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Characteristics of Ultrasensitive Hexagonal-Cored Photonic Crystal Fiber for Hazardous Chemical Sensing

Characteristics of Ultrasensitive Hexagonal-Cored Photonic Crystal Fiber for Hazardous Chemical... hv photonics Article Characteristics of Ultrasensitive Hexagonal-Cored Photonic Crystal Fiber for Hazardous Chemical Sensing 1 , 1 2 3 1 Abdul Mu’iz Maidi *, Norazanita Shamsuddin , Wei-Ru Wong , Shubi Kaijage and Feroza Begum Faculty of Integrated Technologies, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, Bandar Seri Begawan BE1410, Brunei; norazanita.shamsudin@ubd.edu.bn (N.S.); feroza.begum@ubd.edu.bn (F.B.) Department of Electrical Engineering, Faculty of Electrical Engineering, Universiti Malaya, Kuala Lumpur 50603, Malaysia; weiru@um.edu.my School of Computational and Communication Science and Engineering, Nelson Mandela African Institution of Science and Technology, Arusha 23311, Tanzania; shubi.kaijage@nm-aist.ac.tz * Correspondence: 17b4010@ubd.edu.bn Abstract: A highly sensitive non-complex cored photonic crystal fiber sensor for hazardous chemical sensing with water, ethanol, and benzene analytes has been proposed and is numerically analyzed using a full-vector finite element method. The proposed fiber consists of a hexagonal core hole and two cladding air hole rings, operating in the lower operating wavelength of 0.8 to 2.6 m. It has been shown that the structure has high relative sensitivity of 94.47% for water, 96.32% for ethanol and 9 10 99.63% for benzene, and low confinement losses of 7.31  10 dB/m for water, 3.70  10 dB/m ethanol and 1.76  10 dB/m benzene. It also displays a high power fraction and almost flattened chromatic dispersion. The results demonstrate the applicability of the proposed fiber design for chemical sensing applications. Keywords: photonic crystal fiber; chemical sensor; relative sensitivity; confinement loss Citation: Maidi, A.M.; Shamsuddin, N.; Wong, W.-R.; Kaijage, S.; Begum, F. Characteristics of Ultrasensitive 1. Introduction Hexagonal-Cored Photonic Crystal In both industry and academic sectors, photonic crystal fibers (PCFs) are one of the Fiber for Hazardous Chemical most interested research areas in the field of fiber optics. The huge popularity of PCF arises Sensing. Photonics 2022, 9, 38. from its characteristics of low loss in optical signal, more flexibility and lower weight [1]. https://doi.org/10.3390/ These benefits mean that various materials can be incorporated to form the structure of photonics9010038 the PCF to promote a photonic band gap and modified total internal reflection (m-TIR) Received: 10 December 2021 propagation mode due to the high refractive index difference. It, additionally, is not Accepted: 3 January 2022 restrained to communication applications but also can be effectively employed in different Published: 10 January 2022 promising applications, such as astronomy, security and imaging [2,3]. Moreover, PCF can Publisher’s Note: MDPI stays neutral be used in diverse chemical and biological sensing applications such as temperature [4], with regard to jurisdictional claims in pressure [5], mechanical [6], gas [7] and liquid [8] sensors. PCF can be employed as a sensor published maps and institutional affil- by incorporating the core air holes with different test analytes; thus, it is applicable in iations. various sectors. One of the most popular operations of PCF in the field of sensing includes its use as a chemical sensor, where a group of pioneering researchers have introduced diverse designs with varying performance over the years. A group of researchers [9] introduced a sensor design composed of three layers of Copyright: © 2022 by the authors. cladding air holes in a circular lattice with an array of elliptical holes as the core for Licensee MDPI, Basel, Switzerland. chemical sensing, with ethanol as the test analyte. The relative sensitivity was 29.25% and This article is an open access article confinement loss was in the order of 10 dB/m, acquired at 1.5 m operating wavelength. distributed under the terms and In reference [10], a hexagonal grid PCF sensor, with four cladding air hole rings and a conditions of the Creative Commons single core elliptical hole, for liquid detection with a water analyte, has been proposed. It Attribution (CC BY) license (https:// shows values of  = 1.3 m, low relative sensitivity of 41.37% and an order of 10 dB/m creativecommons.org/licenses/by/ for confinement loss. Bin Murshed Leon et al. [11] also proposed a PCF design with water 4.0/). Photonics 2022, 9, 38. https://doi.org/10.3390/photonics9010038 https://www.mdpi.com/journal/photonics Photonics 2022, 9, 38 2 of 14 as the test analyte. The design of the PCF structure consists of four rings of cladding air holes in a hexagonal arrangement and an array of nine circular holes designated as the core. Such a sensor design allowed a relative sensitivity of 44.45% and confinement loss of approximately 10 dB/m at a 1.3 m operating wavelength. The same research group [12] also introduced a design with four cladding air hole rings and four circular holes arranged as the core of the fiber, with a similar liquid analyte: water. At an optimum wavelength of 1.3 m, it results in a low relative sensitivity of 49.13% and confinement loss of order 10 dB/m. Islam et al. [13] suggested a chemical analyte sensor with water, ethanol and benzene, which yielded relative sensitivity results of 48.19%, 53.22% and 55.56% for water, ethanol and benzene, respectively, achieved at a wavelength of 1.3 m. Then, reference [14] reported relative sensitivities of 56.75% for water, 52.07% for ethanol and 58.86% for benzene and a confinement loss of approximately 10 dB/m for all the test analytes, at  = 1.33 m, with five ring cladding holes in an octagonal lattice and nine core holes in a square configuration, proposed as the PCF chemical sensor. A PCF structure with three cladding air hole rings has also been proposed by Maidi et al. [15]. In contrast to the comparatively simple chemical sensor with water, ethanol and benzene marked on the three elliptical core holes, the PCF exhibits decent results, with relative sensitivities of 62.60%, 65.34% and 74.50% for water, ethanol and benzene, respectively, with confinement 7 8 11 losses in the order of 10 dB/m, 10 dB/m and 10 dB/m for water, ethanol and benzene, respectively, at  = 1.3 m. Notably, a group of researchers [16] recommended an impressively performing PCF structure of one hexagonal core and five cladding rings in a circular form for chemical sensing, demonstrating high relative sensitivities. Relative sensitivities of 88.93%, 91.87% and 97.89% were achieved for water, ethanol and benzene, respectively, and the confinement losses for the PCF were in the order of approximately 10 dB/m for all test analytes. These values were obtained at an optimum wavelength of 1.55 m. In the literature [9–16], researchers focused on implementing elaborative PCF structures, which consist of intricate core designs and multiple layers of cladding holes to produce good outcomes in the simulated optical parameters. With such expressive designs, this increases the difficulty of manufacturing the PCFs and may affect the sensing results due to the fabrication tolerances. Fabrication of PCFs is subject to manufacturing errors and prone to issues such as inaccuracy of hole sizes due to the irregular shape and positioning of the desired holes [17,18]. Furthermore, a single inaccuracy in an air hole will affect surrounding air holes as well, which can be problematic in elaborate designs with intricate fiber core structures and numerous air holes [19]. In this work, a noncomplex PCF structure is proposed that maintain impressive results of optical properties, particularly its relative sensitivity and confinement loss. Results of the effective refractive index, relative sensitivity, power fraction, confinement loss and chromatic dispersion are investigated, as well, over the infrared region from 0.8 to 2.6 m operating wavelength. Water, ethanol and benzene are selected as the test analytes for the study. 2. Design The sensing principles for PCF sensors are based on the interaction between the optical signal and the analyte in the propagation core region [20]. The evanescent field of light is imposed on the PCF and extends to the located analyte to be sensed. The presence of cladding air holes allows near-total confinement of light to promote sufficient light–analyte interaction. Thus, an appropriate geometry of the proposed PCF sensor was configured and is presented in Figure 1, which consists of a core, cladding and the perfectly matched layer (PML). Silica was chosen for the background material established for the cladding and PML, marked in red and blue colors, respectively. Likewise, the white color indicates air for the cladding air holes and the test analytes are shown in yellow at the core. Photonics 2022, 9, x FOR PEER REVIEW 3 of 15 The core of the fiber is a hollow hexagonal hole, where the selective test analyte is suggested to be administered for chemical sensing. The corner-to-corner length of the hex- agonal hole is denoted as l. The cladding consists of multiple air holes positioned through- out its region, and each circular air hole is denoted as d. To offer a symmetrical design, the cladding holes are situated equidistantly from each other, with a pitch distance denoted as Λ = 3.0 µm and air-filling fraction (AFF) of 0.97. The cladding has a total of 18 air holes arranged in 2 rings. The PML is imposed on the fiber structure to absorb light leaked from the core and cladding region. The dimension of the core l = 3.32 µm, and the diameter of each cladding air hole d = 2.91 µm. The PML is enhanced to be 10% of the fiber diameter to meet the boundary condition. The proposed PCF sensor can detect various chemical analytes; however, the selected test analytes in this paper are water, ethanol and benzene. The air-filling fraction of the cladding is kept at a high value to acquire an optically dense Photonics 2022, 9, 38 3 of 14 core compared to the cladding, which preserves the modified total internal reflection (m- TIR) as the guiding mechanism. Figure 1. Schematic of the design proposed for the PCF. Figure 1. Schematic of the design proposed for the PCF. The core of the fiber is a hollow hexagonal hole, where the selective test analyte is There are various possible fabrication methods that have been introduced, such as suggested to be administered for chemical sensing. The corner-to-corner length of the the sol–gel technique [21], stacking [22], drilling [23], 3D printing [24] and extrusion [25]. hexagonal hole is denoted as l. The cladding consists of multiple air holes positioned The fabrication of this PCF sensor design can be performed using the extrusion method throughout its region, and each circular air hole is denoted as d. To offer a symmetrical as it allows the fabrication of intricate designs with high accuracy. Additionally, the infil- design, the cladding holes are situated equidistantly from each other, with a pitch distance tration of the test chemical analyte into the hollow holes can be achieved by using the denoted as L = 3.0 m and air-filling fraction (AFF) of 0.97. The cladding has a total of selective infiltration technique, which has been experimentally introduced by researchers 18 air holes arranged in 2 rings. The PML is imposed on the fiber structure to absorb light [26–30]. This technique is capable of injecting liquids into the micro-structured core and leaked from the core and cladding region. The dimension of the core l = 3.32 m, and the cladding holes in the PCF. Numerous methods for injecting liquid analytes have been diameter of each cladding air hole d = 2.91 m. The PML is enhanced to be 10% of the fiber proposed by researchers throughout the years, including the multi-step injection-cure- diameter to meet the boundary condition. The proposed PCF sensor can detect various cleave process [26], fusion splicer [27], lateral filling [28], femtosecond laser micromachin- chemical analytes; however, the selected test analytes in this paper are water, ethanol ing [29] and focused ion beam micromachining [30]. and benzene. The air-filling fraction of the cladding is kept at a high value to acquire an optically dense core compared to the cladding, which preserves the modified total internal reflection (m-TIR) as the guiding mechanism. There are various possible fabrication methods that have been introduced, such as the sol–gel technique [21], stacking [22], drilling [23], 3D printing [24] and extrusion [25]. The fabrication of this PCF sensor design can be performed using the extrusion method as it allows the fabrication of intricate designs with high accuracy. Additionally, the infiltration of the test chemical analyte into the hollow holes can be achieved by using the selective infiltration technique, which has been experimentally introduced by researchers [26–30]. This technique is capable of injecting liquids into the micro-structured core and cladding holes in the PCF. Numerous methods for injecting liquid analytes have been proposed by researchers throughout the years, including the multi-step injection-cure-cleave process [26], fusion splicer [27], lateral filling [28], femtosecond laser micromachining [29] and focused ion beam micromachining [30]. 3. Methodology A simulation of the proposed PCF has been conducted applying the full-vector finite element method (FV-FEM) for numerical analysis using COMSOL Multiphysics software version 5.5. A finer meshing type has been selected for the design to be correctly mapped. Photonics 2022, 9, x FOR PEER REVIEW 4 of 15 3. Methodology A simulation of the proposed PCF has been conducted applying the full-vector finite element method (FV-FEM) for numerical analysis using COMSOL Multiphysics software Photonics 2022, 9, 38 4 of 14 version 5.5. A finer meshing type has been selected for the design to be correctly mapped. The complete mesh consists of 14,370 triangular elements, 1352 edge elements and 86 ver- tex elements. The proposed PCF is intended for detecting chemicals, particularly water, The complete mesh consists of 14,370 triangular elements, 1352 edge elements and 86 vertex ethanol and benzene. Figure 2 shows the refractive index of silica and the test analytes elements. The proposed PCF is intended for detecting chemicals, particularly water, ethanol (water, ethanol and benzene) with respect to a micrometer wavelength of 0.8–2.6 µm [31– and benzene. Figure 2 shows the refractive index of silica and the test analytes (water, 34]. ethanol and benzene) with respect to a micrometer wavelength of 0.8–2.6 m [31–34]. Figure 2. Figure 2.Refra Refractive ctive index index of of silica silica and and test test analy analytes, tes, watwater er, ethanol and b , ethanol and enzene, at benzene, 0.8–2 at 0.8–2.6 .6 µm op- m erating wavelength [31–34]. operating wavelength [31–34]. Evaluation of the performance and practicability of the proposed PCF design is con- Evaluation of the performance and practicability of the proposed PCF design is con- ducted through investigating the respective optical properties: effective refractive index, ducted through investigating the respective optical properties: effective refractive index, relative sensitivity, power fraction, confinement loss and chromatic dispersion. relative sensitivity, power fraction, confinement loss and chromatic dispersion. With silica as the background material, hollow air holes and core holes that have been With silica as the background material, hollow air holes and core holes that have been set with the test analytes, the effective refractive index n can be quantified and modeled set with the test analytes, the effective refractive index neff ef can f be quantified and modeled using Sellmeier ’s equation given by [35]: using Sellmeier’s equation given by [35]: 2 2 2 B l B l B l 𝐵 𝜆 𝐵 𝜆 𝐵 𝜆 1 2 3 n (l) = 1 + + + (1) (1) 𝑛 ef(𝜆 f) = 1+ + + 2 2 2 l C l C l C 𝜆 −𝐶 1𝜆 −𝐶 𝜆 2 −𝐶 3 where l is the operating wavelength and B and C (i = 1,2 and 3) are the Sellmeier coeffi- i i where λ is the operating wavelength and Bi and Ci (i = 1,2 and 3) are the Sellmeier coeffi- cients for the specific material. cients for the specific material. Relative sensitivity S determines the practicability of the PCF sensor to detect analytes Relative sensitivity S determines the practicability of the PCF sensor to detect ana- by matching the refractive indices and achieved by measuring the light intensity that lytes by matching the refractive indices and achieved by measuring the light intensity that interacts with the analyte to be detected. It is defined as [15,36,37]: interacts with the analyte to be detected. It is defined as [15,36,37]: S =  P (2) 𝑆= ×𝑃 n (2) eff where n is the refractive index of the sensed material and P is the power fraction. The variation in relative sensitivity is closely related to the effective refractive index and power fraction. Power fraction P is a measure of the amount of power flowing through the PCF at a specific region, and it is defined as the ratio of power in a chemical-filled region to that of the total fiber by integration. It is expressed by Poynting’s theorem as [15,36,37]: (sample) Re E H E H dxdy x y y x P =  100 (3) total Re E H E H dxdy ( ) x y y x Photonics 2022, 9, x FOR PEER REVIEW 5 of 15 where nr is the refractive index of the sensed material and P is the power fraction. The variation in relative sensitivity is closely related to the effective refractive index and power fraction. Power fraction P is a measure of the amount of power flowing through the PCF at a specific region, and it is defined as the ratio of power in a chemical-filled region to that of the total fiber by integration. It is expressed by Poynting’s theorem as [15,36,37]: (𝑠𝑎𝑚𝑝𝑙𝑒) 𝐻 −𝐸 𝐻 Photonics 2022, 9, 38 5 of 14 𝑃= × 100 (3) ( ) 𝑡𝑜𝑡𝑎𝑙 𝐻 −𝐸 𝐻 where Ex, Ey and Hx, Hy are the transverse electric and magnetic fields of the guided mode, where E , E and H , H are the transverse electric and magnetic fields of the guided mode, x y x y respectively. The integral in the numerator is selected over the analyte at the core, whilst respectively. The integral in the numerator is selected over the analyte at the core, whilst the integral in the denominator is over all fiber regions. the integral in the denominator is over all fiber regions. Confinement loss Lc describes the phenomenon of leakage of light from the core to Confinement loss L describes the phenomenon of leakage of light from the core to the the cladding, contributed by the structural design of the fiber. It quantifies the portion of cladding, contributed by the structural design of the fiber. It quantifies the portion of light light loss from the core area to the cladding, and is defined as [38–40]: loss from the core area to the cladding, and is defined as [38–40]: 40𝜋 𝐿 = Im 𝑛 ×10 (4) 40p ln (10)𝜆 L = Im[n ]  10 (4) c eff ln(10)l where Im[neff] is the imaginary part of the effective mode index. The variations in the op- where Im[n ] is the imaginary part of the effective mode index. The variations in the eff erating wavelength and effective refractive index determine the confinement loss. operating wavelength and effective refractive index determine the confinement loss. Chromatic dispersion D is a measure of the light-guiding capabilities of the fiber and Chromatic dispersion D is a measure of the light-guiding capabilities of the fiber and the degradation of the mode in the fiber. It is defined as [10,38,40]: the degradation of the mode in the fiber. It is defined as [10,38,40]: 𝜆 𝑑 (5) 𝐷= − l d D =𝑐 𝑑𝜆 Re[n ] (5) eff c dl where c is the speed of light and Re[neff] is the real part of the effective refractive index. where c is the speed of light and Re[n ] is the real part of the effective refractive index. eff 4. Results and Discussion 4. Results and Discussion Figure 3 illustrates the mode profiles for the different chemical-infiltrated analytes in Figure 3 illustrates the mode profiles for the different chemical-infiltrated analytes in the core, with an operating wavelength of 1.3 µm. The interaction of light occurs through the core, with an operating wavelength of 1.3 m. The interaction of light occurs through the core region, with the mode field completely confined at the core for all three test ana- the core region, with the mode field completely confined at the core for all three test analytes: lytes: water, ethano water, ethanol l and benzene. and benzene. (a) (b) (c) Figure 3. Mode profile of the proposed PCF for (a) water, (b) ethanol and (c) benzene. Figure 3. Mode profile of the proposed PCF for (a) water, (b) ethanol and (c) benzene. Theor Theoret etically ically, , the theef ef ffec ective tiver efractive refractive index index decr decre eases ases with with an an incr inc ease rease in in the th operating e operat- wavelength, ing wavelengand th, and a a similar similar tren trend is d established is established as well for the as well for the pr pr oposed oposed PCF PCF shown shown in in Figure 4, with the effective refractive index declining as the operating wavelength is Figure 4, with the effective refractive index declining as the operating wavelength is in- incr creas eased, ed, for for all allthe the se selected lected an analytes: alytes: w water ater, ,eth ethanol anol and ben and benzene. zene. This behav This behavior ior ar arises ises where smaller electromagnetic wavelengths propagate through the high refractive index where smaller electromagnetic wavelengths propagate through the high refractive index region. Moreover, it can be observed that the effective refractive index of water is the lowest, region. Moreover, it can be observed that the effective refractive index of water is the followed by ethanol and benzene, being the highest, as established from their respective refractive indices, as seen in Figure 2. It can be seen from Figure 5 that the relative sensitivity for benzene decreases over the scale of set wavelengths from 0.8 to 2.6 m; however, the trend for water and ethanol increases from 0.8 to 1.3 m and then subsequently decreases as the wavelength is increased further. Relative sensitivity is closely related to the effective refractive index and power fraction; hence, benzene has the highest relative sensitivity, followed by ethanol and water. At the operating wavelength of 1.3 m, relative sensitivities are 94.47%, 96.32% and 99.63% for water, ethanol and benzene, respectively. Since the operating wavelength of 1.3 m yielded the optimum relative sensitivities for water and ethanol, other optical properties 𝑛𝑅𝑒 𝑑𝑥𝑑𝑦 𝐸𝑅𝑒 𝑑𝑥𝑑𝑦 𝐸𝑅𝑒 Photonics 2022, 9, x FOR PEER REVIEW 6 of 15 lowest, followed by ethanol and benzene, being the highest, as established from their re- spective refractive indices, as seen in Figure 2. It can be seen from Figure 5 that the relative sensitivity for benzene decreases over the scale of set wavelengths from 0.8 to 2.6 µm; however, the trend for water and ethanol increases from 0.8 to 1.3 µm and then subsequently decreases as the wavelength is in- creased further. Relative sensitivity is closely related to the effective refractive index and power fraction; hence, benzene has the highest relative sensitivity, followed by ethanol Photonics 2022, 9, 38 and water. At the operating wavelength of 1.3 µm, relative sensitivities are 94.47%, 96.32% 6 of 14 and 99.63% for water, ethanol and benzene, respectively. Since the operating wavelength of 1.3 µm yielded the optimum relative sensitivities for water and ethanol, other optical properties for the proposed PCF were considered at this optimum wavelength. Moreover, for the proposed PCF were considered at this optimum wavelength. Moreover, as seen as seen from Figure 1, the dimension of the core hole is larger than the surrounding air from Figure 1, the dimension of the core hole is larger than the surrounding air holes in holes in the cladding, which allows more test analyte to be injected into the core hole; this the cladding, which allows more test analyte to be injected into the core hole; this leads to leads to a stronger interaction between light and the test analyte. Hence, the PCF leads to a stronger interaction between light and the test analyte. Hence, the PCF leads to higher higher relative sensitivity. relative sensitivity. Photonics 2022, 9, x FOR PEER REVIEW 7 of 15 Figure 4. Effective refractive index of the proposed design against operating wavelength for water, Figure 4. Effective refractive index of the proposed design against operating wavelength for water, ethanol and benzene. ethanol and benzene. Figure 5. Proposed PCF sensor results for relative sensitivity with respect to wavelength for water, Figure 5. Proposed PCF sensor results for relative sensitivity with respect to wavelength for water, ethanol and benzene. ethanol and benzene. Figure 6 shows the power fraction of the proposed PCF sensor against different op- Figure 6 shows the power fraction of the proposed PCF sensor against different erating wavelengths for water, ethanol and benzene. The amount of power flowing operating wavelengths for water, ethanol and benzene. The amount of power flowing through at the core of the PCF is quantified with this property. It can be seen that the through at the core of the PCF is quantified with this property. It can be seen that the power power fractions for water and ethanol present an increasing behavior initially as the op- fractions for water and ethanol present an increasing behavior initially as the operating erating wavelength increases between 0.8 and 1.3 µm, before drastically decreasing with further increases in the operating wavelength, whereas the power fraction trend for ben- zene decreases as the wavelength increases. The decreasing behavior results in optical power leaks from the core region to the surrounding cladding as the wavelength in- creases. The proposed PCF yields power fractions of 92.91%, 94.64% and 97.84% for water, ethanol and benzene, respectively, at a wavelength of 1.3 µm. Figure 6. Power fraction of the PCF sensor with respect to wavelength for water, ethanol and ben- zene. Photonics 2022, 9, x FOR PEER REVIEW 7 of 15 Figure 5. Proposed PCF sensor results for relative sensitivity with respect to wavelength for water, ethanol and benzene. Figure 6 shows the power fraction of the proposed PCF sensor against different op- erating wavelengths for water, ethanol and benzene. The amount of power flowing Photonics 2022, 9, 38 7 of 14 through at the core of the PCF is quantified with this property. It can be seen that the power fractions for water and ethanol present an increasing behavior initially as the op- erating wavelength increases between 0.8 and 1.3 µm, before drastically decreasing with wavelength increases between 0.8 and 1.3 m, before drastically decreasing with further further increases in the operating wavelength, whereas the power fraction trend for ben- increases in the operating wavelength, whereas the power fraction trend for benzene zene decreases as the wavelength increases. The decreasing behavior results in optical decreases as the wavelength increases. The decreasing behavior results in optical power power leaks from the core region to the surrounding cladding as the wavelength in- leaks from the core region to the surrounding cladding as the wavelength increases. The creases. The proposed PCF yields power fractions of 92.91%, 94.64% and 97.84% for water, proposed PCF yields power fractions of 92.91%, 94.64% and 97.84% for water, ethanol and ethanol and benzene, respectively, at a wavelength of 1.3 µm. benzene, respectively, at a wavelength of 1.3 m. Figure 6. Power fraction of the PCF sensor with respect to wavelength for water, ethanol and ben- Figure 6. Power fraction of the PCF sensor with respect to wavelength for water, ethanol and benzene. zene. Figure 7 demonstrates the relationship between confinement loss and operating wave- length. Confinement loss is a measure of light leakage from the core to the cladding, and, in theory, confinement losses generally increase as light tends to leak out of the cladding with respect to the increase in operating wavelength; this characteristic can be seen in the 9 10 figure. Confinement losses are 7.31  10 dB/m for water, 3.70  10 dB/m for ethanol and 1.76  10 dB/m for benzene, at an operating wavelength of 1.3 m. Furthermore, with the benefit of a definite hexagonal core and surrounding air hole configuration, it influences the careful confinement of light, as seen in the results. Figure 8 shows the relationship between the chromatic dispersion of the proposed PCF and the operating wavelength with water, ethanol and benzene. It can be observed that the obtained dispersion is especially low and nearly flattened for all test analytes. This indicates a good result in the interaction between the light signal and the chemical analytes. At a 1.3 m wavelength, the chromatic dispersions are 0.0053 ps/nm.km for water, 0.0049 ps/nm.km for ethanol and 0.0045 ps/nm.km for benzene. This evaluation of chromatic dispersions is achieved due to the narrow width of the waveguide. Additionally, regarding the fabrication of the proposed PCF sensor, a tolerance analysis is performed by varying the global parameters—the pitch and diameter of the holes—and examining the effects on the variations in the optical properties: relative sensitivity and con- finement loss. Analyses in the order of 1%, 2% and 4% are applied on the parameters of the proposed PCF, which is shown in Table 1. A very small effect is seen on the optical properties. In terms of the values of relative sensitivities and confinement losses, they decrease as the percentage variations are increased and they increase when the variations are decreased. Photonics 2022, 9, x FOR PEER REVIEW 8 of 15 Figure 7 demonstrates the relationship between confinement loss and operating wavelength. Confinement loss is a measure of light leakage from the core to the cladding, and, in theory, confinement losses generally increase as light tends to leak out of the clad- ding with respect to the increase in operating wavelength; this characteristic can be seen −9 −10 in the figure. Confinement losses are 7.31 × 10 dB/m for water, 3.70 × 10 dB/m for eth- −13 anol and 1.76 × 10 dB/m for benzene, at an operating wavelength of 1.3 µm. Further- more, with the benefit of a definite hexagonal core and surrounding air hole configuration, it influences the careful confinement of light, as seen in the results. Figure 8 shows the relationship between the chromatic dispersion of the proposed PCF and the operating wavelength with water, ethanol and benzene. It can be observed that the obtained dispersion is especially low and nearly flattened for all test analytes. This indicates a good result in the interaction between the light signal and the chemical analytes. At a 1.3 µm wavelength, the chromatic dispersions are −0.0053 ps/nm.km for Photonics 2022, 9, 38 8 of 14 water, −0.0049 ps/nm.km for ethanol and −0.0045 ps/nm.km for benzene. This evaluation of chromatic dispersions is achieved due to the narrow width of the waveguide. Photonics 2022, 9, x FOR PEER REVIEW 9 of 15 Figure 7. Confinement loss of the PCF sensor with respect to wavelength for water, ethanol and Figure 7. Confinement loss of the PCF sensor with respect to wavelength for water, ethanol and benzene. benzene. Figure 8. Figure C 8.hChr rom omatic atic dispersi dispersion on of the propos of the proposed ed de design sign with with respect respectto wav to wavelength elength for water, etha- for water, ethanol nol and benzene. and benzene. Table 1. Comparison among the variation in global parameters on optimum parameters at  = 1.3 m. Additionally, regarding the fabrication of the proposed PCF sensor, a tolerance anal- ysis is performed by varying the global parameters—the pitch and diameter of the holes— Relative Sensitivity (%) Confinement Loss (dB/m) and examining the effects on the variations in the optical properties: relative sensitivity Change in Global Parameters Water Ethanol Benzene Water Ethanol Benzene and confinement loss. Analyses in the order of ±1%, ±2% and ±4% are applied on the pa- 9 10 14 rameters of the proposed PCF, which is shown in Table 1. A very small effect is seen on +4% 94.40 96.32 99.64 2.60  10 1.05  10 7.62  10 9 10 13 the optical properties. In terms of the values of relative sensitivities and confinement +2% 94.44 96.32 99.63 4.37  10 1.78  10 1.28  10 9 10 13 +1% 94.46 96.32 99.63 5.58  10 2.71  10 1.72  10 losses, they decrease as the percentage variations are increased and they increase when 9 10 13 Optimum 94.47 96.32 99.63 7.31  10 3.70  10 1.76  10 the variations are decreased. 9 10 13 1% 94.49 96.31 99.63 9.54  10 4.62  10 4.82  10 8 10 13 2% 94.50 96.31 99.62 1.25  10 6.78  10 5.46  10 Table 1. Comparison among the variation in global parameters on optimum parameters at λ = 1.3 8 9 13 4% 94.51 96.30 99.62 2.16  10 1.25  10 6.71  10 µm. Relative Sensitivity (%) Confinement Loss (dB/m) Change in Global Parameters Water Ethanol Benzene Water Ethanol Benzene −9 −10 −14 +4% 94.40 96.32 99.64 2.60 × 10 1.05 × 10 7.62 × 10 −9 −10 −13 +2% 94.44 96.32 99.63 4.37 × 10 1.78 × 10 1.28 × 10 −9 −10 −13 +1% 94.46 96.32 99.63 5.58 × 10 2.71 × 10 1.72 × 10 −9 −10 −13 Optimum 94.47 96.32 99.63 7.31 × 10 3.70 × 10 1.76 × 10 −9 −10 −13 −1% 94.49 96.31 99.63 9.54 × 10 4.62 × 10 4.82 × 10 −8 −10 −13 −2% 94.50 96.31 99.62 1.25 × 10 6.78 × 10 5.46 × 10 −8 −9 −13 −4% 94.51 96.30 99.62 2.16 × 10 1.25 × 10 6.71 × 10 Figure 9a–c show the relative sensitivity variations of order ±1%, ±2% and ±4% for water, ethanol and benzene, respectively. Meanwhile, Figure 10a–c illustrate the varia- tions in confinement loss in the order of ±1%, ±2% and ±4% for water, ethanol and benzene, respectively. With such modification made to the dimensions of the pitch and air holes’ diameter, Figures 9 and 10 demonstrate minute alterations in the results of the optical properties. Photonics 2022, 9, 38 9 of 14 Figure 9a–c show the relative sensitivity variations of order 1%, 2% and 4% for water, ethanol and benzene, respectively. Meanwhile, Figure 10a–c illustrate the vari- ations in confinement loss in the order of 1%, 2% and 4% for water, ethanol and Photonics 2022, 9, x FOR PEER REVIEW 10 of 15 benzene, respectively. With such modification made to the dimensions of the pitch and air holes’ diameter, Figures 9 and 10 demonstrate minute alterations in the results of the optical properties. (a) (b) Figure 9. Cont. Photonics 2022, 9, x FOR PEER REVIEW 11 of 15 Photonics 2022, 9, x FOR PEER REVIEW 11 of 15 Photonics 2022, 9, 38 10 of 14 (c) (c) Figure 9. (a) Tolerance analysis of relative sensitivity for water in the variations of ±1%, ±2% and Figure 9. ±4%. (b) To (a) Figure T lera olerance analy nce analy 9. (a) Tolerance sis of sis of relative analysis relat sens ive of s relative e iti nsitiv vity fo sensitivity ity r e for thanol in the water in for water the v variatio in the ariations variations ns of ±1% of ±1 of , ±2% %, ±2% 1%, and ±4%.  and 2% and ±4%. ( (c) To b) To lerance a lera 4%. nce analy n (alysis o b) Tolerance sf i relat s ofanalysis relative ive sen of sens sitivity f relative itivity sensitivity or benzene in t for ethanol in the for ethanol he variations o in variatio the variations ns of ±1% f ±1%, ±2% and ±4%. of  , ±2% 1%, and ±4%. 2% and 4%. (c) Tolerance a (c) T nolerance alysis ofanalysis relative sen of relative sitivity f sensitivity or benzene in t for benzene he variations o in the variations f ±1%, ±2% and ±4%. of 1%, 2% and 4%. (a) (a) Figure 10. Cont. Photonics 2022, 9, x FOR PEER REVIEW 12 of 15 Photonics 2022, 9, 38 11 of 14 (b) (c) Figure 10. Figure (a) Tolerance analysis of 10. (a) Tolerance analysis confine of confinement ment loss for loss for water in the variations of ±1 water in the variations of 1%, %, ±2% and 2% and 4%. (b) Tolerance analysis of confinement loss for ethanol in the variations of 1%, 2% and 4%. ±4%. (b) Tolerance analysis of confinement loss for ethanol in the variations of ±1%, ±2% and ±4%. (c) Tolerance analysis of confinement loss for benzene in the variations of 1%, 2% and 4%. (c) Tolerance analysis of confinement loss for benzene in the variations of ±1%, ±2% and ±4%. Lastly, a comparison between prior PCF chemical sensors and the proposed PCF Lastly, a comparison between prior PCF chemical sensors and the proposed PCF de- design is presented in Table 2. It can be observed from the table that the proposed PCF has sign is presented in Table 2. It can be observed from the table that the proposed PCF has a comparatively simple layout of a single core hole with two cladding rings, in contrast a comparatively simple layout of a single core hole with two cladding rings, in contrast to to the prior PCFs with additional cladding rings and intricate core designs. With regard the prior PCFs with additional cladding rings and intricate core designs. With regard to to the design, the proposed PCF demonstrates the highest relative sensitivity and low the design, the proposed PCF demonstrates the highest relative sensitivity and low con- finement loss, with all the chemical analytes. Therefore, the novelty of the proposed PCF is the simplicity of design, which aids in the ease of fabrication and leads to better numer- ically analyzed results. Photonics 2022, 9, 38 12 of 14 confinement loss, with all the chemical analytes. Therefore, the novelty of the proposed PCF is the simplicity of design, which aids in the ease of fabrication and leads to better numerically analyzed results. Table 2. Comparison of structure and performance among prior PCFs and proposed PCF at  = 1.3 m. Structure Relative Confinement No. of Rings Sensitivity (%) Loss (dB/m) Core Cladding Ref. [9] 3 6 core holes Circular holes in circle 26.23 (E) ~10 (E) Ref. [10] 4 1 core hole Circular holes in hexagon 41.37 (W) ~10 (W) Ref. [11] 4 9 core holes Circular holes in hexagon 44.45 (W) ~10 (W) Ref. [12] 4 4 core holes Circular holes in hexagon 49.13 (W) ~10 (W) 48.19 (W) Ref. [13] 3 7 core holes Circular holes in hexagon 53.22 (E) - 55.56 (B) 52.07 (W) ~10 (W) Ref. [14] 5 9 core holes Circular holes in octagon 56.75 (E) ~10 (E) 58.86 (B) ~10 (B) 62.60 (W) ~10 (W) Ref. [15] 3 3 core holes Circular holes in hexagon 65.34 (E) ~10 (E) 74.50 (B) ~10 (B) 90.14 (W) ~10 (W) Ref. [16] 5 1 core hole Circular holes in hexagon 93.85 (E) ~10 (E) 98.11 (B) ~10 (B) 94.47 (W) ~10 (W) Proposed PCF 2 1 core hole Circular holes in hexagon 96.32 (E) ~10 (E) 99.63 (B) ~10 (B) where W refers to water, E refers to ethanol and B refers to benzene. 5. Conclusions The proposal of a simple PCF sensor for hazardous chemical detection has been intro- duced, which is composed of a single hexagonal hole for the core and 18 imposed cladding air holes, positioned in a hexagon-shaped lattice. Operating at the lower wavelengths of 0.8–2.6 m, the designed chemical sensor with water, ethanol and benzene has been numerically analyzed with the aid of a FV-FEM simulation method on COMSOL Multi- physics to investigate its optical properties: effective refractive index, relative sensitivity, power fraction, confinement loss and chromatic dispersion. The optimum results have been obtained at a 1.3 m operating wavelength, with high relative sensitivities of 94.47%, 96.32% and 99.63% for water, ethanol and benzene, respectively, and confinement losses 9 10 13 of 7.31  10 dB/m, 3.70  10 dB/m and 1.76  10 dB/m for water, ethanol and benzene, respectively. The investigated results are noteworthy as they indicate the practica- bility of the proposed PCF for sensing applications in the medical sector, chemical industry, security and defense by sensing unknown analytes, as well as in optical communication through the desirable results of chromatic dispersion. Furthermore, this research shall potentially proceed to fabrication and experimental testing as future work. Author Contributions: Conceptualization, A.M.M. and F.B.; methodology, A.M.M. and F.B.; software, A.M.M., S.K. and F.B.; validation, W.-R.W. and F.B.; formal analysis, A.M.M. and F.B.; investigation, A.M.M. and F.B.; resources, F.B.; data curation, A.M.M. and F.B.; writing—original draft preparation, A.M.M.; writing—review and editing, W.-R.W. and F.B.; visualization, F.B.; supervision, F.B.; project administration, F.B.; funding acquisition, F.B. and N.S. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by UNIVERSITI BRUNEI DARUSSALAM, grant number UBD/RSCH/1.3/FICBF(b)/2019/008. Institutional Review Board Statement: Not applicable. Photonics 2022, 9, 38 13 of 14 Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest. References 1. Habib, A.; Anower, S.; Haque, I. Highly Sensitive Hollow Core Spiral Fiber for Chemical Spectroscopic Applications. Sens. Int. 2020, 1, 100011. [CrossRef] 2. Abbott, D.; Zhang, X.C. Scanning the Issue: T-Ray Imaging, Sensing, and Retection. Proc. IEEE 2007, 95, 1509–1513. [CrossRef] 3. Habib, M.A.; Reza, M.S.; Abdulrazak, L.F.; Anower, M.S. Extremely High Birefringent and Low Loss Microstructure Optical Waveguide: Design and Analysis. Opt. Commun. 2019, 446, 93–99. [CrossRef] 4. Chang, Y.H.; Jhu, Y.Y.; Wu, C.J. Temperature Dependence of Defect Mode in a Defective Photonic Crystal. Opt. Commun. 2012, 285, 1501–1504. [CrossRef] 5. Bock, W.J.; Jiahua, C.; Eftimov, T.; Urbanczyk, W. A Photonic Crystal Fiber Sensor for Pressure Measurements. Conf. Rec.-IEEE Instrum. Meas. Technol. Conf. 2005, 2, 1177–1181. [CrossRef] 6. Chengkuo, L.; Thillaigovindan, J. Optical Nanomechanical Sensor Using a Silicon Photonic Crystal Cantilever Embedded with a Nanocavity Resonator. Appl. Opt. 2009, 48, 1797–1803. [CrossRef] 7. Morshed, M.; Imran Hassan, M.; Roy, T.K.; Uddin, M.S.; Abdur Razzak, S.M. Microstructure Core Photonic Crystal Fiber for Gas Sensing Applications. Appl. Opt. 2015, 54, 8637. [CrossRef] 8. Ademgil, H.; Haxha, S. PCF Based Sensor with High Sensitivity, High Birefringence and Low Confinement Losses for Liquid Analyte Sensing Applications. Sensors 2015, 15, 31833–31842. [CrossRef] 9. Asaduzzaman, S.; Ahmed, K. Microarray-Core Based Circular Photonic Crystal Fiber for High Chemical Sensing Capacity with Low Confinement Loss. Opt. Appl. 2017, 47, 41–49. [CrossRef] 10. Arif, M.F.H.; Hossain, M.M.; Islam, N.; Khaled, S.M. A Nonlinear Photonic Crystal Fiber for Liquid Sensing Application with High Birefringence and Low Confinement Loss. Sens. Bio-Sens. Res. 2019, 22, 100252. [CrossRef] 11. Bin Murshed Leon, M.J.; Abedin, S.; Kabir, M.A. A Photonic Crystal Fiber for Liquid Sensing Application with High Sensitivity, Birefringence and Low Confinement Loss. Sens. Int. 2021, 2, 100061. [CrossRef] 12. Leon, M.J.B.M.; Kabir, M.A. Design of a Liquid Sensing Photonic Crystal Fiber with High Sensitivity, Bireferingence & Low Confinement Loss. Sens. Bio-Sens. Res. 2020, 28, 100335. [CrossRef] 13. Islam, S.; Kumar, B.; Ahmed, K. Liquid-Infiltrated Photonic Crystal Fiber for Sensing Purpose: Design and Analysis. Alexandria Eng. J. 2018, 57, 1459–1466. [CrossRef] 14. Ahmed, K.; Morshed, M.; Asaduzzaman, S.; Arif, M.F.H. Optimization and Enhancement of Liquid Analyte Sensing Performance Based on Square-Cored Octagonal Photonic Crystal Fiber. Optik 2017, 131, 687–696. [CrossRef] 15. Maidi, A.M.; Yakasai, I.; Abas, P.E.; Nauman, M.M.; Apong, R.A.; Kaijage, S.; Begum, F. Design and Simulation of Photonic Crystal Fiber for Liquid Sensing. Photonics 2021, 8, 16. [CrossRef] 16. Eid, M.M.A.; Habib, M.A.; Anower, M.S.; Rashed, A.N.Z. Highly Sensitive Nonlinear Photonic Crystal Fiber Based Sensor for Chemical Sensing Applications. Microsyst. Technol. 2020, 27, 1007–1014. [CrossRef] 17. Buczynski, R. Photonic Crystal Fibers. Acta Phys. Pol. Ser. A 2004, 106, 141–167. [CrossRef] 18. Wang, P.; Farrell, G.; Semenova, Y.; Rajan, G. Influence of Fiber Manufacturing Tolerances on the Spectral Response of a Bend Loss Based All-Fiber Edge Filter. Appl. Opt. 2008, 47, 2921. [CrossRef] 19. Amouzad Mahdiraji, G.; Chow, D.M.; Sandoghchi, S.R.; Amirkhan, F.; Dermosesian, E.; Yeo, K.S.; Kakaei, Z.; Ghomeishi, M.; Poh, S.Y.; Yu Gang, S.; et al. Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study. Fiber Integr. Opt. 2014, 33, 85–104. [CrossRef] 20. Lee, H.W.; Schmidt, M.A.; Uebel, P.; Tyagi, H.; Joly, N.Y.; Scharrer, M.; Russell, P.S.J. Optofluidic Refractive-Index Sensor in Step-Index Fiber with Parallel Hollow Micro-Channel. Opt. Express 2011, 19, 8200. [CrossRef] [PubMed] 21. El Hamzaoui, H.; Ouerdane, Y.; Bigot, L.; Bouwmans, G.; Capoen, B.; Boukenter, A.; Girard, S.; Bouazaoui, M. Sol-Gel Derived Ionic Copper-Doped Microstructured Optical Fiber: A Potential Selective Ultraviolet Radiation Dosimeter. Opt. Express 2012, 20, 29751. [CrossRef] [PubMed] 22. Kim, J.-C.; Kim, H.-K.; Paek, U.-C.; Lee, B.-H.; Eom, J.-B. The Fabrication of a Photonic Crystal Fiber and Measurement of Its Properties. J. Opt. Soc. Korea 2003, 7, 79–83. [CrossRef] 23. Zhang, P.; Zhang, J.; Yang, P.; Dai, S.; Wang, X.; Zhang, W. Fabrication of Chalcogenide Glass Photonic Crystal Fibers with Mechanical Drilling. Opt. Fiber Technol. 2015, 26, 176–179. [CrossRef] 24. Bertoncini, A.; Liberale, C. 3D Printed Waveguides Based on Photonic Crystal Fiber Designs for Complex Fiber-End Photonic Devices. Optica 2020, 7, 1487. [CrossRef] 25. Kiang, K.M.; Frampton, K.; Monro, T.M.; Moore, R.; Tucknott, J.; Hewak, D.W.; Richardson, D.J.; Rutt, H.N. Extruded Singlemode Non-Silica Glass Holey Optical Fibres. Electron. Lett. 2002, 38, 546–547. [CrossRef] 26. Huang, Y.; Xu, Y.; Yariv, A. Fabrication of Functional Microstructured Optical Fibers through a Selective-Filling Technique. Appl. Phys. Lett. 2004, 85, 5182–5184. [CrossRef] Photonics 2022, 9, 38 14 of 14 27. Xiao, L.; Jin, W.; Demokan, M.S.; Ho, H.L.; Hoo, Y.L.; Zhao, C. Fabrication of Selective Injection Microstructured Optical Fibers with a Conventional Fusion Splicer. Opt. Express 2005, 13, 9014. [CrossRef] 28. Cordeiro, C.M.B.; dos Santos, E.M.; Brito Cruz, C.H.; de Matos, C.J.; Ferreiira, D.S. Lateral Access to the Holes of Photonic Crystal Fibers–Selective Filling and Sensing Applications. Opt. Express 2006, 14, 8403. [CrossRef] 29. Wang, Y.; Liu, S.; Tan, X.; Jin, W. Selective-Fluid-Filling Technique of Microstructured Optical Fibers. J. Light. Technol. 2010, 28, 3193–3196. [CrossRef] 30. Wang, F.; Yuan, W.; Hansen, O.; Bang, O. Selective Filling of Photonic Crystal Fibers Using Focused Ion Beam Milled Microchannels. Opt. Express 2011, 19, 17585. [CrossRef] 31. Arif, M.F.H.; Asaduzzaman, S.; Ahmed, K.; Morshed, M. High Sensitive PCF Based Chemical Sensor for Ethanol Detection. In Proceedings of the 2016 5th International Conference on Informatics, Electronics and Vision (ICIEV), Dhaka, Bangladesh, 13–14 May 2016; pp. 6–9. [CrossRef] 32. Malitson, I.H. Interspecimen Comparison of the Refractive Index of Fused Silica*,†. J. Opt. Soc. Am. 1965, 55, 1205. [CrossRef] 33. Hale, G.M.; Querry, M.R. Bladder Cancers Respond to EGFR Inhibitors. Cancer Discov. 2014, 4, 980–981. [CrossRef] 34. Moutzouris, K.; Papamichael, M.; Betsis, S.C.; Stavrakas, I.; Hloupis, G.; Triantis, D. Refractive, Dispersive and Thermo-Optic Properties of Twelve Organic Solvents in the Visible and near-Infrared. Appl. Phys. B Lasers Opt. 2014, 116, 617–622. [CrossRef] 35. Akowuah, E.K.; Gorman, T.; Ademgil, H.; Haxha, S.; Robinson, G.K.; Oliver, J.V. Numerical Analysis of a Photonic Crystal Fiber for Biosensing Applications. IEEE J. Quantum Electron. 2012, 48, 1403–1410. [CrossRef] 36. Yakasai, I.K.; Abas, P.E.; Ali, S.; Begum, F. Modelling and Simulation of a Porous Core Photonic Crystal Fibre for Terahertz Wave Propagation. Opt. Quantum Electron. 2019, 51, 1–16. [CrossRef] 37. Yakasai, I.; Abas, P.E.; Kaijage, S.F.; Caesarendra, W.; Begum, F. Proposal for a Quad-Elliptical Photonic Crystal Fiber for Terahertz Wave Guidance and Sensing Chemical Warfare Liquids. Photonics 2019, 6, 78. [CrossRef] 38. Begum, F.; Abas, P.E. Near Infrared Supercontinuum Generation in Silica Based Photonic Crystal Fiber. Prog. Electromagn. Res. C 2019, 89, 149–159. [CrossRef] 39. Begum, F.; Namihira, Y.; Kinjo, T.; Kaijage, S. Supercontinuum Generation in Photonic Crystal Fibres at 1.06, 1.31, and 1.55m Wavelengths. Electron. Lett. 2010, 46, 1518–1520. [CrossRef] 40. Begum, F.; Namihira, Y.; Razzak, S.M.A.; Kaijage, S.F.; Hai, N.H.; Miyagi, K.; Higa, H.; Zou, N. Flattened Chromatic Dispersion in Square Photonic Crystal Fibers with Low Confinement Losses. Opt. 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Characteristics of Ultrasensitive Hexagonal-Cored Photonic Crystal Fiber for Hazardous Chemical Sensing

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hv photonics Article Characteristics of Ultrasensitive Hexagonal-Cored Photonic Crystal Fiber for Hazardous Chemical Sensing 1 , 1 2 3 1 Abdul Mu’iz Maidi *, Norazanita Shamsuddin , Wei-Ru Wong , Shubi Kaijage and Feroza Begum Faculty of Integrated Technologies, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong, Bandar Seri Begawan BE1410, Brunei; norazanita.shamsudin@ubd.edu.bn (N.S.); feroza.begum@ubd.edu.bn (F.B.) Department of Electrical Engineering, Faculty of Electrical Engineering, Universiti Malaya, Kuala Lumpur 50603, Malaysia; weiru@um.edu.my School of Computational and Communication Science and Engineering, Nelson Mandela African Institution of Science and Technology, Arusha 23311, Tanzania; shubi.kaijage@nm-aist.ac.tz * Correspondence: 17b4010@ubd.edu.bn Abstract: A highly sensitive non-complex cored photonic crystal fiber sensor for hazardous chemical sensing with water, ethanol, and benzene analytes has been proposed and is numerically analyzed using a full-vector finite element method. The proposed fiber consists of a hexagonal core hole and two cladding air hole rings, operating in the lower operating wavelength of 0.8 to 2.6 m. It has been shown that the structure has high relative sensitivity of 94.47% for water, 96.32% for ethanol and 9 10 99.63% for benzene, and low confinement losses of 7.31  10 dB/m for water, 3.70  10 dB/m ethanol and 1.76  10 dB/m benzene. It also displays a high power fraction and almost flattened chromatic dispersion. The results demonstrate the applicability of the proposed fiber design for chemical sensing applications. Keywords: photonic crystal fiber; chemical sensor; relative sensitivity; confinement loss Citation: Maidi, A.M.; Shamsuddin, N.; Wong, W.-R.; Kaijage, S.; Begum, F. Characteristics of Ultrasensitive 1. Introduction Hexagonal-Cored Photonic Crystal In both industry and academic sectors, photonic crystal fibers (PCFs) are one of the Fiber for Hazardous Chemical most interested research areas in the field of fiber optics. The huge popularity of PCF arises Sensing. Photonics 2022, 9, 38. from its characteristics of low loss in optical signal, more flexibility and lower weight [1]. https://doi.org/10.3390/ These benefits mean that various materials can be incorporated to form the structure of photonics9010038 the PCF to promote a photonic band gap and modified total internal reflection (m-TIR) Received: 10 December 2021 propagation mode due to the high refractive index difference. It, additionally, is not Accepted: 3 January 2022 restrained to communication applications but also can be effectively employed in different Published: 10 January 2022 promising applications, such as astronomy, security and imaging [2,3]. Moreover, PCF can Publisher’s Note: MDPI stays neutral be used in diverse chemical and biological sensing applications such as temperature [4], with regard to jurisdictional claims in pressure [5], mechanical [6], gas [7] and liquid [8] sensors. PCF can be employed as a sensor published maps and institutional affil- by incorporating the core air holes with different test analytes; thus, it is applicable in iations. various sectors. One of the most popular operations of PCF in the field of sensing includes its use as a chemical sensor, where a group of pioneering researchers have introduced diverse designs with varying performance over the years. A group of researchers [9] introduced a sensor design composed of three layers of Copyright: © 2022 by the authors. cladding air holes in a circular lattice with an array of elliptical holes as the core for Licensee MDPI, Basel, Switzerland. chemical sensing, with ethanol as the test analyte. The relative sensitivity was 29.25% and This article is an open access article confinement loss was in the order of 10 dB/m, acquired at 1.5 m operating wavelength. distributed under the terms and In reference [10], a hexagonal grid PCF sensor, with four cladding air hole rings and a conditions of the Creative Commons single core elliptical hole, for liquid detection with a water analyte, has been proposed. It Attribution (CC BY) license (https:// shows values of  = 1.3 m, low relative sensitivity of 41.37% and an order of 10 dB/m creativecommons.org/licenses/by/ for confinement loss. Bin Murshed Leon et al. [11] also proposed a PCF design with water 4.0/). Photonics 2022, 9, 38. https://doi.org/10.3390/photonics9010038 https://www.mdpi.com/journal/photonics Photonics 2022, 9, 38 2 of 14 as the test analyte. The design of the PCF structure consists of four rings of cladding air holes in a hexagonal arrangement and an array of nine circular holes designated as the core. Such a sensor design allowed a relative sensitivity of 44.45% and confinement loss of approximately 10 dB/m at a 1.3 m operating wavelength. The same research group [12] also introduced a design with four cladding air hole rings and four circular holes arranged as the core of the fiber, with a similar liquid analyte: water. At an optimum wavelength of 1.3 m, it results in a low relative sensitivity of 49.13% and confinement loss of order 10 dB/m. Islam et al. [13] suggested a chemical analyte sensor with water, ethanol and benzene, which yielded relative sensitivity results of 48.19%, 53.22% and 55.56% for water, ethanol and benzene, respectively, achieved at a wavelength of 1.3 m. Then, reference [14] reported relative sensitivities of 56.75% for water, 52.07% for ethanol and 58.86% for benzene and a confinement loss of approximately 10 dB/m for all the test analytes, at  = 1.33 m, with five ring cladding holes in an octagonal lattice and nine core holes in a square configuration, proposed as the PCF chemical sensor. A PCF structure with three cladding air hole rings has also been proposed by Maidi et al. [15]. In contrast to the comparatively simple chemical sensor with water, ethanol and benzene marked on the three elliptical core holes, the PCF exhibits decent results, with relative sensitivities of 62.60%, 65.34% and 74.50% for water, ethanol and benzene, respectively, with confinement 7 8 11 losses in the order of 10 dB/m, 10 dB/m and 10 dB/m for water, ethanol and benzene, respectively, at  = 1.3 m. Notably, a group of researchers [16] recommended an impressively performing PCF structure of one hexagonal core and five cladding rings in a circular form for chemical sensing, demonstrating high relative sensitivities. Relative sensitivities of 88.93%, 91.87% and 97.89% were achieved for water, ethanol and benzene, respectively, and the confinement losses for the PCF were in the order of approximately 10 dB/m for all test analytes. These values were obtained at an optimum wavelength of 1.55 m. In the literature [9–16], researchers focused on implementing elaborative PCF structures, which consist of intricate core designs and multiple layers of cladding holes to produce good outcomes in the simulated optical parameters. With such expressive designs, this increases the difficulty of manufacturing the PCFs and may affect the sensing results due to the fabrication tolerances. Fabrication of PCFs is subject to manufacturing errors and prone to issues such as inaccuracy of hole sizes due to the irregular shape and positioning of the desired holes [17,18]. Furthermore, a single inaccuracy in an air hole will affect surrounding air holes as well, which can be problematic in elaborate designs with intricate fiber core structures and numerous air holes [19]. In this work, a noncomplex PCF structure is proposed that maintain impressive results of optical properties, particularly its relative sensitivity and confinement loss. Results of the effective refractive index, relative sensitivity, power fraction, confinement loss and chromatic dispersion are investigated, as well, over the infrared region from 0.8 to 2.6 m operating wavelength. Water, ethanol and benzene are selected as the test analytes for the study. 2. Design The sensing principles for PCF sensors are based on the interaction between the optical signal and the analyte in the propagation core region [20]. The evanescent field of light is imposed on the PCF and extends to the located analyte to be sensed. The presence of cladding air holes allows near-total confinement of light to promote sufficient light–analyte interaction. Thus, an appropriate geometry of the proposed PCF sensor was configured and is presented in Figure 1, which consists of a core, cladding and the perfectly matched layer (PML). Silica was chosen for the background material established for the cladding and PML, marked in red and blue colors, respectively. Likewise, the white color indicates air for the cladding air holes and the test analytes are shown in yellow at the core. Photonics 2022, 9, x FOR PEER REVIEW 3 of 15 The core of the fiber is a hollow hexagonal hole, where the selective test analyte is suggested to be administered for chemical sensing. The corner-to-corner length of the hex- agonal hole is denoted as l. The cladding consists of multiple air holes positioned through- out its region, and each circular air hole is denoted as d. To offer a symmetrical design, the cladding holes are situated equidistantly from each other, with a pitch distance denoted as Λ = 3.0 µm and air-filling fraction (AFF) of 0.97. The cladding has a total of 18 air holes arranged in 2 rings. The PML is imposed on the fiber structure to absorb light leaked from the core and cladding region. The dimension of the core l = 3.32 µm, and the diameter of each cladding air hole d = 2.91 µm. The PML is enhanced to be 10% of the fiber diameter to meet the boundary condition. The proposed PCF sensor can detect various chemical analytes; however, the selected test analytes in this paper are water, ethanol and benzene. The air-filling fraction of the cladding is kept at a high value to acquire an optically dense Photonics 2022, 9, 38 3 of 14 core compared to the cladding, which preserves the modified total internal reflection (m- TIR) as the guiding mechanism. Figure 1. Schematic of the design proposed for the PCF. Figure 1. Schematic of the design proposed for the PCF. The core of the fiber is a hollow hexagonal hole, where the selective test analyte is There are various possible fabrication methods that have been introduced, such as suggested to be administered for chemical sensing. The corner-to-corner length of the the sol–gel technique [21], stacking [22], drilling [23], 3D printing [24] and extrusion [25]. hexagonal hole is denoted as l. The cladding consists of multiple air holes positioned The fabrication of this PCF sensor design can be performed using the extrusion method throughout its region, and each circular air hole is denoted as d. To offer a symmetrical as it allows the fabrication of intricate designs with high accuracy. Additionally, the infil- design, the cladding holes are situated equidistantly from each other, with a pitch distance tration of the test chemical analyte into the hollow holes can be achieved by using the denoted as L = 3.0 m and air-filling fraction (AFF) of 0.97. The cladding has a total of selective infiltration technique, which has been experimentally introduced by researchers 18 air holes arranged in 2 rings. The PML is imposed on the fiber structure to absorb light [26–30]. This technique is capable of injecting liquids into the micro-structured core and leaked from the core and cladding region. The dimension of the core l = 3.32 m, and the cladding holes in the PCF. Numerous methods for injecting liquid analytes have been diameter of each cladding air hole d = 2.91 m. The PML is enhanced to be 10% of the fiber proposed by researchers throughout the years, including the multi-step injection-cure- diameter to meet the boundary condition. The proposed PCF sensor can detect various cleave process [26], fusion splicer [27], lateral filling [28], femtosecond laser micromachin- chemical analytes; however, the selected test analytes in this paper are water, ethanol ing [29] and focused ion beam micromachining [30]. and benzene. The air-filling fraction of the cladding is kept at a high value to acquire an optically dense core compared to the cladding, which preserves the modified total internal reflection (m-TIR) as the guiding mechanism. There are various possible fabrication methods that have been introduced, such as the sol–gel technique [21], stacking [22], drilling [23], 3D printing [24] and extrusion [25]. The fabrication of this PCF sensor design can be performed using the extrusion method as it allows the fabrication of intricate designs with high accuracy. Additionally, the infiltration of the test chemical analyte into the hollow holes can be achieved by using the selective infiltration technique, which has been experimentally introduced by researchers [26–30]. This technique is capable of injecting liquids into the micro-structured core and cladding holes in the PCF. Numerous methods for injecting liquid analytes have been proposed by researchers throughout the years, including the multi-step injection-cure-cleave process [26], fusion splicer [27], lateral filling [28], femtosecond laser micromachining [29] and focused ion beam micromachining [30]. 3. Methodology A simulation of the proposed PCF has been conducted applying the full-vector finite element method (FV-FEM) for numerical analysis using COMSOL Multiphysics software version 5.5. A finer meshing type has been selected for the design to be correctly mapped. Photonics 2022, 9, x FOR PEER REVIEW 4 of 15 3. Methodology A simulation of the proposed PCF has been conducted applying the full-vector finite element method (FV-FEM) for numerical analysis using COMSOL Multiphysics software Photonics 2022, 9, 38 4 of 14 version 5.5. A finer meshing type has been selected for the design to be correctly mapped. The complete mesh consists of 14,370 triangular elements, 1352 edge elements and 86 ver- tex elements. The proposed PCF is intended for detecting chemicals, particularly water, The complete mesh consists of 14,370 triangular elements, 1352 edge elements and 86 vertex ethanol and benzene. Figure 2 shows the refractive index of silica and the test analytes elements. The proposed PCF is intended for detecting chemicals, particularly water, ethanol (water, ethanol and benzene) with respect to a micrometer wavelength of 0.8–2.6 µm [31– and benzene. Figure 2 shows the refractive index of silica and the test analytes (water, 34]. ethanol and benzene) with respect to a micrometer wavelength of 0.8–2.6 m [31–34]. Figure 2. Figure 2.Refra Refractive ctive index index of of silica silica and and test test analy analytes, tes, watwater er, ethanol and b , ethanol and enzene, at benzene, 0.8–2 at 0.8–2.6 .6 µm op- m erating wavelength [31–34]. operating wavelength [31–34]. Evaluation of the performance and practicability of the proposed PCF design is con- Evaluation of the performance and practicability of the proposed PCF design is con- ducted through investigating the respective optical properties: effective refractive index, ducted through investigating the respective optical properties: effective refractive index, relative sensitivity, power fraction, confinement loss and chromatic dispersion. relative sensitivity, power fraction, confinement loss and chromatic dispersion. With silica as the background material, hollow air holes and core holes that have been With silica as the background material, hollow air holes and core holes that have been set with the test analytes, the effective refractive index n can be quantified and modeled set with the test analytes, the effective refractive index neff ef can f be quantified and modeled using Sellmeier ’s equation given by [35]: using Sellmeier’s equation given by [35]: 2 2 2 B l B l B l 𝐵 𝜆 𝐵 𝜆 𝐵 𝜆 1 2 3 n (l) = 1 + + + (1) (1) 𝑛 ef(𝜆 f) = 1+ + + 2 2 2 l C l C l C 𝜆 −𝐶 1𝜆 −𝐶 𝜆 2 −𝐶 3 where l is the operating wavelength and B and C (i = 1,2 and 3) are the Sellmeier coeffi- i i where λ is the operating wavelength and Bi and Ci (i = 1,2 and 3) are the Sellmeier coeffi- cients for the specific material. cients for the specific material. Relative sensitivity S determines the practicability of the PCF sensor to detect analytes Relative sensitivity S determines the practicability of the PCF sensor to detect ana- by matching the refractive indices and achieved by measuring the light intensity that lytes by matching the refractive indices and achieved by measuring the light intensity that interacts with the analyte to be detected. It is defined as [15,36,37]: interacts with the analyte to be detected. It is defined as [15,36,37]: S =  P (2) 𝑆= ×𝑃 n (2) eff where n is the refractive index of the sensed material and P is the power fraction. The variation in relative sensitivity is closely related to the effective refractive index and power fraction. Power fraction P is a measure of the amount of power flowing through the PCF at a specific region, and it is defined as the ratio of power in a chemical-filled region to that of the total fiber by integration. It is expressed by Poynting’s theorem as [15,36,37]: (sample) Re E H E H dxdy x y y x P =  100 (3) total Re E H E H dxdy ( ) x y y x Photonics 2022, 9, x FOR PEER REVIEW 5 of 15 where nr is the refractive index of the sensed material and P is the power fraction. The variation in relative sensitivity is closely related to the effective refractive index and power fraction. Power fraction P is a measure of the amount of power flowing through the PCF at a specific region, and it is defined as the ratio of power in a chemical-filled region to that of the total fiber by integration. It is expressed by Poynting’s theorem as [15,36,37]: (𝑠𝑎𝑚𝑝𝑙𝑒) 𝐻 −𝐸 𝐻 Photonics 2022, 9, 38 5 of 14 𝑃= × 100 (3) ( ) 𝑡𝑜𝑡𝑎𝑙 𝐻 −𝐸 𝐻 where Ex, Ey and Hx, Hy are the transverse electric and magnetic fields of the guided mode, where E , E and H , H are the transverse electric and magnetic fields of the guided mode, x y x y respectively. The integral in the numerator is selected over the analyte at the core, whilst respectively. The integral in the numerator is selected over the analyte at the core, whilst the integral in the denominator is over all fiber regions. the integral in the denominator is over all fiber regions. Confinement loss Lc describes the phenomenon of leakage of light from the core to Confinement loss L describes the phenomenon of leakage of light from the core to the the cladding, contributed by the structural design of the fiber. It quantifies the portion of cladding, contributed by the structural design of the fiber. It quantifies the portion of light light loss from the core area to the cladding, and is defined as [38–40]: loss from the core area to the cladding, and is defined as [38–40]: 40𝜋 𝐿 = Im 𝑛 ×10 (4) 40p ln (10)𝜆 L = Im[n ]  10 (4) c eff ln(10)l where Im[neff] is the imaginary part of the effective mode index. The variations in the op- where Im[n ] is the imaginary part of the effective mode index. The variations in the eff erating wavelength and effective refractive index determine the confinement loss. operating wavelength and effective refractive index determine the confinement loss. Chromatic dispersion D is a measure of the light-guiding capabilities of the fiber and Chromatic dispersion D is a measure of the light-guiding capabilities of the fiber and the degradation of the mode in the fiber. It is defined as [10,38,40]: the degradation of the mode in the fiber. It is defined as [10,38,40]: 𝜆 𝑑 (5) 𝐷= − l d D =𝑐 𝑑𝜆 Re[n ] (5) eff c dl where c is the speed of light and Re[neff] is the real part of the effective refractive index. where c is the speed of light and Re[n ] is the real part of the effective refractive index. eff 4. Results and Discussion 4. Results and Discussion Figure 3 illustrates the mode profiles for the different chemical-infiltrated analytes in Figure 3 illustrates the mode profiles for the different chemical-infiltrated analytes in the core, with an operating wavelength of 1.3 µm. The interaction of light occurs through the core, with an operating wavelength of 1.3 m. The interaction of light occurs through the core region, with the mode field completely confined at the core for all three test ana- the core region, with the mode field completely confined at the core for all three test analytes: lytes: water, ethano water, ethanol l and benzene. and benzene. (a) (b) (c) Figure 3. Mode profile of the proposed PCF for (a) water, (b) ethanol and (c) benzene. Figure 3. Mode profile of the proposed PCF for (a) water, (b) ethanol and (c) benzene. Theor Theoret etically ically, , the theef ef ffec ective tiver efractive refractive index index decr decre eases ases with with an an incr inc ease rease in in the th operating e operat- wavelength, ing wavelengand th, and a a similar similar tren trend is d established is established as well for the as well for the pr pr oposed oposed PCF PCF shown shown in in Figure 4, with the effective refractive index declining as the operating wavelength is Figure 4, with the effective refractive index declining as the operating wavelength is in- incr creas eased, ed, for for all allthe the se selected lected an analytes: alytes: w water ater, ,eth ethanol anol and ben and benzene. zene. This behav This behavior ior ar arises ises where smaller electromagnetic wavelengths propagate through the high refractive index where smaller electromagnetic wavelengths propagate through the high refractive index region. Moreover, it can be observed that the effective refractive index of water is the lowest, region. Moreover, it can be observed that the effective refractive index of water is the followed by ethanol and benzene, being the highest, as established from their respective refractive indices, as seen in Figure 2. It can be seen from Figure 5 that the relative sensitivity for benzene decreases over the scale of set wavelengths from 0.8 to 2.6 m; however, the trend for water and ethanol increases from 0.8 to 1.3 m and then subsequently decreases as the wavelength is increased further. Relative sensitivity is closely related to the effective refractive index and power fraction; hence, benzene has the highest relative sensitivity, followed by ethanol and water. At the operating wavelength of 1.3 m, relative sensitivities are 94.47%, 96.32% and 99.63% for water, ethanol and benzene, respectively. Since the operating wavelength of 1.3 m yielded the optimum relative sensitivities for water and ethanol, other optical properties 𝑛𝑅𝑒 𝑑𝑥𝑑𝑦 𝐸𝑅𝑒 𝑑𝑥𝑑𝑦 𝐸𝑅𝑒 Photonics 2022, 9, x FOR PEER REVIEW 6 of 15 lowest, followed by ethanol and benzene, being the highest, as established from their re- spective refractive indices, as seen in Figure 2. It can be seen from Figure 5 that the relative sensitivity for benzene decreases over the scale of set wavelengths from 0.8 to 2.6 µm; however, the trend for water and ethanol increases from 0.8 to 1.3 µm and then subsequently decreases as the wavelength is in- creased further. Relative sensitivity is closely related to the effective refractive index and power fraction; hence, benzene has the highest relative sensitivity, followed by ethanol Photonics 2022, 9, 38 and water. At the operating wavelength of 1.3 µm, relative sensitivities are 94.47%, 96.32% 6 of 14 and 99.63% for water, ethanol and benzene, respectively. Since the operating wavelength of 1.3 µm yielded the optimum relative sensitivities for water and ethanol, other optical properties for the proposed PCF were considered at this optimum wavelength. Moreover, for the proposed PCF were considered at this optimum wavelength. Moreover, as seen as seen from Figure 1, the dimension of the core hole is larger than the surrounding air from Figure 1, the dimension of the core hole is larger than the surrounding air holes in holes in the cladding, which allows more test analyte to be injected into the core hole; this the cladding, which allows more test analyte to be injected into the core hole; this leads to leads to a stronger interaction between light and the test analyte. Hence, the PCF leads to a stronger interaction between light and the test analyte. Hence, the PCF leads to higher higher relative sensitivity. relative sensitivity. Photonics 2022, 9, x FOR PEER REVIEW 7 of 15 Figure 4. Effective refractive index of the proposed design against operating wavelength for water, Figure 4. Effective refractive index of the proposed design against operating wavelength for water, ethanol and benzene. ethanol and benzene. Figure 5. Proposed PCF sensor results for relative sensitivity with respect to wavelength for water, Figure 5. Proposed PCF sensor results for relative sensitivity with respect to wavelength for water, ethanol and benzene. ethanol and benzene. Figure 6 shows the power fraction of the proposed PCF sensor against different op- Figure 6 shows the power fraction of the proposed PCF sensor against different erating wavelengths for water, ethanol and benzene. The amount of power flowing operating wavelengths for water, ethanol and benzene. The amount of power flowing through at the core of the PCF is quantified with this property. It can be seen that the through at the core of the PCF is quantified with this property. It can be seen that the power power fractions for water and ethanol present an increasing behavior initially as the op- fractions for water and ethanol present an increasing behavior initially as the operating erating wavelength increases between 0.8 and 1.3 µm, before drastically decreasing with further increases in the operating wavelength, whereas the power fraction trend for ben- zene decreases as the wavelength increases. The decreasing behavior results in optical power leaks from the core region to the surrounding cladding as the wavelength in- creases. The proposed PCF yields power fractions of 92.91%, 94.64% and 97.84% for water, ethanol and benzene, respectively, at a wavelength of 1.3 µm. Figure 6. Power fraction of the PCF sensor with respect to wavelength for water, ethanol and ben- zene. Photonics 2022, 9, x FOR PEER REVIEW 7 of 15 Figure 5. Proposed PCF sensor results for relative sensitivity with respect to wavelength for water, ethanol and benzene. Figure 6 shows the power fraction of the proposed PCF sensor against different op- erating wavelengths for water, ethanol and benzene. The amount of power flowing Photonics 2022, 9, 38 7 of 14 through at the core of the PCF is quantified with this property. It can be seen that the power fractions for water and ethanol present an increasing behavior initially as the op- erating wavelength increases between 0.8 and 1.3 µm, before drastically decreasing with wavelength increases between 0.8 and 1.3 m, before drastically decreasing with further further increases in the operating wavelength, whereas the power fraction trend for ben- increases in the operating wavelength, whereas the power fraction trend for benzene zene decreases as the wavelength increases. The decreasing behavior results in optical decreases as the wavelength increases. The decreasing behavior results in optical power power leaks from the core region to the surrounding cladding as the wavelength in- leaks from the core region to the surrounding cladding as the wavelength increases. The creases. The proposed PCF yields power fractions of 92.91%, 94.64% and 97.84% for water, proposed PCF yields power fractions of 92.91%, 94.64% and 97.84% for water, ethanol and ethanol and benzene, respectively, at a wavelength of 1.3 µm. benzene, respectively, at a wavelength of 1.3 m. Figure 6. Power fraction of the PCF sensor with respect to wavelength for water, ethanol and ben- Figure 6. Power fraction of the PCF sensor with respect to wavelength for water, ethanol and benzene. zene. Figure 7 demonstrates the relationship between confinement loss and operating wave- length. Confinement loss is a measure of light leakage from the core to the cladding, and, in theory, confinement losses generally increase as light tends to leak out of the cladding with respect to the increase in operating wavelength; this characteristic can be seen in the 9 10 figure. Confinement losses are 7.31  10 dB/m for water, 3.70  10 dB/m for ethanol and 1.76  10 dB/m for benzene, at an operating wavelength of 1.3 m. Furthermore, with the benefit of a definite hexagonal core and surrounding air hole configuration, it influences the careful confinement of light, as seen in the results. Figure 8 shows the relationship between the chromatic dispersion of the proposed PCF and the operating wavelength with water, ethanol and benzene. It can be observed that the obtained dispersion is especially low and nearly flattened for all test analytes. This indicates a good result in the interaction between the light signal and the chemical analytes. At a 1.3 m wavelength, the chromatic dispersions are 0.0053 ps/nm.km for water, 0.0049 ps/nm.km for ethanol and 0.0045 ps/nm.km for benzene. This evaluation of chromatic dispersions is achieved due to the narrow width of the waveguide. Additionally, regarding the fabrication of the proposed PCF sensor, a tolerance analysis is performed by varying the global parameters—the pitch and diameter of the holes—and examining the effects on the variations in the optical properties: relative sensitivity and con- finement loss. Analyses in the order of 1%, 2% and 4% are applied on the parameters of the proposed PCF, which is shown in Table 1. A very small effect is seen on the optical properties. In terms of the values of relative sensitivities and confinement losses, they decrease as the percentage variations are increased and they increase when the variations are decreased. Photonics 2022, 9, x FOR PEER REVIEW 8 of 15 Figure 7 demonstrates the relationship between confinement loss and operating wavelength. Confinement loss is a measure of light leakage from the core to the cladding, and, in theory, confinement losses generally increase as light tends to leak out of the clad- ding with respect to the increase in operating wavelength; this characteristic can be seen −9 −10 in the figure. Confinement losses are 7.31 × 10 dB/m for water, 3.70 × 10 dB/m for eth- −13 anol and 1.76 × 10 dB/m for benzene, at an operating wavelength of 1.3 µm. Further- more, with the benefit of a definite hexagonal core and surrounding air hole configuration, it influences the careful confinement of light, as seen in the results. Figure 8 shows the relationship between the chromatic dispersion of the proposed PCF and the operating wavelength with water, ethanol and benzene. It can be observed that the obtained dispersion is especially low and nearly flattened for all test analytes. This indicates a good result in the interaction between the light signal and the chemical analytes. At a 1.3 µm wavelength, the chromatic dispersions are −0.0053 ps/nm.km for Photonics 2022, 9, 38 8 of 14 water, −0.0049 ps/nm.km for ethanol and −0.0045 ps/nm.km for benzene. This evaluation of chromatic dispersions is achieved due to the narrow width of the waveguide. Photonics 2022, 9, x FOR PEER REVIEW 9 of 15 Figure 7. Confinement loss of the PCF sensor with respect to wavelength for water, ethanol and Figure 7. Confinement loss of the PCF sensor with respect to wavelength for water, ethanol and benzene. benzene. Figure 8. Figure C 8.hChr rom omatic atic dispersi dispersion on of the propos of the proposed ed de design sign with with respect respectto wav to wavelength elength for water, etha- for water, ethanol nol and benzene. and benzene. Table 1. Comparison among the variation in global parameters on optimum parameters at  = 1.3 m. Additionally, regarding the fabrication of the proposed PCF sensor, a tolerance anal- ysis is performed by varying the global parameters—the pitch and diameter of the holes— Relative Sensitivity (%) Confinement Loss (dB/m) and examining the effects on the variations in the optical properties: relative sensitivity Change in Global Parameters Water Ethanol Benzene Water Ethanol Benzene and confinement loss. Analyses in the order of ±1%, ±2% and ±4% are applied on the pa- 9 10 14 rameters of the proposed PCF, which is shown in Table 1. A very small effect is seen on +4% 94.40 96.32 99.64 2.60  10 1.05  10 7.62  10 9 10 13 the optical properties. In terms of the values of relative sensitivities and confinement +2% 94.44 96.32 99.63 4.37  10 1.78  10 1.28  10 9 10 13 +1% 94.46 96.32 99.63 5.58  10 2.71  10 1.72  10 losses, they decrease as the percentage variations are increased and they increase when 9 10 13 Optimum 94.47 96.32 99.63 7.31  10 3.70  10 1.76  10 the variations are decreased. 9 10 13 1% 94.49 96.31 99.63 9.54  10 4.62  10 4.82  10 8 10 13 2% 94.50 96.31 99.62 1.25  10 6.78  10 5.46  10 Table 1. Comparison among the variation in global parameters on optimum parameters at λ = 1.3 8 9 13 4% 94.51 96.30 99.62 2.16  10 1.25  10 6.71  10 µm. Relative Sensitivity (%) Confinement Loss (dB/m) Change in Global Parameters Water Ethanol Benzene Water Ethanol Benzene −9 −10 −14 +4% 94.40 96.32 99.64 2.60 × 10 1.05 × 10 7.62 × 10 −9 −10 −13 +2% 94.44 96.32 99.63 4.37 × 10 1.78 × 10 1.28 × 10 −9 −10 −13 +1% 94.46 96.32 99.63 5.58 × 10 2.71 × 10 1.72 × 10 −9 −10 −13 Optimum 94.47 96.32 99.63 7.31 × 10 3.70 × 10 1.76 × 10 −9 −10 −13 −1% 94.49 96.31 99.63 9.54 × 10 4.62 × 10 4.82 × 10 −8 −10 −13 −2% 94.50 96.31 99.62 1.25 × 10 6.78 × 10 5.46 × 10 −8 −9 −13 −4% 94.51 96.30 99.62 2.16 × 10 1.25 × 10 6.71 × 10 Figure 9a–c show the relative sensitivity variations of order ±1%, ±2% and ±4% for water, ethanol and benzene, respectively. Meanwhile, Figure 10a–c illustrate the varia- tions in confinement loss in the order of ±1%, ±2% and ±4% for water, ethanol and benzene, respectively. With such modification made to the dimensions of the pitch and air holes’ diameter, Figures 9 and 10 demonstrate minute alterations in the results of the optical properties. Photonics 2022, 9, 38 9 of 14 Figure 9a–c show the relative sensitivity variations of order 1%, 2% and 4% for water, ethanol and benzene, respectively. Meanwhile, Figure 10a–c illustrate the vari- ations in confinement loss in the order of 1%, 2% and 4% for water, ethanol and Photonics 2022, 9, x FOR PEER REVIEW 10 of 15 benzene, respectively. With such modification made to the dimensions of the pitch and air holes’ diameter, Figures 9 and 10 demonstrate minute alterations in the results of the optical properties. (a) (b) Figure 9. Cont. Photonics 2022, 9, x FOR PEER REVIEW 11 of 15 Photonics 2022, 9, x FOR PEER REVIEW 11 of 15 Photonics 2022, 9, 38 10 of 14 (c) (c) Figure 9. (a) Tolerance analysis of relative sensitivity for water in the variations of ±1%, ±2% and Figure 9. ±4%. (b) To (a) Figure T lera olerance analy nce analy 9. (a) Tolerance sis of sis of relative analysis relat sens ive of s relative e iti nsitiv vity fo sensitivity ity r e for thanol in the water in for water the v variatio in the ariations variations ns of ±1% of ±1 of , ±2% %, ±2% 1%, and ±4%.  and 2% and ±4%. ( (c) To b) To lerance a lera 4%. nce analy n (alysis o b) Tolerance sf i relat s ofanalysis relative ive sen of sens sitivity f relative itivity sensitivity or benzene in t for ethanol in the for ethanol he variations o in variatio the variations ns of ±1% f ±1%, ±2% and ±4%. of  , ±2% 1%, and ±4%. 2% and 4%. (c) Tolerance a (c) T nolerance alysis ofanalysis relative sen of relative sitivity f sensitivity or benzene in t for benzene he variations o in the variations f ±1%, ±2% and ±4%. of 1%, 2% and 4%. (a) (a) Figure 10. Cont. Photonics 2022, 9, x FOR PEER REVIEW 12 of 15 Photonics 2022, 9, 38 11 of 14 (b) (c) Figure 10. Figure (a) Tolerance analysis of 10. (a) Tolerance analysis confine of confinement ment loss for loss for water in the variations of ±1 water in the variations of 1%, %, ±2% and 2% and 4%. (b) Tolerance analysis of confinement loss for ethanol in the variations of 1%, 2% and 4%. ±4%. (b) Tolerance analysis of confinement loss for ethanol in the variations of ±1%, ±2% and ±4%. (c) Tolerance analysis of confinement loss for benzene in the variations of 1%, 2% and 4%. (c) Tolerance analysis of confinement loss for benzene in the variations of ±1%, ±2% and ±4%. Lastly, a comparison between prior PCF chemical sensors and the proposed PCF Lastly, a comparison between prior PCF chemical sensors and the proposed PCF de- design is presented in Table 2. It can be observed from the table that the proposed PCF has sign is presented in Table 2. It can be observed from the table that the proposed PCF has a comparatively simple layout of a single core hole with two cladding rings, in contrast a comparatively simple layout of a single core hole with two cladding rings, in contrast to to the prior PCFs with additional cladding rings and intricate core designs. With regard the prior PCFs with additional cladding rings and intricate core designs. With regard to to the design, the proposed PCF demonstrates the highest relative sensitivity and low the design, the proposed PCF demonstrates the highest relative sensitivity and low con- finement loss, with all the chemical analytes. Therefore, the novelty of the proposed PCF is the simplicity of design, which aids in the ease of fabrication and leads to better numer- ically analyzed results. Photonics 2022, 9, 38 12 of 14 confinement loss, with all the chemical analytes. Therefore, the novelty of the proposed PCF is the simplicity of design, which aids in the ease of fabrication and leads to better numerically analyzed results. Table 2. Comparison of structure and performance among prior PCFs and proposed PCF at  = 1.3 m. Structure Relative Confinement No. of Rings Sensitivity (%) Loss (dB/m) Core Cladding Ref. [9] 3 6 core holes Circular holes in circle 26.23 (E) ~10 (E) Ref. [10] 4 1 core hole Circular holes in hexagon 41.37 (W) ~10 (W) Ref. [11] 4 9 core holes Circular holes in hexagon 44.45 (W) ~10 (W) Ref. [12] 4 4 core holes Circular holes in hexagon 49.13 (W) ~10 (W) 48.19 (W) Ref. [13] 3 7 core holes Circular holes in hexagon 53.22 (E) - 55.56 (B) 52.07 (W) ~10 (W) Ref. [14] 5 9 core holes Circular holes in octagon 56.75 (E) ~10 (E) 58.86 (B) ~10 (B) 62.60 (W) ~10 (W) Ref. [15] 3 3 core holes Circular holes in hexagon 65.34 (E) ~10 (E) 74.50 (B) ~10 (B) 90.14 (W) ~10 (W) Ref. [16] 5 1 core hole Circular holes in hexagon 93.85 (E) ~10 (E) 98.11 (B) ~10 (B) 94.47 (W) ~10 (W) Proposed PCF 2 1 core hole Circular holes in hexagon 96.32 (E) ~10 (E) 99.63 (B) ~10 (B) where W refers to water, E refers to ethanol and B refers to benzene. 5. Conclusions The proposal of a simple PCF sensor for hazardous chemical detection has been intro- duced, which is composed of a single hexagonal hole for the core and 18 imposed cladding air holes, positioned in a hexagon-shaped lattice. Operating at the lower wavelengths of 0.8–2.6 m, the designed chemical sensor with water, ethanol and benzene has been numerically analyzed with the aid of a FV-FEM simulation method on COMSOL Multi- physics to investigate its optical properties: effective refractive index, relative sensitivity, power fraction, confinement loss and chromatic dispersion. The optimum results have been obtained at a 1.3 m operating wavelength, with high relative sensitivities of 94.47%, 96.32% and 99.63% for water, ethanol and benzene, respectively, and confinement losses 9 10 13 of 7.31  10 dB/m, 3.70  10 dB/m and 1.76  10 dB/m for water, ethanol and benzene, respectively. The investigated results are noteworthy as they indicate the practica- bility of the proposed PCF for sensing applications in the medical sector, chemical industry, security and defense by sensing unknown analytes, as well as in optical communication through the desirable results of chromatic dispersion. Furthermore, this research shall potentially proceed to fabrication and experimental testing as future work. Author Contributions: Conceptualization, A.M.M. and F.B.; methodology, A.M.M. and F.B.; software, A.M.M., S.K. and F.B.; validation, W.-R.W. and F.B.; formal analysis, A.M.M. and F.B.; investigation, A.M.M. and F.B.; resources, F.B.; data curation, A.M.M. and F.B.; writing—original draft preparation, A.M.M.; writing—review and editing, W.-R.W. and F.B.; visualization, F.B.; supervision, F.B.; project administration, F.B.; funding acquisition, F.B. and N.S. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by UNIVERSITI BRUNEI DARUSSALAM, grant number UBD/RSCH/1.3/FICBF(b)/2019/008. Institutional Review Board Statement: Not applicable. Photonics 2022, 9, 38 13 of 14 Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest. References 1. Habib, A.; Anower, S.; Haque, I. Highly Sensitive Hollow Core Spiral Fiber for Chemical Spectroscopic Applications. Sens. Int. 2020, 1, 100011. [CrossRef] 2. Abbott, D.; Zhang, X.C. Scanning the Issue: T-Ray Imaging, Sensing, and Retection. Proc. IEEE 2007, 95, 1509–1513. [CrossRef] 3. Habib, M.A.; Reza, M.S.; Abdulrazak, L.F.; Anower, M.S. Extremely High Birefringent and Low Loss Microstructure Optical Waveguide: Design and Analysis. Opt. Commun. 2019, 446, 93–99. [CrossRef] 4. Chang, Y.H.; Jhu, Y.Y.; Wu, C.J. Temperature Dependence of Defect Mode in a Defective Photonic Crystal. Opt. Commun. 2012, 285, 1501–1504. [CrossRef] 5. Bock, W.J.; Jiahua, C.; Eftimov, T.; Urbanczyk, W. A Photonic Crystal Fiber Sensor for Pressure Measurements. Conf. Rec.-IEEE Instrum. Meas. Technol. Conf. 2005, 2, 1177–1181. [CrossRef] 6. Chengkuo, L.; Thillaigovindan, J. Optical Nanomechanical Sensor Using a Silicon Photonic Crystal Cantilever Embedded with a Nanocavity Resonator. Appl. Opt. 2009, 48, 1797–1803. [CrossRef] 7. Morshed, M.; Imran Hassan, M.; Roy, T.K.; Uddin, M.S.; Abdur Razzak, S.M. Microstructure Core Photonic Crystal Fiber for Gas Sensing Applications. Appl. Opt. 2015, 54, 8637. [CrossRef] 8. Ademgil, H.; Haxha, S. PCF Based Sensor with High Sensitivity, High Birefringence and Low Confinement Losses for Liquid Analyte Sensing Applications. Sensors 2015, 15, 31833–31842. [CrossRef] 9. Asaduzzaman, S.; Ahmed, K. Microarray-Core Based Circular Photonic Crystal Fiber for High Chemical Sensing Capacity with Low Confinement Loss. Opt. Appl. 2017, 47, 41–49. [CrossRef] 10. Arif, M.F.H.; Hossain, M.M.; Islam, N.; Khaled, S.M. A Nonlinear Photonic Crystal Fiber for Liquid Sensing Application with High Birefringence and Low Confinement Loss. Sens. Bio-Sens. Res. 2019, 22, 100252. [CrossRef] 11. Bin Murshed Leon, M.J.; Abedin, S.; Kabir, M.A. A Photonic Crystal Fiber for Liquid Sensing Application with High Sensitivity, Birefringence and Low Confinement Loss. Sens. Int. 2021, 2, 100061. [CrossRef] 12. Leon, M.J.B.M.; Kabir, M.A. Design of a Liquid Sensing Photonic Crystal Fiber with High Sensitivity, Bireferingence & Low Confinement Loss. Sens. Bio-Sens. Res. 2020, 28, 100335. [CrossRef] 13. Islam, S.; Kumar, B.; Ahmed, K. Liquid-Infiltrated Photonic Crystal Fiber for Sensing Purpose: Design and Analysis. Alexandria Eng. J. 2018, 57, 1459–1466. [CrossRef] 14. Ahmed, K.; Morshed, M.; Asaduzzaman, S.; Arif, M.F.H. Optimization and Enhancement of Liquid Analyte Sensing Performance Based on Square-Cored Octagonal Photonic Crystal Fiber. Optik 2017, 131, 687–696. [CrossRef] 15. Maidi, A.M.; Yakasai, I.; Abas, P.E.; Nauman, M.M.; Apong, R.A.; Kaijage, S.; Begum, F. Design and Simulation of Photonic Crystal Fiber for Liquid Sensing. Photonics 2021, 8, 16. [CrossRef] 16. Eid, M.M.A.; Habib, M.A.; Anower, M.S.; Rashed, A.N.Z. Highly Sensitive Nonlinear Photonic Crystal Fiber Based Sensor for Chemical Sensing Applications. Microsyst. Technol. 2020, 27, 1007–1014. [CrossRef] 17. Buczynski, R. Photonic Crystal Fibers. Acta Phys. Pol. Ser. A 2004, 106, 141–167. [CrossRef] 18. Wang, P.; Farrell, G.; Semenova, Y.; Rajan, G. Influence of Fiber Manufacturing Tolerances on the Spectral Response of a Bend Loss Based All-Fiber Edge Filter. Appl. Opt. 2008, 47, 2921. [CrossRef] 19. Amouzad Mahdiraji, G.; Chow, D.M.; Sandoghchi, S.R.; Amirkhan, F.; Dermosesian, E.; Yeo, K.S.; Kakaei, Z.; Ghomeishi, M.; Poh, S.Y.; Yu Gang, S.; et al. Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study. Fiber Integr. Opt. 2014, 33, 85–104. [CrossRef] 20. Lee, H.W.; Schmidt, M.A.; Uebel, P.; Tyagi, H.; Joly, N.Y.; Scharrer, M.; Russell, P.S.J. Optofluidic Refractive-Index Sensor in Step-Index Fiber with Parallel Hollow Micro-Channel. Opt. Express 2011, 19, 8200. [CrossRef] [PubMed] 21. El Hamzaoui, H.; Ouerdane, Y.; Bigot, L.; Bouwmans, G.; Capoen, B.; Boukenter, A.; Girard, S.; Bouazaoui, M. Sol-Gel Derived Ionic Copper-Doped Microstructured Optical Fiber: A Potential Selective Ultraviolet Radiation Dosimeter. Opt. Express 2012, 20, 29751. [CrossRef] [PubMed] 22. Kim, J.-C.; Kim, H.-K.; Paek, U.-C.; Lee, B.-H.; Eom, J.-B. The Fabrication of a Photonic Crystal Fiber and Measurement of Its Properties. J. Opt. Soc. Korea 2003, 7, 79–83. [CrossRef] 23. Zhang, P.; Zhang, J.; Yang, P.; Dai, S.; Wang, X.; Zhang, W. Fabrication of Chalcogenide Glass Photonic Crystal Fibers with Mechanical Drilling. Opt. Fiber Technol. 2015, 26, 176–179. [CrossRef] 24. Bertoncini, A.; Liberale, C. 3D Printed Waveguides Based on Photonic Crystal Fiber Designs for Complex Fiber-End Photonic Devices. Optica 2020, 7, 1487. [CrossRef] 25. Kiang, K.M.; Frampton, K.; Monro, T.M.; Moore, R.; Tucknott, J.; Hewak, D.W.; Richardson, D.J.; Rutt, H.N. Extruded Singlemode Non-Silica Glass Holey Optical Fibres. Electron. Lett. 2002, 38, 546–547. [CrossRef] 26. Huang, Y.; Xu, Y.; Yariv, A. Fabrication of Functional Microstructured Optical Fibers through a Selective-Filling Technique. Appl. Phys. Lett. 2004, 85, 5182–5184. [CrossRef] Photonics 2022, 9, 38 14 of 14 27. Xiao, L.; Jin, W.; Demokan, M.S.; Ho, H.L.; Hoo, Y.L.; Zhao, C. Fabrication of Selective Injection Microstructured Optical Fibers with a Conventional Fusion Splicer. Opt. Express 2005, 13, 9014. [CrossRef] 28. Cordeiro, C.M.B.; dos Santos, E.M.; Brito Cruz, C.H.; de Matos, C.J.; Ferreiira, D.S. Lateral Access to the Holes of Photonic Crystal Fibers–Selective Filling and Sensing Applications. Opt. Express 2006, 14, 8403. [CrossRef] 29. Wang, Y.; Liu, S.; Tan, X.; Jin, W. Selective-Fluid-Filling Technique of Microstructured Optical Fibers. J. Light. Technol. 2010, 28, 3193–3196. [CrossRef] 30. Wang, F.; Yuan, W.; Hansen, O.; Bang, O. Selective Filling of Photonic Crystal Fibers Using Focused Ion Beam Milled Microchannels. Opt. Express 2011, 19, 17585. [CrossRef] 31. Arif, M.F.H.; Asaduzzaman, S.; Ahmed, K.; Morshed, M. High Sensitive PCF Based Chemical Sensor for Ethanol Detection. In Proceedings of the 2016 5th International Conference on Informatics, Electronics and Vision (ICIEV), Dhaka, Bangladesh, 13–14 May 2016; pp. 6–9. [CrossRef] 32. Malitson, I.H. Interspecimen Comparison of the Refractive Index of Fused Silica*,†. J. Opt. Soc. Am. 1965, 55, 1205. [CrossRef] 33. Hale, G.M.; Querry, M.R. Bladder Cancers Respond to EGFR Inhibitors. Cancer Discov. 2014, 4, 980–981. [CrossRef] 34. Moutzouris, K.; Papamichael, M.; Betsis, S.C.; Stavrakas, I.; Hloupis, G.; Triantis, D. Refractive, Dispersive and Thermo-Optic Properties of Twelve Organic Solvents in the Visible and near-Infrared. Appl. Phys. B Lasers Opt. 2014, 116, 617–622. [CrossRef] 35. Akowuah, E.K.; Gorman, T.; Ademgil, H.; Haxha, S.; Robinson, G.K.; Oliver, J.V. Numerical Analysis of a Photonic Crystal Fiber for Biosensing Applications. IEEE J. Quantum Electron. 2012, 48, 1403–1410. [CrossRef] 36. Yakasai, I.K.; Abas, P.E.; Ali, S.; Begum, F. Modelling and Simulation of a Porous Core Photonic Crystal Fibre for Terahertz Wave Propagation. Opt. Quantum Electron. 2019, 51, 1–16. [CrossRef] 37. Yakasai, I.; Abas, P.E.; Kaijage, S.F.; Caesarendra, W.; Begum, F. Proposal for a Quad-Elliptical Photonic Crystal Fiber for Terahertz Wave Guidance and Sensing Chemical Warfare Liquids. Photonics 2019, 6, 78. [CrossRef] 38. Begum, F.; Abas, P.E. Near Infrared Supercontinuum Generation in Silica Based Photonic Crystal Fiber. Prog. Electromagn. Res. C 2019, 89, 149–159. [CrossRef] 39. Begum, F.; Namihira, Y.; Kinjo, T.; Kaijage, S. Supercontinuum Generation in Photonic Crystal Fibres at 1.06, 1.31, and 1.55m Wavelengths. Electron. Lett. 2010, 46, 1518–1520. [CrossRef] 40. Begum, F.; Namihira, Y.; Razzak, S.M.A.; Kaijage, S.F.; Hai, N.H.; Miyagi, K.; Higa, H.; Zou, N. Flattened Chromatic Dispersion in Square Photonic Crystal Fibers with Low Confinement Losses. Opt. Rev. 2009, 16, 54–58. [CrossRef]

Journal

Photonics – Multidisciplinary Digital Publishing Institute

Published: Jan 10, 2022

Keywords: photonic crystal fiber; chemical sensor; relative sensitivity; confinement loss

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