In recent years, sensing of a high toxic analyte using Photonic Crystal Fibre (PCF) has gained interest among researchers due to the increasing demand for testing at the point of need of a particular analyte with improved sensitivity. Although various types of detection mechanisms, namely, electrochemical biosensors, acoustic sensors, optical sensors, magnetic sensor, micro-electro-mechanical systems-based sensor, radio frequency identification based capacitive sensor and thermometric sensors are available in the literature, they suffer from sensitivity and selectivity of the sensing due to the dimensional and temporal aspects of the sensing mechanism. Moreover, the sensor should detect the analyte in either of the gas, liquid, and solid forms. This motivated us to design a novel photonic crystal fiber sensor that allows the analyte and sensing materials to interact using the sensing mechanisms. The photonic crystal fiber is principally a fiber with an arrangement of air holes that achieves uniform features that are imaginary in standard optical fibers [1–4].
Photonic crystal fiber has an exceptional degree of changing the fundamental parameters of conventional fiber and thus demonstrating the wonderful structure adaptability. The auxiliary parameters limit the light in the core that influences the propagation features. Likewise, compact size, reduced cost, and resilience in perilous situations make PCF-based gadgets useful in different situations [6–11]. The optical fiber is known as waveguides that apply to light transference applications. In PCF, the center portion of the optical fiber is encircled by a layer called cladding that is depicted by a refractive index which is less concerning the centered core refractive index. The arrangement of core and cladding in PCF enables the total internal reflection for the propagation of light inside the waveguide [13–24].
The authors in  have made a detailed review of the design of PCF for sensing toxic and non-toxic gases. The importance of hollow-core PCF towards the detection of acetylene, methane, ammonia, nitrogen, oxygen, propane, ethane, carbon dioxide, toluene, acetone, hydrogen cyanide, hydrogen, carbon monoxide, and nitrous oxide has been discussed in detail. The fundamental limits in terms of the wavelength of operation, sensing principle, fiber length, response time, and detection limit have been formulated. The authors in  have designed hexagonal structured circular air holes with asymmetrical circular core regions. The core region consists of two different air holes to detect human mucosa and glucose analyte. These analyte display a sensitivity of 47.31% and 47.59% at the wavelength ranging between 0.6 µm and 1.3 µm. Moreover, the PCF structure displays a confinement loss of 6.54x10-4 dB/m with a birefringence of 0.0027.
For sensing ethanol, benzene, and water, the authors in [3, 36] have designed a five-layered heptagonal cladding with circular air hole PCF that operates at 1 THz frequency range. The PCF consists of a three-layered circular rotated hexa-core with a confinement loss between 1.92 dB/m to 2.13 dB/m and sensitivity ranging between 66.78–69.20%. The authors in  have designed a circular cladding with rectangular slotted core-based PCF for sensing carbon dioxide gas. It exhibits a maximum sensitivity of 24%, confinement loss of 12x10-4 dB/m, non-linearity of 0.6 W-1m-1, and birefringence of 0.035. The authors in  have designed an index-guided PCF with a circular cladding region and having an arrangement of the hexagon for detecting temperature and strain. The PCF consists of a hollow core with an elliptical structure at the outermost region of the core. The center of the PCF has two different elliptical rings that are arranged on the upper and lower side so that the PCF exhibits high birefringence of 1.5x10-2 for a wavelength of 1550 nm.
The authors in  have designed a three-layered nano solid core PCF to identify liquid glycerol, ethanol, and toluene analyte in wavelength ranging between 1.4 µm and 1.65 µm. The cladding consists of a five-layered circular structure with circular holes. The sensitivity of the structure ranges between 6.165–65.16% for a confinement loss of 9.2 x 10− 6 dB/m and an effective area of 3.07 µm2. The authors in  designed PCF using circular structured core and cladding air hole to detect formalin. The sensitivity of the PCF varies between 22–29% for the wavelength between 600 nm to 1600 nm. The authors in  have made a detailed analysis of the hybrid structured circular and elliptical air holes with the hexagonal arrangement in the cladding region. In this PCF, the inner three layers and the outer two layers of the cladding are made of the circular ring and the middle layer is made of elliptical rings. The core part of the PCF consists of circular rings that are arranged in porous form for sensing ethanol analyte. The hybrid PCF provides a sensitivity of 62.19% with a confinement loss of 5.56x10-11 at the wavelength of 1330 nm.
The authors in  have designed non-linear PCF with hexagonal cladding that consists of five layers of homogeneous circular air holes. The hollow core consists of a single hexagonal structure and the design is capable of detecting benzene, chloroform, ethanol, and water at the wavelength of 1.55 µm. The confinement loss in the structure is found to be 10–10 dB/m. The non-linearity of the structure varies between 29 W-1 km-1 to 33 W-1 km-1 with an efficiency between 88.93–97.89%. The authors in  have designed a two-layered PCF with gold-coated nano-film-based biosensor using the principle of surface plasma resonance. Both the core and cladding part of the biosensor follows a circular air hole with fused silica as the base material. The biosensor provides a birefringence of 1.9x102 with improved sensitivity.
Although various photonic crystal fiber-based sensors have been suggested in the literature, the structural arrangement is commonly homogeneous that limits the operating wavelength and the type of analyte to be sensed [27–29]. On a very basic level, the structural arrangement of core and cladding in PCF resolve the operating wavelength, sensitivity, absorbance, birefringence, number of modes, dispersing, confinement loss, non-linearity, effective area, and polarization [31–36]. Hence, this paper proposes a hybrid arrangement of circular and hexagonal holes in the arrangement of honeycomb. Moreover, the proposed hybrid PCF provides the detection of methyl salicylate, arsenic trichloride, and ethylbenzene with improved sensitivity. In this structure, the hollow core is made circular and it is filled with the above liquids and the cladding consists of silica substrate with air holes.
The remainder of the paper is planned as follows: The requirement for the detection of methyl salicylate, arsenic trichloride, and ethylbenzene has been detailed in Section 2. Section 3 describes the strategy of the hybrid honey-comb photonic crystal fiber sensor. Results and discussion is described in Section IV and Section V concludes the major findings of the manuscript.