Bio-inspired butterfly core-shaped photonic crystal fiber-based refractive index sensor

Md. Mashrafi; Md. Mashrafi; Q. M. Kamrunnahar; Q. M. Kamrunnahar; Firoz Haider; Firoz Haider; Rakib Haider; Rifat Ahmmed Aoni; Rajib Ahmed

doi:10.1364/OSAC.416953

1. Introduction

Simple structure and fast-response with a small change of surrounding medium and label-free detection process of SPR technology catch the researcher’s attention for many years. In 1982, Nylander et al. [1] first theoretically and experimentally introduced an SPR gas sensor. At that time, conventional prism coupling based SPR sensors (Kretschmann and Otto configuration) were used which worked based on the principle of attenuated total reflection (ATR) [2,3]. Though Kretschmann configuration had excellent sensing ability, some limitations (bulky, non-portable, incapability to remote sensing) raised the demand for new technology [4,5]. Optical fiber solved most of these problems by miniaturization and remote sensing [6]. Recently, PCF added a new dimension due to having design flexibility and light guidance capability [7,8]. Potential low cost and ease of use employed the PCF-based SPR sensors in numerous applications like medical diagnostics, biosensing, bioimaging, environment monitoring, water quality testing, food quality control, gas detection, virus detection, biomedical applications and so on [9–12]. When the imposing light passes through the core, some electromagnetic field scatters through the cladding that generates an evanescent field. This evanescent field hits the plasmonic layer and excites the free electrons of the metal surface [13]. SPR occurs with the collective oscillation of free electrons on the metal-dielectric interface [9,14]. Therefore, choosing the appropriate plasmonic material is vital to establish the SPR phenomenon. Several materials like Gold (Au), Silver (Ag), Copper (Cu), Aluminium (Al), and some oxides (Indium tin oxide, TiO2), etc. are currently utilized in SPR sensors [15,16]. Silver and gold are the most familiar among them. Silver could be a dormant candidate for its highly sensitive nature, but chemical anxiety and oxidation issues limit its performance [17,18]. Besides, gold is the most favored as it is chemically firm, biocompatible, easily functionalized, and free from oxidation in an aqueous solution [19].

To ease the detection and improve sensitivity, various PCF-based SPR sensors like internal sensing structure, D-shaped structure, slotted-microfluidic fiber, two-side polished structure, externally metal-coated structure, etc. are have been reported [4,7,10,20]. Liu et al. proposed an analyte-filled internal metal-coated plasmonic sensor that offers WS of 6300 nm/RIU within an ultrawide RI detection range (1.0 to 1.43) [21]. Li et al. introduced another internally metal-coated PCF structure that works in a narrow RI range of 1.40 to 1.44 [22]. This sensor exhibits a maximum WS of 9,180 nm/RIU and AS of 1,739.28 RIU^-1. Though they expose good sensitive nature, the deposition of the plasmon layer on the tiny air-hole surface is quite challenging. However, the D-shaped structure assists to enhance the sensitivity of a sensor by increasing light coupling intensity with the metal layer. Recently, Liu et al. suggested an SPR based D-shaped PCF sensor that offers WS of 15,000 nm/RIU and poor AS of 442.47 RIU^-1 within a broad RI detection range [9]. Singh et al. proposed another D-shaped fiber with a maximum WS of 33,500 nm/RIU [7]. However, they skip the AS investigation which is a cost-effective sensing method. Though, the reduced distance between core and metal improved sensitivity in the D-shaped structure, precise polishing increases fabrication complexity. Some slotted microfluidic structures are now coming to light with enhanced sensitivity [23–26]. Nevertheless, design complexity and placement of plasmonic material on the selected region make them tricky. An external coating approach can resolve this by placing the plasmonic and dielectric layers on the outer surface of the PCF structure. Liu et al. proposed a simple square lattice external coated structure that achieved the maximum WS of 7,250 nm/RIU and resolution of 1.1 × 10⁻⁵ RIU [27]. Recently, Haider et al. proposed a modified sold-core plasmonic sensor that exhibits a maximum WS of 11,000 nm/RIU, AS of 631 RIU^-1 along high resolution [4]. Jia et al. has proposed an polarization dependent a plasmonic sensor for low RI detection where the sensor presents the maximum WS of 7,738 nm/RIU in the RI range of 1.20 to 1.33 [3]. Firoz et al. very recently introduced a Alphabetic-core based external-coated SPR sensor that obtained a maximum WS of 12,000 nm/RIU and AS of 933 RIU^-1 [11]. This alphabetic-core structure reduces the confinement loss, but incident of the light through the core is very difficult.

Here a bio-inspired butterfly PCF-based highly sensitive externally gold-coated plasmonic sensor is proposed to detect unknown analytes in a wide RI range of 1.33 to 1.42. The bio-inspired plasmonic structure is used to enhance sensor performance by controlling the light propagation, comprehensive detection range, cost-effective, and fabrication feasibility. Simple air-hole arrangement and external metal-dielectric layer make the sensor fabrication feasible. Further, the proposed sensor works in the visible to the near-infrared region where cost-effective light sources are commercially available. Moreover, we have analyzed all geometric parameters up to ±10% to increase the performance accuracy of the proposed sensor.

2. Methodology of the design sensor

Figure 1(a) depicts the cross-section view of the proposed bio-inspired plasmonic sensor. The sensor consists of four circular air-hole rings in a hexagonal arrangement to form a butterfly shape. The light propagates through the proposed PCF by following modified-total internal reflection (M-TIR). First air hole ring is omitted to make fiber core and confine the light in the core. Some of the air holes are omitted from the second (two air-holes), third (four air-holes) and fourth (four air-holes) rings for easy light penetration and generating evanescent field to hit on the plasmonic metal surface which excite the free electrons of the metal surface. Also, the cladding region supports to confine light in the core that propagates to the open space. A scaled-down air hole is used in the center of the fiber for generating more evanescent field. To prevent the direct coupling, two scaled-down air-holes are used along the y-axis. The FEM based COMSOL Multiphysics software is used to investigate the sensing performance. The regular air-hole diameter, small air-hole diameter, center air-hole diameter, pitch (center to center distance between two conjugate air-hole), and the gold layer thickness are defined as d, d_s, d_c, Λ, and t, respectively. These parameters are optimized to d=0.85Λ, d_s=0.35Λ, d_c=0.4Λ, Λ=1.80µm and t=40nm. The process of optimization is followed by changing one parameter (ʌ) while other parameters (d, ds, dc and t) value remaining same. After getting the optimized value for one parameter and fixed it. Then we have to change another parameter and the process will continue until optimized all the parameters. However, we used the silica as background material and the RI of silica is obtained from the Sellmeir equation [23];

(1)$${n^2}(\lambda )= \; 1 + \frac{{{B_1}{\lambda ^2}}}{{{\lambda ^2} - {C_1}}} + \frac{{{B_2}{\lambda ^2}}}{{{\lambda ^2} - {C_2}}} + \frac{{{B_3}{\lambda ^2}}}{{{\lambda ^2} - {C_{3\; }}}}$$

here n and λ indicate the RI of silica and the wavelength in µm, respectively. The co-efficient values of B₁, B₂, B₃, C₁, C₂ and C₃ are taken from Ref. [24]. Plasmonic material is crucial as it helps to increase the sensing performance. We have used gold as plasmonic material due to having excellent features and employed the optical properties by following the Drude-Lorenz model [10];

(2)$${\mathrm{\varepsilon} _{Au}} = {\mathrm{\varepsilon} _\alpha } - \frac{{\mathrm{\omega}_D^2}}{{\mathrm{\omega}({\mathrm{\omega} + j{\gamma_D}} )}} - \frac{{\Delta \mathrm{\varepsilon} \varOmega _L^2}}{{({{\mathrm{\omega}^2} - \varOmega_L^2} )+ j {\Gamma _L}\mathrm{\omega}}}$$

here ɛ_Au is the permittivity of gold, and all constant values are taken from the Ref. [20]. The RI of gold changes with the change of wavelength. The stack preform of the proposed sensor is illustrated in Fig. 1(b). Here, the regular air-holes are defined as thin wall capillary and small air-holes as thicker wall capillary. The schematic of possible experimental set-up is shown in Fig. 1(c). A broadband light source can be used to propagate light through the proposed PCF core that excites the mode of analyte channel. The liquid infiltration to the sensing channel can be done using a syringe pump by employing tapered head micro-capillary needles. The optical spectrum analyzer (OSA) can be used to observe the loss spectrum. Due to change of analyte RI, loss spectrum will show either blue or read shifts. The stack and draw method can be employed for the fabrication of PCF [28]. A standard diameter of PCF based SPR sensor is 125 μm which is consist of core, cladding and jacket [29,30]. The parameters (core, cladding and jacket) size depend on the designed fiber. For the proposed sensor, a set of capillaries can be considered with 1.25 mm diameter. Then the capillaries will be stacked as a four-ring PCF using commercially available 19/25, 17.5/19, 18/20, 16/20 mm (inner to outer diameter) tube. The stacked capillaries need to be the same inner-to-outer diameter ratio. The capillaries (removed air holes) will be replaced with a similar size glass rod.

Fig. 1. (a) Cross-section view and (b) stack preforms of the bio-inspired butterfly core-shaped plasmonic RI sensor, and (c) Conceptual diagram of possible experimental set-up.

Download Full Size | PDF

Later, the PCF preform will be drawn into around 2 mm diameter canes [29]. Then the proposed PCF will be drawn. During the fiber drawing process, the air-hole size will be adjusted by controlling the drawing temperature and applied pressure to the holes [28]. Finally, vacuum pressure will be applied to collapse the jacket with the PCF cane [31]. After getting the designed PCF structure (125 μm) with four air hole rings, need to polish the outer part (jacket) to make the desired PCF structure for placing the plasmonic layer and sensing channel. In terms of fabrication, plasmonic layer deposition on the PCF surface is a very challenging task. Several coating methods exist like radio frequency sputtering, wet-chemistry deposition, thermal evaporation, etc. However, excessive roughness limits them. Chemical Vapor Deposition (CVD) can replace them as it offers uniform coating with the least roughness [32,33]. An analyte layer and the Perfectly Matched Layer (PML) is placed over the PCF surface. PML and Scattering Boundary Conditions (SBC) are employed to absorb the reflected light. Extremely fine mesh is applied for simulation accuracy, which contains 73,370 domain elements for the proposed sensor.

3. Results and discussions

Figure 2 displays the electric field distribution and the coupling relation between the core-guided mode and SPP mode. Figures 2(a), 2(c) present the core-guided modes, and Figs. 2(b), 2(d) show the SPP modes for the x- and y-polarized modes, respectively. SPR phenomena happens when the evanescent field interacts with the free electrons of the metal surface. Mathematically, when the real effective index value of the core-guided mode converges with the SPP mode then a resonance peak appears which is known as phase matching condition where the maximum energy transfers from the core-guided mode to the SPP mode. Figure 2(e) represents the dispersion relation at analyte RI 1.33. Also, Fig. 2(e) reveals that the x-polarized mode generates strong coupling than the y-polarized mode. Therefore, the x-polarized mode is considered for the performance analysis of the sensor. For analyte RI 1.33, resonance happens at wavelength 600 nm. The confinement loss is observed at resonant wavelength of 21.5 dB/cm and 1.3 dB/cm for analyte RI of 1.33 in x- and y-polarized modes, respectively.

Fig. 2. Electric field distribution of the core-guided mode and SPP mode for the (a, b) x-polarized, (c, d) y-polarized modes, respectively at analyte RI of 1.33, and (e) the dispersion relationship of the proposed sensor at analyte RI 1.33.

Download Full Size | PDF

Moreover, Fig. 3(a) shows the sensor birefringence (B) properties where the values of B (differences between x-and y-polarized modes at a certain RI) gradually increase accordingly increase of wavelengths. According to Fig. 3, it notices that the sensor is more sensitive in a single polarized mode due to the gradual increment of B. Figure 3(b) depicts the proposed sensor's loss spectrum for analyte RI of 1.33 to 1.42. Confinement loss (CL) plays a very significant role in evaluating other sensing performances. The confinement loss can be calculated from the following equation [34];

(3)$$\alpha ({dB/cm} )\; = \; 8.686 \times {k_0}Im({{n_{eff}}} )\times {10^4}$$

where k₀=2π/λ denotes the wave number at free space, $Im({{n_{eff}}} )$ denotes the imaginary part of the effective refractive index, and λ is the wavelength in the micron. The ${n_{eff}}$ of SPP changes with any small changes in analyte RI [11]. Therefore, resonant wavelength shifts with the variation of analyte RIs. From this wavelength shift, unknown analyte RI can be detected. Also, Fig. 3(b) clarifies that resonant peak shifts toward the higher wavelength with analyte RI increment. Moreover, CL increases with the forward shift of analyte RI. After a specific range, it starts to reduce again. Thus, we can specify the RI detection range. The sensor obtains the lowest CL of 21 dB/cm and the highest loss of 153 dB/cm for analyte RI of 1.33 and 1.41, respectively. The sensing performance of the sensor are evaluated based on wavelength and amplitude interrogation methods. A sensor shows the higher sensitivity and detection range in the wavelength interrogation method [35]. The WS is obtained from [36];

(4)$${S_\lambda }(\lambda )\; = \; \Delta {\lambda _{peak}}/\Delta {n_a}$$

here $\Delta {n_a}$ and $\Delta {\lambda _{peak}}$ symbolizes the difference between two consecutive RIs and resonant wavelength peak, respectively. Maximum resonant wavelength shifts from 1030 nm to 1590 nm when analyte RI shift from 1.41 to 1.42 which leads to the maximum WS of 56,000 nm/RIU (see Table 1). Also, maximum sensor resolution can be calculated from the maximum WS which indicates the detection of the smallest change in analyte RI variation. The sensor resolution can be calculated from [37];

(5)$$R({RIU} )= \frac{{\Delta {n_a} \times \Delta {\lambda _{min}}}}{{\Delta {\lambda _{peak}}}}$$

here $\Delta {n_a},\; \Delta {\lambda _{peak}}$ and $\Delta {\lambda _{min}}$ denote the RI variation, maximum peak wavelength shift, and the minimum sensor resolution. The sensor obtains the maximum sensor resolution of 1.8 × 10⁻⁶ RIU when $\Delta {\lambda _{peak}}$=560 nm, $\Delta {\lambda _{min}}$=0.1 and $\Delta {n_a}$=0.01. So, the sensor is capable of detecting the tiny change of RI in the measurement scale of 10⁻⁶. Moreover, the external noises are avoided by observing the resolution. Figure 3(c) depicts the sensor length of the proposed sensor. Sensor length is realized from the following equation [4];

(6)$$L = \frac{1}{{\alpha ({\lambda ,{n_a}} )}}$$

Fig. 3. (a) Birefringence property of the butterfly core-shaped sensor, (b) loss spectrum for the analyte RI of 1.33 to 1.42, (c) sensor length, and (d) amplitude sensitivity for the RI variation.

Download Full Size | PDF

Table 1. Performance analysis of the proposed sensor.

View Table | View all tables in this article

From Eq. (7), it is evident that the sensor length is inverse to the loss. Sensor length decreases with the increment of loss. Practically input light will lose on the way to output if the CL is so high [22]. Moreover, the high confinement loss limits the sensor length. On the contrary, coupling strength defines the sensor performance. As a result, an optimized response is desirable which will provide high sensitivity with optimal confinement loss. However, according to the Fig. 3(c) propose sensor can detect analyte RI in sensing range scale of cm to mm. Another important sensing method is the amplitude interrogation method which is cost-effective compared to wavelength interrogation (requires the full spectrum of the detection signal). In amplitude interrogation, it detects the amplitude variation at a single wavelength [11,38]. AS can be measured using the following equation [23];

(7)$${S_A}(\lambda )[{RI{U^{ - 1}}} ]={-} \frac{1}{{\alpha ({\lambda ,{n_a}} )}}\frac{{\partial \alpha ({\lambda ,{n_a}} )}}{{\partial {n_a}}}$$

here $\alpha ({\lambda ,{n_a}} )$ is the loss for a particular wavelength of any RI, $\partial \alpha ({\lambda ,{n_a}} )\; $ is the loss difference between two consecutive RIs, and $\partial {n_a}$ denotes the change in analyte RIs.

Figure 3(d) illustrates the sensor AS for analyte RI of 1.33 to 1.42. The sensor offers the highest AS of 1,584 RIU^-1 at 870 nm and the lowest AS of 128 RIU^-1 at 620 nm for analyte RI of 1.33 and 1.39, respectively (see Table 1). Figure 4(a) depicts the proposed sensor polynomial fitting as a function of resonant wavelength and analyte RI. The sensor exhibits the value of R²=0.99 for the RI of 1.33 to 1.39 and R² = 1 for the 1.40 to 1.42 which are very close to unity. According to R² value, it indicates that the proposed sensor has a good consistent sensing response in the RI range of 1.33 to 1.42. As we increased RI values, the resonance wavelength shifts exponentially following 2^nd order polynomial equation as shown in Fig. 4(a). Further, the proposed sensor shows a good correlation between analyte RI variation and resonant peak wavelength values. Another significant parameter is FOM, which defines the detection capability of the sensor. FOM is obtained from [13];

(8)$$FOM = \frac{{{S_\lambda }({nm/RIU} )}}{{FWHM}}$$

here, ${S_\lambda }\; $ defines the wavelength sensitivity of individual analyte RI and FWHM indicates the full width at half maxima. The FWHM decline with the increment of RI; therefore, FOM increases. The sensor displays a maximum FOM of 691 RIU^-1 at an analyte RI of 1.41 (see Table 1). High FOM defines the highly sensitive nature of a sensor. All calculated values of the sensing parameters (Peak loss, resonant peak wavelength, WS, WR, FWHM, AS and FOM) are summarized in Table 1. The performance evaluation of our proposed sensor with the existing sensors in the literature is summarized in Table 2. Furthermore, plasmonic material layer thickness has a strong influence on CL and sensitivity. Figures 4(c), 4(d) describes the effect of gold layer thickness variation (t=30, 40, and 50nm) on WS and AS for analyte RI of 1.33 and 1.34.

Fig. 4. (a) 2^nd order polynomial fitting of the sensor with the analyte variation from 1.33 to 1.42, (b) FOM and FWHM as a function of wavelength variation, (c) spectrum of gold layer thickness variation, and (d) corresponding amplitude sensitivity.

Download Full Size | PDF

Table 2. Performance comparison of the proposed PCF sensor with the existing sensors.

View Table | View all tables in this article

It seems that the loss depth decreases with the increment of t due to the damping effect of gold [21,39]. The sensor exhibits the maximum CL of 30, 21 and 12 dB/cm while the gold thickness is 30, 40 and 50 nm, respectively at the analyte RI of 1.33. Similarly, at analyte RI 1.34, the sensor obtains the maximum CL of 41, 26 and 15 dB/cm with the gold thickness of 30, 40 and 50 nm, respectively. The WS remains the same for t=30 and 40nm but swings for t=50nm. With the increase of gold thickness, the resonant wavelength shows a red shift. Also, the loss value decreases significantly with the increase of gold thickness as the light can’t penetrate through the thicker gold surface. With the presence of gold surface, the core-guided light hit on the free electrons of the gold surface and generate SPP mode. During light-coupling, the inherent optical properties of gold is changed which leads to resonant wavelength shift. As a result, the proposed sensor shows the WS 1,000 nm/RIU at the gold thickness of 30 and 40 nm.

However, sensor shows larger wavelength shift for 50 nm and leads to WS of 2,000 nm/RIU. Generally, the resonant shift is ununiform with the increase of gold thickness. As a result, it is important to optimize the gold thickness for a new sensor structure. The similar difficulties are also observed in the previously reported PCF based SPR sensors [22,40]. Moreover, the confinement loss increases with the analyte RI increase and decreases with the increase of Au thickness. This is happened due to the RI contrast between the sensor core RI and analyte RI. The stated sensor obtained the maximum AS of 110, 127 and 131 RIU^-1 with t=30, 40 and 50nm variation, respectively [see Fig. 4(d)]. According to the observation, the selected optimum value is t=40nm.

Moreover, we have investigated the effect of center air hole, two side scale-down air hole, thickness of analyte channel and PML layer on sensing performance. The centre air hole is used to generate evanescent field as shown in Fig. 5(a). The strong evanescent field was observed, when we used an air hole in the center of PCF core. As a result, strong light-metal coupling for RI 1.37 [see inset Fig. 5(a)(i)] is observed. Further, the sensor shows a very week light-metal coupling [see inset Fig. 5(a)(ii, iii)] while air hole is removed from the core resulting incident light confines into the fiber core. Figure 5(b) shows the effect of two scale-down side air holes on confinement loss. It seems that the sensor shows low confinement loss (66 < 119 dB/cm) and resonant peak at higher wavelength (690 > 670 nm) for having two side air holes compare to empty one (direct coupling). Also, low confinement loss helps to increase the limit of the fiber length. Figure 5(c) shows the effect of analyte channel variation where seems that the sensor shows lower confinement loss and resonant peak at 0.5µm. But the sensor shows a similar response while thickness is varied from 1 to 2 µm with step 0.5 µm and considered 1.5 µm as optimum. PML layer has significant effects to get accurate sensing performance. But from Fig. 5(d), it is visible that PML layer has no significant effect on external PCF SPR sensing (proposed sensor) performance as the outer side of the fiber has a liquid/ sensing medium.

Fig. 5. (a) Centre air hole effect on generating evanescent field, (b) scale-down two side air holes effect on loss depth phenomena, (c) analyte channel thickness variation effect on sensing, and (d) PML layer effect on sensing for the proposed sensor.

Download Full Size | PDF

Other sensor parameters (regular air-hole diameter, center air-hole diameter, small air-hole diameter, and pitch) also significantly impact the sensing performance. Practically, the fabrication of PCF with the exact sensor parameter value is a challenging task. Usually, ±2% variations of structural parameters from the optimum value are considered [41]. However, we investigate up to ±10% variation from the optimum values of each parameter which is summarized in Fig. 6. Figure 6(a) depicts the loss spectrum with a ±10% variation of Λ from the optimum (Λ=1.65µm). From Fig. 6(a), the loss depth increases while the pitch value decreases 5%. In contrast, loss peak decreases with 5% and 10% increments of the Λ. The resonant peak remains in the same position (600 nm) for +5% and +10% variation but shifts for -5% variation (600 to 610 nm) of Λ. Therefore, it is evident that the loss peak shift forward with the decrement of Λ and vice-versa. Figure 6(b) illustrates the loss depth intensity with a ±10% shift of d from the optimum value (d = 0.85 Λ). Also, Fig. 6(b) shows that the loss peak increases with 5% and 10% increment of d. The loss depth increases as the ${n_{eff}}$ decreases with the enhancement of d [42]. In addition, while the cladding air holes size are increased, light can’t penetrate through the cladding region as a result confine through the core strongly. However, we introduced the central air-hole which leads to scattered light resulting leads to achieve strong coupling between the core-guided mode and SPP mode [4,43]. The strong coupling indicates the high confinement loss as well improve response sensitivity. The effect of center air-hole diameter (up to ±10% variation) is displayed in Fig. 6(c) where the loss depth decreases with scaling down of d_c and vice-versa. Theoretically, scaling down air holes diameter (d_c) helps concentrate more light on the core resulting in reduce the CL. However, the enhancement of d_c helps to spread the light to the surface that raises the CL. The position of the resonant peak remains constant, so WS will not change with this variation. CL intensity with ±5% to 10% variation of d_s is pictured in Fig. 6(d). This figure shows that the CL increases with the reduction of d_s as scaling down of d_s helps to penetrate more light to the metal surface. On the other hand, enlargement of d_s restricts the light and concentrates more light in the core, which results in reduced CL. According to the figure, the resonant peak remains steady, so there is no change in WS. Following the above investigation, we conclude that the sensor can show potential performance up to ±10% alteration of structural parameters as they have minimal impact on the performance.

Fig. 6. Fabrication tolerance investigation by ${\pm} 10\%$ alteration of (a) pitch value, (b) regular air-hole diameter, (c) center air-hole diameter, and (d) the small air-hole diameter, respectively.

Download Full Size | PDF

4. Conclusion

A highly sensitive bio-inspired butterfly core-shaped PCF based SPR sensor is introduced and numerically studied using FEM in the visible to near-infrared region. Gold is placed on the outer surface of the PCF to build strong coupling resulting in a significant improvement in the performance of wavelength and amplitude interrogation methods. The sensor manifests the maximum WS of 56,000nm/RIU where an average WS of 10,666 nm/RIU. Also, the sensor obtains the maximum AS of 1,584 RIU^-1 along with the sensor resolution of 1.8 × 10⁻⁶ RIU. In addition, the sensor can detect 10⁻⁶ smallest changes of analyte RI within the RI range of 1.33 to 1.42. Moreover, the proposed sensor extends the maximum FOM of 691 RIU^-1 that defines strong sensing capability. Furthermore, the sensor can detect analyte RI strongly in the maximum sensing length of 4.5 mm. Finally, we anticipate that the proposed sensor can be employed as a possible solution in the applications of real-time biomolecules detection.

Disclosures

The authors ensure that there are no conflicts of interest.

References

1. C. Nylander, B. Liedberg, and T. Lind, “Gas detection by means of surface plasmon resonance,” Sens. Actuators 3, 79–88 (1982). [CrossRef]

2. L. Li, Y. Liang, J. Guang, W. Cui, X. Zhang, J.-F. Masson, and W. Peng, “Dual Kretschmann and Otto configuration fiber surface plasmon resonance biosensor,” Opt. Express 25(22), 26950–26957 (2017). [CrossRef]

3. J. Wang, L. Pei, L. Wu, J. Wang, Z. Ruan, and J. Zheng, “A polarization-independent SPR sensor based on photonic crystal fiber for low RI detection,” Plasmonics 15(2), 327–333 (2020). [CrossRef]

4. F. Haider, M. Mashrafi, R. Haider, R. A. Aoni, and R. Ahmed, “Asymmetric core-guided polarization-dependent plasmonic biosensor,” Appl. Opt. 59(26), 7829–7835 (2020). [CrossRef]

5. E. Haque, A. Al Noman, M. A. Hossain, N. H. Hai, Y. Namihira, and F. Ahmed, “Highly Sensitive D-Shaped Plasmonic Refractive Index Sensor for a Broad Range of Refractive Index Detection,” IEEE Photonics J. (2021).

6. S. Vyas, T. Tanabe, M. Tiwari, and G. Singh, “Chalcogenide photonic crystal fiber for ultraflat mid-infrared supercontinuum generation,” Chin. Opt. Lett. 14(12), 123201 (2016). [CrossRef]

7. S. Singh and Y. Prajapati, “Highly sensitive refractive index sensor based on D-shaped PCF with gold-graphene layers on the polished surface,” Appl. Phys. A 125(6), 437 (2019). [CrossRef]

8. Y.-L. Yu, S.-K. Laiw, H. Kishikawa, and N. Goto, “D-shaped silicon core fiber-based surface plasmon-resonance refractive index sensor in 2 µm,” Appl. Opt. 59(18), 5539–5546 (2020). [CrossRef]

9. C. Liu, J. Wang, F. Wang, W. Su, L. Yang, J. Lv, G. Fu, X. Li, Q. Liu, and T. Sun, “Surface plasmon resonance (SPR) infrared sensor based on D-shape photonic crystal fibers with ITO coatings,” Opt. Commun. 464, 125496 (2020). [CrossRef]

10. J. Lu, Y. Li, Y. Han, Y. Liu, and J. Gao, “D-shaped photonic crystal fiber plasmonic refractive index sensor based on gold grating,” Appl. Opt. 57(19), 5268–5272 (2018). [CrossRef]

11. F. Haider, R. A. Aoni, R. Ahmed, W. J. Chew, and G. A. Mahdiraji, “Alphabetic-Core Assisted Microstructure Fiber Based Plasmonic Biosensor,” Plasmonics 15(6), 1949–1958 (2020). [CrossRef]

12. V. Sandeep, T. Takasumi, S. Ghanshyam, and T. Manish, “Ultraflat broadband supercontinuum in highly nonlinear Ge11. 5As24Se64. 5 photonic crystal fibres,” Ukr. J. Phys. Opt. 17(3), 132–139 (2016). [CrossRef]

13. Y. Wang, S. Li, J. Li, Z. Zhang, S. Zhang, and J. Wu, “High-sensitivity photonic crystal fiber refractive index sensor based on directional coupler,” Opt. Fiber Technol. 49, 16–21 (2019). [CrossRef]

14. E. Haque, M. A. Hossain, Y. Namihira, and F. Ahmed, “Microchannel-based plasmonic refractive index sensor for low refractive index detection,” Appl. Opt. 58(6), 1547–1554 (2019). [CrossRef]

15. F. Wu, P. Thomas, V. Kravets, H. Arola, M. Soikkeli, K. Iljin, G. Kim, M. Kim, H. Shin, and D. Andreeva, “Layered material platform for surface plasmon resonance biosensing,” Sci. Rep. 9(1), 20286 (2019). [CrossRef]

16. P. O. Patil, G. R. Pandey, A. G. Patil, V. B. Borse, P. K. Deshmukh, D. R. Patil, R. S. Tade, S. N. Nangare, Z. G. Khan, and A. M. Patil, “Graphene-based nanocomposites for sensitivity enhancement of surface plasmon resonance sensor for biological and chemical sensing: A review,” Biosens. Bioelectron. 139, 111324 (2019). [CrossRef]

17. H. Farmani, A. Farmani, and Z. Biglari, “A label-free graphene-based nanosensor using surface plasmon resonance for biomaterials detection,” Phys. E (Amsterdam, Neth.) 116, 113730 (2020). [CrossRef]

18. X. Meng, J. Li, Y. Guo, Y. Liu, S. Li, H. Guo, W. Bi, H. Lu, and T. Cheng, “Experimental study on a high-sensitivity optical fiber sensor in wide-range refractive index detection,” J. Opt. Soc. Am. B 37(10), 3063–3067 (2020). [CrossRef]

19. K. Kang and D. Kim, “Effective optical properties of nanoparticle-mediated surface plasmon resonance sensors,” Opt. Express 27(3), 3091–3100 (2019). [CrossRef]

20. A. Yasli and H. Ademgil, “Geometrical comparison of photonic crystal fiber-based surface plasmon resonance sensors,” Opt. Eng. 57(03), 1 (2018). [CrossRef]

21. C. Liu, W. Su, F. Wang, X. Li, Q. Liu, H. Mu, T. Sun, P. K. Chu, and B. Liu, “Birefringent PCF-based SPR sensor for a broad range of low refractive index detection,” IEEE Photonics Technol. Lett. 30(16), 1471–1474 (2018). [CrossRef]

22. D. Li, W. Zhang, H. Liu, J. Hu, and G. Zhou, “High sensitivity refractive index sensor based on multicoating photonic crystal fiber with surface plasmon resonance at near-infrared wavelength,” IEEE Photonics J. 9(2), 1–8 (2017). [CrossRef]

23. M. N. Sakib, S. R. Islam, T. Mahendiran, L. F. Abdulrazak, M. S. Islam, I. M. Mehedi, Q. Kamrunnahar, M. Momtaj, M. W. Hassan, and I. Amiri, “Numerical Study of Circularly Slotted Highly Sensitive Plasmonic Biosensor: A Novel Approach,” Results Phys. 17, 103130 (2020). [CrossRef]

24. M. Momtaj, J. R. Mou, Q. Kamrunnahar, and M. A. Islam, “Open-channel-based dual-core D-shaped photonic crystal fiber plasmonic biosensor,” Appl. Opt. 59(28), 8856–8865 (2020). [CrossRef]

25. S. I. Azzam, M. F. O. Hameed, R. E. A. Shehata, A. Heikal, and S. S. Obayya, “Multichannel photonic crystal fiber surface plasmon resonance based sensor,” Opt. Quantum Electron. 48(2), 142 (2016). [CrossRef]

26. M. R. Islam, A. Iftekher, K. R. Hasan, M. J. Nayen, S. B. Islam, R. Islam, R. L. Khan, E. Moazzam, and Z. Tasnim, “Surface plasmon resonance based highly sensitive gold coated PCF biosensor,” Appl. Phys. A 127(2), 118 (2021). [CrossRef]

27. M. Liu, X. Yang, B. Zhao, J. Hou, and P. Shum, “Square array photonic crystal fiber-based surface plasmon resonance refractive index sensor,” Mod. Phys. Lett. B 31(36), 1750352 (2017). [CrossRef]

28. G. Amouzad Mahdiraji, D. M. Chow, S. Sandoghchi, F. Amirkhan, E. Dermosesian, K. S. Yeo, Z. Kakaei, M. Ghomeishi, S. Y. Poh, and S. Yu Gang, “Challenges and solutions in fabrication of silica-based photonic crystal fibers: an experimental study,” Fiber Integr. Opt. 33(1-2), 85–104 (2014). [CrossRef]

29. D. Pysz, I. Kujawa, R. Stępień, M. Klimczak, A. Filipkowski, M. Franczyk, L. Kociszewski, J. Buźniak, K. Haraśny, and R. Buczyński, “Stack and draw fabrication of soft glass microstructured fiber optics,” Bull. Pol. Acad. Sci.: Tech. Sci. 62(4), 667–682(2014). [CrossRef]

30. A. A. Rifat, F. Haider, R. Ahmed, G. A. Mahdiraji, F. M. Adikan, and A. E. Miroshnichenko, “Highly sensitive selectively coated photonic crystal fiber-based plasmonic sensor,” Opt. Lett. 43(4), 891–894 (2018). [CrossRef]

31. M. F. Azman, G. A. Mahdiraji, W. R. Wong, R. A. Aoni, and F. R. M. Adikan, “Design and fabrication of copper-filled photonic crystal fiber based polarization filters,” Appl. Opt. 58(8), 2068–2075 (2019). [CrossRef]

32. F. Haider, R. A. Aoni, R. Ahmed, G. A. Mahdiraji, M. F. Azman, and F. R. M. Adikan, “Mode-multiplex plasmonic sensor for multi-analyte detection,” Opt. Lett. 45(14), 3945–3948 (2020). [CrossRef]

33. J. Liao, Z. Ding, Y. Xie, X. Wang, Z. Zeng, and T. Huang, “Ultra-broadband and highly sensitive surface plasmon resonance sensor based on four-core photonic crystal fibers,” Opt. Fiber Technol. 60, 102316 (2020). [CrossRef]

34. Q.-l. Wu, Y. Zhao, Y.-n. Zhang, and Y. Yang, “Characteristics of a new multi-channel sensing device based on C-type photonic crystal fibers,” Opt. Laser Technol. 134, 106622 (2021). [CrossRef]

35. Y. Guo, J. Li, X. Wang, S. Zhang, Y. Liu, J. Wang, S. Wang, X. Meng, R. Hao, and S. Li, “Highly sensitive sensor based on D-shaped microstructure fiber with hollow core,” Opt. Laser Technol. 123, 105922 (2020). [CrossRef]

36. R. A. Kadhim, L. Yuan, H. Xu, J. Wu, and Z. Wang, “Highly sensitive D-shaped optical fibre surface plasmon resonance refractive index sensor based on Ag-α-Fe2O3 grating,” IEEE Sens. J. (2020).

37. H. Han, D. Hou, N. Luan, Z. Bai, L. Song, J. Liu, and Y. Hu, “Surface Plasmon Resonance Sensor Based on Dual-Side Polished Microstructured Optical Fiber with Dual-Core,” Sensors 20(14), 3911 (2020). [CrossRef]

38. M. Al Mahfuz, M. A. Hossain, E. Haque, N. H. Hai, Y. Namihira, and F. Ahmed, “Dual-core photonic crystal fiber-based plasmonic RI sensor in the visible to near-IR operating band,” IEEE Sens. J. 20(14), 7692–7700 (2020). [CrossRef]

39. M. De, C. Markides, V. K. Singh, C. Themistos, and B. Rahman, “Analysis of a Single Solid Core Flat Fiber Plasmonic Refractive Index Sensor,” Plasmonics 15(5), 1429–1437 (2020). [CrossRef]

40. F. Haider, R. A. Aoni, R. Ahmed, W. J. Chew, and G. A. Mahdiraji, “Plasmonic micro-channel based highly sensitive biosensor in visible to mid-IR,” Opt. Laser Technol. 140, 107020 (2021). [CrossRef]

41. A. K. Paul, “Design and analysis of photonic crystal fiber plasmonic refractive Index sensor for condition monitoring of transformer oil,” OSA Continuum 3(8), 2253–2263 (2020). [CrossRef]

42. S. Perret, C. Poudel, A. N. Ghosh, G. Fanjoux, L. Provino, T. Taunay, A. Monteville, D. Landais, C. Kaminski, and J. M. Dudley, “Silica-based photonic crystal fiber for the generation of broad band UV radiation,” OSA Continuum 3(1), 31–42 (2020). [CrossRef]

43. Z. Rahman, W. Hassan, T. Rahman, N. Sakib, and S. Mahmud, “Highly sensitive tetra-slotted gold-coated spiral plasmonic biosensor with a large detection range,” OSA Continuum 3(12), 3445–3459 (2020). [CrossRef]

Ref.	Structure type	Wave. Sen. (nm/RIU)	Wav. Res. (RIU)	Amp. Sen. (RIU^-1)	FOM (RIU^-1)	Sensor Length (mm)
[4]	Asymmetric core-guided biosensor	11,000	$9.09 \times 10^{- 6}$	631	157	0.80
[7]	D-shaped PCF with gold-graphene layer	33,500	$2.98 \times 10^{- 5}$	N/A	N/A	N/A
[9]	D-shaped PCF SPR sensor	15,000	$6.67 \times 10^{- 6}$	442.5	N/A	N/A
[21]	Analyte filling PCF based SPR sensor	6,300	$1.587 \times 10^{- 5}$	N/A	N/A	N/A
[22]	Internally metal-coated PCF sensor	9,600	$1.09 \times 10^{- 5}$	1739.3	407	N/A
[24]	Modified external PCF SPR sensor	17,000	$5.88 \times 10^{- 6}$	34,00	320	N/A
[26]	Gold coated PCF based SPR sensor	14,700	$6.9 \times 10^{- 6}$	4738	387	0.80
[27]	Externally metal-coated PCF sensor	7,250	$1.1 \times 10^{- 5}$	N/A	N/A	N/A
This work	Butterfly core PCF based SPR sensor	56,000	$1.8 \times 10^{- 6}$	1584	691	4.5

Ref.	Structure type	Wave. Sen. (nm/RIU)	Wav. Res. (RIU)	Amp. Sen. (RIU^-1)	FOM (RIU^-1)	Sensor Length (mm)
[4]	Asymmetric core-guided biosensor	11,000	$9.09 \times 10^{- 6}$	631	157	0.80
[7]	D-shaped PCF with gold-graphene layer	33,500	$2.98 \times 10^{- 5}$	N/A	N/A	N/A
[9]	D-shaped PCF SPR sensor	15,000	$6.67 \times 10^{- 6}$	442.5	N/A	N/A
[21]	Analyte filling PCF based SPR sensor	6,300	$1.587 \times 10^{- 5}$	N/A	N/A	N/A
[22]	Internally metal-coated PCF sensor	9,600	$1.09 \times 10^{- 5}$	1739.3	407	N/A
[24]	Modified external PCF SPR sensor	17,000	$5.88 \times 10^{- 6}$	34,00	320	N/A
[26]	Gold coated PCF based SPR sensor	14,700	$6.9 \times 10^{- 6}$	4738	387	0.80
[27]	Externally metal-coated PCF sensor	7,250	$1.1 \times 10^{- 5}$	N/A	N/A	N/A
This work	Butterfly core PCF based SPR sensor	56,000	$1.8 \times 10^{- 6}$	1584	691	4.5

Bio-inspired butterfly core-shaped photonic crystal fiber-based refractive index sensor

Abstract

1. Introduction

2. Methodology of the design sensor

3. Results and discussions

4. Conclusion

Disclosures

References

Cited By

Figures (6)

Tables (2)

Equations (8)

OSA Continuum

Analyte RI	Peak Loss (dB/cm)	Res. Peak Wave. (nm)	Res. Peak Shift (nm)	Wavelength Sensitivity (nm/RIU)	Wavelength Resolution (RIU)	FWHM	Amp.Sens. (RIU^-1)	FOM (RIU^-1)
1.33	21	600	10	1,000	1.0×10⁻⁴	41	128	24
1.34	26	610	20	2,000	5.0×10⁻⁵	41	206	49
1.35	35	630	30	3,000	3.3×10⁻⁵	36	376	83
1.36	49	660	30	3,000	3.3 ×10⁻⁵	32	561	94
1.37	66	690	40	4,000	2.5×10⁻⁵	30	807	133
1.38	87	730	50	5,000	2.0×10⁻⁵	30	959	152
1.39	105	780	80	8,000	1.3×10⁻⁵	33	1,584	242
1.40	109	860	170	17,000	5.9×10⁻⁶	34	1,222	500
1.41	153	1030	560	56,000	1.8×10⁻⁶	81	206	691
1.42	73	1590	N/A	N/A	N/A	N/A	N/A	N/A