Dataset of surface plasmon resonance based on photonic crystal fiber for chemical sensing applications

In this research work a perfectly circular lattice Photonic Crystal Fiber (PCF) based surface Plasmon resonance (SPR) based sensor has been proposed. The investigation process has been successfully carried out using finite element method (FEM) based commercial available software package COMSOL Multiphysics version 4.2. The whole investigation module covers the wider optical spectrum ranging from 0.48 µm to 1.10 µm. Using the wavelength interrogation method the proposed model exposed maximum sensitivity of 9000 nm/RIU(Refractive Index Unit) and using the amplitude interrogation method it obtained maximum sensitivity of 318 RIU−1. Moreover the maximum sensor resolution of 1.11×10−5 in the sensing ranges between 1.34 and 1.37. Based on the suggested sensor model may provide great impact in biological area such as bio-imaging.


a b s t r a c t
In this research work a perfectly circular lattice Photonic Crystal Fiber (PCF) based surface Plasmon resonance (SPR) based sensor has been proposed. The investigation process has been successfully carried out using finite element method (FEM) based commercial available software package COMSOL Multiphysics version 4.2. The whole investigation module covers the wider optical spectrum ranging from 0.48 µm to 1.10 µm. Using the wavelength interrogation method the proposed model exposed maximum sensitivity of 9000 nm/RIU(Refractive Index Unit) and using the amplitude interrogation method it obtained maximum sensitivity of 318 RIU −1 . Moreover the maximum sensor resolution of 1.11×10 −5 in the sensing ranges between 1 The presented simple designs and data analysis can support the researchers to reduce the complexity and implement high robust SPR sensor designs.
Dataset is highly suitable for the benchmark of different liquid as well as chemical sensing application using PCF based SPR sensor.
Presented senor model is experienced with superior performance than the previous existing sensor model.

Data
This article demonstrates the implementation of the photonic crystal Fiber (PCF) based sensor with cross sectional view. Table 1 is illustrating the data set for gold thickness of the structure; Table 2 is demonstrating the dataset for PML depth on fiber properties; Table 3 is describing about different chemical area; Table 4 is illustrating the data set for various radius of the center air hole; Table 5 is describing the dataset for different pitch value.
The data which describes above tables are comparable with the articles [1-3].

Experimental design, materials and methods
Recently, various kinds of SPR based structures are also proposed [4][5][6] to obtain the high performance. Fig. 1(a) shows a circular lattice PCF sensor structure of cross sectional view. There have two layers of air holes in this structure where two air holes are missing in each layer. Comparatively two small air holes are placed in the second ring and one air hole is placed in the center. Here in the proposed structure, the distance between center-to-center is defined by the p, the radius of the center air hole is defined by r c, r 2 is defined as the radius of the small air holes which is equal to r c , r 1 is the radius of rest of the air holes and the thickness of the gold layer is defined by d g . A larger central air-hole r c is used to reduce the effective index of the core guided and as a result deteriorate the guidance along the core [7]. The gold film layer is placed at the outside of the fused silica layer where the thickness d g of the gold film layer is 35 nm. The analyte layer is placed outside the gold film layer which thickness is 0.965 µm. In this raised structure the size of r 1 is 0.4 µm. Last outer most layers are Perfectly Match Layer (PML) which thickness is 7.2 µm. The back ground layer of the structure is fused silica. Fig. 1(b) and (c) presents the surface mode and at wavelength λ¼0.70 µm and n a ¼1.37 nm.
In this raised structure we used a thin gold layer as an active plasmonic material outside the outermost air holes layer. Since gold is chemically inactive in hydrous atmosphere and represents rich resonance peak shift [8]. An analyte layer is also used outside the gold layer which will help to make a Table 1 Variations on several Gold thicknesses to observe the modal properties of the proposed PCF the operating wavelength lambda (λ) ¼0.48 µm to 1.10 µm. The diameter of center air hole at the first layer and other two air hole at the second layer are r c ¼r 2 ¼ 0.2 µm. The rest air holes are denoted by r 1 where, r 1 ¼ 0.4 µm. The air holes inside the ring are organized by maintaining a fixed distance (p) where, p ¼1.8 µm. The thickness d g of the gold layer, analyte layer and PML layer is 30-40 nm, 0.965 µm and 7.2 µm respectively.   fiber structure easier and straight forward for fabrication process. we considered only one fiber core mode in the data set because this core mode is only eligible to provide high performance. On the other side, another mode provides abject performance and is not presence for all wavelength λ (lambda). That's why we neglect another mode. By following step by step analyzing process the operating selected mode can be achieved.
The following Sellmeier equation [8] is used to obtain the refractive index, where n is denoted refractive index of fused silica that dependent on wavelength (λ), λ is the wavelength in µm. B 1 , B 2 , B 3 , C 1 , C 2 and C 3 are denoted the Sellmeier constants. The values of corresponding constants are respectively 0.69616300, 0.407942600, 0.897479400, 0.00467914826, 0.0135120631, and 97.9340025 for fused silica.
The following Drude-Lorenz model [9] is used to obtain the dielectric constant of the gold, where the permittivity of gold is denoted by ϵ Au , ϵα is the permittivity at high frequency that has a value of 5.9673, ω is the angular frequency that is defined as ω¼2πc/λ, c is the velocity of light in vacuum, ω D is denoted the plasma frequency, the damping frequency is denoted by γD, where ω D ¼ 4227.2π THz, γD¼31.84π THz and weighting factor Δϵ ¼1.09. The spectral width ΓL¼209.72π THz and oscillator strength Ω L ¼1300.14π THz respectively.
The following equation [10] is used to obtain the sensor's performance, α dB m where k 0 ¼2π/λ is denoted the number of free space, operating wavelength is denoted by λ and the imaginary part of the effective refractive index denoted by Im(n eff ).
To obtain the sensitivity of the PCF-based SPR sensor the following formula [11] is used, where Δλ peak is used to indicate the distinction of wavelength peak shifts and Δn a is used to indicate the difference of analyte refractive index RI.
To obtain the resolution of the raised structure the following formula [12] is used, where Δn a ¼0.01, Δλ min ¼0.1 nm, and Δλ peak ¼90 nm; as a result a high value of sensor resolution is obtained as high as 1.11×10 −5 . The following formula [13] is used to obtain the amplitude sensitivity, where α(λ, n a ) is denoted the overall propagation loss at a specific refractive index (RI) of analyte and ∂α(λ, n a ) is indicated the difference between the two loss spectra. Fig. 3(a) shows the consequent loss spectra for different gold layer thickness at analyte 1.36 and 1.37 as described in Table 1. From this analysis we can see that the proposed structure provide highest  loss for gold thickness 35 nm. On the other hand, Fig. 2(b) presents the corresponding amplitude sensitivity with the variation of gold thickness. It easily clarify that the proposed structure is also provides highest amplitude sensitivity for gold layer thickness 35 nm.

Financial support
No financial support was provided to any of the authors for this research work.