A unique wheel-shaped exposed core LSPR-PCF sensor for dual-peak sensing: Applications in the optical communication bands, M-IR region and biosensing

Abstract

Photonic Crystal Fibers (PCF) effectiveness in practice decreases if the fabrication of the sensor becomes too complex. Keeping this in mind, we propose a one-of-a-kind wheel shaped PCF sensor with an exposed core containing only three air holes with exceptional sensing features. The sensor is equipped with dual plasmonic layers, Indium Tin Oxide (ITO, 10 % wt) and silver (Ag) with a coating of TiO₂ to enhance the sensing capabilities and provide protection against oxidation. The sensor's distinctive configuration enables it to exhibit two distinct peaks within a range of refractive index from 1.32 to 1.38 for y-polarization and from 1.35 to 1.38 for x-polarization. The sensor specifications have been optimized to achieve the maximum levels of wavelength sensitivity (WS) and double peak shift sensitivity (DPSS). The sensor portrays a WS of 50,652 nm/RIU and the highest DPSS ever recorded, measuring 50,000 nm/RIU. Additionally, the sensor exhibits a significantly high scale of amplitude sensitivity (AS) of 1668.34 RIU^-1 which is a very remarkable value considering silver as plasmonic material along with an outstanding figure of merit (FOM) of 1017.11 RIU^-1. In addition, our sensor is able to manifest resolutions in the order of 10^-6, demonstrating a resolution of 5.94 × 10^-6 RIU with the deployment of amplitude interrogation method and 1.97 × 10^-6 RIU with the wavelength interrogation method. The design spans an extensive spectrum, covering ultraviolet to mid-infrared wavelengths, enabling detection of biomolecules and biochemicals, along with operation in the optical communication band.

Keywords: Amplitude sensitivity (AS); Biosensing; Double peak shift sensitivity (DPSS); Dual peak sensing; Optical communication band; Wavelength sensitivity (WS).

Fig. 1

(a) 2-dimensional and (b) 3-dimensional layout of our proposed design.

Fig. 2

Potential fabrication steps.

Fig. 3

(a) Dispersion relationship of the double peak displayed with the CL (b) SPP along ITO layer (c) SPP mode along Ag + TiO₂ layer (d) x-pol (e) y-pol for an analyte RI of 1.37.

Fig. 4

(a) CL vs wavelength plot for varying $t_{ITO}$ at RI 1.36 & 1.37 (b) Effect of DPSS with $t_{ITO}$ (c) WS of 1st peak and (d) 2nd peak respectively.

Fig. 5

(a) CL vs wavelength plot for varying $t_{Ag}$ at RI 1.36 & 1.37 (b) Effect of DPSS with varying $t_{Ag}$ (c) WS of 1st peak and (d) 2nd peak respectively.

Fig. 6

(a) CL vs wavelength plot for varying $t_{Ti{O}_2}$ at RI 1.36 and 1.37 (b) Effect of DPSS with varying $t_{Ti{O}_2}$ (c) WS of 1st peak and (d) 2nd peak respectively.

Fig. 7

(a) CL vs wavelength plot for varying pitch at RI 1.36 & 1.37 (b) Effect of DPSS with varying pitch (c) WS of 1st peak and (d) WS of 2nd peak respectively.

Fig. 8

Difference of RW along the (a) x polarization and (b) y polarization.

Fig. 9

Relation of RI with the difference of the loss peak intensity across (a) x-polarization and (b) y-polarization.

Fig. 10

CL vs wavelength along (a) x-pol at a range of 1.35–1.39 and (b) 1.32–1.39 RI for y-pol.

Fig. 11

Amplitude sensitivity for (a) x-polarization and (b) y-polarization.

Fig. 12

Polynomial modelling for the Ag peak across (a) x-polarization and (b) y-polarization.