High Sensitivity Refractive Index Sensor Based on the Excitation of Long-Range Surface Plasmon Polaritons in H-Shaped Optical Fiber

Abstract

In this paper, we propose and numerically analyze a novel design for a high sensitivity refractive index (RI) sensor based on long-range surface plasmon resonance in H-shaped microstructured optical fiber with symmetrical dielectric-metal-dielectric waveguide (DMDW). The influences of geometrical and optical characteristics of the DMDW on the sensor performance are investigated theoretically. A large RI analyte range from 1.33 to 1.39 is evaluated to study the sensing characteristics of the proposed structure. The obtained results show that the DMDW improves the coupling between the fiber core mode and the plasmonic mode. The best configuration shows 27 nm of full width at half maximum with a resolution close to 1.3 × 10 - 5 nm, a high sensitivity of 7540 nm/RIU and a figure of merit of 280 RIU - 1 . Additionally, the proposed device has potential for multi-analyte sensing and self-reference when dissimilar DMDWs are deposited on the inner walls of the side holes. The proposed sensor structure is simple and presents very competitive sensing parameters, which demonstrates that this device is a promising alternative and could be used in a wide range of application areas.

Keywords: optical fiber sensor; optical waveguides; refractive index (RI) sensor; surface plasmon polariton (SPP); surface plasmon resonance.

Figure 1

Structural parameters of the microstructured optical fiber (MOF): (a) with dielectric–metal–dielectric waveguide (DMDW) and (b) without DMDW.

Figure 2

Schematic of the sensor fabrication process.

Figure 3

Proposed sensor setup for practical sensing. PC: Polarization controller; SMF: Single mode fiber; OSA: Optical spectrum analyzer.

Figure 4

(a) Calculated loss spectra for the fiber core mode with $n_a$ = 1.36, d = 1 $\mathsf{\mu }$m, $d_m$= 60 nm, $d_{d1}$ = 0.1 $\mathsf{\mu }$m (Ch1), $d_{d1}$ = 0.2 $\mathsf{\mu }$m (Ch2). (b) Normalized electric field.

Figure 5

Loss spectra of the fiber core mode having a DMDW in each hole. (a) Two different values of $n_d$ and $d_d$, while varying the thickness $d_m$ of the gold layer. (b) Two different values of $d_d$, with $d_m$ = 45 nm, while increasing the refractive index (RI) of the DMDW dielectrics. d = 1 $\mathsf{\mu }$m and $n_a$ = 1.36 were constant for all cases. Solid lines: Ch1. Dashed lines: Ch2.

Figure 6

(a) Self-referencing and/or multi-analyte operation with $d_m$ = 45 nm, $d=1\mathsf{\mu }$m. Black line: $d_{d1}=d_{d2}$ = 0.1 $\mathsf{\mu }$m. Red line: $d_{d1}$ = 0.1 $\mathsf{\mu }$m, $d_{d2}$ = 0.2 $\mathsf{\mu }$m. (b) Loss spectra with different values of $n_a$ in Ch1 and Ch2. $d_m$ = 45 nm, d = 1 $\mathsf{\mu }$m, $d_{d1}$ = 0.1 $\mathsf{\mu }$m, $\Delta n_1$ = 0; $d_{d2}$ = 0.2 $\mathsf{\mu }$m, $\Delta n_2$ = 0.006.

Figure 7

Operation of the RI sensor based on long-range surface plasmon polaritons (LRSPPs). (a) ${\lambda }_{RES}$, (b) S_n with $d_m$ = 30, nm, d = 1$\mathsf{\mu }$m. Black lines: Ch1. Red lines: Ch2. Green line: Ch1 without DMDW (Reference).

Figure 8

Performance of the RI sensor based on LRSPP. (a) S${}_n$, (b) FWHM and (c) FOM with $d_m$ = 30, nm, d = 1 $\mathsf{\mu }$m. Black lines: Ch1. Red lines: Ch2. Green line: Ch1 without DMDW (Reference).