Au nanorod-coupled microfiber optical humidity sensors.

N Zhou,Y P Wang,P Wang,L M Tong,J R Qiu,Y X Gao,Y Xie,Y X Yang,L Zhang,Z X Shi,X Guo,D W Cai

doi:10.1364/oe.27.008180

Abstract

We demonstrate a high-sensitivity relative humidity (RH) sensor taking advantage of single-band narrow plasmon resonance of a single Au nanorod coupled to a whispering gallery cavity mode of a polyacrylamide microfiber. From the resonance peak shift, the sensor could achieve a sensitivity up to 0.51 nm/% RH with a cavity size of about 2 μm. By coupling multiple Au nanorods along the microfiber axis, we demonstrate a position-dependent microfiber optical humidity sensor with a 1.5-mm spatial resolution, which can be potentially reduced to micrometer level, paving a way toward high-resolution distributed microfiber optical sensors.

Highlights

Monitoring and controlling of relative humidity (RH) is crucial in diverse fields from electronics industry, corrosion protection, to disease diagnosis, among which humidity sensors with high sensitivity, fast response, low cost and compact size are highly desired
After the Au NR was coupled to a 2.1-μm-diameter microfiber, the linewidth of the dominant localized surface plasmon resonance (LSPR) peak reduced to 8.0 nm (Fig. 2(b))
LSPR scattering from the three nanorods, as shown in Fig. 4(b), gives different spectral shifts, clearly showing the RH gradient along the microfiber length, and confirming the possibility of developing distributed microfiber optical sensors with spatial resolution much higher than conventional fiber-optic sensors [42]

Summary

Introduction

Monitoring and controlling of relative humidity (RH) is crucial in diverse fields from electronics industry, corrosion protection, to disease diagnosis, among which humidity sensors with high sensitivity, fast response, low cost and compact size are highly desired. By replacing the silica microfiber used in previous work [22,23,24] with a moisturesensitive polyacrylamide (PAM) microfiber, we obtained single-band 10-nm-linewidth plasmon resonance from the coupled WGM and LSPR modes of the hybrid structure, with a cavity size of about 2 μm.

Results

Conclusion