Cavity-Length Spectrum Sensing (CLSS) based on multi fiber Fabry-Pérot(F-P) cavities for refractive index monitoring

Abstract

A Cavity-Length Spectrum Sensing (CLSS) based on multi fiber Fabry-Pérot(F-P) cavities is proposed for detecting refractive index. Traditional wavelength spectrum sensing (WSS) achieves refractive index monitoring by demodulating the wavelength shifting with changing of refractive index under fixed F-P cavity with a certain length. Fixing the wavelength as a reference, changing the refractive index and observing the intensity of wavelength, the curve shifting with length of the cavity, Length as the independent variable is called CLSS. Eight F-P cavities were fabricated and used to reconstruct the cavity-length spectrum. CLSS only need a single-frequency laser and photodetector, and avoid some expensive equipments, such as spectrometers and broadband lasers. On the other hand, compared to optical intensity sensing, CLSS remains immune to laser power fluctuations and allows for software-adjustable sensitivity, utilizing the sampling vernier effect. By demodulating the shifting of the interference dips, the refractive index of glucose solutions of different concentrations can be monitored. Experimental results show that when λ= 1550.00nm, the sensitivity can reach −75.9778μm/RIU near a glucose solution with a refractive index of 1.341. In addition, the sampling vernier effect was utilized, and the sensitivity can be increased −2089.9705μm/RIU by changing the sampling interval. CLSS has low system cost, excellent stability and adjustable sensitivity, which has great potential applications in biomedical analysis, drug discovery, chemical production, etc.