Temperature-insensitive miniaturized fiber inline Fabry-Perot interferometer for highly sensitive refractive index measurement

Tao Wei,Hai-Lung Tsai,Yukun Han,Yanjun Li,Hai Xiao

doi:10.1364/oe.16.005764

Abstract

We report a miniaturized fiber inline Fabry-Perot interferometer (FPI), with an open micro-notch cavity fabricated by one-step fs laser micromachining, for highly sensitive refractive index measurement. The device was tested for measurement of the refractive indices of various liquids including isopropanol, acetone and methanol at room temperature, as well as the temperature-dependent refractive index of deionized water from 3 to 90 degrees C. The sensitivity for measurement of refractive index change of water was 1163 nm/RIU at the wavelength of 1550 nm. The temperature cross-sensitivity of the device was about 1.1x10(-6) RIU/degrees C. The small size, all-fiber structure, small temperature dependence, linear response and high sensitivity, make the device attractive for chemical and biological sensing.

Highlights

Miniaturized and robust optical sensors capable of accurate and reliable measurement of refractive index of liquids have attracted tremendous interest in recent years due to their broad applications in chemical and biological sensing
We report a miniaturized fiber inline Fabry-Perot interferometer (FPI), with an open micro-notch cavity fabricated by one-step fs laser micromachining, for highly sensitive refractive index measurement
Characterized as the resonance wavelength shift in response to refractive index changes, it has been reported that long period fiber gratings (LPFG) can provide a sensitivity as high as 6000 nm/RIU while microresonators can reach 800 nm/RIU [6]

Summary

Introduction

Miniaturized and robust optical sensors capable of accurate and reliable measurement of refractive index of liquids have attracted tremendous interest in recent years due to their broad applications in chemical and biological sensing These devices shall have a small size, high sensitivity, fast response time and large dynamic range. Ran, et al, described a refractive index sensor by adding a sealed Fabry-Perot cavity near the tip of a single-mode fiber [12]. In this case, the sealed FPI itself was not a sensing device and only served as a signal modulator. We report our experimental investigations on its capability for temperature-insensitive refractive index sensing

Sensor fabrication and principle of operation

Experiment and discussion

Conclusion