High sensitivity of taper-based Mach–Zehnder interferometer embedded in a thinned optical fiber for refractive index sensing

Abstract

A taper-based Mach-Zehnder interferometer (MZI) embedded in a thinned optical fiber is demonstrated as a highly sensitive refractive index (RI) sensor. A RI sensitivity of 2210.84 nm/RIU (refractive index unit) is obtained at the external RI of 1.40, which is ten times higher than that of normal taper- and long-period fiber grating (LPFG)-based sensors. The sensitivity can be further improved by decreasing the diameter of the thinned fiber and increasing the interferometer length of the MZI. The proposed MZIs have lower temperature sensitivities compared with normal fiber sensors, which is a desirable merit for RI sensors to reduce the cross sensitivity caused by thermal drift.

Recent Developments in Micro-Structured Fiber Optic Sensors

“…S-taper itself could form the interferometer with excitation and coupling of cladding modes through two bending regions along the tapering length, which has been studied and demonstrated with higher sensitivities than normal abrupt taper-based interferometer sensors [60][61][62][63][64]. Other novel abrupt taperbased interferometers include three cascaded normal abrupt tapers [65], tapered thin optical fibers [66], and tapered hollow fibers [67]. …”

Temperature effects of Mach-Zehnder interferometer using a liquid crystal-filled fiber

“…There are many ways to realize an in-fiber MZI. A common method is to induce and recombine the core mode and cladding modes of a SMF by using double fiber corners [6], long-period fiber grating (LPFG) [7,8], optical fiber taper [9][10][11], misalign spliced joint [12], microstructure collapsing on a photonic crystal fiber [13], imbedded micro air-cavity in fiber [14,15], etc. However, these techniques require complicated process or expensive fabrication apparatus, which knowingly limit their practical applications.…”

Mach–Zehnder interferometer formed by a large core-offset splicing fiber for temperature and displacement measurement

“…In addition, it also had been extensively studied in various physical and chemical sensing applications, such as temperature [1], displacement [2,3], curvature [4][5][6][7], stress [8,9], vibration [10], refractive index (RI) [1,11], etc. One method to realize an all-fiber MZI was using specialty fibers splicing structure, such as Single-mode-Multimode-Single-mode fiber (SMS) structure [8], SMF-small-core SMF(SCSMF)-SMF structure [12], SMF-doublecore fiber-SMF structure [3,10], SMF-PCF-SMF structure [13][14][15], SMF-HC-PCF-SMF structure [16], SMF-FBG-SMF structure [17], etc.…”