Combined Long-Period Fiber Grating and Microcavity In-Line Mach–Zehnder Interferometer for Refractive Index Measurements with Limited Cross-Sensitivity

Abstract

This work discusses sensing properties of a long-period grating (LPG) and microcavity in-line Mach–Zehnder interferometer (µIMZI) when both are induced in the same single-mode optical fiber. LPGs were either etched or nanocoated with aluminum oxide (Al2O3) to increase its refractive index (RI) sensitivity up to ≈2000 and 9000 nm/RIU, respectively. The µIMZI was machined using a femtosecond laser as a cylindrical cavity (d = 60 μm) in the center of the LPG. In transmission measurements for various RI in the cavity and around the LPG we observed two effects coming from the two independently working sensors. This dual operation had no significant impact on either of the devices in terms of their functional properties, especially in a lower RI range. Moreover, due to the properties of combined sensors two major effects can be distinguished—sensitivity to the RI of the volume and sensitivity to the RI at the surface. Considering also the negligible temperature sensitivity of the µIMZI, it makes the combination of LPG and µIMZI sensors a promising approach to limit cross-sensitivity or tackle simultaneous measurements of multiple effects with high efficiency and reliability.

Long Period Grating Mach–Zehnder Interferometer Based Immunosensor with Temperature and Bulk Refractive Index Compensation

“…For example, a plasmonic sensor with gold film deposited on the surface of tilted fibre Bragg grating (FBG) can discriminate the surface RI and bulk RI [ 7 ]. The same function can be implemented using an LPG with a micro-cavity in the middle [ 8 ]. A core-offset Mach–Zehnder interferometer fabricated in series with an FBG can implement a simultaneous monitoring of temperature during RI measurement [ 9 ], as does an LPG fabricated in series with an FBG [ 10 ].…”

Single Wavelength Strain Sensing Based on Double Taper Mach-Zehnder Interferometer

“…The fabrication deficiencies and design parameters of abrupt tapers have been the subject of recent studies [2]- [5]. The versatility of abrupt tapers has shown their application in diverse configurations combined with other optical sensing devices such as Fiber Bragg Gratings (FBG) [6] and Long Period Gratings (LPG) [7].…”

Spectral Modal Decomposition of Abrupt Fiber Tapers Based on Simulated Annealing Method

“…It has been shown through [1] that MZIs can be implemented with just one strand of fiber using modal interferometry. A variety of in-line MZIs are implemented using different fiber devices such as Fiber Tapers (FTs) [2], long-period grating (LPG) [3], fiber Bragg-grating (FBG) [4], photonic crystal fiber (PCF) [5], and multimode fiber (MMF) [6]. Abrupt tapered fiber has the lowest fabrication complexity and cost, involving a common single-mode fiber (SMF) compatible fusion splicer.…”