In-fiber Mach-Zehnder interferometer with piecewise interference spectrum based on hole-assisted dual-core fiber for refractive index sensing

Abstract

We demonstrate theoretically and experimentally a novel in-fiber Mach-Zehnder interferometer (MZI) with piecewise interference spectrum. The interferometer is constructed by splicing a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) to two single mode fibers (SMFs) with a lateral-offset. Due to the offset splicing and the small distance between cores, different core modes in two cores of the SEHADCF can be excited to form interference at the different wavelength ranges. The discontinuous region of the interference spectrum can be employed as a mark to identify the order of the interference valley. The in-fiber MZI is experimentally investigated as a refractive index sensor, the sensitivity of 353.9 nm/RIU is obtained in the RI range of 1.335 ~1.395. The in-fiber MZI with a high sensitivity has a great potential in biological and chemical applications. Especially, due to the ability to identify the order of interference valleys by the discontinuous region, the proposed in-fiber MZI can improve the reliability of fiber sensors in remote monitoring applications.

Fiber Reshaping-Based Refractive Index Sensor Interrogated through Both Intensity and Wavelength Detection

“…The average sensitivities and operating ranges of the sensor, which is interrogated through the wavelength shift, are given in Table 2. The achieved sensitivities in average are much higher than the conventional heterostructure-based designs [19,21,22,23,24,25,26].…”

“…Thus far, a substantial number of fiber-optic designs for RI sensing have been presented. These include tapered multimode fiber (MMF) tips [3,4]; bent fibers incorporating a plastic MMF with a large numerical aperture (NA) [5], standard single-mode fibers (SMFs) with a reduced cladding diameter [6], and dual-channel SMF bending [7]; fiber Bragg gratings (FBGs), including long-period gratings, surface FBGs, macro-bent FBGs, and tilted moiré FBGs [8,9,10,11]; side-polished or D-shaped fibers [12,13,14,15]; waist-deformed fiber tapers fabricated by heat or chemical tapering [16,17,18]; heterostructures formed by the splicing of hetero-core fibers, including MMF-SMF-MMF [19], SMF-MMF-SMF [20], SMF-tapered claddingless fiber-SMF [21], SMF-hole-assisted dual-core fiber-SMF [22], and cascaded single-mode-no-core-hollow-core-no-core-single-mode structures [23].…”

Dual-Core Fiber-Based Interferometer for Detection of Gas Refractive Index

“…The as-drawn fiber has a Ge-doped silica core with a diameter of~9 µm and a hollow core with a diameter of~35 µm ( Figure 1a). The refractive index of the Ge-doped silica core of the DCF is~1.457 at the wavelength of 632.8 nm, and refractive index of the cladding is 0.00425 lower [26]. The typical distance between the two cores is~60 µm.…”

Underwater Pressure and Temperature Sensor Based on a Special Dual-Mode Optical Fiber

“…Traditional barometric pressure fiber optic sensors [2]- [5], which commonly are constructed with open cavities, trenches or holes fabricated by chemical etching or laser micro-machining techniques (to allow the media on which the measurements are made easy to be placed within (and removed from) the FPI cavity used), may not be well suited to marine applications, because these etched structures are thus physically weakened and may be fragile: so they may be sensitive to ambient environmental vibrations, and errors also can occur in their use due to the variation of the salinity of the seawater or the presence of contaminants from the water samples in the open FPI cavities thus created. Measuring errors also exist in fiber in-line Mach-Zehnder Interferometer (MZI) designs, which have a common characteristic of RI sensitivity to the liquid analyte: thus the following features 1) the sensor is used with a bare fiber core [6]; and 2) a thin clad fiber structure, which has a large evanescent field exposed to the surrounding [7]; 3) the sensor is based on cladding mode and core mode interference, which usually is formed by employing two heterogenic fibers (e.g., multimode fiber [8] or PCF [9]) or abnormal fiber fusion splicing (e.g., core offset [10], Sshaped [11] or peanut-like [12] arrangements), used to excite the high order/cladding modes propagating in the sensing fiber, which lead to a relatively large energy spread out of the doped core -as a result, the silica cladding acts as the "core" of the sensing structure. In light of this, noting previous work where similar cases were seen and where extrinsic FP cavity structures were proposed [13] - [17], particular attention needs to be paid to the use of specialized materials and the process of packaging shell design, essential for marine applications.…”