Refractive index sensor based on etched D-fibres with wavelength adjustable operating point and resolution

Abstract

Silica based fibre-optic refractive index sensors are gaining acceptance over conventional refractometers and finding applications in chemical/biological sensing due to many of their desirable properties. Here we present an optical fibrebased refractive index sensor that uses the power transmission through etched D-shaped fibres. The sensor's operating point and resolution can be tailored for a specific application by selecting the correct combination of the operating wavelength and the cladding thickness of the etched fibre. The sensor's power transmission depends on the surrounding refractive index in which the sensor head is immersed. The sensor presented has a maximum resolution on the order of 10 -6 in its "high resolution" region and on the order of 10 -4 in its "low resolution" region. The refractive index at which the maximum resolution occurs in the high resolution region can be shifted by ~0.012 and by ~0.027 in the low resolution region. To date, such high resolutions have been reported over narrow ranges and/or for fibre Bragg grating based sensors, which require optical spectral analysis which typically, is costly.

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

“…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].…”