Optical microfiber mode interferometer for temperature-independent refractometric sensing

Abstract

We report on a functional optical microfiber mode interferometer and its applications for absolute, temperature-insensitive refractive index sensing. A standard optical fiber was tapered down to 10 μm. The central part of the taper, i.e., the microfiber, is connected to the untapered regions with two identical abrupt transitions. The transmission spectrum of our device exhibited a sinusoidal pattern due to the beating between modes. In our interferometer the period of the pattern-an absolute parameter-depends strongly on the surrounding refractive index but it is insensitive to temperature changes. The period, hence the external index, can be accurately measured by taking the fast Fourier transform (FFT) of the detected interference pattern. The measuring refractive index range of the device here proposed goes from 1.33 to 1.428 and the maximum resolution is on the order of 3.7×10(-6).

Adaptable Optical Fiber Displacement-Curvature Sensor Based on a Modal Michelson Interferometer with a Tapered Single Mode Fiber

“…In the aforementioned in-fiber structures, the use of two mode coupler devices is necessary to construct an MZI, however, the fabrication process for FBGs, LPFGs, and spliced spherical shape structures is not quite as simple. In the case of fiber tapers, also by means of just one taper, an MZI can be constructed [11], but the taper needs to be abrupt, increasing the thinness and fragility of the tapered fiber. Furthermore, the use of special fibers to generate both arms of the MZI has been used for bending measurement, e.g., multicore fiber [2,12] and photonic crystal fiber [13].…”

High-Visibility Photonic Crystal Fiber Interferometer as Multifunctional Sensor

“…To fabricate a modal interferometer one needs a mechanism to couple light from the core into two or more modes and another mechanism to recombine them. To this end, different approaches have been proposed including for example, combination of different optical fibers [1–3], tapering techniques [4–6], or long period gratings [7,8]. Another approach consists of collapsing the voids of a photonic crystal fiber (PCF) over a microscopic region [9–11].…”

A Refractive Index Sensor Based on the Resonant Coupling to Cladding Modes in a Fiber Loop

“…Fiber-based technology provides feasible, simple, low cost, and highly sensitive alternatives. Product of this interest, several RI sensors, based on mature fiber technologies, such as highly sensitive long period fiber gratings [1], core-exposed fiber Bragg gratings [2,3], modal all-fiber interferometers [4], or fiber tapers [5,6], have been recently proposed. Furthermore, attractive approaches have been reported taking the new possibilities opened by the advent of the holey fibers [7].…”