All-fiber multimode interference micro-displacement sensor

Abstract

We report an all-fiber micro-displacement sensor based on multimode interference (MMI) effects. The micro-displacement sensor consists of a segment of No-Core multimode fiber (MMF) with one end spliced to a segment of single mode fiber (SMF) which acts as the input. The other end of the MMF and another SMF are inserted into a capillary ferrule filled with index matching liquid. Since the refractive index of the liquid is higher than that of the ferrule, a liquid MMF with a diameter of 125 μm is formed between the fibers inside the ferrule. When the fibers are separated this effectively increases the length of the MMF. Since the peak wavelength response of MMI devices is very sensitive to changes in the MMF's length, this can be used to detect micro-displacements. By measuring spectral changes we have obtained a sensing range of 3 mm with a sensitivity of 25 nm mm −1 and a resolution of 20 μm. The sensor can also be used to monitor small displacements by using a single wavelength to interrogate the transmission of the MMI device close to the resonance peak. Under this latter regime we were able to obtain a sensitivity of 7000 mV mm −1 and a sensing range of 100 μm, with a resolution up to 1 μm. The simplicity and versatility of the sensor make it very suitable for many diverse applications.

Applications of Modal Interferences in Optical Fiber Sensors Based on Mismatch Methods

“…[12] The single-mode fiber-multimode fiber structure was inserted into a capillary ferrule filled with index matching liquid, as shown as Figure 1a. Compared with the previous design, [10] this FIGURE 1 (a) Schematic of the modal interference micro-displacement sensor.…”

“…Compared with the previous design, [10] this FIGURE 1 (a) Schematic of the modal interference micro-displacement sensor. [12] (b) Sensing illustration of single-mode-multimode-single-mode (SMS) fiber microphone [15] . system avoided the error caused by the tilt mirror, eliminated interferences introduced by the air cavity and fiber end that formed a Fabry-Perot cavity, and solved the difficulty to ensure coaxiality.…”

Low Cutoff Wavelength Etched SMS Structures Towards Verification of the Quality of Automotive Antifreeze

“…Optical fiber sensors can be used in many applications due their interesting properties: small size, multiplexing capability and immunity to electromagnetic interferences [1][2][3][4][5][6][7]. Different fiber optic configurations have been studied for these purposes, such as those based on gratings (fiber Bragg gratings, long period gratings and tilted fiber Bragg gratings) or interferometers (Mach-Zender, Fabry-Pérot and Michelson) [1].…”

Temperature-insensitive refractometer based on an RI-modulated singlemode-multimode-singlemode fibre structure

“…The SMS fibre structure is a very common fibre heterostructure which relies on MMI as its underling operating principle, and SMS fibre structures have been widely applied in telecommunications [13,14]. In the optical fibre sensing field, SMS fibre structures have also proven to be capable of performing measurements of a wide range of parameters, including temperature [15,16], humidity [17], displacement [18,19], curvature [20], strain [21,22], magnetic field [23] and RI [24][25][26] etc. A disadvantage of a simple SMS structure is that the cladding layer prevents direct access to the evanescent field by the external environment, thus traditional SMS fibre structures have not been used to directly measure external RI variations.…”