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

Abstract

A compact, highly sensitive optical fiber displacement and curvature radius sensor is presented. The device consists of an adiabatic bi-conical fused fiber taper spliced to a single-mode fiber (SMF) segment with a flat face end. The bi-conical taper structure acts as a modal coupling device between core and cladding modes for the SMF segment. When the bi-conical taper is bent by an axial displacement, the symmetrical bi-conical shape of the tapered structure is stressed, causing a change in the refractive index profile which becomes asymmetric. As a result, the taper adiabaticity is lost, and interference between modes appears. As the bending increases, a small change in the fringe visibility and a wavelength shift on the periodical reflection spectrum of the in-fiber interferometer is produced. The displacement sensitivity and the spectral periodicity of the device can be adjusted by the proper selection of the SMF length. Sensitivities from around 1.93 to 3.4 nm/mm were obtained for SMF length between 7.5 and 12.5 cm. Both sensor interrogations, wavelength shift and visibility contrast, can be used to measure displacement and curvature radius magnitudes.

Fiber Microsphere Coupled in a Taper for a Large Curvature Range

“…); to the direction of the input and output beams that are controlled by the curvature of the input and output tapers, respectively. Currently, for curvature sensors formed by a multimode fiber placed between two single-mode fibers, the sensitivity is of the order of 10 pm km in a range of hundreds of km −1 and, for a structure consisting of a taper placed in the center of the curve for curvatures between 4.5 km −1 and 16.3 km −1 , have a sensitivity of 340 pm km [12][13][14].…”

Wavelength switching and tuning of fiber lasers by using a modifiable intra-cavity filter based on a modal Michelson interferometer

“…So, the generated phase difference between modes for every wavelength depends on the different effective refractive indexes of the core and cladding propagated modes. The phase difference can be approximately calculated by [35][36][37][38]: where λ is the wavelength of the core and cladding mode, L is the SMF piece length, n effcore is the effective refractive index of the core mode corresponding to the wavelength λ, and n effcladding is the effective refractive index of the cladding mode corresponding to the wavelength λ.…”

An Optical Interferometric Triaxial Displacement Sensor for Structural Health Monitoring: Characterization of Sliding and Debonding for a Delamination Process

“…In comparison to traditional sensing technologies, optical fiber sensors offer great advantages, such as immunity to electromagnetic field, high sensitivity, small size, ease of fabrication, and robustness to harsh environments [ 11 , 12 , 13 , 14 ]. Given several choices of sensing mechanisms, such as wavelength modulation, phase modulation, and intensity modulation, optical fiber displacement sensors thrive on structural diversity and sensing properties [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. The majority of the reported optical fiber displacement sensors work in a one-dimensional fashion, meaning it is impossible to measure interfacial sliding and debonding at the same time [ 15 , 16 , 17 , 18 , 19 , 20 ].…”

“…Given several choices of sensing mechanisms, such as wavelength modulation, phase modulation, and intensity modulation, optical fiber displacement sensors thrive on structural diversity and sensing properties [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. The majority of the reported optical fiber displacement sensors work in a one-dimensional fashion, meaning it is impossible to measure interfacial sliding and debonding at the same time [ 15 , 16 , 17 , 18 , 19 , 20 ]. Several two- and three-dimensional (2D, 3D) optical fiber displacement sensors have been demonstrated [ 21 , 22 , 23 ].…”

“…The distance between the two reflecting surfaces can directly affect the reflection spectrum of an EFPI [ 24 ]. With proper structure design and packaging, EFPI sensors could be considered excellent candidates for accurately measuring displacements [ 14 , 18 , 24 , 25 ].…”