A simple ultrasensitive displacement sensor based on a high bend loss single-mode fibre and a ratiometric measurement system

Abstract

An all-fibre displacement sensor with a simple configuration and capable of monitoring sub-50 nm displacements is proposed and investigated experimentally. The proposed fibre displacement sensor consists of a half-loop structure of bare high bend loss single-mode fibre 1060XP and a ratiometric power interrogation system. By measuring the change in transmission ratio in the ratiometric system, a change in displacement can be measured. The displacement sensor is sensitive to temperature and an experimental investigation of this sensitivity is presented. It is found that the peak shift response has a linear variation with temperature; therefore, temperature dependence can be mitigated by a suitable displacement correction process. The proposed macrobending fibre based displacement sensor benefits from simplicity and low cost and achieves a comparable resolution as compared with other conventional fibre optic sensors.

An Intrinsic Fiber-Optic Single Loop Micro-Displacement Sensor

“…It is well known that temperature variations affect the performance of any optical fiber sensor [ 12 ]. When temperature changes there are thermo-optic and thermal expansion effects that may modify the power transmission characteristics which may manifest as an undesirable attenuation in the whole spectral range or the wavelength shift of a given spectral notch.…”

“…This observation coincides with a measurement made by using a white light source, where we observed that at a given position the increase of temperature from 25 °C to 36 °C resulted in ∼0.1 dB loss. A more accurate measurement will require the use of a setup where the optical power source variations are compensated such as that proposed in reference [ 12 ].…”

“…In general, in most intrinsic fiber sensors the displacement produces a deformation which bends the sensible portion of the fiber, thus affecting the optical transmission properties of the fiber. The sensible portion of the fiber may consist of fiber Bragg gratings [ 8 , 9 ], long-period fiber gratings [ 10 ], two-core fibers [ 11 ], single mode fibers with high bend loss at the measurement wavelength [ 12 ], tapered fibers [ 13 – 15 ], among others. In reference [ 11 ], an intrinsic micro-displacement sensor based on a two core fiber is proposed, where the sensitivity depends on the bending deformation suffered by multiple fiber loops.…”

“…In reference [ 11 ], an intrinsic micro-displacement sensor based on a two core fiber is proposed, where the sensitivity depends on the bending deformation suffered by multiple fiber loops. In [ 12 ] an ultrasensitive intrinsic fiber sensor based on the macrobending loss at 1.55 μm in a single-mode fiber with wavelength cutoff around 1,060 nm was demonstrated. In this case the measurement range was in the order of 250 μm and a maximum resolution in the order of 40 nm is claimed.…”

Cladding-Mode Backward-Recoupling-Based Displacement Sensor Incorporating Fiber Up Taper and Bragg Grating

“…Optical fiber sensor, by virtue of its passive operation and immunity to electro-magnetic interference, opens up plentiful opportunities for displacement sensing applications in hard-to-reach circumstances. From the intuitive bending induced attenuation [1] to the sophisticated but highly sensitive fiber birefringence based interferometer [2], displacement information can be interrogated through the power change or the wavelength shift. Fiber Bragg grating (FBG), as one of the most widely used fiber sensor devices, also provides the displacement measurement solutions either by using an edge filter to interrogate the resonant wavelength [3] or a cantilever to transfer the displacement into the chirp profile of the FBG [4].…”