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Abstract
A micro-displacement sensor consisting of a fiber-loop made with a tapered fiber is reported. The sensor operation is based on the interaction between the fundamental cladding mode propagating through the taper waist and higher order cladding modes excited when the taper is deformed to form a loop. As a result, a transmission spectrum with several notches is observed, where the notch wavelength resonances shift as a function of the loop diameter. The loop diameter is varied by the spatial displacement of one end of the fiber-loop attached to a linear translation stage. In a displacement range of 3.125 mm the maximum wavelength shift is 360.93 nm, with 0.116 nm/μm sensitivity. By using a 1,280 nm broadband low-power LED source and a single Ge-photodetector in a power transmission sensor setup, a sensitivity in the order of 2.7 nW/μm is obtained in ∼1 mm range. The proposed sensor is easy to implement and has a plenty of room to improve its performance.
Highlights
Many industrial and scientific processes require measurement of micro-displacements
We may distinguish two types of fiber optic displacement sensors: extrinsic sensors, where the fiber merely transports the signal from the object being displaced as in reflective [1,2,3,4] or interferometric [5,6,7] sensors; and intrinsic sensors, where the fiber sensitive element experiences displacement, as in those based on fiber Bragg gratings [8,9], or long-period fiber gratings [10]
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
Summary
Many industrial and scientific processes require measurement of micro-displacements. Optical fiber sensors have been applied with success in measurements of micro- and nano-displacements offering. 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. In Reference [13] the bending angle is taken as a measure of displacement which is used as an indirect method to implement acoustic, magnetic, and electric sensors In this case, the bending is applied directly to the taper at the center of the waist by using a capillary tube, which may perturb the interaction between modes at the waist of the taper. Using a monocromatic higher power light source and a higher order sensitivity photodetection system we may significantly increase the resolution of our device
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