Compact fiber-optic vector inclinometer

Department of Electronics, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6.
Optics Letters (Impact Factor: 3.29). 04/2010; 35(7):1034-6. DOI: 10.1364/OL.35.001034
Source: PubMed


What we believe to be a novel fiber-optical inclinometer based on a dual-path core-to-cladding mode coupling mechanism is demonstrated. Both the amplitude and tilt direction of bends about a 2-mm-long flexure joint in an optical fiber can be determined. The sensor head consists of a nonadiabatic abrupt taper cascaded with a weakly tilted fiber Bragg grating. Measured bend angles of up to 12 degrees are demonstrated, as well as a method to increase the sensitivity for bend angles smaller than 4 degrees.

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    • "PTICAL fiber inclinometer is useful for many applications, including structural health monitoring, angle measurement under special environment, geotechnical measurements. Usually, optical fiber inclinometer is based on fiber Bragg gratings[1], [2], [3], phase-shift Bragg gratings[4], taper Michelson interferometer[5], long-period fiber gratings[6], and abrupt taper[7], [8]. B. O. Guan[1] reported a vertical-pendulum based fiber Bragg grating tilt sensor, which has an accuracy of 0.1ºand the resolution of 0.007 º . "
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    ABSTRACT: An optical fiber inclinometer applying modal interference based on an abrupt tapering cascading a peanut-shape configuration is proposed. The abrupt taper splits part of the core mode into cladding modes and the interference occurs when the peanut-shape recombines the cladding modes and core mode together. Four inclinometers with different lengths have been fabricated and characterized, and the high sensitivities of −1.76 and −4.49 nm/° are obtained in the angle range of 0°–3° and 3°–6.66°, respectively.
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    • "Several schemes of optical fiber curvature sensors based on chirped fiber Bragg gratings (CFBG) [7] [8], tilted fiber Bragg gratings (TFBG) [9], long period fiber gratings (LPFG) [10], or Mach–Zehnder fiber interferometers [11] have been demonstrated. However, these systems are complex and expensive. "
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    ABSTRACT: An optical fiber curvature sensor based on interference between LP01–LP02 modes of a circularly symmetric few mode fiber (FMF) is presented. The device consists of two single-mode fiber and a 10-cm FMF. The two single-mode fiber is offset-spliced to each end of the FMF. When the optical fiber is kept straight and fixed, the interference pattern appears in the transmitted spectrum. As the fiber device is bent, the visibility of the interference fringes (at 1530 nm) decreases, reaching values close to 0.3. The dynamic range of the device can be tailored by the proper selection of the length of FMF. The relationship between the fringe visibility and the curvature is linear while the curvature is between 11 m−1 and 16 m−1. The result indicates that the compact sensor can be used in the measurement of large curvature, which is also important in structural health monitoring.
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    • "TFBG refractometers operating in reflection mode were then proposed originally by using cleaved fiber end and metallic coating [8] [11], but the measurements were still based on wavelength shift [8]. Power-referenced designs operating in reflection mode are recently proposed by employing an offset splicing or fiber taper in front of the TFBG to recouple the backforward-propagating cladding modes into the backforwardpropagating core mode [12] [16]. However, the mode coupling structures in these reflection mode designs weaken the fiber strength and introduce high insertion loss that reduces the signal power seriously. "
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    ABSTRACT: A power-referenced refractometer operating in reflection mode is proposed and experimentally demonstrated based on a tilted-fiber Bragg grating (TFBG) cascaded by a reflection-band-matched chirped-fiber Bragg grating (CFBG). The optical signal reflected by the CFBG passes twice through the TFBG that enhances sensitivity of the refractometer. In addition, the optical signal is propagating all the way in the fiber core so that the extra insertion loss is low. Refractive index measurement with sensitivity up to 597.2 μW/R.I.U. is achieved within the range from 1.333 to ~1.42. The maximum detectable refractive index is ~1.45.
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