An optical fiber sensor system for localization of a vibrational disturbance along the fiber is presented. The sensor system is based on a serial array of identical Fabry-Perot interferometers, formed directly in the single mode SMF-28e fiber by pairs of fiber Bragg gratings with reflectivity of 0.04% each. Interferometers were interrogated by an intensity modulated distributed feedback diode laser. We present a signal processing algorithm for localization of a disturbed interferometer and experimental results for a serial array of 14 in-fiber interferometers. Simple sensor configuration and the use of low-frequency components make it potentially inexpensive and suitable for applications where continuous monitoring for appearance of vibrations is required.Index Terms-Fiber Bragg grating, low-finesse Fabry-Perot interferometer, optical fiber sensor.
In this work, two novel stable multi-wavelength fiber laser configurations are proposed and demonstrated by using a spool of a single-mode fiber as an optical loop mirror and one or two fiber ring cavities, respectively. The lasers are comprised of fiber Bragg grating reflectors as the oscillation wavelength selecting filters. The influence of the length of the spool of fiber on the laser stability both in terms of wavelength and laser output power was investigated. An application for temperature measurement is also shown.
We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented using an array of ultra-low-reflectivity fiber Bragg gratings as weak reflectors.
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