US 12,345,585 B2
Few-mode Rayleigh-based distributed fiber sensor for simultaneous temperature and strain sensing
Jian Fang, Princeton, NJ (US); and Ting Wang, West Windsor, NJ (US)
Assigned to NEC Corporation, Tokyo (JP)
Filed by NEC Laboratories America, Inc., Princeton, NJ (US)
Filed on Oct. 16, 2022, as Appl. No. 17/966,869.
Claims priority of provisional application 63/270,218, filed on Oct. 21, 2021.
Prior Publication US 2023/0125375 A1, Apr. 27, 2023
Int. Cl. G01L 1/24 (2006.01); G01K 11/32 (2021.01); G01K 11/3206 (2021.01); G01K 1/26 (2006.01)
CPC G01L 1/242 (2013.01) [G01K 11/32 (2013.01); G01K 11/3206 (2013.01); G01K 1/26 (2013.01)] 5 Claims
OG exemplary drawing
 
1. A few-mode, wavelength-scanning, coherent optical time domain reflectometry system comprising:
a wavelength-tunable light source configured to generate light;
a modulator configured to generate light pulses from light received from the wavelength-tunable light source;
a controller configured to control/tune wavelength(s) of light output by the wavelength tunable light source and control light pulse generation by the modulator;
a first amplifier configured to amplify the light pulses generated by the modulator;
a filter configured to filter the amplified light pulses;
a sensing media comprising a few-mode fiber (FMF) that supports N spatial modes;
a mode-selective multiplexer (MUX)/demultiplexer (DEMUX) configured to couple/convert an optical signal from the fundamental mode in a single mode fiber (SMF) to a particular spatial mode in the FMF, the MUX/DEMUX located in an optical path between the filter and the FMF; and
a first switch configured to selectively excite a desired spatial mode via the MUX/DEMUX, said first switch located in an optical path between the filter and the MUX/DEMUX;
said system configured to
launch a particular spatial mode into the FMF while Rayleigh scattering propagates backward;
convert backscattered signals of various spatial modes into fundamental modes by the MUX/DEMUX;
selecting, by a second switch, a particular fundamental mode to collect; and
directing the collected fundamental mode to a detector, the detector configured to provide output to an analog-to-digital converter, the digital output of which is directed to the controller for processing;
said system further comprising a second amplifier positioned in an optical path between the second switch and the detector, said second amplifier configured to amplify selected scattering modes prior to detection;
wherein the light source is one selected from the group consisting of distributed feedback (DFB) laser, external cavity laser and another wavelength-tunable light source;
wherein the controller is configured to control wavelength tuning of m different wavelengths;
wherein the first that amplifies the pulses generated by the modulator is an acousto-optic-modulator (AOM), or a semiconductor optical amplifier (SOA);
wherein said system is configured to selectively launch light of one spatial mode i, and collect Rayleigh backscatter of a particular spatial mode j, wherein the launch mode i and the collected mode j, form one mode-pair u=i−j; and
wherein the mode-pair corresponds to intramodal Rayleigh scattering if i=j and corresponds to intermodal if i≠j.