Few-mode Rayleigh-based distributed fiber sensor for simultaneous temperature and strain sensing
Aspects of the present disclosure describe Rayleigh-based DTSS that utilizes few-mode fiber (FMF), which supports multiple spatial modes. For each spatial mode, a wavelength-scanning configuration gives the relative wavelength (or frequency) shift between two consecutive measurements. The temperature and strain changes can therefore be separated through different temperature/strain sensitivities of various mode-pairs. Advantageously, Rayleigh-based DTSS according to aspects of the present disclosure removes temperature-strain ambiguity, enhances measurement accuracy, reduces errors. and enables new features for multi-parameter sensing.
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.
2. The system of claim 1 wherein the detector is a coherent receiver.
3. 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 system is configured to scan the wavelength of the light source and the stack detector output signals a 2-dimensional Rayleigh pattern of mode-pairs is constructed.
4. The system of claim 3 configured to adjust wavelength shift vs. temperature/strain change.
5. The system of claim 3 wherein the detector is a coherent receiver.