CN115235367B - High-precision double-frequency optical frequency domain reflectometer with large strain measurement range - Google Patents
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
- G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means
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- G—PHYSICS
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
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- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
- G01D5/35387—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques using wavelength division multiplexing
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Abstract
The invention discloses a high-precision double-frequency optical frequency domain reflectometer with a large strain measurement range, which comprises: the optical modulation module is used for combining continuous light beams and modulating double-frequency continuous light into sweep continuous light; the optical interference module is used for interfering the backward scattered light emitted by the optical fiber to be detected with the sweep continuous light and adjusting the polarization state of the backward scattered light to obtain interference light; the photoelectric conversion module is used for converting the interference light into an electric signal; and the acquisition and processing module is connected with the photoelectric conversion module and is used for acquiring data and analyzing and processing the data. The dual-frequency optical frequency domain reflectometer utilizes the phase difference of two frequency optical waves to carry out strain measurement, solves the problem that the maximum dynamic strain measurable by a single-frequency optical system is limited by optical frequency under the condition that the sweep frequency repetition frequency and the applied strain vibration frequency are unchanged, and maintains high-precision measurement.
Description
Technical Field
The patent belongs to the field of optical fiber sensing, and particularly relates to a high-precision double-frequency optical frequency domain reflectometer with a large strain measurement range.
Background
The distributed optical fiber sensing technology has the advantages of electromagnetic interference resistance, high sensitivity, easiness in implementation and the like, and has been widely applied to the fields of perimeter security, structural health monitoring, seismic wave detection and the like. When the optical fiber to be measured is disturbed by an external environment (such as dynamic strain), the length, the core diameter and the refractive index characteristics of the optical fiber change, so that the amplitude and the phase of the Rayleigh scattered light in the optical fiber are changed; the detection of the disturbance signals is further realized by analyzing the Rayleigh scattering signals before and after the disturbance event. In early sensing systems, one merely achieved the localization of disturbance events based on the relative changes in the rayleigh scattering signal intensities, and no quantitative measurement could be achieved. Further studies have shown that the amount of change in the phase of the Rayleigh scattering signal is linear with the amount of strain applied to the fiber, and thus the amount of dynamic strain can be quantitatively measured by demodulating the phase change of the probe light.
Among the detection modes, the phase sensitive optical frequency domain reflectometer is widely focused due to the advantages of high resolution, high sensitivity and the like. The optical frequency domain reflection technology uses frequency modulation continuous wave as detection light, the spatial resolution depends on the sweep frequency range, and the problem that the spatial resolution and the detection distance are mutually restricted in a pulse detection mode is solved. The phase sensitive optical frequency domain reflectometer demodulates the phase spectrum of the Rayleigh scattering signal, and performs phase difference before and after a strain event to obtain the magnitude of phase change, so as to demodulate the dynamic strain applied on the optical fiber.
In measuring dynamic strain using a phase sensitive optical frequency domain reflectometer, unwrapping algorithms are required to unwrap the phase measurements to make the phases continuous. However, a precondition for proper demodulation using the unwrapping algorithm is that the absolute value of the phase change of adjacent measurement points cannot exceed pi (pi threshold condition), which limits the maximum range of measurable dynamic strain. Assuming that the applied dynamic strain is a single frequency sinusoidal signal, based on the pi threshold condition, the system measurable dynamic strain is derived as:
wherein f p Frequency sweep repetition frequency f for optical frequency domain reflectometer ε To apply a strained vibration frequency. In the prior art, the phase sensitive optical frequency domain reflection system adopts single-frequency light with the wavelength of light being about 1550nm (optical frequency-193.5 THz), and the maximum measurable dynamic strain is limited by the optical frequency v under the condition that the sweep repetition frequency and the applied strain vibration frequency are unchanged.
Disclosure of Invention
In order to solve the problem that the measurable maximum dynamic strain is limited by the optical frequency v under the condition that the sweep frequency repetition frequency and the applied strain vibration frequency are unchanged, the invention provides a high-precision double-frequency optical frequency domain reflectometer which is used for strain measurement by utilizing the phase difference of two frequency optical waves. This approach is equivalent to forming a low frequency carrier in the measurement system, increasing the measurement range of strain; the measuring system adopts Fourier phase spectrum for demodulation, and leads single-frequency optical phase unwrapping by means of phase difference between double-frequency lights, thereby realizing high-precision measurement of large dynamic strain range.
In order to achieve the above object, the present invention provides the following solutions: a high-accuracy dual-frequency optical frequency domain reflectometer with a large strain measurement range, comprising:
the optical modulation module is used for converging the continuous light emitted by the laser into double-frequency continuous light and modulating the double-frequency continuous light into sweep continuous light;
the optical interference module is used for interfering the backward scattered light emitted by the optical fiber to be detected with the sweep continuous light and adjusting the polarization state of the backward scattered light to obtain interference light;
the photoelectric conversion module is used for converting the interference light into an electric signal;
and the acquisition and processing module is connected with the photoelectric conversion module and is used for analyzing and processing the electric signals.
Preferably, the light modulation module is connected with the light interference module through a first optical coupler;
the optical interference module is connected with the photoelectric conversion module through a second optical coupler;
the first optical coupler and the second optical coupler are used for branching the light.
Preferably, the light modulation module comprises a beam combination unit and a conversion unit;
the beam combining unit is used for combining continuous light into double-frequency continuous light;
the conversion unit is used for modulating the dual-frequency continuous light into sweep frequency continuous light.
Preferably, the beam combining unit comprises a narrow linewidth laser and a first wavelength division multiplexer;
the narrow linewidth laser comprises a first narrow linewidth laser and a second narrow linewidth laser;
the first narrow linewidth laser is used for emitting continuous light with a first optical frequency;
the second narrow linewidth laser is used for emitting continuous light with a second optical frequency;
the first wavelength division multiplexer is used for combining the continuous light of the first optical frequency and the continuous light of the second optical frequency.
Preferably, the conversion unit comprises an arbitrary waveform generator, a radio frequency amplifier and a modulator;
the arbitrary waveform generator is used for sending out a sweep frequency signal;
the radio frequency amplifier is connected with the arbitrary waveform generator and is used for amplifying the sweep frequency signal;
the modulator is connected with the radio frequency amplifier and used for modulating the dual-frequency continuous light into sweep frequency continuous light.
Preferably, the optical interference module comprises a first optical coupler, an optical amplifier, an optical fiber to be tested, an optical circulator, a polarization controller and a second optical coupler;
the first optical coupler is used for splitting light waves, wherein one path is a detection path and the other path is a reference path;
the optical amplifier is connected with the first optical coupler and is used for increasing the optical power of the incoming fiber;
the optical fiber to be tested is used for generating backward Rayleigh scattered light;
the optical circulator is respectively connected with the optical amplifier, the optical fiber to be tested and the polarization controller and is used for injecting light waves into the optical fiber to be tested, receiving backward Rayleigh scattered light generated by the optical fiber to be tested and then outputting the backward Rayleigh scattered light to the polarization controller;
the polarization controller is used for adjusting the polarization state.
The second optical coupler is used for interfering the optical wave combination beams of the detection path and the reference path.
Preferably, the photoelectric conversion module comprises a second wavelength division multiplexer, a third wavelength division multiplexer, a first photoelectric detector and a second photoelectric detector;
the second wavelength division multiplexer and the third wavelength division multiplexer are connected with the second optical coupler and are used for wavelength division multiplexing;
the first photoelectric detector is respectively connected with the second wavelength division multiplexer and the third wavelength division multiplexer and is used for receiving beat frequency signals of a first optical frequency;
the second photoelectric detector is respectively connected with the second wavelength division multiplexer and the third wavelength division multiplexer and is used for receiving beat frequency signals of a second optical frequency.
The invention discloses the following technical effects:
1. the phase sensitive optical frequency domain reflectometer can adjust the sweep frequency range to obtain high spatial resolution, and solves the problem that the spatial resolution and the detection distance cannot be considered in a pulse detection mode; and the demodulation is carried out by adopting the frequency domain Fourier phase, so that the method has the advantage of high sensitivity.
2. The dual-frequency measurement system provided by the invention utilizes the phase difference between two frequencies for demodulation, and compared with the traditional single-frequency optical detection mode, the dual-frequency measurement system greatly improves the measurement range of dynamic strain. The method comprises the steps of detecting continuous light with the frequency of a first frequency and a second frequency, and increasing the measurable dynamic strain of the dual-frequency measurement system to be the frequency of the first frequency divided by the frequency difference times (or the frequency of the second frequency divided by the frequency difference times) of the single-frequency measurement system.
3. In order to improve the measurement accuracy, the phase difference between the dual-frequency light is used for guiding the single-frequency light phase to unwind during phase demodulation, so that the measurement accuracy of the dual-frequency light system is improved to the single-frequency light system level. The high-precision dual-frequency optical frequency domain reflectometer provided by the invention provides an effective detection means for application scenes with large strain and high vibration frequency.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a system structure of a dual-band optical frequency domain reflectometer according to an embodiment of the present invention;
in the figure: a first narrow linewidth laser, a second narrow linewidth laser, a first Wavelength Division Multiplexer (WDM), a modulator (4), an arbitrary waveform generator (5), a radio frequency amplifier (6), a first optical coupler (7), an optical amplifier (8), a 9-optical circulator (9), an optical fiber to be tested (10), a polarization controller (11), a second optical coupler (12), a second WDM, a third WDM (WDM), a first photoelectric detector (15), a second photoelectric detector (16) and a data acquisition and processor (17).
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
As shown in FIG. 1, the invention provides a high-precision dual-frequency optical frequency domain reflectometer with a large strain measurement range, and the system structure is as follows: the first narrow linewidth laser 1 and the second narrow linewidth laser 2 respectively emit a frequency v 1 And v 2 Is combined by a first wavelength division multiplexer 3, and the first wavelength division multiplexer 3 is connected with an optical input port of a modulator 4; the arbitrary waveform generator 5 is connected with the radio frequency amplifier 6, the output end of the radio frequency amplifier 6 is connected with the radio frequency input end of the modulator 4, the combined beam is modulated into sweep continuous light, the light output port of the modulator 4 is connected with the first optical coupler 7, the first optical coupler 7 is divided into two paths, one path is a detection path, the other path is sequentially connected with the optical amplifier 8 and the port a of the optical circulator 9, the port b of the optical circulator 9 is connected with the optical fiber 10 to be detected, and the port c is connected with the polarization controller 11; the other path of the output of the first optocoupler 7 serves as a reference path. The detection path and the reference path are connected with a second optical coupler 12, two output ports of the second optical coupler 12 are respectively connected with a second wavelength division multiplexer 13 and a third wavelength division multiplexer 14, and the two wavelength division multiplexers are used for converting the frequency v into the frequency v 1 And v 2 Is connected to the first photodetector 15 and the second photodetector 16, respectively, converts the optical signal into an electrical signal, and is connected to the data acquisition and processor 17.
Further optimizing scheme, the optical frequency v of the first narrow linewidth laser 1 And the optical frequency v of the second narrow linewidth laser 2 May differ by hundreds of GHz to THz.
Further optimizing the scheme, wherein the splitting ratio of the first optical coupler 7 is 90:10 or 80:20; the split ratio of the second optocoupler 12 is 50:50.
Further, in the optimized scheme, the optical fiber 10 to be measured may be a common single mode fiber, a polarization maintaining fiber, an FBG fiber, a rayleigh scattering enhancement fiber, etc.
Further optimizing the scheme, the demodulation method of the signal is as follows:
firstly, time domain beat frequency signals acquired in each sweep frequency period are subjected to Fourier transformation to be analyzed in a frequency domain, the magnitude of the beat frequency reflects the position information of an optical fiber, and the Fourier phase at a certain frequency reflects the phase information at a corresponding position;
the second step, extracting Fourier phase information of the frequency domain signals in each sweep frequency period under two single frequencies respectively, and obtaining winding values of phase change caused by strain under each moment under two single frequencies respectively by difference on a distance axis and a slow change time axis
And->
Step three, the phase difference of two single-frequency lights is obtained
The method comprises the following steps:
where n is the refractive index of the fiber, κ is the strain coefficient of the fiber, L is the length of the strain region, ε is the strain magnitude, and c is the speed of light in vacuum. Where Δν=ν 1 -ν 2 Is the frequency difference between the two light waves. From the above, compared with single-frequency light, the phase caused by the same strain in the dual-frequency measurement systemVariation of
Reduced, and thus a greater range of dynamic strain can be measured. With frequency v 1 And v 2 When continuous light of (1) is detected, the measurable dynamic strain of the dual-frequency measurement system is improved to single-frequency v 1 V under measurement system 1 The multiple of [ delta ] v (or single frequency v 2 V under measurement system 2 /Deltav times);
fourth, in order to improve the measurement accuracy in the dual-frequency system, the phase difference between the dual-frequency light is used
Guiding the single frequency optical phase to unwind. At frequency v 1 For example, the single frequency light is a strain-induced phase change after single frequency light unwinds +.>
For winding phase->
Adding an integer multiple of 2 pi, i.e. +.>
The unwrapping is converted into a wrapped integer k 1 Is a value of (2); let the scale factor M 1 ＝ν 1 Deltav, according to formula->
Obtaining integer k 1 And further demodulating to obtain
The precision under single-frequency light measurement is maintained;
and fifthly, obtaining the strain epsilon according to the linear relation between the phase change and the strain, and correspondingly demodulating the strain epsilon at each moment on a slow-change time axis to obtain a strain curve which changes with time and is caused by vibration.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.
Claims (7)
1. A high-accuracy dual-frequency optical frequency domain reflectometer with a large strain measurement range, comprising:
the optical modulation module is used for converging the continuous light emitted by the laser into double-frequency continuous light and modulating the double-frequency continuous light into sweep continuous light;
the optical interference module is used for interfering the backward scattered light emitted by the optical fiber to be detected with the sweep continuous light and adjusting the polarization state of the backward scattered light to obtain interference light;
the photoelectric conversion module is used for converting the interference light into an electric signal;
and the acquisition and processing module is connected with the photoelectric conversion module and is used for analyzing and processing the electric signals.
2. The high-precision dual-frequency optical frequency domain reflectometer with large strain measurement range as claimed in claim 1,
the light modulation module is connected with the light interference module through a first optical coupler in the light interference module;
the optical interference module is connected with the photoelectric conversion module through a second optical coupler in the optical interference module.
3. The high-precision dual-frequency optical frequency domain reflectometer with large strain measurement range as claimed in claim 1,
the light modulation module comprises a beam combining unit and a conversion unit;
the beam combining unit is used for combining continuous light into double-frequency continuous light;
the conversion unit is used for modulating the dual-frequency continuous light into sweep frequency continuous light.
4. A high-precision dual-frequency optical frequency domain reflectometer with large strain measurement range as claimed in claim 3,
the beam combining unit comprises a narrow linewidth laser and a first wavelength division multiplexer;
the narrow linewidth laser comprises a first narrow linewidth laser and a second narrow linewidth laser;
the first narrow linewidth laser is used for emitting continuous light with a first optical frequency;
the second narrow linewidth laser is used for emitting continuous light with a second optical frequency;
the first wavelength division multiplexer is used for combining the continuous light of the first optical frequency and the continuous light of the second optical frequency.
5. A high-precision dual-frequency optical frequency domain reflectometer with large strain measurement range as claimed in claim 3,
the conversion unit comprises an arbitrary waveform generator, a radio frequency amplifier and a modulator;
the arbitrary waveform generator is used for sending out a sweep frequency signal;
the radio frequency amplifier is connected with the arbitrary waveform generator and is used for amplifying the sweep frequency signal;
the modulator is connected with the radio frequency amplifier and used for modulating the dual-frequency continuous light into sweep frequency continuous light.
6. The high-precision dual-frequency optical frequency domain reflectometer with large strain measurement range as claimed in claim 1,
the optical interference module comprises a first optical coupler, an optical amplifier, an optical fiber to be tested, an optical circulator, a polarization controller and a second optical coupler;
the first optical coupler is used for splitting light waves, wherein one path is a detection path and the other path is a reference path;
the optical amplifier is connected with the first optical coupler and is used for increasing the optical power of the incoming fiber;
the optical fiber to be tested is used for generating backward Rayleigh scattered light;
the optical circulator is respectively connected with the optical amplifier, the optical fiber to be tested and the polarization controller and is used for injecting light waves into the optical fiber to be tested, receiving backward Rayleigh scattered light generated by the optical fiber to be tested and then outputting the backward Rayleigh scattered light to the polarization controller;
the polarization controller is used for adjusting the polarization state;
the second optical coupler is used for interfering the optical wave combination beams of the detection path and the reference path.
7. The high-precision dual-frequency optical frequency domain reflectometer with large strain measurement range as claimed in claim 1,
the photoelectric conversion module comprises a second wavelength division multiplexer, a third wavelength division multiplexer, a first photoelectric detector and a second photoelectric detector;
the second wavelength division multiplexer and the third wavelength division multiplexer are connected with the second optical coupler and are used for wavelength division multiplexing;
the first photoelectric detector is respectively connected with the second wavelength division multiplexer and the third wavelength division multiplexer and is used for receiving beat frequency signals of a first optical frequency;
the second photoelectric detector is respectively connected with the second wavelength division multiplexer and the third wavelength division multiplexer and is used for receiving beat frequency signals of a second optical frequency.
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| CA1145927A (en) * | 1981-10-23 | 1983-05-10 | Marc Bage | Method and apparatus for optical fiber fault location |
| JP3262311B2 (en) * | 1996-02-09 | 2002-03-04 | 日本電信電話株式会社 | Frequency sweep error detection method and circuit, optical frequency sweep light source, and optical frequency domain reflection measurement circuit |
| GB0409865D0 (en) * | 2004-05-01 | 2004-06-09 | Sensornet Ltd | Direct measurement of brillouin frequency in distributed optical sensing systems |
| CN103984184B (en) * | 2014-05-19 | 2016-08-24 | 上海交通大学 | Light pulse compressive reflexes device |
| CN205453695U (en) * | 2016-01-05 | 2016-08-10 | 上海交通大学 | Optical frequency territory reflect meter based on frequency synthesis |
| EP3658859B1 (en) * | 2017-07-26 | 2024-06-05 | Terra15 Pty Ltd | Distributed optical sensing systems and methods |
| CN107990997B (en) * | 2017-11-20 | 2019-08-09 | 大连理工大学 | A kind of double light source self-correction formula fiber optic Distributed Temperature Fast measurement systems and method |
| JP7331373B2 (en) * | 2019-02-12 | 2023-08-23 | 日本電信電話株式会社 | Optical frequency reflection measurement device and its measurement method |
| CN110375779B (en) * | 2019-07-29 | 2021-06-04 | 武汉昊衡科技有限公司 | Device and method for improving OFDR frequency domain sampling rate |
| EP3916365A1 (en) * | 2020-05-25 | 2021-12-01 | Aragon Photonics Labs, S.L.U. | Method and system for interrogating optical fibers |
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