CN113686366A - Optical frequency domain reflectometer device based on Fourier domain mode locking and measuring method - Google Patents
Optical frequency domain reflectometer device based on Fourier domain mode locking and measuring method Download PDFInfo
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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
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- 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
Abstract
The invention provides an optical frequency domain reflectometer device based on Fourier domain mode locking and a measuring method, and belongs to the field of optical frequency domain reflectometers. The problems that the conventional optical frequency domain reflectometer device and method are limited by slow tuning speed of a tuning light source, small tuning range and polarization sensitivity are solved. The Fourier domain mode-locking tuning light source is respectively connected with an auxiliary interferometer, a double-shaft working polarization splitting prism and a polarization-maintaining optical amplifier after sequentially passing through a second optical isolator and a second polarization-maintaining optical fiber coupler, the auxiliary interferometer is connected with a signal processing module, the double-shaft working polarization splitting prism is respectively connected with a fourth polarization-maintaining optical fiber coupler and a fifth polarization-maintaining optical fiber coupler, and the polarization-maintaining optical amplifier and a second delay line are respectively connected with the fourth polarization-maintaining optical fiber coupler and the fifth polarization-maintaining optical fiber coupler after sequentially passing through a polarization-maintaining circulator and a single-shaft working polarization splitting prism. It is mainly used for optical frequency domain reflectometer.
Description
Technical Field
The invention belongs to the field of optical frequency domain reflectometers, and particularly relates to an optical frequency domain reflectometer device and a measuring method based on Fourier domain mode locking.
Background
In recent years, with the deepening of the functions of the intelligent flexible structure in the fields of aerospace, smart cities, smart medical treatment and the like, how to perform operations such as structural health monitoring, adaptive control and the like on the intelligent flexible structure becomes one of the problems to be solved urgently. On the one hand, the optical fiber sensor with the characteristics of flexibility, light weight, electromagnetic shielding and the like has good compatibility with the intelligent flexible structure; furthermore, the optical fiber itself can serve as a good medium for optical signal transmission, which enables the fiber sensor to perform distributed measurement of stress/strain conditions in the intelligent flexible structure.
The existing distributed optical fiber measuring device and method mainly comprise two types of optical time domain reflectometers and optical frequency domain reflectometers. The method is mainly limited in that the pulse width of the pulse reference beam cannot be limited to be free of limited pressure, the spatial resolution of the pulse reference beam is usually dozens of centimeters or even meters, and the measurement requirement of an intelligent flexible structure cannot be met. The optical frequency domain reflectometer measures using a continuous reference beam with a tunable center wavelength and locates by calculating the beat frequency between the backscattered beam generated by the continuous reference beam and the continuous reference beam. The optical frequency domain reflectometer replaces the requirement of the optical time domain reflectometer on a pulse reference beam by appointing a tuning curve between a time domain and a frequency domain, the spatial resolution of the optical frequency domain reflectometer mainly depends on the tuning range and the tuning precision of a pump beam/reference beam, and the optical frequency domain reflectometer is expected to reach the millimeter order. Therefore, the key point that the optical frequency domain reflectometer can work fast, with high spatial resolution and high precision is to realize the large-range and high-precision pump light book/reference beam tuning.
However, the external cavity laser tuning technology ECL, the vertical cavity surface emitting laser tuning technology VCSEL, the distributed bragg reflection laser tuning technology DBR and the like adopted in the conventional optical frequency domain reflectometer apparatus and method implement pump beam tuning by repeatedly starting and stopping different laser longitudinal modes, so that the introduced time delay and phase noise restrict the improvement of the tuning speed and the tuning precision of the pump light source. In addition, when the measuring signal of the optical frequency domain reflectometer apparatus and method is demodulated by using an interference method, the deviation of the polarization state between the reference beam and the measuring beam will also cause the accuracy of the measurement result to be lowered.
Disclosure of Invention
The invention provides an optical frequency domain reflectometer device and a measuring method based on Fourier domain mode locking, aiming at solving the problems in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme: a Fourier domain mode locking based optical frequency domain reflectometer device comprises a Fourier domain mode locking tuning light source, a second optical isolator, a second polarization-maintaining optical fiber coupler, an auxiliary interferometer, a double-shaft working polarization beam splitter prism, a fourth polarization-maintaining optical fiber coupler, a first balance detector, a signal processing module, a second balance detector, a fifth polarization-maintaining optical fiber coupler, a single-shaft working polarization beam splitter prism, a polarization-maintaining circulator, a second delay line and a polarization-maintaining optical amplifier, wherein the Fourier domain mode locking tuning light source is respectively connected with the auxiliary interferometer, the double-shaft working polarization beam splitter prism and the polarization-maintaining optical amplifier after passing through the second optical isolator and the second polarization-maintaining optical fiber coupler in sequence, the auxiliary interferometer is connected with the signal processing module, the double-shaft working polarization beam splitter prism is respectively connected with the fourth polarization-maintaining optical fiber coupler and the fifth polarization-maintaining optical fiber coupler, the polarization maintaining optical amplifier and the second delay line are sequentially connected with a fourth polarization maintaining optical fiber coupler and a fifth polarization maintaining optical fiber coupler after passing through the polarization maintaining circulator and the single-axis working polarization splitting prism, the fourth polarization maintaining optical fiber coupler is connected with the first balance detector and the signal processing module to form a passage, and the fifth polarization maintaining optical fiber coupler is connected with the second balance detector and the signal processing module to form a passage.
Furthermore, the Fourier domain mode-locked tuned light source comprises an optical amplifier, a tunable optical filter, a polarization dispersion management delay line, a first optical isolator, a first polarization-maintaining fiber coupler and a narrow-linewidth optical filter which are sequentially connected, wherein the tunable optical filter is connected with the function generator, and the narrow-linewidth optical filter is connected with a second optical isolator.
Furthermore, the transmission and polarization characteristics of the polarization dispersion management delay line are adjustable.
Furthermore, the polarization dispersion management delay line regulates and controls transmission and polarization characteristics by means of writing a chirped grating, a series dispersion displacement optical fiber, a dispersion compensation optical fiber, a glass slide, an optical fiber cone or a polarization controller.
Furthermore, supplementary interferometer includes third polarization maintaining fiber coupler, first delay line, photoelectric detector, first Faraday speculum and second Faraday speculum, second polarization maintaining fiber coupler links to each other with third polarization maintaining fiber coupler, third polarization maintaining fiber coupler links to each other with photoelectric detector, first Faraday speculum and second Faraday speculum respectively, be provided with first delay line between third polarization maintaining fiber coupler and the first Faraday speculum, photoelectric detector links to each other with signal processing module.
The invention also provides a measuring method of the optical frequency domain reflectometer device based on Fourier domain mode locking, which comprises the following steps:
step 1: the second optical isolator and the second polarization-maintaining fiber coupler are divided into a trigger beam T, a reference beam R and a pumping beam P, and the three beams respectively flow into the auxiliary interferometer, the double-shaft working polarization beam splitter prism and the polarization-maintaining optical amplifier;
step 2: the trigger light beam T enters the signal processing module after being processed by the auxiliary interferometer and is used as a trigger signal of the signal processing module;
and step 3: the reference beam R is divided into a slow axis alignment reference beam R1 and a fast axis alignment reference beam R2 with equal amplitude through a biaxial working polarization beam splitter prism;
and 4, step 4: the pump light beam P flows into a second delay line through a port 1 and a port 2 of the polarization-maintaining circulator, and the pump light beam P and the second delay line generate a measuring light beam S through Rayleigh scattering interaction;
and 5: the measuring beam S is divided into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2 through a single-axis working polarization beam splitter prism;
step 6: after the slow axis alignment reference beam R1 and the slow axis alignment measuring beam S1 are combined and interfered by the fourth polarization maintaining fiber coupler, the combined and interfered beams are converted into a slow axis interference signal A by the first balanced detector and input into the signal processing module;
and 7: the fast axis alignment reference beam R2 and the fast axis alignment measuring beam S2 are combined and interfered by the fifth polarization maintaining fiber coupler, converted into a fast axis interference signal B by the second balanced detector and input into the signal processing module;
and 8: and the signal processing module integrates the slow axis interference signal A and the fast axis interference signal B to obtain the stress/strain information to be measured.
Further, the measuring beam S in step 5 is an arbitrarily polarized beam, wherein
A polarization mode and
the polarization mode is divided into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2 by a single axis working polarization beam splitter prism.
Further, the signal processing method of the signal processing module in step 8 includes the following steps:
step 8.1: the signal processing module records | A | in a single wavelength tuning period by calculating the square sum of the slow axis interference signal A and the fast axis interference signal B2+|B|2Trend over time;
step 8.2: utilizing fast Fourier transform to tune | A in a single wavelength tuning period2+|B|2Processing the time variation trend to obtain | A2+|B|2The distribution of different beat frequency components;
step 8.3: combining each sensing position in the second delay line with | A2+|B|2By making the Y component correspond to the Y component one by one2+|B|2The beat frequency component in (1) is subjected to local inverse fast Fourier transform to access each sensing position in the second delay line, and the local inverse fast Fourier transform results in the presence or absence of stress/strain are subjected to mutual processingAnd (4) performing a correlation operation to obtain stress/strain information of the sensing position.
Furthermore, when continuous and repetitive spectral analysis is required, the output waveform of the function generator is set to be sawtooth-shaped.
Compared with the prior art, the invention has the beneficial effects that: the invention solves the problems that the existing optical frequency domain reflectometer device and method are limited by slow tuning speed of a tuning light source, small tuning range and polarization sensitivity, and the measurement speed, the spatial resolution and the measurement precision are difficult to improve.
According to the invention, the transmission and polarization characteristics of the polarization dispersion management delay line are regulated, the material dispersion and the polarization mode dispersion among longitudinal mode modes in the Fourier domain mode-locked tuned light source are inhibited, and the reference beam, the pump beam and the trigger beam can be controlled to be linear polarization beams; by matching the tuning period of the function generator with the one-way transition time of each longitudinal mode in the Fourier domain mode locking tuning light source, each longitudinal mode can be stably evolved in the Fourier domain mode locking tuning light source; and controlling the longitudinal mode modes to be output sequentially according to the wavelength sequence through the tunable optical filter. The invention avoids the repeated oscillation starting and oscillation stopping of the reference beam, the pumping beam and the trigger beam in the measuring process in the conventional optical frequency domain reflectometer device and method, can realize large-range, quick and stable tuning of the reference beam, the pumping beam and the trigger beam, and further improves the measuring speed and the spatial resolution of the optical frequency domain reflectometer.
The invention divides the linearly polarized reference beam into the equal-amplitude slow axis alignment reference beam and the fast axis alignment reference beam through the double-axis working polarization beam splitter prism; in the measuring beam by a single-axis working polarizing beam splitter prism
A polarization mode and
the polarization mode is divided into a slow axis alignment measuring beam and a fast axis alignment measuring beam; by a first balanced detector and a second balanced detectorIndependent detection of slow axis interference signals and fast axis interference signals enables optical frequency domain reflectometry apparatus and methods to be spared from
A polarization mode and
the influence of polarization mode crosstalk further improves the measurement precision of the optical frequency domain reflectometer.
Drawings
FIG. 1 is a schematic structural diagram of an optical frequency domain reflectometer apparatus based on Fourier domain mode locking according to the present invention;
FIG. 2 is a schematic view of a biaxial working polarizing beam splitter prism according to the present invention;
FIG. 3 is a schematic view of a single-axis working polarizing beam splitter prism according to the present invention;
FIG. 4 is a schematic diagram of a signal processing method according to the present invention;
FIG. 5 is a schematic diagram of the output waveform of the function generator according to the present invention.
1-Fourier domain mode-locked tuned light source, 101-optical amplifier, 102-tunable optical filter, 103-function generator, 104-polarization dispersion management delay line, 105-first optical isolator, 106-first polarization-maintaining fiber coupler, 107-narrow linewidth optical filter, 2-second optical isolator, 3-second polarization-maintaining fiber coupler, 4-auxiliary interferometer, 401-third polarization-maintaining fiber coupler, 402-first delay line, 403-photoelectric detector, 404-first Faraday mirror, 405-second Faraday mirror, 5-biaxial working polarization splitting prism, 6-fourth polarization-maintaining fiber coupler, 7-first balance detector, 8-signal processing module, 9-second balance detector, 10-a fifth polarization maintaining fiber coupler, 11-a single-axis working polarization beam splitting prism, 12-a polarization maintaining circulator, 13-a second delay line, 14-a polarization maintaining optical amplifier, R-reference beams, R1-slow axis alignment reference beams, R2-fast axis alignment reference beams, S-measuring beams, S1-slow axis alignment measuring beams, S2-fast axis alignment measuring beams, T-trigger beams, P-pumping beams, A-slow axis interference signals and B-fast axis interference signals.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely explained below with reference to the drawings in the embodiments of the present invention.
Referring to fig. 1 to illustrate the present embodiment, a fourier domain mode-locked optical frequency domain reflectometer apparatus includes a fourier domain mode-locked tuning light source 1, a second optical isolator 2, a second polarization maintaining fiber coupler 3, an auxiliary interferometer 4, a biaxial working polarization splitting prism 5, a fourth polarization maintaining fiber coupler 6, a first balance detector 7, a signal processing module 8, a second balance detector 9, a fifth polarization maintaining fiber coupler 10, a uniaxial working polarization splitting prism 11, a polarization maintaining circulator 12, a second delay line 13, and a polarization maintaining optical amplifier 14, wherein the fourier domain mode-locked tuning light source 1 is connected to the auxiliary interferometer 4, the biaxial working polarization splitting prism 5, and the polarization maintaining optical amplifier 14 after passing through the second optical isolator 2 and the second polarization maintaining fiber coupler 3 in sequence, the auxiliary interferometer 4 is connected to the signal processing module 8, and the biaxial working polarization maintaining fiber coupler 5 is connected to the fourth polarization maintaining fiber coupler 6 and the fifth polarization maintaining fiber coupler 6, respectively The polarization maintaining optical fiber coupler is characterized in that the polarization maintaining optical fiber coupler 10 is connected, the polarization maintaining optical amplifier 14 and the second delay line 13 are sequentially connected with the polarization maintaining circulator 12 and the single-shaft working polarization splitting prism 11 and then are respectively connected with the fourth polarization maintaining optical fiber coupler 6 and the fifth polarization maintaining optical fiber coupler 10, the fourth polarization maintaining optical fiber coupler 6 is connected with the first balance detector 7 and the signal processing module 8 to form a channel, and the fifth polarization maintaining optical fiber coupler 10 is connected with the second balance detector 9 and the signal processing module 8 to form a channel.
The fourier domain mode-locked tuned light source 1 of this embodiment includes an optical amplifier 101, a tunable optical filter 102, a polarization dispersion management delay line 104, a first optical isolator 105, a first polarization maintaining fiber coupler 106, and a narrow linewidth optical filter 107, which are connected in sequence, where the tunable optical filter 102 is connected to a function generator 103, the narrow linewidth optical filter 107 is connected to a second optical isolator 2, the polarization dispersion management delay line 104 has adjustable transmission and polarization characteristics, and the polarization dispersion management delay line 104 is formed by writing a chirped grating, a serial dispersion shifted fiber, a dispersion compensating fiber, a glass fiber, and a chirped gratingThe transmission and polarization characteristics are regulated and controlled by a sheet, an optical fiber cone or a polarization controller, on one hand, the material dispersion among longitudinal mode modes in the Fourier domain mode-locked tuned light source 1 is inhibited, and on the other hand, the material dispersion among longitudinal mode modes in the Fourier domain mode-locked tuned light source 1 is limited
Polarization mode transmission in the Fourier-domain mode-locked tuned light source 1, thereby suppressing
A polarization mode and
polarization mode dispersion between polarization modes and the ability to control the polarization states of the reference beam R, the pump beam P and the trigger beam T is shown in fig. 2.
The auxiliary interferometer 4 comprises a third polarization maintaining fiber coupler 401, a first delay line 402, a photoelectric detector 403, a first Faraday reflector 404 and a second Faraday reflector 405, the second polarization maintaining fiber coupler 3 is connected with the third polarization maintaining fiber coupler 401, the third polarization maintaining fiber coupler 401 is respectively connected with the photoelectric detector 403, the first Faraday reflector 404 and the second Faraday reflector 405, the first delay line 402 is arranged between the third polarization maintaining fiber coupler 401 and the first Faraday reflector 404, and the photoelectric detector 403 is connected with the signal processing module 8.
The transmission and polarization characteristics of the polarization dispersion management delay line 104 are adjustable, the material dispersion and the polarization mode dispersion between longitudinal mode modes in the fourier domain mode-locked tuned light source 1 can be inhibited, and the output light beam of the fourier domain mode-locked tuned light source 1 can be controlled to be a linear polarization light beam; the tuning period of the function generator 103 is matched with the one-way transition time of each longitudinal mode in the Fourier domain mode locking tuned light source 1, and each longitudinal mode can be stably evolved in the Fourier domain mode locking tuned light source 1 by matching the tuning period of the function generator 103 with the one-way transition time of each longitudinal mode in the Fourier domain mode locking tuned light source 1; the tunable optical filter 102 controls each longitudinal mode in the fourier domain mode-locked tuned light source 1 to be output sequentially in the order of wavelength. The tunable optical filter 102 controls each longitudinal mode to be output sequentially according to the wavelength sequence, so that the repeated oscillation starting and oscillation stopping of the reference beam R, the pump beam P and the trigger beam T in the measurement process in the conventional coherent spectrum analysis device and method are avoided, the large-range, quick and stable tuning of the reference beam R, the pump beam P and the trigger beam T can be realized, and the measurement speed and the spatial resolution of the optical frequency domain reflectometer are further improved.
The embodiment is a measuring method of an optical frequency domain reflectometer device based on Fourier domain mode locking, which comprises the following steps:
step 1: the second optical isolator 2 and the second polarization-maintaining fiber coupler 3 are divided into a trigger beam T, a reference beam R and a pumping beam P, and the three beams respectively flow into the auxiliary interferometer 4, the biaxial working polarization beam splitter prism 5 and the polarization-maintaining amplifier 14;
step 2: the trigger beam T enters the signal processing module 8 after being processed by the auxiliary interferometer 4, and is used as a trigger signal of the signal processing module 8;
and step 3: the reference beam R is divided into a slow axis alignment reference beam R1 and a fast axis alignment reference beam R2 with equal amplitude through a biaxial working polarization beam splitter prism 5;
and 4, step 4: the pump light beam P flows into the second delay line 13 through the port 1 and the port 2 of the polarization-maintaining circulator 12, and the pump light beam P and the second delay line 13 generate a measuring light beam S through Rayleigh scattering interaction;
and 5: the measuring beam S is divided into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2 through the single-axis working polarization beam splitter 11;
step 6: after being combined and interfered by the fourth polarization maintaining fiber coupler 6, the slow axis alignment reference beam R1 and the slow axis alignment measuring beam S1 are converted into a slow axis interference signal A by the first balanced detector 7 and input into the signal processing module 8;
and 7: the fast axis alignment reference beam R2 and the fast axis alignment measuring beam S2 are converged and interfered by the fifth polarization maintaining fiber coupler 10, converted into a fast axis interference signal B by the second balanced detector 9, and input into the signal processing module 8;
and 8: and the signal processing module 8 integrates the slow axis interference signal A and the fast axis interference signal B to obtain the stress/strain information to be measured.
In the embodiment, the measuring beam S in the step 5 is an arbitrarily polarized beam
A polarization mode and
the polarization mode is split into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2 by a single axis working polarization beam splitter prism 11. As shown in fig. 2 and 3, the two-axis working polarization splitting prism 5 splits the linearly polarized reference beam R into a slow-axis alignment reference beam R1 and a fast-axis alignment reference beam R2 of equal amplitude; the single-axis working polarization beam splitter prism 11 measures the light beam S
A polarization mode and
the polarization mode is divided into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2; the first balanced detector 7 and the second balanced detector 9 respectively and independently detect the slow axis interference signal A and the fast axis interference signal B, and the detection method can prevent the coherent spectrum analysis device and the method from being used
A polarization mode and
the influence of polarization mode crosstalk further improves the measurement precision of the optical frequency domain reflectometer.
As shown in fig. 4, the signal processing method of the signal processing module 8 in step 8 includes the following steps:
step 8.1: the signal processing module 8 records | A | in a single wavelength tuning period by calculating the square sum of the slow axis interference signal A and the fast axis interference signal B2+|B|2Trend over time;
step 8.2: tuning | A through a single wavelength within a period using a Fast Fourier Transform (FFT)2+|B|2Processing the time variation trend to obtain | A2+|B|2The distribution of different beat frequency components;
step 8.3: coupling the sensing positions in the second delay line 13 with | A2+|B|2By making the Y component correspond to the Y component one by one2+|B|2The beat frequency component in (1) is subjected to local inverse fast fourier transform (local iFFT) to access each sensing position in the second delay line 13, and the stress/strain information of the sensing position is obtained by performing cross correlation operation on the local inverse fast fourier transform (local iFFT) result in the presence or absence of stress/strain.
When continuous, repetitive spectral analysis is required, the output waveform of the function generator 103 is set in a sawtooth shape as shown in fig. 5.
The optical frequency domain reflectometer device and the optical frequency domain reflectometer measuring method based on the Fourier domain mode locking are introduced in detail, a specific example is applied in the text to explain the principle and the implementation mode of the invention, and the description of the embodiment is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
Claims (9)
1. The utility model provides an optical frequency domain reflectometer device based on mode locking in Fourier domain which characterized in that: the device comprises a Fourier domain mode-locking tuning light source (1), a second optical isolator (2), a second polarization-maintaining optical fiber coupler (3), an auxiliary interferometer (4), a double-shaft working polarization beam splitter prism (5), a fourth polarization-maintaining optical fiber coupler (6), a first balance detector (7), a signal processing module (8), a second balance detector (9), a fifth polarization-maintaining optical fiber coupler (10), a single-shaft working polarization beam splitter prism (11), a polarization-maintaining circulator (12), a second delay line (13) and a polarization-maintaining optical amplifier (14), wherein the Fourier domain mode-locking tuning light source (1) is respectively connected with the auxiliary interferometer (4), the double-shaft working polarization beam splitter prism (5) and the polarization-maintaining optical amplifier (14) after sequentially passing through the second optical isolator (2) and the second polarization-maintaining optical fiber coupler (3), the auxiliary interferometer (4) is connected with the signal processing module (8), the double-shaft working polarization splitting prism (5) is respectively connected with a fourth polarization-maintaining optical fiber coupler (6) and a fifth polarization-maintaining optical fiber coupler (10), the polarization-maintaining optical amplifier (14) and the second delay line (13) are respectively connected with the fourth polarization-maintaining optical fiber coupler (6) and the fifth polarization-maintaining optical fiber coupler (10) after sequentially passing through the polarization-maintaining circulator (12) and the single-shaft working polarization splitting prism (11), the fourth polarization-maintaining optical fiber coupler (6) is connected with the first balance detector (7) and the signal processing module (8) to form a passage, and the fifth polarization-maintaining optical fiber coupler (10) is connected with the second balance detector (9) and the signal processing module (8) to form a passage.
2. The apparatus of claim 1, wherein the optical frequency domain reflectometer is based on Fourier-domain mode locking, and comprises: the Fourier domain mode-locked tuned light source (1) comprises an optical amplifier (101), a tunable optical filter (102), a polarization dispersion management delay line (104), a first optical isolator (105), a first polarization maintaining fiber coupler (106) and a narrow linewidth optical filter (107) which are sequentially connected, wherein the tunable optical filter (102) is connected with a function generator (103), and the narrow linewidth optical filter (107) is connected with a second optical isolator (2).
3. An optical frequency domain reflectometry apparatus based on fourier domain mode locking as claimed in claim 2, wherein: the transmission and polarization characteristics of the polarization dispersion managed delay line (104) are tunable.
4. An optical frequency domain reflectometry apparatus based on Fourier domain mode locking as in claim 3, wherein: the polarization dispersion management delay line (104) regulates and controls transmission and polarization characteristics by means of writing chirped gratings, series dispersion displacement optical fibers, dispersion compensation optical fibers, glass slides, optical fiber cones or polarization controllers.
5. The apparatus of claim 1, wherein the optical frequency domain reflectometer is based on Fourier-domain mode locking, and comprises: the auxiliary interferometer (4) comprises a third polarization-maintaining optical fiber coupler (401), a first delay line (402), a photoelectric detector (403), a first Faraday reflector (404) and a second Faraday reflector (405), the second polarization-maintaining optical fiber coupler (3) is connected with the third polarization-maintaining optical fiber coupler (401), the third polarization-maintaining optical fiber coupler (401) is respectively connected with the photoelectric detector (403), the first Faraday reflector (404) and the second Faraday reflector (405), the first delay line (402) is arranged between the third polarization-maintaining optical fiber coupler (401) and the first Faraday reflector (404), and the photoelectric detector (403) is connected with the signal processing module (8).
6. A method for measuring an optical frequency domain reflectometry apparatus based on fourier domain mode locking as in claim 1, wherein: it comprises the following steps:
step 1: the second optical isolator (2) and the second polarization-maintaining optical fiber coupler (3) are divided into a trigger beam T, a reference beam R and a pumping beam P, and the three beams respectively flow into the auxiliary interferometer (4), the biaxial working polarization beam splitter prism (5) and the polarization-maintaining optical amplifier (14);
step 2: the trigger light beam T enters a signal processing module (8) after being processed by the auxiliary interferometer (4) and is used as a trigger signal of the signal processing module (8);
and step 3: the reference beam R is divided into a slow axis alignment reference beam R1 and a fast axis alignment reference beam R2 with equal amplitude through a biaxial working polarization beam splitter prism (5);
and 4, step 4: the pump light beam P flows into a second delay line (13) through a port 1 and a port 2 of the polarization-maintaining circulator (12), and the pump light beam P and the second delay line (13) generate a measuring light beam S through Rayleigh scattering interaction;
and 5: the measuring beam S is divided into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2 through a single-axis working polarization beam splitter prism (11);
step 6: after being combined and interfered by a fourth polarization-maintaining fiber coupler (6), a slow-axis alignment reference beam R1 and a slow-axis alignment measuring beam S1 are converted into a slow-axis interference signal A by a first balanced detector (7) and input into a signal processing module (8);
and 7: the fast axis alignment reference beam R2 and the fast axis alignment measuring beam S2 are combined and interfered by a fifth polarization maintaining fiber coupler (10), converted into a fast axis interference signal B by a second balanced detector (9) and input into a signal processing module (8);
and 8: and the signal processing module (8) integrates the slow axis interference signal A and the fast axis interference signal B to obtain the stress/strain information to be measured.
7. The method for measuring an optical frequency domain reflectometry apparatus based on Fourier domain mode locking as claimed in claim 6, wherein: the measuring beam S in the step 5 is a beam with any polarization, wherein
A polarization mode and
the polarization mode is split into a slow axis alignment measuring beam S1 and a fast axis alignment measuring beam S2 by a single axis working polarization beam splitter prism (11).
8. The method for measuring an optical frequency domain reflectometry apparatus based on Fourier domain mode locking as claimed in claim 6, wherein: the signal processing method of the signal processing module (8) in the step 8 comprises the following steps:
step 8.1: the signal processing module (8) records | A | calcualty in a single wavelength tuning period by calculating the square sum of the slow axis interference signal A and the fast axis interference signal B2+|B|2Trend over time;
step 8.2: utilizing fast Fourier transform to tune | A in a single wavelength tuning period2+|B|2Processing the time variation trend to obtain | A2+|B|2The distribution of different beat frequency components;
step 8.3: passing each sensing position and | A! N in the second delay line (13)2+|B|2By making the Y component correspond to the Y component one by one2+|B|2The beat frequency component in the second delay line (13) is subjected to local inverse fast Fourier transform to access each sensing position, and the stress/strain information of the sensing position is obtained by performing cross correlation operation on the local inverse fast Fourier transform result in the presence or absence of stress/strain.
9. The method for measuring an optical frequency domain reflectometry apparatus based on Fourier domain mode locking as claimed in claim 6, wherein: when continuous and repetitive spectral analysis is required, the output waveform of the function generator (103) is set to be zigzag.
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