CN117288426A - Polarization dimming-free vector analysis device based on cascade polarization-preserving interferometer - Google Patents
Polarization dimming-free vector analysis device based on cascade polarization-preserving interferometer Download PDFInfo
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Abstract
The invention provides a polarization dimming-free vector analysis device based on a cascade polarization-preserving interferometer, which belongs to the field of optical fiber device measurement, and comprises a tunable laser, a polarization-preserving orthogonal polarization generation module, a polarization diversity detection module, a measurement interferometer module, an auxiliary interferometer module and a signal acquisition analysis module, and is characterized in that: after the linear sweep light output by the tunable laser passes through the 45-degree polarizer, an optical signal is averagely injected into the fast and slow axes of the polarization maintaining optical fiber, and then a pair of orthogonal polarized light with equivalent intensity is constructed by utilizing the characteristics of the polarization maintaining polarization beam splitter and the polarization maintaining polarization combining device to serve as query light. And realizing balanced polarization alignment of a polarization diversity system by using 45-degree optical fiber fusion. The device obtains the transmission matrix of the device to be tested through testing, and then demodulates to obtain the optical parameters of the device. The device utilizes the characteristics of the polarization maintaining device and the polarization stability of the polarization maintaining optical fiber to realize polarization adjustment-free, and fundamentally eliminates the polarization adjustment error of the traditional light vector analyzer.
Description
Technical Field
The invention belongs to the technical field of optical fiber measurement, and relates to a vector characteristic measuring device of an optical fiber device.
Technical Field
The new generation of optical information systems is pressing to require photonic devices capable of multi-dimensional and high-definition manipulation of optical signals. An Optical Vector Analyzer (OVA) is a technique that can measure the amplitude, phase and polarization response of an optical device. Based on these responses, various parameters such as insertion loss, dispersion, group delay, polarization dependent loss, etc., can be obtained at once.
There are two more sophisticated measuring methods for the light vector analyzer, namely the electrical modulation method and the optical interferometry method. The main principle of the electric modulation method is that the ultra-fine frequency scanning of the electric domain is converted into the optical domain by electro-optic modulation. Through research test, the frequency resolution can reach 334Hz, and the dynamic range reaches 90dB. However, the test range is only 1THz, and at most only covers the C-band [ T.Qing, S.Li, Z.Tang, B.Gao, S.Pan, "Optical vector analysis with attometer resolution,90-dB dynamic range and THz bandwidth" Nature Communication,10 (1), 5135 (2019) ].
An Optical Vector Analyzer (OVA) of the optical interferometry is a scheme that uses a pair of orthogonal-polarized linear swept-continuous lasers with a fixed time delay as interrogation light and performs coherent detection using a polarization diversity detection scheme. A Tunable Laser (TLS) has a wide wavelength scanning range so that it can completely cover the c+l band. However, the frequency resolution of the optical interferometry is limited to 200MHz, which is limited by the wavelength scanning accuracy of TLS.
The light vector analyzer can simultaneously demodulate the vector transmission characteristics of the amplitude, the phase and the polarization of the optical device to be tested along with the change of frequency. Such as: the company LUNA in united states of america in 2005 discloses an apparatus and method for complete characterization of optics including loss, dispersion and dispersion effects [ Apparatus and method for the complete characterization of optical devices including loss, birefringence and dispersion effects, US7042573B2]. The method is a scheme of using a pair of orthogonal polarized linear sweep continuous lasers with fixed time delay as interrogation light and using a polarization diversity detection scheme for coherent detection. The spectral measurements are digitized and curve fitted to provide an optical power versus optical frequency curve. Each curve characterizes the jones matrix of the device under test by fourier transformation, calculating four constant arrays.
In the measurement of optical fiber devices in a traditional light vector analyzer, a Tunable Laser (TLS) has a wide wavelength scanning range, so that the optical fiber device can completely cover the c+l band. However, the frequency resolution of the optical interferometry is limited to 200MHz, which is limited by the wavelength scanning accuracy of TLS. The test needs to realize orthogonal polarization alignment and polarization equilibrium alignment, and the polarization controllers are required to be adjusted in the two alignments, so that during the actual test, the polarization state can be changed due to the influence of environmental disturbance factors or the influence of bending deformation of light rays, and the incoming error of polarization imbalance is increased.
The invention provides a polarization dimming-free vector analysis device based on a cascade polarization-preserving interferometer, which fundamentally eliminates polarization imbalance errors in the traditional OVA. The polarization maintaining polarization beam splitter and the polarization maintaining polarization beam combiner are used for guaranteeing orthogonal polarization output, and 45-degree fusion is used for equally dividing orthogonal polarized light to the p detector and the s detector. The whole light path is in a polarization stable state, and accurate measurement can be realized without adjustment. The insertion loss and group delay of the gas absorption chamber can be measured in the wavelength range 1525 to 1610 nm. The frequency resolution of 50MHz was verified by measuring the free spectral range of a Michelson Interferometer (MI) with a 2.1m arm length difference. The proposed approach is likely to be the dominant approach to characterizing various emerging optics and provides support for many leading edge type studies.
Disclosure of Invention
The invention is based on the use of polarization maintaining polarization beam splitters and polarization maintaining polarization beam combiners to create orthogonal polarized light, and the 45-degree optical fiber fusion technology is utilized to equally divide the orthogonal polarized light to a p detector and an s detector, so as to provide a measurement device of a polarization-free adjusting light vector analyzer with high frequency resolution and for measuring the spectral response of an optical device.
The utility model provides a polarization is exempted from vector analysis device that adjusts luminance based on cascade polarization-preserving interferometer, includes tunable laser 1, polarization-preserving orthogonal polarization generation module 2, measures interferometer module 3, polarization diversity detection module 4, auxiliary interferometer module 5, signal acquisition analysis module 6, characterized by:
the continuous sweep light emitted by the tunable laser 1 is split into two beams by the first coupler 101, one beam is injected into the auxiliary interferometer module 5, and the other beam is injected into the polarization-preserving orthogonal polarization generating module 2, so as to generate a pair of orthogonal polarized light aa with fixed time delay.
The orthogonal polarized light aa is used as interrogation light to be injected into the measurement interferometer module 3, the first polarization maintaining coupler 301 divides the orthogonal polarized light aa into two beams, one beam is used as reference light to be injected into the first output port 303 of the first polarization maintaining coupler, and 45-degree optical fiber fusion 305 is carried out after the reference light passes through the second delay optical fiber 304, namely, the polarization maintaining optical fiber fast and slow axis 310 is subjected to optical fiber fusion with the polarization maintaining optical fiber fast and slow axis 311 after being rotated by 45 degrees, so that the orthogonal polarized light aa can be projected to the P end 308 and the S end 309 of the second polarization maintaining polarization beam splitter 307 in a balanced manner, and balanced polarization alignment without adjustment is realized; the other beam of light is injected into the second output port 302 of the first polarization maintaining coupler and passes through the device under test 300, and the two parts of light are output by the second polarization maintaining coupler 306. After passing through the second polarization maintaining polarization beam splitter 401, interference occurs between the P-terminal 402 and the S-terminal 403. The interference signals of the auxiliary interferometer module 5, the P end 402 and the S end 403 are injected into the signal acquisition and analysis module 6, so that the transmission characteristics of the device are obtained.
The polarization-preserving orthogonal polarization generating module 1 is characterized in that:
injecting an optical signal into a fast axis m and a slow axis n of a polarization-maintaining optical fiber by a 45 DEG polarizer, then dividing light into two beams by a first polarization-maintaining polarization beam splitter 202, wherein one beam is injected into a first output end 203 of the first polarization-maintaining polarization beam splitter to transmit the slow axis light n1, and the other beam is injected into a second output end 204 of the first polarization-maintaining polarization beam splitter to transmit the fast axis light m1 to pass through a first delay optical fiber 205, the two beams are in an orthogonal polarization state, and a pair of orthogonal polarized light aa with fixed time delay is output by a polarization-maintaining polarization beam combiner 206, wherein the introduced time delay of the first delay optical fiber 205 is tau;
the first polarization maintaining beam splitter 202 is characterized in that:
the output end of the first polarization maintaining beam splitter 202 only works uniaxially, i.e. the first polarization maintaining beam splitter first output port 203 only outputs on the slow axis n, and the first polarization maintaining beam splitter second output port 204 only outputs on the block axis m. The polarization maintaining polarization beam splitter first input port 207 is only slow axis n in and the polarization maintaining polarization beam splitter first input port 208 is only fast axis m in.
The measuring interferometer module 3 is characterized in that:
the pigtail of the device 300 to be tested can be a polarization maintaining fiber or a single mode fiber, and the delay τ introduced by the second delay fiber 304 D ＞3τ；
The auxiliary interferometer module 5 is characterized in that:
the second coupler 501 divides the light into two parts, one beam is injected into the first output end 501a of the second coupler as reference light, the other beam is injected into the second output end 501b of the second coupler as test light and passes through the delay optical fiber 502, the two beams are divided into two beams after being combined in the third coupler 305, and the first balance detector 504 performs differential detection
The signal acquisition and analysis module 6 is characterized in that:
the acquisition module 601 performs data acquisition and storage on interference signals of the auxiliary interferometer module 5, the P end 402 and the S end 403, corrects the nonlinear sweep frequency problem of the laser through the correction module 602, inputs the signals into the transfer function acquisition module 603 to obtain a transfer function of the device, and then demodulates the transfer function to obtain an amplitude frequency response and a phase frequency response of the device through the frequency response calculation module 604;
the correction module 602 is characterized in that:
the processing method of the correction unit 602 carries out nonlinear sweep correction of the laser on the interference signal of the acquisition module by a resampling algorithm.
The frequency response calculation module 604 demodulates the amplitude frequency response and the phase frequency response of the device, and then the calculation formula of the Insertion Loss (IL) is:
the calculation formula of the Group Delay (GD) is:
the formula for calculating the Polarization Dependent Loss (PDL) is:
T max and T min The eigenvalues of the matrix obtained by multiplying the jones matrix of the device with the conjugate transpose matrix, respectively.
Calculation formula of polarization dispersion (PMD):
wherein ρ is 1 And ρ2 Is that H(ω+Δω)H(ω) -1 Is a characteristic value of (a).
Since the jones matrix and the time domain impulse response 606 are related to each other by discrete fourier transforms, the filter window width 607 determines the resolution of the data in the frequency domain. If the filter window width 607 is deltat f And in ns, the resolution bandwidth in GHz is
RBW(GHz)＝1/Δt f (8)
Since the filter window width 607 is Δt f If the arm length difference of the polarization maintaining orthogonal polarization generating module 2 must be less than or equal to the corresponding time delay τ, the frequency resolution can be increased by increasing the arm length difference of the polarization maintaining orthogonal polarization generating module 2, and in order to distinguish the time domain impulse response 606, the arm length difference of the measurement interferometer module 3 is correspondingly increased.
Compared with the prior art, the invention has the advantages that:
1) The invention relates to a polarization light-free vector analysis device based on a cascade polarization-preserving interferometer, which is based on an optical frequency domain interference principle, creates orthogonal polarized light through a polarization-preserving polarization beam splitter and a polarization-preserving polarization beam combiner, and equally divides the orthogonal polarized light by utilizing a 45-degree optical fiber fusion technology, thereby realizing polarization-free adjustment and fundamentally eliminating polarization measurement errors of a traditional light vector analyzer.
2) Compared with the traditional light vector analyzer, the invention can easily improve the frequency resolution by increasing the arm length difference of the measurement interferometer by utilizing the polarization stability of the polarization maintaining optical fiber. The frequency resolution of 50MHz was verified by measuring the free spectral range of a Michelson Interferometer (MI) with an arm length difference of 2.1 m.
Drawings
FIG. 1 is a diagram of a polarization dimming-free vector analysis (PAF-OVA) device based on a cascade polarization-preserving interferometer;
FIG. 2 is a schematic diagram of a post-fast Fourier transform of an interference signal for P-sounding
FIG. 3 is a graph of insertion loss versus results for PAF-OVA and LUNA OVA5100 test chambers;
FIG. 4 is a graph of group delay versus results for PAF-OVA and LUNA OVA5100 test chambers;
FIG. 5 is a spectral diagram of a spectrometer testing arm length difference of Michelson Interferometer (MI) of 2.1 m;
FIG. 6 is a spectral plot of MI with a PAF-OVA test arm length difference of 2.1 m;
FIG. 7 is a graph of group delay results of PAF-OVA test arm length difference MI of 2.1 m.
Detailed Description
For clarity of description of the method for testing optical performance of polarization maintaining fiber, the present invention will be further described with reference to examples and drawings, but the scope of protection of the present invention should not be limited thereto.
A polarization dimming-free vector analysis (PAF-OVA) device based on a cascade polarization-preserving interferometer is shown in fig. 1.
The main photoelectric device of the device is selected and parameters thereof are as follows:
the light source is a narrow linewidth tunable laser source, the model is Keysight-81606A, the wavelength tuning range is 1510-1610 nm, the sweep rate is 50nm/s, and the sweep time is 2s;
the model of the detector is aoshow-PDB1001, the detection bandwidth is 15MHz, and the saturated differential detection power is 7uW;
the model of the acquisition card is M4i:4471-x8, 16 bit sampling rate setting 11.25MHz, sampling point number 22.5M, sampling time 2s, triggering by LabVIEW software;
the first coupler 101 has a split ratio of 1:99, extinction ratios of more than 20dB, insertion loss of less than 0.5dB, and an operating wavelength covering 1550nm band;
the extinction ratio of all the polarization maintaining polarization beam splitters and polarization maintaining polarization beam combiners is more than 23dB, the insertion loss is less than 0.6dB, and the working wavelength covers 1550nm wave bands;
the split ratio of the first polarization maintaining coupler 301 and the second polarization maintaining coupler 306 is 50:50, the insertion loss is less than 3.8dB, and the working wavelength covers 1550nm wave band;
the polarizer 201 has the working wavelength of 1550nm, the angle of 45 degrees, the insertion loss of less than 1dB and the extinction ratio of more than 30dB;
the utility model provides a polarization is exempted from vector analysis device that adjusts luminance based on cascade polarization-preserving interferometer, includes tunable laser 1, polarization-preserving orthogonal polarization generation module 2, measures interferometer module 3, polarization diversity detection module 4, auxiliary interferometer module 5, signal acquisition analysis module 6, characterized by:
the continuous sweep light emitted by the tunable laser 1 is split into two beams by the first coupler 101, one beam is injected into the auxiliary interferometer module 5, and the other beam is injected into the polarization-preserving orthogonal polarization generating module 2, so as to generate a pair of orthogonal polarized light aa with fixed time delay.
The orthogonal polarized light aa is used as interrogation light to be injected into the measurement interferometer module 3, the first polarization maintaining coupler 301 divides the orthogonal polarized light aa into two beams, one beam is used as reference light to be injected into the first output port 303 of the first polarization maintaining coupler, and 45-degree optical fiber fusion 305 is carried out after the reference light passes through the second delay optical fiber 304, namely, the polarization maintaining optical fiber fast and slow axis 310 is subjected to optical fiber fusion with the polarization maintaining optical fiber fast and slow axis 311 after being rotated by 45 degrees, so that the orthogonal polarized light aa can be projected to the P end 308 and the S end 309 of the second polarization maintaining polarization beam splitter 307 in a balanced manner, and balanced polarization alignment without adjustment is realized; the other beam of light is injected into the second output port 302 of the first polarization maintaining coupler and passes through the device under test 300, and the two parts of light are output by the second polarization maintaining coupler 306. After passing through the second polarization maintaining polarization beam splitter 401, interference occurs between the P-terminal 402 and the S-terminal 403. The interference signals of the auxiliary interferometer module 5, the P end 402 and the S end 403 are injected into the signal acquisition and analysis module 6, so that the transmission characteristics of the device are obtained.
The polarization-preserving orthogonal polarization generating module 1 is characterized in that:
injecting an optical signal into a fast axis m and a slow axis n of a polarization-maintaining optical fiber by a 45 DEG polarizer, then dividing light into two beams by a first polarization-maintaining polarization beam splitter 202, wherein one beam is injected into a first output end 203 of the first polarization-maintaining polarization beam splitter to transmit the slow axis light n1, and the other beam is injected into a second output end 204 of the first polarization-maintaining polarization beam splitter to transmit the fast axis light m1 to pass through a first delay optical fiber 205, the two beams are in an orthogonal polarization state, and a pair of orthogonal polarized light aa with fixed time delay is output by a polarization-maintaining polarization beam combiner 206, wherein the introduced time delay of the first delay optical fiber 205 is tau;
the first polarization maintaining beam splitter 202 is characterized in that:
the output end of the first polarization maintaining beam splitter 202 only works uniaxially, i.e. the first polarization maintaining beam splitter first output port 203 only outputs on the slow axis n, and the first polarization maintaining beam splitter second output port 204 only outputs on the block axis m. The polarization maintaining polarization beam splitter first input port 207 is only slow axis n in and the polarization maintaining polarization beam splitter first input port 208 is only fast axis m in.
The measuring interferometer module 3 is characterized in that:
the pigtail of the device under test 300 may be a polarization maintaining fiber or a single mode fiber, where the length of the first delay fiber 205 is L 1 Length L of second delay fiber 304=4.8m 2 =30m; according to the corresponding time delay tau D ＞3τ
The auxiliary interferometer module 5 is characterized in that:
the second coupler 501 divides the light into two parts, one beam is injected into the first output end 501a of the second coupler as reference light, the other beam is injected into the second output end 501b of the second coupler as test light and passes through the delay optical fiber 502, the two beams are divided into two beams after being combined in the third coupler 305, and the first balance detector 504 performs differential detection
The signal acquisition and analysis module 6 is characterized in that:
the acquisition module 601 performs data acquisition and storage on interference signals of the auxiliary interferometer module 5, the P end 402 and the S end 403, corrects the nonlinear sweep frequency problem of the laser through the correction module 602, inputs the signals into the transfer function acquisition module 603 to obtain a transfer function of the device, and then demodulates the transfer function to obtain an amplitude frequency response and a phase frequency response of the device through the frequency response calculation module 604;
the correction module 602 is characterized in that:
the processing method of the correction unit 602 carries out nonlinear sweep correction of the laser on the interference signal of the acquisition module by a resampling algorithm.
One device to be tested is an air chamber (wavelength reference QUAD-4/2/150/150), wherein the input and output tail fibers of the air chamber are all single-mode fibers and are used for testing and verifying the accuracy of PAF-OVA insertion loss and group delay; the other is a Michelson Interferometer (MI) with an arm length difference of 2.1m, which is used for verifying the frequency resolution of 50 MHz;
the auxiliary interferometer module 4 adopts a Mach-Zehnder fiber interferometer module, wherein the length L of the third delay fiber 402 3 ＝10m；
The 45-degree optical fiber fusion 305 adopts a rattan bin FSM100P+ optical fiber fusion machine to ensure that the polarization maintaining optical fiber fast and slow axis 310 rotates for 45 degrees and then is fused with the polarization maintaining optical fiber fast and slow axis 311, so that orthogonal polarized light can be projected to the P end 402 and the s end 403 of the second polarization maintaining polarization beam splitter 401 in a balanced manner;
the air chamber is tested first, and the effective resolution of the test is 200MHz. FIG. 3 is a graph comparing the insertion loss of the chambers of PAF-OVA and commercial OVA instrument-LUNA OVA5100, wherein the PAF-OVA test chamber insertion loss results (701) are consistent with the OVA5100 test chamber insertion loss results (702). Fig. 4 is a graph of chamber group delay comparisons for PAF-OVA and commercial OVA instrument-LUNA OVA5100, where the PAF-OVA test chamber group delay results (703) are consistent with the OVA5100 test chamber group delay results (704). And the PAF-OVA can be verified to effectively test the amplitude-frequency response and the phase-frequency response of the device.
The MI with a difference in arm length of 2.1m was then tested to verify that the PAF-OVA had a frequency resolution of 50MHz. FIG. 5 is a graph of the results of a spectrum analyzer (OSA-APEX-AP 2081A, maximum resolution 5 MHz) versus a Michelson interferometer with a 2.1m arm length difference, where the spectrum results (705) of the spectrometer can be seen to show only its basic profile. FIGS. 6 and 7 are graphs of insertion loss and group delay results for MI with a PAF-OVA test arm length difference of 2.1m, where PAF-OVA test MI spectral results (706) and PAF-OVA test MI group delay results (707) were observed, with a free spectral range of 49.19MHz, which effectively illustrates PAF-OVA test frequency resolution up to 50MHz.
Claims (7)
1. The utility model provides a polarization exempts from vector analysis device that adjusts luminance based on cascade polarization-preserving interferometer, includes tunable laser (1), polarization-preserving orthogonal polarization generation module (2), measures interferometer module (3), polarization diversity detection module (4), supplementary interferometer module (5), signal acquisition analysis module (6), characterized by:
the continuous sweep light emitted by the tunable laser (1) is split into two beams by a first coupler (101), one beam is injected into the auxiliary interferometer module (5), and the other beam is injected into the polarization-preserving orthogonal polarization generating module (2) to generate a pair of orthogonal polarized light (aa) with fixed time delay.
The orthogonal polarized light (aa) is used as interrogation light to be injected into a measurement interferometer module (3), the first polarization maintaining coupler (301) divides the orthogonal polarized light (aa) into two beams, one beam is used as reference light to be injected into a first output port (303) of the first polarization maintaining coupler, 45-degree optical fiber fusion (305) is carried out after passing through a second delay optical fiber (304), namely, an optical fiber fast and slow axis (310) of the polarization maintaining optical fiber rotates by 45 degrees and then is subjected to optical fiber fusion with an optical fiber fast and slow axis (311) of the polarization maintaining optical fiber, so that the orthogonal polarized light (aa) can be symmetrically projected to a P end (308) and an S end (309) of a second polarization maintaining polarization beam splitter (307), and balanced polarization alignment without adjustment is realized; the other beam of light is injected into a second output port (302) of the first polarization maintaining coupler and passes through the device (300) to be tested, and the two parts of light are output by the second polarization maintaining coupler (306). After passing through the second polarization maintaining polarization beam splitter (401), interference occurs between the P end (402) and the S end (403). The interference signals of the auxiliary interferometer module (5), the P end (402) and the S end (403) are injected into the signal acquisition and analysis module (6) to obtain the transmission characteristic of the device.
2. The polarization dimming-free vector analysis device based on the cascade polarization-preserving interferometer as claimed in claim 1, wherein the polarization dimming-free vector analysis device is characterized in that:
the polarization maintaining orthogonal polarization generating module (2) comprises a 45-degree polarizer (201), a first polarization maintaining beam splitter (202), a first delay optical fiber (205) and a polarization maintaining polarization beam combiner (206), wherein the 45-degree polarizer (201) injects optical signals into a fast axis (m) and a slow axis (n) of the polarization maintaining optical fiber, then the first polarization maintaining beam splitter (202) divides light into two beams, one beam is injected into a first output end (203) of the first polarization maintaining beam splitter to transmit slow axis light (n 1), the other beam is injected into a second output end (204) of the first polarization maintaining beam splitter to transmit fast axis light (m 1) to pass through the first delay optical fiber (205), the two beams are in an orthogonal polarization state, and the polarization maintaining polarization beam combiner (206) outputs a pair of orthogonal polarized light (aa) with fixed time delay, and the time delay of introduction of the first delay optical fiber (205) is τ.
3. The polarization dimming-free vector analysis device based on the cascade polarization-preserving interferometer as claimed in claim 2, wherein the polarization dimming-free vector analysis device is characterized in that:
the output end of the first polarization maintaining beam splitter (202) only works in a single axis, namely the first output port (203) of the first polarization maintaining beam splitter only outputs in a slow axis (n), and the second output port (204) of the first polarization maintaining beam splitter only outputs in a block axis (m). The first input port (207) of the polarization maintaining polarization splitter is only input by a slow axis (n), and the first input port (208) of the polarization maintaining polarization splitter is only input by a fast axis (m).
4. The polarization dimming-free vector analysis device based on the cascade polarization-preserving interferometer as claimed in claim 1, wherein the polarization dimming-free vector analysis device is characterized in that:
the measurement interferometer module (3) comprises a first polarization maintaining coupler (301), a second polarization maintaining coupler (306) and a device to be measured(300) The second delay optical fiber (304) and the 45-degree optical fiber fusion splice (305), wherein the tail fiber of the device (300) to be tested can be a polarization maintaining optical fiber or a single-mode optical fiber, and the delay introduced by the second delay optical fiber (304) is tau D Demanding tau D ＞3τ。
5. The polarization dimming-free vector analysis device based on the cascade polarization-preserving interferometer as claimed in claim 1, wherein the polarization dimming-free vector analysis device is characterized in that:
the auxiliary interferometer module (5) comprises a second coupler (501), a delay optical fiber (502), a third coupler (305) and a first balance detector (504), wherein the second coupler (501) divides light into two parts, one beam is injected into a first output end (501 a) of the second coupler as reference light, the other beam is injected into a second output end (501 b) of the second coupler as test light and passes through the delay optical fiber (502) in the second output end, and the two beams are divided into two beams after being combined in the third coupler (305), and the two beams are detected differentially by the first balance detector (504).
6. The polarization dimming-free vector analysis device based on the cascade polarization-preserving interferometer as claimed in claim 1, wherein the polarization dimming-free vector analysis device is characterized in that:
the signal acquisition analysis module (6) comprises an acquisition module (601), a correction module (602), a transfer function acquisition module (603) and a frequency response calculation module (604), wherein the acquisition module (601) acquires and stores interference signals of the auxiliary interferometer module (5), the P end (402) and the S end (403), the correction module (602) corrects the nonlinear sweep problem of the laser, then the signal is input into the transfer function acquisition module (603) to obtain a transfer function of the device, and then the frequency response and the phase frequency response of the device are obtained through demodulation of the frequency response calculation module (604).
7. The polarization dimming-free vector analysis device based on the cascade polarization-preserving interferometer, as claimed in claim 6, is characterized in that:
the processing method of the correction unit (602) carries out nonlinear sweep correction of the laser on the interference signal of the acquisition module by a resampling algorithm.
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