Polarization adjustment-free frequency shift interference type light vector analysis device

Abstract

The invention provides a polarization-adjustment-free frequency shift interference type optical vector analysis device, which belongs to the technical field of optical testing, and comprises a tunable laser, an offset frequency protection orthogonal polarization generation module, an offset frequency protection interference measurement module, a polarization diversity detection module, an auxiliary interferometer module and a signal acquisition demodulation module, the method is characterized in that a pair of orthogonal polarized light is constructed as inquiry light by utilizing the characteristics of a polarization beam splitter and a polarization beam combiner, and balanced polarization alignment of a polarization diversity system can be realized without polarization regulation and control by utilizing 45-degree axis welding of a polarization maintaining optical fiber. According to the device, the polarization adjustment error of a traditional light vector analysis device is eliminated by utilizing the characteristics of the polarization maintaining device and the polarization stability of the polarization maintaining optical fiber. The device utilizes the frequency shifter to replace an extended optical fiber, so that phase noise caused by the long polarization-maintaining extended optical fiber can be reduced, and the effective frequency resolution of the device is greatly increased.

Description

Technical Field

[0001] The invention belongs to the technical field of optical testing and relates to a polarization-free frequency-shift interference optical vector analysis device. Technical Background

[0002] Optical vector analyzer (OVA) is an instrument used to analyze vector information in optical signals. In the fields of optical communication, optical sensing, spectroscopy, etc., vector information usually includes parameters such as the polarization state, phase relationship, and frequency distribution of light waves, which are of great significance for analyzing and optimizing optical signals.

[0003] There are two relatively mature measurement methods for optical vector analyzers, namely the electrical modulation method and the optical interference method. The main principle of the electrical modulation method is to use the beat frequency of the optical carrier and the first-order sideband, and then obtain the fine vector transmission characteristics of the device in the electrical domain. In 2019, Pan Shilong and others from Nanjing University of Aeronautics and Astronautics obtained the highest test frequency resolution of 334Hz and the dynamic range of 90dB based on this scheme. However, the test range is only 1THz, which can only cover the C band at most [T. Qing, S. Li, Z. Tang, B. Gao, S. Pan, “Optical vector analysis with attometer resolution, 90-dB dynamic range and THz bandwidth”, NatureCommunication, 10(1), 5135 (2019)].

[0004] The optical vector analyzer of the optical interferometry method uses a pair of linearly swept continuous lasers with orthogonal polarizations with fixed time delay as interrogation light, and uses a polarization diversity detection scheme for coherent detection. Two interferometers are cascaded, the first interferometer produces orthogonal polarization light, and the second interferometer is used as a test interferometer. Then the spectra in the two polarization directions are tested respectively, and the spectral measurement values ​​are digitized and curve fitting is performed to provide optical power and optical frequency curves. Each curve characterizes the Jones matrix of the device under test through Fourier transform to calculate four constant arrays. In 2005, LUNA Company of the United States disclosed an apparatus and method for the complete characterization of optical devices including loss, birefringence and dispersion effects [Apparatus and methodfor the complete characterization of optical devices including loss, birefringence and dispersion effects, US7042573B2]. Due to the wide wavelength scanning range of the tunable laser (TLS), this scheme can fully cover the C+L band. However, due to the wavelength scanning accuracy of TLS, the frequency resolution of the optical interferometry method is limited to 200 MHz.

[0005] When testing traditional interferometric optical vector analyzers, orthogonal polarization alignment and polarization equalization alignment are required. Both alignments require adjustment of the polarization controller. During actual testing, the polarization state will change due to environmental disturbance factors or the bending and deformation of the light itself, thereby increasing the error caused by polarization misalignment. In 2023, Yu Zhangjun and others from Guangdong University of Technology proposed an online polarization alignment method [an online polarization aligned optical vector analyzer device and method, CN116222979A], which effectively suppresses the error caused by polarization adjustment; in the same year, the same research group proposed an OVA scheme based on polarization-maintaining fiber [a polarization-free optical vector analyzer based on a cascaded polarization-maintaining interferometer, 202310422850.X], which uses the characteristics of polarization-maintaining devices and the polarization stability of polarization-maintaining fibers to achieve polarization-free adjustment, effectively suppress polarization errors, and expand the effective frequency resolution to 50MHz. However, due to the accumulated phase noise of long optical fibers, it is difficult to improve the frequency scanning accuracy. Since two interferometers will generate four interference peaks in the frequency domain, two of the four interference peaks are related to the transmission matrix information of the device. In order to prevent the four interference peaks from overlapping and to arrange them in order of position, there are certain requirements for the arm length difference of the two interferometers. In the past, extended optical fiber was used to ensure that the interference information did not overlap, but the phase noise of the long extended optical fiber would accumulate and be difficult to eliminate. The use of polarization-maintaining optical fiber can only bring polarization stability and guarantee the suppression of polarization-related errors to a certain extent, but it cannot eliminate the phase noise caused by the light source. The phase noise will degrade the information of the four interference peaks, making it impossible to extract and affecting the accuracy.

[0006] The present invention provides a polarization-free frequency-shift interferometric optical vector analysis device, which uses a polarization beam splitter and a polarization beam combiner to ensure the output of orthogonal polarized light, and uses polarization-maintaining optical fibers to be 45° axially welded to evenly project the orthogonal polarized light to a p detector and an s detector. The entire optical path is always in a polarization-stable state, which fundamentally eliminates the polarization misalignment error in traditional OVA. Using a frequency shifter instead of an extended optical fiber can reduce the phase noise problem caused by a long polarization-maintaining extended optical fiber, and can effectively increase the effective frequency resolution of the device. Summary of the invention

[0007] The present invention utilizes the characteristics and polarization stability of polarization-maintaining devices and polarization-maintaining optical fibers to realize polarization-free OVA, and utilizes a frequency shifter to replace the extended optical fiber. The purpose is to provide a polarization-free optical vector analyzer measuring device with high frequency resolution and capable of measuring the spectrum response of optical devices.

[0008] A polarization-free frequency-shift interferometry optical vector analysis device comprises a tunable laser 1, an offset-frequency-maintaining orthogonal polarization generation module 2, an offset-frequency-maintaining interferometry measurement module 3, a polarization diversity detection module 4, an auxiliary interferometer module 5, and a signal acquisition and demodulation module 6, and is characterized in that:

[0009] The linear continuous frequency sweeping light whose frequency changes with time at a rate γ generated by the tunable laser 1 is divided 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 offset frequency maintaining orthogonal polarization generating module 2;

[0010] The shift-frequency-maintaining orthogonal polarization generating module 2 comprises a 45° polarizer 201, a polarization beam splitter 202, a first frequency shifter 205, a polarization beam combiner 206, and a first driver 209;

[0011] The 45° polarizer 201 injects the optical signal into the fast axis (m) and the slow axis (n) of the polarization-maintaining optical fiber in a balanced manner. Then, the first polarization beam splitter 202 splits the light into two beams, one of which is injected into the first output end 203 of the first polarization beam splitter and passes through the first input end 207 of the polarization-maintaining beam combiner; the other beam is injected into the second output end 204 of the first polarization beam splitter for transmission, passes through the first frequency shifter 205, and outputs light with a frequency shift amount Ω1 to the second input end 208 of the polarization-maintaining beam combiner, wherein the first driver 209 provides the first frequency shifter 205 with a driving signal frequency of Ω1; the two beams are combined in the polarization beam combiner 206, and then a pair of orthogonal polarized lights with a fixed frequency difference are output to the offset frequency-maintaining interferometric measurement module 3, the time delay difference between the upper and lower arms of the offset frequency-maintaining orthogonal polarization generating module 2 is τ, and the frequency difference between the upper and lower arms of the offset frequency-maintaining orthogonal polarization generating module 2 is ΔΩ1=Ω1+γτ;

[0012] The shift frequency interferometry measurement module 3 comprises a first polarization-maintaining coupler 301, a device to be measured 300, a second frequency shifter 304, a second driver 305, a second polarization-maintaining coupler 306, and a polarization-maintaining optical fiber 45° axial fusion point 307; a pair of orthogonal polarization lights with a fixed frequency difference output by the polarization-maintaining orthogonal polarization generating module 2 is divided into two beams after passing through the first polarization-maintaining coupler 301, one beam is injected into the first output port 303 of the first polarization-maintaining coupler as a reference light, and passes through the second frequency shifter 304 with a frequency shift amount Ω2, wherein the second driver 305 gives the second polarization-maintaining coupler 306 a reference light. The driving signal frequency provided by 04 is Ω2, and the output light is input into the second polarization-maintaining coupler 306 after passing through the 45° axial fusion point 307 of the polarization-maintaining optical fiber; another beam of light output by the first polarization-maintaining coupler 301 is injected into the second output port 302 of the first polarization-maintaining coupler, and is input into the second polarization-maintaining coupler 306 after passing through the device under test 300; the two beams of light combined in the second polarization-maintaining coupler 306 are injected into the second polarization beam splitter 401, and are respectively injected into the p detector 402 and the s detector 403 after beam splitting; the time delay difference between the upper and lower arms of the offset frequency interferometry measurement module 3 is τ D , the frequency difference between the upper and lower arms of the offset frequency interferometry module 4 is ΔΩ2=Ω2+γτ D ;

[0013] The auxiliary interferometer module 5 includes a second coupler 501, a delay fiber 502, a third coupler 503, and a first balanced detector 504, wherein the second coupler 501 divides the light into two parts, one beam is injected into the first output end 501a of the second coupler, and the other beam is injected from the second output end 501b of the second coupler and passes through the delay fiber 502 therein, the two beams of light are combined in the third coupler 503 and then divided into two beams, and differential detection is performed by the first balanced detector 504, and the interference fringe signal after photoelectric conversion is injected into the information acquisition module 601, and is used as a sampling trigger signal after square wave shaping therein;

[0014] The signal acquisition and demodulation module 6 includes an information acquisition module 601, a filter extraction module 602, a transfer function acquisition module 603, and a spectrum response demodulation module 604;

[0015] The frequency difference introduced by the offset frequency maintaining interferometry module 3 is ΔΩ2 and the frequency difference introduced by the offset frequency maintaining orthogonal polarization generation module 2 is ΔΩ1, which requires that: ΔΩ2≥3ΔΩ1.

[0016] The pigtail fibers of the first frequency shifter 204 and the second frequency shifter 304 are both polarization-maintaining fibers; the pigtail fiber of the device under test 300 can be either a polarization-maintaining fiber or a single-mode fiber.

[0017] The output end of the first polarization beam splitter 202 works only in a single axis, that is, the first output end 203 of the first polarization beam splitter only outputs the slow axis (n), and the second output end 204 of the first polarization beam splitter only outputs the fast axis (m); the input end 200 of the first polarization beam splitter works in two axes. The first input end 207 of the polarization beam combiner only inputs the slow axis (n), and the second input end 208 of the polarization beam combiner only inputs the fast axis (m). The output end 210 of the polarization beam combiner works in two axes.

[0018] The auxiliary interferometer module 5 includes a second coupler 501, a delay fiber 502, a third coupler 305, and a first balanced detector 504, wherein the second coupler 501 divides the light into two parts, one beam is injected into the first output end 501a of the second coupler, and the other beam is injected from the second output end 501b of the second coupler and passes through the delay fiber 502. The two beams of light are combined in the third coupler 503 and then divided into two beams, which are differentially detected by the first balanced detector 504.

[0019] The interference fringes collected by the auxiliary interferometer module 5 are subjected to photoelectric conversion, and the interference fringe signals enter the information collection module 601, where they are square-wave shaped and used as sampling trigger signals.

[0020] A digital bandpass filter is designed according to the frequency difference between the frequency-shifted orthogonal polarization generating module 2 and the frequency-shifted interferometric measurement module 3, wherein the center frequency of the first unilateral digital bandpass filter 6021 is ΔΩ2-ΔΩ1, and the bandwidth is ΔΩ1; the center frequency of the second unilateral digital bandpass filter 6022 is ΔΩ2+ΔΩ1, and the bandwidth is ΔΩ1.

[0021] The information acquisition module 601 collects and stores data on the interference signals of the auxiliary interferometer module 5, the p detector 402 and the s detector 403; the p-polarized interference fringes 601a and the s-polarized interference fringes 601b output by the information acquisition module 601 can establish a functional relationship with the angular frequency of the linear frequency sweeping light, respectively. p (ω) and I s (ω), in the filtering and extraction module 602, the p-polarized interference fringe 601a passes through the first unilateral digital bandpass filter 6021 to obtain a first complex signal 602a, denoted as h 11 (ω), the p-polarized interference fringe 601a passes through the second unilateral digital bandpass filter 6022 to obtain a second complex signal 602b, denoted as h 12 (ω), the s-polarized interference fringe 601b passes through the first unilateral digital bandpass filter 6021 to obtain a third complex signal 602c, denoted as h 21 (ω), the s-polarized interference fringe 601b passes through the second unilateral digital bandpass filter 6021 to obtain a fourth complex signal 602d, denoted as h 22(ω), and then the device transfer matrix 603a is formed in the transfer function acquisition module 603, which is recorded as H(ω)=[h ij (ω)] 2×2 Finally, the amplitude transmission characteristic, phase transmission characteristic, and polarization transmission characteristic of the device are calculated in the spectrum response demodulation module (604), specifically:

[0022] The calculation formula for insertion loss (IL) is:

[0023]

[0024] The formula for calculating group delay (GD) is:

[0025] GD ( oh ) = arg [ ∑ h ij ( oh ) h ij * ( oh − D oh ) ] D oh

[0026] The calculation formula for polarization dependent loss (PDL) is:

[0027]

[0028] T max and T min are the eigenvalues ​​of the matrix obtained by multiplying the Jones matrix of the device and its conjugate transposed matrix;

[0029] The calculation formula for polarization mode dispersion (PMD) is:

[0030]

[0031] in, and yes The characteristic value of .

[0032] The polarization-free frequency-shift interferometry optical vector analysis device according to claim 1 is characterized in that:

[0033] The center frequency of the first unilateral digital bandpass filter 6021 is ΔΩ2-ΔΩ1, and the bandwidth is ΔΩ1; the center frequency of the second unilateral digital bandpass filter 6022 is ΔΩ2+ΔΩ1, and the bandwidth is ΔΩ1.

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] 1) The present invention uses polarization-maintaining devices to realize polarization-free optical vector analyzer, uses the characteristics of polarization beam splitter and polarization beam combiner to construct a pair of orthogonal polarized lights as interrogation lights, and uses polarization-maintaining optical fibers to 45° axially fused to realize balanced polarization alignment of polarization diversity system, thus realizing polarization-free adjustment and eliminating polarization adjustment errors introduced by traditional OVA;

[0036] 2) The optical vector analysis device based on frequency shift interferometry of the present invention utilizes a frequency shifter to replace the extended optical fiber, thereby reducing the phase noise problem caused by the long polarization-maintaining extended optical fiber and significantly increasing the effective frequency resolution of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a polarization-free frequency-shift interferometry optical vector analysis device.

[0038] Figure 1 In: 1—tunable laser; 2—offset frequency maintaining orthogonal polarization generation module; 3—offset frequency maintaining interferometry measurement module; 4—polarization diversity detection module; 5—auxiliary interferometer module; 6 signal acquisition and demodulation module; 101—first coupler; 201—45° polarizer; 200—first polarization beam splitter input end; 202—first polarization beam splitter; 203—first polarization beam splitter first output end; 204—first polarization beam splitter second output end; 205—first frequency shifter; 206—polarization beam combiner; 207—first polarization beam combiner input end; 208—second polarization beam combiner input end; 209—first driver; 301—first polarization maintaining coupler; 302—first A first output end of a polarization-maintaining coupler; 303—a second output end of the first polarization-maintaining coupler; 304—a second frequency shifter; 305—a second driver; 306—a second polarization-maintaining coupler; 307—a 45° axial fusion point of a polarization-maintaining optical fiber; 401—a second polarization beam splitter; 402—a p detector; 403—an s detector; 501—a second coupler; 501a—a first output end of the second coupler; 501b—a second output end of the second coupler; 502—a delayed optical fiber; 503—a third coupler; 504—a first balanced detector; 601—an information acquisition module; 602—a filter extraction module; 603—a transfer function acquisition module; 604—a spectrum response demodulation module.

[0039] Figure 2 This is a schematic diagram of 45° axial fusion of polarization-maintaining optical fibers;

[0040] Figure 3 is the frequency domain interference image of the p detector and the s detector,

[0041] Figure 3 In the middle: A—the frequency difference ΔΩ1 corresponding to the peak of the frequency shifting orthogonal polarization generating module 2; B—the frequency difference ΔΩ2-ΔΩ1 corresponding to the peak of the frequency shifting interference test module 4 and the frequency shifting orthogonal polarization generating module 2; C—the frequency difference ΔΩ2 corresponding to the peak of the frequency shifting interference test module 4; D—the sum of the frequency differences ΔΩ2+ΔΩ1 corresponding to the peak of the frequency shifting interference test module 4 and the frequency shifting orthogonal polarization generating module 2; 6021—the first unilateral digital bandpass filter; 6022—the second unilateral digital bandpass filter. DETAILED DESCRIPTION

[0042] In order to clearly illustrate the method for testing optical performance of polarization-maintaining optical fiber of the present invention, the present invention is further described in conjunction with examples and drawings, but the protection scope of the present invention shall not be limited thereto.

[0043] A polarization-free frequency-shift interferometry optical vector analysis device Figure 1 shown.

[0044] The selection and parameters of the main optoelectronic devices of this device are as follows:

[0045] 1) The light source is a narrow linewidth tunable laser source, model Santec TSL-770, with a wavelength tuning range of 1510nm~1590nm, a sweep rate of 80nm / s, and a sweep time of 1s;

[0046] 2) The detector model is Newport-2107-FC, the detection bandwidth is 10MHz, and the saturated differential detection power is 7μW;

[0047] 3) The acquisition card model is M4i:4471-x8, the 16-bit sampling rate is set to 200MHz, the number of sampling points is 200M, and the sampling time is 1s;

[0048] 4) The splitting ratio of the first coupler 101 is 1:99, wherein 99% of the light is input to the offset frequency-maintaining orthogonal polarization generating module 2, and 1% of the light is input to the auxiliary interferometer module 5, with an operating wavelength of 1550±40nm;

[0049] 5) The extinction ratio of all polarization beam splitters and polarization beam combiners is greater than 23dB, the insertion loss is less than 0.6dB, and the operating wavelength covers the 1550nm band;

[0050] 6) The splitting ratio of the first polarization-maintaining coupler 301 and the second polarization-maintaining coupler 306 is 50:50, and the operating wavelength is 1550±40nm;

[0051] 7) The polarizer 201 has an operating wavelength of 1550±40nm, an angle of 45°, an insertion loss of less than 1dB, and an extinction ratio of greater than 30dB;

[0052] 8) The first frequency shifter 205 is of model SGTF20-1550-1P, with an operating frequency of 20 MHz, and the second frequency shifter 405 is of model SGTF80-1550-1P, with an operating frequency of 80 MHz; the first driver 204 and the second driver 404 are low-power N-type acousto-optic drivers, the first driver is of model SGY20-33-N-1D, with an operating frequency of 20 MHz, and the second driver is of model SGY80-33-N-1D, with an operating frequency of 80 MHz;

[0053] 9) The device under test is a dense wavelength division multiplexer (DWDM) with a test port operating center wavelength of 1550nm, a length of 10m, and a refractive index of 1.456.

[0054] The linear continuous frequency sweeping light whose frequency changes with time at a rate γ generated by the tunable laser 1 is divided 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 offset frequency maintaining orthogonal polarization generating module 2;

[0055] The 45° polarizer 201 injects the optical signal into the fast axis (m) and the slow axis (n) of the polarization-maintaining optical fiber in a balanced manner. Then, the first polarization beam splitter 202 splits the light into two beams, one of which is injected into the first output end 203 of the first polarization beam splitter and passes through the first input end 207 of the polarization-maintaining beam combiner. The other beam is injected into the second output end 204 of the first polarization beam splitter and transmitted through the first frequency shifter 205 to output the light with the frequency shift amount Ω1 to the first input end 208 of the polarization-maintaining beam combiner. The first driver The driving signal frequency provided by the device 209 to the first frequency shifter 205 is Ω1; the two beams are combined in the polarization beam combiner 206, and then a pair of orthogonal polarized lights with a fixed frequency difference are output to the offset frequency maintaining interferometry measurement module 3, the time delay difference between the upper and lower arms of the offset frequency maintaining orthogonal polarization generation module 2 is τ, and the frequency difference between the upper and lower arms of the offset frequency maintaining orthogonal polarization generation module 2 is ΔΩ1=Ω1+γτ=20.097MHz (in this example, Ω1 is 20MHz and γ is 80nm / s);

[0056] A pair of orthogonal polarized lights with a fixed frequency difference output by the polarization-maintaining orthogonal polarization generating module 2 is divided into two beams after passing through the first polarization-maintaining coupler 301, one beam is injected into the first output port 303 of the first polarization-maintaining coupler as a reference light, and passes through the second frequency shifter 304 with a frequency shift amount Ω2, wherein the frequency provided to the second frequency shifter 304 by the second driver 305 is Ω2; the output light passes through the 45° axial fusion point 307 of the polarization-maintaining optical fiber and is input into the second polarization-maintaining coupler 306; another beam of light output by the first polarization-maintaining coupler 301 is injected into the second output port 302 of the first polarization-maintaining coupler, and is input into the second polarization-maintaining coupler 306 after passing through the device to be measured 300; the two beams of light combined in the second polarization-maintaining coupler 306 are injected into the second polarization beam splitter 401, and are respectively injected into the p detector 402 and the s detector 403 after being split; the time delay difference between the upper and lower arms of the offset frequency interferometry measurement module 3 is τ D , the frequency difference between the upper and lower arms of the offset frequency interferometry module 4 is ΔΩ2=Ω2+γτ D =80.485MHz (in this case, Ω2 is 80MHz and γ is 80nm / s);

[0057] Delay τ and τ D The calculation formula is ; Where L is the difference in length between the two arms, n is the refractive index, and c is the speed of light in a vacuum.

[0058] A digital bandpass filter is designed according to the frequency difference between the frequency-shifted orthogonal polarization generating module 2 and the frequency-shifted interferometric measurement module 3, wherein the center frequency of the first unilateral digital bandpass filter 6021 is ΔΩ2-ΔΩ1, and the bandwidth is ΔΩ1; the center frequency of the second unilateral digital bandpass filter 6022 is ΔΩ2+ΔΩ1, and the bandwidth is ΔΩ1.

[0059] The second coupler 501 divides the light into two parts, one beam is injected into the first output end 501a of the second coupler, and the other beam is injected into the second output end 501b of the second coupler and passes through the delay optical fiber 502. The two beams are combined in the third coupler 503 and then divided into two beams, which are differentially detected by the first balanced detector 504. The interference fringe signal after photoelectric conversion is injected into the information acquisition module 601, where it is used as a sampling trigger signal after square wave shaping.

[0060] The information acquisition module 601 collects and stores the interference signals of the auxiliary interferometer module 5, the P terminal 402 and the S terminal 403; the p-polarized interference fringes 601a and the s-polarized interference fringes 601b output by the information acquisition module 601 can establish a functional relationship with the angular frequency of the linear sweep light, respectively. p (ω) and I s (ω), in the filtering and extraction module 602, the p-polarized interference fringe 601a passes through the first unilateral digital bandpass filter 6021 to obtain a first complex signal 602a, denoted as h 11 (ω), the p-polarized interference fringe 601a passes through the second unilateral digital bandpass filter 6022 to obtain a second complex signal 602b, denoted as h 12 (ω), the s-polarized interference fringe 601b passes through the first unilateral digital bandpass filter 6021 to obtain a third complex signal 602c, denoted as h 21 (ω), the s-polarized interference fringe 601b passes through the second unilateral digital bandpass filter 6021 to obtain a fourth complex signal 602d, denoted as h 22 (ω), and then the device transfer matrix 603a is formed in the transfer function acquisition module 603, which is recorded as H(ω)=[h ij (ω)] 2×2 Finally, the amplitude transmission characteristic, phase transmission characteristic, and polarization transmission characteristic of the device can be calculated in the spectrum response demodulation module (604), specifically:

[0061] The calculation formula for insertion loss (IL) is:

[0062]

[0063] The formula for calculating group delay (GD) is:

[0064] GD ( oh ) = arg [ ∑ h ij ( oh ) h ij * ( oh − D oh ) ] D oh

[0065] The calculation formula for polarization dependent loss (PDL) is:

[0066]

[0067] T max and T min are the eigenvalues ​​of the matrix obtained by multiplying the Jones matrix of the device and its conjugate transposed matrix;

[0068] The calculation formula for polarization mode dispersion (PMD) is:

[0069]

[0070] in, and yes The characteristic value of .

Claims

1. A polarization-free frequency-shift interferometry optical vector analysis device, comprising a tunable laser (1), an offset-frequency-maintaining orthogonal polarization generation module (2), an offset-frequency-maintaining interferometry measurement module (3), a polarization diversity detection module (4), an auxiliary interferometer module (5), and a signal acquisition and demodulation module (6). Its characteristics are: The linear continuous frequency sweeping light whose frequency changes with time at a rate γ generated by the tunable laser (1) is divided into two beams through a first coupler (101), one beam is injected into the auxiliary interferometer module (5), and the other beam is injected into the offset frequency maintaining orthogonal polarization generation module (2); The polarization-maintaining orthogonal polarization generating module (2) comprises a 45° polarizer (201), a polarization beam splitter (202), a first frequency shifter (205), a polarization beam combiner (206), and a first driver (209), wherein the 45° polarizer (201) injects an optical signal into the fast axis (m) and the slow axis (n) of the polarization-maintaining optical fiber in a balanced manner, and then the first polarization beam splitter (202) splits the light into two beams, one of which is injected into the first output end (203) of the first polarization beam splitter and passes through the first input end (207) of the polarization-maintaining beam combiner, and the other is injected into the second output end (204) of the first polarization beam splitter for transmission and passes through the first frequency shifter (205) to output a light beam with a frequency shift amount Ω. 1 The light is transmitted to the second input end (208) of the polarization-maintaining beam combiner, wherein the frequency of the driving signal provided by the first driver (209) to the first frequency shifter (205) is Ω 1 The two beams of light are combined in the polarization beam combiner (206), and then a pair of orthogonal polarized lights with a fixed frequency difference are output to the offset frequency maintaining interferometry measurement module (3), the time delay difference between the upper and lower arms of the offset frequency maintaining orthogonal polarization generation module (2) is τ, and the frequency difference between the upper and lower arms of the offset frequency maintaining orthogonal polarization generation module (2) is ΔΩ 1 =Ω 1 +γτ; The shift frequency interferometry module (3) comprises a first polarization-maintaining coupler (301), a device to be tested (300), a second frequency shifter (304), a second driver (305), a second polarization-maintaining coupler (306), and a polarization-maintaining optical fiber 45° axial fusion point (307), wherein a pair of orthogonal polarization lights with a fixed frequency difference output by the polarization-maintaining orthogonal polarization generating module (2) are divided into two beams after passing through the first polarization-maintaining coupler (301), one beam is injected into the first output port (303) of the first polarization-maintaining coupler as a reference light, and the second beam is divided into two beams after passing through the frequency shift amount Ω 2 The second frequency shifter (304) is a second frequency shifter (304), wherein the second driver (305) provides a driving signal with a frequency of Ω 2 , the output light passes through the 45° axial fusion point (307) of the polarization-maintaining optical fiber and is input into the second polarization-maintaining coupler (306); another beam of light output from the first polarization-maintaining coupler (301) is injected into the second output port (302) of the first polarization-maintaining coupler, passes through the device under test (300) and is input into the second polarization-maintaining coupler (306); the two beams of light combined in the second polarization-maintaining coupler (306) are injected into the second polarization beam splitter (401), and after beam splitting, are respectively injected into the p detector (402) and the s detector (403); the time delay difference between the upper and lower arms of the offset frequency interferometry measurement module (3) is τ D , the frequency difference ΔΩ between the upper and lower arms of the offset frequency interferometry module (4) 2 =Ω 2 +γτ D ; The auxiliary interferometer module (5) comprises a second coupler (501), a delay optical fiber (502), a third coupler (503), and a first balanced detector (504), wherein the second coupler (501) divides light into two parts, one beam is injected into the first output end (501a) of the second coupler, and the other beam is injected from the second output end (501b) of the second coupler and passes through the delay optical fiber (502), the two beams of light are combined in the third coupler (503) and then divided into two beams, which are differentially detected by the first balanced detector (504), and the interference fringe signal after photoelectric conversion is injected into the information acquisition module (601), where it is square-wave shaped and used as a sampling trigger signal; The signal acquisition and demodulation module (6) comprises an information acquisition module (601), a filter extraction module (602), a transfer function acquisition module (603), and a spectrum response demodulation module (604).

2. The polarization-free frequency-shift interferometry optical vector analysis device according to claim 1, Its characteristics are: The frequency difference introduced by the offset frequency interferometry module (3) is ΔΩ 2 , the frequency difference introduced by the offset frequency orthogonal polarization generating module (2) is ΔΩ 1 , the requirement is: ΔΩ 2 ≥3ΔΩ 1 .

3. The polarization-free frequency-shift interferometry optical vector analysis device according to claim 1, Its characteristics are: The pigtail fibers of the first frequency shifter (204) and the second frequency shifter (304) are both polarization-maintaining optical fibers.

4. The polarization-free frequency-shift interferometry optical vector analysis device according to claim 1, Its characteristics are: The output end of the first polarization beam splitter (202) works only in a single axis, that is, the first output end (203) of the first polarization beam splitter outputs only in a slow axis (n), and the second output end (204) of the first polarization beam splitter outputs only in a fast axis (m); the input end (200) of the first polarization beam splitter works in a dual axis; the first input end (207) of the polarization beam combiner inputs only in a slow axis (n), and the second input end (208) of the polarization beam combiner inputs only in a fast axis (m); and the output end (210) of the polarization beam combiner works in a dual axis.

5. The polarization-free frequency-shift interferometry optical vector analysis device according to claim 1, Its characteristics are: The information acquisition module (601) acquires and stores data on interference signals of the auxiliary interferometer module (5), the p detector (402) and the s detector (403); the p-polarized interference fringes (601a) and the s-polarized interference fringes (601b) output by the information acquisition module (601) can establish functional relationships with the angular frequencies of the linear frequency sweeping light, which are I p (ω) and I s (ω), in the filtering and extraction module (602), the p-polarized interference fringes (601a) pass through the first unilateral digital bandpass filter (6021) to obtain a first complex signal (602a), which is denoted as h 11 (ω), the p-polarized interference fringes (601a) pass through the second unilateral digital bandpass filter (6022) to obtain a second complex signal (602b), denoted as h 12 (ω), the s-polarized interference fringes (601b) pass through the first unilateral digital bandpass filter (6021) to obtain a third complex signal (602c), denoted as h 21 (ω), the s-polarized interference fringes (601b) pass through the second unilateral digital bandpass filter (6021) to obtain a fourth complex signal (602d), denoted as h 22 (ω), and then the device transfer matrix (603a) is formed in the transfer function acquisition module (603), which is recorded as H(ω)=[h ij (ω)] 2×2 Finally, the amplitude transmission characteristic, phase transmission characteristic, and polarization transmission characteristic of the device are calculated in the spectrum response demodulation module (604), specifically: The calculation formula for insertion loss (IL) is: The formula for calculating group delay (GD) is: GD ( ω ) = arg [ ∑ h ij ( ω ) h ij * ( ω − Δ ω ) ] Δ ω The calculation formula for polarization dependent loss (PDL) is: T max and T min are the eigenvalues ​​of the matrix obtained by multiplying the Jones matrix of the device and its conjugate transposed matrix; The calculation formula for polarization mode dispersion (PMD) is: in, and yes The characteristic value of .

6. The polarization-free frequency-shift interferometry optical vector analysis device according to claim 1, Its characteristics are: The center frequency of the first unilateral digital bandpass filter (6021) is ΔΩ 2 -ΔΩ 1 , bandwidth is ΔΩ 1 ; The center frequency of the second unilateral digital bandpass filter (6022) is ΔΩ 2 +ΔΩ 1 , bandwidth is ΔΩ 1 .

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