A swept polarization sensitive optical coherence tomography system and method

Abstract

The application discloses a swept frequency polarization sensitive optical coherence tomography system and method, and the swept frequency polarization sensitive optical coherence tomography system comprises a swept frequency light source, a polarization maintaining optical fiber, a spatial coupling collimator, a full spatial polarization light path module, an observation imaging module and a data processing module. The swept frequency light is converted into free space collimated light after being input into the spatial coupling collimator through the polarization maintaining optical fiber; the collimated light is divided into sample light and reference light through a first unpolarized beam splitting cube, the sample light is converted into circularly polarized light through a first quarter wave plate and irradiates a sample. After the sample return light and the reference light are combined through a second unpolarized beam splitting cube, the sample return light and the reference light are respectively decomposed into horizontal and vertical polarization components through a polarization beam splitter and are differentially collected by two balanced detectors. The data processing module calculates Stokes parameters, phase delay, optical axis and polarization uniformity according to a double-channel complex signal. The full spatial polarization light path module adopts a rigid free space light path, reduces dynamic polarization drift caused by deformation of a moving optical fiber and improves stability of moving imaging.

Description

Technical Field

[0001] This invention relates to the field of optical coherence tomography and polarization measurement technology, and in particular to a frequency-sweeping polarization-sensitive optical coherence tomography system and method suitable for mobile or handheld probes. Background Technology

[0002] Polarization-sensitive optical coherence tomography (PS-OCT) can acquire information about the structure of tissues or materials, and also measure parameters such as phase retardation, optical axis, and polarization uniformity to characterize birefringent structures and spatial variations in polarization states. Swept-source PS-OCT (SS-PS-OCT) uses a narrow-linewidth light source with wavelength scanning over time, making it suitable for high-speed and deep-range imaging.

[0003] Existing single-input polarization-state PS-OCT typically uses two orthogonal polarization detection channels to recover the complex amplitude of the returned light. If a relatively long single-mode fiber is retained within the moving probe, fiber bending, twisting, and stress will alter the system's Jones matrix, causing the sample polarization information to couple with the system polarization drift. Active polarization control can compensate for this change, but it increases hardware and control complexity.

[0004] Using polarization-maintaining fiber can improve the stability of the input polarization state, but it may introduce differential group delay and polarization mode dispersion when simultaneously exciting the fast and slow axes. Using multiple input polarization states can improve sample matrix recovery capability, but it typically requires electro-optic modulators, acousto-optic modulators, or polarization state switching between adjacent A-scans, increasing synchronization requirements and reducing the effective acquisition rate for each input polarization state.

[0005] Therefore, there is a need for an SS-PS-OCT system that reduces the propagation length of deformable optical fibers inside the moving probe, adopts a rigid free-space polarization optical path, and combines polarization diversity balanced detection to improve the stability of the dual-channel polarization interference signal during probe movement. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a swept-frequency polarization-sensitive optical coherence tomography system and method. This invention uses polarization-maintaining fiber only for polarization-preserving transmission from the swept-frequency light source to the probe entrance, and employs rigidly mounted free-space sample arm, reference arm, and polarization diversity balanced probe optical path inside the probe, thereby reducing dynamic polarization drift caused by probe movement.

[0007] In a first aspect, the present invention provides a swept-frequency polarization-sensitive optical coherence tomography system, comprising:

[0008] Frequency sweeping light source, polarization-maintaining fiber, spatial coupling collimator, full-space polarization optical path module, observation and imaging module, and data processing module;

[0009] The swept frequency light source is connected to the spatial coupling collimator through the polarization-maintaining fiber. The spatial coupling collimator is used to receive the swept frequency beam output by the swept frequency light source and convert it into a free space collimated beam.

[0010] The full-space polarization optical path module includes a first non-polarization beam splitter cube, a sample arm, a reference arm, a sample return optical path, and a polarization diversity balanced detection optical path; the first non-polarization beam splitter cube splits the free-space collimated beam into a sample detection beam and a reference beam;

[0011] The sample arm includes a first quarter-wave plate, a two-dimensional galvanometer, and an OCT focusing objective arranged in sequence. The sample probe beam is converted into a circularly polarized probe beam by the first quarter-wave plate and then illuminates the sample under test after passing through the two-dimensional galvanometer and the OCT focusing objective. The backscattered beam of the sample under test returns to the first unpolarized beam splitter cube along the sample arm.

[0012] The reference arm includes a second mirror and a second quarter-wave plate. The reference beam is reflected by the second mirror and its polarization state is adjusted by the second quarter-wave plate before entering the second unpolarized beam splitter cube. The sample return optical path includes a first mirror. The backscattered beam is guided to the second unpolarized beam splitter cube via the first mirror.

[0013] The second non-polarized beam splitter cube combines the backscattered beam with the reference beam and outputs two complementary interference beams. The two complementary interference beams enter the first polarization beam splitter and the second polarization beam splitter, respectively. The horizontal polarization components output by the first polarization beam splitter and the second polarization beam splitter are connected to the horizontal polarization balance detector, and the vertical polarization components output by the first polarization beam splitter and the second polarization beam splitter are connected to the vertical polarization balance detector. The horizontal polarization differential interference signal and the vertical polarization differential interference signal are obtained through the horizontal polarization balance detector and the vertical polarization balance detector.

[0014] The data processing module is connected to the horizontal polarization balance detector and the vertical polarization balance detector, and is used to generate structural and polarization parameter images based on the horizontal polarization differential interference signal and the vertical polarization differential interference signal.

[0015] Preferably, the diameter of the parallel free-space collimated beam output by the spatial coupling collimator is 3 mm.

[0016] Preferably, the fast axis of the first quarter-wave plate forms a 45° angle with the polarization direction of the incident linearly polarized light, thereby converting the sample probe beam into a circularly polarized probe beam, wherein the circularly polarized probe beam satisfies:

[0017] ;

[0018] In the formula, The Jones vector of the circularly polarized probe light. The Jones matrix for the first quarter-wave plate; The Jones vector of the incident ray-polarized light. The amplitude of the incident light field. The imaginary unit and .

[0019] Preferably, the observation and imaging module includes a CCD, an imaging lens group, and the spectral splitter; the spectral splitter combines the visible observation light and the OCT detection light into a shared two-dimensional galvanometer and OCT focusing objective, for real-time observation of the sample to be tested and positioning of the OCT scanning field of view.

[0020] Preferably, under the reciprocal coordinate convention, the round-trip polarization transport of the sample arm satisfies:

[0021] ;

[0022] In the formula, The Jones vector of the sample backscattered light. The Jones matrix represents the forward system from the first unpolarized beam splitter cube to the sample under test. For transpose operation, Let be the equivalent Jones matrix of the sample to be tested and its reflection process.

[0023] Preferably, the two complementary interference beams output by the second non-polarized beam-splitting cube are represented as follows:

[0024] ;

[0025] ;

[0026] In the formula, , These are two complementary interference beams; , These are the sample light field and the reference light field entering the second unpolarized beam splitter cube, respectively.

[0027] The horizontal polarization balance detector and the vertical polarization balance detector perform differential analysis on the same polarization components of the two complementary interference beams to eliminate the DC term and retain the coherent cross term.

[0028] Preferably, the spatial coupling collimator, the full-space polarization optical path module, and the observation imaging module are rigidly mounted in the same probe housing, and the polarization-maintaining fiber is fixed to the input end of the spatial coupling collimator to reduce the influence of fiber bending and twisting on the detection polarization state when the probe moves.

[0029] Preferably, the data processing module is configured as follows:

[0030] Background removal, wavenumber linearization, and complex signal analysis are performed on the horizontally polarized differential interference signal and the vertically polarized differential interference signal to obtain the horizontally polarized complex signal and the vertically polarized complex signal;

[0031] Calculate the Stokes parameters based on the horizontally polarized complex signal and the vertically polarized complex signal;

[0032] Within a preset three-dimensional space window, the normalized Stokes parameters are smoothed, and the polarization uniformity (DOPU) is calculated. The structural image, phase retardation image, optical axis image, and DOPU image of the sample under test are then generated.

[0033] Secondly, the present invention provides a swept-frequency polarization-sensitive optical coherence tomography method, comprising:

[0034] The linearly polarized swept light is converted into free-space collimated light, which is then converted into a circularly polarized probe beam by a first quarter-wave plate. The two-dimensional galvanometer is controlled to complete the two-dimensional scan, and the horizontal polarization balance detector and the vertical polarization balance detector simultaneously acquire the horizontal polarization differential interference signal and the vertical polarization differential interference signal.

[0035] Background removal, wavenumber linearization, dispersion compensation, and complex signal analysis are performed on the horizontally polarized differential interference signal and the vertically polarized differential interference signal to obtain the horizontally polarized complex signal and the vertically polarized complex signal.

[0036] An initial Jones vector is constructed based on the horizontal and vertical polarization complex signals and converted into Stokes parameters. Polarization coordinates are then corrected based on the system calibration results.

[0037] Within a preset three-dimensional space window, the normalized Stokes parameters are smoothed, and the polarization uniformity DOPU is calculated.

[0038] The phase delay, optical axis, and depolarization index of the sample under test are calculated based on the normalized Stokes parameters, and structural images, phase delay images, optical axis images, and DOPU images are generated.

[0039] The beneficial technical effects of this invention are as follows:

[0040] 1. The probe mainly adopts a rigid free space optical path to reduce the system polarization change caused by deformable optical fibers inside the moving probe and improve the stability of polarization imaging.

[0041] 2. By utilizing the complementary output of the second non-polarization beam splitter cube for dual-channel polarization diversity balanced detection, the relative intensity noise of the light source and DC background can be suppressed, thereby improving the signal-to-noise ratio of the interference signal.

[0042] 3. Synchronous horizontal and vertical polarization complex signals are obtained in a single scan, eliminating the need to switch the input polarization state between adjacent A-scans, which facilitates rapid imaging under conditions of sample movement and handheld probe. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the system framework according to an embodiment of the present invention;

[0044] Figure 2 This is a flowchart illustrating the method of an embodiment of the present invention;

[0045] 1-Sweeping frequency light source; 2-Polarization-maintaining fiber; 3-Spatial coupling collimator; 4-First unpolarized beam splitter cube; 5-First quarter-wave plate; 6-Two-dimensional galvanometer; 7-OCT focusing objective; 8-CCD; 9-Second reflecting mirror; 10-Second quarter-wave plate; 11-First reflecting mirror; 12-Second unpolarized beam splitter cube; 13-First polarization beam splitter; 14-Second polarization beam splitter; 15-Horizontal polarization balance detector; 16-Vertical polarization balance detector; 17-Data processing module. Detailed Implementation

[0046] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0047] like Figure 1 As shown, this embodiment provides a swept-frequency polarization-sensitive optical coherence tomography system, including a swept-frequency light source 1, a polarization-maintaining fiber 2, a spatially coupled collimator 3, a full-space polarization optical path module, an observation and imaging module, and a data processing module. The full-space polarization optical path module includes a first non-polarization beam splitter cube 4, a sample arm, a reference arm, a sample return optical path, and a polarization diversity balanced detection optical path.

[0048] The sample arm comprises a first quarter-wave plate 5, a two-dimensional galvanometer 6, and an OCT focusing objective lens 7 arranged sequentially. The reference arm comprises a second reflecting mirror 9 and a second quarter-wave plate 10.

[0049] The sample return optical path includes a first reflector 11.

[0050] The polarization diversity balanced detection optical path includes a first polarization beamsplitter 13 and a second polarization beamsplitter 14, as well as a horizontal polarization balanced detector 15 and a vertical polarization balanced detector 16.

[0051] The swept-frequency light source 1 outputs linearly polarized swept-frequency light. This light is transmitted via polarization-maintaining fiber 2 to a spatially coupled collimator 3, which outputs a parallel free-space collimated beam with a diameter of approximately 3 mm. The output polarization direction of the polarization-maintaining fiber 2 is aligned at a 45° angle with the fast axis direction of the first quarter-wave plate 5.

[0052] The free-space collimated beam enters the first unpolarized beam-splitting cube 4 and is split into a sample probe beam and a reference beam. The sample probe beam passes sequentially through a first quarter-wave plate 5, a two-dimensional galvanometer 6, and an OCT focusing objective lens 7. When the fast axis of the first quarter-wave plate 5 forms a 45° angle with the polarization direction of the incident beam, the circularly polarized probe beam at the sample satisfies:

[0053]

[0054] In the formula, The Jones vector of the circularly polarized probe light. The Jones matrix for the first quarter-wave plate; The Jones vector of the incident ray-polarized light. The amplitude of the incident light field. The imaginary unit and .

[0055] The two-dimensional galvanometer 6 performs an XY two-dimensional scan of the circularly polarized probe beam, and the OCT focusing objective 7 focuses the scanned beam onto the sample to be tested. The backscattered light from the sample to be tested returns along the original sample arm to the first unpolarized beam splitter cube 4, and is guided by the first reflecting mirror 11 to the second unpolarized beam splitter cube 12.

[0056] The reference beam is output from the first unpolarized beam splitter cube 4, reflected by the second mirror 9, and its polarization state and polarization component ratio are adjusted by the second quarter-wave plate 10 before entering the second unpolarized beam splitter cube 12. The optical path of the reference arm is matched by the position of the second mirror 9 or by an additional optical path adjustment mechanism.

[0057] The first reflecting mirror 11 is located in the sample return optical path, and the second reflecting mirror 9 is located in the reference arm; the above names and paths are consistent with... Figure 1 To maintain consistency, the sample arm, reference arm, and polarization diversity balanced probe optical path are rigidly fixed inside the probe housing.

[0058] Under the reciprocal coordinate convention, let This represents the forward system Jones matrix from the first unpolarized beam splitter cube 4 to the sample under test. The equivalent Jones matrix representing the sample under test and its reflection process, under the reciprocal coordinate convention, satisfies the following for the round-trip polarization transport of the sample arm:

[0059] ;

[0060] In the formula, The Jones vector of the sample backscattered light. The Jones matrix represents the forward system from the first unpolarized beam splitter cube to the sample under test. For transpose operation, Let be the equivalent Jones matrix of the sample to be tested and its reflection process.

[0061] During system calibration, coordinate rotation, polarization-dependent loss, and fixed phase offset can be determined using calibration samples with known polarization states, and corrected in the data processing module 17. For the polarization response caused by the two-dimensional galvanometer 6 that varies with the scanning angle, the calibration matrix at different scanning positions can be pre-measured and compensated using a lookup table or fitting model.

[0062] The two complementary interference beams output by the second unpolarized beam-splitting cube 12 are represented as follows:

[0063] ;

[0064] ;

[0065] In the formula, , These are two complementary interference beams; , These are the sample light field and the reference light field entering the second unpolarized beam splitter cube 12, respectively;

[0066] The horizontal polarization balance detector 15 and the vertical polarization balance detector 16 respectively perform differential analysis on the same polarization components of the two complementary interference beams to eliminate the DC term and retain the coherent cross term.

[0067] The first polarization beam splitter 13 and the second polarization beam splitter 14 process the two complementary interference beams respectively. , Its horizontal polarization projection matrix and vertical polarization projection matrix for:

[0068] ;

[0069] The two complementary interference beams , The horizontal polarization component is connected to the horizontal polarization balance detector 15 to obtain the horizontal polarization differential interference signal. ,Right now:

[0070] ;

[0071] The two complementary interference beams , The vertical polarization component is connected to the vertical polarization balanced detector 16 to obtain the vertical polarization differential interference signal. ,Right now:

[0072] ;

[0073] In the formula, The modulus is squared.

[0074] The above differential operation eliminates the same-direction DC terms in the two outputs and retains the coherent cross terms. The data processing module 17 samples the horizontally polarized differential interference signal and the vertically polarized differential interference signal, and constructs the horizontally polarized complex signal and the vertically polarized complex signal through background removal, wavenumber linearization, dispersion compensation, Fourier transform, and analytical signal processing.

[0075] The Stokes parameters are constructed based on the horizontally polarized complex signal and the vertically polarized complex signal, i.e.:

[0076]

[0077]

[0078] In the formula, , , , These are the Stokes parameters; , These are horizontally polarized complex signals and vertically polarized complex signals, respectively; the superscript * indicates complex conjugate.

[0079] The Stokes parameters are normalized to obtain the normalized Stokes parameters. ,Right now:

[0080] ;

[0081] In the region where the sample under test can be approximated as a linear phase retarder and the input is circularly polarized light, the phase delay δ and optical axis direction θ under the coordinate convention of this embodiment can be expressed as:

[0082]

[0083] ;

[0084] For two-way reflection measurements, the phase delay δ is the equivalent two-way phase delay in system coordinates. If a single-way phase delay or local birefringence is required, it should be converted by combining refractive index, depth sampling and two-way coefficient.

[0085] To reduce random fluctuations in polarization state caused by speckle, the normalized Stokes parameters are weighted or mean-smoothed within a preset three-dimensional spatial window. The polarization uniformity DOPU is calculated as follows:

[0086] ;

[0087] In the formula, , , Normalized Stokes parameters; This represents the average value within a preset three-dimensional space window;

[0088] A higher DOPU value indicates a more consistent polarization state within the window; a lower DOPU value indicates a stronger spatial variation in polarization states. To display the polarization state in the direction of increasing depolarization degree, a depolarization index can be defined. :

[0089] ;

[0090] The polarization index It is used solely as a display indicator to complement DOPU.

[0091] The observation imaging module acquires the sample surface field of view via CCD 8. The dichroic mirror in the two-dimensional galvanometer 6 selects the transmission or reflection direction based on the visible observation band and the OCT operating band, merging the observation optical path and the OCT sample optical path into the shared two-dimensional galvanometer 6 and OCT focusing objective lens 7. Thus, CCD 8 is used to locate the scanning area, rather than being directly connected to the two-dimensional galvanometer 6 without optical beam combining.

[0092] like Figure 2 As shown, a second embodiment of this application provides a swept-frequency polarization-sensitive optical coherence tomography method, comprising:

[0093] S1: The linearly polarized swept light is converted into free-space collimated light, which is then converted into a circularly polarized probe beam through a first quarter-wave plate. The sample to be tested is located by a CCD, and the two-dimensional galvanometer is controlled to complete the XY two-dimensional scan. The horizontal polarization balance detector and the vertical polarization balance detector simultaneously acquire the horizontal polarization differential interference signal and the vertical polarization differential interference signal.

[0094] S2: Perform background removal, wavenumber linearization, dispersion compensation, and complex signal analysis on the horizontally polarized differential interference signal and the vertically polarized differential interference signal to obtain the horizontally polarized complex signal and the vertically polarized complex signal;

[0095] S3: Construct an initial Jones vector based on the horizontally polarized complex signal and the vertically polarized complex signal and convert it into Stokes parameters. Perform polarization coordinate correction based on the system calibration results to obtain the normalized Stokes parameters.

[0096] S4: Smooth the normalized Stokes parameters within a preset three-dimensional space window and calculate the polarization uniformity DOPU.

[0097] S5: Calculate the phase delay, optical axis, and depolarization index of the sample under test based on the normalized Stokes parameters, and combine this with the Stokes parameters before normalization. Alternatively, horizontally polarized complex signals and vertically polarized complex signals can be used to generate structural images, phase delay images, optical axis images, and DOPU images.

[0098] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of the present invention. Various changes and modifications may be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A swept-frequency polarization-sensitive optical coherence tomography system, characterized in that, It includes a frequency sweeping light source, polarization-maintaining fiber, spatial coupling collimator, full-space polarization optical path module, observation and imaging module, and data processing module; The swept frequency light source is connected to the spatial coupling collimator through the polarization-maintaining fiber. The spatial coupling collimator is used to receive the swept frequency beam output by the swept frequency light source and convert it into a free space collimated beam. The full-space polarization optical path module includes a first non-polarization beam splitter cube, a sample arm, a reference arm, a sample return optical path, and a polarization diversity balanced detection optical path; the first non-polarization beam splitter cube splits the free-space collimated beam into a sample detection beam and a reference beam; The sample arm includes a first quarter-wave plate, a two-dimensional galvanometer, and an OCT focusing objective arranged in sequence. The sample probe beam is converted into a circularly polarized probe beam by the first quarter-wave plate and then illuminates the sample under test after passing through the two-dimensional galvanometer and the OCT focusing objective. The backscattered beam of the sample under test returns to the first unpolarized beam splitter cube along the sample arm. The reference arm includes a second mirror and a second quarter-wave plate. The reference beam is reflected by the second mirror and its polarization state is adjusted by the second quarter-wave plate before entering the second unpolarized beam splitter cube. The sample return optical path includes a first mirror. The backscattered beam is guided to the second unpolarized beam splitter cube via the first mirror. The polarization diversity balanced detection optical path includes a first polarization beamsplitter and a second polarization beamsplitter, as well as a horizontal polarization balanced detector and a vertical polarization balanced detector. The second non-polarization beam splitter cube combines the backscattered beam with the reference beam and outputs two complementary interference beams, which enter the first polarization beams and the second polarization beams, respectively. The horizontal polarization components output by the first polarization beamsplitter and the second polarization beamsplitter are jointly connected to the horizontal polarization balanced detector, and the vertical polarization components output by the first polarization beamsplitter and the second polarization beamsplitter are jointly connected to the vertical polarization balanced detector. Horizontal polarization differential interference signals and vertical polarization differential interference signals are obtained through the horizontal polarization balanced detector and the vertical polarization balanced detector. The data processing module is connected to the horizontal polarization balance detector and the vertical polarization balance detector, and is used to generate structural and polarization parameter images based on the horizontal polarization differential interference signal and the vertical polarization differential interference signal.

2. The swept-frequency polarization-sensitive optical coherence tomography system according to claim 1, characterized in that, The diameter of the parallel free-space collimated beam output by the spatial coupling collimator is 3 mm.

3. The swept-frequency polarization-sensitive optical coherence tomography system according to claim 1, characterized in that, The fast axis of the first quarter-wave plate forms a 45° angle with the polarization direction of the incident linearly polarized light, converting the sample probe beam into a circularly polarized probe beam, which satisfies the following: ； In the formula, The Jones vector of the circularly polarized probe light. The Jones matrix for the first quarter-wave plate; The Jones vector of the incident ray-polarized light. The amplitude of the incident light field. The imaginary unit and .

4. The system according to claim 1, characterized in that, The observation and imaging module includes a CCD, an imaging lens group, and a spectral splitter; the spectral splitter combines the visible observation light and the OCT detection light into a shared two-dimensional galvanometer and OCT focusing objective, which is used to observe the sample under test in real time and locate the OCT scanning field of view.

5. The system according to claim 1, characterized in that, Under the reciprocal coordinate convention, the round-trip polarization transport of the sample arm satisfies: In the formula, The Jones vector of the sample backscattered light. The Jones matrix represents the forward system from the first unpolarized beam splitter cube to the sample under test. For transpose operation, Let be the equivalent Jones matrix of the sample to be tested and its reflection process.

6. The system according to claim 1, characterized in that, The two complementary interference beams output by the second non-polarized beam splitter cube are represented as follows: ； ； In the formula, , These are two complementary interference beams; , These are the sample light field and the reference light field entering the second unpolarized beam splitter cube, respectively. The horizontal polarization balance detector and the vertical polarization balance detector perform differential analysis on the same polarization components of the two complementary interference beams to eliminate the DC term and retain the coherent cross term.

7. The system according to claim 1, characterized in that, The spatial coupling collimator, the full-space polarization optical path module, and the observation imaging module are rigidly mounted in the same probe housing. The polarization-maintaining fiber is fixed to the input end of the spatial coupling collimator to reduce the influence of fiber bending and twisting on the detection polarization state when the probe moves.

8. The system according to claim 1, characterized in that, The data processing module is configured as follows: Background removal, wavenumber linearization, and complex signal analysis are performed on the horizontally polarized differential interference signal and the vertically polarized differential interference signal to obtain the horizontally polarized complex signal and the vertically polarized complex signal; Calculate the Stokes parameters based on the horizontally polarized complex signal and the vertically polarized complex signal; Within a preset three-dimensional space window, the normalized Stokes parameters are smoothed, and the polarization uniformity (DOPU) is calculated. The structural image, phase retardation image, optical axis image, and DOPU image of the sample under test are then generated.

9. A swept-frequency polarization-sensitive optical coherence tomography method, characterized in that, include: The linearly polarized swept light is converted into free-space collimated light, which is then converted into a circularly polarized probe beam by a first quarter-wave plate. The two-dimensional galvanometer is controlled to complete the two-dimensional scan, and the horizontal polarization balance detector and the vertical polarization balance detector simultaneously acquire the horizontal polarization differential interference signal and the vertical polarization differential interference signal. Background removal, wavenumber linearization, dispersion compensation, and complex signal analysis are performed on the horizontally polarized differential interference signal and the vertically polarized differential interference signal to obtain the horizontally polarized complex signal and the vertically polarized complex signal. An initial Jones vector is constructed based on the horizontally polarized complex signal and the vertically polarized complex signal and converted into Stokes parameters. Polarization coordinates are corrected according to the system calibration results to obtain normalized Stokes parameters. Within a preset three-dimensional space window, the normalized Stokes parameters are smoothed, and the polarization uniformity DOPU is calculated. The phase delay, optical axis, and depolarization index of the sample under test are calculated based on the normalized Stokes parameters. The structure image, phase delay image, optical axis image, and DOPU image are generated by combining the Stokes parameters before normalization or the horizontally polarized complex signal and the vertically polarized complex signal.

10. The method according to claim 9, characterized in that, The polarization uniformity DOPU satisfies: ； In the formula, , , Normalized Stokes parameters; This represents the average value within a preset three-dimensional space window; The depolarization index is expressed as: .

Images