Handheld polarization-based optical coherence tomography system and method

Abstract

The application belongs to the technical field of OCT imaging, and provides a handheld optical coherence tomography system and method based on polarization control. The application actively and dynamically controls through a polarization dynamic adjustment module, fundamentally suppresses random fluctuations of the polarization state caused by handheld operation and fiber disturbance, and significantly improves the contrast and stability of the interference signal. The application pre-sets the polarization state and shapes the light beam of the incident light before the handheld probe, effectively improves the interference efficiency and the imaging signal-to-noise ratio, and reduces the influence of posture changes and environmental disturbances on the imaging quality during the handheld operation. The optical path structure supports polarization-sensitive imaging and functional expansion in a compact volume, and is suitable for non-contact and non-invasive high-resolution retinal imaging. Compared with the existing handheld OCT system, the application has the advantages of strong polarization controllability, high imaging stability, high system integration and the like.

Description

Technical Field

[0001] This invention belongs to the field of OCT imaging technology, specifically relating to a handheld optical coherence tomography system and method based on polarization modulation. Background Technology

[0002] In the field of OCT imaging technology, optical coherence tomography (OCT) has evolved from traditional desktop systems to handheld devices to improve its applicability. However, handheld OCT still faces a series of systemic challenges in practical applications, which can be summarized into the following four aspects: 1. Handheld operation leads to polarization instability and degrades interference signal quality: Handheld operation inevitably introduces jitter, attitude changes and fiber bending, which causes random drift in the polarization state of the imaging optical path, severely reducing the interference contrast and stability between the reference light and the sample light, and directly affecting the image signal-to-noise ratio and system reliability.

[0003] 2. Fiber motion and aberration disturbances reduce imaging resolution: The flexible fiber connecting the handheld probe and the main unit is prone to introducing dynamic aberrations and wavefront distortion during movement, leading to a decrease in the focusing quality of the emitted beam. This increases the size of the fundus spot and disperses energy, thus significantly reducing the actual lateral resolution and imaging sensitivity of the system.

[0004] 3. High integration of probes leads to limitations in size and flexibility: Traditional handheld probes often tightly integrate beam shaping, scanning and focusing optical systems, resulting in complex probe structures, large size and increased weight. This is not conducive to flexible handheld operation for a long time and at multiple angles, and also limits their use in confined spaces (such as infant eye sockets and surgical areas).

[0005] 4. Existing correction techniques are difficult to adapt to handheld dynamic environments: Although polarization control and adaptive optics technologies have been applied in desktop OCT, existing solutions are mostly designed for static or quasi-static optical paths. They fail to effectively address the coordination issues between rapid changes in polarization state, real-time aberration disturbances, and system lightweight requirements under handheld conditions, resulting in difficulty in guaranteeing image quality in portable scenarios.

[0006] Compared to existing technologies, traditional handheld optical coherence tomography (OCT) systems typically integrate scanning, focusing, and some beam control functions within the handheld probe, or employ only fixed polarization control and static optical correction structures. In practical applications, handheld operation inevitably introduces posture changes and fiber bending, causing the polarization state in the system to drift randomly with fiber deformation, resulting in reduced interferometric efficiency. Simultaneously, fiber disturbances and system instability introduce dynamic wavefront aberrations, further reducing imaging resolution. Furthermore, integrating the optical correction module into the handheld probe increases its size and weight, negatively impacting stability and flexibility during clinical operation. To address these issues, existing technologies typically only perform local optimization through polarization control or adaptive optics techniques, lacking a coordinated control mechanism for polarization changes and aberration disturbances under dynamic handheld conditions, and failing to rationally allocate probe load and optical correction functions at the system structure level.

[0007] This invention separates the optical correction function from the handheld operating unit by placing the beam quality optimization module before the handheld probe, enabling wavefront correction of the sample arm beam before it enters the probe. This structural separation reduces probe size and weight while improving beam quality stability. Furthermore, a dual-closed-loop control structure for dynamic polarization adjustment and wavefront correction is constructed to collaboratively compensate for polarization drift and wavefront aberrations under dynamic handheld conditions, ensuring stable acquisition of interference signals and consistent imaging quality.

[0008] Furthermore, this invention incorporates an adjustable polarization modulation unit within the sample arm. By dynamically adjusting the polarization state of the incident light, multiple sets of interference signal data are acquired under different polarization states. These multiple sets of data are then jointly processed by a control module, thereby suppressing speckle noise while enhancing tissue structure contrast and polarization characteristic characterization capabilities. This polarization-diversified imaging mechanism, working in conjunction with the dynamic polarization adjustment and wavefront correction structure, further improves the system's anti-disturbance capability and imaging stability in handheld dynamic environments.

[0009] Therefore, this invention not only reduces the load on the handheld probe by using a front beam quality optimization module in the system structure, but also achieves coordinated closed-loop control of polarization and wavefront in the system control mechanism. Combined with multi-polarization state data acquisition and processing strategies, it significantly improves the imaging quality and applicability of the handheld optical coherence tomography system in complex clinical environments. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a handheld optical coherence tomography system and method based on polarization modulation, thereby resolving the issues in the prior art. The technical solution adopted by this invention is as follows: A handheld optical coherence tomography system based on polarization modulation includes a light source and beam splitting module, a reference arm optical path, a sample arm optical path, a polarization dynamic adjustment module, and a detection and control module. The light source and beam splitting module are used to generate low-coherence light, and split the low-coherence light into beams according to a predetermined power ratio, and guide them to the reference arm optical path and the sample arm optical path respectively as imaging light; the imaging light includes the reference beam and the sample beam. The reference arm optical path includes an optical path adjustment module for adjusting the optical path length of the reference arm optical path; The optical path of the sample arm includes a handheld probe module and a beam quality optimization module: the handheld probe module is used to guide and focus the sample beam onto the fundus being tested, and at the same time receive the reflected light from the fundus being tested; the beam quality optimization module is used to perform wavefront correction and beam shaping on the sample beam; the beam quality optimization module is located before the handheld probe module. The polarization dynamic adjustment module is used to preset and adjust the polarization state of the imaging light entering the reference arm optical path and the sample arm optical path in real time, so as to compensate for polarization state changes. The detection and control module is used to acquire interference signals and to control the polarization dynamic adjustment module in real time based on the intensity or contrast of the interference signals; the interference signals are formed based on the reflected return light from the sample arm optical path and the reference arm optical path.

[0011] Furthermore, the polarization dynamic adjustment module includes a first liquid crystal variable delay unit disposed on the optical path of the reference arm and a second liquid crystal variable delay unit disposed on the optical path of the sample arm.

[0012] Furthermore, the light source and beam splitting module includes an OCT light source, an optical isolator, and a first fiber coupler; wherein, the low-coherence light emitted by the OCT light source enters the first fiber coupler after passing through the optical isolator, and is split into a reference beam and a sample beam according to a predetermined power ratio.

[0013] Furthermore, referencing the optical path of the arm: The first fiber coupler outputs a reference beam, which enters port A of the first polarization-maintaining circulator and is then output from port B of the first polarization-maintaining circulator. The beam is converted into spatially collimated light by the first collimator and then passes sequentially through a plano-concave lens, a high-dispersion lens, a first quarter-glass slide, a first liquid crystal variable delay unit, a phase modulator, an attenuator, an achromatic cemented doublet lens, an optical path adjustment module, and a high-precision plane mirror. The high-precision plane mirror forms the reflected return light of the reference arm optical path.

[0014] Furthermore, the optical path adjustment module includes a displacement platform. The reference beam is irradiated onto a high-precision plane mirror through the achromatic doublet lens. The high-precision plane mirror is used to move in the optical axis direction via the displacement platform to achieve continuous or step adjustment of the optical path of the reference arm.

[0015] Furthermore, in the optical path of the sample arm: The first fiber coupler outputs a sample beam, which enters port A of the second polarization-maintaining circulator and then exits from port B of the second polarization-maintaining circulator, entering the beam quality optimization module.

[0016] Furthermore, the beam quality optimization module includes a second collimator, a second quarter glass slide, a second liquid crystal variable retarder, a dichroic mirror, a fast deformable mirror, a curved reflector, a first focusing lens, a second focusing lens, and a wavefront sensor; The sample beam is output from port B of the second polarization-maintaining circulator and passes sequentially through the second collimator, the second quarter glass slide, and the second liquid crystal variable delay unit for dynamic adjustment; the dynamic adjustment signal is generated in real time by the detection and control module based on the intensity and contrast feedback of the interference signal. After dynamic adjustment, the sample beam is transmitted through a dichroic mirror to a fast deformable mirror to achieve initial beam pointing adjustment; the fast deformable mirror reflects the sample beam to a curved mirror, and then after being reflected by the curved mirror, it enters the flexible polarization-maintaining fiber and finally enters the handheld probe module. The handheld probe module generates a reflected return light, which is incident on the flexible polarization-maintaining fiber and then passes in reverse sequentially through a curved reflector, a fast deformable mirror, and a dichroic mirror. The reflected return light in the sample arm optical path is split into two parts when passing through the dichroic mirror: a transmission part and a reflection part. The transmission part passes in sequence through a second liquid crystal variable retarder, a second quarter glass slide, a second collimator, and a second polarization-maintaining circulator, and finally enters the detection and control module from the C port of the second polarization-maintaining circulator. The reflection part passes in sequence through a first focusing lens, a second focusing lens, and a wavefront sensor to acquire the waveform of the reflection part and provide an electrical signal to the fast control reflector to complete the shaping.

[0017] Furthermore, the handheld probe module includes a third collimator, a MEMS mirror, an adjustable lens, and a dispersion-compensating adjustable lens; The sample beam is emitted through a flexible polarization-maintaining fiber and passes sequentially through a third collimator, a MEMS mirror, a dilatation lens, a dispersion-compensating adjustable lens, and the fundus of the eye under test. Finally, the reflected return light of the sample arm optical path is formed by the fundus of the eye under test.

[0018] Furthermore, the detection and control module includes a polarization-maintaining fiber coupler, a polarization beam splitter, a fourth collimator, a fifth collimator, a first grating, a second grating, a third focusing lens, a fourth focusing lens, and a CCD; The reflected return light from the sample arm optical path and the reference arm optical path is incident on the polarization-maintaining fiber coupler and converges to interfere, forming interference light. After entering the polarization beam splitter, the interference light is separated into two orthogonal polarization components. The two orthogonal polarization components are collimated by the fourth collimator and the fifth collimator, respectively, and then undergo spectral dispersion through the first grating and the second grating, respectively. Finally, they are converged to different detection areas of the CCD by the third focusing lens and the fourth focusing lens.

[0019] A handheld optical coherence tomography method based on polarization modulation includes the following steps: Step 1: System initialization and polarization matching calibration: Turn on the OCT light source; the detection and control module drives the curved MEMS mirror to reset to the reference surface shape and completes the calibration of the conjugate relationship between the reference arm optical path and the sample arm optical path; Before the fundus of the eye being tested is connected, the detection and control module simultaneously scans the delay of the first liquid crystal variable delay unit and the second liquid crystal variable delay unit, and monitors the intensity and contrast of the interference signal acquired by the CCD. The state with the maximum amplitude of the interference signal and the balanced energy distribution of the two channels is set as the initial working point for polarization matching of the system. Step 2: Eye alignment and wavefront aberration pre-correction: The handheld probe module is aimed at the fundus of the eye being tested; The detection and control module drives the adjustable lens and the dispersion compensation adjustable lens to perform correction based on the wavefront aberration measured by the wavefront sensor, thereby achieving automatic focusing and low-order aberration compensation. Step 3: Initiate hardware closed-loop dual locking and optimization: During the imaging process, the detection and control module continuously receives interference signals and adjusts the driving parameters of the first and second liquid crystal variable delay devices in real time based on the changes in the intensity and contrast of the interference signals, thereby achieving dynamic locking of the polarization matching state. The wavefront sensor continuously acquires the wavefront information of the reflected return light and feeds it back to the detection and control module. The detection and control module calculates the driving parameters based on the feedback signal and drives the fast deformable mirror to adjust its surface shape. Step 4: OCT structural imaging: The detection and control module triggers the imaging process, drives the handheld probe module to execute a predetermined scanning pattern, and simultaneously triggers the CCD to acquire interference signals. The acquired spectral data is processed by the host computer through Fourier transform and digital dispersion compensation to reconstruct the structural image of the retina.

[0020] The present invention has the following beneficial effects: (1) By actively and dynamically adjusting the polarization dynamic adjustment module, the random fluctuations in polarization state caused by hand operation and fiber disturbance are fundamentally suppressed, significantly improving the contrast and stability of the interference signal and ensuring the imaging reliability of the system under complex operating conditions.

[0021] (2) By integrating an independent beam quality optimization module with deformable mirrors, it can not only correct the aberrations of the system itself, but also directly compensate for the large-span refractive errors (such as -10D to +10D) and higher-order aberrations of the test subject. No additional inserts are required for pre-correction, which greatly simplifies the operation process.

[0022] (3) By uniformly correcting all aberrations through the above wavefront correction method, the actual resolution and focused spot energy density of the system are effectively improved, making it possible to distinguish fine structures such as individual photoreceptor cells.

[0023] (4) By modular design, the beam quality optimization function is moved to the front and independent of the main unit, and connected to the lightweight handheld probe through flexible optical fiber, thus achieving the optimal balance between high system performance and operational flexibility. Attached Figure Description

[0024] Figure 1 This is a structural diagram of the present invention; In the diagram: 1. OCT light source; 2. Optical isolator; 3. First fiber optic coupler; 4. First polarization-maintaining circulator; 5. First collimator; 6. Plano-concave lens; 7. High-dispersion lens; 8. First quarter-glass slide; 9. First liquid crystal variable retarder; 10. Phase modulator; 11. Attenuator; 12. Achromatic cemented doublet lens; 13. High-precision plane mirror; 14. Displacement platform; 15. Second polarization-maintaining circulator; 16. Second collimator; 17. Second quarter-glass slide; 18. Second liquid crystal variable retarder; 19. Dichroic mirror. 20. Rapid deformable mirror; 21. Curved reflector; 22. Polarization-maintaining fiber; 23. Third collimator; 24. Curved MEMS reflector; 25. Adjustable lens; 26. Dispersion-compensating adjustable lens; 27. Fundus of the eye to be tested; 28. First focusing lens; 29. ​​Second focusing lens; 30. Wavefront sensor; 31. Polarization-maintaining fiber coupler; 32. Polarization beam splitter; 33. Fourth collimator; 34. Fifth collimator; 35. First grating; 36. Second grating; 37. Third focusing lens; 38. Fourth focusing lens; 39. CCD. Detailed Implementation

[0025] The following will be described in conjunction with embodiments of the present invention. Figure 1 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0026] like Figure 1This invention proposes a handheld optical coherence tomography system based on polarization modulation, including a light source and beam splitting module, a reference arm optical path, a sample arm optical path, a polarization dynamic adjustment module, and a detection and control module. The light source and beam splitting module are used to generate low-coherence light, and split the low-coherence light into beams according to a predetermined power ratio (e.g., 50:50) and guide them to the reference arm optical path and the sample arm optical path respectively as imaging light; the imaging light includes the reference beam and the sample beam, providing a stable light source basis for subsequent interferometric imaging. The reference arm optical path includes an optical path adjustment module for adjusting the optical path length of the reference arm optical path; The sample arm optical path includes a handheld probe module and a beam quality optimization module: the handheld probe module guides and focuses the sample beam onto the fundus 27 under test, while simultaneously receiving reflected light from the fundus 27; the beam quality optimization module shapes and optimizes the imaging beam to improve its spatial distribution characteristics and focusing performance, thereby enhancing the focusing quality of the imaging beam on the retina and improving the system's lateral resolution and imaging signal-to-noise ratio; the beam quality optimization module is positioned before the handheld probe module; this handheld probe module can adapt to changes in posture and limitations of the usage environment during clinical operation, achieving flexible and stable fundus scanning and imaging, suitable for applications such as pediatric ophthalmology and bedside examinations.

[0027] The polarization dynamic adjustment module is used to preset and adjust the polarization state of the imaging light entering the reference arm optical path and the sample arm optical path in real time, so as to compensate for polarization state changes. The detection and control module is used to acquire interference signals and to control the polarization dynamic adjustment module in real time based on the intensity or contrast of the interference signals; the interference signals are formed based on the reflected return light from the sample arm optical path and the reference arm optical path.

[0028] Specifically, the detection and control module is used to detect, acquire, and process the interference signal formed by the sample arm return light and the reference arm light, and to control the coordinated operation of the light source, polarization dynamic adjustment module, optical path adjustment module, beam quality optimization module, and scanning module. The detection and control module is also configured to control the polarization modulation unit in the sample arm to switch between multiple polarization states, acquire corresponding interference signal data in each polarization state, and jointly process the multiple sets of interference signals to improve imaging stability and image quality.

[0029] The system comprises a dual-loop control structure consisting of a polarization dynamic adjustment module and a beam quality optimization module, used to compensate for polarization drift and wavefront aberrations under handheld dynamic conditions. Specifically, in the polarization adjustment closed loop, the detection and control module extracts signal intensity and contrast information from the dual-channel interference signals acquired by the detection module, constructs polarization matching evaluation parameters, and adjusts the driving voltage of the first and / or second liquid crystal variable delay units in real time according to these parameters. This balances the signal energy of different polarization channels and improves interference contrast, thereby achieving dynamic locking of the polarization state. In the wavefront correction closed loop, the wavefront sensor acquires the wavefront information of the sample arm return light and feeds it back to the detection and control module. The detection and control module calculates the aberration distribution and generates driving parameters based on the wavefront information, driving the fast deformable mirror to adjust its surface shape to generate a compensation wavefront corresponding to the aberrations, thus achieving real-time correction of the system's dynamic wavefront aberrations. The polarization adjustment closed loop and the wavefront correction closed loop work together under a unified control module. Polarization adjustment is used to improve the stability and matching efficiency of the interference signal, while wavefront correction is used to improve the beam focusing quality and imaging resolution. The two work together to compensate for system disturbances caused by handheld operation, thereby improving imaging stability and image quality.

[0030] Furthermore, the polarization dynamic adjustment module includes a first liquid crystal variable delay unit 9 disposed on the optical path of the reference arm and a second liquid crystal variable delay unit 18 disposed on the optical path of the sample arm.

[0031] Furthermore, the light source and beam splitting module includes an OCT light source 1, an optical isolator 2, and a first fiber optic coupler 3; wherein, the low-coherence light emitted by the OCT light source 1 enters the first fiber optic coupler 3 after passing through the optical isolator 2, and is split into a reference beam and a sample beam according to a predetermined power ratio.

[0032] Furthermore, referencing the optical path of the arm: The first fiber coupler 3 outputs a reference beam, which enters port A of the first polarization-maintaining circulator 4 and is then output from port B of the first polarization-maintaining circulator 4. The reference beam is converted into spatially collimated light by the first collimator 5 and then passes sequentially through a plano-concave lens 6, a high-dispersion lens 7, a first quarter-glass slide 8, a first liquid crystal variable delay unit 9, a phase modulator 10, an attenuator 11, an achromatic cemented doublet lens 12, an optical path adjustment module, and a high-precision plane mirror 13. The high-precision plane mirror 13 forms the reflected return light of the reference arm optical path.

[0033] The plano-concave lens 6 is used to perform preliminary divergence or wavefront adjustment on the reference beam to match the beam size and divergence angle of the subsequent optical system; it provides negative spherical aberration to compensate for the positive spherical aberration introduced by other lenses in the system (such as collimating or focusing lenses) and improve beam quality. The high-dispersion lens 7 is used to introduce preset dispersion compensation to balance the dispersion difference between the reference arm and the sample arm, thereby improving the axial resolution of the interference signal. The first quarter-glass slide 8 is used to modulate the polarization state of the reference beam, converting linearly polarized light into circularly polarized light or elliptical polarized light, and realizing the reversible transformation of the polarization state during the return journey to improve interference stability. The phase modulator 10 is used to introduce phase modulation into the reference beam to achieve phase encoding of the interference signal or improve the system's ability to detect weak signals. The attenuator 11 is used to adjust the light intensity of the reference beam so that the light intensity of the reference beam matches that of the sample beam, thereby optimizing the interference contrast. The achromatic doublet lens 12 is used to focus or collimate the reference beam and reduce aberrations caused by chromatic aberration, so as to ensure that beams of different wavelengths have consistent propagation characteristics.

[0034] Furthermore, the optical path adjustment module includes a displacement platform 14. The reference beam is irradiated onto a high-precision plane mirror 13 through the achromatic cemented doublet lens 12. The high-precision plane mirror 13 is used to move along the optical axis via the displacement platform 14 to achieve continuous or step adjustment of the optical path of the reference arm. The achromatic cemented doublet lens (12) is used to focus or collimate the reference beam and reduce aberrations caused by chromatic aberration to ensure that beams of different wavelengths have consistent propagation characteristics.

[0035] Furthermore, in the optical path of the sample arm: The first fiber coupler 3 outputs a sample beam, which enters port A of the second polarization-maintaining circulator 15 and is then output from port B of the second polarization-maintaining circulator 15, entering the beam quality optimization module.

[0036] Furthermore, the beam quality optimization module includes a second collimator 16, a second quarter glass slide 17, a second liquid crystal variable delay 18, a dichroic mirror 19, a fast deformable mirror 20, a curved reflector 21, a first focusing lens 28, a second focusing lens 29, and a wavefront sensor 30. After the sample beam is output from the second polarization-maintaining circulator 15, it first enters the second collimator 16 to convert the diverging light output from the fiber into collimated light, thereby obtaining a stable spatial beam shape. The collimated beam then passes through the second quarter-glass plate 17, which is used to initially modulate the polarization state of the beam, converting linearly polarized light into circularly or ellipsoidally polarized light, and achieving reversible polarization state transformation during the return journey. Subsequently, the beam enters the second liquid crystal variable delay unit 18, which dynamically adjusts the phase delay of the beam under the action of an electronic control signal, thereby achieving real-time control of the polarization state and cooperating with the detection and control module to complete polarization matching and multi-polarization state scanning. The polarization-adjusted beam is transmitted through the dichroic mirror 19 to achieve separation or beam combining of signals from different optical paths or different wavebands, while providing a beam splitting interface for the subsequent wavefront detection optical path. The beam is then incident on the fast deformable mirror 20, which is used for surface shape adjustment under the drive of the control module to achieve rapid fine-tuning of the beam direction and low-order wavefront correction. After being reflected by the rapidly deformable mirror 20, the beam is incident on the curved mirror 21 for further focusing or collimation adjustment and to improve the spatial distribution characteristics of the beam, thereby increasing the beam coupling efficiency. The beam modulated by the curved mirror 21 is transmitted to the handheld probe module through the flexible polarization-maintaining fiber 22. The sample arm return beam propagates in the opposite direction along the same optical path and is divided into a transmission part and a reflection part when passing through the dichroic mirror 19. The transmission part is used for interference detection, and the reflection part enters the wavefront detection channel. The reflection part of the beam passes through the first focusing lens 28 and the second focusing lens 29 in sequence to focus and shape the beam so that it meets the incident requirements of the wavefront sensor. Finally, the beam is incident on the wavefront sensor 30 to collect the wavefront information of the return beam and feed the wavefront information back to the detection and control module. The detection and control module calculates the driving parameters and drives the rapidly deformable mirror 20 to adjust the surface shape, thereby realizing real-time closed-loop correction of the system's wavefront aberration.

[0037] The sample beam is output from port B of the second polarization-maintaining circulator 15 and passes sequentially through the second collimator 16, the second quarter-glass slide 17, and the second liquid crystal variable delay unit 18 for dynamic adjustment. The dynamic adjustment signal is generated in real-time by the detection and control module based on the intensity and contrast feedback of the interference signal, thus forming a closed-loop adjustment path for the polarization state to compensate for polarization drift caused by handheld operation and fiber optic disturbance. The second liquid crystal variable delay unit 18 switches between multiple preset polarization states and acquires corresponding interference signals in each polarization state. Multiple sets of interference signals acquired in different polarization states are then jointly processed to reduce speckle noise and improve imaging contrast.

[0038] After dynamic adjustment, the sample beam is transmitted through the dichroic mirror 19 to the fast deformable mirror 20 to achieve the initial pointing adjustment of the beam; the fast deformable mirror 20 reflects the sample beam to the curved mirror 21, and then after being reflected by the curved mirror 21, it enters the flexible polarization-maintaining fiber 22, and finally enters the handheld probe module. The handheld probe module generates a reflected return light, which is incident on the flexible polarization-maintaining fiber 22 and then passes in reverse sequentially through the curved reflector 21, the fast deformable mirror 20, and the dichroic mirror 19. The reflected return light of the sample arm optical path is divided into two parts when it passes through the dichroic mirror 19: a transmission part and a reflection part. The transmission part passes in sequence through the second liquid crystal variable delay unit 18, the second quarter glass plate 17, the second collimator 16, and the second polarization-maintaining circulator 15, and finally enters the detection and control module from the C port of the second polarization-maintaining circulator 15. The reflection part passes in sequence through the first focusing lens 27, the second focusing lens 28, and the wavefront sensor 29 to collect the waveform of the reflection part and provide an electrical signal to the fast control reflector 20 to complete the shaping.

[0039] Furthermore, the handheld probe module includes a third collimator 23, a MEMS mirror 24, an adjustable lens 25, and a dispersion-compensating adjustable lens 26. The sample beam is emitted through the flexible polarization-maintaining fiber 22 and passes sequentially through the third collimator 23, MEMS mirror 24, adjustable lens 25, dispersion-compensating adjustable lens 26, and fundus under test 27. Finally, the reflected return light of the sample arm optical path is formed by the fundus under test 27.

[0040] To accommodate the refractive states of different subjects, the sample arm is equipped with a refractive lens 25 and a dispersion compensation adjustable lens 26 to achieve preliminary correction and dispersion compensation for a wide range of refractive errors.

[0041] Furthermore, the detection and control module includes a polarization-maintaining fiber coupler 31, a polarization beam splitter 32, a fourth collimator 33, a fifth collimator 34, a first grating 35, a second grating 36, a third focusing lens 37, a fourth focusing lens 38, and a CCD 39; The reflected return light from the sample arm optical path and the reference arm optical path is incident on the polarization-maintaining fiber coupler 31 and converges to interfere, forming interference light. After entering the polarization beam splitter 32, the interference light is separated into two orthogonal polarization components. The two orthogonal polarization components are collimated by the fourth collimator 33 and the fifth collimator 34, respectively, and then spectrally dispersed by the first grating 35 and the second grating 36, respectively. They are then converged by the third focusing lens 37 and the fourth focusing lens 38 to different detection areas of the CCD 39, realizing polarization-sensitive spectral domain interferometric detection.

[0042] The control module, as the core processing unit of the system, is responsible for the unified coordination and synchronous control of all sub-modules. Its functions include: receiving aberration information output by the wavefront sensor 30 and driving the curved MEMS mirror 20 to perform wavefront correction; driving the fast deformable mirror 20 to achieve image stabilization compensation based on the image feedback signal; controlling the displacement platform 14 to complete the optical path scanning of the reference arm; dynamically adjusting the first liquid crystal variable delay unit 9 and the second liquid crystal variable delay unit 18 to maintain polarization matching; and synchronously triggering the OCT light source 1, the scanning mechanism, and the CCD 39 to complete the acquisition of interference signals.

[0043] This invention also proposes a handheld optical coherence tomography method based on polarization modulation, which, based on the aforementioned handheld optical coherence tomography system based on polarization modulation, includes the following steps: Step 1: System initialization and polarization matching calibration.

[0044] 1. Turn on OCT light source 1; the detection and control module drives the curved MEMS mirror 24 to reset to the reference surface shape, and completes the calibration of the conjugate relationship between the reference arm optical path and the sample arm optical path to ensure that the interference optical path is in the initial stable state.

[0045] 2. Before the fundus 27 under test is connected, the detection and control module synchronously scans the delay of the first liquid crystal variable delay unit 9 and the second liquid crystal variable delay unit 18, and at the same time monitors the intensity and contrast of the dual-channel spectral interference signal collected by CCD 39. The state with the maximum amplitude of the interference signal and the balanced energy distribution of the dual channels is set as the initial operating point for polarization matching of the system.

[0046] The state of balanced energy distribution in dual channels means that the intensity of the interference signal detected by CCD39 in the two detection channels after polarization beam splitting is close to the same, so that the difference in signal energy between the two channels is within a preset threshold range, thereby ensuring that the system is in a polarization matching state and obtains a high interference contrast.

[0047] For example: I1 is the intensity of the interference signal detected by the first polarization channel of the CCD; I2 is the intensity of the interference signal detected by the second polarization channel of the CCD; the channel energy balance coefficient is defined as: B=|I1-I2| / (I1+I2B); The system is considered to have reached a dual-channel energy balance state when B < ε. Where: B: channel energy imbalance; ε: preset threshold (usually taken as 0.1–0.2 in engineering).

[0048] Step 2: Eye alignment and wavefront aberration pre-correction.

[0049] 1. Hold the probe module and align it with the fundus 27 to be tested, so that the imaging beam of the sample arm passes through the dispersion-compensated adjustable lens 26 and enters the human eye sample 27.

[0050] 2. The detection and control module drives the adjustable lens 25 and the dispersion compensation adjustable lens 26 to perform large-scale and rapid correction based on the main defocus and astigmatism and other low-order wavefront aberrations quickly measured by the wavefront sensor 30, so as to realize automatic focusing and low-order aberration compensation, thereby replacing the traditional lens insertion refraction process.

[0051] Among them, the measurement is carried out within the range of curvature and focal length according to the golden section method. When the equipment is calibrated and the closed loop converges, the image presented by the wavefront sensor should show that: the grid array is neat and uniform, without distortion; the contour map is flat and uniformly green, without color gradation fluctuations, indicating that the wavefront aberration has been effectively corrected.

[0052] Step 3: Initiate hardware closed-loop dual locking and optimization.

[0053] 1. Polarization dynamic tracking closed loop: During the imaging process, the detection and control module continuously receives interference signal feedback and adjusts the driving parameters of the first liquid crystal variable delay unit 9 and the second liquid crystal variable delay unit 18 in real time based on the intensity and contrast changes of the feedback signal, thereby forming a closed-loop adjustment path consisting of "detection module - control module - polarization modulation unit" to achieve dynamic locking of polarization matching state.

[0054] The contrast of the interference signal can be calculated using the following formula: V = (I max -I min ) / I max +I min The average voltage V = (V1 + V2) / 2 is applied to the two channels. The detection and control module uses the energy balance coefficient B and the interference contrast V as feedback parameters to dynamically adjust the driving voltage of the first liquid crystal variable delay unit 9 and the second liquid crystal variable delay unit 18. Let: the driving voltage of the first liquid crystal variable delay device be U1; and the driving voltage of the second liquid crystal variable delay device be U2.

[0055] The phase delay generated by the liquid crystal retarder can be expressed as: in: For liquid crystal at voltage V i Effective birefringence under action; d i λ represents the thickness of the liquid crystal layer; λ represents the operating wavelength.

[0056] The detection and control module constructs an optimization objective function based on the currently measured energy imbalance B: Where w1 and w2 are weighting coefficients. The driving voltage is then iteratively adjusted based on the control algorithm. Where: α is the adjustment step size.

[0057] Through continuous iteration, the objective function is improved. The goal is to achieve the minimum value, thus realizing the optimal polarization matching state. Under the above control strategy, the system forms a real-time closed-loop adjustment path consisting of a detection and control module and a polarization dynamic adjustment module. Through this closed-loop control mechanism, polarization drift can be compensated in real time when handheld operation causes fiber bending or system attitude changes, achieving dynamic locking of the polarization matching state, thereby improving the stability of the interference signal and the imaging signal-to-noise ratio.

[0058] 2. Adaptive Optical Wavefront Correction Closed Loop: The wavefront sensor 30 continuously acquires the wavefront information of the reflected return light and feeds it back to the detection and control module. The detection and control module calculates the driving parameters based on the feedback signal and drives the fast deformable mirror 20 to adjust its surface shape, thereby forming a closed-loop control path consisting of the wavefront sensor 30, the detection and control module, and the fast deformable mirror 20.

[0059] Step 4: High-resolution OCT structural imaging.

[0060] 1. After the polarization matching state and wavefront correction state are stable, that is, the dual-channel energy distribution is balanced, the detection and control module synchronously triggers the imaging process, drives the scanning mechanism inside the handheld probe to execute the predetermined scanning pattern, and simultaneously triggers the CCD39 to acquire spectral interference signals.

[0061] The scanning mechanism within the handheld probe can be a dual-axis MEMS micromirror chip, fabricated using single-crystal silicon micromachining technology. It integrates a miniature mirror (typically 2–3 mm in diameter) capable of two-dimensional deflection along the X-axis (fast axis) and Y-axis (slow axis). Its driving method commonly employs electrostatic comb drive or electrothermal drive.

[0062] After the control module sends a synchronization trigger signal, the drive circuit applies a resonant sine wave (frequency equal to the mechanical resonant frequency of the MEMS fast axis, typically 1–4 kHz) to the MEMS fast axis, causing the mirror to rapidly reciprocate and achieve a B-scan sampling point scan. Simultaneously, a stepped sawtooth wave (frequency equal to the frame rate divided by the number of B-scan lines per frame, e.g., 30 Hz / 500 lines = 60 Hz) is applied to the slow axis, causing the mirror to step line by line, completing the two-dimensional raster scan.

[0063] During synchronous acquisition, the MEMS fast axis generates a line synchronization signal after each half-cycle of a sine wave (i.e., scanning one line), triggering the CCD 39 to begin exposure and acquire the spectral interference signal of that line. With each step of the slow axis, the system updates the line number, ensuring that each A-scan line in each frame of the image precisely corresponds to the mirror position.

[0064] In addition, to address the jitter that may be introduced by handheld probes, the blank retrace period of the slow-axis sawtooth wave can be used in conjunction with the MEMS built-in sensor signal for real-time motion correction to ensure image registration between adjacent frames.

[0065] 2. The reference arm return light and the sample arm return light are combined at the polarization-maintaining fiber coupler 30 to form a spectral interference signal. The interference signal is then detected by the CCD 39 after passing through the grating beam splitting and focusing optical system.

[0066] 3. The acquired spectral data is processed by the host computer using Fourier transform and digital dispersion compensation to reconstruct a high-resolution tomographic image of the retina, which can clearly distinguish the fine structures of each layer of the retina.

[0067] The beam quality optimization module of this invention incorporates a wavefront correction method, including the following steps: Step S1: Obtaining full-order wavefront aberrations: Wavefront sensors are used to acquire wavefront information of beacon or imaging light returning from inside the eye, which is then reconstructed into a set of Zernike polynomial coefficients: This forms the full-order aberration coefficient vector C; Step S2: Calculation of deformable mirror driving voltage: Call the influence matrix M of the pre-calibrated fast deformable mirror 20 DM Based on the pseudo-inverse M of this influence matrix DM † Calculate the driving voltage vector V DM =M DM † ·C; Step S3: Aberration correction is performed. The driving voltage vector V DM Applying a conjugate wavefront to the fast deformable mirror 20 causes its surface shape to generate a conjugate wavefront, thereby correcting measurement aberrations from low to high order in one step.

[0068] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, alterations, or substitutions made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A handheld optical coherence tomography system based on polarization modulation, characterized in that, It includes a light source and beam splitter module, a reference arm optical path, a sample arm optical path, a polarization dynamic adjustment module, and a detection and control module; The light source and beam splitting module are used to generate low-coherence light, and split the low-coherence light into beams according to a predetermined power ratio, and guide them to the reference arm optical path and the sample arm optical path respectively as imaging light; the imaging light includes the reference beam and the sample beam. The reference arm optical path includes an optical path adjustment module for adjusting the optical path length of the reference arm optical path; The optical path of the sample arm includes a handheld probe module and a beam quality optimization module: the handheld probe module is used to guide and focus the sample beam onto the fundus (27) under test, and at the same time receive the reflected light from the fundus (27) under test; the beam quality optimization module is used to perform wavefront correction and beam shaping on the sample beam; the beam quality optimization module is located in front of the handheld probe module. The polarization dynamic adjustment module is used to preset and adjust the polarization state of the imaging light entering the reference arm optical path and the sample arm optical path in real time, so as to compensate for polarization state changes. The detection and control module is used to acquire interference signals and to control the polarization dynamic adjustment module in real time based on the intensity or contrast of the interference signals. The interference signal is formed based on the reflected return light from the sample arm optical path and the reference arm optical path.

2. The handheld optical coherence tomography system based on polarization modulation according to claim 1, characterized in that, The polarization dynamic adjustment module includes a first liquid crystal variable delay unit (9) disposed on the optical path of the reference arm and a second liquid crystal variable delay unit (18) disposed on the optical path of the sample arm.

3. The handheld optical coherence tomography system based on polarization modulation according to claim 1, characterized in that, The light source and beam splitting module includes an OCT light source (1), an optical isolator (2), and a first fiber coupler (3); wherein, the low coherence light emitted by the OCT light source (1) enters the first fiber coupler (3) after passing through the optical isolator (2), and is split into a reference beam and a sample beam according to a predetermined power ratio.

4. The handheld optical coherence tomography system based on polarization modulation according to claim 2, characterized in that, Reference arm optical path: The first fiber coupler (3) outputs a reference beam, which enters port A of the first polarization-maintaining circulator (4) and is then output from port B of the first polarization-maintaining circulator (4). The beam is converted into spatially collimated light by the first collimator (5) and then passes sequentially through a plano-concave lens (6), a high-dispersion lens (7), a first quarter-glass plate (8), a first liquid crystal variable delay device (9), a phase modulator (10), an attenuator (11), an achromatic cemented doublet lens (12), an optical path adjustment module, and a high-precision plane mirror (13). The high-precision plane mirror (13) forms the reflected return light of the reference arm optical path.

5. The handheld optical coherence tomography system based on polarization modulation according to claim 4, characterized in that, The optical path adjustment module includes a displacement platform (14). The reference beam is irradiated onto a high-precision plane mirror (13) through the achromatic doublet lens (12). The high-precision plane mirror (13) is used to move in the optical axis direction through the displacement platform (14) to realize continuous or step adjustment of the optical path of the reference arm.

6. The handheld optical coherence tomography system based on polarization modulation according to claim 2, characterized in that, In the optical path of the sample arm: The first fiber coupler (3) outputs a sample beam, which enters port A of the second polarization-maintaining circulator (15) and is then output from port B of the second polarization-maintaining circulator (15) into the beam quality optimization module.

7. The handheld optical coherence tomography system based on polarization modulation according to claim 6, characterized in that, The beam quality optimization module includes a second collimator (16), a second quarter glass slide (17), a second liquid crystal variable delay device (18), a dichroic mirror (19), a fast deformable mirror (20), a curved reflector (21), a first focusing lens (28), a second focusing lens (29), and a wavefront sensor (30). The sample beam is output from port B of the second polarization maintaining circulator (15) and passes sequentially through the second collimator (16), the second quarter glass slide (17), and the second liquid crystal variable delay unit (18) for dynamic adjustment; its dynamic adjustment signal is generated in real time by the detection and control module based on the intensity and contrast feedback of the interference signal. After dynamic adjustment, the sample beam is transmitted through a dichroic mirror (19) to a fast deformable mirror (20) to achieve initial beam pointing adjustment; the fast deformable mirror (20) reflects the sample beam to a curved mirror (21), and then after being reflected by the curved mirror (21), it enters the flexible polarization-maintaining fiber (22) and finally enters the handheld probe module. The handheld probe module generates a reflected return light and incident it onto the flexible polarization-maintaining fiber (22), and then passes in reverse sequentially through the curved reflector (21), the fast deformable mirror (20), and the dichroic mirror (19). The reflected return light of the sample arm optical path is divided into two parts when it passes through the dichroic mirror (19), namely the transmission part and the reflection part. The transmission part passes in sequence through the second liquid crystal variable delay unit (18), the second quarter glass plate (17), the second collimator (16), and the second polarization-maintaining circulator (15), and finally enters the detection and control module from the C port of the second polarization-maintaining circulator (15). The reflection part passes in sequence through the first focusing lens (28), the second focusing lens (29), and the wavefront sensor (30) to collect the waveform of the reflection part and provide an electrical signal to the fast control reflector (20) to complete the shaping.

8. The handheld optical coherence tomography system based on polarization modulation according to claim 7, characterized in that, The handheld probe module includes a third collimator (23), a MEMS mirror (24), an adjustable lens (25), and a dispersion-compensating adjustable lens (26). The sample beam is emitted through a flexible polarization-maintaining fiber (22) and passes sequentially through a third collimator (23), a MEMS mirror (24), a dilatancy lens (25), a dispersion-compensating adjustable lens (26), and the fundus of the tested eye (27). Finally, the reflected return light of the sample arm optical path is formed by the fundus of the tested eye (27).

9. The handheld optical coherence tomography system based on polarization modulation according to any one of claims 1-8, characterized in that, The detection and control module includes a polarization-maintaining fiber coupler (31), a polarization beam splitter (32), a fourth collimator (33), a fifth collimator (34), a first grating (35), a second grating (36), a third focusing lens (37), a fourth focusing lens (38), and a CCD (39). The reflected return light from the sample arm optical path and the reference arm optical path is incident on the polarization-maintaining fiber coupler (31), and they converge and interfere to form interference light; After the interference light enters the polarization beam splitter (32), it is separated into two orthogonal polarization components. The two orthogonal polarization components are collimated by the fourth collimator (33) and the fifth collimator (34), respectively. They are then spectrally dispersed by the first grating (35) and the second grating (36), respectively, and converged to different detection areas of the CCD (39) by the third focusing lens (37) and the fourth focusing lens (38).

10. A handheld optical coherence tomography method based on polarization modulation, based on the handheld optical coherence tomography system based on polarization modulation as described in any one of claims 1-9, characterized in that, Includes the following steps: Step 1: System initialization and polarization matching calibration: Turn on the OCT light source (1); the detection and control module drives the curved MEMS mirror (24) to reset to the reference surface shape and completes the calibration of the conjugate relationship between the reference arm optical path and the sample arm optical path; Before the fundus (27) of the eye being tested is connected, the detection and control module simultaneously scans the delay of the first liquid crystal variable delay unit (9) and the second liquid crystal variable delay unit (18), and monitors the intensity and contrast of the interference signal collected by the CCD (39). The state with the maximum amplitude of the interference signal and the balanced energy distribution of the two channels is set as the initial working point of the system polarization matching. Step 2: Eye alignment and wavefront aberration pre-correction: The handheld probe module is aimed at the fundus of the eye being tested (27); The detection and control module drives the adjustable lens (25) and the dispersion compensation adjustable lens (26) to perform correction based on the wavefront aberration measured by the wavefront sensor (30), thereby achieving automatic focusing and low-order aberration compensation. Step 3: Initiate hardware closed-loop dual locking and optimization: During the imaging process, the detection and control module continuously receives interference signals and adjusts the driving parameters of the first liquid crystal variable delay unit (9) and the second liquid crystal variable delay unit (18) in real time based on the changes in the intensity and contrast of the interference signals, so as to achieve dynamic locking of the polarization matching state. The wavefront sensor (30) continuously acquires the wavefront information of the reflected return light and feeds it back to the detection and control module. The detection and control module calculates the driving parameters based on the feedback signal and drives the fast deformable mirror (20) to adjust its surface shape. Step 4: OCT structural imaging: The detection and control module triggers the imaging process, drives the handheld probe module to execute the predetermined scanning pattern, and triggers the CCD (39) to acquire interference signals. The acquired spectral data is processed by the host computer through Fourier transform and digital dispersion compensation to reconstruct the structural image of the retina.

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