Self-stabilizing optical path difference adjusting system and control method thereof

Abstract

Although a traditional optical path difference scanning delay line system can realize variable scanning of optical path difference, a scanning mirror is inevitably deviated from a focal plane of a focusing mirror along with different inclination angles of the scanning mirror, so that optical power returned to a collimator is attenuated to different degrees, and the stability of the whole system becomes poor. In order to solve the problem, a self-stabilizing optical path difference adjusting system and a control method thereof are provided. The self-stabilizing optical path difference adjusting system is characterized by comprising a first reflector and a second reflector, the first reflector and the second reflector are located on the left side and the right side of a collimator, and the self-stabilizing optical path difference adjusting system with two optical paths can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a self-stabilizing optical path difference adjustment system and a control method thereof. Background Art

[0002] Optical delay lines (ODLs) play a pivotal role in modern optics. Their ability to generate stable and rapidly reproducible optical delays has led to their widespread application in a variety of key areas, including optical metrology, pulsed laser characterization, high-speed optical communications, photon signal processing, and low-coherence interferometry. Optical coherence tomography (OCT), a leading application of low-coherence interferometry, leverages the coherence gating capability of a broadband near-infrared light source to obtain information about the reflection intensity distribution across a sample's cross-section, playing a crucial role in biomedical imaging and materials testing. OCT typically has a scanning depth of 1–3 mm and an axial resolution of 1–10 μm. These parameters are influenced by various factors, including the light source's power, bandwidth, central wavelength, and Fourier envelope shape. As research continues to deepen, numerous researchers have explored ODLs extensively. For example, N. Delachenal et al. reported an ODL based on a rotating glass prism in "Constant high-speed optical low-coherence reflectometry over a 0.12 mm scan range." This ODL produces opposite group delays in the sample and reference arms, meeting certain measurement requirements to a certain extent. However, it has numerous drawbacks. The heavy rotating mechanism makes the device bulky and difficult to port. The 12% duty cycle and 76Hz repetition rate limit measurement efficiency. The complex optical components increase system cost and debugging difficulty. Time-varying dispersion further affects measurement accuracy. These shortcomings have severely restricted the further development and application of this type of ODL.

[0003] Meanwhile, in "In vivo video rate optical coherence tomography," AM Rollins et al. proposed a folded Fourier domain rapid scanning optical delay line (RSOD). In this RSODL, the light emitted by the collimator is low-coherence, collimated light. After diffraction by a diffraction grating, its spectrum is dispersed. A focusing lens focuses light of different wavelengths onto a scanning mirror. Tilting the scanning mirror introduces a linear phase ramp in the spectrum. The spectrum is reflected back to the grating via a lens, where it is inverted. The grating then inverts the spectrum, and the light strikes a reflector perpendicularly. The reflector then returns the light along its original path, achieving a change of twice the optical path difference. This unique design offers advantages such as a simple optical structure, low cost, and excellent linearity, while enabling rapid scanning. This RSOD has demonstrated significant practical value when combined with fiber-based OCT systems. Zeiss's fundus OCT systems, based on this principle, have rapidly gained market share due to their ability to rapidly acquire retinal tomographic images. They provide strong technical support for the diagnosis and treatment of ophthalmic diseases and further promote the widespread adoption and development of OCT technology in clinical applications.

[0004] However, while this system can rapidly increase the change in optical path difference, as the scanning mirror tilts, it inevitably deviates from the focal plane of the focusing mirror, causing varying degrees of attenuation of the optical power returning to the collimator. Increasing the scanning mirror's swing angle increases the change in optical path difference, but also increases the defocus introduced, leading to greater fluctuations in the optical power returning to the collimator, which in turn destabilizes the entire system. Summary of the Invention

[0005] The present invention aims to solve the above technical problems, and in particular innovatively proposes a self-stabilizing optical path difference adjustment system and a control method thereof.

[0006] To achieve the above-mentioned object, the present invention provides a self-stabilizing optical path difference adjustment system, characterized in that it includes a collimator, a grating, a lens, a zoom mirror, a scanner, a reflector, and a control system; the grating is located on the focal plane of the lens, and the scanning mirror is located on the focal plane of the lens; the control system controls the zoom mirror and the scanner so that the scanner is always located on the focal plane of the lens throughout the entire scanning cycle;

[0007] The diopter compensation introduced by the zoom mirror in the default state is 0D; the zoom mirror is positioned between the lens and the scanner, or between the lens and the grating, or between the grating and the reflector.

[0008] In a preferred embodiment of the present invention, the grating is preferably a transmission grating; the control system includes a function generator, a control board, and a host computer; and the reflector is a reflector, a corner cube prism, or a right-angle prism.

[0009] The parallel light beam emitted from the collimator is first incident on the grating. The grating disperses the light and then passes through the lens and zoom mirror in sequence before focusing on the scanner. The scanner deflects the light beam by an angle θ, and then passes through the zoom mirror, lens and grating again, and then is incident vertically on the surface of the reflector. The reflector returns the light to each component along the original path and finally returns to the collimator.

[0010] The present invention also provides another embodiment of a self-stabilizing optical path difference adjustment system, characterized in that: the reflector includes a first reflector and a second reflector, the first reflector and the second reflector being located on the left and right sides of a collimator; the zoom lens includes a first zoom lens and a second zoom lens; a parallel light beam emitted from the collimator is first incident on a grating, the grating diffracts light of different wavelengths into light of different diffraction angles, and the dispersed light passes through a lens and is focused on a scanner;

[0011] When the scanner's reflective surface swings at an angle of θ, the light is reflected and passes through the lens, grating, and first zoom mirror in sequence, finally vertically incident on the surface of the first reflector. The first reflector then returns the light back to the collimator along the original path, completing the first light path. The distance between the first reflector and the grating is L1.

[0012] When the reflective surface of the scanner swings at an angle of θ ′ When the light is reflected, it passes through the lens, the grating and the second zoom mirror in sequence, and finally vertically impinges on the surface of the second reflector. The second reflector returns the light to the collimator along the original path again, thus realizing the second light path; wherein, the distance between the second reflector and the grating is L2, and L1 and L2 are not equal.

[0013] When the scanner is a single reflective mirror, it can realize the swing angle θ and the swing angle θ in time sharing. ′ When the scanner is a multi-reflecting mirror, it can simultaneously achieve the swing angle θ and the swing θ ′ angle.

[0014] The present invention also provides another embodiment of a self-stabilizing optical path difference adjustment system, characterized in that the reflector includes a first reflector and a second reflector, the first reflector and the second reflector being located on the left and right sides of a collimator; a parallel light beam emitted from the collimator is first incident on a grating, the grating diffracts light of different wavelengths into light of different diffraction angles, the dispersed light passes through a lens and is focused on a scanner, when the reflective surface of the scanner swings at an angle of θ, the light is reflected, then passes through the lens, the grating and the first zoom mirror in sequence, and finally is incident on the surface of the first reflector at an angle not equal to 90 degrees, the first reflector reflects the light to the first zoom mirror, the grating, the lens and the scanner in sequence; at this time, the light beam is perpendicular to the reflective surface of the scanner; then, the reflective surface of the scanner returns the light to the collimator along its original path, thereby realizing a first light path;

[0015] When the reflective surface of the scanner swings at an angle of θ ′ When the light is reflected, it passes through the lens, grating and second zoom mirror in sequence, and finally enters the surface of the second reflector at an angle not equal to 90 degrees. The second reflector will reflect the light to the second zoom mirror, grating, lens and scanner in sequence. At this time, the light beam is perpendicular to the reflective surface of the scanner. Then, the reflective surface of the scanner returns the light to the collimator along the original path, realizing the second light path. In a preferred embodiment of the present invention, when the scanner is a single reflective mirror, it can realize the swing angle θ and the swing angle θ in time sharing. ′ When the scanner is a multi-reflecting mirror, it can simultaneously achieve the swing angle θ and the swing θ ′ angle.

[0016] The present invention also provides a control method for a self-stabilizing optical path difference adjustment system, which is specifically as follows:

[0017] S1, the host computer synchronously controls the output of the function generator and the control board. The function generator is used to control the swing angle function and swing period of the scanner, and the control board is used to control the refractive change function and period of the zoom lens;

[0018] S2, set the refractive power of the zoom lens to 0D, control the scanner to work in a suitable angle range with a period T, measure and record the numerical curve C1 of the optical power returned to the collimator within one period;

[0019] S3, let the working cycle of the zoom lens be T, and the refractive range be [D 01 D 02 ], record the numerical curve C2 of the optical power returned to the collimator within one cycle;

[0020] S4, extracting the maximum values of C1 and C2 at the same time within a period T, and combining them in sequence to form a new curve C3;

[0021] S5, the host computer continuously adjusts the output signals of the function generator and the control board, repeating steps S2-S4, so that the peak-to-peak value of curve C3 is finally fixed near a certain value and greater than 0.

[0022] The present invention also provides another embodiment of a control method for a self-stabilizing optical path difference adjustment system, which is specifically as follows:

[0023] S21, the host computer synchronously controls the outputs of the function generator and the control board, the function generator is used to control the swing angle function and swing period of the scanner, and the control board is used to control the refractive change function and period of the first zoom lens and the second zoom lens;

[0024] S22, set the refractive power of the first zoom lens and the second zoom lens to 0D, control all the reflective units of the scanner to move within the angle range [θ 11 θ 12 ] within a period of T, measure and record the fluctuation curve C11 of the optical power returned to the collimator; control all the reflective units of the scanner to be within the angle range [θ 11 ′ θ 12 ′ ] operates at a period T within a period of 1, and measures and records the fluctuation curve C12 of the optical power returned to the collimator 1;

[0025] S23, setting the duty cycle of the first zoom lens to T and the diopter variation range to [D1 D2], and recording the fluctuation curve C01 of the optical power returned to the collimator at this time; setting the duty cycle of the second zoom lens to T and the diopter variation range to [D3 D4], and recording the fluctuation curve C02 of the optical power returned to the collimator at this time;

[0026] S24, calculate the first-order derivative DIF1 of C11 and C01; calculate the first-order derivative DIF2 of C12 and C02;

[0027] S25, adjust the output signals of the function generator and the control board so that the maximum values of DIF1 and DIF2 are weakened by half;

[0028] S26, repeat steps S22-S25 until the peak-to-peak values of C11 and C12 approach zero and the amplitudes are greater than zero.

[0029] The present invention provides an OCT system, wherein the reference arm of the OCT system is the self-stabilizing optical path difference adjustment system.

[0030] The present invention has the following advantages:

[0031] (1) The present invention provides a self-stabilizing optical path difference adjustment system that not only increases the amount of optical path difference variation but also, by introducing a zoom lens, improves the stability of the return light power as the optical path difference changes. For example, when used as a reference arm in a time-domain optical coherence tomography (OCT) system, this can directly extend the imaging depth and protect the sensitivity of the OCT system from attenuation due to optical power fluctuations.

[0032] (2) The present invention can achieve different optical path differences between the first optical path and the second optical path, and the two optical paths can operate simultaneously or in a time-sharing manner, which can be used to achieve dual-modality OCT imaging of the anterior and posterior segments of the eye.

[0033] (3) The present invention can optimize the optical path configuration and, without adding any additional components, increase the optical path difference from 2 to 3 times, which can significantly increase the imaging depth of the corresponding OCT and has significant practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of a self-stabilizing optical path difference adjustment system.

[0035] Figure 2 Schematic diagram of a dual-channel self-stabilized optical path difference adjustment system.

[0036] Figure 3 Schematic diagram of a triple-multiplexed self-stabilized optical path difference adjustment system.

[0037] Figure 4 This is the control system schematic.

[0038] Notes on the figures: collimator 1, grating 2, lens 3, zoom mirror 4, first zoom mirror 401, second zoom mirror 402, scanner 5, reflector 6, first reflector 601, second reflector 602, function generator 7, control board 8, host computer 9. DETAILED DESCRIPTION

[0039] Example 1

[0040] like Figure 1Figure 1 shows a self-stabilizing optical path difference adjustment system. The system includes a collimator 1, a grating 2, a lens 3, a zoom mirror 4, a scanner 5, a reflector 6, and a control system, wherein the control system includes a function generator 7, a control board 8, and a host computer 9. A parallel light beam emitted from collimator 1 first impinges on grating 2. Grating 2 diffracts light of different wavelengths into light of different diffraction angles according to the grating equation of Formula 1. The dispersed light passes through lens 3 and zoom mirror 4 and is focused on scanner 5. Grating 2 is located on the focal plane of lens 3, and scanning mirror 5 is located on the focal plane of lens 3. α represents the incident angle of the incident light beam, and β represents the diffraction angle of the diffracted light beam. The sign of the two depends on whether the incident and exit angles are on the same side of the normal or on opposite sides. m represents the grating diffraction order, generally taking the first order diffraction with the highest diffraction efficiency. λ0 represents the central wavelength of the incident light beam, and d is the grating constant. When scanner 5 swings a small angle, the light is reflected and passes through zoom mirror 4, lens 3, and grating 2, finally striking the surface of reflector 6 perpendicularly. At this point, the light is said to have completed one pass through the RSOD optical path. Reflector 6 then returns the light along the same path to collimator 1, completing a second optical pass. This dual-pass solution doubles the RSOD's optical path difference scanning range.

[0041]

[0042] Assume that the first deflection angle of scanner 5 is θ1. When scanner 5 reflects the light beam to lens 3, the height difference between the light beam and the center of lens 3 is h1. The second deflection angle of scanner 5 is θ2. When scanner 5 reflects the light beam to lens 3, the height difference between the light beam and the center of lens 3 is h2. The zoom amount introduced by zoom lens 4 in the default state is zero. The focal length of lens 3 is f. Then the change in optical path difference ΔOPD corresponding to the swing angle of scanner 5 can be approximately expressed as,

[0043] ΔOPD=OPD(θ2)-OPD(θ1)=2(ab+bc) (2)

[0044] from Figure 1 From the geometric relationship in , we can conclude that

[0045] cd=f(tan 2θ2-tan 2θ1) (3)

[0046] bc=cd*tanβ (4)

[0047]

[0048] Combining formulas (1) to (5), and using the small angle approximation, we can obtain:

[0049]

[0050] Here, θ=θ2-θ1 represents the angular variation of the scanner 5 .

[0051] For the traditional RSOD system, as the scanner 5 swings, the problem of the scanner 5 deviating from the focal plane will inevitably occur, resulting in a decrease in the optical power returned to the collimator 1. Although the optical path difference change increases when the swing angle range increases, the defocus introduced also increases, resulting in an increase in the optical power fluctuation in the return collimator 1, which will cause the stability of the entire system to deteriorate. In order to overcome the problems that exist in the traditional RSOD system, the present invention introduces a zoom lens 4, and keeps the refractive modulation period of the zoom lens 4 consistent with the scanning period of the scanner 5. This not only solves the defocus problem of the scanner 5 at different scanning angles, but also makes the scanner 5 in the focal plane position at different angles, so that the power of the light emitted by the scanner from different angles is basically stable, thereby improving the stability of the system. Moreover, when this self-stabilizing system for quickly adjusting the optical path difference is applied to the OCT system, the signal-to-noise ratio of the OCT device can be improved, thereby improving the image quality.

[0052] The collimator 1 collimates the light from the optical fiber; preferably, the lens of the collimator 1 is an aspheric lens with a numerical aperture greater than 0.5.

[0053] The grating is a transmission grating with a diffraction efficiency of over 90%. Because transmission gratings currently have higher diffraction efficiency than reflection gratings, such as Gitterwerk's transmission gratings with a diffraction efficiency of 95%-99%, while traditional blazed gratings have a diffraction efficiency of 60%-85%, using transmission gratings to implement RSOD is very valuable for improving the signal-to-noise ratio in weak-light detection systems such as OCT.

[0054] The zoom lens 4 introduces a diopter compensation of 0D by default. Preferably, the diopter compensation range of the zoom lens 4 is greater than -10D to 10D, and the response speed of the zoom lens 4 needs to be higher than 10kHz. The zoom lens 4 is optimally positioned between the lens 3 and the scanner 5, but can also be positioned between the lens 3 and the grating 2, or between the grating 2 and the first reflector 601.

[0055] The first reflector 601 can be a reflecting mirror, a corner cube, a right-angle prism, etc.

[0056] The scanner 5 is a single reflective mirror such as a scanning galvanometer, a resonant mirror, or a MEMS, and can also be a multi-reflective mirror such as a spatial light modulator or a digital micromirror.

[0057] like Figure 4As shown, host computer 9 is connected to function generator 7 and control board 8, respectively; function generator 7 and scanner 5 are connected to each other; and control board 8 is connected to zoom lens 4. The control system controls the zoom lens and scanner so that the scanner remains in the focal plane of the lens throughout the entire scanning cycle.

[0058] The present invention provides an OCT system, wherein the reference arm of the OCT system is the self-stabilizing optical path difference adjustment system.

[0059] The present invention provides a control method for a self-stabilizing optical path difference adjustment system, which is specifically as follows:

[0060] S1, the host computer synchronously controls the output of the function generator and the control board. The function generator is used to control the swing angle function and swing period of the scanner, and the control board is used to control the refractive change function and period of the zoom lens;

[0061] S2, set the refractive power of the zoom lens to 0D, control the scanner to work in a suitable angle range with a period T, measure and record the numerical curve C1 of the optical power returned to the collimator within one period;

[0062] S3, let the working cycle of the zoom lens be T, and the refractive range be [D 01 D 02 ], record the numerical curve C2 of the optical power returned to the collimator within one cycle;

[0063] S4, extracting the maximum values of C1 and C2 at the same time within a period T, and combining them in sequence to form a new curve C3;

[0064] S5, the host computer continuously adjusts the output signals of the function generator and the control board, repeating steps S2-S4, so that the peak-to-peak value of curve C3 is finally fixed near a certain value and greater than 0.

[0065] Example 2

[0066] like Figure 2 As shown, the present invention provides a schematic diagram of a self-stabilizing optical path difference adjustment system, which has the advantages of two different optical path differences. The system includes a collimator 1, a grating 2, a lens 3, a first zoom mirror 401, a second zoom mirror 402, a scanner 5, a first reflector 601, a second reflector 602, and a control system. The control system includes a function generator 7, a control board 8, and a host computer 9. The host computer 9 is connected to the function generator 7 and the control board 8, respectively; the function generator 7 and the scanner 5 are interconnected; and the control board 8 is connected to the first zoom mirror 401 and the second zoom mirror 402, respectively. The control system controls the first zoom mirror, the second zoom mirror, and the scanner, ensuring that the scanner remains in the focal plane of the lens throughout the entire scanning cycle.

[0067] A parallel light beam emitted from collimator 1 first strikes grating 2, which diffracts light of different wavelengths into light of different diffraction angles. The dispersed light passes through lens 3 and is focused on scanner 5, where grating 2 and scanner mirror 5 are located in the focal plane of lens 3. α represents the angle of incidence of the incident light beam, and β represents the diffraction angle of the diffracted light beam.

[0068] When the reflective surface of scanner 5 swings at an angle of θ, the light is reflected and passes through lens 3, grating 2, and first zoom mirror 401 in sequence, ultimately perpendicularly incident on the surface of first reflector 601. First reflector 601 then returns the light along its original path to collimator 1, completing the first light path. The distance between first reflector 601 and grating 2 is L1.

[0069] When the reflective surface of the scanner 5 swings at an angle of θ ′ When the light is reflected, it passes through lens 3, grating 2, and second zoom lens 402 in sequence, and finally vertically impinges on the surface of second reflector 602. Second reflector 602 also returns the light along the original path to collimator 1, completing the second light path. The distance between second reflector 602 and grating 2 is L2.

[0070] The first reflector 601 and the second reflector 602 are located on the left and right sides of the collimator 1 .

[0071] When the scanner 5 can be a single reflective mirror such as a scanning galvanometer, a resonant mirror, or a MEMS, the swing angle θ and the swing angle θ can be realized in a time-sharing manner. ′ The scanner 5 may also be a spatial light modulator, a digital micromirror or other multi-reflective mirror, which can simultaneously achieve a swing angle θ and a swing θ ′ Angle; the distances L1 and L2 are unequal, which can achieve different optical path differences between the first and second optical pathways; the distance can satisfy L1 = L2 + L3, where L3 is preferably in the range of 5mm to 50mm. In this case, the first optical pathway can serve as the reference arm for anterior segment OCT, and the second optical pathway can serve as the reference arm for posterior segment OCT, achieving dual-modality OCT. The dual-modality OCT can be time-domain OCT, frequency-domain OCT, or swept-band OCT.

[0072] In addition to the advantages of Example 1, this second embodiment also offers the advantages of dual optical paths. The first and second optical paths have different optical path differences, and these two paths can operate simultaneously or in a time-sharing manner, enabling dual-modality OCT imaging of the anterior and posterior segments of the eye. The present invention provides an OCT system whose reference arm utilizes the aforementioned self-stabilizing optical path difference adjustment system.

[0073] The present invention provides a control method for a self-stabilizing optical path difference adjustment system, specifically:

[0074] S21, the host computer synchronously controls the outputs of the function generator and the control board, the function generator is used to control the swing angle function and swing period of the scanner, and the control board is used to control the refractive change function and period of the first zoom lens and the second zoom lens;

[0075] S22, set the refractive power of the first zoom lens and the second zoom lens to 0D, control all the reflective units of the scanner to move within the angle range [θ 11 θ 12 ] within a period of T, measure and record the fluctuation curve C11 of the optical power returned to the collimator; control all the reflective units of the scanner to be within the angle range [θ 11 ′ θ 12 ′ ] operates at a period T within a period of 1, and measures and records the fluctuation curve C12 of the optical power returned to the collimator 1;

[0076] S23, setting the duty cycle of the first zoom lens to T and the diopter variation range to [D1 D2], and recording the fluctuation curve C01 of the optical power returned to the collimator at this time; setting the duty cycle of the second zoom lens to T and the diopter variation range to [D3 D4], and recording the fluctuation curve C02 of the optical power returned to the collimator at this time;

[0077] S24, calculate the first-order derivative DIF1 of C11 and C01; calculate the first-order derivative DIF2 of C12 and C02;

[0078] S25, adjust the output signals of the function generator and the control board so that the maximum values of DIF1 and DIF2 are weakened by half;

[0079] S26, repeat steps S22-S25 until the peak-to-peak values of C11 and C12 approach zero and the amplitudes are greater than zero.

[0080] Example 3

[0081] like Figure 3 The figure shows a schematic diagram of a self-stabilizing optical path difference adjustment system proposed in the present invention, which has the advantages of two different optical path differences and the advantage of increasing the optical path difference from 2 to 3. The system includes a collimator 1, a grating 2, a lens 3, a first zoom mirror 401, a second zoom mirror 402, a scanner 5, a first reflector 601, a second reflector 602, and a control system. The control system includes a function generator 7, a control board 8, and a host computer 9. The host computer 9 is connected to the function generator 7 and the control board 8 respectively; the function generator 7 and the scanner 5 are connected to each other; and the control board 8 is connected to the first zoom mirror 401 and the second zoom mirror 402 respectively.

[0082] A parallel light beam emitted from collimator 1 first strikes grating 2, which diffracts light of different wavelengths into light of different diffraction angles. The dispersed light passes through lens 3 and is focused on scanner 5, where grating 2 and scanner mirror 5 are located in the focal plane of lens 3. α represents the angle of incidence of the incident light beam, and β represents the diffraction angle of the diffracted light beam.

[0083] When the reflective surface of scanner 5 swings at an angle of θ, the light is reflected and then passes through lens 3, grating 2, and first zoom mirror 401 in sequence, finally impinging on the surface of first reflector 601 at an angle not equal to 90 degrees. First reflector 601 then reflects the light in sequence to first zoom mirror 401, grating 2, lens 3, and scanner 5. At this point, the light beam is perpendicular to the reflective surface of scanner 5. The reflective surface of scanner 5 then returns the light along its original path to collimator 1, completing the first optical path. Throughout this process, the light beam makes three round trips, increasing the optical path difference from the traditional 2x to 3x without adding any additional components. The distance between first reflector 601 and grating 2 is L1.

[0084] When the reflective surface of the scanner 5 swings at an angle of θ ′ When the light is reflected, it then passes through lens 3, grating 2, and second zoom mirror 402 in sequence, finally striking the surface of second reflector 602 at an angle not equal to 90 degrees. Second reflector 602 then reflects the light sequentially to second zoom mirror 402, grating 2, lens 3, and scanner 5. At this point, the light beam is perpendicular to the reflective surface of scanner 5. The reflective surface of scanner 5 then returns the light along its original path to collimator 1, completing the second optical path. Throughout this process, the light beam makes three round trips, increasing the optical path difference from the traditional 2x to 3x without adding any additional components. The distance between second reflector 602 and grating 2 is L2.

[0085] The first reflector 601 and the second reflector 602 are located on the left and right sides of the collimator 1 .

[0086] The distances L1 and L2 are unequal, which allows the first and second optical pathways to have different optical path differences. The distances satisfy L1 = L2 + L3, where L3 is preferably in the range of 5 mm to 50 mm. In this case, the first optical pathway can serve as the reference arm for anterior segment OCT, and the second optical pathway can serve as the reference arm for posterior segment OCT, thus achieving dual-modality OCT. The dual-modality OCT can be time-domain OCT, frequency-domain OCT, or swept-frequency OCT. The anterior segment OCT and posterior segment OCT are existing technologies and will not be explained in detail here.

[0087] When the scanner 5 is a single reflective mirror such as a scanning galvanometer, a resonant mirror, or a MEMS, the swing angle θ and the swing angle θ can be realized in a time-sharing manner. ′Angle, can realize two scanning with different optical path differences in time.

[0088] When the scanner 5 is a multi-reflective mirror such as a spatial light modulator or a digital micromirror, the swing angle θ and the swing angle θ can be realized simultaneously. ′ Angle, can realize two scanning with different optical path differences at the same time.

[0089] In addition to the advantages of the second embodiment, the third embodiment has the advantage of increasing the optical path difference change from 2 times to 3 times, which can greatly improve the imaging depth of the corresponding OCT and has great practical application value.

[0090] The present invention provides an OCT system, wherein the reference arm of the OCT system is the self-stabilizing optical path difference adjustment system.

[0091] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A self-stabilizing optical path difference adjustment system, characterized by: It includes a collimator, a grating, a lens, a zoom mirror, a scanner, a reflector, and a control system. The grating is located on the focal plane of the lens, and the scanning mirror is located on the focal plane of the lens. The control system controls the zoom mirror and the scanner so that the scanner is always located on the focal plane of the lens during the entire scanning cycle. The diopter compensation introduced by the zoom mirror in the default state is 0D; the zoom mirror is positioned between the lens and the scanner, or between the lens and the grating, or between the grating and the reflector.

2. The self-stabilizing optical path difference adjustment system according to claim 1, characterized in that: The grating is a transmission grating; the control system includes a function generator, a control board, and a host computer; and the reflector is a reflecting mirror, a corner cube prism, or a right-angle prism.

3. A self-stabilizing optical path difference adjustment system according to claim 1 or 2, characterized in that: The parallel light beam emitted from the collimator is first incident on the grating. The grating disperses the light and then passes through the lens and zoom mirror in sequence before focusing on the scanner. The scanner deflects the light beam by an angle θ, and then passes through the zoom mirror, lens and grating again, and then is incident vertically on the surface of the reflector. The reflector returns the light to each component along the original path and finally returns to the collimator.

4. A self-stabilizing optical path difference adjustment system according to claim 1 or 2, characterized in that: The reflector includes a first reflector and a second reflector, which are located on the left and right sides of the collimator; the zoom lens includes a first zoom lens and a second zoom lens; the parallel light beam emitted from the collimator is first incident on the grating, and the grating diffracts light of different wavelengths into light of different diffraction angles. The dispersed light passes through the lens and is focused on the scanner; When the scanner's reflective surface swings at an angle of θ, the light is reflected and passes through the lens, grating, and first zoom mirror in sequence, finally vertically incident on the surface of the first reflector. The first reflector then returns the light back to the collimator along the original path, completing the first light path. The distance between the first reflector and the grating is L1. When the scanner's reflective surface swings to an angle of θ', the light is reflected and passes through the lens, grating, and second zoom mirror in sequence, finally striking the surface of the second reflector perpendicularly. The second reflector then returns the light back to the collimator along the original path, completing a second optical path. The distance between the second reflector and the grating is L2; L1 and L2 are not equal.

5. The self-stabilizing optical path difference adjustment system according to claim 1 or 2, characterized in that: The reflector includes a first reflector and a second reflector, which are located on the left and right sides of the collimator. The parallel light beam emitted from the collimator is first incident on the grating, and the grating diffracts light of different wavelengths into light of different diffraction angles. The dispersed light passes through the lens and is focused on the scanner. When the scanner's reflective surface swings at an angle of θ, the light is reflected, then passes through the lens, grating, and first zoom mirror in sequence, and finally strikes the surface of the first reflector at an angle not equal to 90 degrees. The first reflector then reflects the light to the first zoom mirror, grating, lens, and scanner in sequence. At this point, the light beam is perpendicular to the scanner's reflective surface. The scanner's reflective surface then returns the light along its original path to the collimator, completing the first light path. When the reflective surface of the scanner swings to an angle of θ′, the light is reflected, then passes through the lens, grating, and second zoom mirror in sequence, and finally impinges on the surface of the second reflector at an angle not equal to 90 degrees. The second reflector will reflect the light to the second zoom mirror, grating, lens, and scanner in sequence; at this time, the light beam is perpendicular to the reflective surface of the scanner; then, the reflective surface of the scanner returns the light to the collimator along the original path, realizing the second light path.

6. A self-stabilizing optical path difference adjustment system according to claim 4 or 5, characterized in that: When the scanner is a single-reflection mirror, it can realize swinging the θ angle and the θ′ angle in a time-sharing manner; when the scanner is a multi-reflection mirror, it can realize swinging the θ angle and the θ′ angle at the same time.

7. A control method for a self-stabilizing optical path difference adjustment system according to any one of claims 1 to 3, comprising: S1, the host computer synchronously controls the output of the function generator and the control board. The function generator is used to control the swing angle function and swing period of the scanner, and the control board is used to control the refractive change function and period of the zoom lens; S2, set the refractive power of the zoom lens to 0D, control the scanner to work in a suitable angle range with a period T, measure and record the numerical curve C1 of the optical power returned to the collimator within one period; S3, let the working cycle of the zoom lens be T, and the refractive range be [D 01 D 02 ], record the numerical curve C2 of the optical power returned to the collimator within one cycle; S4, extracting the maximum values of C1 and C2 at the same time within a period T, and combining them in sequence to form a new curve C3; S5, the host computer continuously adjusts the output signals of the function generator and the control board, repeating steps S2-S4, so that the peak-to-peak value of curve C3 is finally fixed near a certain value and greater than 0.

8. A method for controlling a self-stabilizing optical path difference adjustment system according to any one of claims 4 to 6, comprising: S21, a host computer synchronously controlling outputs of a function generator and a control board, wherein the function generator is used to control a swing angle function and a swing period of a scanner, and the control board is used to control a refractive change function and a period of a first zoom lens and a second zoom lens; S22, set the refractive power of the first zoom lens and the second zoom lens to 0D, control all the reflective units of the scanner to move within the angle range [θ 11 θ 12 ] within a period of T, measure and record the fluctuation curve C11 of the optical power returned to the collimator; control all the reflective units of the scanner to be within the angle range [θ 11 ′ θ 12 ′] works at a period T, measures and records the fluctuation curve C12 of the optical power returning to the collimator 1; S23, setting the duty cycle of the first zoom lens to T and the diopter variation range to [D1 D2], and recording the fluctuation curve C01 of the optical power returned to the collimator at this time; setting the duty cycle of the second zoom lens to T and the diopter variation range to [D3 D4], and recording the fluctuation curve C02 of the optical power returned to the collimator at this time; S24, calculate the first-order derivative DIF1 of C11 and C01; calculate the first-order derivative DIF2 of C12 and C02; S25, adjust the output signals of the function generator and the control board so that the maximum values of DIF1 and DIF2 are weakened by half; S26, repeat steps S22-S25 until the peak-to-peak values of C11 and C12 approach zero and the amplitudes are greater than zero.

9. An OCT system, wherein the reference arm of the system is the self-stabilizing optical path difference adjustment system according to any one of claims 1 to 5.

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