Optical coherence tomography optical path structure and dispersion compensation method thereof

Abstract

The invention discloses an optical coherence tomography optical path structure and a dispersion compensation method thereof. The light path structure comprises a coherent light source, a 2 * 2 optical fiber coupler, a reference light path, a sample light path, an equal-wave-number spectrograph and an upper computer; low-coherence broadband light emitted by the coherent light source is divided into reference light and sample light after passing through the 2 * 2 optical fiber coupler, the reference light and the sample light are sequentially transmitted in a reference light path and a sample light path, the reference light and the sample light are retroreflected through a sample and a reference mirror and are retroreflected to the 2 * 2 optical fiber coupler according to an original light path, interference is generated, and interference light beams are transmitted to the equal-wave-number spectrometer. Interference light beams are split to an upper computer according to equal wave number intervals, and a tomographic image of a sample is obtained through algorithm processing of the upper computer. By means of the structure, the existing dispersion loss problem is solved from the source, most dispersion generated by a light path is solved, other dispersion is eliminated by adding a dispersion compensating mirror made of optical glass materials with certain thickness in the light path through algorithm calculation, the algorithm is simple, convenient and fast, and the imaging speed is high.

Description

Technical Field

[0001] The present invention relates to the field of OCT technology, and in particular to an optical coherence tomography optical path structure and a dispersion compensation method thereof. Background Art

[0002] Optical Coherence Tomography (OCT) is a non-invasive high-resolution tomography technology based on the interference principle of partially coherent light. In theory, the wider the bandwidth of the OCT light source, the higher the axial resolution. However, in practical applications, when the actual optical propagation paths of the reference light and the sample light are not completely consistent, the broadband light will cause dispersion mismatch in the interference signal when propagating in the optical fiber, optical lens group and inside the sample, thereby introducing a dispersion phase into the interference signal. The dispersion phase will broaden the coherence peak of the interference signal, causing the amplitude distribution of adjacent positions to overlap, thereby affecting the resolution of the imaging.

[0003] Existing methods of dispersion compensation are divided into physical (hardware) compensation and numerical (algorithm) compensation. Hardware compensation is to restore the propagation path in the sample arm by adding a suitable optical compensation device to the reference arm optical path. However, the low-cost materials and thickness of the optical compensation device are difficult to test and calculate, which greatly reduces the effect of hardware dispersion compensation. Algorithmic compensation is to offset dispersion through algorithms. Common methods include iterative algorithms and convolution methods. Although both methods are effective, the complex iterative process and large amount of calculation reduce the imaging speed and affect the real-time performance of imaging, which in turn increases the difficulty of process transformation of commercial OCT, thereby limiting the application of algorithm compensation in the field of commercial OCT. Summary of the invention

[0004] The present invention provides an optical coherence tomography optical path structure and a dispersion compensation method thereof, which can solve the dispersion mismatch problem from the source, and the dispersion compensation algorithm is simple, low-cost, convenient and fast, and the imaging speed is fast.

[0005] In a first aspect, an embodiment of the present invention provides an optical coherence tomography optical path structure, comprising: a coherent light source, a 2*2 fiber coupler, a reference optical path, a sample optical path, an equal wave number spectrometer and a host computer;

[0006] The first end of the 2*2 optical fiber coupler is connected to a coherent light source, the second end is connected to a reference optical path, the third end is connected to a sample optical path, the fourth end is connected to an equal wave number spectrometer, and the equal wave number spectrometer is connected to a host computer;

[0007] The reference optical path comprises: a first housing, and a first parabolic reflection collimator, an aperture, a first lens group and a first reflection mirror located in the first housing; the first reflection mirror can move along the optical axis direction of the reference optical path;

[0008] The sample optical path includes: a second shell, and a second parabolic reflection collimator, a scanning galvanometer, a focusing mechanical structure and a second lens group located in the second shell; the scanning galvanometer is connected to the host computer, and the first lens group is the same as the second lens group.

[0009] Optionally, the reference optical path also includes: a slide rail assembly and a drive assembly arranged in the first shell, the first reflector is located on the slide rail assembly, and the drive assembly is used to drive the slide rail assembly to move the first reflector along the optical axis direction of the reference optical path; the drive assembly is connected to the host computer.

[0010] Optionally, the reference optical path further includes: a first collimator bracket, the first collimator bracket includes a first bottom plate and a first side plate, the first bottom plate is fixed to the bottom plate of the first shell, and the first side plate is fixed to the first parabolic reflection collimator.

[0011] Optionally, the reference optical path further includes: a first lens group bracket, the first lens group bracket includes a second bottom plate and a second side plate, the second bottom plate is fixed to the bottom plate of the first shell, and the second side plate is fixed to the first lens group.

[0012] Optionally, the sample optical path further includes: a scanning galvanometer support housing, the scanning galvanometer support housing including a bottom surface, a first side surface and a third side surface, a second side surface and a fourth side surface that are arranged parallel to each other;

[0013] A first galvanometer rotating assembly for driving the first galvanometer to deflect is fixedly disposed on the first side surface, and a second galvanometer rotating assembly for driving the second galvanometer to deflect is fixedly disposed on the adjacent second side surface, wherein the rotation axis of the first galvanometer rotating assembly and the rotation axis of the second galvanometer rotating assembly are perpendicular to each other and are arranged at a preset distance in a direction perpendicular to the bottom surface;

[0014] The third side surface is provided with a mounting hole for mounting a second parabolic reflective collimator;

[0015] The fourth side surface is provided with a mounting hole for mounting the focusing mechanical structure, and the other end of the focusing mechanical structure is fixedly connected to the second lens group.

[0016] Optionally, the equal wave number spectrometer includes: a diffraction grating, an isosceles prism, a focusing lens group and an image acquisition unit.

[0017] In a second aspect, an embodiment of the present invention provides a dispersion compensation method for an optical coherence tomography optical path structure, which is implemented based on the optical coherence tomography optical path structure described in any embodiment of the present invention, wherein the sample to be measured is a second reflector, and the dispersion compensation method includes:

[0018] Controlling the first reflector to move at least one position along the optical axis of the reference optical path, or controlling the second reflector to move at least one position along the optical axis of the sample optical path within the depth of field of the second lens group to obtain at least one interference spectrum signal;

[0019] Performing fast Fourier transform on the interference spectrum signal to obtain a complex frequency domain signal; obtaining a positive amplitude signal based on the complex frequency domain signal;

[0020] Perform inverse fast Fourier transform on the positive amplitude signal to obtain a complex signal;

[0021] Extracting phase information of the complex signal, and unwrapping the phase information to obtain a phase signal after unwrapping;

[0022] Perform a third-order linear fit on the phase signal after phase wrapping to obtain a nonlinear phase term;

[0023] A dispersion model of the dispersion compensating mirror is established, and at least one set of thickness and glass material parameters of the dispersion compensating mirror is obtained based on the dispersion model and the nonlinear phase term.

[0024] Optionally, establishing a dispersion model of the dispersion compensating mirror, and obtaining at least one set of thickness and glass material parameters of the dispersion compensating mirror based on the dispersion model and the nonlinear phase term includes:

[0025] The dispersion model is:

[0026] Where d is the thickness of the dispersion compensation mirror; λ is the wavelength, and B1, B2, B3, C1, C2, C3 are the Sellmeier coefficients of any glass material in the glass library; is the dispersion phase of the dispersion compensation mirror;

[0027] The nonlinear phase term is made identical to the dispersion phase, thereby obtaining at least one set of thickness and glass material parameters of the dispersion compensation mirror.

[0028] Optionally, if multiple sets of thickness and glass material parameters of the dispersion compensation mirror are obtained, the method further includes:

[0029] A dispersion compensation mirror formed based on the i-th group of thickness and glass material parameters is placed in the reference optical path or the sample optical path; i>1;

[0030] Acquire multiple interference spectrum signals, and calculate the longitudinal resolutions of the multiple interference spectrum signals; obtain a first quantity in which the difference between the longitudinal resolution of the interference spectrum signal and the longitudinal resolution of the coherent light source is within a preset range;

[0031] The thickness and glass material parameters corresponding to the maximum value of the first number are screened out in a cycle; and the dispersion compensation mirror formed by the thickness and glass material parameters is used as the final dispersion compensation mirror.

[0032] Optionally, calculating the longitudinal resolution of the plurality of interference spectrum signals includes:

[0033] Controlling the first reflector to move at least one position along the optical axis of the reference optical path, or controlling the second reflector to move at least one position along the optical axis of the sample optical path within the depth of field of the second lens group to obtain at least one interference spectrum signal;

[0034] Performing fast Fourier transform on the interference spectrum signal to obtain a complex frequency domain signal; obtaining a positive amplitude signal based on the complex frequency domain signal;

[0035] The longitudinal resolution of the interference spectrum signal is obtained based on the positive amplitude signal.

[0036] The technical solution of the embodiment of the present invention proposes an optical coherence tomography optical path structure and a dispersion compensation method thereof, wherein the optical path structure includes: a coherent light source, a 2*2 fiber coupler, a reference optical path, a sample optical path, an equal wave number spectrometer and a host computer; wherein the low coherence broadband light emitted by the coherent light source is divided into a reference light and a sample light after passing through a 2*2 fiber coupler, and the reference light and the sample light are transmitted in the reference optical path and the sample optical path in turn, and the two beams of light are reflected back through the sample and the reference mirror according to the original optical path and generate interference, and the interference beam is transmitted to the equal wave number spectrometer, and the equal wave number spectrometer splits the interference beam according to the equal wave number interval to the host computer, and the tomographic image of the sample is obtained through the host computer processing. Through the above optical path structure, most of the dispersion generated by the optical path can be solved, and combined with the dispersion compensation method, the dispersion compensation mirror obtained by the dispersion compensation method is adapted in the optical path to eliminate it, thereby solving the existing dispersion mismatch, low resolution and complex algorithm problems from the source.

[0037] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 A schematic diagram of the structure of the optical coherence tomography optical path structure provided in the first embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the structure of a reference optical path provided in Embodiment 1 of the present invention;

[0041] Figure 3 A schematic diagram of the structure of the sample optical path provided in the first embodiment of the present invention;

[0042] Figure 4 A schematic diagram of the structure of the reference optical path mechanical structure provided in the first embodiment of the present invention;

[0043] Figure 5 A schematic diagram of the structure of the scanning galvanometer mechanical structure provided in the first embodiment of the present invention;

[0044] Figure 6 A schematic diagram of the structure of the propagation direction of the light path in the scanning galvanometer provided in the first embodiment of the present invention;

[0045] Figure 7 A schematic diagram of the structure of a second housing in a sample optical path provided in Embodiment 1 of the present invention;

[0046] Figure 8 A schematic diagram of the structure of the sample optical path and the reference optical path provided in the first embodiment of the present invention;

[0047] Fig. 9 A schematic diagram of the structure of an equal wavenumber spectrometer provided in Embodiment 1 of the present invention;

[0048] Fig.10 This is a flow chart of a method for compensating optical path structure dispersion of optical coherence tomography provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0050] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0051] Embodiment 1

[0052] Figure 1 A schematic diagram of the optical coherence tomography optical path structure provided in the first embodiment of the present invention. Figure 2 A schematic diagram of the structure of the reference optical path provided in the first embodiment of the present invention, Figure 3 This is a schematic diagram of the structure of the sample optical path provided in the first embodiment of the present invention. Figures 1 to 3 As shown, the optical coherence tomography optical path structure includes:

[0053] Coherent light source 401 , 2*2 fiber coupler 402 , reference optical path 415 , sample optical path 416 , equal wave number spectrometer 413 and host computer 414 . Among them, the first end of the 2*2 fiber coupler 402 is connected to the coherent light source 401, the second end is connected to the reference light path 415, the third end is connected to the sample light path 416, and the fourth end is connected to the equal wave number spectrometer 413, and the equal wave number spectrometer 413 is connected to the host computer 414; the reference light path 415 includes: a first shell 1, and a first parabolic reflection collimator 403, an aperture 404, a first lens group 405 and a first reflector 406 located in the first shell 1; the first reflector 406 can move along the optical axis direction of the reference light path 415; the sample light path 416 includes: a second shell 2, and a second parabolic reflection collimator 407, a scanning galvanometer 408, a focusing mechanical structure 417 and a second lens group 411 located in the second shell 2; the scanning galvanometer 408 is connected to the host computer 414, and the first lens group 405 is the same as the second lens group 411.

[0054] Among them, the coherent light source 401 can be a low-coherence SLD light source, a supercontinuum light source, etc., which is used to emit low-coherence broadband light. The first end of the 2*2 fiber coupler 402 is connected to the coherent light source 401, the second end is connected to the reference optical path 415, the third end is connected to the sample optical path 416, and the fourth end is connected to the equal-wavenumber spectrometer 413, which is used to realize the connection, distribution and debugging of electrical signals between different optical fibers. The optical path lengths of the pigtails at the four output ends of the 2*2 fiber coupler 402 must be consistent, which is used to split the light source beam into two beams of light and transmit them to the reference optical path and the sample optical path respectively. The reference optical path 415 is used to transmit the reference light transmitted from the 2*2 optical fiber coupler 402 in the reference optical path, the sample optical path 416 is used to transmit the sample light transmitted from the 2*2 optical fiber coupler 402 in the sample optical path, the equal wavenumber spectrometer 413 is used to evenly distribute the interference spectrum on the pixels of the linear array camera according to equal wavenumber intervals, and the host computer 414 is connected to the equal wavenumber spectrometer 413 to display the tomographic image of the sample 412 to be tested.

[0055] It should be noted that the first parabolic reflection collimator 403 located in the reference light path 415 and the second parabolic reflection collimator 407 in the sample light path 416 are based on a 90° off-axis parabolic reflector, and are a reflective collimator coated with a protective layer, which is mainly used to couple and collimate the incident broadband light so that it can be output as parallel light. Unlike lenses, the focal length of the metal reflector of the first parabolic reflection collimator 403 and the second parabolic reflection collimator 407 can remain unchanged within a wide wavelength range. Due to this characteristic, the first parabolic reflection collimator 403 and the second parabolic reflection collimator 407 can collimate light of different wavelengths without adjustment, so they are very suitable for collimating polychromatic light. The aperture 404 located in the reference light path 415 is used to adjust the energy of the reference arm light.

[0056] The scanning galvanometer 408 located in the sample optical path 416 includes a first galvanometer 409 and a second galvanometer 410. By adjusting the angles of the first galvanometer 409 and the second galvanometer 410, the sample light beam can scan any position of the image plane, thereby detecting each position of the sample; and the sample light beam can also be output in a specific direction, and the spot size is almost the same in the entire image plane field of view. The second lens group 411 located in the sample optical path 416 is composed of a telecentric scanning lens composed of multiple lenses, and the telecentric scanning lens is composed of a telecentric scanning lens composed of multiple lenses. When the incident light angle changes relative to the lens optical axis, the telecentric scanning lens can generate a flat image plane with very small spot size distortion; changing the incident angle allows the focal spot to scan the image plane in the entire field of view. The f-theta distortion is small, and a geometrically corrected scanned image is generated without a large amount of post-image processing. The telecentric scanning lens optical path can also allow the light (signal) scattered or emitted by the sample to enter the detection system to the greatest extent. In addition, the spot size of the image plane is almost the same in the entire field of view, so the imaging resolution of the sample in the entire scanning area is almost unchanged.

[0057] The first lens group 405 is the same as the second lens group 411. Exemplarily, the first lens group 405 and the second lens group 411 can be specifically but not limited to the models of Solebo LSM02 (-BB), LSM03 (-BB), LSM03-VIS, LSM04 (-BB) and LSM05 (-BB). The first lens group 405 is arranged in the reference optical path 415 and is arranged the same as the second lens group 411 in order to compensate for the dispersion caused by the second lens group 411 in the sample optical path 416. Among them, Figure 1 The first lens group 405 in FIG. 4 is for illustration only.

[0058] It should be noted that the first parabolic reflection collimator 403 and the first reflection mirror 406 do not produce dispersion, so the dispersion in the reference light path 415 can be appropriately eliminated; the second parabolic reflection collimator 407 and the scanning galvanometer 408 do not produce dispersion, so the dispersion in the sample light path 416 can be appropriately eliminated.

[0059] Specifically, the low-coherence broadband light emitted by the coherent light source 401 is divided into two beams after passing through the 2*2 fiber coupler 402, namely, the reference light and the sample light. The reference light is transmitted through the optical fiber in the reference light path 415 to the first parabolic reflection collimator 403. The first parabolic reflection collimator 403 transmits the light beam in the optical fiber to the air to form a collimated light beam. The collimated light beam passes through the adjustable aperture 404 and reaches the first lens group 405. The light output after the light beam passes through the first lens group 405 is then transmitted to the first reflector 406. The first reflector 406 6 reflects the reference light and makes it reflect back to the first parabolic reflection collimator 403 along the original optical path. The light beam output by the first parabolic reflection collimator 403 enters the optical fiber for transmission and reaches the 2*2 optical fiber coupler 402. Another beam of sample light is transmitted to the second parabolic reflection collimator 407 via the optical fiber in the sample optical path 416. The second parabolic reflection collimator 407 collimates the light beam to form a collimated light beam. The collimated light beam passes through the scanning galvanometer 408 and the focusing mechanical structure 417 and reaches the second lens group 411. The second lens group 411 The lens group 411 focuses the sample light onto the sample to be tested 412. At the same time, the backscattered light of the sample to be tested 412 is collected by the second lens group 411. The second lens group 411 reflects the collected backscattered light back to the second parabolic reflection collimator 407 along the original optical path. The light beam output by the second parabolic reflection collimator 407 enters the optical fiber for transmission. After reaching the 2*2 optical fiber coupler 402, in the 2*2 optical fiber coupler 402, when the optical path difference of the two light beams is within the coherence length of the light source, the backscattered light will be reflected by the backscattered light. The reference light emitted forms interference; the interference light beam is transmitted to the equal wave number spectrometer 413, and the equal wave number spectrometer 413 evenly distributes the interference light beam on the pixels of the linear array camera according to the equal wave number interval. The interference spectrum signal represents the reflectivity distribution of the sample at different depths, and converts the interference spectrum signal into an electrical signal, which is digitized and input and uploaded to the host computer 414. By performing a transverse scanning on the sample 412 to be tested, the three-dimensional tomographic image of the sample 412 to be tested can be reconstructed, thereby obtaining the structural tomographic image of the sample 412 to be tested.

[0060] Optional, continue to refer to Figure 2 The reference optical path 415 also includes: a slide rail assembly 17 and a drive assembly 14 arranged in the first shell 1, the first reflector 406 is located on the slide rail assembly 17, and the drive assembly 14 is used to drive the slide rail assembly 17 to move the first reflector 406 along the optical axis direction of the reference optical path 415; the drive assembly 14 is connected to the host computer 414.

[0061] Specifically, refer to Figure 2As shown, the reference optical path 415 includes a slide rail assembly 17 and a drive assembly 14 disposed in the first housing 1. The slide rail assembly 17 includes a slide rail end fixing mechanical structure 12 and a slide rail 13, and a slider (not shown in the figure). The slider can be fixedly connected to the first reflector 406, and the drive assembly 14 can be a motor to drive the slider to move on the slide rail 13, thereby driving the first reflector 406 to move along the slide rail 13. In other embodiments, the slide rail assembly 17 can also be a gear and rack transmission mode, wherein the rack is fixed in the slide rail 13, the gear is fixedly connected to the first reflector 406, and the drive assembly 14 drives the rack to rotate, so that the gear moves on the rack, thereby driving the first reflector 406 to move along the slide rail 13.

[0062] The mechanical structure 12 fixed at the end of the slide rail is used to prevent the first reflector 406 from sliding off the rail and causing abnormal imaging. The driving assembly 14 is used to drive the slide rail assembly 17 to move the first reflector 406 along the optical axis direction of the reference optical path 415, that is, to move forward and backward stably and quickly along the optical axis direction of the reference optical path 415 to focus the light beam for imaging. The structure is easy to install and simple to operate, and realizes the stable and rapid movement of the first reflector 406 along the optical axis direction of the reference optical path 415.

[0063] In addition, a first optical fiber connection port 11 is also provided on the first housing 1 for introducing the reference beam into the first parabolic reflection collimator 403 .

[0064] Optional, Figure 4 This is a schematic diagram of the mechanical structure of the reference optical path provided in the first embodiment of the present invention, referring to Figure 4 As shown, the reference optical path 415 also includes: a first collimator bracket 15 , the first collimator bracket 15 includes a first bottom plate 151 and a first side plate 152 , the first bottom plate 151 is fixed to the bottom plate of the first shell 1 , and the first side plate 152 is fixed to the first parabolic reflection collimator 403 .

[0065] Specifically, the first parabolic reflection collimator 403 in the reference optical path 415 includes a first collimator bracket 15, and the first collimator bracket 15 includes a first base plate 151 and a first side plate 152, wherein the first base plate 151 is fixed to the base plate of the first shell 1, and the first side plate 152 is fixed to the first parabolic reflection collimator 403, so as to be more convenient and quick when installing or disassembling the component.

[0066] The first collimator bracket 15 can be formed in one piece, such as an L-shaped piece. The first bottom plate 151 can be fixed to the bottom plate of the first housing 1 by bolts or bonding. A light hole can be set on the first side plate 152 to allow the collimated light beam of the first parabolic reflector collimator 403 to pass through.

[0067] Optional, reference Figure 4As shown, the reference optical path 415 also includes: a first lens group bracket 16, the first lens group bracket 16 includes a second bottom plate 161 and a second side plate 162, the second bottom plate 161 is fixed to the bottom plate of the first shell 1, and the second side plate 162 is fixed to the first lens group 405.

[0068] Specifically, the first lens group 405 in the reference optical path 415 includes a first lens group bracket 16, and the first lens group bracket 16 includes a second bottom plate 161 and a second side plate 162. The second bottom plate 161 is fixed to the bottom plate of the first housing 1, and the second side plate 162 is fixed to the first lens group 405, so that it is more convenient and quick to install or remove the component. Similarly, the first lens group bracket 16 can be a one-time formed L-shaped plate, and the second bottom plate 161 can be fixed to the bottom plate of the first housing 1 by bolts or bonding. A light hole can be set on the second side plate 162 to allow the collimated light beam of the first parabolic reflector collimator 403 to pass through and enter the first lens group 405.

[0069] The centers of the first parabolic reflective collimator 403, the first lens group 405 and the first reflector 406 are coaxial, and the central axes of the three are located on a horizontal straight line to reduce the aberration of the optical path. Figure 2 and Figure 4 As shown, the reference optical path 415 is fixed in the first housing 1 , and the first housing 1 is beneficial for protecting the entire reference optical path 415 .

[0070] It should be noted that the second parabolic reflection collimator 407 and the second lens group 411 in the sample optical path 416 have the same support structure as the first collimator support 15 and the first lens group support 16 included in the reference optical path 415 .

[0071] Optional, Figure 5 This is a schematic diagram of the mechanical structure of the scanning galvanometer provided in the first embodiment of the present invention, referring to Figure 5 As shown, the sample optical path 416 also includes: a scanning galvanometer bracket shell 3, the scanning galvanometer bracket shell 3 includes a bottom surface 31, a first side surface 32 and a third side surface 34 arranged parallel to each other, a second side surface 33 and a fourth side surface 35; a first galvanometer rotation assembly for driving the first galvanometer 409 to deflect is fixedly arranged on the first side surface 32, and a second galvanometer rotation assembly for driving the second galvanometer 410 to deflect is fixedly arranged on the adjacent second side surface 33, the rotation axis of the first galvanometer rotation assembly and the rotation axis of the second galvanometer rotation assembly are perpendicular to each other and are arranged at a preset distance in a direction perpendicular to the bottom surface; the third side surface 34 is provided with a mounting hole for mounting the second parabolic reflection collimator 407; the fourth side surface 35 is provided with a mounting hole for mounting a focusing mechanical structure 417, and the other end of the focusing mechanical structure 417 is fixedly connected to the second lens group 411.

[0072] Specifically, Figure 6 A schematic diagram of the structure of the propagation direction of the optical path in the scanning galvanometer provided in the first embodiment of the present invention, combined with Figure 5 and Figure 6 As shown, a galvanometer motor controller interface is provided on the first galvanometer 409 to control and adjust the angle of the first galvanometer 409, and a galvanometer motor controller interface is provided on the second galvanometer 410 to control and adjust the angle of the second galvanometer 410, so that the light beam can reach any position of the image plane, and the scanning galvanometer bracket shell 3 assembles the second parabolic reflection collimator 407, the second lens group 411 and the focusing mechanical structure 417 together, which is easy to install, compact in structure, and easy to carry, and the second shell 2 can protect the various components in the sample optical path 2.

[0073] Specifically, the sample light is transmitted to the second parabolic reflector collimator 407 via the optical fiber in the sample optical path 416. The second parabolic reflector collimator 407 forms the light beam into a collimated light beam. When the collimated light beam passes through the scanning galvanometer 408, the parallel emitted light beam passes through the first galvanometer 409 and deflects the light path by 90° to reach the second galvanometer 410. The second galvanometer 410 receives the light beam emitted by the first galvanometer 409, and after passing through the second galvanometer 410, the light beam is deflected by 90° again to transmit the light beam to the focusing mechanical structure 417. It should be noted that the rotation axis of the first galvanometer rotating assembly and the rotation axis of the second galvanometer rotating assembly are perpendicular to each other and are set at a preset distance in a direction perpendicular to the bottom surface. The preset distance is determined by the actual diameters of the first galvanometer 409 and the second galvanometer 410 to avoid collision between the two during rotation.

[0074] in, Figure 7 A schematic diagram of the structure of a second housing in a sample optical path provided in Embodiment 1 of the present invention; Figure 8 A schematic diagram of the structure of the sample optical path and the reference optical path provided in the first embodiment of the present invention; Figure 7 and Figure 8 As shown, the second housing 2 is also provided with a second optical fiber connection port 6 , a first galvanometer wire outlet 5 , a second galvanometer wire outlet 4 , and a through hole 7 for the sample light beam to pass through.

[0075] Optional, Fig. 9 This is a schematic diagram of the structure of the equal wave number spectrometer provided in the first embodiment of the present invention, referring to Fig. 9 As shown, the equal wave number spectrometer 413 includes: a diffraction grating 101 , an isosceles prism 102 , a focusing lens group 103 and an image acquisition unit 104 .

[0076] Specifically, the diffraction grating 101 is located in the optical path of the interference light beam transmission, and is used to form a diffraction light beam from the interference light beam; the isosceles prism 102 is located in the optical path of the diffraction light beam transmission, and is used to refract the diffraction light beam to form a refracted light beam; the focusing lens group 103 is located in the optical path of the refracted light beam transmission, and is used to focus the refracted light beam to form a focused light beam; the image acquisition unit 104 is located in the optical path of the focused light beam transmission, and is used to form spectral bands arranged at equal wave number intervals based on the focused light beam.

[0077] Specifically, the 2*2 fiber coupler 402 generates interference between the reflected reference light and the backscattered light reflected by the sample. After the interference signal corresponding to the interference light beam passes through the diffraction grating 101 and the isosceles prism 102 in sequence, the interference signal is split into a spectrum array arranged at equal wave number intervals, and then focused by the focusing lens group 103 onto the image acquisition unit 104 (linear array charge coupled device (CCD)); the image acquisition unit 104 converts the collected interference spectrum signal into an electrical signal, and inputs it into the computer hardware system after digitization. The interference spectrum signal represents the reflectivity distribution of the sample at different depths; after being processed by the demodulation circuit, it is finally collected by the acquisition card to the host computer 414, and the host computer system performs Fourier inverse transformation on the obtained interference spectrum data to obtain the one-dimensional depth information of the sample. On this basis, by scanning the sample horizontally, the three-dimensional tomography image of the sample 412 to be tested can be reconstructed, thereby obtaining the structural tomography of the sample 412 to be tested. It should be noted that the equal wave number spectrometer 413 performs light splitting by combining an isosceles prism 102 with a diffraction grating 101. The equal wave number spectrometer 413 can balance the dispersion in the optical path system and accurately distinguish the light spots of different wavelengths during the light transmission process, thereby avoiding the noise and dispersion introduced from the 2*2 fiber coupler 402 end. Therefore, it has the advantages of low dispersion, high signal-to-noise ratio, and high resolution.

[0078] Therefore, in the optical coherence tomography optical path structure, the second parabolic reflection collimator 407 and the scanning galvanometer 408 are arranged in the sample optical path 416 to eliminate the dispersion on the sample optical path 416. The first parabolic reflection collimator 403 and the first reflector 406 are arranged in the reference optical path 415 to eliminate the dispersion on the reference optical path 415, and the first lens group 405 is arranged in the reference optical path 415 to balance the dispersion caused by the second lens group 411 in the sample optical path 416. Finally, the interference beam is transmitted to the equal wave number spectrometer, and the equal wave number spectrometer splits the interference beam according to the equal wave number interval to the host computer, and the tomographic image of the sample is obtained through the algorithm processing of the host computer. The use of the equal wave number spectrometer can eliminate the dispersion of the imaging optical path, and further, the above optical coherence tomography optical path structure has less dispersion, which can solve the dispersion mismatch problem from the source.

[0079] Embodiment 2

[0080] Fig.10 Flow chart of the dispersion compensation method for optical coherence tomography optical path structure provided in the second embodiment of the present invention. Based on the optical coherence tomography optical path structure described in the first embodiment, in order to better implement the method, the sample to be measured is set as the second reflector, such as Fig.10 As shown, the dispersion compensation method includes:

[0081] S110. Control the first reflector to move at least one position along the optical axis of the reference light path, or control the second reflector to move at least one position along the optical axis of the sample light path, within the depth of field of the second lens group, to obtain at least one interference spectrum signal.

[0082] The depth of field is the distance range of the object in front of and behind the camera lens or other imager that can obtain a clear image. There is a certain length of space in front of the lens (before and after the focus adjustment). When the object is located in this space, its image on the film is located between the two diffusion circles before and after the focus. Interference is the phenomenon that two or more waves overlap in space and superimpose to form a new waveform.

[0083] Specifically, adjust the first reflector of the reference light path or the second reflector of the sample light path so that the first reflector is near zero optical path difference. Within the depth of field of the second lens group, in the reference light path, the first reflector is moved by a driving component on the slide rail along the direction of the optical axis of the reference light path, or in the sample light path, the second reflector is moved by a position along the direction of the optical axis of the sample light path. The reference light and the sample light can interfere in the 2*2 fiber coupler to generate an interference signal. The interference signal will generate an interference spectrum signal in the equal wave number spectrometer to obtain the interference spectrum signal. It should be noted that one position can be moved to obtain one interference spectrum signal, and multiple positions can be moved to obtain multiple interference spectrum signals.

[0084] The obtained interference spectrum signal can be expressed as:

[0085]

[0086] Where n represents the number of depths away from the zero optical path difference position, that is, the number of depths at different depths of field; I0(k) is the autocorrelation term in the interference spectrum signal, S(k) is the spectral density function of the light source, and R sn is the reflectivity of the Nth reflective surface of the sample to be tested, R R is the reflectivity of the reference mirror, k is the wave number, represents the dispersion phase introduced into the system; is the phase difference between the Nth reflection surface of the sample to be tested and the reflection surface of the reference mirror, z nis the phase difference between the Nth reflection surface of the sample to be tested and the reflection surface of the reference mirror, and I(k) is the obtained interference spectrum signal.

[0087] S120, performing fast Fourier transform on the interference spectrum signal to obtain a complex frequency domain signal; and obtaining a positive amplitude signal based on the complex frequency domain signal.

[0088] Among them, Fast Fourier Transform (FFT) is a method for quickly calculating the discrete Fourier transform or its inverse transform of a sequence; the complex frequency domain signal is a three-dimensional coordinate signal obtained after the time domain signal is Fourier transformed; the amplitude signal is a signal when the physical quantity of the vibration may reach the maximum value.

[0089] Specifically, the collected interference spectrum signal is subjected to fast Fourier transform to obtain a complex frequency domain signal I(z), and a bandpass filter is used to extract the positive amplitude signal A(z) of the complex frequency domain signal, which can be specifically expressed as:

[0090]

[0091] Among them, Γ(z) is the Fourier transform result of S(k), δ N is the Dirac equation. The positive amplitude signal A(z) extracted from the complex frequency domain signal can be expressed as:

[0092] S130, performing inverse fast Fourier transform on the positive amplitude signal to obtain a complex signal.

[0093] Specifically, after performing inverse fast Fourier transform on the positive amplitude signal A(z), a complex signal A(k) can be obtained, which can be specifically expressed as:

[0094] S140, extracting phase information of the complex signal, and unwrapping the phase information to obtain a phase signal after unwrapping.

[0095] Among them, phase information is the information that describes the change of signal waveform. To obtain the deformation data of the surface of the sample to be tested, it is necessary to extract the phase information from the speckle fringes, and establish a quantitative relationship between phase and light intensity through an inverse tangent function. In the process of inverse solving the trigonometric function, wrapping is the constraint phenomenon that the phase difference is constrained between "-π, +π". Unwrapping phase is the process of unfolding the phase information wrapped between "-π, +π" and restoring it to continuously changing phase data.

[0096] Specifically, after obtaining the complex signal A(k), the phase information of the complex signal is extracted. The extracted phase information can be expressed as: The phase information is unwrapped, the wrapped phase information is unfolded, and restored to continuously changing phase data to obtain the phase signal after unwrapping, which can be expressed as:

[0097] S150, performing a third-order linear fitting on the phase signal after the phase wrapping is solved to obtain a nonlinear phase term.

[0098] Among them, the third-order linear fitting is to fit the existing information into a third-order continuous curve through mathematical methods, and the nonlinear phase term is a phase term with an independent variable higher than the first order.

[0099] Specifically, the phase signal after phase wrapping is Perform a third-order linear fit and obtain the fitting equation Extract the coefficients a, b, c, d in the third-order linear fitting equation. After obtaining the third-order coefficients a, b, c, d, subtract the linear term φ from the unwrapped phase signal. l =cx+d, we can get the nonlinear phase term The specific formula can be expressed as:

[0100]

[0101] S160, establishing a dispersion model of the dispersion compensating mirror, and obtaining at least one set of thickness and glass material parameters of the dispersion compensating mirror based on the dispersion model and the nonlinear phase term.

[0102] Optionally, establishing a dispersion model of the dispersion compensating mirror, and obtaining at least one set of thickness and glass material parameters of the dispersion compensating mirror based on the dispersion model and the nonlinear phase term includes:

[0103] The dispersion model is:

[0104] Where d is the thickness of the dispersion compensation mirror; λ is the wavelength, and B1, B2, B3, C1, C2, C3 are the Sellmeier coefficients of any glass material in the glass library; is the dispersion phase of the dispersion compensating mirror; the nonlinear phase term is made the same as the dispersion phase to obtain at least one set of thickness and glass material parameters of the dispersion compensating mirror.

[0105] Among them, the dispersion compensation mirror is a compensation mirror with certain thickness and glass material parameters set in the light path to eliminate dispersion during the propagation of the light path; the dispersion model is a model established to eliminate dispersion; the Sellmeier coefficient is an empirical formula that describes the change of the refractive index of the medium with the wavelength, which is used to describe the speed and refractive index of light propagating in the medium.

[0106] Specifically, the glass material parameters B, C and thickness d of the optical glass are used as variables to establish the dispersion model of the optical glass. Right now

[0107] Where d is the thickness of the dispersion compensation mirror; λ is the wavelength, and B1, B2, B3, C1, C2, C3 are the Sellmeier coefficients of any glass material in the glass library; is the dispersion phase of the dispersion compensation mirror. Based on the dispersion model, the Sellmeier coefficient of any glass material in the glass library is obtained to obtain the thickness and material parameters of the glass material. The thickness and material parameters of the glass material are iteratively calculated in the dispersion model by the least squares method. When the calculated dispersion phase With the nonlinear phase term When the same, The thickness and glass material parameters of the group of glass materials are recorded as the thickness and glass material parameters of the dispersion compensation mirror that can eliminate the dispersion.

[0108] Optionally, if multiple groups of thickness and glass material parameters of the dispersion compensating mirror are obtained, it also includes: placing the dispersion compensating mirror formed based on the i-th group of thickness and glass material parameters in the reference light path or the sample light path; i>1; obtaining multiple interference spectrum signals, and calculating the longitudinal resolution of the multiple interference spectrum signals; obtaining a first number in which the difference between the longitudinal resolution of the interference spectrum signal and the longitudinal resolution of the coherent light source is within a preset range; looping in sequence to screen out the thickness and glass material parameters corresponding to the maximum value of the first number; and using the dispersion compensating mirror formed by the thickness and glass material parameters as the final dispersion compensating mirror.

[0109] Among them, the longitudinal resolution can be understood as the ability to distinguish the two closest targets (objects) in the longitudinal direction (ultrasonic wave propagation direction).

[0110] Specifically, the thickness of the glass material and the glass material parameters obtained by the above calculation are processed into a glass flat sheet, which is set between the first lens group and the first reflector in the reference light path or between the second lens group and the second reflector in the sample light path to eliminate a small amount of dispersion in the light path; in order to completely eliminate the dispersion, it is usually necessary to perform multiple calculations and select the glass thickness and glass material parameters. Therefore, within the depth of field of the second lens group, the position of the first reflector or the position of the second reflector is moved to obtain multiple interference spectrum signals, and S110-S120 are repeated to obtain positive amplitude signals, and the longitudinal resolutions of the multiple interference spectrum signals can be calculated through the positive amplitude signals; and according to the theoretical longitudinal resolution of the coherent light source itself, the longitudinal resolutions of the calculated multiple interference spectrum signals are calculated, and the obtained multiple difference data are all within the preset range of the first quantity, and the cycle is repeated in sequence to calculate multiple groups of first quantities whose differences are all within the preset range, and the multiple groups of first quantities are screened to obtain the maximum value of the first quantity, and the glass thickness and glass material parameter corresponding to the maximum value are considered to be the glass thickness and glass material parameter values ​​that can completely eliminate the dispersion.

[0111] In one example, after obtaining a set of thickness and glass material parameters, the glass sheet corresponding to the set of parameters can be placed in a reference optical path or a sample optical path, and then multiple interference spectrum signals are obtained again. If the longitudinal resolution of each interference spectrum signal is the same as the theoretical longitudinal resolution of the coherent light source itself, then the glass sheet corresponding to the set of thickness and glass material parameters is the final compensation mirror. If it is not possible to achieve that the longitudinal resolution of each interference spectrum signal is the same as the theoretical longitudinal resolution of the coherent light source itself, then the glass sheet corresponding to the set of thickness and glass material parameters with the most interference spectrum signals that achieve the same theoretical longitudinal resolution as the coherent light source itself is selected, which is the final compensation mirror.

[0112] Optionally, calculating the longitudinal resolution of multiple interference spectrum signals includes: controlling the first reflector to move at least one position along the optical axis of the reference light path, or controlling the second reflector to move at least one position along the optical axis of the sample light path, within the depth of field of the second lens group, to obtain at least one interference spectrum signal; performing fast Fourier transform on the interference spectrum signal to obtain a complex frequency domain signal; obtaining a positive amplitude signal based on the complex frequency domain signal; and obtaining the longitudinal resolution of the interference spectrum signal based on the positive amplitude signal.

[0113] Specifically, within the depth of field of the second lens group, in the reference light path, the first reflector is moved on the slide rail by a position along the direction of the optical axis of the reference light path, or in the sample light path, the second reflector is moved by a position along the direction of the optical axis of the sample light path, and the reference light and the sample light can interfere in the 2*2 fiber coupler to generate an interference signal, and the interference signal will generate an interference spectrum signal in the equal wave number spectrometer, and the interference spectrum signal is obtained. The obtained interference spectrum signal executes S110-S120 to obtain a positive amplitude signal A(z), that is:

[0114]

[0115] For the positive amplitude signal A(z), the longitudinal resolution of the interference spectrum signal is calculated. When z=z n When , the half-width Δ in the interference spectrum signal, that is, the size of the longitudinal resolution, is calculated.

[0116] In the embodiment of the present invention, by controlling the first reflector within the depth of field of the second lens group, the reflector is moved at least one position along the optical axis of the reference optical path, or the second reflector is moved at least one position along the optical axis of the sample optical path, at least one interference spectrum signal is obtained; the interference spectrum signal is subjected to fast Fourier transform to obtain a complex frequency domain signal; a positive amplitude signal is obtained based on the complex frequency domain signal; a complex signal is obtained by fast Fourier inverse transforming the positive amplitude signal; the phase information of the complex signal is extracted, and the phase information is phase-unwrapped to obtain a phase signal after the phase is unwrapped; a third-order linear fitting is performed on the phase signal after the phase is unwrapped to obtain a nonlinear phase term; a dispersion model of the dispersion compensation mirror is established, and at least one set of thickness and glass material parameters of the dispersion compensation mirror is obtained based on the dispersion model and the nonlinear phase term; the longitudinal resolution is calculated by the positive amplitude signal, and the glass thickness and material parameters corresponding to the maximum value of the first number of differences with the longitudinal resolution of the coherent light source are used as the final dispersion compensation mirror. Through the above method, a dispersion compensation mirror with a certain thickness and material parameters is obtained and arranged in the reference optical path or the sample optical path, and the algorithm is simple, the cost is low, it is convenient and fast, and the imaging speed is fast.

[0117] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0118] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An optical coherence tomography optical path structure, characterized in that: include: Coherent light source, 2*2 fiber coupler, reference optical path, sample optical path, equal wave number spectrometer and host computer; Wherein, the first end of the 2*2 optical fiber coupler is connected to the coherent light source, the second end is connected to the reference optical path, the third end is connected to the sample optical path, the fourth end is connected to the equal wave number spectrometer, and the equal wave number spectrometer is connected to the host computer; The reference optical path comprises: a first housing, and a first parabolic reflection collimator, an aperture, a first lens group and a first reflection mirror located in the first housing; the first reflection mirror can move along the optical axis direction of the reference optical path; The sample optical path includes: a second shell, and a second parabolic reflection collimator, a scanning galvanometer, a focusing mechanical structure and a second lens group located in the second shell; the scanning galvanometer is connected to the host computer, and the first lens group is the same as the second lens group.

2. The optical coherence tomography optical path structure according to claim 1, characterized in that: The reference optical path also includes: a slide rail assembly and a drive assembly arranged in the first shell, the first reflector is located on the slide rail assembly, and the drive assembly is used to drive the slide rail assembly to move the first reflector along the optical axis direction of the reference optical path; the drive assembly is connected to the host computer.

3. The optical coherence tomography optical path structure according to claim 1, characterized in that: The reference optical path further includes: a first collimator bracket, the first collimator bracket includes a first bottom plate and a first side plate, the first bottom plate is fixed to the bottom plate of the first shell, and the first side plate is fixed to the first parabolic reflection collimator.

4. The optical coherence tomography optical path structure according to claim 1, characterized in that: The reference optical path also includes: a first lens group bracket, the first lens group bracket includes a second bottom plate and a second side plate, the second bottom plate is fixed to the bottom plate of the first shell, and the second side plate is fixed to the first lens group.

5. The optical coherence tomography optical path structure according to claim 1, characterized in that: The sample optical path further comprises: a scanning galvanometer support housing, wherein the scanning galvanometer support housing comprises a bottom surface, a first side surface and a third side surface, a second side surface and a fourth side surface which are arranged parallel to each other; A first galvanometer rotating assembly for driving the first galvanometer to deflect is fixedly disposed on the first side surface, and a second galvanometer rotating assembly for driving the second galvanometer to deflect is fixedly disposed on the adjacent second side surface, wherein the rotation axis of the first galvanometer rotating assembly and the rotation axis of the second galvanometer rotating assembly are perpendicular to each other and are arranged at a preset distance in a direction perpendicular to the bottom surface; The third side surface is provided with a mounting hole for mounting the second parabolic reflective collimator; The fourth side surface is provided with a mounting hole for mounting the focusing mechanical structure, and the other end of the focusing mechanical structure is fixedly connected to the second lens group.

6. The optical coherence tomography optical path structure according to claim 1, characterized in that: The equal wave number spectrometer comprises: a diffraction grating, an isosceles prism, a focusing lens group and an image acquisition unit.

7. A method for compensating optical path structure dispersion in optical coherence tomography, characterized in that: The optical coherence tomography optical path structure according to any one of claims 1 to 6 is implemented, wherein the sample to be measured is a second reflector, and the dispersion compensation method comprises: Controlling the first reflector to move at least one position along the optical axis of the reference optical path, or controlling the second reflector to move at least one position along the optical axis of the sample optical path within the depth of field of the second lens group to obtain at least one interference spectrum signal; Performing fast Fourier transform on the interference spectrum signal to obtain a complex frequency domain signal; and obtaining a positive amplitude signal based on the complex frequency domain signal; Performing an inverse fast Fourier transform on the positive amplitude signal to obtain a complex signal; Extracting phase information of the complex signal, and un-phase-wrapping the phase information to obtain a phase signal after phase-wrapping; Performing a third-order linear fit on the phase signal after the phase wrapping is solved to obtain a nonlinear phase term; A dispersion model of the dispersion compensating mirror is established, and at least one set of thickness and glass material parameters of the dispersion compensating mirror is obtained based on the dispersion model and the nonlinear phase term.

8. The method for optical coherence tomography optical path structure dispersion compensation according to claim 7, characterized in that: The step of establishing a dispersion model of the dispersion compensating mirror and obtaining at least one set of thickness and glass material parameters of the dispersion compensating mirror based on the dispersion model and the nonlinear phase term comprises: The dispersion model is: Where d is the thickness of the dispersion compensation mirror; λ is the wavelength, and B1, B2, B3, C1, C2, C3 are the Sellmeier coefficients of any glass material in the glass library; is the dispersion phase of the dispersion compensation mirror; The nonlinear phase term is made equal to the dispersion phase to obtain at least one set of thickness and glass material parameters of the dispersion compensation mirror.

9. The optical coherence tomography optical path structure dispersion compensation method according to claim 7 or 8, characterized in that: If multiple sets of thickness and glass material parameters of the dispersion compensation mirror are obtained, it also includes: placing a dispersion compensation mirror formed based on the thickness and the glass material parameters of the i-th group in the reference optical path or the sample optical path; i>1; Acquire a plurality of interference spectrum signals, and calculate the longitudinal resolutions of the plurality of interference spectrum signals; obtain a first quantity in which the difference between the longitudinal resolution of the interference spectrum signal and the longitudinal resolution of the coherent light source is within a preset range; The thickness and glass material parameters corresponding to the maximum value of the first number are screened out in a cycle; and the dispersion compensating mirror formed by the thickness and the glass material parameters is used as the final dispersion compensating mirror.

10. The optical coherence tomography optical path structure dispersion compensation method according to claim 7, characterized in that: The phase signal after the phase wrapping is subjected to a third-order linear fitting, and the nonlinear phase term obtained includes: A third-order linear fitting is performed on the phase signal after the phase wrapping is solved, and the linear phase is subtracted from the original phase to obtain a nonlinear phase term.

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