Optical coherence tomography light path structure and dispersion compensation method thereof

Abstract

The application discloses an optical coherence tomography light 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-wavenumber spectrometer and an upper computer. Low-coherence broadband light emitted by the coherent light source is divided into reference light and sample light after the 2*2 optical fiber coupler, and the two are transmitted in the reference light path and the sample light path in turn, and after being back-reflected by a sample and a reference mirror, the two are back-reflected to the 2*2 optical fiber coupler according to the original light path and interference is generated. The interference light beam is transmitted to the equal-wavenumber spectrometer, which splits the interference light beam to the upper computer according to equal-wavenumber intervals, and the tomographic image of the sample is obtained through algorithm processing of the upper computer. Through the above structure, the existing dispersion mismatch problem is solved from the source, most of the dispersion generated by the light path is solved, and the remaining dispersion is eliminated by adding a dispersion compensation mirror made of optical glass material with a certain thickness in the light path through algorithm calculation. The algorithm is simple, convenient and fast, and the imaging speed is fast.

Description

TECHNICAL FIELD

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

[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 actual application, when the actual optical propagation paths of the reference light and the sample light are not completely consistent, the wideband light will cause dispersion mismatch problems when propagating in the optical fiber, the optical lens group and the sample inside, 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] The existing dispersion compensation methods are divided into physical (hardware) compensation and numerical (algorithm) compensation. Hardware compensation is to restore the propagation path in the sample arm by adding appropriate optical compensation devices in the reference arm light path. However, due to the low cost of the material and the difficulty in testing and calculating the thickness of the optical compensation device, the effect of hardware dispersion compensation is greatly reduced. Algorithm compensation is to offset the dispersion by using algorithms. Common methods include iterative algorithms and convolution methods. Although the two methods are effective, the complex iterative process and large amount of calculation reduce the imaging speed and affect the real-time performance of the imaging, thereby increasing the process conversion difficulty of the commercial OCT, and thus limiting the application of algorithm compensation in the field of commercial OCT. SUMMARY

[0004] The present application provides an optical coherence tomography light 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 in cost, convenient and fast, and fast in imaging speed.

[0005] In a first aspect, the present application provides an optical coherence tomography light path structure, comprising: a coherent light source, a 2*2 optical fiber coupler, a reference light path, a sample light path, an equal-wavenumber spectrometer and an upper computer;

[0006] The first end of the 2*2 optical fiber coupler is connected with the coherent light source, the second end is connected with the reference light path, the third end is connected with the sample light path, and the fourth end is connected with the equal-wavenumber spectrometer. The equal-wavenumber spectrometer is connected with the upper computer;

[0007] The reference light path comprises: a first shell, and a first parabolic reflecting collimator, an aperture, a first lens group and a first mirror located in the first shell; the first mirror is movable along the optical axis direction of the reference light path;

[0008] The sample light path comprises: a second shell, and a second parabolic reflective collimator, a scanning galvanometer, a focusing mechanical structure and a second lens group located in the second shell; the scanning galvanometer is connected with the upper computer, and the first lens group is identical with the second lens group.

[0009] Optionally, the reference light path further comprises: a sliding rail assembly and a driving assembly arranged in the first shell, the first mirror is located on the sliding rail assembly, and the driving assembly is used to drive the sliding rail assembly to move the first mirror along the optical axis direction of the reference light path; the driving assembly is connected with the upper computer.

[0010] Optionally, the reference light path further comprises: a first collimator support, the first collimator support comprises a first bottom plate and a first side plate, the first bottom plate is fixed with the bottom plate of the first shell, and the first side plate is fixed with the first parabolic reflective collimator.

[0011] Optionally, the reference light path further comprises: a first lens group support, the first lens group support comprises a second bottom plate and a second side plate, the second bottom plate is fixed with the bottom plate of the first shell, and the second side plate is fixed with the first lens group.

[0012] Optionally, the sample light path further comprises: a scanning galvanometer support shell, the scanning galvanometer support shell comprises a bottom surface, first and third side surfaces arranged in parallel with each other, and second and fourth side surfaces.

[0013] A first galvanometer rotation assembly for driving the first galvanometer to deflect is fixedly arranged on the first side surface, a second galvanometer rotation assembly for driving the second galvanometer to deflect is fixedly arranged on the adjacent second side surface, 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.

[0014] The third side surface is provided with a mounting hole for mounting the 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 with the second lens group.

[0016] Optionally, the equal-wavenumber spectrometer comprises: a diffraction grating, an isosceles prism, a focusing lens group and an image acquisition unit.

[0017] In a second aspect, an optical coherence tomography light path structure dispersion compensation method is provided, which is based on the optical coherence tomography light path structure according to any one of the embodiments of the present application, wherein the sample to be measured is a second mirror, and the dispersion compensation method comprises:

[0018] In a depth of field range of the second lens group, at least one of the following is performed: moving the first mirror along an optical axis of the reference light path by at least one position, or moving the second mirror along an optical axis of the sample light path by at least one position, 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; and obtaining a positive amplitude signal based on the complex frequency domain signal;

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

[0021] Extracting phase information of the complex signal, and performing phase unwrapping on the phase information to obtain an unwrapped phase signal;

[0022] Performing third-order linear fitting on the unwrapped phase signal to obtain a nonlinear phase term;

[0023] Establishing a dispersion model of the dispersion compensation mirror, and obtaining at least one set of thickness and glass material parameters of the dispersion compensation mirror based on the dispersion model and the nonlinear phase term.

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

[0025] The dispersion model is:

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

[0027] The nonlinear phase term is the same as the dispersion phase, to obtain the 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 comprises:

[0029] Placing the dispersion compensation mirror formed based on the i-th set of thickness and glass material parameters in the reference light path or the sample light path; i>1;

[0030] Obtaining multiple interference spectrum signals, and calculating a longitudinal resolution of the multiple interference spectrum signals; obtaining a first number of interference spectrum signals whose difference between the longitudinal resolution and the longitudinal resolution of the coherent light source is within a preset range;

[0031] Cyclically selecting the thickness and the glass material parameters corresponding to the maximum value of the first number, and forming a dispersion compensation mirror based on the thickness and the glass material parameters as the final dispersion compensation mirror.

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

[0033] Within the depth of field range of the second lens group, at least one position of the first mirror along the optical axis of the reference light path is controlled to move, or at least one position of the second mirror along the optical axis of the sample light path is controlled to move, to obtain at least one interference spectrum signal;

[0034] The interference spectrum signal is subjected to a fast Fourier transform to obtain a complex frequency domain signal; and a positive amplitude signal is obtained 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 scheme of the embodiment of the present application provides an optical coherence tomography light path structure and a dispersion compensation method thereof, and 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-wavenumber spectrometer and an upper computer; wherein 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 transmitted in the reference light path and the sample light path in turn, and finally the two beams of light are back-reflected to the 2*2 optical fiber coupler according to the original light path and interference is generated, the interference light beam is transmitted to the equal-wavenumber spectrometer, the equal-wavenumber spectrometer splits the interference light beam to the upper computer according to equal-wavenumber intervals, and a tomographic image of the sample is obtained through processing of the upper computer. Through the above light path structure, most of the dispersion generated by the light path can be solved, and in combination with the dispersion compensation method, a dispersion compensation mirror obtained by adapting the dispersion compensation method in the light path is used to eliminate, and then the problems of existing dispersion mismatch, low resolution and complex algorithm are solved from the source.

[0037] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating laborious work.

[0039] Figure 1 The structural schematic diagram of the optical coherence tomography light path structure provided for the first embodiment of the present application;

[0040] Figure 2 The structural schematic diagram of the reference light path provided for the first embodiment of the present application;

[0041] Figure 3 A structure schematic diagram of a sample optical path provided for the embodiment one of the present application is shown in FIG. 1.

[0042] Figure 4 A structure schematic diagram of a reference optical path mechanical structure provided for the embodiment one of the present application is shown in FIG. 2.

[0043] Figure 5 A structure schematic diagram of a scanning galvanometer mechanical structure provided for the embodiment one of the present application is shown in FIG. 3.

[0044] Figure 6 A structure schematic diagram of a propagation direction of the optical path in the scanning galvanometer provided for the embodiment one of the present application is shown in FIG. 4.

[0045] Figure 7 A structure schematic diagram of a second housing in the sample optical path provided for the embodiment one of the present application is shown in FIG. 5.

[0046] Figure 8 A structure schematic diagram of the sample optical path and the reference optical path provided for the embodiment one of the present application is shown in FIG. 6.

[0047] Figure 9 A structure schematic diagram of the equal-wavenumber spectrometer provided for the embodiment one of the present application is shown in FIG. 7.

[0048] Figure 10 A flow chart of the optical coherence tomography optical path structure dispersion compensation method provided for the embodiment two of the present application is shown in FIG. 8. DETAILED DESCRIPTION

[0049] In order to make the personnel in the technical field better understand the present application scheme, the technical scheme in the embodiment of the present application will be described clearly and completely in the following by combining the drawings in the embodiment of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by the person of ordinary skill in the art without making creative labor should belong to the protection scope of the present application.

[0050] It should be noted that the terms "first", "second", etc. in the description 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 numbers 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 clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0051] Example 1

[0052] Figure 1 This is a schematic diagram of the optical coherence tomography optical path structure provided in the first embodiment of the present invention. Figure 2 This is 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 Example 1 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 wavenumber 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] The coherent light source 401 can be a low-coherence SLD light source, an ultra-continuum spectrum light source, etc., for emitting low-coherence broadband light. The 2*2 optical fiber coupler 402 has a first end connected to the coherent light source 401, a second end connected to the reference light path 415, a third end connected to the sample light path 416, and a fourth end connected to the equal-wavenumber spectrometer 413, for realizing the connection, distribution, and debugging of electrical signals between different optical fibers. The tail fiber optical path lengths of the four output ends of the 2*2 optical fiber coupler 402 need to be consistent, which is used to divide the light source beam into two beams of light for transmission to the reference light path and the sample light path, respectively. The reference light path 415 is used for transmitting the reference light transmitted by the 2*2 optical fiber coupler 402 in the reference light path, and the sample light path 416 is used for transmitting the sample light transmitted by the 2*2 optical fiber coupler 402 in the sample light path. The equal-wavenumber spectrometer 413 is used for uniformly distributing the interference spectrum according to equal-wavenumber intervals on the pixels of the line array camera. The host computer 414 is connected to the equal-wavenumber spectrometer 413, for displaying the tomographic image of the sample to be measured 412.

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

[0056] The scanning galvanometer 408 in the sample light 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 be scanned to any position in the image plane, and thus the sample at each position can be detected. In addition, the sample light beam can 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 in the sample light path 416 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, and the spot size distortion is very small. By changing the incident angle, the focal spot can be scanned in the entire field of view image plane. The f-theta distortion is small, and a geometrically corrected scanning image is generated, without the need for a large amount of post-image processing. The telecentric scanning lens light path can also maximize the entry of light (signal) scattered or emitted by the sample into the detection system. 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 entire scanning area of the sample is also almost unchanged.

[0057] The first lens group 405 is the same as the second lens group 411. For example, the first lens group 405 and the second lens group 411 can be, but are not limited to, models such as LSM02(-BB), LSM03(-BB), LSM03-VIS, LSM04(-BB), and LSM05(-BB). The first lens group 405 is arranged in the reference light path 415 and is the same as the second lens group 411, which is arranged to compensate for the dispersion caused by the second lens group 411 in the sample light path 416. Among them, Figure 1 The first lens group 405 in the above is only for illustration.

[0058] It should be noted that the first parabolic reflective collimator 403 and the first mirror 406 do not produce dispersion, which can appropriately eliminate the dispersion in the reference light path 415; the second parabolic reflective 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, which are the reference light and the sample light respectively. The reference light is transmitted to the first parabolic reflective collimator 403 through the optical fiber in the reference light path 415. The first parabolic reflective 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 diaphragm 404 and reaches the first lens group 405. The light output after the light beam passes through the first lens group 405 is transmitted to the first mirror 406. The first mirror 406 reflects the reference light to make it back to the first parabolic reflective collimator 403 along the original light path. The light beam output by the first parabolic reflective collimator 403 enters the optical fiber for transmission and reaches the 2*2 fiber coupler 402. The other beam of sample light is transmitted to the second parabolic reflective collimator 407 through the optical fiber in the sample light path 416. The second parabolic reflective 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 focuses the sample light on the sample to be measured 412. At the same time, the backscattered light of the sample to be measured 412 is collected by the second lens group 411. The second lens group 411 reflects the collected backscattered light back to the second parabolic reflective collimator 407 along the original light path. The light beam output by the second parabolic reflective collimator 407 enters the optical fiber for transmission and reaches the 2*2 fiber coupler 402. In the 2*2 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 interfere with the reflected reference light. The interference light beam is transmitted to the equal-wavenumber spectrometer 413. The equal-wavenumber spectrometer 413 uniformly distributes the interference light beam on the pixels of the line array camera according to equal-wavenumber intervals. The interference spectrum signal represents the reflectivity distribution of different depths of the sample. The interference spectrum signal is converted into an electrical signal, which is digitized and input and uploaded to the upper computer 414. By performing lateral scanning on the sample to be measured 412, the three-dimensional tomographic image of the sample to be measured 412 can be reconstructed, and thus the structural tomographic image of the sample to be measured 412 can be obtained.

[0060] Optionally, with reference to Figure 2 , the reference light path 415 further comprises a slide rail assembly 17 and a driving assembly 14 arranged in the first housing 1. The first mirror 406 is located on the slide rail assembly 17, and the driving assembly 14 is used to drive the slide rail assembly 17 to move the first mirror 406 along the optical axis direction of the reference light path 415. The driving assembly 14 is connected with the upper computer 414.

[0061] Specifically, with reference to Figure 2As shown, the reference light path 415 comprises the slide rail assembly 17 and the driving assembly 14 arranged in the first housing 1. The slide rail assembly 17 comprises the slide rail end fixed mechanical structure 12 and the slide rail 13, and a slide block (not shown in the figure). The slide block can be fixedly connected with the first mirror 406, and the driving assembly 14 can be a motor to drive the slide block to move on the slide rail 13, so as to drive the first mirror 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 with the first mirror 406, and the driving assembly 14 drives the rack to rotate, so that the gear moves on the rack, thereby driving the first mirror 406 to move along the slide rail 13.

[0062] The slide rail end fixed mechanical structure 12 is used to prevent the first mirror 406 from sliding out of the track and causing derailment, so as to avoid abnormal imaging. The driving assembly 14 is used to drive the slide rail assembly 17, so that the first mirror 406 moves along the optical axis direction of the reference light path 415, i.e. stably and quickly moves forward and backward along the optical axis direction of the reference light path 415, so as to focus the light beam. The structure is convenient to install and easy to operate, and realizes the stable and quick movement of the first mirror 406 along the optical axis direction of the reference light path 415.

[0063] In addition, the first optical fiber connection port 11 is arranged on the first housing 1, which is used to guide the reference light beam into the first parabolic reflective collimator 403.

[0064] Optionally, Figure 4 The structure of the reference light path mechanical structure provided by the embodiment one of the present application is shown in the figure, and the reference Figure 4 As shown, the reference light path 415 further comprises a first collimator support 15, and the first collimator support 15 comprises a first bottom plate 151 and a first side plate 152. The first bottom plate 151 is fixed with the bottom plate of the first housing 1, and the first side plate 152 is fixed with the first parabolic reflective collimator 403.

[0065] Specifically, the first parabolic reflective collimator 403 in the reference light path 415 comprises the first collimator support 15, and the first collimator support 15 comprises the first bottom plate 151 and the first side plate 152. The first bottom plate 151 is fixed with the bottom plate of the first housing 1, and the first side plate 152 is fixed with the first parabolic reflective collimator 403, so as to be more convenient and fast when installing or dismounting the component.

[0066] The first collimator support 15 can be formed at one time, such as an L-shaped piece. The first bottom plate 151 can be fixed with the bottom plate of the first housing 1 by means of bolts or adhesion. The first side plate 152 can be provided with a light passing hole, so that the collimated light beam of the first parabolic reflective collimator 403 can pass through.

[0067] Optionally, the reference Figure 4As shown, the reference light path 415 further comprises a first lens group support 16, the first lens group support 16 comprises a second bottom plate 161 and a second side plate 162, the second bottom plate 161 is fixed with the bottom plate of the first shell 1, and the second side plate 162 is fixed with the first lens group 405.

[0068] Specifically, the first lens group 405 in the reference light path 415 comprises a first lens group support 16, the first lens group support 16 comprises a second bottom plate 161 and a second side plate 162, the second bottom plate 161 is fixed with the bottom plate of the first shell 1, and the second side plate 162 is fixed with the first lens group 405, which is more convenient and fast when installing or dismounting the component. Similarly, the first lens group support 16 can be a one-time molded L-shaped plate, and the second bottom plate 161 can be fixed with the bottom plate of the first shell 1 by bolts or adhesion. A light passing hole can be provided on the second side plate 162 to allow the collimated light beam of the first parabolic reflector 403 to pass through and enter the first lens group 405.

[0069] The centers of the first parabolic reflector 403, the first lens group 405 and the first mirror 406 are coaxial, and the center axes of the three are located on a horizontal straight line to reduce the aberration of the light path. Figure 2 And Figure 4 As shown, the reference light path 415 is fixed in the first shell 1, and the first shell 1 is beneficial to protect the entire reference light path 415.

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

[0071] Optionally, Figure 5 The structure schematic diagram of the scanning galvanometer mechanical structure provided for the first embodiment of the present application is shown in Figure 5 As shown, the sample light path 416 further comprises a scanning galvanometer support shell 3, the scanning galvanometer support shell 3 comprises a bottom surface 31, first and third side surfaces 32 and 34 which are arranged parallel to each other, a second side surface 33 and a fourth side surface 35; the first side surface 32 is fixedly provided with a first galvanometer rotating assembly for driving the first galvanometer 409 to deflect, the adjacent second side surface 33 is fixedly provided with a second galvanometer rotating assembly for driving the second galvanometer 410 to deflect, the rotating shaft of the first galvanometer rotating assembly and the rotating shaft of the second galvanometer rotating assembly are perpendicular to each other and are arranged at a predetermined 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 reflector 407; the fourth side surface 35 is provided with a mounting hole for mounting the focusing mechanical structure 417, and the other end of the focusing mechanical structure 417 is fixedly connected with the second lens group 411.

[0072] Specifically,Figure 6 A structure diagram of a light path provided by the embodiment one of the present application in a propagation direction of a scanning galvanometer is shown in FIG. 4. Figure 5 And Figure 6 As shown in FIG. 4, a galvanometer motor controller interface is arranged on the first galvanometer 409 to control the angle of the first galvanometer 409, and a galvanometer motor controller interface is arranged on the second galvanometer 410 to control the angle of the second galvanometer 410, so that the light beam can reach any position of the image plane. The second parabolic reflector 407, the second lens group 411 and the focusing mechanical structure 417 are assembled together by the scanning galvanometer support shell 3, which is convenient to install, compact in structure, convenient to carry, and the second shell 2 can protect each component in the sample light path 2.

[0073] Specifically, the sample light is transmitted to the second parabolic reflector 407 through the optical fiber in the sample light path 416. The second parabolic reflector 407 forms a collimated light beam from the light beam. When the collimated light beam passes through the scanning galvanometer 408, the light beam emitted in parallel is deflected by 90° after passing through the first galvanometer 409 and reaches the second galvanometer 410. The second galvanometer 410 receives the light beam emitted by the first galvanometer 409, and the light beam is deflected by 90° again after passing through the second galvanometer 410 and is transmitted 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 arranged at a preset distance in a direction perpendicular to the bottom surface. The preset distance is determined by the diameter of the actual first galvanometer 409 and the second galvanometer 410, so as to avoid collision during rotation.

[0074] Among them, Figure 7 A structure diagram of the second shell in the sample light path provided by the embodiment one of the present application is shown in FIG. 5. Figure 8 A structure diagram of the sample light path and the reference light path provided by the embodiment one of the present application is shown in FIG. 6. Figure 7 And Figure 8 As shown in FIG. 6, the second shell 2 is further provided with a second optical fiber connection port 6, a first galvanometer outlet 5 and a second galvanometer outlet 4, and a through hole 7 for the sample light beam to pass through.

[0075] Optionally, Figure 9 A structure diagram of the equal-wavenumber spectrometer provided by the embodiment one of the present application is shown in FIG. 7. Figure 9 As shown in FIG. 7, the equal-wavenumber 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 light path of the interference light beam, and is used to form a diffraction light beam from the interference light beam; the isosceles prism 102 is located in the light path of the diffraction light beam, and is used to refract the diffraction light beam to form a refracted light beam; the focusing lens group 103 is located in the light path of the refracted light beam, and is used to focus the refracted light beam to form a focused light beam; and the image acquisition unit 104 is located in the light path of the focused light beam, and is used to form an equal-wave-number-interval-arranged spectral band based on the focused light beam.

[0077] Specifically, the 2*2 optical fiber coupler 402 generates interference between the back-reflected reference light and the backscattered light back-reflected by the sample, and the interference signals corresponding to the interference light beam are sequentially subjected to the diffraction grating 101 and the isosceles prism 102, and the interference signals are split into an equal-wave-number-interval-arranged spectral array, and then focused by the focusing lens group 103 to the image acquisition unit 104 (a linear array charge-coupled device (CCD)). The image acquisition unit 104 converts the collected interference spectral signals into electrical signals, and inputs the digitized electrical signals into a computer hardware system. The interference spectral signals represent the reflectivity distribution of the sample at different depths; after being processed by a demodulation circuit, the one-dimensional depth information of the sample is finally acquired by the acquisition card to the host computer 414, and the host computer system performs inverse Fourier transform on the obtained interference spectral data, so that the one-dimensional depth information of the sample is obtained. On this basis, by performing transverse scanning on the sample, a three-dimensional tomographic image of the sample to be measured 412 can be reconstructed, so that the structural tomographic image of the sample to be measured 412 is obtained. It should be noted that the equal-wave-number spectrometer 413 is a scheme for splitting light by combining the isosceles prism 102 and the diffraction grating 101, the equal-wave-number spectrometer 413 can balance the dispersion on the optical path system, accurately distinguish different wavelength light spots in the light transmission process, so as to avoid the noise and dispersion introduced from the 2*2 optical fiber coupler 402 end, and therefore has the advantages of low dispersion, high signal-to-noise ratio and high resolution.

[0078] Therefore, in the optical coherence tomography light path structure, the second parabolic reflective collimator 407 and the scanning galvanometer 408 arranged in the sample light path 416 can eliminate the dispersion on the sample light path 416. The first parabolic reflective collimator 403 and the first mirror 406 arranged in the reference light path 415 can eliminate the dispersion on the reference light path 415, and the first lens group 405 arranged in the reference light path 415 can balance the dispersion caused by the second lens group 411 in the sample light path 416. Finally, the interference light beam is transmitted to the equal-wave-number spectrometer, the equal-wave-number spectrometer splits the interference light beam according to equal-wave-number intervals 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 light path, and therefore the optical coherence tomography light path structure described above has less dispersion, which can solve the dispersion mismatch problem from the source.

[0079] Embodiment two

[0080] Figure 10 The flow chart of the dispersion compensation method of the optical coherence tomography light path structure provided by the second embodiment of the present application. Based on the optical coherence tomography light path structure implementation described in the first embodiment, in order to better implement the method, the sample to be measured is set as the second mirror, as shown in Figure 10 The dispersion compensation method includes:

[0081] S110, within the depth of field range of the second lens group, the first mirror is controlled to move at least one position along the optical axis of the reference light path, or the second mirror is controlled to move at least one position along the optical axis of the sample light path, and at least one interference spectrum signal is obtained.

[0082] The depth of field is the distance range of the object in front of and behind the camera lens or other imager front along which clear images can be obtained. There is a certain length of space in front of the lens (in front of and behind the focusing point), and when the object to be photographed is located in this space, its image on the film is located between the two diffraction circles in front of and behind the focusing point. Interference is the phenomenon that two or more columns of waves superimpose when they overlap in space, thereby forming a new wave form.

[0083] Specifically, the first mirror of the reference light path or the second mirror of the sample light path is adjusted so that the first mirror is near zero optical path difference. Within the depth of field range of the second lens group, the first mirror is moved by one position in the direction of the optical axis of the reference light path on the slide rail by driving the assembly in the reference light path, or the second mirror is moved by one position in the direction of the optical axis of the sample light path in the sample light path. The reference light and the sample light can interfere in the 2*2 optical fiber coupler to produce an interference signal, and the interference signal can produce an interference spectrum signal in the equal wave number spectrometer, and the interference spectrum signal is obtained. 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, i.e. the number of depths at different depth positions; I0(k) is the autocorrelation term in the interference spectrum signal, S(k) is the light source spectral density function, R sn is the reflectivity of the Nth layer of the sample to be measured, R R is the reflectivity of the reference mirror, k is the wave number, represents the dispersion phase introduced in the system; is the phase difference between the Nth layer of the sample to be measured and the reference mirror, z nA phase difference between the Nth layer of the sample to be measured and a reference mirror, I(k) is an interference spectrum signal obtained.

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

[0088] Wherein, the fast Fourier transform (FFT) is a method for fast computing discrete Fourier transform or its inverse transform of sequence; the complex frequency domain signal is a three-dimensional coordinate signal obtained by Fourier transform of a time domain signal; and the amplitude signal is a signal when a physical quantity of vibration reaches a maximum value.

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

[0090]

[0091] Wherein, Γ(z) is a Fourier transform result of S(k), and δ N The positive amplitude signal A(z) of the complex frequency domain signal can be represented as:

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

[0093] Specifically, the positive amplitude signal A(z) is subjected to inverse fast Fourier transform to obtain a complex signal A(k), which can be specifically represented as:

[0094] S140, phase information of the complex signal is extracted, and the phase information is de-wrapped to obtain a de-wrapped phase signal.

[0095] Wherein, the phase information is information describing a waveform change of a signal, and to obtain deformation data of a surface of a sample to be measured, the phase information needs to be extracted from a speckle fringe, and a quantitative relationship between the phase and light intensity is established through an inverse tangent function. In the process of inverse trigonometric function, the wrapping is a constraint phenomenon that the phase difference is constrained between "-π, +π", and the unwrapped phase is a process of unfolding and restoring the phase data which is continuously changed.

[0096] Specifically, after obtaining the complex signal A(k), the phase information of the complex signal is extracted, and the extracted phase information can be represented as: The phase information is de-wrapped, the wrapped phase information is unfolded, and continuous phase data is restored to obtain a de-wrapped phase signal, which can be expressed as:

[0097] In S150, third-order linear fitting is performed on the de-wrapped phase signal to obtain a nonlinear phase term.

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

[0099] Specifically, the de-wrapped phase signal is subjected to third-order linear fitting to obtain a fitting equation The coefficients a, b, c, and d in the third-order linear fitting equation are extracted to obtain the third-order coefficients a, b, c, and d, and then the linear term φ l = cx+d is subtracted from the de-wrapped phase signal, so that the nonlinear phase term The specific formula can be expressed as:

[0100]

[0101] In S160, 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.

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

[0103] The dispersion model is:

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

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

[0106] Specifically, the glass material parameters B, C and thickness d of the optical glass are taken as variables to establish a dispersion model of the optical glass That is

[0107] wherein, d is the thickness of the dispersion compensation mirror; λ is the wavelength, and B1, B2, B3, C1, C2, C3 are 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 coefficients of any glass material in the glass library are obtained, the thickness and the glass material parameters of the glass material are obtained, and the thickness and the material parameters of the glass material are iteratively calculated in the dispersion model by the least square method, when the calculated dispersion phase is the same as the nonlinear phase term that is the thickness and the glass material parameters of the glass material are recorded as the thickness and the glass material parameters of the dispersion compensation mirror that can eliminate the dispersion.

[0108] Optionally, if multiple sets of thickness and glass material parameters of the dispersion compensation mirror are obtained, then further comprising: placing the dispersion compensation mirror formed based on the i-th set 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 of 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; sequentially cycling, screening out the thickness and the glass material parameters corresponding to the maximum value of the first number; and forming the dispersion compensation mirror with the thickness and the glass material parameters as the final dispersion compensation mirror.

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

[0110] Specifically, for the calculated thickness and glass material parameters of the glass material, a glass flat is processed and arranged between the first lens group and the first mirror in the reference light path or between the second lens group and the second mirror in the sample light path to eliminate a small amount of dispersion existing in the light path; in order to completely eliminate the dispersion, multiple calculations and selection of glass thickness and glass material parameters are usually required, therefore, within the depth of field of the second lens group, the position of the first mirror or the position of the second mirror is moved to obtain multiple interference spectrum signals, and S110-S120 are repeated to obtain a positive amplitude signal, from which the longitudinal resolution of the multiple interference spectrum signals can be calculated; and the theoretical longitudinal resolution of the coherent light source itself is subtracted from the calculated longitudinal resolution of the multiple interference spectrum signals to obtain a first number of multiple difference values within a preset range, which is sequentially cycled to calculate a first number of multiple sets of difference values within the preset range, and the multiple sets of first numbers are screened to obtain a maximum value of the first number, and the glass thickness and glass material parameters corresponding to the maximum value are considered as 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, a glass sheet corresponding to the set of parameters can be placed in the reference light path or the sample light 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 the same longitudinal resolution of each interference spectrum signal 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 that achieves the most interference spectrum signals with the same longitudinal resolution as the theoretical longitudinal resolution of the coherent light source itself is selected as the final compensation mirror.

[0112] Optionally, calculating the longitudinal resolution of the multiple interference spectrum signals comprises: within the depth of field of the second lens group, moving the first mirror at least one position along the optical axis of the reference light path or moving the second mirror at least one position along the optical axis of the sample light path 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, in the depth of field range of the second lens group, the first mirror is moved by a position along the direction of the optical axis of the reference light path in the reference light path by the driving assembly, or the second mirror is moved by a position along the direction of the optical axis of the sample light path in 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, the interference signal generates an interference spectrum signal in the equal wave number spectrometer, and the interference spectrum signal is acquired. The acquired interference spectrum signal performs S110-S120 to obtain the 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 , the half width Δ in the interference spectrum signal is calculated, that is, the size of the longitudinal resolution.

[0116] In the embodiment of the application, by controlling the first mirror in the depth of field range of the second lens group to move at least one position along the optical axis of the reference light path, or the second mirror to move at least one position along the optical axis of the sample light path, at least one interference spectrum signal is acquired; the complex frequency domain signal is obtained by performing fast Fourier transform on the interference spectrum signal; the positive amplitude signal is obtained based on the complex frequency domain signal; the complex signal is obtained by performing inverse fast Fourier transform on the positive amplitude signal; the phase information of the complex signal is extracted, and the phase unwrapping of the phase information is performed to obtain the phase signal after phase unwrapping; the nonlinear phase term is obtained by performing third-order linear fitting on the phase signal after phase unwrapping; the 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 quantity of the difference between the longitudinal resolution and the longitudinal resolution of the coherent light source are taken as the final dispersion compensation mirror. By the above method, the dispersion compensation mirror with certain thickness and material parameters is arranged in the reference light path or the sample light path, 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 flow shown above can be reordered, added or deleted steps. For example, each step described in the present application can be executed in parallel, sequentially or in different order, as long as the desired results of the technical solutions of the present application can be achieved, which is not limited herein.

[0118] The above detailed description does not limit the scope of the application. Various modifications, combinations, sub-combinations and alternatives can be made to the detailed embodiment within the scope of the application. Any modification, equivalent replacement and improvement made without departing from the spirit and principle of the application shall fall within the scope of the application.

Claims

1. An optical coherence tomography optical path structure dispersion compensation method, characterized by, The optical coherence tomography light path structure is realized based on an optical coherence tomography light path structure, which comprises a coherent light source, a 2*2 optical fiber coupler, a reference light path, a sample light path, an equal wave number spectrometer and an upper computer; the first end of the 2*2 optical fiber coupler is connected with the coherent light source, the second end is connected with the reference light path, the third end is connected with the sample light path, and the fourth end is connected with the equal wave number spectrometer; the equal wave number spectrometer is connected with the upper computer; the reference light path comprises a first shell, a first parabolic reflective collimator, an aperture, a first lens group and a first mirror arranged in the first shell; the first mirror can be moved along the optical axis direction of the reference light path; the sample light path comprises a second shell, a second parabolic reflective collimator, a scanning galvanometer, a focusing mechanical structure and a second lens group arranged in the second shell; the scanning galvanometer is connected with the upper computer, and the first lens group is the same as the second lens group; wherein the sample to be measured is a second mirror, and the dispersion compensation method comprises: Within the depth of field range of the second lens group, at least one position of the first mirror is controlled to move along the optical axis of the reference light path, or at least one position of the second mirror is controlled to move along the optical axis of the sample light path, and 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; The positive amplitude signal is subjected to inverse fast Fourier transform to obtain a complex signal; Phase information of the complex signal is extracted, and the phase information is dephased to obtain a dephased phase signal; The dephased phase signal is subjected to third-order linear fitting 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 nonlinear phase term is the same as the dispersion phase, and at least one set of thickness and glass material parameters of the dispersion compensation mirror is obtained; The dispersion model is: ; wherein, is the thickness of the dispersion compensating mirror; is the wavelength, and k is the wave number, is the Sellmeier coefficient of any glass material in the glass library; is the dispersion phase of the dispersion compensating mirror; If multiple sets of thickness and glass material parameters of the dispersion compensation mirror are obtained, the method further comprises: A dispersion compensation mirror formed based on the i-th set of thickness and glass material parameters is placed in the reference light path or the sample light path; i>1; A plurality of interference spectrum signals are obtained, and the longitudinal resolution of the plurality of interference spectrum signals is calculated; a first number of the difference between the longitudinal resolution of the interference spectrum signal and the longitudinal resolution of the coherent light source is obtained; The thickness and glass material parameters corresponding to the maximum value of the first number are selected through circulation, and a dispersion compensation mirror formed based on the thickness and the glass material parameters is used as the final dispersion compensation mirror. The dephased phase signal is subjected to third-order linear fitting to obtain a nonlinear phase term, which comprises:

2. The optical coherence tomography optical path structure dispersion compensation method according to claim 1, characterized in that: ​ Third-order linear fitting is performed on the phase-unwraped phase signal, and a linear phase is subtracted in the original phase to obtain a nonlinear phase term.

3. The method for optical coherence tomography optical path structure dispersion compensation according to claim 1, characterized in that: The reference light path further comprises a slide rail assembly and a driving assembly arranged in the first housing, the first mirror is arranged on the slide rail assembly, and the driving assembly is configured to drive the slide rail assembly to move the first mirror along the optical axis direction of the reference light path; the driving assembly is connected with the upper computer.

4. The method according to claim 1, wherein, The reference light path further comprises a first collimator support, the first collimator support comprises a first bottom plate and a first side plate, the first bottom plate is fixed with the bottom plate of the first housing, and the first side plate is fixed with the first parabolic reflector.

5. The method according to claim 1, wherein the method is a method for dispersion compensation in an optical coherence tomography optical path structure. The reference light path further comprises a first lens group support, the first lens group support comprises a second bottom plate and a second side plate, the second bottom plate is fixed with the bottom plate of the first housing, and the second side plate is fixed with the first lens group.

6. The method according to claim 1, wherein the method is a method for dispersion compensation in an optical coherence tomography optical path structure. The sample light path further comprises a scanning galvanometer support housing, the scanning galvanometer support housing comprises a bottom surface, first and third side surfaces arranged in parallel with each other, and second and fourth side surfaces; A first galvanometer rotating assembly for driving the first galvanometer to deflect is fixed on the first side surface, a second galvanometer rotating assembly for driving the second galvanometer to deflect is fixed on the second side surface adjacent to the first side surface, the rotating shaft of the first galvanometer rotating assembly and the rotating shaft of the second galvanometer rotating assembly are perpendicular to each other and 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 reflector; 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 with the second lens group.

7. The method according to claim 1, wherein the method is a method for dispersion compensation in an optical coherence tomography optical path structure. The equal wave number spectrometer comprises a diffraction grating, an isosceles prism, a focusing lens group and an image acquisition unit.

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