Swept laser and control method thereof, optical coherence tomography system

Abstract

The embodiment of the present application provides a frequency-sweeping laser, a control method thereof and an optical coherence tomography system. The frequency-sweeping laser comprises: a light beam generating component configured to emit a first light beam; an acousto-optic deflector comprising an ultrasonic wave generating element and a crystal, the crystal comprising a first surface and a second surface, the first surface configured to receive the first light beam; the ultrasonic wave generating element configured to transmit a first ultrasonic wave signal to the crystal, the first ultrasonic wave signal being a first nonlinear chirp signal; under the drive of the first nonlinear chirp signal, a medium in the crystal forms a grating varying with the frequency of the first nonlinear chirp signal, so that the first light beam is diffracted to obtain a first-order diffracted light, the first-order diffracted light being emitted from the second surface; and a wavelength-selective reflecting element configured to reflect the first-order diffracted light back to the second surface, a first sub-diffracted light returning to the light beam generating component through the grating and the first surface. The embodiment of the present application can reduce the calculation time of the OCT imaging process and improve the OCT imaging speed.

Description

Technical Field

[0001] This application belongs to the field of laser technology, and in particular relates to a swept-frequency laser and its control method, and an optical coherence tomography system. Background Technology

[0002] Optical coherence tomography (OCT) is a novel non-destructive optical imaging technique. It utilizes the basic principles of weakly coherent optical interferometry, such as detecting the back reflection or scattering signals of incident weakly coherent light at different depths of the sample. By analyzing the interference signals, depth information of the sample is extracted, providing two-dimensional or three-dimensional tomographic images. OCT's advantages include high resolution, high speed, high sensitivity, in vivo detection, non-invasiveness, and independent lateral and longitudinal resolution. Because OCT's axial resolution can reach the micrometer level, it is easily miniaturized, leading to its increasingly widespread applications in skin, cardiovascular diseases, gastrointestinal diseases, and early cancer diagnosis.

[0003] Generally speaking, the OCT imaging process is as follows: First, a rapid wavelength scan is performed using a frequency-sweeping laser. Then, the intensity of the interference signal of the wavelength is detected by a point detector to obtain the interference spectrum. Finally, the microstructure information of the object is obtained by performing a Fourier transform on the interference spectrum, which yields the tomographic image of the sample to be tested.

[0004] However, the inventors of this application have discovered that the interference spectrum obtained from the laser output of the current swept-frequency laser is not easy to perform Fourier transform, which results in the OCT imaging process requiring a lot of computation time and seriously affecting the imaging speed. Summary of the Invention

[0005] This application provides a swept-frequency laser and its control method, as well as an optical coherence tomography (OCT) system, which can reduce the computation time of the OCT imaging process and improve the OCT imaging speed.

[0006] In a first aspect, embodiments of this application provide a swept-frequency laser, comprising: a beam generating assembly for emitting a first beam; and an acousto-optic deflector located in the propagation path of the first beam, the acousto-optic deflector including an ultrasonic generating element and a crystal, the ultrasonic generating element being disposed on one side of the crystal, the crystal including a first surface and a second surface disposed opposite to each other, the first surface receiving the first beam; the ultrasonic generating element being used to generate and transmit a first ultrasonic signal to the crystal, the propagation direction of the first ultrasonic signal being parallel to a first direction, the first direction being a direction parallel to the first surface or the second surface, the first ultrasonic signal being a first nonlinear chirped signal; and the crystal being driven by the first nonlinear chirped signal. The medium forms a grating that varies with the frequency of the first nonlinear chirp signal. The grating extends along a second direction that intersects the first direction. The grating is used to diffract the first beam to obtain the first-order diffracted light of the first beam. The frequency of the first-order diffracted light varies with the frequency of the first nonlinear chirp signal. The first-order diffracted light exits from the second surface. A wavelength-selective reflective element is located on the propagation path of the first-order diffracted light, and the angle between the extension direction of the wavelength-selective reflective element and the first direction is greater than 0 degrees. The wavelength-selective reflective element is used to receive the first-order diffracted light and reflect it back to the second surface. The first sub-diffracted light passes through the grating and the first surface in sequence and returns to the beam generating assembly.

[0007] In a second aspect, embodiments of this application provide a control method for a frequency-sweeping laser. The frequency-sweeping laser includes the frequency-sweeping laser provided in the first aspect. The method includes: for a pre-selected test frequency-sweeping laser, controlling an ultrasonic generating element in the test frequency-sweeping laser to output an initial ultrasonic signal to a crystal in the test frequency-sweeping laser, so that the test frequency-sweeping laser outputs a first laser. Both the initial ultrasonic signal and the first laser are continuous signals within a first time period. The first time period includes multiple time nodes, and the time interval between two adjacent time nodes is a preset first time interval; acquiring the wavenumber of the first laser at each time node; for any one of the multiple time nodes... At i time points, the difference between the wavenumber of the first laser at the i-th time point and the wavenumber of the first laser at the (i+1)-th time point is the first difference. When the difference between the first difference and the preset reference wavenumber interval is greater than the preset error threshold, the frequency of the initial ultrasonic signal at the i-th time point is adjusted until the difference between the first difference and the preset reference wavenumber interval is less than or equal to the preset error threshold, thus obtaining the frequency of the adjusted initial ultrasonic signal at the i-th time point, where i is a positive integer. Based on the frequencies of the adjusted initial ultrasonic signal at multiple time points, the first ultrasonic signal is obtained. The ultrasonic generating element in the frequency sweep laser is controlled to output the first ultrasonic signal.

[0008] Thirdly, embodiments of this application provide an optical coherence tomography system, which includes a swept-frequency laser as provided in the first aspect.

[0009] This application describes a swept-frequency laser and its control method, as well as an optical coherence tomography system. The swept-frequency laser includes: a beam generating component for emitting a first beam; an acousto-optic deflector located in the propagation path of the first beam, the acousto-optic deflector including an ultrasonic generating element and a crystal, the ultrasonic generating element being disposed on one side of the crystal, the crystal including a first surface and a second surface disposed opposite to each other, the first surface receiving the first beam; the ultrasonic generating element generating and transmitting a first ultrasonic signal to the crystal, the propagation direction of the first ultrasonic signal being parallel to a first direction, the first direction being a direction parallel to the first surface or the second surface, the first ultrasonic signal being a first nonlinear chirped signal; and the first nonlinear chirped signal being driven... In this structure, a grating is formed in the medium of the crystal, the frequency of which varies with the first nonlinear chirped signal. The grating extends along a second direction, which intersects the first direction. The grating causes the first beam to diffract, resulting in first-order diffracted light. The frequency of the first-order diffracted light varies with the frequency of the first nonlinear chirped signal. The first-order diffracted light exits from the second surface. A wavelength-selective reflective element is located on the propagation path of the first-order diffracted light, and the angle between the extension direction of the wavelength-selective reflective element and the first direction is greater than 0 degrees. The wavelength-selective reflective element receives the first-order diffracted light and reflects it back to the second surface. The first sub-diffracted light sequentially passes through the grating and the first surface and returns to the beam generating assembly. The inventors of this application have discovered that by adjusting the ultrasonic signal in the acousto-optic deflector from a linear chirped signal to a nonlinear chirped signal, the wavenumber of the laser output by the swept-frequency laser can change linearly. In this way, since the wavenumber of the laser output by the swept laser changes linearly, the interference spectrum obtained based on the linearly changing wavenumber can be directly subjected to Fourier transform. This reduces the process of converting the nonlinear change of the laser wavenumber into a linear change, thereby reducing the calculation time of the OCT imaging process and improving the speed of OCT imaging. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram showing the relationship between the frequency and time of the ultrasonic signal transmitted in an acousto-optic deflector in related technologies.

[0012] Figure 2This is a schematic diagram showing the relationship between the frequency and time of the ultrasonic signal transmitted in the acousto-optic deflector according to an embodiment of this application.

[0013] Figure 3 A schematic diagram of a swept-frequency laser provided in an embodiment of this application;

[0014] Figure 4 A schematic flowchart illustrating a control method for a swept-frequency laser provided in an embodiment of this application;

[0015] Figure 5 This is another structural schematic diagram of the swept-frequency laser provided in the embodiments of this application;

[0016] Figure 6 This is another structural schematic diagram of the swept-frequency laser provided in the embodiments of this application;

[0017] Figure 7 This is another structural schematic diagram of the swept-frequency laser provided in the embodiments of this application. Detailed Implementation

[0018] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0019] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0020] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0021] Before describing the technical solutions provided in the embodiments of this application, in order to facilitate understanding of the embodiments of this application, this application first specifically explains the problems existing in the prior art:

[0022] As mentioned earlier, the OCT imaging process is as follows: First, a rapid wavelength scan is performed using a swept-frequency laser. Then, the intensity of the interference signal at each wavelength is detected using a point detector to obtain the interference spectrum. Finally, the microstructure information of the object is obtained by performing a Fourier transform on the interference spectrum, thus obtaining the tomographic image of the sample. The inventors of this application have discovered that the interference spectrum obtained from the laser output of current swept-frequency lasers is not easily subjected to Fourier transform, resulting in a significant computational time required for the OCT imaging process, severely impacting the imaging speed.

[0023] Specifically, the inventors of this application have discovered that the ultrasonic signal transmitted in the acousto-optic deflector in the related technology is a linear chirped signal, meaning that the frequency of the signal changes linearly with time. For example... Figure 1 As shown, Figure 1 The horizontal axis in the graph represents time. Figure 1 The vertical axis in the figure represents the frequency of the ultrasonic signal transmitted in the acousto-optic deflector in the related technology, which is... Figure 1 It can be seen that there is a linear relationship between the frequency and time of the ultrasonic signal transmitted in the acousto-optic deflector in the relevant technology; that is, the frequency of the ultrasonic signal changes uniformly with time. When the ultrasonic signal transmitted in the acousto-optic deflector is a linearly chirped signal, the wavenumber of the laser output by the swept-frequency laser changes non-linearly. However, Fourier transform cannot directly process data with non-linearly changing wavenumbers, so it is necessary to first convert the non-linearly changing wavenumber data into linearly changing wavenumber data before performing the Fourier transform. This conversion process involves a large number of mathematical calculations, which leads to a significant amount of computation time required in the OCT imaging process, severely affecting the imaging speed.

[0024] The inventors of this application discovered a correlation between the frequency of the ultrasonic signal transmitted in the acousto-optic deflector and the wavenumber of the laser output by the swept-frequency laser. When the frequency of the ultrasonic signal is adjusted at a certain moment or over a certain time period, the wavenumber of the laser output by the swept-frequency laser also changes accordingly. In other words, by adjusting the mapping relationship between the frequency and time of the ultrasonic signal, the mapping relationship between the wavenumber and time of the laser can be adjusted, achieving a linear change in the wavenumber of the output laser.

[0025] In view of the inventors’ above-mentioned research findings, the embodiments of this application provide a swept-frequency laser and its control method, and an optical coherence tomography system, which can solve the technical problems of OCT imaging process requiring a lot of computing time and low OCT imaging speed in related technologies.

[0026] The technical concept of this application embodiment lies in: by adjusting the ultrasonic signal in the acousto-optic deflector from a linear chirped signal to a nonlinear chirped signal, the wavenumber of the laser output by the swept-frequency laser changes linearly. The so-called nonlinear chirped signal refers to a signal whose frequency changes nonlinearly with time. For example... Figure 2 As shown, Figure 2 The horizontal axis in the graph represents time. Figure 2 The vertical axis in the figure represents the frequency of the ultrasonic signal transmitted in the acousto-optic deflector of this application embodiment, which is determined by... Figure 2 It can be seen that there is a nonlinear relationship between the frequency and time of the ultrasonic signal transmitted in the acousto-optic deflector of this application embodiment, that is, the frequency of the ultrasonic signal changes non-uniformly with time. Since the wavenumber of the laser output by the swept-frequency laser changes linearly, the interference spectrum obtained based on the linearly transformed wavenumber of the laser can be directly subjected to Fourier transform, reducing the process of converting the nonlinear change of the laser wavenumber to a linear change, thereby reducing the calculation time of the OCT imaging process and improving the OCT imaging speed.

[0027] The frequency-sweeping laser provided in the embodiments of this application will be described below.

[0028] like Figure 3 As shown, the swept-frequency laser 20 provided in this application embodiment includes a beam generating component 201, an acousto-optic deflector 202, and a wavelength selective reflector 203. Exemplarily, the beam generating component 201 may be a component including a laser gain medium and a pump source; for example, the beam generating component 201 may include a laser gain chip, but this application embodiment does not limit this. The beam generating component 201 is used to emit a beam; for ease of distinction and description, the beam emitted by the beam generating component 201 is referred to here as the first beam s.

[0029] The acousto-optic deflector 202 is located on the propagation path L1 of the first light beam s. The acousto-optic deflector 202 includes an ultrasonic wave generating element 2021 and a crystal 2022. The crystal 2022 includes a first surface a and a second surface b disposed opposite to each other. The first surface a receives the first light beam s. The ultrasonic wave generating element 2021 is disposed on one side of the crystal 2022 and is used to generate and transmit a first ultrasonic wave signal to the crystal 2022. The propagation direction of the first ultrasonic wave signal is perpendicular to a first direction (e.g., [missing information]). Figure 3 The X direction shown is parallel to the first surface a or the second surface b.

[0030] It is worth noting that, in this embodiment, the first ultrasonic signal generated by the ultrasonic generating element 2021 is a nonlinear chirped signal. For ease of distinction and description, this nonlinear chirped signal is referred to here as the first nonlinear chirped signal. Driven by the first nonlinear chirped signal, the dielectric in the crystal 2022 forms a grating G that varies with the frequency of the first nonlinear chirped signal. The grating G is along a second direction (e.g., Figure 3 The first beam (s) extends in the Y direction (as shown), and the second direction intersects the first direction. A grating G is used to diffract the first beam s, resulting in a first-order diffracted beam s1. The frequency of the first-order diffracted beam s1 varies with the frequency of the first nonlinear chirped signal, or in other words, the wavenumber of the first-order diffracted beam s1 varies with the frequency of the first nonlinear chirped signal. The first-order diffracted beam s1 exits from the second surface b of the crystal 2022.

[0031] The wavelength-selective reflective element 203 is located on the propagation path L2 of the first-order diffracted light s1. The extension direction of the wavelength-selective reflective element 203 (e.g., Figure 3 The Y1 direction shown) and the first direction (as shown) Figure 3 The angle between the first beam and the first beam (Y direction shown) is greater than 0 degrees. Therefore, since the wavelength-selective reflective element 203 is tilted, i.e., at a certain angle to the first direction, the first-order diffracted light s1 will be reflected back to the beam generating assembly 201 in a littrow mode by the wavelength-selective reflective element 203. Specifically, the wavelength-selective reflective element 203 can receive the first-order diffracted light s1 and reflect it back to the second surface b of the crystal 2022 along the propagation path L2 when the first-order diffracted light s1 is incident on the wavelength-selective reflective element 203. Subsequently, the first sub-diffracted light s1 passes sequentially through the grating G in the acousto-optic deflector 202 and the first surface of the crystal 2022, and returns to the beam generating assembly 201 along the propagation path L1 of the first beam s, thereby selecting the first-order diffracted light s1 of a preset wavelength from the first beam s.

[0032] For example, the wavelength-selective reflective element 203 may be a mirror with a stepped or inclined structure on its reflective surface, which can be used to reflect the first sub-diffracted light s1. In some specific examples, the wavelength-selective reflective element 203 may include a grating.

[0033] In this embodiment, by adjusting the first ultrasonic signal propagating in the acousto-optic deflector 202 from a linear chirped signal to a nonlinear chirped signal, the wavenumber of the laser output by the swept-frequency laser 20 can change linearly. Since the wavenumber of the laser output by the swept-frequency laser 20 changes linearly, the interference spectrum obtained based on the linearly transformed wavenumber can be directly subjected to Fourier transform, reducing the process of converting the nonlinear change of the laser wavenumber to a linear change. This reduces the computation time of the OCT imaging process and improves the speed of OCT imaging.

[0034] To facilitate understanding, the process of determining the first nonlinear chirp signal will be explained below with reference to some embodiments.

[0035] According to some embodiments of this application, optionally, both the first nonlinear chirped signal and the laser output from the swept-frequency laser are continuous signals within a first time period. The first time period may include multiple time nodes t1 to tn, and the time interval between any two adjacent time nodes is a preset first time interval Δt. For example, the time interval between the first time node t1 and the second time node t2 is the first time interval Δt, the time interval between the second time node t2 and the third time node t3 is the first time interval Δt, ..., and the time interval between the last second time node tn-1 and the last first time node tn is the first time interval Δt. The specific value of the first time interval Δt can be flexibly adjusted according to actual conditions, and this application does not limit it in this respect.

[0036] For any i-th time node ti among multiple time nodes t1 to tn, the difference between the wavenumber of the laser output by the swept laser at time node ti and the wavenumber of the laser output by the swept laser at time node (i+1)ti+1 is the first difference. The frequency of the first nonlinear chirped signal at time node ti can be determined based on the relationship between the first difference and a preset reference wavenumber interval, where i is a positive integer. For example, when the first difference is greater than the reference wavenumber interval, the first difference can be reduced by adjusting the frequency of the first nonlinear chirped signal at time node ti. In this way, the difference in wavenumber between any two adjacent time nodes of the laser output by the swept laser can be equal to or approximately equal to the same reference wavenumber interval, making the wavenumber of the laser output by the swept laser change linearly.

[0037] Figure 4This is a schematic flowchart of a control method for a swept-frequency laser provided in an embodiment of this application. The determination process of the first nonlinear chirp signal will be described below in conjunction with the control method for a swept-frequency laser provided in an embodiment of this application.

[0038] like Figure 4 As shown, the control method for the swept laser provided in this application embodiment includes the following steps S101 to S105.

[0039] S101. For a pre-selected test sweep laser, control the ultrasonic generating element in the test sweep laser to output an initial ultrasonic signal to the crystal in the test sweep laser, so that the test sweep laser outputs the first laser.

[0040] It is easy to understand that before S101, a preset number of swept-frequency lasers can be selected as test swept-frequency lasers. The test swept-frequency lasers can be understood as the swept-frequency lasers used during the test. The first laser is simply a laser; for ease of distinction and description, the laser output by the test swept-frequency laser is referred to as the first laser. In this embodiment, both the initial ultrasonic signal and the first laser can be continuous signals within a first time period. The first time period can include multiple time nodes t1 to tn, and the time interval between two adjacent time nodes is a preset first time interval Δt.

[0041] S102. Obtain the wavenumber of the first laser at each time point.

[0042] S103. For any i-th time node ti among multiple time nodes t1 to tn, the difference between the wavenumber of the first laser at the i-th time node ti and the wavenumber of the first laser at the (i+1)-th time node ti+1 is the first difference. When the difference between the first difference and the preset reference wavenumber interval is greater than the preset error threshold, the frequency of the initial ultrasonic signal at the i-th time node is adjusted until the difference between the first difference and the preset reference wavenumber interval is less than or equal to the preset error threshold, and the frequency of the adjusted initial ultrasonic signal at the i-th time node is obtained, where i is a positive integer.

[0043] In S103, by adjusting the frequency of the initial ultrasonic signal at the i-th time node, the difference between the wavenumber of the first laser at the i-th time node ti and the wavenumber of the first laser at the (i+1)-th time node ti+1 (i.e., the first difference) and the preset reference wavenumber interval are made less than or equal to a preset error threshold. The preset error threshold can be flexibly adjusted according to the actual situation; for example, the preset error threshold can be equal to 0. This embodiment of the application does not limit this.

[0044] For example, by adjusting the frequency of the initial ultrasonic signal at the second time node, the difference between the wavenumber of the first laser at the second time node and the wavenumber of the first laser at the third time node is equal to the reference wavenumber interval. Similarly, by adjusting the frequency of the initial ultrasonic signal at the third time node, the difference between the wavenumber of the first laser at the third time node and the wavenumber of the first laser at the fourth time node is equal to the reference wavenumber interval. In this way, the frequency of the initial ultrasonic signal at each of the multiple time nodes can be determined.

[0045] S104. Based on the frequencies of the adjusted initial ultrasonic signal at multiple time points, a first ultrasonic signal is obtained. Specifically, after adjusting the frequencies of the initial ultrasonic signal at multiple time points, the adjusted initial ultrasonic signal is determined as the first ultrasonic signal.

[0046] S105, Control the ultrasonic generating element in the frequency sweep laser to output the first ultrasonic signal.

[0047] In this way, by outputting a first ultrasonic signal with a nonlinear chirped signal to the crystal in the acousto-optic deflector, the difference in wavenumber between any two adjacent time points of the laser output by the swept laser can be equal to or approximately equal to the same reference wavenumber interval, so that the wavenumber of the laser output by the swept laser changes linearly.

[0048] like Figure 5 As shown, according to some embodiments of this application, optionally, the swept-frequency laser 20 may further include a radio frequency (RF) signal generating component 401, which is electrically connected to the ultrasonic wave generating element 2021. The RF signal generating component 401 can be used to generate an RF signal. It is worth noting that the RF signal is a nonlinear chirped signal; for ease of distinction, this nonlinear chirped signal is referred to as the second nonlinear chirped signal. Accordingly, the ultrasonic wave generating element 2021 is specifically used to receive the RF signal and generate a first ultrasonic signal based on the RF signal. In some specific examples, the ultrasonic wave generating element 2021 may be, for example, an ultrasonic transducer, which converts the RF signal emitted by the RF signal generating component 401 into the first ultrasonic signal. In some specific examples, the RF signal generating component 401 may be a combination of an arbitrary waveform generator and an RF amplifier.

[0049] Combination Figure 4 and Figure 5As shown, correspondingly, during the test, the radio frequency signal generating component 401 can be used to generate an initial radio frequency signal, and the ultrasonic wave generating element in the test sweep laser can specifically be used to generate an initial ultrasonic wave signal based on the initial radio frequency signal. In S103, adjusting the frequency of the initial ultrasonic wave signal at the i-th time node until the difference between the first difference and the preset reference wavenumber interval is less than or equal to a preset error threshold can specifically include: adjusting the frequency of the initial radio frequency signal at the i-th time node until the difference between the first difference and the preset reference wavenumber interval is less than or equal to the preset error threshold. Since the initial ultrasonic wave signal is generated based on the initial radio frequency signal, adjusting the frequency of the initial radio frequency signal at the i-th time node can adjust the frequency of the initial ultrasonic wave signal at the i-th time node.

[0050] See also Figure 5 According to some embodiments of this application, optionally, the swept-frequency laser 20 may further include a control element 402, which is electrically connected to the radio frequency signal generating component 401. The control element 402 can be used to generate a control signal. It is worth noting that the control signal is a nonlinear chirped signal. For ease of distinction, this nonlinear chirped signal is referred to as the third nonlinear chirped signal. Accordingly, the radio frequency signal generating component 401 can specifically be used to receive the control signal and generate a radio frequency signal based on the control signal. That is, firstly, the control element 402 generates a control signal with a nonlinear chirped signal, then the radio frequency signal generating component 401 generates a radio frequency signal with a nonlinear chirped signal based on the control signal, and finally, the ultrasonic wave generating element 2021 generates a first ultrasonic wave signal with a nonlinear chirped signal based on the radio frequency signal, and transmits the first ultrasonic wave signal to the crystal 2022.

[0051] It is readily understood that in S103 of some embodiments, the frequency of the initial ultrasonic signal at the i-th time node can be adjusted by adjusting the frequency of the control signal at the i-th time node.

[0052] like Figure 6 As shown, according to some embodiments of this application, optionally, the swept-frequency laser 20 may further include a collimating lens 501 located on the propagation path of the first beam s between the beam generating assembly 201 and the first surface a of the crystal 2022. The collimating lens 501 includes a third surface c and a fourth surface d disposed opposite to each other, with the third surface c receiving the first beam s. The first beam s may include multiple sub-beams. The multiple sub-beams in the first beam s emitted from the beam generating assembly 201 are typically scattered in multiple directions. The collimating lens 501 can be used to convert the first beam s incident on the third surface c into a first beam s with multiple sub-beams parallel to each other, i.e., converting the scattered light into parallel light. The first beam s with multiple parallel sub-beams exits from the fourth surface d.

[0053] In this way, by adding a collimating lens 501, the first beam s emitted from the beam generating component 201 can be converted from scattered light into parallel light, so that more sub-beams can be incident into the acousto-optic deflector 202, thereby increasing the output power of the laser.

[0054] like Figure 7 As shown, according to some embodiments of this application, optionally, the beam generating assembly 201 may include a fifth surface e and a sixth surface f disposed opposite to each other. The fifth surface e emits a first beam s, and the sixth surface f is provided with an optical fiber output end 601 for emitting laser light. The swept-frequency laser 20 may further include an optical fiber isolator 602 and a laser output port 603. The input end of the optical fiber isolator 602 is electrically connected to the optical fiber output end 601, and the output end of the optical fiber isolator 602 is electrically connected to the laser output port 603, for preventing laser light from the laser output port 603 side from entering the optical fiber output end 601.

[0055] In this way, by adding the fiber optic isolator 602, the laser from the laser output port 603 side can be prevented from entering the fiber output end 601, that is, the laser from the laser output port 603 side can be prevented from entering the beam generating component 201 and causing oscillation, thus ensuring that the sweep laser can output a stable laser.

[0056] See also Figure 7 According to some embodiments of this application, optionally, the swept-frequency laser 20 may further include a booster fiber amplifier 604, the input end of which is electrically connected to the output end of the fiber isolator 602, and the output end of which is electrically connected to the laser output port 603, for amplifying the power of the laser emitted from the fiber output port 601 to the target power.

[0057] In this way, by adding a booster fiber amplifier 604, the power of the laser emitted from the fiber output end 601 can be amplified to the target power to meet the output requirements of different power levels.

[0058] See also Figure 7 According to some embodiments of this application, optionally, the sweep laser 20 may also include at least one of an antireflective coating 605 and a semi-transparent and semi-reflective coating 606, wherein the antireflective coating 605 may be attached to the fifth surface e and the semi-transparent and semi-reflective coating 606 may be attached to the sixth surface f.

[0059] In this way, by adding the antireflective coating 605, the light extraction efficiency of the beam generating component 201 can be increased, thereby improving the output power of the laser. By adding the semi-transparent and semi-reflective coating 606, part of the laser can be output through the semi-transparent and semi-reflective coating 606, while the other part of the laser is reflected back to the beam generating component 201 and undergoes multiple optical amplifications through the acousto-optic deflector 202 and the wavelength selective reflection element 203.

[0060] Based on the frequency-sweeping laser 20 provided in the above embodiments, correspondingly, this application also provides an optical coherence tomography system. The frequency-sweeping laser 20 provided in this application can include the frequency-sweeping laser 20 provided in the above embodiments.

[0061] Furthermore, in conjunction with the control method for the swept laser in the above embodiments, this application embodiment can provide a computer-readable storage medium for implementation. This computer-readable storage medium stores computer program instructions; when these computer program instructions are executed by a processor, they implement any of the swept laser control methods in the above embodiments. Examples of computer-readable storage media include non-transitory computer-readable storage media, such as electronic circuits, semiconductor memory devices, ROM, random access memory, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, and hard disks.

[0062] It should be clarified that this application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of this application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of this application.

[0063] The functional blocks shown in the above-described block diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this application are programs or code segments used to perform the required tasks. Programs or code segments can be stored on a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried on a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0064] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0065] The aspects of this application have been described above with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It should be understood that each block in the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that these instructions, executable via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions / actions specified in one or more blocks of the flowchart illustrations and / or block diagrams. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor, or a field-programmable logic circuit. It is also understood that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can also be implemented by dedicated hardware performing the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0066] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A swept-frequency laser, characterized in that, include: A beam generating assembly for emitting a first beam; An acousto-optic deflector is located in the propagation path of the first light beam. The acousto-optic deflector includes an ultrasonic generating element and a crystal. The ultrasonic generating element is disposed on one side of the crystal. The crystal includes a first surface and a second surface disposed opposite to each other. The first surface receives the first light beam. The ultrasonic generating element is used to generate and transmit a first ultrasonic signal to the crystal. The propagation direction of the first ultrasonic signal is parallel to a first direction, which is a direction parallel to the first surface or the second surface. The first ultrasonic signal is a first nonlinear chirped signal. Driven by the first nonlinear chirp signal, the medium in the crystal forms a grating that varies with the frequency of the first nonlinear chirp signal. The grating extends along a second direction that intersects with the first direction. The grating is used to cause the first beam to diffract, resulting in first-order diffracted light of the first beam. The frequency of the first-order diffracted light varies with the frequency of the first nonlinear chirp signal. The first-order diffracted light exits from the second surface. A wavelength-selective reflective element is located on the propagation path of the first-order diffracted light, and the angle between the extension direction of the wavelength-selective reflective element and the first direction is greater than 0 degrees. The wavelength-selective reflective element is used to receive the first-order diffracted light and reflect the first-order diffracted light back to the second surface. The first-order diffracted light passes through the grating and the first surface in sequence and returns to the beam generating assembly. The swept-frequency laser also includes a radio frequency signal generating component, which is electrically connected to the ultrasonic generating element and is used to generate a radio frequency signal, which is a second nonlinear chirped signal. The ultrasonic generating element is specifically used to receive the radio frequency signal and generate the first ultrasonic signal based on the radio frequency signal.

2. The swept-frequency laser according to claim 1, characterized in that, Both the first nonlinear chirped signal and the laser output by the swept laser are continuous signals within a first time period. The first time period includes multiple time nodes, and the time interval between two adjacent time nodes is a preset first time interval. For any i-th time node among the plurality of time nodes, the frequency of the first nonlinear chirped signal at the i-th time node is determined according to the relationship between a first difference and a preset reference wavenumber interval. The first difference is the difference between the wavenumber of the laser output by the swept laser at the i-th time node and the wavenumber of the laser output by the swept laser at the (i+1)-th time node, where i is a positive integer.

3. The swept-frequency laser according to claim 1, characterized in that, The swept laser further includes a collimating lens located on the propagation path of the first beam between the beam generating component and the first surface. The collimating lens includes a third surface and a fourth surface disposed opposite to each other. The third surface receives the first beam, which includes a plurality of sub-beams. The collimating lens is used to convert the first beam incident on the third surface into a first beam in which the plurality of sub-beams are parallel. The first beam in which the plurality of sub-beams are parallel is emitted from the fourth surface.

4. The swept-frequency laser according to claim 1, characterized in that, The beam generating component includes a fifth surface and a sixth surface arranged opposite to each other. The fifth surface emits the first beam, and the sixth surface is provided with an optical fiber output end for emitting laser light. The swept-frequency laser also includes an optical fiber isolator and a laser output port. The input end of the optical fiber isolator is electrically connected to the output end of the optical fiber, and the output end of the optical fiber isolator is electrically connected to the laser output port, which is used to prevent laser from the laser output port side from entering the optical fiber output end.

5. The swept-frequency laser according to claim 4, characterized in that, The swept-frequency laser also includes a booster fiber amplifier, the input end of which is electrically connected to the output end of the fiber isolator, and the output end of which is electrically connected to the laser output port, for amplifying the power of the laser emitted from the fiber output end to the target power.

6. The swept-frequency laser according to claim 1, characterized in that, The beam generating component includes a fifth surface and a sixth surface disposed opposite to each other, wherein the fifth surface emits the first beam; The swept-frequency laser further includes at least one of an antireflective coating and a semi-transparent and semi-reflective coating, wherein the antireflective coating is attached to the fifth surface and the semi-transparent and semi-reflective coating is attached to the sixth surface.

7. A control method for a swept-frequency laser, characterized in that, The swept-frequency laser includes the swept-frequency laser as described in any one of claims 1-6, and the method includes: For a pre-selected test sweep laser, the ultrasonic generating element in the test sweep laser is controlled to output an initial ultrasonic signal to the crystal in the test sweep laser, so that the test sweep laser outputs a first laser. The initial ultrasonic signal and the first laser are both continuous signals within a first time period. The first time period includes multiple time nodes, and the time interval between two adjacent time nodes is a preset first time interval. Obtain the wavenumber of the first laser at each time node; For any i-th time node among the multiple time nodes, the difference between the wavenumber of the first laser at the i-th time node and the wavenumber of the first laser at the (i+1)-th time node is the first difference. When the difference between the first difference and the preset reference wavenumber interval is greater than the preset error threshold, the frequency of the initial ultrasonic signal at the i-th time node is adjusted until the difference between the first difference and the preset reference wavenumber interval is less than or equal to the preset error threshold, thus obtaining the adjusted frequency of the initial ultrasonic signal at the i-th time node, where i is a positive integer. The first ultrasonic signal is obtained based on the frequency of the adjusted initial ultrasonic signal at multiple time points; The ultrasonic generating element in the frequency sweep laser is controlled to output the first ultrasonic signal.

8. The method according to claim 7, characterized in that, The swept-frequency laser also includes a radio frequency signal generating component, which is electrically connected to the ultrasonic wave generating element and is used to generate an initial radio frequency signal. The ultrasonic wave generating element is specifically used to generate the initial ultrasonic wave signal based on the initial radio frequency signal. The step of adjusting the frequency of the initial ultrasonic signal at the i-th time node until the difference between the first difference and the preset reference wavenumber interval is less than or equal to the preset error threshold specifically includes: The frequency of the initial radio frequency signal at the i-th time node is adjusted until the difference between the first difference and the preset reference wavenumber interval is less than or equal to the preset error threshold.

9. An optical coherence tomography system, characterized in that, Includes the frequency-sweeping laser as described in any one of claims 1-6.

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