CN115963060A - Swept-frequency laser, control method thereof and optical coherence tomography system - Google Patents
Swept-frequency laser, control method thereof and optical coherence tomography system Download PDFInfo
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Abstract
The embodiment of the application provides a frequency-swept laser, a control method thereof and an optical coherence tomography system, wherein the frequency-swept laser comprises: the light beam generating assembly is used for emitting a first light beam; an acousto-optic deflector comprising an ultrasonic generating element and a crystal, the crystal comprising a first surface and a second surface, the first surface receiving the first light beam; the ultrasonic wave generating element is used for transmitting a first ultrasonic wave signal to the crystal, and the first ultrasonic wave signal is a first nonlinear chirp signal; under the drive of the first nonlinear chirp signal, a medium in the crystal forms a grating which is changed along with the frequency of the first nonlinear chirp signal, so that the first beam is diffracted to obtain first-order diffracted light, and the first-order diffracted light is emitted from the second surface; and the wavelength selective reflecting element is used for reflecting the first-order diffracted light to the second surface, and the first-order diffracted light returns to the light beam generating component through the grating and the first surface. According to the OCT imaging method and device, the calculation time of the OCT imaging process can be shortened, and the OCT imaging speed is improved.
Description
Technical Field
The application belongs to the technical field of laser, and particularly relates to a frequency-sweeping laser, a control method thereof and an optical coherence tomography system.
Background
Optical Coherence Tomography (OCT) is a novel non-destructive Optical imaging technique. The method utilizes the basic principle of the weak coherent light interferometer, for example, can detect back reflection or scattering signals of incident weak coherent light at different depth levels of a sample to be detected, extracts the depth information of the sample to be detected through the analysis of interference signals, and provides two-dimensional tomographic image or three-dimensional image information of the sample to be detected. Advantages of OCT include high resolution, high speed, high sensitivity, in vivo, non-invasive, and independent lateral and longitudinal resolution. Because the axial resolution of the OCT can reach micron level and is easy to miniaturize, its application and research in the aspects of skin, cardiovascular diseases, gastrointestinal diseases, early diagnosis of cancer, etc. is also becoming widespread.
Generally, the OCT imaging process is as follows: firstly, fast wavelength scanning is carried out through a frequency scanning laser, and then intensity detection is carried out on interference signals of the wavelength by matching with a point detector to obtain an interference spectrum; and finally, carrying out Fourier transform on the interference spectrum to obtain microstructure information of the object, and obtaining the chromatographic image of the sample to be detected.
However, the inventor of the present application finds that the interference spectrum obtained based on the laser output by the current swept-frequency laser is not easy to perform fourier transform, so that the OCT imaging process needs to consume a large amount of computing time, and the imaging speed is seriously affected.
Disclosure of Invention
The embodiment of the application provides a swept-frequency laser, a control method thereof and an optical coherence tomography system, which can reduce the calculation time of an OCT imaging image process and improve the OCT imaging speed.
In a first aspect, an embodiment of the present application provides a swept-frequency laser, including: the light beam generating assembly is used for emitting a first light beam; the acousto-optic deflector is positioned on a propagation path of the first light beam and comprises an ultrasonic wave generating element and a crystal, wherein the ultrasonic wave generating element is arranged on one side of the crystal, the crystal comprises a first surface and a second surface which are oppositely arranged, and the first surface receives the first light beam; the ultrasonic wave generating element is used for generating and transmitting a first ultrasonic wave signal to the crystal, the propagation direction of the first ultrasonic wave signal is parallel to a first direction, the first direction is a direction parallel to the first surface or the second surface, and the first ultrasonic wave signal is a first nonlinear chirp signal; under the drive of the first nonlinear chirp signal, a medium in the crystal forms a grating which changes along with the frequency of the first nonlinear chirp signal, the grating extends along a second direction, the second direction is crossed with the first direction, the grating is used for enabling the first light beam to be diffracted to obtain first-order diffracted light of the first light beam, the frequency of the first-order diffracted light changes along with the frequency change of the first nonlinear chirp signal, and the first-order diffracted light is emitted from the second surface; and the wavelength selective reflecting element is positioned on the propagation path of the first-order diffracted light, the angle between the extension direction of the wavelength selective reflecting element and the first direction is larger than 0 degree, the wavelength selective reflecting element is used for receiving the first-order diffracted light and reflecting the first-order diffracted light to the second surface, and the first-sub diffracted light returns to the light beam generating component through the grating and the first surface in sequence.
In a second aspect, an embodiment of the present application provides a method for controlling a swept-frequency laser, where the swept-frequency laser includes the swept-frequency laser provided in the first aspect, and the method includes: for a pre-selected test frequency-swept laser, controlling an ultrasonic wave generating element in the test frequency-swept laser to output an initial ultrasonic wave signal to a crystal in the test frequency-swept laser so as to enable the test frequency-swept laser to output first laser, wherein the initial ultrasonic wave signal and the first laser are continuous signals within a first time period, the first time period comprises a plurality of time nodes, and the time intervals between two adjacent time nodes are preset first time intervals; acquiring the wave number of the first laser at each time node; for any ith time node in the multiple time nodes, the difference value between the wave number of the first laser at the ith time node and the wave number of the first laser at the (i + 1) th time node is a first difference value, when the difference value between the first difference value and a preset reference wave number interval is greater than a preset error threshold value, the frequency of the initial ultrasonic signal at the ith time node is adjusted until the difference value between the first difference value and the preset reference wave number interval is less than or equal to the preset error threshold value, the frequency of the adjusted initial ultrasonic signal at the ith time node is obtained, and i is a positive integer; obtaining a first ultrasonic signal according to the adjusted frequency of the initial ultrasonic signal at a plurality of time nodes; and controlling an ultrasonic wave generating element in the sweep-frequency laser to output a first ultrasonic wave signal.
In a third aspect, embodiments of the present application provide an optical coherence tomography system that includes a swept-frequency laser as provided in the first aspect.
The sweep-frequency laser, the control method thereof and the optical coherence tomography system of the embodiment of the application have the following advantages that: the light beam generating assembly is used for emitting a first light beam; the acousto-optic deflector is positioned on a propagation path of the first light beam and comprises an ultrasonic wave generating element and a crystal, wherein the ultrasonic wave generating element is arranged on one side of the crystal, the crystal comprises a first surface and a second surface which are oppositely arranged, and the first surface receives the first light beam; the ultrasonic wave generating element is used for generating and transmitting a first ultrasonic wave signal to the crystal, the propagation direction of the first ultrasonic wave signal is parallel to a first direction, the first direction is a direction parallel to the first surface or the second surface, and the first ultrasonic wave signal is a first nonlinear chirp signal; under the drive of the first nonlinear chirp signal, a medium in the crystal forms a grating which changes along with the frequency of the first nonlinear chirp signal, the grating extends along a second direction, the second direction is crossed with the first direction, the grating is used for enabling the first light beam to be diffracted to obtain first-order diffracted light of the first light beam, the frequency of the first-order diffracted light changes along with the frequency change of the first nonlinear chirp signal, and the first-order diffracted light is emitted from the second surface; and the wavelength selective reflecting element is positioned on the propagation path of the first-order diffracted light, the angle between the extension direction of the wavelength selective reflecting element and the first direction is larger than 0 degree, the wavelength selective reflecting element is used for receiving the first-order diffracted light and reflecting the first-order diffracted light to the second surface, and the first-sub diffracted light returns to the light beam generating component through the grating and the first surface in sequence. The inventor of the present application finds that the wave number of the laser output by the frequency-swept laser can be changed linearly by adjusting the ultrasonic signal in the acousto-optic deflector from the linear chirp signal to the nonlinear chirp signal. Therefore, because the wave number of the laser output by the sweep frequency laser is changed in a linear mode, the interference spectrum obtained based on the laser with the wave number in a linear conversion mode can be directly subjected to Fourier conversion, the process of converting the wave number of the laser from nonlinear change to linear change is reduced, the calculation time of the OCT imaging process is shortened, and the OCT imaging speed is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram showing the relationship between the frequency and time of an ultrasonic signal transmitted in an acousto-optic deflector according to the related art;
FIG. 2 is a schematic diagram illustrating the relationship between the frequency and the time of the ultrasonic signal transmitted in the acousto-optic deflector according to the embodiment of the present application;
fig. 3 is a schematic structural diagram of a swept-frequency laser provided in an embodiment of the present application;
fig. 4 is a schematic flowchart of a control method of a swept-frequency laser according to an embodiment of the present disclosure;
fig. 5 is a schematic structural diagram of another swept-frequency laser provided in an embodiment of the present application;
fig. 6 is a schematic structural diagram of a swept-frequency laser provided in an embodiment of the present application;
fig. 7 is a schematic structural diagram of another swept-frequency laser provided in the embodiment of the present application.
Detailed Description
Features and exemplary embodiments of various aspects of the present application will be described in detail below, and in order to make objects, technical solutions and advantages of the present application more apparent, the present 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 merely illustrative of, and not restrictive on, the present application. It will be apparent to one skilled in the art that the present application may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present application by illustrating examples thereof.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising … …" does not exclude the presence of another like element in a process, method, article, or apparatus that comprises the element.
It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
Before explaining the technical solutions provided by the embodiments of the present application, in order to facilitate understanding of the embodiments of the present application, the present application first specifically explains the problems existing in the prior art:
as previously mentioned, the OCT imaging process is as follows: firstly, fast wavelength scanning is carried out through a frequency scanning laser, and then intensity detection is carried out on interference signals of the wavelength by matching with a point detector to obtain an interference spectrum; and finally, carrying out Fourier transform on the interference spectrum to obtain microstructure information of the object, and obtaining the chromatographic image of the sample to be detected. The inventor of the application finds that the interference spectrum obtained based on the laser output by the current sweep frequency laser is not easy to carry out Fourier transform, so that a great amount of calculation time is consumed in the OCT imaging process, and the imaging speed is seriously influenced.
Specifically, the inventors of the present application have found that the ultrasonic signal transmitted in the acousto-optic deflector in the related art is a linear chirp signal, i.e., a signal whose frequency varies linearly with time. As shown in fig. 1, the horizontal axis of fig. 1 represents time, and the vertical axis of fig. 1 represents the frequency of the ultrasonic wave signal transmitted in the acousto-optic deflector in the related art, it can be seen from fig. 1 that there is a linear relationship between the frequency of the ultrasonic wave signal transmitted in the acousto-optic deflector in the related art and time, that is, the frequency of the ultrasonic wave signal changes uniformly with the change of time. When the ultrasonic signal transmitted in the acousto-optic deflector is a linear chirp signal, the wave number of the laser output by the sweep-frequency laser varies nonlinearly. However, since the fourier transform cannot directly process data in which the wave number changes nonlinearly, it is necessary to convert the data in which the wave number changes nonlinearly into data in which the wave number changes linearly, and then perform the fourier transform. This conversion process involves a large number of mathematical operations, which results in a large amount of computation time required for the OCT imaging process, and significantly affects the imaging speed.
The inventor of the present application finds that there is a correlation between the frequency of the ultrasonic signal transmitted in the acousto-optic deflector and the wave number of the laser light output by the swept-frequency laser. When the frequency of the ultrasonic signal at a certain moment or a certain time period is adjusted, correspondingly, the wave number of the laser output by the sweep-frequency laser at the corresponding moment or the corresponding time period also changes. In other words, by adjusting the mapping relationship between the frequency and the time of the ultrasonic signal, the mapping relationship between the wave number and the time of the laser can be adjusted, and the output laser wave number is changed linearly.
In view of the above research of the inventor, the embodiment of the present application provides a swept-frequency laser, a control method thereof, and an optical coherence tomography system, which can solve the technical problems that the OCT imaging process needs to consume a large amount of computation time and the OCT imaging speed is low in the related art.
The technical idea of the embodiment of the application is as follows: the wave number of the laser output by the sweep-frequency laser is changed linearly by adjusting the ultrasonic signal in the acousto-optic deflector from a linear chirp signal to a nonlinear chirp signal. So-called non-linear chirp signals are signals whose frequency varies non-linearly with time. As shown in fig. 2, the horizontal axis in fig. 2 represents time, and the vertical axis in fig. 2 represents the frequency of the ultrasonic signal transmitted in the acousto-optic deflector according to the embodiment of the present application, it can be seen from fig. 2 that there is a non-linear relationship between the frequency of the ultrasonic signal transmitted in the acousto-optic deflector according to the embodiment of the present application and time, that is, the frequency of the ultrasonic signal varies non-uniformly with time. Because the wave number of the laser output by the sweep frequency laser is changed in a linear mode, the interference spectrum obtained based on the laser with the wave number in the linear conversion mode can be subjected to Fourier conversion directly, the process that the wave number of the laser is converted from nonlinear change to linear change is reduced, the calculation time of the OCT imaging process is reduced, and the OCT imaging speed is improved.
The swept-frequency laser provided by the embodiment of the application is described below.
As shown in fig. 3, the swept-frequency laser 20 provided by the embodiment of the present application includes a beam generating assembly 201, an acousto-optic deflector 202, and a wavelength selective reflecting element 203. Illustratively, the beam generation assembly 201 may be an assembly including a laser gain medium and a pump source, for example, the beam generation assembly 201 may include a laser gain chip, which is not limited in this application. The light beam generating assembly 201 is used for emitting light beams, and for the convenience of distinction and description, the light beams emitted by the light beam generating assembly 201 are referred to as first light beams s herein.
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 including a first surface a and a second surface b disposed opposite to each other, the first surface a receiving a first light beam s. The ultrasonic wave generating element 2021 is disposed at one side of the crystal 2022, and the ultrasonic wave generating element 2021 is used for generating and transmitting a first ultrasonic wave signal to the crystal 2022, and the propagation direction of the first ultrasonic wave signal is parallel to a first direction (X direction shown in fig. 3), wherein the first direction is a direction parallel to the first surface a or the second surface b.
It is to be noted that, in the embodiment of the present application, the first ultrasonic wave signal generated by the ultrasonic wave generating element 2021 is a nonlinear chirp signal, and for convenience of distinction and presentation, the nonlinear chirp signal is referred to as a first nonlinear chirp signal herein. Driven by the first nonlinear chirp signal, the medium in the crystal 2022 forms a grating G that varies with the frequency of the first nonlinear chirp signal, the grating G extending in a second direction (Y direction as shown in fig. 3) that intersects the first direction. The grating G is used for diffracting the first beam s to obtain a first order diffracted light s1 of the first beam s. The frequency of the first-order diffracted light s1 may vary with the frequency of the first nonlinear chirp signal, or the wave number of the first-order diffracted light s1 may vary with the frequency of the first nonlinear chirp signal. The first-order diffracted light s1 exits from the second surface b of the crystal 2022.
The wavelength selective reflecting element 203 is located on the propagation path L2 of the first-order diffracted light s1. The angle between the extending direction (Y1 direction shown in fig. 3) of the wavelength selective reflection element 203 and the first direction (Y direction shown in fig. 3) is larger than 0 degree, so that the first order diffracted light s1 is reflected by the wavelength selective reflection element 203 back into the beam generating member 201 in littrow mode because the wavelength selective reflection element 203 is inclined, i.e., has a certain angle with the first direction. Specifically, the wavelength selective reflecting element 203 may receive the first-order diffracted light s1 and reflect the first-order diffracted light s1 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 reflecting element 203, and then the first-sub diffracted light s1 sequentially passes 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 light beam s to select the first-order diffracted light s1 of the preset wavelength from the first light beam s.
Illustratively, the wavelength selective reflecting element 203 may be a mirror having a reflecting surface provided with a stepped structure or a slanted structure, which may be used to reflect the first sub diffracted light s1. In some specific examples, the wavelength selective reflective element 203 may comprise a grating.
In the embodiment of the present application, the wave number of the laser output by the swept-frequency laser 20 can be changed linearly by adjusting the first ultrasonic signal transmitted in the acousto-optic deflector 202 from the linear chirp signal to the nonlinear chirp signal. In this way, since the wave number of the laser output by the swept-frequency laser 20 varies linearly, the interference spectrum obtained based on the laser whose wave number varies linearly can be directly fourier transformed, which reduces the process of converting the wave number of the laser from nonlinear variation to linear variation, thereby reducing the calculation time of the OCT imaging process and increasing the OCT imaging speed.
For ease of understanding, the following description will be made with reference to some embodiments for determining the first non-linear chirp signal.
According to some embodiments of the application, optionally, the first nonlinear chirp signal and the laser light output by the swept-frequency laser are continuous signals in the first time period. The first time period may include a plurality of time nodes t1 to tn, and time intervals between two adjacent time nodes are preset first time intervals Δ t. For example, the time interval between the first time node t1 and the second time node t2 is a first time interval Δ t, the time interval between the second time node t2 and the third time node t3 is a first time interval Δ t, … …, and the time interval between the last second time node tn-1 and the last first time node tn is a first time interval Δ t. The specific value of the first time interval Δ t may be flexibly adjusted according to the actual situation, which is not limited in the embodiment of the present application.
For any ith time node ti among the multiple time nodes t1 to tn, a difference value between a wave number of laser light output by the swept-frequency laser at the ith time node ti and a wave number of laser light output by the swept-frequency laser at an i +1 th time node ti +1 is a first difference value, a frequency of the first nonlinear chirp signal at the ith time node ti may be determined according to a relationship between the first difference value and a preset reference wave number interval, and i is a positive integer. For example, when the first difference value is larger than the reference wave number interval, the first difference value may be made smaller by adjusting the frequency of the first nonlinear chirp signal at the i-th time node ti. In this way, the difference of the wave numbers of the laser output by the swept-frequency laser at any two adjacent time nodes can be equal to or approximately equal to the same reference wave number interval, so that the wave number of the laser output by the swept-frequency laser changes linearly.
Fig. 4 is a schematic flowchart of a control method of a swept-frequency laser according to an embodiment of the present disclosure. The following describes a determination process of the first nonlinear chirp signal with reference to a control method of the swept-frequency laser provided in the embodiment of the present application.
As shown in fig. 4, the method for controlling a swept-frequency laser provided in the embodiment of the present application includes the following steps S101 to S105.
S101, for the pre-selected test swept-frequency laser, controlling an ultrasonic wave generating element in the test swept-frequency laser to output an initial ultrasonic wave signal to a crystal in the test swept-frequency laser so that the test swept-frequency laser outputs first laser.
It is easily understood that, before S101, a preset number of swept-frequency lasers may be selected as the test swept-frequency lasers, and the test swept-frequency lasers may be understood as swept-frequency lasers used in the test process. The first laser is laser, and for convenience of distinction and expression, the laser output by the test swept-frequency laser is referred to as the first laser. In the embodiment of the present application, the initial ultrasonic signal and the first laser may be both continuous signals in the first period of time. The first time period may include a plurality of time nodes t1 to tn, and the time intervals between two adjacent time nodes are both preset first time intervals Δ t.
And S102, acquiring the wave number of the first laser at each time node.
S103, for any ith time node ti in the multiple time nodes t1 to tn, the difference value between the wave number of the first laser at the ith time node ti and the wave number of the first laser at the (i + 1) th time node ti +1 is a first difference value, when the difference value between the first difference value and the preset reference wave number interval is greater than a preset error threshold value, the frequency of the initial ultrasonic signal at the ith time node is adjusted until the difference value between the first difference value and the preset reference wave number interval is less than or equal to the preset error threshold value, the frequency of the adjusted initial ultrasonic signal at the ith time node is obtained, and i is a positive integer.
In S103, the frequency of the initial ultrasonic signal at the ith time node is adjusted, so that the difference between the wave number of the first laser at the ith time node ti and the wave number of the first laser at the (i + 1) th time node ti +1 (i.e. the first difference) and the preset reference wave number interval is less than or equal to the preset error threshold. The preset error threshold may be flexibly adjusted according to an actual situation, for example, the preset error threshold may be equal to 0, which is not limited in this embodiment of the application.
For example, by adjusting the frequency of the initial ultrasonic signal at the 2 nd time node, the difference between the wave number of the first laser at the 2 nd time node and the wave number of the first laser at the 3 rd time node is made equal to the reference wave number interval. The difference between the wave number of the first laser at the 3 rd time node and the wave number of the first laser at the 4 th time node is made equal to the reference wave number interval by adjusting the frequency of the initial ultrasonic signal at the 3 rd time node. In this manner, the frequency of the initial ultrasonic signal at each of the plurality of time nodes may be determined.
And S104, obtaining a first ultrasonic signal according to the adjusted frequency of the initial ultrasonic signal at a plurality of time nodes. Specifically, after the initial ultrasonic signal has adjusted the frequencies of the plurality of time nodes, the adjusted initial ultrasonic signal is determined as the first ultrasonic signal.
And S105, controlling an ultrasonic wave generating element in the sweep frequency laser to output a first ultrasonic wave signal.
In this way, by outputting the first ultrasonic signal in the form of a nonlinear chirp signal to the crystal in the acousto-optic deflector, the difference in wave number of the laser light output by the swept-frequency laser at any two adjacent time nodes can be made equal or approximately equal to the same reference wave number interval, so that the wave number of the laser light output by the swept-frequency laser changes linearly.
As shown in fig. 5, according to some embodiments of the present application, optionally, the swept-frequency laser 20 may further include a radio-frequency signal generating component 401, the radio-frequency signal generating component 401 is electrically connected to the ultrasonic wave generating element 2021, and the radio-frequency signal generating component 401 may be configured to generate a radio-frequency signal. It should be noted that the rf signal is a non-linear chirp signal, and for convenience of distinction, the non-linear chirp signal is referred to as a second non-linear chirp signal. Accordingly, the ultrasonic wave generating element 2021 is specifically configured to receive the radio frequency signal and generate a first ultrasonic wave signal based on the radio frequency signal. In some specific examples, the ultrasonic wave generating element 2021 may be, for example, an ultrasonic transducer for converting the radio frequency signal emitted by the radio frequency signal generating assembly 401 into the first ultrasonic wave signal. In some specific examples, the radio frequency signal generation component 401 may be any combination of waveform generator and radio frequency amplifier.
As shown in fig. 4 and 5, correspondingly, during the test, the radio frequency signal generating assembly 401 may be used to generate an initial radio frequency signal, and the ultrasonic wave generating element in the test swept laser may be specifically used to generate an initial ultrasonic wave signal based on the initial radio frequency signal. In S103, adjusting the frequency of the initial ultrasonic signal at the ith time node until the difference between the first difference and the preset reference wave number interval is less than or equal to a preset error threshold, which may specifically include: and adjusting the frequency of the initial radio frequency signal at the ith time node until the difference between the first difference and the preset reference wave number interval is less than or equal to a preset error threshold. Since the initial ultrasonic signal is generated based on the initial radio frequency signal, the frequency of the initial ultrasonic signal at the ith time node can be adjusted by adjusting the frequency of the initial radio frequency signal at the ith time node.
With continued reference to fig. 5, according to some embodiments of the present application, the swept-frequency laser 20 may optionally further include a control element 402, the control element 402 being electrically connected to the radio-frequency signal generating assembly 401, the control element 402 may be used to generate a control signal. It should be noted that the control signal is a non-linear chirp signal, and for convenience of distinction, the non-linear chirp signal is referred to as a third non-linear chirp signal. Accordingly, the radio frequency signal generating component 401 may be specifically configured to receive the control signal and generate the radio frequency signal based on the control signal. That is, the control element 402 generates a control signal with a non-linear chirp signal, the rf signal generating module 401 generates an rf signal with a non-linear chirp signal based on the control signal, and the ultrasonic wave generating element 2021 generates a first ultrasonic wave signal with a non-linear chirp signal based on the rf signal and sends the first ultrasonic wave signal to the crystal 2022.
It is easily understood that, in S103 of some embodiments, the frequency of the initial ultrasonic signal at the ith time node may be adjusted by adjusting the frequency of the control signal at the ith time node.
As shown in fig. 6, according to some embodiments of the present application, the swept-frequency laser 20 may optionally further include a collimating lens 501, and the collimating lens 501 is located on a propagation path of the first light 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 oppositely, the third surface c receiving the first light beam s. The first light beam s may comprise a plurality of sub-beams. The sub-beams of the first light beam s emitted from the light beam generating assembly 201 are generally scattered in multiple directions. The collimating lens 501 may be configured to convert the first light beam s incident on the third surface c into a first light beam s in which a plurality of sub-beams are parallel, i.e., to convert scattered light into parallel light. The plurality of sub-beams of parallel first light beams s exit from the fourth surface d.
In this way, by adding the collimating lens 501, the first light beam s emitted from the light beam generating assembly 201 can be converted into parallel light by scattered light, so that more sub-light beams enter the acousto-optic deflector 202, and the output power of the laser is improved.
As shown in fig. 7, according to some embodiments of the present application, the beam generation assembly 201 may optionally include a fifth surface e and a sixth surface f, which are oppositely disposed, the fifth surface e emits the first beam s, the sixth surface f is provided with a fiber output end 601, and the fiber output end 601 is used for emitting laser light. The swept-frequency laser 20 may further include a fiber isolator 602 and a laser output port 603, an input end of the fiber isolator 602 is electrically connected to the fiber output port 601, and an output end of the fiber isolator 602 is electrically connected to the laser output port 603, for preventing laser light from one side of the laser output port 603 from entering the fiber output port 601.
Therefore, by additionally arranging the optical fiber isolator 602, the laser from the laser output port 603 side can be prevented from entering the optical fiber output end 601, that is, the laser from the laser output port 603 side is prevented from entering the beam generating assembly 201 to oscillate, and the stable laser can be output by the frequency-swept laser.
With continued reference to fig. 7, according to some embodiments of the present application, the swept-frequency laser 20 may further optionally include a boosting fiber amplifier 604, an input end of the boosting fiber amplifier 604 is electrically connected to an output end of the fiber isolator 602, and an output end of the boosting fiber amplifier 604 is electrically connected to the laser output port 603, for amplifying the power of the laser light emitted from the fiber output end 601 to a target power.
Therefore, by additionally arranging the boosting optical fiber amplifier 604, the power of the laser emitted from the optical fiber output end 601 can be amplified to the target power, so as to meet the output requirements of different powers.
With continued reference to fig. 7, according to some embodiments of the present disclosure, the swept-frequency laser 20 may further optionally include at least one of an antireflection film 605 and a transflective film 606, where the antireflection film 605 may be attached on the fifth surface e and the transflective film 606 is attached on the sixth surface f.
In this way, by adding the antireflection film 605, the light-emitting rate of the light beam generation assembly 201 can be increased, and the output power of the laser can be improved. By adding the transflective film 606, a part of the laser light can be output through the transflective film 606, and another part of the laser light is reflected back to the beam generating assembly 201 and is amplified multiple times by the acousto-optic deflector 202 and the wavelength selective reflecting element 203.
Based on the swept-frequency laser 20 provided in the foregoing embodiment, correspondingly, the embodiment of the present application further provides an optical coherence tomography system, and the swept-frequency laser 20 provided in the embodiment of the present application may include the swept-frequency laser 20 provided in the foregoing embodiment.
In addition, in combination with the control method of the swept-frequency laser in the foregoing embodiments, the embodiments of the present application may be implemented by providing a computer-readable storage medium. The computer readable storage medium having stored thereon computer program instructions; the computer program instructions, when executed by a processor, implement a method of controlling a swept-frequency laser as in any of the above embodiments. Examples of the computer-readable storage medium include non-transitory computer-readable storage media such as electronic circuits, semiconductor memory devices, ROMs, random access memories, flash memories, erasable ROMs (EROMs), floppy disks, CD-ROMs, optical disks, and hard disks.
It is to be understood that the present application is not limited to the particular arrangements and instrumentality described above and shown in the attached drawings. A detailed description of known methods is omitted herein for the sake of brevity. In the above embodiments, several specific steps are described and shown as examples. However, the method processes of the present application are not limited to the specific steps described and illustrated, and those skilled in the art can make various changes, modifications, and additions or change the order between the steps after comprehending the spirit of the present application.
The functional blocks shown in the above-described structural block diagrams may be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it may be, for example, an electronic Circuit, an Application Specific Integrated Circuit (ASIC), suitable firmware, plug-in, function card, or the like. When implemented in software, the elements of the present application are the programs or code segments used to perform the required tasks. The program or code segments may be stored in a machine-readable medium or transmitted by a data signal carried in a carrier wave over a transmission medium or a communication link. A "machine-readable medium" may include any medium that can store or transfer information. Examples of a machine-readable medium include an electronic circuit, a semiconductor memory device, a ROM, a flash memory, an Erasable ROM (EROM), a floppy disk, a CD-ROM, an optical disk, a hard disk, an optical fiber medium, a Radio Frequency (RF) link, and so forth. The code segments may be downloaded via computer networks such as the internet, intranet, etc.
It should also be noted that the exemplary embodiments mentioned in this application describe some methods or systems based on a series of steps or devices. However, the present application is not limited to the order of the above steps, that is, the steps may be performed in the order mentioned in the embodiments, may be performed in an order different from the order in the embodiments, or may be performed at the same time.
Aspects of the present application are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each block of 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 may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions/acts specified in the flowchart and/or block diagram block or blocks. Such a processor may be, but is not limited to, a general purpose processor, a special purpose processor, an application specific processor, or a field programmable logic circuit. It will also be understood that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware for performing the specified functions or acts, or combinations of special purpose hardware and computer instructions.
As described above, only the specific embodiments of the present application are provided, and it can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working processes of the system, the module and the unit described above may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again. It should be understood that the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the present application, and these modifications or substitutions should be covered within the scope of the present application.
Claims (10)
1. A swept-frequency laser, comprising:
the light beam generating assembly is used for emitting a first light beam;
an acousto-optic deflector located in a propagation path of the first light beam, the acousto-optic deflector comprising an ultrasonic wave generating element and a crystal, the ultrasonic wave generating element being disposed on one side of the crystal, the crystal comprising a first surface and a second surface disposed opposite to each other, the first surface receiving the first light beam; the ultrasonic wave generating element is used for generating and transmitting a first ultrasonic wave signal to the crystal, the propagation direction of the first ultrasonic wave signal is parallel to a first direction, the first direction is a direction parallel to the first surface or the second surface, and the first ultrasonic wave signal is a first nonlinear chirp signal;
under the driving of the first nonlinear chirp signal, a medium in the crystal forms a grating which is changed along with the frequency of the first nonlinear chirp signal, the grating extends along a second direction, the second direction is crossed with the first direction, the grating is used for diffracting the first light beam to obtain first-order diffracted light of the first light beam, the frequency of the first-order diffracted light is changed along with the frequency change of the first nonlinear chirp signal, and the first-order diffracted light is emitted from the second surface;
and the wavelength selective reflecting element is positioned on a propagation path of the first-order diffracted light, an angle between the extension direction of the wavelength selective reflecting element and the first direction is larger than 0 degree, the wavelength selective reflecting element is used for receiving the first-order diffracted light and reflecting the first-order diffracted light to the second surface, and the first sub-diffracted light returns to the light beam generation component after sequentially passing through the grating and the first surface.
2. The swept-frequency laser of claim 1, wherein the first nonlinear chirp signal and the laser output by the swept-frequency laser are continuous signals within a first time period, the first time period comprises a plurality of time nodes, and the time intervals between two adjacent time nodes are preset first time intervals;
for any ith time node in the plurality of time nodes, the frequency of the first nonlinear chirp signal at the ith time node is determined according to a relationship between a first difference value and a preset reference wave number interval, the first difference value is a difference value between the wave number of the laser output by the swept-frequency laser at the ith time node and the wave number of the laser output by the swept-frequency laser at the (i + 1) th time node, and i is a positive integer.
3. The swept-frequency laser of claim 1, further comprising a radio frequency signal generating component electrically connected to the ultrasonic wave generating element for generating a radio frequency signal, wherein the radio frequency signal is a second nonlinear chirp signal;
the ultrasonic wave generating element is specifically configured to receive the radio frequency signal and generate the first ultrasonic wave signal based on the radio frequency signal.
4. The swept laser of claim 1, further comprising a collimating lens located in a propagation path of the first beam between the beam generating assembly and the first surface, the collimating lens comprising third and fourth oppositely disposed surfaces, the third surface receiving the first beam, the first beam comprising a plurality of sub-beams, the collimating lens configured to convert the first beam incident on the third surface into the first beam in which the plurality of sub-beams are parallel, the first beam in which the plurality of sub-beams are parallel exiting from the fourth surface.
5. The swept-frequency laser of claim 1, wherein the beam generation assembly comprises a fifth surface and a sixth surface arranged oppositely, the fifth surface emitting the first beam, the sixth surface being provided with a fiber output end for emitting laser light;
the swept-frequency laser further comprises an optical fiber isolator and a laser output port, wherein the input end of the optical fiber isolator is electrically connected with the optical fiber output end, and the output end of the optical fiber isolator is electrically connected with the laser output port and used for preventing laser from entering the optical fiber output end from one side of the laser output port.
6. The swept-frequency laser of claim 5, further comprising a booster fiber amplifier, wherein an input end of the booster fiber amplifier is electrically connected to an output end of the fiber isolator, and an output end of the booster fiber amplifier is electrically connected to the laser output port, and is configured to amplify the power of the laser light emitted from the output end of the fiber to a target power.
7. The swept-frequency laser of claim 1, wherein the beam generation assembly comprises oppositely disposed fifth and sixth surfaces, the fifth surface emitting the first beam;
the swept-frequency laser further comprises at least one of an antireflection film and a semi-transparent and semi-reflective film, wherein the antireflection film is attached to the fifth surface, and the semi-transparent and semi-reflective film is attached to the sixth surface.
8. A method of controlling a swept-frequency laser, the swept-frequency laser comprising the swept-frequency laser of any one of claims 1-7, the method comprising:
for a pre-selected test frequency-swept laser, controlling an ultrasonic wave generating element in the test frequency-swept laser to output an initial ultrasonic wave signal to a crystal in the test frequency-swept laser, so that the test frequency-swept laser outputs first laser, wherein the initial ultrasonic wave signal and the first laser are continuous signals within a first time period, the first time period comprises a plurality of time nodes, and time intervals between two adjacent time nodes are preset first time intervals;
acquiring the wave number of the first laser at each time node;
for any ith time node in the plurality of time nodes, setting a difference value between the wave number of the first laser at the ith time node and the wave number of the first laser at the (i + 1) th time node as a first difference value, when the difference value between the first difference value and a preset reference wave number interval is greater than a preset error threshold value, adjusting the frequency of the initial ultrasonic signal at the ith time node until the difference value between the first difference value and the preset reference wave number interval is less than or equal to the preset error threshold value, and obtaining the adjusted frequency of the initial ultrasonic signal at the ith time node, wherein i is a positive integer;
obtaining the first ultrasonic signal according to the adjusted frequency of the initial ultrasonic signal at a plurality of time nodes;
controlling the ultrasonic wave generating element in the swept-frequency laser to output the first ultrasonic wave signal.
9. The method of claim 8, wherein the swept-frequency laser further comprises a radio-frequency signal generating component electrically connected to the ultrasonic-wave generating element for generating an initial radio-frequency signal, the ultrasonic-wave generating element being specifically configured to generate the initial ultrasonic-wave signal based on the initial radio-frequency signal;
the adjusting the frequency of the initial ultrasonic signal at the ith time node until the difference between the first difference and a preset reference wave number interval is less than or equal to the preset error threshold specifically includes:
and adjusting the frequency of the initial radio-frequency signal at the ith time node until the difference between the first difference and a preset reference wave number interval is less than or equal to the preset error threshold.
10. An optical coherence tomography system comprising a swept-frequency laser according to any one of claims 1 to 7.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117119643A (en) * | 2023-10-20 | 2023-11-24 | 光越科技(深圳)有限公司 | Sweep frequency light source and sweep frequency optical coherence tomography system |
| CN117389200A (en) * | 2023-12-08 | 2024-01-12 | 迈为技术(珠海)有限公司 | Laser control system, method and computer equipment based on acousto-optic deflector |
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2021
- 2021-10-13 CN CN202111193389.2A patent/CN115963060A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117119643A (en) * | 2023-10-20 | 2023-11-24 | 光越科技(深圳)有限公司 | Sweep frequency light source and sweep frequency optical coherence tomography system |
| CN117119643B (en) * | 2023-10-20 | 2024-04-02 | 光越科技(深圳)有限公司 | Sweep frequency light source and sweep frequency optical coherence tomography system |
| CN117389200A (en) * | 2023-12-08 | 2024-01-12 | 迈为技术(珠海)有限公司 | Laser control system, method and computer equipment based on acousto-optic deflector |
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