Collimation device and method for optical resonant cavity

Abstract

The invention provides a collimation device and method for an optical resonant cavity, which can be applied to the technical field of laser. According to the device, a polarization unit adjusts the polarization direction of laser to obtain circularly polarized light; the four-quadrant photoelectric detector collects reflected light obtained after the circularly polarized light is reflected by the first reflector, the second reflector, the optical resonant cavity and the polarization unit for multiple times, and the incident coordinate of the reflected light incident to the four-quadrant photoelectric detector is obtained; the photoelectric tube performs photoelectric conversion on output light after the circularly polarized light sequentially passes through the first reflecting mirror, the second reflecting mirror and the optical resonant cavity to obtain a voltage value; the controller generates a first control signal according to the incident coordinate and a preset coordinate; and according to a plurality of voltage values corresponding to the laser at different frequencies, a second control signal is generated, so that the first reflector rotates under the control of the second control signal, and the incident light incident to the optical resonant cavity is adjusted to coincide with the central axis of the optical resonant cavity.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and more specifically, to a collimation device and method for an optical resonant cavity. Background Art

[0002] Ultrastable lasers play an important role in quantum precision measurement, gravitational wave detection, basic physics testing, etc. Stability and mobility are the two main research directions of ultrastable lasers.

[0003] However, the environmental sensitivity of ultra-stable lasers makes their stability and robustness contradictory. This makes highly stable ultra-stable lasers only work in laboratories and difficult to spatialize and move. Therefore, how to fix and adjust the system corresponding to the ultra-stable laser to simultaneously ensure the high impact robustness and low vibration sensitivity of the ultra-stable laser has become an urgent problem to be solved. Summary of the invention

[0004] In view of this, the present invention provides a collimation device and method for an optical resonant cavity.

[0005] According to one aspect of the present invention, a collimation device for an optical resonant cavity is provided, comprising: a polarization unit for adjusting the polarization direction of a laser to obtain circularly polarized light; a four-quadrant photodetector for collecting reflected light obtained after the circularly polarized light is reflected multiple times by a first reflector, a second reflector, an optical resonant cavity, and the polarization unit, and obtaining an incident coordinate of the reflected light incident on the four-quadrant photodetector; a phototube for performing photoelectric conversion on the output light of the circularly polarized light after it passes through the first reflector, the second reflector, and the optical resonant cavity in sequence, and obtaining a voltage value; a controller for generating a first control signal according to the incident coordinate and a preset coordinate, so that the second reflector rotates under the control of the first control signal to adjust the incident coordinate to the preset coordinate; and generating a second control signal according to a plurality of voltage values ​​corresponding to lasers at different frequencies, so that the first reflector rotates under the control of the second control signal to adjust the incident light incident on the optical resonant cavity to coincide with the central axis of the optical resonant cavity.

[0006] According to another aspect of the present invention, a collimation method for an optical resonant cavity is provided, which is applied to the collimation device for the optical resonant cavity, and the method comprises: a polarization unit adjusts the polarization direction of the laser to obtain circularly polarized light; a four-quadrant photodetector collects reflected light obtained after the circularly polarized light is reflected multiple times by a first reflector, a second reflector, the optical resonant cavity and the polarization unit, and obtains the incident coordinates of the reflected light incident on the four-quadrant photodetector; a controller generates a first control signal according to the incident coordinates and a preset coordinate, so that the second reflector rotates under the control of the first control signal to adjust the incident coordinates to the preset coordinates; a photoelectric tube performs photoelectric conversion on the output light of the circularly polarized light after it passes through the first reflector, the second reflector and the optical resonant cavity in sequence to obtain a voltage value; and a controller generates a second control signal according to a plurality of voltage values ​​corresponding to lasers at different frequencies, so that the first reflector rotates under the control of the second control signal to adjust the incident light incident on the optical resonant cavity to coincide with the central axis of the optical resonant cavity.

[0007] According to the collimation device for an optical resonant cavity provided by an embodiment of the present invention, a polarization unit is used to adjust the polarization direction of a laser to obtain circularly polarized light, and a four-quadrant photodetector is used to collect reflected light obtained after the circularly polarized light is reflected multiple times by a first reflector, a second reflector, an optical resonant cavity and a polarization unit to obtain the incident coordinates of the reflected light incident on the four-quadrant photodetector. A controller is used to generate a first control signal according to the incident coordinates and preset coordinates so that the second reflector rotates under the control of the first control signal. The technical means of adjusting the incident coordinates to the preset coordinates can adjust the incident coordinates to the preset coordinates while adjusting the incident light incident on the optical resonant cavity to normal incidence, and will not introduce cumulative errors. In addition, there is no need to use a CCD to accurately measure the incident coordinates of the reflected light during the adjustment process, and the structure is simple and the cost is low.

[0008] According to the collimation device for an optical resonant cavity provided by an embodiment of the present invention, a voltage value is obtained by performing photoelectric conversion on the output light of circularly polarized light after passing through a first reflector, a second reflector and an optical resonant cavity in sequence by using a photoelectric tube, and a second control signal is generated by using a controller according to a plurality of voltage values ​​corresponding to lasers at different frequencies, so that the first reflector rotates under the control of the second control signal. The technical means of adjusting the incident light incident to the optical resonant cavity to coincide with the central axis of the optical resonant cavity can automatically adjust the incident light to coincide with the central axis of the optical resonant cavity without the need for an additional CCD to detect the spot shape and the resonant mode, thereby realizing automatic collimation and outputting output light with high robustness and stability, while greatly simplifying the optical path, having a simple structure and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0010] Figure 1 A schematic structural diagram of a collimation device for an optical resonant cavity according to an embodiment of the present invention is shown.

[0011] Figure 2A FIG. 4 is a schematic diagram showing incident light obliquely incident into an optical resonant cavity according to an embodiment of the present invention.

[0012] Figure 2B FIG. 1 is a schematic diagram showing incident light incident on an optical resonant cavity according to an embodiment of the present invention.

[0013] Figure 3 A schematic diagram of a transmission spectrum according to an embodiment of the present invention is shown.

[0014] Figure 4 A flow chart of a method for aligning an optical resonant cavity according to an embodiment of the present invention is shown.

[0015] Figure 5A FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention. Figure 5B FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention.

[0016] Figure 5C FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention.

[0017] Figure 5D FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention.

[0018] Figure 5E FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention.

[0019] Fig. 5F FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention.

[0020] Figure 6 A schematic structural diagram of a collimation device for an optical resonant cavity according to another embodiment of the present invention is shown.

[0021] Figure 7 A flow chart of a method for aligning an optical resonant cavity according to another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0022] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0023] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0024] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0025] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0026] Ultrastable lasers play an important role in quantum precision measurement, gravitational wave detection, basic physics testing and other fields. Stability and mobility are the two main directions of research on ultrastable lasers. In recent years, the stability of ultrastable lasers has made great progress. At present, the stability of the best ultrastable lasers has reached the order of 4e-17 seconds. At the same time, many mobile ultrastable lasers and space ultrastable lasers have been developed one after another, laying the foundation for the application of ultrastable lasers in complex environments such as space and field.

[0027] However, the environmental sensitivity of ultra-stable lasers makes their stability and robustness contradictory. This means that highly stable ultra-stable lasers can only work in laboratories and are difficult to be spatialized and mobile. The precise optical system corresponding to the ultra-stable laser may not be able to withstand the severe vibration of the external environment and thus fail. For example, the severe vibration of the external environment can be vibration during transportation, impact during rocket launch, etc.

[0028] Although using a more rigid mounting structure in an ultra-temperature laser can effectively resist external shocks and make it more robust, it will couple in more environmental noise when the ultra-stable laser is working, making it less stable. For example, when the ambient temperature changes, the stress release of a more rigid mounting structure will cause the coupling efficiency of the laser to deteriorate, thereby making the frequency stability of the ultra-stable laser worse or even fail.

[0029] How to simultaneously ensure the high shock robustness and low vibration sensitivity of ultra-stable lasers has become an important factor restricting the development of mobile optical clocks. Although the use of shorter resonant cavities and special resonant cavity shapes and mounting structures in ultra-stable lasers can bring better vibration robustness, it will bring greater thermal noise. Another idea is to directly avoid this problem through all-fiber coupling. However, optical fibers and optical fiber devices will introduce additional noise. For example, additional noise can come from the phase jitter of the optical fiber itself, the residual amplitude modulation of the electro-optic modulator connected to the optical fiber, etc. In addition, if the alignment shift occurs due to environmental vibration, the locking noise of PDH (Pound-Drever-Hall) using active feedback adjustment technology will deteriorate or even fail completely.

[0030] In addition to improving the vibration tolerance of the ultra-stable laser, active re-collimation can also be used to obtain an ultra-temperature laser with high shock robustness and low vibration sensitivity.

[0031] The active realignment method in the related art uses four rotating prisms to adjust the direction of the light beam in the optical resonant cavity, uses two CCDs (Charge-coupled Devices) to measure the position and point of the reflected light in front of the cavity, and uses another CCD and a photoelectric tube behind the cavity to measure the coupling mode and coupling efficiency. This method calculates the deflection angle and offset distance of the cavity based on the coupling mode and efficiency, as well as the position and direction of the light beam, and then provides feedback to the rotating prism to achieve zero deflection angle and offset distance.

[0032] However, this method has many defects in ultra-stable laser systems in long-term unattended environments such as space optical clocks. First, the coupling method has cumulative errors that cannot be eliminated. Secondly, this method requires CCD imaging and requires the use of multiple CCD cameras, which takes up a lot of space and has high requirements for CCDs and high costs, limiting its application in aerospace projects. In addition, the collimation range of this method is limited by the refractive angle of the rotating prism, and it is impossible to achieve automatic collimation in a larger range.

[0033] In order to solve the technical problems existing in the related art, the embodiments of the present invention provide a collimation device and method for an optical resonant cavity, which can be applied to the field of laser technology. The collimation device and method for an optical resonant cavity provided by the embodiments of the present invention can realize ultra-stable laser automatic collimation with no cumulative error, no CCD imaging requirements, high robustness, and large collimation offset tolerance in a long-term unattended environment such as space.

[0034] Figure 1 A schematic structural diagram of a collimation device for an optical resonant cavity according to an embodiment of the present invention is shown.

[0035] like Figure 1 As shown, the collimating device for an optical resonant cavity may include a polarization unit 110 , a four-quadrant photodetector 120 , a phototube 150 , and a controller 160 .

[0036] The polarization unit 110 can be used to adjust the polarization direction of the laser to obtain circularly polarized light.

[0037] For example, the polarization unit 110 may include a polarizing beam splitter (PBS) and a quarter wave plate. The polarizing beam splitter may be used to transmit laser light in a horizontal polarization direction, and the quarter wave plate may adjust the polarization direction of the laser light in a horizontal polarization direction to obtain circularly polarized light.

[0038] The polarization unit 110 can transmit light with a horizontal polarization direction and can reflect light with a vertical polarization direction.

[0039] The quadrant photodetector (QPD) 120 can be used to collect reflected light obtained after circularly polarized light is reflected multiple times by the first reflector 130 , the second reflector 140 , the optical resonant cavity 101 and the polarization unit 110 , and obtain the incident coordinates of the reflected light incident on the quadrant photodetector 120 .

[0040] For example, the optical resonant cavity 101 may be a Fabry-Perot cavity (FP cavity). The first reflector 130 and the second reflector 140 may both be 45-degree reflectors.

[0041] For example, the circularly polarized light may be reflected by the first reflector 130, the second reflector 140, and the optical resonant cavity 101, and then reflected back to the second reflector 140, and then reflected by the second reflector 140 and the first reflector 130 in sequence, and then reflected to the polarization unit 110. Finally, after the polarization direction is adjusted and reflected by the polarization unit 110, the circularly polarized light is reflected to the four-quadrant photodetector 120.

[0042] For example, the four-quadrant photodetector 120 may be pre-calibrated for normal incidence, so that when the circularly polarized light passes through the first reflector 130 and the second reflector 140 and is incident on the optical resonant cavity 101 perpendicular to the end surface of the optical resonant cavity 101 (i.e., normal incidence), the incident coordinates of the reflected light incident on the four-quadrant photodetector 120 are preset coordinates. That is, when the incident light incident on the optical resonant cavity 101 is incident normally into the optical resonant cavity 101, the reflected light will return to the preset coordinates on the four-quadrant photodetector 120. The preset coordinates may be, for example, the coordinates (0, 0).

[0043] By using a four-quadrant photodetector 120 that has been pre-calibrated for normal incidence to measure the incident coordinates of the reflected light, there is no need to use a CCD to accurately measure the incident coordinates of the reflected light. Compared with the related technology that requires the use of a CCD to accurately measure the incident coordinates of the reflected light, the optical path is simplified, the structure is simple and the cost is low.

[0044] The controller 160 can be used to generate a first control signal according to the incident coordinate and the preset coordinate, so that the second reflector 140 rotates under the control of the first control signal to adjust the incident coordinate to the preset coordinate. When the second reflector 140 rotates under the control of the first control signal, the incident coordinate of the reflected light incident on the four-quadrant photodetector 120 will change, and the incident coordinate can be adjusted to the preset coordinate. When the second reflector 140 rotates under the control of the first control signal, the light path in front of the second reflector 140 will not change.

[0045] When ensuring that the optical path in front of the second reflector 140 does not change, the normal incidence calibration point, i.e., the preset coordinates, does not change at any time. Therefore, by using the controller 160 to generate a first control signal according to the incident coordinates and the preset coordinates, so that the second reflector 140 rotates under the control of the first control signal, the technical means of adjusting the incident coordinates to the preset coordinates can adjust the incident coordinates to the preset coordinates while adjusting the incident light incident to the optical resonant cavity 101 to normal incidence, and at the same time, no cumulative error is introduced.

[0046] Figure 2A FIG. 4 is a schematic diagram showing incident light obliquely incident into an optical resonant cavity according to an embodiment of the present invention.

[0047] like Figure 2AAs shown, when the cavity of the optical resonant cavity 101 is tilted, the inclination angle of the cavity of the optical resonant cavity 101 is θ. The angle between the incident light incident to the optical resonant cavity 101, that is, the reflected light after being reflected by the second reflector 140, and the central axis 1011 of the optical resonant cavity 101 is also θ, so the reflected light will not return along the original path. At this time, the incident coordinate of the reflected light hitting the four-quadrant photodetector 120 is proportional to the inclination angle θ of the cavity of the optical resonant cavity 101. The controller 160 can read the incident coordinate of the four-quadrant photodetector 120, and use a digital proportional-integral (PI, Proportional Integral) algorithm to process the incident coordinate and the preset coordinate, generate a first control signal, and feed the first control signal back to the second reflector 140, so that the second reflector 140 rotates under the control of the first control signal, and adjusts the incident coordinate to the preset coordinate, so that the incident light incident to the optical resonant cavity 101 is incident into the optical resonant cavity 101. The process of feeding back the first control signal to the second reflector 140 to ensure normal incidence is referred to as normal incidence convergence in the mode convergence algorithm.

[0048] For example, the controller 160 may generate a first control signal based on the incident coordinates and the preset coordinates, which may include: the controller 160 may loop through the following operations until the deviation between the incident coordinates and the preset coordinates is within a preset deviation threshold range: compare whether the deviation between the current incident coordinates and the preset coordinates is within the preset deviation threshold range, and if the deviation between the current incident coordinates and the preset coordinates is not within the preset deviation threshold range, generate the current first control signal based on the deviation.

[0049] Figure 2B FIG. 1 is a schematic diagram showing incident light incident on an optical resonant cavity according to an embodiment of the present invention.

[0050] like Figure 2B As shown, when the incident light is incident on the optical resonant cavity 101, the incident light is parallel to the central axis 1011 of the optical resonant cavity 101. The offset between the incident light and the central axis 1011 of the optical resonant cavity 101 along the x-axis direction is Δx. Similarly, the offset between the incident light and the central axis 1011 of the optical resonant cavity 101 along the y-axis direction is Δy.

[0051] Depend on Figure 2B It can be seen that, under the condition that the incident light incident on the optical resonant cavity 101 is always incident on the optical resonant cavity 101, it is only necessary to adjust the incident light for the misalignment caused by the cavity translation of the optical resonant cavity 101. In this way, the four degrees of freedom (θ x ,θ y, Δx, Δy) are reduced to two degrees of freedom, Δx and Δy, which are controlled independently. Since the process of adjusting Δx and Δy is carried out separately and independently, both can be controlled separately, and the control dimension of each feedback is reduced to 1 dimension, which greatly reduces the complexity of the collimation algorithm. x is the angle of the incident light relative to the x-axis, θ y is the angle between the incident light and the y-axis, Δx is the offset between the incident light and the central axis of the optical resonant cavity along the x-axis, and Δy is the offset between the incident light and the central axis of the optical resonant cavity along the y-axis, wherein the x-axis and the y-axis are both coordinate axes in the coordinate system corresponding to the central axis of the optical resonant cavity. The central axis of the optical resonant cavity is perpendicular to the x-axis and the y-axis.

[0052] The photoelectric tube 150 can be used to perform photoelectric conversion on the output light of the circularly polarized light after it passes through the first reflector 130 , the second reflector 140 and the optical resonant cavity 101 in sequence, and obtain a voltage value.

[0053] For example, the photoelectric tube 150 can perform photoelectric conversion on the circularly polarized light that is reflected by the first reflector 130 and the second reflector 140 in sequence and then normally incident on the optical resonant cavity 101 and then output by the optical resonant cavity 101 to obtain a voltage value.

[0054] For example, the photoelectric tube 150 may be a PD (Photo-Diode).

[0055] The controller 160 can be used to generate a second control signal according to a plurality of voltage values ​​corresponding to lasers at different frequencies, so that the first reflector 130 rotates under the control of the second control signal to adjust the incident light incident on the optical resonant cavity 101 to coincide with the central axis 1011 of the optical resonant cavity 101. The controller 160 generates the second control signal according to a plurality of voltage values ​​corresponding to lasers at different frequencies, which is a cyclic control process.

[0056] After the incident light enters the optical resonant cavity 101, for each laser light at different frequencies, the polarization unit 110 can obtain the circularly polarized light corresponding to the laser light, and the photoelectric tube 150 can obtain the voltage value corresponding to the circularly polarized light, and then obtain the voltage value corresponding to the laser light. Therefore, the laser light at different frequencies corresponds to multiple voltage values ​​one by one.

[0057] For example, the controller 160 can determine the voltage value corresponding to the target frequency based on multiple voltage values ​​corresponding to lasers at different frequencies, and then find the target frequency based on the voltage value. The target frequency corresponds to the target resonance mode of the optical resonant cavity 101. The controller 160 can generate a second control signal to adjust the angle of the first reflector 130 according to the second control signal to reduce the offset between the incident light and the central axis of the optical resonant cavity. At this time, the voltage value corresponding to the target frequency will increase, and when the voltage value corresponding to the target frequency reaches the maximum, the current offset between the incident light and the central axis of the optical resonant cavity is determined, which can ensure that the intensity of the output light corresponding to the target resonance mode reaches the maximum, and stop generating the second control signal for the target resonance mode. When the target mode is the fundamental mode and the intensity of the output light reaches the maximum, it is determined that the current offset between the incident light and the central axis of the optical resonant cavity is adjusted to 0. At this time, the incident light is adjusted to coincide with the central axis 1011 of the optical resonant cavity 101.

[0058] For example, the first reflector 130 and the second reflector 140 can be both mounted on a piezoelectric motor mirror mount, and the controller 160 can send a first control signal and a second control signal to the piezoelectric motor mirror mount, and the piezoelectric motor mirror mount can adjust the rotation angles of the first reflector 130 and the second reflector 140 according to the first control signal and the second control signal. The optical resonant cavity 101 can be fixed in a clamping manner.

[0059] According to the collimation device for an optical resonant cavity provided by an embodiment of the present invention, a polarization unit is used to adjust the polarization direction of a laser to obtain circularly polarized light, and a four-quadrant photodetector is used to collect reflected light obtained after the circularly polarized light is reflected multiple times by a first reflector, a second reflector, an optical resonant cavity and a polarization unit to obtain the incident coordinates of the reflected light incident on the four-quadrant photodetector. A controller is used to generate a first control signal according to the incident coordinates and preset coordinates so that the second reflector rotates under the control of the first control signal. The technical means of adjusting the incident coordinates to the preset coordinates can adjust the incident coordinates to the preset coordinates while adjusting the incident light incident on the optical resonant cavity to normal incidence, and will not introduce cumulative errors. In addition, there is no need to use a CCD to accurately measure the incident coordinates of the reflected light during the adjustment process, and the structure is simple and the cost is low.

[0060] The invention uses a photoelectric tube to perform photoelectric conversion on the output light of the circularly polarized light after passing through the first reflector, the second reflector and the optical resonant cavity in sequence to obtain a voltage value, and uses a controller to generate a second control signal according to multiple voltage values ​​corresponding to lasers at different frequencies, so that the first reflector rotates under the control of the second control signal, and the technical means of adjusting the incident light incident to the optical resonant cavity to coincide with the central axis of the optical resonant cavity can automatically adjust the incident light to coincide with the central axis of the optical resonant cavity without the need for an additional CCD to detect the spot shape and the resonant mode, thereby realizing automatic collimation and outputting output light with high robustness and stability, while greatly simplifying the optical path, having a simple structure and low cost.

[0061] The collimation device for an optical resonant cavity provided in an embodiment of the present invention has no CCD imaging requirement, is simple in structure and low in cost, and can avoid the problem of CCD limitation and selection in space applications.

[0062] The controller 160 generates a second control signal based on multiple voltage values ​​corresponding to lasers at different frequencies, which may include: determining a target frequency based on multiple voltage values ​​corresponding to lasers at different first preset frequencies; generating a second control signal based on multiple voltage values ​​corresponding to lasers at different second preset frequencies, wherein the center frequency of the multiple second preset frequencies is the target frequency.

[0063] According to the embodiment of the present invention, the first preset frequency and the second preset frequency can be selected according to actual conditions and are not limited here.

[0064] According to an embodiment of the present invention, the target frequency is determined based on multiple voltage values ​​corresponding to lasers at different first preset frequencies, and the target frequency corresponds to the target resonance mode of the optical resonant cavity, so that the target resonance mode can be further determined to achieve mode selection. In the process of adjusting the collimation, it is not necessary to clearly know the specific resonance mode, and the selection of the target resonance mode is not unique, which significantly improves the fault tolerance and reduces the requirements for the measurement accuracy of the transmission intensity corresponding to the output light, that is, reduces the requirements for the photoelectric tube.

[0065] By generating a second control signal according to multiple voltage values ​​corresponding to lasers at different second preset frequencies, the center frequency of the multiple second preset frequencies is the target frequency, and the first reflector is adjusted according to the second control signal to reduce the offset between the incident light and the central axis of the optical resonant cavity, increase the voltage value corresponding to the target frequency, and when the voltage value corresponding to the target frequency is adjusted to the maximum, the intensity of the output light corresponding to the target resonance mode can be guaranteed to reach the maximum. This step is called mode enhancement in the mode convergence algorithm.

[0066] The controller 160 determines the target frequency according to multiple voltage values ​​corresponding to the laser at different first preset frequencies, including: generating a transmission spectrum according to multiple voltage values ​​corresponding to the laser at different first preset frequencies, wherein the ordinate of the transmission spectrum is the voltage value, and the abscissa of the transmission spectrum is the first preset frequency; searching for peaks in the transmission spectrum to obtain multiple transmission peaks; when the number of the multiple transmission peaks is greater than a preset threshold, determining a minimum transmission peak from the multiple transmission peaks; determining a target transmission peak according to transmission peaks adjacent to the minimum transmission peak; and determining a target frequency corresponding to the target transmission peak according to the transmission spectrum.

[0067] According to the embodiment of the present invention, the preset threshold value can be selected according to actual conditions and is not limited here. For example, the preset threshold value can be 2.

[0068] According to an embodiment of the present invention, when the number of multiple transmission peaks is greater than a preset threshold, it indicates that the intensity of the output light corresponding to some target resonance modes has not yet reached the maximum, and the current offset between the incident light and the central axis of the optical resonance cavity is not yet 0. Therefore, it is necessary to continue to find these target resonance modes, and continue to adjust the angle of the first reflector 130 for these target resonance modes to further reduce the current offset between the incident light and the central axis of the optical resonance cavity, increase the intensity of the output light corresponding to these target resonance modes, and adjust the intensity of the output light corresponding to these target resonance modes to the maximum. When the number of multiple transmission peaks is equal to the preset threshold, it indicates that the intensity of the output light corresponding to each target resonance mode has reached the maximum. At this time, it can be determined that the current offset between the incident light and the central axis 1011 of the optical resonance cavity 101 is adjusted to 0.

[0069] For example, multiple first preset frequencies correspond to multiple first preset voltages one by one. Multiple first preset voltages can be between -10V and +10V, with an interval of 1V. Lasers at different first preset frequencies can be lasers output by the laser generating unit in time-sharing under the control of multiple first preset voltages respectively. After the circularly polarized light corresponding to each laser at the first preset frequency is incident on the optical resonant cavity 101, the optical resonant cavity 101 outputs the output light corresponding to each laser at the first preset frequency. The photoelectric tube 150 can perform photoelectric conversion on the output light corresponding to each laser at the first preset frequency to obtain a voltage value corresponding to each laser at the first preset frequency.

[0070] Similarly, the lasers at different second preset frequencies can be lasers output by the laser generating unit in time division under the control of multiple second preset voltages. After the circularly polarized light corresponding to each laser at the second preset frequency is incident on the optical resonant cavity 101, the optical resonant cavity 101 outputs the output light corresponding to each laser at the second preset frequency. The photoelectric tube 150 can perform photoelectric conversion on the output light corresponding to each laser at the second preset frequency to obtain a voltage value corresponding to each laser at the second preset frequency.

[0071] According to an embodiment of the present invention, a transmission spectrum is generated according to a plurality of voltage values ​​corresponding to lasers at different first preset frequencies; a peak is searched for the transmission spectrum to obtain a plurality of transmission peaks; when the number of the plurality of transmission peaks is greater than a preset threshold, a minimum transmission peak is determined from the plurality of transmission peaks; a target transmission peak is determined according to a transmission peak adjacent to the minimum transmission peak; and a technical means of determining a target frequency corresponding to the target transmission peak according to the transmission spectrum is used to select a target frequency through the intensity distribution law of the transmission spectrum, wherein the target frequency corresponds to a target resonance mode of the optical resonant cavity, thereby further selecting a mode through the intensity distribution law of the transmission spectrum, without the need for CCD imaging of the output light and image recognition to select a mode, and the structure is simple and the cost is low.

[0072] According to an embodiment of the present invention, the target resonance mode corresponding to the target frequency is a high-order mode, and this step is mode selection in the mode convergence algorithm. This shows that the collimation device for an optical resonant cavity provided by an embodiment of the present invention has the ability to couple to high-order modes.

[0073] Figure 3 A schematic diagram of a transmission spectrum according to an embodiment of the present invention is shown.

[0074] like Figure 3 As shown in the figure, the ordinate of the transmission spectrum is the voltage value, and the abscissa of the transmission spectrum is the first preset frequency. The two voltage values ​​corresponding to the two adjacent first preset frequencies cannot be distinguished in the transmission spectrum. Therefore, in the actual transmission spectrum, for the positions of the two adjacent first preset frequencies, only the larger voltage value of the two voltage values ​​corresponding to the two adjacent first preset frequencies can be seen. Figure 3 In the example, the transmission peak marked by the star can be determined as the target transmission peak, and the target frequency can be determined according to the target transmission peak. The two voltage values ​​corresponding to the two first preset frequencies that are adjacent to each other are Figure 3 Indicated by different colors.

[0075] According to an embodiment of the present invention, after obtaining the target frequency, the target resonance mode can be determined according to the target frequency, thereby realizing the resonance mode selection. After completing the resonance mode selection, the transmission intensity corresponding to the output light can be measured, and the first reflector 130 can be fed back. At the same time, the normal incidence convergence is used to ensure the normal incidence, and the PI algorithm is used to maximize the transmission intensity of the current resonance mode.

[0076] The controller 160 generates the second control signal according to the multiple voltage values ​​corresponding to the laser at a different second preset frequency, which may include: determining a first voltage value corresponding to the target frequency from the multiple voltage values ​​of the first wheel for the target coordinate axis in the coordinate system corresponding to the plane where the central axis of the optical resonant cavity is located, and generating a first control sub-signal so that the first reflector 130 rotates in the first direction under the control of the first control sub-signal to adjust the offset between the incident light and the central axis of the optical resonant cavity along the target coordinate axis, and the photoelectric tube 150 obtains the multiple voltage values ​​of the second wheel; determines the second voltage value corresponding to the target frequency from the multiple voltage values ​​of the second wheel; determines the target rotation direction according to the first voltage value and the second voltage value; and The target rotation direction and the preset rotation angle are used to cyclically generate the second control sub-signal, so that the first reflector 130, under the control of the second control sub-signal, rotates in turn to the target rotation direction by different multiples of the preset rotation angle, and the phototube 150 obtains a plurality of voltage values ​​of the third wheel corresponding to different multiples of the preset rotation angle; when the voltage values ​​corresponding to the target frequency determined in sequence from the plurality of voltage values ​​corresponding to different multiples of the preset rotation angle of the third wheel begin to decrease, the second control sub-signal is stopped from being generated, and the controller 160 is returned to determine the operation of the target frequency according to the plurality of voltage values ​​corresponding to the lasers at different first preset frequencies, wherein the second control signal includes the first control sub-signal and the second control sub-signal.

[0077] When the target coordinate axes are different, the first directions corresponding to the different target coordinate axes are different. The target rotation direction is a direction that reduces the offset between the incident light and the central axis of the optical resonant cavity along the target coordinate axis.

[0078] According to an embodiment of the present invention, the multiple second preset frequencies corresponding to the multiple voltage values ​​of the first round, the multiple second preset frequencies corresponding to the multiple voltage values ​​of the second round and the multiple second preset frequencies corresponding to the multiple voltage values ​​of the third round are the same.

[0079] For example, when the first voltage value is greater than the second voltage value, the second direction can be determined as the target rotation direction. When the first voltage value is less than the second voltage value, the first direction can be determined as the target rotation direction. The first direction is opposite to the second direction. The target rotation direction is the direction in which the voltage value corresponding to the target frequency increases, the direction in which the incident light approaches the central axis of the optical resonant cavity, and the direction in which the offset between the incident light and the central axis of the optical resonant cavity along the target coordinate axis direction is reduced.

[0080] According to an embodiment of the present invention, when the first voltage value is greater than the second voltage value, the first direction is characterized as a direction in which the voltage value corresponding to the target frequency decreases. When the first voltage value is less than the second voltage value, the first direction is characterized as a direction in which the voltage value corresponding to the target frequency increases.

[0081] According to an embodiment of the present invention, when the voltage values ​​corresponding to the target frequency determined in sequence begin to decrease, it indicates that the voltage value corresponding to the target frequency has reached the maximum. When the first reflector 130 is rotated in the target rotation direction, the voltage value corresponding to the target frequency will decrease.

[0082] For example, the target coordinate axis in the coordinate system corresponding to the central axis 1011 of the optical resonant cavity 101 may be the x-axis or the y-axis.

[0083] For example, the controller 160 determines the first voltage value corresponding to the target frequency from the multiple voltage values ​​of the first round, and generates the first control sub-signal, which may include: according to the first direction and the preset first rotation angle, cyclically generating the first control sub-signal, so that the first reflector rotates in turn in the first direction by different multiples of the preset first rotation angle under the control of the first control sub-signal, and the photoelectric tube 150 obtains multiple voltage values ​​of the second round corresponding to the different multiples of the preset first rotation angle. The number of cycles for cyclically generating the first control sub-signal can be selected according to actual conditions and is not limited here. For example, the number of cycles for cyclically generating the first control sub-signal can be 2, 3, 4, 5, 10 or 15, etc.

[0084] The controller 160 determines the second voltage value corresponding to the target frequency from the multiple voltage values ​​of the second wheel, which may include: determining multiple voltage values ​​corresponding to the target frequency according to the multiple voltage values ​​of the second wheel corresponding to different multiples of the preset first rotation angle; determining the second voltage value according to the multiple voltage values ​​corresponding to the target frequency. For example, the multiple voltage values ​​corresponding to the target frequency may be averaged to obtain the second voltage value. Alternatively, the multiple voltage values ​​corresponding to the target frequency may be median to obtain the second voltage value.

[0085] According to an embodiment of the present invention, a controller is used to cyclically generate a first control sub-signal according to a first direction and a preset first rotation angle, so that the first reflector, under the control of the first control sub-signal, rotates in sequence in the first direction by different multiples of the preset first rotation angle to adjust the offset between the incident light and the central axis of the optical resonant cavity along the target coordinate axis. The photoelectric tube obtains a plurality of voltage values ​​of the second wheel corresponding to different multiples of the preset first rotation angle; a plurality of voltage values ​​corresponding to the target frequency are determined according to the plurality of voltage values ​​of the second wheel corresponding to different multiples of the preset first rotation angle; a plurality of voltage values ​​corresponding to the target frequency are determined according to the plurality of voltage values ​​corresponding to the target frequency. The technical means of determining the target rotation direction according to the first voltage value and the second voltage value can be used to determine the mode convergence direction, that is, the target rotation direction, by using multiple feedback results when the signal-to-noise ratio of the transmission signal corresponding to the output light is very low and there is serious mode competition, which makes it difficult to accurately measure the transmission intensity, that is, when the voltage value corresponding to the output light is difficult to accurately measure using a phototube, and then adjust in the convergence direction until the transmission intensity reaches the maximum, that is, the voltage value corresponding to the target frequency reaches the maximum, which can solve the problem of reduced convergence speed or even inability to converge caused by inaccurate transmission measurement due to mode competition at low signal-to-noise ratio. This step is called mode enhancement in the mode convergence algorithm.

[0086] According to the embodiment of the present invention, the preset first rotation angle and the preset rotation angle can be selected according to actual conditions and are not limited here.

[0087] According to an embodiment of the present invention, after completing mode enhancement, when the number of multiple transmission peaks is greater than a preset threshold, the transmission spectrum is rescanned and mode selection-mode enhancement is performed, and this cycle is repeated until the transmission spectrum has only the fundamental mode and the number of multiple transmission peaks is equal to the preset threshold, and automatic coupling is completed.

[0088] When the number of the plurality of transmission peaks is equal to the preset threshold, the first reflector 130 adjusts the offset between the incident light and the central axis 1011 of the optical resonant cavity 101 along the target coordinate axis to 0 under the control of the second control sub-signal.

[0089] After the first reflector 130 rotates under the control of each second control signal, the controller 160 generates a first control signal according to the incident coordinates and the preset coordinates.

[0090] Figure 4 A flow chart of a method for aligning an optical resonant cavity according to an embodiment of the present invention is shown.

[0091] like Figure 4 As shown, in operation S401, mode convergence begins.

[0092] In operation S402, the direction of the incident light obtained after the laser passes through the polarization unit, the first reflector, and the second reflector is adjusted so that the incident light is incident normally into the optical resonant cavity, thereby completing normal incidence convergence.

[0093] For example, for operation S402, adjusting the direction of the incident light obtained after the laser passes through the polarization unit, the first reflector, and the second reflector so that the incident light is incident on the optical resonant cavity may include the following operations: adjusting the polarization direction of the laser by using the polarization unit to obtain circularly polarized light. Collecting the reflected light obtained after the circularly polarized light is reflected multiple times by the first reflector, the second reflector, the optical resonant cavity, and the polarization unit by using a four-quadrant photodetector to obtain the incident coordinates of the reflected light incident on the four-quadrant photodetector. Using a controller, generating a first control signal according to the incident coordinates and the preset coordinates, so that the second reflector rotates under the control of the first control signal, and adjusting the incident coordinates to the preset coordinates, so that the incident light incident on the optical resonant cavity is incident on the optical resonant cavity.

[0094] In operation S403, the output light of the circularly polarized light after passing through the first reflector, the second reflector and the optical resonant cavity in sequence is subjected to photoelectric conversion to obtain a voltage value. For example, a photoelectric tube can be used to perform photoelectric conversion on the output light of the circularly polarized light after passing through the first reflector, the second reflector and the optical resonant cavity in sequence to obtain a voltage value.

[0095] In operation S404, a transmission spectrum is generated according to a plurality of voltage values ​​corresponding to lasers at different first preset frequencies.

[0096] In operation S405, a peak is searched for the transmission spectrum to obtain a plurality of transmission peaks.

[0097] In operation S406 , it is determined whether the number of transmission peaks is equal to a preset threshold.

[0098] If not, then perform operation S407, determine the target transmission peak according to the transmission peak adjacent to the minimum transmission peak, and determine the target frequency corresponding to the target transmission peak according to the transmission spectrum. Complete mode selection. Perform operation S408, generate a second control signal according to multiple voltage values ​​corresponding to lasers at different second preset frequencies, so that the first reflector rotates under the control of the second control signal, and adjusts the voltage value corresponding to the target frequency to the maximum, wherein the center frequency of the multiple second preset frequencies is the target frequency. Complete mode enhancement. After performing operation S408, return to operation S403.

[0099] For example, with respect to operation S408, generating a second control signal according to a plurality of voltage values ​​corresponding to the laser at a different second preset frequency may include: with respect to a target coordinate axis in a coordinate system corresponding to the central axis of the optical resonant cavity, determining a first voltage value corresponding to the target frequency from a plurality of voltage values ​​of the first round, and generating a first control sub-signal so that the first reflector rotates in a first direction under the control of the first control sub-signal to adjust the offset between the incident light and the central axis of the optical resonant cavity in the direction of the target coordinate axis, and obtaining a plurality of voltage values ​​of the second round by the photoelectric tube; determining a second voltage value corresponding to the target frequency from a plurality of voltage values ​​of the second round; value; determine the target rotation direction according to the first voltage value and the second voltage value; cyclically generate the second control sub-signal according to the target rotation direction and the preset rotation angle, so that the first reflector, under the control of the second control sub-signal, rotates in turn to the target rotation direction by different multiples of the preset rotation angle, and the photoelectric tube obtains a plurality of voltage values ​​of the third wheel corresponding to different multiples of the preset rotation angle; when the voltage values ​​corresponding to the target frequency determined in sequence from the plurality of voltage values ​​corresponding to different multiples of the preset rotation angle of the third wheel start to decrease, stop generating the second control sub-signal, and determine to adjust the voltage value corresponding to the target frequency to the maximum.

[0100] After the first reflector rotates under the control of each second control signal, the controller will perform an operation of generating a first control signal according to the incident coordinates and the preset coordinates.

[0101] If yes, operation S409 is performed to determine that the offset between the incident light incident on the optical resonant cavity and the central axis of the optical resonant cavity along the target coordinate axis is adjusted to 0, thereby completing mode convergence.

[0102] In accordance with Figure 4 The collimation method for an optical resonant cavity shown in the figure adjusts the incident light to coincide with the central axis of the optical resonant cavity when the offsets between the incident light and the central axis of the optical resonant cavity along each target coordinate axis direction are adjusted to 0, thereby achieving automatic collimation.

[0103] Figure 5A FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention. Figure 5B FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention. Figure 5C FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention. Figure 5D FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention. Figure 5E FIG. 5 is a schematic diagram showing a transmission spectrum according to another embodiment of the present invention. Fig. 5F FIG. 1 is a schematic diagram of a transmission spectrum according to another embodiment of the present invention, wherein the transmission peak marked with a star is the target transmission peak.

[0104] FIG. 5A to FIG. 5C A collimation device for an optical resonant cavity provided according to an embodiment of the present invention generates a transmission spectrum according to multiple voltage values ​​corresponding to lasers at different first preset frequencies when adjusting the offset between the incident light and the central axis of the optical resonant cavity along the x-axis direction. Figure 5A This is the transmission spectrum before adjustment. Figure 5B is the transmission spectrum after the first adjustment. Figure 5C This is the transmission spectrum after the adjustment is completed (also after the second adjustment).

[0105] Depend on FIG. 5A to FIG. 5C It can be seen that the collimation device for an optical resonant cavity provided in an embodiment of the present invention, after adjusting the incident light incident to the optical resonant cavity to normal incidence, quickly and accurately adjusts the offset between the incident light and the central axis of the optical resonant cavity in the x-axis direction to 0 based on the mode convergence algorithm.

[0106] FIG. 5D to FIG. 5F A collimation device for an optical resonant cavity provided according to an embodiment of the present invention generates a transmission spectrum according to a plurality of voltage values ​​corresponding to lasers at different first preset frequencies when adjusting the offset between the incident light and the central axis of the optical resonant cavity along the y-axis direction. Figure 5D This is the transmission spectrum before adjustment. Figure 5E is the transmission spectrum after the first adjustment. Fig. 5F This is the transmission spectrum after the adjustment is completed (also after the second adjustment).

[0107] Depend on FIG. 5D to FIG. 5F It can be seen that the collimation device for an optical resonant cavity provided in an embodiment of the present invention, after adjusting the incident light incident to the optical resonant cavity to normal incidence, quickly and accurately adjusts the offset between the incident light and the central axis of the optical resonant cavity in the y-axis direction to 0 based on the mode convergence algorithm.

[0108] right Figure 5A and Figure 5C By comparison, it can be seen that according to the transmission spectrum before adjustment, the fourth-order resonance mode is selected along the x-axis direction. Figure 5D and Fig. 5F By comparison, it can be seen that according to the transmission spectrum before adjustment, a high-order resonance mode is selected along the y-axis direction. Figure 5A , Figure 5B , Figure 5D and Figure 5E It can be seen that after a round of collimation, the transmission spectrum is transformed into an aliased spectrum with a higher signal-to-noise ratio. Figure 5B and Figure 5E From the transmission spectrum in the figure, we can see that the lowest order resonance mode, the fundamental mode, is accurately selected in both the x-axis direction and the y-axis direction. Figure 5Cand Fig. 5F From the transmission spectrum in , we can see that after the second round of collimation, the voltage value corresponding to the fundamental mode is successfully coupled to the strongest, achieving automatic coupling, i.e., automatic collimation. At this stage, the transmission spectrum is the fundamental mode spectrum of only the fundamental mode.

[0109] Depend on FIG. 5A to FIG. 5F It can be seen that the collimation device for an optical resonant cavity provided in an embodiment of the present invention, after adjusting the incident light incident to the optical resonant cavity to normal incidence, quickly and accurately adjusts the incident light to coincide with the central axis of the optical resonant cavity based on a mode convergence algorithm, thereby achieving automatic collimation.

[0110] Figure 6 A schematic structural diagram of a collimation device for an optical resonant cavity according to another embodiment of the present invention is shown.

[0111] like Figure 6 As shown, the collimating device for an optical resonant cavity may include a polarization unit, a four-quadrant photodetector 120, a first reflecting mirror 130, a second reflecting mirror 140, a photoelectric tube 150, and a controller.

[0112] The polarization unit can adjust the polarization direction of the laser to obtain circularly polarized light. The polarization unit can include a polarization beam splitter 1101 and a quarter wave plate 1102. The polarization beam splitter 1101 can transmit the laser in the horizontal polarization direction, and the quarter wave plate 1102 can adjust the polarization direction of the laser in the horizontal polarization direction to obtain circularly polarized light.

[0113] The first reflector 130 can be used to reflect the circularly polarized light to obtain the first reflected light. The second reflector 140 can be used to reflect the first reflected light to obtain the second reflected light, so that the optical resonant cavity 101 reflects the second reflected light to obtain the third reflected light. The second reflector 140 can also be used to reflect the third reflected light to obtain the fourth reflected light. The first reflector 130 can also be used to reflect the fourth reflected light to obtain the fifth reflected light.

[0114] For example, the cavity length of the optical resonant cavity 101 may be 10 cm, and the finesse may be 300000. The vacuum of the optical resonant cavity 101 may be approximately 2e-2 mbar.

[0115] The polarization unit can also be used to adjust the polarization direction of the fifth reflected light and reflect it to obtain reflected light. For example, the polarization direction of the fifth reflected light can be adjusted using the quarter wave plate 1102 to obtain vertically polarized light, and the vertically polarized light can be reflected using the polarization beam splitter 1101 to obtain reflected light.

[0116] Figure 6The controller can also be used to output multiple first preset voltages so that the laser generating unit outputs lasers at different first preset frequencies under the control of the multiple first preset voltages. The multiple first preset voltages correspond to the multiple first preset frequencies one by one. The controller can also be used to output multiple second preset voltages so that the laser generating unit outputs lasers at different second preset frequencies under the control of the multiple second preset voltages. The multiple second preset voltages correspond to the multiple second preset frequencies one by one.

[0117] like Figure 6 As shown, the collimating device for the optical resonant cavity may further include a third reflecting mirror 170 and a fourth reflecting mirror 180 .

[0118] The third reflector 170 can be used to reflect the reflected light so that the reflected light enters the four-quadrant photodetector 120 . The fourth reflector 180 can be used to reflect the output light so that the output light enters the photoelectric tube 150 .

[0119] The laser generating unit may include a laser 1021, a first fiber coupler 1022, an acousto-optic modulator 1023, a second fiber coupler 1024, an electro-optic modulator 1025, and a radio frequency source 1026. The laser generating unit is a standard PDH-based frequency-stabilized optical path.

[0120] The laser 1021 is used to generate initial laser light according to the voltage output by the controller. For example, the laser 1021 may be a 1397 nm tunable semiconductor laser.

[0121] The acousto-optic modulator 1023 is used to perform acousto-optic modulation on the initial laser to obtain a laser with stable power. After the initial laser passes through the first fiber coupler 1022, the acousto-optic modulator 1023, and the second fiber coupler 1024 in sequence, a laser with stable power is output. The RF source 1026 is used to output a sine wave. The electro-optic modulator 1025 is used to phase-modulate the laser with stable power according to the sine wave output by the RF source 1026, generate two sidebands, the sideband frequency is the same as the frequency of the sine wave, and output a laser at a preset frequency.

[0122] Figure 6 The controller may include a motion control unit 161 , a data acquisition unit 162 , a host 163 , a first control subunit 164 , a second control subunit 165 , a semi-transparent mirror 166 , a photodiode 167 and a mixer 168 .

[0123] The data acquisition unit 162 is used to collect the analog signal corresponding to the incident coordinate output by the four-quadrant photoelectric detector 120, and perform analog-to-digital conversion, input the incident coordinate after analog-to-digital conversion to the host 163, and transmit it to the first control subunit 164 through the host 163.

[0124] The first control subunit 164 can be used to generate a first control signal according to the incident coordinates and the preset coordinates. The first control subunit 164 can also be used to collect the voltage value output by the photoelectric tube 150 and generate a second control signal according to multiple voltage values ​​corresponding to lasers at different frequencies.

[0125] The motion control unit 161 can receive the first control signal and the second control signal output by the first control subunit 164, and send the first control signal to the second reflector 140, and send the second control signal to the first reflector 130, so that the second reflector 140 rotates under the control of the first control signal, and the first reflector 130 rotates under the control of the second control signal.

[0126] The semi-transparent and semi-reflective mirror 166 can be used to semi-transmit and semi-reflect the reflected light, transmit the reflected light to the third reflector 170, and transmit the transmitted light to the photodiode 167. The photodiode 167 is used to perform photoelectric conversion on the transmitted light, and output the converted voltage value to the mixer 168. The mixer 168 can generate an error signal according to the sine wave output by the RF source 1026 and the voltage value output by the mixer 168, wherein the error signal is proportional to the frequency difference between the frequency of the laser 1021 and the resonant frequency of the optical resonant cavity 101.

[0127] The second control subunit 165 can receive the error signal, generate a preset current, and output the preset current to the laser 1021 under the control of the preset current generation control signal output by the host 163, so that the laser 1021 performs laser frequency locking under the control of the preset current.

[0128] The first control subunit 164 can also generate a preset voltage under the control of the preset voltage generation control signal output by the host 163, and output the preset voltage to the laser 1021, so that the laser 1021 adjusts the laser frequency under the control of the preset voltage. The preset voltage includes a first preset voltage and a second preset voltage. The laser 1021 generates an initial laser according to the voltage output by the controller, which may include: generating an initial laser according to a preset current and a preset voltage.

[0129] According to the collimation device for an optical resonant cavity provided by an embodiment of the present invention, the incident light and the central axis of the optical resonant cavity are adjusted to coincide based on the mode convergence algorithm, and the mode convergence radius reaches the theoretical limit, that is, the incident light and the central axis of the optical resonant cavity can be adjusted to coincide when the offset between the incident light and the central axis of the optical resonant cavity in the x-axis direction is 1.2 mm and the offset between the incident light and the central axis of the optical resonant cavity in the y-axis direction is 0.9 mm. And the maximum automatic coupling angle reaches 0.16 degrees, which mainly depends on the sensitive area of ​​the four-quadrant photodetector and its distance from the cavity of the optical resonant cavity.

[0130] According to the collimation device for an optical resonant cavity provided in an embodiment of the present invention, the incident light and the central axis of the optical resonant cavity are adjusted to coincide based on a mode convergence algorithm, and the maximum fundamental mode coupling efficiency reaches 0.94, which is close to the theoretical expectation of 0.95, and has an extremely ideal high-precision FP cavity automatic coupling effect.

[0131] Based on the above-mentioned collimation device for an optical resonant cavity, an embodiment of the present invention further provides a collimation method for an optical resonant cavity.

[0132] Figure 7 FIG. 4 is a flow chart showing a method for aligning an optical resonant cavity according to another embodiment of the present invention. Figure 7 The collimation method for optical resonant cavities in Figure 1 and Figure 6 A collimation device for an optical resonant cavity.

[0133] like Figure 7 As shown, the alignment method for an optical resonant cavity may include operations S710 to S750.

[0134] In operation S710, a polarization unit adjusts the polarization direction of the laser to obtain circularly polarized light.

[0135] In operation S720, the four-quadrant photodetector collects reflected light obtained after the circularly polarized light is reflected multiple times by the first reflector, the second reflector, the optical resonant cavity, and the polarization unit, and obtains the incident coordinates of the reflected light incident on the four-quadrant photodetector.

[0136] In operation S730, the controller generates a first control signal according to the incident coordinates and the preset coordinates, so that the second reflective mirror rotates under the control of the first control signal to adjust the incident coordinates to the preset coordinates.

[0137] In operation S740, the photoelectric tube performs photoelectric conversion on the output light of the circularly polarized light after passing through the first reflector, the second reflector and the optical resonant cavity in sequence to obtain a voltage value.

[0138] In operation S750, the controller generates a second control signal according to a plurality of voltage values ​​corresponding to lasers at different frequencies, so that the first reflector rotates under the control of the second control signal to adjust the incident light incident to the optical resonant cavity to coincide with the central axis of the optical resonant cavity.

[0139] It should be noted that the collimation method part for the optical resonant cavity in the embodiment of the present invention corresponds to the collimation device part for the optical resonant cavity in the embodiment of the present invention. The description of the collimation method part for the optical resonant cavity specifically refers to the collimation device part for the optical resonant cavity, which will not be repeated here.

[0140] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present invention. In this regard, each box in the flowchart or block diagram may represent a module, a program segment, or a part of a code, and the above-mentioned module, program segment, or a part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in an order different from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions. It can be understood by those skilled in the art that the features recorded in the various embodiments of the present invention can be combined and / or combined in various ways, even if such a combination or combination is not explicitly recorded in the present invention. In particular, without departing from the spirit and teachings of the present invention, the features recorded in the various embodiments of the present invention can be combined and / or combined in various ways. All these combinations and / or combinations fall within the scope of the present invention.

[0141] The embodiments of the present invention have been described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present invention. Although each embodiment has been described above, this does not mean that the measures in each embodiment cannot be advantageously used in combination. The scope of the present invention is limited by the attached embodiments and their equivalents. Without departing from the scope of the present invention, those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present invention.

Claims

1. A collimation device for an optical resonant cavity, characterized in that: include: A polarization unit, used to adjust the polarization direction of the laser to obtain circularly polarized light; A four-quadrant photoelectric detector is used to collect reflected light obtained after the circularly polarized light is reflected multiple times by the first reflector, the second reflector, the optical resonant cavity and the polarization unit, and obtain the incident coordinates of the reflected light incident on the four-quadrant photoelectric detector; a photoelectric tube, used for performing photoelectric conversion on the output light of the circularly polarized light after it passes through the first reflector, the second reflector and the optical resonant cavity in sequence, to obtain a voltage value; The controller is used to generate a first control signal according to the incident coordinate and the preset coordinate, so that the second reflector rotates under the control of the first control signal to adjust the incident coordinate to the preset coordinate; and generate a second control signal according to the multiple voltage values ​​corresponding to the lasers at different frequencies, so that the first reflector rotates under the control of the second control signal to adjust the incident light incident to the optical resonant cavity to coincide with the central axis of the optical resonant cavity.

2. The device according to claim 1, wherein: The controller generates a second control signal according to a plurality of voltage values ​​corresponding to lasers at different frequencies, comprising: determining a target frequency according to a plurality of voltage values ​​corresponding to lasers at different first preset frequencies; The second control signal is generated according to a plurality of voltage values ​​corresponding to lasers at different second preset frequencies, wherein a center frequency of the plurality of second preset frequencies is the target frequency.

3. The device according to claim 2, characterized in that The controller determines the target frequency according to the plurality of voltage values ​​corresponding to the lasers at different first preset frequencies, comprising: Generate a transmission spectrum according to a plurality of voltage values ​​corresponding to lasers at different first preset frequencies, wherein the ordinate of the transmission spectrum is the voltage value and the abscissa of the transmission spectrum is the first preset frequency; searching for peaks in the transmission spectrum to obtain a plurality of transmission peaks; When the number of the plurality of transmission peaks is greater than a preset threshold, determining a minimum transmission peak from the plurality of transmission peaks; Determining a target transmission peak according to a transmission peak adjacent to the minimum transmission peak; The target frequency corresponding to the target transmission peak is determined according to the transmission spectrum.

4. The device according to claim 3, characterized in that The controller generates a second control signal according to a plurality of voltage values ​​corresponding to lasers at different second preset frequencies, comprising: for a target coordinate axis in a coordinate system corresponding to a central axis of the optical resonant cavity, Determining a first voltage value corresponding to the target frequency from the plurality of voltage values ​​of the first round, and generating a first control sub-signal, so that the first reflector rotates in a first direction under the control of the first control sub-signal to adjust the offset between the incident light and the central axis of the optical resonant cavity along the target coordinate axis, and the photoelectric tube obtains a plurality of voltage values ​​of the second round; Determining a second voltage value corresponding to the target frequency from the plurality of voltage values ​​of the second round; determining a target rotation direction according to the first voltage value and the second voltage value; According to the target rotation direction and the preset rotation angle, a second control sub-signal is cyclically generated, so that the first reflector is rotated in sequence by different multiples of the preset rotation angle toward the target rotation direction under the control of the second control sub-signal, and the photoelectric tube obtains a plurality of voltage values ​​of the third wheel corresponding to the different multiples of the preset rotation angle; When the voltage values ​​corresponding to the target frequency determined in sequence from the multiple voltage values ​​corresponding to different multiples of the preset rotation angle of the third wheel start to decrease, the generation of the second control sub-signal is stopped, and the controller returns to the operation of determining the target frequency based on the multiple voltage values ​​corresponding to the laser at different first preset frequencies, wherein the second control signal includes the first control sub-signal and the second control sub-signal.

5. The device according to claim 4, characterized in that When the number of the multiple transmission peaks is equal to a preset threshold, the first reflector, under the control of the second control sub-signal, adjusts the offset between the incident light and the central axis of the optical resonant cavity along the target coordinate axis to 0.

6. The device according to claim 4, characterized in that After the first reflector rotates under the control of each second control signal, the controller will perform an operation of generating a first control signal according to the incident coordinates and the preset coordinates.

7. The device according to claim 1, characterized in that Also includes: The first reflector is used to reflect the circularly polarized light to obtain a first reflected light; reflecting the fourth reflected light to obtain a fifth reflected light; The second reflector is used to reflect the first reflected light to obtain the second reflected light, so that the optical resonant cavity reflects the second reflected light to obtain the third reflected light; and reflects the third reflected light to obtain the fourth reflected light; The polarization unit is further used to adjust the polarization direction of the fifth reflected light and reflect it to obtain the reflected light.

8. The device according to claim 2, characterized in that The controller is also used to output multiple first preset voltages so that the laser generating unit outputs lasers at different first preset frequencies under the respective control of the multiple first preset voltages, wherein the multiple first preset voltages correspond one-to-one to the multiple first preset frequencies.

9. The device according to claim 2, characterized in that The controller is also used to output multiple second preset voltages so that the laser generating unit outputs lasers at different second preset frequencies under the respective control of the multiple second preset voltages, wherein the multiple second preset voltages correspond one-to-one to the multiple second preset frequencies.

10. A collimation method for an optical resonant cavity, applied to the collimation device for an optical resonant cavity according to any one of claims 1 to 9, characterized in that: The method comprises: The polarization unit adjusts the polarization direction of the laser to obtain circularly polarized light; The four-quadrant photoelectric detector collects reflected light obtained after the circularly polarized light is reflected multiple times by the first reflector, the second reflector, the optical resonant cavity and the polarization unit, and obtains the incident coordinates of the reflected light incident on the four-quadrant photoelectric detector; The controller generates a first control signal according to the incident coordinate and the preset coordinate, so that the second reflector rotates under the control of the first control signal to adjust the incident coordinate to the preset coordinate; The photoelectric tube performs photoelectric conversion on the output light of the circularly polarized light after it passes through the first reflector, the second reflector and the optical resonant cavity in sequence to obtain a voltage value; The controller generates a second control signal according to the multiple voltage values ​​corresponding to the lasers at different frequencies, so that the first reflector rotates under the control of the second control signal to adjust the incident light entering the optical resonant cavity to coincide with the central axis of the optical resonant cavity.

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