Tunable photogenerated microwave source system

Abstract

The present disclosure provides a tunable photogenerated microwave source system, which relates to the field of photogenerated microwave technology, and includes: an optical heterodyne module, which is used to generate a microwave signal using an output laser beam based on an optical heterodyne method; a frequency stabilization and frequency measurement module, which is used to modulate the microwave signal into a light wave containing a negative first-order sideband, and then split the light wave into two paths and measure the relationship between the power ratio of the two paths of light waves and the frequency; a feedback control module, which is used to calculate the actual frequency value of the microwave signal according to the relationship between the power ratio and the frequency, compare the actual frequency value with the preset frequency value of the microwave signal, and adjust the laser beam frequency according to the comparison result, so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value. Based on the tunable photogenerated microwave source system, microwave signals can be tuned in a large range, and microwave signals with high frequency stability can be generated.

Description

Technical Field

[0001] The present disclosure relates to the technical field of photogenerated microwaves, and in particular to a tunable photogenerated microwave source system. Background Art

[0002] Microwave source refers to a device that generates microwave energy. Photonic microwave technology is an optical technology that carries microwave millimeter wave signals in optical signals to transmit radio frequency signals in optical transmission media such as optical fibers. In optical radio frequency systems, the generation, conversion and modulation of radio frequency signals are achieved by regulating laser signals. High-precision, broadband tunable microwave sources are one of the key technologies in radar, optical wireless communication, satellite communication and other systems, and are also the basis for the widespread application of these systems.

[0003] However, the series of photogenerated microwave systems currently used are unable to generate highly stable and tunable microwave signals over a large range, which limits the application of the system to a certain extent. Summary of the invention

[0004] In view of the above problems, the present disclosure provides a tunable photogenerated microwave source system, so that the microwave source can be tuned within a larger range and generate a microwave signal with high frequency stability.

[0005] The present disclosure provides a tunable optical microwave source system, comprising: an optical heterodyne module, which is used to generate a microwave signal by using an output laser beam based on an optical heterodyne method; a frequency stabilization and frequency measurement module, which is used to modulate the microwave signal into a light wave containing a negative first-order sideband, and then measure the power values ​​of the two light waves after splitting the light wave into two paths, and obtain the relationship between the power ratio of the two light waves and the frequency through a pre-test; and a feedback control module, which is used to calculate the actual frequency value of the microwave signal according to the relationship between the power ratio and the frequency and the power values ​​of the two light waves, compare the actual frequency value with the preset frequency value of the microwave signal, and adjust the laser beam frequency according to the comparison result, so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value.

[0006] Optionally, the optical heterodyne module also includes: a first laser module, used to generate a first laser beam; a second laser module, used to generate a second laser beam; a beam splitter, used to split the second laser beam into two paths; a coupler, used to couple the first laser beam with one of the second laser beams to obtain a third laser beam; a detection module, used to convert the third laser beam into a microwave signal; and a power divider, used to split the microwave signal into multiple paths.

[0007] Optionally, the frequency stabilization and frequency measurement module includes: a laser modulator, which is used to use one of the second laser light beams as a carrier to convert the microwave signal input to the frequency stabilization and frequency measurement module into a light wave containing frequency components of positive and negative first-order sidebands; an optical bandpass filter, which is used to filter out the positive first-order sideband in the light wave; a micro-ring-assisted Mach-Zehnder interferometer, which is used to split the light wave output by the optical bandpass filter into two light waves and then respectively measure the transmission spectra corresponding to the two light waves, and obtain the relationship between the power ratio of the two light waves and the frequency according to the transmission spectra of the two light waves; a power detection module, which is used to measure the power values ​​of the two light waves output by the micro-ring-assisted Mach-Zehnder interferometer, and feed back to the feedback control module.

[0008] Optionally, the frequency stabilization and measurement module further includes a polarization controller, the input end of the polarization controller is connected to the output end of the optical bandpass filter, and the output end of the polarization controller is connected to the input end of the micro-ring assisted Mach-Zehnder interferometer.

[0009] Optionally, the micro-ring assisted Mach-Zehnder interferometer includes: a Mach-Zehnder interferometer; two micro-rings are provided, and the two micro-rings are respectively provided on the upper arm and the lower arm of the Mach-Zehnder interferometer; three electrodes are provided, two of which are respectively provided on the two micro-rings, and the other electrode is provided on the upper arm / lower arm of the Mach-Zehnder interferometer.

[0010] Optionally, the circumference of the micro-ring is 2.5-3.5 mm, and the error of the circumference is less than 1 μm.

[0011] Optionally, the laser modulator is a Mach-Zehnder modulator.

[0012] Optionally, the power value in the transmission spectrum of one of the light waves first decreases and then increases within a certain frequency range, and the power value in the transmission spectrum of the other light wave first increases and then decreases within the same frequency range. A monotonic interval in which the power values ​​in the transmission spectra of the two light waves change in opposite directions is selected to calculate the power ratio, and a monotonic relationship between the power ratio and frequency is obtained.

[0013] Optionally, the preset microwave signal frequency value is the difference between the frequency values ​​of two laser light beams generated by the first laser module and the second laser module.

[0014] Optionally, the comparison result is an error value between the actual frequency value and the preset frequency value, and the frequency value of the first laser beam is regulated according to the error value so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value.

[0015] The at least one technical solution adopted in the embodiment of the present disclosure includes at least the following beneficial effects:

[0016] By introducing a frequency stabilization and frequency measurement module and a feedback control module into the tunable photogenerated microwave source system, the frequency stabilization and frequency measurement module can realize instantaneous and accurate measurement of the microwave signal frequency. After comparing the actual frequency value of the microwave signal with the preset frequency value, the laser beam frequency is adjusted to make the actual frequency value of the microwave signal output by the optical heterodyne module equal to the preset frequency value, thereby making the output microwave signal frequency have higher stability; at the same time, it also replaces the phase detection part in the traditional optical phase locking, thereby increasing the tunable range of the system.

[0017] Furthermore, by introducing a micro-ring-assisted Mach-Zehnder interferometer in the frequency stabilization and measurement module and utilizing microwave photonic technology, the instantaneous and accurate measurement of the microwave signal frequency can be achieved, and the frequency of the laser beam can be adjusted according to the real-time frequency measurement results, thereby obtaining a stable microwave signal.

[0018] Furthermore, the optical heterodyne method is used in the optical heterodyne module of the system to generate microwave signals. By changing the frequency of one of the laser beams, the frequency of the microwave signal can be adjusted to achieve the tunability of the microwave signal. At the same time, the bandwidth of the microwave signal is only limited by the response bandwidth of the detection module, so the microwave signal has a wider tunable frequency range.

[0019] In addition, the system has a simple structure and is easy to integrate into a single chip, which is beneficial to reducing the volume of the system and facilitating its promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a more complete understanding of the present disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, in which:

[0021] Figure 1 A block diagram of a tunable photogenerated microwave source system provided by an embodiment of the present disclosure is schematically shown;

[0022] Figure 2 The structure of a micro-ring-assisted Mach-Zehnder interferometer provided by an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] 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.

[0025] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] In the description of the present invention, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the subsystem or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0027] Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or configurations will be omitted when they may cause confusion in the understanding of the present invention. The shapes, sizes, and positional relationships of the components in the drawings do not reflect the actual size, proportion, and actual positional relationship. In addition, in the claims, any reference symbol between brackets shall not be construed as a limitation to the claims.

[0028] Similarly, in order to simplify the present invention and help understand one or more of the various disclosed aspects, in the above description of exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. The description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0029] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0030] The present disclosure provides a tunable photogenerated microwave source system, referring to Figure 1 The tunable optical microwave source system includes: an optical heterodyne module, which is used to generate a microwave signal using an output laser beam based on an optical heterodyne method; a frequency stabilization and frequency measurement module, which is used to modulate the microwave signal into a light wave containing a negative first-order sideband, and then split the light wave into two paths to measure the power values ​​of the two light waves, and obtain the relationship between the power ratio of the two light waves and the frequency through a preliminary test; a feedback control module, which is used to calculate the actual frequency value of the microwave signal according to the relationship between the power ratio and the frequency and the power values ​​of the two light waves, compare the actual frequency value with the preset frequency value of the microwave signal, and adjust the laser beam frequency according to the comparison result, so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value.

[0031] In some embodiments, the comparison result is an error value between the actual frequency value and the preset frequency value, and the frequency value of the first laser beam is adjusted according to the error value so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value.

[0032] In some embodiments, continue to refer to Figure 1 The optical heterodyne module also includes: a first laser module for generating a first laser beam; a second laser module for generating a second laser beam; a beam splitter for dividing the second laser beam into two paths; a coupler for coupling the first laser beam with one of the second laser beams to obtain a third laser beam; a detection module for converting the third laser beam into a microwave signal; and a power divider for dividing the microwave signal into multiple paths.

[0033] In some embodiments, the preset microwave signal frequency value is the difference between the frequency values ​​of the two laser beams generated by the first laser module and the second laser module.

[0034] In some embodiments, continue to refer to Figure 1The frequency stabilization and frequency measurement module includes: a laser modulator, an optical bandpass filter, a polarization controller, a micro-ring-assisted Mach-Zehnder interferometer and a power detection module arranged in sequence along the optical path; the laser modulator is used to use one of the second laser beams as a carrier to convert the microwave signal input to the frequency stabilization and frequency measurement module into a light wave containing positive and negative first-order sidebands as frequency components; the optical bandpass filter is used to filter out the positive first-order sideband in the light wave; the polarization controller is used to control the polarization characteristics of the light wave output from the optical bandpass filter; the micro-ring-assisted Mach-Zehnder interferometer is used to divide the light wave output by the polarization controller into two light waves and then respectively measure the transmission spectra corresponding to the two light waves, and obtain the relationship between the power ratio between the two light waves and the frequency according to the transmission spectra of the two light waves; the power detection module is used to measure the power values ​​of the two light waves output by the micro-ring-assisted Mach-Zehnder interferometer, and feed them back to the feedback control module.

[0035] In some embodiments, continue to refer to Figure 1 and Figure 2 The micro-ring-assisted Mach-Zehnder interferometer includes: a Mach-Zehnder interferometer; two micro-rings are provided, and the two micro-rings are respectively provided on the upper arm and the lower arm of the Mach-Zehnder interferometer; three electrodes are provided, wherein two electrodes are respectively provided on the two micro-rings, and the other electrode is provided on the upper arm / lower arm of the Mach-Zehnder interferometer.

[0036] In some embodiments, continue to refer to Figure 1 and Figure 2 , the circumference of the microring is 2.5-3.5mm, and the error of the circumference is less than 1μm.

[0037] In some embodiments, the circumference of the microring is 3 mm, and the present disclosure does not make specific limitations on the circumference of the microring. When the circumference of the microring changes by 1 μm, the influence on the power ratio obtained by the frequency stabilization and frequency measurement module as a function of the frequency change is relatively large, which may cause the monotonicity of the curve to change or lose its monotonicity. The function of the microring and the electrode is mainly to change the phase of the light wave after it has been transmitted along the microring for one cycle. After the entire system is manufactured, it needs to be debugged first to determine the voltages that need to be applied to the three electrodes. The size of the microring and the voltage of the electrode jointly determine the range and accuracy of the frequency measurement. The error caused by the microring process is reduced by adjusting the voltage applied to the electrode, thereby obtaining a trend of monotonic changes in the light wave power with the frequency within a certain frequency range.

[0038] In some embodiments, the laser modulator is a Mach-Zehnder modulator.

[0039] In some embodiments, the power value in the transmission spectrum of one light wave first decreases and then increases within a certain frequency range, and the power value in the transmission spectrum of the other light wave first increases and then decreases within the same frequency range. A monotonic interval in which the power values ​​in the transmission spectra of the two light waves change in opposite directions is selected to calculate the power ratio, and a monotonic relationship between the power ratio and frequency is obtained.

[0040] The specific working process of a tunable photogenerated microwave source system provided by an embodiment of the present disclosure is as follows: a first laser module generates a first laser beam, a second laser module generates a second laser beam, the frequencies of the first laser beam and the second laser beam are different, a beam splitter divides the second laser beam into two paths with the same frequency, a coupler couples the first laser beam with one of the second laser beams to obtain a third laser beam, the third laser beam is incident on a detection module, and the third laser beam is converted into a microwave signal; the microwave signal is input into a power splitter and then divided into multiple microwave signals with the same frequency.

[0041] Since the system will be disturbed by the external environment, the frequency of the microwave signal generated will fluctuate within a certain range, causing the instability of the microwave signal. In order to stabilize the output microwave signal, a frequency stabilization and frequency measurement module is introduced.

[0042] One of the microwave signals and one of the second laser beams are input into the Mach-Zehnder modulator, and the second laser beam is used as a carrier to modulate the microwave signal through the Mach-Zehnder modulator. An appropriate DC bias voltage is set for the Mach-Zehnder modulator so that the Mach-Zehnder modulator works in the carrier suppressed double sideband modulation mode. After the microwave signal is modulated by the Mach-Zehnder modulator, a carrier suppressed double sideband modulated light wave is obtained. When the high-order sidebands of the light wave are ignored, the frequency components contained in the light wave are positive and negative first-order sidebands, and the difference between the frequency value of the negative first-order sideband and the frequency value of the carrier is equal to the frequency value of the microwave signal input into the modulator. The modulated light wave is input into an optical bandpass filter to filter out the positive first-order sideband of the light wave and retain only the negative first-order sideband. The light wave output from the optical bandpass filter passes through a polarization controller to control the polarization characteristics of the light wave, and then is output to a micro-ring assisted Mach-Zehnder interferometer.

[0043] The main body of the micro-ring assisted Mach-Zehnder interferometer is a 2×2 Mach-Zehnder interferometer structure. A micro-ring is added to the upper and lower arms of the Mach-Zehnder interferometer structure to control the light wave transmission. At the same time, an electrode is set on the two micro-rings and the upper arm of the Mach-Zehnder interferometer structure to control the additional phase shift of the light wave (the positions of the three electrodes are Figure 2The position of one electrode can be any position of the upper arm and the lower arm of the Mach-Zehnder interferometer structure. In the embodiment of the present application, the specific position of the electrode in the upper arm or the lower arm of the Mach-Zehnder interferometer structure is not limited; the light wave enters through the lower input port of the micro-ring assisted Mach-Zehnder interferometer, and is propagated through the upper and lower arms respectively after being split by the directional coupler in the micro-ring assisted Mach-Zehnder interferometer, and a resonance phenomenon is generated at the micro-ring. The phase change of the light wave during the propagation process is controlled by designing the size structure of the micro-ring during system design and adjusting the voltage applied to the three electrodes. Finally, the two light waves are output from the output ends of the upper and lower arms respectively after passing through the directional coupler. Due to the introduction of the micro-ring and the control of the additional phase shift, two transmission spectra with opposite changes can be obtained at the output ends of the upper and lower arms. The power value in the transmission spectrum of the light wave output by the upper arm first decreases and then increases within a certain frequency range, and the power value in the transmission spectrum of the light wave output by the lower arm first increases and then decreases within the same frequency range. The monotonic interval in which the power values ​​in the transmission spectra of the two light waves change in opposite directions is selected to calculate the power ratio, and the monotonic relationship between the power ratio and the frequency is obtained. The monotonic relationship between the power ratio and the frequency is pre-input into the feedback control module. Finally, the light waves output by the upper and lower arms of the micro-ring-assisted Mach-Zehnder interferometer are input into the power detection module, and the power values ​​of the light waves output by the upper and lower arms of the micro-ring-assisted Mach-Zehnder interferometer are measured and fed back to the feedback control module.

[0044] The feedback control module first calculates the power ratio of the light waves output by the upper and lower arms of the pre-microring-assisted Mach-Zehnder interferometer according to the power values ​​of the light waves output by the upper and lower arms, and then calculates the frequency value according to the monotonic relationship between the power ratio and the frequency input in advance, and the frequency value is the actual frequency value of the microwave signal. The actual frequency value is compared with the preset frequency value of the microwave signal, and the comparison result is the error value between the actual frequency value and the preset frequency value. The frequency value of the first laser beam is adjusted according to the error value, so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value, thereby generating a stable microwave signal.

[0045] The tunability of the system is controlled by adjusting the frequency of the second laser beam output by the second laser module. Since the frequency of the generated microwave signal is equal to the difference between the frequencies of the first laser beam and the second laser beam, the frequency of the output microwave signal can be adjusted by the frequency of the second laser beam.

[0046] The frequency interval in which the transmission spectra of the two light waves output by the micro-ring-assisted Mach-Zehnder interferometer show a monotonic change in the opposite direction is only about 7 GHz, and the measurable frequency range is small, that is, the microwave frequency range that can be obtained is small. However, the design of this system can solve this defect. Considering that the passband range of the bandpass filter will not change, when the frequency of the output microwave signal is increased (or decreased) in advance, the frequency of the second laser beam needs to be increased (or decreased), which also means that the carrier frequency of the frequency stabilization and frequency measurement module is increased (or decreased). After modulation by the Mach-Zehnder modulator, because the carrier frequency and the microwave signal frequency are increased (or decreased) at the same time, the frequency value of the negative first-order sideband can be stably present in the passband of the bandpass filter, and is not affected by the change of the microwave signal and the frequency of the second laser beam. Similarly, the final light wave frequency will be maintained within the interval in which the transmission spectra of the two light waves output by the micro-ring-assisted Mach-Zehnder interferometer show a monotonic change in the opposite direction, so the frequency measurement range can be expanded. It is only necessary to change the corresponding relationship between power and frequency in the feedback control module accordingly to obtain the new actual frequency value of the microwave signal. The feedback control module can directly add or subtract the frequency mapped by the same power according to the change in the frequency of the optical heterodyne module, thereby obtaining a new mapping. Based on this, the effective range of the frequency of the frequency stabilization and frequency measurement module can be effectively expanded, thereby increasing the frequency adjustment range of the generated microwave signal from the original 0-7GHz to about 0-40GHz, expanding the measurement frequency range of the microwave signal.

[0047] The specific embodiments described above further illustrate the technical solutions of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A tunable photogenerated microwave source system, characterized in that: include: An optical heterodyne module, used for generating a microwave signal using an output laser beam based on an optical heterodyne method; The frequency stabilization and frequency measurement module is used to modulate the microwave signal into a light wave containing a negative first-order sideband, and then measure the power values ​​of the two light waves after splitting the light wave into two paths, and obtain the relationship between the power ratio of the two light waves and the frequency through pre-testing; A feedback control module, used for calculating the actual frequency value of the microwave signal according to the relationship between the power ratio and the frequency and the power values ​​of the two optical waves, comparing the actual frequency value with the preset frequency value of the microwave signal, and regulating the laser beam frequency according to the comparison result so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value; Wherein, the optical heterodyne module further includes: A first laser module, used to generate a first laser beam; A second laser module, used to generate a second laser beam; A beam splitter, used for splitting the second laser beam into two paths; a coupler, used for coupling the first laser beam with one of the second laser beams to obtain a third laser beam; A detection module, used for converting the third laser beam into a microwave signal; Power divider, used to divide microwave signals into multiple paths; The frequency stabilization and frequency measurement module comprises: A laser modulator, used for converting the microwave signal input to the frequency stabilization and frequency measurement module into a light wave containing frequency components of positive and negative first-order sidebands by using one of the second laser beams as a carrier; An optical bandpass filter, used for filtering out the positive first-order sideband in the optical wave; A micro-ring-assisted Mach-Zehnder interferometer is used to split the light wave output by the optical bandpass filter into two light waves and then respectively measure the transmission spectra corresponding to the two light waves, and obtain the relationship between the power ratio of the two light waves and the frequency according to the transmission spectra of the two light waves; A power detection module, used to measure the power values ​​of the two optical waves output by the micro-ring assisted Mach-Zehnder interferometer, and feed back the power values ​​to the feedback control module; A polarization controller, wherein the input end of the polarization controller is connected to the output end of the optical bandpass filter, and the output end of the polarization controller is connected to the input end of the micro-ring assisted Mach-Zehnder interferometer; The micro-ring assisted Mach-Zehnder interferometer comprises: Mach-Zehnder interferometer; Two microrings are provided, and the two microrings are respectively provided on the upper arm and the lower arm of the Mach-Zehnder interferometer; There are three electrodes, two of which are respectively arranged on the two micro-rings, and the other electrode is arranged on the upper arm / lower arm of the Mach-Zehnder interferometer.

2. The tunable photogenerated microwave source system according to claim 1, characterized in that: The circumference of the micro-ring is 2.5-3.5 mm, and the error of the circumference is less than 1 μm.

3. The tunable photogenerated microwave source system according to claim 1, characterized in that: The laser modulator is a Mach-Zehnder modulator.

4. The tunable photogenerated microwave source system according to claim 1, characterized in that: The power value in the transmission spectrum of one of the light waves first decreases and then increases within a certain frequency range, and the power value in the transmission spectrum of the other light wave first increases and then decreases within the same frequency range. A monotonic interval in which the power values ​​in the transmission spectra of the two light waves change in opposite directions is selected to calculate the power ratio, and a monotonic relationship between the power ratio and frequency is obtained.

5. The tunable photogenerated microwave source system according to claim 1, characterized in that: The preset frequency value is the difference between the frequency values ​​of the two laser beams generated by the first laser module and the second laser module.

6. The tunable photogenerated microwave source system according to claim 1, characterized in that: The comparison result is the error value between the actual frequency value and the preset frequency value. The frequency value of the first laser beam is regulated according to the error value so that the actual frequency value of the microwave signal output by the optical heterodyne module is equal to the preset frequency value.

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