Continuous-wave swept laser based on cyclic frequency shifting

Abstract

The present invention provides a continuous wave frequency sweeping laser based on cyclic frequency shifting, comprising a cyclic frequency shifting loop, the cyclic frequency shifting loop comprising a gain medium, a coupler, a filter and a variable frequency shifter, the output end of the gain medium is connected to the input end of the coupler, the first output end of the coupler is connected to the input end of the gain medium through the filter and the variable frequency shifter in sequence; the gain medium generates a multi-longitudinal mode laser under the excitation of a pump source, the coupler transmits a part of the multi-longitudinal mode laser, and transmits another part of the multi-longitudinal mode laser to the filter; the filter selects a single longitudinal mode laser of a corresponding frequency from the multi-longitudinal mode laser; the single longitudinal mode laser is frequency shifted by the variable frequency shifter, amplified by the gain medium and transmitted to the coupler, the coupler transmits a part of the single longitudinal mode laser, and the other part of the single longitudinal mode laser is transmitted to the variable frequency shifter through the filter for cyclic frequency shifting. The frequency sweeping curve followed by the laser frequency sweeping of the present invention is adjustable.

Description

Technical Field

[0001] The invention belongs to the field of frequency sweeping lasers, and in particular relates to a continuous wave frequency sweeping laser based on cyclic frequency shifting. Background Art

[0002] Frequency-swept lasers have many advantages, such as continuous frequency shifting, wide tuning range, fast tuning speed, low insertion loss, and easy preparation, and are therefore widely used in the fields of optical communications and sensing. However, existing frequency-swept lasers mainly achieve continuous scanning of the laser longitudinal mode frequency by changing the cavity length through mechanical devices, with slow tuning speed and the flexibility of laser frequency regulation needs to be improved. Summary of the invention

[0003] The invention provides a continuous wave frequency sweeping laser based on cyclic frequency shifting, so as to solve the problems of slow tuning speed and poor flexibility of the current frequency sweeping laser.

[0004] According to a first aspect of an embodiment of the present invention, there is provided a continuous wave frequency sweeping laser based on cyclic frequency shifting, comprising a cyclic frequency shifting loop, wherein the cyclic frequency shifting loop comprises a gain medium, a coupler, a filter and a variable frequency shifter, wherein the output end of the gain medium is connected to the input end of the coupler, the first output end of the coupler is connected to the input end of the gain medium through the filter and the variable frequency shifter in sequence, and the second output end of the coupler serves as the laser output end of the frequency sweeping laser;

[0005] The gain medium generates multi-longitudinal mode laser light under the excitation of the pump source and transmits the multi-longitudinal mode laser light to the coupler; the coupler transmits a part of the multi-longitudinal mode laser light and transmits another part of the multi-longitudinal mode laser light to the filter; the filter selects a single longitudinal mode laser light of a corresponding frequency from the multi-longitudinal mode laser light and provides the single longitudinal mode laser light to the variable frequency shifter; the variable frequency shifter performs frequency shift processing on the single longitudinal mode laser light and transmits the single longitudinal mode laser light after the frequency shift processing back to the gain optical fiber;

[0006] The gain optical fiber performs gain amplification on the single longitudinal mode laser, and transmits the gain-amplified single longitudinal mode laser to the coupler. The coupler transmits a portion of the single longitudinal mode laser, and the other portion of the single longitudinal mode laser is transmitted to the variable frequency shifter through the filter for cyclic frequency shifting until all of the single longitudinal mode laser is output from the second output end of the coupler in the cyclic frequency shift loop.

[0007] In an optional implementation, the frequency shift amount of the single longitudinal mode laser output from the second output end of the coupler is related to the time it takes for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop, the number of cyclic transmissions in the cyclic frequency shift loop, and the frequency shift amount of the single longitudinal mode laser each time it passes through the variable frequency shifter.

[0008] In another optional implementation, the frequency shift amount of the single longitudinal mode laser output from the second output end of the coupler is adjusted by changing at least one of the time the single longitudinal mode laser is transmitted once in the cyclic frequency shift loop, the splitting ratio of the coupler, and the frequency shift amount sweep curve of the variable frequency shifter, thereby adjusting the frequency sweep curve of the single longitudinal mode laser.

[0009] In another optional implementation, changing the frequency shift sweep curve of the variable frequency shifter includes changing the waveform of the frequency shift sweep curve, and changing the amplitude and period of the frequency shift sweep curve without changing the waveform of the frequency shift sweep curve; adjusting the sweep curve of the single longitudinal mode laser includes adjusting the waveform, amplitude and period of the sweep curve.

[0010] In another optional implementation, the variable frequency shifter is an adjustable acousto-optic frequency shifter, comprising a first adjustable acousto-optic frequency shift unit and a second adjustable acousto-optic frequency shift unit connected in series, wherein the first free end of the first adjustable acousto-optic frequency shift unit and the second adjustable acousto-optic frequency shift unit connected in series are connected to the output end of the filter, and the second free end is connected to the input end of the gain medium; the first adjustable acousto-optic frequency shift unit is used to generate a fixed frequency shift amount, and the second adjustable acousto-optic frequency shift unit is used to generate an initial frequency shift amount sweep curve; the initial frequency shift amount sweep curve is subtracted from the fixed frequency shift amount to obtain the frequency shift amount sweep curve starting from zero frequency, and the variable frequency shifter uses the frequency shift amount sweep curve to perform frequency shift processing on the single longitudinal mode laser.

[0011] In another optional implementation, the frequency shift amount Δf of the single longitudinal mode laser during one cycle frequency shift is:

[0012] Δf=f2-f1,

[0013] Wherein, f2 represents the frequency shift amount of the single longitudinal mode laser after passing through the second adjustable acousto-optic frequency shift unit, and f1 represents the frequency shift amount of the single longitudinal mode laser after passing through the first adjustable acousto-optic frequency shift unit. By adjusting the size of f1 and / or f2, the frequency shift amount Δf can be arbitrarily changed with time near the zero frequency;

[0014] according to It is deduced that the cumulative frequency shift f of the single longitudinal mode laser in the previous cyclic frequency shift processes is:

[0015]

[0016] Where τ represents the time it takes for a single longitudinal mode laser to transmit once in the cyclic frequency shift loop. Represents the frequency shift rate of single longitudinal mode laser.

[0017] In another optional implementation, the filter is an adjustable acousto-optic filter, which is used to adjust the frequency range of the single longitudinal mode laser selected from the multi-longitudinal mode laser.

[0018] In another optional implementation, the frequency shift sweep curve is a frequency shift sine curve that starts from zero frequency. The time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop is equal to one frequency shift period in the frequency shift sine curve. At this time, the single longitudinal mode laser is frequency shifted according to the cosine curve, thereby obtaining a single longitudinal mode cosine swept laser.

[0019] In another optional implementation, an isolator is provided between the variable frequency shifter and the input end of the gain medium.

[0020] In another optional implementation, it also includes a control circuit, which is respectively connected to the filter and the variable frequency shifter, and is used to output a first control signal to control the filter so as to adjust the frequency range of the single longitudinal mode laser selected by the filter from the multi-longitudinal mode laser; the control circuit is also used to output a second control signal to control the variable frequency shifter so as to adjust the frequency shift sweep curve provided by the variable frequency shifter.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention designs a cyclic frequency shift loop, firstly selects a single longitudinal mode laser of corresponding frequency from the generated multi-longitudinal mode lasers, so that the frequency sweeping law of the single longitudinal mode laser is completely determined by the cyclic frequency shift loop. In the cyclic frequency shift loop, the frequency sweeping curve of the single longitudinal mode laser can be changed by adjusting three parameters: the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop, the number of cyclic transmissions of the single longitudinal mode laser in the cyclic frequency shift loop, and the frequency shift sweeping curve provided by the variable frequency shifter. Even if the frequency shift structure remains unchanged and the corresponding frequency shift sweeping curve waveform remains unchanged, the waveform of the frequency sweeping curve that the single longitudinal mode laser can follow can be changed by adjusting the two parameters: the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop and the number of cyclic transmissions in the cyclic frequency shift loop. It can be seen that the frequency sweeping curve followed by the laser frequency sweeping of the present invention is adjustable, especially the waveform of the laser frequency sweeping curve is adjustable, so the frequency sweeping laser of the present invention has better versatility, faster tuning speed and better flexibility.

[0023] 2. The present invention can adjust the frequency range of single longitudinal mode laser by setting an adjustable acousto-optic filter;

[0024] 3. The present invention provides a first adjustable acousto-optic frequency shifting unit and a second adjustable acousto-optic frequency shifting unit, and subtracts the initial frequency shifting sweeping curve generated by the second adjustable acousto-optic frequency shifting unit from the fixed frequency shifting amount generated by the first adjustable acousto-optic frequency shifting unit, thereby obtaining a frequency shifting sweeping curve starting from zero frequency, and the two frequency shifting units are adjustable, so that the frequency shifting sweeping curve can be adjusted;

[0025] 4. The present invention can ensure that the single longitudinal mode laser is transmitted along a preset route by setting an isolator;

[0026] 5. The present invention can control the filter to adjust the frequency range of the single longitudinal mode laser by setting a control circuit; and can control the variable frequency shifter to adjust the frequency shift sweep curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of an embodiment of a continuous wave frequency sweeping laser based on cyclic frequency shifting of the present invention;

[0028] Figure 2 It is a structural schematic diagram of another embodiment of the continuous wave frequency sweeping laser based on cyclic frequency shifting of the present invention;

[0029] Figure 3 is a schematic diagram of an embodiment of a frequency shift sweep curve of the present invention;

[0030] Figure 4 It is a schematic diagram of an embodiment of the frequency sweep curve of the present invention. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0032] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] See also Figure 1, is a schematic diagram of the structure of an embodiment of a continuous wave frequency sweeping laser based on cyclic frequency shifting of the present invention. The continuous wave frequency sweeping laser based on cyclic frequency shifting may include a cyclic frequency shifting loop, which includes a gain medium 2, a coupler 3, a filter 4 and a variable frequency shifter 5. The output end of the gain medium 2 is connected to the input end of the coupler 3, and the first output end of the coupler 3 is connected to the input end of the gain medium 2 through the filter 4 and the variable frequency shifter 5 in sequence. The second output end of the coupler 3 serves as the laser output end of the frequency sweeping laser; under the excitation of the pump source, the gain medium 2 generates a multi-longitudinal mode laser and transmits the multi-longitudinal mode laser to the coupler 3, and the coupler 3 transmits a part of the multi-longitudinal mode laser to the coupler 3, and the other part of the multi-longitudinal mode laser is transmitted to the coupler 3. filter 4; the filter 4 selects a single longitudinal mode laser of a corresponding frequency from the multi-longitudinal mode laser and provides the single longitudinal mode laser to the variable frequency shifter 5; the variable frequency shifter 5 performs frequency shifting on the single longitudinal mode laser and transmits the single longitudinal mode laser after frequency shifting back to the gain fiber 2; the gain fiber 2 performs gain amplification on the single longitudinal mode laser and transmits the gain-amplified single longitudinal mode laser to the coupler 3, the coupler 3 transmits a part of the single longitudinal mode laser, and transmits the other part of the single longitudinal mode laser to the variable frequency shifter 5 through the filter 4 for cyclic frequency shifting, until all the single longitudinal mode lasers are output from the second output end of the coupler 3 in the cyclic frequency shifting loop.

[0034] In this embodiment, the frequency shift amount of the single longitudinal mode laser output from the second output end of the coupler is related to the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop, the number of cyclic transmissions in the cyclic frequency shift loop, and the frequency shift amount of the single longitudinal mode laser each time it passes through the variable frequency shifter. The present invention can adjust the frequency shift amount of the single longitudinal mode laser output from the second output end of the coupler by changing at least one of the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop, the splitting ratio of the coupler, and the frequency shift amount sweep curve of the variable frequency shifter, thereby adjusting the frequency sweep curve of the single longitudinal mode laser. Among them, a delay device can be provided in the cyclic frequency shift loop to adjust the time for a single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop; changing the splitting ratio of the coupler can adjust the number of cyclic transmissions in the single longitudinal mode laser re-circulating frequency shift loop; changing the frequency shift amount sweep curve of the variable frequency shifter can adjust the frequency shift amount of the single longitudinal mode laser each time it passes through the variable frequency shifter; changing the frequency shift amount sweep curve of the variable frequency shifter can include replacing the variable frequency shifter to change the waveform of the frequency shift amount sweep curve, and changing the amplitude and period of the frequency shift amount sweep curve without replacing the variable frequency shifter and without changing the waveform of the frequency shift amount sweep curve; adjusting the sweep frequency curve of the single longitudinal mode laser can include adjusting the waveform, amplitude and period of the sweep frequency curve.

[0035] In this embodiment, for the corresponding amount of multi-longitudinal mode laser generated by the gain medium under the excitation of the pump source, the corresponding amount of single longitudinal mode laser is obtained after passing through the filter. In the process of passing through the cyclic frequency shift loop, part of the single longitudinal mode laser is continuously gain-amplified and its frequency shift amount is continuously accumulated and changed. When the part of the single longitudinal mode laser is output from the second output end of the coupler, the frequency shift amount of the part of the single longitudinal mode laser is equal to the sum of the frequency shift amounts of the single longitudinal mode laser in the previous transmission process of the cyclic frequency shift loop. Since the gain medium will continuously generate multi-longitudinal mode laser under the excitation of the pump source, the frequency shift amount of the selected single longitudinal mode laser from the multi-longitudinal mode laser generated subsequently during the transmission of the cyclic frequency shift loop is closely related to the frequency shift amount sweep curve provided by the variable frequency shifter. In addition, in order to quickly obtain the laser that sweeps according to the corresponding curve, the multi-longitudinal mode laser generated by the gain medium can be gain-amplified multiple times in the cyclic frequency shift loop before the filter and the variable frequency shifter start working.

[0036] It can be seen from the above embodiments that, conventionally, the frequency shift sweep curve waveform that can be output by the variable frequency shifter is single. In order to obtain frequency shift sweep curves with more waveforms, the variable frequency shifter needs to be redesigned. The structure is relatively complex and one frequency shift structure can only generate a frequency shift sweep curve with one waveform in a targeted manner. The frequency shift structure is not universal. The present invention designs a cyclic frequency shift loop, firstly selects a single longitudinal mode laser of corresponding frequency from the generated multi-longitudinal mode lasers, so that the frequency sweeping law of the single longitudinal mode laser is completely determined by the cyclic frequency shift loop, and in the cyclic frequency shift loop, the frequency sweeping curve of the single longitudinal mode laser can be changed by adjusting three parameters, namely, the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop, the number of cyclic transmissions of the single longitudinal mode laser in the cyclic frequency shift loop, and the frequency shift amount sweeping curve provided by the variable frequency shifter. Even if the frequency shift structure remains unchanged and the corresponding frequency shift amount sweeping curve waveform remains unchanged, the waveform of the frequency sweeping curve that the single longitudinal mode laser can follow can be changed by adjusting the two parameters, namely, the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop and the number of cyclic transmissions in the cyclic frequency shift loop. It can be seen that the frequency sweeping curve followed by the laser frequency sweeping of the present invention is adjustable, especially the waveform of the laser frequency sweeping curve is adjustable, so the frequency sweeping laser of the present invention has better versatility, faster tuning speed and better flexibility.

[0037] See also Figure 2 , is a schematic structural diagram of another embodiment of a continuous wave frequency-sweeping laser based on cyclic frequency shifting. Figure 2 and Figure 1The difference between the continuous wave frequency sweeping laser based on cyclic frequency shift shown in the figure is that the filter 4 is an adjustable acousto-optic filter, which is used to adjust the frequency range of the single longitudinal mode laser selected from the multi-longitudinal mode laser. The present invention can achieve single longitudinal mode laser frequency range adjustment by setting an adjustable acousto-optic filter. In addition, the variable frequency shifter 5 can be an adjustable acousto-optic frequency shifter, including a first adjustable acousto-optic frequency shift unit 51 and a second adjustable acousto-optic frequency shift unit 52 connected in series, the first free ends of the first adjustable acousto-optic frequency shift unit 51 and the second adjustable acousto-optic frequency shift unit 52 connected in series are connected to the output end of the filter 4, and the second free ends are connected to the input end of the gain medium 2; the first adjustable acousto-optic frequency shift unit 51 is used to generate a fixed frequency shift amount, and the second adjustable acousto-optic frequency shift unit 52 is used to generate an initial frequency shift amount sweep curve; the initial frequency shift amount sweep curve is subtracted from the fixed frequency shift amount to obtain the frequency shift amount sweep curve that starts from zero frequency, and the variable frequency shifter 5 uses the frequency shift amount sweep curve to perform frequency shift processing on the single longitudinal mode laser. Generally, it is difficult for a variable frequency shifter to generate a frequency shift sweep curve starting from zero frequency. The present invention provides a first adjustable acousto-optic frequency shift unit and a second adjustable acousto-optic frequency shift unit, and subtracts the initial frequency shift sweep curve generated by the second adjustable acousto-optic frequency shift unit from the fixed frequency shift generated by the first adjustable acousto-optic frequency shift unit, thereby obtaining a frequency shift sweep curve starting from zero frequency. The two frequency shift units are adjustable, so the frequency shift sweep curve can be adjusted, and the adjustment amount can start from zero frequency, with a larger adjustment range. In one embodiment, the frequency shift sweep curve can be a frequency shift sinusoidal curve starting from zero frequency, such as Figure 3 As shown, the time for a single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop is equal to one frequency shift period in the frequency shift amount sine curve. At this time, the single longitudinal mode laser is frequency shifted according to the cosine curve, thereby obtaining a single longitudinal mode cosine swept laser, as shown in FIG. Figure 4 shown.

[0038] In this embodiment, the frequency shift amount Δf of the single longitudinal mode laser during one cycle frequency shift is:

[0039] Δf=f2-f1,

[0040] Wherein, f2 represents the frequency shift amount of the single longitudinal mode laser after passing through the second adjustable acousto-optic frequency shift unit, and f1 represents the frequency shift amount of the single longitudinal mode laser after passing through the first adjustable acousto-optic frequency shift unit. By adjusting the size of f1 and / or f2, the frequency shift amount Δf can be arbitrarily changed with time near the zero frequency;

[0041] according to It is deduced that the cumulative frequency shift f of the single longitudinal mode laser in the previous cyclic frequency shift processes is:

[0042]

[0043] Where τ represents the time it takes for a single longitudinal mode laser to transmit once in the cyclic frequency shift loop. Represents the frequency shift rate of single longitudinal mode laser.

[0044] Figure 2 and Figure 1 The difference of the continuous wave frequency sweeping laser based on cyclic frequency shift shown is that an isolator 1 is provided between the variable frequency shifter and the input end of the gain medium. By providing the isolator, the present invention can ensure that the single longitudinal mode laser is transmitted along a preset route. Figure 2 The continuous wave frequency sweeping laser based on cyclic frequency shifting shown in the figure also includes a control circuit 7, which is connected to the filter 4 and the variable frequency shifter 5 respectively, and is used to output a first control signal 61 to control the filter 4, so as to adjust the frequency range of the single longitudinal mode laser selected by the filter 4 from the multi-longitudinal mode laser; the control circuit is also used to output a second control signal 62 to control the variable frequency shifter 5, so as to adjust the frequency shift amount sweeping curve provided by the variable frequency shifter 5. By setting a control circuit, the present invention can control the filter to achieve the adjustment of the frequency range of the single longitudinal mode laser; and can control the variable frequency shifter to achieve the adjustment of the frequency shift amount sweeping curve.

[0045] It can be seen from the above embodiments that the present invention designs a cyclic frequency shift loop to first select a single longitudinal mode laser of corresponding frequency from the generated multi-longitudinal mode lasers, so that the frequency sweeping law of the single longitudinal mode laser is completely determined by the cyclic frequency shift loop. In the cyclic frequency shift loop, the frequency sweeping curve of the single longitudinal mode laser can be changed by adjusting three parameters: the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop, the number of cyclic transmissions of the single longitudinal mode laser in the cyclic frequency shift loop, and the frequency shift amount sweeping curve provided by the variable frequency shifter. Even if the frequency shift structure remains unchanged and the corresponding frequency shift amount sweeping curve waveform remains unchanged, the waveform of the frequency sweeping curve that the single longitudinal mode laser can follow can be changed by adjusting the two parameters: the time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop and the number of cyclic transmissions in the cyclic frequency shift loop. It can be seen that the frequency sweeping curve followed by the laser frequency sweeping of the present invention is adjustable, especially the waveform of the laser frequency sweeping curve is adjustable. Therefore, the frequency sweeping laser of the present invention has better versatility, faster tuning speed and better flexibility.

[0046] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0047] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. A continuous wave frequency-sweeping laser based on cyclic frequency shifting, characterized in that: The invention comprises a cyclic frequency shift loop, wherein the cyclic frequency shift loop comprises a gain medium, a coupler, a filter and a variable frequency shifter, wherein the output end of the gain medium is connected to the input end of the coupler, the first output end of the coupler is connected to the input end of the gain medium through the filter and the variable frequency shifter in sequence, and the second output end of the coupler serves as the laser output end of the frequency sweeping laser; The gain medium generates a multi-longitudinal mode laser under the excitation of the pump source and transmits the multi-longitudinal mode laser to the coupler, the coupler transmits a part of the multi-longitudinal mode laser and transmits another part of the multi-longitudinal mode laser to the filter; the filter selects a single longitudinal mode laser of a corresponding frequency from the multi-longitudinal mode laser and provides the single longitudinal mode laser to the variable frequency shifter; the variable frequency shifter performs frequency shift processing on the single longitudinal mode laser and transmits the single longitudinal mode laser after the frequency shift processing back to the gain medium; The gain medium performs gain amplification on the single longitudinal mode laser, and transmits the gain-amplified single longitudinal mode laser to the coupler, the coupler transmits a portion of the single longitudinal mode laser, and transmits another portion of the single longitudinal mode laser to the variable frequency shifter through the filter for cyclic frequency shifting, until all of the single longitudinal mode laser is output from the second output end of the coupler in the cyclic frequency shift loop; The variable frequency shifter is an adjustable acousto-optic frequency shifter, comprising a first adjustable acousto-optic frequency shift unit and a second adjustable acousto-optic frequency shift unit connected in series, wherein the first free end of the first adjustable acousto-optic frequency shift unit and the second adjustable acousto-optic frequency shift unit connected in series are connected to the output end of the filter, and the second free end is connected to the input end of the gain medium; the first adjustable acousto-optic frequency shift unit is used to generate a fixed frequency shift amount, and the second adjustable acousto-optic frequency shift unit is used to generate an initial frequency shift amount sweep curve; the initial frequency shift amount sweep curve is subtracted from the fixed frequency shift amount to obtain the frequency shift amount sweep curve that starts frequency shifting from zero frequency, and the variable frequency shifter uses the frequency shift amount sweep curve to perform frequency shift processing on the single longitudinal mode laser.

2. The continuous wave frequency sweeping laser based on cyclic frequency shifting according to claim 1, characterized in that: The frequency shift amount of the single longitudinal mode laser output from the second output end of the coupler is related to the time the single longitudinal mode laser is transmitted once in the cyclic frequency shift loop, the number of cyclic transmissions in the cyclic frequency shift loop, and the frequency shift amount of the single longitudinal mode laser each time it passes through the variable frequency shifter.

3. The continuous wave frequency sweeping laser based on cyclic frequency shifting according to claim 2, characterized in that: By changing at least one of the time that the single longitudinal mode laser is transmitted once in the cyclic frequency shift loop, the splitting ratio of the coupler, and the frequency shift sweep curve of the variable frequency shifter, the frequency shift amount of the single longitudinal mode laser output from the second output end of the coupler is adjusted, thereby adjusting the frequency sweep curve of the single longitudinal mode laser.

4. The continuous wave frequency sweeping laser based on cyclic frequency shift according to claim 3, characterized in that: Changing the frequency shift sweep curve of the variable frequency shifter includes changing the waveform of the frequency shift sweep curve, and changing the amplitude and period of the frequency shift sweep curve without changing the waveform of the frequency shift sweep curve; adjusting the sweep curve of the single longitudinal mode laser includes adjusting the waveform, amplitude and period of the sweep curve.

5. The continuous wave frequency sweeping laser based on cyclic frequency shift according to any one of claims 1 to 4, characterized in that: The filter is an adjustable acousto-optic filter, which is used to adjust the frequency range of the single longitudinal mode laser selected from the multi-longitudinal mode laser.

6. The continuous wave frequency sweeping laser based on cyclic frequency shifting according to claim 1, characterized in that: The frequency shift amount Δf during the one-cycle frequency shift of the single longitudinal mode laser is: Δf=f2-f1, Wherein, f2 represents the frequency shift amount of the single longitudinal mode laser after passing through the second adjustable acousto-optic frequency shift unit, and f1 represents the frequency shift amount of the single longitudinal mode laser after passing through the first adjustable acousto-optic frequency shift unit. By adjusting the size of f1 and / or f2, the frequency shift amount Δf can be arbitrarily changed with time near the zero frequency; according to It is deduced that the cumulative frequency shift f of the single longitudinal mode laser in the previous cyclic frequency shift processes is: Where τ represents the time it takes for a single longitudinal mode laser to transmit once in the cyclic frequency shift loop. Represents the frequency shift rate of single longitudinal mode laser.

7. The continuous wave frequency sweeping laser based on cyclic frequency shifting according to claim 6, characterized in that: The frequency shift sweep curve is a frequency shift sine curve that shifts frequency from zero frequency. The time for the single longitudinal mode laser to be transmitted once in the cyclic frequency shift loop is equal to one frequency shift period in the frequency shift sine curve. At this time, the single longitudinal mode laser is frequency shifted according to the cosine curve, thereby obtaining a single longitudinal mode cosine swept laser.

8. The continuous wave frequency sweeping laser based on cyclic frequency shifting according to claim 1, characterized in that: An isolator is provided between the variable frequency shifter and the input end of the gain medium.

9. The continuous wave frequency sweeping laser based on cyclic frequency shifting according to claim 1, characterized in that: It also includes a control circuit, which is connected to the filter and the variable frequency shifter respectively, and is used to output a first control signal to control the filter so as to adjust the frequency range of the single longitudinal mode laser selected by the filter from the multi-longitudinal mode laser; the control circuit is also used to output a second control signal to control the variable frequency shifter so as to adjust the frequency shift sweep curve provided by the variable frequency shifter.

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