Narrow-linewidth continuous frequency sweeping Brillouin laser based on mode following principle

Abstract

The invention provides a narrow linewidth continuous frequency sweeping Brillouin laser based on a mode following principle, which comprises a tunable pumping laser source, a Brillouin ring cavity and a feedback control unit, and is characterized in that the output end of the tunable pumping laser source is connected with the input end of the Brillouin ring cavity; the first output end of the feedback control unit is connected with the control end of the Brillouin ring cavity; the tunable pump laser source transmits pump laser to the Brillouin annular cavity, the pump laser generates a stimulated Brillouin scattering signal in the transmission process in the Brillouin annular cavity, and the Brillouin annular cavity tunes a cavity mode in the Brillouin annular cavity according to a first control signal provided by the feedback control unit. The tunable pump laser source is used for pumping the Brillouin ring cavity, so that the tuning speed of the tunable pump laser source is matched with the tuning speed of a cavity mode in the Brillouin ring cavity, a Brillouin frequency sweeping signal obtained after cavity mode tuning is circularly amplified to an intra-cavity threshold value in the Brillouin ring cavity, and then the Brillouin frequency sweeping signal serves as Brillouin frequency sweeping laser to be output. The Brillouin laser breaks through the range limitation of continuous tuning of the Brillouin laser.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber lasers, and in particular relates to a narrow-linewidth continuous-frequency-sweeping Brillouin laser based on a mode-following principle. Background Art

[0002] With the continuous development of science and technology, fiber optic sensing technology has become increasingly important, and the core device involved in fiber optic sensing technology is the continuous frequency sweeping laser. At present, most of the commercial frequency sweeping lasers that are widely used on the market are based on external cavity tuning. This frequency sweeping laser relies on a sophisticated MEMS electronic control system, which is expensive, and the laser line width is usually in the order of 100kHz. The fiber laser based on Brillouin can well achieve narrow linewidth laser output of kHz and below thanks to the narrowband gain characteristics of Brillouin. In addition, the frequency sweeping laser based on the Brillouin all-fiber structure has the advantages of simple structure and low cost. The way to achieve frequency tuning based on the Brillouin frequency sweeping laser is mainly to introduce a stress stretching device into the cavity, wrap the gain fiber around the piezoelectric ceramic, and apply a driving signal to the piezoelectric ceramic to generate periodic resonance, drive the laser cavity length to change, and achieve continuous tuning of the output laser. The frequency tuning range that can be finally achieved by this technical solution is usually tens of MHz. The size of the continuous tuning range is mainly limited by the free spectral range FSR of the Brillouin ring cavity and the size of the Brillouin gain bandwidth. When the longitudinal mode tuning range corresponding to the tuned laser exceeds an FSR or Brillouin gain bandwidth range, mode hopping will occur, resulting in phase discontinuity of the output laser. Summary of the invention

[0003] The invention provides a narrow-linewidth continuous frequency-sweeping Brillouin laser based on the mode following principle, so as to solve the problem that the continuous tuning range of the current frequency-sweeping laser is limited.

[0004] According to a first aspect of an embodiment of the present invention, there is provided a narrow linewidth continuous frequency swept Brillouin laser based on a mode following principle, comprising a tunable pump laser source, a Brillouin ring cavity and a feedback control unit, wherein the output end of the tunable pump laser source is connected to the input end of the Brillouin ring cavity, and the first output end of the feedback control unit is connected to the control end of the Brillouin ring cavity;

[0005] The tunable pump laser source transmits the pump laser to the Brillouin ring cavity. The pump laser generates a stimulated Brillouin scattering signal during the transmission process in the Brillouin ring cavity. The Brillouin ring cavity tunes the cavity mode in the Brillouin ring cavity according to the first control signal provided by the feedback control unit, so that the tuning speed of the tunable pump laser source matches the tuning speed of the cavity mode in the Brillouin ring cavity. The Brillouin swept-frequency signal of the corresponding frequency band obtained after the cavity mode is tuned is cyclically amplified in the Brillouin ring cavity until it reaches the intracavity threshold, and then is output as the Brillouin swept-frequency laser of the frequency band.

[0006] In an optional implementation, the device further includes a first coupler and a second coupler, wherein the output end of the Brillouin ring cavity is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the feedback control unit, and the second output end serves as the Brillouin frequency sweep laser output end; the Brillouin ring cavity divides the Brillouin frequency sweep laser into two paths through the first coupler, one path is directly output, and the other path is transmitted to the feedback control unit;

[0007] The output end of the tunable pump laser source is connected to the input end of the second coupler, the first output end of the second coupler is connected to the input end of the Brillouin ring cavity, and the second output end is connected to the second input end of the feedback control unit; the tunable pump laser source transmits the pump laser to the Brillouin ring cavity and the feedback control unit respectively through the second coupler;

[0008] The feedback control unit determines whether mode hopping occurs in the Brillouin swept laser. If so, the magnitude relationship between the tuning speed of the tunable pump laser source and the tuning speed of the Brillouin ring cavity is determined, and a first control signal including the magnitude relationship is sent to the Brillouin ring cavity, and the feedback control unit returns to continue to determine whether mode hopping occurs in the Brillouin swept laser; otherwise, it indicates that the tuning speed of the tunable pump laser source matches the cavity mode tuning speed of the Brillouin ring cavity.

[0009] In another optional implementation, an optical amplifier is further included, and the optical amplifier is arranged between the first output end of the second coupler and the input end of the Brillouin ring cavity.

[0010] In another optional implementation, the Brillouin ring cavity includes a circulator, a Brillouin gain medium, a cavity mode tuning device and a third coupler, wherein the first end of the circulator serves as the input end of the Brillouin ring cavity, the second end is connected to the first output end of the third coupler through the Brillouin gain medium, the third end is connected to the input end of the third coupler through the cavity mode tuning device, the second output end of the third coupler serves as the output end of the Brillouin ring cavity and is connected to the input end of the first coupler; the control end of the cavity mode tuning device serves as the control end of the Brillouin ring cavity and is connected to the first output end of the feedback control unit;

[0011] The pump laser is transmitted to the Brillouin gain medium through the circulator, and a stimulated Brillouin scattering signal is generated during the transmission of the pump laser along the Brillouin gain medium, and the stimulated Brillouin scattering signal is transmitted back to the circulator; the circulator transmits the stimulated Brillouin scattering signal to the cavity mode tuning device, and the cavity mode tuning device frequency-modulates the stimulated Brillouin scattering signal to obtain a Brillouin frequency sweeping signal, and the Brillouin frequency sweeping signal is transmitted to the Brillouin gain medium through the third coupler, and the Brillouin frequency sweeping signal is amplified by the Brillouin gain medium, and this cycle is repeated until the Brillouin frequency sweeping signal is amplified to the intracavity threshold, and then output as a Brillouin frequency sweeping laser from the second output end of the third coupler.

[0012] In another optional implementation, by setting the length of the Brillouin gain medium, the laser is ensured to be in a single longitudinal mode operation state while the laser construction cost is low. Although increasing the length of the Brillouin gain medium can reduce the intracavity threshold, it will cause the laser to be in a multi-longitudinal mode operation state, making it more likely to produce mode hopping. Although shortening the length of the Brillouin gain medium can ensure that the laser is in a single longitudinal mode operation state, it will increase the intracavity threshold, which will increase the laser construction cost accordingly.

[0013] In another optional implementation, a first coupler is further included, wherein the output end of the Brillouin ring cavity is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the feedback control unit, and the second output end is connected to the output wire;

[0014] The Brillouin ring cavity divides the Brillouin frequency sweep laser into two paths through the first coupler, one path is output through the output wire, and the other path is transmitted to the feedback control unit; wherein the sum of the time delay of the first coupler transmitting the Brillouin frequency sweep laser to the feedback control unit and the time delay of the feedback control unit transmitting the first control signal to the Brillouin ring cavity is equal to the time delay of the output wire;

[0015] After receiving the Brillouin swept laser of the previous frequency band, the feedback control unit sends the first control signal to the Brillouin ring cavity, so that the Brillouin ring cavity immediately enters the next frequency band sweep after the Brillouin swept laser of the previous frequency band is output.

[0016] In another optional implementation, a second coupler is further included, the output end of the tunable pump laser source is connected to the output end of the second coupler, the first output end of the second coupler is connected to the input end of the Brillouin ring cavity, and the second output end is connected to the second input end of the feedback control unit; the second output end of the feedback control unit is connected to the control end of the tunable pump laser source; the tunable pump laser source transmits the pump laser to the Brillouin ring cavity and the feedback control unit respectively through the second coupler;

[0017] For each tuning of the tunable pump laser source, the feedback control unit determines the line width of the corresponding stimulated Brillouin scattering signal according to the line width of the pump laser output by this tuning, takes the moment of first receiving the Brillouin swept laser of the first frequency band as the first moment, determines the reception time difference of the Brillouin swept lasers of two adjacent frequency bands, and determines the reception moment of the Brillouin swept laser of the last frequency band in the stimulated Brillouin scattering signal corresponding to the pump laser output by this tuning according to the determined line width, the first moment and the reception time difference of the stimulated Brillouin scattering signal; the time from the output of the pump laser from the tunable pump laser source to the transmission of the corresponding stimulated Brillouin scattering signal to the cavity mode tuning device is taken as the first time length, and the first time length is subtracted from the determined reception moment to obtain The method comprises the steps of: obtaining the second moment; determining the moment and line width of the next tuning according to the second moment and the line width of the pump laser output by the current tuning, and sending a second control signal including the moment and line width of the next tuning to the tunable pump laser source, so that the tunable pump laser source is tuned according to the moment and outputs the pump laser of the corresponding line width, so as to avoid mode hopping and realize continuous frequency sweeping output, wherein when the moment of the next tuning is equal to the second moment, the line width of the next tuning makes the line widths of the stimulated Brillouin scattering signals corresponding to the two adjacent tuned output pump lasers continuous or overlapped; and when the moment of the next tuning is earlier than the second moment, the line width of the next tuning makes the line widths of the stimulated Brillouin scattering signals corresponding to the two adjacent tuned output pump lasers overlapped.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention is provided with a feedback control unit, which provides a first control signal to the Brillouin ring cavity. The Brillouin ring cavity tunes the tuning speed of the cavity mode therein according to the first control signal, so that the tuning speed of the tunable pump laser source can be matched with the tuning speed of the cavity mode in the Brillouin ring cavity. In this way, the tuning range of the laser is no longer limited by the free spectrum range and the Brillouin gain bandwidth of the Brillouin ring cavity, breaking through the range limitation of the continuous tuning of the laser, so that the laser can be continuously tuned over a wide range in any band; in addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve kHz-level narrow linewidth swept-frequency laser output;

[0020] 2. The present invention can ensure that the laser is in a single longitudinal mode operation state by setting the length of the Brillouin gain medium, while making the laser construction cost lower;

[0021] 3. The first control signal provided to the Brillouin ring cavity of the present invention is used to control the start of each frequency sweep. The Brillouin ring cavity starts the next frequency sweep after receiving the first control signal. The second control signal provided to the tunable pump laser source controls the tuning time and line width of the next tuning of the tunable pump laser source. The tunable pump laser source of the present invention only needs to start the next tuning when the last tuning output pump laser corresponding to the stimulated Brillouin scattering signal is about to complete the sweep of all frequency bands. The tunable pump laser source does not need to be tuned continuously without interruption, thereby reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of an embodiment of a narrow linewidth continuous frequency swept Brillouin laser based on the mode following principle of the present invention;

[0023] Figure 2 It is a schematic structural diagram of another embodiment of the narrow linewidth continuous frequency sweeping Brillouin laser based on the mode following principle of the present invention;

[0024] Figure 3 It is a schematic structural diagram of another embodiment of the narrow-linewidth continuous-frequency swept Brillouin laser based on the mode following principle of the present invention. DETAILED DESCRIPTION

[0025] 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.

[0026] 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.

[0027] See also Figure 1 , is a schematic diagram of an embodiment of the structure of a narrow linewidth continuous frequency sweeping Brillouin laser based on the mode following principle of the present invention. The laser may include a tunable pump laser source 1, a Brillouin ring cavity A and a feedback control unit 2, wherein the output end of the tunable pump laser source 1 is connected to the input end of the Brillouin ring cavity A, and the first output end of the feedback control unit 2 is connected to the control end of the Brillouin ring cavity A; the tunable pump laser source 1 transmits the pump laser to the Brillouin ring cavity A, and the pump laser generates a stimulated Brillouin scattering signal during the transmission process in the Brillouin ring cavity A, and the Brillouin ring cavity A tunes the cavity mode in the Brillouin ring cavity A according to the first control signal provided by the feedback control unit 2 (thereby frequency modulating the stimulated Brillouin scattering signal), so that the tuning speed of the tunable pump laser source 1 matches the tuning speed of the cavity mode in the Brillouin ring cavity A, and the Brillouin frequency sweeping signal of the corresponding frequency band obtained after the cavity mode is tuned is cyclically amplified in the Brillouin ring cavity A until the intracavity threshold is reached, and then output as the Brillouin frequency sweeping laser of the frequency band.

[0028] In this embodiment, the tunable pump laser source can be a commercial tunable laser source based on external cavity tuning or a tunable laser source based on external frequency modulation; the commercial tunable laser source based on external cavity tuning is mainly composed of a semiconductor gain chip, an external cavity Littrow or Littman external cavity tuning structure and a control circuit; the tunable laser source based on external frequency modulation is mainly composed of a single-frequency laser source, an EOM electro-optical modulator and a signal generator.

[0029] As can be seen from the above embodiments, the present invention is provided with a feedback control unit, and the feedback control unit provides a first control signal to the Brillouin ring cavity, and the Brillouin ring cavity tunes the tuning speed of the cavity mode therein according to the first control signal, so that the tuning speed of the tunable pump laser source can be matched with the tuning speed of the cavity mode in the Brillouin ring cavity, so that the tuning range of the laser is no longer limited by the free spectrum range and the Brillouin gain bandwidth of the Brillouin ring cavity, breaking through the range limitation of the continuous tuning of the laser, so that the laser can be continuously tuned over a wide range in any band; in addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve narrow linewidth swept-frequency laser output of the kHz order.

[0030] In one embodiment, the tunable pump laser source can be tuned continuously at a corresponding speed and the tuning speed is constant. Before the laser is officially put into use, the feedback control unit gradually adjusts the tuning speed of the cavity mode in the Brillouin ring cavity while monitoring the mode hopping phenomenon. According to whether the mode hopping phenomenon occurs, it is determined whether the tuning speed of the tunable pump laser source matches the tuning speed of the cavity mode in the Brillouin ring cavity. If the mode hopping phenomenon does not occur, it indicates that the tuning speeds of the two match. To this end, combined with Figure 2 As shown, Figure 2 and Figure 1 The difference between the illustrated embodiments is that the Brillouin laser may further include a first coupler 3 and a second coupler 4, the output end of the Brillouin ring cavity A is connected to the input end of the first coupler 3, the first output end of the first coupler 3 is connected to the first input end of the feedback control unit 2, and the second output end serves as the Brillouin swept laser output end; the Brillouin ring cavity A divides the Brillouin swept laser into two paths through the first coupler 3, one path is directly output, and the other path is transmitted to the feedback control unit; the output end of the tunable pump laser source 1 is connected to the input end of the second coupler 4, the first output end of the second coupler 4 is connected to the input end of the Brillouin ring cavity A, and the second output end is connected to the second input end of the feedback control unit 2; the tunable pump laser source 1 transmits the pump laser to the Brillouin ring cavity A and the feedback control unit 2 respectively through the second coupler. The feedback control unit 2 determines whether the Brillouin swept laser has mode hopping. If so, the magnitude relationship between the tuning speed of the tunable pump laser source and the tuning speed of the Brillouin ring cavity is determined, and a first control signal including the magnitude relationship is sent to the Brillouin ring cavity A, and the feedback control unit 2 returns to continue to determine whether the Brillouin swept laser has mode hopping. Otherwise, it indicates that the tuning speed of the tunable pump laser source 1 matches the cavity mode tuning speed of the Brillouin ring cavity A (the line width change of the pump laser will cause the Brillouin gain spectrum to shift, and the cavity mode in the Brillouin ring cavity needs to match the displacement of the center position of the Brillouin gain spectrum).

[0031] in addition, Figure 2 and Figure 1The difference of the embodiment shown is that the Brillouin laser can also include an optical amplifier 5, which can be arranged between the first output end of the second coupler 4 and the input end of the Brillouin ring cavity A, and is used to amplify the power of the pump laser. The optical amplifier can adopt an erbium-doped fiber amplifier (EDFA), and its main structure includes a 980nm pump laser source and a section of erbium gain fiber. The Brillouin ring cavity A can include a circulator 6, a Brillouin gain medium 7, a cavity mode tuning device 8 and a third coupler 9, wherein the first end of the circulator 6 serves as the input end of the Brillouin ring cavity A, the second end is connected to the first output end of the third coupler 9 through the Brillouin gain medium 7, and the third end is connected to the input end of the third coupler 9 through the cavity mode tuning device 8. The second output end of the third coupler 9 serves as the output end of the Brillouin ring cavity A and is connected to the input end of the first coupler 3; the control end of the cavity mode tuning device 8 serves as the control end of the Brillouin ring cavity A and is connected to the first output end of the feedback control unit 2.

[0032] The pump laser is transmitted to the Brillouin gain medium 7 through the circulator 6. During the transmission of the pump laser along the Brillouin gain medium 7, a stimulated Brillouin scattering signal is generated. The stimulated Brillouin scattering signal is transmitted back to the circulator 6 (at this time, the pump laser injected into the Brillouin ring cavity A is transmitted to the third end of the circulator 6 through the third coupler 9 and the cavity mode tuning device 8 in sequence, and is isolated at the third end of the circulator 6); the circulator 6 transmits the stimulated Brillouin scattering signal to the cavity mode tuning device 8, and the cavity mode tuning device 8 frequency modulates the stimulated Brillouin scattering signal to obtain a Brillouin frequency sweeping signal, which is transmitted to the Brillouin gain medium 7 through the third coupler 9, and the Brillouin frequency sweeping signal is amplified by the Brillouin gain medium 7, and this cycle is repeated until the Brillouin frequency sweeping signal is amplified to the intracavity threshold, and then output as a Brillouin frequency sweeping laser from the second output end of the third coupler 9. In this embodiment, the first output end and the second output end of the first coupler 3 are respectively a 1% output end and a 99% output end; the first output end and the second output end of the second coupler 4 are respectively a 99% output end and a 1% output end; the first output end and the second output end of the third coupler 9 are respectively a 90% output end and a 10% output end; the feedback control unit can adopt a PID control circuit.

[0033] Among them, the length of the Brillouin gain medium in the Brillouin ring cavity A has a great influence on the performance parameters of the laser, such as the laser threshold and the laser operating state (single longitudinal mode or multi-longitudinal mode operation). Although the increase in the length of the Brillouin gain medium can reduce the threshold in the cavity, it will cause the laser to be in a multi-longitudinal mode operating state, which is more likely to cause mode hopping, which is not conducive to the realization of a mode-hopping-free sweep signal; although the length of the Brillouin gain medium is shortened, although it can ensure that the laser is in a single longitudinal mode operating state, it will increase the threshold in the cavity, corresponding to the increase in the selection specifications of the optical amplifier, thereby increasing the construction cost of the laser; the length of the Brillouin gain medium is set to ensure that the laser is in a single longitudinal mode operating state, while making the optical amplifier selection specifications lower and the laser construction cost lower.

[0034] As can be seen from the above embodiments, the present invention is provided with a feedback control unit, and the feedback control unit provides a first control signal to the Brillouin ring cavity, and the Brillouin ring cavity tunes the tuning speed of the cavity mode therein according to the first control signal, so that the tuning speed of the tunable pump laser source can be matched with the tuning speed of the cavity mode in the Brillouin ring cavity, so that the tuning range of the laser is no longer limited by the free spectrum range and the Brillouin gain bandwidth of the Brillouin ring cavity, breaking through the range limitation of the continuous tuning of the laser, so that the laser can be continuously tuned over a wide range in any band; in addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve narrow linewidth swept-frequency laser output of the kHz order.

[0035] In the above embodiment, the tunable pump laser source needs to adapt to the frequency sweeping band and continuously tune at the corresponding speed. Continuous tuning will increase energy consumption. To this end, the present invention also proposes a method for matching the tuning speed of the tunable pump laser source and the Brillouin ring cavity. In this method, the tunable pump laser source does not need to continuously tune the frequency, thereby reducing energy consumption. Figure 3 As shown, Figure 3 and Figure 1The difference between the illustrated embodiment is that it can also include a first coupler 3 and a second coupler 4, the output end of the Brillouin ring cavity A is connected to the input end of the first coupler 3, the first output end of the first coupler 3 is connected to the first input end of the feedback control unit 2, and the second output end is connected to the output wire; the Brillouin ring cavity A divides the Brillouin swept laser into two paths through the first coupler 3, one path is output through the output wire, and the other path is transmitted to the feedback control unit 2; wherein the sum of the time delay of the first coupler 3 transmitting the Brillouin swept laser to the feedback control unit 2 and the time delay of the feedback control unit 2 transmitting the first control signal to the Brillouin ring cavity A is equal to the time delay of the output wire. After receiving the Brillouin swept laser of the previous frequency band, the feedback control unit 2 sends the first control signal to the Brillouin ring cavity A, so that the Brillouin ring cavity A immediately enters the next frequency band sweep after receiving the first control signal, that is, the Brillouin swept laser of the previous frequency band is output.

[0036] The output end of the tunable pump laser source 1 is connected to the output end of the second coupler 4, the first output end of the second coupler 4 is connected to the input end of the Brillouin ring cavity A, and the second output end is connected to the second input end of the feedback control unit 2; the second output end of the feedback control unit 2 is connected to the control end of the tunable pump laser source 1; the tunable pump laser source 1 transmits the pump laser to the Brillouin ring cavity A and the feedback control unit 2 respectively through the second coupler 4; for each tuning of the tunable pump laser source, the feedback control unit 2 determines the line width of the corresponding stimulated Brillouin ring cavity according to the line width of the pump laser output by this tuning. The line width of the stimulated Brillouin scattering signal (a line width model of the pump laser and the stimulated Brillouin scattering signal can be established. Based on the line width model, the line width of the stimulated Brillouin scattering signal is obtained according to the line width of the received pump laser. The Brillouin ring cavity modulates the stimulated Brillouin scattering signal within the line width. The Brillouin swept signal of the corresponding frequency band obtained after each frequency sweep can generate the Brillouin swept laser of the frequency band in the Brillouin ring cavity). The moment when the first frequency band Brillouin swept laser is received for the first time (the Brillouin swept laser is the laser after the Brillouin swept laser of the corresponding frequency band obtained after the frequency sweep is cyclically amplified to the threshold value in the cavity) is taken as the first time the Brillouin swept laser of the first frequency band is received. At a moment, determine the receiving time difference of the Brillouin swept lasers of two adjacent frequency bands, and determine the receiving time of the Brillouin swept laser of the last frequency band in the stimulated Brillouin scattering signal corresponding to the pump laser output of this tuning according to the determined line width of the stimulated Brillouin scattering signal, the first moment and the receiving time difference; the time from the output of the pump laser from the tunable pump laser source to the transmission of the corresponding stimulated Brillouin scattering signal to the cavity mode tuning device is taken as the first time length, and the determined receiving moment is subtracted from the first time length to obtain the second moment; according to the second moment and the line width of the pump laser output of this tuning, determine the moment and line width of the next tuning width, sending a second control signal including the moment of next tuning and the line width to the tunable pump laser source, so that the tunable pump laser source is tuned according to the moment, and outputs a pump laser with a corresponding line width, so as to avoid mode hopping and realize continuous frequency sweeping output, wherein when the moment of next tuning is equal to the second moment, the line width of the next tuning makes the line widths of stimulated Brillouin scattering signals corresponding to two adjacent tuned output pump lasers continuous or overlapped; when the moment of next tuning is earlier than the second moment, the line width of the next tuning makes the line widths of stimulated Brillouin scattering signals corresponding to two adjacent tuned output pump lasers overlapped.

[0037] in addition, Figure 3 and Figure 1The difference between the illustrated embodiments is that the Brillouin laser can also include an optical amplifier 5, which can be arranged between the first output end of the second coupler 4 and the input end of the Brillouin ring cavity A, and is used to amplify the power of the pump laser. The Brillouin ring cavity A can include a circulator 6, a Brillouin gain medium 7, a cavity mode tuning device 8 and a third coupler 9, wherein the first end of the circulator 6 serves as the input end of the Brillouin ring cavity A, the second end is connected to the first output end of the third coupler 9 through the Brillouin gain medium 7, and the third end is connected to the input end of the third coupler 9 through the cavity mode tuning device 8, and the second output end of the third coupler 9 serves as the output end of the Brillouin ring cavity A, connected to the input end of the first coupler 3; the control end of the cavity mode tuning device 8 serves as the control end of the Brillouin ring cavity A, and is connected to the first output end of the feedback control unit 2.

[0038] The pump laser is transmitted to the Brillouin gain medium 7 through the circulator 6. During the transmission of the pump laser along the Brillouin gain medium 7, a stimulated Brillouin scattering signal is generated. The stimulated Brillouin scattering signal is transmitted back to the circulator 6 (at this time, the pump laser injected into the Brillouin ring cavity A is transmitted to the third end of the circulator 6 through the third coupler 9 and the cavity mode tuning device 8 in sequence, and is isolated at the third end of the circulator 6); the circulator 6 transmits the stimulated Brillouin scattering signal to the cavity mode tuning device 8, and the cavity mode tuning device 8 frequency modulates the stimulated Brillouin scattering signal to obtain a Brillouin frequency sweeping signal, which is transmitted to the Brillouin gain medium 7 through the third coupler 9, and the Brillouin frequency sweeping signal is amplified by the Brillouin gain medium 7, and this cycle is repeated until the Brillouin frequency sweeping signal is amplified to the intracavity threshold, and then output as a Brillouin frequency sweeping laser from the second output end of the third coupler 9.

[0039] As can be seen from the above embodiments, the present invention is provided with a feedback control unit, and the feedback control unit provides a first control signal to the Brillouin ring cavity, and the Brillouin ring cavity tunes the tuning speed of the cavity mode therein according to the first control signal, so that the tuning speed of the tunable pump laser source can be matched with the tuning speed of the cavity mode in the Brillouin ring cavity, so that the tuning range of the laser is no longer limited by the free spectrum range and the Brillouin gain bandwidth of the Brillouin ring cavity, breaking through the range limitation of the continuous tuning of the laser, so that the laser can be continuously tuned over a wide range in any band; in addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve narrow linewidth swept-frequency laser output of the kHz order. The first control signal provided to the Brillouin ring cavity of the present invention is used to control the start of each frequency sweep, and the Brillouin ring cavity starts the frequency sweep of the next frequency band after receiving the first control signal; the second control signal provided to the tunable pump laser source controls the tuning time and line width of the next tuning of the tunable pump laser source. The tunable pump laser source of the present invention only starts the next tuning when the stimulated Brillouin scattering signal corresponding to the pump laser outputted in the last tuning is about to complete the frequency sweep of all frequency bands, and the tunable pump laser source does not need to be tuned continuously without interruption, thereby reducing energy consumption.

[0040] 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.

[0041] 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 narrow linewidth continuously swept Brillouin laser based on the mode following principle, characterized in that: It comprises a tunable pump laser source, a Brillouin ring cavity and a feedback control unit, wherein the output end of the tunable pump laser source is connected to the input end of the Brillouin ring cavity, and the first output end of the feedback control unit is connected to the control end of the Brillouin ring cavity; The tunable pump laser source transmits the pump laser to the Brillouin ring cavity. The pump laser generates a stimulated Brillouin scattering signal during the transmission process in the Brillouin ring cavity. The Brillouin ring cavity tunes the cavity mode in the Brillouin ring cavity according to the first control signal provided by the feedback control unit, so that the tuning speed of the tunable pump laser source matches the tuning speed of the cavity mode in the Brillouin ring cavity. The Brillouin swept-frequency signal of the corresponding frequency band obtained after the cavity mode is tuned is cyclically amplified in the Brillouin ring cavity until it reaches the intracavity threshold, and then is output as the Brillouin swept-frequency laser of the frequency band.

2. The narrow linewidth continuous frequency swept Brillouin laser based on the mode following principle according to claim 1, characterized in that: It also includes a first coupler and a second coupler, wherein the output end of the Brillouin ring cavity is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the feedback control unit, and the second output end serves as an output end of the Brillouin frequency-sweeping laser; the Brillouin ring cavity divides the Brillouin frequency-sweeping laser into two paths through the first coupler, one path is directly output, and the other path is transmitted to the feedback control unit; The output end of the tunable pump laser source is connected to the input end of the second coupler, the first output end of the second coupler is connected to the input end of the Brillouin ring cavity, and the second output end is connected to the second input end of the feedback control unit; the tunable pump laser source transmits the pump laser to the Brillouin ring cavity and the feedback control unit respectively through the second coupler; The feedback control unit determines whether the Brillouin swept laser has mode hopping, and if so, determines the magnitude relationship between the tuning speed of the tunable pump laser source and the tuning speed of the Brillouin ring cavity, sends a first control signal including the magnitude relationship to the Brillouin ring cavity, and returns to continue determining whether the Brillouin swept laser has mode hopping; Otherwise, it indicates that the tuning speed of the tunable pump laser source matches the cavity mode tuning speed of the Brillouin ring cavity.

3. The narrow linewidth continuous frequency swept Brillouin laser based on the mode following principle according to claim 1 or 2, characterized in that: It also includes an optical amplifier, which is arranged between the first output end of the second coupler and the input end of the Brillouin ring cavity.

4. The narrow linewidth continuously swept Brillouin laser based on the mode following principle according to claim 1, characterized in that: The Brillouin ring cavity comprises a circulator, a Brillouin gain medium, a cavity mode tuning device and a third coupler, wherein the first end of the circulator serves as the input end of the Brillouin ring cavity, the second end is connected to the first output end of the third coupler through the Brillouin gain medium, the third end is connected to the input end of the third coupler through the cavity mode tuning device, the second output end of the third coupler serves as the output end of the Brillouin ring cavity and is connected to the input end of the first coupler; the control end of the cavity mode tuning device serves as the control end of the Brillouin ring cavity and is connected to the first output end of the feedback control unit; The pump laser is transmitted to the Brillouin gain medium through the circulator, and a stimulated Brillouin scattering signal is generated during the transmission of the pump laser along the Brillouin gain medium, and the stimulated Brillouin scattering signal is transmitted back to the circulator; the circulator transmits the stimulated Brillouin scattering signal to the cavity mode tuning device, and the cavity mode tuning device frequency-modulates the stimulated Brillouin scattering signal to obtain a Brillouin frequency sweeping signal, and the Brillouin frequency sweeping signal is transmitted to the Brillouin gain medium through the third coupler, and the Brillouin frequency sweeping signal is amplified by the Brillouin gain medium, and this cycle is repeated until the Brillouin frequency sweeping signal is amplified to the intracavity threshold, and then output as a Brillouin frequency sweeping laser from the second output end of the third coupler.

5. The narrow linewidth continuous frequency swept Brillouin laser based on the mode following principle according to claim 4, characterized in that: By setting the length of the Brillouin gain medium, the laser is ensured to be in a single longitudinal mode operation state while the construction cost of the laser is low. Although increasing the length of the Brillouin gain medium can reduce the intracavity threshold, it will cause the laser to be in a multi-longitudinal mode operation state, making it more likely to generate mode hopping. Although shortening the length of the Brillouin gain medium can ensure that the laser is in a single longitudinal mode operation state, it will increase the intracavity threshold, which will increase the construction cost of the laser accordingly.

6. The narrow linewidth continuous frequency swept Brillouin laser based on the mode following principle according to claim 1, characterized in that: It also includes a first coupler, wherein the output end of the Brillouin ring cavity is connected to the input end of the first coupler, the first output end of the first coupler is connected to the first input end of the feedback control unit, and the second output end is connected to the output wire; The Brillouin ring cavity divides the Brillouin frequency sweep laser into two paths through the first coupler, one path is output through the output wire, and the other path is transmitted to the feedback control unit; wherein the sum of the time delay of the first coupler transmitting the Brillouin frequency sweep laser to the feedback control unit and the time delay of the feedback control unit transmitting the first control signal to the Brillouin ring cavity is equal to the time delay of the output wire; After receiving the Brillouin swept laser of the previous frequency band, the feedback control unit sends the first control signal to the Brillouin ring cavity, so that the Brillouin ring cavity immediately enters the next frequency band sweep after the Brillouin swept laser of the previous frequency band is output.

7. The narrow linewidth continuous frequency swept Brillouin laser based on the mode following principle according to claim 6, characterized in that: It also includes a second coupler, wherein the output end of the tunable pump laser source is connected to the output end of the second coupler, the first output end of the second coupler is connected to the input end of the Brillouin ring cavity, and the second output end is connected to the second input end of the feedback control unit; the second output end of the feedback control unit is connected to the control end of the tunable pump laser source; the tunable pump laser source transmits the pump laser to the Brillouin ring cavity and the feedback control unit respectively through the second coupler; For each tuning of the tunable pump laser source, the feedback control unit determines the line width of the corresponding stimulated Brillouin scattering signal according to the line width of the pump laser output by this tuning, takes the moment of first receiving the Brillouin swept laser of the first frequency band as the first moment, determines the reception time difference of the Brillouin swept lasers of two adjacent frequency bands, and determines the reception time of the Brillouin swept laser of the last frequency band in the stimulated Brillouin scattering signal corresponding to the pump laser output by this tuning according to the determined line width, the first moment and the reception time difference of the stimulated Brillouin scattering signal; the pump laser is output from the tunable pump laser source until the corresponding stimulated Brillouin scattering signal is transmitted to the cavity mode tuning The time length of the tuning device is the first time length, the determined receiving time is subtracted from the first time length to obtain the second time length; according to the second time length and the line width of the pump laser output by the current tuning, the time and line width of the next tuning are determined, and the second control signal including the time and line width of the next tuning is sent to the tunable pump laser source, so that the tunable pump laser source is tuned according to the time length and outputs the pump laser of the corresponding line width, so as to avoid mode hopping and realize continuous frequency sweeping output, wherein when the time length of the next tuning is equal to the second time length, the line width of the next tuning makes the line widths of the stimulated Brillouin scattering signals corresponding to the two adjacent tuned output pump lasers continuous or overlapped; When the time of the next tuning is earlier than the second time, the line width of the next tuning makes the line widths of stimulated Brillouin scattering signals corresponding to two adjacent tuning output pump lasers overlap.

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