Narrow-linewidth continuous-wave brillouin laser based on mode-following principle

Abstract

The application provides a narrow linewidth continuous sweep Brillouin laser based on a mode following principle, which comprises a tunable pump laser source, a Brillouin ring cavity and a feedback control unit, the output end of the tunable pump laser source is connected with the input end of the Brillouin ring cavity, and 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 ring cavity, the pump laser generates a stimulated Brillouin scattering signal during the transmission 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, and the Brillouin sweep signal obtained after the tuning of the cavity mode is cyclically amplified to the threshold value in the Brillouin ring cavity, and then is taken as the Brillouin sweep laser output. The application breaks through the range limitation of the continuous tuning of the Brillouin laser.

Description

Technical Field

[0001] This invention belongs to the field of fiber lasers, specifically relating to a narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle. Background Technology

[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 sweep laser. Currently, most commercially available sweep lasers are based on external cavity tuning. These sweep lasers rely on sophisticated MEMS electronic control systems, are expensive, and typically have linewidths on the order of 100kHz. In contrast, Brillouin-based fiber lasers, benefiting from the narrowband gain characteristics of Brillouin, can effectively achieve narrow linewidth laser output in the kHz and below order. Furthermore, sweep lasers based on the Brillouin all-fiber structure have advantages such as simple structure and low cost. Frequency tuning of Brillouin-based sweep lasers is mainly achieved by introducing a stress-stretching device within the cavity, winding the gain fiber around a piezoelectric ceramic, and applying a driving signal to the piezoelectric ceramic to induce periodic resonance, thereby changing the cavity length of the laser and achieving continuous tuning of the output laser. This technical solution can typically achieve a frequency tuning range of 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 one FSR or Brillouin gain bandwidth range, mode hopping will occur, resulting in phase discontinuity of the output laser. Summary of the Invention

[0003] This invention provides a narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle to solve the problem of limited continuous tuning range of current sweep lasers.

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

[0005] The tunable pump laser source transmits pump laser to the Brillouin ring cavity. During its transmission within the Brillouin ring cavity, the pump laser generates stimulated Brillouin scattering (SBS) signals. The Brillouin ring cavity tunes its cavity modes according to a 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 modes within the Brillouin ring cavity. The Brillouin sweep signal obtained after cavity mode tuning is cyclically amplified within the Brillouin ring cavity until it reaches the cavity threshold, after which it is output as the Brillouin sweep laser for that frequency band.

[0006] In one optional implementation, a first coupler and a second coupler are also included. 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 swept laser output end. The Brillouin ring cavity splits the Brillouin swept 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 of the tunable pump laser source is connected to the input of the second coupler, the first output of the second coupler is connected to the input of the Brillouin ring cavity, and the second output is connected to the second input 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 the Brillouin swept laser exhibits mode hopping. If so, it determines the relationship between the tuning speed of the tunable pump laser source and the tuning speed of the Brillouin ring cavity, and sends a first control signal including this relationship to the Brillouin ring cavity, then returns to continue determining whether the Brillouin swept laser exhibits 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.

[0009] In another alternative implementation, an optical amplifier is also included, which is disposed between the first output of the second coupler and the input 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. The first end of the circulator serves as the input of the Brillouin ring cavity, the second end is connected to the first output of the third coupler via the Brillouin gain medium, and the third end is connected to the input of the third coupler via the cavity mode tuning device. The second output of the third coupler serves as the output of the Brillouin ring cavity and is connected to the input 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 of the feedback control unit.

[0011] The pump laser is transmitted to the Brillouin gain medium through the circulator. During its transmission along the Brillouin gain medium, the pump laser generates a stimulated Brillouin scattering signal, which is then transmitted back to the circulator. The circulator transmits the stimulated Brillouin scattering signal to the cavity mode tuning device, which modulates the frequency of the stimulated Brillouin scattering signal to obtain a Brillouin sweep signal. This Brillouin sweep signal is transmitted to the Brillouin gain medium through the third coupler, where it is amplified. This process is repeated until the Brillouin sweep signal is amplified to the intracavity threshold, after which it is output as the Brillouin sweep laser from the second output terminal of the third coupler.

[0012] In another alternative implementation, by setting the length of the Brillouin gain medium, the laser can be kept in a single-mode operation while maintaining a low construction cost. While increasing the length of the Brillouin gain medium can lower the intracavity threshold, it can also cause the laser to operate in multiple modes, making it more prone to mode hopping. Conversely, while shortening the length of the Brillouin gain medium can ensure that the laser operates in a single-mode operation, it can increase the intracavity threshold, thereby increasing the laser construction cost.

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

[0014] The Brillouin ring cavity splits the Brillouin swept 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. The sum of the time delay of the first coupler in transmitting the Brillouin swept laser to the feedback control unit and the time delay of the feedback control unit in 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 sweep laser from 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 sweep laser from the previous frequency band is output.

[0016] In another optional implementation, a second coupler is further included, wherein the output of the tunable pump laser source is connected to the output of the second coupler, the first output of the second coupler is connected to the input of the Brillouin ring cavity, and the second output is connected to the second input of the feedback control unit; the second output of the feedback control unit is connected to the control terminal 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 linewidth of the corresponding stimulated Brillouin scattering (SBS) signal based on the linewidth of the output pump laser during this tuning. The moment when the first frequency band of the Brillouin sweep laser is received is taken as the first moment. The reception time difference between two adjacent frequency bands of the Brillouin sweep laser is determined. Based on the determined linewidth of the SBS signal, the first moment, and the reception time difference, the reception moment of the last frequency band of the SBS signal corresponding to the output pump laser during this tuning is determined. The time from the output of the pump laser from the tunable pump laser source to the transmission of the corresponding SBS signal to the cavity mode tuning device is taken as the first duration. The determined reception moment is subtracted from the first duration to obtain the result. The second time point is obtained; based on the second time point and the linewidth of the current tuned output pump laser, the time and linewidth of the next tuning are determined, and a second control signal including the time and linewidth 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 point and outputs a pump laser with the corresponding linewidth to avoid mode hopping and achieve continuous frequency sweep output. When the time of the next tuning is equal to the second time point, the linewidth of the next tuning makes the linewidths of the stimulated Brillouin scattering signals corresponding to the two adjacent tuned output pump lasers continuous or overlapping; when the time of the next tuning is earlier than the second time point, the linewidth of the next tuning makes the linewidths of the stimulated Brillouin scattering signals corresponding to the two adjacent tuned output pump lasers overlap.

[0018] The beneficial effects of this invention are:

[0019] 1. This invention includes a feedback control unit that provides a first control signal to the Brillouin ring cavity. The Brillouin ring cavity tunes its cavity mode tuning speed according to the first control signal, allowing the tuning speed of the tunable pump laser source to match the tuning speed of the cavity mode within the Brillouin ring cavity. Thus, the tuning range of the laser is no longer limited by the free spectral range of the Brillouin ring cavity and the Brillouin gain bandwidth, breaking through the limitations of continuous laser tuning and enabling the laser to be continuously tuned over a wide range in any wavelength band. Furthermore, based on the narrowband gain characteristics of Brillouin, this invention can achieve narrow-linewidth swept-frequency laser output in the kHz range.

[0020] 2. By setting the length of the Brillouin gain medium, this invention can ensure that the laser operates in a single longitudinal mode while keeping the laser construction cost low.

[0021] 3. The first control signal provided to the Brillouin ring cavity in this invention is used to control the start of each frequency sweep. The Brillouin ring cavity starts the next frequency band sweep upon receiving the first control signal. The second control signal provided to the tunable pump laser source controls the tuning time and linewidth of the next tuning of the tunable pump laser source. The tunable pump laser source of this invention only starts the next tuning when the stimulated Brillouin scattering signal corresponding to the pump laser output of the previous tuning is about to complete the frequency sweep of all frequency bands. The tunable pump laser source does not need to be continuously tuned without interruption, thus reducing energy consumption. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of an embodiment of the narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle of the present invention;

[0023] Figure 2 This is a schematic diagram of another embodiment of the narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle of the present invention;

[0024] Figure 3 This is a schematic diagram of another embodiment of the narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle of the present invention. Detailed Implementation

[0025] 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 objectives, features and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] In the description of this invention, unless otherwise specified and limited, it should be noted that the term "connection" should be interpreted broadly. For example, it can be a mechanical connection or an electrical connection, or it can be a connection between two internal components. It can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above term according to the specific circumstances.

[0027] See Figure 1 This is a schematic diagram of an embodiment of the narrow-linewidth continuous-sweep 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. The output of the tunable pump laser source 1 is connected to the input of the Brillouin ring cavity A, and the first output of the feedback control unit 2 is connected to the control terminal of the Brillouin ring cavity A. The tunable pump laser source 1 transmits pump laser light to the Brillouin ring cavity A. During its transmission within the Brillouin ring cavity A, the pump laser generates a stimulated Brillouin scattering signal. The Brillouin ring cavity A tunes its cavity mode according to the first control signal provided by the feedback control unit 2 (thereby frequency modulation of the stimulated Brillouin scattering signal) to match the tuning speed of the tunable pump laser source 1 with the tuning speed of the cavity mode within the Brillouin ring cavity A. The Brillouin sweep signal obtained after cavity mode tuning is cyclically amplified within the Brillouin ring cavity A until an intracavity threshold is reached, after which it is output as the Brillouin sweep laser for that frequency band.

[0028] In this embodiment, the tunable pump laser source can be a commercially available tunable laser source based on external cavity tuning or a tunable laser source based on external frequency modulation. The commercially available tunable laser source based on external cavity tuning mainly consists 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 mainly consists of a single-frequency laser source, an EOM electro-optic modulator, and a signal generator.

[0029] As can be seen from the above embodiments, the present invention provides a feedback control unit, which provides a first control signal to the Brillouin ring cavity. The Brillouin ring cavity tunes its cavity mode tuning speed according to the first control signal, which can match the tuning speed of the tunable pump laser source 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 spectral range of the Brillouin ring cavity and the Brillouin gain bandwidth, breaking through the limitation of the continuous tuning range of the laser and enabling the laser to be continuously tuned over a wide range in any wavelength band. In addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve narrow linewidth swept frequency laser output in the kHz range.

[0030] In one embodiment, the tunable pump laser source can be continuously tuned at a constant speed. Before the laser is put into use, the feedback control unit gradually adjusts the tuning speed of the cavity mode within the Brillouin cavity while monitoring for mode hopping. The presence or absence of mode hopping determines whether the tuning speed of the tunable pump laser source matches the tuning speed of the cavity mode within the Brillouin cavity. The absence of mode hopping indicates that the two tuning speeds are matched. Therefore, in conjunction with... Figure 2 As shown, Figure 2 and Figure 1 The difference in the illustrated embodiment 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 splits 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 exhibits mode hopping. If so, it determines the relationship between the tuning speed of the tunable pump laser source and the tuning speed of the Brillouin ring cavity, and sends a first control signal including this relationship to the Brillouin ring cavity A, then returns to continue determining whether the Brillouin swept laser exhibits 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 linewidth change of the pump laser will cause a shift in the Brillouin gain spectrum, and the cavity mode in the Brillouin ring cavity needs to match the shift of the center position of the Brillouin gain spectrum).

[0031] in addition, Figure 2 and Figure 1The difference in the illustrated embodiment is that the Brillouin laser may further include an optical amplifier 5, which can be disposed between the first output terminal of the second coupler 4 and the input terminal of the Brillouin ring cavity A, for power amplification of the pump laser. This optical amplifier may be an erbium-doped fiber amplifier (EDFA), whose main structure includes a 980nm pump laser source and a section of erbium gain fiber. The Brillouin ring cavity A may include a circulator 6, a Brillouin gain medium 7, a cavity mode tuning device 8, and a third coupler 9. The first end of the circulator 6 serves as the input terminal of the Brillouin ring cavity A, the second end is connected to the first output terminal of the third coupler 9 via the Brillouin gain medium 7, and the third end is connected to the input terminal of the third coupler 9 via the cavity mode tuning device 8. The second output terminal of the third coupler 9 serves as the output terminal of the Brillouin ring cavity A and is connected to the input terminal of the first coupler 3. The control terminal of the cavity mode tuning device 8 serves as the control terminal of the Brillouin ring cavity A and is connected to the first output terminal of the feedback control unit 2.

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

[0033] The length of the Brillouin gain medium in the Brillouin ring cavity A has a significant impact on the laser's performance parameters, such as the laser threshold and the laser's operating state (single-mode or multi-mode operation). Increasing the length of the Brillouin gain medium can lower the threshold within the cavity, but it will cause the laser to operate in a multi-mode state, making it more prone to mode hopping and hindering the realization of mode-hopping-free sweep signals. Shortening the length of the Brillouin gain medium can ensure that the laser operates in a single-mode state, but it will increase the threshold within the cavity, requiring a higher specification of optical amplifier and thus increasing the laser's construction cost. Setting the length of the Brillouin gain medium allows for a lower specification of optical amplifier while ensuring the laser operates in a single-mode state, resulting in a lower laser construction cost.

[0034] As can be seen from the above embodiments, the present invention provides a feedback control unit, which provides a first control signal to the Brillouin ring cavity. The Brillouin ring cavity tunes its cavity mode tuning speed according to the first control signal, which can match the tuning speed of the tunable pump laser source 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 spectral range of the Brillouin ring cavity and the Brillouin gain bandwidth, breaking through the limitation of the continuous tuning range of the laser and enabling the laser to be continuously tuned over a wide range in any wavelength band. In addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve narrow linewidth swept frequency laser output in the kHz range.

[0035] In the above embodiments, the tunable pump laser source needs to be adapted to a swept frequency band and continuously tuned at a corresponding speed, which increases energy consumption. Therefore, this invention also proposes a method to match 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 be continuously tuned, thereby reducing energy consumption. Figure 3 As shown, Figure 3 and Figure 1The difference in the illustrated embodiment is that it may also include a first coupler 3 and a second coupler 4. The output terminal of the Brillouin ring cavity A is connected to the input terminal of the first coupler 3, the first output terminal of the first coupler 3 is connected to the first input terminal of the feedback control unit 2, and the second output terminal is connected to the output wire. The Brillouin ring cavity A splits 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. The sum of the time delay of the first coupler 3 in transmitting the Brillouin swept laser to the feedback control unit 2 and the time delay of the feedback control unit 2 in 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, i.e., after the Brillouin swept laser of the previous frequency band is output.

[0036] The output of the tunable pump laser source 1 is connected to the output of the second coupler 4. The first output of the second coupler 4 is connected to the input of the Brillouin ring cavity A, and the second output is connected to the second input of the feedback control unit 2. The second output of the feedback control unit 2 is connected to the control terminal 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 through the second coupler 4. For each tuning of the tunable pump laser source, the feedback control unit 2 determines the corresponding stimulated Brillouin ring cavity A based on the linewidth of the output pump laser during this tuning. The linewidth of the stimulated Brillouin scattering (SBS) signal can be determined by establishing linewidth models for the pump laser and stimulated Brillouin scattering (SBS). Based on this model, the linewidth of the stimulated Brillouin scattering (SBS) signal is obtained according to the linewidth of the received pump laser. The Brillouin ring cavity modulates the SBS signal within this linewidth. After each frequency sweep, the corresponding frequency band of the Brillouin sweep signal can be generated within the Brillouin ring cavity to produce the corresponding frequency band of Brillouin sweep laser. The moment when the first frequency band of Brillouin sweep laser is received (the Brillouin sweep laser is the laser obtained after the frequency sweep and cyclically amplified to the threshold value within the cavity) is taken as the first... At a given moment, the receiving time difference between two adjacent frequency bands of Brillouin sweep lasers is determined. Based on the determined linewidth of the stimulated Brillouin scattering signal, the first moment, and the receiving time difference, the receiving moment of the last frequency band of the stimulated Brillouin scattering signal corresponding to the current tuning output pump laser is determined. 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 defined as the first duration. The first duration is subtracted from the determined receiving moment to obtain the second moment. Based on the second moment and the linewidth of the current tuning output pump laser, the timing and linewidth of the next tuning are determined. The second control signal, including the next tuning time and linewidth, is sent to the tunable pump laser source so that the tunable pump laser source is tuned according to the time and outputs a pump laser with the corresponding linewidth to avoid mode hopping and achieve continuous frequency sweep output. When the next tuning time is equal to the second time, the linewidth of the next tuning makes the linewidth of the stimulated Brillouin scattering signal corresponding to the pump laser output of two adjacent tunings continuous or overlapping; when the next tuning time is earlier than the second time, the linewidth of the next tuning makes the linewidth of the stimulated Brillouin scattering signal corresponding to the pump laser output of two adjacent tunings overlap.

[0037] in addition, Figure 3 and Figure 1The difference in the illustrated embodiment is that the Brillouin laser may further include an optical amplifier 5, which can be disposed between the first output terminal of the second coupler 4 and the input terminal of the Brillouin ring cavity A, for power amplification of the pump laser. The Brillouin ring cavity A may include a circulator 6, a Brillouin gain medium 7, a cavity mode tuning device 8, and a third coupler 9. The first end of the circulator 6 serves as the input terminal of the Brillouin ring cavity A, the second end is connected to the first output terminal of the third coupler 9 via the Brillouin gain medium 7, and the third end is connected to the input terminal of the third coupler 9 via the cavity mode tuning device 8. The second output terminal of the third coupler 9 serves as the output terminal of the Brillouin ring cavity A and is connected to the input terminal of the first coupler 3. The control terminal of the cavity mode tuning device 8 serves as the control terminal of the Brillouin ring cavity A and is connected to the first output terminal of the feedback control unit 2.

[0038] The pump laser is transmitted to the Brillouin gain medium 7 through the circulator 6. During its transmission along the Brillouin gain medium 7, the pump laser generates a stimulated Brillouin scattering signal, which is then transmitted back to the circulator 6 (at this time, the pump laser injected into the Brillouin ring cavity A is transmitted sequentially through the third coupler 9 and the cavity mode tuning device 8 to the third end of the circulator 6, where it is isolated). The circulator 6 transmits the stimulated Brillouin scattering signal to the cavity mode tuning device 8, which modulates the frequency of the stimulated Brillouin scattering signal to obtain a Brillouin sweep signal. This Brillouin sweep signal is transmitted to the Brillouin gain medium 7 through the third coupler 9, where it is amplified. This process is repeated until the Brillouin sweep signal is amplified to the intracavity threshold, after which it is output as the Brillouin sweep laser from the second output end of the third coupler 9.

[0039] As can be seen from the above embodiments, the present invention provides a feedback control unit, which provides a first control signal to the Brillouin ring cavity. The Brillouin ring cavity tunes its cavity mode tuning speed according to the first control signal, which can match the tuning speed of the tunable pump laser source 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 spectral range of the Brillouin ring cavity and the Brillouin gain bandwidth, breaking through the limitation of the continuous tuning range of the laser and enabling the laser to be continuously tuned over a wide range in any wavelength band. In addition, based on the narrowband gain characteristics of Brillouin, the present invention can achieve narrow linewidth swept frequency laser output in the kHz range. The invention provides a first control signal to the Brillouin ring cavity to control the start of each frequency sweep. Upon receiving the first control signal, the Brillouin ring cavity begins the next frequency sweep. A second control signal is provided to the tunable pump laser source to control the tuning time and linewidth 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 stimulated Brillouin scattering signal corresponding to the pump laser output in the previous tuning is about to complete the frequency sweep of all frequency bands. The tunable pump laser source does not need to be continuously tuned without interruption, thus reducing energy consumption.

[0040] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.

[0041] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is defined solely by the appended claims.

Claims

1. A narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle, characterized in that, It includes a tunable pumped laser source, a Brillouin ring cavity, and a feedback control unit. The output terminal of the tunable pumped laser source is connected to the input terminal of the Brillouin ring cavity, and the first output terminal of the feedback control unit is connected to the control terminal of the Brillouin ring cavity. The tunable pump laser source transmits pump laser to the Brillouin ring cavity. During the transmission of the pump laser within the Brillouin ring cavity, stimulated Brillouin scattering signals are generated. The Brillouin ring cavity tunes the cavity mode within 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 within the Brillouin ring cavity. The Brillouin sweep signal of the corresponding frequency band obtained after cavity mode tuning is cyclically amplified within the Brillouin ring cavity until it reaches the cavity threshold, and then outputs as the Brillouin sweep laser of that frequency band. It also includes a first coupler and a second coupler. 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. The second output end serves as the Brillouin sweep laser output end. The Brillouin ring cavity splits the Brillouin 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. The output of the tunable pump laser source is connected to the input of the second coupler, the first output of the second coupler is connected to the input of the Brillouin ring cavity, and the second output is connected to the second input 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 exhibits mode hopping. If so, it determines the relationship between the tuning speed of the tunable pump laser source and the tuning speed of the Brillouin ring cavity, and sends a first control signal including the relationship to the Brillouin ring cavity, then returns to continue determining whether the Brillouin swept laser exhibits 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.

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 an optical amplifier, which is disposed between the first output of the second coupler and the input of the Brillouin ring cavity.

3. The narrow-linewidth continuous-frequency swept Brillouin laser based on the mode-following principle according to claim 1, characterized in that, The Brillouin ring cavity includes a circulator, a Brillouin gain medium, a cavity mode tuning device, and a third coupler. The first end of the circulator serves as the input of the Brillouin ring cavity; the second end is connected to the first output of the third coupler via the Brillouin gain medium; the third end is connected to the input of the third coupler via the cavity mode tuning device; the second output of the third coupler serves as the output of the Brillouin ring cavity and is connected to the input 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 of the feedback control unit. The pump laser is transmitted to the Brillouin gain medium through the circulator. During its transmission along the Brillouin gain medium, the pump laser generates a stimulated Brillouin scattering signal, which is then transmitted back to the circulator. The circulator transmits the stimulated Brillouin scattering signal to the cavity mode tuning device, which modulates the frequency of the stimulated Brillouin scattering signal to obtain a Brillouin sweep signal. This Brillouin sweep signal is transmitted to the Brillouin gain medium through the third coupler, where it is amplified. This process is repeated until the Brillouin sweep signal is amplified to the intracavity threshold, after which it is output as the Brillouin sweep laser from the second output terminal of the third coupler.

4. The narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle according to claim 1, characterized in that, It also includes a first coupler, the output of the Brillouin annular cavity is connected to the input of the first coupler, the first output of the first coupler is connected to the first input of the feedback control unit, and the second output is connected to the output wire; The Brillouin ring cavity splits the Brillouin swept 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. The sum of the time delay of the first coupler in transmitting the Brillouin swept laser to the feedback control unit and the time delay of the feedback control unit in transmitting the first control signal to the Brillouin ring cavity is equal to the time delay of the output wire. After receiving the Brillouin sweep laser from 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 sweep laser from the previous frequency band is output.

5. The narrow-linewidth continuous-sweep Brillouin laser based on the mode-following principle according to claim 4, characterized in that, It also includes a second coupler, the output of the tunable pump laser source is connected to the output of the second coupler, the first output of the second coupler is connected to the input of the Brillouin ring cavity, and the second output is connected to the second input of the feedback control unit; the second output of the feedback control unit is connected to the control terminal 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 linewidth of the corresponding stimulated Brillouin scattering signal based on the linewidth of the output pump laser in this tuning. The moment when the first frequency band of the Brillouin sweep laser is received is taken as the first moment. The reception time difference between two adjacent frequency bands of the Brillouin sweep laser is determined. Based on the determined linewidth of the stimulated Brillouin scattering signal, the first moment, and the reception time difference, the reception time of the last frequency band of the Brillouin sweep laser in the stimulated Brillouin scattering signal corresponding to the output pump laser in this tuning is determined. The pump laser is output from the tunable pump laser source until the corresponding stimulated Brillouin scattering signal is transmitted to the cavity mode tuner. The duration of the tuning device is used as the first duration. The determined receiving time is subtracted from the first duration to obtain the second time. Based on the second time and the linewidth of the current tuned output pump laser, the time and linewidth of the next tuning are determined. A second control signal including the time and linewidth 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 and outputs a pump laser with a corresponding linewidth to avoid mode skipping and achieve continuous frequency sweep output. When the time of the next tuning is equal to the second time, the linewidth of the next tuning makes the linewidth of the stimulated Brillouin scattering signal corresponding to the two adjacent tuned output pump lasers continuous or overlapping. When the next tuning occurs earlier than the second tuning moment, the linewidth of the next tuning causes the linewidths of the stimulated Brillouin scattering signals corresponding to the output pump lasers of the two adjacent tunings to overlap.

Images