A kind of injection-locked based cascaded stimulated brillouin scattering multi-wavelength laser and its implementation method

Abstract

The application relates to a kind of based on injection locking cascade stimulated Brillouin scattering multi-wavelength laser and its implementation method, cascade stimulated Brillouin scattering multi-wavelength laser includes: laser, the output end of laser is connected with first optical coupler, and first optical coupler introduces the output light of laser into main pump branch and phase modulation branch;Main pump branch includes: second optical coupler, second optical coupler is sequentially connected with erbium-doped fiber amplifier, circulator, first polarization controller, single-mode optical fiber and optical isolator;Wherein, circulator is also connected with third optical coupler, to form Brillouin laser ring feedback cavity;Phase modulation branch includes: second polarization controller, second polarization controller is sequentially connected with phase modulator and fourth optical coupler;Wherein, there is phase modulator and is also connected with microwave source, and fourth optical coupler is also connected with optical isolator, to inject main pump branch.

Description

Technical Field

[0001] This invention relates to the fields of fiber lasers, microwave photonics, and multi-wavelength light sources, and in particular to a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking and its implementation method. Background Technology

[0002] In fiber optic sensing, dual-comb ranging, coherent measurement, and microwave photonic channelized receiving systems, narrow-linewidth, uniformly spaced channel frequencies, and phase-coherent multi-wavelength light sources are the core requirements for achieving high-precision signal processing and long-term stable operation.

[0003] Currently, multi-wavelength light source implementation schemes are mainly divided into two categories: semiconductor laser arrays and multi-wavelength fiber lasers. Among them, semiconductor laser arrays can output multiple wavelengths, but each laser usually requires independent temperature control and wavelength locking devices. As the number of channels increases, the system complexity, power consumption and cost increase significantly, while also facing problems such as thermal crosstalk and difficulties in wavelength consistency control.

[0004] In contrast, multi-wavelength fiber lasers can generate multiple wavelength outputs using a single ring cavity. Each channel is constrained by the same light source and cavity, offering advantages such as consistent overall drift and compact structure, thus attracting widespread attention in recent years. Multi-wavelength fiber lasers are mainly classified according to their implementation methods into those based on active modulation technology, intensity-dependent loss technology, and fiber nonlinear effect technology. Among these, multi-wavelength fiber lasers based on stimulated Brillouin scattering (SBS) can utilize a single pump source and the Brillouin gain in the fiber to achieve cascaded Stokes light generation, offering advantages such as narrow linewidth and low threshold voltage.

[0005] However, traditional cascaded stimulated Brillouin scattering (SBS) multiwavelength lasers have two inherent drawbacks: first, the wavelength spacing of each Stokes beam gradually narrows with increasing order, making it impossible to maintain uniformity; second, there is a lack of coherence between Stokes beams of different orders due to the random phase evolution during the SBS process. These problems make it difficult for this type of light source to meet the stringent requirements of the aforementioned system for channel spacing uniformity and phase coherence.

[0006] Therefore, how to achieve wavelength spacing uniformity and multi-channel phase locking while maintaining the advantages of narrow linewidth and low threshold is a technical challenge that needs to be solved in multi-wavelength Brillouin fiber lasers. Summary of the Invention

[0007] To address the problems existing in the prior art, the present invention aims to provide a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking and its implementation method. With a simple phase modulation injection structure, it simultaneously achieves single longitudinal mode output of Brillouin laser, active control of multi-wavelength spacing, and generation of equally spaced multi-wavelength lasers with good coherence. It also has the advantages of simple structure, finely adjustable frequency spacing, good multi-wavelength coherence, and easy cascading expansion.

[0008] To achieve the above objectives, the present invention provides the following solution: A cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking, comprising: a laser, the output end of which is connected to a first optical coupler, the first optical coupler introducing the output light of the laser into a main pump branch and a phase modulation branch; The main pump branch includes: a second optical coupler, which is sequentially connected to an erbium-doped fiber amplifier, a circulator, a first polarization controller, a single-mode fiber, and an optical isolator; wherein, the circulator is also connected to a third optical coupler to form a Brillouin laser ring feedback cavity; The phase modulation branch includes: a second polarization controller, which is sequentially connected to a phase modulator and a fourth optical coupler; wherein the phase modulator is also connected to a microwave source, and the fourth optical coupler is also connected to the optical isolator, for injection into the main pump branch.

[0009] To achieve the above objectives, the present invention also provides a method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking, comprising: A cascaded stimulated Brillouin scattering multi-wavelength laser is configured. The single-frequency continuous light of the laser is split into phase light and pump light by the first optical coupler and then introduced into the phase modulation branch and the main pump branch in sequence. The phase light is phase-modulated based on the phase modulation branch to generate a phase modulation sideband that matches the Brillouin frequency shift, and the phase modulation sideband is introduced into the Brillouin laser ring feedback cavity as injection light. The pump light is subjected to cascaded stimulated Brillouin scattering through the main pump branch to output multi-wavelength laser light.

[0010] Optionally, generating the phase modulation sideband includes: The phase light is input to the second polarization controller of the phase modulation branch. After the polarization state is adjusted by the second polarization controller, it enters the phase modulator. The microwave source loads the target radio frequency signal into the phase modulator, so that the optical carrier generates the phase modulation sideband.

[0011] Optionally, the output frequency of the microwave source is adjustable. The output frequency is set to the target Brillouin frequency shift corresponding to the target Stokes light, so as to continuously adjust the phase modulation sideband frequency by adjusting the output frequency of the microwave source, thereby realizing the repetition frequency adjustment of the output Stokes light comb.

[0012] Optionally, introducing the phase modulation sideband as injection light into the Brillouin laser ring feedback cavity includes: The phase modulation sideband is used as injection light and introduced into the Brillouin laser ring feedback cavity through a fourth optical coupler.

[0013] Optionally, outputting the multi-wavelength laser includes: The pump light passes through the first port of the second optical coupler, and is output from the third port of the second optical coupler to the erbium-doped fiber amplifier, then enters the first port of the circulator, and is output from the second port of the circulator to the first polarization controller, then enters the single-mode fiber. When the pump power exceeds the SBS threshold, a first-order Stokes light propagating in the reverse direction is generated in the single-mode fiber. The first-order Stokes beam is returned through the second port of the circulator and split into two beams. One beam is input from the first and third ports of the circulator to the third port of the erbium-doped fiber amplifier and the third optical coupler, respectively, and is further output from the first port of the third optical coupler to the fourth optical coupler. The other beam circulates unidirectionally in the Brillouin laser ring feedback cavity. At the same time, the optical signal output from the second port of the third optical coupler is input to the second port of the second optical coupler and output from the third and fourth ports of the second optical coupler. The output from the third port of the second optical coupler is amplified by the erbium-doped fiber amplifier and used as the pump light for the next-stage Stokes beam. The output from the fourth port of the second optical coupler is used as the multi-wavelength laser.

[0014] Optionally, the method further includes: When the injection sideband frequency of the injected light is within the locked range and the injection power meets the locking condition, the target Stokes light is locked; the frequency and phase of the target Stokes light are consistent with the phase-modulated sideband light. The target Stokes beam is fed back into the ring cavity and can be used as the pump light for the next-order SBS to generate a second-order Stokes beam. At the same time, it is injected and locked by the modulation sideband of the phase modulator. This cycle can be repeated to generate injection-locked multi-order Stokes beams.

[0015] The beneficial effects of this invention are as follows: This invention utilizes a single laser to split the beam into a main pump beam and a phase-modulated injection beam, ensuring a definite frequency relationship and good phase correlation between the phase-modulated sideband and the main pump beam. By using the phase-modulated sideband as coherent injection beam to frequency-push and phase-lock the target Stokes beam, non-target longitudinal mode suppression and single-longitudinal-mode Brillouin laser output are achieved. Active control of the wavelength spacing of the multi-wavelength Brillouin laser is achieved by adjusting the microwave source driving frequency. The locked low-order Stokes beam is used to excite cascaded stimulated Brillouin scattering, ultimately obtaining multi-wavelength laser output with equal frequency spacing and good coherence. Therefore, this invention simultaneously achieves single-longitudinal-mode output of a Brillouin laser, active control of multi-wavelength wavelength spacing, and generation of coherent, equally spaced multi-wavelength lasers with a simple phase-modulated injection structure, combining advantages such as simple structure, finely adjustable frequency spacing, good multi-wavelength coherence, and ease of cascading expansion. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a cascaded stimulated Brillouin scattering multiwavelength laser structure based on injection locking, according to an embodiment of the present invention. Figure 2 This is a spectrum diagram of the Selfie signal output by a single-wavelength Brillouin laser in an embodiment of the present invention when it is not injected and locked. Figure 3 This is the output spectrum of a multi-wavelength Brillouin laser after injection locking according to an embodiment of the present invention; Figure 4 This is a spectrum diagram of the output Selfie signal of a multi-wavelength Brillouin laser after injection locking, according to an embodiment of the present invention. Among them, 1-laser, 2-first optical coupler, 3-second optical coupler, 4-erbium-doped fiber amplifier, 5-circulator, 6-first polarization controller, 7-single-mode fiber, 8-optical isolator, 9-fourth optical coupler, 10-second polarization controller, 11-phase modulator, 12-microwave source, 13-third optical coupler. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown, this embodiment discloses a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking. The proposed structure includes: a laser, a first optical coupler, a second optical coupler, a third optical coupler, a fourth optical coupler, an erbium-doped fiber amplifier, a circulator, a single-mode fiber, a phase modulator (PM), a polarization controller, an optical isolator, and a microwave source. The output end of the laser is connected to the first optical coupler, which splits the output light into a main pump branch and a phase modulation branch. The main pump branch is sequentially connected to the second optical coupler, the erbium-doped fiber amplifier, the circulator, the first polarization controller, the single-mode fiber, and the optical isolator, and forms a Brillouin laser ring feedback cavity through the third optical coupler. The phase modulation branch is sequentially connected to the second polarization controller and the phase modulator, and is injected into the main pump branch through the fourth optical coupler. The microwave source is connected to the phase modulator to provide the phase modulator with a radio frequency drive signal. This method generates a modulation sideband that matches the Brillouin frequency shift through a phase modulation branch, and injects this sideband as injection light into the Brillouin laser resonator. This allows the free oscillating longitudinal modes within the Brillouin gain spectrum that match the sideband to dominate in gain competition, thereby achieving injection locking of the target Stokes beam. Through step-by-step injection locking, multi-wavelength laser output with uniform frequency spacing and good wavelength coherence can be obtained.

[0021] This embodiment discloses a method for implementing a cascaded stimulated Brillouin scattering (SBS) multi-wavelength laser based on injection-locked propagation, comprising the following steps: The single-frequency continuous light output from laser 1 is split into two paths by a first optical coupler 2. One path enters a phase modulation branch for phase modulation, and the other path enters a main pump branch. In the phase modulation branch, the phase light signal enters a phase modulator 11 after its polarization state is adjusted by a second polarization controller 10. A microwave source 12 loads a radio frequency signal with a frequency near the Brillouin shift onto the phase modulator 11, causing the optical carrier to generate a phase modulation sideband. In the main pump branch, the pump light sequentially passes through a second optical coupler 3 and an erbium-doped fiber amplifier 4 before entering port 1 of a circulator and exiting from port 2. After passing through a first polarization controller 6, it enters a single-mode fiber 7. When the pump power exceeds the SBS threshold, a first-order Stokes beam propagating in the reverse direction is generated in the single-mode fiber 7. The Stokes beam returns through port 2 of the circulator and exits through port 3 of the circulator 5. Part of it is output through port 1 of the third optical coupler, while the other part circulates unidirectionally within the ring cavity composed of the fourth optical coupler 9, the optical isolator 8, the single-mode fiber 7, and the first polarization controller 2. Part of the output optical signal from port 2 of the third optical coupler is amplified by the erbium-doped fiber amplifier through port 3 of the second optical coupler and used as the pump light for the next stage of the Stokes beam. The other part is used as the multi-wavelength laser output of the system through port 4 of the second optical coupler.

[0022] The modulated light output from the phase modulation branch is injected into the Brillouin ring cavity via the fourth optical coupler. Since the frequency of the modulated sideband light matches the frequency of a certain longitudinal mode within the Brillouin gain spectrum, this longitudinal mode has an advantage in gain competition. When the injected sideband frequency is within the locking range and the injection power ratio meets the corresponding optical injection locking condition, the target Stokes beam is locked, and its frequency and phase are consistent with the phase modulation sideband light. The locked first-order Stokes beam continues to feed back in the ring cavity and can be used as the pump light for the next-order SBS to generate a second-order Stokes beam, which is also injected and locked by the phase modulator's modulation sideband. This cycle repeats to further generate multi-order injected and locked Stokes beams.

[0023] As a preferred method, the phase modulation branch and the main pump branch are obtained by splitting the same laser. Since the phase modulation sideband and the main pump light originate from the same continuous optical carrier, they have a definite frequency relationship and phase correlation. This method eliminates the need for additional dual-laser frequency locking, reducing system complexity and improving the coherence between the Stokes beam and the pump beam after injection locking.

[0024] As a preferred method, the output frequency of the microwave source is adjustable, and its output frequency is set near the Brillouin frequency shift corresponding to the target Stokes light. By adjusting the output frequency of the microwave source, the phase modulation sideband frequency can be continuously adjusted, thereby achieving adjustment of the repetition frequency of the output Stokes light comb.

[0025] In one possible implementation, this embodiment discloses a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking, including a laser, an optical coupler, a phase modulator, a section of single-mode fiber, a circulator, a polarization controller, an optical isolator, and a microwave source.

[0026] Laser 1 outputs a single-frequency continuous beam with a center wavelength of 1550 nm and an output power of 18 dBm. This beam is split into two paths by a first optical coupler 2 with a splitting ratio of 20:80. One path enters the main pump branch via a second optical coupler 3 with a splitting ratio of 95:5; the other path enters the phase modulation branch. In the main pump branch, the pump light is amplified to 20 dBm by an erbium-doped fiber amplifier 4, then enters port 2 of a circulator 5 through port 1, and finally enters a 5100 m long single-mode fiber 7 via a first polarization controller 6. When the pump light power exceeds the stimulated Brillouin scattering threshold, a first-order Stokes beam propagating in the reverse direction of the pump light is generated in the single-mode fiber. The first-order Stokes light enters port 3 from port 2 of circulator 5. Part of it circulates unidirectionally within the ring feedback cavity, while the other part is fed back to the main pump branch via a 90:10 third optical coupler 13. After being amplified again by an erbium-doped fiber amplifier, it serves as the pump light for the next stimulated Brillouin scattering process. Once the power of this first-order Stokes light reaches the Brillouin threshold, it continues to generate a second-order Stokes light in reverse propagation within the main pump circuit. This process repeats until the power of the higher-order Stokes light falls below the Brillouin threshold. As the feedback process continues, the lower-order Stokes light, after power amplification, sequentially serves as the pump light for the higher-order stimulated Brillouin scattering process, progressively exciting even higher-order Stokes light, thus forming a cascaded multi-wavelength Brillouin laser output. In the phase modulation branch, the optical signal, after its polarization state is adjusted by the second polarization controller 10, enters a phase modulator 11 with a bandwidth of 20 GHz. The phase modulator 11 is driven by a microwave source 12, and its output frequency is set near the Brillouin frequency shift corresponding to the Stokes light to be locked; in this embodiment, it is set to fb = 10.859 GHz. Phase modulation generates multiple optical sidebands. The low-frequency first-order sideband BS1′ matches the frequency of the first-order Stokes beam BS1, while the higher-order low-frequency sidebands correspond to the injection frequencies of the higher-order Stokes beams. The phase-modulated optical signal is injected into the main pump branch through a 50:50 fourth optical coupler 9. During stimulated Brillouin scattering, the injected light gains an advantage in mode competition, locking each Stokes beam to its corresponding modulation sideband, achieving frequency pulling and phase locking. Since the frequency spacing between the modulation sidebands is determined by the microwave source frequency fb, the locked Stokes beams have equal frequency spacing. Therefore, injection locking not only suppresses gain competition within the cavity but also improves the uniformity of frequency spacing and phase coherence among the multi-order Stokes beams.

[0027] Without optical injection locking, the single-wavelength Brillouin laser output was connected to a photodetector with a bandwidth of 20 GHz for beat frequency analysis, and the beat frequency spectrum was measured using an electrical spectrum analyzer. The obtained beat frequency spectrum is as follows: Figure 2 As shown in the figure. At this time, both the center frequency and output power of the beat frequency signal fluctuate significantly, indicating that the system is in a free-running state.

[0028] Figure 3 This is a multi-wavelength Brillouin laser spectrum output by the system after injection locking. The signal is input to a photodetector for beat frequency analysis, and then measured by a spectrum analyzer. Figure 4 The spectrum is shown. The results show that the Brillouin beat frequency signal is equal to the frequency of the modulated microwave source, stabilizing at 10.8598 GHz without significant frequency drift, and the power is stable at -52 dBm. The clean spectrum indicates that a stable frequency relationship has been established between the Stokes beams of different orders, and the injection lock was successful. This also demonstrates that the phase modulation sideband effectively achieved injection lock for the Stokes beams of different orders, improved the phase consistency between them, and ultimately obtained a multi-wavelength Brillouin laser output with uniform frequency spacing.

[0029] As can be seen from specific examples, the present invention provides a multi-wavelength Brillouin fiber laser based on injection locking and its implementation method. This method introduces phase modulation sidebands to perform optical domain frequency pulling and phase locking on the cascaded stimulated Brillouin scattering process, which can effectively suppress intracavity longitudinal mode competition and random phase drift, and has the advantages of strictly equal spacing of multi-wavelength frequency combs, good phase coherence, and single longitudinal mode output.

[0030] This invention is not limited to the above-described embodiments, and several equivalent modifications and substitutions can be made. The center wavelength of the single-frequency continuous-wave laser is not limited to 1550nm, the type of optical fiber providing stimulated Brillouin gain is not limited to ordinary single-mode optical fiber (if highly nonlinear optical fiber is used, the cavity length can be further shortened and the start-up threshold reduced), the fiber length is not limited to 5100m, and the output frequency of the microwave source is not limited to around 10.8598GHz (it can be tuned according to the actual Brillouin frequency shift of the specific optical fiber). Various simplifications and modifications within the scope of the principles and methods of this invention are all protected by this invention.

[0031] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking, characterized in that, include: A laser, the output of which is connected to a first optical coupler, the first optical coupler introducing the output light of the laser into the main pump branch and the phase modulation branch; The main pump branch includes: a second optical coupler, which is sequentially connected to an erbium-doped fiber amplifier, a circulator, a first polarization controller, a single-mode fiber, and an optical isolator; wherein, the circulator is also connected to a third optical coupler to form a Brillouin laser ring feedback cavity; The phase modulation branch includes: a second polarization controller, which is sequentially connected to a phase modulator and a fourth optical coupler; wherein the phase modulator is also connected to a microwave source, and the fourth optical coupler is also connected to the optical isolator, for injection into the main pump branch.

2. A method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking, used to implement the cascaded stimulated Brillouin scattering multi-wavelength laser of claim 1, characterized in that, include: A cascaded stimulated Brillouin scattering multi-wavelength laser is configured. The single-frequency continuous light of the laser is split into phase light and pump light by the first optical coupler and then introduced into the phase modulation branch and the main pump branch in sequence. The phase light is phase-modulated based on the phase modulation branch to generate a phase modulation sideband that matches the Brillouin frequency shift, and the phase modulation sideband is introduced into the Brillouin laser ring feedback cavity as injection light. The pump light is subjected to cascaded stimulated Brillouin scattering through the main pump branch to output multi-wavelength laser light.

3. The method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking according to claim 2, characterized in that, Generating the phase modulation sideband includes: The phase light is input to the second polarization controller of the phase modulation branch. After the polarization state is adjusted by the second polarization controller, it enters the phase modulator. The microwave source loads the target radio frequency signal into the phase modulator, so that the optical carrier generates the phase modulation sideband.

4. The method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking according to claim 3, characterized in that, The output frequency of the microwave source is adjustable. The output frequency is set to the target Brillouin frequency shift corresponding to the target Stokes light. By adjusting the output frequency of the microwave source, the phase modulation sideband frequency is continuously adjusted to achieve the repetition frequency adjustment of the output Stokes light comb.

5. The method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking according to claim 2, characterized in that, Introducing the phase modulation sideband as injection light into the Brillouin laser ring feedback cavity includes: The phase modulation sideband is used as injection light and introduced into the Brillouin laser ring feedback cavity through a fourth optical coupler.

6. The method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking according to claim 2, characterized in that, The output of the multi-wavelength laser includes: The pump light passes through the first port of the second optical coupler, and is output from the third port of the second optical coupler to the erbium-doped fiber amplifier, then enters the first port of the circulator, and is output from the second port of the circulator to the first polarization controller, then enters the single-mode fiber. When the pump power exceeds the SBS threshold, a first-order Stokes light propagating in the reverse direction is generated in the single-mode fiber. The first-order Stokes beam is returned through the second port of the circulator and split into two beams. One beam is input from the first and third ports of the circulator to the third port of the erbium-doped fiber amplifier and the third optical coupler, respectively, and is further output from the first port of the third optical coupler to the fourth optical coupler. The other beam circulates unidirectionally in the Brillouin laser ring feedback cavity. At the same time, the optical signal output from the second port of the third optical coupler is input to the second port of the second optical coupler and output from the third and fourth ports of the second optical coupler. The output from the third port of the second optical coupler is amplified by the erbium-doped fiber amplifier and used as the pump light for the next-stage Stokes beam. The output from the fourth port of the second optical coupler is used as the multi-wavelength laser.

7. The method for implementing a cascaded stimulated Brillouin scattering multi-wavelength laser based on injection locking according to claim 5, characterized in that, The method also includes: When the injection sideband frequency of the injected light is within the locked range and the injection power meets the locking condition, the target Stokes light is locked; the frequency and phase of the target Stokes light are consistent with the phase-modulated sideband light. The target Stokes beam is fed back into the ring cavity and can be used as the pump light for the next-order SBS to generate a second-order Stokes beam. At the same time, it is injected and locked by the modulation sideband of the phase modulator. This cycle can be repeated to generate injection-locked multi-order Stokes beams.

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