Apparatus and method for increasing the stimulated brillouin scattering threshold of a fiber amplifier

Abstract

The application provides a device and method for improving the stimulated Brillouin scattering threshold of a fiber amplifier, wherein the device comprises a single-frequency seed source, a first fiber amplifier, a first fiber circulator, a passive fiber, a second fiber circulator and a single-frequency pump laser connected in sequence; the single-frequency laser signal emitted by the single-frequency seed source is amplified by the first fiber amplifier and meets the single-frequency pump laser signal emitted by the single-frequency pump laser on the passive fiber to generate stimulated Brillouin amplification. Under the same output power, the effective fiber length required by the application is shorter, the application can be superimposed and multiplexed with the current method for improving the stimulated Brillouin scattering threshold of a fiber amplifier, the stimulated Brillouin scattering threshold of the fiber amplifier can be further improved, thereby further improving the output power of the signal light, in addition, compared with the commercial fiber amplifier on the market, the application only changes the fiber optical path and does not have other auxiliary measures, the implementation scheme is simple in structure, low in cost and high in reliability.

Description

Technical Field

[0001] This invention relates to the field of fiber laser technology, and in particular to an apparatus and method for improving the stimulated Brillouin scattering threshold of a fiber amplifier. Background Technology

[0002] High-power single-frequency continuous (or pulsed) fiber lasers have broad application prospects in coherent Doppler lidar, nonlinear frequency conversion, and gas detection. These lasers typically employ a single-frequency seed source followed by master oscillator power amplification (MOPA) optical path structure, characterized by extremely narrow output laser linewidth, high power, and an all-fiber optical path. However, due to the limitation of the nonlinear effect of stimulated Brillouin scattering (SBS) excited by the narrow-linewidth laser in the fiber amplifier, the rapidly growing reverse Brillouin laser, amplified from quantum noise, consumes the signal laser, hindering further signal laser growth. This limits the maximum output power of such lasers to approximately 500W (continuous beam) and 750W (peak power, ns long pulse). Since the stimulated Brillouin scattering threshold is proportional to the effective mode area of ​​the fiber and inversely proportional to the effective fiber length and Brillouin gain coefficient, methods to improve the stimulated Brillouin scattering threshold of the fiber amplifier mainly fall into three categories.

[0003] 1. Increase the fiber core diameter. The larger the fiber core diameter, the larger its effective mode field area. However, in order to keep the number of modes in large mode field fibers to a small extent, a fiber structure with a smaller numerical aperture is required. The extremely small numerical aperture not only places more stringent requirements on fiber manufacturing, but also makes the fiber very sensitive to bending, losing the advantage of flexible bending. Therefore, the maximum core diameter of commercially available gain fibers is generally 30µm, and it has not been further increased.

[0004] II. Employing highly doped gain fiber to reduce effective fiber length. The effective fiber length of a fiber amplifier includes both gain fiber and passive fiber, with a total effective fiber length of approximately 1m. Given that the passive fiber of the fiber amplifier has already been optimized to its optimal length, employing highly doped gain fiber can reduce the gain fiber length, thereby reducing the effective fiber length of the fiber amplifier. However, due to limitations imposed by effects such as ion aggregation, concentration quenching, and photon darkening, it is difficult to further increase the doping concentration of the gain fiber.

[0005] III. Reducing the Effective Brillouin Gain Coefficient. Applying a temperature or stress gradient along the fiber axis shifts the Brillouin gain peak at different locations in the fiber, thereby reducing the accumulation of stimulated Brillouin scattering in the fiber, which is equivalent to reducing the Brillouin gain coefficient. This method has a relatively complex device, and its engineering application is quite difficult. Alternatively, a high-peak-power pulsed laser can be injected in the reverse direction. By cross-phase modulation between this pulsed laser and the backward-propagating stimulated Brillouin scattering light, the spectrum of the stimulated Brillouin scattering light can be broadened, thus reducing the Brillouin gain coefficient. This method is simple in structure and easy to implement, but it requires a high-peak-power reverse light to generate sufficient cross-phase modulation. Furthermore, the reverse light must be selected at a wavelength that the gain fiber does not absorb or emit, which carries the risk of exciting reverse amplification or self-excitation, potentially damaging the amplification optical path.

[0006] The methods described above for increasing the stimulated Brillouin scattering threshold of fiber amplifiers can all achieve certain results, but their ability to increase the threshold is limited and still cannot meet the application requirements for further increasing the output power of fiber lasers.

[0007] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0008] This invention provides a solution to the technical problem that current methods for increasing the stimulated Brillouin scattering threshold of fiber amplifiers have limited ability to further improve the output power of fiber lasers.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides an apparatus for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, the apparatus comprising:

[0011] The single-frequency seed source 1, the first fiber amplifier 2, the first fiber circulator 3, the passive fiber 4, the second fiber circulator 5, and the single-frequency pump laser 6 are connected in sequence.

[0012] The single-frequency laser signal emitted by the single-frequency seed source 1 is amplified by the first fiber amplifier 2 and then meets the single-frequency pump laser signal emitted by the single-frequency pump laser 6 on the passive fiber 4 to generate stimulated Brillouin amplification; wherein, the amplified single-frequency laser signal is output from the second fiber circulator 5, and the consumed single-frequency pump laser signal is output from the first fiber circulator 3.

[0013] Preferably, the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is consistent with the maximum output power of the single-frequency pump laser 6.

[0014] Preferably, the difference between the frequency of the single-frequency laser signal emitted by the single-frequency seed source 1 and the frequency of the single-frequency pump laser signal emitted by the single-frequency pump laser 6 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4.

[0015] Preferably, the wavelength of the single-frequency laser signal emitted by the single-frequency seed source 1 is between 1 and 2 μm, and the linewidth of the single-frequency laser signal emitted by the single-frequency seed source 1 is less than 10 MHz.

[0016] Based on the same general technical concept as the first aspect, in a second aspect, the present invention provides a method for increasing the stimulated Brillouin scattering threshold of an optical fiber amplifier, using the apparatus for increasing the stimulated Brillouin scattering threshold of an optical fiber amplifier described in the first aspect, the method comprising:

[0017] Connect the single-frequency seed source 1, the first fiber amplifier 2, the first fiber circulator 3, the passive fiber 4, the second fiber circulator 5, and the single-frequency pump laser 6 in sequence.

[0018] Ensure that the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is consistent with the maximum output power of the single-frequency pump laser 6.

[0019] Ensure that the frequency difference between the single-frequency laser signal emitted by the single-frequency seed source 1 and the single-frequency pump laser signal emitted by the single-frequency pump laser 6 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4, so that the single-frequency laser signal emitted by the single-frequency seed source 1, after being amplified by the first fiber amplifier 2, meets the single-frequency pump laser signal emitted by the single-frequency pump laser 6 on the passive fiber 4 to generate stimulated Brillouin amplification.

[0020] Based on the same general technical concept as the first aspect, in a third aspect, the present invention provides an apparatus for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, the apparatus comprising:

[0021] The single-frequency seed source 1, the first fiber amplifier 2, the first fiber optic circulator 3, the passive fiber 4, and the second fiber optic circulator 5 are connected in sequence; and,

[0022] Fiber optic coupler 7 connected in series between single-frequency seed source 1 and first fiber amplifier 2;

[0023] Frequency shifter 8 and second fiber amplifier 9 are connected in series between fiber coupler 7 and second fiber circulator 5;

[0024] The single-frequency laser signal emitted by the single-frequency seed source 1 is split into two paths by the fiber coupler 7. One path, amplified by the first fiber amplifier 2, meets the other path, amplified by the frequency shifter 8 and the second fiber amplifier 9, on the passive fiber 4, generating stimulated Brillouin amplification. The amplified single-frequency laser signal is output from the second fiber circulator 5, and the consumed single-frequency laser signal is output from the first fiber circulator 3.

[0025] Preferably, the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is the same as the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the second fiber amplifier 9.

[0026] Preferably, the difference between the frequency of the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the first fiber amplifier 2 and the frequency of the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the frequency shifter 8 and the second fiber amplifier 9 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4.

[0027] Preferably, the wavelength of the single-frequency laser signal emitted by the single-frequency seed source 1 is between 1 and 2 μm, and the linewidth of the single-frequency laser signal emitted by the single-frequency seed source 1 is less than 10 MHz.

[0028] Based on the same general technical concept as the third aspect, in a fourth aspect, the present invention provides a method for increasing the stimulated Brillouin scattering threshold of an optical fiber amplifier, using the apparatus for increasing the stimulated Brillouin scattering threshold of an optical fiber amplifier described in the third aspect, the method comprising:

[0029] Connect the single-frequency seed source 1, the first fiber amplifier 2, the first fiber circulator 3, the passive fiber 4, and the second fiber circulator 5 in sequence.

[0030] Fiber optic coupler 7 is connected in series between single-frequency seed source 1 and first fiber optic amplifier 2, and frequency shifter 8 and second fiber optic amplifier 9 are connected in series between fiber optic coupler 7 and second fiber optic circulator 5.

[0031] Ensure that the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is consistent with the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the second fiber amplifier 9.

[0032] Ensure that the frequency difference between the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the first fiber amplifier 2 and the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the frequency shifter 8 and the second fiber amplifier 9 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4, so that the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the first fiber amplifier 2 meet on the passive fiber 4 and generate stimulated Brillouin amplification.

[0033] In view of the shortcomings of the prior art, the beneficial effects that the present invention can achieve are as follows:

[0034] This invention proposes a new technical solution for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier. The technical solution of this invention can be superimposed and reused with current methods for improving the stimulated Brillouin scattering threshold of optical fiber amplifiers, which can further improve the stimulated Brillouin scattering threshold of the optical fiber amplifier, thereby further improving the output power of the signal light.

[0035] At the same output power, compared with the technical solution of using highly doped gain fiber (e.g., rare earth ion doped fiber) to reduce the effective fiber length, the present invention requires a shorter effective fiber length. In addition, compared with the commercial fiber amplifiers currently on the market that only change the fiber optical path without other auxiliary measures, the present invention has a simple structure, low cost and high reliability. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0037] Figure 1 This is a schematic diagram of a device structure for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, provided in Embodiment 1 of the present invention.

[0038] Figure 2 This is a schematic flowchart of a method for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier according to Embodiment 2 of the present invention;

[0039] Figure 3 This is a schematic diagram of a device structure for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, provided in Embodiment 3 of the present invention.

[0040] Figure 4 This is a schematic flowchart of a method for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, provided in Embodiment 4 of the present invention.

[0041] In the accompanying drawings, the same reference numerals are used to denote the same parts or structures, wherein:

[0042] 1-Single-frequency seed source; 2-First fiber amplifier; 3-First fiber circulator; 4-Passive fiber; 5-Second fiber circulator; 6-Single-frequency pump laser; 7-Fiber coupler; 8-Frequency shifter; 9-Second fiber amplifier. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0044] In the description of this invention, the terms "inner", "outer", "longitudinal", "lateral", "upper", "lower", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and do not require that this invention must be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0045] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] Example 1:

[0047] To address the limitation of current methods for increasing the stimulated Brillouin scattering threshold of fiber amplifiers, which hinders further improvements in fiber laser output power, this embodiment 1 provides a device for increasing the stimulated Brillouin scattering threshold of fiber amplifiers, such as... Figure 1 As shown, it includes:

[0048] The system is sequentially connected to a single-frequency seed source 1, a first fiber amplifier 2, a first fiber circulator 3, a passive fiber 4, a second fiber circulator 5, and a single-frequency pump laser 6. The single-frequency laser signal emitted from the single-frequency seed source 1 is amplified by the first fiber amplifier 2 and then encounters the single-frequency pump laser signal emitted from the single-frequency pump laser 6 on the passive fiber 4, generating stimulated Brillouin amplification. In this embodiment, the single-frequency laser signal emitted from the single-frequency seed source 1 undergoes two amplifications: first by the first fiber amplifier 2, and second by the stimulated Brillouin amplification generated when it encounters the single-frequency pump laser signal emitted from the single-frequency pump laser 6 on the passive fiber 4. Compared to the traditional method, this adds an extra amplification stage. This amplification stage can be superimposed and multiplexed with current methods for increasing the stimulated Brillouin scattering threshold of fiber amplifiers, enabling... The stimulated Brillouin scattering threshold of the fiber amplifier is further increased, thereby further increasing the output power of the signal light based on the first fiber amplifier 2. The effective fiber length required in this embodiment is limited by the sum of the pigtail lengths required for the fusion of the first fiber circulator 3 and the second fiber circulator 5, which is approximately 20 cm. At the same output power, compared with the technical solution of using highly doped gain fiber (e.g., rare earth ion-doped fiber) to reduce the effective fiber length, the effective fiber length required in this embodiment is shorter, and the stimulated Brillouin scattering threshold that can be achieved is higher. Therefore, the power output by the circulator 5 is greater than the power output by the first fiber amplifier 2 alone. The amplified single-frequency laser signal is output from the second fiber circulator 5, and the consumed single-frequency pump laser signal is output from the first fiber circulator 3.

[0049] In specific implementation, the single-frequency seed source 1 uses a semiconductor laser, fiber laser, or other fiber-coupled laser. The single-frequency laser signal produced by the single-frequency seed source 1 is a continuous (or pulsed) laser signal. The wavelength of the single-frequency laser signal emitted by the single-frequency seed source 1 is between 1-2 μm, preferably 1.0 μm, 1.5 μm, or 2.0 μm. The single-frequency laser signal emitted by the single-frequency seed source 1 has a narrow linewidth, preferably less than 10 MHz. The first fiber amplifier 2 is one of a ytterbium-doped fiber amplifier, an erbium-doped fiber amplifier, an erbium-ytterbium co-doped fiber amplifier, a thulium-doped fiber amplifier, or a thulium-holmium co-doped fiber amplifier. The first fiber circulator 3 and the second fiber circulator 5 are both high-power fiber circulators. In this embodiment, they can be three-port or four-port circulators. The passive fiber 4 is one of a quartz fiber, a phosphate fiber, or a silicate fiber.

[0050] To better facilitate stimulated Brillouin amplification by allowing the single-frequency laser signal emitted by the single-frequency seed source 1 and the single-frequency pump laser signal emitted by the single-frequency pump laser 6 to meet on the passive fiber 4, the wavelength of the single-frequency pump laser signal emitted by the single-frequency pump laser 6 is shorter than that of the single-frequency laser signal emitted by the single-frequency seed source 1. In practical applications, to obtain greater output power, it is necessary to maximize the output power. Preferably, the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after amplification by the first fiber amplifier 2 is consistent with the maximum output power of the single-frequency pump laser 6. Furthermore, the difference between the frequency of the single-frequency laser signal emitted by the single-frequency seed source 1 and the frequency of the single-frequency pump laser signal emitted by the single-frequency pump laser 6 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4 (approximately 11 GHz).

[0051] This embodiment 1 provides a device for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, and its overall optical path transmission implementation is as follows:

[0052] The single-frequency seed source 1 emits a single-frequency (continuous or pulsed) laser signal, which is amplified by the first fiber amplifier 2 and connected to port 3-1 of the first fiber circulator 3. The signal is then output from port 3-2 of the first fiber circulator 3, transmitted forward through the passive fiber 4, and input to port 5-2 of the second fiber circulator 5. It is then output from port 5-3 of the second fiber circulator 5. Simultaneously, the single-frequency pump laser 6 generates a single-frequency pump laser signal for Brillouin amplification, which is input from port 5-1 of the second fiber circulator 5 and output from port 5-3 of the second fiber circulator 5. The single-frequency pump laser signal propagating in reverse and the single-frequency laser signal propagating in forward meet in space in the passive fiber 4, generating stimulated Brillouin amplification. The optical power of the forward-propagating single-frequency laser signal is further amplified and output from port 5-3 of the second fiber circulator 5, while the single-frequency pump laser signal propagating in reverse is partially consumed. The remaining single-frequency pump laser signal propagating in reverse is injected through port 3-2 of the first fiber circulator 3 and output from port 3-3 of the first fiber circulator 3.

[0053] Example 2:

[0054] Based on the same overall technical concept as Embodiment 1, Embodiment 2 provides a method for increasing the stimulated Brillouin scattering threshold of an optical fiber amplifier, using the apparatus for increasing the stimulated Brillouin scattering threshold of an optical fiber amplifier described in Embodiment 1, such as... Figure 2 As shown, the method includes:

[0055] S201, connect the single-frequency seed source 1, the first fiber amplifier 2, the first fiber circulator 3, the passive fiber 4, the second fiber circulator 5, and the single-frequency pump laser 6 in sequence.

[0056] S202 ensures that the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is consistent with the maximum output power of the single-frequency pump laser 6.

[0057] S203 ensures that the frequency difference between the single-frequency laser signal emitted by the single-frequency seed source 1 and the single-frequency pump laser signal emitted by the single-frequency pump laser 6 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4, so that the single-frequency laser signal emitted by the single-frequency seed source 1, after being amplified by the first fiber amplifier 2, meets the single-frequency pump laser signal emitted by the single-frequency pump laser 6 on the passive fiber 4 to generate stimulated Brillouin amplification.

[0058] In terms of ensuring the method, it can be achieved through the selection of components and their testing and verification.

[0059] Example 3:

[0060] To address the limitation of current methods for increasing the stimulated Brillouin scattering threshold of fiber amplifiers, which hinders further improvements in fiber laser output power, and based on the same overall technical concept as in Embodiment 1, this Embodiment 3 provides a device for increasing the stimulated Brillouin scattering threshold of a fiber amplifier. This device aims to adjust the frequency difference between the two laser signals generating stimulated Brillouin amplification, thereby achieving better and more reliable technical results. Figure 3As shown, the device includes: a single-frequency seed source 1, a first fiber amplifier 2, a first fiber circulator 3, a passive fiber 4, and a second fiber circulator 5 connected in sequence; and a fiber coupler 7 connected in series between the single-frequency seed source 1 and the first fiber amplifier 2; a frequency shifter 8 and a second fiber amplifier 9 connected in series between the fiber coupler 7 and the second fiber circulator 5; the single-frequency laser signal emitted by the single-frequency seed source 1 is split into two paths by the fiber coupler 7, one path of the single-frequency laser signal amplified by the first fiber amplifier 2 and the other path of the single-frequency laser signal amplified by the frequency shifter 8 and the second fiber amplifier 9 meet on the passive fiber 4 to generate stimulated Brillouin amplification; wherein, the amplified single-frequency laser signal is output from the second fiber circulator 5, and the consumed single-frequency laser signal is output from the first fiber circulator 3; in this embodiment Instead of using the single-frequency pump laser 6 in Embodiment 1, a frequency shifter 8 and a second fiber amplifier 9 are used. Through the application of the frequency shifter 8, the frequency of one of the single-frequency laser signals can be precisely adjusted, that is, the frequency difference of the single-frequency laser signals can be precisely adjusted. Similarly, the single-frequency laser signal emitted by the single-frequency seed source 1 is also amplified twice. The required effective fiber length is limited by the sum of the pigtail lengths required for the fusion of the first fiber circulator 3 and the second fiber circulator 5, which is about 20 cm. At the same output power, compared with the technical solution of using highly doped gain fiber (e.g., rare earth ion-doped fiber) to reduce the effective fiber length, this embodiment requires a shorter effective fiber length and can achieve a higher stimulated Brillouin scattering threshold, that is, the power output by the circulator 5 is greater.

[0061] In specific implementation, the implementation scheme of single-frequency seed source 1, first fiber amplifier 2, first fiber circulator 3, passive fiber 4 and second fiber circulator 5 is similar to that of embodiment 1; the fiber coupler 7 is preferably a 1×2 coupler, and the frequency shifter 8 shown is preferably an electro-optic modulator to generate a positive frequency shift. Preferably, the model and performance of the second fiber amplifier 9 are consistent with those of the first fiber amplifier 2.

[0062] In practical applications, similarly, the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is the same as the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the second fiber amplifier 9; furthermore, the difference between the frequency of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 and the frequency of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the frequency shifter 8 and the second fiber amplifier 9 is the same as the frequency shift at the Brillouin peak gain of the passive fiber 4 (approximately 11 GHz).

[0063] This embodiment 3 provides a device for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, and its overall optical path transmission implementation is as follows:

[0064] The single-frequency seed source 1 emits a single-frequency (continuous or pulsed) laser signal, which is connected to the input 7-1 of the fiber coupler 7. The signal is then split into two beams, outputting through ports 7-2 and 7-3 of the fiber coupler 7, respectively. The beam output from port 7-3 serves as the signal beam, connected to the input of the first fiber amplifier 2. After amplification by the first fiber amplifier 2, it is connected to port 3-1 of the first fiber circulator 3, and then output from port 3-2. After forward propagation in the passive fiber 4, it is input to port 5-2 of the second fiber circulator 5, and then output from port 5-3. Simultaneously, the beam output from port 7-2 is frequency-shifted by the frequency shifter 8 before... The power of the laser signal is amplified by the second fiber amplifier 9 to the same output power as the first fiber amplifier 2, serving as the pump laser for stimulated Brillouin amplification. It is input through port 5-1 of the second fiber circulator 5 and injected into the passive fiber 4 through port 5-2. In the passive fiber 4, the laser signal propagating in the reverse direction meets the laser signal propagating in the forward direction in space, resulting in stimulated Brillouin amplification. The optical power of the forward-propagating laser signal is further amplified and output from port 5-3 of the second fiber circulator 5. The optical power of the reverse-propagating laser signal is partially consumed, and the remaining reverse-propagating laser signal is injected through port 3-2 of the first fiber circulator 3 and output from port 3-3 of the first fiber circulator 3.

[0065] Example 4:

[0066] Based on the same overall technical concept as Embodiment 3, Embodiment 4 provides a method for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, using the apparatus for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier described in Embodiment 3. The method includes:

[0067] S401, connect the single-frequency seed source 1, the first fiber amplifier 2, the first fiber circulator 3, the passive fiber 4, and the second fiber circulator 5 in sequence; connect the fiber coupler 7 in series between the single-frequency seed source 1 and the first fiber amplifier 2, and connect the frequency shifter 8 and the second fiber amplifier 9 in series between the fiber coupler 7 and the second fiber circulator 5 in sequence.

[0068] S402, ensure that the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the first fiber amplifier 2 is consistent with the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source 1 after being amplified by the second fiber amplifier 9.

[0069] S403 ensures that the frequency difference between the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the first fiber amplifier 2 and the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the frequency shifter 8 and the second fiber amplifier 9 is consistent with the frequency shift at the Brillouin peak gain of the passive fiber 4, so that the single-frequency laser signal emitted by the single-frequency seed source 1 and amplified by the first fiber amplifier 2 meet on the passive fiber 4 to generate stimulated Brillouin amplification.

[0070] Similarly, in terms of ensuring the quality of equipment, this can be achieved through the selection of appropriate components and their testing and verification.

[0071] In summary, this invention provides an apparatus and method for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier. At the same output power, this invention requires a shorter effective optical fiber length and can be superimposed and multiplexed with current methods for improving the stimulated Brillouin scattering threshold of optical fiber amplifiers, thereby further increasing the stimulated Brillouin scattering threshold of the optical fiber amplifier and thus further increasing the output power of the signal light. In addition, compared with commercially available optical fiber amplifiers on the market, this invention only changes the optical fiber path without other auxiliary measures, resulting in a simple structure, low cost, and high reliability.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, characterized in that, include: The single-frequency seed source (1), the first fiber amplifier (2), the first fiber circulator (3), the passive fiber (4), the second fiber circulator (5) and the single-frequency pump laser (6) are connected in sequence. The single-frequency laser signal emitted by the single-frequency seed source (1) is amplified by the first fiber amplifier (2) and meets the single-frequency pump laser signal emitted by the single-frequency pump laser (6) on the passive fiber (4) to generate stimulated Brillouin amplification; wherein, the amplified single-frequency laser signal is output from the second fiber circulator (5), and the consumed single-frequency pump laser signal is output from the first fiber circulator (3). The maximum output power of the single-frequency laser signal emitted by the single-frequency seed source (1) after being amplified by the first fiber amplifier (2) is the same as the maximum output power of the single-frequency pump laser (6); The difference between the frequency of the single-frequency laser signal emitted by the single-frequency seed source (1) and the frequency of the single-frequency pump laser signal emitted by the single-frequency pump laser (6) is consistent with the frequency shift at the Brillouin peak gain of the passive fiber (4).

2. The apparatus for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier according to claim 1, characterized in that, The wavelength of the single-frequency laser signal emitted by the single-frequency seed source (1) is between 1 and 2 μm, and the linewidth of the single-frequency laser signal emitted by the single-frequency seed source (1) is less than 10 MHz.

3. A method for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, characterized in that, The apparatus for raising the stimulated Brillouin scattering threshold of an optical fiber amplifier according to any one of claims 1 or 2 comprises: Connect the single-frequency seed source (1), the first fiber amplifier (2), the first fiber circulator (3), the passive fiber (4), the second fiber circulator (5), and the single-frequency pump laser (6) in sequence. Ensure that the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source (1) after being amplified by the first fiber amplifier (2) is consistent with the maximum output power of the single-frequency pump laser (6); Ensure that the frequency difference between the single-frequency laser signal emitted by the single-frequency seed source (1) and the single-frequency pump laser signal emitted by the single-frequency pump laser (6) is consistent with the frequency shift at the Brillouin peak gain of the passive fiber (4), so that the single-frequency laser signal emitted by the single-frequency seed source (1) is amplified by the first fiber amplifier (2) and meets the single-frequency pump laser signal emitted by the single-frequency pump laser (6) on the passive fiber (4) to generate stimulated Brillouin amplification.

4. A device for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, characterized in that, include: A single-frequency seed source (1), a first fiber amplifier (2), a first fiber optic circulator (3), a passive fiber (4), and a second fiber optic circulator (5) are connected in sequence; and, Fiber optic coupler (7) connected in series between single-frequency seed source (1) and first fiber amplifier (2); A frequency shifter (8) and a second fiber amplifier (9) are connected in series between the fiber coupler (7) and the second fiber circulator (5). The single-frequency laser signal emitted by the single-frequency seed source (1) is split into two paths by the fiber coupler (7). One path, amplified by the first fiber amplifier (2), meets the other path, amplified by the frequency shifter (8) and the second fiber amplifier (9), on the passive fiber (4) to generate stimulated Brillouin amplification. The amplified single-frequency laser signal is output from the second fiber circulator (5), and the consumed single-frequency laser signal is output from the first fiber circulator (3). The maximum output power of the single-frequency laser signal emitted by the single-frequency seed source (1) after being amplified by the first fiber amplifier (2) is the same as the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source (1) after being amplified by the second fiber amplifier (9). The frequency difference between the single-frequency laser signal emitted by the single-frequency seed source (1) and amplified by the first fiber amplifier (2) and the single-frequency laser signal emitted by the single-frequency seed source (1) and amplified by the frequency shifter (8) and the second fiber amplifier (9) is consistent with the frequency shift at the Brillouin peak gain of the passive fiber (4).

5. The apparatus for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier according to claim 4, characterized in that, The wavelength of the single-frequency laser signal emitted by the single-frequency seed source (1) is between 1 and 2 μm, and the linewidth of the single-frequency laser signal emitted by the single-frequency seed source (1) is less than 10 MHz.

6. A method for improving the stimulated Brillouin scattering threshold of an optical fiber amplifier, characterized in that, The apparatus for raising the stimulated Brillouin scattering threshold of an optical fiber amplifier according to any one of claims 4 or 5 includes: Connect the single-frequency seed source (1), the first fiber amplifier (2), the first fiber circulator (3), the passive fiber (4), and the second fiber circulator (5) in sequence; Connect the fiber coupler (7) in series between the single-frequency seed source (1) and the first fiber amplifier (2), and connect the frequency shifter (8) and the second fiber amplifier (9) in series between the fiber coupler (7) and the second fiber circulator (5). Ensure that the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source (1) after being amplified by the first fiber amplifier (2) is consistent with the maximum output power of the single-frequency laser signal emitted by the single-frequency seed source (1) after being amplified by the second fiber amplifier (9); Ensure that the frequency difference between the single-frequency laser signal emitted by the single-frequency seed source (1) and amplified by the first fiber amplifier (2) and the single-frequency laser signal emitted by the single-frequency seed source (1) and amplified by the frequency shifter (8) and the second fiber amplifier (9) is consistent with the frequency shift at the Brillouin peak gain of the passive fiber (4), so that the single-frequency laser signal emitted by the single-frequency seed source (1) and amplified by the first fiber amplifier (2) and the single-frequency laser signal emitted by the single-frequency seed source (1) and amplified by the frequency shifter (8) and the second fiber amplifier (9) meet on the passive fiber (4) to generate stimulated Brillouin amplification.

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