Fiber grating structure, laser and self-oscillation suppression method

Abstract

The invention belongs to the field of lasers, provides a fiber grating structure, a laser and a self-oscillation suppression method, and relates to the field of lasers. The fiber bragg grating structure comprises a high-reflectivity grating, a first gain fiber, a low-reflectivity grating, a second gain fiber and an inclined grating module which are sequentially arranged in the first direction, the inclined grating module comprises at least one inclined grating, the at least one inclined grating has an inclined angle relative to the second direction, the second direction is perpendicular to the first direction, and the first gain fiber is arranged in the first direction. The second gain fiber is longer than the first gain fiber. According to the fiber grating structure, the laser and the self-oscillation suppression method, the self-oscillation suppression ratio can be improved, so that the self-oscillation power of the laser is reduced.

Description

Technical Field

[0001] This application relates primarily to the field of lasers, and more particularly to a fiber grating structure, a laser, and a method for suppressing self-excited oscillations. Background Technology

[0002] In the field of lasers, the ability to resolve the self-oscillation problem has always been a crucial factor affecting laser stability. Taking thulium-doped fiber lasers (FDFSLs) as an example, FDFSLs have attracted significant attention in medical, materials processing, and lidar fields due to their high-efficiency output in the 2μm wavelength range. However, FDFSLs are highly susceptible to generating parasitic light in the 1980nm–2400nm wavelength range during spontaneous emission amplification. This parasitic light forms parasitic resonant cavities between reflection points such as the gain fiber endface and melting point. This parasitic light competes with the signal light, consuming population inversion energy, leading to mode instability, beam quality degradation, and limited laser output power. In severe cases, it can damage optical components and cause laser system failure. Therefore, resolving the self-oscillation problem is paramount for achieving safe, stable, and reliable fiber lasers. Summary of the Invention

[0003] The technical problem to be solved by this application is to provide a fiber grating structure that can improve the self-oscillation suppression ratio, thereby reducing the self-oscillation power of the laser.

[0004] To address the aforementioned technical problems, this application provides a fiber optic grating structure, comprising a high-reflection grating, a first-gain fiber, a low-reflection grating, a second-gain fiber arranged sequentially along a first direction, and a tilted grating module. The tilted grating module includes at least one tilted grating, which has a tilt angle relative to a second direction, the second direction being perpendicular to the first direction. The length of the second-gain fiber is greater than the length of the first-gain fiber.

[0005] Optionally, the tilted grating module includes a tilted grating array consisting of multiple tilted gratings, each tilted grating having a tilt angle of 10° to 15°.

[0006] Optionally, multiple tilted gratings may have different center wavelengths.

[0007] Optionally, the first gain fiber and the second gain fiber are made of the same material and have an absorption coefficient α. The sum of the lengths L of the first gain fiber and the second gain fiber has the following relationship with the absorption coefficient α: the product of L and α is between 10dB and 30dB, where the unit of L is m and the unit of α is dB / m.

[0008] Optionally, the first gain fiber and the second gain fiber are doped with thulium.

[0009] Optionally, the difference between the length of the second gain fiber and the length of the first gain fiber is 1m to 10m.

[0010] To address the aforementioned technical problems, this application provides a laser, including a pump source and the aforementioned fiber optic grating structure, wherein the pump source is connected to a high-reflectivity grating in the fiber optic grating structure.

[0011] Optionally, it also includes a beam combiner connected between the pump source and the high-reflectivity grating, wherein the pump source and the beam combiner are an integrated device.

[0012] Optionally, it also includes a front tilt grating located in the first direction on the side of the pump source further away from the high-reflectivity grating, the front tilt grating having a tilt angle relative to a second direction perpendicular to the first direction.

[0013] Optionally, it also includes a cladding stripper and an end cap, which are integrated devices.

[0014] Optionally, it also includes a monitoring and feedback module, which includes a monitoring unit, a logic unit, and an execution unit. The monitoring unit is configured to monitor the power data of the laser; the logic unit is configured to compare the power data with a preset safety value and then generate a control command; and the execution unit is configured to receive the control command and control the working state of the pump source according to the control command.

[0015] Optionally, the monitoring unit is connected to the fiber optic grating structure, and the monitoring unit includes a photodiode, which is configured to monitor power data.

[0016] Optionally, the preset safety value includes a pump source shutdown threshold, and the logic unit is configured to generate a first control command suitable for shutting down the pump source when the power data is determined to be higher than the pump source shutdown threshold.

[0017] Optionally, the power data includes the output laser power, the preset safety value includes the output power fluctuation threshold, and the logic unit is configured to generate a second control command suitable for making the ratio not greater than the output power fluctuation threshold when the absolute value of the difference between the output laser power and the output power reference value is greater than the output power fluctuation threshold.

[0018] Optionally, the power data includes the output laser power and the return laser power, the preset safety value includes the return light ratio threshold, and the logic unit is configured to generate a third control command suitable for making the ratio not greater than the return light ratio threshold when it is determined that the ratio of the return laser power to the output laser power is greater than the return light ratio threshold.

[0019] To address the aforementioned technical problems, this application provides a self-oscillation suppression method applicable to lasers. The laser includes a fiber grating structure, comprising a high-reflection grating, a first-gain fiber, a low-reflection grating, a second-gain fiber, and a tilted grating module arranged sequentially along a first direction. The tilted grating module includes at least one tilted grating, which has a tilt angle relative to a second direction perpendicular to the first direction. The length of the second-gain fiber is greater than the length of the first-gain fiber. The self-oscillation suppression method includes the following steps: determining a first center wavelength of at least one self-oscillating light generated by the laser; and setting a second center wavelength of the at least one tilted grating to be equal to the first center wavelength of the corresponding self-oscillating light.

[0020] Optionally, the laser also includes a beam combiner and a pump source, the beam combiner being connected between the pump source and the high-reflectivity grating, and the self-oscillation suppression method further includes the following steps: determining the third center wavelength of the returned laser generated by the laser, and setting a forward tilting grating on the side of the pump source further away from the high-reflectivity grating in a first direction, wherein the fourth center wavelength of the forward tilting grating is equal to the third center wavelength; and / or setting the beam combiner and the pump source as an integrated device.

[0021] Optionally, the laser also includes a cladding stripper and an end cap, and the self-oscillation suppression method further includes the following steps: depositing an antireflection coating on the end cap; and / or setting the cladding stripper and the end cap as an integrated device.

[0022] Compared with existing technologies, this application has the following advantages: By making the first gain fiber shorter, it achieves a higher self-excitation threshold, enabling it to suppress parasitic laser oscillations (i.e., self-excitation) while initially amplifying the optical signal. Furthermore, by incorporating a second gain fiber and making the first gain fiber longer, the second gain fiber further amplifies the optical signal output from the first gain fiber. Since the first gain fiber effectively controls parasitic laser oscillations, the parasitic laser oscillations in the optical signal output from the second gain fiber are also smaller. Moreover, by connecting a tilted grating module including a tilted grating after the second gain fiber, self-excited oscillation signals of the corresponding wavelengths in the optical signal output from the second gain fiber can be further filtered out, achieving further suppression of parasitic laser oscillations. Attached Figure Description

[0023] The accompanying drawings are included to provide a further understanding of this application; they are incorporated into and constitute a part of this application. The drawings illustrate embodiments of this application and, together with this specification, serve to explain the principles of this application. In the drawings:

[0024] Figure 1 This is a schematic diagram of a fiber Bragg grating structure according to an embodiment of this application;

[0025] Figure 2 This is a schematic diagram of the structure of a laser according to an embodiment of this application;

[0026] Figure 3 yes Figure 2 The spectrum of the output signal light generated by the laser after eliminating self-oscillation;

[0027] Figure 4 It is a spectrum of the output signal light containing self-excited oscillation generated by a common laser in the prior art;

[0028] Figure 5 This is a flowchart illustrating a self-excited oscillation suppression method according to an embodiment of this application; and

[0029] Figure 6 This is a flowchart illustrating a self-excited oscillation suppression method according to another embodiment of this application. Detailed Implementation

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0031] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0032] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0033] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0034] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0035] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0036] It should be understood that when a component is referred to as "on another component," "connected to another component," "coupled to another component," or "in contact with another component," it can be directly on, connected to, coupled to, or in contact with that other component, or there may be an intervening component. In contrast, when a component is referred to as "directly on another component," "directly connected to," "directly coupled to," or "directly in contact with" another component, there is no intervening component. Similarly, when a first component is referred to as "electrically contacting" or "electrically coupled to" a second component, there is an electrical path between the first and second components that allows current to flow. This electrical path may include capacitors, coupled inductors, and / or other components that allow current to flow, even if there is no direct contact between the conductive components.

[0037] Reference Figure 1 One embodiment of this application proposes a fiber grating structure 10. For example... Figure 1 As shown, the fiber optic grating structure 10 includes a high-reflection grating 11, a first-gain fiber 12, a low-reflection grating 13, a second-gain fiber 14, and a tilted grating module 15 arranged sequentially along a first direction (x-direction). The tilted grating module 15 includes at least one tilted grating, which has a tilt angle relative to a second direction (y-direction), and the second direction is perpendicular to the first direction. More preferably, in this embodiment, the length of the second-gain fiber 14 is greater than the length of the first-gain fiber 12.

[0038] In the above embodiment, the high-reflection grating 11, the first gain fiber 12, and the low-reflection grating 13 constitute a resonant cavity, which generates a first laser beam when pump light is injected into the resonant cavity. Since the first gain fiber 12 has a shorter length than the second gain fiber 14, it generates fewer upper-level inversion particles and produces a lower laser power. Consequently, the first gain fiber 12 has a higher self-excitation threshold and a lower operating temperature. It is understood that the higher self-excitation threshold allows the first gain fiber 12 to suppress parasitic laser oscillations (i.e., self-excitation) while simultaneously amplifying the absorbed pump light to generate the first laser beam. Furthermore, the lower operating temperature prevents the first gain fiber 12 from forming a parasitic resonant cavity due to refractive index changes caused by thermal accumulation, thus suppressing the self-excitation problem of the first gain fiber 12 from another perspective.

[0039] Continue to refer to Figure 1 The unabsorbed pump light and the first laser beam from the first gain fiber 12 are received by the second gain fiber 14 after passing through the low-reflection grating 13. Because the second gain fiber 14 is longer than the first gain fiber 12, it can generate a larger number of upper-level inversion particles after absorbing the pump light, thus further amplifying the first laser beam and generating an optical signal containing the second laser beam and a self-oscillating optical signal. Although the self-oscillation threshold of the second gain fiber 14 is low, the parasitic laser oscillation has been effectively controlled by the first gain fiber 12, therefore the optical signal output from the second gain fiber 14 contains a smaller amount of self-oscillating optical signal generated by the parasitic laser oscillation. Furthermore, by connecting a tilted grating module 15, including a tilted grating, after the second gain fiber 14, the self-oscillating optical signal in the optical signal can be further filtered out, ensuring that the second laser beam can pass through with low loss, thereby further suppressing the parasitic laser oscillation.

[0040] Continue to refer to Figure 1 In some embodiments, the high-reflectivity grating 11 has a center wavelength of 1900nm~2000nm, a 3dB bandwidth of 1nm~5nm, and a reflectivity of not less than 99.9%. In some embodiments, the low-reflectivity grating 13 has a center wavelength of 1900nm~2000nm, a 3dB bandwidth of 0.5nm~1nm, and a reflectivity of not more than 20%.

[0041] Continue to refer to Figure 1In some embodiments, the tilted grating module 15 includes a tilted grating array composed of multiple tilted gratings, and the tilt angle of each tilted grating is 10°~15°, that is, the tilted grating has a large tilt angle, thereby achieving a better filtering effect. It should be noted that this application does not limit the number of tilted gratings; the minimum can be one. It does not limit whether the tilt angles of different tilted gratings are consistent. In some instances, multiple tilted gratings in the tilted grating module 15 have the same tilt angle, and in some instances, each tilted grating in the tilted grating module 15 has a different tilt angle. Continuing to refer to... Figure 1 In some embodiments, multiple tilted gratings have different center wavelengths, thereby enabling targeted filtering of corresponding self-oscillating optical signals. For example, the center wavelength of each tilted grating is 1900 nm to 2400 nm. In some embodiments, the first gain fiber 12 and the second gain fiber 14 are doped with thulium, making the laser containing the fiber grating structure 10 a thulium-doped fiber laser. This thulium-doped fiber laser has high-efficiency output in the 2 μm band, enabling its application in fields such as medicine, materials processing, and lidar.

[0042] Continue to refer to Figure 1 In some embodiments, the first gain fiber 12 and the second gain fiber 14 are made of the same material and have an absorption coefficient α. Preferably, the sum L of the lengths of the first gain fiber 12 and the second gain fiber 14 has the following relationship with the absorption coefficient α: the product of L and α is between 10dB and 30dB, where L is in meters and α is in dB / m. By setting the product of L and α, i.e., the total absorption of the first gain fiber 12 and the second gain fiber 14, between 10dB and 30dB, 90% to 97.5% of the pump light can be absorbed, thereby improving the pump light absorption rate of the fiber grating structure 10 and avoiding pump light waste. Furthermore, in some embodiments, the difference between the length of the second gain fiber 14 and the length of the first gain fiber 12 is 1m to 10m. For example, the length of the first gain fiber 12 is 1m to 3m, the length of the second gain fiber 14 is 4m to 7m, and the absorption coefficient α is 2dB / m to 3dB / m. Referring to the example above, the length of the first gain fiber 12 is shortened compared to the length of the second gain fiber 14, thereby achieving a higher self-excitation threshold. This results in the loss of the self-lasing generated by the first gain fiber 12 being greater than its gain, thus improving the competitiveness of the signal light generated by the first gain fiber 12. In other words, the first gain fiber 12 can suppress the self-excitation problem. Furthermore, the shortened first gain fiber 12 can also suppress the overshoot problem, thereby reducing the impact of the overshoot problem on the stability of the fiber grating structure 10 or reducing the damage caused by the overshoot problem to the fiber grating structure 10.

[0043] One aspect of this application also proposes a laser, referring to Figure 2 In one embodiment of this application, the laser 100 includes a fiber Bragg grating structure 10 and a pump source 30. In this embodiment, the pump source 30 is used to provide pump light, thereby enabling the fiber Bragg grating structure 10 to generate a corresponding laser signal according to the pump light. Continuing to refer to... Figure 2 In this embodiment, the pump source 30 is connected to the high-reflectivity grating 11 in the fiber optic grating structure 10. In some embodiments, the pump source 30 includes a plurality of semiconductor lasers 31, and each semiconductor laser 31 is connected to the high-reflectivity grating 11. It should be noted that... Figure 2 The image contains multiple semiconductor lasers 31, but only one semiconductor laser 31 is exemplarily labeled. It is understood that the semiconductor laser 31 can generate sub-lasers, and the coordinated operation of multiple semiconductor lasers 31 can generate pump light with greater power. In this embodiment, the laser 100 also includes a beam combiner 40, which is connected between the pump source 30 and the high-reflectivity grating 11. That is, the sub-lasers generated by each semiconductor laser 31 are concentrated by the beam combiner 40 and then transmitted to the high-reflectivity grating 11. In other words, the beam combiner 40 is adapted to converge the multiple sub-lasers generated by the multiple semiconductor lasers 31 into a single combined laser beam, i.e., the pump light, thereby enabling the laser 100 to generate a higher-power laser signal.

[0044] It should be noted that in the above embodiment, the semiconductor lasers 31 in the pump source 30 are fused with optical fibers to the combiner 40, resulting in multiple fusion points. These fusion points can cause Fresnel reflections, leading to self-oscillation, i.e., self-excitation. To address this, in the above embodiment, the pump source 30 and the combiner 40 are integrated devices, thereby reducing the number of fusion points and suppressing the self-excitation problem caused by fusion points. It should be noted that in this embodiment, an integrated device means that multiple devices are fabricated on the same segment of optical fiber, rather than being connected by multiple segments of optical fiber; therefore, there are no fusion points in the integrated device.

[0045] Continue to refer to Figure 2In some embodiments, the laser 100 further includes a front-tilted grating 20, which is located on the side of the pump source 30 further away from the high-reflectivity grating 11 in the first direction, i.e., the x-direction. The front-tilted grating 20 has a tilt angle relative to the second direction, i.e., the y-direction, which is perpendicular to the first direction. For example, the tilt angle of the front-tilted grating 20 is 10°~15°, and the bandwidth is 1nm~5nm. It should be noted that while the fiber grating structure 10 absorbs pump light to generate a laser signal, it also generates a reflected laser signal, which is transmitted to the combiner 40. This reflected laser signal can damage the pump source 30 and cause self-oscillation. In some embodiments, the center wavelength of the front tilt grating 20 is set to be equal to the center wavelength of the returned laser signal, and the front tilt grating 20 is connected to the returning arm of the beam combiner 40. This allows the front tilt grating 20 to filter out the returned laser signal, thereby cutting off potential self-excited paths to suppress self-excited oscillations and reducing interference with the pump source 30 to reduce the possibility of damage to the pump source 30.

[0046] Continue to refer to Figure 2 In some embodiments, the laser 100 further includes a cladding stripper 50 and an end cap 60, and the cladding stripper 50 and the end cap 60 are integrated devices, thereby eliminating the fusion point between the cladding stripper 50 and the end cap 60, and thus suppressing the self-excitation problem caused by the fusion point. In some embodiments, the end cap 60 is also coated with an anti-reflection film, thereby reducing end-face reflection and further suppressing the self-excitation problem.

[0047] Overall, in the laser 100, the tilted grating in the tilted grating module 15, due to its tilted grating surface, can disrupt the Bragg reflection condition in the fiber grating structure 10 and couple light into the cladding. Therefore, in this embodiment, the tilted grating can be configured with appropriate tilt angles, grating periods, and other parameters according to the actual operating requirements of the laser 100. This allows the tilted grating to couple out the self-excited oscillating light signal with a specific center wavelength generated by the fiber grating structure 10, thereby further suppressing parasitic laser oscillations. Specifically, as the laser propagates in the fiber core, the tilted grating can couple unwanted self-excited wavelengths into the cladding, which are then filtered out by the cladding light stripper 50, thus achieving self-excitation suppression.

[0048] The above briefly describes the various settings for suppressing self-oscillation in laser 100. The following example illustrates the effectiveness of laser 100 in suppressing self-oscillation. In one example, the center wavelength of the pre-tilted grating 20 is 1940 nm, the 3dB bandwidth is 1 nm, and the reflectivity is 10%. The pump source 30 contains six semiconductor lasers 31, and the pump light from the pump source 30 has a wavelength of 793 nm, an output power greater than 200 W, and the core diameter, cladding diameter, and numerical aperture of the output pigtail are 220 μm, 242 μm, and 0.22, respectively. Pump source 30 is positively pumped. The corresponding combiner 40 has six pump fibers and one signal fiber. The core diameter, cladding diameter, and numerical aperture of the output pigtail of the pump fiber are 220 μm, 242 μm, and 0.22, respectively. The core diameter, cladding diameter, and numerical aperture of the output pigtail of the signal fiber are 25 μm, 400 μm, and 0.09, respectively. The high-reflectivity grating 11 has a center wavelength of 1940 nm, a 3dB bandwidth of 1 nm, and a reflectivity of 99.9%. The core diameter, cladding diameter, and numerical aperture of the output pigtails of the first gain fiber 12 and the second gain fiber 14 are 25 μm, 400 μm, and 0.09, respectively. The product of the sum of the lengths of the first gain fiber 12 and the second gain fiber 14 (L) and α is 13 dB. The low-reflectivity grating 13 has a center wavelength of 1940 nm and a 3dB bandwidth of 1 nm. The tilted grating module 15 includes three tilted gratings: a first tilted grating, a second tilted grating, and a third tilted grating. The first tilted grating has a tilt angle of 10°, a bandwidth of 1nm, and a center wavelength of 2370nm; the second tilted grating has a tilt angle of 12°, a bandwidth of 5nm, and a center wavelength of 2220nm; and the third tilted grating has a tilt angle of 15°, a bandwidth of 5nm, and a center wavelength of 2000nm. This allows for the sequential filtering of self-oscillating optical signals with center wavelengths of 2370nm, 2220nm, and 2000nm. The output pigtail of the cladding stripper 50 has a core diameter, cladding diameter, and numerical aperture of 25μm, 400μm, and 0.09, respectively, and a cladding stripping efficiency greater than 20dB. The end cap 60 is made of quartz and has a 1940nm antireflection coating.

[0049] Further reference Figure 3 , Figure 3 This is the spectrum of the output signal light generated by the laser 100 in the example above, which eliminates self-oscillation. Figure 3 In the mid-spectral graph, the horizontal axis represents wavelength in nm, and the vertical axis represents laser intensity in dBm. For example... Figure 3As shown, in the light wave output by laser 100, the ratio between the intensity of the target laser wave at a wavelength of 1940nm and the intensity of the wavelengths that need to be eliminated, i.e., clutter wavelengths, is 42dB. This means the energy of the clutter wavelengths is less than one ten-thousandth of the total output energy. Clearly, laser 100 effectively suppresses the self-oscillation problem through the above settings. (Continue referring to...) Figure 4 , Figure 4 It is the spectrum of the output signal light containing self-excited oscillation generated by a conventional laser without the antireflection coating configured with the front tilt grating 20, the tilt grating module 15 and the end cap 60, and with the first gain fiber 12 and the second gain fiber 14 replaced with ordinary gain fibers. Figure 4 In the spectral graph, the horizontal axis represents wavelength in nm, and the vertical axis represents laser intensity in dBm. For example... Figure 4 As shown, Figure 4 The laser intensity corresponding to the 1940nm wavelength did not surpass that of other wavelengths, indicating that the ordinary laser suffered from severe self-oscillation interference. The self-oscillating wavelength dominated this interference, preventing the ordinary laser from effectively outputting the target wavelength. Therefore, in this example, by incorporating a pre-tilted grating 20, a first gain fiber 12, a second gain fiber 14, a tilted grating module 15, and an anti-reflection coating with an end cap 60 in the laser 100, self-oscillating light can be effectively suppressed.

[0050] Continue to refer to Figure 2 In some embodiments, the laser 100 further includes a monitoring feedback module 70, which includes a monitoring unit 71, a logic unit 72, and an execution unit 73. Specifically, the monitoring unit 71 is configured to monitor the power data of the laser 100, the logic unit 72 is configured to compare the power data with a preset safety value and generate a control command, and the execution unit 73 is configured to receive the control command and control the working state of the pump source 30 according to the control command. In this embodiment, by setting a monitoring feedback module, the pump source 30 can be controlled according to the real-time power data of the laser, thereby making the laser 100 operate in a stable state. It should be noted that this application does not limit the control method of the execution unit 73 on the pump source 30. In some embodiments, the execution unit 73 controls all pump sources 30 to be in the same working state, and in some embodiments, the execution unit 73 controls each pump source 30 to be in a different working state.

[0051] Continue to refer to Figure 2In some embodiments, the monitoring unit 71 is connected to the fiber optic grating structure 10. The monitoring unit 71 includes a photodiode and is configured to monitor power data via the photodiode. That is, the photodiode converts the optical signal generated in the laser into an electrical signal, thereby determining the power data of the corresponding optical signal, thus achieving accurate monitoring of the power state of the laser 100. In some embodiments, the execution unit 73 includes a pump source driver, and the pump source driver is configured to control the pump source 30 to open or close, or to control the pump source 30 to adjust its drive current, according to a control command. It is understood that, on the one hand, by controlling the pump source 30 to open or close via the pump source driver, the execution unit 73 can adjust the output power of the laser 100 or cut off an out-of-control pump source 30 to prevent the laser 100 from suffering more serious damage. On the other hand, by controlling the pump source 30 via the pump source driver, the execution unit 73 can control the pump source 30 to adjust its drive current, thereby more precisely adjusting the output laser power of the laser 100, thus improving the adjustable range of the output laser of the laser 100.

[0052] Continue to refer to Figure 2 In some embodiments, the preset safety value includes a pump source shutdown threshold. The corresponding logic unit 72 is configured to generate a first control command suitable for shutting down the pump source 30 when the power data is determined to be higher than the pump source shutdown threshold. It is understood that when the power data is higher than the pump source shutdown threshold, the laser 100 is in an unstable operating state, requiring it to stop working or have its output power reduced for observation. Therefore, the logic unit 72 generates a corresponding first control command and executes the first control command through the execution unit 73 to shut down some or all of the pump sources 30. Alternatively, the logic unit 72 can also generate a corresponding control command to turn on some or all of the pump sources 30 after determining that the anomaly has been eliminated, i.e., the power data is not higher than the pump source shutdown threshold, thereby allowing the laser 100 to continue operating in a normal state.

[0053] Continue to refer to Figure 2In some embodiments, the power data includes the output laser power, and the preset safety value includes an output power fluctuation threshold. Accordingly, the logic unit 72 is configured to generate a second control command suitable for ensuring that the ratio of the absolute value of the difference between the output laser power and the output power reference value to the output power reference value is greater than the output power fluctuation threshold when the latter is greater than the output power fluctuation threshold. That is, after detecting that the power fluctuation of the output laser generated by the laser 100 exceeds the output power fluctuation threshold, the logic unit 72 generates a corresponding second control command to cause the pump source 30 to adjust its operating state, thereby reducing the output laser power fluctuation. It should be noted that the output power reference value is a preset value, but this application does not limit the method of obtaining the output power reference value. In some examples, the output power reference value is the rated output power of the corresponding laser 100; in some examples, the corresponding output power reference value is determined based on the detected output power range of the laser 100.

[0054] In one example, when the output power fluctuation threshold is 15%, the output laser power fluctuation is greater than 15%, and the laser 100 is single-ended pumped, the execution unit 73 gradually reduces the driving current of the corresponding pump source 30 according to the corresponding second control command at a preset safety slope until the execution unit 73 no longer receives the second control command. It should be noted that the safety slope is the rate at which the driving current decreases, and this safety slope is 5% to 10% of the maximum allowable operating current of the pump source 30. In another example, when the output power fluctuation threshold is 15%, the output laser power fluctuation is greater than 15%, and the laser 100 is bidirectional pumped, the execution unit 73 reduces the forward pump power and controls the backward pump power according to the corresponding second control command until the execution unit 73 no longer receives the second control command.

[0055] Understandably, logic unit 72 can generate a second control command in real time based on the magnitude of the real-time fluctuation of the output laser power and the control algorithm until the real-time fluctuation of the output laser power does not exceed the output power fluctuation threshold. It should be noted that this application does not limit the type of control algorithm; in some embodiments, the control algorithm includes a PID control algorithm. Specifically, logic unit 72 generates a corresponding second control command based on the difference between the real-time fluctuation of the output laser power and the output power fluctuation threshold.

[0056] Continue to refer to Figure 2In some embodiments, the power data includes output laser power and return laser power, and the preset safety value includes a return light ratio threshold. Logic unit 72 is configured to generate a third control instruction suitable for making the ratio not greater than the return light ratio threshold when it determines that the ratio of the return laser power to the output laser power is greater than the return light ratio threshold. In one example, the return light ratio threshold is 5%. Accordingly, when the ratio of the return laser power to the output laser power is greater than the return light ratio threshold, it indicates that the optical feedback of laser 100 is abnormal or has signs of instability. Accordingly, execution unit 73 adjusts the drive current according to the corresponding third control instruction and a preset power reduction curve until no more third control instructions are received, i.e., the ratio of the return laser power to the output laser power is not greater than the return light ratio threshold. It should be noted that the power reduction curve is the rate of decrease of the drive current, and the slope of the power reduction curve is 5% to 10% of the maximum allowable operating current of pump source 30.

[0057] Another aspect of this application proposes a method for suppressing self-excited oscillations. (Refer to...) Figure 2 and Figure 5 A self-oscillation suppression method 200 according to an embodiment of this application is applicable to a laser 100. The laser 100 includes a fiber grating structure 10, which comprises a high-reflection grating 11, a first gain fiber 12, a low-reflection grating 13, a second gain fiber 14, and a tilted grating module 15 arranged sequentially along a first direction. The tilted grating module 15 includes at least one tilted grating, which has a tilt angle relative to a second direction, and the length of the second gain fiber is greater than the length of the first gain fiber. Figure 5 As shown, the self-oscillation suppression method 200 includes the following steps: Step S1 is to determine the first center wavelength of at least one self-oscillating light generated by the laser 100. Step S2 is to set the second center wavelength of at least one tilted grating to be equal to the first center wavelength of the corresponding self-oscillating light. Through the above steps S1 and S2, the self-oscillation suppression method 200 can filter out the corresponding self-oscillating light through the tilted grating, thereby suppressing the self-oscillation problem of the laser 100.

[0058] Continue to refer to Figure 6In some embodiments, the laser 100 further includes a beam combiner 40 and a pump source 30, with the beam combiner 40 connected between the pump source 30 and the high-reflectivity grating 11. The corresponding self-oscillation suppression method 200 further includes the following steps: Step S3 is to determine the third center wavelength of the returned laser generated by the laser 100, and to set a forward tilt grating 20 on the side of the pump source 30 further away from the high-reflectivity grating 11 in a first direction, wherein the fourth center wavelength of the forward tilt grating 20 is equal to the third center wavelength. Step S4 is to configure the beam combiner 40 and the pump source 30 as an integrated device. In the above embodiments, the self-oscillation suppression method 200, through step S3, can filter out the returned laser signal in the laser 100 to suppress the self-oscillation problem from one aspect; furthermore, through step S4, it can reduce the number of fusion points in the laser 100 to suppress the self-oscillation problem from another aspect.

[0059] Continue to refer to Figure 6 In some embodiments, the laser further includes a cladding stripper 50 and an end cap 60. Correspondingly, the self-oscillation suppression method 200 further includes the following steps: Step S5 is to deposit an anti-reflection coating on the end cap 60. Step S6 is to integrate the cladding stripper 50 and the end cap 60 into a single device. In the above embodiments, the self-oscillation suppression method 200 reduces end-face reflection through step S5, thereby suppressing the self-oscillation problem. Furthermore, step S6 reduces the number of fusion points in the laser 100, thus suppressing the self-oscillation problem from another perspective.

[0060] The basic concepts have been described above. Obviously, for those skilled in the art, the above disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore remain within the spirit and scope of the exemplary embodiments of this application.

[0061] Flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, various steps can be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0062] Furthermore, this application uses specific terms to describe embodiments of the application. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of the application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0063] Similarly, it should be noted that, in order to simplify the description of the present application and thus aid in the understanding of one or more embodiments, the foregoing description of the embodiments of the present application sometimes combines multiple features into a single embodiment, drawing, or description thereof. However, this disclosure method does not imply that the subject matter of the present application requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of the single embodiments disclosed above.

[0064] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of scope in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

[0065] Some aspects of this application can be executed entirely by hardware, entirely by software (including firmware, resident software, microcode, etc.), or by a combination of hardware and software. The aforementioned hardware or software may be referred to as a "data block," "module," "engine," "unit," "component," or "system." The processor may be one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DAPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or combinations thereof. Furthermore, aspects of this application may manifest as computer products residing in one or more computer-readable media, including computer-readable program code. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disks, floppy disks, magnetic tapes, etc.), optical discs (e.g., compressed CDs, digital multifunction DVDs, etc.), smart cards, and flash memory devices (e.g., cards, sticks, key drives, etc.).

[0066] A computer-readable medium may contain a propagated data signal containing computer program code, for example, on baseband or as part of a carrier wave. This propagated signal may take various forms, including electromagnetic, optical, and so on, or suitable combinations thereof. A computer-readable medium can be any computer-readable medium other than a computer-readable storage medium, which can be connected to an instruction execution system, apparatus, or device to enable communication, propagation, or transmission of a program for use. The program code located on the computer-readable medium can be propagated through any suitable medium, including radio, cable, fiber optic cable, radio frequency signals, or similar media, or any combination of the above media.

[0067] Although this application has been described with reference to specific embodiments, those skilled in the art should recognize that the above embodiments are only used to illustrate this application, and various equivalent changes or substitutions can be made without departing from the spirit of this application. Therefore, any changes or modifications to the above embodiments within the essential spirit of this application will fall within the scope of the claims of this application.

Claims

1. A fiber grating structure, characterized by, The fiber grating structure comprises a high reflection grating, a first gain fiber, a low reflection grating, a second gain fiber, and an inclined grating module arranged in sequence along a first direction, wherein the inclined grating module comprises at least one inclined grating having an inclined angle relative to a second direction perpendicular to the first direction. The length of the second gain fiber is greater than the length of the first gain fiber.

2. The fiber grating structure of claim 1, wherein, The inclined grating module comprises an inclined grating array composed of a plurality of inclined gratings, and each inclined grating has an inclined angle of 10°-15°.

3. The fiber grating structure of claim 2, wherein, The plurality of inclined gratings have different central wavelengths.

4. The fiber grating structure of claim 1, wherein, The first gain fiber and the second gain fiber are made of the same material and have an absorption coefficient α, and the sum L of the lengths of the first gain fiber and the second gain fiber satisfies the following relationship with the absorption coefficient α: the product of L and α is between 10 dB and 30 dB, wherein the unit of L is m and the unit of α is dB / m.

5. The fiber grating structure of claim 1, wherein, The first gain fiber and the second gain fiber are doped with thulium elements.

6. The fiber grating structure of any one of claims 1 to 5, wherein, The difference between the length of the second gain fiber and the length of the first gain fiber is 1 m-10 m.

7. A laser characterized by, The fiber grating structure comprises a pump source and a fiber grating structure according to any one of claims 1-6, wherein the pump source is connected to the high reflection grating in the fiber grating structure.

8. The laser of claim 7, wherein, Further comprising a combiner connected between the pump source and the high reflection grating, wherein the pump source and the combiner are integrated devices.

9. The laser of claim 8, wherein, Further comprising a pre-inclined grating located on the side of the pump source farther away from the high reflection grating in the first direction, and the pre-inclined grating has an inclined angle relative to a second direction perpendicular to the first direction.

10. The laser of claim 7, wherein, Further comprising a cladding light stripper and an end cap, wherein the cladding light stripper and the end cap are integrated devices.

11. The laser as claimed in any one of claims 7 to 10, characterized in that Further comprising a monitoring feedback module, wherein the monitoring feedback module comprises a monitoring unit, a logic unit, and an execution unit. The monitoring unit is configured to monitor power data of the laser. The logic unit is configured to generate a control instruction after comparing the power data with a preset safety value. The execution unit is configured to accept the control instruction and control the working state of the pump source according to the control instruction.

12. The laser of claim 11, wherein, The monitoring unit is connected to the fiber grating structure, and the monitoring unit comprises a photodiode, and the monitoring unit is configured to monitor the power data through the photodiode.

13. The laser of claim 11, wherein, The preset safety value comprises a pump source shutdown threshold, and the logic unit is configured to generate a first control instruction suitable for shutting down the pump source when it is judged that the power data is higher than the pump source shutdown threshold.

14. The laser of claim 11, wherein, The power data comprises output laser power, the preset safety value comprises an output power fluctuation threshold, and the logic unit is configured to generate a second control instruction suitable for making the ratio of the absolute value of the difference between the output laser power and an output power reference value to the output power reference value not greater than the output power fluctuation threshold when it is judged that the ratio is greater than the output power fluctuation threshold.

15. The laser of claim 11, wherein, The power data includes output laser power and return laser power, the preset safety value includes a return light proportion threshold, and the logic unit is configured to generate a third control instruction suitable for making the ratio of the return laser power to the output laser power not greater than the return light proportion threshold when it is judged that the ratio is greater than the return light proportion threshold.

16. A self-excited oscillation suppression method characterized by comprising: The laser includes a fiber grating structure, the fiber grating structure includes a high reflection grating, a first gain fiber, a low reflection grating, a second gain fiber and an inclined grating module arranged in sequence along a first direction, the inclined grating module includes at least one inclined grating, the at least one inclined grating has an inclination angle compared with a second direction, the second direction is perpendicular to the first direction, wherein the length of the second gain fiber is greater than the length of the first gain fiber, and the self-excited oscillation suppression method includes the following steps: Determine the first center wavelength of at least one self-excited oscillation light generated by the laser; Set the second center wavelength of the at least one inclined grating to be equal to the first center wavelength of the corresponding self-excited oscillation light.

17. The self-excited oscillation suppression method according to claim 16, wherein The laser also includes a combiner and a pump source, the combiner is connected between the pump source and the high reflection grating, and the self-excited oscillation suppression method further includes the following steps: Determine the third center wavelength of the return laser generated by the laser, and set a front inclined grating on the side of the pump source farther away from the high reflection grating in the first direction, wherein the fourth center wavelength of the front inclined grating is equal to the third center wavelength; and / or Set the combiner and the pump source as an integrated device.

18. The self-excited oscillation suppression method according to claim 16, wherein The laser also includes a cladding light stripper and an end cap, and the self-excited oscillation suppression method further includes the following steps: Coat an anti-reflection film on the end cap; and / or Set the cladding light stripper and the end cap as an integrated device.

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