A pump lock device for fiber lasers

Abstract

The application discloses a pump wave-locked device of a fiber laser and belongs to the field of fiber lasers. The pump wave-locked device comprises a wave-locked control system and a pump drift detection module, wherein the pump drift detection module comprises at least a pair of cladding pumping light detection modules; the wave-locked control system controls the refrigeration effect of a pump cooling platform on a pump system according to the signal strength of a first photosensitive detector and a second photosensitive detector in the pair of cladding pumping light detection modules, so as to control the output wavelength of the pump system in real time.

Description

Technical Field

[0001] This invention belongs to the field of fiber lasers, and specifically relates to a pump-locking device for fiber lasers. Background Technology

[0002] 976nm pump technology boasts very high gain conversion efficiency, but it also suffers from a relatively narrow absorption bandwidth. Therefore, this technology demands extremely high stability of the pump light wavelength. Traditional 976nm fiber lasers typically employ direct wave-locking with pump coatings to control the wavelength. However, this method places very high demands on the pump diode. In real-world applications, changes in current, cooling water temperature, and the aging of the diode coating itself can cause significant wavelength variations in the diode, ultimately reducing the overall efficiency of the laser system. Furthermore, when the diode wavelength changes significantly, traditional direct wave-locking with pump coatings cannot adjust the output wavelength in real time. Summary of the Invention

[0003] The purpose of this invention is to provide a pump-locking device for fiber lasers, which can be used to control the pump wavelength in fiber lasers within a stable range and can also be used to realize tunable wavelocking of fiber lasers.

[0004] To achieve the above objectives, the present invention provides a pump-locking device for a fiber laser. The pump-locking device includes a pump system, a gain cavity module, a pump drift detection module, a pump cooling platform, and a wave-locking control system. The pump drift detection module includes at least one pair of cladding pump light detection modules. Each pair of cladding pump light detection modules includes a first reflective filter and a first photodetector connected thereto, as well as a second reflective filter and a second photodetector connected thereto. The reflection center wavelength of the first reflective filter is smaller than the peak pump wavelength of the gain cavity module, and the reflection wavelength of the second reflective filter is larger than the peak pump wavelength of the gain cavity module. The first and second reflective filters are used to filter the separated pump residue and to allow the transmitted pump residue to be incident on the first and second photodetectors, respectively. The wave-locking control system controls the cooling effect of the pump cooling platform on the pump system according to the signal strength of the first and second photodetectors, thereby controlling the output wavelength of the pump system.

[0005] Preferably, each pair of cladding pump light detection modules further includes a first cladding pump light separation element and a second cladding pump light separation element, which are respectively connected to the first reflective filter and the second reflective filter. The cladding pump light separation element is used to separate the pump residue in the fiber cladding.

[0006] Preferably, each pair of cladding pump light detection modules further includes a cladding pump light separation element connected together with the first reflective filter and the second reflective filter. The cladding pump light separation element is used to separate the pump residue in the fiber cladding.

[0007] Preferably, the cladding pump light separation element is a cladding light stripper, a beam splitter, or a reverse beam combiner.

[0008] Preferably, the sum of the differences between the reflection center wavelength and the peak pump wavelength of the two reflective filters in each pair of cladding pump light detection modules is between -2 and 2.

[0009] Preferably, the peak pump wavelength is the median of the reflection center wavelengths of the two reflective filters in each pair of cladding pump light detection modules.

[0010] Preferably, the wave-locking control system controls the cooling effect so that the sum of the signal strengths received by each first photodetector is equal to the sum of the signal strengths received by each second photodetector.

[0011] Preferably, the wave-locking control system controls the cooling effect so that the signal strength difference between the first photodetector and the second photodetector in one of the pair of cladding pump photodetector modules is a preset value, which is not 0.

[0012] Preferably, the cladding pump light detection module further includes a filtering device that filters out the peak pump wavelength light before the pump residue enters each reflective filter.

[0013] Preferably, the reflective filter is a fiber grating or a filter sheet.

[0014] The beneficial effects of this invention are as follows:

[0015] (1) The present invention can intuitively show the distribution of pump wavelength in fiber laser system and adjust the wavelength of pump system in real time.

[0016] (2) The present invention can achieve the selection of any control wavelength median within a certain range by setting it, thereby realizing multiple selections of arbitrary efficiency of fiber laser system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the pump-lock device for a fiber laser proposed in this invention;

[0018] Figure 2 This is a schematic diagram of the pump drift detection system;

[0019] Figure 3 This is a schematic diagram of a multi-section pump-locked wave system;

[0020] Figure 4 This is a schematic diagram of the wave-locking control system's method for implementing wave-locking. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, this invention proposes a pump-locking device for a fiber laser, used to control the pump wavelength in the fiber laser within a stable range. The pump-locking device includes: a pump system 1, a pump cooling platform 2, a beam combiner module 4, a gain cavity module, a pump drift detection module 8, an output optical cable 9, and a wave-locking control system. The pump system 1, beam combiner module 4, gain cavity module, output optical cable 9, and pump cooling platform 2 constitute a typical fiber laser system. In another embodiment, the device further includes an indicator laser 11.

[0023] Pump system 1 consists of N semiconductor lasers, which are used to provide pump light to the gain cavity module, where N≥1.

[0024] The pump cooling platform 2 is used to dissipate heat and cool the semiconductor laser in the pump system 1. The pump cooling platform 2 uses air cooling or refrigerant cooling, where refrigerant cooling includes water cooling. The pump cooling platform 2 can be composed of a channel-type water-cooled plate.

[0025] The beam combining module 4 can be an optical fiber beam combiner, used to combine the pump light output from N semiconductor lasers.

[0026] The gain cavity module includes a grating pair consisting of gratings 5 ​​and 7 and a gain fiber 6. The gain fiber 6 is used to absorb the pump light provided by the pump system 1 and amplify the gain. The reflection center of the grating pair corresponds to the resonant wavelength of the resonant cavity.

[0027] In different implementations, semiconductor lasers with different output wavelengths are selected to provide pump light based on the gain fiber. The doping elements in the gain fiber can be Yb, Er, Th, Ho, Tm, or any combination thereof. The output wavelength of the semiconductor laser is 915 nm, 976 nm, 981 nm, 1480 nm, 1560 nm, or any combination thereof. The gain cavity module may also include frequency shifting elements such as nonlinear optical crystals and Raman fibers.

[0028] The pump drift detection system 8 includes at least one pair of cladding pump light detection modules, i.e., it can include 1, 2, 3...N pairs of cladding pump light detection modules. Each pair of cladding pump light detection modules includes two sets of cladding pump light detection modules, and each set of cladding pump light detection modules includes a reflective filter and a photodetector connected in sequence. The reflection center wavelength of the reflective filter in one set is less than the peak pump wavelength of the gain cavity module, and the reflection wavelength of the reflective filter in the other set is greater than the peak pump wavelength of the gain cavity module, where the peak pump wavelength refers to the optimal absorption wavelength of the pump light by the gain fiber. Preferably, the peak pump wavelength is the median of the reflection center wavelengths of the two reflective filters in each pair of cladding pump light detection modules. However, it is not strictly required that the peak pump wavelength be the median of the reflection center wavelengths of the two reflective filters in each pair of cladding pump light detection modules. In one embodiment, the sum of the differences between the reflection center wavelengths of the two reflective filters in each pair of cladding pump light detection modules and the peak pump wavelength is between -2 and 2. For example, if the emission spectrum of the pump system or the absorption of the gain fiber is not symmetrical about the peak pump wavelength, the difference can be determined based on the emission spectrum distribution of the pump system and the absorption of the gain fiber.

[0029] In one embodiment, each cladding pump light detection module further includes a cladding pump light separation element for separating pump remnants from the cladding. This cladding pump light separation element can be a cladding optical stripper (CPS), a beam splitter, or a reverse beam combiner. In another embodiment, multiple cladding pump light detection modules share a single cladding pump light separation element. Preferably, multiple cladding pump light detection modules perform detection at the same CPS, so that the detection positions of the two sets of cladding pump light detection modules are relatively close, reducing detection errors between the two detectors.

[0030] Reflective filters are used for filtering, allowing the pump residue of the desired wavelength to be incident on the photodetector. They can be fiber Bragg gratings or filter sheets. Preferably, reflective filters use reflective fiber Bragg gratings, so that a shorter wavelength bandwidth can be achieved through minimal etching during grating fabrication.

[0031] The output optical cable 9 is the output part of the entire laser system. The output optical cable 9 may include a transmission optical fiber, a quartz cone mirror, and an armor structure.

[0032] like Figure 4 As shown, the wave lock control system controls the cooling effect of the pump cooling platform 2 based on the feedback from the pump drift detection system 8, thereby controlling the output wavelength of the pump system. In one embodiment, the wave lock control system controls the electrically controlled regulating valve 3 at the water inlet of the pump cooling platform 2 based on the feedback from the pump drift detection system 8.

[0033] Example 1:

[0034] like Figure 2 As shown, the pump drift detection module 8 includes a cladding light stripper 80, a 971nm fiber grating 81 and corresponding photodetectors 83 and 981nm fiber grating 82 and corresponding photodetectors 84. The cladding light stripper strips the cladding pump light that is not absorbed by the gain cavity. The two gratings collect the stripped cladding pump light and transmit it to the two photodetectors, which then perform signal conversion. The fiber gratings with appropriate bandwidth can be selected according to the actual application requirements. Preferably, the fiber grating bandwidth is 3nm (±1.5nm).

[0035] The working principle of the wave lock control system is as follows:

[0036] During normal operation of the fiber laser, residual pump light energy is generated that is not completely absorbed by the gain cavity. Based on the absorption characteristics of ytterbium-doped fiber in the gain cavity for 976nm pump light, the residual pump light energy is mainly distributed at 971nm and 981nm. This residual light energy is stripped from the fiber cladding by the CPS in the pump drift detector 8. A portion of this light energy enters the detection end faces of the 971nm fiber grating 81 and 981nm fiber grating 82, which are pre-placed near the CPS stripping area. The two gratings will perform total internal reflection for the corresponding wavelengths, preventing them from passing through. If the residual pump light energy at 971nm is predominant, most of the residual pump light incident on the 971nm fiber grating 81 will be reflected back to the CPS direction by the grating. However, most of the residual pump light entering the 981nm fiber grating 82 will not be reflected by the grating, but will be transmitted to the other end of the 981nm fiber grating 82 and enter the photodetector 84.

[0037] When the unabsorbed pump light wavelength is biased towards 971nm, the photodetector 84 corresponding to the 981nm fiber grating 82 will receive a larger signal, while the photodetector 83 corresponding to the 971nm fiber grating 81 will only receive a smaller signal. Conversely, when the unabsorbed pump light wavelength is biased towards 981nm, the photodetector 83 corresponding to the 971nm fiber grating 81 will receive a larger signal, while the photodetector 84 corresponding to the 981nm fiber grating 82 will only receive a smaller signal. The signals received by the two photodetectors will form a difference. The closer the difference is to 0, the closer the residual pump light energy of 971nm and 981nm generated in the gain cavity system is to that of the pump, meaning the gain cavity is in a relatively good absorption state. The wave-locked control system will calculate in real time based on the feedback from the two photodetectors in the pump drift detection system 8. The calculation formula is Pfb(971)-Pfb(981)=P(move). Then we will get the following three cases: P(move)>0; P(move)=0; P(move)<0.

[0038] The wave-locking control system sends different adjustment signals to the regulating valve 3 at the inlet of the pump cooling platform 2 based on the three scenarios described above, adjusting the flow rate of the cooling water by increasing or decreasing it. When the residual wavelength of the pump deviates to 971nm, the wave-locking control system obtains a comparison result of P(move) < 0, and then sends a command to the regulating valve 3 to reduce the flow rate. By reducing the water cooling flow, the temperature of the pump diode is increased, causing its output wavelength to red-shift, thereby achieving the purpose of wave-locking the output wavelength of the pump diode and maintaining the gain cavity in an optimal state. In the air-cooled embodiment, the wave-locking control system adjusts the air volume or air temperature according to the difference P(move).

[0039] When the pump residual wavelength deviates to 981nm, the wave-locking control system will obtain a comparison result of P(move)>0, and then send a command to the regulating valve 3 to increase the flow rate. By increasing the water cooling flow rate, the temperature of the pump diode is reduced, causing its output wavelength to blue shift, thereby achieving the purpose of wave-locking the output wavelength of the pump diode and keeping the gain cavity in the optimal state.

[0040] When P(move) = 0, it indicates that the gain cavity is in a good absorption state, so there is no need to change the water cooling flow rate.

[0041] Furthermore, since the efficiency of a fiber laser is directly proportional to the absorption rate of the gain fiber at different wavelengths, when the peak pump wavelength is 976nm, the pump light center wavelength can be red-shifted or blue-shifted relative to 976nm by setting the signal value of photodetector 83 to be greater than or less than the signal value of photodetector 84 by comparing P(move) with the preset value and controlling the cooling effect based on the comparison result. The amount of red-shift or blue-shift depends on the difference between the two photodetector signals; the larger the difference, the greater the shift relative to 976nm, resulting in lower fiber laser efficiency and lower output laser power. Therefore, the above structure allows for controllable changes in the luminous efficiency of the fiber laser to meet the requirements for adjustable laser power in different application scenarios.

[0042] Example 2:

[0043] The difference between Example 2 and Example 1 is that in Example 2, a 976nm fiber grating is set before the 971nm fiber grating 81 and the 981nm fiber grating 82, respectively, to reduce the optical power incident on the photodetectors 83 and 84 and prevent the energy incident on the photodetectors from being too high.

[0044] Example 3:

[0045] like Figure 3As shown, the difference between Embodiment 3 and Embodiment 1 is that the pump drift detection module in Embodiment 3 includes two pairs of cladding pump light detection modules, i.e., four sets of cladding pump light detection modules. The center wavelengths of fiber Bragg gratings 85, 86, 87, and 88 are 971nm, 973nm, 979nm, and 981nm, respectively, corresponding to four photosensitive detectors 89, 90, 91, and 92 with different incident light powers. Preferably, the grating bandwidth of the fiber Bragg grating is 2nm (±1nm).

[0046] The calculation formula is as follows: (Pfb(971)+Pfb(973))-(Pfb(979)+Pfb(981))=P(move). The method of controlling the regulating valve 3 in the wave-locking control system is the same as in Example 1. Compared with Example 1, using four sets of cladding pump light detection modules can achieve a more accurate pump frequency band detection and control effect. With the corresponding parameter control, adjustable wave-locking in multiple wavelength ranges can be realized.

[0047] A preset value is set for the signal value of photodetector 89 to be greater than or less than the signal value of photodetector 92, and another preset value is set for the signal value of photodetector 90 to be greater than or less than the signal value of photodetector 91. When adjusting the luminous efficiency of the fiber laser, the cooling effect of the pump cooling platform is controlled by the detection results of any pair of cladding pump light detection modules. When different pairs of cladding pump light detection modules are used, the direction (i.e., blue shift or red shift) and / or amplitude of the pump light center wavelength shift are different, thereby achieving adjustable wavelength locking in multiple ranges.

[0048] It is worth mentioning that other embodiments also include three or more pairs of cladding pump light detection modules, which will not be described in detail here.

[0049] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A pump-locking device for a fiber laser, characterized in that, The pump-locking device includes a pump system, a gain cavity module, a pump drift detection module, a pump cooling platform, and a wave-locking control system. The pump drift detection module includes at least one pair of cladding pump light detection modules. Each pair of cladding pump light detection modules includes a first reflective filter and a first photodetector connected thereto, as well as a second reflective filter and a second photodetector connected thereto. The reflection center wavelength of the first reflective filter is smaller than the peak pump wavelength of the gain cavity module, and the reflection center wavelength of the second reflective filter is larger than the peak pump wavelength of the gain cavity module. The first and second reflective filters are used to filter the separated pump residue and allow the transmitted pump residue to be incident on the first and second photodetectors, respectively. The wave-locking control system controls the cooling effect of the pump cooling platform on the pump system based on the signal strength of the first and second photodetectors, thereby controlling the output wavelength of the pump system.

2. The pump-locking device for a fiber laser according to claim 1, characterized in that, Each pair of cladding pump light detection modules further includes a first cladding pump light separation element and a second cladding pump light separation element, which are respectively connected to the first reflective filter and the second reflective filter. The cladding pump light separation element is used to separate the pump residue in the fiber cladding.

3. The pump-locking device for a fiber laser according to claim 1, characterized in that, Each pair of cladding pump light detection modules further includes a cladding pump light separation element connected together with the first reflective filter and the second reflective filter. The cladding pump light separation element is used to separate the pump residue in the fiber cladding.

4. The pump-locking device for a fiber laser according to claim 2 or 3, characterized in that, The cladding pump light separation element is a cladding light stripper, beam splitter, or reverse beam combiner.

5. The pump-locking device for a fiber laser according to claim 1, characterized in that, The sum of the differences between the reflection center wavelength and the peak pump wavelength of the two reflective filters in each pair of cladding pump light detection modules is between -2 and 2.

6. The pump-locking device for a fiber laser according to claim 1, characterized in that, The peak pump wavelength is the median of the reflection center wavelengths of the two reflective filters in each pair of cladding pump light detection modules.

7. The pump-locking device for a fiber laser according to claim 1, characterized in that, The wave-locking control system controls the cooling effect so that the sum of the signal strengths received by each first photodetector is equal to the sum of the signal strengths received by each second photodetector.

8. The pump-locking device for a fiber laser according to claim 1, characterized in that, The wave-locking control system controls the cooling effect so that the signal strength difference between the first photodetector and the second photodetector in one of the pair of cladding pump photodetector modules is a preset value, which is not 0.

9. The pump-locking device for a fiber laser according to claim 1, characterized in that, The cladding pump light detection module also includes a filtering device that filters out the peak pump wavelength light before the pump residue enters each reflective filter.

10. The pump-locking device for a fiber laser according to claim 1, characterized in that, The reflective filter is a fiber optic grating or a filter sheet.

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