A pulse injection coherent beam combining laser system based on a ring feedback structure

Abstract

This invention provides a pulse-injection coherent beam combining laser system based on a ring feedback structure, comprising: a pulse injection module, a preamplification module, a beam splitter module, an amplification module, a beam combiner module, a feedback module, and an output module. The beam splitter module, amplification module, and beam combiner module are connected sequentially. The feedback module connects the input end of the beam splitter module and the output end of the beam combiner module, forming a closed ring feedback structure. This invention features an all-fiber structure, a compact system, and achieves pulse synchronization without complex phase control methods, resulting in high-energy, high-power pulsed laser output. Furthermore, thanks to the pulse injection method, various frequencies, pulse widths, and waveforms of the pulse injection system can be selected to achieve coherent beam combining output, without being limited by the single cavity length or structure of the pulse system.

Description

[0001] This invention is a divisional application of the invention patent filed on November 25, 2019, entitled "A pulse injection coherent beam combining laser system based on a ring feedback structure" with application number 201911166916.3. Technical Field

[0002] This invention relates to the field of fiber lasers, specifically to a pulse injection coherent beam combining laser system based on a ring feedback structure. Background Technology

[0003] Pulsed fiber lasers offer advantages such as high beam quality, compact structure, convenient thermal management, and high conversion efficiency. In addition, they feature high peak pulse power, high single-pulse energy, and adjustable pulse width. Pulsed lasers provide short processing times, high precision, low cost, and high speed in industrial processing. Therefore, they are widely used in various fields including optical communication, laser medicine, industrial marking, cutting and welding, strong-field physics, frequency conversion, and lidar.

[0004] From the perspective of pulsed laser application requirements, achieving high-brightness laser output at the 100-kilowatt level has always been the goal of pulsed lasers. Currently, single-channel pulsed fiber lasers have achieved average power output at the kilowatt level or pulse energy output at the millijoule level. However, single-channel systems struggle to simultaneously achieve high average power and high pulse energy, often sacrificing one performance indicator to maximize the other. Furthermore, limitations imposed by nonlinear effects, optical damage, and mode instability within the fiber restrict the potential for power or energy increases in a single channel. For silicon fiber, the self-focusing effect (threshold peak power of approximately 4MW) is the ultimate limiting factor for peak power increases within fiber amplifiers. Coherent combining technology is a crucial technique for overcoming the performance limits of single-channel systems and achieving high-energy, high-power, high-pulse laser output, and the key to coherent combining lies in phase control technology.

[0005] Common coherent synthesis techniques include:

[0006] Active coherent combining: This method is mostly based on a MOPA cascaded amplification structure, using active phase detection and feedback control for phase synchronization to achieve coherent output of the array laser. The main methods for controlling the phase include heterodyne HC detection, SPGD algorithm, and dithering.

[0007] Passive coherent combining: Utilizing the self-organizing phase-locked characteristic of fiber lasers, automatic compensation for phase fluctuations in each laser path is achieved. Based on the phase-locked method, it is mainly divided into evanescent wave coupling, mutual injection coupling, and ring feedback coupling, etc.

[0008] Active phase-locked loop (PLL) requires clear theoretical guidance and theoretically has the potential to coherently combine more than 100 beams. However, it necessitates complex optical path control measures, and the combining effect is closely related to the optical path control capability. High-brightness laser output at the 100-kilowatt level requires the construction of hundreds of fiber laser arrays, with each channel needing an output power exceeding 1 kilowatt. Furthermore, active control requires narrow-linewidth seed light, and increasing power is limited by the SBS effect. Compared to active coherent combining technology,

[0009] Passive coherent combining systems are simple in structure, require no complex electrical signal feedback, and do not need narrow-linewidth seed sources. They can use broadband lasers, effectively suppress SBS in fiber amplifiers, and improve output power, making them a feasible solution for high-power fiber laser coherent combining. In passive structures, mutual injection feedback and evanescent wave coupling are based on standing-wave cavities. Mutual injection feedback uses different seed lights, resulting in poor stability. Evanescent wave coupling requires multi-core fiber coupling devices, which are difficult to fabricate, and the power is concentrated in the coupling section, limiting output power. Ring-type feedback coupling cavities are based on traveling-wave cavities, can use the same seed light, and under the same conditions, the phase difference of traveling-wave cavities is smaller than that of standing-wave cavities, resulting in better phase-locked stability and at least twice the number of combining paths compared to standing-wave cavities. Currently, ring-type composite cavities have kilowatt-level output capabilities in continuous-wave passive coherent combining experiments, but research on their application in pulsed lasers is relatively lacking.

[0010] CN103441419A discloses a passive coherent beam combiner system for fiber lasers based on a Dammann grating. This system includes: an N-channel fiber amplifier array, a beam splicing system comprising a beam collimator group and a laser high-reflectivity mirror group, a first planar beam splitter, a second planar beam splitter, a feedback fiber, a CCD camera, a fiber preamplifier, a fiber coupler, a semiconductor laser diode, and a 1×N fiber beam splitter. It also features a phase compensation plate, Fourier lenses, Dammann gratings, and an adjustable aperture stop. This system overcomes the drawback of multi-level sidelobes in the far-field coherent beam output of traditional passive coherent beam combiners. However, this system includes non-all-fiber components such as Fourier lenses, Dammann gratings, laser high-reflectivity mirror groups, and planar beam splitters. The system's compactness is limited by the working distance of these components, resulting in poor integration. Furthermore, the system's ring feedback cavity employs a spatial coupling structure, making coupling adjustment difficult, and the quality of the synthesized beam is limited by the dispersion of the far-field output energy.

[0011] CN108429121A discloses a passive coherent beamforming all-fiber laser based on a ring cavity structure, which largely overcomes the shortcomings of the aforementioned patents. Through an integrated ring cavity structure laser and phase-locked loop system, it relies on its automatic mode selection mechanism to select the commonly oscillating modes, achieving phase locking and coherent beamforming output without any manual operation. However, the larger the length difference ΔL between the fibers in this laser, the more difficult it is to synchronize the pulses, resulting in lower coherent beamforming efficiency. Improving beamforming efficiency places high demands on the manufacturing process. Furthermore, the output light pulse of this laser is achieved by a pulsed power supply driving a pump diode, and the pump pulse is then modulated into continuous light to achieve pulse output. The pulse frequency and pulse width obtained by this method are limited by the electrical pulse, thus restricting the improvement of pulse power and energy. Summary of the Invention

[0012] This invention discloses a pulse injection coherent beam combining laser system based on a ring feedback structure, eliminating the need for complex phase control structures. All pulsed laser beams originate from the same pulsed laser. The ring feedback structure splits a small portion of the output light from each pulsed laser beam and feeds it back into the respective pulsed laser system as injection seeds. The ring feedback coupling causes low-loss modes to oscillate, acting as self-organizing filters and mode selection, thereby achieving phase locking. The length difference between the various optical fibers is controlled by an optically variable delay line, reducing the phase difference between the pulses and improving efficiency.

[0013] This system improves pulse beam combining efficiency while reducing process requirements. Phase-synchronized pulsed lasers are coherently superimposed at the beam combining module, and the combined laser beam is output through the output module. Furthermore, the system employs a pulse injection method, allowing for the selection of various frequencies, pulse widths, and waveforms to achieve coherent beam combining output, without being limited by a single cavity length or structure of the pulse system.

[0014] The present invention discloses a pulse injection coherent beam combining laser system based on a ring feedback structure, comprising: a pulse injection module, a pre-amplification module, a beam splitting module, an amplification module, a beam combining module, a feedback module, and an output module. The beam splitting module, the amplification module, and the beam combining module are connected in sequence. The feedback module connects the input end of the beam splitting module and the output end of the beam combining module to form a closed ring feedback structure.

[0015] The pulse injection module includes a pulsed laser and a polarization-independent isolator.

[0016] The pre-amplification module includes a laser, a pump combiner, an active optical fiber, and a polarization-independent isolator.

[0017] The beam splitter module includes an optical fiber coupler;

[0018] The amplification module includes at least two amplifiers connected in parallel, each amplifier including an optical variable delay line, a laser, a pump combiner, and an active optical fiber;

[0019] The beam combining module includes an optical fiber coupler;

[0020] The feedback module includes an optical fiber coupler and a polarization-independent isolator.

[0021] Preferably, the pulse injection module, the preamplification module, the ring feedback structure, and the output module are connected in sequence.

[0022] Furthermore, the fiber optic coupler of the beam splitter module includes two input terminals, and its input coupling ratio is 1:1.

[0023] Preferably, the pre-amplification module is located within the feedback module, and the two share a single linear polarization-independent isolator.

[0024] Furthermore, the feedback module also includes another fiber optic coupler through which the pulse injection module injects into the preamplification module.

[0025] Furthermore, the other fiber optic coupler includes two input terminals with an input coupling ratio of 1:1.

[0026] Preferably, the output fiber type of the pulsed laser in the pulse injection module matches the input fiber type of the linear polarization-independent isolator.

[0027] Preferably, the forward withstand power of the polarization-independent isolator of the pulse injection module is not less than the power of the pulsed laser.

[0028] Preferably, each amplifier in the preamplifier module and / or amplification module has one or more amplification stages. Preferably, the amplifiers in the preamplifier module and / or amplification module further include a cladding optical filter. Preferably, the laser in the preamplifier module and / or amplification module is a laser diode.

[0029] Preferably, the active optical fiber of the preamplifier module and / or amplification module is a rare-earth-doped gain fiber. Further, the active optical fiber of the preamplifier module and / or amplification module is a double-clad ytterbium-doped fiber.

[0030] Furthermore, the active fiber core / cladding diameter of the pre-amplification module and / or amplification module is 30μm / 250μm, 50μm / 400μm, or 20μm / 400μm.

[0031] Furthermore, the active fiber core / cladding diameter of the pre-amplification module and / or amplification module is 50μm / 400μm.

[0032] Further, the active fiber length of the preamplifier module and / or amplification module is 1.3–2 m. Even further, the active fiber length of the preamplifier module and / or amplification module is 1.5 m. Preferably, the pump combiner of the preamplifier module includes at least one pump input end.

[0033] Preferably, the pump input fiber of the pre-amplification module's pump combiner is matched with the output fiber of the laser.

[0034] Preferably, the input fiber of the pump combiner signal fiber of the pre-amplification module is matched with the output fiber of the pulse injection module.

[0035] Preferably, the output fiber type of the pump combiner of the pre-amplification module matches the active fiber type.

[0036] Preferably, the forward withstand power of the polarization-independent isolator of the pre-amplification module is not less than the pre-amplification power.

[0037] Preferably, the number of output ends of the fiber optic coupler of the beam splitter module is at least two, and their output coupling ratios are equal, thereby ensuring that the seed power entering each amplifier is equal, thus improving the coherent beam combining efficiency.

[0038] Preferably, the amplification module includes 2 to 5 amplifiers connected in parallel.

[0039] Preferably, the lasers of each amplifier in the amplification module are driven by the same power supply.

[0040] Preferably, the amplifier of the amplification module has at least two pump input terminals in its pump combiner.

[0041] Preferably, all devices of the same type in the amplification module are of the same model and batch.

[0042] Preferably, the length difference of the pigtails of the same type of devices in each amplifier of the amplification module does not exceed 0.5 mm.

[0043] Preferably, the total length difference between all components of each amplifier in the amplification module during the welding process does not exceed 5mm.

[0044] Preferably, the optical variable delay line of the amplification module controls the cavity length difference ΔL of each amplifier to be 5.7mm to 10mm.

[0045] Preferably, the fiber optic coupler of the bundle combining module has at least two input ends, and their input coupling ratios are equal to ensure that the output power of each amplifier is equal, thereby improving the coherent bundle combining efficiency.

[0046] Furthermore, the formula for calculating the coherent beam combining efficiency η is:

[0047] η=a*b / (ΔP*ΔL) (1)

[0048] Where a is the synchronization coefficient of each amplifier pulse, b is the pump synchronization coefficient of each amplifier, ΔP is the power difference of each amplifier pulse, and ΔL is the cavity length difference of each amplifier. Preferably, 90% to 99% of the light output from one output port of the feedback module fiber coupler is input to the output module for outputting coherent combined laser beams, and 1% to 10% of the light output from the other output port is used as feedback light input to the feedback module. That is, the feedback module fiber coupler.

[0049] The output coupling ratio is 99:1 to 9:1.

[0050] Furthermore, 99% of the light output from one output port of the fiber coupler of the feedback module is used to output coherent combined laser beams in the output module, and 1% of the light output from the other output port is used as feedback light in the feedback module. That is, the output coupling ratio of the fiber coupler of the feedback module is 99:1.

[0051] Preferably, the output module includes a QBH output optical cable for outputting combined pulsed laser light. The beneficial technical effects of this invention are as follows:

[0052] (1) The present invention has a simple structure and does not require a complex phase control structure, and has the advantages of simple implementation and low cost.

[0053] (2) The present invention has an all-fiber structure, which is compact and easy to integrate;

[0054] (3) The present invention has multiple expandability and can realize high-energy and high-power pulsed laser output.

[0055] (4) This invention is a pulse injection type, which can easily realize the pulse diversity output of the laser system. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of a pulse injection coherent beam combining laser system based on a ring feedback structure according to the present invention.

[0057] In the diagram: 101 is a pulsed laser, 102, 107, and 117 are linear polarization-independent isolators, 103 and 110 are laser diodes, 104 and 111 are pump combiners, 105 and 112 are active optical fibers, 106 and 113 are cladding optical filters, 108, 114, and 115 are fiber couplers, 109 is an optical variable delay line, and 116 is a QBH output optical cable.

[0058] Figure 2This is a schematic diagram of another structure of the pulse injection coherent beam combining laser system based on a ring feedback structure according to the present invention.

[0059] In the diagram: 201 is a pulsed laser, 202 and 208 are linear polarization-independent isolators, 204 and 211 are laser diodes, 205 and 212 are pump combiners, 206 and 213 are active optical fibers, 207 and 214 are cladding optical filters, 203, 209, 215 and 216 are fiber couplers, 210 is an optical variable delay line, and 217 is a QBH output optical cable. Detailed Implementation

[0060] This invention discloses a pulse-injection coherent beam combining laser system based on a ring feedback structure. The ring feedback coupling causes low-loss modes to oscillate, acting as self-organizing filters and mode selection, thereby achieving phase locking. The phase-synchronized amplified pulsed lasers coherently superimpose at the beam combining module, and the combined laser beam is output through the output module. Figure 1 For example, this invention includes a pulse injection module, a preamplification module, a beam splitter module, an amplification module, a beam combiner module, a feedback module, and an output module. The beam splitter module, amplification module, and beam combiner module are connected in sequence, and the feedback module connects the input end of the beam splitter module and the output end of the beam combiner module to form a closed loop feedback structure. The pulse injection module, preamplification module, loop feedback structure, and output module are connected in sequence.

[0061] The pulse injection module includes a pulsed laser 101 and a linear polarization-independent isolator 102. The fiber type at the output end of the pulsed laser is matched with the fiber type at the input end of the linear polarization-independent isolator 102. The forward withstand power of the linear polarization-independent isolator 102 is not less than the power of the pulsed laser.

[0062] The preamplification module includes a laser diode 103, a pump combiner 104, an active fiber 105, a cladding optical filter 106, and a linear polarization-independent isolator 107. The pump combiner 104 includes at least one pump input, which matches the output fiber type of the laser diode. The input of the pump combiner matches the output fiber type of the pulse injection module, and the output matches the active fiber type. The forward withstand power of the linear polarization-independent isolator 107 is not less than the preamplification power. The active fiber is a rare-earth-doped gain fiber, and the preamplification module has one or more amplification stages.

[0063] The beam splitting module includes an optical fiber coupler 108. The optical fiber coupler 108 has at least two output terminals with equal output coupling ratios to ensure that the seed power entering each amplification path is equal, thereby improving coherent beam combining efficiency. The optical fiber coupler 108 also includes two input terminals with an input coupling ratio of 1:1.

[0064] The amplification module includes at least two parallel amplifiers, preferably two to five parallel amplifiers. Each amplifier includes: an optical variable delay line 109, a laser diode 110, a pump combiner 111, an active fiber 112, and a cladding filter 113. All laser diodes in each amplifier of the amplification module are driven by the same power supply. The pump combiner 111 contains at least two pump input fibers. The active fiber is a rare-earth-doped gain fiber. All components of the same type involved in the amplification module are of the same model and batch. The length difference of the pigtails of the same type of components in each amplifier must not exceed 0.5 mm. The total length difference generated by all components in each amplifier of the amplification module during the splicing process does not exceed 5 mm. The optical variable delay line 109 controls the cavity length difference ΔL of each amplifier to be within the range of 5.7 mm to 10 mm. Each amplifier in the amplification module has one or more amplification stages.

[0065] The beam combining module includes fiber optic couplers 114. Fiber optic couplers 114 have at least two input terminals with equal input coupling ratios to ensure equal output power for each amplifier, thereby improving the coherent beam combining efficiency η. The calculation of η...

[0066] The formula is as follows:

[0067] η=a*b / (ΔP*ΔL) (1)

[0068] Where a is the synchronization coefficient of each amplifier pulse, b is the pump synchronization coefficient of each amplifier, ΔP is the power difference of each amplifier pulse, and ΔL is the cavity length difference of each amplifier.

[0069] The feedback module includes a fiber coupler 115 and a linear polarization-independent isolator 117. One output port of the fiber coupler 115 outputs 90%–99% of the light as input to the output module for coherent combined laser output, while the other output port outputs 1%–10% of the light as feedback light as input to the feedback module. Therefore, the output coupling ratio of the fiber coupler in the feedback module is 99:1–9:1. The linear polarization-independent isolator 117 isolates reverse light, protecting the optics, while simultaneously ensuring unidirectional transmission within the ring feedback cavity.

[0070] The output module includes a QBH output optical cable 116 for outputting combined pulsed laser.

[0071] In another embodiment of the invention, the preamplification module is located within the feedback module, and the two share a single linear polarization-independent isolator. Figure 2For example, the pulse injection module includes: a pulsed laser 201 and a linear polarization-independent isolator 202; the preamplification module includes: a laser diode 204, a pump combiner 205, an active fiber 206, a cladding optical filter 207, and a linear polarization-independent isolator 208; the beam splitting module includes: an optical fiber coupler 209; the amplifiers in each channel of the amplification module include: an optical variable delay line 210, a laser diode 211, a pump combiner 212, an active fiber 213, and a cladding optical filter 214; the beam combining module includes: an optical fiber coupler 215; the feedback module includes: an optical fiber coupler 216, an optical fiber coupler 203, and a preamplification module; and the output module includes: a QBH output optical cable 217. In this configuration, the output fiber of fiber coupler 215 is fused to the input port of fiber coupler 216 of the feedback module, and the output fiber of fiber coupler 216 is fused to the input port of another fiber coupler 203. The output end of fiber coupler 203 is connected to the preamplifier module, preventing the output fiber of the preamplifier module from being fused to the bundle combining module, thus forming a closed loop feedback structure. In this case, the pulse injection module injects into the preamplifier module through another fiber coupler 203.

[0072] The output fiber type of the pulsed laser 201 in the pulse injection module matches the input fiber type of the linear polarization-independent isolator 202, and the forward withstand power of the linear polarization-independent isolator 202 is not less than the power of the pulsed laser.

[0073] The pulsed laser 201 of the pulse injection module has an output pulse width range of 100ns to 500us, a repetition frequency of 1kHz to 4MHz, and no limit on waveform type.

[0074] The preamplification module pump combiner 205 includes at least one pump input, which matches the output fiber type of the laser diode 204. The signal fiber type input of the pump combiner 205 matches the output fiber type of the pulse injection module, and the output end matches the active fiber type 206. The forward withstand power of the linear polarization-independent isolator 208 is not less than the preamplification power. The active fiber is a rare-earth-doped gain fiber, and the preamplification module has one or more amplification stages.

[0075] The fiber optic coupler 209 of the beam splitter module contains at least two output terminals with equal output coupling ratios, thereby ensuring that the seed power entering each amplification path is equal, thus improving the coherent beam combining efficiency.

[0076] The amplification module includes at least two parallel amplifiers. All laser diodes in each amplifier are driven by the same power supply. The pump combiner 212 contains at least two pump input fibers. The active fiber is a rare-earth-doped gain fiber. All components of the same type involved in the amplification module are of the same model and batch. The length difference of the pigtails of the same type of components in each amplifier must not exceed 0.5 mm. The total length difference generated by all components in each amplifier during the splicing process must not exceed 5 mm. The optical variable delay line 210 controls the cavity length difference ΔL of each amplifier to be within the range of 5.7 mm to 10 mm. Each amplifier in the amplification module has one or more amplification stages.

[0077] The beam combining module includes an optical fiber coupler 215. The optical fiber coupler 215 has at least two input terminals with equal input coupling ratios to ensure that the output power of each amplifier is equal, thereby improving the coherent beam combining efficiency η. The formula for calculating η is shown in Equation (1).

[0078] One output port of the feedback module fiber coupler 216 outputs 90%–99% of the light to the output module for coherent beam combining laser output, while the other output port outputs 1%–10% of the light as feedback light coupled into the feedback module. That is, the output coupling ratio of the feedback module fiber coupler is 99:1–9:1. The feedback module and preamplifier module share a linear polarization-independent isolator 208, used to isolate reverse light and protect optical components, while ensuring unidirectional transmission in the ring feedback cavity. The other fiber coupler 203 of the feedback module includes two input ports with an input coupling ratio of 1:1.

[0079] The output module includes a QBH output optical cable 116 for outputting combined pulsed laser.

[0080] Example 1:

[0081] The output fiber of the pulsed laser 101 is fused to the input fiber of the linearly polarized isolator 102 to form a pulse injection module. The linearly polarized isolator 102 isolates the reverse transmission light to protect the pulsed laser 101. The input fiber of the pump combiner 104 of the preamplifier module is fused to the output fiber of the linearly polarized isolator 102 of the pulse injection module. The laser diode 103 of the preamplifier module is coupled into the active fiber 105 through the pump combiner 104 to achieve pre-amplification of the injected pulse. The output fiber of the active fiber 105 is fused to the input fiber of the cladding optical filter 106. The cladding optical filter 106 filters out the remaining pump light to protect the devices after the preamplifier module. The linearly polarized isolator 107 isolates the reverse transmission light to protect the preamplifier module. In this embodiment, the amplification module includes two amplifiers connected in parallel. The fiber coupler 108 of the beam splitter module is a 2×2 coupler with an input coupling ratio of 1:1. One input port is fused to the output fiber of the cladding optical filter 106 of the preamplifier module, and the other input port is fused to the output fiber of the linear polarization-independent isolator 117 of the feedback module, forming a closed-loop feedback structure for unidirectional transmission. The output coupling ratio of the fiber coupler 108 is 1:1 (i.e., equal ratio) to ensure that the pulse light entering each amplifier of the amplification module after beam splitting is of equal power. The output fibers are fused to the input fibers of the optical variable delay line 109 of the amplification module. The optical variable delay line 109 is used to fine-tune the cavity length of each amplifier to compensate for the cavity length difference caused by the process. Here, the process ensures that the cavity lengths of each amplifier are almost equal. The optical variable delay line 109 controls the cavity length difference ΔL of each amplifier to be 5.7mm to 10mm. Laser diode 110 is coupled into active fiber 112 via pump combiner 111 to achieve pulse amplification. The output fiber of active fiber 112 is fused to the input fiber of cladding optical filter 113. Cladding optical filter 113 filters out residual pump light to protect devices after the amplification module. The fiber coupler 114 of the combiner module has a 2×1 structure with an input coupling ratio of 1:1 (i.e., equal ratio), where the output pulses of each amplifier are coherently superimposed. The output fiber of fiber coupler 114 is fused to the input port of fiber coupler 115 of the feedback module, and the output coupling ratio of fiber coupler 115 is 99:1. 1% of the output fiber of fiber coupler 115 of the feedback module is fused to the input fiber of linear polarization-independent isolator 117, and the output fiber of linear polarization-independent isolator 117 is fused to the other input port of fiber coupler 108 of the beam splitter module to form a closed loop feedback structure for unidirectional transmission. The ring feedback coupling causes the low-loss mode to oscillate, which plays a role in self-organizing filtering and mode selection, thereby achieving phase locking, that is, phase synchronization of each amplification ring cavity, so as to achieve coherent superposition at the point where the output pulse lasers of each amplifier converge (fiber coupler 114 of the beam combining module); 99% of the fiber output of the feedback module fiber coupler 115 is fused with the fiber input of the QBH output optical cable 116 of the output module, and the beam combining pulse laser is output at the output end of the QBH output optical cable 116.

[0082] The injected pulse repetition frequency is 30kHz, the pulse width is 100ns, the average power is 5W, and the waveform is a square wave.

[0083] The linear polarization-independent isolator 117 has a maximum power handling capacity of 30W.

[0084] Both active optical fibers 105 and 112 are double-clad ytterbium-doped fibers with core / cladding diameters of 30μm / 250μm.

[0085] The laser diode 110 has a maximum output power of 70W and an output wavelength of 975nm. It is driven by the same power supply for both of the aforementioned amplification modules.

[0086] The amplifiers in the amplification module are all consistent in terms of model, batch, and fiber optic cable length.

[0087] The coherent beam combining laser system outputs a pulse repetition frequency of 30kHz, a pulse width of 100ns, an average power of 100W, and a square wave waveform.

[0088] In this embodiment, the amplification module may also include three amplifiers connected in parallel. At this time, other parts of the invention remain unchanged, but the fiber optic coupler 108 of the beam splitting module is changed to a 2×3 coupler with an output coupling ratio of 1:1:1 (i.e., equal ratio); the fiber optic coupler 114 of the beam combining module is changed to a 3×1 structure with an input coupling ratio of 1:1:1 (i.e., equal ratio).

[0089] In this embodiment, the output coupling ratio of the fiber optic coupler 115 in the feedback module can also be set to 9:1, meaning that 10% of the fiber output from the fiber optic coupler 115 is fused to the input fiber of the linearly polarization-independent isolator 117, and 90% of the fiber output is fused to the input fiber of the QBH output optical cable 116 of the output module. In this embodiment, the active optical fibers of the preamplifier module and the amplification module can also be erbium-doped optical fibers.

[0090] The core / cladding diameters are 30μm / 250μm, 20μm / 400μm, or 50μm / 400μm, etc.

[0091] In this embodiment, the pulsed laser of the pulse injection module has an output pulse width range of 100ns to 500μs, a repetition frequency of 1kHz to 4MHz, and no limit on the waveform type.

[0092] Example 2:

[0093] The output fiber of the pulsed laser 201 is fused to the input fiber of the linearly polarization-independent isolator 202, and coupled into the feedback module through the 50% input port of the 2×1 fiber coupler 203. The output fiber of the fiber coupler 203 is fused to the signal input fiber of the pump combiner 205 of the preamplifier module. The laser diode 204 of the preamplifier module is coupled into the active fiber 206 through the pump input fiber of the pump combiner 205 to achieve pre-amplification of the injected pulse. The output fiber of the active fiber 206 is fused to the input fiber of the cladding optical filter 207. The cladding optical filter 207 filters out the remaining pump light to protect the devices after the preamplifier module. The linearly polarization-independent isolator 208 isolates the reverse transmission light to protect the preamplifier module while ensuring unidirectional transmission in the ring feedback cavity. Therefore, the preamplifier module is located within the feedback module. The output fiber of the linearly polarization-independent isolator 208 of the preamplifier module is fused to the single-port input fiber of the fiber coupler 209 of the beam splitter module to achieve beam splitting of the pulsed laser. In this embodiment, the amplification module includes two parallel amplifiers. The fiber coupler 209 of the beam splitter module is a 1×2 coupler with an output coupling ratio of 1:1 (i.e., equal ratio) to ensure that the pulse light entering each amplifier in the amplification module after beam splitting is of equal power. The output fiber is fused to the input fiber of the optical variable delay line 210 of the amplification module. The optical variable delay line 210 is used to fine-tune the cavity length of each amplifier to compensate for the cavity length difference caused by the process. Here, the process ensures that the cavity length of each amplifier is almost equal. Here, the optical variable delay line 109 controls the cavity length difference ΔL of each amplifier to be 5.7mm to 10mm. The laser diode 211 is coupled into the active fiber 213 through the pump combiner 212 to realize pulse amplification. The output fiber of the active fiber 213 is fused to the input fiber of the cladding optical filter 214. The cladding optical filter 214 filters out the remaining pump light to protect the devices after the amplification module. The fiber coupler 215 of the combining module has a 2×1 structure with an input coupling ratio of 1:1 (i.e., equal ratio), where the output pulses of each amplifier are coherently superimposed. The output fiber of fiber coupler 215 is fused to the input port of fiber coupler 216 of the feedback module. The output coupling ratio of fiber coupler 216 is 99:1. 1% of the output fiber of fiber coupler 216 of the feedback module is fused to the 50% input port of fiber coupler 203. After passing through the preamplifier module and the combining module, they are fused together to form a closed loop feedback structure. The loop feedback coupling causes the low-loss mode to oscillate, which plays a role in self-organizing filtering and mode selection, thereby achieving phase locking, that is, phase synchronization of each amplification loop cavity, thus achieving coherent superposition at the point where the output pulse lasers of each amplifier converge (fiber coupler 215 of the combining module). The 99% output port of fiber coupler 216 of the feedback module is fused to the input fiber of QBH output optical cable 217 of the output module, and the combined pulse laser is output at the output end of QBH output optical cable 217.

[0094] The injected pulse repetition frequency is 200kHz, the pulse width is 200ns, the average power is 20W, and the waveform is Gaussian.

[0095] The 208 linear polarization-independent isolator has a maximum power handling capacity of 60W.

[0096] Active fiber 206 is a double-clad ytterbium-doped fiber with a core / cladding diameter of 30μm / 250μm, and active fiber 213 is a double-clad ytterbium-doped fiber with a core / cladding diameter of 50μm / 400μm.

[0097] The laser diode 211 has a maximum output power of 140W and an output wavelength of 975nm. It is driven by the same power supply for both of the aforementioned amplification modules.

[0098] The coherent beam combining laser system outputs a pulse repetition frequency of 200kHz, a pulse width of 220ns, an average power of 200W, and a Gaussian waveform.

[0099] The amplifiers in the amplification module are all of the same type and have the same model, batch, and pigtail length. In this embodiment, the amplification module may also include three amplifiers connected in parallel. In this case, other parts of the invention remain unchanged, but the fiber optic coupler 209 of the beam splitter module is changed to a 1×3 coupler with an output coupling ratio of 1:1:1 (i.e., equal ratio); the fiber optic coupler 215 of the beam combiner module is changed to a 3×1 structure with an input coupling ratio of 1:1:1 (i.e., equal ratio).

[0100] In this embodiment, the output coupling ratio of the feedback module fiber coupler 216 can also be set to 9:1, that is, 10% of the fiber output of the fiber coupler 216 is fused with 50% of the input port of the fiber coupler 203, and 90% of the fiber output is fused with the QBH output optical cable 217 of the output module.

[0101] In this embodiment, the active optical fiber of the pre-amplification module and the amplification module can also be erbium-doped fiber, with a core / cladding diameter of 30μm / 250μm, 20μm / 400μm, or 50μm / 400μm, etc.

[0102] In this embodiment, the pulsed laser of the pulse injection module has an output pulse width range of 100ns to 500μs, a repetition frequency of 1kHz to 4MHz, and no limit on the waveform type.

[0103] The above description is for illustration and explanation only and is not intended to limit the invention. Any improvements and modifications made to the invention without departing from its principles fall within the scope of protection of the invention. For example, when the amplification module includes multiple parallel amplifiers, the number of ports in the corresponding beam splitting and combining modules increases accordingly; the preamplifier and each amplifier have one or more amplification stages.

Claims

1. A pulse-injection coherent beam combining laser system based on a ring feedback structure, comprising: The pulse injection module, preamplification module, beam splitting module, amplification module, beam combining module, feedback module, and output module are characterized in that: the beam splitting module, amplification module, and beam combining module are connected in sequence, and the feedback module connects the input end of the beam splitting module and the output end of the beam combining module to form a closed ring feedback structure. The pulse injection module includes a pulsed laser and a first linear polarization-independent isolator, wherein the pulse injection module injects a pulsed light signal; The preamplification module includes a first laser, a first pump combiner, a first active optical fiber, a second linear polarization-independent isolator, and a first cladding optical filter. The first laser is a first laser diode. The first laser diode of the preamplification module is coupled into the first active optical fiber through the first pump combiner to achieve preamplification of the injected pulse. The output of the first active optical fiber is fused to the input of the first cladding optical filter. The first cladding optical filter filters out the remaining pump light to protect the devices after the preamplification module. The second linear polarization-independent isolator isolates the reverse transmission light to protect the preamplification module. The beam splitting module includes a first fiber coupler, one of which is fused to the output fiber of the second linear polarization-independent isolator of the preamplifier module, and the other input port is fused to the output fiber of the third linear polarization-independent isolator of the feedback module, forming a closed loop feedback structure for unidirectional transmission. The output fibers are fused to the input fibers of the multi-channel optical variable delay line of the amplification module respectively. The amplification module includes at least two amplifiers connected in parallel. Each amplifier includes an optical variable delay line, a second laser, a second pump combiner, a second active fiber, and a second cladding optical filter. The second laser is a second laser diode. The second laser diode is coupled into the second active fiber through the second pump combiner to achieve pulse amplification. The output fiber of the second active fiber is fused to the input fiber of the second cladding optical filter. The second cladding optical filter filters out the remaining pump light to protect the devices after the amplification module. The optical variable delay line is used to delay the amplified pulse light signal so that the feedback light is synchronized with the next pulse and to control the cavity length difference of each amplifier. The beam combining module includes a second fiber coupler, which is used to combine the output pulses of each amplifier so that the output pulses of each amplifier can be coherently superimposed at this point. The feedback module includes a third fiber coupler and a third linear polarization-independent isolator. The output fiber of the second fiber coupler is fused to the input port of the third fiber coupler of the feedback module. The first active fiber output of the third fiber coupler of the feedback module is fused to the input fiber of the third linear polarization-independent isolator. The output fiber of the third linear polarization-independent isolator is fused to the other input port of the first fiber coupler of the beam splitter module to form a closed loop feedback structure for unidirectional transmission. The phases of each amplification loop cavity are synchronized, thereby achieving coherent superposition in the fiber coupler of the beam combining module. The second active fiber output of the third fiber coupler of the feedback module is fused to the input fiber of the output cable of the output module, and the beam combining pulse laser is output at the output end of the output cable. The input coupling ratio of the third fiber coupler is proportional to ensure that the output power of each amplifier is equal, thereby improving the coherent beam combining efficiency η. The formula for calculating η is as follows: n=a b / (ΔP ΔL)(1) Where a is the synchronization coefficient of each amplifier pulse, b is the pump synchronization coefficient of each amplifier, ΔP is the power difference of each amplifier pulse, and ΔL is the cavity length difference of each amplifier.

2. The pulse injection coherent beam combining laser system based on a ring feedback structure according to claim 1, characterized in that: The third fiber coupler has an output coupling ratio of 99:1, the first active fiber has an output light intensity ratio of 1% to 10%, and the second active fiber has an output light intensity ratio of 90% to 99%.

3. The pulse injection coherent beam combining laser system based on a ring feedback structure according to claim 1, characterized in that: The number of output ends of the fiber optic coupler in the beam splitting module and the number of input ends of the fiber optic coupler in the beam combining module are each at least 2, and the output coupling ratio of the fiber optic coupler in the beam splitting module and the input coupling ratio of the fiber optic coupler in the beam combining module are both proportional.

4. The pulse injection coherent beam combining laser system based on a ring feedback structure according to claim 1, characterized in that: The injection module has an injection pulse repetition frequency of 30kHz, a pulse width of 100ns, an average power of 5W, and a square wave waveform. The coherent beam combining laser system outputs a pulse repetition frequency of 30kHz, a pulse width of 100ns, an average power of 100W, and a square wave waveform.

5. A pulse-injection coherent beam combining laser system based on a ring feedback structure, comprising: The pulse injection module, beam splitting module, amplification module, beam combining module, feedback module, and output module are characterized in that: the beam splitting module, amplification module, and beam combining module are connected in sequence, and the feedback module connects the input end of the beam splitting module and the output end of the beam combining module to form a closed ring feedback structure. The pulse injection module includes a pulsed laser and a first online polarization-independent isolator. The pulsed light signal injected by the pulse injection module is fused to the output fiber of the pulsed laser and the input fiber of the first online polarization-independent isolator, and coupled into the feedback module through the first input port of a 2×1 fiber coupler. The feedback module includes a third fiber coupler and a preamplification module. The preamplification module includes a first laser, a first pump combiner, a first active fiber, a first cladding optical filter, and a second polarization-independent isolator. The first laser is a first laser diode. The first laser diode of the preamplification module and the output fiber of the 2×1 fiber coupler are coupled into the first active fiber through the first pump combiner to achieve preamplification of the injected pulse. The output fiber of the first active fiber is fused to the input fiber of the first cladding optical filter. The first cladding optical filter filters out the remaining pump light to protect the devices after the preamplification module. The second polarization-independent isolator isolates the reverse transmission light to protect the preamplification module. The second input port of the 2×1 fiber coupler is fused to the output fiber of the first active fiber of the third fiber coupler. The beam splitting module includes a first fiber beam splitter, one of whose input ports is fused with the output fiber of the second linear polarization-independent isolator of the preamplification module to form a closed loop feedback structure for unidirectional transmission. The output fiber is fused with the input fiber of the optical variable delay line of the multiple amplification modules respectively. The amplification module includes at least two amplifiers connected in parallel. Each amplifier includes an optical variable delay line, a second laser, a second pump combiner, a second active fiber, and a second cladding optical filter. The second laser is a second laser diode. The second laser diode is coupled into the second active fiber through the second pump combiner to achieve pulse amplification. The output fiber of the second active fiber is fused to the input fiber of the second cladding optical filter. The second cladding optical filter filters out the remaining pump light to protect the devices after the amplification module. The optical variable delay line is used to delay the amplified pulse light signal so that the feedback light is synchronized with the next pulse and to control the cavity length difference of each amplifier. The beam combining module includes a second fiber coupler, which is used to combine the output pulses of each amplifier so that the output pulses of each amplifier can be coherently superimposed at this point. The output fiber of the second fiber coupler is fused to the input port of the third fiber coupler of the feedback module. The second active fiber output of the third fiber coupler of the feedback module is fused with the output fiber input of the output fiber cable of the output module, and a combined pulse laser is output at the output end of the output fiber cable. The input coupling ratio of the third fiber coupler is proportional to ensure that the output power of each amplifier is equal, thereby improving the coherent beam combining efficiency η. The formula for calculating η is as follows: n=a b / (ΔP ΔL)(1) Where a is the synchronization coefficient of each amplifier pulse, b is the pump synchronization coefficient of each amplifier, ΔP is the power difference of each amplifier pulse, and ΔL is the cavity length difference of each amplifier.

6. The pulse injection coherent beam combining laser system based on a ring feedback structure according to claim 5, characterized in that: The third fiber coupler has an output coupling ratio of 99:1, the first active fiber has an output light intensity ratio of 1% to 10%, and the second active fiber has an output light intensity ratio of 90% to 99%.

7. The pulse injection coherent beam combining laser system based on a ring feedback structure according to claim 5, characterized in that: The number of output ends of the fiber optic coupler in the beam splitting module and the number of input ends of the fiber optic coupler in the beam combining module are each at least 2, and the output coupling ratio of the fiber optic coupler in the beam splitting module and the input coupling ratio of the fiber optic coupler in the beam combining module are both proportional.

8. The pulse injection coherent beam combining laser system based on a ring feedback structure according to claim 5, characterized in that: The injection module has an injection pulse repetition frequency of 30kHz, a pulse width of 100ns, an average power of 5W, and a square wave waveform. The coherent beam combining laser system outputs a pulse repetition frequency of 30kHz, a pulse width of 100ns, an average power of 100W, and a square wave waveform.

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