CN112838467B

CN112838467B - Pulse injection type coherent beam combination laser system based on annular feedback structure

Info

Publication number: CN112838467B
Application number: CN201911166916.3A
Authority: CN
Inventors: 李骁军; 谭小妹; 李文涛; 严超; 白云娜; 刘广柏
Original assignee: Nanjing Light Laser Technology Co ltd
Current assignee: Nanjing Light Laser Technology Co ltd
Priority date: 2019-11-25
Filing date: 2019-11-25
Publication date: 2022-12-16
Anticipated expiration: 2039-11-25
Also published as: CN116191178A; CN112838467A

Abstract

A pulse injection type coherent beam combination laser system based on an annular feedback structure comprises: the pulse injection module, the pre-amplifier module, the beam splitting module, the amplifier module, the beam combining module, the feedback module and the output module are sequentially connected, 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 annular feedback structure. The invention has the advantages of full optical fiber structure, compact system, no need of complex phase control mode, pulse synchronization, high-energy and high-power pulse laser output, and selection of pulse injection systems with various frequencies, pulse widths and waveforms to realize coherent beam combination output without being limited by single cavity length or structure of the pulse system due to the pulse injection mode.

Description

Pulse injection type coherent beam combination laser system based on annular feedback structure

Technical Field

The invention relates to the field of fiber lasers, in particular to a pulse injection type coherent beam combination laser system based on an annular feedback structure.

Background

The pulse fiber laser has the advantages of good beam quality, compact structure, convenient heat management, high conversion efficiency and the like, and has the characteristics of high pulse peak power, large single pulse energy, adjustable pulse width and the like. The pulse laser has short action time in industrial processing, high processing precision, low cost and high speed. Therefore, the laser marking device is widely applied to a plurality of fields such as optical communication, laser medical treatment, industrial marking, cutting and welding, high-field physics, frequency conversion, laser radar and the like.

From the application requirement of pulse laser, the realization of high-brightness laser output of hundreds of kilowatts is always the target of pulse laser. At present, a single-path pulse fiber laser has realized output of an average power kilowatt level or a pulse energy millifocal level, but a single-path system is difficult to consider both high average power and high pulse energy, and often another performance index has to be sacrificed in order to realize maximization of a certain performance index. In addition, the power or energy boosting space of a single path is very limited due to nonlinear effects, optical damage, mode instability, and the like in the optical fiber. For silicon fiber, the self-focusing effect (threshold peak power of about 4 MW) is the ultimate limiting factor in peak power boosting in fiber amplifiers. The coherent synthesis technology is an important technical means for breaking through the performance limit of a single-path system and realizing high-energy high-power large-pulse-energy laser output, and the key of coherent synthesis is the phase control technology.

Common coherent synthesis techniques are:

active coherent synthesis: most of the systems are based on MOPA cascade amplification structures, and active phase detection and feedback control phase synchronization are carried out so as to achieve the purpose of coherent output of array laser. Methods for controlling the phase mainly include heterodyne H-C detection, SPGD algorithm, dither method, and the like.

Passive coherent synthesis: the self-organizing phase-locking characteristic of the fiber laser is utilized to realize the automatic compensation of the fluctuation of the laser phases of all paths. The phase-locking method is mainly divided into evanescent wave coupling, mutual injection coupling, annular feedback coupling and the like.

The active phase lock needs clear theoretical guidance and has potential greater than one hundred-beam coherent synthesis theoretically, but complex optical path control measures need to be adopted, the synthesis effect is closely related to the optical path control capability, hundreds of paths of fiber laser arrays need to be built for hundreds of paths of high-brightness laser output, and the output power of each path needs to be increased to more than kilowatt. Moreover, active control requires narrow linewidth seed light, and increasing power is limited by the SBS effect. Compared with an active coherent synthesis technology, the passive coherent synthesis system has a simple structure, does not need complex electric signal feedback, and does not need a narrow line width seed source; the wide-spectrum laser can be used, SBS in the optical fiber amplifier can be effectively inhibited, the output power is improved, and the method is a feasible high-power optical fiber laser coherent synthesis implementation scheme. Mutual injection feedback and evanescent coupling in passive structures is based on standing wave cavities. Different seed lights are adopted for mutual injection feedback, and the stability is poor. The coupling device used for evanescent wave coupling adopts multi-core optical fiber, is difficult to manufacture, has power concentrated in a coupling part and is limited in output power. The annular feedback coupling cavity is based on a traveling wave cavity, can adopt the same seed light, has the phase difference of the traveling wave cavity smaller than that of the standing wave cavity under the same condition, has good phase locking stability, and has the synthetic path number at least twice of that of the standing wave cavity. At present, an annular composite cavity has the kilowatt-level output capability in a continuous light passive coherent synthesis experiment, but the research of the annular composite cavity applied to pulse laser is relatively lacked.

CN103441419A discloses a fiber laser all-optical feedback passive coherent beam combining system based on dammann grating, which includes: the optical fiber splicing system comprises an N-path optical fiber amplifier array, a light beam splicing system comprising a light beam collimator group and a laser high-reflection lens group, a first plane beam splitter, a second plane beam splitter, a feedback optical fiber, a CCD camera, an optical fiber preamplifier, an optical fiber coupler, a semiconductor laser diode and a 1 XN optical fiber beam splitter, and is characterized by further comprising a phase compensation plate. Fourier lens, dammann grating and adjustable aperture diaphragm. The system overcomes the defect that multi-stage side lobes exist in far-field coherent light spots output by the traditional passive coherent beam combining system. However, the system comprises non-all-fiber elements such as a fourier lens, a dammann grating, a laser high-reflection lens group, a planar beam splitter and the like, and the compactness of the system is limited by the working distance of the elements and the poor integration level. In addition, the annular feedback cavity of the system adopts a space coupling structure, the coupling adjustment is difficult, and the quality of the combined light beam is limited by the dispersion degree of far-field output energy.

CN108429121A discloses a passive coherent beam-combining all-fiber laser based on a ring cavity structure, which substantially overcomes the disadvantages of the above patents. Through the integrated annular cavity structure laser and the phase locking system, a mode of common oscillation starting is selected by means of an automatic mode selection mechanism, and the functions of phase locking and coherent beam combination output are achieved without any operation. However, the larger the length difference Δ L between the optical fibers of the laser, the more difficult it is to synchronize the pulses, and the lower the coherent beam combination efficiency. This places high process demands on the beam-forming efficiency. In addition, the output light pulse of the laser is realized by the following modes: the pulse power supply drives the pumping diode, and the pumping pulse remodulates the continuous light to realize pulse output. The pulse frequency and pulse width obtained in this way are limited by the electrical pulses, thereby limiting the increase in pulse power and energy.

Disclosure of Invention

The invention discloses a pulse injection type coherent beam combination laser system based on an annular feedback structure, which does not need a complex phase control structure. Each path of pulse laser is from the same pulse laser, a small part of the output light of each path of pulse laser is separated by an annular feedback structure and is respectively fed back to each path of pulse laser system to be used as a part of injection seeds, and the mode with low loss is oscillated by annular feedback coupling to play the roles of self-organizing filtering and mode selection, so that the phase locking is realized. The length difference of each path of optical fiber is controlled by the optical variable delay line, so that the phase difference of each path of pulse is reduced, the pulse beam combination efficiency is improved, and the requirement on the process is reduced. And coherent superposition of each path of pulse laser with synchronous phases is realized at the junction of the beam combining modules, and the output of the beam combining laser is realized through the output module. In addition, the system adopts a pulse injection mode, can select a pulse injection system with various frequencies, pulse widths and waveforms to realize coherent beam combination output, and is not limited by the single cavity length or structure of the pulse system.

The invention relates to a pulse injection type coherent beam combination laser system based on an annular feedback structure, which comprises: the pulse feedback device comprises a pulse injection module, a pre-amplifier module, a beam splitting module, an amplifier module, a beam combining module, a feedback module and an output module, wherein the beam splitting module, the amplifier module and the beam combining module are sequentially connected, 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 annular feedback structure;

the pulse injection module comprises a pulse laser and an online polarization-independent isolator;

the pre-amplifier module comprises a laser, a pumping beam combiner, an active optical fiber and an online polarization-independent isolator;

the beam splitting module comprises a fiber coupler;

the amplification module comprises at least 2 paths of amplifiers which are connected in parallel, and each path of amplifier comprises an optical variable delay line, a laser, a pumping beam combiner and an active optical fiber;

the beam combining module comprises an optical fiber coupler;

the feedback module includes a fiber coupler and an in-line polarization independent isolator.

Preferably, the pulse injection module, the pre-discharge module, the annular feedback structure and the output module are connected in sequence.

Further, the fiber coupler of the splitting module comprises 2 input ends, and the input coupling ratio is 1.

Preferably, the pre-amplifier module is located in the feedback module, and the pre-amplifier module and the feedback module share an in-line polarization-independent isolator.

Further, the feedback module further comprises another optical fiber coupler, and the pulse injection module is injected into the pre-amplification module through the optical fiber coupler.

Further, the other fiber coupler includes two input ends, and has an input coupling ratio of 1.

Preferably, the type of the output end optical fiber of the pulse laser of the pulse injection module is matched with the type of the input end optical fiber of the online polarization-independent isolator.

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

Preferably, the amplification level of each amplifier of the pre-amplification module and/or the amplification module is 1 level or more.

Preferably, the amplifier of the pre-amplifier module and/or the amplifier module further comprises a cladding light filter.

Preferably, the laser of the pre-amplifier module and/or the amplifier module is a laser diode.

Preferably, the active fiber of the pre-amplifier module and/or the amplifying module is a rare-earth ion doped gain fiber.

Further, the active optical fiber of the pre-amplifier module and/or the amplifier module is a double-clad ytterbium-doped optical fiber.

Further, the active fiber core/outer cladding diameter of the pre-amplifier module and/or the amplifier module is 30 μm/250 μm,50 μm/400 μm, or 20 μm/400 μm.

Still further, the active fiber core/outer cladding diameter of the pre-amplifier module and/or amplifier module is 50/400 μm.

Further, the active fiber length of the pre-amplifier module and/or the amplifier module is 1.3-2 m.

Further, the active fiber length of the pre-amplifier module and/or the amplifier module is 1.5m.

Preferably, the pump combiner of the pre-amplifier module comprises at least 1 pump input end.

Preferably, the model of the pump input end optical fiber of the pump beam combiner of the pre-amplifier module is matched with the model of the output optical fiber of the laser.

Preferably, the model of the input end of the pump beam combiner signal fiber of the pre-amplifier module is matched with the model of the output optical fiber of the pulse injection module.

Preferably, the type of the output end optical fiber of the pump combiner of the pre-amplifier module is matched with that of the active optical fiber.

Preferably, the forward withstand power of the in-line polarization-independent isolator of the pre-discharge module is not less than the pre-discharge power.

Preferably, the number of the output ends of the fiber coupler of the beam splitting module is at least 2, and the output coupling ratio is equal proportion, so that the seed power entering each path of amplifier is ensured to be equal, and the coherent beam combination efficiency is improved.

Preferably, the amplifying module comprises 2-5 parallel amplifiers.

Preferably, the lasers of the amplifiers of the amplifying modules are driven by the same power supply.

Preferably, the pump combiner of the amplifier of the amplifying module comprises at least 2 pump inputs.

Preferably, the types and batches of all the devices of the same type of the amplifying module are consistent.

Preferably, the length difference of tail fibers of the same type of devices of each path of amplifier of the amplifying module is not more than 0.5mm.

Preferably, the difference of the total length of all the devices of each amplifier of the amplifying module generated in the fusion process is not more than 5mm.

Preferably, the optical variable delay line of the amplifying module controls the cavity length difference Δ L of each path of amplifier to be 5.7 mm-10 mm.

Preferably, the number of the input ends of the beam combining module fiber coupler is at least 2, and the input coupling ratio is equal proportion, so that the output power of each path of amplifier is ensured to be equal, and the coherent beam combining efficiency is improved.

Further, the coherent beam combination efficiency η is calculated by the following formula:

η＝a*b/(ΔP*ΔL) (1)

wherein, a is the synchronous coefficient of each path of amplifier pulse, b is the pumping synchronous coefficient of each path of amplifier, Δ P is the power difference of each path of amplifier pulse, and Δ L is the cavity length difference of each path of amplifier. Preferably, one output port of the feedback module fiber coupler outputs 90% to 99% of light to the output module for outputting coherent beam combination laser, and the other output port outputs 1% to 10% of light as feedback light to the feedback module. Namely, the output coupling ratio of the feedback module fiber coupler is 99.

Furthermore, one output port of the fiber coupler of the feedback module outputs 99% of light, which is accessed to the output module to output coherent combined beam laser, and the other output port outputs 1% of light, which is used as feedback light, which is accessed to the feedback module, that is, the fiber coupler output coupling ratio of the feedback module is 99.

Preferably, the output module comprises a QBH output optical cable for outputting the combined beam of pulsed laser light.

The invention has the following beneficial technical effects:

(1) The invention has simple structure, does not need a complex phase control structure, and has the advantages of simple and convenient implementation, low cost and the like;

(2) The invention is of an all-fiber structure, and has compact system and convenient integration;

(3) The invention has multi-path expansibility and can realize high-energy and high-power pulse laser output.

(4) The invention is of a pulse injection type, and can conveniently realize the pulse diversity output of a laser system.

Drawings

Fig. 1 is a schematic structural diagram of a pulse injection type coherent beam combination laser system based on an annular feedback structure according to the present invention.

In the figure: 101 is a pulse laser, 102, 107, 117 is an online polarization independent isolator, 103, 110 are laser diodes, 104, 111 are pump beam combiners, 105, 112 are active fibers, 106, 113 are cladding light filters, 108, 114, 115 are fiber couplers, 109 is an optical variable delay line, and 116 is a QBH output cable.

Fig. 2 is another structural diagram of the pulse injection type coherent beam combination laser system based on the annular feedback structure.

In the figure: 201 is a pulse laser, 202, 208 are online polarization independent isolators, 204, 211 are laser diodes, 205, 212 are pump beam combiners, 206, 213 are active optical fibers, 207, 214 are cladding light filters, 203, 209, 215, 216 are fiber couplers, 210 is an optical variable delay line, and 217 is a QBH output optical cable.

Detailed Description

According to the pulse injection type coherent beam combination laser system based on the annular feedback structure, the annular feedback coupling enables the mode with low loss to oscillate, and the functions of self-organizing filtering and mode selection are achieved, so that phase locking is achieved. Each path of amplified pulse laser with synchronous phase realizes coherent superposition at the junction of the beam combining modules, and the output of the beam combining laser is realized through the output module. Taking fig. 1 as an example, the present invention includes a pulse injection module, a pre-amplifier module, a beam splitting module, an amplifier module, a beam combining module, a feedback module, and an output module. The beam splitting module, the amplifying module and the beam combining module are sequentially connected, and the feedback module connects the input end of the beam splitting module with the output end of the beam combining module to form a closed annular feedback structure. The pulse injection module, the pre-discharge module, the annular feedback structure and the output module are connected in sequence.

The pulse injection module comprises a pulse laser 101 and an online polarization-independent isolator 102, the model of an output end optical fiber of the pulse laser is matched with the model of an input end optical fiber of the online polarization-independent isolator 102, and the forward tolerable power of the online polarization-independent isolator 102 is not less than the power of the pulse laser.

The pre-amplifier module comprises a laser diode 103, a pumping beam combiner 104, an active fiber 105, a cladding light filter 106 and an online polarization-independent isolator 107, wherein the pumping beam combiner 104 at least comprises 1 pumping input end which is matched with the output fiber model of the laser diode, the signal fiber model input end of the pumping beam combiner is matched with the output fiber model of the pulse injection module, the output end of the pumping beam combiner is matched with the active fiber model, and the forward tolerance power of the online polarization-independent isolator 107 is not less than the pre-amplifier power. The active optical fiber is a rare earth ion doped gain optical fiber, and the amplification stage number of the pre-amplification module is 1 stage or more.

The splitting module includes a fiber coupler 108. The fiber coupler 108 includes at least 2 output ends, and the output coupling ratio thereof is equal proportion, thereby ensuring that the power of the amplified seeds entering each path is equal, and thus improving the efficiency of coherent beam combination. The fiber coupler 108 includes two input ends with an input coupling ratio of 1.

The amplifying module comprises at least 2 parallel amplifiers, preferably 2-5 parallel amplifiers, each amplifier comprises: the optical variable delay line 109, the laser diode 110, the pumping beam combiner 111, the active optical fiber 112, the cladding light filter 113, all the laser diodes of each amplifier of the amplification module are driven by the same power supply, the pumping beam combiner 111 at least comprises 2 pumping input fibers, the active optical fiber is a rare earth ion doped gain optical fiber, the models and batches of all the devices of the same type related to the amplification module are consistent, the length difference of the tail fiber of the same type device of each amplifier cannot exceed 0.5mm, the total length difference generated in the fusion process of all the devices of each amplifier of the amplification module is not more than 5mm, and the optical variable delay line 109 controls the cavity length difference delta L of each amplifier to be 5.7 mm-10 mm. The amplification stage number of each amplifier of the amplification module is 1 stage or more.

The beam combining module includes a fiber coupler 114. The fiber coupler 114 at least includes 2 input ends, the input coupling ratio of which is equal in proportion, so as to ensure that the output power of each path of amplifier is equal, thereby improving the coherent beam combination efficiency η, and the calculation formula of η is as follows:

η＝a*b/(ΔP*ΔL) (1)

wherein, a is the synchronous coefficient of each path of amplifier pulse, b is the pumping synchronous coefficient of each path of amplifier, Δ P is the power difference of each path of amplifier pulse, and Δ L is the cavity length difference of each path of amplifier.

The feedback module comprises an optical fiber coupler 115 and an online polarization-independent isolator 117, wherein one output port of the optical fiber coupler 115 outputs 90% -99% of light to an output module for outputting coherent beam combination laser, and the other output port outputs 1% -10% of light as feedback light to a feedback module, namely the output coupling ratio of the feedback module optical fiber coupler is 99-9. The in-line polarization independent isolator 117 isolates the reverse photoprotective optics while ensuring unidirectional transmission of the annular feedback cavity.

The output module includes a QBH output optical cable 116 for outputting the combined pulse laser.

In another embodiment of the present invention, the pre-amplifier module is located in the feedback module and both modules share an in-line polarization independent isolator. Taking fig. 2 as an example, the pulse injection module includes: a pulsed laser 201, an in-line polarization independent isolator 202; the pre-placing module comprises: a laser diode 204, a pump beam combiner 205, an active fiber 206, a cladding light filter 207, and an in-line polarization-independent isolator 208; the beam splitting module includes: a fiber coupler 209; each amplifier of the amplifying module comprises: an optical variable delay line 210, a laser diode 211, a pump beam combiner 212, an active fiber 213, a cladding light filter 214; the beam combining module comprises: a fiber coupler 215; the feedback module comprises: the optical fiber coupler 216, the optical fiber coupler 203 and the pre-amplifier module; the output module includes: QBH output cable 217. The output optical fiber of the optical fiber coupler 215 is welded with the input port of the optical fiber coupler 216 of the feedback module, the output optical fiber of the optical fiber coupler 216 is welded with the input port of the other optical fiber coupler 203, the output end of the optical fiber coupler 203 is connected with the pre-amplifier module, and the module output and the beam combining module are prevented from being welded, so that a closed annular feedback structure is formed. In this case, the pulse injection module is injected into the preamplifier module through another fiber coupler 203.

The type of the output end optical fiber of the pulse injection module pulse laser 201 is matched with the type of the input end optical fiber of the online polarization-independent isolator 202, and the forward tolerable power of the online polarization-independent isolator 202 is not less than the power of the pulse laser.

The output pulse width range of the pulse laser 201 of the pulse injection module is 100 ns-500 us, the repetition frequency is 1 kHz-4 MHz, and the waveform type is not limited.

The pre-amplifier module pump combiner 205 at least comprises 1 pump input end which is matched with the output fiber model of the laser diode 204, the signal fiber model input end of the pump combiner 205 is matched with the output fiber model of the pulse injection module, the output end of the pump combiner 205 is matched with the active fiber 206 model, and the forward tolerance power of the online polarization independent isolator 208 is not less than the pre-amplifier power. The active optical fiber is a gain optical fiber doped with rare earth ions, and the amplification stage number of the pre-amplification module is 1 or more.

The fiber coupler 209 of the beam splitting module at least comprises 2 output ends, and the output coupling ratio of the output ends is equal proportion, so that the power of the amplified seeds entering each path is ensured to be equal, and the coherent beam combination efficiency is improved.

The amplifying module comprises at least 2 paths of amplifiers connected in parallel, all laser diodes of all paths of amplifiers of the amplifying module are driven by the same power supply, the pumping beam combiner 212 at least comprises 2 pumping input fibers, the active optical fiber is a rare earth ion-doped gain optical fiber, the models and batches of all devices of the same type related to the amplifying module are consistent, the length difference of tail fibers of the devices of the same type of all paths of amplifiers is not more than 0.5mm, the total length difference generated by all devices of all paths of amplifiers of the amplifying module in the fusion welding process is not more than 5mm, and the optical variable delay line 210 controls the cavity length difference delta L of all paths of amplifiers to be 5.7-10 mm. The amplification stage number of each amplifier of the amplification module is 1 stage or more.

The beam combining module includes a fiber coupler 215. The fiber coupler 215 includes at least 2 input ends, and the input coupling ratio thereof is equal to ensure that the output power of each amplifier is equal, so as to improve the coherent beam combination efficiency η, the calculation formula of η is shown in formula (1).

One output port of the feedback module optical fiber coupler 216 outputs 90% -99% of light to the access output module for outputting coherent beam combination laser, and the other output port outputs 1% -10% of light as feedback light to be coupled into the access feedback module. Namely, the output coupling ratio of the feedback module fiber coupler is 99. The feedback module and the pre-amplifier module share an in-line polarization independent isolator 208 for isolating the reverse light protection optics while ensuring unidirectional transmission of the annular feedback cavity. The other fiber coupler 203 of the feedback module comprises two input ends, and the input coupling ratio is 1.

Example 1:

the outgoing fiber of the pulse laser 101 is fused with the incoming fiber of the on-line polarization independent isolator 102 to form a pulse injection module, and the on-line polarization independent isolator 102 isolates the reverse transmission light to protect the pulse laser 101. The input fiber of a pump beam combiner 104 of the pre-amplifier module is welded with the output fiber of an online polarization-independent isolator 102 of the pulse injection module, a laser diode 103 of the pre-amplifier module is coupled into an active fiber 105 through the pump beam combiner 104 so as to realize pre-amplification of an injection pulse, the output fiber of the active fiber 105 is welded with the input fiber of a cladding light filter 106, the cladding light filter 106 filters residual pump light to protect devices behind the pre-amplifier module, and the online polarization-independent isolator 107 isolates a reverse transmission light protection pre-amplifier module. In this embodiment, the amplifying module includes 2 parallel amplifiers, the fiber coupler 108 of the splitting module is a 2 × 2 coupler, and the input coupling ratio is 1, wherein one input port is fusion-spliced with the outgoing fiber of the cladding light filter 106 of the pre-amplifying module, and the other input port is fusion-spliced with the outgoing fiber of the on-line polarization-independent isolator 117 of the feedback module, so as to form a closed loop feedback structure with unidirectional transmission; the output coupling ratio of the optical fiber coupler 108 is 1 (i.e. equal ratio), so as to ensure that the pulsed light entering each path of amplifier of the amplification module after beam splitting is of equal power, and the outgoing fibers are respectively fused with the incoming 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 the cavity length difference caused by the process, wherein the process ensures that the cavity length of each amplifier is almost equal, and the optical variable delay line 109 controls the cavity length difference Δ L of each amplifier to be 5.7 mm-10 mm. The laser diode 110 is coupled into the active fiber 112 through the pump beam combiner 111 to realize pulse amplification, the outgoing fiber of the active fiber 112 is fused with the incoming fiber of the cladding light filter 113, and the cladding light filter 113 filters the residual pump light to protect the device behind the amplification module. The fiber coupler 114 of the beam combining module is of a 2 × 1 structure, the input coupling ratio is 1 (namely equal proportion), and coherent superposition is realized at the position where the output pulses of each path of amplifier are output; the output fiber of the fiber coupler 114 is fusion-spliced with the input port of the fiber coupler 115 of the feedback module, and the output coupling ratio of the fiber coupler 115 is 99. The output fiber of 1% of the feedback module optical fiber coupler 115 is welded with the input fiber of the online polarization independent isolator 117, and the output fiber of the online polarization independent isolator 117 is welded with the other input port of the optical fiber coupler 108 of the beam splitting module to form a closed loop feedback structure for unidirectional transmission. The ring feedback coupling enables the mode with low loss to oscillate, and the functions of self-organizing filtering and mode selection are realized, so that phase locking is realized, namely the phases of all amplification ring cavities are synchronous, and coherent superposition is realized at the junction of pulse laser output by each path of amplifier (the optical fiber coupler 114 of the beam combination module); 99% of the output fibers of the feedback module fiber coupler 115 are fused with the input fibers of the QBH output optical cable 116 of the output module, and the combined pulse laser is output at the output end of the QBH output optical cable 116.

The injection pulse repetition frequency is 30kHz, the pulse width is 100ns, the average power is 5W, and the waveform is square wave.

The in-line polarization independent isolator 117 withstands up to a power of 30W.

The

active fibers

105, 112 are double-clad ytterbium-doped fibers with a core/outer cladding diameter of 30 μm/250 μm.

The maximum output power of the laser diode 110 is 70W, the output wavelength is 975nm, and two paths of the amplifying modules are driven by the same power supply.

The types, batches and tail fiber lengths of all paths of amplifiers of the amplifying module are kept consistent.

The output pulse repetition frequency of the coherent beam combination laser system is 30kHz, the pulse width is 100ns, the average power is 100W, and the waveform is a square wave.

In this embodiment, the amplification module may also include 3 amplifiers connected in parallel. At this time, the other parts of the invention are not changed, the fiber coupler 108 of the beam splitting module is changed into a 2 × 3 coupler, and the output coupling ratio is 1; the fiber coupler 114 of the beam combining module is changed into a 3 × 1 structure, and the input coupling ratio is 1.

The output coupling ratio of the feedback module fiber coupler 115 of this embodiment can also be set to 9, that is, 10% of the output fibers of the fiber coupler 115 are fused with the input fibers of the online polarization-independent isolator 117, and 90% of the output fibers are fused with the input fibers of the QBH output optical cable 116 of the output module. The active fibers of the pre-amplifier module and the amplifying module of the embodiment can also be erbium-doped fibers, and the diameters of the fiber cores/outer claddings are 30 μm/250 μm,20 μm/400 μm or 50 μm/400 μm, etc.

The output pulse width range of the pulse laser of the pulse injection module of the embodiment is 100 ns-500 mus, the repetition frequency is 1 kHz-4 MHz, and the waveform type is not limited.

Example 2:

the output of the pulse laser 201 is fused with the input of the in-line polarization-independent isolator 202, and is coupled into the feedback module through 50% of the input port of the 2 × 1 fiber coupler 203. The output fiber of the optical fiber coupler 203 is fused with the signal input fiber of the pump beam combiner 205 of the pre-amplifier module, the laser diode 204 of the pre-amplifier module is coupled into the active optical fiber 206 through the pump input fiber of the pump beam combiner 205 so as to realize the pre-amplification of the injection pulse, the output fiber of the active optical fiber 206 is fused with the input fiber of the cladding light filter 207, the cladding light filter 207 filters the residual pump light to protect the device behind the pre-amplifier module, and the online polarization-independent isolator 208 isolates the reverse transmission light to protect the pre-amplifier module and simultaneously ensures the unidirectional transmission of the annular feedback cavity. It can be seen that the pre-amplifier module is located within the feedback module. The outgoing fiber of the online polarization-independent isolator 208 of the pre-amplifier module is welded with the single-port incoming fiber of the fiber coupler 209 of the beam splitting module to realize the beam splitting of the pulse laser. In this embodiment, the amplifying module includes 2 parallel amplifiers, the fiber coupler 209 of the splitting module is a 1 × 2 coupler, and the output coupling ratio is 1 (i.e., equal proportion), so as to ensure that the pulsed light entering each amplifier of the amplifying module after beam splitting is of equal power, and the outgoing fibers are respectively fused with the incoming fibers of the optical variable delay line 210 of the amplifying module. The optically variable delay line 210 is used to fine tune the cavity length of each amplifier to compensate for process induced cavity length differences, where the process ensures that the cavity lengths of the amplifiers are nearly equal. The optical variable delay line 109 controls the cavity length difference Δ L of each amplifier to be 5.7 mm-10 mm. The laser diode 211 is coupled into the active fiber 213 through the pump beam combiner 212 to realize pulse amplification, the output fiber of the active fiber 213 is fused with the input fiber of the cladding light filter 214, and the cladding light filter 214 filters the residual pump light to protect the device after the amplification module. The fiber coupler 215 of the beam combining module is of a 2 × 1 structure, the input coupling ratio is 1 (namely equal proportion), and coherent superposition is realized at the input coupling ratio where the output pulses of each path of amplifier are output; the output fiber of the fiber coupler 215 is welded with the input port of the fiber coupler 216 of the feedback module, the output coupling ratio of the fiber coupler 216 is 99, 1% of the output fibers of the fiber coupler 216 of the feedback module are welded with 50% of the input port of the fiber coupler 203, and the output fibers are welded with the input port of the pre-amplifier module and the beam combining module to form a closed annular feedback structure. The ring feedback coupling enables the mode with low loss to oscillate, and the functions of self-organizing filtering and mode selection are realized, so that phase locking is realized, namely the phases of all the amplifying ring cavities are synchronized, and coherent superposition is realized at the junction of the pulse lasers output by all the amplifiers (the optical fiber coupler 215 of the beam combining module). 99% of output ports of the feedback module optical fiber coupler 216 are in fiber fusion with the QBH output optical cable 217 of the output module, and the output end of the QBH output optical cable 217 outputs the combined pulse laser.

The injection pulse repetition frequency is 200kHz, the pulse width is 200ns, the average power is 20W, and the waveform is Gaussian.

The in-line polarization independent isolator 208 withstands up to 60W of power.

The active fiber 206 is a double-clad ytterbium-doped fiber with a core/outer cladding diameter of 30 μm/250 μm, and the active fiber 213 is a double-clad ytterbium-doped fiber with a core/outer cladding diameter of 50 μm/400 μm.

The laser diode 211 has the maximum output power of 140W and the output wavelength of 975nm, and the two amplifying modules are driven by the same power supply.

The output pulse repetition frequency of the coherent beam combination laser system is 200kHz, the pulse width is 220ns, the average power is 200W, and the waveform is Gaussian.

The type, batch and tail fiber length of each path of amplifier similar type device of the amplification module are kept consistent. In this embodiment, the amplifying module may also include 3 parallel amplifiers. At this time, the other parts of the present invention are not changed, the fiber coupler 209 of the beam splitting module is changed to 1 × 3 coupler, and the output coupling ratio is 1; the fiber coupler 215 of the beam combining module is changed into a 3 × 1 structure, and the input coupling ratio is 1.

The output coupling ratio of the feedback module fiber coupler 216 of this embodiment may also be set to 9, that is, 10% of the output fibers of the fiber coupler 216 are fused to 50% of the input ports of the fiber coupler 203, and 90% of the output fibers are fused to the input fibers of the QBH output optical cable 217 of the output module.

The active fibers of the pre-amplifier module and the amplifying module of the embodiment can also be erbium-doped fibers, and the diameters of the fiber cores/outer claddings are 30 μm/250 μm,20 μm/400 μm or 50 μm/400 μm, etc.

The foregoing description is provided to illustrate and explain the present invention and should not be used to limit the present invention. Without departing from the principle of the invention, several modifications and variations of the invention are within the scope of the invention. Such as: when the amplifying module comprises a plurality of paths of amplifiers connected in parallel, the ports of the corresponding beam splitting and combining modules are increased; the amplification stages of the pre-amplifier and each amplifier are 1 stage or more.

Claims

1. A pulse injection type coherent beam combination laser system based on an annular feedback structure comprises: pulse injection module, put module, beam splitting module, amplification module, beam combination module, feedback module and output module in advance, its characterized in that: the beam splitting module, the amplifying module and the beam combining module are sequentially connected, and the feedback module connects the input end of the beam splitting module with the output end of the beam combining module to form a closed annular feedback structure;

the pulse injection module comprises a pulse laser and a first online polarization-independent isolator, wherein the injection pulse repetition frequency of the pulse injection module is 30kHz, the pulse width is 100ns, the average power is 5W, and the waveform is square wave;

the pre-amplifier module comprises a first laser, a first pump beam combiner, a first active optical fiber, a second online polarization-independent isolator and a first cladding optical filter, wherein the first laser is a first laser diode, the first laser diode of the pre-amplifier module is coupled into the first active optical fiber through the first pump beam combiner so as to realize pre-amplification of an injection pulse, an output fiber of the first active optical fiber is fused with an input fiber of the first cladding optical filter, the first cladding optical filter filters residual pump light so as to protect devices behind the pre-amplifier module, and the second online polarization-independent isolator isolates a reverse transmission light protection pre-amplifier module;

the beam splitting module comprises a first optical fiber coupler, the first optical fiber coupler is a 2 x 2 coupler, the input coupling ratio is 1, one input port is welded with the output fiber of the second online polarization-independent isolator of the pre-amplifier module, the other input port is welded with the output fiber of the third online polarization-independent isolator of the feedback module to form a closed annular feedback structure for unidirectional transmission, and the output fibers are respectively welded with the optical variable delay line input fibers of the amplifier module;

the amplification module comprises at least 2 amplifiers connected in parallel, each amplifier comprises an optical variable delay line, a second laser, a second pumping beam combiner, a second active optical fiber and a second cladding light filter, the second laser is a second laser tube, a second laser diode is coupled into the second active optical fiber through the second pumping beam combiner so as to realize pulse amplification, the output fiber of the second active optical fiber is fused with the input fiber of the second cladding light filter, and the second cladding light filter filters residual pumping light so as to protect devices behind the amplification module;

the beam combining module comprises a second optical fiber coupler which is of a 2 x 1 structure, and the input coupling ratio is 1;

the feedback module comprises a third optical fiber coupler and a third online polarization-independent isolator, an output optical fiber of the second optical fiber coupler is welded with an input port of the third optical fiber coupler of the feedback module, the output coupling ratio of the third optical fiber coupler is 99, 1% of output fibers of the third optical fiber coupler of the feedback module are welded with input fibers of the third online polarization-independent isolator, and the output fibers of the third online polarization-independent isolator are welded with the other input port of the first optical fiber coupler of the beam splitting module to form a closed loop feedback structure for unidirectional transmission; the phases of the amplifying ring cavities are synchronous, so that coherent superposition is realized at the optical fiber coupler of the beam combining module); 99% of output fibers of the third optical fiber coupler of the feedback module are fused with input fibers of a QBH output optical cable of the output module, and the output end of the QBH output optical cable outputs combined pulse laser;

the optical variable delay line of the amplification module controls the cavity length difference delta L of each path of amplifier to be 5.7 mm-10mm, the active optical fiber length of the pre-amplification module and/or the amplification module is 1.5m, the length difference of tail fibers of the same type of devices of each path of amplifier of the amplification module is not more than 0.5mm, and the total length difference of all devices of each path of amplifier of the amplification module in the welding process is not more than 5mm.

2. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the pulse injection module, the pre-discharge module, the annular feedback structure and the output module are sequentially connected.

3. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the third in-line polarization independent isolator withstands up to 30W of power.

4. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the first and second active fibers are double-clad ytterbium-doped fibers with a core/outer cladding diameter of 30/250 μm.

5. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the maximum output power of the second laser diode is 70W, the output wavelength is 975nm, and the two paths of amplification modules are driven by the same power supply.

6. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the types, batches and tail fiber lengths of all paths of amplifiers of the amplifying module are consistent.

7. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the number of the output ends of the beam splitting module optical fiber couplers and the number of the input ends of the beam combining module optical fiber couplers are at least 2 respectively, and the output coupling ratio of the beam splitting module optical fiber couplers and the input coupling ratio of the beam combining module optical fiber couplers are in equal proportion.

8. The pulsed injection coherent beam combination laser system based on the ring feedback structure of claim 1, wherein: the output pulse repetition frequency of the coherent beam combination laser system is 30kHz, the pulse width is 100ns, the average power is 100W, and the waveform is square wave.