CN111193167A - Fractal-based coherent fiber laser array and generation system thereof - Google Patents

Fractal-based coherent fiber laser array and generation system thereof Download PDF

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Publication number
CN111193167A
CN111193167A CN202010148390.2A CN202010148390A CN111193167A CN 111193167 A CN111193167 A CN 111193167A CN 202010148390 A CN202010148390 A CN 202010148390A CN 111193167 A CN111193167 A CN 111193167A
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array
fractal
laser
beams
light
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周朴
侯天悦
马鹏飞
安毅
来文昌
常洪祥
龙金虎
张雨秋
黄龙
宋家鑫
黄良金
李�灿
吴坚
姜曼
粟荣涛
马阎星
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National University of Defense Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2316—Cascaded amplifiers
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/0994—Fibers, light pipes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0071—Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0085—Modulating the output, i.e. the laser beam is modulated outside the laser cavity

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Abstract

The coherent fiber laser array comprises N circles of light beams which are annularly arranged from inside to outside around the center of an array fiber, each circle of light beam comprises the same number of sub-light beams, and each sub-light beam in the same circle of light beam has the same optical parameter and is uniformly arranged along an angular direction. At least two or more continuous light beams in the N circles of light beams form a fractal arrangement laser array; in any two adjacent circles of light beams in the fractal distribution laser array, the beam waist radius, the beam caliber and the distance between the beam center and the array fiber center of each sub-light beam in the circle of light beams close to the inner side are reduced in equal ratio to the beam waist radius, the beam caliber and the distance between the beam center and the array fiber center of each sub-light beam in the circle of light beams close to the outer side. The invention can expand the array filling mode of the system and improve the optical parameter regulation and control capability of the laser array, thereby improving the synthesis efficiency and the mode purity of the structured light generated by the coherent fiber laser array.

Description

Fractal-based coherent fiber laser array and generation system thereof
Technical Field
The invention relates to the technical field of coherent synthesis of fiber laser, in particular to a coherent fiber laser array based on fractal and a generating system thereof.
Background
The fiber laser coherent synthesis is one of the important methods for obtaining high-brightness laser coherent synthesis, has wide application prospects in the fields of space optical communication, scientific research, national defense and the like, and is a research hotspot in the current laser technical field. The coherent synthesis of the fiber laser is an effective way to realize the laser output with high average power and high beam quality, and has wide application prospect in the fields of medical treatment and health, industrial processing, scientific research, national defense safety and the like. In recent years, with the rapid development of laser technology, not only high-power laser is required in the fields of long-distance space optical communication, nonlinear frequency conversion, laser ablation, material processing and the like, but also further requirements are provided for the amplitude, phase and polarization state space structures of optical fields, such as vortex beams, column vector beams, non-diffraction beams and the like, the optical fields with special space structures of optical parameters are collectively called as structure optical fields, and the coherent synthesis of fiber laser arrays also provides an effective technical approach for generating high-power structured light.
In the fiber laser array coherent combining technology, the construction of array beams directly influences the coherent combining effect. In the prior art, a regular hexagon or circular arrangement mode is generally adopted, the calibers of all light beams are the same, and the distances between adjacent light beams are consistent and are unit distances R. Referring to fig. 1, taking a circular uniformly-arranged laser array as an example, a circle of light beams in the uniformly-arranged laser array, which is the innermost circle of light beams, is a circle of light beams from inside to outside, and the circle of light beams is a circle of light beams 1, a circle of light beams 2 …. The existing uniform array beam construction method is as shown in fig. 1, firstly constructing a unit beam at the origin of a cartesian coordinate system with a beam waist radius of w0The wavelength is lambda, the aperture of the light beam is d, then N circles of annularly arranged light beams are sequentially constructed from inside to outside, wherein the Nth circle comprises 6N sub-light beams which are the same as the unit light beam at the origin, all the sub-light beams are uniformly arranged along the angular direction, namely, one sub-light beam is arranged at intervals of pi/3N from 0 to 2 pi, and the distance between the center of each sub-light beam and the origin of the Nth circle is RNR is unit spacing. The circular laser array including N circles of circularly arranged beams constructed according to the method of fig. 1 has a total aperture D1: d1＝2NR+d。
However, the existing array beam construction method limits the filling mode of the array beam in the field of traditional coherent synthesis, so that the side lobe of the synthesized beam is difficult to further eliminate, and the improvement of the energy concentration degree of the synthesized beam is influenced. The problem is more obvious in the field of high-power structured light generated by a fiber laser array, for example, vortex beams are generated, the side lobe of a synthesized beam is difficult to further eliminate by the existing array beam construction method, so that the limitation of power improvement is influenced, and the mode purity of the generated vortex beams is influenced. Therefore, the existing array beam construction method brings difficulty to further optimization of the fiber laser array coherent combination system.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a fractal-based coherent fiber laser array and a generating system thereof, by adopting the fractal-based coherent fiber laser array, the array filling mode of the system can be expanded, and the optical parameter regulation and control capability of the laser array can be improved, so that the synthesis efficiency of the coherent fiber laser array for generating structured light and the mode purity of the generated structured light can be improved.
In order to achieve the technical purpose, the invention adopts the following specific technical scheme:
the fractal-based coherent fiber laser array comprises N circles of light beams which are annularly arranged around the center of the array fiber from inside to outside, wherein each circle of light beam comprises the same number of sub-light beams, and each sub-light beam in the same circle of light beam has the same optical parameter and is uniformly arranged along an angular direction.
At least two or more continuous light beams in the N circles of light beams form a fractal arrangement laser array; in any two adjacent circles of light beams in the fractal arrangement laser array, the beam waist radius, the beam caliber and the distance between the beam center and the array optical fiber center of each sub-light beam in the circle of light beams close to the inner side are reduced in equal ratio relative to the beam waist radius, the beam caliber and the distance between the beam center and the array optical fiber center of each sub-light beam in the circle of light beams close to the outer side, wherein the equal ratio of reduction is t, and t is more than 0.
Furthermore, the 1 st circle of light beam in the fractal distribution laser array is the outermost circle of light beam, and the 1 st circle of light beam and the 2 nd circle of light beam … are sequentially arranged from outside to inside. The proportion t of geometric scale reduction of any adjacent n-1 th light beam and n-th light beam in the fractal arrangement laser array is not more than rn/rn-1Wherein r isn-1Is the distance between the beam center of each sub-beam in the n-1 th beam and the center of the array fiber, rnThe distance between the beam center of each sub-beam in the nth beam and the center of the array fiber.
Further, in the present invention, rnAnd rn-1And the geometric series general formula is satisfied.
Furthermore, the invention also comprises a uniformly distributed laser array, wherein at least two or more continuous circles of light beams in the N circles of light beams form the uniformly distributed laser array.
Further, in the invention, the beam waist radii of all the sub-beams in the uniformly arranged laser array are w0The wavelengths are lambda, the beam apertures are d, and the distances between adjacent rings of beams in the uniformly distributed laser array are the same.
Further, in the invention, the fractal arrangement laser arrays and the uniform arrangement laser arrays are alternately arranged.
Furthermore, in the invention, the coherent fiber laser array is arranged in a regular hexagon or a circle.
In another aspect, the present invention provides a method for generating a coherent fiber laser array based on fractal, including:
generating a laser beam;
amplifying the generated laser beam;
expanding the amplified laser beams to generate multiple paths of laser beams and amplifying the generated multiple paths of laser beams;
carrying out phase regulation and control on each path of amplified laser beams;
a plurality of fiber laser collimators are spliced in a fractal arrangement mode to form a fractal-based beam collimator array, each path of light beam after phase regulation corresponds to one fiber laser collimator in the beam collimator array one by one, each path of light beam after phase regulation is emitted through the beam collimator array, beam expansion and collimation of laser from fiber waveguide to free space light beam are realized, and meanwhile, splicing of the fractal-based coherent fiber laser array light beam is realized.
The invention provides a coherent fiber laser array generating system based on fractal, which can generate any coherent fiber laser array based on fractal.
Furthermore, the invention provides a fractal-based coherent fiber laser array generation system, which comprises a seed source, a pre-amplification module, a beam splitter module, a cascade amplification module, a phase modulator array and a collimation and beam combination module. The seed source is used for generating laser beams, the laser beams output by the seed source seeds are amplified through the pre-amplification module and then enter the beam splitter module for beam expansion, and multiple paths of laser beams are generated; and the multi-path laser beams split by the beam splitter module are amplified by the cascade amplification module, and the amplified laser beams are injected into the phase modulator array for phase regulation and control. And each path of laser beam regulated and controlled by the phase modulator array is output to a collimation and beam combination module, and each path of laser beam is collimated and output by the collimation and beam combination module and spliced into a coherent fiber laser array beam based on fractal. The collimating and beam combining module comprises a plurality of fiber laser collimators, each path of laser beam corresponds to one fiber laser collimator, the fiber laser collimators of multiple paths of beams are spliced in a fractal arrangement mode (namely the fiber laser collimators are arranged according to the arrangement mode of the corresponding fractal arrangement laser arrays) to form a fractal-based beam collimator array, and the beam is emitted through the beam collimator array, so that beam expansion and collimation of laser from a fiber waveguide to a free space beam can be realized, and meanwhile, splicing of the fractal-based coherent fiber laser array beam can be realized. Further, the device also comprises a composite beam processing module, a photoelectric detection module and a control system; part of light beams of the coherent fiber laser array light beam based on fractal output by the collimation and beam combination module after passing through the combined light beam processing module are incident to the photoelectric detection module. The photoelectric detection module converts the received optical signals into electric signals and transmits the electric signals to the control system. The control system generates a phase control signal according to the received electric signal and transmits the phase control signal to the phase modulator array, so that the locking and the regulation of the phase between each path of light beam are realized. The synthetic light beam processing module consists of a high reflector, a focusing lens and a beam splitter and has the functions of extracting light field information of the synthetic light beam and observing light intensity distribution of the synthetic light beam. The light beams output by the collimation and beam combination module pass through the high reflector, the high reflector reflects most energy light beams and transmits the energy light beams in a free space, the light beams containing a small part of energy are transmitted, the transmitted light beams containing the small part of energy pass through the focusing lens and then are split by the beam splitter, one part of light beams are focused to the photoelectric detector for extracting light field information, and the other part of light beams are focused to the light spot analyzer for observing the light intensity distribution of the combined light beams.
The invention has the following beneficial effects:
1. the invention ensures that the number of the sub-beams in each circle of annularly arranged beams is consistent, and solves the defect of low purity of vortex beams generated by the conventional uniform array beam construction method.
2. Compared with the laser array which is uniformly distributed, the invention can be filled with more paths of sub-beams in the same caliber, and has the potential of improving power.
3. The fractal array laser array is compatible with the uniform array laser array, can be combined with the uniform array laser array, and flexibly regulates and controls the light beam optical field distribution of the emitting area array in practical engineering application.
Drawings
FIG. 1 is a schematic view of a circular array beam;
FIG. 2 is a schematic structural view of embodiment 1 of the present invention;
FIG. 3 is a schematic structural view of example 2 of the present invention;
FIG. 4 is a schematic structural diagram of embodiment 3 of the present invention;
fig. 5 is a light intensity distribution and phase distribution diagram of two circles of array light beams in uniform annular arrangement, one circle of array light beams in uniform annular arrangement and two circles of array light beams in fractal annular arrangement;
FIG. 6 is a focal plane light intensity distribution diagram of two circles of uniformly annularly arranged array light beams, one circle of uniformly annularly arranged array light beams and two circles of fractal annularly arranged array light beams;
fig. 7 is an OAM mode spectrum distribution diagram of focal planes of two circles of array beams uniformly and annularly arranged, one circle of array beams uniformly and annularly arranged, and two circles of fractal array beams annularly arranged.
Fig. 8 is an OAM mode spectrum distribution diagram of an effective part of a vortex light beam generated by two circles of array light beams uniformly and annularly arranged, one circle of array light beams uniformly and annularly arranged, and two circles of fractal array light beams focal planes.
Fig. 9 is a schematic structural diagram of a fractal-based coherent fiber laser array generation system according to an embodiment of the present invention.
Fig. 10 is a schematic structural diagram of a fractal-based coherent fiber laser array generation system according to an embodiment of the present invention.
Detailed Description
In order to make the technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Referring to fig. 2, fig. 2 is a schematic structural diagram of embodiment 1 of the present invention. A coherent fiber laser array based on fractal is distributed in the center, namely the center of an array fiber, and comprises N circles of light beams which are annularly distributed around the center of the array fiber from inside to outside, wherein each circle of light beam comprises the same number of sub-light beams, and each sub-light beam in the same circle of light beam has the same optical parameter and is uniformly distributed along the angular direction.
In the embodiment shown in fig. 2, N circles of light beams form a fractal arrangement laser array; in any two adjacent circles of light beams in the fractal arrangement laser array, the beam waist radius, the beam caliber and the distance between the beam center and the array optical fiber center of each sub-light beam in the circle of light beams close to the inner side are reduced in equal ratio relative to the beam waist radius, the beam caliber and the distance between the beam center and the array optical fiber center of each sub-light beam in the circle of light beams close to the outer side, wherein the equal ratio of reduction is t, and t is more than 0. In this embodiment, a circular fractal arrangement laser array of N circles of light beams is constructed according to the schematic diagram of circular uniformly arranged array light beams shown in fig. 1. According to the distance R between the center of the Nth circle of sub-beams and the origin in FIG. 1NAnd the distance R between the center of the N-1 th circle sub-beam and the originN-1Determining the fractal ratio t-R of the coherent fiber laser array based on fractal in the embodimentN-1/RNDue to RNThe proportional scaling of the geometric reduction in this example is calculated as t ═ NR (N-1)/N.
In the embodiment shown in fig. 2, the 1 st circle of light beams of the fractal distribution laser array is the outermost circle of light beams, and the 1 st circle and the 2 nd circle of light beams … are sequentially arranged from outside to inside. Each circle of light beams comprises 6N sub-light beams, and each sub-light beam in each circle of light beams is uniformly distributed along the angle direction, namely, one sub-light beam is distributed at intervals of pi/3N from 0 to 2 pi.
Given a unit interval R, the beam waist radius of each sub-beam in the 1 st circle of beams is set as w0The aperture of the light beam is d, and the distance between the center of each sub-light beam in the 1 st circle of light beam and the center of the array fiber is r1NR. The beam waist radius w of each sub-beam of the nth beam in the fractal arrangement laser arraynDiameter of light beam dnAnd the distance r between the center of each sub-beam and the center of the array fibernAre each tn- 1w0，tn-1d and tn-1NR。
Then, the center-to-center distance between the n +1 th circle sub-beam and the n th circle sub-beam at the same angular position is:
Figure BDA0002401571690000081
it can be seen that the center-to-center distances of the sub-beams in the n +1 th circle of beams at the same angular position and the sub-beams in the n th circle of beams satisfy the geometric progression general expression. In a coherent fiber laser array based on fractal, a circularly arranged laser array comprising n circles of annularly arranged light beams has a total caliber D when n approaches infinity2The calculation can be based on the superposition of the distances between the centers of the sub-beams at the same angular position in adjacent turns, as follows:
Figure BDA0002401571690000082
it can be seen that FIG. 2 showsThe total caliber D is obtained by corresponding calculation in the embodiment 12＝2r1And + d is 2NR + d, which is the same as the total aperture of the circularly uniformly arranged array beam shown in fig. 1. Therefore, when N approaches infinity, the sub-beams will cover the whole caliber and the number of the sub-beams (6N) of the circularly arranged laser array comprising N circles of annularly arranged beams constructed by the construction method of the fractal-based coherent fiber laser arraynApproaching infinity.
The laser array transmitting surface optical field distribution constructed according to the fractal-based coherent fiber laser array construction method is as follows:
Figure BDA0002401571690000083
wherein the content of the first and second substances,
Figure BDA0002401571690000091
x, y are the abscissa and ordinate of the emitting surface in the cartesian coordinate system, z is the transmission distance of the array beam, and k represents the ordinal number of each term in the summation formula.
The fractal-arranged laser array and the uniformly-arranged laser array in the fractal-based coherent fiber laser array can be compatible, and the laser array can be constructed by combining two modes of the fractal-arranged laser array and the uniformly-arranged laser array according to actual engineering requirements. For example, under the application requirements of limited synthetic path number and determined synthetic aperture, the fractal number of turns n of the fractal-arranged laser array can be determined firstlymaxConstructing fractal arrangement laser array, and then using nth ordermaxAnd constructing a uniformly-arranged laser array comprising the single-path light beam at the origin position and the N-1 circle of annular sub-light beams in the unfilled aperture by taking the parameters of the circle of sub-light beams as a reference. As shown in fig. 3, refer to fig. 3, which is a schematic structural diagram of embodiment 2 of the present invention. A coherent fiber laser array based on fractal comprises a laser array and a laser array, wherein the laser array is uniformly distributed, and the laser array is arranged outside the fractal array. Firstly, constructing unit beams and units at the origin of a Cartesian coordinate systemBeam waist radius of the beam is w0The wavelength is lambda, the aperture of the light beam is d, then an evenly-distributed laser array formed by n circles of annularly-distributed light beams is sequentially constructed from inside to outside, the nth circle of light beam is used as the outermost circle of light beam of the evenly-distributed laser array, and meanwhile, the nth circle of light beam is also the first circle of light beam of the fractal-distributed laser array. And a plurality of circles of light beams which are annularly arranged outwards from the nth circle form a fractal arrangement laser array.
FIG. 4 is a schematic structural diagram of embodiment 3 of the present invention; a coherent fiber laser array based on fractal comprises a uniformly distributed laser array and a fractal distributed laser array. Under the application requirements of limited synthetic path number and determined synthetic aperture, the array fiber can be constructed in an array fiber arrangement mode of uniformly arranging laser arrays inside and fractal-arranged laser arrays outside. The array fiber can also be constructed by adopting an array fiber arrangement mode of uniformly arranging the laser arrays inside and outside the fractal arrangement laser arrays. For different requirements in practical engineering application, the arrangement and construction of the array optical fiber can be realized by adopting a mode of alternately arranging the laser arrays with uniform arrangement and the laser arrays with fractal arrangement, as shown in fig. 4.
The following is a calculation example of the present invention to further describe the technical effects of the present invention:
to generate a vortex beam with a topological charge number of 3, a uniform circular array comprising 2 turns, N, was constructed according to the present uniformly arrayed laser array construction shown in fig. 1, wherein: the parameters of the optical fiber laser aperture-dividing coherent synthesis system are the number of array units 19 and the waist radius w of the laser beam0The diameter d of the light beam is 23mm, the unit distance R is 25mm, and the working wavelength lambda of the laser is 1064 nm. On the basis, two circles of array beams uniformly and annularly arranged can be obtained by removing the unit beams at the origin, and the light intensity distribution and the phase distribution of the array beams are shown in the accompanying fig. 5(a) and fig. 5 (d); the unit light beam at the origin and the first 6 unit light beams arranged in a ring shape are removed to obtain a ring of array light beams arranged in a uniform ring shape, and the light intensity distribution and the phase distribution of the array light beams are shown in the accompanying fig. 5(b) and fig. 5 (e); removing the unit light beam at the origin and the first 6-path annularly-arranged unit light beams, and constructing by using the fractal-based coherent fiber laser arrayBy the method, 2-turn fractal ring array light beams can be obtained, and the light intensity distribution and the phase distribution of the fractal ring array light beams are shown in the attached fig. 5(c) and the attached fig. 5 (f).
By placing a lens with a focal length of 20m behind the array beam, the far field characteristics of the array beam can be studied at the lens focal plane. And (3) obtaining the light field distribution of the array light beam transmitted to the lens focal plane through the lens by using an angular spectrum transmission method through numerical simulation. The light intensity distribution of the two circles of array light beams which are uniformly and annularly arranged, the light intensity distribution of the one circle of array light beams which are uniformly and annularly arranged and the two circles of array light beams which are fractal and annularly arranged on the focal plane of the lens are shown in the attached drawings 6(a), 6(b) and 6 (c). The calculation result shows that compared with two circles of array beams which are uniformly and annularly arranged and one circle of array beams which are uniformly and annularly arranged, the light energy distribution of the vortex light beams generated by the two circles of fractal and annularly arranged array beams on the focal plane of the lens is more concentrated. A first-order bright ring for generating a structured light field, namely an effective part for generating a vortex light beam, can be collected in a circular area with the focus as the center and the diameter of 0.95mm on the focal plane of the lens. Further calculation results show that for two circles of uniformly and annularly arranged array light beams, one circle of uniformly and annularly arranged array light beams and two circles of fractal and annularly arranged array light beams, the ratio of the first-order bright ring power for generating a structural light field collected in a circular area is 0.482, 0.427 and 0.501.
The OAM mode spectrum distribution of one circle of uniform annularly arranged array beams and two circles of fractal annularly arranged array beams at the lens focal plane is shown in fig. 7(a), fig. 7(b), and fig. 7 (c). The calculation result shows that the OAM +3 mode intensity ratio of the two circles of the array light beams which are uniformly and annularly arranged, the one circle of the array light beams which are uniformly and annularly arranged and the two circles of the fractal and annularly arranged array light beams which are transmitted to the lens focal plane optical field distribution is 0.617, 0.681 and 0.681, and the main factor influencing the OAM mode spectrum distribution is the density degree of the innermost circle array of the array light beams which are angularly arranged.
The OAM mode spectrum distribution of the effective part of the vortex optical beam generated by one circle of uniform circular array beam and two circles of fractal circular array beam at the lens focal plane is shown in fig. 8(a), fig. 8(b), and fig. 8 (c). The calculation result shows that the OAM +3 mode intensity ratio of the effective part of the two circles of uniform annular arrangement array light beams, the one circle of uniform annular arrangement array light beams and the two circles of fractal annular arrangement array light beams which are transmitted to the focal plane of the lens to generate the vortex light beams is 0.907, 0.995 and 0.997, and the OAM +3 mode intensity ratio of the effective part of the two circles of fractal annular arrangement array light beams distributed in the focal plane light field and the OAM +3 mode intensity ratio of the effective part of the vortex light beams have advantages.
Referring to fig. 9, the present embodiment provides a fractal-based coherent fiber laser array generation system, which includes a seed source, a pre-amplification module, a beam splitter module, a cascade amplification module, a phase modulator array, and a collimation and beam combination module. The seed source is used for generating laser beams, the laser beams output by the seed source seeds are amplified through the pre-amplification module and then enter the beam splitter module for beam expansion, and multiple paths of laser beams are generated; and the multi-path laser beams split by the beam splitter module are amplified by the cascade amplification module, and the amplified laser beams are injected into the phase modulator array for phase regulation and control. And each path of laser beam regulated and controlled by the phase modulator array is output to a collimation and beam combination module, and each path of laser beam is collimated and output by the collimation and beam combination module and spliced into a coherent fiber laser array beam based on fractal. The collimating and beam combining module comprises a plurality of fiber laser collimators, each path of laser beam corresponds to one fiber laser collimator, the fiber laser collimators of multiple paths of beams are spliced in a fractal arrangement mode (namely the fiber laser collimators are arranged according to the arrangement mode of the corresponding fractal arrangement laser arrays) to form a fractal-based beam collimator array, and the beam is emitted through the beam collimator array, so that beam expansion and collimation of laser from a fiber waveguide to a free space beam can be realized, and meanwhile, splicing of the fractal-based coherent fiber laser array beam can be realized.
Referring to fig. 10, the present embodiment provides a coherent fiber laser array generation system based on fractal, which includes a seed source, a pre-amplification module, a beam splitter module, a cascade amplification module, a phase modulator array, a collimation and beam combination module, a combined light beam processing module, a photoelectric detection module, and a control system. The seed source is used for generating laser beams, the laser beams output by the seed source seeds are amplified through the pre-amplification module and then enter the beam splitter module for beam expansion, and multiple paths of laser beams are generated; and the multi-path laser beams split by the beam splitter module are amplified by the cascade amplification module, and the amplified laser beams are injected into the phase modulator array for phase regulation and control. And each path of laser beam regulated and controlled by the phase modulator array is output to a collimation and beam combination module, and each path of laser beam is collimated and output by the collimation and beam combination module and spliced into a coherent fiber laser array beam based on fractal. And transmitting the coherent fiber laser array beam based on fractal to a far field to form an interference light spot. Part of light beams of the coherent fiber laser array light beam based on fractal output by the collimation and beam combination module after passing through the combined light beam processing module are incident to the photoelectric detection module. The photoelectric detection module converts the received optical signals into electric signals and transmits the electric signals to the control system. The control system generates a phase control signal according to the received electric signal and transmits the phase control signal to the phase modulator array, so that the locking and the regulation of the phase between each path of light beam are realized. The synthetic light beam processing module consists of a high reflector, a focusing lens and a beam splitter and has the functions of extracting light field information of the synthetic light beam and observing light intensity distribution of the synthetic light beam. The light beams output by the collimation and beam combination module pass through the high reflector, the high reflector reflects most energy light beams and transmits the energy light beams in a free space, the light beams containing a small part of energy are transmitted, the transmitted light beams containing the small part of energy pass through the focusing lens and then are split by the beam splitter, one part of light beams are focused to the photoelectric detector for extracting light field information, and the other part of light beams are focused to the light spot analyzer for observing the light intensity distribution of the combined light beams.
In summary, although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.

Claims (10)

1. The fractal-based coherent fiber laser array is characterized in that: the coherent fiber laser array is distributed in the center, namely the center of the array fiber, and comprises N circles of light beams which are annularly distributed from inside to outside around the center of the array fiber, wherein each circle of light beam comprises the same number of sub-light beams, and each sub-light beam in the same circle of light beam has the same optical parameter and is uniformly distributed along the angular direction;
at least two or more continuous light beams in the N circles of light beams form a fractal arrangement laser array; in any two adjacent circles of light beams in the fractal arrangement laser array, the beam waist radius, the beam caliber and the distance between the beam center and the array optical fiber center of each sub-light beam in the circle of light beams close to the inner side are reduced in equal ratio relative to the beam waist radius, the beam caliber and the distance between the beam center and the array optical fiber center of each sub-light beam in the circle of light beams close to the outer side, wherein the equal ratio of reduction is t, and t is more than 0.
2. The fractal-based coherent fiber laser array of claim 1, wherein: the 1 st circle of light beam in the fractal arrangement laser array is the outermost circle of light beam, and the 1 st circle of light beam and the 2 nd circle of light beam … are sequentially arranged from outside to inside; the proportion t of geometric scale reduction of any adjacent n-1 th light beam and n-th light beam in the fractal arrangement laser array is not more than rn/rn-1Wherein r isn-1Is the distance between the beam center of each sub-beam in the n-1 th beam and the center of the array fiber, rnThe distance between the beam center of each sub-beam in the nth beam and the center of the array fiber.
3. The fractal-based coherent fiber laser array of claim 2, wherein: r isnAnd rn-1And the geometric series general formula is satisfied.
4. The fractal-based coherent fiber laser array according to claim 1, 2 or 3, wherein: the laser array is uniformly distributed, and the N circles of light beams have at least two or more continuous circles of light beams to form the uniformly distributed laser array.
5. The fractal-based coherent fiber laser array according to claim 4, wherein: the beam waist radii of all the sub-beams in the uniformly distributed laser array are w0The wavelengths are lambda, the beam apertures are d, and the distances between adjacent rings of beams in the uniformly distributed laser array are the same.
6. The fractal-based coherent fiber laser array according to claim 4, wherein: the fractal arrangement laser arrays and the uniform arrangement laser arrays are alternately arranged.
7. The fractal-based coherent fiber laser array according to claim 5, wherein: the coherent fiber laser array is arranged in a regular hexagon or a circle.
8. A method for generating a coherent fiber laser array based on fractal comprises the following steps:
generating a laser beam;
amplifying the generated laser beam;
expanding the amplified laser beams to generate multiple paths of laser beams and amplifying the generated multiple paths of laser beams;
carrying out phase regulation and control on each path of amplified laser beams;
a plurality of fiber laser collimators are spliced in a fractal arrangement mode to form a fractal-based beam collimator array, each path of light beam after phase regulation corresponds to one fiber laser collimator in the beam collimator array one by one, each path of light beam after phase regulation is emitted through the beam collimator array, beam expansion and collimation of laser from fiber waveguide to free space light beam are realized, and meanwhile, splicing of the fractal-based coherent fiber laser array light beam is realized. And splicing to form coherent fiber laser array beams based on fractal.
9. A coherent fiber laser array generation system based on fractal is characterized in that: the device comprises a seed source, a pre-amplification module, a beam splitter module, a cascade amplification module, a phase modulator array and a collimation and beam combination module; the seed source is used for generating laser beams, the laser beams output by the seed source seeds are amplified through the pre-amplification module and then enter the beam splitter module for beam expansion, and multiple paths of laser beams are generated; the multi-path laser beams split by the beam splitter module are amplified by the cascade amplification module, and the amplified laser beams are injected into the phase modulator array for phase regulation and control; and each path of laser beam regulated and controlled by the phase modulator array is output to a collimation and beam combination module, and each path of laser beam is collimated and output by the collimation and beam combination module and spliced into a coherent fiber laser array beam based on fractal.
10. The fractal-based coherent fiber laser array generation system according to claim 9, wherein: the device also comprises a composite light beam processing module, a photoelectric detection module and a control system; part of light beams of the coherent fiber laser array light beam based on fractal output by the collimation and beam combination module after passing through the combined light beam processing module are incident to the photoelectric detection module; the photoelectric detection module converts the received optical signal into an electric signal and transmits the electric signal to the control system; the control system generates a phase control signal according to the received electric signal and transmits the phase control signal to the phase modulator array, so that the locking and the regulation of the phase between each path of light beam are realized.
CN202010148390.2A 2020-03-05 2020-03-05 Fractal-based coherent fiber laser array and generation system thereof Pending CN111193167A (en)

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