CN116197524A - Optical phased array axial focus regulation and control method and system - Google Patents

Optical phased array axial focus regulation and control method and system Download PDF

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Publication number
CN116197524A
CN116197524A CN202310335557.XA CN202310335557A CN116197524A CN 116197524 A CN116197524 A CN 116197524A CN 202310335557 A CN202310335557 A CN 202310335557A CN 116197524 A CN116197524 A CN 116197524A
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laser
array
equivalent
focal length
lens
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张雨秋
常洪祥
殳博王
粟荣涛
冷进勇
吴坚
李�灿
姜曼
周朴
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National University of Defense Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
    • B23K26/046—Automatically focusing the laser beam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0643—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising mirrors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0648—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising lenses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/70—Auxiliary operations or equipment
    • B23K26/702—Auxiliary equipment

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Laser Beam Processing (AREA)

Abstract

The invention provides an optical phased array axial focus regulation and control method and system, which firstly compensates phase differences and phase noises among unit beams in array laser to control the phases among the unit beams to be consistent; determining the focal depth of the array laser on a processed workpiece; calculating expected array distribution of the array laser according to the expected equivalent focal length; and finally, applying the expected array distribution to the array laser, and changing the focusing position of the array laser on the processed workpiece. The invention has no mechanical moving part, can be suitable for high power output, improves the focal depth regulating and controlling speed, and can improve the processing efficiency of high power laser in application scenes such as industrial cutting and the like.

Description

Optical phased array axial focus regulation and control method and system
Technical Field
The invention mainly relates to the technical field of optical fiber laser coherent synthesis, in particular to an optical phased array axial focus regulation and control method and system.
Background
Fiber lasers have been widely used in laser cutting, welding, medical treatment, laser three-dimensional printing, and other fields. In certain specific applications, such as biomedical imaging, three-dimensional imaging, laser machining, etc., the axial focal position of the laser needs to be quickly adjustable. For example, in biomedical imaging applications, a rapidly adjustable depth of focus may disperse optical power along the optical axis to different focal points, thereby avoiding phototoxicity. In advanced manufacturing, when high-power laser is used for cutting thick metal, the adjustable focusing depth can enable the cutting surface to be smoother, and the processing efficiency is improved.
Zoom optical elements are typically based on principles of mechanical motion, electro-mechanical, refractive index gradients, and bragg diffraction. Conventional approaches use mechanical means to move the position of the lens to change the focus, which reduces the dynamic response of the optical system. Axial focus manipulation methods of non-mechanical or microelectromechanical systems have made it possible to shorten response times, including liquid crystal lenses, tunable acoustic gradient index lenses, deformable mirrors, and the like. The speed of these devices can be on the order of sub-milliseconds and microseconds. Although the methods have better performance, the method still has the limitations of element size, high-power heat absorption, alignment precision and the like in practical application. In addition, the output power of a monolithic fiber laser is limited due to nonlinear effects and mode instabilities, while laser processing requires more and more output power and flexibility of the fiber laser.
Therefore, a regulation and control method with rapid and adjustable axial focus, high power application, good thermal performance and convenient and accurate regulation is needed.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides an optical phased array axial focus regulation and control method and system.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
in one aspect, the present invention provides a method for adjusting and controlling an axial focus of an optical phased array, including:
compensating phase difference and phase noise among the unit light beams in the array laser to control the phases among the unit light beams to be consistent;
determining the focal depth of the array laser on a processed workpiece;
calculating expected array distribution of the array laser according to the expected equivalent focal length;
the desired array profile is applied to the array laser to alter the focus of the array laser on the location where the workpiece is being processed.
Further, the array laser is focused on a processing workpiece after passing through the focusing lens, the distance between the focus and the focusing lens is f, and the expected equivalent focal length corresponding to the nth step is f if the axial step distance of each focus is dz equ ＝f+n·dz,n＝0,1,2…。
Further, in a preferred embodiment of the present invention: calculating a desired array profile of the array laser from the desired equivalent focal length, comprising:
the array laser and the focusing lens are equivalent to a lens combination consisting of two lenses, the phase of the equivalent lens in the lens combination corresponds to the phase of the array laser, and the focal length of the equivalent lens is f 2 The focal length of the focusing lens is f, and the distance between the equivalent lens and the focusing lens is s;
calculating the focal length f of the equivalent lens according to the expected equivalent focal length and the equivalent focal length of the lens combination 2 ；
According to the focal length f of the equivalent lens 2 The desired laser array phase profile is derived.
Further, in a preferred embodiment of the present invention: focal length f of the equivalent lens 2 Determined by the following formula:
Figure BDA0004156313220000021
further, in a preferred embodiment of the present invention, the desired laser array phase distribution is:
Figure BDA0004156313220000022
where x and y represent the spatial coordinates of the laser light distribution in the x-direction and y-direction, respectively, k=2pi/λ is wavenumber, and λ is the array laser wavelength.
In another aspect, the present invention provides an optical phased array axial focus adjustment system, comprising:
the array laser coherent combining light path is used for realizing coherent combination and output of multiple paths of unit light beams;
the high-reflection mirror is arranged on the output path of the array laser coherent combining light path, most of laser output by the array laser coherent combining light path is reflected by the high-reflection mirror, and the small part of the laser is transmitted by the high-reflection mirror;
the array laser reflected from the high-reflection mirror is focused on a processing workpiece through the focusing lens;
the signal acquisition module is used for acquiring the optical signals transmitted from the high-reflection mirror and converting the optical signals into electric signals;
the data processing module is used for realizing the compensation of phase difference and phase noise among the unit light beams in the array laser based on the electric signals output by the signal acquisition module so as to control the phases among the unit light beams to be consistent; after the phases of the unit beams are controlled to be consistent, determining the focal depth of the array laser on the processed workpiece; calculating expected array distribution of the array laser according to the expected equivalent focal length; the desired array profile is applied to the array laser to alter the focus of the array laser on the location where the workpiece is being processed.
Further, in a preferred embodiment of the present invention: the array laser coherent combining light path comprises a seed laser, a 1 XN beam splitter, N phase modulators, N optical fiber amplifiers and a laser beam combining device; the laser output by the seed laser is divided into N paths of unit beams by a 1 XN beam splitter, each path of unit beam is respectively subjected to phase modulation and amplification by a corresponding phase modulator and an optical fiber amplifier, and the N paths of unit beams after the phase modulation and amplification are synthesized and output by a laser beam combining device.
Further, in a preferred embodiment of the present invention: the data processing module is in control connection with the phase modulator of each path of unit light beam.
Further, in a preferred embodiment of the present invention: the array laser reflected from the high-reflection mirror is focused on a processing workpiece after passing through a focusing lens, the distance between a focus and the focusing lens is f, and if the axial stepping distance of each focus is dz, the expected equivalent focal length corresponding to the nth step is f equ ＝f+n·dz,n＝0,1,2…；
The array laser and the focusing lens are equivalent to a lens combination consisting of two lenses, the phase of the equivalent lens in the lens combination corresponds to the phase of the array laser, and the focal length of the equivalent lens is f 2 The focal length of the focusing lens is f, and the distance between the equivalent lens and the focusing lens is s;
calculating the focal length f of the equivalent lens according to the expected equivalent focal length and the equivalent focal length of the lens combination 2 ；
According to the focal length f of the equivalent lens 2 The desired laser array phase profile is derived.
The invention utilizes the array laser phase distribution to simulate the lens phase distribution and realize the lens combination with equivalent variable focal length with the long-focus focusing lens combination, so that the focal depth shifts on a processed workpiece after the array laser is interfered, thereby improving the processing efficiency of the processes such as laser cutting and the like.
The invention utilizes a plurality of high-power fiber lasers to form an array, and realizes rapid, accurate and rapid laser focus regulation by carrying out high-speed regulation and control on the piston phase of the laser array. Compared with the prior art, the method has no mechanical moving part compared with the traditional method, can be suitable for high-power output, improves the focal depth regulating and controlling speed, and can improve the processing efficiency of high-power laser in application scenes such as industrial cutting and the like.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of an embodiment;
FIG. 2 is a schematic diagram of an equivalent lens assembly principle in one embodiment;
FIG. 3 is a schematic diagram of an embodiment;
FIG. 4 is a graph showing the results of numerical simulation obtained in one embodiment, wherein (a) is the phase profile of an equivalent lens; (b) is a sampled array phase profile;
fig. 5 is a comparison of energy distribution in the optical axis direction before and after the optical phased array axial focus adjustment in an embodiment, where (a) shows the optical axis energy distribution before the focus adjustment, (b) shows the optical axis energy distribution after the focus adjustment, and (c) shows a comparison of the two cross-sectional views.
The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the spirit of the present disclosure will be clearly described in the following drawings and detailed description, and any person skilled in the art, after having appreciated the embodiments of the present disclosure, may make alterations and modifications by the techniques taught by the present disclosure without departing from the spirit and scope of the present disclosure. The exemplary embodiments of the present invention and the descriptions thereof are intended to illustrate the present invention, but not to limit the present invention.
Referring to fig. 1, in one embodiment, an optical phased array axial focus adjustment method is provided, including:
compensating phase difference and phase noise among the unit light beams in the array laser to control the phases among the unit light beams to be consistent;
determining the focal depth of the array laser on a processed workpiece;
calculating expected array distribution of the array laser according to the expected equivalent focal length;
the desired array profile is applied to the array laser to alter the focus of the array laser on the location where the workpiece is being processed.
It is understood that the phase difference and phase noise between the unit beams in the array laser are compensated in the present invention, and the phase compensation method may be any one of array laser coherent synthesis phase control algorithms commonly used or customary in the art, such as near-field interference fringe extraction, heterodyne method, and various optimization algorithms. The purpose of this is to control the phase between the individual unit beams to be uniform by phase control.
Taking an optimization algorithm as an example without losing generality, the energy of a main lobe of a far-field interference fringe of the array laser is collected by utilizing a photoelectric detector and is converted into an electric signal. Based on the electric signal, by executing an optimization algorithm such as a random parallel gradient descent method, a dithering method, etc., the phase error between the unit light beams of each path is calculated and the corresponding control voltage u is output to the phase modulator (u= { u) corresponding to each path unit light beam 1 ，u 2 ，…，u N N is the total number of unit beams) such that the array beam interference main lobe energy detected by the photodetector reaches a maximum. The phase between the individual unit beams will be controlled to be uniform at this time.
The shift speed of the focal depth is related to the phase modulation device, and different devices are selected according to requirements. The shift range of the focal depth is related to the focal length of the focusing lens and the size of the single unit beam, and the larger the focal length of the focusing lens and the smaller the size of the single beam, the larger the shift range of the focal depth. The specific depth of focus offset range should be designed for the unit beam size and focal length of the focusing lens according to the application requirements.
In one embodiment, the array laser is focused onto the work piece after passing through a focusing lens. By the phase compensation control, the phases of the unit beams in the array laser are consistent, the distance between the focus and the focusing lens is f, and the focus falls on a processing workpiece. Assuming that the axial stepping distance of each time of the focus is dz, the expected equivalent focal length corresponding to the nth step is f equ ＝f+n·dz,n＝0,1,2…。
In an embodiment, taking laser cutting as an example, the array laser is focused on the upper surface of the machined workpiece after passing through the focusing lens, the laser cutting operation is performed on the machined workpiece, and after the surface cutting of the machined workpiece is completed, the depth of focus is expected to move downwards so as to realize the focusing of laser energy in the machined workpiece, and the machining efficiency is improved. First, the phase of each unit beam in the array laser is uniform by the phase compensation control. The array laser is focused on the upper surface of the processing workpiece after passing through the focusing lens, and the distance between the focus and the focusing lens is f, namely the focus falls on the upper surface of the processing workpiece. Assuming that the axial stepping distance of each time of the focus is dz, the expected equivalent focal length corresponding to the nth step is f equ ＝f+n·dz,n＝0,1,2…。
In a preferred embodiment: calculating a desired array profile of the array laser from the desired equivalent focal length, comprising:
referring to fig. 2, the array laser and the focusing lens are equivalent to a lens combination composed of two lenses. The equivalent lens combination comprises a focusing lens and an equivalent lens, the phase of the equivalent lens in the lens combination corresponds to the phase of the array laser, and the focal length of the equivalent lens is f 2 The focal length of the focusing lens is f, and the distance between the equivalent lens and the focusing lens is s.
Calculating the focal length f of the equivalent lens according to the expected equivalent focal length and the equivalent focal length of the lens combination 2 ；
Figure BDA0004156313220000061
According to the focal length f of the equivalent lens 2 The desired laser array phase profile is derived.
Figure BDA0004156313220000062
Where x and y represent the spatial coordinates of the laser light distribution in the x-direction and y-direction, respectively, k=2pi/λ is the wavenumber, and λ is the wavelength of the wave array laser light.
Referring to fig. 3, an embodiment of the present invention provides an optical phased array axial focus adjustment system, including:
the array laser coherent combining light path is used for realizing coherent combination and output of multiple paths of unit light beams;
the high-reflection mirror 106 is arranged on the output path of the array laser coherent combining light path, most of laser output by the array laser coherent combining light path is reflected by the high-reflection mirror, and the small part is transmitted by the high-reflection mirror;
a long focal lens 107 for focusing the array laser reflected from the high reflection mirror on the workpiece to be processed after passing through the focusing lens;
the signal acquisition module is used for acquiring the optical signals transmitted from the high-reflection mirror and converting the optical signals into electric signals;
the data processing module is used for realizing the compensation of phase difference and phase noise among the unit light beams in the array laser based on the electric signals output by the signal acquisition module so as to control the phases among the unit light beams to be consistent; after the phases of the unit beams are controlled to be consistent, determining the focal depth of the array laser on the processed workpiece; calculating expected array distribution of the array laser according to the expected equivalent focal length; the desired array profile is applied to the array laser to alter the focus of the array laser on the location where the workpiece is being processed.
Referring to fig. 3, the array laser coherent combining optical path includes a seed laser 101, a 1×n beam splitter 102, N phase modulators 103, N fiber amplifiers 104, and a laser beam combining device 105.
The output of the seed laser 101 is connected to the input of a 1 xn beam splitter 102.
The 1 xn beam splitter 102 has one input port and N output ports for splitting a laser beam into N laser beams.
The N outputs of the 1 xn splitter 102 are connected to N phase modulators 103, respectively.
The N phase modulators 103 have one input port and one output port for applying phase modulation to the laser light. The working principle of the phase modulation device is not limited, and the phase modulation device can be a piezoelectric ceramic device, a crystal device and the like, and is specifically selected according to the bandwidth requirement of the device.
The outputs of the N phase modulators 103 are connected to N optical fiber amplifiers 104.
The N optical fiber amplifiers 104 are used to amplify the power of the input laser signal.
The N optical fiber amplifiers 104 are connected to the laser beam combining device 5.
The laser beam combining device 105 is a collimator array which is two-dimensionally arranged, and has the function of collimating output laser. The collimator array arrangement in the beam combining device 105 is not limited. The shape of the laser array is not limited, and can be rectangular distribution, circular distribution, regular hexagonal distribution, spiral line distribution and the like. Preferably, the light beam combining device 105 is arranged in a regular hexagon.
The laser beam output by the seed laser 101 is split into N unit beams by the 1×n beam splitter 102, each unit beam is phase modulated and amplified by the corresponding phase modulator 103 and optical fiber amplifier 104, and the N unit beams after phase modulation and amplification are synthesized and output by the laser beam combiner 105.
The collimated array laser is emitted from the laser beam combining device 105 into free space, sampled by the high-reflection mirror 106, and most of the laser is reflected and a small part of the laser is transmitted.
The high reflection mirror 106 is a film plating optical device, and the material is not limited, so that most of the incident laser light can be reflected, and a small part of the incident laser light can be transmitted. The high reflectivity of the mirror is such that the ratio of reflected laser light to transmitted laser light is greater than 99.
The lens materials sampled in the invention are not limited, and can be optical crystal materials such as K9, fused quartz and the like, and the focal length of the lens is about 1m. The array lasers are converged by the lens and then interfere to generate interference fringes with a central main lobe.
The reflected laser beam is focused by the tele focusing lens 107, and the focused laser beam reaches the surface of the processing workpiece 108.
The focal length of the long-focus focusing lens 107 is f, and the focal length is 1m without losing generality. The focal length of the long-focus focusing lens 107 is selected in relation to the focal depth adjusting range, and the longer the focal length is, the larger the adjusting range is, so that the long-focus focusing lens 107 with different focal lengths can be selected according to requirements.
Laser light transmitted from the high mirror passes through 50:50 beam splitter 109 divides into two laser beams, the two laser beams are focused by focusing lens 110 respectively, and one laser beam is input into photoelectric detector 111 after being focused, for detecting the phase of array laser; the other laser beam is focused and then input into the camera 112 for detecting the spot shape.
The 50: the 50 beam splitter 109 is a film-plating optical device, and can split the input laser into two lasers with the same power.
The focal length of the focusing lens 110 is not limited.
The photodetector 111 is used to convert an optical signal into an electrical signal.
The camera 112 is used to observe the morphology of the array laser after focusing.
The photodetector 111 converts the optical signal into an electrical signal and then sends the electrical signal to the data processing unit 113. The output of the data processing unit is connected to the N phase modulators.
The data processing unit 113 is preloaded with a phase compensation algorithm, on the one hand with a systematic phase noise compensation capability, and on the other hand the data processing unit 113 is able to apply a given phase distribution to the array laser on the basis of compensating the phase noise. After the phases of the lasers are controlled to be consistent, the position of the final array laser focused on the processing workpiece can be changed by changing the phase distribution of the array laser.
Specifically, the data processing unit realizes the focus position regulation and control in the following four steps:
step one: for each unit beam in the systemThe phase difference and the phase noise are compensated. The compensation method can be any array laser coherent synthesis phase control algorithm, such as near-field interference fringe extraction, heterodyne method, optimization algorithm and the like. Taking the optimization algorithm as an example, the far-field interference fringe main lobe energy is converted into an electric signal by the photodetector 111 in fig. 3 and sent to the data processing unit 113. The data processing unit 113 calculates a phase error between the respective unit light beams by executing an optimization algorithm such as random parallel gradient descent and outputs a corresponding control voltage u to the phase modulator (u= { u 1 ，u 2 ，…，u N N is the number of sub-beams) such that the array beam interference main lobe energy detected by the photodetector reaches a maximum. The phase between the individual unit beams will be controlled to be uniform at this time.
Step two: the depth of focus of the array laser on the work piece is determined.
The upper surface of the workpiece to be processed is placed at a distance f from the focusing lens 107. In the case where the laser phases of the respective unit beams are identical, the distance between the focal point and the focusing lens 107 is f, that is, the focal point falls on the upper surface of the workpiece to be processed. Taking laser cutting as an example, the laser cutting operation is carried out on the workpiece to be processed, after the surface cutting of the workpiece to be processed is completed, the depth of focus is expected to move downwards so as to realize the focusing of laser energy in the workpiece to be processed, and the processing efficiency is improved. Let the focal point step distance be dz, the desired system equivalent focal length be f equ ＝f+n·dz,n＝0,1,2…。
Step three: the desired array profile of the array laser is calculated from the desired system equivalent focal length.
Fig. 2 provides a schematic diagram of the equivalent principle, and the equivalent lens combination includes a focusing lens 201 and an equivalent lens 202. The focal length of the focusing lens 201 is f, which corresponds to the tele focusing lens 107 in the schematic structural diagram shown in fig. 3. The phase of the equivalent lens 202 corresponds to the phase of the array laser emitted from the laser beam combining device 105 in the schematic structural diagram shown in fig. 3, and the focal length is f 2 . The equivalent focal length f is expected from the step two known system equ From the equivalent focal length calculation formula of the two lens combinations of formula (1), the equivalent can be deducedFocal length f of lens 202 2 。
Figure BDA0004156313220000091
S in the formula (1) is a distance between two lenses.
From the derived equivalent lens 202 focal length f 2 It can be further derived that the desired laser array phase distribution should satisfy equation (2)
Figure BDA0004156313220000101
In the formula (2), x and y are space coordinates, and k=2pi/λ is wave number.
Since the unit beam controlled phase is the piston phase, the equivalent lens phase cannot be completely simulated, and the equivalent lens phase is sampled by the array laser unit beam center. FIG. 4 is a schematic diagram of an embodiment of an array laser phase generation method consisting of 37 unit beams. The aperture diameter of a single unit beam is set to be 3mm, the distance between the unit beams is 3.16mm, the duty ratio of the array is about 95%, the focal length of the focusing lens is 1m, the system focus stepping value is 1mm, the array beams are transmitted to the focusing lens in parallel, and the distance s between the array laser and the long-focus focusing lens is ignored. If the focal position is moved to 1.001m, the equivalent lens focal length f is calculated according to formula (1) 2 The phase distribution of the equivalent lens can be calculated from equation (2) as shown in fig. 4 (a). Sampling the phase distribution of the equivalent lens by using the central position of the array laser beam composed of 37 unit beams to obtain the corresponding array phase distribution in FIG. 4 (b)
Figure BDA0004156313220000102
Figure BDA0004156313220000103
I.e. array phase distribution required by 1mm of equivalent focus of the system, the corresponding control voltage offset is Deltau= { Deltau 1 ，Δu 2 ，…，Δu 37 }。
Step four: the generated phase profile is applied to the array laser.
In step one, the phase error existing in the system is already compensated by the applied control voltage u, and the required control voltage offset is added to the control voltage u to obtain the control voltage output u+Δu required for focal depth regulation. To ensure the accuracy of the desired phase distribution, the system phase noise needs to be periodically compensated for the update control voltage u. During the updating of the control voltage u, the focal position is temporarily restored to the upper surface of the workpiece to be machined, and the system can still move the focal point to the desired position for a large part of the time due to the short time required for the phase noise compensation. The optimization algorithm is only one embodiment of the method provided by the invention, and the required phase distribution deltau can be applied while the control voltage u is updated by adopting a direct phase method such as a near-field interference fringe extraction method, a heterodyne method and the like, so that the focus is not required to be temporarily moved back to the initial position for phase noise correction.
Fig. 5 is a schematic diagram showing the energy distribution in the optical axis direction before and after the focal point adjustment based on the parameters of fig. 4, fig. 5 (a) shows the energy distribution in the optical axis before the focal point adjustment, fig. 5 (b) shows the energy distribution in the optical axis after the focal point adjustment, and fig. 5 (c) shows the cross-sectional views of the two. Therefore, the method provided by the invention can change the energy distribution of the focus in the optical axis direction at high speed, and takes 80% energy as an evaluation standard, compared with a fixed focus processing mode, the method provided by the invention can provide 3 times of focus depth, has more advantages in thick material processing, and can improve processing efficiency.
In summary, the invention utilizes a plurality of fiber lasers to form array output, and changes the focusing position of output laser by regulating and controlling the phase distribution of the array, thereby providing a non-mechanical, high-speed, accurate and high-output-power axial focus regulating and controlling method. The invention solves the problems of low output power and long response time of the existing axial focus control method and improves the accuracy of axial focus control.
The invention is not a matter of the known technology.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples merely represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.

Claims (10)

1. The method for regulating the axial focus of the optical phased array is characterized by comprising the following steps of:
compensating phase difference and phase noise among the unit light beams in the array laser to control the phases among the unit light beams to be consistent;
determining the focal depth of the array laser on a processed workpiece;
calculating expected array distribution of the array laser according to the expected equivalent focal length;
the desired array profile is applied to the array laser to alter the focus of the array laser on the location where the workpiece is being processed.
2. The method for adjusting and controlling an axial focus of an optical phased array according to claim 1, wherein the array laser is focused on the workpiece to be processed after passing through the focusing lens, a distance between the focus and the focusing lens is f, and if an axial stepping distance of each time of the focus is dz, a desired equivalent focal length corresponding to an nth step is f equ ＝f+n·dz,n＝0,1,2…。
3. The method of claim 2, wherein calculating the desired array profile of the array laser from the desired equivalent focal length comprises:
the array laser and the focusing lens are equivalent to a lens combination consisting of two lenses, the phase of the equivalent lens in the lens combination corresponds to the phase of the array laser, and the focal length of the equivalent lens is f 2 The focal length of the focusing lens is f, and the distance between the equivalent lens and the focusing lens is s;
calculating the focal length f of the equivalent lens according to the expected equivalent focal length and the equivalent focal length of the lens combination 2 ；
According to the focal length f of the equivalent lens 2 The desired laser array phase profile is derived.
4. The method of claim 3, wherein the focal length f of the equivalent lens 2 Determined by the following formula:
Figure FDA0004156313210000011
5. the method of claim 3, wherein the desired laser array phase profile is:
Figure FDA0004156313210000012
where x and y represent the spatial coordinates of the laser light distribution in the x-direction and y-direction, respectively, k=2pi/λ is wavenumber, and λ is the array laser wavelength.
6. The optical phased array axial focus regulation and control system is characterized by comprising:
the array laser coherent combining light path is used for realizing coherent combination and output of multiple paths of unit light beams;
the high-reflection mirror is arranged on the output path of the array laser coherent combining light path, most of laser output by the array laser coherent combining light path is reflected by the high-reflection mirror, and the small part of the laser is transmitted by the high-reflection mirror;
the array laser reflected from the high-reflection mirror is focused on a processing workpiece through the focusing lens;
the signal acquisition module is used for acquiring the optical signals transmitted from the high-reflection mirror and converting the optical signals into electric signals;
the data processing module is used for realizing the compensation of phase difference and phase noise among the unit light beams in the array laser based on the electric signals output by the signal acquisition module so as to control the phases among the unit light beams to be consistent; after the phases of the unit beams are controlled to be consistent, determining the focal depth of the array laser on the processed workpiece; calculating expected array distribution of the array laser according to the expected equivalent focal length; the desired array profile is applied to the array laser to alter the focus of the array laser on the location where the workpiece is being processed.
7. The optical phased array axial focus adjustment system of claim 6, wherein the array laser coherent combining optical path comprises a seed laser, a 1 xn beam splitter, N phase modulators, N fiber amplifiers, and a laser beam combining device; the laser output by the seed laser is divided into N paths of unit beams by a 1 XN beam splitter, each path of unit beam is respectively subjected to phase modulation and amplification by a corresponding phase modulator and an optical fiber amplifier, and the N paths of unit beams after the phase modulation and amplification are synthesized and output by a laser beam combining device.
8. The optical phased array axial focus adjustment system of claim 7, wherein the data processing module is in control connection with a phase modulator of each of the individual unit beams.
9. The system according to claim 6, 7 or 8, wherein the array laser reflected from the high-reflection mirror is focused on the workpiece after passing through the focusing lens, the distance between the focus and the focusing lens is f, and the nth step is provided that the axial step distance of each time of the focus is dzThe corresponding expected equivalent focal length is f equ ＝f+n·dz,n＝0,1,2…；
The array laser and the focusing lens are equivalent to a lens combination consisting of two lenses, the phase of the equivalent lens in the lens combination corresponds to the phase of the array laser, and the focal length of the equivalent lens is f 2 The focal length of the focusing lens is f, and the distance between the equivalent lens and the focusing lens is s;
calculating the focal length f of the equivalent lens according to the expected equivalent focal length and the equivalent focal length of the lens combination 2 ；
According to the focal length f of the equivalent lens 2 The desired laser array phase profile is derived.
10. The optical phased array axial focus adjustment system of claim 9, wherein the focal length f of the equivalent lens 2 Determined by the following formula:
Figure FDA0004156313210000031
the desired laser array phase profile is:
Figure FDA0004156313210000032
where x and y represent the spatial coordinates of the laser light distribution in the x-direction and y-direction, respectively, k=2pi/λ is wavenumber, and λ is the array laser wavelength.
CN202310335557.XA 2023-03-31 2023-03-31 Optical phased array axial focus regulation and control method and system Pending CN116197524A (en)

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