A continuous surface fiber laser collimation beam combining device

Abstract

The application relates to a continuous surface fiber laser collimation beam combining device, belonging to the field of high-energy laser beam combining. The device comprises a fiber QBH interface backboard, a mechanical lens barrel and a continuous surface compound eye lens. The continuous surface compound eye lens is a free surface lens comprising a plurality of aspheric collimation units, and the collimation units are smoothly connected through an optimized Zernike polynomial fitting method. The collimation unit adopts a convex aspheric plano-convex lens structure, and the aperture amplification ratio is selected according to the relationship between the waist diameter multiple of a Gaussian beam and the in-circle energy ratio. The fiber QBH interface backboard comprises a plurality of QBH interfaces connected with fiber end caps, and the position of each interface corresponds to the object focal point of each collimation unit. The mechanical lens barrel is a hollow cylindrical structure, one end of which is connected with the fiber QBH interface backboard, and the other end is connected with the continuous surface compound eye lens. The application can realize higher laser energy transmission and obtain longer stable light emission time under the condition of ensuring the consistency and stability of the system outgoing optical axis.

Description

TECHNICAL FIELD

[0001] The present application relates to a continuous surface fiber laser collimation beam combining device, belonging to the field of high-energy laser beam combining. BACKGROUND

[0002] In the military field, laser weapons generally refer to weapons that can destroy enemy attacking targets or important photoelectric systems of attacking targets, and the main features include fast attack speed, high hit rate, flexible turning, and small collateral damage. The power demand of military high-energy lasers has reached the order of tens of thousands of W to hundreds of thousands of W, and the theoretical output power limit of single-mode wide-spectrum fiber lasers is only tens of kW. It can be seen that the scheme of developing high-energy laser equipment using a single fiber laser is currently impossible to implement. Therefore, using laser beam combining technology to effectively combine the outgoing laser beams of multiple fiber lasers and achieving higher laser power to the target while maintaining the quality of the laser beam is the key direction for developing high-energy laser equipment.

[0003] At present, the aperture beam combining scheme mainly includes the fiber collimator array bundle beam combining scheme and the discrete collimating element beam combining scheme. Figure 1 The fiber collimator array bundle beam combining scheme is shown. Multiple fiber collimators are densely arranged into a polygonal array to achieve synthesis in the far field. Due to the characteristics of Gaussian laser beams, there is still a small amount of energy outside the beam waist radius. Therefore, when this beam combining method is continuously operated, the metal cylinder wall will absorb part of the laser energy and produce thermal deformation, causing the optical axes of each collimator to deviate from their original positions, resulting in the dispersion of the laser spot to the target and the decline of the beam combining effect. Figure 2 The discrete collimating element beam combining scheme is shown. Compared with the collimator array bundle beam combining method, this beam combining device eliminates the mechanical cylinder wall between the collimating elements, effectively solving the problem of deviation of the collimating light paths caused by heat absorption of the metal cylinder wall, and improving the duty cycle and the concentration of the light beam. At this time, the metal mirror frame of hard aluminum material at the laser exit end face becomes the main heat absorption area of the system. The thermal expansion coefficients of fused quartz and hard aluminum differ by tens of times, so when this device is continuously operated, the metal mirror frame of hard aluminum material between the fused quartz lens units will produce a large thermal deformation, which will further press the lenses and cause the optical axes of the collimating lenses to deviate from each other, reducing the beam combining effect and affecting the stable light output time.

[0004] In summary, at present, laser beam combining technology is a high-energy laser implementation scheme that can achieve higher total laser power while maintaining the quality of the laser beam. However, the current two types of aperture beam combining schemes have the problem of dispersion of the laser spot to the target and reduction of energy concentration due to the difficulty in solving the thermal-optical deformation caused by the absorption of high-energy laser by the mechanical structure of the collimator, which is greatly limited in practical application.

[0005] The following problems exist in the traditional aperture beam combining method:

[0006] Main problem: According to the property of single-mode laser Gaussian beam, there is still energy distribution outside the beam waist diameter, therefore, the way of fiber collimator array bundle combining will absorb part of the strong laser to heat and produce thermal deformation, which will cause the deviation angle between the optical axes of each collimator, and reduce the effect of beam combining; the way of discrete collimating element beam combining will produce large thermal deformation in the metal connecting area between the fused quartz lenses due to the difference of several tens times in the thermal expansion coefficient between hard aluminum and fused quartz, which will squeeze the lenses and cause the optical axes of each collimating lens to deviate from each other, and reduce the effect of beam combining. Therefore, when the two kinds of laser beam combining devices are used continuously, the far-field spot will be scattered and the energy concentration will be reduced due to thermal-optical deformation, which will directly affect the stable light output time.

[0007] Secondary problem: the traditional aperture beam combining scheme is difficult to ensure the consistency and stability of the optical axis of the system due to the structure of the discrete collimating unit: in practical application, real-time adjustment is required, which is difficult to ensure the consistency of the optical axis of each lens, affecting the beam combining quality; in the adjustment process, it will also be affected by the dynamic environment, and the performance in the moving state is not as good as in the static state. SUMMARY

[0008] The purpose of the present application is to solve the problems of the existing aperture beam combining scheme, such as serious thermal-optical deformation, poor optical axis consistency and low space occupation ratio, and to provide a continuous surface fiber laser collimating beam combining device. The device uses a continuous surface fly-eye lens instead of traditional discrete collimating units as the laser exit surface of the fiber collimating beam combiner. The collimating unit adopts a convex surface aspherical plano-convex lens structure, and the optical surface fitting method is used to smoothly transition between each collimating unit. In the process of processing, the optical axis consistency of each collimating unit is corrected, and the mechanical cylinder wall and the metal obstruction such as lens frame in the center area of the laser exit surface between the collimating units are removed, which can greatly alleviate the problem of collimator optical axis consistency change caused by thermal-optical deformation in the aperture beam combining scheme, improve the laser resistance and increase the stable light output time.

[0009] The purpose of the present application is achieved by the following technical scheme.

[0010] A continuous surface fiber laser collimating beam combining device, the device comprises a fiber QBH interface backplate, a mechanical lens barrel and a continuous surface fly-eye lens; the mechanical lens barrel is a hollow cylindrical structure, one end of which is connected to the fiber QBH interface backplate; the other end is connected to the continuous surface fly-eye lens.

[0011] The continuous surface fly-eye lens is a continuous free-form surface lens containing several aspherical collimating units, which is made of materials with high transmittance, high damage threshold, high temperature resistance and low expansion coefficient, such as fused quartz, sapphire and calcium fluoride.

[0012] The collimation unit adopts a convex aspherical plano-convex lens structure. The light emitted by the point light source passes through the plano-convex lens and is emitted, obtaining an approximately collimated light beam. The aperture of the collimation unit is selected. Firstly, the light beam divergence aperture of the fiber laser at the front surface of the lens is calculated. Then, according to the relationship between the waist diameter multiple of the Gaussian beam and the energy ratio in the circle, the magnification of the collimation unit aperture is determined based on the evaluation standard of laser energy transmittance. Under the condition of ensuring the on-axis point to remove spherical aberration, the corresponding convex aspherical collimation unit surface shape is obtained as the optimization index of the minimum exit light wavefront aberration.

[0013] The transition area between the collimation units adopts an optical curved surface fitting method for smooth transition.

[0014] The curved surface fitting method is an optimized Zernike polynomial fitting method. Firstly, the relative position and surface height data of each collimation unit are taken as the reference coordinates. The continuous curved surface is obtained by fitting the basic Zernike polynomial through the least square method. The number of terms with non-zero weight in the coefficient matrix of the Zernike polynomial is selected as the Zernike effective term of this fitting. By comparing the aberration pattern corresponding to the Zernike effective term with the position distribution characteristics of each collimation unit, the characteristics of the term number of the Zernike effective term with higher correlation degree to the position distribution characteristics of each collimation unit are summarized. The term number of more required Zernike effective terms is extrapolated, and the characteristic equation of the corresponding term is calculated and generated. Finally, the characteristic equation of the Zernike effective term is composed into a new Zernike polynomial matrix, which is used as an independent orthogonal coordinate system for surface fitting. The continuous surface free-form compound eye lens surface structure is constructed by fitting.

[0015] The fiber QBH interface backboard includes a plurality of QBH interfaces connected with the fiber end cap. The position of each interface corresponds to the object focal point of each collimation unit of the continuous surface compound eye lens.

[0016] The continuous surface compound eye lens is fixed on the right end exit surface of the mechanical lens barrel through the right threaded compression ring and the left step. The fiber QBH interface backboard is screwed to the mechanical lens barrel.

[0017] Beneficial effects:

[0018] (1) High laser resistance. The transition between the collimation units of the beam combining system is smooth by curved surface fitting, without seams and singular points, effectively avoiding the absorption of specific energy points; the mechanical barrel and the metal mirror frame of the laser exit surface between the collimation units are removed, the laser energy absorbed by the lens barrel and the exit end surface is reduced, the problem of change of collimator optical axis consistency caused by thermal-optical deformation is effectively improved, higher energy laser irradiation can be tolerated, and the stable light emission time is increased.

[0019] (2) Good optical axis consistency. The optical axis consistency of the system is adjusted in advance and fixed in the processing, the outgoing light waves of each collimation unit are detected and polished with the same reference, which physically ensures the accurate consistency of the outgoing optical axis of each unit, and is beneficial to improve the control accuracy of the system.

[0020] (3) Strong structural reliability. The mechanical barrel wall and the water-cooling heat dissipation system between the collimation units are removed, the light beams of each path are concentrated in the middle, the optical and mechanical structure is more compact, and the volume and weight are obviously reduced; without complex operations such as adjustment of the consistency of the optical axis of each path, the system will not change due to environmental changes such as vibration and temperature in the field operation, and has high reliability.

[0021] (4) The continuous surface fiber laser collimation beam combining device can realize higher laser energy transmission and obtain longer stable light emission time under the condition of ensuring the consistency and stability of the outgoing optical axis of the system. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Figure 1 is a schematic diagram of the bundled beam combining mode of the fiber collimator array; (a) is a sectional view, and (b) is a physical diagram;

[0023] Figure 2 Figure 2 is a schematic diagram of the beam combining mode of the discrete collimation element; (a) is a sectional view, and (b) is a physical diagram;

[0024] Figure 3 Figure 3 is a sectional view of the continuous surface fiber laser collimation beam combining device of the present application;

[0025] Figure 4 Figure 4 is a front view of the continuous surface compound eye lens of the present application;

[0026] Figure 5 Figure 5 is a schematic diagram of the optical path structure of the collimation unit;

[0027] Figure 6 Figure 6 is a collimation wavefront diagram after optimization;

[0028] Figure 7 Figure 7 is a non-spherical surface height diagram after optimization.

[0029] In the figure, 1 is a fiber end cap, 2 is a fiber QBH interface back plate, 3 is a mechanical lens barrel, 4 is a threaded compression ring, 5 is a continuous surface compound eye lens, 6 is a collimation unit, and 7 is a transition zone. DETAILED DESCRIPTION

[0030] In order to better illustrate the purpose and advantages of the present application, the content of the application will be further described below in combination with the drawings and examples.

[0031] Example 1:

[0032] Figure 3 It is a cross-sectional view of the continuous surface fiber laser collimation beam combining device. The device mainly includes a fiber QBH interface backboard, a mechanical lens barrel, and a continuous surface compound eye lens. The continuous surface compound eye lens is fixed on the right end of the mechanical lens barrel through the right screw pressure ring and the left step, and the fiber QBH interface backboard is screwed to the mechanical lens barrel. The interface position of the fiber QBH interface backboard corresponds to the object focal point of each collimation unit of the continuous surface compound eye lens. In the working state, kilowatt-level laser is emitted from the fiber end cap in the form of an approximate point source, passes through the opening of the fiber QBH interface backboard, irradiates the continuous surface compound eye lens at the right end of the mechanical lens barrel, and most of the laser energy is transmitted through each collimation unit, and the remaining small part of the energy is transmitted out by the smooth transition inter-lens transition area of the same material.

[0033] Figure 4 It is a continuous free-form surface lens containing seven aspheric collimation units. The area inside the dashed circle is the collimation unit area, and the area outside the dashed line is the smooth fitting inter-lens transition area. The continuous surface compound eye lens is a continuous free-form surface lens containing several aspheric collimation units, which is made of a material with high transmittance, high damage threshold, high temperature resistance, and low expansion coefficient. Here, fused quartz is selected. The ratio of the thickness to the aperture of the compound eye lens should be not less than 1 / 10 to ensure sufficient mechanical processing strength and laser damage resistance.

[0034] The collimation unit adopts a convex aspherical plano-convex lens structure. The light emitted by the point source is emitted through the plano-convex lens to obtain an approximately collimated light beam.

[0035] Figure 5 It is a schematic diagram of the optical path structure of the collimation unit. According to the characteristics of the kilowatt fiber laser QBH interface, the light beam divergence aperture of the fiber laser on the front surface of the lens is calculated. The fiber tail fiber diameter is 30 μm, the fiber numerical aperture NA is 0.06, the tail fiber verticality error is ±0.01°, the end cap length (end cap cone tip to laser exit surface) is 20 mm, and the end cap diameter is 8.2 mm.

[0036] The calculation shows that the beam aperture on the exit surface of the end cap is:

[0037] a = 2 x 20 x 0.06 = 2.4 mm (1)

[0038] The beam aperture (beam waist diameter) of the front surface of the collimation unit is:

[0039] D = 2 x 132.4 x tan α + 2.4 ≈ 18.3 mm (2)

[0040] As shown in Table 1, according to the property of energy distribution outside the waist diameter of the Gaussian beam of the single-mode laser, the aperture of the collimation unit is selected according to the waist diameter, and then 13.5% of the light energy hits the barrel wall and other structures. For a high-power fiber laser of 3kW, the unemitted energy accumulates, and the deformation or damage caused by the unemitted energy seriously reduces the performance of the emission system. Meanwhile, the pupil obstruction causes the ringing phenomenon of the far-field spot, which is not conducive to improving the energy concentration of the far-field spot. If the aperture of the collimation unit is too large, the spacing of the multi-beam will increase, and the volume and weight of the system will also increase. Therefore, it is necessary to optimize the selection of the aperture of the collimation unit.

[0041] Table 1

[0042]

[0043] Here, the collimation unit is designed with 1.86 times the waist diameter to ensure sufficient laser energy transmittance. That is, when the aperture of the collimation unit satisfies D≥34.04mm, the beam transmittance can reach 99.9%. In Zemax, the lens model of the collimation unit is established. In order to reduce the wavefront aberration of the outgoing light wave as much as possible, a convex lens structure with a convex surface is adopted, the glass material is fused quartz with high temperature resistance and low expansion coefficient, the lens aperture is selected as 35mm, the thickness is 20mm, and the optimized wavefront diagram is shown in Figure 6 The peak-to-valley value of the wavefront of the light emitted by the point light source collimated by the plano-convex lens is 0.0016λ, which meets the requirements of the beam quality. The surface height diagram of the aspheric surface is drawn, and the result is shown in Figure 7 . Taking the edge of the aspheric surface as the reference, when the effective lens aperture is 35mm, the convex height is 2.14mm, and the design of the single-channel collimation unit is completed.

[0044] On this basis, the transition area between the collimation units is designed, and the method of optical surface fitting is used for smooth transition.

[0045] The surface fitting method is the optimized Zernike polynomial fitting method. As shown in Figure 4As shown, for the transition area outside the dashed circle, firstly, the relative positions and surface height data of each collimating unit inside the dashed circle are taken as the reference coordinates, a continuous surface is obtained by fitting the basic Zernike polynomial through the least square method, the number of terms with non-zero weight in the Zernike polynomial coefficient matrix is selected as the Zernike effective term of this fitting. By analyzing the aberration pattern corresponding to the Zernike effective term and comparing it with the position distribution characteristics of each collimating unit, the characteristics of the term number of the Zernike effective term with higher correlation with the position distribution characteristics of each collimating unit are summarized, more required term numbers of the Zernike effective term are extrapolated, and the characteristic equation of the corresponding term is calculated and generated. Finally, the characteristic equation of the Zernike effective term obtained is composed into a new Zernike polynomial matrix, which is used as an independent orthogonal coordinate system for surface fitting, and a continuous surface of the compound eye lens surface structure is constructed.

[0046] The specific implementation method is as follows:

[0047] Step one, select the Zernike effective term.

[0048] According to the weight distribution of the coefficient matrix obtained by fitting the basic Zernike polynomial through the least square method, the number of terms with non-zero weight in the coefficient matrix is selected as the Zernike effective term of this fitting. Since the seven collimating units are in a regular hexagonal distribution, by observing the aberration pattern corresponding to the selected Zernike effective term, it can be known through comparative analysis that the aberration pattern is the Zernike term number of each order spherical aberration and the angle direction is an integer multiple of six, which is exactly the number of terms with non-zero weight in the coefficient matrix, that is, the Zernike effective term required for fitting.

[0049] Step two, obtain the term number of the Zernike effective term.

[0050] The aberration function of an optical system with a circular pupil and no rotational symmetry axis can be expanded into a complete set of Zernike circular polynomials, and these terms are orthogonal in the unit circle and have the following expression form:

[0051]

[0052] Where a j is the expansion term coefficient, n and m are positive integers containing zero, n-m>0 and even, (ρ,θ) are the pupil polar coordinates. Here n represents the highest order of the polynomial, m represents the azimuthal frequency, and there is Z j The orthogonal Zernike polynomial expansion is:

[0053]

[0054] where the radial circular polynomial can be expanded as:

[0055]

[0056] is a polynomial of n-th order of ρ n , ρ n-2 , …, and ρ m .

[0057] Therefore, different order n and azimuthal frequency m determine the term number of Zernike terms.

[0058] Firstly, the term number of each order of spherical aberration is determined. For each even order n, the term number j of Zernike effective terms is:

[0059] j1=1+(n+1)(n+2) / 2 (6)

[0060] Secondly, the aberration pattern is obtained. The term number of Zernike terms with angle direction being an integer multiple of six is obtained. Since the azimuthal frequency m varies with the order n, the azimuthal frequency m needs to be divided into two cases according to the different orders n.

[0061] Case one: the polynomial order n starts from 1 and every interval is 4. The term number j of Zernike effective terms is:

[0062] j2=6×floor((n+1) / 6)+(n+1)(n+2) / 2+1 (7)

[0063] Case two: the polynomial order n starts from 3 and every interval is 4. The term number j of Zernike effective terms is:

[0064] j3=6×floor((n+1) / 6-1)+(n+1)(n+2) / 2+6 (8)

[0065] In summary, the term numbers j1, j2, j3 of the obtained Zernike effective terms are arranged in ascending order to obtain the term number j of the aberration pattern with the highest order n (max) .

[0066] Step three: generate the characteristic equation corresponding to the Zernike effective terms.

[0067] According to the obtained term number j, the corresponding order n is obtained:

[0068]

[0069] The azimuthal frequency m is obtained according to the item number j:

[0070] The obtaining of the azimuthal frequency m is divided into two cases:

[0071] When n is even:

[0072] m 偶 = 2 x floor((2j+1-n(n+1)) / 4) (10)

[0073] When n is odd:

[0074] m 奇 = 2 x floor((2j+1-n(n+1)) / 4)+(-1) α (11)

[0075] Wherein the positive and negative of a is judged as follows:

[0076] 1) In the case that (n+1) can be divided by 4, when (n+j) is even, a = 1, when (n+j) is odd, a = 0;

[0077] 2) In the case that (n+1) cannot be divided by 4, when (n+j) is even, a = 0, when (n+j) is odd, a = 1;

[0078] Therefore, according to the order of j from small to large, substitute into formula (9), (10), (11) in turn, obtain the order n and the azimuthal frequency m corresponding to each item number j, and then bring into formula (4) to obtain the characteristic equation of the corresponding Zernike effective term.

[0079] Finally, the obtained characteristic equation is composed into a new Zernike polynomial matrix, which is an independent orthogonal coordinate system participating in the optimization of surface fitting, that is, the compound eye lens surface shape structure of continuous free-form surface can be fitted and constructed.

[0080] Taking the laser transmittance of fused quartz at 1080 nm as 99.9%, and the aperture of the collimating unit as D = 35 mm, the laser transmittance of the collimating beam combiner using continuous surface compound eye lens under the condition of dense arrangement of collimating units can reach:

[0081]

[0082] That is, under the irradiation of 7 paths of 3 kW high-energy laser, this beam combining scheme has only 22.43 W of laser energy loss in theory.

[0083] Taking the laser beam waist diameter of the front focal surface of the collimating unit, that is, D = 18.3 mm, as the aperture of the collimating unit, the laser transmittance of the discrete collimating unit is calculated:

[0084]

[0085] Laser transmittance of collimating combiner with continuous surface fly's eye lens:

[0086]

[0087] Under the irradiation of 7-path 3kW high-energy laser, the collimating combiner with continuous surface fly's eye lens can realize the increase of laser energy transmission of about:

[0088] T 连续-分立 =7*3000*(86.38%-97.48%)≈2331.83W (15)

[0089] It can be seen that the collimating combiner with continuous surface fly's eye lens can realize higher laser energy transmission. At the same time, the mechanical barrel wall and the metal mirror frame of the laser exit surface between the collimating units are removed, the laser energy absorbed by the lens barrel and the exit end surface is reduced, thereby realizing higher laser load capacity and longer stable light output time.

[0090] In addition, since the optical axis consistency between the collimating units of the continuous surface fly's eye lens is corrected during processing, the problem of collimator optical axis consistency change caused by thermal-optical deformation is effectively improved, and the optical axis consistency is higher.

[0091] Finally, the mechanical barrel wall and the water-cooling heat dissipation system between the discrete collimating units are removed, the light beams of each path are concentrated in the middle, the optical and mechanical structure is more compact, the volume and weight are obviously reduced, and the complex operation of adjusting the optical axis consistency of each path is not needed, the structure is more reliable and will not change due to the vibration, temperature and other environmental changes in the field.

[0092] Therefore, the continuous surface fiber laser collimating combiner device of the present application can realize higher laser energy transmission and longer stable light output time under the condition of ensuring the system exit optical axis consistency and stability.

[0093] The above specific description further describes the purpose, technical scheme and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and does not limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A continuous surface fiber laser collimation beam combining device, characterized by: The application relates to a continuous surface compound eye lens, which comprises a fiber QBH interface backboard, a mechanical lens barrel and a continuous surface compound eye lens. The mechanical lens barrel is a hollow cylindrical structure, one end of which is connected with the fiber QBH interface backboard; The other end of the mechanical lens barrel is connected with the continuous surface compound eye lens. The continuous surface compound eye lens is a free surface lens comprising a plurality of aspheric collimating units. The aspheric collimating units are smoothly connected with each other through an optical surface fitting method. The collimating unit is a convex aspheric plano-convex lens structure. The aperture selection method of the aspheric collimating unit is as follows: Step one: the beam divergence aperture of the fiber laser on the front surface of the lens is calculated; Step two: according to the relationship between the waist diameter multiple of the Gaussian beam and the energy ratio in the circle, the magnification of the collimating unit aperture is determined according to the laser energy transmittance as the evaluation standard.

2. The continuous surface fiber laser collimating beam combining apparatus of claim 1, wherein: The fiber QBH interface backboard comprises a plurality of QBH interfaces connected with fiber end caps, and the position of each interface corresponds to the object focal point of each collimating unit of the continuous surface compound eye lens.

3. The continuous surface fiber laser collimating beam combining apparatus of claim 1, wherein: The continuous surface compound eye lens is fixed on the right end of the aluminum mechanical lens barrel through the right screw pressure ring and the left step.

4. A continuous surface fiber laser collimating beam combining device as claimed in claim 1, wherein: The surface fitting method is an optimized Zernike polynomial fitting method, which comprises the following steps: Step one: taking the relative position and surface height data of each collimating unit as the reference coordinates, the continuous surface is obtained through the least square fitting of the basic Zernike polynomial, the coefficient matrix of the Zernike polynomial participating in the fitting is analyzed, the number of terms with non-zero weight in the coefficient matrix is selected as the Zernike effective term of this fitting; Step two: the aberration pattern corresponding to the Zernike effective term obtained in step one is compared with the position distribution characteristics of each collimating unit, and the item number characteristics of the Zernike effective term with higher correlation with the position distribution characteristics of each collimating unit are summarized, more required item number characteristics of the Zernike effective term are extrapolated, and the characteristic equation of the corresponding term is calculated and generated; Step three: the characteristic equation of the Zernike effective term obtained in step two is composed into a new Zernike polynomial matrix, which is used as an independent orthogonal coordinate system participating in the surface fitting, and a continuous surface free surface compound eye lens surface structure is constructed.

5. The collimating beam of continuous surface fiber laser device of claim 4, wherein the optimized Zernike polynomial fitting method is characterized by: The specific implementation method is as follows: Step one: selecting the Zernike effective term; For the case that the seven collimating units are distributed in a regular hexagon, the Zernike terms with the aberration pattern of each order spherical aberration and the angle direction being an integer multiple of six are selected as the Zernike effective term; Step two: obtaining the item number characteristics of the Zernike effective term and calculating and generating the characteristic equation of the Zernike effective term; Firstly, the item number characteristics of each order spherical aberration are determined, and for each even order n, the item number characteristics j of the Zernike effective term are as follows: j1=1+(n+1)(n+2) / 2 (1) Secondly, the item number characteristics of the Zernike term with the angle direction being an integer multiple of six are obtained, and because the azimuth frequency m changes with the order n, the azimuth frequency m needs to be divided into two cases according to the order n. Case one, n starts from 1 and every 4 polynomial order n, the number of Zernike effective term is j: floor represents the down rounding j2=6*floor((n+1) / 6)+(n+1)(n+2) / 2+1 (2) Case two, n starts from 3 and every 4 polynomial order n, the number of Zernike effective term is j: j3=6*floor((n+1) / 6-1)+(n+1)(n+2) / 2+6 (3) In summary, the obtained Zernike effective term number j1, j2, j3 is arranged in ascending order, and the highest order number n is obtained (max) At this time, the aberration pattern is each level of spherical aberration and the Zernike term number j whose angle direction is an integer multiple of six; According to the obtained term number j, the corresponding order n is obtained: According to the term number j, the azimuthal frequency m is obtained: The acquisition of the azimuthal frequency m is divided into two cases: When n is even: m 偶 = 2 x floor((2j + 1 - n(n + 1)) / 4) (5) When n is odd: m 奇 = 2 x floor((2j + 1 - n(n + 1)) / 4) + (-1) α (6) Where the positive and negative of a is judged as follows: 1) In the case of (n+1) can be divided by 4, (n+j) is even, a=1, (n+j) is odd, a=0; 2) In the case of (n+1) can not be divided by 4, (n+j) is even, a=0, (n+j) is odd, a=1; Therefore, according to the order of j from small to large, substitute into formula (4), (5), (6) in turn, obtain the order n and the azimuthal frequency m corresponding to each term number j, and then bring into formula (7) to obtain the characteristic equation of the corresponding Zernike effective term; Zernike polynomial expansion formula: where (p, q) are pupil polar coordinates, radial circular polynomials The expansion is for ρ n , ρ n-2 ,..., and ρ m n times polynomial; Step three, the obtained characteristic equation is composed into a new Zernike polynomial matrix, which is an independent orthogonal coordinate system participating in the optimization of surface fitting, and a continuous surface free-form compound eye lens surface structure is constructed.

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