Illuminating system based on double-conical-surface lens and composite ellipsoid cavity and design method thereof

Abstract

The invention discloses an illumination system based on a double-conical-surface lens and a composite ellipsoidal cavity and a design method thereof.The illumination system comprises the double-conical-surface lens and the composite ellipsoidal cavity which are coaxially arranged front and back between a laser light source and a target receiving surface, the front end of the double-conical-surface lens is a convex conical surface, the rear end of the double-conical-surface lens is a concave conical surface, and the conical degree of the concave conical surface is larger than that of the convex conical surface; light rays are refracted by the double-conical-surface lens to form annular converged light rays with a certain focal depth, the composite ellipsoid cavity is of an out-of-focus structure and corresponds to focus distribution of the double-conical-surface lens, and the annular converged light rays form uniform light spots on a target receiving surface after passing through the composite ellipsoid cavity; according to the illumination system, center accumulated energy of a point light source is transferred to an edge area through the double-conical-surface lens to form annular irradiance distribution with a specific defocusing amount, annular irradiation energy is evenly distributed on a target receiving surface through the matched designed composite ellipsoid cavity, and the illumination system is simple in structure, easy to design and machine and small in energy loss; the design algorithm simplifies and optimizes a free-form surface design algorithm.

Description

Technical Field

[0001] The present invention relates to the technical field of non-imaging light concentration, and specifically refers to an illumination system based on a bi-conical lens and a compound ellipsoidal cavity and a design method thereof. Background Art

[0002] Uneven target illuminance and a large illuminance dynamic range are key factors affecting imaging quality. A uniform illumination system can effectively eliminate background interference, extract the target from a complex background, improve imaging quality, reduce the difficulty of image processing, and increase the information extraction speed and imaging quality. Since the energy distribution of a laser beam is Gaussian, it brings many adverse effects to direct illumination. By shaping the laser beam with a Gaussian energy distribution into a laser beam with a super-Gaussian or flat-top energy distribution through laser beam shaping technology, the laser illumination quality can be effectively improved.

[0003] Existing laser shaping technologies usually adopt methods such as aspherical lens group shaping, microlens array shaping, and diffractive optical elements. The aspherical lens group shaping method has a relatively simple structure and little light energy loss, but it requires a sufficiently high order to achieve complex illumination and it is difficult to achieve precise control of the light beam; the microlens array shaping method has a relatively high homogenization degree, but the structure is relatively complex and the energy loss is large; diffractive optical elements have a large design freedom and high diffraction efficiency, but the manufacturing difficulty is relatively large; and currently commonly used laser shaping technologies are mostly applied to uniform illumination in a small field of view. For uniform illumination in a large field of view, a light source array structure and a free-form surface design are mostly adopted. Among them, the array structure design is relatively simple, but there are problems such as large volume and poor uniformity; the free-form surface has a variety of structures and a large design freedom, but a relatively complex mathematical model and optimization algorithm are required in the design process.

[0004] In view of the problems of complex design and poor uniform illumination effect for a large field of view with a small aperture existing in the existing laser beam homogenization technology, it is difficult to meet the application requirements of laser processing and laser illumination. The present design proposes an illumination system based on a bi-conical lens and a compound ellipsoidal cavity and a design method thereof. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide an illumination system based on a bi-conical lens and a compound ellipsoidal cavity and a design method thereof to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] An illumination system based on a bi-conical lens and a compound ellipsoidal cavity, in which a bi-conical lens and a compound ellipsoidal cavity are coaxially arranged in sequence before and after between a laser light source and a target receiving surface. The target receiving surface is perpendicular to the optical axis. The front end surface of the bi-conical lens is a convex conical surface, and the rear end surface is a concave conical surface. The taper of the concave conical surface is greater than that of the convex conical surface. After the light rays of the laser light source are refracted by the bi-conical lens, an annular converging light with a certain depth of focus is formed behind it. The compound ellipsoidal cavity is an off-focus structure, and its focal point distribution corresponds to that of the bi-conical lens. The annular converging light is reflected and shaped by the compound ellipsoidal cavity to form a uniform light spot on the target receiving surface.

[0008] Furthermore, the bi-conical lens satisfies and In the formula: ɑ1 is the angle between the concave conical surface and the optical axis, ɑ2 is the angle between the concave conical surface and the optical axis; δ is the angle between the optical path of the laser light source and the optical axis, h is the radius of the bi-conical lens, and f is the distance from the laser light source to the vertex of the concave conical surface.

[0009] A design method for an illumination system based on a bi-conical lens and a compound ellipsoidal cavity, which includes the following contents:

[0010] I. Establish a virtual coordinate system between the laser light source and the bi-conical lens, and solve the focal point change coordinate formula of the annular converging light after being refracted by the bi-conical lens;

[0011] The coordinates of the laser light source on the concave conical surface are (x k , y k ), and their coordinate relationship is shown in formula (1):

[0012]

[0013] Among them, f n is the distance from the laser light source to the coordinate origin, and f k is the distance from the laser light source to the vertex of the concave conical surface;

[0014] Establish the refraction light equation (2) in the bi-conical lens, and the angle between the refraction light and the optical axis β = 90° - ɑ1 - γ2;

[0015] y = tan(β)x + y k -tan(β)x k (2)

[0016] According to the geometric relationship, establish the convex conical surface equation (3);

[0017] y = -tan(a2)x + (f k +d)tan(a2) (3)

[0018] Among them, d is the distance between the vertex of the concave conical surface and the vertex of the convex conical surface;

[0019] Solve the refraction point coordinate formula (4) of the refracted light on the convex conical surface from the refracted light equation (2) and the convex conical surface equation (3);

[0020]

[0021] According to the geometric relationship, and by simultaneously solving formulas (1) and (4), obtain the focal point change coordinate formula (5) of the annular converging light after refraction by the bi-conical lens;

[0022]

[0023] where, θ is the angle between the optical path of the annular converging light and the optical axis.

[0024] II. Design algorithm of the composite ellipsoidal cavity based on SQM:

[0025] Take the focal point of each optical path of the bi-conical lens as the focal point for the design of the micro-ellipsoidal surface of the composite ellipsoidal cavity. At the same time, set the width and the central diameter R′ of several consecutive mapped light spot rings on the target receiving surface i , divide the annular converging light into several consecutive incremental light beams, and the angle between the center of the light beam and the optical axis is θ' i , according to formula (5), the focal point F of the micro-ellipsoidal surface can be solved from θ' i , according to the optical path characteristics and the optical characteristics of the ellipse, use the distance L from the target receiving surface to the origin, the central diameter R′ i , the angle θ' between the center of the light beam and the optical axis i , and the focal point F i and solve the relevant parameters of each micro-ellipsoidal surface Eq i . i

[0026] Furthermore, considering the mapping superposition uniformity on the target receiving surface, divide the annular converging light by an arithmetic progression, as shown in formula (6),

[0027]

[0028] then θ′ i =(θ i +θ i+1 ) / 2.

[0029] Even further, within the angle between θ i and θ i+1 , the radiant flux of the light beam is approximately Gaussian distributed, and its radiation peak is located at θ′ i , the corresponding peak position mapped to the target receiving surface is R′ i , the outer diameter of its mapped light spot ring is R i , and the inner diameter is R i+1, the width of the mapped light spot ring is equal to the full width at half maximum of the Gaussian beam peak on the target receiving surface, and the adjacent mapped light spot rings have radiation peak regions and radiation trough regions, i.e., R′ i serves as the outer diameter of the next mapped light spot ring, and R i+1 serves as the central diameter of the next mapped light spot ring. Accordingly, the relevant parameters of each micro-ellipsoid Eq i are solved.

[0030] Furthermore, an adjustment factor ξ is introduced to correct the superposition uniformity of the mapped light spot ring in the immediate vicinity of the optical axis itself, and R N+1 = Ltan(ξ×θ N ).

[0031] Compared with the prior art, the illumination system based on a bi-conical lens and a compound ellipsoidal cavity and its design method of the present invention have the following beneficial effects:

[0032] This illumination system transfers the central accumulated energy of the point light source to the edge region through the bi-conical lens to form an annular irradiance distribution with a specific defocus amount, overcoming the spot center energy accumulation effect caused by the Gaussian beam transmission energy gradient in the traditional coaxial illumination system. The designed compound ellipsoidal cavity evenly distributes the annular irradiation energy on the target receiving surface. This optical system has a simple structure, is easy to design and process, has a streamlined optical path, has less energy loss during shaping and uniform distribution, and can achieve uniform illumination of a large field of view of the point light source;

[0033] The design algorithm of this illumination system is based on the optical characteristics of the bi-conical lens and the ellipsoid and the geometric optical method, minimizing the radiation energy loss during the light transmission and shaping process and improving the uniformity of the shaped light spot. The compound ellipsoidal cavity is designed using the SQM method, simplifying the free-form surface design algorithm and the optimization algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of the structure of the invention system and its light homogenization optical path disclosed in the present invention;

[0035] Figure 2 is Figure 1 a schematic diagram of the principle of the light deflection optical path of the bi-conical lens in

[0036] Figure 3 is Figure 1 a mapping relationship diagram of the compound ellipsoidal cavity in

[0037] Figure 4 is Figure 1 a structural design flow chart of the compound ellipsoidal cavity in

[0038] Figure 5 is Figure 1 a schematic diagram of the energy homogenization principle on the target receiving surface in

[0039] In the figure: 1. Laser light source; 2. Biconical lens; 3. Compound ellipsoidal cavity; 4. Target receiving surface. Specific embodiments

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only the best embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] The present invention discloses an illumination system based on a biconical lens and a compound ellipsoidal cavity, as Figure 1 shown. The laser light source 1 preferably uses an 808 nm laser source, and the irradiance energy of its light source is Gaussian-distributed. In order to form a desired uniform irradiance distribution on the target receiving surface 4, a biconical lens 2 and a compound ellipsoidal cavity 3 are coaxially arranged in sequence before and after between the laser light source 1 and the target receiving surface 4. The common optical axis of the biconical lens 2 and the compound ellipsoidal cavity 3 is perpendicular to the target receiving surface 4. Referring again to Figure 1 and Figure 2 , both end faces of the biconical lens 2 are conical surfaces, where the front end face is a convex conical surface and the rear end face is a concave conical surface. The laser light source 1 is located on the optical axis of the biconical lens 2. After the point light source is refracted by the biconical lens 2 at the front end, the Gaussian energy distribution is converted into an annular energy distribution, forming an annular irradiance distribution with a specific defocus amount, and converging annular converging light is formed behind the biconical lens 2 with a certain depth of focus.

[0042] In the design, the distance between the laser light source 1 and the vertex of the concave conical surface and the radius of the biconical lens 2 should be respectively adapted to the radiation angle of the laser light source 1, and in order to form converging light, the taper of the concave conical surface is greater than that of the convex conical surface; in addition, according to the optical transmission principle, total reflection will occur when light travels from an optically dense medium to an optically sparse medium. When δ = 0°, the value of γ3 is the largest. In order to reduce energy loss, the angle of γ3 should be less than the critical angle, and the establishment of the compound ellipsoidal cavity 3 should increase θ as much as possible, but θ is limited by the radius h of the biconical lens 2. Therefore, the structural design of the biconical lens 2 needs to satisfy Equation (1) and Equation (2):

[0043]

[0044] In the formula: ɑ1 is the angle between the concave conical surface and the optical axis, ɑ2 is the angle between the concave conical surface and the optical axis, n1 is the refractive index of light entering the biconical lens 2 from air, n2 is the refractive index of light entering air from the biconical lens 2; δ is the angle between the optical path of the laser light source 1 and the optical axis, h is the radius of the biconical lens 2, and f is the distance from the laser light source 1 to the vertex of the concave conical surface;

[0045] The compound ellipsoidal cavity 3 is used for shaping and homogenizing the mapped energy to obtain uniform illumination on the target receiving surface 4. The compound ellipsoidal surface of the compound ellipsoidal cavity 3 is defocused, that is, the foci of the micro-ellipsoidal surfaces are discretized along the optical axis, and the foci of the micro-ellipsoidal surfaces of the compound ellipsoidal cavity 3 are respectively designed based on the focal coordinates of the bi-conical lens 2. That is, the light beam located at the focus after being refracted by the bi-conical lens 2 is projected onto the micro-ellipsoidal surface corresponding to the focus.

[0046] The free ellipsoidal surface design of the compound ellipsoidal cavity 3 adopts the SQM method. The first focus at the front end of the focal depth of the annular converging light is used as the first focus of the micro-ellipsoidal surface at the entrance end of the compound ellipsoidal cavity 3. Combining with the irradiance distribution design of the target receiving surface 4, the focal coordinates of the micro-ellipsoidal surfaces of the compound ellipsoidal cavity 3 are sequentially determined through the reverse optical path tracing algorithm, and then the ellipsoidal surface parameters of the defocused compound ellipsoidal cavity 3 are obtained. The specific design method of its illumination system design is as follows:

[0047] I. Establish a virtual coordinate system between the laser light source 1 and the bi-conical lens 2, and solve the focal change coordinate formula of the annular converging light after being refracted by the bi-conical lens 2;

[0048] Assume that the coordinates of the light beam of the laser light source 1 on the concave conical surface are (x k , y k ), as Figure 2 shown, the coordinate relationship is as shown in formula (1):

[0049]

[0050] Among them, f n is the distance from the laser light source 1 to the origin of coordinates, and f k is the distance from the laser light source 1 to the vertex of the concave conical surface;

[0051] Establish the refraction light equation (2) in the bi-conical lens 2, and the angle β between the refraction light and the optical axis is β = 90° - ɑ1 - γ2;

[0052] y = tan(β)x + y k -tan(β)x k (2)

[0053] According to the geometric relationship, establish the convex conical surface equation (3);

[0054] y = -tan(a2)x + (f k + d)tan(a2) (3)

[0055] Among them, d is the distance between the vertex of the concave conical surface and the vertex of the convex conical surface;

[0056] From the refraction light equation (2) and the convex conical surface equation (3), solve the refraction point coordinate formula (4) of the refraction light on the convex conical surface;

[0057]

[0058] According to the law of refraction and Figure 2 the geometric relationship shown in the figure, and by simultaneously solving formulas (1) and (4), the focus change coordinate formula (5) of the annular converging light after refraction by the biconical lens 2 is obtained;

[0059]

[0060] where θ is the angle between the optical path of the annular converging light and the optical axis.

[0061] Second, the design algorithm of the compound ellipsoidal cavity 3 is based on the existing surface design method SQM method (support quadratic surface method), and its specific calculation process is as Figure 4 shown:

[0062] Taking the first focus of the annular converging light as the first focus of the entrance of the compound ellipsoidal cavity 3, discretizing the focal depth, and obtaining the divergence angle and coordinates of the discrete foci through the Figure 2 geometric relationship and formula (10) shown in the figure. Taking the annular converging light as the incident light source of the compound ellipsoidal cavity 3, dividing its radiation angle, and considering the total radiation flux Φ All and the radiation flux Φ i within each divided angle range are determined by formula (III) and formula (IV) respectively:

[0063]

[0064] Since the annular area of the mapped light ring on the target receiving surface 4 has a non-linear increasing relationship with the radius, under the same radiation flux, the larger the annular area, the less conducive to achieving the superposition of energy. Therefore, the incident angle of the discretized annular converging light is segmented by an arithmetic progression to form a continuous incremental light beam, as shown in formula (6), so as to balance the change of the mapped ring area and further achieve the uniformity of regional superposition;

[0065]

[0066] Then the angle between the center of the segmented light beam and the optical axis is θ′ i =(θ i +θ i+1 ) / 2;

[0067] In addition, the radiation flux of the light beam segmented by the angle between θ i and θ i+1 is approximately Gaussian distributed. The micro-mapping relationship between the mapped light spot ring formed on the target receiving surface 4 and the discretized incident angle corresponds to the peak position on the target receiving surface 4 as R′ i , and at the same time, the mapped light spot ring is Gaussian-like distributed, and the full width at half maximum of the peak in this region is set as its ring width Ri+1 -R i , so as to facilitate uniform superposition. The adjacent mapped light spot rings achieve uniform illumination through the superposition of the radiation peak region and the radiation trough region, that is, R′ i serves as the outer diameter of the next mapped light spot ring, and R i+1 serves as the central diameter of the next mapped light spot ring;

[0068] For the distance L from the target receiving surface 4 to the origin, according to the optical path characteristics and the optical characteristics of the ellipse, using the central diameter R′ i , the included angle θ' between the beam center and the optical axis i and the focus F i solve the relevant parameters of each micro-ellipsoid Eq i ;

[0069] As Figure 3 shown, in the xoz coordinate system, the intersection point of the mapped light ray reflected by the composite ellipsoidal cavity 3 of the split beam center and the optical axis is the second focus F ci , and its coordinates are (0, c′ i ), that is, (0, 2c i ). This mapped light ray intersects with the outgoing light ray at the θ′ i angle at the F i focus and intersects at A′ i on the micro-ellipsoid (z′ i , x′ i ). According to the ellipse relationship, determine the parameters (ɑ′ i , b′ i , c′ i ) of Eq i ;

[0070] In order to achieve the uniform illumination design of the mapped light spot ring, adjacent micro-ellipsoids have a common coordinate point A′ i+1 (z i+1 , x i+1 ). Taking this coordinate point as the condition for the parameters (ɑ′ i+1 , b′ i+1 , c′ i+1 ) of the next micro-ellipsoid equation Eq i+1 , according to the Figure 4 shown logical relationship, find all the micro-ellipsoid parameters and fit to generate a continuous and smooth elliptical surface.

[0071] As Figure 5 shown in, when the mapped light spot rings in the innermost neighborhood of the optical axis overlap, since its central region is its own superposition region, it is easy to present a peak-valley distribution phenomenon in this region, resulting in uneven central energy. Therefore, it is necessary to adjust the inner ring radius of the innermost mapped light spot ring. Introduce the adjustment factor ξ, then its inner diameter R N+1 = L×tan(ξ×θ N) to correct the superposition uniformity of the innermost ring mapped light spot ring.

[0072] The directional or positional terms such as "front", "rear", "end", "side", "x", "y", "z", etc. mentioned in this article are respectively based on Figures 1 - 3 the coordinate or positional relationship shown in. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation, or be constructed and operated in a specific orientation;

[0073] Moreover, in addition to being used to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the terms "upper", "inner", etc. may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0074] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An illumination system based on a biconical lens and a composite ellipsoidal cavity, characterized by: A double - cone lens and a compound ellipsoidal cavity are coaxially arranged in sequence between the laser light source and the target receiving surface. The target receiving surface is perpendicular to the optical axis. The front end surface of the double - cone lens is a convex conical surface, and the rear end surface is a concave conical surface. The taper of the concave conical surface is greater than that of the convex conical surface. After the light rays of the laser light source are refracted by the double - cone lens, an annular converging light with a certain depth of focus is formed behind it. The compound ellipsoidal cavity is an off - focus structure, and its focal point distribution corresponds to that of the double - cone lens. The annular converging light is reflected and shaped by the compound ellipsoidal cavity to form a uniform light spot on the target receiving surface.

2. The illumination system based on a bi-conical lens and a compound ellipsoidal cavity according to claim 1, wherein: The biconical lens satisfies and Wherein: ɑ1 is the angle between the concave cone surface and the optical axis, ɑ2 is the angle between the concave cone surface and the optical axis; δ is the angle between the optical path of the laser light source and the optical axis, h is the radius of the biconical lens, and f is the distance from the laser light source to the vertex of the concave cone surface.

3. A lighting system design method, based on the lighting system of a double conical surface lens and a compound ellipsoidal cavity according to claim 1 or 2, characterized in that, It includes the following contents:

1. Establish a virtual coordinate system between the laser light source and the double - cone lens, and solve the focal point change coordinate formula of the annular converging light after being refracted by the double - cone lens; The coordinates of the laser light source on the concave conical surface are (x k , y k ), and the coordinate relationship is as shown in formula (1): Among them, f n is the distance from the laser light source to the origin of coordinates, and f k is the distance from the laser light source to the vertex of the concave conical surface; Establish the refraction light equation (2) in the double - cone lens, and the angle β between the refraction light and the optical axis is β = 90° - ɑ1 - γ2; y = tan(β)x + y k -tan(β)x k (2) According to the geometric relationship, establish the convex conical surface equation (3); y = -tan(a2)x+(f k +d)tan(a2) (3) Where d is the distance between the vertex of the concave conical surface and the vertex of the convex conical surface; From the refraction light equation (2) and the convex conical surface equation (3), solve the refraction point coordinate formula (4) of the refraction light on the convex conical surface; According to the geometric relationship, and by combining formula (1) and (4), obtain the focal point change coordinate formula (5) of the annular converging light after being refracted by the double - cone lens; Where θ is the angle between the optical path of the annular converging light and the optical axis.

2. The design algorithm of the compound ellipsoidal cavity based on the SQM method: Taking the focus of each optical path of the bi-conical lens as the focus of the design of the compound ellipsoidal cavity micro-ellipsoid, and at the same time, setting the widths and the central diameter R' of several consecutive mapped light spot rings on the target receiving surface i , dividing the annular converging light into several consecutive incremental light beams, with the angle between the beam center and the optical axis being θ' i , according to formula (5), the focus F of the micro-ellipsoid can be obtained by solving from θ' i i , according to the optical path characteristics and the optical characteristics of the ellipse, using the distance L from the target receiving surface to the origin, the central diameter R' i , the angle θ' between the beam center and the optical axis i and the focus F i to solve the relevant parameters of each micro-ellipsoid Eq i .​ 4. The lighting system design method according to claim 3, wherein: Considering the mapping superposition uniformity on the target receiving surface, the annular converging light is segmented by an arithmetic progression, as shown in formula (6). Then θ′ i =(θ i + θ i+1 ) / 2。 5. The lighting system design method according to claim 4, wherein: θ i to θ i+1 The radiation flux of the beam within the angle is approximately Gaussian, and its radiation peak is located at θ′ i The peak position corresponding to the target receiving surface is R′ i , the outer diameter of the mapping spot ring is R i , inner diameter is R i+1 , the width of the mapping spot ring is equal to the half-height width of the Gaussian beam peak on the target receiving surface, and the radiation peak area and radiation valley area of adjacent mapping spot rings overlap, that is, R′ i As the outer diameter of the next mapping spot ring, R i+1 As the center diameter of the next mapping spot ring, solve each micro-ellipsoid Eq. i Related parameters.

6. The lighting system design method according to claim 5, wherein: Introduce a regulation factor ξ to correct the superposition uniformity of the mapping light spot ring in the immediate neighborhood of the optical axis, R N+1 = Ltan(ξ × θ N ).

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