Freeform surface collimator and its freeform surface configuration method and application

Abstract

The application discloses a free-form surface collimator, a free-form surface configuration method and application thereof, and belongs to the field of optical engineering. The free-form surface collimator comprises a total internal reflection lens and a free-form surface light mixing rod. The free-form surface light mixing rod comprises a free transmission section at a front end, a free-form surface reflection section at a middle section and a uniform light exit section at a rear end. The free-form surface reflection section is a gradually changing diameter curved surface connecting the free transmission section and the uniform light exit section. The free-form surface configuration method comprises the following steps: setting the lengths of the front end and the rear end of the light mixing rod, determining the starting point of the free-form surface section; calculating the incident angles of light rays reaching the free-form surface reflection section at different exit points; calculating the average incident angle of the reflection point according to the radiation intensity weight; obtaining the slope of the reflection point and the coordinates of the next reflection point according to the average incident angle; repeating the above steps until the preset final reflection point is reached; fitting the reflection points into a curve to obtain the outer contour line of the free-form surface reflection section of the light mixing rod, and integrally modeling the light mixing rod. The collimator can greatly reduce the divergence angle of the LED light beam, improve the light beam uniformity and effectively increase the transmission distance.

Description

Technical Field

[0001] This invention relates to an optical device, specifically to a freeform surface collimator, its construction and forming method, and its application. Background Technology

[0002] Light-emitting diodes (LEDs), as a new generation of light source, have advantages such as small size, low power consumption, long lifespan, high brightness, low heat generation, and strong controllability. They are widely used in various indicator lights, indoor and outdoor lighting, and solar simulators. LEDs can also be used as a light source in long-distance visible light wireless power transmission systems. However, in field illumination, the existing reflector-type focusing and collimating effects are poor, limiting the brightness of long-distance directional lighting. When using LEDs for long-distance visible light power transmission and visible light communication, the beam diverges, resulting in an excessively large light spot, making reception difficult and reducing light energy utilization. When used in solar simulators, current LED solar simulators have very short transmission distances and small illumination areas, making them unsuitable for the overall testing of large-area solar cell arrays.

[0003] In the aforementioned typical application scenarios, beams with high parallelism and good collimation are required to accommodate long-distance energy transmission from LED light sources. However, LED light sources have large divergence angles and large emitting surfaces, making it difficult for existing focusing collimation systems to further improve the collimation of LED light sources. This results in significant beam divergence, very low power density, and difficulties in light energy reception during long-distance applications. Therefore, those skilled in the art have conducted extensive research and constructed various collimation systems in hopes of improving the collimation of LED light sources.

[0004] Chinese patent application number 202223178202.4, entitled "A Novel LED Collimation System", includes a light source and two collimating lenses distributed on the light emission channel of the light source. The light emitted by the LED is collimated by combining two separate plano-convex lenses. This system has a complex structure and is inconvenient to install. When the lens radius is small, the light utilization rate is low. The collimation effect of the beam is poor and the transmission efficiency is low when transmitting the beam over long distances.

[0005] Chinese patent application number 202221521857.4, entitled "A High Collimation and High Uniformity LED Optical System," includes a support device and a reflector. An LED light source is mounted on the support device, and the reflector performs secondary collimation on the beam emitted by the LED. This system is used for calibration testing during LED light source production to improve collimation performance. The device is complex in structure, bulky, and cumbersome to operate.

[0006] Chinese patent application number 202221620981.6, entitled "A Collimation Structure for LEDs," includes a circuit board and an LED light source equipped with a primary lens, a parabolic reflector, and a secondary collimating lens. The light emitted by the LED first passes through the primary lens, then is refracted by the secondary collimating lens to reach the parabolic reflector, and is collimated and emitted after reflection by the reflector, or is directly emitted after refraction by the secondary collimating lens. This device can reduce the divergence angle of LED light, but the structure is complex and it is difficult to adapt to the collimation of extended light sources. Summary of the Invention

[0007] To address the problems existing in the prior art, the technical problem to be solved by this invention is to provide a freeform surface collimator that can collimate and converge divergent light to achieve uniform light, reduce the divergence angle of the light source, and improve the light energy utilization rate and light spot uniformity of the light source during long-distance transmission. This invention also provides a method for constructing and shaping this freeform surface. Furthermore, it provides an application of this freeform surface collimator in LED light source collimation.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a freeform collimator, comprising a total internal reflection lens (TIR) ​​and a freeform surface mixing rod (hereinafter referred to as "mixing rod") attached to the upper end face of the TIR lens. The TIR lens is a cone with a cavity at the bottom, and the freeform surface mixing rod is a variable diameter cylinder. The freeform surface mixing rod consists of a free transmission section at the front end, a freeform surface reflection section in the middle, and a uniform light emission section at the rear end, from bottom to top. The diameter of the free transmission section is smaller than the diameter of the uniform light emission section, and the freeform surface reflection section is a gradually changing diameter surface connecting the free transmission section and the uniform light emission section.

[0010] Secondly, the present invention provides a method for constructing a freeform surface collimator, comprising the following steps:

[0011] Step 1: Set the lengths of the free transmission section and the uniform light emission section; determine the coordinates of the starting point of the freeform surface reflection section. The x-coordinate of the starting point is the radius of the free transmission section, and the y-coordinate of the starting point is the sum of the lengths of the total internal reflection lens and the free transmission section along the principal optical axis.

[0012] Step 2: Calculate the nth reflection point P on the freeform surface reflection segment when different light-emitting points of the LED light source reach along different optical paths. n At that time, the angle of the incident light ray;

[0013] Step 3: Calculate the radiation intensity distribution function of the Lambert radiator to reach P. n The radiant intensity weights of light rays at different incident angles are used to calculate the average value of the incident angles according to the radiant intensity weights of the incident rays, thus obtaining P. n Average angle of incidence at point

[0014] Step 4, according to P n Calculate P based on the average incident angle of the point. n The slope of the tangent line at the point k n Combined with P n Point coordinates and k n And the pre-set P n With P n+1 The difference in the horizontal coordinates ΔX yields P n+1 The coordinates of the point;

[0015] Step 5: Determine P at this time. n+1 Does the x-coordinate of the point reach the radius of the preset uniform light emission segment? If yes, proceed to step 6; otherwise, return to step 2.

[0016] Step 6: Fit the outer contour line of the freeform surface reflection segment based on the coordinates of all reflection points calculated iteratively in Step 5, and then perform integrated modeling of the three-segment light mixing rod.

[0017] Thirdly, the present invention also provides the application of the above-mentioned freeform surface collimator in LED light source collimation.

[0018] The basic working principle of LED light source collimation is:

[0019] Total internal reflection (TIR) ​​lenses can adjust the light emitted from a point light source to be parallel to the principal optical axis through reflection and refraction. However, actual LED light sources are not ideal point light sources. Even after the TIR lens shapes the beam, there will still be a large angle between the light rays and the principal optical axis, which increases the overall divergence angle of the TIR lens output. Therefore, a freeform surface reflection section is added to the light mixing bar to perform secondary shaping on the beam with a large deviation angle in the light mixing bar, thereby reducing the overall divergence angle of the collimator, improving the light energy utilization rate of the receiving surface, and improving the uniformity of the light spot on the target plane by relying on the total internal reflection on the side of the light uniform output section of the light mixing bar.

[0020] The technical effects of this invention are:

[0021] 1. A freeform surface light mixing bar is used as the main structure, which improves the collimation performance of the LED light source during long-distance transmission, and the uniformity of the light spot on the target plane can be improved through the uniform light emission section of the light mixing bar.

[0022] 2. The incident end adopts a total internal reflection structure, which improves the utilization rate of the light emitted by the LED and the light utilization rate of the LED emission system.

[0023] 3. The overall structure of the present invention is simple and can be manufactured in one piece or made in sections and then seamlessly connected.

[0024] 4. The integrated structure forming method proposed in this invention can be customized according to different LED light sources. Therefore, this invention can be used in fields such as long-distance lighting, visible light energy transmission and sunlight simulation to achieve light mixing and collimation of single LED light sources and multi-LED light source arrays. Attached Figure Description

[0025] The accompanying drawings of this invention are described below:

[0026] Figure 1 This is a structural diagram illustrating the collimation principle of the freeform surface collimator of the present invention;

[0027] Figure 2 This is a schematic diagram showing the distribution of the collimator beam converged by the collimator of the present invention;

[0028] Figure 3 for Figure 1 A schematic diagram illustrating the calculation principle of the contour line of the reflection segment of a freeform surface;

[0029] Figure 4 for Figure 1 Flowchart for calculating the contour line of the reflection segment of a freeform surface;

[0030] Figure 5 A comparison diagram of the radial distribution of light spot and light intensity at a distance of 5m between the collimator of the present invention and a cylindrical collimator;

[0031] (a) The light spot of the present invention; (b) The light spot of the cylindrical collimator;

[0032] (c) Light intensity of the present invention; (d) Light intensity of the cylindrical collimator.

[0033] In the diagram: 1. Total internal reflection lens; 2. Freeform surface light mixing bar; 21. Free transmission section; 22. Freeform surface reflection section; 23. Uniform light emission section; 3. LED light source; 4. Receiving plane. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0035] To clearly describe the invention, this patent application uses the directional terms "upper" and "lower" for distinction. The terms "upper" and "lower" are determined based on the arrangement of the above figures. When the actual use direction of the invention changes, the terminology of the orientation will change accordingly, and this should not be regarded as a limitation on the scope of patent protection.

[0036] like Figure 1As shown, the freeform collimator of the present invention includes a total internal reflection lens 1 and a freeform surface mixing rod 2 attached to the upper end face of the total internal reflection lens 1. The total internal reflection lens 1 is a cone with a cavity at the bottom, which is used to place a light source. The freeform surface mixing rod 2 is a variable diameter cylinder. From bottom to top, the freeform surface mixing rod 2 consists of a free transmission section 21 at the front end, a freeform surface reflection section 22 in the middle, and a uniform light emission section 23 at the rear end. The diameter of the free transmission section 21 is smaller than the diameter of the uniform light emission section 23. The freeform surface reflection section 22 is a gradually changing diameter surface connecting the free transmission section 21 and the uniform light emission section 23.

[0037] The entire invention is solid, and is made of glass or acrylic. The three sections of the freeform surface light mixing rod 2 can be manufactured separately or integrally; the total internal reflection lens 1 and the freeform surface light mixing rod 2 can also be manufactured separately or integrally. The freeform surface collimator of the present invention can be coated with a reflective material to avoid light leakage.

[0038] Since the light source is not an ideal point light source, but an extended light source of different shapes, the surface shapes of the total internal reflection lens 1 and the freeform surface reflection section 22 in the middle section of the light mixing rod are formed by optimized calculations using the freeform surface construction method of this invention. The diameter of the free transmission section 21 at the front end of the light mixing rod should depend on the surface shape parameters of the total internal reflection lens 1, so that the light emitted from the upper end surface of the total internal reflection lens 1 is coupled into the free transmission section 21 at the front end of the light mixing rod to the maximum extent.

[0039] See Figure 2 The light emitted by the LED is first collimated and focused by the total internal reflection lens 1, then collimated a second time by the free-form surface reflection section 22 in the middle of the light mixing rod, and then homogenized by the uniform light output section 23 at the rear end. The light is emitted with a small divergence angle and high light intensity uniformity, and reaches the target plane 4 to obtain a converging light spot.

[0040] The forming principle of the freeform surface reflective segment 22 of the present invention:

[0041] Because the LED extended light source has a large divergence angle, the beam collimated by the total internal reflection lens 1 still diverges at a large angle. Therefore, it is necessary to shape the free surface of the free reflection section 22 in the middle of the light mixing rod and perform a second collimation.

[0042] See Figure 3 For each defined point P on the freeform surface reflection segment 22 n Multiple light-emitting points on the LED extended light source have their light rays passing through the total internal reflection lens 1 and the free transmission section 21, reaching P at different angles and along different paths. n Point, these rays of light reach P n The angle between the point and the principal optical axis varies, making it impossible to find a P-axis. n The angle of the tangent plane at the point makes all points reaching P... nThe light rays from point P all emerge at an angle parallel to the principal axis, so for rays reaching P... n The angle of the ray from the point is used to calculate P based on the radiation intensity distribution function of the Lambertian radiator. n The radiation intensity weights of light rays at different incident angles are calculated, and the average value is obtained by averaging the radiation intensity weights of the incident rays over the incident angles to obtain P. n The average incident angle of the point. Then, the freeform surface of the reflection segment 22 is solved; the solution process is described in [link to solution procedure]. Figure 4 .

[0043] like Figure 4 As shown, the freeform surface collimator construction method of the present invention includes the following steps:

[0044] Step 1: Set the lengths of the free transmission section 21 and the uniform light emission section 23, as well as the maximum radius x of the light mixing rod. max Set the maximum radius x of the light mixing rod. max Not less than 1.2 times the minimum radius x1 at the starting end. Set the maximum radius x of the mixing rod. max It should be considered that if its value is too small, the freeform surface reflection section will reflect too little light, reducing the collimation performance of the system, but x max The value of x should not be too large; an excessively large x max This will lead to an increase in the size of the device and an excessively large aperture at the transmitting end, thus reducing the homogenizing effect of the homogenizing section. Determine the coordinates (x1, y1) of the starting point P1 of the freeform surface reflection section 22, where x1 is the radius of the free transmission section of the mixing rod, and y1 is the sum of the lengths of the total internal reflection lens 1 and the free transmission section 21 along the principal optical axis.

[0045] Step 2: Using the relationship obtained from the optical path calculation, calculate the nth reflection point P from different exit points on the LED extended light source through the total internal reflection lens 1 and the free transmission section 21 to the freeform surface reflection section 22. n The angle of incidence of the ray of light at a point.

[0046] Step 3: According to the radiation intensity distribution function of the Lambertian radiator, I = I0 cosα (α is the angle between the ray from the emitting point and the normal to the LED emitting surface, and I0 is the ray intensity along the normal direction of the emitting point on the LED; for simplicity, the ray intensity along the normal direction of the entire LED emitting surface is considered to be equal), for each determined point P... n Different beams of light emitted from different points on the luminous surface will reach P via different paths. n Point, these beams reach P n At point P, the angle θ of incidence of the incident ray at that point is also different for each point. n The incident angle θ of all light rays from a point is averaged according to their radiant intensity weights. Get Pn Average angle of incidence at point

[0047]

[0048] Where the subscript j represents the j-th light-emitting point of the LED, α j Let θ be the angle between the ray from the j-th emitting point and the normal to the LED emitting surface. j For the light ray from the j-th emitting point to reach P n The angle of incidence at the point, cosα j For the j-th emitting point at P n Radiation intensity weight at a given location.

[0049] Step 4, according to P n Average angle of incidence at point Find P n The slope of the tangent line at the point k n Combined with P n Point coordinates, k n and P n With P n+1 The difference in the horizontal coordinates ΔX yields P n+1 The coordinates of the point.

[0050] The value of ΔX can be adjusted according to the actual situation. The larger the value of ΔX, the lower the precision requirement of the processing equipment. The smaller the value of ΔX, the stronger the collimation capability of the system.

[0051] Step 5: Determine P at this time. n+1 Does the x-coordinate of the point reach the preset radius x of the uniform light output section 23 of the rear section of the light mixing rod? max If yes, proceed to step 6; otherwise, return to step 2.

[0052] Step 6: Fit the obtained series of coordinates into a curve to obtain the outer contour of the free surface reflection section 22 of the light mixing rod, and perform integrated modeling of the free transmission section 21 and the uniform light emission section 23 of the light mixing rod.

[0053] In step 1, for the free-transmission section 21 of the light mixing rod, both excessively short and excessively long lengths will result in less light beam received by the freeform surface reflection section 22, thus reducing the collimation effect of the freeform surface. Based on simulation and considering the relatively small collimator volume, a length of 1.4-1.6 times its diameter for the free-transmission section 21 yields better collimation results.

[0054] If the uniform beam output section 23 is too short, the uniformity of the output beam will decrease; if it is too long, the system size will increase, reducing portability. A uniform beam output section 23 with a length twice that of the free transmission section 21 can achieve a better uniform beam effect.

[0055] It should be noted that, in the embodiments of the present invention, based on a given LED extended light source, the preferred range of length dimensions and proportional relationships is given by simulation. However, based on different LED extended light sources, this method can still be used to design freeform surfaces, and the size design is not limited to the above-mentioned proportional relationships.

[0056] The freeform surface collimator of the present invention is used in the collimation of LED light sources.

[0057] See Figure 1 The LED light source 3 is installed at the center of the cavity at the bottom of the cone of the total internal reflection lens 1. The LED extended light source located in the cavity of the total internal reflection lens 1 emits a light beam a with a small angle to the principal optical axis, which enters the free transmission section 21 of the mixing rod after being refracted by the total internal reflection lens 1; the light beam b with a large angle to the principal optical axis is first refracted into the total internal reflection lens 1, and then reflected by the total internal reflection lens 1 before entering the free transmission section 21 of the mixing rod.

[0058] After the light beam enters the free propagation section 21, it travels a certain distance. The beam that deviates significantly from the principal optical axis will reach the freeform surface reflection section 22 in the middle of the mixing rod. After reflection by the freeform surface reflection section, the angle between the beam and the principal optical axis is reduced, thereby achieving collimation. Then, the beam undergoes several total internal reflections through the wall of the mixing rod in the homogenization exit section 23 at the rear of the mixing rod, improving the uniformity of the final emitted light spot.

[0059] like Figure 5 As shown, the collimator spot distribution of the present invention, under the same transmission distance, is described in [reference needed]. Figure 5 (a) See the image spot distribution effect of a conventional cylindrical collimator. Figure 5 (b) As can be seen, the implementation effect of the present invention results in a smaller beam divergence angle and a more uniform beam spot, which can significantly improve the visible light transmission distance and distribution uniformity. For the intensity distribution of the collimator beam spot of the present invention, please refer to [link to relevant documentation]. Figure 5 (c) For the intensity distribution of the light spot in a conventional cylindrical collimator, see [reference needed]. Figure 5 (d) The light intensity of the present invention is significantly enhanced.

Claims

1. A freeform surface collimator, characterized in that: It includes a total internal reflection lens (1) and a free-form surface mixing rod (2) attached to the upper end face of the total internal reflection lens (1); the total internal reflection lens (1) is a cone with a cavity at the bottom; the free-form surface mixing rod (2) is a variable diameter cylinder, and the free-form surface mixing rod (2) consists of a free transmission section (21) at the front end, a free-form surface reflection section (22) in the middle section and a uniform light emission section (23) at the rear end from bottom to top. The diameter of the free transmission section (21) is smaller than the diameter of the uniform light emission section (23), and the free-form surface reflection section (22) is a gradually changing diameter surface connecting the free transmission section (21) and the uniform light emission section (23).

2. The freeform surface collimator according to claim 1, characterized in that: The freeform collimator has a reflective material coated on its surface.

3. The method for constructing a freeform surface collimator as described in claim 1 or 2, characterized in that: it includes... The following steps: Step 1: Set the lengths of the free transmission section and the uniform light emission section; determine the coordinates of the starting point of the freeform surface reflection section. The x-coordinate of the starting point is the radius of the free transmission section, and the y-coordinate of the starting point is the sum of the lengths of the total internal reflection lens and the free transmission section along the principal optical axis. Step 2: Calculate the nth reflection point P on the freeform surface reflection segment when different light-emitting points of the LED light source reach along different optical paths. n At that time, the angle of the incident ray; Step 3: Calculate the radiation intensity distribution function of the Lambert radiator to reach P. n The radiant intensity weights of light rays at different incident angles are used to calculate the average value of the incident angles according to the radiant intensity weights of the incident rays, thus obtaining P. n The average incident angle θ of the point; Step 4, according to P n Calculate P based on the average incident angle of the point. n The slope of the tangent line at the point k n Combined with P n Point coordinates and k n And the pre-set P n With P n+1 The difference in the horizontal coordinates ΔX yields P n+1 The coordinates of the point; Step 5: Determine P at this time. n+1 Does the x-coordinate of the point reach the radius of the preset uniform light emission segment? If yes, proceed to step 6; otherwise, return to step 2. Step 6: Fit the outer contour line of the freeform surface reflection segment based on the coordinates of all reflection points calculated iteratively in Step 5, and then perform integrated modeling of the three-segment light mixing rod.

4. The method for constructing freeform surfaces according to claim 3, characterized in that: In step 3, P n Average angle of incidence at point In the formula, the subscript j represents the j-th light-emitting point of the LED, and α j Let θ be the angle between the ray from the j-th emitting point and the normal to the LED emitting surface. j For the light ray from the j-th emitting point to reach P n The angle of incidence at the point, cosα j For the j-th emitting point at P n Radiation intensity weight at a location; cosα j =I j / I0,I j I0 is the radiation intensity distribution function value of the Lambertian radiator, and I0 is the luminous intensity in the direction normal to the LED emitting surface.

5. The method for constructing freeform surfaces according to claim 4, characterized in that: in In step 1, the length of the free transmission section is 1.4-1.6 times the diameter of the free transmission section, and the length of the uniform light emission section is twice the length of the free transmission section.

6. The freeform surface collimator as described in claim 1 or 2 is applied to the collimation of LED light sources.

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