Collimation system for diffraction waveguide and application thereof

Abstract

The invention discloses a collimation system for a diffraction waveguide. The collimation system sequentially comprises a first lens group, a diaphragm, a second lens group, a prism equivalent lens, a window protection sheet and an image plane position from an object space to an image space along an optical axis. The first lens group is composed of a positive-focal-power biconvex lens, a negative-focal-power meniscus lens and a balsaming lens. And the second lens group comprises a negative-focal-power biconcave lens, a positive-focal-power meniscus lens and a biconvex / biconcave lens combination to form a double-Gaussian symmetric structure. The total length of the system is less than 90mm, and a full-spherical mirror design is adopted, so that a focal length proportional relation (0.5 lt; f1 / F0lt; 2.5 1t, 2.5 1t; f2 / F0lt; 4.5), the ratio gt of the rear working distance to the focal length; 2. According to the invention, aiming at diffraction waveguide technology optimization, the balsaming lens has stronger chromatic aberration correction capability, and the double-Gaussian structure improves the relative illuminance (gt; 90%), and the overall length of the system is shorter (lt; 90 mm), adapts to the requirement of a diffraction grating for high angle precision of parallel light, is suitable for scenes such as AR glasses and vehicle-mounted HUD, and has the advantages of high collimation and low distortion; 0.15%) and compactness.

Description

Technical Field

[0001] The present invention relates to the field of optical display technology, and specifically to a collimation system for a diffraction waveguide, which is specially designed for the diffraction waveguide technology. By optimizing the lens group structure and the optical focal length distribution, the problems of large chromatic aberration, low edge illumination and volume redundancy in the diffraction grating coupling of the existing collimation system are solved. The collimation system is suitable for scenes such as AR glasses and vehicle-mounted HUD. Background Art

[0002] Optical waveguide technology uses a dielectric substrate to make light input under certain conditions produce total reflection inside the waveguide, and uses specific optical elements to control the direction and intensity of the light, ultimately presenting the image at the display position. Due to its excellent display effect and performance characteristics, optical waveguide technology is expected to be applied to AR glasses, head-up displays, tablet computers and other fields in the future.

[0003] Optical waveguide technology can be divided into geometric waveguide and diffraction waveguide technology, which requires the in-coupling grating to input parallel light of a certain angle, which is modulated by the in-coupling grating and then totally reflected inside the waveguide to transmit the light, and finally the out-coupling grating exit pupil realizes the imaging effect. The key factor of the imaging quality of the waveguide system lies in the imaging quality of the collimation system. Therefore, the design of the collimation system is crucial in the optical waveguide display system. At the same time, the design of the collimation system also needs to comprehensively consider the type of optical machine, the size of the optical waveguide coupling, the waveguide display field of view, etc. It is expected that the ideal collimation system has a compact structure and good cost control. Therefore, designing a collimating lens with a compact structure, controllable cost and high imaging quality is one of the key and difficult points of optical design in this field.

[0004] In summary, traditional compact waveguide collimation systems mostly use a symmetrical double Gaussian structure, but its cemented lens design is not optimized for the dispersion characteristics of the diffraction waveguide, resulting in low coupling efficiency; and the total length of the system is usually more than 100mm, which is difficult to adapt to the miniaturization requirements of optical machines. The present invention introduces a double convex-meniscus cemented lens combination and a double concave lens beam expander, combined with strict focal length ratio control, to significantly improve the chromatic aberration correction capability and compactness. Summary of the invention

[0005] Purpose of the invention: In view of the above existing background, a collimation system for a diffraction waveguide is proposed, which can be used to generate collimated light at different angles required for the in-coupling grating of the waveguide system. Under the premise of meeting high imaging quality, it solves the problems of chromatic aberration and edge illumination, effectively reduces the lens cost, and at the same time, the compact design simplifies the system optical components and reduces the system optical volume.

[0006] Technical solution: A collimation system for a diffraction waveguide, the system along the optical axis from the object side to the image side is respectively a first lens group, an aperture, a second lens group, a prism equivalent lens, a window protective sheet and an image plane position; the first lens group includes a first lens, a second lens, a third lens and a fourth lens, the first lens is a biconvex lens with positive focal power, the second lens is a meniscus lens with negative focal power, the third lens with positive focal power and the fourth lens with negative focal power form a cemented lens, the third lens is a meniscus lens, and the fourth lens is a biconvex lens; the second lens group includes a fifth lens, a sixth lens, a seventh lens and an eighth lens. The fifth lens is a biconcave lens with negative focal power, the sixth lens is a meniscus lens with positive focal power, the seventh lens is a biconvex lens with positive focal power, and the eighth lens is a biconcave lens with negative focal power. The aperture aperture is located between the fourth lens and the fifth lens, the prism equivalent lens is located between the eighth lens and the image plane position, and the window protective sheet is located between the prism equivalent lens and the image plane position.

[0007] Furthermore, the lens surfaces of the collimating system lens group are all composed of spherical mirrors.

[0008] Furthermore, the collimating system lenses are all made of optical glass with a refractive index ranging from 1.50 to 1.85 and an Abbe number of 30 to 65.

[0009] Furthermore, the object-side light of the collimation system is incident with parallel light characteristics and is focused on the image plane through the collimation system.

[0010] Furthermore, when the collimation system is working, light is emitted from the image plane, and after being modulated by the lens, it is incident on the waveguide coupling grating surface in the form of parallel light at different angles.

[0011] Furthermore, the equivalent focal length of the projection lens of the collimating system, the focal length of the first lens group, and the focal length of the second lens group satisfy the following relationship:

[0012] 0.5<|F1 / F0|<2.5;

[0013] 2.5<|F2 / F0|<4.5;

[0014] Wherein, F0 represents the equivalent focal length of the projection lens, F1 represents the focal length of the first lens group, and F2 represents the focal length of the second lens group.

[0015] Furthermore, the rear working distance of the collimation system and the equivalent focal length of the projection lens satisfy the following relationship:

[0016] |BFL / F0|>2;

[0017] Wherein, F0 represents the equivalent focal length of the projection lens, and BFL represents the back working distance of the projection lens.

[0018] In the technical solution of the present invention, the first lens group S1 includes a first lens 11, a second lens 12, a third lens 13 and a fourth lens 14. The first lens 11 is a biconvex lens with positive focal power, which preliminarily changes the angle of light, corrects aberrations, and converges the light to the next lens next to it. The second lens 12 is a meniscus lens with negative focal power, which has a smaller divergent effect on the light, prevents the first lens from causing excessive convergence, and appropriately increases the optical distance of the system. The third lens with positive focal power and the fourth lens with negative focal power form a cemented lens, which can correct chromatic aberration and further converge the light to the aperture. The third lens 13 is a meniscus lens, and the fourth lens 14 is a biconvex lens; the second lens group S2 includes a fifth lens 21, a sixth lens 22, a seventh lens 23 and an eighth lens 24. The fifth lens 21 is a biconcave lens with negative focal power. The sixth lens 22 is a meniscus lens with positive power, the seventh lens 23 is a double convex lens with positive power, and the eighth lens 24 is a double concave lens with negative power. The three lenses together form a symmetrical structure, which reduces the difficulty of correcting the aberration of the system. The four lenses inside the second lens group S2 together form a double Gaussian symmetrical structure, which can effectively suppress the aberration of the system and reasonably increase the total length of the system to meet the size requirements of the waveguide optical machine.

[0019] Furthermore, the chromatic aberration correction capability of the cemented lens satisfies that the axial chromatic aberration in the wavelength range of Δλ<5nm is less than 0.1mm.

[0020] Furthermore, the system is adapted to introduce diffraction waves into a coupling grating, the divergence angle of the output parallel light is less than 0.5°, and the relative illumination of the edge field of view is greater than 90%.

[0021] Furthermore, the incident surface and the exit surface of the prism equivalent lens are coated with an anti-reflection film, the transmittance is greater than 99.5%, and the ratio of its thickness to the total optical path of the system is 1:6 to 1:8.

[0022] The present invention also provides an AR glasses, characterized in that: the collimation system for the diffraction waveguide is integrated in the optical waveguide module, the working band is visible light (400-700nm), and the mixed output of RGB three-color light sources is supported.

[0023] The present invention also provides a vehicle-mounted head-up display (HUD), comprising the collimation system for the diffraction waveguide, wherein the virtual image distortion rate is less than 0.15%, and the thickness of the optical machine module is less than 25 mm.

[0024] Beneficial effects: The first lens group (double convex + meniscus + cemented lens) in the present invention corrects axial chromatic aberration and performs preliminary collimation; the second lens group (double concave + meniscus + double convex / double concave) forms a double Gaussian structure to suppress field curvature and distortion; the total length of the system is <90mm, and the focal length ratio (F1 / F0, F2 / F0) and the back working distance (BFL / F0) meet the strict requirements of the diffraction grating for the uniformity and angle of the light spot. Compared with the prior art, the present invention can effectively suppress various aberrations of the optical system when the collimated light of the waveguide system is generated, and collimate the light emitted from the image source surface into parallel light, which can meet the high-quality collimated light output required by the waveguide display, and the relative illumination of the edge field of view reaches more than 90%. At the same time, combined with the actual optical machine lens installation restrictions, a compact design is realized. Under the condition of meeting the hardware size, all spherical mirrors are used, which effectively reduces the lens cost. At the same time, the compact design simplifies the system optical components and reduces the system optical volume. It can be installed in the waveguide display system as a collimating element. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the optical structure of a collimation system for a diffraction waveguide is created for the present invention;

[0026] Figure 2 A modulation transfer function (MTF) graph of a collimation system for a diffractive waveguide created for the present invention;

[0027] Figure 3 A relative illumination graph of a collimation system for a diffractive waveguide is created for the present invention;

[0028] Figure 4 A grid distortion diagram of a collimation system for a diffractive waveguide is created for the present invention;

[0029] Figure 5 A schematic diagram of the optical path of a collimation system for a diffraction waveguide is created for the present invention.

[0030] Among them, S1-first lens group, S2-second lens group, 11-first lens, 12-second lens, 13-third lens, 14-fourth lens, 21-fifth lens, 22-sixth lens, 23-seventh lens, 24-eighth lens, 3-prism equivalent lens, 4-window protection plate, 5-image plane position. DETAILED DESCRIPTION

[0031] The present invention will be further explained below in conjunction with the accompanying drawings.

[0032] The diffraction waveguide collimation system of the present invention satisfies the high-quality collimated light output required for waveguide display, while achieving a compact design and effectively reducing the lens cost. It can be used as a collimation element for optical waveguide display systems and can ultimately be used in the fields of smart glasses, flat panel displays, and vehicle-mounted head-up displays.

[0033] Example 1

[0034] like Figure 1 A collimation system for a diffraction waveguide is shown, and the system comprises a first lens group, an aperture, a second lens group, a prism equivalent lens, a window protection sheet and an image plane position along the optical axis from the object side to the image side; the first lens group comprises a first lens, a second lens, a third lens and a fourth lens, the first lens is a biconvex lens with positive focal power, the second lens is a meniscus lens with negative focal power, the third lens with positive focal power and the fourth lens with negative focal power form a cemented lens, the third lens is a meniscus lens, and the fourth lens is a biconvex lens; the second lens group comprises a fifth lens, a sixth lens, a seventh lens and an eighth lens. The fifth lens is a biconcave lens with negative focal power, the sixth lens is a meniscus lens with positive focal power, the seventh lens is a biconvex lens with positive focal power, and the eighth lens is a biconcave lens with negative focal power. The lenses in the collimation system are all spherical lenses. By reasonably allocating the focal length and surface shape of each lens, the collimation ability of the lens is effectively improved, and a high degree of collimation of the light output is achieved. The object side light of the collimation system is incident with parallel light characteristics. It is focused on the image plane through the collimation system and is suitable for optical waveguide display systems.

[0035] Example 2

[0036] Furthermore, on the basis of Embodiment 1, the lens group further includes: the first lens 11, the second lens 12, the third lens 13, the fourth lens 14, the fifth lens 21, the sixth lens 22, the seventh lens 23 and the eighth lens 24, all of which have lens surfaces composed of spherical mirrors, and all of which have lens materials composed of glass materials.

[0037] Example 3

[0038] Furthermore, on the basis of Embodiment 1, the method further includes: the equivalent focal length of the projection lens of the collimating system, the focal length of the first lens group, and the focal length of the second lens group satisfy the following relationship:

[0039] 0.5<|F1 / F0|<2.5;

[0040] 2.5<|F2 / F0|<4.5;

[0041] Wherein, F0 represents the equivalent focal length of the projection lens, F1 represents the focal length of the first lens group, and F2 represents the focal length of the second lens group.

[0042] Example 4

[0043] Furthermore, on the basis of Embodiment 1, the method further includes: the rear working distance of the collimation system and the equivalent focal length of the projection lens satisfy the following relationship:

[0044] |BFL / F0|>2;

[0045] Wherein, F0 represents the equivalent focal length of the projection lens, and BFL represents the back working distance of the projection lens.

[0046] In the present invention, the first lens 11 is a meniscus lens with positive focal power, and the second lens 12 is a meniscus lens with positive focal power, which preliminarily changes the angle of the light. The double-layer meniscus lens can correct aberrations more effectively. The third lens with negative focal power and the fourth lens with negative focal power form a cemented lens, which can correct chromatic aberration. The third lens 13 is a biconcave lens, and the fourth lens 14 is a biconvex lens; the fifth lens 21 is a biconcave lens with negative focal power, which expands the collimated light and expands the focal length of the system to meet the optical machine size length requirements. The sixth lens 22 is a meniscus lens with positive focal power, the seventh lens 23 is a biconvex lens with positive focal power, and the eighth lens 24 is a biconvex lens with positive focal power. The three lenses together form a symmetrical structure, which reduces the difficulty of correcting aberrations in the system.

[0047] The cemented lens 13-14 is a combination of H-ZF52 and H-LAK53 glass, with an Abbe number difference of >30, and a dispersion correction capability improved by 30%; the prism equivalent lens (3) is coated with a broadband anti-reflection film (average transmittance of 99.7% in 400-700nm).

[0048] In the present invention, in the first lens group S1, the first lens 11 is a biconvex lens with positive focal power, which preliminarily changes the angle of light, corrects aberrations, and converges the light to the next lens next to it. The second lens 12 is a meniscus lens with negative focal power, which has a smaller divergent effect on the light, prevents the first lens from causing excessive convergence, and appropriately increases the optical distance of the system. The third lens with positive focal power and the fourth lens with negative focal power form a cemented lens, which can correct chromatic aberration and further converge the light to the aperture. The third lens 13 is a meniscus lens, and the fourth lens 14 is a biconvex lens; in the second lens group S2, the fifth lens 21 is a biconcave lens with negative focal power. The sixth lens 22 is a meniscus lens with positive focal power, the seventh lens 23 is a double convex lens with positive focal power, and the eighth lens 24 is a double concave lens with negative focal power. The three lenses together form a symmetrical structure, which reduces the difficulty of correcting aberrations of the system. The four lenses inside the second lens group S2 together form a double Gaussian symmetrical structure, which can effectively suppress system aberrations and reasonably increase the total length of the system to meet the size requirements of the waveguide optical machine.

[0049] In the present invention, the optical parameters of each lens are shown in the figure:

[0050]

[0051] In the present invention, reference is made to Figure 1 : The order of light rays in the collimation system from left to right is: 11-first lens, 12-second lens, 13-third lens, 14-fourth lens, 21-fifth lens, 22-sixth lens, 23-seventh lens, 24-eighth lens, 3-prism equivalent lens, 4-window protection sheet, 5-image plane position for imaging.

[0052] In the present invention, reference is made to Figure 2 : Modulation transfer function of the collimation system. When the cutoff frequency is 66lp / mm, the MTF values ​​under different fields of view are all higher than 0.6. The MTF curve is uniform and decreases slowly, indicating that high-quality collimation effect can be achieved.

[0053] In the present invention, reference is made to Figure 3 : The relative illumination curve of the collimation system shows that the relative illumination under different fields of view is greater than 0.95, indicating that the relative illumination is high, the brightness difference between the imaging center and the edge is small, and the brightness distribution is uniform.

[0054] In the present invention, reference is made to Figure 4 :The grid distortion of the collimation system is controlled within 0.15%, which can effectively control the distortion and improve the imaging quality.

[0055] The compact waveguide collimation system in the present invention can effectively suppress various aberrations of the optical system when the waveguide system generates collimated light, collimate the light emitted from the image source surface into parallel light, and meet the high-quality collimated light output required by the waveguide display. At the same time, the relative illumination of the edge field of view reaches more than 90%. At the same time, combined with the actual optical machine lens installation restrictions, a compact design is achieved. Under the condition of meeting the hardware size, spherical mirrors are used in full, which effectively reduces the lens cost. At the same time, the compact design simplifies the system optical components and reduces the system optical volume. It can be installed in the waveguide display system as a collimation element.

[0056] Example 5

[0057] In this embodiment, the diffraction waveguide collimation system is integrated into the optical waveguide display module of augmented reality (AR) glasses. The light emitted by the micro-projection light source (such as micro-LED or laser diode) forms highly collimated parallel light after passing through the collimation system, and is coupled to the inside of the optical waveguide sheet through the in-coupling grating. The optical waveguide sheet is made of high-refractive index glass material (refractive index ≥ 1.8), and the light is transmitted internally by total reflection, and finally guided to the imaging area of ​​the human eye by the out-coupling grating.

[0058] Optical path details: The image plane position 5 of the collimation system is aligned with the in-coupling grating of the optical waveguide to ensure that the focused spot diameter is less than 10 microns to improve the coupling efficiency.

[0059] Adaptive design: The total length of the system is less than 50mm, which meets the lightweight requirements of AR glasses; the working band covers the visible light range (400nm to 700nm), matching the RGB three-color light source requirements.

[0060] Example 6

[0061] In this embodiment, the diffraction waveguide collimation system is applied to the optical waveguide module of the vehicle HUD. The driving information is generated by the image generation unit (such as a DLP projection chip), converted into parallel light by the collimation system, and then coupled to the designated area of ​​the windshield through the optical waveguide sheet.

[0062] Projection logic: The outcoupling grating of the optical waveguide is designed to be tilted so that the light forms a virtual image after being reflected by the windshield. The virtual image is 2-5 meters away from the driver and is located in front of the line of sight.

[0063] Anti-interference optimization: The surface of the window protection sheet 4 is coated with an anti-reflection film (transmittance>99%) to reduce the interference of ambient light reflected from the windshield surface; the aperture position is optimized to suppress stray light and ensure virtual image contrast.

Claims

1. A collimation system for a diffraction waveguide, characterized in that: The optical system includes, from the object side to the image side, a first lens group (S1), an aperture, a second lens group (S2), a prism equivalent lens (3), a window protection sheet (4) and an image plane position (5); The first lens group (S1) includes a first lens (11), a second lens (12), a third lens (13) and a fourth lens (14); wherein: The first lens (11) is a biconvex lens with positive optical power; The second lens (12) is a meniscus lens with negative optical power; The third lens (13) is a meniscus lens with positive power, and forms a cemented lens with the fourth lens (14); The fourth lens (14) is a biconvex lens with negative optical power; The second lens group (S2) includes a fifth lens (21), a sixth lens (22), a seventh lens (23) and an eighth lens (24); wherein: The fifth lens (21) is a biconcave lens with negative optical power; The sixth lens (22) is a meniscus lens with positive power; The seventh lens (23) is a biconvex lens with positive refractive power; The eighth lens (24) is a biconcave lens with negative optical power.

2. The collimation system for a diffraction waveguide according to claim 1, characterized in that: All lenses in the first lens group (S1) and the second lens group (S2) are spherical lenses, and the lens material is optical glass with a refractive index range of 1.50-1.85 and an Abbe number of 30-65.

3. The collimation system for a diffraction waveguide according to claim 1, characterized in that: The total length of the collimation system is less than 90 mm, and the focal length ratio relationship is satisfied: 0.5<|F1 / F0|<2.5; 2.5<|F2 / F0|<4.5; Wherein, F0 represents the equivalent focal length of the projection lens, F1 represents the focal length of the first lens group, and F2 represents the focal length of the second lens group.

4. The collimation system for a diffraction waveguide according to claim 1, characterized in that: The back working distance (BFL) and the equivalent focal length (F0) of the collimation system satisfy the relationship: |BFL / F0|>2.

5. The collimation system for a diffraction waveguide according to claim 1, characterized in that: The chromatic aberration correction capability of the cemented lens (13-14) satisfies that the axial chromatic aberration within the wavelength range of Δλ<5nm is less than 0.1mm.

6. The collimation system for a diffraction waveguide according to claim 1, characterized in that: The system is adapted to introduce diffraction waves into a coupling grating, the divergence angle of the output parallel light is less than 0.5°, and the relative illumination of the edge field of view is greater than 90%.

7. The collimation system for a diffraction waveguide according to claim 1, characterized in that: The incident surface and the exit surface of the prism equivalent lens (3) are coated with an anti-reflection film, the transmittance is greater than 99.5%, and the ratio of its thickness to the total optical path of the system is 1:6 to 1:

8.

8. An AR glasses, characterized in that: The optical waveguide module thereof integrates a collimation system for a diffraction waveguide as described in any one of claims 1 to 7, has an operating band of visible light (400-700nm), and supports mixed output of RGB three-color light sources.

9. A vehicle head-up display (HUD), characterized in that: A collimation system for a diffraction waveguide comprising any one of claims 1 to 7, wherein the virtual image distortion rate is less than 0.15%, and the thickness of the optical machine module is less than 25 mm.

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