Collimation system for a diffractive waveguide and use thereof

Abstract

The application discloses a collimation system for a diffraction waveguide, which comprises, in order from the object side to the image side along the optical axis, a first lens group, a diaphragm, a second lens group, a prism equivalent lens, a window protection sheet and an image plane position. The first lens group is composed of a positive focal power lenticular lens, a negative focal power meniscus lens and a cemented lens; the second lens group comprises a negative focal power biconcave lens, a positive focal power meniscus lens and a double convex / biconcave lens combination, forming a double Gauss symmetric structure. The total length of the system is less than 90 mm, a global surface mirror design is adopted, the focal length ratio relationship (0.5<|F1 / F0|<2.5, 2.5<|F2 / F0|<4.5) is met, and the ratio of the rear working distance to the focal length is greater than 2. The application is optimized for the diffraction waveguide technology, the cemented lens has stronger chromatic aberration correction ability, the double Gauss structure improves the relative luminance of the edge field of view (>90%), and the total length of the system is shorter (<90 mm), which meets the high-angle precision requirement of the diffraction grating to parallel light, is suitable for AR glasses, vehicle HUD and other scenes, and has the advantages of high collimation, low distortion (<0.15%) and compactness.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical display technology, in particular to a collimation system for diffractive waveguide, which is specially designed for diffractive waveguide technology. By optimizing the structure and power distribution of the lens group, the problems of large chromatic aberration, low edge illumination and redundant volume in the existing collimation system in the coupling of diffraction grating are solved, and it is suitable for AR glasses, vehicle HUD and other scenes. BACKGROUND

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

[0003] Optical waveguide technology can be divided into geometric waveguide and diffractive waveguide technology. It requires that the input coupling grating input parallel light at a certain angle, and after modulation by the input coupling grating, the light is totally reflected inside the waveguide for transmission, and finally the out-coupling grating out-pupil realizes the imaging effect. The key factor of the imaging quality of the waveguide system is 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 consider the optical-mechanical type, the waveguide input coupling size, the waveguide display field angle, etc. The ideal collimation system structure is compact and cost controllable, and the imaging quality is high, so designing a collimation lens with compact structure, controllable cost and high imaging quality is one of the difficulties in optical design in this field.

[0004] In summary, the traditional compact waveguide collimation system mostly adopts a symmetric double-Gaussian structure, but the cemented lens design is not optimized for the chromatic dispersion characteristics of diffractive waveguide, resulting in low coupling efficiency. And the total length of the system usually exceeds 100mm, which is difficult to adapt to the miniaturization needs of the optical machine. The present application introduces a double-convex-crescent cemented lens combination and a double-concave lens expansion, combined with strict focal length ratio control, which significantly improves the chromatic aberration correction ability and compactness. SUMMARY

[0005] The present application is a collimation system for diffractive waveguide, which can be used to generate collimated light of different angles required by the input coupling grating of the waveguide system. It solves the problems of chromatic aberration and edge illumination under the premise of meeting high imaging quality, effectively reduces the cost of the lens, and at the same time, the compact design simplifies the optical components of the system and reduces the optical volume of the system.

[0006] Technical solution: a kind of collimating system for diffractive waveguide, system is first lens group, diaphragm, second lens group, prism equivalent lens, window protection piece and image plane position from object side to image plane along optical axis;The first lens group includes first lens, second lens, third lens and fourth lens, the first lens is double convex lens with positive focal power, second lens is meniscus lens with negative focal power, third lens with positive focal power and fourth lens with negative focal power form cemented lens, third lens is meniscus lens, and fourth lens is double convex lens;The second lens group includes fifth lens, sixth lens, seventh lens and eighth lens.Fifth lens is double concave lens with negative focal power, sixth lens is meniscus lens with positive focal power, seventh lens is double convex lens with positive focal power, and eighth lens is double concave lens with negative focal power.The aperture diaphragm is located between fourth lens and fifth lens, the prism equivalent lens is located between eighth lens and image plane position, and the window protection piece is located between prism equivalent lens and image plane position.

[0007] Further, the lens surface of the collimating system lens group is composed of spherical mirror.

[0008] Further, the collimating system lens is optical glass, and the refractive index range is 1.50-1.85, and the Abbe number is 30-65.

[0009] Further, the collimating system object side light is incident with parallel light characteristics, and is focused on the image plane position by collimating system.

[0010] Further, the collimating system light is emitted at the image plane during operation, and is incident on the waveguide incoupling grating surface in the form of parallel light with different angles after lens modulation.

[0011] Further, 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] Further, the back working distance of the collimating 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, 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 light angle, corrects aberration, and converges light to the next lens, the second lens 12 is a meniscus lens with negative focal power, which has a small diverging effect on light, prevents the first lens from causing excessive convergence, and appropriately increases the system optical distance. 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 light to the stop. 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 double concave lens with negative focal power. 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 double concave lens with negative focal power. The three lenses together form a symmetric structure, which reduces the difficulty of correcting aberration of the system. The four lenses in the second lens group S2 together form a double Gauss symmetric structure, which can effectively suppress system aberration and reasonably increase the total length of the system to meet the size requirements of the waveguide optical machine.

[0019] Further, 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] Further, the system is adapted to a diffractive waveguide incoupling grating, the divergence angle of the output parallel light is less than 0.5°, and the relative luminance of the edge field of view is greater than 90%.

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

[0022] The application also provides an AR glasses, characterized in that: the light waveguide module of the AR glasses is integrated with the collimation system for diffractive waveguide, and the working waveband is visible light (400-700nm), and the AR glasses supports mixed output of RGB three-color light sources.

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

[0024] Beneficial effects: the first lens group (biconvex + meniscus + cemented lens) in the application corrects axial chromatic aberration and preliminarily collimates; the second lens group (biconcave + meniscus + biconvex / biconcave) forms a double-Gauss structure, suppresses field curvature and distortion; the total length of the system is less than 90mm, the focal length ratio (F1 / F0, F2 / F0) and the back working distance (BFL / F0) meet the stringent requirements of the diffraction grating on spot uniformity and angle. Compared with the prior art, the application can effectively suppress various aberrations of the optical system when generating collimated light in the waveguide system, can collimate the light emitted by the image source into parallel light, can meet the requirement of high-quality collimated light output for waveguide display, and can make the relative luminance of the edge field of view reach more than 90%. Meanwhile, combined with the actual optical lens mounting restriction, the compact design is realized, all spherical mirrors are used in the case of meeting the hardware size, the lens cost is effectively reduced, the system optical components are simplified by the compact design, and the system optical volume is reduced. The application can be installed in a waveguide display system as a collimating element. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 An optical structure schematic diagram of a collimating system for a diffraction waveguide is created for the application.

[0026] Figure 2 A modulation transfer function (MTF) curve diagram of the collimating system for the diffraction waveguide is created for the application.

[0027] Figure 3 A relative luminance curve diagram of the collimating system for the diffraction waveguide is created for the application.

[0028] Figure 4 A grid distortion diagram of the collimating system for the diffraction waveguide is created for the application.

[0029] Figure 5 An optical path schematic diagram of the collimating system for the diffraction waveguide is created for the application.

[0030] Wherein S1 is a first lens group, S2 is a second lens group, 11 is a first lens, 12 is a second lens, 13 is a third lens, 14 is a fourth lens, 21 is a fifth lens, 22 is a sixth lens, 23 is a seventh lens, 24 is an eighth lens, 3 is a prism equivalent lens, 4 is a window protection sheet, and 5 is an image plane position. DETAILED DESCRIPTION

[0031] The application will be further explained in combination with the drawings.

[0032] The collimating system for the diffraction waveguide in the application meets the requirement of high-quality collimated light output for waveguide display, realizes compact design, effectively reduces lens cost, can be used as a collimating element of an optical waveguide display system, and can be finally used in the fields of smart glasses, flat panel display, vehicle head-up display, etc.

[0033] Embodiment 1

[0034] As Figure 1 shown in a collimating system for a diffractive waveguide, the system along the optical axis from the object side to the image side is a first lens group, an aperture, a second lens group, a prism equivalent lens, a window protection 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 double convex 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 double convex lens; the second lens group includes a fifth lens, a sixth lens, a seventh lens, and an eighth lens. The fifth lens is a double concave lens with negative focal power, the sixth lens is a meniscus lens with positive focal power, the seventh lens is a double convex lens with positive focal power, and the eighth lens is a double concave lens with negative focal power. All lenses in the collimating system are spherical mirrors, and by reasonably allocating the focal power and surface shape of each lens, the collimating ability of the lens is effectively improved, the light output performance with high collimation is realized, and the object side light of the collimating system is incident with parallel light characteristics. And focus on the image plane position through the collimating system, suitable for waveguide display system.

[0035] Embodiment 2

[0036] Further, on the basis of embodiment 1, further comprising: the lens group first lens 11, second lens 12, third lens 13, fourth lens 14, fifth lens 21, sixth lens 22, seventh lens 23 and eighth lens 24, the lens surface is composed of spherical mirror. And its lens material is composed of glass material.

[0037] Embodiment 3

[0038] Further, on the basis of embodiment 1, further comprising: the equivalent focal length of the collimating system projection lens, 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] Embodiment 4

[0043] Further, on the basis of embodiment 1, further comprising: the back working distance of the collimating 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 application, the first lens 11 is a meniscus lens with positive refractive power, the second lens 12 is a meniscus lens with positive refractive power, the light ray angle is preliminarily changed, the double-layer meniscus lens can correct aberration more effectively, the third lens with negative refractive power and the fourth lens with negative refractive power form a cemented lens, and chromatic aberration can be corrected. The third lens 13 is a double-concave lens, and the fourth lens 14 is a double-convex lens; the fifth lens 21 is a double-concave lens with negative refractive power, and the collimated light is expanded, and the system focal length is expanded to meet the length requirement of the optical-mechanical size. The sixth lens 22 is a meniscus lens with positive refractive power, the seventh lens 23 is a double-convex lens with positive refractive power, and the eighth lens 24 is a double-convex lens with positive refractive power, and the three lenses together form a symmetrical structure, which reduces the difficulty of correcting aberration of the system.

[0047] The cemented lens 13-14 is combined by H-ZF52 and H-LAK53 glasses, the Abbe number difference is greater than 30, and the dispersion correction ability is increased by 30%; the prism equivalent lens (3) is coated with a broadband anti-reflection film (400-700nm average transmittance 99.7%).

[0048] In the application, in the first lens group S1, the first lens 11 is a double-convex lens with positive refractive power, the light ray angle is preliminarily changed, aberration is corrected, and the light rays are converged to the next lens, the second lens 12 is a meniscus lens with negative refractive power, the light rays are slightly diverged, the first lens is prevented from converging too much, and the optical distance of the system is appropriately increased. The third lens with positive refractive power and the fourth lens with negative refractive power form a cemented lens, which can correct chromatic aberration and further converge the light rays to the diaphragm. The third lens 13 is a meniscus lens, and the fourth lens 14 is a double-convex lens; in the second lens group S2, the fifth lens 21 is a double-concave lens with negative refractive power. The sixth lens 22 is a meniscus lens with positive refractive power, the seventh lens 23 is a double-convex lens with positive refractive power, and the eighth lens 24 is a double-concave lens with negative refractive power, and the three lenses together form a symmetrical structure, which reduces the difficulty of correcting aberration of the system, the four lenses in the second lens group S2 together form a double-Gauss symmetrical structure, which can effectively suppress system aberration, and the total length of the system is reasonably increased to meet the size requirement of the optical-mechanical device

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

[0050]

[0051] In the present application, reference is made to Figure 1 : the light sequence of 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 application, reference is made to Figure 2 : the modulation transfer function of the collimation system, the MTF values of different fields of view are all higher than 0.6 when the cut-off frequency is 66 lp / mm, the MTF curve is uniform and slowly declining, which shows that high-quality collimation effect can be achieved.

[0053] In the present application, reference is made to Figure 3 : the relative luminance curve of the collimation system, the relative luminance of different fields of view is all greater than 0.95, which shows that the relative luminance is high, the brightness difference between the center and the edge of the image is not large, and the display luminance distribution is uniform.

[0054] In the present application, 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 application can effectively suppress various aberrations of the optical system when generating collimated light of the waveguide system, collimate the light emitted by the image source into parallel light, meet the requirement of high-quality collimated light output for waveguide display, and achieve a relative luminance of the edge field of view of more than 90%. In combination with the actual optical lens installation restriction, the compact design is realized, all spherical mirrors are used under the condition of meeting the hardware size, the lens cost is effectively reduced, the system optical components are simplified by the compact design, and the system optical volume is reduced. The compact waveguide collimation system can be installed in a waveguide display system as a collimation element.

[0056] Example 5

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

[0058] Light path details: the image plane position 5 of the collimation system is aligned with the in-coupling grating of the light waveguide sheet, so as to ensure that the diameter of the focused light spot is less than 10 microns, thereby improving the coupling efficiency.

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

[0060] Embodiment 6

[0061] In this embodiment, the collimating system for diffractive waveguide is applied to the light waveguide module of vehicle HUD. The driving information is generated by the image generation unit (such as DLP projection chip), and after being converted into parallel light by the collimating system, it is coupled to the specified area of the windshield through the light waveguide sheet.

[0062] Projection logic: the out-coupling grating of the light waveguide sheet is designed with an inclination angle, so that the light reflected by the windshield forms a virtual image, which is 2-5 meters away from the driver and 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%), which reduces the interference of ambient light reflected by the surface of the windshield; the position of the diaphragm is optimized to suppress stray light and ensure the contrast of the virtual image.

Claims

1. A collimating system for a diffractive waveguide, characterized by: Composed of 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) in order from the object side to the image side along the optical axis; The first lens group (S1) is composed of 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 focal power; The second lens (12) is a meniscus lens with negative focal power; The third lens (13) is a meniscus lens with positive focal power, and forms a cemented lens with the fourth lens (14); The fourth lens (14) is a biconvex lens with negative focal power; The second lens group (S2) is composed of a fifth lens (21), a sixth lens (22), a seventh lens (23) and an eighth lens (24); wherein, The fifth lens (21) is a double concave lens with negative focal power; The sixth lens (22) is a meniscus lens with positive focal power; The seventh lens (23) is a biconvex lens with positive focal power; The eighth lens (24) is a double concave lens with negative focal power; The total length of the collimation system is less than 90mm, 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 collimation system, F1 represents the focal length of the first lens group, and F2 represents the focal length of the second lens group.

2. The collimating system for diffractive waveguides of claim 1, wherein, All lenses in the first lens group (S1) and the second lens group (S2) are spherical mirrors, 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 collimating system for diffractive waveguides of claim 1, wherein, The back working distance BFL of the collimation system and the equivalent focal length satisfy the relationship: |BFL / F0|>2.

4. The collimating system for diffractive waveguides of claim 1, wherein: The chromatic aberration correction ability of the cemented lens (13-14) satisfies the condition that the axial chromatic aberration in the wavelength range of Δλ<5nm is less than 0.1mm.

5. The collimating system for diffractive waveguides of claim 1, wherein, The system is adapted to a diffractive waveguide incoupling grating, and the divergence angle of the output parallel light is less than 0.5°, and the relative luminance of the edge field is greater than 90%.

6. The collimating system for diffractive waveguides of claim 1, wherein: The entrance surface and the exit surface of the prism equivalent lens (3) are coated with an anti-reflection film with a transmittance of greater than 99.5%, and the ratio of its thickness to the total optical path of the system is 1:6 to 1:

8.

7. An AR eyeglass, characterized by: The light waveguide module integrates the collimation system for diffractive waveguide of any one of claims 1-6, and the working waveband is visible light 400-700nm, supporting RGB three-color light source mixed output.

8. A heads-up display for a vehicle, comprising: The collimation system for diffractive waveguide of any one of claims 1-6 is included, the virtual image distortion rate is less than 0.15%, and the optical mechanical module thickness is less than 25mm.

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