Off-axis catadioptric projection optical lens group and near-to-eye display system using same

Abstract

The invention discloses an off-axis catadioptric miniature projection optical lens group suitable for near-to-eye display of a one-dimensional waveguide, which comprises an optical prism and an optical lens which are sequentially arranged from an exit pupil position side to an image source side, and is characterized in that image light emitted by an image source is propagated to the exit pupil position through the optical lens and the optical prism; according to the projection optical lens group provided by the invention, the optical prism and the optical lens are preferably selected to be in a free-form surface form, so that the size and the weight of the whole device are more suitable for the whole integrated glasses form of a waveguide system, and the size and the weight of the whole device are more suitable for the whole integrated glasses form of the waveguide system. The earphone is more suitable for daily wearing and use.

Description

Technical Field

[0001] The present invention relates to the technical field of miniaturized optical projection for augmented reality applications, and specifically to an off-axis catadioptric projection optical lens group, which is applied to a one-dimensional waveguide near-eye display system. Background Art

[0002] Since the advent of near-eye display technology for augmented reality, a variety of optical display technology routes have been developed. For optical transmissive augmented reality near-eye displays, in the optical display modules adopted by current market products, as shown in Figure 1, there are mainly three methods: (a) the method using a coaxial Birdbath optical path, (b) the method using a free-form prism to project light into the human eye, and (c) the method of a micro-projection optical system projecting light onto a one-dimensional or two-dimensional pupil-expanded waveguide and then entering the human eye.

[0003] Currently, in this type of device, the light energy utilization rate of the Birdbath solution is very low, and the free-form prism solution has problems such as a small exit pupil diameter, thick lenses, and being unfavorable for the fashionable appearance of daily wear. To achieve daily long-term wear closest to corrective spectacle lenses, the waveguide display solution has become the first choice for consumer products in augmented reality technology due to its advantages such as a large exit pupil diameter, light weight, thin and moldable lenses, and easy to carry.

[0004] In a waveguide display system, the optical waveguide plate only provides the functions of conducting light and expanding the one-dimensional or two-dimensional exit pupil diameter for the human eye, and has no function of correcting the imaging quality in principle. Therefore, when integrating this system, a projection optical lens group needs to be matched to achieve the imaging function of the system. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an off-axis catadioptric projection optical lens group with a thin and light structure. To achieve the above technical purpose, the present invention adopts the following technical solutions:

[0006] An off-axis catadioptric micro-projection optical lens group applicable to a near-eye display one-dimensional waveguide according to the present invention includes an optical prism and an optical lens arranged in sequence from the side of the exit pupil position to the image source side. The diameter of the optical lens matches the size of the image source, and the image light emitted by the image source is focused and transmitted towards the light incident surface of the optical prism. The optical prism includes at least three effective optical surfaces, where the light incident surface faces the image source side and the light exit surface faces the exit pupil position;

[0007] The focal length of this optical lens group is f, satisfying 11mm < f < 13mm, the length of the exit pupil range is greater than 15mm, the width is less than 5mm, and the exit pupil distance is 0.25mm.

[0008] The two outer edge positions where the projection optical lens group reaches the maximum thickness are respectively distributed on the optical lens and the optical prism, and the maximum thickness T satisfies T ≤ 8mm.

[0009] Preferably, the optical prism in the lens assembly comprises a first surface, a second surface, and a third surface arranged on the optical path from the exit pupil plane to the image source, and the first surface and the second surface are free-form optical surfaces.

[0010] Preferably, the optical lens comprises a fourth surface and a fifth surface, the surface shapes of which can be selected as spherical, aspherical, free-form or other optical surface shapes, and the fourth surface faces the third surface of the optical prism;

[0011] The image light emitted by the image source enters the optical lens through the fifth surface and is then emitted from the fourth surface. The image light emitted from the fourth surface is transmitted through the third surface into the optical prism and is then totally internally reflected at the first surface. Thereafter, the image light is reflected by the second surface and is emitted through the first surface.

[0012] In one embodiment, as a way to avoid stray light, the third surface of the optical prism is formed as a stepped surface to limit stray light entering the third surface at a predetermined angle from propagating toward the third surface.

[0013] The present invention also provides a near-eye display device worn in front of a person's eyes, which is in the form of glasses and includes a micro-projection optical lens group and a one-dimensional waveguide plate. The projection optical lens group is wrapped in a part of the frame near the temples, and the one-dimensional waveguide plate is placed in the frame.

[0014] According to the projection optical lens assembly of the present invention, a combination scheme is adopted in which both the optical prism and the optical lens have free-form surfaces as the surface morphology, so that the volume and weight of the overall device are more suitable for the overall integrated glasses form with the waveguide system, and as a near-eye display device, it is more suitable for daily wear. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a schematic diagram of the optical display technology principle of existing augmented reality near-eye display technology;

[0016] Figure 2 This is a schematic diagram of the optical path and structure provided by the present invention;

[0017] FIG3(a) and FIG3(b) are schematic diagrams showing two optical path principles of the projection optical lens assembly with a tilted exit pupil shown in FIG1;

[0018] Figure 4 Schematic diagram of a one-dimensional waveguide display system using the projection optical lens assembly of the present invention. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0021] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features specified as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0022] According to the off-axis catadioptric micro-projection optical lens assembly suitable for near-eye display of a one-dimensional waveguide provided by the present invention, the image source is projected toward the entrance pupil position of the one-dimensional waveguide sheet through the lens assembly, thereby realizing near-eye display of augmented reality.

[0023] The following is a detailed description of the embodiments of the present invention with reference to the accompanying drawings. Figure 2 The optical lens assembly shown in the figure establishes a spatial rectangular coordinate system with the center of the exit pupil as the origin, and uses this as the world coordinate system, so that the Z axis of the coordinate system is parallel to the optical axis direction, and the system is symmetrical about the YOZ plane. Figure 2 A microdisplay 30 is added for illustration purposes, providing an image light source for the optical lens assembly. Microdisplay 30 can be selected from self-luminous screens such as MicroOLED, MicroLED, MicroLCD, and FrontLit-LCoS. The size of a microdisplay is generally no larger than 1 inch (diagonal). In waveguide near-eye display systems, the microdisplay is typically selected from approximately 0.13 inches, 0.23 inches, or 0.3-0.4 inches.

[0024] Regarding the size requirements of the coupling end of the one-dimensional waveguide, it is necessary to perform optical pupil expansion in one dimension (one-dimensional extension replication of the entrance pupil) to meet the requirements of the coupling end of the long strip area with a certain aspect ratio.

[0025] like Figure 2 As shown, the optical lens assembly includes an optical prism 10 and an optical lens 20 which are sequentially arranged from the exit pupil plane 40 toward the micro display screen 30 .

[0026] The optical prism 10 includes a first surface 101, a second surface 102 and a third surface 103 arranged on the optical path from the exit pupil plane 40 to the micro display screen 30. These three effective optical surfaces and other auxiliary surfaces constitute the overall shape of the optical prism 10, making it the outer shape of the prism.

[0027] The function of the optical prism 10 is to fold the optical path and provide the primary optical power for the projection optical lens assembly. While the optical surfaces of the optical prism 10 can be spherical, aspherical, free-form, or other optical surface shapes, it is preferred that all three surfaces of the optical prism 10 be free-form surfaces to better balance aberrations and provide a higher-quality image at the exit pupil.

[0028] In order to meet the optical path requirements, a total reflection film is coated on the second surface 102 of the optical prism 10 to ensure that light is reflected when it propagates in the optical prism 10 and reaches the second surface.

[0029] like Figure 2 In the relative position shown, the optical lens 20 is located between the third surface 103 of the optical prism 10 and the micro-display 30. It directly receives the image light emitted by the micro-display 30 and provides the ability to correct aberrations, thereby achieving higher imaging quality in conjunction with the optical prism 10. The optical lens 20 includes two effective optical surfaces: a fourth surface 201 and a fifth surface 202.

[0030] The fourth surface 201 and the fifth surface 202 of the optical lens 20 can be spherical, aspherical, free-form, or other optical surface types. In this embodiment, both surfaces of the optical lens 20, like the effective optical surfaces of the optical prism 10, are designed as free-form surfaces to compensate for the aberrations of the optical prism and achieve balanced image quality.

[0031] In order to reduce the weight of the micro-projection optical lens assembly, the optical prism 10 and the optical lens 20 in this embodiment are both made of optical resin material and produced based on an injection molding process.

[0032] like Figure 2As shown in the optical path, the image light emitted by the micro display screen 30 includes image information provided to the human eye and is emitted to the fifth surface 202 of the optical lens 20; the image light passing through the fifth surface 202 propagates within the thickness of the optical lens 20 to the fourth surface 201, and the image light exits the optical lens through the fourth surface 201 and is emitted to the optical prism 10; the third surface 103 of the optical prism 10 is arranged opposite to the fourth surface 202, and the image light enters the optical prism through the third surface 103 (i.e., the light incident surface) due to the incident angle. It propagates toward the first surface 101, is totally internally reflected by the first surface 101, and is emitted toward the second surface 102 of the optical prism. It is then reflected by the second surface 102 and returns to the first surface 101. At this time, since the incident angle no longer meets the total reflection condition, it is emitted through the first surface 101 to the exit pupil plane 40. At the exit pupil plane 40, it is coupled to the entrance pupil position of the one-dimensional waveguide. The specific light exit position on the exit pupil plane 40 (i.e., the exit pupil position) is close to the lower edge of the first surface 101 (i.e., the light exit surface) of the optical prism 10.

[0033] The optical prism 10 is made of a light-transmitting resin material. Light will be refracted on both the first surface 101 and the third surface 103 of the optical prism. In this embodiment, an anti-reflection film is applied to the first surface 101 and the third surface 103 to improve the overall light efficiency of the system and reduce stray light.

[0034] Since the light energy utilization rate of the waveguide system for augmented reality is usually very low, in order to reduce light energy loss, it is preferred to coat the fourth surface 201 and the fifth surface 202 of the optical lens 20 with an anti-reflection film to maximize the image light energy entering the projection optical lens assembly.

[0035] In this embodiment, the optical surfaces of the optical lens assembly are labeled as follows: Figure 2 Marked and described in the figure, based on the free-form surface of this embodiment, the free-form surface expression adopted is in the form of XY polynomial, and the surface equation is:

[0036]

[0037] Where c is the inverse of the radius of curvature, r is the radial distance of a point on the surface, k is the quadratic constant, and Cj are the coefficients of the XY polynomial.

[0038] The parameters are shown in the following tables, where Table 1 shows the first-order parameters and eccentric tilt data of each optically effective surface, and Table 2 shows the coefficients of the XY polynomial in the surface equation of each optically effective surface.

[0039] Table 1 First-order parameters and eccentric tilt data of the optical effective surface in the embodiment

[0040] Surface marking Surface type radius Y global coordinate Z global coordinate ALPHA Tilt 101 XY Polynomial -23.1 2.96 1.01 3.12 102 XY Polynomial -24.8 1.30 5.09 -21.68 103 XY Polynomial 4.43 7.47 2.45 52.45 201 XY Polynomial 3.09 8.55 3.95 43.26 202 XY Polynomial 2.71 11.05 5.44 53.50 display / / 11.95 6.91 51.83

[0041] Table 2 XY polynomial coefficients in the surface equations of each optically effective surface in the embodiments

[0042]

[0043]

[0044] In this embodiment, in order to obtain a smaller volume, the relative surfaces 103 and 201 of the optical prism 10 and the optical lens 20 form an angle of approximately 9 degrees in the normal direction.

[0045] The main features of this type of projection lens group are small volume, light weight, and large exit pupil size. As can be seen from Figure 2 it can be exactly enclosed by a rectangle in the YOZ plane. When the short side of the drawn envelope rectangle reaches the minimum value, this envelope rectangle is the most compact envelope rectangle 70. The length of the short side of this rectangle is defined as the thickness T of the micro-projection optical lens group, and the long side is defined as the length L of the lens group, satisfying T≤8mm and L<18mm; the focal length of the optical lens group is f, satisfying 11mm < f < 13mm; the exit pupil diameter is equal to 17mm (X direction) × 4mm (Y direction), the exit pupil distance is 0.25mm, and the field angle is 30°. This is convenient for the overall integration of the system and reduces the system volume.

[0046] For the projection optical lens group of this embodiment, preferably, it further includes a protective shell (not shown) that fixes the relative positions of the optical lens 20 and the optical prism 10 in the minimum outer envelope manner. The optical prism 10 can only partially expose from the protective shell, so that the image light passing through the projection optical lens group is coupled to the incident surface of the coupling end of a predetermined one-dimensional waveguide sheet at the exit pupil position, while excluding stray light in other emission directions.

[0047] Modifications

[0048] According to the optical lens group of this embodiment, as shown in Fig. 3(a), there is stray light 50 formed due to the light emitted by the micro-display entering the optical lens group and undergoing unexpected reflections; the path of the stray light is that the image light emitted by the micro-display 30 normally passes through the optical lens 20, enters the optical prism 10 from the third surface 103 of the optical prism 10, is incident on the second surface 102, is reflected and then incident on the first surface 101, is reflected again and then incident on the second surface 102 for the second time, and is reflected again and then exits from the first surface 101 and enters the exit pupil plane 40. The distribution range of such stray light is outside the expected imaging range, and when it reaches the exit pupil position, it will cause unwanted coupling at the waveguide coupling end and will ultimately be observed by the human eye.

[0049] To this end, as shown in FIG3( b ), part of the material of the first prism 10 is removed near the position of the intersection of the second surface 102 and the third surface 103 of the optical prism 10, so that the third surface 103 forms a step surface and is discontinuous. The two intersecting surfaces 601 and 602 constitute a step surface, thereby cutting off the optical path where the stray light 50 may be distributed as a measure to eliminate the above-mentioned stray light 50, so as to limit the stray light emitted at a predetermined angle to the third surface and prevent it from propagating to the third surface. The surface shape of these two surfaces can be set according to factors such as the prism shape, stray light elimination effect, and processing difficulty, without having to be described in a mathematical way that conforms to optical design. The method of removing material can be to adjust the shape of the mold cavity during injection molding, directly inject molding, or remove it by machining after molding.

[0050] After removing the material, the minimum distance between the light and the lens surface should be no less than 0.1mm, so as not to affect the optical effect of the surface.

[0051] One-dimensional waveguide near-eye display system

[0052] The projection optical lens assembly according to the embodiment of the present invention can be used in a one-dimensional waveguide display system for augmented reality, such as Figure 4 As shown, the exit pupil plane 40 of the projection optical lens assembly is positioned overlying the entrance pupil of the one-dimensional waveguide. Image light emitted by the micro-display 30 is coupled into the one-dimensional waveguide through the projection optical lens assembly, propagating through the one-dimensional waveguide to the exit pupil plane before exiting to the eye, allowing the wearer to see a clear, magnified virtual image. This one-dimensional waveguide display system is typically configured as eyeglasses, with the projection optical lens assembly positioned near the temples of the frame and the one-dimensional waveguide positioned within the frame, forming the form of eyeglass lenses.

[0053] In summary, the optical lens assembly provided by the present invention folds the image light path by combining a free-form prism and a free-form lens, thereby greatly reducing the system volume. At the same time, by selecting suitable materials, the system mass is reduced while ensuring a large exit pupil range of the system. When used in conjunction with a suitable waveguide, the system exit pupil size is expanded.

[0054] The above describes in detail the off-axis catadioptric projection optical lens assembly and the near-eye display system using the same provided by the present invention. For those skilled in the art, any obvious modifications made thereto without departing from the essence of the present invention would constitute an infringement of the present invention's patent rights and would incur corresponding legal liability.

Claims

1. An off-axis catadioptric micro-projection optical lens assembly suitable for near-eye display of one-dimensional waveguides, characterized in that: It includes an optical prism and an optical lens arranged in sequence from the exit pupil position side to the image source side. The diameter of the optical lens matches the size of the image source. The optical lens focuses the image light emitted by the image source and transmits it towards the light incident surface of the optical prism. The optical prism includes at least three effective optical surfaces, where the light incident surface faces the image source side and the light exit surface faces the exit pupil position. The focal length of the optical lens group is f, satisfying 11mm < f < 13mm. The length of the exit pupil range is greater than 15mm and the width is less than 5mm. The exit pupil distance is 0.25mm.

2. The micro-projection optical lens assembly according to claim 1, wherein: The maximum thickness T of the projection optical lens group satisfies T ≤ 8mm. The two outer edge positions where the maximum thickness is achieved are respectively distributed on the optical lens and the optical prism.

3. The micro-projection optical lens assembly according to claim 2, wherein: The optical prism includes a first surface, a second surface, and a third surface arranged on the optical path from the exit pupil plane towards the image source direction. The first surface and the second surface are optical surface types of free-form surfaces.

4. The micro-projection optical lens assembly according to claim 3, wherein: The optical lens includes a fourth surface and a fifth surface. The surface types of both can be selected as spherical surfaces, aspherical surfaces, free-form surfaces, or other forms of optical surface types. The fourth surface faces the third surface of the optical prism. The image light emitted by the image source enters the optical lens through the fifth surface and exits through the fourth surface. The image light exiting from the fourth surface is transmitted through the third surface and enters the optical prism, and then undergoes total internal reflection at the first surface. After that, it is reflected by the second surface and exits through the first surface.

5. The micro-projection optical lens assembly according to claim 4, wherein: The included angle between the third surface of the optical prism and the fourth surface of the optical lens is approximately 9°.

6. The micro-projection optical lens assembly according to claim 3, wherein: The third surface of the optical prism is formed as a stepped surface to limit the stray light incident on the third surface at a predetermined angle and prevent it from propagating towards the third surface.

7. The micro-projection optical lens assembly according to claim 3, wherein: The second surface is covered with a total reflection film.

8. The micro-projection optical lens assembly according to any one of claims 1 to 7, wherein: It further includes a protective shell that can fix the relative positions of the optical lens and the optical prism. Only a part of the optical prism is exposed from the protective shell so that the image light passing through the projection optical lens group is coupled to the incident surface of the input end of a predetermined one-dimensional waveguide sheet at the exit pupil position.

9. The micro-projection optical lens assembly according to claim 8, wherein: The exit pupil position is close to the lower edge of the light exit surface of the optical prism.

10. A near-eye display device worn in front of a person's eyes, in the form of glasses, includes the micro-projection optical lens group as described in any one of claims 1-9 and a one-dimensional waveguide sheet. The projection optical lens group is wrapped in a part of the frame close to the temple, and the one-dimensional waveguide sheet is placed in the frame.

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