A foldable micro-projection lens

Abstract

The present invention belongs to the field of virtual realization technology, specifically a lens for AR. In order to solve the problem of large volume and high weight of existing projection lenses, a refractive micro-projection lens is disclosed, which is arranged in order from the exit pupil side to the image source side along the optical axis. The first lens, the second lens, and the third lens are all meniscus lenses with concave surfaces facing the exit pupil side, and the surface shape of the image source side of the third lens is a superposition of a diffraction surface and an even-order aspheric surface. The beneficial effects of the present invention are as follows: a diffraction surface is superimposed on the image source side surface of the third lens, and the chromatic aberration of the lens is corrected by optimizing the parameters of the diffraction surface. The use of the diffraction surface replaces the traditional double-cemented lens. Compared with the traditional projection lens, the number of lenses is reduced while ensuring the imaging quality of the projection lens, and the weight of the projection lens is reduced. Its application in augmented reality glasses can improve the comfort of the wearer and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of virtual realization, and in particular relates to a projection lens for AR. Background Art

[0002] The micro-projection optical system is mainly composed of LED light source, light source shaping lighting system, image source (LCOS or DMD), projection system, heat dissipation system and other mechanisms. With the emergence of head-mounted optical systems represented by augmented reality glasses AR and virtual reality glasses in recent years, there are higher requirements for the volume, weight, brightness and other indicators of the micro-projection optical system.

[0003] Currently, the projection lenses used for augmented reality glasses on the market basically adopt multi-piece structures, especially aspherical structures with more than four pieces. Although such projection lenses have good effects, they are prone to problems such as large size, high overall weight, and high difficulty in processing and assembly. Summary of the invention

[0004] The object of the present invention is to provide a diffractive micro-projection lens to solve the problems raised in the above background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a diffractive micro-projection lens, comprising: a silicon-based liquid crystal image source, a polarization beam splitter cube, and a projection lens group, wherein the light emitted by the silicon-based liquid crystal image source passes through the projection lens group after passing through the polarization beam splitter cube, and enters the human eye from the exit pupil as parallel light at different angles; the characteristic is that: the side close to the human eye when worn is the exit pupil side, the side of the silicon-based liquid crystal image source is the image source side, and the projection lens group includes a first lens, a second lens, and a third lens in sequence along the direction from the exit pupil side to the image source side along the optical axis; wherein the first lens, the second lens, and the third lens are all configured as meniscus lenses with concave surfaces facing the exit pupil side; the optical focal length of the first lens is positive and is used to deflect light with a large field of view; the image source side of the third lens is configured as a superposition of a diffraction surface and an even-order aspheric surface; the second lens and the third lens are used together to balance the field curvature, distortion, chromatic aberration, and aberration of the projection lens group.

[0006] The silicon-based liquid crystal image source includes: mobile phone color screen. Color screen types include: TFT, TFD, UFB, STN, OLED, AMOLED, SLCD.

[0007] Preferably, the first lens and the third lens are made of optical plastic, and the second lens is made of optical glass.

[0008] Preferably, the focal length F1 of the first lens and the focal length F2 of the second lens of the projection lens assembly satisfy the relationship: F1 / F2≤4.

[0009] Preferably, the focal length F1 of the first lens and the focal length F3 of the third lens of the projection lens assembly satisfy the relationship: -2≤F1 / F3≤-1.

[0010] Preferably, the back focus Fb of the projection lens group and the total length TTL of the projection lens group satisfy the relationship: 0.4≤Fb / TTL.

[0011] Preferably, the polarization beam splitter cube is a wire grid polarization beam splitter cube with a refractive index of 1.52 and an Abbe constant of 64.2.

[0012] Preferably, the refractive index of the first lens is 1.49, and the Abbe constant is 57.4; the refractive index of the second lens is 1.57, and the Abbe constant is 63.0; the refractive index of the third lens is 1.49, and the Abbe constant is 57.4.

[0013] Preferably: the phase expression of the diffraction surface is:

[0014]

[0015] Among them, A 2 and A 4 is the phase parameter, r is the distance from a point on the third lens to the center of the lens, and r' is the clear aperture of the third lens.

[0016] Preferred: A 2 and A 4 The phase parameters are -1071.89 and 160.26 respectively.

[0017] When the technical solution is used, the silicon-based liquid crystal image source is placed on the image source side, passes through the projection lens group after passing through the polarization beam splitter cube, and exits from the exit pupil with parallel light at different angles. After the exit pupil, it is connected to the diffraction light guide plate, etc., and the image at the exit pupil is magnified and enters the human eye, so that the human eye receives the image on the LCOS image source. Since the three lenses used in the projection lens group are all meniscus lenses with the concave surface facing the exit pupil side, the length of the optical system is greatly shortened, and the convex surface on the image source side of the third lens is set to be a superposition of the diffraction surface and the even-order aspheric surface, the chromatic aberration of the lens is corrected by the diffraction surface, the number of lenses is reduced, and the weight of the projection lens is reduced. The projection lens of the present invention is applied to the AR glasses system, and with the corresponding hardware circuit and software, it can be used in daily life such as classroom teaching and family entertainment.

[0018] Beneficial Effects

[0019] The diffractive projection lens provided by the present invention has a diffractive surface superimposed on the image source side surface of the third lens. The chromatic aberration of the lens is corrected by optimizing the parameters of the diffractive surface. The use of the diffractive surface replaces the traditional double-cemented lens. Compared with the traditional projection lens, the number of lenses is reduced while the imaging quality of the projection lens is guaranteed, and the weight of the projection lens is reduced. Applying it to augmented reality glasses can improve the comfort of the wearer and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is an optical structure diagram of the present invention;

[0021] Figure 2 It is the light trend diagram of the present invention;

[0022] Figure 3 It is a schematic diagram of the 0° field of view MTF curve of the present invention;

[0023] Figure 4 It is a schematic diagram of the MTF curve of 10° field of view of the present invention;

[0024] Figure 5 It is a schematic diagram of the MTF curve of 20° field of view of the present invention;

[0025] Figure 6 is a schematic diagram of a distortion curve of the present invention;

[0026] Figure 7 is a relative illumination schematic diagram of the present invention;

[0027] Figure 8 It is a schematic diagram of Example 2 of the present invention.

[0028] Reference numerals

[0029] ST-exit pupil side, IMA-image source side, G1-first lens, G2-second lens, G3-third lens, G4-polarization beam splitter cube, S1-exit pupil side surface of the first lens, S2-image source side surface of the first lens, S3-exit pupil side surface of the second lens, S4-image source side surface of the second lens, S5-exit pupil side surface of the third lens, S6-image source side surface of the third lens. DETAILED DESCRIPTION

[0030] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0031] Example 1

[0032] like Figure 1 As shown, in this embodiment, a folding micro-projection lens, such as Figure 1As shown, a silicon-based liquid crystal image source, a polarization beam splitter cube G4, and a projection lens group. The light emitted by the silicon-based liquid crystal image source passes through the polarization beam splitter cube and then passes through the projection lens group, and is emitted from the exit pupil into the human eye as parallel light at different angles; the side close to the human eye when worn is the exit pupil side, and the silicon-based liquid crystal image source side is the image source side; along the optical axis from the exit pupil side ST to the image source side IMA, in order, the first lens is a meniscus lens G1, and the exit pupil side surface S1 is a concave surface; the second lens is a meniscus lens G2, and the exit pupil side surface S3 is a concave surface; the third lens is a meniscus lens G3, and the exit pupil side surface S5 is a concave surface; the image source side S6 of the third lens is a superposition of a diffraction surface and an even-order aspheric surface; the optical power of the first lens is positive, and is used to deflect light with a large field of view; the second lens and the third lens are used together to balance the field curvature, distortion, chromatic aberration, and aberration of the projection lens group.

[0033] The application optical path of the lens is as follows Figure 2 As shown, the light from the illumination system is reflected by the polarization beam splitter cube G4 to the image source surface, that is, the liquid crystal surface of LCOS. After being reflected by LCOS, the phase of the incident light is flipped, and it passes through the polarization beam splitter cube G4, the third lens G3, the second lens G2, and the first lens G1 in sequence, and then is emitted from the exit pupil side ST as parallel light at different angles and enters the human eye.

[0034] The first lens G1 and the second lens G2 both have positive refractive power, and are used to converge light from different fields of view and then project them into the third lens G3.

[0035] The refractive power of the third lens G3 is opposite to that of the first lens G1 and the second lens G2, and is used to balance aberrations.

[0036] The back focus of the first lens G1, the second lens G2, and the third lens G3 and the total length of the first lens G1, the second lens G2, and the third lens G3 satisfy the relationship: 0.4≤back focus / total length. Through such a setting, the overall length of the lens can be compressed, and sufficient distance can be left for adding a polarization beam splitter cube to the projection lens.

[0037] The materials of the first lens G1 and the third lens G2 are both optical plastic PMMA, whose refractive index and Abbe number are 1.49 and 57.4 respectively. The material of the second lens G2 is H-ZF1, whose refractive index and Abbe number are 1.57 and 63.0 respectively. The material of the polarization beam splitter cube G4 is H-K9L, whose refractive index and Abbe number are 1.52 and 64.2 respectively. The polarization beam splitter cube G4 is a wire grid type polarization beam splitter cube.

[0038] Both optical surfaces of the second lens G2 and the two optical surfaces of the third lens G3 are even-order aspherical surfaces, which can effectively reduce the aberration of the entire projection lens. Since the third lens G3 is made of optical plastic, a diffraction surface is superimposed on the surface S6 on the third image source side of the third lens G3. By optimizing the parameters of the diffraction surface, the chromatic aberration of the lens is corrected. At the same time, because the material of the third lens G3 is optical plastic, it can be processed by high-precision diamond turning. The use of the diffraction surface replaces the traditional double-cemented lens. Compared with the traditional projection lens, while ensuring the imaging quality of the projection lens, the number of lenses is reduced and the weight of the projection lens is reduced. Applying it to augmented reality glasses can improve the comfort of the wearer and has broad application prospects.

[0039] The expression of the sag height of an even-order aspheric surface is:

[0040]

[0041] Among them, h represents the y-axis coordinate of each point on the lens surface relative to the center of the lens, c is the curvature of the lens, k is the cone coefficient, and a 4 , a 6 , a 8 , a 12 , a 14 are the high-order coefficients of even-order aspheric surfaces, Z ref It is the vector height of the lens surface along the optical axis when the y-axis coordinate is h.

[0042] When the substrate is a plane, the expression of the sagittal height of the diffraction surface is:

[0043]

[0044] Where λ is the central wavelength of the optical system design wavelength, n is the refractive index of the lens, and m is the ring zone serial number;

[0045] φ(r) is the phase expression of the diffraction surface,

[0046]

[0047] Among them, A 2 and A 4 is the phase parameter, r is the distance from a point on the third lens to the center of the lens, and r' is the clear aperture of the third lens.

[0048] The third image source side S6 of the third lens G3 is a superposition of a diffraction surface and an even-order aspheric surface, so the final sagittal height after the superposition of the two is:

[0049] Z=Z dif +Z ref

[0050] Table 1, Table 2 and Table 3 together show the specific parameters of each lens:

[0051] Table 1:

[0052]

[0053] Table 2:

[0054] Face number A4 A6 S3 -1.028E-03 -7.401E-05 S4 1.126E-03 -2.234E-05 S5 4.765E-03 -6.821E-05 S6 3.552E-03 -3.692E-05

[0055] Table 3 is the diffraction surface data of Example 1:

[0056] Face number Diffraction order Polynomial order Diffraction surface radius <![CDATA[A 2 ]]> <![CDATA[A 4 ]]> S6 1 2 5 -1017.897 160.261

[0057] Figures 3 to 5 The figure shows the MTF curve of this example under different fields of view (0°, 10°, 20°). In this example, the pixel size of LCOS is 5um, which is greater than 0.2 at 100lp / mm, and the overall curve is relatively stable, which reflects that the imaging quality of the refractive projection lens in this example is good.

[0058] Figure 6 This is a distortion curve. The distortion of the lens does not affect the image clarity but will affect the final imaging effect, especially for the optical system with the exit pupil being the human eye. It can be seen from the figure that the overall distortion of the lens is less than 5%, which can meet the distortion requirements of the human eye.

[0059] Figure 7 This is an overall illumination curve. The overall illumination of this example reaches more than 90% under the full field of view, which can avoid the problem of insufficient illumination at the exit pupil due to the loss of light energy in the system.

[0060] Example 2

[0061] like Figure 8 As shown, in a diffractive micro-projection lens based on Example 1, among the first lens G1, the second lens G2, and the third lens G3, the first focal length of the first lens G1 and the second focal length of the second lens G2 satisfy the relationship: first focal length / second focal length=3.8, among the first lens G1, the second lens G2, and the third lens G3, the first focal length of the first lens G1 and the third focal length of the third lens G3 satisfy the relationship: first focal length / third focal length=-0.17, and the back focus of the first lens G1, the second lens G2, and the third lens G3 and the total length of the projection lens satisfy the relationship: back focus / total length of the projection lens=0.52.

[0062] Table 4 below shows the radius of curvature, thickness, refractive index, Abbe number and cone coefficient of each lens of the optical lens of Example 2. Table 5 below shows the high-order coefficients A4 and A6 of the aspheric lens surface that can be used in Example 2.

[0063] Table 4:

[0064]

[0065]

[0066] Table 5:

[0067] Face number A4 A6 S3 -1.261E-03 -8.235E-05 S4 1.246E-03 -2.863E-05 S5 4.929E-03 -9.201E-05 S6 3.353E-03 -4.543E-05

[0068] Table 3 is the diffraction surface data of Example 2:

[0069] Face number Diffraction order Polynomial order Diffraction surface radius <![CDATA[A 2 ]]> <![CDATA[A 4 ]]> S6 1 2 5 -915.176 115.684

[0070] Embodiments 1 and 2 take projection lenses as examples to describe examples of optical lenses according to the embodiments of the present application. However, it should be understood that these projection lenses are merely application examples of the optical lenses according to the above-mentioned embodiments of the present application and should not be understood as limitations. The optical lenses can also be used in other fields as needed.

[0071] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the invention content within the protection scope of the present invention.

Claims

1. A foldable micro-projection lens, comprising: A silicon-based liquid crystal image source, a polarization beam splitter cube, and a projection lens group. The light emitted by the silicon-based liquid crystal image source passes through the polarization beam splitter cube and then passes through the projection lens group, and enters the human eye from the exit pupil as parallel light at different angles. The characteristics are as follows: the side close to the human eye when worn is the exit pupil side, the side of the silicon-based liquid crystal image source is the image source side, and along the direction from the exit pupil side to the image source side along the optical axis, the projection lens group includes a first lens, a second lens, and a third lens in sequence; wherein the first lens, the second lens, and the third lens are all meniscus lenses with concave surfaces facing the exit pupil side; the optical focal length of the first lens is positive and is used to deflect light with a large field of view; the image source side of the third lens is a diffraction lens. The projection surface is superimposed with the even-order aspheric surface; the second lens and the third lens are used together to balance the field curvature, distortion, chromatic aberration and aberration of the projection lens group; the focal length F1 of the first lens and the focal length F2 of the second lens satisfy the relationship: F1 / F2≤4; the focal length F1 of the first lens and the focal length F3 of the third lens satisfy the relationship: -2≤F1 / F3≤-1; the back focus Fb of the projection lens group and the total length TTL of the projection lens group satisfy the relationship: 0.4≤Fb / TTL; the second lens has a positive optical focal length, which is used to converge light from different fields of view and then project it into the third lens; the optical focal length of the third lens is opposite to that of the first lens, which is used to balance the aberration.

2. The folded micro-projection lens according to claim 1, characterized in that: The materials of the first lens and the third lens are optical plastics, and the material of the second lens is optical glass.

3. The folded micro-projection lens according to claim 1, characterized in that: The polarization beam splitter cube is a wire grid polarization beam splitter cube with a refractive index of 1.52 and an Abbe constant of 64.

2.

4. The folded micro-projection lens according to claim 1, characterized in that: The refractive index of the first lens is 1.49, and the Abbe constant is 57.4; the refractive index of the second lens is 1.57, and the Abbe constant is 63.0; the refractive index of the third lens is 1.49, and the Abbe constant is 57.

4.

5. The folded micro-projection lens according to claim 1, characterized in that: The phase expression of the diffraction surface is: Wherein, A2 and A4 are phase parameters, r is the distance from a point on the third lens to the center of the lens, and r' is the clear aperture of the third lens.

6. The folded micro-projection lens according to claim 5, characterized in that: The phase parameters of A2 and A4 are -1071.89 and 160.26 respectively.

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