CN111487777A - Refraction and diffraction type miniature projection lens - Google Patents

Abstract

The invention belongs to the technical field of virtual implementation, and particularly relates to an AR (augmented reality) shadow camera. The first lens, the second lens and the third lens are arranged along an optical axis from an exit pupil side to an image source side in sequence, the first lens, the second lens and the third lens are meniscus lenses with concave surfaces facing the exit pupil side, and the surface shape of the image source side of the third lens is the superposition of a diffraction surface and an even aspheric surface. The invention has the beneficial effects that: the diffraction surface is superposed on the side surface of the image source of the third lens, the chromatic aberration of the lens is corrected by optimizing the parameters of the diffraction surface, the traditional double-cemented lens is replaced by the diffraction surface, and compared with the traditional projection lens, the projection lens reduces the number of lenses while ensuring the imaging quality of the projection lens, lightens the weight of the projection lens, can improve the comfort level of a wearer by applying the projection lens to the augmented reality glasses, and has wide application prospect.

Description

Refraction and diffraction type miniature projection lens

Technical Field

The invention belongs to the technical field of virtual implementation, and particularly relates to a projection lens for AR.

Background

The micro projection optical system is mainly composed of L ED light source, light source shaping illumination system, image source (L COS or DMD), projection system, heat dissipation system, and so on, and with the recent appearance of head-mounted optical systems represented by augmented reality glasses AR and virtual reality glasses, there are higher demands for indexes of the micro projection optical system such as volume, weight, and brightness.

The projection lens used for augmented reality glasses and the like in the current market basically adopts a multi-piece type, particularly an aspheric surface structure with more than four pieces, and the projection lens has good effect, but easily causes the problems of large volume, high total weight, high processing and adjusting difficulty and the like.

Disclosure of Invention

The present invention is directed to a diffractive micro projection lens to solve the above problems.

In order to achieve the purpose, the invention provides the following technical scheme: a diffractive micro projection lens, comprising: the device comprises a silicon-based liquid crystal image source, a polarization beam splitting cube and a projection lens group, wherein light emitted by the silicon-based liquid crystal image source passes through the polarization beam splitting cube and then passes through the projection lens group, and parallel light with different angles is emitted from an exit pupil and enters human eyes; the method is characterized in that: the projection lens group sequentially comprises a first lens, a second lens and a third lens from the exit pupil side to the image source side along the optical axis, wherein one side of the projection lens group, which is close to human eyes when the projection lens group is worn, is the exit pupil side, and one side of the silicon-based liquid crystal image source is the image source side; the first lens, the second lens and the third lens are provided with meniscus lenses with concave surfaces facing the exit pupil side; the focal power of the first lens is positive and is used for deflecting the light rays with a large visual field; the image source side of the third lens is arranged to be superposed by a diffraction surface and an even aspheric surface; the second lens and the third lens are used together to balance the curvature of field, distortion, chromatic aberration and aberration of the projection lens group.

The color screen type comprises a TFT, a TFD, a UFB, an STN, an O L ED, an AMO L ED and an S L CD.

Preferably: the first lens and the third lens are made of optical plastics, and the second lens is made of optical glass.

Preferably: the focal length F1 of the first lens and the focal length F2 of the second lens of the projection lens group satisfy the following relation: F1/F2 is less than or equal to 4.

Preferably: the focal length F1 of the first lens and the focal length F3 of the third lens of the projection lens group satisfy the following relation: F1/F3 is more than or equal to-2 and less than or equal to-1.

Preferably, the rear intercept Fb of the projection lens group and the total length TT L of the projection lens group satisfy the relation that Fb/TT L is more than or equal to 0.4.

Preferably: the polarization beam splitting cube is a wire grid type polarization beam splitting cube, the refractive index is 1.52, and the Abbe constant is 64.2.

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 was 1.49, and the abbe constant was 57.4.

Preferably: the phase expression of the diffraction surface is as follows:

wherein A is₂And A₄And 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.

Preferably: a is described₂And A₄Are-1071.89 and 160.26, respectively.

When the technical scheme 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 splitting cube, is emitted from the exit pupil by parallel light with different angles, is connected into the diffraction light guide plate and the like after the exit pupil, and is amplified to enter human eyes, so that the human eyes receive L images on the COS image source.

Advantageous effects

According to the refraction and diffraction type projection lens provided by the invention, the diffraction surface is superposed on the image source side surface of the third lens, the chromatic aberration of the lens is corrected by optimizing the parameters of the diffraction surface, the diffraction surface is used for replacing the traditional double-cemented lens, and compared with the traditional projection lens, the number of lenses is reduced while the imaging quality of the projection lens is ensured, the weight of the projection lens is reduced, the comfort of a wearer can be improved when the refraction and diffraction type projection lens is applied to augmented reality glasses, and the refraction and diffraction type projection lens has a wide application prospect.

Drawings

FIG. 1 is an optical block diagram of the present invention;

FIG. 2 is a ray tracing diagram of the present invention;

FIG. 3 is a schematic view of the MTF curve at 0 ° field of view of the present invention;

FIG. 4 is a schematic representation of the 10 field MTF curve of the present invention;

FIG. 5 is a schematic representation of the 20 field MTF curve of the present invention;

FIG. 6 is a schematic diagram of a distortion curve of the present invention;

FIG. 7 is a diagram illustrating relative illumination according to the present invention;

FIG. 8 is a schematic view of example 2 of the present invention.

Reference numerals

ST-exit pupil side, IMA-image source side, G1-first lens, G2-second lens, G3-third lens, G4-polarizing beam splitting cube, S1-first lens exit pupil side surface, S2-first lens image source side surface, S3-second lens exit pupil side surface, S4-second lens image source side surface, S5-third lens exit pupil side surface, S6-third lens image source side surface.

Detailed Description

The following are specific examples of the present invention and further describe the technical solutions of the present invention, but the present invention is not limited to these examples.

Example 1

As shown in fig. 1, in the present embodiment, a diffractive micro projection lens, as shown in fig. 1, includes a liquid crystal on silicon image source, a polarization beam splitter cube G4, and a projection lens set, wherein light emitted from the liquid crystal on silicon image source passes through the polarization beam splitter cube and then passes through the projection lens set, and exits from an exit pupil to enter a human eye as parallel light with different angles; one side close to human eyes is taken as an exit pupil side when the device is worn, and one side of a silicon-based liquid crystal image source is taken as an image source side; the first lens is a meniscus lens G1, the exit pupil side surface S1 is a concave surface, the second lens is a meniscus lens G2, the exit pupil side surface S3 is a concave surface, the third lens is a meniscus lens G3, the exit pupil side surface S5 is a concave surface, and the image source side S6 of the third lens is the superposition of a diffraction surface and an even aspheric surface; the focal power of the first lens is positive and is used for deflecting the light rays with a large visual field; the second lens and the third lens are used together to balance the curvature of field, distortion, chromatic aberration and aberration of the projection lens group.

As shown in fig. 2, an application optical path of the lens is that light from the illumination system is reflected to an image source surface, that is, a liquid crystal surface of L COS, by a polarization beam splitter cube G4, the phase of incident light is reversed after being reflected by L COS, the incident light successively passes through the polarization beam splitter cube G4, a third lens G3 and a second lens G2, and parallel light with different angles exits from an exit pupil side ST after passing through a first lens G1, and enters human eyes.

The first lens G1 and the second lens G2 both have positive powers, and focus light of different fields of view and project the light into the third lens G3.

The third lens G3 has an optical power opposite to that of the first lens G1 and the second lens G2, and is used for balancing aberrations.

The rear intercepts 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 following relations: and the rear intercept/total length is more than or equal to 0.4, so that the whole length of the lens can be compressed, and a sufficient distance can be reserved for adding a polarization beam splitting cube into the projection lens.

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

Two optical surfaces of the second lens G2 and two optical surfaces of the third lens G3 are even aspheric surfaces, aberration of the whole projection lens can be effectively reduced, the third lens G3 is made of optical plastic, a diffraction surface is superposed on the surface of the third image source side S6 of the third lens G3, chromatic aberration of the lens is corrected by optimizing parameters of the diffraction surface, meanwhile, the third lens G3 is made of optical plastic, processing can be carried out through high-precision diamond turning, the diffraction surface is used for replacing a traditional double-cemented lens, compared with the traditional projection lens, the number of lenses is reduced while imaging quality of the projection lens is guaranteed, weight of the projection lens is reduced, comfort of a wearer can be improved when the third lens is applied to augmented reality glasses, and the projection lens has a wide application prospect.

The rise expression for an even aspheric surface is:

wherein h represents the y-axis coordinate of each point on the lens surface relative to the lens center, c is the curvature of the lens, k is the conic coefficient, a₄，a₆，a₈，a₁₂，a₁₄Higher order coefficients, Z, of even-order aspheric surfaces, respectively_refIs the rise of the lens surface in the optical axis direction at the y-axis coordinate h.

The saggital expression of the diffraction plane when the substrate is a plane is:

wherein lambda is the central wavelength of the optical system design wavelength, n is the refractive index of the lens, and m is the annulus serial number;

phi (r) is a phase expression of the diffraction plane,

wherein A is₂And A₄And 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.

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 rise after the superposition of the two is:

Z＝Z_dif+Z_ref

table 1, table 2 and table 3 collectively represent specific parameters for each lens:

table 1:

table 2:

flour mark	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

Table 3 shows the diffraction surface data of example 1:

flour mark	Diffraction order	Polynomial order	Radius of diffraction surface	A2	A4
						S6	1	2	5	-1017.897	160.261

Fig. 3 to fig. 5 show MTF curves of the present example under different fields of view (0 °, 10 °, and 20 °), where the pixel size of the L COS in the present example is 5um, and is greater than 0.2 at 100lp/mm, and the trend of the overall curve is relatively smooth, which can reflect that the imaging quality of the diffractive projection lens in the present example is relatively good.

Fig. 6 is a distortion curve diagram, where the distortion of the lens does not affect the image sharpness but affects the final image effect, and especially for an optical system with an exit pupil of human eyes, it can be seen that the overall distortion of the lens is less than 5%, which can meet the requirement of human eyes for distortion.

Fig. 7 is a graph of the overall illumination, which is more than 90% in the full field of view, and can avoid the problem of insufficient illumination at the exit pupil due to the loss of light energy of the system.

Example 2

As shown in fig. 8, in the first lens G1, the second lens G2, and the third lens G3 of the diffractive micro projection lens based on embodiment 1, a first focal length of the first lens G1 and a second focal length of the second lens G2 satisfy a relationship: the first focal length/the second focal length is 3.8, and of 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: the first focal length/the third focal length is-0.17, and the rear focal length of the first lens G1, the second lens G2 and the third lens G3 and the total length of the projection lens satisfy the following relation: the rear intercept/total projection lens length is 0.52.

Table 4 below shows the radius of curvature, thickness, refractive index, abbe number, and conic coefficient of each lens of the optical lens of example 2. Table 5 below shows the high-order term coefficients a4 and a6 of the aspherical lens surface that can be used in example 2.

Table 4:

table 5:

flour mark	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

Table 3 shows the diffraction surface data of example 2:

flour mark	Diffraction order	Polynomial order	Radius of diffraction surface	A2	A4
						S6	1	2	5	-915.176	115.684

Examples 1 and 2 describe examples of the optical lens according to the embodiment of the present application by taking the projection lens as an example, but it should be understood that these projection lenses are only examples of the application of the optical lens according to the above embodiment of the present application, and should not be construed as a limitation, and the optical lens can also be applied to other fields as needed.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the content of the present invention within the scope of the protection of the present invention.

Claims (9)

1. A diffractive micro projection lens, comprising: the device comprises a silicon-based liquid crystal image source, a polarization beam splitting cube and a projection lens group, wherein light emitted by the silicon-based liquid crystal image source passes through the polarization beam splitting cube and then passes through the projection lens group, and parallel light with different angles is emitted from an exit pupil and enters human eyes; the method is characterized in that: the projection lens group sequentially comprises a first lens, a second lens and a third lens from the exit pupil side to the image source side along the optical axis, wherein one side of the projection lens group, which is close to human eyes when the projection lens group is worn, is the exit pupil side, and one side of the silicon-based liquid crystal image source is the image source side; the first lens, the second lens and the third lens are provided with meniscus lenses with concave surfaces facing the exit pupil side; the focal power of the first lens is positive and is used for deflecting the light rays with a large visual field; the image source side of the third lens is arranged to be superposed by a diffraction surface and an even aspheric surface; the second lens and the third lens are used together to balance the curvature of field, distortion, chromatic aberration and aberration of the projection lens group.

2. The diffractive micro projection lens according to claim 1, wherein the first lens and the third lens are made of optical plastic, and the second lens is made of optical glass.

3. The catadioptric miniature projection lens of claim 1 wherein the focal length of the first lens of the projection lens group F1 and the focal length of the second lens F2 satisfy the relationship: F1/F2 is less than or equal to 4.

4. The catadioptric miniature projection lens of claim 1 wherein the focal length of the first lens of the projection lens group F1 and the focal length of the third lens F3 satisfy the relationship: F1/F3 is more than or equal to-2 and less than or equal to-1.

5. The catadioptric miniature projection lens of claim 1 wherein the rear intercept Fb of the projection lens group and the total length TT L of the projection lens group satisfy the relationship of 0.4 ≦ Fb/TT L.

6. The diffractive micro projection lens according to claim 1, wherein 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.

7. The diffractive micro projection lens according to claim 1, wherein the refractive index of the first lens is 1.49, 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 was 1.49, and the abbe constant was 57.4.

8. The diffractive micro projection lens according to claim 1, wherein the phase expression of the diffraction surface is:

wherein A is₂And A₄And 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.

9. The catadioptric miniature projection lens of claim 8, wherein a is₂And A₄Are-1071.89 and 160.26, respectively.

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