Refraction and diffraction mixed type folded optical path head-mounted display

Abstract

The invention discloses a refraction and diffraction mixed type folded light path head-mounted display, relates to the technical field of head-mounted displays, and aims to solve the problem of low imaging resolution caused by difficulty in chromatic aberration correction of a head-mounted display with a large eye pupil space and a large view field in the prior art. A display screen, a first imaging assembly, a second imaging assembly and a third imaging assembly are sequentially arranged in the optical axis direction. The first imaging assembly comprises a first lens L1 and a semi-reflecting and semi-transmitting film L2; the second imaging assembly comprises a second lens L3; the third imaging assembly comprises a third lens L4, a polarization reflector plate L6, a quarter-wave plate L5 and a polaroid L7; according to the invention, folding of a light path is realized through combination of the light splitting element and the polarization optical element; a diffractive optical element is introduced into the polarization folded light path to form a refractive-diffractive hybrid folded light path head-mounted display; the invention has the advantages of large eye pupil space, large field of view, high resolution, small volume and light weight, and can improve excellent immersion and comfort for wearers.

Description

Technical Field

[0001] The present invention relates to the technical field of head-mounted displays, and in particular to a refractive-diffractive hybrid folded optical path head-mounted display. Background Art

[0002] The development of virtual reality (VR) technology has greatly expanded the boundaries of human perception, driving the rapid evolution of concepts such as the metaverse, digital twins, and spatial computing. It also demonstrates enormous application potential in fields such as education, healthcare, entertainment, and manufacturing. As the core device of VR technology, VR head-mounted displays (HMDs) rely on microdisplays and optical systems. Key research focuses on improving wearing comfort and immersion. This requires optical systems to possess a large pupil area, a wide field of view, high resolution, a compact size, and low weight.

[0003] By folding the optical path using polarization elements, the polarization-folded optical path structure achieves a large field of view while maintaining a small size, making it ideal for head-mounted displays (HMDs). However, while achieving a large field of view, the polarization-folded optical path structure inevitably introduces significant chromatic aberration. This is especially true when the pupil space is increased to accommodate pupil shift scenarios. Chromatic aberration has a more severe impact on image quality. Pupil shift can lead to a sharp increase in lateral chromatic aberration, reducing the HMD's imaging resolution and causing chromatic aberration artifacts, which can seriously affect the comfort and immersion of the HMD.

[0004] In the journal Laser Technology, Bai Xianghu, Zhu Xiangbing, and others published an article titled "Optical Design of a Head-Mounted Display with a Folded Optical Path Structure." Based on a polarization-based folded optical path structure, this article designed a head-mounted display with a large field of view and large pupil space, including a 96° field of view, a 10mm exit pupil diameter, and a 14.94mm exit pupil distance. The head-mounted display in the article exhibited a maximum vertical chromatic aberration of 13.84μm, a resolution of 1600×1600, and a modulation transfer function (MTF) greater than 0.2 at a Nyquist frequency of 20.83 lp / mm. However, the head-mounted display in the article lacked means to correct chromatic aberration, which significantly impacted image quality, resulting in low resolution. This low resolution led to a screen door effect, severely impacting comfort and immersion. Summary of the Invention

[0005] In order to solve the problem of low imaging resolution caused by difficulty in chromatic aberration correction in existing head-mounted displays with large pupil space and large field of view, the present invention proposes a hybrid refractive-diffractive folded optical path head-mounted display.

[0006] The technical solution of the present invention to solve the technical problem is:

[0007] A refractive-diffractive hybrid folded optical path head-mounted display, characterized in that a display screen, a first imaging component, a second imaging component, and a third imaging component are arranged in sequence along the optical axis direction;

[0008] The first imaging assembly includes a first lens L1 and a semi-reflective semi-transparent membrane L2; the first lens L1 is a refractive-diffractive hybrid lens, and the front surface S1 of the first lens L1 is a diffractive surface; the semi-reflective semi-transparent membrane L2 forms a membrane on the back surface S2 of the first lens L1;

[0009] The second imaging assembly includes a second lens L3;

[0010] The third imaging assembly includes a third lens L4, a polarizing reflector L6, a quarter-wave plate L5, and a polarizer L7;

[0011] The refractive powers of the first lens L1 and the third lens L4 are both positive, and the refractive power of the second lens L3 is negative;

[0012] The quarter-wave plate L5, the polarizing reflector L6, and the polarizer L7 form a composite film on the rear surface S6 of the third lens L4, and are arranged in the order of the quarter-wave plate L5, the polarizing reflector L6, and the polarizer L7 in the optical axis direction;

[0013] The right-handed circularly polarized light emitted by the display screen passes through the first imaging component, the second imaging component and the third lens L4 of the third imaging component in sequence, and then reaches the quarter-wave plate L5 for the first time, and the right-handed circularly polarized light is converted into horizontally polarized light; the light reaches the polarizing reflector L6 for the first time, which reflects the horizontally polarized light; the light reaches the quarter-wave plate L5 for the second time, and the horizontally polarized light is converted into right-handed circularly polarized light; the light passes through the third lens L4 and the second lens L3 for the second time and reaches the semi-reflective semi-transparent membrane L2, and the left-handed circularly polarized light is reflected by the semi-reflective semi-transparent membrane L2; then the light passes through the second lens L3 and the third lens L4 and reaches the quarter-wave plate L5 for the third time, and the left-handed circularly polarized light is converted into vertically polarized light by the quarter-wave plate L5; the light passes through the polarizing reflector L6 for the second time; the vertically polarized light after passing through reaches the polarizer L7, and light other than the vertically polarized light is filtered out; finally, the light reaches the pupil of the human eye in the polarization state of vertically polarized light.

[0014] Beneficial effects of the present invention: The present invention realizes the folding of the optical path through the combination of a spectroscopic element and a polarization optical element. The polarization folded optical path facilitates achieving a large field of view while taking into account a small size and light weight. A diffraction optical element is introduced into the polarization folded optical path to form a refractive-diffractive hybrid folded optical path head-mounted display. Based on the special negative dispersion characteristics of the diffractive optical element, it is combined with a refractive optical element to form a refractive-diffractive hybrid lens, which can efficiently correct chromatic aberration. The present invention has good chromatic aberration correction in a large pupil space and high imaging resolution. Based on the above characteristics, the present invention has the advantages of a large pupil space, a large field of view, a high resolution, a small size and a light weight, which can provide the wearer with an excellent sense of immersion and comfort. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of a refractive-diffractive hybrid folded optical path head-mounted display according to the present invention;

[0016] Figure 2 A schematic diagram of pupil displacement of a refractive-diffractive hybrid folded optical path head-mounted display according to the present invention;

[0017] Figure 3 A schematic diagram of six specific pupil positions in the pupil space of a refractive-diffractive hybrid folded optical path head-mounted display according to the present invention;

[0018] Figure 4 A structural light path diagram of six specific pupil positions in the pupil space according to a specific embodiment of the present invention;

[0019] Figure 5 is a characteristic parameter curve of the diffraction surface of a specific embodiment of the present invention;

[0020] Figure 6 is the MTF of six specific pupil positions in the pupil space of a specific embodiment of the present invention;

[0021] Figure 7 φ is the vertical chromatic aberration of six specific pupil positions in the pupil space according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, a refractive-diffractive hybrid folded optical path head-mounted display comprises a display screen 1, a first imaging component 2, a second imaging component 3 and a third imaging component 4 arranged in sequence along the optical axis direction.

[0024] The optical axis direction is the direction from the display screen 1 to the position of the human eye.

[0025] The first imaging assembly 2 includes a first lens L1 and a semi-reflective semi-transparent film L2. The first lens L1 is a refractive / diffractive hybrid lens. The front surface S1 of the first lens L1 is a diffractive surface. The semi-reflective semi-transparent film L2 forms the film on the back surface S2 of the first lens L1.

[0026] The second imaging assembly 3 includes a second lens L3.

[0027] The third imaging assembly 4 includes a third lens L4, a polarizing reflector L6, a quarter-wave plate L5 and a polarizer L7.

[0028] The refractive powers of the first lens L1 and the third lens L4 are both positive, and the refractive power of the second lens L3 is negative.

[0029] The quarter-wave plate L5, the polarizing reflector L6 and the polarizer L7 form a composite film on the rear surface S6 of the third lens L4, and are arranged in the order of the quarter-wave plate L5, the polarizing reflector L6 and the polarizer L7 in the optical axis direction.

[0030] The display screen 1 is configured to emit right-handed circularly polarized light.

[0031] The semi-reflective and semi-transmissive film L2 is a film with a spectroscopic property. When light passes through, part of the light is transmitted and part of the light is reflected, and the intensity of the transmitted light and the reflected light each accounts for 50%.

[0032] The quarter-wave plate L5 is made of birefringent material and adjusts the polarization state of the light beam by introducing phase delay.

[0033] The polarizing reflector L6 is an optical element that reflects or transmits light according to its polarization state, and achieves selective transmission of light by distinguishing between horizontally polarized light and vertically polarized light.

[0034] The polarizer L7 transmits only vertically polarized light, thereby effectively filtering out stray light and improving the imaging quality of the head-mounted display.

[0035] The semi-reflective and semi-transparent film L2, the quarter-wave plate L5 and the polarized reflective plate L6 fold the optical path to shorten the total optical length and realize the miniaturization and lightweight design of the head-mounted display.

[0036] The workflow of the present invention is as follows:

[0037] The display screen 1 emits right-handed circularly polarized light, which passes through the first imaging component 2, the second imaging component 3 and the third lens L4 of the third imaging component 4 in sequence. The light then reaches the quarter-wave plate L5 for the first time, and the right-handed circularly polarized light is converted into horizontally polarized light. The light reaches the polarizing reflector L6 for the first time, which reflects the horizontally polarized light. The light reaches the quarter-wave plate L5 for the second time, and the horizontally polarized light is converted into right-handed circularly polarized light. The light passes through the third lens L4 and the second lens L3 for the second time, and reaches the semi-reflective and semi-transparent membrane L2 of the first imaging component 2. The left-handed circularly polarized light is reflected by the semi-reflective and semi-transparent membrane L2. The light then passes through the second lens L3 and the third lens L4 and reaches the quarter-wave plate L5 for the third time, and the left-handed circularly polarized light is converted into vertically polarized light by the quarter-wave plate L5. The light passes through the polarizing reflector L6 for the second time. The vertically polarized light after passing through reaches the polarizer L7, and light other than the vertically polarized light is filtered out. Finally, the light reaches the pupil of the human eye in the polarization state of vertically polarized light.

[0038] The front and rear surfaces S1 and S2 of the first lens L1 and the front and rear surfaces S3 and S4 of the second lens L3 are all high-order aspheric surfaces. The equation of the high-order aspheric surface is:

[0039]

[0040] Where z is the height of the high-order aspheric surface, c is the basic curvature at the vertex of the high-order aspheric surface, r is the radial coordinate of the point on the high-order aspheric surface, k is the conic section constant, and a1, a2, a3, a4, and a5 are the aspheric coefficients.

[0041] The front surface S1 of the first lens L1 is a diffraction surface, and the phase distribution formula is:

[0042]

[0043] Where c1, c2, ... and c n is the number of terms of the binary diffraction surface, and r is the normalized radial radius.

[0044] The total number of ring zones on the diffraction surface is:

[0045]

[0046] Example:

[0047] like Figure 3 As shown, the present invention provides a refractive-diffractive hybrid folded optical path head-mounted display that allows the human pupil to shift by ±3 mm in the direction of the optical axis and the direction perpendicular to the optical axis; when pupil shift is not considered, the exit pupil size is 4 mm and the exit pupil distance is 15 mm; the pupil shift range allowed in the vertical axis direction is 10 mm, and the pupil shift range allowed in the optical axis direction is 12 to 18 mm.

[0048] like Figure 4 As shown, the Z axis of the pupil space of a refractive-diffractive hybrid folded optical path head-mounted display of the present invention is the optical axis direction, and the Y axis is the vertical axis direction; the six specific pupil positions include points A, B, C, D, E and F; point A is the pupil position without pupil offset, that is, the origin, point B is the pupil position offset by -3mm in the optical axis direction, point C is the pupil position offset by 3mm in the optical axis direction, point D is the pupil position offset by -3mm in the vertical axis direction, point E is the pupil position offset by -3mm in both the optical axis direction and the vertical axis direction, and point F is the pupil position offset by 3mm in both the optical axis direction and the vertical axis direction.

[0049] The dielectric material of the lenses in the refractive-diffractive hybrid folded optical path head-mounted display of the present invention is plastic, which is convenient for processing and manufacturing high-order aspheric surfaces and diffractive surfaces and can be processed and manufactured using injection molding technology.

[0050] The structural optical path diagram of the six specific pupil positions in the pupil space of a specific embodiment of a refractive-diffractive hybrid folded optical path head-mounted display of the present invention is as follows: Figure 4 shown.

[0051] The display screen 1 has an aspect ratio of 1:1, a resolution of 2280×2280, and a pixel size of 12 μm.

[0052] Some parameters of the specific embodiment are as follows:

[0053]

[0054]

[0055] The curvature radius in the table is the curvature radius of the standard sphere and the basic curvature radius at the vertex of the higher-order aspheric surface. The thickness in the table is the distance between adjacent mirror vertices on the imaging optical path. The material in the table is the dielectric material of the optical lens.

[0056] The front and rear surfaces S1 and S2 of the first lens L1 and the front and rear surfaces S3 and S4 of the second lens L3 are all high-order aspheric surfaces. The equation of the high-order aspheric surface is:

[0057]

[0058] Where z is the height of the high-order aspheric surface, c is the basic curvature at the vertex of the high-order aspheric surface, r is the radial coordinate of the point on the high-order aspheric surface, k is the conic section constant, and a1, a2, a3, a4, and a5 are the aspheric coefficients.

[0059] The mirror coefficients of the aspheric surfaces in the embodiment are shown in the following table:

[0060] surface Cone coefficient 4th-order term 6th-order term 8th-order term S4 0.336 -3.120E-06 4.132E-09 -1.440E-12 S3 0.801 -3.543E-06 2.324E-09 3.272E-12 S2 3.097 -1.402E-06 2.652E-09 -1.969E-12 S1 - -2.090E-05 3.202E-10 -1.931E-13

[0061] The front surface S1 of the first lens L1 is a diffraction surface, and the phase distribution formula is:

[0062]

[0063] Where c1, c2, ... and c n is the number of terms of the binary diffraction surface, and r is the normalized radial radius.

[0064] The total number of ring zones on the diffraction surface is:

[0065]

[0066] The diffraction surface uses the first two terms of the binary diffraction surface, where c1 is -1708.602 and c2 is 194.983. The total number of ring zones is 192. The characteristic parameters of the diffraction surface are as follows: Figure 5 As shown, the minimum periodic ring zone spacing is 83.572μm, and precision diamond turning technology is used to meet the requirements of processing accuracy.

[0067] All lens dielectric materials are optical plastics to achieve lightweight head-mounted display. Lens L1 is APL5014CL, lens L3 is EP9000, and lens L4 is COC.

[0068] The embodiment of the present invention has a focal length of 25mm, a full field of view angle of 96°, an exit pupil size of 4mm, an exit pupil distance of 15mm, an imaging band of 0.45-0.65μm, and a total optical length of 21mm, and has the advantages of a large field of view and a small size.

[0069] The MTF of the embodiment of the present invention at different viewing fields at six specific pupil positions in the pupil space is as follows: Figure 6 As shown, the MTF value at the Nyquist frequency of 42lp / mm is greater than 0.2, and high-quality imaging is achieved within a 96° field of view angle, a 12-18mm optical axis pupil offset range, and a 10mm vertical axis pupil offset range, enabling high resolutions of 2K for monocular and 4K for binocular.

[0070] The vertical axis chromatic aberration of six specific pupil positions in the pupil space according to the embodiment of the present invention is as follows: Figure 7 As shown, the vertical chromatic aberration at points A, B, and C on the axis is smaller than the Airy disk size (4.5μm) across the entire field of view. Point E has the largest vertical chromatic aberration of all positions, with a maximum value of 11.85mm, which is smaller than the size of a pixel. The vertical chromatic aberration is effectively controlled within the allowable pupil offset range. Image preprocessing only requires addressing distortion, eliminating the need for additional processing of the vertical chromatic aberration, greatly facilitating image preprocessing.

Claims

1. A refractive-diffractive hybrid folded optical path head-mounted display, characterized in that: A display screen (1), a first imaging component (2), a second imaging component (3) and a third imaging component (4) are sequentially arranged along the optical axis direction; The first imaging component (2) comprises a first lens L1 and a semi-reflective semi-transparent film L2; The first lens L1 is a refractive-diffractive hybrid lens, and the front surface S1 of the first lens L1 is a diffractive surface; the semi-reflective and semi-transparent film L2 constitutes a film on the back surface S2 of the first lens L1; The second imaging assembly (3) includes a second lens L3; The third imaging assembly (4) includes a third lens L4, a polarizing reflector L6, a quarter-wave plate L5, and a polarizer L7; The refractive powers of the first lens L1 and the third lens L4 are both positive, and the refractive power of the second lens L3 is negative; The quarter-wave plate L5, the polarizing reflector L6, and the polarizer L7 form a composite film on the rear surface S6 of the third lens L4, and are arranged in the order of the quarter-wave plate L5, the polarizing reflector L6, and the polarizer L7 in the optical axis direction; The display screen (1) emits right-handed circularly polarized light, which passes through the first imaging component (2), the second imaging component (3), and the third lens L4 of the third imaging component (4) in sequence. The light then reaches the quarter-wave plate L5 for the first time, and the right-handed circularly polarized light is converted into horizontally polarized light. The light then reaches the polarizing reflector L6 for the first time, and the horizontally polarized light is reflected. The light then reaches the quarter-wave plate L5 for the second time, and the horizontally polarized light is converted into right-handed circularly polarized light. The light then reaches the semi-reflective and semi-transparent membrane L2 for the second time, and the left-handed circularly polarized light is reflected by the semi-reflective and semi-transparent membrane L2. The light then passes through the second lens L3 and the third lens L4 before reaching the quarter-wave plate L5 for the third time. The left-handed circularly polarized light is converted into vertical linearly polarized light by the quarter-wave plate L5. The light then passes through the polarizing reflector L6 for the second time. The vertically polarized light after passing through reaches the polarizer L7, and light other than the vertically polarized light is filtered out; finally, the light reaches the pupil of the human eye in the polarization state of vertically polarized light.

2. The refractive-diffractive hybrid folded optical path head-mounted display according to claim 1, characterized in that: The display screen (1) is configured to emit right-handed circularly polarized light.

3. The hybrid refractive-diffractive folded optical path head-mounted display according to claim 1, characterized in that: The semi-reflective and semi-transmissive film L2 is a film with a spectroscopic property. When light passes through, part of the light is transmitted and part of the light is reflected, and the intensity of the transmitted light and the reflected light each accounts for 50%.

4. The refractive-diffractive hybrid folded optical path head-mounted display according to claim 1, characterized in that: The quarter-wave plate L5 is made of birefringent material and adjusts the polarization state of the light beam by introducing phase delay.

5. The hybrid refractive-diffractive folded optical path head-mounted display according to claim 1, characterized in that: The polarizing reflector L6 is an optical element that reflects or transmits light according to its polarization state, and achieves selective transmission of light by distinguishing between horizontally polarized light and vertically polarized light.

6. The refractive-diffractive hybrid folded optical path head-mounted display according to claim 1, characterized in that: The polarizer L7 transmits only vertically polarized light.

7. The refractive-diffractive hybrid folded optical path head-mounted display according to claim 1, characterized in that: The front and rear surfaces S1 and S2 of the first lens L1 and the front and rear surfaces S3 and S4 of the second lens L3 are all high-order aspheric surfaces. The equation of the high-order aspheric surface is: Where z is the height of the high-order aspheric surface, c is the basic curvature at the vertex of the high-order aspheric surface, r is the radial coordinate of the point on the high-order aspheric surface, k is the conic section constant, and a1, a2, a3, a4, and a5 are the aspheric coefficients.

8. The refractive-diffractive hybrid folded optical path head-mounted display according to claim 1, characterized in that: The front surface S1 of the first lens L1 is a diffraction surface, and the phase distribution formula is: Where c1, c2, ... and c n is the number of terms of the binary diffraction surface, r is the normalized radial radius; The total number of ring zones on the diffraction surface is:

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