An extremely thin virtual reality liquid crystal holographic optical system

Abstract

The present application relates to virtual reality display technical field, disclose a kind of very light and thin virtual reality liquid crystal holographic optical system, the system includes display panel, half reflection half transmission film, reflective cholesteric liquid crystal holographic lens and at least one geometric phase liquid crystal lens;Half reflection half transmission film and reflective cholesteric liquid crystal holographic lens constitute optical folding cavity between, at least one geometric phase liquid crystal lens is set in cavity, the rest can be flexibly arranged in cavity or specific position outside cavity;Panel emitted light enters folding cavity, by multiple transmission and polarization state alternative conversion, is finally shot out after being reflected by holographic lens.The present application utilizes liquid crystal lens and folding cavity to shorten physical total length and achieve light and thin, introduces high-order phase function to accurately correct wavefront aberration, and through precise polarization state control and wavelength alignment design of three cholesteric lenses, significantly improves light energy utilization and color reproduction degree.

Description

Technical Field

[0001] This invention relates to the field of virtual reality display technology, specifically to an ultra-thin virtual reality liquid crystal holographic optical system. Background Technology

[0002] The optical system of a virtual reality head-mounted display device plays a crucial role in magnifying the displayed image and guiding it to the human eye. Traditional optical systems typically use solid glass or injection-molded resin lenses. These curved refractive lenses inevitably have a large physical thickness and weight, resulting in a bulky overall size of the head-mounted device. This can easily cause user fatigue and makes it difficult to meet the development needs of thinner and lighter hardware devices.

[0003] To shorten the overall physical length of optical systems, the industry currently employs folded optical path architectures and is beginning to explore the introduction of liquid crystal optical elements to replace traditional solid lenses. However, several technical limitations still exist in existing folded optical systems built on liquid crystal elements. First, folded optical paths rely on light undergoing multiple reflections and transmissions between the semi-reflective film and the mirror, requiring extremely precise control over the polarization state evolution of the light. The polarization state conversion process in existing systems is not precise enough, and polarization errors can easily occur when light passes through the lens multiple times, resulting in ghosting and crosstalk, which leads to a decrease in the overall light energy utilization and contrast of the system.

[0004] Secondly, while diffraction-based liquid crystal optical systems significantly reduce system thickness, the difficulty of correcting wavefront aberrations increases. Multiple propagations of light within the folded cavity accumulate and amplify chromatic and monochromatic aberrations. Existing liquid crystal phase modulation structures often lack sufficient design freedom, making it difficult to effectively compensate for higher-order wavefront aberrations in the optical system, resulting in insufficient edge field-of-view sharpness in the final image. Furthermore, for full-color displays, existing liquid crystal holographic reflection structures typically struggle to achieve precise broadband reflection matching with the peak wavelengths of the red, green, and blue primary colors emitted by the display panel. This directly leads to energy loss in some wavelength bands, affecting the color reproduction of the displayed image. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an ultra-thin virtual reality liquid crystal holographic optical system. This system solves the problems of existing virtual reality optical systems being bulky due to the use of traditional solid lenses, as well as the difficulties in effectively correcting wavefront aberrations, inaccurate polarization state control, and low multi-band light energy utilization encountered in the process of achieving a thinner optical system and folded optical path.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: including a display panel, a semi-reflective and semi-transparent film, a reflective cholesteric liquid crystal holographic lens, and at least one geometric phase liquid crystal lens, wherein an optical reflection folding cavity is formed between the semi-reflective and semi-transparent film and the reflective cholesteric liquid crystal holographic lens; The at least one geometric phase liquid crystal lens is disposed within the reflective folding cavity, and the additional geometric phase liquid crystal lens optional arrangement areas are respectively located between the display panel and the semi-reflective semi-transparent film, between the semi-reflective semi-transparent film and the reflective cholesteric liquid crystal holographic lens, and between the reflective cholesteric liquid crystal holographic lens and the eye box.

[0007] One embodiment of the present invention is as follows: The system includes a display panel, a fifth geometric phase liquid crystal lens, a semi-reflective and semi-transparent film, a fourth geometric phase liquid crystal lens, a third geometric phase liquid crystal lens, a second geometric phase liquid crystal lens, a reflective cholesteric liquid crystal holographic lens, and a first geometric phase liquid crystal lens arranged sequentially along the optical axis propagation direction. The semi-reflective and semi-transparent film and the reflective cholesteric liquid crystal holographic lens form an optical reflection folding cavity.

[0008] The display panel emits right-handed circularly polarized light, which is incident on the fifth geometric phase liquid crystal lens and converted into left-handed circularly polarized light. This left-handed circularly polarized light transmits through the semi-reflective membrane into the optical reflection folding cavity, then through the fourth, third, and second geometric phase liquid crystal lenses, reaching the reflective cholesteric liquid crystal holographic lens and being reflected. The reflected light then travels in the opposite direction through the second, third, and fourth geometric phase liquid crystal lenses, is reflected again by the semi-reflective membrane, and propagates towards the first geometric phase liquid crystal lens. This propagating light then passes through the fourth, third, and second geometric phase liquid crystal lenses again, transmits through the reflective cholesteric liquid crystal holographic lens, and exits through the first geometric phase liquid crystal lens.

[0009] The first to fifth geometric phase liquid crystal lenses are all transmission diffraction optical elements. A circular polarization structure is attached to the light-emitting surface of the display panel. The circular polarization structure is composed of a linear polarization film and a quarter-wave plate stacked together. The fast axis of the quarter-wave plate is at a 45-degree angle to the transmission axis of the linear polarization film.

[0010] The first to fifth geometrical phase liquid crystal lenses are all disposed on a transparent substrate. A light alignment layer is coated on the transparent substrate, and multiple liquid crystal layers are stacked on top of the light alignment layer. The multiple liquid crystal layers include a first liquid crystal layer located at the bottom and in direct contact with the light alignment layer, and an Nth liquid crystal layer located at the top. The multiple liquid crystal layers contain liquid crystal molecules. At the contact surfaces between the first to Nth liquid crystal layers, the liquid crystal molecules maintain a co-directional arrangement. Each layer in the multiple liquid crystal layers has a helical structure in a direction perpendicular to the transparent substrate.

[0011] The semi-reflective and semi-transparent film is bonded and fixed to the substrate surfaces of the fifth geometric phase liquid crystal lens and the fourth geometric phase liquid crystal lens using optically transparent adhesive. The semi-reflective and semi-transparent film consists of a transparent support substrate and an optical beam-splitting film attached to the surface of the transparent support substrate. The transmittance and reflectance of the optical beam-splitting film are both controlled within the range of 45% to 55%.

[0012] The reflective cholesteric liquid crystal holographic lens employs a multi-layered structure, including a transparent substrate and three cholesteric liquid crystal layers stacked sequentially along the optical axis on the transparent substrate. Each of the three cholesteric liquid crystal layers contains a spiral structure. The light emitted by the display panel includes the dominant wavelength peaks of blue, green, and red light. The reflection center wavelengths of the first, second, and third cholesteric liquid crystal layers are aligned with the dominant wavelength peaks of blue, green, and red light, respectively.

[0013] The first to fifth geometric phase liquid crystal lenses all contain liquid crystal molecules. The molecular orientation angles of the liquid crystal molecules have a two-dimensional spatial distribution. The two-dimensional spatial distribution satisfies the phase distribution function requirement, which includes a higher-order phase term distribution function. The higher-order phase term distribution function is used for wavefront aberration correction. The higher-order phase term distribution function is characterized by an even-order aspherical polynomial or a Zernike polynomial.

[0014] The first, second, and third cholesteric liquid crystal layers each contain an orientation layer and cholesteric liquid crystal molecules. The orientation layer guides the continuous change of the azimuth angle of the cholesteric liquid crystal molecules. The first, second, and third cholesteric liquid crystal layers each have independent high-order phase term distribution functions for wavefront aberration correction.

[0015] When left-handed circularly polarized light passes through the fourth geometric phase liquid crystal lens, the third geometric phase liquid crystal lens, and the second geometric phase liquid crystal lens, its polarization state undergoes three alternating transformations. After passing through the fourth geometric phase liquid crystal lens, it is converted into right-handed circularly polarized light. After passing through the third geometric phase liquid crystal lens, it is converted into left-handed circularly polarized light. After passing through the second geometric phase liquid crystal lens, it is converted back into right-handed circularly polarized light. The light that reaches the surface of the reflective cholesteric liquid crystal holographic lens maintains its right-handed circular polarization state and is reflected.

[0016] This invention provides an extremely thin and light virtual reality liquid crystal holographic optical system. It has the following beneficial effects: 1. This invention constructs an optical reflection and folding cavity using a semi-reflective and semi-transparent film and a reflective cholesteric liquid crystal holographic lens. This allows light to pass through multiple reflections and transmission folds within the system, shortening the total physical length required by the optical system. The lenses used in the system are all geometric phase liquid crystal lenses and cholesteric liquid crystal lenses made from stacked liquid crystal layers on a transparent substrate and a light-alignment layer. These transmissive diffractive optical elements replace traditional solid curved glass lenses, reducing the overall weight and volume of the system and meeting the structural requirements for lightweight virtual reality hardware.

[0017] 2. This invention achieves aberration correction by controlling the spatial arrangement of liquid crystal molecules. The two-dimensional spatial distribution of liquid crystal molecules inside the first to fifth geometric phase liquid crystal lenses satisfies the requirements of higher-order phase term distribution functions and is characterized using even-order aspherical polynomials or Zernike polynomials. Simultaneously, the three cholesteric liquid crystal layers inside the reflective cholesteric liquid crystal holographic lens each have independent higher-order phase term distribution functions for wavefront aberration correction at different wavelengths. This design, which independently adjusts the molecular azimuth angle for different lenses and different wavelengths of light, suppresses chromatic aberration and monochromatic aberration in the optical path transmission, improving the clarity of the system's imaging.

[0018] 3. This invention improves light energy utilization and color performance through polarization state evolution control and wavelength alignment mechanisms. The system uses various geometric phase liquid crystal lenses to perform multiple precise conversions between left- and right-hand circularly polarized light, ensuring that the light maintains a right-hand circularly polarized state when it reaches the reflective cholesteric liquid crystal holographic lens. This achieves high-efficiency reflection and reduces light energy loss caused by polarization misalignment. Simultaneously, the three cholesteric liquid crystal layers contained in the reflective cholesteric liquid crystal holographic lens have their reflection center wavelengths aligned with the peak wavelengths of the blue, green, and red light from the display panel, respectively, ensuring the system's reflection efficiency for each primary color and the color reproduction accuracy of the image. Attached Figure Description

[0019] Figure 1 This is a diagram illustrating the optical path evolution of a liquid crystal holographic optical system according to an embodiment of the present invention. Figure 2 This is a characteristic diagram of the geometric phase liquid crystal lens according to an embodiment of the present invention; Figure 3 This is a characteristic diagram of the reflective cholesteric liquid crystal holographic lens according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the orientation layer arrangement according to an embodiment of the present invention; Figure 5 This is a structural diagram of a liquid crystal lens according to an embodiment of the present invention; Figure 6 This is a structural diagram of a reflective cholesteric liquid crystal holographic lens according to an embodiment of the present invention; Figure 7 This is a structural diagram of a liquid crystal holographic optical system according to an embodiment of the present invention; Figure 8 This is an example of the optical path at a wavelength of 454nm according to an embodiment of the present invention; Figure 9 This is an example of the optical path at a wavelength of 530nm according to an embodiment of the present invention; Figure 10 This is an example of the optical path at a wavelength of 630nm according to an embodiment of the present invention; Figure 11 This is an optical transfer function curve corresponding to a 0.5D virtual image distance at a wavelength of 454nm in an embodiment of the present invention; Figure 12 This is an optical transfer function curve corresponding to a 0.5D virtual image distance at a wavelength of 530nm in an embodiment of the present invention; Figure 13 This is an optical transfer function curve corresponding to a 0.5D virtual image distance at a wavelength of 630nm in an embodiment of the present invention; Figure 14 This is an optical transfer function curve for a wavelength of 454nm at an exit pupil offset of 2mm, according to an embodiment of the present invention. Figure 15 This is an optical transfer function curve for a wavelength of 530nm at an exit pupil offset of 2mm according to an embodiment of the present invention. Figure 16 This is an optical transfer function curve for a wavelength of 630nm at an exit pupil offset of 2mm, according to an embodiment of the present invention.

[0020] Among them, 101 is the space between the reflective cholesteric liquid crystal holographic lens and the eye box; 102 is the space between the semi-reflective and semi-transparent film and the reflective cholesteric liquid crystal holographic lens; 103 is the space between the display panel and the semi-reflective and semi-transparent film; 401 is the liquid crystal molecule; 501 is the light alignment layer; 502 is the first liquid crystal layer; 503 is the Nth liquid crystal layer; 504 is the spiral structure; 601 is the reflective cholesteric liquid crystal holographic lens; and 602 is the narrow-band cholesteric liquid crystal layer. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See attached document Figure 1 This invention provides an extremely thin and light virtual reality liquid crystal holographic optical system, combined with... Figure 7 This includes display panels arranged sequentially along the optical axis propagation direction. Figure 7The components include a display screen, a fifth geometrical phase liquid crystal lens (PBL5), a semi-reflective and semi-transparent film, a fourth geometrical phase liquid crystal lens (PBL4), a third geometrical phase liquid crystal lens (PBL3), a second geometrical phase liquid crystal lens (PBL2), a reflective cholesteric liquid crystal holographic lens 601 (CLC), and a first geometrical phase liquid crystal lens (PBL1). All five geometrical phase liquid crystal lenses are transmission diffraction optical elements. The reflective cholesteric liquid crystal holographic lens 601 possesses the optical property of reflecting specific chiral circularly polarized light. An optical reflection folding cavity is formed between the semi-reflective and semi-transparent film and the reflective cholesteric liquid crystal holographic lens 601.

[0023] See attached document Figure 7 This invention provides an optical path transmission method for a virtual reality liquid crystal holographic optical system, comprising the following steps: S10, the display panel emits image light in the form of right-hand circularly polarized light (RCP). The light enters the fifth geometric phase liquid crystal lens, and after passing through the fifth geometric phase liquid crystal lens, the polarization state is reversed and converted into left-hand circularly polarized light (LCP). S20, the left-hand circularly polarized light continues to propagate along the optical axis, passes through the semi-reflective and semi-transparent film and enters the optical reflection folding cavity, and passes through the fourth geometric phase liquid crystal lens, the third geometric phase liquid crystal lens and the second geometric phase liquid crystal lens in sequence. S30, when light passes through the fourth geometric phase liquid crystal lens, the third geometric phase liquid crystal lens and the second geometric phase liquid crystal lens in succession, the polarization state undergoes three alternating transformations. After passing through the fourth geometric phase liquid crystal lens, it is converted into right-hand circularly polarized light. After passing through the third geometric phase liquid crystal lens, it is converted into left-hand circularly polarized light. After passing through the second geometric phase liquid crystal lens, it is converted back into right-hand circularly polarized light. S40, light rays with a right-hand circular polarization state reach the reflective cholesteric liquid crystal holographic lens 601, are reflected on the surface of the reflective cholesteric liquid crystal holographic lens 601, and the propagation direction is reversed while maintaining the right-hand circular polarization state. S50, the reflected light propagates in the opposite direction along the optical axis, and passes through the second geometric phase liquid crystal lens, the third geometric phase liquid crystal lens and the fourth geometric phase liquid crystal lens in reverse in sequence. The polarization state of the light undergoes three alternating reversals, and when it reaches the interface of the semi-reflective and semi-transparent film, it is transformed into left-handed circularly polarized light. S60, the light undergoes a second reflection on the surface of the semi-reflective and semi-transparent membrane, and the propagation direction is redirected to the observation end. During the reflection process, the polarization state of the light changes and is converted into right-hand circularly polarized light. S70, the light that has been refracted passes through the fourth geometric phase liquid crystal lens, the third geometric phase liquid crystal lens and the second geometric phase liquid crystal lens in sequence, and the polarization state is converted into left-hand circularly polarized light through three inversions; S80, the left-handed circularly polarized light reaches the reflective cholesteric liquid crystal holographic lens 601 again, and is directly transmitted through the reflective cholesteric liquid crystal holographic lens 601 to reach the first geometric phase liquid crystal lens. After being modulated by the end wavefront of the first geometric phase liquid crystal lens, it is emitted in the form of approximately parallel light.

[0024] In this embodiment, a display panel is positioned at the starting point of the optical system along the direction of light propagation. The display panel is located on the object plane of the near-eye display system and is used to project an initial light wave carrying image information onto the subsequent optical reflective folding cavity.

[0025] As a specific implementation, the display panel can be a micro-display device with high-resolution display capabilities, such as a micro-organic light-emitting diode display panel, a micro-light-emitting diode display panel, or a silicon-based liquid crystal display panel.

[0026] For the arrangement of the active matrix pixel array and the specific electrical driving method inside the display panel, those skilled in the art can make conventional selections based on the set resolution indicators. The underlying image addressing and light emission control principles are well-known technologies in this field and will not be elaborated here.

[0027] To ensure that the optical path folding and geometric phase modulation within the system can close the loop according to the expected path, the beam emitted from the display panel needs to have a specific spectral distribution and polarization state. The geometric phase liquid crystal lens in the subsequent optical path relies on specific circularly polarized light to achieve phase modulation and chiral inversion, while the cholesteric liquid crystal holographic lens relies on the physical matching of a fixed spectral peak and the liquid crystal helical pitch to achieve selective reflection of specific wavelengths. Therefore, the light wave emission and initial state configuration process at this end includes the following steps: S101, emits image light waves with discrete wavelength peaks. Controls the display panel to emit broadband image light waves. This emission spectrum contains three independent dominant wavelength peaks in the visible light band: red, green, and blue. The specific values ​​of these three dominant wavelength peaks can be determined based on the inherent physical properties of the display panel's light-emitting material. In a specific embodiment, the dominant wavelength peaks for blue, green, and red light are 454nm, 530nm, and 630nm, respectively. These spectral peaks are pre-aligned with the reflection response band of the reflective cholesteric liquid crystal holographic lens 601 in the system, providing source-end support for subsequent low-color-difference full-color image modulation.

[0028] S102, Modulate the initial polarization state. The optical system sets the reference state of the light emitted from the display panel side to right-hand circularly polarized light. Since conventional micro-organic light-emitting diode display panels typically emit unpolarized light, a circularly polarized structure is attached to the light-emitting surface of the display panel. This structure consists of a linearly polarizing film and a quarter-wave plate stacked on top of each other. By aligning the fast axis of the quarter-wave plate at a 45-degree angle to the transmission axis of the linearly polarizing film, the emitted unpolarized light wave is converted into right-hand circularly polarized light. If a display device that emits intrinsically linearly polarized light, such as a silicon-based liquid crystal, is used in the implementation, only a quarter-wave plate with a matching fast axis angle needs to be placed at its light-emitting end to complete the conversion of right-hand circularly polarized light.

[0029] S103, Beam Emission and Spatial Orientation. After polarization conversion, right-handed circularly polarized light carrying image information is emitted from the display panel surface as a diverging beam. The diverging beam propagates along the optical axis to the observer's side, enters the adjacent fifth geometric phase liquid crystal lens interface, and then enters the subsequent spatial polarization alternation and wavefront modulation stage.

[0030] See attached document Figure 4 See attached Figure 5 The first to fifth geometric phase liquid crystal lenses configured in the optical system share commonalities in their microscopic physical architecture and light wave modulation mechanism. Each lens entity relies on the 401 orientation distribution of liquid crystal molecules in the plane to perform wavefront modulation on the incident light wave.

[0031] Specifically, the liquid crystal molecules 401 inside the liquid crystal lens act as optical half-wave plates in a microscopic local region. When a circularly polarized light wave passes through this microscopic region, not only is its polarization chirality reversed, but a geometric phase related to the azimuth angle of the principal axis of the liquid crystal molecules 401 at that location is also added. By continuously and regularly changing the azimuth angle of the liquid crystal molecules 401 on a macroscopic two-dimensional plane, the system can modulate the wavefront phase of the incident light wave across the entire surface, converging it from a diverging beam into a target beam.

[0032] The specific workflow and structural parameters of this optical component are described below: S201, Constructing a multilayer liquid crystal structure. The geometric phase liquid crystal lens is built on a transparent substrate. This transparent substrate can be an ultra-thin glass substrate with a thickness of 0.2 mm, or a thinner flexible transparent polymer substrate, thereby reducing the overall thickness of the system. (See attached diagram.) Figure 5 It is known that a bottom light alignment layer 501 is coated on the substrate, and N liquid crystal layers are stacked on the light alignment layer 501, including the first liquid crystal layer 502 located at the bottom and in direct contact with the light alignment layer 501, and the Nth liquid crystal layer 503 located at the top. Figure 5The ellipsis between the two indicates that multiple intermediate liquid crystal layers may also be included. For the spin-coating and UV-curing film-forming process of liquid crystal materials, those skilled in the art can perform conventional processing according to the set refractive index parameters. The process is well-known in the field and will not be described in detail here.

[0033] In terms of internal microstructure, the bottom layer liquid crystal molecules 401 within the first liquid crystal layer 502 are arranged according to the preset light alignment field of the light alignment layer, and the liquid crystal molecules 401 at the contact surfaces between each liquid crystal layer maintain a unidirectional arrangement. Each liquid crystal layer possesses a spontaneous helical structure 504 in a direction perpendicular to the substrate. (Setting variables) This is the hierarchical index of the spatial liquid crystal layer. The value is a positive integer from 1 to N. In order for the lens to cover a wide range of visible light wavelengths, the number of layers N is usually greater than or equal to 3.

[0034] With hierarchical index The increasing, the first The liquid crystal layer is set with a specific rotation angle and thickness in the vertical direction, which are defined as the rotation angle. With physical thickness For example, combined with appendix Figure 5 It can be seen that the bottom first liquid crystal layer 502 (i.e. When =1, it has a turning angle. and physical thickness The top Nth liquid crystal layer 503 (i.e. When =N, it has a turning angle. and physical thickness The combination of rotation angle and thickness parameters for each layer must ensure that the geometric phase liquid crystal lens has a diffraction efficiency greater than 90% in the visible light band. In practical implementation, the optimal thickness and rotation angle parameters for each liquid crystal layer can be determined through iterative optimization using a coupled-wave analysis algorithm, combined with the target spectral bandwidth and the target diffraction efficiency threshold.

[0035] S202 performs chiral modulation of the polarization state and geometric phase addition. When light carrying polarization characteristics passes through the liquid crystal lens, the phase of the light wave is controlled by the orientation of the liquid crystal molecules 401. The calculation model for this process uses the following formula: ; In this computational model, Jones matrix representing the geometric phase of a liquid crystal lens; column vectors and These represent the circularly polarized Jones vectors of the incident and outgoing light waves, respectively, with positive and negative signs corresponding to left-hand and right-hand polarization chirality, respectively. This represents the local orientation angle of liquid crystal molecule 401 in a two-dimensional plane parallel to the substrate, i.e., the molecular orientation angle. This represents the imaginary unit in a complex number context. The results of this calculation model show that after left-handed and right-handed circularly polarized light passes through a geometric phase liquid crystal lens, their polarization chirality is interchanged. Furthermore, the transmitted light wave has a phase addition equal to twice the molecular azimuth angle added to its original phase. The sign of this phase addition is determined by the specific polarization chirality of the incident light wave.

[0036] S203, configure the spatial phase distribution function. The macroscopic phase modulation distribution obtained by the light wave is directly determined by the arrangement array of the underlying contact liquid crystal molecules 401. In order to achieve beam focusing and aberration correction, the molecular azimuth angle of the liquid crystal molecules 401 in the plane is... The two-dimensional spatial distribution within the lens aperture needs to satisfy specific phase function configuration conditions. Its mathematical model is as follows: ; In this spatial distribution model, and These are two-dimensional orthogonal spatial coordinate components established on the physical plane of the lens; The design focal length set for this geometric phase liquid crystal lens at the reference wavelength; The calculated wavelength of the incident light wave; This is the distribution function of the higher-order phase term used for wavefront aberration correction. In specific embodiments, this higher-order phase term distribution function can be characterized using even-order aspherical polynomials or Zernike polynomials. The specific values ​​of the polynomial coefficients are generated by optical design software through spatial ray tracing and aberration balance optimization calculations, taking into account the preset field-of-view parameters and eyebox size parameters of the entire optical system. By configuring the higher-order phase terms at each microscopic coordinate position, the lens can achieve the wavefront convergence and aberration compensation capabilities of a traditional aspherical lens within a planar physical form.

[0037] S204 provides the longitudinal dispersion response. In the above spatial phase distribution model, due to the focal length design in the formula... Located in the denominator, it is related to the calculated wavelength of the incident light wave. This exhibits a mathematically negative correlation characteristic. This causes the geometric phase liquid crystal lens to display chromatic aberration behavior in the visible light band that is opposite to that of conventional refractive glass lenses. Specifically, the focal length of the lens when parallel red light is incident is less than that when parallel green light is incident, and the focal length when parallel green light is incident is less than that when parallel blue light is incident. This specific longitudinal chromatic aberration distribution provides the underlying physical basis for coordinated chromatic aberration compensation in the wavelength dimension through multilayer reflective holographic elements in the system.

[0038] A semi-reflective and semi-transparent film is positioned between the fifth and fourth geometric phase liquid crystal lenses. In a specific physical assembly configuration, the semi-reflective and semi-transparent film can be bonded and fixed to the substrate surface of adjacent geometric phase liquid crystal lenses using optically transparent adhesive to eliminate additional interface reflection stray light caused by air gaps. The semi-reflective and semi-transparent film, together with the reflective cholesteric liquid crystal holographic lens 601 near the observation end, defines the physical boundary of the internal optical reflection folding cavity of the system. Since the optical system needs to extend the actual propagation path of light within a limited physical thickness, the semi-reflective and semi-transparent film acts as an amplitude divider, distributing the optical power of the incident light wave through transmission and reflection in a specific ratio. Simultaneously, it introduces a fixed phase jump at the reflection interface, thereby changing the polarization chirality of the light wave and forcing the light to shuttle back and forth within the cavity.

[0039] The specific construction and physical workflow of this optical module are as follows: S301, Structural Arrangement and Physical Film System Fabrication. The semi-reflective and semi-transparent film mainly consists of a transparent support substrate and an optical beam-splitting film attached to its surface. In a specific implementation, the transparent support substrate is made of optical-grade resin or ultra-thin glass. The optical beam-splitting film on its surface can be a metal semi-transparent film or a dielectric multilayer film, formed by vacuum evaporation or magnetron sputtering. To balance the final light energy utilization rate of the system and suppress stray light in the folded-back cavity, the transmittance and reflectance of the optical beam-splitting film are configured at a baseline ratio of 50% to 50%. In actual optical film fabrication, considering the tolerance of the coating process, the specific values ​​of transmittance and reflectance are controlled between 45% and 55%. This threshold range ensures that the energy product of forward transmitted light and backward reflected light fluctuates around the theoretical maximum value of 25%, achieving optimal overall light efficiency. For the specific design of the number of film layers and the refractive index matching process of dielectric multilayer films, those skilled in the art can perform conventional optical coating design based on the set visible light working band. The film growth control is a well-known technology in the field and will not be elaborated here.

[0040] S302, forward transmission and energy splitting enter the cavity. Left-handed circularly polarized light, modulated by the fifth geometric phase liquid crystal lens, reaches the front surface of the semi-reflective and semi-transparent film. The semi-reflective and semi-transparent film splits the energy of the incident electromagnetic light wave, with approximately half of the light power directly transmitting through the thin film layer and entering the optical reflection folding cavity. In this spatial transmission path, the dielectric material of the semi-reflective and semi-transparent film does not exert any additional modulation effect on the polarization state of the light; the transmitted light wave continues to maintain its original left-handed circular polarization state and continues to propagate along the set optical axis towards the fourth geometric phase liquid crystal lens.

[0041] S303, Back Reflection and Polarization Chiral Reversal. Light rays are reflected back through the rear-stage reflective surface within the optical reflection folding cavity and arrive again at the rear surface of the semi-reflective membrane. Here, the rear surface of the semi-reflective membrane acts as a reflecting mirror in the system's optical path. According to the boundary conditions of the electromagnetic wave reflection interface, circularly polarized light undergoes a phase jump in the electric field component during reflection at a conventional dielectric or metal interface. This physical process of polarization reversal can be mathematically characterized using the Jones reflection matrix, and its calculation model is as follows: ; In this computational model, The ideal Jones reflection matrix representing the reflective interface of the semi-reflective membrane; column vectors Jones vector representing left-handed circularly polarized light; column vector Represents the Jones vector of right-handed circularly polarized light; constant elements in the diagonal matrix. and The reflective interface represents the phase reversal of the two orthogonal electric field components of the incident light wave. From the matrix derivation above, it can be seen that after left-handed circularly polarized light is reflected from the surface of the semi-reflective and semi-transparent film, its polarization chirality is reversed, converting it into right-handed circularly polarized light. The propagation direction of the light simultaneously reverts back towards the observation end. This physical polarization reversal provides the polarization matching condition for the light to smoothly penetrate the subsequent geometric phase liquid crystal lens and ultimately exit the folded cavity.

[0042] See attached document Figure 3 See attached Figure 6 A reflective cholesteric liquid crystal holographic lens 601 is disposed between the second geometric phase liquid crystal lens and the first geometric phase liquid crystal lens. From an optical principle perspective, the molecules inside the cholesteric liquid crystal material exhibit a helical periodic arrangement, and this structure possesses the optical property of selective Bragg reflection of light waves of specific wavelengths and specific circular polarization states.

[0043] The specific construction and physical workflow of this optical module are as follows: S401 constructs a multi-layered band-selective physical structure. To match the broadband full-color image light waves emitted by the display panel, it is combined with... Figure 6 It is known that the reflective cholesteric liquid crystal holographic lens 601 adopts a multi-layer stacked structure. On a transparent substrate, a first cholesteric liquid crystal layer corresponding to the blue light band, a second cholesteric liquid crystal layer corresponding to the green light band, and a third cholesteric liquid crystal layer corresponding to the red light band are sequentially stacked along the optical axis. All three layers are structurally narrow-band cholesteric liquid crystal layers 602. The reflection center wavelength of each liquid crystal layer is determined by the pitch of its internal helical structure 504, and their physical relationship follows the Bragg reflection condition. The mathematical model is as follows: ; In this formula, The wavelength representing the center of reflection of the narrow-band cholesteric liquid crystal layer 602; This represents the average refractive index of the cholesteric liquid crystal material, which is typically between 1.5 and 1.7 in practical engineering applications. This represents the helical pitch of the cholesteric liquid crystal molecules. In practice, by adding chiral dopants of different mass fractions to the nematic liquid crystal substrate, the helical pitch of each layer can be precisely controlled and solidified. This ensures that the reflection center wavelengths of the three layers are aligned with the peak wavelengths of the blue, green, and red light specified in the display panel. Regarding the specific liquid crystal material ratios and spin-coating curing process, those skilled in the art can adjust the process according to the target wavelength using conventional methods. The material preparation process is well-known in the field and will not be elaborated upon here.

[0044] S402 performs selective reflection and transmission based on polarization state. This optical module is configured during physical fabrication to have a single set of helical chirality, for example, a right-handed helical structure 504. When an image light wave with a right-handed circularly polarized state arrives at this lens, selective Bragg reflection occurs inside the lens because the polarization chirality of the light wave matches the helical chirality of the liquid crystal layer, and the wavelength of the light wave is within the set reflection band. Since the rotation direction of the incident circularly polarized light vector is consistent with the spatial helical direction of the cholesteric liquid crystal molecules, the light wave is strongly coupled with the periodic structure and reflected back. This reflection mechanism based on a volume holographic grating does not cause half-wave loss of the electric field vector. The calculation model for this physical process uses the following formula: ; In this computational model, The ideal Jones reflection matrix representing the 601 reflective cholesteric liquid crystal holographic lens is mathematically expressed as a second-order identity matrix; column vectors This represents the Jones vector of right-handed circularly polarized light. This mechanism ensures that right-handed circularly polarized light is refracted back and maintains its original polarization state. When light undergoes a polarization chirality reversal within the system's front-stage folded cavity and arrives at the lens again as left-handed circularly polarized light, the light wave is no longer reflected because its polarization chirality is opposite to that of the liquid crystal spiral structure; instead, it is directly transmitted through the multilayer structure.

[0045] S403, custom independent phase distribution for chromatic aberration compensation. Each narrow-band cholesteric liquid crystal layer 602 constituting this optical module not only possesses spectral reflectance but also independent phase distribution control capability within a two-dimensional physical plane. Similar to the aforementioned transmissive geometric phase liquid crystal lens, the bottom layer of each cholesteric liquid crystal layer is also configured with an alignment layer. This alignment layer guides the continuous change of the azimuth angle of local cholesteric liquid crystal molecules, thereby forming the lens phase on the macroscopic surface. The mathematical model of the phase distribution function for each layer is as follows: ; In this phase distribution model, To correspond to the narrow-band cholesteric liquid crystal layer 602, in the form of and The macroscopic additional phase provided at the coordinate points formed; The wavelength representing the center of reflection of the narrow-band cholesteric liquid crystal layer 602; The design focal length for this layer at a specific wavelength; This is the distribution function of the higher-order phase term used for wavefront aberration correction. The system utilizes the physical characteristic of the aforementioned geometric phase liquid crystal lens exhibiting anomalous longitudinal dispersion response at different wavelengths. By setting different design focal lengths and higher-order phase terms for aberration correction for each of the three narrow-band cholesteric liquid crystal layers 602, differentiated target wavefront phase compensation amounts are provided for red, green, and blue light during selective reflection of light waves. In specific implementations… and The specific coefficients were obtained through multi-wavelength configuration optimization using optical design software in conjunction with ray tracing data from the front-stage lens. This physical mechanism of independently controlling the wavefront for different bands offsets the chromatic aberration accumulated by the broadband image beam as it passes through the geometric phase liquid crystal lens multiple times, reducing the overall longitudinal chromatic aberration of the system.

[0046] Combined with appendix Figure 6 It can be known that ( Figure 6 The horizontal axis represents wavelength, and the vertical axis represents diffraction efficiency. The multi-layer structure achieves efficient reflection of blue, green, and red light bands respectively.

[0047] See attached document Figure 2 See attached Figures 8 to 10 See attached Figures 11 to 16 In this embodiment, the display panel, geometric phase liquid crystal lens, semi-reflective and semi-transparent film, and reflective cholesteric liquid crystal holographic lens 601 are arranged in space along the optical axis of the system to jointly construct an optical reflection folding cavity. The optical reflection folding cavity utilizes the conversion characteristics of different polarization states in the interface reflection and liquid crystal modulation process to allow light to refract and shuttle back and forth multiple times within a limited physical space, thereby extending the equivalent optical path.

[0048] Because light undergoes alternating forward and reverse propagation during its reflection, and each reflection is accompanied by a reversal of polarization chirality, the initial physical conditions of the light are different each time it passes through the same lens. Therefore, the physical components need to be configured in a system-wide phase coordination manner to ensure that the total wavefront of the light wave after multiple transmissions and reflections meets the requirements for human eye observation.

[0049] The cooperative mechanism and specific configuration parameters of the optical reflective folded cavity are described below: S501 utilizes a polarization- and direction-dependent diffraction order response mechanism. When light passes through a geometric phase liquid crystal lens multiple times within the folded cavity, the macroscopic diffraction order provided by the lens exhibits dependence on polarization chirality and incident direction, based on the underlying physical properties of the geometric phase. When circularly polarized light is incident from the front of the lens, if the lens acts as a positive lens for right-handed circularly polarized light (corresponding to...) Figure 2 In the +f), it acts as a negative lens for left-handed circularly polarized light (corresponding to...). Figure 2 (-f) Meanwhile, since the azimuth distribution of the liquid crystal molecules 401 on the lens surface is fixed in the spatial coordinate system, when circularly polarized light of the same chirality enters from the back of the lens, the mirror flip of the observation coordinate system causes the sign of the equivalent optical power presented by the lens to also be reversed. This physical response process can be characterized by the following model: ; In this model, This represents the equivalent actual focal length of the liquid crystal lens under the current specific incident conditions; This represents the absolute value of the design focal length of the lens for the reference polarization state and normal incidence conditions; This is the direction factor; its value is 1 when the light is incident from the front and 1 / 2 when it is incident from the back. 1; This is the polarization coefficient. When the light wave is in a right-hand circularly polarized state, this coefficient is 1; when it is in a left-hand circularly polarized state, it is 1. 1. This response law provides a mathematical basis for the joint phase allocation of multiple lenses in the system.

[0050] S502 employs a collaborative compensation design with multiple phase folding. The second to fourth geometrical phase liquid crystal lenses within the system are positioned between the semi-reflective and semi-transparent film and the reflective cholesteric liquid crystal holographic lens 601. Due to the folding of the optical path, the image beam passes through the lens group a total of three times. In this collaborative configuration, the system superimposes the wavefront phases of the multi-stage transmissive and reflective lenses along with their spatial propagation distances. The overall equivalent optical power of the system is set to... Its mathematical model is as follows: ; In this model, This represents the total number of times a light wave passes through the transmissive geometric phase liquid crystal lens within the cavity. and All are positive integer index variables representing the order of penetration; Representing the first wave of light The equivalent actual focal length when passing through a certain level of geometric phase liquid crystal lens; The additional optical power provided by the reflective cholesteric liquid crystal holographic lens 601 when the light wave undergoes Bragg reflection; Representing the The second modulation and the first The actual physical propagation distance between submodulations; and Representing the light waves respectively Next and first The equivalent actual focal length when the liquid crystal lens with the corresponding geometric phase is penetrated by the secondary penetration; This represents the average refractive index of the filling medium over that distance. By introducing the spatial distance term, the system can more accurately calculate the wavefront curvature change caused by light waves propagating in free space.

[0051] To achieve specific aberration balance and optical path control, based on the benchmark of spatial surface characterization using even-order polynomial phase, Table 1 gives the higher-order diffraction coefficients of the five geometric phase liquid crystal lenses (PBL1 to PBL5) in this embodiment, and Table 2 gives the higher-order diffraction coefficients of the reflective cholesteric liquid crystal holographic lens 601 (corresponding to the red, green, and blue band layers): Table 1. Diffraction coefficients of geometric phase liquid crystal lenses Table 2. Diffraction coefficients of CLC Note: The " / " in Table 1 indicates that the diffraction coefficient of the corresponding geometric phase liquid crystal lens at this order is 0, that is, the higher-order term was not used for surface configuration.

[0052] S503, setting physical dimensions and verifying optical transfer performance. Under the aforementioned diffraction coefficient configuration, the total system thickness, from the emitting surface of the display panel to the emitting surface of the first geometric phase liquid crystal lens closest to the observation end, is significantly reduced to approximately 6.8 mm. The system's field of view is configured at 70°, the exit pupil diameter is set at 4 mm, the exit pupil distance within the eyebox is maintained at 12 mm, and the eyebox's vertical fluctuation range is 8 mm. For the actual imaging quality evaluation of the optical system under this spatial constraint, a modulation transfer function is used for quantitative verification. (See attached...) Figures 11 to 13 The given MTF curves for a virtual image distance of 0.5D, and attached... Figures 14 to 16The MTF curves given with a 2mm offset from the exit pupil position show that (in the attached figures, the horizontal axis represents spatial frequency, the vertical axis represents modulation transfer function value, the legend shows the diffraction limit, T and R represent the meridional and sagittal directions respectively, and ANG deg represents the field of view angle), under the aforementioned dimensions and field of view parameters, the system maintains a stable modulation transfer function value above 0.2 for both the central and peripheral fields of view at a spatial frequency of 20 lp / mm. In near-eye display engineering evaluation, a modulation transfer function value of 0.2 is a conventional threshold benchmark for determining whether the human eye can distinguish high-contrast image features. These results demonstrate that the system, through the combined modulation of transmissive and reflective elements, suppresses chromatic aberration caused by a broadband light source, achieving the goal of providing full-color display in an extremely thin and lightweight form.

Claims

1. An ultra-thin virtual reality liquid crystal holographic optical system, characterized in that, It includes a display panel, a semi-reflective and semi-transparent film, a reflective cholesteric liquid crystal holographic lens (601), and at least one geometric phase liquid crystal lens, wherein the semi-reflective and semi-transparent film and the reflective cholesteric liquid crystal holographic lens (601) form an optical reflection folding cavity. The at least one geometric phase liquid crystal lens is disposed in the reflective folding cavity, and the additional geometric phase liquid crystal lens optional arrangement areas are respectively located between the display panel and the semi-reflective semi-transparent film (103), between the semi-reflective semi-transparent film and the reflective cholesteric liquid crystal holographic lens (102), and between the reflective cholesteric liquid crystal holographic lens and the eye box (101). The image light emitted by the display panel enters the optical reflection folding cavity through the semi-reflective and semi-transparent film and propagates back; The at least one geometric phase liquid crystal lens performs geometric phase wavefront modulation and circular polarization chiral conversion on the image light in the propagation path of the image light; The reflective cholesteric liquid crystal holographic lens selectively reflects or transmits image light in a predetermined circularly polarized state and a predetermined wavelength band, so that the image light after folding and propagation is emitted from the exit side.

2. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The at least one geometric phase liquid crystal lens is a transmission diffraction optical element.

3. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The light-emitting surface of the display panel is fitted with a circular polarization structure, which is composed of a linear polarization film and a quarter-wave plate stacked together. The fast axis direction of the quarter-wave plate is at a 45-degree angle to the light transmission axis direction of the linear polarization film.

4. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The geometric phase liquid crystal lens is built on a transparent substrate, and a light alignment layer (501) is coated on the transparent substrate. Multiple liquid crystal layers are stacked on the light alignment layer (501). The multilayer liquid crystal layer includes a first liquid crystal layer (502) located at the bottom and in direct contact with the light alignment layer (501), and an Nth liquid crystal layer (503) located at the top. The multilayer liquid crystal layer contains liquid crystal molecules (401). At the contact surface between the first liquid crystal layer (502) and the Nth liquid crystal layer (503), the liquid crystal molecules (401) are arranged in the same direction. Each layer of the multilayer liquid crystal layer has a spiral structure (504) in a direction perpendicular to the transparent substrate.

5. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The semi-reflective and semi-transparent film is bonded and fixed to the substrate surface of the geometric phase liquid crystal lens by optical transparent adhesive; The semi-reflective and semi-transparent membrane is composed of a transparent support substrate and an optical beam-splitting film attached to the surface of the transparent support substrate. The transmittance and reflectance of the optical beam-splitting film are both controlled within the range of 45% to 55%.

6. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The reflective cholesteric liquid crystal holographic lens (601) adopts a multi-layer stacked structure. The reflective cholesteric liquid crystal holographic lens (601) includes a transparent substrate, and a first cholesteric liquid crystal layer, a second cholesteric liquid crystal layer and a third cholesteric liquid crystal layer stacked sequentially on the transparent substrate along the optical axis propagation direction. The first cholesteric liquid crystal layer, the second cholesteric liquid crystal layer and the third cholesteric liquid crystal layer all have a spiral structure (504) inside.

7. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 6, characterized in that, The light emitted by the display panel includes the peak wavelengths of blue light, green light, and red light, and the reflection center wavelengths of the first cholesteric liquid crystal layer, the second cholesteric liquid crystal layer, and the third cholesteric liquid crystal layer are aligned with the peak wavelengths of blue light, green light, and red light, respectively.

8. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The geometric phase liquid crystal lens contains liquid crystal molecules (401), and the molecular orientation angles of the liquid crystal molecules (401) have a two-dimensional spatial distribution. The two-dimensional spatial distribution satisfies the phase distribution function requirement that includes a higher-order phase term distribution function. The higher-order phase term distribution function is used for wavefront aberration correction. The higher-order phase term distribution function is characterized by an even-order aspherical polynomial or a Zernike polynomial.

9. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 6, characterized in that, The first, second, and third cholesteric liquid crystal layers each contain an orientation layer and cholesteric liquid crystal molecules. The orientation layer guides the cholesteric liquid crystal molecules to continuously change their azimuth angle. The first, second, and third cholesteric liquid crystal layers each have an independent high-order phase term distribution function for wavefront aberration correction.

10. The ultra-thin virtual reality liquid crystal holographic optical system according to claim 1, characterized in that, The circularly polarized light undergoes a polarization state change when it passes through the geometric phase liquid crystal lens; The light rays arriving at the surface of the reflective cholesteric liquid crystal holographic lens (601) are reflected while maintaining a right-handed circular polarization state.

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