Polarizer holographic optical waveguide-based ghosting-eliminating head-up display system
By introducing a highly selective P-light reflective film and a circular polarizer into the head-up display system, combined with a polarizing holographic waveguide structure, the ghosting problem of holographic diffraction waveguide head-up displays was solved, achieving high-quality imaging and lightweight design.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHEAST UNIV
- Filing Date
- 2026-02-11
- Publication Date
- 2026-05-15
AI Technical Summary
Existing holographic diffractive waveguide head-up display systems suffer from ghosting issues, affecting display clarity and brightness uniformity. Furthermore, these systems are large and complex, hindering lightweight design.
By employing a highly selective P-light reflective film, a circular polarizer, and a polarizing body holographic waveguide structure, and by adjusting the incident angle and polarization state of the projected image source, combined with the volume and pupil expansion advantages of the waveguide, ghosting is eliminated.
It effectively suppresses or eliminates ghosting, improves imaging clarity and brightness uniformity, while reducing system size and complexity, lowering production difficulty and cost, and is suitable for mass production environments.
Smart Images
Figure CN122043747A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a system for a ghosting-free head-up display based on a polarizing holographic waveguide, belonging to the field of optical display device technology. Background Technology
[0002] With the increasing demand for head-up display (HUD) systems in the automotive, aerospace, and augmented reality (AR) industries, achieving high brightness, a wide field of view, and clear imaging within limited spaces has become a key research focus. Traditional HUDs often employ freeform surface mirrors or beam splitters, resulting in bulky and complex systems that are not conducive to lightweight and compact designs. Furthermore, traditional optical components are prone to introducing ghost images and stray light during multiple reflections or refractions, leading to reduced contrast and impacting the visual experience and safety of drivers and other users.
[0003] In recent years, head-up displays based on holographic diffractive waveguides have gradually become a research hotspot. These waveguides utilize holographic gratings to couple, guide, transmit, and emit light, significantly reducing system thickness and weight, and offering advantages such as a large field of view and high transmittance. However, existing holographic diffractive waveguide head-up displays still suffer from ghosting problems. This is because after the light beam exits the waveguide structure, it undergoes refraction and reflection when it hits the first layer of windshield glass. The refracted beam and the beam reflected multiple times within the windshield create ghosting, reducing display clarity.
[0004] To address these issues, there is an urgent need to develop a new technical solution that can improve imaging clarity and brightness uniformity while maintaining the advantages of waveguide systems in terms of thinness, high transmittance, and wide field of view, and effectively suppress or eliminate ghosting. Summary of the Invention
[0005] Objective: To address the common problem of ghosting in existing polarized holographic waveguide head-up displays, this invention provides a ghosting-eliminating head-up display system based on polarized holographic waveguides. By adding a circular polarizer, the display quality is effectively improved, avoiding the special design of the projection image source in traditional methods. Furthermore, the incident angle of the projection image source can be effectively adjusted according to actual conditions, increasing the design dimensionality. At the same time, by combining the volume and pupil expansion advantages of the waveguide, it overcomes the problem of the volume limitation of existing head-up display structures restricting the human eye's observation range.
[0006] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:
[0007] A head-up display system based on polarized holographic waveguide for ghosting elimination includes: a highly selective P-light reflective film, a circular polarizer, a polarized holographic waveguide structure, a projection image source, and a head-up display windshield.
[0008] The head-up display windshield is equipped with a highly selective P-light reflective film.
[0009] The emitted light from the projection image source enters the input coupling grating of the polarizing holographic waveguide structure, and then enters the circular polarizer through the output coupling grating of the polarizing holographic waveguide structure. The emitted light from the circular polarizer is reflected by the high-selectivity P-light reflective film inside the head-up display windshield.
[0010] Optionally, highly selective P-light reflective films include, but are not limited to, circularly polarized beam-splitting films based on nematic liquid crystals and chiral dopants, circularly polarized light-splitting films based on cholesteric liquid crystals, and extended structures based on these two types of films.
[0011] Optionally, the highly selective P-light reflective film is a cholesteric liquid crystal highly selective circular polarization reflective film, and the polarization direction of the reflected light is consistent with the rotation direction controlled by the input coupling grating and output coupling grating of the polarizing body holographic waveguide structure.
[0012] Optionally, the in-coupler grating can be circular.
[0013] Optionally, the types of projection image sources include, but are not limited to, Micro LED, TFT-LCD, LCOS, MicroOLED, and DLP.
[0014] Optionally, it also includes a preset optical path, in which the imaging beam emitted by the projection image source is coupled and incident on the input coupling grating of the polarizer holographic waveguide structure along the preset optical path. The preset optical path includes, but is not limited to, a collimation optical path and an image quality correction optical path inside the projection image source.
[0015] Optionally, the distance control between the projection image source and the polarizing holographic waveguide structure requires that all the light rays in the projection image source enter the ingress coupling grating of the polarizing holographic waveguide structure.
[0016] Optionally, the size of the coupling grating can be set by determining the eyebox size and the required FOV of the target, as shown in the following formula:
[0017]
[0018]
[0019]
[0020]
[0021]
[0022] in, These are the side lengths of the output coupling grating of the polarizer holographic waveguide structure. These are the side lengths of the four sides of the eye box. for and as well as and The corresponding edge That is, the vertical field of view. for and as well as and The corresponding edge That is, the horizontal field of view. It is the sum of the horizontal straight-line distance between the position of the human eye and the high-selectivity circularly polarized light reflective film and the vertical straight-line distance between the high-selectivity circularly polarized light reflective film and the installation position of the polarizing holographic waveguide structure. Let be the perpendicular distance from the point of incidence of the incident light on the glass medium to the exit of the coupling grating. The distance between the windshield and the surface of the high-selectivity P-light reflective film for the head-up display. The perpendicular distance from the point of reflection of the reflected light on the glass medium to the center of the eye box. 2 is the angle of refraction of the incident light in the windshield.
[0023] Optionally, the input coupling grating and output coupling grating of the polarizing holographic waveguide structure adopt a two-dimensional pupil expansion structure.
[0024] Optionally, the incident angle of the projected image source can be adjusted as needed, wherein the angle between the outgoing light and the normal at the intersection of the incident and coupled gratings after the outgoing light enters the waveguide must be at least greater than the critical angle of total internal reflection, to ensure that the light propagates in the polarizing holographic waveguide.
[0025] Optionally, the head-up display windshield is a curved windshield, and the angle of incidence is measured by the angle between the tangent line at the point where the light beam hits the windshield and the incident light.
[0026] Beneficial Effects: This invention provides a head-up display system based on a polarizing holographic waveguide to eliminate ghosting. Through the polarization state modulation of the polarizing holographic grating and the synergistic reflection mechanism of the P-ray reflective film, it fundamentally eliminates the ghosting problem caused by multi-interface reflection from the windshield. Simultaneously, it retains the volume advantages and pupil expansion advantages of existing waveguides, significantly reducing the difficulty and cost of industrial production. This invention provides methods and ideas for the design and image quality optimization of existing diffractive waveguide-based head-up displays, improving imaging quality. By leveraging the volume advantage of diffractive waveguides and reducing process complexity, it is expected to achieve an optical system that balances optical efficiency and low ghosting, providing technical support for the development of near-eye display devices. Compared to existing technologies, the advantages of this invention are as follows:
[0027] 1. This invention proposes a ghosting suppression scheme for head-up display systems based on holographic diffraction waveguides, which differs from traditional freeform surface lenses. This scheme maximizes the advantages of volume and significantly reduces system complexity and manufacturing costs. The method is highly compatible with existing process platforms, meets the precision control requirements of mass production environments, ensures the engineering feasibility of the optimization results, and avoids a disconnect between design goals and process capabilities.
[0028] 2. This invention avoids the drawback of requiring special design for specific models and enhances the applicability and compatibility of the method under different grating configurations and waveguide parameters. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the structure of a head-up display system based on a polarizing body holographic waveguide for ghosting elimination according to the present invention.
[0030] Figure 2 This is a schematic diagram of the polarizing holographic waveguide structure of the present invention.
[0031] Figure 3 This is a schematic diagram of the polarization body holographic waveguide structure and HUD structure parameters of the present invention.
[0032] Figure 4 This is a diagram showing the polarization characteristics of the emitted light from the polarizing body holographic waveguide structure of the present invention.
[0033] Figure 5 This is a diagram showing the incident light angle response characteristics of the polarizing holographic waveguide structure of the present invention.
[0034] Figure 6 This is a simulation diagram showing the ghosting reduction effect of a head-up display (HUD) ghosting reduction device. Figure 6 Image (a) shows the imaging effect of a holographic diffraction waveguide head-up display without ghosting removal. Figure 6 Image (b) shows the imaging effect of the holographic diffraction waveguide head-up display of the present invention. Detailed Implementation
[0035] The technical solutions 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 protection scope of the present invention.
[0036] The present invention will be further described below with reference to specific embodiments.
[0037] Example 1:
[0038] This embodiment introduces a system for ghosting-eliminating head-up display based on polarizing holographic waveguides, such as... Figure 1 As shown, it includes: a highly selective P-light reflective film 1, a circular polarizer 2, a polarizing holographic waveguide structure 3, a projection image source 4, and a head-up display windshield 5.
[0039] The head-up display windshield 5 is equipped with a highly selective P-light reflective film 1, which is deposited inside the windshield 5 to prevent interference with the selective reflection effect caused by external forces on the inner or outer side of the windshield. The highly selective P-light reflective film is an optical thin film with selective reflection characteristics for polarized light. It achieves high reflectivity for specific polarization states (such as P-polarized light) while having relatively low reflectivity for other polarization states (such as S-polarized light).
[0040] The emitted light from the projection image source 4 enters the input coupling grating 301 of the polarizer holographic waveguide structure 3, and then enters the circular polarizer 2 through the output coupling grating 302 of the polarizer holographic waveguide structure 3. The emitted light from the circular polarizer 2 is reflected by the high-selectivity P-light reflective film 1 inside the head-up display windshield 5.
[0041] Furthermore, the highly selective P-light reflective film 1 includes, but is not limited to, circularly polarized beam splitting films based on nematic liquid crystals and chiral dopants, circularly polarized light separating films based on cholesteric liquid crystals, and extended structures based on these two types of films.
[0042] Furthermore, the highly selective P-light reflective film 1 is superior to the cholesteric liquid crystal highly selective circular polarization reflective film, and the polarization direction of the reflected light is consistent with the rotation direction controlled by the polarization holographic grating (input coupling grating 301 and output coupling grating 302) of the polarization holographic waveguide structure 3, so that the reflectivity is as high as possible.
[0043] like Figure 2 As shown, the polarizing holographic waveguide structure 3 has dimensions of 200 mm × 120 mm, a refractive index of 1.57, and a thickness of 1 mm. The input coupling grating 301 is a circular grating with a radius of 8 mm and a thickness of 6 μm. The output coupling grating 302 has dimensions of 100 mm × 100 mm and a thickness of 0.3 μm. The refractive index and waveguide 303 thickness of the polarizing holographic waveguide structure are related to the propagation of light in the waveguide, ensuring that both the refractive index and waveguide thickness meet the total internal reflection condition. The input coupling grating should be circular to ensure compatibility with the lens of the projection image source and should be as thick as possible to maximize diffraction efficiency and allow light to propagate in the waveguide. The output coupling grating should be as large as possible and as thin as possible to ensure a larger pupil expansion range. The polarizing holographic waveguide structure can expand the eyebox size by increasing the exit pupil area.
[0044] Furthermore, the projection image source types include, but are not limited to, Micro LED, TFT-LCD, LCOS, MicroOLED, and DLP, and can be replaced with different projection image sources according to different needs.
[0045] Furthermore, it also includes a preset optical path, in which the imaging beam emitted by the projection image source is coupled and incident on the input coupling grating of the polarizer holographic waveguide structure along the preset optical path. The preset optical path includes, but is not limited to, a collimation optical path and an image quality correction optical path inside the projection image source.
[0046] Furthermore, the distance control between the projection image source and the polarizing holographic waveguide structure requires that all the light rays in the projection image source enter the ingress coupling grating of the polarizing holographic waveguide structure.
[0047] Furthermore, such as Figure 3 As shown, the size of the eye box is determined by the lengths of its four sides. And the required FOV of the target, thereby setting the size of the coupling grating to determine the optical waveguide structure design, the specific formula is as follows:
[0048]
[0049]
[0050]
[0051]
[0052]
[0053] in, These are the side lengths of the output coupling grating of the polarizer holographic waveguide structure. These are the side lengths of the four sides of the eye box. for and as well as and The corresponding edge That is, the vertical field of view. for and as well as and The corresponding edge That is, the horizontal field of view. It is the sum of the horizontal straight-line distance between the position of the human eye and the high-selectivity circularly polarized light reflective film and the vertical straight-line distance between the high-selectivity circularly polarized light reflective film and the installation position of the polarizing holographic waveguide structure. Let be the perpendicular distance from the point of incidence of the incident light on the glass medium to the exit of the coupling grating. The distance between the windshield and the surface of the high-selectivity P-light reflective film for the head-up display. The perpendicular distance from the point of reflection of the reflected light on the glass medium to the center of the eye box. 2 is the angle of refraction of the incident light in the windshield. 1 is the angle of incidence of the incident light on the windshield.
[0054] Furthermore, the polarization holographic waveguide structure 3 employs a two-dimensional pupil-expanding structure for its polarization holographic grating, including but not limited to a cross-shaped structure and a butterfly-shaped structure. The polarization diffraction characteristics and angular bandwidth of the polarization holographic grating are as follows: Figure 4 and Figure 5 As shown, where, Figure 4 The figure shows the relationship between the diffraction efficiency and polarization state of a polarizing holographic grating. In the figure, (-45, 90) and (-45, -90) correspond to left-handed and right-handed circularly polarized light, respectively. The corresponding diffraction efficiencies are close to 0 for left-handed circularly polarized light and close to 1 for right-handed circularly polarized light. Figure 5 The figure shows the relationship between the incident angle and diffraction efficiency of a polarizing holographic grating. The center wavelength of the incident light in the figure is 530 nm.
[0055] Furthermore, the incident angle of the projected image source can be adjusted as needed, wherein the angle between the outgoing light and the normal at the intersection of the incident and coupled gratings after the outgoing light enters the waveguide must be at least greater than the critical angle of total internal reflection, to ensure that the light propagates in the polarizing holographic waveguide.
[0056] Furthermore, the head-up display windshield 5 is a curved windshield, and the angle of incidence is measured by the angle between the tangent line at the point where the light beam hits the windshield and the incident light.
[0057] Furthermore, the circular polarizer is generally composed of a linear polarizer and a quarter-wave plate. The circular polarizer should be placed in reverse so that the incident circularly polarized light is first converted into linearly polarized light, and then the direction of the linear polarizer is adjusted so that the light passing through the circular polarizer is P-light.
[0058] Furthermore, the highly selective P-light reflective film includes, but is not limited to, multilayer dielectric film systems, metal-dielectric composite films, etc., and is required to have the highest possible P-light reflectivity.
[0059] Furthermore, the head-up display windshield 5 includes a first windshield and a second windshield, with the high-selectivity P-light reflective film positioned between the parallel first and second windshield layers.
[0060] Example 2:
[0061] This embodiment describes the working principle of a system for ghosting-eliminating head-up display based on a polarizing holographic waveguide, specifically including:
[0062] The imaging beam emitted from the projection image source is coupled and incident on the input coupling grating of the polarizing holographic waveguide structure along a preset optical path.
[0063] The core diffraction element in the polarizing holographic waveguide structure is the polarizing holographic grating. By utilizing the polarization-selective diffraction characteristics of the grating on the incident light, the non-polarized imaging beam is modulated into a circularly polarized outgoing light with a single rotation direction (left-hand or right-hand).
[0064] Ensure that the incident angle of the beam emitted from the output coupling grating region onto the windshield is Brewster's angle, so that the P-beam is not reflected when entering the first layer of windshield glass.
[0065] A circular polarizer is placed on the path of the emitted beam from the output coupling grating to ensure that the entire emitted beam passes through the circular polarizer and that the beam after passing through the circular polarizer is entirely P-beam.
[0066] A highly selective P-light reflective film is added inside the head-up display windshield to ensure that most of the light entering the windshield is reflected once by the reflective film and then exits into the eye box area.
[0067] Through a series of optimization methods, by adjusting the highly selective P-light reflective film, the polarizing holographic waveguide, and the projected image source, the best ghosting elimination effect was obtained after comparison.
[0068] The present invention employs a projection image source for outputting an imaging beam, a core light guide and polarization control component namely a polarizing holographic waveguide structure, a head-up display windshield as an imaging reflection interface, a circular polarizer, and a circularly polarized light reflection film fixed inside the windshield.
[0069] The aforementioned head-up display device uses a traditional optical waveguide head-up display structure as its core diffraction element, while the anti-ghosting device uses a polarizing holographic optical waveguide head-up display structure as its core diffraction element. A comparison of the imaging effects of the two devices is shown in the figure below. Figure 6 As shown, Figure 6 (a) is an image of the holographic diffraction waveguide head-up display without ghosting removal processing. Figure 6 (b) is a diagram of the above-mentioned holographic diffraction waveguide head-up display imaging effect.
[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A system for ghosting-eliminating head-up display based on polarizing holographic waveguide, characterized in that: include: High-selectivity P-light reflective film, circular polarizer, polarizing body holographic waveguide structure, projection image source, head-up display windshield; The head-up display windshield is equipped with a highly selective P-light reflective film. The emitted light from the projection image source enters the input coupling grating of the polarizing holographic waveguide structure, and then enters the circular polarizer through the output coupling grating of the polarizing holographic waveguide structure. The emitted light from the circular polarizer is reflected by the high-selectivity P-light reflective film inside the head-up display windshield.
2. The system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The highly selective P-light reflective film includes, but is not limited to, a circularly polarized beam splitter based on nematic liquid crystal and chiral dopants, a circularly polarized light separation film based on cholesteric liquid crystal, and extended structures based on these two films.
3. The system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The highly selective P-light reflective film is a cholesteric liquid crystal highly selective circular polarization reflective film, and the polarization direction of the reflected light is consistent with the rotation direction controlled by the input coupling grating and output coupling grating of the polarizing body holographic waveguide structure.
4. The system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The types of projection image sources include, but are not limited to, Micro LED, TFT-LCD, LCOS, Micro OLED, and DLP.
5. The system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: It also includes a preset optical path, in which the imaging beam emitted by the projection image source is coupled and incident on the input coupling grating of the polarizer holographic waveguide structure along the preset optical path. The preset optical path includes, but is not limited to, a collimation optical path and an image quality correction optical path inside the projection image source.
6. The system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The distance control between the projection image source and the polarizing holographic waveguide structure requires that all the light rays in the projection image source enter the ingress coupling grating of the polarizing holographic waveguide structure.
7. The system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: By determining the eyebox size and the required field of view (FOV) of the target, the size of the coupling grating is set, using the following formula: ； ； ； ； ； in, These are the side lengths of the output coupling grating of the polarizer holographic waveguide structure. These are the side lengths of the four sides of the eye box. for and as well as and The corresponding edge That is, the vertical field of view. for and as well as and The corresponding edge That is, the horizontal field of view. It is the sum of the horizontal straight-line distance between the position of the human eye and the high-selectivity circularly polarized light reflective film and the vertical straight-line distance between the high-selectivity circularly polarized light reflective film and the installation position of the polarizing holographic waveguide structure; Let be the perpendicular distance from the point of incidence of the incident light on the glass medium to the exit of the coupling grating. The distance between the windshield and the surface of the high-selectivity P-light reflective film for the head-up display. The perpendicular distance from the point of reflection of the reflected light on the glass medium to the center of the eye box. 2 is the angle of refraction of the incident light in the windshield.
8. A system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The input and output coupling gratings of the polarizing holographic waveguide structure adopt a two-dimensional pupil expansion structure.
9. A system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The incident angle of the projection image source can be adjusted according to the requirements. The angle between the outgoing light and the normal at the intersection of the incident light and the coupling grating must be at least greater than the critical angle of total internal reflection to ensure that the light propagates in the polarizing holographic waveguide.
10. A system for ghosting-eliminating head-up display based on polarizing body holographic waveguide according to claim 1, characterized in that: The head-up display windshield is a curved windshield, and the angle of incidence is measured by the angle between the tangent line at the point where the light beam hits the windshield and the incident light beam.