Head-up display system and projection method of head-up display image

Abstract

The invention relates to the field of novel display, in particular to a head-up display system and a projection method of a head-up display image. The head-up display system comprises an image generation device and an optical waveguide, image light rays are transmitted to a coupling-out area through the optical waveguide after being emitted from the image generation device, the image light rays firstly enter an image correction device after being emitted from the coupling-out area, and the image correction device is a reflective optical element, preferably a free-form surface reflector. The reflecting element is used for adjusting the direction of image light, so that the image light enters an eye observation area of a driver in an optimized state after being incident to the windshield and reflected by the windshield, the problems of graphic distortion and binocular parallax caused by the curvature of the windshield are effectively compensated, and meanwhile, the characteristic of small size of a waveguide display system is considered. The invention has the advantages of compact structure, small dispersion, high luminous efficiency and the like, and is suitable for various types of vehicle-mounted head-up display systems.

Description

Technical Field

[0001] This invention relates to the field of novel displays, and more particularly to a head-up display system and a method for projecting head-up display images. Background Technology

[0002] With the development of intelligent cockpits in automobiles, HUDs have become an important component for improving driving safety and user experience. AR-HUDs, in particular, can overlay navigation and driver assistance information onto the road ahead, allowing drivers to drive safely with their eyes on the road and hands on the steering wheel. Traditional AR-HUDs typically use a two-stage magnifying mirror optical structure, resulting in a bulky system that is difficult to install in ordinary passenger vehicles. In recent years, HUD solutions using optical waveguide technology have emerged. While these reduce size, the parallel light emitted directly onto the curved windshield causes astigmatism and binocular parallax, leading to blurred images.

[0003] To achieve a sufficiently large field of view (FOV) and virtual image distance, traditional AR-HUDs often employ two stages of freeform surface mirrors to magnify the image, resulting in system volumes exceeding 10 liters, and sometimes even reaching over 20 liters. Such a large size makes installation difficult within the compact dashboard space of ordinary passenger vehicles; therefore, currently only some luxury and large cars come standard with large-field-of-view AR-HUD display systems. Therefore, the industry urgently needs to develop more compact HUD optical solutions to reduce size and weight.

[0004] In recent years, AR-HUD solutions have emerged that utilize optical waveguides to replace the traditional freeform surface secondary reflection. An optical waveguide is a novel device that decouples optical imaging from transmission functions. It is typically a planar substrate where light propagates and expands within the thin plate through total internal reflection. The advantages of optical waveguide HUDs lie in their significantly reduced size and flattened structure, while maintaining a large exit pupil (eyebox) and field of view.

[0005] However, while significantly reducing the size of the HUD, the optical waveguide solution introduces new technical challenges: imaging inconsistencies caused by the freeform surface of the windshield. In practical applications, the windshield itself is a non-ideal optical element. A typical automotive windshield is a laminated curved glass with a complex freeform surface curvature. Specifically, optical waveguides typically transmit image light in a "parallel light in, parallel light out" manner. The collimated image beam generated by the PGU remains essentially parallel after being coupled out through the waveguide. If these parallel lights are directly projected onto the curved windshield, the curvature at different locations on the glass will cause the reflected beams to converge or diverge to varying degrees, resulting in changes in optical focal length. This means that an ideally projected virtual image at infinity may deviate from its original focal plane after passing through the windshield, and the inconsistency in the entrance pupil light between the left and right eyes further leads to binocular parallax and aberration problems. Therefore, existing pure optical waveguide HUDs may experience problems such as blurred imaging, misalignment of double images, and reduced eye box range on vehicles with large windshield curvature. How to maintain the compact advantage of waveguide solutions while addressing the optical focus deviation caused by the freeform surface of the windshield has become a key challenge that needs to be overcome for the mass production application of AR-HUD.

[0006] Therefore, it is necessary to provide a new head-up display system and image correction device to solve the practical application problems of the aforementioned waveguide head-up display. Summary of the Invention

[0007] Objective: To address the shortcomings of the aforementioned background technology, this invention provides a head-up display (HUD) system and a method for projecting HUD images. By adding a reflective image correction device between the waveguide transmitting end and the windshield, optical aberrations introduced by the curved surface of the windshield are accurately compensated, thereby solving the surface adaptation problem of the waveguide HUD system. This solution combines the advantages of a highly free-form surface mirror design and novel waveguide transmission, significantly reducing the system size while achieving clear and distortion-free long-distance virtual image display, meeting the application requirements of various vehicle platforms.

[0008] Technical solution: To achieve the above objectives, the present invention provides a head-up display system for projecting image information onto the windshield of a vehicle and reflecting it through the windshield for the driver to view virtual images, comprising: an image generation device, an optical waveguide, and an image correction device;

[0009] The image generating device is used to provide input light containing HUD display image information;

[0010] The optical waveguide has an input region and an output region. The input region is aligned with the image generating device and is used to couple the input light into the optical waveguide, and after propagation and pupil dilation via total internal reflection, it is transmitted to the output region and then output.

[0011] The image correction device is a reflective optical element, disposed between the coupling area of ​​the optical waveguide and the vehicle windshield, and aligned with the coupling area. It is used to receive light emitted from the coupling area, reflect and optically correct it, and then guide the corrected light to the windshield.

[0012] Furthermore, the optical power change introduced by the image correction device to the image light is opposite in direction and matched in magnitude to the optical power change introduced by the windshield reflecting the image light, so that after the combined effect of the image light being reflected by the image correction device and the windshield, the net optical power change of the image light is compensated for or eliminated.

[0013] Furthermore, the image correction device is configured such that a parallel beam incident upon it is reflected by it and then by the windshield, and is converted back into a parallel beam or converged to a virtual image plane with a fixed focal length, thereby causing the image light received by the driver's left and right eyes to converge at a distance, presenting a virtual image with a consistent focal plane to reduce binocular parallax.

[0014] Furthermore: the image correction device is a freeform surface mirror with at least one non-rotationally symmetric freeform surface reflective working surface, the working surface being coated with a high reflectivity film; the mirror surface shape of the freeform surface mirror is defined by a polynomial function containing second-order and higher-order coefficients, and the aberration correction of image light is achieved by adjusting the coefficients of each order of the polynomial to match the curvature distribution of different windshields.

[0015] Furthermore, the image correction device includes a reflective holographic optical element, which changes the propagation direction and convergence of image light rays through holographic diffraction, and its diffraction characteristics compensate for the optical power characteristics of the windshield, so that the image light rays after being diffracted by the reflective holographic optical element and reflected by the windshield are restored to collimation.

[0016] Furthermore: the optical waveguide includes an incident coupling element and an outgoing coupling element, which are used to guide image light into and out of the optical waveguide, respectively; the incident coupling element and the outgoing coupling element are one of the following structures: a partial mirror array, a surface relief grating, a volume holographic grating, or a polarizing volume holographic grating.

[0017] The present invention also provides a method for projecting a head-up display image, applied to the aforementioned head-up display system, comprising the following steps:

[0018] S1: The image generating device generates light representing image information, and after collimation by the projection optical system, outputs a parallel image beam;

[0019] S2: The parallel image beam is coupled into the interior of the optical waveguide through the coupling region of the optical waveguide, so that it is transmitted to the coupling region by total internal reflection;

[0020] S3: The image beam is coupled out from the coupling region and propagated to the image correction device;

[0021] S4: Use the image correction device to perform a single reflection on the image beam to adjust its propagation direction and convergence;

[0022] S5: The adjusted image beam is projected onto the windshield, and after being reflected, it enters the driver's observation area to form a virtual image.

[0023] The present invention also provides a vehicle cockpit head-up display system, including the head-up display system installed in the vehicle dashboard, wherein the image correction device is configured to project the image information output by the image generation device onto the windshield after processing by the optical waveguide and the image correction device, and reflect it into the driver's field of vision.

[0024] The present invention also provides a method for manufacturing an image correction device, for manufacturing the freeform surface mirror, comprising the following steps performed in sequence:

[0025] System modeling and initial definition steps: In optical design software (such as Zemax OpticStudio, CodeV, etc.), create a complete HUD optical path model including the image generation device, optical waveguide, windshield surface model, and eyebox position. Define an initial surface shape image correction device within this model. The windshield surface can be defined as an extended polynomial surface according to actual vehicle parameters, or it can be imported from a CAD model. The initial freeform mirror can be assumed to be a plane or a low-order aspherical surface, placed at a predetermined position between the waveguide aperture and the windshield.

[0026] Optical simulation and performance analysis steps: Perform ray tracing simulation based on the optical path model to obtain the imaging error of the uncorrected image at the eye box position. The imaging error includes distortion, astigmatism and binocular parallax.

[0027] Iterative optimization steps for surface parameters: With the goal of compensating for the imaging error, the surface parameters of the image correction device are set as optimization variables. Iterative calculations are performed through optimization algorithms to finally obtain a dataset of final surface parameters of the freeform surface that makes the system imaging performance meet the preset index.

[0028] Lens substrate processing steps: Based on the final surface parameter dataset, the corresponding freeform surface lens is processed on the optical substrate using ultra-precision processing technology;

[0029] High-reflectivity film preparation steps: A high-reflectivity optical film is deposited on the surface of the processed freeform mirror body through a vacuum coating process to form the image correction device.

[0030] In the iterative optimization step of the surface shape parameters, the optimization variables are polynomial coefficients used to define the freeform surface, and slope constraints related to processing capability are introduced during the optimization process to ensure that the final surface shape parameter dataset obtained by optimization is manufacturable. Based on the surface shape defined by the final surface shape parameter dataset, any of the following processes are used to realize it: using single-point diamond turning technology to directly cut and shape on a metal or plastic substrate; or using CNC grinding and polishing technology to process on an optical glass substrate; or first processing a high-precision master mold based on the final surface shape parameter data, and then using injection molding, embossing, or ultraviolet lithography resin replication processes for mass replication production.

[0031] The present invention also provides a method for manufacturing an image correction device, for manufacturing the aforementioned reflective holographic optical element, comprising the following steps:

[0032] Optical function design steps: Determine the optical function to be realized by the reflective holographic optical element in the optical design software, so that its diffraction characteristics and the optical power characteristics of the target windshield can compensate for each other;

[0033] Interference recording steps: Based on the designed optical function, construct the corresponding interference optical path between the object light and the reference light, and perform holographic exposure recording on the photosensitive material;

[0034] Post-processing steps: The exposed photosensitive material is developed, fixed, UV cured and encapsulated to form the reflective holographic optical element.

[0035] Beneficial effects:

[0036] 1. This invention proposes a novel HUD system architecture that combines an image generation device, an optical waveguide, and a reflective image correction device. The core of this architecture lies in inserting a specially designed reflective image correction device between the light output path of the optical waveguide (for miniaturization) and the windshield. This successfully resolves the contradiction between the compactness of the optical waveguide and the aberrations caused by the curvature of the windshield. Traditional solutions can only choose between size and image quality, while this invention achieves both simultaneously for the first time in a waveguide HUD.

[0037] This solution fully utilizes the characteristics of folded optical paths in waveguides to significantly reduce the physical size of the optical engine, enabling it to be easily installed in the compact dashboard of ordinary passenger vehicles, thus solving the industry pain point of excessively large size of traditional AR-HUDs. Through the image correction device in the subsequent stage, it effectively compensates for changes in optical focal length, astigmatism, and distortion caused by the freeform surface of the windshield, ultimately providing the driver with a clear, distortion-free, parallax-free (or low parallax) long-distance virtual image, greatly improving driving safety and display experience.

[0038] 2. This invention proposes two specific implementation schemes to construct the image correction device:

[0039] Option A: Use a freeform surface mirror, whose surface shape is defined by a polynomial containing higher-order terms (such as a Zernike polynomial). Through optical optimization design, its surface shape is precisely matched with the curvature of the windshield of a specific car model.

[0040] Option B: Use a reflective holographic optical element (HOE) to modulate light waves through holographic diffraction. Its diffraction wavefront is designed to be conjugate and compensate for the optical properties of the windshield.

[0041] The above solutions provide efficient, reliable, and mass-producible aberration correction methods. Freeform mirrors are widely applicable and highly efficient; HOEs are thinner and lighter, offering flexibility and versatility in system design.

[0042] Both methods can achieve high-precision correction of astigmatism, field curvature, and distortion caused by windshield curvature, ensuring a clear and sharp virtual image. By designing the correction device to introduce optical power equal in magnitude but opposite in sign to that introduced by the windshield, the final outgoing light is collimated or converged to a fixed focal plane, ensuring that the virtual image seen by both eyes is on the same focal plane, avoiding visual fatigue and misjudgment. The reflective method (especially the freeform metal film mirror) has a much higher optical efficiency than the transmissive correction method and avoids chromatic aberration, ensuring image brightness and color fidelity.

[0043] 3. This invention provides a complete design, optimization, and verification process for image correction devices based on optical simulation software (such as Zemax). This method incorporates the actual curvature of the windshield, the light-emitting characteristics of the optical waveguide, and the position of the eyepiece into a unified model for overall optimization. It solves the matching problem between the image correction device and a specific windshield and optical waveguide, ensuring the performance of the final system from the design stage.

[0044] The above solution, through a closed-loop process of "modeling-simulation-optimization-verification," can accurately predict system performance before processing, significantly improving design success rate and efficiency, and reducing development costs and time. During the optimization process, processing constraints such as mirror slope and light deflection angle can be controlled to ensure that the designed freeform surface or HOE can be reliably manufactured by existing processing technologies (such as single-point diamond turning and holographic exposure) and has mass production potential.

[0045] 4. This invention treats the aforementioned head-up display system as a single module, defining its application scenarios and installation locations in the vehicle cabin (installed inside the dashboard, with the correction device located near the bottom of the windshield). This transforms an optical technology innovation into a component solution that can be directly adopted by OEMs.

[0046] The above solution provides automakers with an optically optimized, ready-to-use, compact AR-HUD module, accelerating the widespread adoption of advanced display technology in the automotive field. Enhancing the overall technological feel and safety of the vehicle: Vehicles equipped with this system can provide drivers with a more intuitive and safer way of displaying information, becoming one of the core selling points of the smart cockpit. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the head-up display device of the present invention;

[0048] Figure 2 This is a schematic diagram of the head-up display device according to Embodiment 1 of the present invention;

[0049] Figure 3 This is a schematic diagram of the head-up display device according to Embodiment 2 of the present invention;

[0050] Figure 4 This is a flowchart of the optical path transmission of the head-up display device of the present invention;

[0051] Figure 5 This is a flowchart illustrating the design of the image correction device for the head-up display device of the present invention.

[0052] Annotation instructions:

[0053] 010 Windshield; 020 Head-up display system; 021 Image generation device; 022 Optical waveguide; 023 Image correction device; 030 Eyebox position; 040 Virtual image position.

[0054] 110 Windshield; 120 Head-up display system; 121 Flat panel display image source; 122 Optical waveguide; 123 Collimation system; 124 Freeform surface reflector; 130 Driver's eye observation area (eyebox position); 140 Virtual image position.

[0055] 210 Windshield; 220 Head-up display system; 221 DLP projection device; 222 Optical waveguide; 223 Collimation system; 224 Reflective holographic optical element; 230 Eyebox position; 240 Virtual image position. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0057] Example 1: An image correction device based on a freeform surface mirror and its head-up display system.

[0058] like Figure 2 As shown, this embodiment provides a waveguide vehicle head-up display system 120 (HUD) suitable for curved windshields. The structure mainly includes an image generation module (including a planar display 121 and a collimation system 123), an optical waveguide 122, a freeform surface reflector 124, and a windshield 110. The image light sequentially passes through the planar display 121 and collimation system 123, the optical waveguide 122, the freeform surface reflector 124, and the windshield 110 before finally entering the driver's eye observation area (eye box) 130.

[0059] In this embodiment, the image generation module preferentially uses a high-brightness flat panel display panel as the image source 121, and outputs a parallel beam in conjunction with the collimating optical system 123. The beam is incident on the coupling region of the optical waveguide 122.

[0060] In this embodiment, the flat panel display can be selected from TFT-LCD transmissive display or OLED / Micro-LED self-emissive display. In this embodiment, an OLED panel is preferred as the image source 121.

[0061] In this embodiment, the collimated beam enters the waveguide 122 after passing through the grating in the coupling region, undergoes multiple total internal reflections in the waveguide, and finally exits from the decoupling region.

[0062] In this embodiment, the optical waveguide 122 can be selected from geometrical optical waveguides, surface relief grating waveguides, volume holographic grating waveguides, or polarizing volume holographic optical waveguides, etc. In this embodiment, a polarizing volume holographic optical waveguide is preferred as the optical waveguide 122.

[0063] In this embodiment, to compensate for image distortion and focal length deviation caused by the curvature of the windshield 110, the image light emitted from the coupling region of the optical waveguide 122 first enters a freeform surface reflector 124 disposed inside the dashboard. This reflector is a monolithic optical element, and its surface shape is optimized by freeform surface design software such as ZEMAX, so that the characteristics of its reflected light can accurately compensate for the optical effects of the windshield 110 of a specific vehicle model.

[0064] In this embodiment, the image correction device is a freeform surface reflector 124. The reflector 124 can be made of optical glass or plastic substrate, the working surface is a precision-machined curved surface, and a high-reflectivity optical film layer (such as aluminum, silver or other metal film or dielectric reflective film) is coated on the surface.

[0065] As a preferred implementation, the reflector 124 is preferably made of aluminum-based material, and its smooth curved surface is formed by ultra-precision single-point diamond turning. Subsequently, a high-reflectivity metal coating (such as reinforced aluminum or silver) is deposited on its reflective surface, followed by anti-oxidation encapsulation treatment. Its freeform surface shape is optimized using ZEMAX optical design software based on the curvature model of the windshield 110. The manufacturing method of this freeform reflector 124 includes:

[0066] System Modeling and Optimization: A complete optical path model including image source 121, optical waveguide 122, windshield 110 curved surface model, and eyebox 130 is established in optical design software. The surface shape of mirror 124 is defined as a freeform surface, and its polynomial coefficients are used as variables for optimization. The goal is to eliminate aberrations and binocular parallax at the eyebox and obtain the final surface shape parameters.

[0067] Substrate processing: Aluminum metal is selected as the substrate for the mirror body. Based on the optimized final surface parameters, ultra-precision single-point diamond turning technology is used to directly cut and form the free-form mirror body on the aluminum base blank.

[0068] Coating: On the surface of the free-form mirror body, an enhanced aluminum high-reflection film and a silicon dioxide (SiO2) protective film are sequentially deposited through a vacuum coating process to form the final image correction device 124.

[0069] The reflector 124 measures approximately 120mm × 600mm and has a thickness of 4mm.

[0070] In this embodiment, the freeform reflector 124 performs a precise reflection of the image light. This reflection process causes the light that was originally converged or diverged due to the curvature of the windshield to regain its collimation direction after entering the windshield 110. As a result, the image light reflected to the driver's eye observation area 130 forms a virtual image 140 3m in front of the eye box position, ultimately achieving an image display with a field of view of 15°×9° without significant binocular parallax.

[0071] Example 2:

[0072] An image correction device based on a reflective holographic optical element and its head-up display system.

[0073] like Figure 3As shown, this embodiment provides a waveguide vehicle head-up display system 220 (HUD) suitable for curved windshields. The structure mainly includes an image generation module (including a projection device 221 and a collimation system 223), an optical waveguide 222, a reflective holographic optical element 224, and a windshield 210. The image light sequentially passes through the projection device 221 and collimation system 223, the optical waveguide 222, the reflective holographic optical element 224, and the windshield 210 before finally entering the driver's eye observation area (eye box) 230.

[0074] In this embodiment, the image generation module preferentially uses a projection device 221, such as a DLP digital light processing device, as the image source. The image light generated by the device is output as a parallel beam after passing through a collimating optical system 223. The beam is incident on the coupling region of the optical waveguide 222.

[0075] In this embodiment, the projection display device can be selected from DLP digital light processing projection, LCoS silicon-based liquid crystal projection, or laser scanning display. The projection device 221, together with a light-diffusing element (such as a diffuser), serves as the image generation unit. The light source can be an LED array or an RGB laser, etc., the specific selection depending on power consumption and brightness requirements. In this embodiment, DLP digital light processing projection is preferred as the image source 221.

[0076] In this embodiment, the parallel beam from the collimation system 223 is coupled into the waveguide through the coupling region (such as a grating) of the optical waveguide 222, undergoes multiple total internal reflections in the waveguide 222 and completes pupil expansion, and finally exits from the coupling region.

[0077] In this embodiment, the optical waveguide 222 can be selected from geometrical optical waveguides, surface relief grating waveguides, volume holographic grating waveguides, or polarizing volume holographic optical waveguides, etc. In this embodiment, a polarizing volume holographic optical waveguide is preferred as the optical waveguide 222.

[0078] In this embodiment, to compensate for image distortion and focal length deviation caused by the curvature of the windshield 210, the image light rays, after exiting the coupling region, first incident on a reflective holographic optical element 224. The surface wavefront distribution of this element is optimized using ZEMAX optical design software to ensure that its diffraction characteristics compensate for the optical focal length characteristics of the windshield. Subsequently, the optimized optical function is recorded in a photosensitive material using holographic interference recording technology. After steps such as darkroom exposure, ultraviolet curing, and encapsulation, the reflective holographic optical element 224 is fabricated.

[0079] In this embodiment, the image correction device is a reflective holographic optical element 224, which can be selected from surface relief gratings, volume holographic gratings, or polarizing volume holographic gratings, etc. In this embodiment, a polarizing volume holographic grating is preferably selected as the reflective holographic optical element 224.

[0080] In this embodiment, a polarizing holographic grating is selected as the reflective holographic optical element 224, and its manufacturing method includes the following steps:

[0081] Optical function design: The optical function to be implemented by the holographic optical element 224 is determined based on optical simulation, so that its diffraction characteristics are accurately compensated with the curvature (optical power) of the target windshield 210.

[0082] Interference recording: Based on the designed optical function, an interference optical path of the corresponding object light wave and reference light wave is constructed in a dark room, and holographic exposure recording is performed on a substrate coated with a photosensitive polymer (such as acrylate-based photosensitive resin).

[0083] Post-processing: The exposed photosensitive material is developed, fixed, and UV cured to stabilize the grating structure. Finally, it is encapsulated to form the reflective holographic optical element 224.

[0084] The grating 224 measures approximately 100mm × 500mm and has a thickness of 10mm.

[0085] In this embodiment, the reflective holographic optical element 224 diffracts and reflects the image light once. The diffraction effect makes the light collimated again after being reflected by the windshield 210, so that the image light reflected to the driver's eye observation area 230 remains parallel, and finally achieves image display with a field of view of 10°×6° without obvious binocular parallax.

[0086] In summary, this invention effectively solves the aberration problem when matching the waveguide-emitted parallel light with the curved windshield by introducing a specific image correction device (freeform mirror or reflective holographic optical element) into the aforementioned waveguide HUD architecture. While maintaining system compactness, it significantly improves virtual image quality and reduces binocular parallax. The head-up display system and image correction device described in this invention are suitable for automotive AR-HUD applications with high requirements for size and image quality.

Claims

1. A head-up display system for projecting image information onto the windshield of a vehicle and reflecting it back onto the windshield for the driver to view virtual images, characterized in that, include: Image generation device, optical waveguide, and image correction device; The image generating device is used to provide input light containing HUD display image information; The optical waveguide has an input region and an output region. The input region is aligned with the image generating device and is used to couple the input light into the optical waveguide, and after propagation and pupil dilation via total internal reflection, it is transmitted to the output region and then output. The image correction device is a reflective optical element, disposed between the coupling area of ​​the optical waveguide and the vehicle windshield, and aligned with the coupling area. It is used to receive light emitted from the coupling area, reflect and optically correct it, and then guide the corrected light to the windshield.

2. The head-up display system according to claim 1, characterized in that: The optical power change introduced by the image correction device to the image light is opposite in direction and matched in magnitude to the optical power change introduced by the windshield reflecting the image light, so that the net optical power change of the image light is compensated or eliminated after the combined effect of the reflection by the image correction device and the reflection by the windshield.

3. The head-up display system according to claim 1, characterized in that: The image correction device is configured such that a parallel beam incident upon it is reflected by it and then by the windshield, and is then converted back into a parallel beam or converged to a virtual image plane with a fixed focal length, thereby causing the image light received by the driver's left and right eyes to converge at a distance, presenting a virtual image with a consistent focal plane to reduce binocular parallax.

4. The head-up display system according to claim 1, characterized in that: The image correction device is a freeform mirror with at least one non-rotationally symmetric freeform reflective working surface, which is coated with a high reflectivity film. The mirror surface shape of the freeform mirror is defined by a polynomial function containing coefficients of second and higher orders, and the aberration correction of the image light is achieved by adjusting the coefficients of each order of the polynomial to match the curvature distribution of different windshields.

5. The head-up display system according to claim 1, characterized in that: The image correction device includes a reflective holographic optical element, which changes the propagation direction and convergence of image light rays by holographic diffraction. Its diffraction characteristics and the optical power characteristics of the windshield compensate for each other, so that the image light rays after being diffracted by the reflective holographic optical element and reflected by the windshield are restored to collimation.

6. The head-up display system according to claim 1, characterized in that: The optical waveguide includes an incident coupling element and an outgoing coupling element, which are used to guide image light into and out of the optical waveguide, respectively; the incident coupling element and the outgoing coupling element are one of the following structures: a partial mirror array, a surface relief grating, a volume holographic grating, or a polarizing volume holographic grating.

7. A method for projecting a head-up display image, applied to the head-up display system according to any one of claims 1-6, characterized in that, Includes the following steps: S1: The image generating device generates light representing image information, and after collimation by the projection optical system, outputs a parallel image beam; S2: The parallel image beam is coupled into the interior of the optical waveguide through the coupling region of the optical waveguide, so that it is transmitted to the coupling region by total internal reflection; S3: The image beam is coupled out from the coupling region and propagated to the image correction device; S4: Use the image correction device to perform a single reflection on the image beam to adjust its propagation direction and convergence; S5: The adjusted image beam is projected onto the windshield, and after being reflected, it enters the driver's observation area to form a virtual image.

8. A vehicle cockpit head-up display system, characterized in that: The head-up display system according to any one of claims 1-6, which is installed in the dashboard of a vehicle, wherein the image correction device is configured to project the image information output by the image generating device onto the windshield after processing by the optical waveguide and the image correction device, and reflect it into the driver's field of vision.

9. A method for manufacturing an image correction device, used to manufacture the freeform surface mirror as described in claim 4, characterized in that, The steps are executed in the following order: System modeling and initial definition steps: In the optical design software, establish a complete optical path model that includes the image generation device, optical waveguide, windshield curved surface model and eye box position, and define an image correction device with an initial surface shape in this model; Optical simulation and performance analysis steps: Perform ray tracing simulation based on the optical path model to obtain the imaging error of the uncorrected image at the eye box position. The imaging error includes distortion, astigmatism and binocular parallax. Iterative optimization steps for surface parameters: With the goal of compensating for the imaging error, the surface parameters of the image correction device are set as optimization variables. Iterative calculations are performed through optimization algorithms to finally obtain a dataset of final surface parameters of the freeform surface that makes the system imaging performance meet the preset index. Lens substrate processing steps: Based on the final surface parameter dataset, the corresponding freeform surface lens is processed on the optical substrate using ultra-precision processing technology; High reflectivity film preparation steps: A high reflectivity optical film is deposited on the surface of the processed freeform mirror body by vacuum coating process to form the image correction device. In the iterative optimization step of the surface parameters, the optimization variables are polynomial coefficients used to define the freeform surface, and slope constraints related to machining capability are introduced during the optimization process to ensure that the final surface parameter dataset obtained by optimization is manufacturable; based on the surface defined by the final surface parameter dataset, any of the following processes are used to achieve the shape: cutting and shaping directly on a metal or plastic substrate using single-point diamond turning technology; Alternatively, CNC grinding and polishing technology can be used to process the optical glass substrate; or a high-precision master mold can be processed first according to the final surface shape parameter data, and then mass production can be carried out by injection molding, embossing or ultraviolet lithography resin replication process.

10. A method for manufacturing an image correction device, used to manufacture the reflective holographic optical element as described in claim 5, characterized in that, Includes the following steps: Optical function design steps: Determine the optical function to be realized by the reflective holographic optical element in the optical design software, so that its diffraction characteristics and the optical power characteristics of the target windshield can compensate for each other; Interference recording steps: Based on the designed optical function, construct the corresponding interference optical path between the object light and the reference light, and perform holographic exposure recording on the photosensitive material; Post-processing steps: The exposed photosensitive material is developed, fixed, UV cured and encapsulated to form the reflective holographic optical element.

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