Compact wide-field windshield head-up display with hybrid reflective intermediate image screen

Abstract

A windshield head-up display system for a vehicle occupant comprises: a picture generation unit having a light source, the picture generation unit generating light for the head-up display system in a first optical path; a hybrid reflective intermediate image screen characterized by at least i) a field correction term that defines a carrier shape of the hybrid reflective intermediate image screen and ii) a diffuser term that defines a surface structure on the hybrid reflective intermediate image screen, the hybrid reflective intermediate image screen receiving the light from the picture generation unit; and at least one mirror in a second optical path that receives the light after reflection and diffusion at the hybrid reflective intermediate image screen; and the head-up display system is configured such that the vehicle windshield receives the light after reflection at the mirror and reflects the light towards the occupant.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Patent Application No. 63 / 384,668, filed November 22, 2022, and entitled "COMPACT WIDE FIELD OF VIEW HEAD UP DISPLAY WITH CURVED REFLECTING SCATTERING INTERMEDIATE IMAGE PLANE," the disclosure of which is incorporated herein by reference in its entirety.

[0002] This document relates to a compact wide field of view windshield head-up display with a hybrid reflective intermediate image screen. [Background technology]

[0003] In the automotive industry, several attempts have been made to design windshield head-up displays (HUDs) for vehicles, typically to provide drivers with driving-related information. While these previous systems all involve projecting an image onto the vehicle's windshield, they typically lack any form of intermediate image plane in windshield HUD systems. A windshield HUD may include a picture generating unit (PGU), several adjustable folding mirrors that project the image from the PGU onto a virtual image plane, and elements for handling stray light. In most windshield HUDs, the PGU, e.g., a thin-film transistor (TFT) display, is projected onto the virtual image plane. Therefore, these systems do not support wide-angle projection at high brightness that also provides a sufficiently long virtual image distance (VID). For example, they are often limited to a VID of approximately 2.5 meters or at least less than 8 meters. In some windshield HUDs, the PGU projects the image onto an additional transparent intermediate image screen, which allows for more freedom in the optical design. They usually require an additional field lens to correct the illumination angle of view to achieve good brightness and uniformity at the eyebox, and also require packaging space to allow for the necessary optical distance between the IIP and the projection optics.

[0004] Some previous HUD systems have relied on TFT displays with light-emitting diode (LED) illumination. However, these systems are typically susceptible to sunlight on the TFT display, which can result in damage. While TFT systems may be capable of producing a relatively long VID, this requires significant magnification, substantially reducing brightness. As a result, much more sophisticated LED lighting designs may be required, and due to the high magnification, the solar load that can be reversed in the projection path and focused onto the display can be significantly higher. Summary of the Invention

[0005] In one aspect, a windshield head-up display system for a vehicle occupant includes a picture generation unit having a light source, the picture generation unit generating light for the head-up display system in a first optical path; a hybrid reflective intermediate image screen characterized by at least i) a field correction term that defines a carrier shape of the hybrid reflective intermediate image screen and ii) a diffuser term that defines a surface structure on the hybrid reflective intermediate image screen, the hybrid reflective intermediate image screen receiving the light from the picture generation unit; and at least one mirror in a second optical path that receives the light after reflection and diffusion at the hybrid reflective intermediate image screen; and the head-up display system is configured such that the vehicle windshield receives the light after reflection at the mirror and reflects the light toward the occupant.

[0006] Implementations may include any or all of the following features: The carrier shape of the hybrid reflective intermediate image screen is curved. The field correction term is described as an optical freeform. The optical freeform is a two-dimensional polynomial function. The field correction term is described as a biconic surface function. The field correction term is described as a cylindrical surface function. The hybrid reflective intermediate image screen has a radius of curvature of approximately 1000 to 300 millimeters and is convex. The field correction term is described by an anamorphic lens function. The hybrid reflective intermediate image screen has a convex shape pointing toward the origin of the first optical path. The surface structures have a total height of at least 2.5 times the longest illumination wavelength used, and lateral structure sizes exceed 5 times the longest illumination wavelength. The diffuser term is realized by a deterministic, non-stochastic, calculated surface according to a specified height profile. The surface structures have no steps, jumps, or edges in both lateral directions, and the first derivative of the surface height function is continuous. The surface structure is described by the repetition of one or more unit cells. The unit cells are calculated using an iterative Fourier transform algorithm. The first optical path intersects the second optical path. The windshield head-up display system further includes a second mirror in a third optical path that receives the light after reflection from the first mirror, at least one of the first or second mirrors being curved. The first mirror is flat and the second mirror is curved. The first mirror faces away from the occupant, and the second mirror faces toward the occupant. The origin of the first optical path is located below the first and second mirrors in the z direction of a vehicle coordinate system. The origin of the first optical path is located between the first and second mirrors in the x direction of the vehicle coordinate system. The second mirror is positioned forward of the first mirror in the x direction of the vehicle coordinate system. The windshield head-up display system further includes a glare trap positioned between the second mirror and the windshield. The glare trap is formed in part by a transparent polymer cover.The origin of the first optical path is located below the hybrid reflective intermediate image screen in the z-direction of the vehicle coordinate system. The windshield head-up display system is configured to generate a virtual image for the occupant, the virtual image being positioned approximately 10 to 30 meters from the occupant. The field of view of the head-up display system is specified as a first angle multiplied by a second angle, the first angle being approximately 10 to 20 degrees and the second angle being approximately 3 to 10 degrees. The hybrid reflective intermediate image screen is formed by a plurality of unit cells satisfying a periodic boundary condition. The hybrid reflective intermediate image screen is formed by a plurality of unit cells that are all identical to one another. The hybrid reflective intermediate image screen is formed by a plurality of unit cells that are not all identical to one another. The hybrid reflective intermediate image screen includes a volume holographic polymer element. The volume holographic polymer element includes a photopolymer film and a carrier substrate. The carrier substrate includes at least one selected from the group consisting of polycarbonate and polyethylene. The windshield head-up display system further comprises a cover layer positioned on an opposite side of the photopolymer film from where the carrier substrate is positioned. The hybrid reflective intermediate image screen comprises curved volume holographic polymer elements. The hybrid reflective intermediate image screen comprises planar volume holographic polymer elements. The hybrid reflective intermediate image screen is formed by grayscale lithography. The surface structure is formed in a material selected from the group consisting of polymers or plastics. The material is coated with a reflective layer. The reflective layer comprises a metal. The reflective layer comprises a combination of a metal and a dielectric layer. [Brief explanation of the drawings]

[0007] [Figure 1A] FIG. 1 illustrates a schematic example of a windshield head-up display (HUD) system using a hybrid reflective intermediate image plane. [Figure 1B]FIG. 1 illustrates a schematic example of a windshield head-up display (HUD) system using a hybrid reflective intermediate image plane. [Figure 1C] FIG. 1 illustrates a schematic example of a windshield head-up display (HUD) system using a hybrid reflective intermediate image plane.

[0008] [Figure 2] FIG. 1B illustrates an example of a light path in the windshield HUD system of FIG. 1A.

[0009] [Figure 3A] FIG. 1B illustrates another example of the light path in the windshield HUD system of FIG. 1A.

[0010] [Figure 3B] FIG. 3B shows an example of a rectangular diffuser diffusion for the hybrid reflective IIS of FIG. 3A.

[0011] [Figure 4] FIG. 1 illustrates an example of a non-stochastic micro-optical computational surface that can be used with the diffusers described herein.

[0012] [Figure 5] FIG. 1 illustrates an example of a unit cell for a diffuser that can be used with the windshield HUD systems described herein.

[0013] [Figure 6] FIG. 6 shows an example of a height profile of the non-stochastic micro-optical computational surface of FIG. 5.

[0014] [Figure 7A] FIG. 6 illustrates an example of the non-stochastic micro-optical computational surface of FIG. 5. [Figure 7B] FIG. 6 illustrates an example of the non-stochastic micro-optical computational surface of FIG. 5.

[0015] [Figure 8A] FIG. 10 shows an example of how a reflection structure can be calculated and organized. [Figure 8B] FIG. 10 shows an example of how a reflection structure can be calculated and organized. [Figure 8C] FIG. 10 shows an example of how a reflection structure can be calculated and organized. [Figure 8D] FIG. 10 shows an example of how a reflection structure can be calculated and organized. [Figure 8E] FIG. 10 shows an example of how a reflection structure can be calculated and organized. [Figure 8F] FIG. 10 shows an example of how a reflection structure can be calculated and organized. [Figure 8G] FIG. 10 shows an example of how a reflection structure can be calculated and organized.

[0016] [Figure 9] FIG. 10 shows an example of placement of unit cells in a 4×4 array through repetition.

[0017] [Figure 10] 1A-1C illustrate examples of diffuser arrangements that can be formed from unit cells. [Figure 11] 1A-1C illustrate examples of diffuser arrangements that can be formed from unit cells.

[0018] [Figure 12] FIG. 10 shows an example of diffuser specifications regarding eyebox size and position.

[0019] [Figure 13] FIG. 6 shows an example of intensity distribution in the far field for the non-stochastic micro-optical computational surface of FIG. 5.

[0020] [Figure 14] FIG. 10 is a diagram illustrating an example of irradiance in the eye box.

[0021] [Figure 15A] FIG. 1 illustrates an example of a hybrid reflective IIS. [Figure 15B] FIG. 1 illustrates an example of a hybrid reflective IIS. [Figure 15C] FIG. 1 illustrates an example of a hybrid reflective IIS.

[0022] [Figure 16A] FIG. 1 illustrates an example of a windshield HUD system. [Figure 16B] FIG. 1 illustrates an example of a windshield HUD system.

[0023] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE INVENTION

[0024] This document describes example systems and techniques for a compact windshield HUD system that provides a wide field of view using a hybrid reflective intermediate image screen (IIS) characterized by at least a field correction term and a diffuser term. The geometry of the hybrid reflective IIS can be decomposed into a specific mirror curvature and a specific calculated diffuser height profile (e.g., with feature sizes in the micrometer range for the VIS) that provides a specific scattering distribution. The curvature can be described using a lens function, such as a two-dimensional freeform (e.g., described by a polynomial function), or it can be a biconic or cylindrical shape (e.g., with a radius of curvature of approximately 1000 to 300 millimeters, e.g., approximately 500 mm). The curvature and calculated diffuser height profile can be designed so that the optical paths of all field points of the image coming from the PGU and projected onto the hybrid reflective IIS match the illumination required at the eyebox (the area where the driver's / passenger's eyes should be located to observe the virtual image). For example, this can enable high system efficiency with low light attenuation of the virtual image toward the sides (with significantly reduced vignetting) and high perceived brightness and uniformity throughout the eyebox. Hybrid reflective IIS can be based on deterministic scattering, for example, by using a tuned or otherwise calculated reflective diffuser. Achromatic diffusers can be designed with low granularity to enable high-brightness and sharp virtual images. The feature size can then be very low and shallow. Starting with a regular structure (e.g., a microlens array or a specific 2D wave structure) that provides an orthogonal distribution, a specific pattern can then be calculated, for example, as described in U.S. Pat. No. 10,254,449. The reflective structure can provide a specific, e.g., rectangular, angular distribution with high suppression of the retroreflected component to avoid light from the screen traveling back to the projection unit. The reflective structure can improve the sun resistance because the light coming from the sun will be scattered in the opposite direction from the virtual image and only a very small amount will pass into the PGU.In some implementations, the reflective lens function is recorded in a volume hologram, providing a polymer film that reflects only the design wavelengths for the HUD and transmits all other wavelengths, which is further beneficial for solar load management. In some implementations, the present subject matter can provide a windshield HUD system with an improved field of view (FOV). For example, the FOV can be approximately 13 by 5 degrees. In some implementations, the present subject matter can provide a windshield HUD system with a reduced packaging volume. Having a hybrid reflective IIS can be beneficial for packaging because the beam path can be folded and the optical volume of the projection path can be reused. The packaging volume can be as small as approximately 14 liters, even when the system provides significantly improved VID and / or FOV. For example, a VID of approximately 15 meters can be achieved, which may allow the driver / passenger to view the HUD content with little or no redirection of attention. In the present subject matter, sunlight can instead be focused onto the hybrid reflective IIS, which can improve solar load management. Only a small fraction of sunlight may actually reach the PGU. The system can provide better cooling and reduce the risk of thermal damage to the PGU. The present subject matter can provide an advantageously large image (e.g., approximately 60 millimeters multiplied by 100 millimeters, or 60 x 100 mm) on the midplane, which also reduces glare issues and solar loading effects compared to smaller image sizes. The eyebox area can be advantageously increased. For example, an eyebox of approximately 180 x 120 mm can be achieved. Furthermore, a windshield HUD with IIS can support better contrast and / or color gamut compared to TFT-based systems.

[0025] Examples described herein refer to vehicles. A vehicle is a machine that transports passengers, cargo, or both. A vehicle can have one or more motors that use at least one type of fuel or other energy source (e.g., electricity). Examples of vehicles include, but are not limited to, cars, trucks, and buses. The number of wheels can vary between vehicle types, and one or more (e.g., all) of the wheels can be used to propel the vehicle, or the vehicle can be unpowered (e.g., when a trailer is attached to another vehicle). A vehicle can include a passenger compartment that accommodates one or more people. A person traveling with a vehicle can be characterized as a driver and / or passenger. For simplicity, a user of the system described herein will be referred to as a passenger, regardless of whether the person performs any driving tasks with the vehicle.

[0026] The examples described herein refer to a hybrid reflective intermediate image screen. As used herein, a hybrid reflective intermediate image screen is an image screen positioned intermediately between an image source (e.g., a picture generation unit) and a vehicle windshield. The term "hybrid" refers to an element derived by a combination of traditional optical ray tracing optimization and diffractive components calculated, for example, by an iterative Fourier transform algorithm (IFTA). A hybrid reflective intermediate image screen is characterized by at least a field correction term and a diffuser term. The field correction term can be calculated / optimized with traditional sequential ray tracing to correct the direction of light coming from the PGU so that each point on the image screen illuminates the entire eyebox and as little light as possible is lost outside the eyebox. Without this field correction term, the eyebox location and size would vary from image point to image point because the chief ray of the illumination coming from the PGU does not necessarily coincide with the chief ray of the optical system that forms the virtual image. The field correction term can be characterized by a lens function, for example a two-dimensional freeform (e.g., described by a polynomial function), or it can be a biconical shape, where the surface z(x,y) is given by:

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[0027] Examples described herein refer to top, bottom, front, side, or back. These and similar expressions identify things or aspects relative to one another based on an explicit or arbitrary notion of perspective. That is, these terms are merely exemplary and are used for illustrative purposes and do not necessarily represent the only possible positions, orientations, etc.

[0028] 1A-1C illustrate schematic examples of windshield HUD systems 100, 120, and 140, respectively. Any or all of windshield HUD systems 100, 120, or 140 can be used with one or more other examples described elsewhere herein. For simplicity, windshield HUD systems 100, 120, and 140 are illustrated schematically, and some components are omitted or illustrated schematically. Windshield HUD systems 100, 120, or 140 can be configured for installation within a vehicle, most of which are also omitted in the respective illustrations. Some features of windshield HUD systems 100, 120, and 140 are described with reference to a Cartesian coordinate system, roughly oriented in FIG. 1A. This coordinate system indicates an x-direction (e.g., the direction along which a vehicle may travel), a y-direction (e.g., the direction across the vehicle), and a z-direction (e.g., vertical to the vehicle).

[0029] Starting with FIG. 1A , the windshield HUD system 100 includes a PGU 102 that provides illumination and image content. The PGU 102 has a light source based on one or more illumination technologies. In some implementations, the PGU provides illumination using one or more LEDs. For example, multiple colors (e.g., red, green, and blue) of LEDs can be provided. In some implementations, the PGU 102 can generate an image using a liquid crystal on silicon (LCOS) projector. One or more other approaches can be used, including, but not limited to, a digital micromirror device (DMD) and / or a microelectronic mechanical system (MEMS) projector. For example, the PGU 102 can use one or more optical elements, including, but not limited to, lenses and / or mirrors, between the light source and the LCOS / DMD / MEMS device and / or elsewhere.

[0030] The windshield HUD system 100 includes a hybrid reflective IIS 104. The hybrid reflective IIS 104 can receive light from the PGU 102. The PGU 102 cannot generate the angular spread required to fill the eyebox 114. Therefore, two things are required: First, the spread required to fill the size of the eyebox 114 is required. For example, a diffuser (e.g., with a non-stochastic micro-optically calculated surface height profile) placed on the surface of the hybrid reflective IIS 104 can be adjusted to create a rectangular scattering profile. The non-stochastically calculated diffuser increases the pupil area provided by the PGU to the desired eyebox shape and size where the virtual image 116 is visible to the driver. Using the hybrid reflective IIS 104, the virtual image 116 can be visible in a specific area, here the eyebox 114, which can be shaped as needed to accommodate different driver head positions (e.g., the eyebox is rectangular with a spread of 180 x 120 mm). Therefore, a diffuser on the IIS surface can create rectangular diffusion to match, for example, a rectangular eyebox. Still, if the hybrid reflective IIS 104 were flat, the diffusion generated from the diffuser for different field points would not perfectly overlap in the eyebox. This would result in light attenuation for higher field points for outer eyebox positions. Alternatively, the total diffuser diffusion would need to be increased, which would reduce efficiency and add more light in outer areas where light is not needed or even obstructive. Therefore, secondly, a field correction term is needed to determine the overall shape / curvature of the hybrid reflective IIS 104 to correct for the primary (central) field angle. This causes the generated (rectangular) diffusion for all field points to (ideally, perfectly) overlap in the rectangular eyebox. In this way, the brightness of the virtual image can be increased because the light is shaped to the required eyebox area.For example, the brightness may be greater than about 15,000 candelas per square meter. The surface structure may be defined or tailored according to a specified height profile.

[0031] The curvature can be free-form; because the eyebox 114 is typically rectangular to accommodate all possible head positions, this requires an anamorphic optical lens function, such as a biconic or cylindrical lens term. The curvature and resulting lens function incorporated into the IIS 104 can be designed so that the illumination optical path of all field points of the image on the hybrid reflective IIS 104 of light coming from the PGU 102 matches the optical path provided by the HUD projection system toward the eyebox, enabling tailored illumination at the eyebox 114, enabling high system efficiency with low optical attenuation of the virtual image 116 toward the sides. Therefore, the shape of the IIS 104 and the corresponding field correction term include the angular beam shift required to match the PGU illumination path to the HUD projection beam path. This typically results in a convex shape for the hybrid reflective IIS 104. This leads to easier manufacturing and better surface quality in terms of grain size, since the required lens function will generally result in a higher frequency (smaller structure size) or higher depth of the microstructures.

[0032] The reflective hybrid reflective IIS 104 can provide advantages in reducing the volume of packaging space required for the windshield HUD system 100 due to folding the beam and passing through the volume at least twice. The hybrid reflective IIS 104 can have a curved carrier shape (with a one- or two-dimensional lens function, such as a biconic or a polynomial freeform (e.g., based on Chebyshev polynomials)) or a cylindrical shape. It can be realized, for example, by a polymer with a reflective metal coating. As another example, the IIS 104 can have a planar carrier shape, where a field-corrected phase term is added to the phase distribution of the diffuser term. The resulting phase term is then transferred in a diffuser surface height profile that can be added on top of the carrier shape. As another example, the hybrid reflective IIS 104 can be realized as a curved or planar volume holographic polymer element. This transparent polymer can be realized so that it reflects only the required lens function for the design wavelength (e.g., the specific spectrum of the RGB LED used in the PGU).

[0033] The windshield HUD system 100 can include a mirror 106. The presence and location of the mirror 106 is highly dependent on the optical specifications and the given package volume. In the illustrated windshield HUD system 100, the mirror 106 is a planar / flat folding mirror to adjust the beam path within the given package volume and reduce the overall required volume of the windshield HUD system 100. The mirror 106 need not have optical power and can function to fit the package. The mirror 106 can receive light scattered from the hybrid reflective IIS 104 with a lens function. The mirror 106 can include any substrate with reflective properties that allow sufficient light generated at the PGU 102 to be reflected. For some applications, the mirror 106 can be characterized as a freeform mirror. For example, the mirror 106 can have a lens function (e.g., biconic, spherical, aspherical, or freeform, based on a polynomial description (e.g., Chebyshev polynomials)). For example, a freeform surface can be described by a base radius of curvature and a sequence of Chebyshev polynomials. The mirror 106 can include coatings to improve efficiency, color, stray light / solar suppression, or contrast. For example, the mirror 106 can have a cold mirror coating that allows only light below a certain wavelength threshold to be reflected. Longer wavelengths, such as infrared light from the sun, will be transmitted and can be placed on an absorber. Additionally, coatings that improve reflectivity can be used. Additionally, polarizing films (e.g., wave plates or polarizers) can be placed on the mirror to improve contrast or suppress stray light (e.g., sunlight).

[0034] The windshield HUD system 100 includes a freeform mirror 108, which can either receive light reflected from the mirror 106 or, in the case where the mirror 106 is not present, directly receive scattered light from the hybrid reflective IIS 104. The freeform mirror 108 can include any substrate with reflective properties that allow sufficient light generated at the PGU 102 to be reflected. The freeform mirror 108 acts as a magnifying mirror and compensates for the shape of the windshield; therefore, the freeform mirror 108 can have a lens function (e.g., biconic, spherical, aspherical, or freeform, such as one based on a 2D polynomial). For example, the freeform surface can be described by a base radius of curvature and a sequence of Chebyshev polynomials. The mirror 106 and / or the freeform mirror 108 can include one or more of the same or different coatings to improve efficiency, color, stray light / solar suppression, or contrast. For example, if the windshield HUD system 100 includes a mirror 106, the coating may preferably be disposed on the mirror 106.

[0035] The windshield HUD system 100 includes a cover 110 used as a glare trap. For example, the cover 110 is made of a transparent polymer material. The cover 110, which partially forms a glare trap, can have a specific shape designed to avoid glare problems from sunlight in the windshield HUD system 100. For example, the shape can be such that any light arriving from outside that strikes the cover 110 does not reach the occupant's eyebox. The cover 110 can be positioned between the freeform mirror 108 and the vehicle's windshield 112. The cover 110 can include one or more coatings to improve efficiency, color, stray light / sunlight suppression, and / or contrast. For example, the cover 110 can have a hot mirror coating that allows only light below a certain wavelength to pass through the cover. For example, infrared light from the sun would be reflected. Coatings that improve transmittance can be used. A polarizing coating / film (e.g., a wave plate or polarizer) can be placed on the mirror to improve contrast or suppress stray light (e.g., sunlight).

[0036] The windshield HUD system 100 can project light that, when reflected by the windshield 112 and subsequently observed by the occupant, creates the appearance of a virtual image 116 for the occupant. The virtual image 116 can be characterized as being located at a VID from the eyebox 114. The VID can be approximately 10 to 30 meters. For example, the VID can be approximately 15 meters. Having a significant VID can be beneficial to enable the occupant to view the content generated by the windshield HUD system 100 (i.e., the virtual image 116) with no or only a small redirection of attention from observing objects in traffic or otherwise near the vehicle. This can allow the virtual image 116 to blend practically into the surroundings from the occupant's perspective. Another advantage of having a VID greater than approximately 10 meters is that the virtual image 116 cannot be perceived as a double image by the occupant because the windshield 112 is relatively close to the pupil zone of the eyebox 114 (i.e., to the occupant) compared to the VID distance.

[0037] The virtual image 116 can be characterized in terms of its FOV relative to the occupant. The FOV can be specified using a horizontal angle and a vertical angle. In some implementations, the horizontal angle can be approximately 10-20 degrees, e.g., approximately 13 degrees. In some implementations, the vertical angle can be approximately 3-10 degrees, e.g., approximately 5 degrees. Having a wide FOV can facilitate the presentation of augmented reality (AR) content by the windshield HUD system 100. For example, the AR content can highlight or otherwise depict pedestrians, house numbers, and / or street signs. In particular, achieving a wide FOV while simultaneously providing a long VID can present challenges in terms of package space and / or achievable brightness for available PGU technology.

[0038] The windshield HUD system 100 has a folded beam path for light traveling from the PGU 102 to the hybrid reflective IIS 104, the mirror 106, and the freeform mirror 108, reusing the same optical volume between the mirror 106 and the freeform mirror 108. This may be possible, in part, because the PGU 102 can project toward the hybrid reflective IIS 104 (e.g., through an opening in the housing), and this optical volume is also traversed by light propagating from the mirror 106 toward the freeform mirror 108. That is, this packaging space can be reused because the same optical volume is used twice, thereby reducing packaging space and making the windshield HUD system 100 more compact. That is, the hybrid reflective IIS 104, and some or all of the mirror 106 and freeform mirror 108 can be curved and folded relative to one another (beam folding) to minimize packaging space. For example, mirror 106 can face away from the occupant and freeform mirror 108 can face towards the occupant. As another example, freeform mirror 108 can be positioned in front of mirror 106 relative to the x-direction of the vehicle coordinate system.

[0039] Generally, a HUD system requires at least a PGU (which can already provide the picture itself for a TFT with rear lighting) and a magnifying lens (mirror) that compensates for the windshield shape as well. FIG. 1B shows an example of a windshield HUD system 120, including a PGU 102; a hybrid reflective IIS 104; a freeform mirror 108; a cover 110; and a windshield 112. In FIGS. 1B and 1C, the cylindrical convex shape of the IIS 104 is emphasized. The radius is not to scale. The PGU 102 can generate light (i.e., one or more images) that enters the hybrid reflective IIS 104 and is reflected and diffused thereby. The freeform mirror 108 receives light from the hybrid reflective IIS 104 and reflects it through the cover 110 and toward the windshield 112. The windshield 112 reflects the light from the freeform mirror 108, making the reflected light visible to the occupant in the eyebox 114. To the occupant, the light reflected by the windshield 112 appears as a virtual image 116 positioned in the VID in front of the eyebox 114. That is, windshield HUD system 120, compared to windshield HUD system 100, at least omits mirror 106.

[0040] FIG. 1C illustrates an example windshield HUD system 140 including a PGU 102, a curved hybrid reflective IIS 104, a mirror 106, a freeform mirror 108, a cover 110, and a windshield 112. That is, in the present subject matter, the hybrid reflective IIS 104 can be flat or curved. The PGU 102 can generate light (i.e., one or more images) that is incident on the hybrid reflective IIS 104 and is reflected and diffused thereby. The mirror 106 receives light from the hybrid reflective IIS 104. The freeform mirror 108 receives light from the mirror 106 and reflects it through the cover 110 and toward the windshield 112. The windshield 112 reflects the light from the freeform mirror 108, making the reflected light visible to the occupant at an eyebox 114. To the occupant, the light reflected by the windshield 112 appears as a virtual image 116 positioned in the VID forward of the eyebox 114.

[0041] 2 shows an example light path 200 in the windshield HUD system 100 of FIG. 1A. Light path 200 can be used with one or more other examples described elsewhere herein. Light path 200 represents the chief ray for different field points. For example, this can include the outer corners (i.e., maximum angle) and center of virtual image 116. Hybrid reflective IIS 104 and mirror 106 and freeform mirror 108 are shown here relative to location 202 (shown schematically) where PGU 102 introduces light.

[0042] As mentioned, the hybrid reflective IIS 104 can have a specially calculated curvature. When using a rectangular eyebox to accommodate all possible head positions, an anamorphic optical lens function is used (e.g., a biconic). In some implementations, the hybrid reflective IIS 104 has a radius of curvature (ROC) of approximately planar to 300 mm in one direction and planar to approximately 300 mm in the other direction. For example, the ROC can be approximately 500 mm in one direction and planar in the other direction, resulting in a cylindrical carrier shape for the IIS 104. An ROC such as that exemplified above can avoid light attenuation toward the sides / edges of the virtual image. This ROC can be calculated based on the rest of the windshield HUD system 100 to fit the optical design. In some implementations, the ROC can be designed to match the aperture of the PGU 102 (e.g., at location 202). For example, this can enable higher brightness for higher field points (e.g., at higher angles). The ROC can provide an optical illumination path from the aperture of the PGU 102. The size of the hybrid reflective IIS 104 can be approximately 40-150 mm horizontally and approximately 20-80 mm vertically. For example, the hybrid reflective IIS 104 can have a size of approximately 85 x 45 mm. The hybrid reflective IIS 104 can provide better cooling with respect to solar loads. With respect to solar loads, a small amount of light may enter the windshield HUD system 100 under the angle at which the virtual image is located and travel a reverse optical path back to the hybrid reflective IIS 104. This amount of light is further scattered upon impinging on the hybrid reflective IIS 104, keeping the amount of light reaching the PGU 102 very low, thereby reducing the risk of introducing stray light visible as glare to the driver and, in the worst case, thermal damage to the PGU 102. The windshield HUD system 100 can provide a larger intermediate image (on the hybrid reflective IIS 104), thereby reducing the amount of magnification required to generate the final virtual image.The lower magnification of the system reduces problems with solar load, glare and visible grain.

[0043] This illustration shows multiple chief rays, each propagating from location 202 (i.e., the exit surface from PGU 102) to hybrid reflective IIS 104, from there to mirror 106, from there to freeform mirror 108, from there to windshield 112, and from there to eyebox 114. For simplicity, the propagation of one of these chief rays will be described.

[0044] The chief ray may include optical path 204A from location 202 to hybrid reflective IIS 104. Hybrid reflective IIS 104 may have a convex shape facing toward the origin of optical path 204A (e.g., facing toward location 202). The origin of optical path 204A (e.g., location 202) may be located below mirror 106 and freeform mirror 108 in the z-direction of the vehicle coordinate system. The origin of optical path 204A (e.g., location 202) may be located between mirror 106 and freeform mirror 108 in the x-direction of the vehicle coordinate system. The origin of optical path 204A (e.g., location 202) may be located below hybrid reflective IIS 104 in the x-direction of the vehicle coordinate system. The chief ray may include optical path 204B from hybrid reflective IIS 104 to mirror 106. The chief ray may include optical path 204C from mirror 106 to freeform mirror 108. Light path 204C intersects with light path 204A. For example, light paths 204A and 204C occupy the same point in space within the optical volume of windshield HUD system 100. The chief ray can include light path 204D from the freeform mirror 108 to the windshield 112. The chief ray can include light path 204E from the windshield 112 to the eyebox 114.

[0045] The above example shows that a head-up display system (e.g., windshield HUD system 100) can include: a picture generation unit (e.g., PGU 102) including a light source that generates light for the head-up display system in a first optical path (e.g., optical path 204A); a hybrid reflective intermediate image screen (e.g., hybrid reflective IIS 104) that receives light from the picture generation unit; a first mirror (e.g., mirror 106) that receives the light after scattering at the hybrid reflective image screen in a second optical path (e.g., optical path 204B); and a second mirror (e.g., freeform mirror 108) that receives the light after reflecting at the first mirror in a third optical path (e.g., optical path 204C). The third optical path intersects the first optical path, and at least one of the first or second mirrors is curved.

[0046] 3A shows another example of a light path 300 in the windshield HUD system 100 of FIG. 1A. The light path 300 can be used with one or more other examples described elsewhere herein. The windshield HUD system 100 is shown here from a different angle and with additional example details. The windshield HUD system 100 can be tuned (e.g., optimized) by using an instance of a windshield 112 having a wedge-shaped profile and / or by providing one or more polarizing coatings on the windshield 112.

[0047] Light path 300 may originate in a PGU (e.g., PGU 102 in FIG. 1A ), which is not shown in this diagram for simplicity. Rather, in this illustration, light path 300 is shown from the point where it is scattered by hybrid reflective IIS 104. It illustrates the exit beam path / bundle from one field point coming from IIS 104 toward eyebox 114. The shape and diffusion characteristics of IIS 104 allow a ray bundle coming from the IIS with the required size and shape to (ideally) completely fill eyebox 114. Coming from the IIS, the light is further reflected by mirror 106, freeform mirror 108, and windshield 112, while also traveling through cover 110. Scattering ensures that the area of ​​eyebox 114 is filled with light path 300. In contrast, FIG. 2 does not show scattering, which is why the illustration shows all rays intersecting at a small spot in the pupil plane of the eyebox.

[0048] 3B shows an example of rectangular diffuser diffusion for the hybrid reflective IIS 104 of FIG. 3A for a small number of field points. Multiple light bundles 302 are shown starting from the hybrid reflective IIS 104 and reaching the mirror 106, while the remainder of the windshield HUD system is omitted here for clarity.

[0049] FIG. 4 illustrates an example of a section of an achromatic diffuser area 400 that can be used with the windshield HUD system described herein. This illustration shows multiple repetitions of a unit cell. The achromatic diffuser area 400 can be part of a component such as the hybrid reflective IIS 104 and, therefore, can be placed on a carrier geometry given by the field correction terms of the IIS. In some implementations, the carrier geometry includes a curvature (e.g., with a specific ROC). In some implementations, the carrier geometry can be a planar geometry, and the field correction phase terms are already integrated into the diffuser optical function. Light rays 402 are incident from the PGU, and scattered light 404 is coming from the achromatic diffuser area 400. The light rays 402 and scattered light 404 are shown here schematically as respective arrows.

[0050] The unit cell of the achromatic diffuser area 400 can have a size that depends at least in part on the total angular distribution (eyebox shape) and the angular resolution required and perceived granularity. For example, having an excessively small unit cell can result in a grating effect (visual color effect). For example, the unit cell of the achromatic diffuser area 400 can have sides of about 250 microns to 5 mm, e.g., about 1 mm. The feature size (e.g., the size from a single hillock) is about 1 to 100 microns, and the total maximum structure depth is about 0.5 to several microns. The surface profile is not stochastic, but rather has a deterministic structure. The surface structure is continuous in both lateral directions and does not have jumps, steps, or edges. The first derivative of the surface height function should be continuous. This deterministic microstructure can be calculated, for example, as described in U.S. Pat. No. 10,254,449. The structure is designed so that the unit cell can be periodically repeated in both lateral directions. To avoid granularity, different unit cells with the same boundary conditions (to allow for smooth transitions between unit cells) can be calculated and randomly placed on the diffuser surface. A diffuser containing multiple instances of a unit cell is configured for its optical purpose: to provide a reflective surface that scatters light to create a particular size and uniformity of illumination in the eyebox.

[0051] The achromatic diffuser area 400 can be formed on any of a variety of substrates, including, but not limited to, metal, composite, polymer, or glass, or a combination of the listed materials. For example, the surface structure can be formed as one or more layers or coatings on the surface. Because the achromatic diffuser area 400 is reflective, the outermost layer of the surface structure can be a reflective material such as metal. The structure can be a micro-optically calculated surface profile with a microstructured pattern. The surface structure can be formed using any of several techniques, including, but not limited to, wafer or roll-to-roll processes, including lithography, etching, imprinting, embossing, molding, or coating techniques. For example, wafer processing means that a lithography step (e.g., grayscale lithography) is performed on a wafer (with a polymer resist on top) using dedicated machines. For example, grayscale laser lithography can be used. In some implementations, grayscale lithography (e.g., with electron beam lithography, laser writing, or LED grayscale lithography) can be used to generate master structures that can be copied and transferred to generate submasters out of polymers (e.g., silicone) or metals (e.g., nickel or steel). Using those submasters, the structures can be copied (e.g., by embossing, imprinting, or compression or injection molding) into the polymer or plastic. The structures can then be coated, for example, with a highly reflective metal coating or a combination of metal and dielectric layers. In another implementation, a structured polymer layer containing a specific height profile for a transparent computational diffuser can be added onto a curved carrier mirror.

[0052] Furthermore, the required optical function can be implemented in a curved or planar holographic volume diffuser film. A volume holographic optical element (VHOE) can be used to reflect only design wavelengths, such as 633 nm, 532 nm, and 457 nm. While the VHOE reflects light at the design wavelength (within the Bragg condition), it is transparent to all other wavelengths (off the Bragg condition). This enables superior performance for solar suppression because sunlight has a broad spectrum, and only light at the design wavelength is reflected, while the main solar load passes through the VHOE and lands on the absorber. Photopolymer films can be applied directly to the curved or planar surface of the IIS. The combined optical function, including the field correction term and the diffuser term, can be recorded in the photopolymer by holographic interference lithography. Here, the required scattering profile (e.g., uniform scattering in a rectangular angular intensity distribution, as in Figure 13) is created by an external setup that creates such an angular distribution (e.g., generated by a collimated coherent source, e.g., a pulsed laser, plus a diffuser) and then copied into photopolymer for all design wavelengths by holographic recording. Another approach is to copy the diffuser function into photopolymer using a contact copying method. Here, a master diffuser is created by a writing / lithography process (e.g., grayscale lithography, e-beam lithography, or another lithography process). This master is placed in a defined position (usually near contact) toward the VHOE photopolymer film (later replica / copy), allowing the master's optical phase function to be copied into the photopolymer film. This recording process is performed for all design wavelengths (e.g., using a pulsed laser / coherent source with the appropriate pulse dose).

[0053] FIG. 5 shows an example of a non-stochastic micro-optical computational unit cell 500 that can be used to form a diffuser as described herein. FIG. 6 shows an example of a height profile 600 taken along line 502 of the non-stochastic micro-optical computational unit cell 500 of FIG. 5. The height profile 600 can be used with one or more other examples described elsewhere herein. The non-stochastic micro-optical computational unit cell 500 is the smallest unit that does not exhibit any repetition. For example, for a grating, a unit cell is one grating period. The height profile 600 has a non-stochastic pattern of maxima and minima that can make the non-stochastic micro-optical computational unit cell 500 a diffuse, smooth surface. The non-stochastic pattern can be contrasted, for example, with wood grain, which typically has a random / stochastic structure. FIGS. 7A-7B show the same (enlarged) section of area from the unit cell 500 from FIG. 5, examples 700 and 702, respectively, in two different ways to highlight the specified computational surface profile. Examples 700 and 702 each illustrate a different height of a surface. In example 700, the height is illustrated using shading, where light (e.g., white) shading corresponds to a low height (e.g., down to zero) and dark (e.g., black) shading corresponds to a higher height (e.g., up to a maximum). For example, the shape of each of examples 700 and 702 may resemble the shape of a distorted egg container. That is, a hybrid reflective IIS (e.g., hybrid reflective IIS 104) can be characterized by at least i) a field correction term that defines the carrier shape of the hybrid reflective IIS and ii) a diffuser term that defines the surface structure on the hybrid reflective IIS. The surface structure does not have steps, jumps, or edges in both lateral directions. Moreover, the first derivative of the surface height function is continuous.

[0054] 8A-8G show examples of how reflective structures can be calculated and organized. FIG. 8A shows an example of defining a scattering profile in the form of a target eyebox 800. The target eyebox 800 can be defined relative to an area 802. For example, the area 802 can include a coordinate system with axes that define the height and width of the target eyebox 800 at a particular position of the driver, in which case the scattering profile can be calculated in angular coordinates. In another example, the area 802 can include a coordinate system with axes that define the angular spread of the target eyebox 800, indicating the required maximum angle for diffuser spread.

[0055] The reflective surface profile can be defined so that the height difference between the lowest and highest points of the surface profile introduces a phase shift in the reflection that exceeds 2.5 times the longest wavelength used. The lateral extension can be at least about 5 times the longest wavelength used. The structure of the unit cell can be derived by first calculating a starting distribution with a specific wave structure that produces the required angular diffusion of the diffuser, but still has problems with grating effects (which result in color effects).

[0056] FIG. 8B shows an example of a height function 804. The height function 804 uses shading to indicate different heights on a surface. For example, shading 806 can correspond to a high (or low) height, and shading 808, which is different from shading 806, can correspond to a low (or high) height. The height function 804 defines different heights across the surface of a unit cell. For example, the height function 804 can be a starting height function for forming a continuous height profile. The starting distribution can be derived by a specific randomization of a regular pattern. The starting functions are established such that when placed next to each other in any direction, the height profile is still continuous and does not exhibit abrupt steps in the height profile.

[0057] The height function 804 can generate a scattering profile 810, as illustrated in Figure 8C. The scattering profile 810 can indicate the behavior of a grating formed according to the height function 804. For example, the scattering profile 810 can be compared to a target eyebox 800 to assess the light distribution.

[0058] 8D shows an example of a height function 812 that can be obtained after performing a special iterative Fourier transform algorithm (IFTA) on function 804 (as described in U.S. Pat. No. 10,254,449). Height function 804 uses shading to indicate different heights of the surface and differs from height function 804 in various ways. For example, height function 812 can be the final height function in forming a continuous height profile. The final structure provides a uniform scattering distribution.

[0059] The height function 812 can generate a scattering profile 814, as illustrated in Figure 8E. The scattering profile 814 can indicate the behavior of a grating formed according to the height function 812. For example, the scattering profile 814 can be compared to a target eyebox 800 to assess the light distribution.

[0060] Instances of height function 804 and / or height function 812 can be placed next to each other or repeated in multiple directions to form a continuous height profile within the desired diffuser area. The calculated cells can be placed next to each other to form a continuous surface profile. A multiple N of these structures (e.g., N = 1 to 1000) can be calculated using the same interface between cells to enable a continuous height profile without steps when cells are placed next to each other. The arrangement can have any of a number of shapes, including, but not limited to, rectangular or hexagonal. Figure 8F shows an example of a continuous height profile 816 formed by placing instances of height function 804 next to each other. Figure 8G shows an example of a continuous height profile 818 formed by placing instances of height function 812 next to each other.

[0061] 9 shows an example of a diffuser area 900. The diffuser area 900 can be used with one or more other examples described elsewhere herein. The diffuser area 900 can be fabricated using multiple unit cells 902. In some implementations, the unit cells 902 can be arranged in a grid pattern (e.g., in a 4x4 grid as shown, or in another pattern). For example, each of the unit cells 902 can include an instance of the non-stochastic micro-optical computing unit cell 500 in FIG. 5. The unit cells 902 can satisfy periodic boundary conditions.

[0062] 10-11 show examples of diffuser arrangements 1000 and 1100 that can be formed from unit cells. Diffuser arrangement 1000 is here formed from unit cells 1002 that are all identical to one another (i.e., only a single unit cell is used for diffuser arrangement 1000). For example, unit cell 902 in FIG. 9 can be used for each of unit cells 1002.

[0063] The diffuser arrangement 1100 is now formed from unit cells 1102 that are not all identical to one another. Different numbers marked on the unit cells 1102 indicate different types of unit cells. Continuous profiles of the different subcells can be used. For example, profiles can be calculated such that the boundaries are continuous and have no steps.

[0064] 12 shows an example of a diffuser specification 1200 for eyebox size and position. In some implementations, the diffuser specification 1200 may specify a height 1202 and a width 1204. For example, the diffuser specification 1200 may ensure that the eyes of both a tall person 1206 and a short person 1208 fall within the defined eyebox.

[0065] FIG. 13 shows an example of an angular intensity distribution 1300 in the far field for the non-stochastic micro-optical computational unit cell 500 of FIG. 5. The intensity distribution 1300 can be used with one or more other examples described elsewhere herein. The intensity distribution 1300 is shown in a graph, where the horizontal and vertical axes represent angles according to arbitrary units (e.g., degrees). The intensity distribution 1300 uses shading to indicate different light intensities. For example, shading 1302 can correspond to high intensity, and shading 1304, which is different from shading 1302, can correspond to low intensity. For example, the specularly reflected portion of the incident light ray 402 from FIG. 4 can correspond to the center of illumination of the intensity distribution 1300. The intensity distribution 1300 can be generated when light from the PGU 102 is incident on the hybrid reflection IIS 104 in the optical system. The intensity distribution 1300 can be matched to the eyebox 114 (e.g., FIG. 1A) so that the windshield HUD system projects its light to the occupant in the most efficient presentation of image content. Therefore, the surface structure of the unit cells (see, e.g., the multiple unit cells in the achromatic diffuser area 400 in FIG. 4) can be calculated so that the intensity distribution 1300 fits into the eyebox 114 and does not allow a significant amount of light to reside outside of the eyebox. The angular spread of the intensity distribution 1300 can have any shape (e.g., rectangular). Referring to FIG. 1A, the angular spread of the diffuser for a HUD system depends on the magnification of the image on the hybrid reflective IIS 104 relative to the virtual image in the eyebox 114. It can be, for example, 10 to 50 degrees horizontally and 5 to 30 degrees vertically. In some implementations, in the horizontal direction, the intensity distribution 1300 has a spread 1306 of approximately 35 degrees, and in the vertical direction, the intensity distribution 1300 has a spread 1308 of approximately 18 degrees. The diffuser spread can therefore be approximately 35 x 18 degrees.

[0066] 14 shows an example of irradiance 1400 at an eyebox position. The irradiance 1400 is shown in a graph, where the horizontal and vertical axes represent length (e.g., width and height) according to arbitrary units (e.g., mm). The irradiance 1400 uses shading to indicate different light irradiance. For example, shading 1402 can correspond to high irradiance, and shading 1404, which is different from shading 1402, can correspond to low irradiance.

[0067] 15A-15C show example hybrid reflective IISs 1500, 1502, and 1520, respectively. Any or all of the hybrid reflective IISs 1500, 1502, and 1520 can be used with one or more other example hybrid reflective IISs described elsewhere herein. Only a portion of each hybrid reflective IIS 1500, 1502, and 1520 is shown. The curvatures shown are used for illustrative purposes only. Each of the hybrid reflective IISs 1500, 1502, and 1520 is characterized by at least a field correction term and a diffuser term.

[0068] The hybrid reflective IIS 1500 includes a body 1504 and an outer surface 1506. The body 1504 is shaped with a height profile that defines the surface structure of the hybrid reflective IIS. For example, the body 1504 is made of a plastic material or another polymer. In some implementations, the outer surface 1506 can be a high-reflectivity layer. The outer surface 1506 can conform to the shape of the body 1504 and thus present a reflective surface with a height profile. For example, the outer surface 1506 can include a metal coating or a combination of metal and dielectric layers. In the case of an outer surface metal coating, the diffuser structure height profile h R (x,y) can be calculated from the calculated diffuser phase profile ΔΦ(x,y) using:

number

[0069] The hybrid reflective IIS 1502 includes a body 1508, a reflective mirror 1510, and an outer surface 1512. The body 1508 can include a curved substrate (e.g., having a smooth surface). The reflective mirror 1510 includes a reflective material that can be applied onto the body 1508. The outer surface 1512 can include a polymer microstructure on the reflective mirror 1510. For example, the outer surface 1512 can be a structured polymer layer that provides a specific height profile for a transparent computational diffuser. The diffuser structure height profile h in the case of a structured polymer layer on a metal layer can be P (x,y) can be calculated from the calculated diffuser phase profile ΔΦ(x,y) using:

number

[0070] In some implementations, the required optical function can be implemented in a curved or planar holographic volume diffuser film. For example, this can be done by holographic interference lithography or by contact copying an existing diffuser master onto the holographic volume diffuser film. FIG. 15C shows an example of a volume holographic optical element, a hybrid reflective IIS 1520. The hybrid reflective IIS 1520 includes a curved substrate 1522 and a photopolymer film 1524 on the curved substrate 1522. The curved substrate 1522 can include a transparent carrier film. For example, the transparent carrier film can include polycarbonate and / or polyethylene. The hybrid reflective IIS 1520 can include a cover layer 1526 positioned on the photopolymer film 1524 opposite the carrier substrate 1522. For example, the cover layer 1526 can include polyethylene. The contact copying process can be used as a method for mass-producing the hybrid reflective IIS 1520.

[0071] 16A-16B illustrate an example windshield HUD system 1600. The windshield HUD system 1600 can be used with one or more other examples described elsewhere herein. The windshield HUD system 1600 has a housing 1602. For example, the housing 1602 can include a bezel for stray light reduction. The windshield HUD system 1600 can include the PGU 102, the hybrid reflective IIS 104, the mirror 106, the freeform mirror 108, and the cover 110, similar to reference to FIG. 1A or 1C .

[0072] As used throughout this specification, the terms "substantially" and "about" are used to describe and take into account small variations, such as those due to processing variations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. Also, as used herein, indefinite articles such as "a" or "an" mean "at least one."

[0073] It should be understood that all combinations of the foregoing concepts, and additional concepts discussed in more detail below, (provided that such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.

[0074] Although multiple implementations have been described, it will be understood that various modifications may be made without departing from the spirit and scope of the present specification.

[0075] Additionally, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Additionally, other processes may be provided or processes may be eliminated from the described flows, and other components may be added to or deleted from the described systems. Accordingly, other implementations are within the scope of the following claims.

[0076] While certain features of the described implementations have been shown and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It should therefore be understood that the appended claims are intended to cover all such modifications and variations that fall within the scope of these implementations. They have been presented by way of example only, and not limitation, and it should be understood that various changes in form and detail may be made. Except for mutually exclusive combinations, any portions of the apparatus and / or methods described herein may be combined in any combination. The implementations described herein may include various combinations and / or subcombinations of the functions, components, and / or features of the different implementations described.

Claims

1. 1. A windshield head-up display system for a vehicle occupant, the windshield head-up display system comprising: a picture generation unit having a light source, the picture generation unit generating light for the windshield head-up display system in a first light path; a hybrid reflective intermediate image screen characterized by at least i) a field correction term that defines a carrier shape of the hybrid reflective intermediate image screen and ii) a diffuser term that defines a surface structure on the hybrid reflective intermediate image screen, the hybrid reflective intermediate image screen receiving the light from the picture generation unit; and in a second optical path, at least one mirror that receives the light after reflection and diffusion at the hybrid reflective intermediate image screen; wherein the windshield head-up display system is configured such that a windshield of the vehicle receives the light after reflection on the mirror and reflects the light toward the occupant.

2. The windshield head-up display system of claim 1 , wherein the carrier shape of the hybrid reflective intermediate image screen is curved.

3. A windshield head-up display system according to any one of claims 1 to 2, wherein the field correction terms are described as optical freeforms.

4. The windshield head-up display system of claim 3 , wherein the optical freeform is a two-dimensional polynomial function.

5. The windshield head-up display system according to any one of claims 1 to 2, wherein the field correction term is described as a biconic surface function.

6. The windshield head-up display system according to any one of claims 1 to 2, wherein the field correction term is described as a cylindrical surface function.

7. 7. The windshield head-up display system of claim 6, wherein the hybrid reflective intermediate image screen has a radius of curvature of approximately 1000 to 300 millimeters and is convex.

8. A windshield head-up display system according to any one of claims 1 to 2, wherein the field correction term is described by an anamorphic lens function.

9. 3. A windshield head-up display system according to claim 1, wherein the hybrid reflective intermediate image screen has a convex shape facing towards the origin of the first optical path.

10. 3. The windshield head-up display system of claim 1, wherein the surface structures have a total height of at least 2.5 times the longest illumination wavelength used, and a lateral structure size is greater than 5 times the longest illumination wavelength.

11. The windshield head-up display system according to any one of claims 1 to 2, wherein the diffuser term is realized by a deterministic non-probabilistic computational surface according to a specified height profile.

12. 12. The windshield head-up display system of claim 11, wherein the surface structure has no steps, jumps or edges in both lateral directions and the first derivative of the surface height function is continuous.

13. The windshield head-up display system of claim 11 , wherein the surface structure is described by one or more repeating unit cells.

14. The windshield head-up display system of claim 13 , wherein the unit cell is calculated by an iterative Fourier transform algorithm.

15. The windshield head-up display system according to any one of claims 1 to 2, wherein the first optical path intersects with the second optical path.

16. 3. The windshield head-up display system of claim 1, further comprising a second mirror in a third optical path that receives the light after reflection at the first mirror, and at least one of the first mirror or the second mirror is curved.

17. 17. The windshield head-up display system of claim 16, wherein the first mirror is flat and the second mirror is curved.

18. 17. The windshield head-up display system of claim 16, wherein the first mirror faces away from the occupant and the second mirror faces towards the occupant.

19. 17. The windshield head-up display system of claim 16, wherein an origin of the first optical path is located below the first mirror and the second mirror in the z direction of a vehicle coordinate system.

20. 17. The windshield head-up display system of claim 16, wherein an origin of the first optical path is located between the first mirror and the second mirror in the x-direction of a vehicle coordinate system.

21. 17. The windshield head-up display system of claim 16, wherein the second mirror is positioned forward of the first mirror relative to the x-direction of a vehicle coordinate system.

22. 17. The windshield head-up display system of claim 16, further comprising a glare trap positioned between the second mirror and the windshield.

23. 23. The windshield head-up display system of claim 22, wherein the glare trap is formed in part by a transparent polymer cover.

24. 3. A windshield head-up display system according to claim 1, wherein the origin of the first optical path is located below the hybrid reflective intermediate image screen in the z-direction of a vehicle coordinate system.

25. 3. The windshield head-up display system of claim 1, wherein the windshield head-up display system is configured to generate a virtual image for the occupant, the virtual image being positioned approximately 10 to 30 meters from the occupant.

26. 3. The windshield head-up display system of claim 1, wherein a field of view of the windshield head-up display system is specified as a first angle multiplied by a second angle, the first angle being approximately 10 to 20 degrees, and the second angle being approximately 3 to 10 degrees.

27. 3. A windshield head-up display system according to claim 1, wherein the hybrid reflective intermediate image screen is formed by a plurality of unit cells satisfying periodic boundary conditions.

28. A windshield head-up display system according to any one of claims 1 to 2, wherein the hybrid reflective intermediate image screen is formed by a plurality of unit cells that are all identical to one another.

29. A windshield head-up display system according to any one of claims 1 to 2, wherein the hybrid reflective intermediate image screen is formed by a plurality of unit cells that are not all identical to one another.

30. A windshield head-up display system according to any one of claims 1 to 2, wherein the hybrid reflective intermediate image screen comprises a volume holographic polymer element.

31. 31. The windshield head-up display system of claim 30, wherein the volume holographic polymer element comprises a photopolymer film and a carrier substrate.

32. 32. The windshield head-up display system of claim 31, wherein the carrier substrate comprises at least one selected from the group consisting of polycarbonate and polyethylene.

33. 32. The windshield head-up display system of claim 31, further comprising a cover layer positioned on an opposite side of the photopolymer film from where the carrier substrate is positioned.

34. 31. The windshield head-up display system of claim 30, wherein the hybrid reflective intermediate image screen comprises a curved volume holographic polymer element.

35. 31. The windshield head-up display system of claim 30, wherein the hybrid reflective intermediate image screen comprises a planar volume holographic polymer element.

36. A windshield head-up display system according to any one of claims 1 to 2, wherein the hybrid reflective intermediate image screen is formed by greyscale lithography.

37. The windshield head-up display system according to any one of claims 1 to 2, wherein the surface structure is formed in a material selected from the group consisting of polymers or plastics.

38. 38. The windshield head-up display system of claim 37, wherein the material is coated with a reflective layer.

39. 39. The windshield head-up display system of claim 38, wherein the reflective layer comprises a metal.

40. 39. The windshield head-up display system of claim 38, wherein the reflective layer comprises a combination of a metal and a dielectric layer.

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