Hologram manufacturing process

Abstract

This document describes a method and apparatus for testing and / or manufacturing holograms. Specifically, a method for manufacturing and / or testing holograms on a planar or substantially planar substrate or on a cylindrical roller is provided, the method comprising the steps of: generating a target holographic optical element (HOE) based on input geometric parameters and input system parameters; generating a digital master printer control file and test pass / fail criteria; printing a master hologram; testing the master hologram, and if the master hologram passes the test criteria: generating a first witness replica from the master hologram; testing the replica hologram, and if the replica hologram passes the test criteria: mass-producing replica copies on a curved substrate using the master and / or replica holograms.

Description

Technical Field

[0001] This invention relates to apparatus and methods for manufacturing and / or testing and / or characterizing the performance of holograms. More specifically, this invention relates to the manufacturing and / or measurement and / or testing of reflective or transmissive holograms, for example, configured as reflective diffusers or general-purpose reflective holographic optical elements (HOEs). Background Technology

[0002] There is a need in the prior art for a universal process for mass-producing holograms (e.g., reflective holograms) and integrating them into curved glass substrates, such as automotive windshields. By unfolding and mapping the curved hologram surface into a planar substrate for the final application, each point on the hologram can be processed independently. The entire manufacturing process relies on the creation, replication, and testing of a point-by-point digital master of the hologram on the planar substrate. This approach offers flexibility, allowing each new curved hologram design to be produced using the same set of planar substrate manufacturing tools.

[0003] There is a need in the prior art for a testing apparatus to characterize holograms (e.g., reflective holograms). The testing apparatus described in this application aims to capture all relevant diffraction characteristics of transparent display (TD) products. This testing apparatus can be used for process control of reflective hologram manufacturing steps, covering the entire process from digital mastering to subsequent replica holograms.

[0004] An example application of transparent display components includes applying transparent displays to the inner surface of vehicle windshields or embedding them within the windshield itself, thereby providing a display within the windshield itself. A primary advantage of such displays is improved driving safety; because the display can be seen on the windshield surface, the driver can simultaneously see the display and the road outside without looking down at a traditional dashboard, thus avoiding distraction. Another potential application area for transparent displays is for passenger entertainment information displays. The advantage of using transparent displays in this area is that it can reduce motion sickness in passengers. This significantly enhances safety and represents an improvement in overall road safety.

[0005] The application of transparent displays is not limited to car windshields; it can be easily implemented in other scenarios, such as, but not limited to, traditional architectural windows, as well as other vehicle windows, such as side and rear windows. Other applications include turn signals, brake lights, logo projectors—in fact, any scenario requiring holograms to produce beams with clearly defined diffraction angles is suitable.

[0006] The transparent display operates by having a projector generate an image on its surface. The display then redirects (diffuses) the light emitted from the image into a pre-defined "eyebox" for the driver to view. This eyebox represents an adjustable angular space that can be achieved through digital holographic printing technology. The shape of the eyebox can be designed as any polygon or ellipse, depending on the requirements of the final application.

[0007] The light source for a projector can be based on a light-emitting diode (LED) or a laser. Furthermore, transparent display technology is not picky about the type of microdisplay at the core of the projector; for example, digital light processing (DLP), liquid crystal on silicon (LCOS), laser-based microelectromechanical systems (MEMS) scanners, thin-film transistors (TFTs), and micro-LED displays are all applicable.

[0008] By inputting relevant video signals into a projector, transparent displays can be used to display a variety of content, such as movies, video calls, entertainment information, driver information (vehicle speed, direction, etc.). Therefore, transparent display technology combines the advantages of hardware, application, and installation flexibility through holographic technology, and achieves flexibility in displayed content by using standard and readily available projection technology.

[0009] The key requirement of this invention is the need to produce large-sized displays with bright and uniform brightness and color to meet user acceptance. These requirements necessitate a deep understanding of the microscopic details of holograms, which has led the applicant to develop a novel testing instrument for measuring component performance.

[0010] The following abbreviations will be used throughout this application: AOI, Angle of Incidence. CD (Compact Disk); DLP stands for Digital Light Projector. DUT, Device under test; FWHM, Full Width Half Maximum. HOE stands for Holographic Optical Element. HUD, Head-Up Display. LCOS, Liquid Crystal On Silicon. LD stands for Laser diode. LED, Light Emitting Diode. MEMs, Micro Electro-Mechanical Systems. TD stands for Transparent Display; and TFT stands for Thin Film Transistor Liquid Crystal Display.

[0011] US Patent 7,839,547 B2 (Miura et al.) describes a system for ensuring that a holographic printing medium displays an image as intended. That application shows illumination performed at a predetermined angle, while this application allows for the use of an adjustable angle. Furthermore, that patent does not describe an analysis of diffraction efficiency, nor does it measure the angular response.

[0012] US Patent 9,036,153 B1 (Gupta et al.) describes an apparatus and method for measuring the reflectivity of materials, without mentioning or discussing holograms. However, the device under test in that patent is mounted on a rotating support and includes a spherical surface. The integrating sphere in that patent is reflective, while in this application, the integrating sphere is transmissive. Furthermore, the sample dimensions, configuration, and mounting details in that patent are completely different from those in this application.

[0013] Therefore, there is a need in the existing technology to overcome the above problems. Summary of the Invention

[0014] According to a first aspect, a method is provided for manufacturing and / or testing holograms on a planar or substantially planar substrate, or on a cylindrical roller, the method comprising the following steps: Generate a target holographic optical element (HOE) based on the input geometric parameters and the input system parameters; Generate digital printer control files and pass / fail criteria for testing; Print master hologram; The master hologram is tested, and the criteria are defined if the master hologram passes the test: Then, a first witness replica is generated from the master hologram. The hologram of the replica is tested, and the criteria for if the replica hologram passes the test are as follows: Then, the master and / or replica hologram are used to mass-produce replicas on a curved substrate.

[0015] Mass production of replicas on curved substrates using master and / or replica holograms can be performed once, or more than once, or in multiple rounds or generations.

[0016] The method may also include generating a replicator control file and pass / fail criteria for the test.

[0017] This method may also include generating control files and pass / fail criteria for the test.

[0018] To deliver a fully functional and acceptable HOE in the final windshield and achieve high productivity, the following points were found to be crucial: - Manufacturing and testing systems are performed on a planar or near-planar (or cylindrical roller-like) substrate, and mastering and testing are carried out on a point-by-point (e.g., pixel-by-pixel) basis.

[0019] The curvature applied at the end is used to create control files for the mastering, copying, and testing systems. These control files are based on a point-to-point (pixel-to-pixel) basis, adjusting the recorded laser beam angle and test angle of the processed HOE.

[0020] The flexibility of the HOE testing system is crucial for providing performance feedback at every stage of the HOE manufacturing process, providing pass / fail criteria for each mastering and replication stage before mass production. At the initial stage of process design, digital device control files are created for digital printers, replicators, and testers to control mastering, replication, and testing angles and wavelengths of the master and replica holograms. These files include pass / fail criteria controlling diffraction efficiency, diffraction angle, and diffraction eyebox size, all customized for planar test substrates.

[0021] The substrate of the plane or substantially plane can be a flat or substantially flat planar structure.

[0022] The cylindrical roller can rotate about a mechanical axis, and an unexposed photopolymer layer is wound onto the cylindrical roller. Within the range of an extremely fine replica laser beam, the surface of the roller is virtually flat.

[0023] The copy is made by the master and / or replicated onto a curved substrate, which may be concave or convex.

[0024] The input geometric parameters can be at least one of the following or any combination thereof: windshield curvature; projector position; transparent display size; eye box position and size; and / or windshield composition.

[0025] Holograms can be composed of patterned diffusers of image shape, and when illuminated by a simple LED light source, the image can be viewed in an eye box.

[0026] Tests can be conducted on a point-by-point or pixel-by-pixel basis.

[0027] The substrate curvature of the final replica can be used to create at least one or more control files, which can be used to record the beam angle and test angle of the processed HOE.

[0028] The input system parameters can be at least one of the following or any combination thereof: target display brightness value; projector lumen output; and / or projector light source spectrum.

[0029] Holograms can be either reflection holograms or transmission holograms.

[0030] If the master hologram fails the test criteria, it can be reprinted and the test repeated. This test may include feedback to the master hologram production or the creation of a copy.

[0031] If the replica hologram fails to meet the test criteria, it can be regenerated from the master hologram and the test repeated.

[0032] According to another aspect, an apparatus for manufacturing and / or testing holograms is provided, the apparatus comprising: A substrate containing the holographic optical element (HOE) to be tested. A light source is used to provide an illumination area on the holographic optical element (HOE) under test, wherein the light source is disposed spaced apart from the substrate and can be moved relative to the substrate to control the incident position and incident angle of the illumination area on the holographic optical element (HOE) under test; The optics are collected to capture images of the illumination area of ​​the holographic optical element (HOE) under test and to capture the angular range and / or shape of the diffractive eyebox, wherein the collected optics can be repositioned to various angular locations to represent a range of final eyebox positions; and An optical integrator, comprising an entrance aperture, an illumination area, and a spectrometer, is connected to the optical integrator to measure the transmission spectrum of a holographic optical element (HOE) under test.

[0033] An angular range can be defined as the angular dimensions of an object; in this case, it could be the dimensions of the eye box.

[0034] The entrance aperture can be located near the illumination area of ​​the holographic optical element (HOE) to allow light to enter the light integration device.

[0035] The light source can be a collimated light source. It can originate from a laser, LED, or halogen bulb. The light source can emit white light, or any other color or wavelength. There are no limitations on the wavelength range; the light source can also be infrared or near-infrared light. The light source can be any wavelength of light.

[0036] Holographic optical elements (HOEs) can be transparent and / or transmissive displays, or reflective holographic optical elements (HOEs).

[0037] The light source can be mounted on a multi-axis robotic arm.

[0038] The robotic arm can be a 6-axis robotic arm.

[0039] The collecting optical device may include a detection device, which may include multiple cameras.

[0040] The substrate can be translated in the horizontal and / or vertical planes to allow the illuminated area to move relative to the holographic optical element (HOE) under test. Alternatively, the test equipment and light source can be translated while the HOE remains stationary, thus creating the same relative movement between the illuminated area and the HOE.

[0041] The illuminated area can be a spot of light.

[0042] The substrate can be a substantially flat glass plate onto which the holographic optical element (HOE) can be laminated. Alternatively, the holographic optical element can be an inherent component of the substrate (just as music is an inherent component of a CD).

[0043] The collecting optics can be repositioned to various angular locations to represent a series of final eyebox positions.

[0044] An optical integrator can be an optical integrator sphere.

[0045] In another aspect, a method for manufacturing holograms is provided, the method comprising the following steps: Generate a target holographic optical element (HOE) based on the input geometric parameters and the input system parameters; Generate digital printer control files and pass / fail criteria for testing; Print master hologram; The master hologram is tested, and the criteria are defined if the master hologram passes the test: Generate and copy device control files and the pass / fail criteria for testing; The first witness replica was generated from the master hologram; The hologram of the replica is tested, and the criteria for if the replica hologram passes the test are as follows: This master hologram is used to mass-produce replicas.

[0046] It should be noted that in the above method, the master hologram can be used to produce multiple generations of replicas.

[0047] The input geometric parameters can be at least one of the following or any combination thereof: windshield curvature; projector position; transparent display size and / or eye box position and size. The input geometric parameters can be any other parameters related to the geometry of the device under test. For example, the input geometric parameters can include windshield composition data, such as glass type—clear, light green, medium green, dark green, etc.; glass thickness; any glass coatings; additional intermediate layers.

[0048] The input system parameters can be at least one of the following or any combination thereof: target display brightness value; projector lumen output; and / or projector light source spectrum. Other input system parameters that are obvious to those skilled in the art may also be included.

[0049] Holograms can be reflective and / or transmissive. Any type of hologram can be tested using the aforementioned apparatus and methods.

[0050] If the master hologram fails the test criteria, it can be reprinted and the test repeated. This step can be repeated until a suitable master is produced. The test may include feedback for master creation or replication.

[0051] If the replica hologram fails the test criteria, it can be regenerated from the master hologram and the test repeated. This step can be repeated until a suitable replica hologram is produced. The test may include creating a master hologram or providing feedback on the replication process.

[0052] The aforementioned device can be used to perform tests on the master hologram.

[0053] In another aspect, a method is provided for manufacturing and / or testing and / or characterizing the performance of a holographic optical element (HOE) using any of the foregoing apparatus, the method comprising: The illumination area is moved point by point to a unique location on the hologram under test, thereby analyzing the entire hologram.

[0054] The method described above can also be applied to a subset of the complete measurement scan, i.e., measuring a specific region of interest. This is particularly useful when only a portion of the HOE needs to be analyzed.

[0055] Holograms can be reflective or transmissive.

[0056] Each time the illumination area is moved, the collecting optics can rotate accordingly to precisely capture the image of the holographic optical element (HOE).

[0057] The illumination area can be moved relative to the holographic optical element (HOE) by moving the substrate containing the holographic optical element (HOE) in both horizontal and vertical planes. Alternatively, the illumination area can be moved only in any direction in the vertical plane.

[0058] This invention relates to reflective holograms configured as diffuser elements (TDs) or more generally holographic elements (HOEs). The invention also relates to an apparatus for characterizing the performance of such holograms.

[0059] The advantages of this testing device include the ability to simultaneously capture all TD characteristics related to manufacturing process control, specifically: the diffraction efficiency of red, green, and blue light and their corresponding peak wavelengths; the full width at half maximum (FWHM) spectral bandwidth of the diffracted light; the shape of the eye box and the angular distribution of the diffracted light; and the near-field pixel "fill factor" image of the monochrome hologram pixels generated by the digital hologram printer.

[0060] The device can examine one illuminated area (e.g., an illumination spot) on a hologram at a time and can scan the entire surface of the component to construct a two-dimensional image of, for example, the performance of the hologram.

[0061] Some end applications require transparent displays to be applied to composite curved surfaces. Typically, the manufacturing process uses a planar substrate, meaning that mastering, replication, and testing processes are all performed on a planar substrate.

[0062] Because testing is performed by scanning the entire hologram surface, it provides a local "prescription file" that takes into account any curvature in the final application. Therefore, the hologram can be printed, replicated, and tested on a planar substrate before being applied to the final surface required for the application.

[0063] The test instrument can also be reconfigured to allow testing of a wide range of geometric parameters represented by the projector position and eyebox position relative to the TD component. The flexible robotically positioned illumination source allows it to represent angles from 0 degrees to approximately 80 degrees relative to the hologram surface normal. o The projector angle of incidence (AOI) is within the range. Furthermore, the optics of the eyebox collection module can be repositioned to accommodate a wide variety of system geometric requirements.

[0064] In another aspect, the holographic testing device may include: Collimated broadband "white" light source produced by, for example, a "halogen" light bulb; The collimated light source can be mounted on a 6-axis robotic arm, thereby giving complete control over the position and angle of incidence of the illumination spot on the hologram; The reflective holographic element under test can be a transparent display (TD) or a reflective HOE; A set of displacement stages for moving the hologram under test so that the hologram can be inspected point by point; A set of independent collecting optics and cameras is used to capture digitally printed holographic pixel images, as well as the angular range and shape of the eyebox diffracted by the holographic elements; The collecting optics can also be repositioned to various angular locations to represent a wide range of final application eyebox locations; and / or The combination of an integrating sphere and a spectrometer can be used to measure the transmission spectrum of a hologram. The transmission spectrum can then be converted into the diffraction spectrum present at the eyebox.

[0065] Various novel features of the present invention will now be discussed, and these features may be applied to any of the features discussed in this application.

[0066] The robotic arm positions the illumination source, enabling 6-axis positioning of the collimated light source. This means the robotic arm can move freely in three spatial coordinates and three angular coordinates. This allows the system to illuminate the hologram from any point and at any angle.

[0067] This robotic arm positioning also enables dynamic adjustment of lighting across the entire hologram, i.e., spatially varying lighting during measurement. Because the robotic arm has six free axes, the device's operation is not limited in any way; for example, it is not confined to a specific plane, around a spatial axis, or at a single point.

[0068] For large holograms, it is essential to ensure that a set, calibrated distance (i.e., "light source distance") is maintained between the illumination source and the DUT plane. It is also crucial to ensure that the angles are calibrated. The applicant has developed the necessary calibration techniques to ensure that the light source distance is maintained and the angles are calibrated, thereby guaranteeing that all parts of the hologram receive proper illumination.

[0069] The illuminated area (e.g., the illumination spot) may typically be much smaller than the complete hologram. This allows the entire DUT to be measured in blocks according to the "prescription file." This is a feature not available in the prior art, but it allows the system to scan DUTs of various sizes accurately and efficiently.

[0070] The DUT can be a reflective diffuse hologram used in transparent display (TD) applications. These holograms can be extremely large. Each hologram pixel is individually programmed to optimally redirect light from the projector onto the entire eyepiece. The hologram is not "attached" to the medium; it is an inherent component of the photopolymer film structure, just as music is an inherent component of a CD.

[0071] The DUT is considered a planar stacked structure, but it will typically be applied / used in curved geometries. Simply put, it's flat for evaluation but curved for use. This needs to be taken into account in practical applications.

[0072] Similarly, when the application uses a replica copied from the master, the hologram used may be of a different generation than the one used in the final application; for example, the master is being measured. This must also be taken into account when determining the pass / fail criteria for this section.

[0073] The device under test (DUT) can be a transparent photopolymer, attached to a transparent substrate to adhere to a transparent carrier (e.g., glass), and secured by a test frame. The entire DUT can be a rigid planar stacked structure.

[0074] Reference markers can be placed on the DUT. Therefore, consistency between measurement results and actual world application usage can be achieved. This process can be automated to account for differences between any parts or measurements.

[0075] This invention can also measure diffraction efficiency in the transmission state. This can be achieved by using an integrating sphere with a large angular range to collect the transmitted light (i.e., it has a wide tolerance for illumination angles), meaning the transmitted light detector can be fixed in one position. This simplifies the system mechanically. The effect is that the hologram can be measured by observing how much light from the transmitted source is "missing" in the transmission due to diffraction. These measurements can be compared with reference specifications as a pass / fail standard.

[0076] Based on the recorded images, measure the center angle and angular range of the eyebox (reflected diffracted light). This can be compared with reference specifications as a pass / fail standard.

[0077] The near-field behavior of hologram pixels is reported as a pixel “fill factor,” encompassing all red / green / blue components in the vertical and / or horizontal directions of the print. This is closely related to the final diffraction efficiency. This can be compared to a reference specification as a pass / fail criterion.

[0078] Other benefits and advantages of this invention are listed below. The hologram in this invention can be integrated inside a photopolymer, such as Bayfol (registered trademark) photopolymer. Illumination can be implemented at any adjustable angle. This invention uses a single light source. In this invention, diffraction efficiency and angular response can both be measured and verified.

[0079] The embodiments described herein will be better understood in conjunction with the following description.

[0080] Illustrative examples are provided on the following pages. Attached Figure Description

[0081] Embodiments of the invention will now be described by way of example only, with reference to the following figures: Figure 1 An overview of an example system according to an embodiment of the present invention is shown; Figure 2 A method flowchart according to an embodiment of the present invention is shown; Figure 3 This illustrates the concept of compensating for holographic curvature during manufacturing and testing steps using a method according to an embodiment of the invention; Figure 4 Examples of the range of motion and angles of various subsystems within a test system according to an embodiment of the present invention are shown; Figure 5 The components of a hologram testing apparatus according to an embodiment of the present invention are shown; Figure 6 , Figure 7 and Figure 10 An example hologram dataset collected by an example test device according to an embodiment of the present invention is shown; Figure 8 Another configuration of HOE (603) in a head-up display (HUD) application is shown, which can also be tested through embodiments of the present invention; Figure 9 This illustrates another advantage of embodiments of the present invention; Figure 11 shows an example of a prior art method; Figure 12 Compensation for non-uniform intensity or color variations in image projection units is shown; Figure 13 This demonstrates the process of directly recording a reflection hologram onto an unexposed photopolymer using a large laser beam; Figure 14 An example of digitally printed pixels is shown; Figure 15 The overall manufacturing process is shown; Figure 16 A holographic replication method using a rotating drum is shown; and Figure 17 The equivalent flat-panel holographic replication process is shown. Detailed Implementation

[0082] This invention relates to the use of a testing system to measure the performance of holographic elements at various stages of the manufacturing process, such as digital mastering and replication.

[0083] This testing system is used to verify each step of the manufacturing process. The manufacturing process flow is as follows: Figure 2 A more detailed demonstration was provided in the text.

[0084] Figure 1 One application of transparent display (TD) holograms is shown, and the various components of the system are labeled. Figure 1 A hologram (103) of a TD is shown, illuminated by a projection light source (101), and an image (104) is formed on its surface.

[0085] An example ray (102) falls on a specific location on the surface of the TD (103), and each location of the TD scatters / diffracts the ray into a set of multiple rays (107), thus forming a unique eyebox shape (105) that conforms to the final application specification (204). The eyebox (105) represents a unique solid angle scattering cone emanating from each location of the TD (103). If an observer (106) places both eyes (or at least one eye) within the solid angle range of the eyebox (105), the image (104) will be visible. Once the observer (106) moves out of the eyebox (105) range, the image (104) will be invisible.

[0086] Figure 2 The manufacturing process for holographic digital printing, replication, and testing at each stage is illustrated, and it is shown that at the start of the process (201), the required input geometric parameters (202) and other system performance parameters (203) are needed to generate the application-specific holographic optical element (HOE) specifications (204). The input geometric parameters (202) may include windshield curvature, projector position / location, TD display size, and the position and size of the eye box.

[0087] According to this specification (204), machine control files (205) for all digital printers, copiers, and testers can be generated for the “planar” substrate manufacturing process. Since the digital printing process is a pixel-based process and each pixel is uniquely designed, any curvature of the final application design substrate can be compensated for at this stage for printing on the planar substrate.

[0088] The next stage is to print the master hologram pixel by pixel (213), where the angle of any recording laser beam is modulated as the hologram is recorded into a photopolymer material (such as Covestro's Bayfol (registered trademark)).

[0089] Subsequently, the entire surface of the master hologram is scanned and tested (206) to verify whether it meets the pass / fail criteria (205). Once passed, the master hologram (213) will be used to create a witness holographic copy using a replication device (207), which will again be used to verify (209) that the holographic replication device is set up correctly before mass production of the replica copy (211) is initiated.

[0090] To reiterate, testing equipment is crucial for the successful mass production of holographic components.

[0091] Figure 3 The concept of compensating for holographic curvature during the manufacturing and testing steps is demonstrated. The advantage of this testing system is that it can simultaneously measure digitally printed master holograms (213) and any witness replicas (207) or subsequent generations of replicas on a planar substrate on a point-by-point basis.

[0092] Each point on the hologram (e.g., point (308)) has a unique illumination ray (306) from the projector and a diffracted ray (307) pointing towards the center of the eyebox (105). The surface normal (305) at point (308) is defined by the curvature of the substrate (304) (e.g., a car windshield). The illumination AOI (301) and diffraction angle (302) are unique to that point (308) on the TD. These angles (301, 302) are reproduced in digital printing, replication, and testing apparatus, but all on a planar glass substrate (303) and point-by-point across the entire surface. In effect, the curved surface and the surface normal of each pixel are unfolded onto the planar substrate for hologram fabrication. Note that although Figure 3 The diagrams are presented in two dimensions, but it is obvious that the angle can be extended to three-dimensional space.

[0093] Figure 4 A range of motion and angles of the various subsystems within the testing system are demonstrated. Holographic elements (409) are laminated onto a planar glass substrate (408). For point-by-point scanning, the glass substrate (408) is mounted on a displacement stage that can move in both horizontal and vertical directions.

[0094] An illumination source is mounted on a robotic arm, such as a multi-axis robotic arm (e.g., a 6-axis robotic arm) (402), allowing illumination of a point at the AOI (301) required for the final application. The robotic arm (402) adjusts the AOI as the entire surface of the HOE (409) is scanned. The final range of motion required by the testing system is the final range of motion of the collecting optics (413), which is responsible for imaging the light diffracted by the hologram.

[0095] The collecting optics (413) has a limited optical aperture that needs to be rotated to capture the diffracted beam (307) at the diffraction angle (302). The collecting optics includes a beam splitter (412) that allows light to be transmitted to a camera (415) and reflected by the camera (406) to the diffraction eyebox. The aperture of the collecting optics (307) is large enough to capture the full range of angles represented by the design of a particular eyebox (105), and this range of angles is generated across the entire surface of the HOE (409) as the point-by-point scan proceeds.

[0096] Figure 5 Details of the hologram tester components of this application are shown. A point (410) on the hologram (409) is illuminated. The illumination consists of a broadband light source (401), such as a halogen bulb or a multi-wavelength LED system. The light is coupled into a flexible multimode fiber optic cable (407), which transmits the light to the mounting head of a multi-axis robotic arm (402).

[0097] The output aperture of the fiber optic cable is then re-imaged (405) onto the holographic spot (410) under test. Thus, light from the light source (401) is transmitted from the fiber optic cable (407) at the lower left corner of the image to the upper right corner, and illuminates the holographic spot (410) under test there.

[0098] As the tester substrate (408) moves to scan the entire surface of the hologram (409), the robotic arm (402) adjusts the AOI of the illumination beam (405) to follow the projector beam AOI (301) required by the application specifications (204) and the tester control document (205).

[0099] Please note that, although Figure 5 The diagrams are presented in two dimensions, but it is obvious that the angle can be extended to three-dimensional space.

[0100] Another subsystem of the testing apparatus is represented by the collecting optics (413). The collecting optics uses a camera (415) to image the digitally printed pixels of the test point (410) and a camera (406) to image the solid angle of the diffraction eyebox.

[0101] The final subsystem of the test apparatus is shown as a combination of an integrating sphere (402) with an entrance aperture (414), a spectrometer (403), and an optical fiber cable (404) that samples light from within the integrating sphere and provides it to the spectrometer (403). This spectrometer system allows for the measurement of the transmission spectrum of the hologram (409) within the bandwidth of a broadband light source (401).

[0102] Figure 6 , Figure 7 and Figure 10 A more detailed description of the data captured by the testing device is shown.

[0103] At each measured point (410), a color image (801) of the digitally printed pixel is captured by a camera (405). The pixel “fill factor” of each color (typically red, green, and blue) of the reflective hologram is recorded. The goal is usually to maximize the “fill factor” of the hologram pixels, and any pixels below the manufacturing quality pass / fail threshold are recorded and used to optimize the digital printer settings.

[0104] The collecting optics (413) also uses a camera (406) to record color images (802) of the eye box. The eye box images (802) are angularly calibrated to measure the angular range and shape of the generated eye box (105), and then compared with the design pass / fail criteria (205) of the hologram under test.

[0105] A spectrometer (403) provides additional testing information by comparing the light transmitted from the HOE (409) at point (410) with the spectrum of the illumination light (405). The spectrum of the HOE diffraction (707) can then be calculated and compared again with the design pass / fail standard (205). This diffraction spectrum (707) typically consists of multiple spectral peaks, usually a red peak (706), a green peak (705), and a blue peak (704), which are matched to the spectrum of the light source of the projector (101) in the final application.

[0106] The hologram (409) may be designed to produce only one diffraction peak for a monochromatic element, but in any given design, there may be two, three or more independent peaks. The testing setup determines the peak diffraction efficiency (702), center wavelength (703), and full width at half maximum (FWHM) (701) for each independent spectral component of the HOE.

[0107] Figure 8 Another configuration of the holographic element HOE (603) in a head-up display (HUD) application is shown, which can also be tested using the present invention. Figure 8A picture generation unit (PGU) (601) is shown, where an image (603) is generated on its output surface. In this configuration, the image is not formed on the surface of the HOE element; the HOE acts as an optical mirror, both reflecting light from the PGU and generating a magnified virtual image (602), which an observer (106) can view at a distance from the HOE surface. Essentially, each point of the HOE (603) diffracts unique light rays from the PGU (601). This is consistent with... Figure 1 Unlike the previously described TD component (103), in which each point of the TD scatters a set of light rays to form its eyebox (105).

[0108] The invention described in this application can measure and evaluate both types of holographic elements, namely TD (103) and HOE (603). TD is a specific example of a general HOE.

[0109] It will be apparent to those skilled in the art that the constructed virtual image (602) can be used in various applications, such as in road vehicles. In this case, the HOE (603) can be the vehicle's windshield, so the virtual image (602) can be projected into the driver's field of vision, appearing in front of the vehicle. From a safety perspective, this is highly beneficial because the driver can see important information without having to take their eyes off the road ahead.

[0110] Figure 9 Another advantage of this testing system is outlined. The testing system must be flexible enough to measure the position of the projector (101) and the position of the eyebox (105) relative to the hologram (103) design with a wide range.

[0111] The extreme AOI (902) of the illumination beam from the projector (102) can range from approximately 0 degrees to 80 degrees. Therefore, the robotic arm (402) of the tester must be able to cover this AOI range of the illumination beam (405). Furthermore, the extreme diffraction angle (901) of the eyebox (105) generated by the light (107) can also range from 0 degrees to approximately 80 degrees. Therefore, the angular position of the collecting optics module (413) must be adjusted according to each hologram geometry provided in the HOE specification (205).

[0112] Examples of prior art recording holographic elements in laminated automotive glass can be found in U.S. Patent Application Publication No. US20210373492A1, "Laminated Holographic Display and Manufacturing Thereof." Paragraphs 0016 to 0019 are particularly noteworthy. Figure 1 The existing technology Figure 1 and Figure 2It has been incorporated into Figure 11 of this application.

[0113] This application describes a manufacturing process in which an unrecorded photopolymer film is placed between two glass layers of an automotive windshield. The subsequent hologram is recorded using a conventional two-beam laser simulation interferometry method. Because the recording beams are very large, covering the entire hologram, this method has the following limitations: 1. The centers of the two recording beams will experience natural Gaussian intensity attenuation, resulting in non-uniform diffraction efficiency curves in the recorded hologram. In final applications, this manifests as a gradual decrease in brightness towards the edges of the hologram (see this application). Figure 13 Simply put, an uneven recording beam will produce an uneven display product.

[0114] 2. The complete assembly and lamination of the windshield must be carried out under dark conditions to avoid premature exposure of the photopolymer layer. This is extremely difficult to achieve on a windshield manufacturing site.

[0115] 3. Holographic recording requires a minimum laser energy density (joules / cm²) to initiate the fringe recording process. As the laser beam expands to cover the holographic area (e.g., 30 cm x 15 cm), the illuminance (watts / cm²) naturally decreases. Therefore, to achieve the desired target laser energy density, the holographic exposure time will be between approximately 10 seconds and several minutes. During this period, maintaining the stability of the laser fringes between the two interfering beams is extremely difficult, again leading to a reduction in holographic diffraction efficiency. Any windshield manufacturing site will require stations capable of minimizing arbitrary vibrations in an attempt to stabilize the laser fringes during holographic recording. This will be a low-yield process during manufacturing, resulting in a significant increase in cost.

[0116] In contrast, the applicant used digital holographic pixel recording, in which the entire laser beam is focused within an area of ​​approximately 0.25 square millimeters, resulting in higher illuminance and reducing the exposure time required to form the pixel hologram to less than 1 millisecond (see [link to relevant documentation]). Figure 14 When the exposure time is less than 1 millisecond, stripe stability and holographic recording are relatively easy to control. Furthermore, the applicant's method involves manufacturing and mass-producing holograms before integrating them into any windshield, with only qualified holograms used for subsequent windshield lamination.

[0117] 4. This holographic recording system, covering the entire HOE area, requires a custom set of optics to switch from one vehicle / HOE combination design to another. Each new design requires expensive, large, custom optics (comparable in size to the HOE) to record the HOE. This is extremely slow, costly, and impractical.

[0118] Some advantages of the system and method according to the present invention are now presented.

[0119] The aforementioned prior art methods attempt to directly record holograms onto a curved windshield without image quality loss. However, as mentioned above, this is a low-yield and high-cost method.

[0120] The digital holographic printing, copying, and manufacturing process employed by the applicant is a more robust method for mass production of holograms on curved windshields with high yield.

[0121] The entire manufacturing process is based on using a planar glass substrate to record, replicate, and test holograms. Figure 15 This "fixed" and stable hologram is only introduced into the lamination process of the curved windshield in the final step. The windshield lamination plant does not require dark conditions or vibration-free analog recording equipment because the hologram has already been fabricated and is provided as a fixed photopolymer layer on a stable and flexible carrier substrate.

[0122] Other advantages of digital printing technology include: 1. The entire process is software-controlled. The same set of printer tools is used for each new hologram design for each vehicle. The only change is the printer control file, which adjusts the incident angle of the two interference beams recorded at each pixel position of the hologram.

[0123] 2. The maximum size of the hologram is scalable, limited only by the travel range of a two-dimensional displacement stage used to move a planar glass substrate to the coverage area of ​​the hologram.

[0124] 3. No need for expensive and time-consuming large custom optics. The digital printing process can be quickly reconfigured by adjusting the software and then the pixel printing control file, making it a completely digital process from the vehicle design CAD file that defines the HOE (House of Image) in the car to the digital printing control file.

[0125] 4. Most vehicle windshields produced today contain composite curvatures that can vary across the windshield surface. Simulation methods described in the prior art attempt to compensate for this curvature or freeform shape by directly simulating and recording holograms into an unexposed photopolymer laminated within the curved windshield. Digital printing processes, with their flexible angle control, allow for the printing of holograms on a flat glass substrate while maintaining the angular relationship between the two hologram recording beams and the glass normal, thus meeting the requirements of the final curved windshield application.

[0126] 5. The diffraction efficiency (or grayscale) of each pixel can be locally controlled, for example, by adjusting the energy density, which can be achieved by changing the laser power at the pixel or by adjusting the pixel exposure time. In this way, defects in the final projector used to illuminate the HOE in the vehicle can be compensated for, such as intensity attenuation or red / green / blue color variations in the projected image. Controlling the relative diffraction efficiency of the red, green, and blue HOEs at each pixel can be used to compensate for such defects. In this way, the final image seen by the driver can achieve uniform brightness and color across the entire HOE surface.

[0127] 6. Multiple HOE masters can be recorded on a single photopolymer film. Each HOE represents a transparent display (TD), illuminated by its own independent projector image. Different areas can also be printed with fixed image symbols and scenes, requiring only simple light source illumination to display the image to the driver. Digital printing technology allows for the mosaic and splicing of such different elemental HOEs within the same photopolymer film.

[0128] As previously mentioned, the master hologram printed on a planar glass substrate is then used to produce mass-produced HOEs. Unexposed layers are laminated onto the master, whether on a planar substrate or on roll-to-roll rollers. The master can be replicated in several ways. For example, a laser line can be swept across the entire laminated (master / original photopolymer) surface, thereby creating a replica of the HOE in the original film. Since laser line replication is aligned top-down along the axis of any roller in roll-to-roll replication, it is equivalent to the planar substrate replication method.

[0129] The key to producing a fully functional and acceptable HOE in the final windshield and achieving high yield lies in: - The manufacturing and testing system is completed on a planar (or equivalent cylindrical roller) substrate, and the mastering and testing are carried out on a point-by-point (pixel-by-pixel) basis.

[0130] The curvature applied at the end is used to create control files for the mastering, copying, and testing systems. These control files adjust the recorded laser beam angle and test angle of the processed HOE on a point-by-point (pixel-by-pixel) basis.

[0131] The flexibility of the HOE testing system is crucial, providing performance feedback at every stage of the HOE manufacturing process and offering pass / fail criteria for each mastering and replication stage before mass production. At the start of the design process, digital control files are created for the digital printer and testers to control the test angles and wavelengths of the master and replica holograms, including pass / fail criteria for diffraction efficiency, diffraction angle, and diffraction eyebox size—all tailored to the planar test substrate.

[0132] A simplified description of the manufacturing process using holographic digital mastering and replication equipment is as follows: Figure 14 and Figure 15 As shown in these figures, the incident angles of the two recording beams (1405 and 1406) remain constant throughout the fabrication process at a specific pixel location (1402). However, it is well known in the field of holography that these angles vary during the fabrication process and depend on the following parameters: - The laser wavelength used to create master holograms and replica holograms.

[0133] - The peak wavelength of the final replica hologram created (this wavelength is expected to match the light source wavelength of the projection unit that generates the main image on the hologram surface).

[0134] - Any shrinkage of the photopolymer during holographic recording.

[0135] The key point is that the incident angle 1406 from the projector and the angle entering the diffraction eyebox 1405 meet design requirements when integrated into the curved windshield of the application. These values ​​are unique for each printed pixel position on the hologram. Furthermore, the central peak of the diffraction spectrum must match the dominant wavelength of the projector, regardless of whether the projector is an LED, laser, or other light source.

[0136] Figure 11 illustrates an example of a prior art method that directly laser-holographically records HOE display elements onto a previously unexposed photopolymer layer, which is then laminated into the windshield.

[0137] Figure 12 Compensation for non-uniform intensity or color variation 1201 in image projection unit 1202 is shown. The diffraction efficiency of the multiplexed red, green, and blue holograms 1203 can be adjusted at each pixel location 1402. The final improved display brightness uniformity 1204 observed by the driver is the result of the combined effect of projector intensity and compensated hologram efficiency.

[0138] Figure 13 This illustrates the direct recording of a reflection hologram onto an unexposed laser beam of an optical polymer 1302, simulated by a large laser beam. The optical polymer 1302 is laminated between two glass shells 1301 and 1303 of an automotive windshield. The significant variations in the intensity of the two laser beams on the surface of the holographic element are represented by 1304 and 1305, highlighting the difficulty of achieving uniform diffraction efficiency on a large-area hologram.

[0139] Figure 14An example of a digitally printed pixel 1402 is shown. The size diameter of pixel 1402 can range from 0.1 mm to 10 mm. An unexposed photopolymer layer 1302 is laminated onto a planar glass substrate 1401. Two recording laser beams (1404 and 1403) are focused into the tiny pixel region 1402, and their corresponding incident angles (1405 and 1406) are controlled by the printer's optomechanical mechanism to match the desired application design.

[0140] As the pixels of the printing process move on the HOE surface, the intensity and / or exposure time of the two recording beams 1404 and 1403 can be adjusted to compensate for any defects in the HOE or the final projector, i.e., to adjust the local diffraction efficiency of any multiplexed red, green, and blue holograms.

[0141] Figure 15 An overall manufacturing process according to an example of the present invention is described.

[0142] Step 1 (1501): Hologram Design: Design is performed for each pixel 1502 on the entire curved hologram surface 1503, and digital printing, copying, and testing control files are created for their respective devices. The angle of incidence at each pixel is determined by the beam from the projector 1504 and the angle pointing towards the eye box 1505 relative to the local windshield normal direction 1508.

[0143] Step 2 (1507): The original curved surface 1503 is unfolded onto a flat surface 1506, preparing it for the digital printing process. At each pixel location, the design AOI (1405, 1406) is maintained relative to the surface normal.

[0144] Step 3 (1509): The master hologram is now tested using the HOE testing system. The tester examines the two AOIs (1405, 1406) on the hologram surface pixel by pixel (1502), as well as the diffraction efficiency spectrum and peak efficiency. Again, this is performed on a planar glass substrate (1506).

[0145] Step 4 (1510): Using the original unexposed photopolymer film laminated onto the surface of the master HOE, multiple copies are generated by using a digitally printed master hologram. Again, the replication is achieved on a planar or roller surface 1506.

[0146] Step 5 (1511): Now evaluate the performance of the replicated HOE using the HOE test system, also using the planar substrate 1506.

[0147] Step 6 (1512): The final step is to laminate the exposed HOE replica between the curved glass shells (1301, 1303) of the windshield to conform to the curved profile of the original design 1503.

[0148] Figure 16 A hologram replication method using a rotating roller 1601 is illustrated. This allows for the creation of multiple copies of a master hologram using a roll-to-roll process. A digitally printed master hologram 1602, generated using process 1507, is wrapped around the outside of roller 1601.

[0149] Next, a layer of unexposed holographic photopolymer material 1603 is laminated onto the master hologram 1602. A linear laser line 1604 is generated using an incident laser beam 1608 and a scanning mirror system 1605, and this line illuminates the master hologram 1602 and the unexposed photopolymer layer 1603. The master hologram 1602 diffracts the incident laser line 1604, generating a beam 1606 that creates the eyebox 1607. Subsequently, two interfering laser beams 1604 and 1606 record a copy of the master hologram into the photopolymer layer 1603.

[0150] It is important to emphasize that the illumination laser line 1604 is substantially parallel to the mechanical axis 1609 of the roller. In this way, the line illumination of the master hologram 1603 and the copy 1603 is equivalent to a flatbed replication process. Figure 17 This means that the laser scanning line appears to be illuminating a planar substrate.

[0151] Figure 17 An equivalent planar holographic replication process is illustrated. Both the master hologram 1602 and the replica hologram 1603 are laminated onto a planar substrate 1701. Again, a laser scanning line 1604 sweeps across the hologram stack via a linear translation of the planar substrate 1701, which is equivalent to a replication process using a rotating drum 1601.

[0152] Any feature in any embodiment may be combined with any embodiment shown in any way.

[0153] Although specific embodiments of the present invention have been described above, it should be understood that modifications to the described embodiments may still fall within the protection scope of the present invention.

Claims

1. A method for manufacturing and / or testing holograms on a planar or substantially planar substrate or on a cylindrical roller, the method comprising the following steps: Generate a target holographic optical element (HOE) based on input geometric parameters and input system parameters; Generate digital printer control files and test pass / fail criteria; Print master hologram; The master hologram is tested, and the criteria for the master hologram to pass the test are as follows: Then a first witness replica is generated from the master hologram; The test involves replicating the hologram, and defining the criteria for if the replica passes the test: The master and / or replica holograms are then used to mass-produce replicas on a curved substrate.

2. The method according to claim 1, characterized in that, The method also includes generating replicator control files and testing pass / fail criteria.

3. The method according to claim 1, characterized in that, The planar or substantially planar substrate is a flat or substantially flat planar structure.

4. The method according to claim 1, characterized in that, The cylindrical roller is rotatable about a mechanical axis, wherein the substrate is wound onto the cylindrical roller.

5. The method according to any of the preceding claims, characterized in that, The copy is made into a master and / or replicated onto a curved substrate, which is either concave or convex.

6. The method according to any of the preceding claims, characterized in that, The input geometric parameters are: windshield curvature; projector position; The size of the transparent display; the position and size of the eye box; and / or the composition of the windshield, etc., are geometric parameters that include at least one or any combination of several.

7. The method according to any of the foregoing claims, characterized in that, The tests are conducted on a point-by-point or pixel-by-pixel basis.

8. The method according to any of the preceding claims, characterized in that, The curvature of the replica of the substrate is used to create at least one or more control files for adjusting the beam recording angle and test angle of the processed HOE.

9. The method according to any of the preceding claims, characterized in that, The input system parameters are at least one or any combination of several of the following: target display brightness value; projector lumen output; and / or projector light source spectrum.

10. The method according to any of the preceding claims, characterized in that, The hologram is either a reflection hologram or a transmission hologram.

11. The method according to any of the preceding claims, characterized in that, If the master hologram fails the test, the master hologram is reprinted and the test is repeated.

12. The method according to any of the preceding claims, characterized in that, If the replica hologram fails the test criteria, the replica hologram is regenerated from the master hologram and the test is repeated.

13. An apparatus for manufacturing and / or testing holograms, the apparatus comprising: A substrate, the substrate including a holographic optical element (HOE) to be tested; A light source is used to provide an illuminated area on a holographic optical element (HOE) under test, wherein the light source is spaced apart from the substrate and is movable relative to the substrate to control the position and angle of incidence of the illuminated area on the holographic optical element (HOE) under test. Collecting optics to capture images of the illuminated area of ​​the holographic optical element (HOE) under test and to capture the angular range and / or shape of the diffractive eyebox, wherein the collecting optics can be repositioned to various angular positions to represent a series of final eyebox positions; as well as An optical integrating device, the optical integrating device including an entrance aperture, wherein the illumination area and a spectrometer are connected to the optical integrating device to measure the transmission spectrum of a holographic optical element (HOE) under test.

14. The apparatus according to claim 13, characterized in that, The substrate is a planar or substantially planar substrate, or a cylindrical roller.

15. The apparatus according to claim 13 or 14, characterized in that, The light source is a collimated light source.

16. The apparatus according to any one of claims 13 to 15, characterized in that, The holographic optical element (HOE) is a transparent and / or transmissive display, or a reflective holographic optical element (HOE).

17. The apparatus according to any one of claims 12 to 15, characterized in that, The light source is connected to a multi-axis positioning system, such as a multi-axis robotic arm.

18. The apparatus according to claim 17, characterized in that, The robotic arm is a 6-axis multi-axis positioning system, such as a 6-axis robotic arm.

19. The apparatus according to any one of claims 13 to 18, characterized in that, The collecting optical device includes multiple detection devices, such as a camera.

20. The apparatus according to any one of claims 13 to 19, characterized in that, The substrate can be translated in a vertical plane to allow the illumination area (e.g., illumination spot) to move relative to the holographic optical element (HOE) under test.

21. The apparatus according to any one of claims 13 to 20, characterized in that, The substrate is a planar or nearly planar glass plate, or a sheet wound on a cylindrical roller, onto which holographic optical elements (HOEs) can be laminated.

22. The apparatus according to any one of claims 13 to 21, characterized in that, The collecting optics can be repositioned to various angular positions to represent a series of final eyebox positions.

23. The apparatus according to any one of claims 13 to 22, characterized in that, The optical integrating device is an optical integrating sphere.

24. A method for characterizing the performance of a holographic optical element (HOE) using the apparatus according to any one of claims 13 to 23, the method comprising: The illumination area (e.g., illumination spot) is moved point-by-point to a unique location on the hologram to be tested in order to analyze the entire hologram.

25. The method according to claim 23, characterized in that, The hologram is either reflective or transmissive.

26. The method according to claim 24, characterized in that, Each time the illumination area is moved, the collecting optics are rotated to accurately capture an image of the holographic optical element (HOE).

27. The method according to any one of claims 23 to 25, characterized in that, The illumination area is moved relative to the holographic optical element (HOE) by moving the substrate containing the holographic optical element (HOE) in a horizontal and / or vertical plane.

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