Optical arrangement with holographic display and further holographic element for stray light reduction

Abstract

An optical arrangement (3) comprising a holographic display (4) is described, wherein the holographic display (4) includes at least one holographic optical element (6) for diffracting light towards a defined viewing area (10) and wherein the holographic display (3) has a first side (8) and a second side (9). At least one further holographic optical element (7) is arranged on the first side (8) and / or the second side (9), which is designed to diffract undiffracted light (13) from the at least one holographic optical element (6) of the holographic display (4) such that the diffracted light (14) is totally reflected at least once at an interface (8, 9, 16, 17, 18) of the optical arrangement (3).

Description

[0001] The present invention relates to an optical arrangement comprising a holographic display and an image reproduction device, e.g. in the form of a projection device.

[0002] Displays are used in a wide variety of applications, including in conjunction with display or projection devices. These displays incorporate holographic optical elements for diffracting incident light towards a viewer or an "eyebox." Using appropriate display or projection devices, image content can be projected onto a display plane and be visually perceptible within that plane. The display plane can act as a diffuser, or it can generate image content that is perceived as virtual. An eyebox is understood to be a spatial area from which an image or representation is visually perceptible to a viewer, either as a virtual or real image.

[0003] Display or projection devices that use holographic optical elements can include, for example, screens, projection windows, projection walls, head-up displays (HUDs), or demonstrators. In applications where light from an image source or projector is directed onto a display or projection surface and diffracted by holographic optical elements towards a viewer, particularly in so-called holodisplays, it can happen that light not diffracted by the holographic optical elements is emitted into the surroundings as unwanted stray light or is generated within the respective optical system. This can be countered, for example, by using crossed polarizing filters in the beam path.However, the use of polarizing filters results in a relatively strong filtering effect, significantly reducing the light intensity emitted by the display. This is especially true for displays designed as transparent sheets. Polarizing filters make the sheet less transparent.

[0004] Against this background, the object of the present invention is to provide an advantageous optical arrangement which, in particular, offers an alternative to the use of polarizing filters for reducing or avoiding stray light. A further object is to provide an advantageous image display device.

[0005] The aforementioned problems are solved by an optical arrangement according to claim 1 and an image display device according to claim 12. The dependent claims contain further advantageous embodiments of the invention.

[0006] The optical arrangement according to the invention comprises a holographic display. A holographic display is understood to be an element or surface designed to emit light diffracted by means of at least one hologram. The holographic display comprises at least one holographic optical element for diffracting light, e.g., light emitted from an image transmitter or projector, towards a defined viewing area. A viewing area is understood to be a spatial area in which a viewer must be located in order to visually perceive image content emitted by, displayed by, or projected by the holographic display.The projected image content can be perceived on the surface of the holographic display or as virtual images in a spatial area located at a distance from the holographic display, or in one or more image planes. In the case of generating virtual or real images, the viewing area is designed as an eyebox.

[0007] The holographic display has a first side, e.g., a front, and a second side, e.g., a back. At least one further holographic optical element is arranged on the first side, e.g., the front, and / or the second side, e.g., the back. This at least one further holographic optical element is designed to diffract light not diffracted by the at least one holographic optical element of the holographic display, e.g., light transmitted through the holographic optical element of the holographic display, such that the diffracted light undergoes total internal reflection at least once at an interface of the optical arrangement.In other words, the design of the optical arrangement, and in particular the further holographic optical element, ensures that light is diffracted by the further holographic optical element in such a way that the diffracted light subsequently strikes an interface at an angle of incidence greater than the critical angle for total internal reflection. This interface can be an outer surface of the optical arrangement or a surface located within the optical arrangement between two media.

[0008] The optical arrangement according to the invention has the advantage that it reduces or prevents the emission of light, e.g., of an undiffracted diffraction order and / or unwanted scattered light, from the optical arrangement. This is possible without a significant loss or reduction in the intensity of the emitted light. However, there is always a small loss due to absorption or Fresnel reflection. Furthermore, the solution according to the invention is simple and cost-effective to implement and simultaneously ensures very efficient stopping of unwanted light escaping from the optical arrangement.

[0009] The use of holographic optical elements for stray light reduction also has the advantage that, on the one hand, holographic optical elements require virtually no installation space and, on the other hand, can be very precisely adapted to the respective optical requirements and, in particular, the specific properties of the expected stray light. A further advantage is that, compared to the polarization filters described earlier, a holographic stopper significantly reduces the display's transparency.

[0010] The at least one holographic optical element of the holographic display can comprise at least one transmission hologram and / or at least one reflection hologram. In other words, at least one of the holograms can be designed to diffract light into reflection and / or transmission, i.e., to efficiently diffract light into reflection and / or transmission. For example, in the case of a transmission hologram, more than 95 percent of the light can be diffracted into transmission, i.e., transmitted, and / or in the case of a reflection hologram, more than 95 percent can be diffracted into reflection. The at least one further holographic optical element can, as described below, also comprise at least one corresponding transmission hologram and / or reflection hologram.The choice of whether to use a transmission hologram or a reflection monogram in a specific application can depend on the specific geometric requirements of the beam path and on the desired wavelength selectivity.

[0011] In another variant, the optical arrangement can be designed in such a way that the light diffracted by the further holographic optical element is passed on within the optical arrangement, e.g. by total internal reflection, and optionally absorbed.

[0012] The holographic display can have a substrate with a front side facing the viewing area, e.g., an eyebox, and a back side facing away from the viewing area, e.g., an eyebox. The holographic optical element can be located on the front side and the other holographic optical element on the back side of the substrate. The substrate can comprise or consist of glass and / or a polymer. The described variant is particularly easy and inexpensive to manufacture.

[0013] As mentioned above, the additional holographic optical element can comprise at least one transmission hologram, which is advantageous in combination with a broadband light source with respect to wavelength selectivity, and / or at least one reflection hologram, which is advantageous in combination with a narrowband light source with respect to wavelength selectivity. This allows for the targeted use of the specific properties of transmission holograms and / or reflection holograms, in particular their respective wavelength selectivity and angle-of-incidence selectivity. Furthermore, this enables adaptation to the spectrum of the light emitted by an image source for projection.

[0014] In another variant, a surface of the additional holographic optical element facing away from the viewing area, e.g. the eyebox, and / or a surface of the at least one holographic optical element facing the viewing area can be designed for total internal reflection, in particular for total internal reflection of light of a defined wavelength range.

[0015] The additional holographic optical element can be configured to diffract a light wavefront into a plane light wavefront. In particular, the additional holographic optical element can be configured to diffract a spherical wavefront and / or a spherically or aspherically shaped light wavefront and / or a freeform light wavefront into a plane light wavefront. Precise shaping of the diffracted wavefront facilitates the efficient and complete transmission of light within the optical arrangement. Preferably, the optical arrangement includes a device, e.g., in the form of a beam trap, for consuming, in particular for transmission and / or absorption, light diffracted by the additional holographic optical element and / or totally reflected within the optical arrangement.

[0016] The at least one holographic optical element of the holographic display and / or the at least one further holographic optical element can be designed for diffraction, preferably for efficient diffraction, of light in a defined wavelength range, which can be, for example, a maximum of 50 nanometers, in particular a maximum of 10 nanometers, and is, for example, approximately 5 nanometers wide, and / or for diffracting light in a defined angle of incidence range. In this way, for example, in a monochrome imager, the further holographic optical element can be specifically adapted to expected light that is not diffracted by the holographic display.

[0017] The image display device according to the invention, which may be, for example, a projection device, comprises an image transmitter or projector and an optical arrangement according to the invention as previously described. The optical arrangement according to the invention is arranged in the beam path downstream of the image transmitter or projector, i.e., downstream of it. The image transmitter may be a laser projector, e.g., a monochromatic laser, or a projector designed to emit multicolored light. The image display device according to the invention has the features and advantages already described in connection with the optical arrangement according to the invention.

[0018] The image display device, e.g., a projection device, can be designed as a head-up display, projection panel, projection screen, or projection window. The image display device can be designed for or be a component of a motor vehicle. In another variant, the image display device can be designed as a diffuser, e.g., as a side window diffuser for a motor vehicle.

[0019] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying figures. Although the invention is illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention.

[0020] The figures are not necessarily detailed or to scale and may be enlarged or reduced to provide a better overview. Therefore, the functional details disclosed here are not to be understood as limiting, but merely as an illustrative basis to guide those skilled in this field of technology in using the present invention in a variety of ways.

[0021] The expression "and / or" used here, when used in a series of two or more elements, means that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. For example, when describing a composition containing the components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination. Fig. Figure 1 schematically shows a first variant of an image reproduction device according to the invention. Fig. Figure 2 schematically shows a second variant of an image reproduction device according to the invention.

[0022] The Fig. Figure 1 schematically shows a first variant of an image display device 1 according to the invention. The image display device 1 comprises an image transmitter or projector 2 and an optical arrangement 3 according to the invention.

[0023] The optical arrangement 3 according to the invention comprises a holographic display 4. The holographic display 4 comprises a substrate 5 and at least one holographic optical element 6. The substrate 5 has a front side 21 facing a viewing area 10 and a back side 22 facing away from the viewing area 10. The substrate 5 can comprise glass, for example, the N-BK7 or BF33 glass from Schott AG, or a polymer, or be made of such a material.

[0024] In the depicted variant, the holographic optical element 6 is designed as a reflection hologram and is configured to diffract or reflect light 11 emitted by the projector 1 onto the optical arrangement 3 in the direction of the viewing area 10, for example, towards an eyebox. An alternative configuration of the holographic optical element 6 as a transmission hologram is also possible. The diffracted or reflected light is labeled with the reference numeral 12 and schematically represented as an intensity distribution. The viewing area 10 defines the spatial region from which image content to be projected by the image display device 1 is visually perceptible.

[0025] The holographic optical element 6 of the holographic display 4 is arranged on the front side 21 of the substrate 5, e.g., laminated or glued to the front side 21 of the substrate. The holographic display 4 has a first side 8, e.g., a front side facing the image generator 2 and / or the viewing area 10, and a second side 9, e.g., a back side facing away from the image generator 2 and / or the viewing area 10. At least one further holographic optical element 7 is arranged on the second side 9. The further holographic optical element 7 can, for example, be laminated or glued to the second side or back side 9 of the substrate 5.

[0026] The further holographic optical element 7 is designed to diffract non-diffracted light 13 from the at least one holographic optical element 6 of the holographic display 4 such that the diffracted light 14 is totally internally reflected at least once at an interface, in the example shown at the first side 8 of the holographic display 4, of the optical arrangement 3. The totally internally reflected light 15 can then be passed through a [missing information] in the Fig. One beam trap, not explicitly shown, is absorbed. A corresponding beam trap can, for example, be arranged on the underside of the optical arrangement 3 in the variant shown.

[0027] The additional holographic optical element 7 can be configured as an edge-lit spherical planar reflection grating, i.e., as a holographic "stopper," and used as a blocking element for the zeroth diffraction order of the holographic optical element 6. In other words, the light of the zeroth diffraction order of the holographic optical element 6 is diffracted by the holographic optical element 7 in such a way that it undergoes total internal reflection in the further path of the beam, e.g., at the holographic optical element 6. A spherical planar reflection grating diffraction of light from a point light source, i.e., a spherical wavefront, into a plane wavefront.

[0028] The one in Fig. The variant shown is particularly suitable for projectors 2 in the form of monochrome (narrowband) or laser projectors.

[0029] The Fig. Figure 2 schematically shows a second variant of an image display device 1 according to the invention. This variant differs from the one shown in the Fig. The variant shown in Figure 1 differs in that the further holographic optical element 7 comprises at least one transmission hologram. The light 14, which in this case is diffracted in transmission, is then totally reflected at an interface 16, which in the example shown forms the outer surface or back side of the optical arrangement 3. Subsequently, a further total reflection occurs at the first side or front 8 of the holographic display 4. Furthermore, the variant shown in Figure 1... Fig. The second variant shown has the same features as the one in the Fig. The first variant shown is shown.

[0030] In the in the Fig. 1 and Fig. In the variants shown, total internal reflection of the diffracted light 14 can also occur at another interface, for example at an interface 17 between the substrate 5 and the holographic optical element 6 and / or at an interface 18 between the substrate 5 and the further holographic optical element 7.

[0031] The one in Fig. The variant shown is advantageous in connection with the use of broadband emitting image transmitters or projectors, because the wavelength selectivity of holographic transmission diffraction gratings is more broadband, e.g. with a width of about 10 nm, than that of holographic reflection diffraction gratings, which have a higher wavelength selectivity, e.g. with a width of about 2 nm.

[0032] The in the Fig. 1 and Fig.The image display devices shown in Figure 2 can be used in the consumer or home tech sector or in connection with automotive applications, for example as a head-up display or side window diffuser of a motor vehicle, or in connection with display devices designed as diffusers, which can be integrated into windows, panels or walls, for example. Reference symbol list 1 Image display device 2 Image transmitters / projector 3 optical arrangement 4 holographic displays 5 Substrat 6 holographic optical element 7 additional holographic optical element 8 first page / front / surface 9 second page / back 10 Viewing area / Eyebox 11 Light emitted by the image sensor 12 Light diffracted by the holographic optical element 13 Light not diffracted by the holographic optical element 14 diffracted light 15 Totally reflected light 16 Outer surface, back 17 Interface 18 Interface 21 Front 22 Back

Claims

[1] Optical arrangement (3) comprising a holographic display (4), wherein the holographic display (4) comprises at least one holographic optical element (6) for diffracting light towards a defined viewing space area (10), wherein the holographic display (3) has a first side (8) and a second side (9), characterized by , that at least one further holographic optical element (7) is arranged on the first side (8) and / or the second side (9), which is designed to diffract non-diffracted light (13) from the at least one holographic optical element (6) of the holographic display (4) in such a way that the diffracted light (14) is totally reflected at least once at an interface (8, 9, 16, 17, 18) of the optical arrangement (3). [2] Optical arrangement (3) according to claim 1, characterized by, that the at least one holographic optical element (6) of the holographic display (4) comprises at least one transmission hologram and / or at least one reflection hologram. [3] Optical arrangement (3) according to claim 1 or 2, characterized by , that the optical arrangement (3) is constructed such that the light (14) diffracted by the further holographic optical element (7) is passed on within the optical arrangement (3). [4] Optical arrangement (3) according to any one of claims 1 to 3, characterized by , that the holographic display (4) has a substrate (5) which has a front (21) facing the viewing area (10) and a back (22) facing away from the viewing area (10), wherein the holographic optical element (6) is located on the front (21) and the further holographic optical element (7) is located on the back (22) of the substrate (5). [5] Optical arrangement (3) according to any one of claims 1 to 4, characterized by , that the further holographic optical element (7) comprises at least one reflection hologram. [6] Optical arrangement (3) according to any one of claims 1 to 5, characterized by , that the further holographic optical element (7) comprises at least one transmission hologram. [7] Optical arrangement (3) according to any one of claims 1 to 6, characterized by , that a surface (16) of the further holographic optical element (7) facing away from the viewing space area (10) and / or a surface (8) of the holographic optical element (6) facing the viewing space area (10) is designed for total internal reflection. [8] Optical arrangement (3) according to any one of claims 1 to 7, characterized by , that the further holographic optical element (7) is designed to diffract a light wavefront into a plane light wavefront (15). [9] Optical arrangement (3) according to claim 8, characterized by , that the further holographic optical element (7) is configured to diffract a spherical wavefront and / or a spherically or aspherically shaped light wavefront and / or a freeform light wavefront into a planar light wavefront (15). [10] Optical arrangement (3) according to any one of claims 1 to 9, characterized by , that the optical arrangement (3) comprises a device for consuming light (15) diffracted by the further holographic optical element (7) and / or totally reflected within the optical arrangement. [11] Optical arrangement (3) according to any one of claims 1 to 10, characterized by, that the at least one holographic optical element (6) of the holographic display (4) and / or the at least one further holographic optical element (7) is designed to diffract light in a specified wavelength range and / or to diffract light in a specified angle of incidence range. [12] Image display device (1) comprising an image sensor (2) and an optical arrangement (3) according to any one of claims 1 to 10, wherein the optical arrangement (3) is arranged in the beam path after the image sensor (2). [13] Image display device (1) according to claim 12, characterized by , that the image display device (1) is designed as a head-up display or projection panel or projection wall or projection window. [14] Image display device (1) according to claim 12 or 13, characterized by , that the image display device (1) is designed as a diffuser.

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