Light guide arrangement, imaging optical unit, head mounted display and method for improving imaging quality of imaging optical unit

Abstract

In order to improve the imaging quality of an imaging optical unit having a light guide arrangement for transmitting at least one color channel (I, II, III) having a spectral maximum and a spectral bandwidth, the light guide arrangement (3) reduces the spectral bandwidth of the at least one color channel (I, II, III) during the transmission of the at least one color channel (I, II, III).

Description

[0001] The invention relates to a light guide arrangement with a light waveguide for transmitting at least one color channel, in particular at least one first color channel and one second color channel, wherein the color channels have corresponding spectral maxima and corresponding spectral bandwidths. The invention also relates to an imaging optical unit for forming a virtual image of an original image presented on an image generator, and to a head-mounted display having such an imaging optical unit.

[0002] Light guide arrangements of the type mentioned at the outset can be used in head-mounted displays and in particular in smart glasses. Smart glasses in the sense of the present description are a specific form of head-mounted display that is able to combine electronic images with directly perceived images of the surroundings and thus present the electronic images to the user without impeding the direct perception of the surroundings. When combining electronic images with directly perceived images of the surroundings, a distinction is made essentially between the following principles on which this combination can be based:

[0003] 1. Use ordinary glasses with a beam combiner (e.g. a beamsplitting cube) attached to the front.

[0004] 2. Direct coupling of light from the side, from the top or from the bottom by reflection on the inside of the eyeglass lenses, with diffraction gratings, Fresnel elements etc. being used in a supporting manner.

[0005] 3. guiding the light of the electronic image by reflection in the spectacle lens, in particular by total reflection, and combining the beam path of the electronic image with a direct image of the surroundings by means of an output coupling structure, which is arranged in the spectacle lens and is used to couple the beam path of the electronic image out of the spectacle lens in the direction of the eye.

[0006] Although the first principle works very well optically, it has very low social acceptance due to the fact that the beam combiner attached to the front is very visible and large outwards. In addition, the glasses thus become front-heavy. The second principle can only be realized if the distance between the glasses and the head is greatly increased, which is likewise unacceptable. Therefore, a more promising approach is to start from the third principle, i.e. to guide the light as an optical waveguide in the eyeglass lens. In this case, the output coupling structure can be configured as a diffraction grating, as a partially transparent tilting mirror or in the form of a partially transparent Fresnel element. In the case of a diffraction grating, the beam path of the electronic image is coupled out of the eyeglass lens, for example, via the first-order diffraction maximum, while the observation light can pass through the output coupling structure with as little attenuation as possible via the zero-order diffraction maximum. Examples of smart glasses that guide the light of an electronic image to an output coupling structure by reflection in the glasses lens, in particular by total internal reflection, are described, for example, in the following documents: DE 10 2013 207 257 A1, DE 10 2013 223 963 A1, DE 10 2013 223 964 B3, DE 10 2015 117 557 A1, DE 10 2016 124 538 A1, US 2006 / 0126181 A1, US 2010 / 0220295 A1, and US 2012 / 0002294 A1.

[0007] Smart glasses are also intended to be able to present especially colored electronic images. Therefore, the imaging optical unit having an optical waveguide as part of it is usually optimized for several specific wavelengths, for example for wavelengths in the red spectral range, wavelengths in the green spectral range, and wavelengths in the blue spectral range. That is, the input coupling structure for coupling into the optical waveguide, the output coupling structure for coupling out from the optical waveguide, and the reflection of the imaging beam path within the optical waveguide are optimized with respect to these specific wavelengths.

[0008] However, a polychromatic image generator (i.e., an image generator that can generate color images) does not emit only the three specific wavelengths for which the imaging optical unit is optimized, but rather emits three wavelength ranges, for example a red wavelength range, a green wavelength range, and a blue wavelength range, each wavelength range having a spectral width. Then, the three specific wavelengths for which the imaging optical unit is optimized are typically selected to correspond to the spectral maxima of these wavelength ranges or to be close to the corresponding spectral maxima. Since the imaging optical unit is optimized for a few specific wavelengths, the spectral bandwidth of the wavelength ranges emitted by the polychromatic image generator results in poor imaging quality.

[0009] Therefore, the object of the present invention is to provide a light guide arrangement, an imaging optical unit, and a head mounted display that produce a high imaging quality even with a multicolor image generator. Furthermore, the object of the present invention is to provide a method for improving the imaging quality of an imaging optical unit when transmitting color channels with a spectral bandwidth.

[0010] The first object is achieved by the light guide arrangement of the present invention, the imaging optical unit of the present invention, and the head mounted display of the present invention. The second object is achieved by the method of the present invention for improving the imaging quality of the imaging optical unit. The present invention also comprises advantageous configurations of the present invention.

[0011] The light guide arrangement according to the present invention comprises a light waveguide for transmitting at least one color channel having a spectral maximum and a spectral bandwidth. However, in particular, the light waveguide can be implemented as a light waveguide for transmitting at least one first color channel and a second color channel, wherein these color channels have corresponding spectral maximums and corresponding spectral bandwidths, and wherein the positions of the spectral maximums in the spectrum are different from each other. The light waveguide is typically configured to transmit three color channels of this type. According to the present invention, the light guide arrangement comprises a device for reducing the spectral bandwidth of the color channel, or reducing the spectral bandwidth of these color channels in the case of at least two color channels. In the context of this description, the light waveguide should be considered to cover any of the following elements consisting of a transparent material, which transmits light in its interior, for example, by total internal reflection at the outer surface of the element or at the internal interface of the material. However, reflection can also be achieved on a partially or completely reflective layer, rather than by total reflection. In the context of this description, the color channel is considered to be the primary colors of the color space used to generate a multicolor image, in particular. The primary colors can be, for example, red, green and blue here. However, other primary colors are also possible, such as cyan, magenta and yellow. Furthermore, in principle, the color space may also include more or less than three primary colors, and thus there may be more or less than three color channels. Furthermore, in the context of the present description, the situation when a monochrome image is generated is also intended to be covered by the color channels. The color channels then determine the color of the monochrome image.

[0012] The present invention is based on the following insights:

[0013] Each color channel of the multicolor image generator to be transmitted by the light guide arrangement is typically formed by a specific wavelength range with a spectral maximum, whose wavelength defines the primary color of the color channel. In this case, each wavelength range has a certain spectral width, wherein, for each color channel, the material dispersion of the light guide causes the light in the wavelength range to have different reflection angles depending on the wavelength of the light. Since the light guide arrangement is optimized only for one wavelength in each wavelength range (typically for the wavelength defining the primary color of the color channel, but this is not mandatory), the remaining wavelengths in this wavelength range are not reflected at the optimal reflection angle. In addition, in the case where the imaging beam path is coupled into the light waveguide by a diffraction grating and / or the imaging beam path is coupled out of the light waveguide, the diffraction grating for input coupling and / or output coupling of the color channel is optimized in each case for a specific wavelength in the corresponding wavelength range, so that the wavelength deviating from the wavelength range is coupled out in a slightly different direction. The result of these two effects is that, for the color channel, not all wavelengths in the relevant wavelength range are focused to the same point during imaging. A measure of the extent to which a point of the original image is focused again to a point in the image is the point spread function (PSF). Due to the above-mentioned wavelength-dependent dispersion and diffraction of each color channel, the full width at half maximum of the point spread function increases. This leads to a reduction in the resolution of the image generated based on the original image and a loss of contrast of the image.

[0014] The means for reducing the spectral bandwidth of the color channels counteracts the broadening of the point spread function of each color channel. The imaging optical unit with the light guide arrangement according to the invention can in this respect be configured such that each color channel is reduced to a narrow spectral range around the corresponding spectral maximum of the wavelength range of the multicolor image generator. By means of the light guide arrangement according to the invention, for each color channel, reducing the spectral bandwidth of the color channel prevents the transmission of those wavelengths of the wavelength range assigned to said color channel that contribute most to poor imaging quality.

[0015] In the case of an optimization of the color channels of the imaging optical unit for the wavelength of the spectral maximum of the wavelength range of the polychromatic image generator, the contribution of the wavelengths in the wavelength range to the poor image quality is greater the further these wavelengths are from the spectral maximum. Therefore, the more the spectral bandwidth is reduced, i.e. the narrower the spectral range of the color channel becomes, the more the imaging quality of the imaging optical unit is improved. However, the intensity in the imaging beam path is also lost due to the reduction of the spectral bandwidth of the color channel. Therefore, the extent to which the spectral bandwidth of the color channel is advantageously reduced by means of the device for reducing the spectral bandwidth is generally a compromise between the desired image intensity and the desired imaging quality. If a very high imaging quality is desired, the spectral bandwidth of the color channel is greatly reduced, but a significant intensity loss also occurs. However, such an intensity loss can be compensated by increasing the luminous intensity of the display. If the main emphasis is on the intensity of the image generated by the imaging optical unit, the reduction of the spectral bandwidth of the color channel will be smaller. Therefore, the extent to which the spectral bandwidth is reduced typically depends on the respective application.

[0016] Although the invention can already be advantageously applied in the case of multicolor imaging when there are at least two color channels, the invention is typically used in an imaging optical unit with three color channels, for example in an imaging optical unit with a red channel, a green channel and a blue channel. However, the light guide arrangement according to the invention can also be used in an imaging optical unit to transmit more than three color channels.

[0017] Although the present invention is particularly advantageous in the context of multicolor imaging, it can also improve imaging quality in the context of monochromatic imaging if the image generator used for monochromatic imaging emits a large spectral bandwidth around the wavelength selected for monochromatic imaging. Thus, the present invention can use a broadband image generator in the case of monochromatic imaging.

[0018] The device for reducing the spectral bandwidth of the one or more color channels can be integrated into the optical waveguide. In this case, the optical waveguide arrangement can be configured to be particularly compact. Alternatively, there is also the possibility that the device for reducing the spectral bandwidth of the one or more color channels is a reducing element arranged upstream or downstream of the optical waveguide, for example in the form of a spectral filter element. This can especially prevent the device for reducing the spectral bandwidth from changing the color perception of the surrounding environment when viewing through the optical waveguide. However, there is the possibility that the device for reducing the spectral bandwidth of the one or more color channels is partially integrated into the optical waveguide and partially implemented as a reducing element arranged upstream or downstream of the optical waveguide, for example in the form of a spectral filter element. For example, for one color channel, the device for reducing the spectral bandwidth can be integrated into the optical waveguide, while for other color channels, the device for reducing the spectral bandwidth is implemented as a reducing element arranged upstream or downstream of the optical waveguide. Finally, for at least one color channel or for each color channel, there is also the possibility of combining a device for reducing the spectral bandwidth integrated into the optical waveguide and a device for reducing the spectral bandwidth configured in the form of a reducing element arranged upstream or downstream of the optical waveguide with one another in such a way that a reduction in the spectral bandwidth of the color channel is achieved by the interaction of the element integrated into the optical waveguide with the reducing element arranged upstream or downstream of the optical waveguide.

[0019] The device for reducing the spectral bandwidth of the one or more color channels may include one or more transmission filters, no matter in the form of one or more transmission filters integrated into the optical waveguide and / or in the form of one or more transmission filters arranged upstream or downstream of the optical waveguide. The at least one transmission filter constitutes a spectral filter that only allows a specific wavelength range to pass through. It can be implemented as an absorption filter or an interference filter in particular. If the transmission filter is integrated into the optical waveguide, there is especially the possibility that the at least one transmission filter is realized by a light waveguide input surface with a transmission filter characteristic and / or a light waveguide output surface with a transmission filter characteristic. In this case, the light waveguide input surface is the surface through which the imaging beam path enters the optical waveguide, and the light waveguide output surface is the surface through which the imaging beam path passes from the light waveguide. Since the light waveguide entrance surface is typically located outside the field of view of the user of smart glasses provided with the light waveguide or at least at the edge of the field of view to a certain extent, so that the color distortion of the ambient light passing through the light waveguide will not be perceived as disturbing, equipping the light waveguide entrance surface with transmission filter characteristics provides an advantage over equipping the light waveguide entrance surface with transmission filter characteristics, namely, the color perception will not be distorted when looking at the surrounding environment.

[0020] In addition or in lieu of the at least one transmission filter, the device for reducing the spectral bandwidth of the one or more color channels may include at least one spectrally selective reflective element. Such an element may, for example, be implemented as a dichroic reflective element or a reflective element that absorbs a specific wavelength.

[0021] The means for reducing the spectral bandwidth of the one or more color channels can be implemented as at least one coating of at least a portion of the optical waveguide or of the reducing element arranged upstream or downstream of the optical waveguide. In this way, no additional transmissive or reflective elements are required in the beam path of the optical waveguide arrangement. In this case, absorption layers and / or interference layers can be used.

[0022] In the light guide arrangement according to the invention, the device for reducing the spectral bandwidth of the one or more color channels may include at least one narrowband filter, that is, one narrowband spectral filter and / or at least one narrowband spectral selective reflective element. In particular, for each color channel, there may be a narrowband filter or a narrowband spectral selective reflective element. The narrowband filter or the corresponding narrowband spectral selective reflective element then transmits the wavelength of the primary color defining the corresponding color channel, and the wavelength range immediately adjacent to the wavelength, and blocks all other wavelengths. The width of the selected wavelength range depends on the desired imaging quality on the one hand and on the desired intensity of the transmitted light on the other hand. The narrower the selected wavelength range, the more the imaging quality is improved, but at the expense of the intensity of the transmitted light. In principle, there is also the possibility of using a single narrowband filter or a corresponding single narrowband spectral selective reflective element, which transmits or reflects a narrow spectral range near the wavelength of the primary color defining the corresponding color channel for each color channel. In this way, reducing the bandwidth of multiple color channels can be achieved with a single transmission filter or a corresponding single spectral selective reflective element.

[0023] In addition to or instead of at least one narrow-band filter or at least one narrow-band spectrally selective reflective element, the means for reducing the spectral bandwidth of the one or more color channels may comprise at least:

[0024] - two broadband filters,

[0025] - two broadband spectrally selective reflective elements, or

[0026] - a broadband filter and a broadband spectrally selective reflective element,

[0027] They each transmit a wavelength of a primary color defining a color channel and a wavelength range adjacent to said wavelength, wherein the wavelength ranges are different from one another.

[0028] In the context of this description, a broadband filter is understood to refer to a transmission filter that transmits only a portion of the spectrum bounded on one side of a transmission color channel (e.g., a transmission filter that transmits only short-wave light or only long-wave light of the spectrum of a transmission color channel), or a transmission filter that transmits at least half of the spectrum of a transmission color channel. Accordingly, in the context of this description, a broadband spectrally selective reflective element is understood to refer to a reflective element that reflects only a portion of the spectrum bounded on one side (e.g., an element that reflects only short-wave light or only long-wave light of a reflection color channel), or a reflective element that reflects at least half of the spectrum of a reflection color channel. Then, these two broadband filters, or these two broadband spectrally selective reflective elements, or broadband filters and broadband spectrally selective reflective elements jointly cause a reduction in the spectral bandwidth of the one or more color channels. In this case, in principle, there is the following possibility: there are at least two broadband filters or at least two broadband spectrally selective reflective elements, or at least one broadband filter and one broadband spectrally selective reflective element for each color channel. However, there is also the possibility that two broadband filters or two broadband spectrally selective reflective elements, or one broadband filter and one broadband spectrally selective reflective element, each together cause a reduction in the spectral bandwidth of more than one color channel. Broadband filters or, respectively, broadband spectrally selective reflective elements are generally simpler to produce than narrowband filters or, respectively, narrowband selective reflective elements.

[0029] In the light guide arrangement according to the invention, the optical waveguide can in particular be a spectacle lens. Such a spectacle lens can advantageously be used in smart glasses.

[0030] The imaging optical unit according to the invention for forming a virtual image of an original image presented on an image generator comprises a light guide arrangement according to the invention and at least one imaging optical element for forming an image of the original image. However, the imaging optical unit may also comprise a plurality of imaging optical elements, wherein these imaging optical elements then jointly form an image of the original image. In this case, the imaging optical unit may comprise at least one imaging optical element integrated into the optical waveguide. Additionally or alternatively, the imaging optical unit may comprise at least one imaging optical element arranged upstream or downstream of the optical waveguide. In the latter case, the device for reducing the spectral bandwidth contained in the light guide arrangement may be fully or partially integrated into the imaging optical element arranged upstream or downstream.

[0031] Advantages in terms of imaging quality that are achievable with respect to the light guide arrangement according to the invention can be achieved with the imaging optical unit according to the invention. Reference is therefore made to the explanations with respect to the light guide arrangement according to the invention.

[0032] The head-mounted display according to the present invention, which may be specifically smart glasses, comprises an image generator for presenting an original image, and an imaging optical unit according to the present invention for forming a virtual image of the original image presented on the image generator. Due to the use of the imaging optical unit according to the present invention, the head-mounted display according to the present invention can realize the formation of a multi-color virtual image with high imaging quality.

[0033] The present invention also provides a method for improving the imaging quality of an imaging optical unit when transmitting at least one color channel having a spectral maximum and a spectral bandwidth, wherein the at least one color channel is transmitted by a light-guiding arrangement of the imaging optical unit. According to the present invention, during the transmission of the at least one color channel by the light-guiding arrangement, the spectral bandwidth of the at least one color channel is reduced. In particular, in the context of the method according to the present invention, at least one first color channel and one second color channel are transmitted, which color channels have corresponding different spectral maxima and corresponding spectral bandwidths, wherein the spectral bandwidth of the color channels is reduced during the transmission of the color channels by the light-guiding arrangement. Reducing the spectral bandwidth of the one or more color channels during the transmission by the light-guiding arrangement can improve the imaging quality of the imaging optical unit when the imaging optical unit generates a virtual image of the original image, as already described with respect to the light-guiding arrangement according to the present invention. Therefore, reference is made to the explanations regarding the light-guiding arrangement according to the present invention.

[0034] In order to compensate for the distortions in the image present at the wavelengths of the spectral maximum, which distortions are generated during the transmission of the corresponding color channel by the optical system, the original image on which the imaging is based can be presented on the display with a certain distortion, which corresponds to the inverse of the distortion caused by the transmission of the corresponding color channel. Such a distorted presentation on the display is also referred to as chromaticity precorrection.

[0035] Further features, characteristics, and advantages of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

[0036] Figure 1 An example of smart glasses is shown.

[0037] Figure 2 An example of the basic optical components of smart glasses is shown in a schematic diagram.

[0038] Figure 3 Schematic representation of the spectral bandwidths of the color channels of a multicolor display.

[0039] Figure 4 The transmission characteristics of the light waveguide incident surface of the light waveguide of the light guide arrangement according to the first exemplary embodiment are shown.

[0040] Figure 5The transmission characteristics of the light waveguide incident surface of the light waveguide of the light guide arrangement according to the second exemplary embodiment are shown.

[0041] Figure 6 The reflection characteristics of the first reflection surface of the light guide arrangement of the second exemplary embodiment are shown.

[0042] Figure 7 The reflection characteristics of the second reflection surface of the light guide arrangement of the second exemplary embodiment are shown.

[0043] Figure 8 The transmission characteristics of the light waveguide incident surface of the light waveguide of the light guide arrangement according to the third exemplary embodiment are shown.

[0044] Fig. 9 The reflection characteristics of the first reflection surface of the light guide arrangement of the third exemplary embodiment are shown.

[0045] Fig.10 The reflection characteristics of the second reflection surface of the light guide arrangement of the third exemplary embodiment are shown.

[0046] Fig.11 Smart glasses with a light guide arrangement according to a fourth exemplary embodiment are shown.

[0047] The following will refer to Figures 1 to 4 A first exemplary embodiment of smart glasses with a light guide arrangement according to the invention is described. In this case, Figure 1 shows smart glasses, and Figure 2 The basic optical elements of the light guide arrangement 3 of the smart glasses are shown. In addition, Figure 2 A display 1 is shown and the eye lens 15 and the retina 17 of a user of the smart glasses are shown highly schematically.

[0048] Figure 1 An exemplary embodiment of smart glasses 20 is shown. The smart glasses include a glasses frame 21, in which two glasses lenses 22 and 23 are mounted. Display ( Figure 1 The display (not shown) is arranged in the temple of the glasses, and the display displays the original image intended to be imaged onto the retina of the user of the smart glasses by the imaging optical unit of the smart glasses 20. In the present exemplary embodiment, the imaging optical unit of the smart glasses 20 is formed by the glasses lenses 22 and 23, which are simultaneously used as optical waveguides. However, the imaging optical unit can also include optical elements outside the glasses lenses. Such elements are especially arranged between the temples 24, 25 of the glasses and the glasses lenses 22, 23.

[0049] The spectacle lenses 22 , 23 of the smart glasses are each part of a light guiding arrangement of the smart glasses 20 or form the light guiding arrangement. Figure 2The basic optical elements of such a light guide arrangement 3 are shown. Each light guide arrangement 3 is assigned a multicolor display 1, on which a multicolor original image can be displayed. Each light guide arrangement 3 comprises a light waveguide 4, which has a light waveguide entrance surface 5 and a light waveguide exit surface 7. A light beam 9 emitted from the original image displayed on the display 1 enters the light waveguide 4 via the light waveguide entrance surface 5 and is reflected multiple times at a plurality of reflection surfaces 11a to 11f in the light waveguide and is guided to a transparent or at least partially transparent output coupling structure 13 by these reflections. With the aid of the output coupling structure 13 (in the present exemplary embodiment, implemented as a reflective Fresnel structure), the light beam 9 is finally coupled out through the light waveguide exit surface 7 in the direction toward the eye lens 15, and the light beam 9 is finally focused onto the retina 17. In this case, the reflective Fresnel structure is formed by a plurality of inclined partially reflective surfaces, which form a structure with a profile similar to a sawtooth. By segmentation, the partially reflective surfaces forming the output coupling structure 13 can be configured to have a small depth. However, instead of a reflective Fresnel structure, an unsegmented mirror or a diffraction grating or a holographic optical element (HOE) can also be used for the purpose of outcoupling. Incoupling can also be achieved via a diffraction grating or a HOE. The outcoupling structure can be arranged on the side of the optical waveguide 4 facing away from the eye lens 15, such as Figure 2 As shown. In principle, however, the outcoupling structure can also be arranged on the side of the optical waveguide 4 facing the eye lens 15 and in this case in particular can also be integrated into the optical waveguide exit surface 7. In this case, the outcoupling structure has a refractive effect instead of a partially reflective effect and guides the beam path 9 by refraction in the direction towards the eye lens 15. Partially reflective outcoupling structures are described, for example, in US 2012 / 0002294 A1 and refractive outcoupling structures are described, for example, in DE 10 2015 117 557 A1. Diffraction gratings as outcoupling structures are described in US 2006 / 0126181 A1 and US 2010 / 0220295 A1. With regard to possible configurations of the outcoupling structure 13, reference is therefore made to the cited literature. Diffractive outcoupling can be achieved by an outcoupling structure 13 arranged at the side of the optical waveguide 4 facing away from the eye lens 15 , or by an outcoupling structure arranged at the side of the optical waveguide 4 facing the eye lens 15 .

[0050] exist Figure 1 and Figure 2In the exemplary embodiment shown in , each optical waveguide 4 is formed by a spectacle lens 22, 23. The reflective surfaces 11a and 11c to 11f are located at the inner surface (i.e. facing the eye lens 15) and the outer surface (i.e. facing away from the eye lens 15) of the respective spectacle lens 22, 23. In this case, the geometry and arrangement of the reflective surfaces 11a to 11f are selected so that at the reflective surfaces 11c, 11d, 11e and 11f, total reflection occurs at the interface between the respective spectacle lens 22, 23 and the surrounding medium (usually air). The conditions for the occurrence of total reflection are known to those skilled in the art and are not described in detail here. Since the total reflection occurs inside the spectacle lens, it is also called total internal reflection. Since the light is guided inside the spectacle lens by total internal reflection and the output coupling structure 13 is embodied as at least partially transparent, the observation of the surrounding environment is not hindered or is only hindered to a minimum extent. In particular, the obstruction of the observation of the surrounding environment can be minimized by a suitable configuration of the output coupling structure 13. However, in principle, the optical waveguide 4 (i.e., the eyeglass lenses 22, 23) can also be configured so that the reflection does not occur by total reflection. In this case, the optical waveguide 4 has a reflective coating, but the coating is selected as far as possible so that they have an angle-selective effect and thus block as little light from the surrounding environment as possible that passes through the optical waveguide 4.

[0051] Instead of being implemented in the form of spectacle lenses 22, 23 as in the present exemplary embodiment, the optical waveguide 4 can in principle also be implemented in the form of a visor or the like. Therefore, when smart glasses are mentioned in the context of the present invention, the term can also cover head-mounted displays having a visor-like structure, even if this structure is not explicitly mentioned.

[0052] As mentioned, a multicolor image generator 1 is used in the smart glasses 20 according to the present invention. The multicolor image generator typically emits three wavelength ranges, each wavelength range representing a color channel. A wavelength range centered in the blue spectral range, a wavelength range centered in the green spectral range, and a wavelength range centered in the red spectral range are conventional. Figure 3 spectral emission characteristics of a typical multicolor display are shown. In the latter, each image point has a blue light source, a green light source, and a red light source. In this exemplary embodiment, the wavelength range of the light emitted by the blue light source has a maximum value of approximately 450nm, the light emitted by the green light source has a maximum value of approximately 540nm, and the light emitted by the red light source has a maximum value of approximately 630nm. In addition, each light source also emits wavelengths adjacent to the maximum value, and therefore each light source has a spectral bandwidth. Figure 3Spectrum I of a blue light source, spectrum II of a green light source, and spectrum III of a red light source are shown, and for better comparability, the intensity of the maximum value is normalized to 1. Spectra I to III represent the three color channels of the display.

[0053] The light guide arrangement 4 of the smart glasses 20 is optimized to transmit those wavelengths of the respective color channels that correspond to the maximum values ​​of the color channels. In the present example, this means that the light guide arrangement is optimized to transmit light with a wavelength of 450 nm, a wavelength of 540 nm, and a wavelength of 630 nm. Reflection at the various elements of the light guide arrangement, and / or possible refraction in other embodiments, and / or possible diffraction in other embodiments, are configured here so that light rays with wavelengths of 450 nm, 540 nm, and 630 nm emanating from an image point of the original image (i.e., from different image points of the display in the case of chromatic pre-correction) are focused to the same point on the retina.

[0054] However, due to the dispersion occurring in the optical waveguide, light rays with different wavelengths are refracted differently when entering and exiting the optical waveguide 3. In particular, the refraction occurring when passing through the optical waveguide incident surface 5 causes the refracted light rays to have different directions in the optical waveguide 3 according to the wavelength of the light, and thus causes the light rays with different wavelengths to hit the reflective surfaces 11a to 11f at different angles, which causes different distortions of the color images (here, the blue image, the green image and the red image) transmitted by different color channels. Therefore, for all colors, the light rays emitted from the image points of the display do not combine at the same point on the retina. In the context of optimizing the optical waveguide arrangement 4, this influence of individual wavelengths, such as the wavelength of the maximum value of the color channel, can be counteracted, for example, by separating the color channels in the optical waveguide from each other, for example by causing the color channels to be guided through different sections of the optical waveguide 3 and only to be combined again when exiting the optical waveguide. Additionally or alternatively, for individual wavelengths, such as the wavelength of the maximum value of the color channel, a chromaticity pre-correction can be achieved in the context of presenting the original image on the display. In the case of chromatic precorrection, mutually corresponding image points of the color image are not represented by the same image point of the display. Therefore, distortions of the color image in the original image can be taken into account, which are generated during the transmission of the corresponding color channel by the optical system. For this purpose, the color original image (here the original image at 450 nm, the original image at 540 nm and the original image at 630 nm) is represented on the display with generally different distortions, which correspond to the inverse of the distortion caused by the transmission of the corresponding color channel and thus compensate for the distortion occurring in the color channel. Therefore, the mutually corresponding image points of the color image of the original image, which are represented by different image points of the display, are focused on the same point on the retina.

[0055] For those wavelengths of the color channels which deviate from their wavelength of maximum, despite optimization of the light guide arrangement 4 and / or despite chromatic precorrection, the problems associated with the dispersion still exist, which results in each color channel containing light rays with a wavelength deviating from its wavelength of maximum, which rays are not focused to the same point on the retina as the light rays with the wavelength of maximum, whereby the resolution of the generated image is reduced and the sharpness is reduced. In the case of diffractive in- and / or out-coupling of light into and / or out of the optical waveguide 3, the wavelength dependence of the diffraction angle additionally results in different propagation directions of light rays with different wavelengths, which likewise results in a loss of resolution and contrast of the generated image.

[0056] In order to offset the loss of resolution and contrast, in this exemplary embodiment, the light waveguide incident surface 5 is provided with a coating having a transmissive property, such as Figure 4 Schematic display. The coating realized by the interference layer in the present exemplary embodiment forms a spectral filter with three narrowly defined transmission ranges A, B, C. In the present exemplary embodiment, the spectral width of the transmission range is limited to 20nm in each case and is centered on the maximum wavelength of the corresponding imaging channel. Therefore, in the present exemplary embodiment, the first transmission range A extends from 440 to 460nm, the second transmission range B extends from 530 to 550nm, and the third transmission range C extends from 620 to 640nm. The remaining wavelengths are blocked by the coating of the light waveguide incident surface 5. Obviously, the coating of the light waveguide incident surface acts as a narrowband spectral filter with three narrowly defined spectral transmission ranges. Such a transmission filter can be realized with a steep slope and a transmittance of almost 100% for the transmission ranges A, B, C. In the remaining ranges, such a transmission filter has a transmittance close to 0.

[0057] Reducing the spectral bandwidth of the individual color channels by means of a coating applied to the light waveguide entrance surface 5 masks the wavelengths of the individual color channels that most contribute to a loss of resolution and contrast, thereby increasing the resolution and contrast of the image generated on the retina.

[0058] In the present exemplary embodiment, the spectral filter described is implemented by an interference layer of the light waveguide incident surface 5, and it is therefore a so-called interference filter. In an interference filter, those wavelengths intended to be blocked by the filter are reduced by destructive interference. However, the spectral filter can also be implemented as an absorption filter. In the case of such a filter, the reduction of undesirable wavelengths is not accomplished by destructive interference, but by absorption of light with the corresponding wavelength in the filter layer.

[0059] References below Figures 5 to 7 The second exemplary embodiment of the smart glasses according to the present invention is explained. The structural design of the second exemplary embodiment corresponds to the one already mentioned in reference Figure 1 and Figure 2 The structural design of the first exemplary embodiment described. Therefore, with regard to the structural elements, reference is made to Figure 1 and Figure 2 The components shown in .

[0060] Compared with the first exemplary embodiment, in the second exemplary embodiment, the light waveguide incident surface 5 is provided with a coating having a wide transmission range (see Figure 5 ). The transmission range of the coating covers most of the visible spectrum, namely the range from 440 to 640 nm. All wavelengths in this range are transmitted almost unhindered by the layer, while the remaining wavelengths are blocked by the layer as much as possible.

[0061] In the present second exemplary embodiment, a coating is also applied to the reflective surface 11a. The coating suppresses reflection in the wavelength range between 460 and 530 nm (see Figure 6 ). The suppression of this reflection can be achieved by an interference layer or by an absorption layer. Therefore, the first reflective surface 11a only reflects light with a wavelength of <460nm and >530nm.

[0062] Furthermore, in the present exemplary embodiment, a coating is also applied to the reflective surface 11b. The coating suppresses reflection in the wavelength range between 550 and 620 nm (see Figure 7 ). Therefore, the first reflective surface 11b only reflects light with a wavelength of <550nm and >620nm. The coating on the reflective surface 11b can also be realized by an interference layer or an absorption layer.

[0063] The interaction of the coating applied to the light waveguide incident surface 5, the coating applied to the reflective surface 11a, and the coating applied to the reflective surface 11b blocks the lightguide arrangement from transmitting wavelengths outside the wavelength ranges of 440 to 460 nm, 530 to 550 nm, and 620 to 640 nm. Thus, only the spectral range of 440 to 460 nm is transmitted for the blue channel, only the spectral range of 530 to 550 nm is transmitted for the green channel, and only the spectral range of 620 to 640 nm is transmitted for the red channel. The resulting reduction in the spectral bandwidth of the color channels results in an improvement in the resolution and contrast of the image appearing on the retina.

[0064] References below Figures 8 to 10 A third exemplary embodiment of smart glasses according to the present invention is described. In this exemplary embodiment, the same elements as in the second exemplary embodiment are provided with coatings. Only the coatings differ from those in the second exemplary embodiment.

[0065] In this third exemplary embodiment, the light waveguide incident surface 5 is coated with a coating that blocks all wavelengths below 440 nm and all wavelengths in the range of 460 to 530 nm and transmits all remaining wavelengths (see Figure 8 ). A coating is applied to the reflective surface 11a, which suppresses reflection in the wavelength range between 460 nm and 530 nm and in the wavelength range between 550 nm and 620 nm, but on the contrary does not suppress reflection of the remaining wavelengths (see Fig. 9 ), and a coating is applied to the reflective surface 11b, which suppresses reflection in the wavelength range between 550nm and 620nm and reflection of all wavelengths above 640nm, but on the contrary does not suppress reflection of the remaining wavelengths (see Fig.10 ). Due to the interaction of these three coatings, the light guide arrangement of the third exemplary embodiment provides for each color channel only a narrow transmission range of 20 nm in width, centered around the primary color of the corresponding color channel. Thus, for the blue channel only the spectral range of 440 to 460 nm is transmitted, for the green channel only the spectral range of 530 to 550 nm is transmitted, and for the red channel only the spectral range of 620 to 640 nm is transmitted. As in the other exemplary embodiments, the coating of the third exemplary embodiment can be realized by an interference layer or an absorption layer.

[0066] In exemplary embodiments 1 to 3, at least one of the reflective surfaces 11a to 11f, and / or the light waveguide entrance surface 5, and / or the surface of the output coupling structure 13, and / or the light waveguide exit surface 7, individually or collectively has imaging properties. If one surface individually has imaging properties, this should be understood to mean that the corresponding surface is configured in such a way that it generates an image on the retina 19 when it interacts with the eye lens 17 individually. If a plurality of surfaces collectively have imaging properties, this should be understood to mean that the image on the retina is generated by the interaction of these surfaces with the eye lens 17.

[0067] Fig.11 A fourth exemplary embodiment of smart glasses according to the present invention is shown. Elements of the fourth exemplary embodiment corresponding to elements of the first exemplary embodiment are shown in Fig.11 Chinese Figure 2 The same reference numerals are used and will not be described again to avoid repetition. In fact, the only difference between the fourth exemplary embodiment and the first exemplary embodiment is that Figure 4The transmission behavior shown is not achieved by a coating of the light waveguide incident surface 5, but by a spectral filter element 19 arranged between the image generator 1 and the light waveguide incident surface 5, which acts as a reducing element for reducing the spectral bandwidth of the color channel. The spectral filter element 19 (which can be implemented as an interference filter or an absorption filter) has the following characteristics: Figure 4 Such transmission characteristics can in particular also be achieved by a coating applied to the light waveguide entrance surface 5, which in a first exemplary embodiment is applied to a separate transparent element which is then arranged as a spectral filter element 19 between the display 1 and the light waveguide entrance surface 5.

[0068] As in the first three exemplary embodiments, also in the fourth exemplary embodiment, at least one of the reflective surfaces 11a to 11f, and / or the light waveguide entrance surface 5, and / or the surface of the output coupling structure 13, and / or the light waveguide exit surface 7, alone or together, has imaging properties. Additionally or alternatively, the spectral filter element 19 may have imaging properties by itself or together with at least one of the above elements.

[0069] The present invention has been described in detail based on exemplary embodiments for illustrative purposes. However, the skilled person recognizes that it is possible to depart from these exemplary embodiments without departing from the teachings of the present invention. For example, the skilled person recognizes that even though three color channels are described in each exemplary embodiment, the present invention can also be implemented with less than or more than three color channels. In particular, the present invention can also be implemented with only one color channel. This opens up the possibility of generating monochrome images with high resolution and high contrast, for example, using an image generator with a wide emission spectrum. In addition, the skilled person also recognizes that the light guide arrangement according to the present invention can also be used in a head-mounted display that is not implemented as smart glasses, i.e., the head-mounted display cannot directly perceive the surrounding environment. Therefore, the present invention is not intended to be limited to the configuration described with reference to the exemplary embodiments, but the present invention is intended to be limited only by the claims.

[0070] List of Reference Numerals

[0071] 1 Display

[0072] 3 Light guide arrangement

[0073] 4 Optical waveguide

[0074] 5 Light waveguide incident surface

[0075] 7 Light waveguide incident surface

[0076] 9 Beam

[0077] 11a-f Reflective surfaces

[0078] 13 Output coupling structure

[0079] 15. Lens of the eye

[0080] 17 Retina

[0081] 19 Spectral filter elements

[0082] 20. Smart Glasses

[0083] 21. Eyeglass frames

[0084] 22 Eyeglass lenses

[0085] 23. Eyeglass lenses

[0086] 24 Glasses temples

[0087] 25 glasses temples

Claims

1. An imaging optical unit for forming a virtual image of an original image presented on an image generator (1), characterized in that The imaging optical unit comprises a light guide arrangement (3) having a light waveguide (4) for transmitting one or more color channels, and at least one imaging optical element; wherein the one or more color channels respectively have a spectral maximum and a spectral bandwidth, and the light guide arrangement (3) comprises means for reducing the spectral bandwidth of the one or more color channels; wherein the imaging optical unit comprises at least one imaging optical element arranged upstream or downstream of the optical waveguide (4), wherein the device for reducing the spectral bandwidth of the one or more color channels is fully or partially integrated into the at least one imaging optical element arranged upstream or downstream of the optical waveguide (4); The invention is characterized in that the optical waveguide arrangement has an optical waveguide (4) for transmitting at least one first color channel and one second color channel, wherein the first color channel and the second color channel have corresponding spectral maxima and corresponding spectral bandwidths, the positions of the spectral maxima of the first color channel and the second color channel in the spectrum are different from each other, and the optical waveguide arrangement (3) has a device for reducing the spectral bandwidth of the one or more color channels, and the device is configured to reduce the spectral bandwidth of the first color channel and the second color channel.

2. The imaging optical unit according to claim 1, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels is integrated into the optical waveguide (4).

3. The imaging optical unit according to claim 1 or 2, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels is a reducing element arranged upstream or downstream of the optical waveguide (4).

4. The imaging optical unit according to claim 1 or 2, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels comprises at least one transmissive filter.

5. The imaging optical unit according to claim 4, characterized in that: The at least one transmission filter is realized by a light waveguide incident surface (5) having transmission filter properties.

6. The imaging optical unit according to claim 1 or 2, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels comprises at least one spectrally selective reflective element (11a, 11b).

7. The imaging optical unit according to claim 1 or 2, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels are implemented as at least one coating of at least a portion of the optical waveguide (4) or of a reducing element arranged upstream or downstream of the optical waveguide (4).

8. The imaging optical unit according to claim 1 or 2, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels comprises at least one narrowband filter and / or a narrowband spectrally selective reflective element.

9. The imaging optical unit according to claim 1 or 2, characterized in that: The means for reducing the spectral bandwidth of the one or more color channels comprises at least: - two broadband filters, - two broadband spectrally selective reflective elements, or - a broadband filter and a broadband spectrally selective reflective element, Together they cause a reduction in the spectral bandwidth of the one or more color channels.

10. The imaging optical unit according to claim 1 or 2, characterized in that: The optical waveguide (4) is a spectacle lens (22, 23).

11. The imaging optical unit according to claim 1 or 2, characterized in that: The imaging optical unit comprises at least one imaging optical element integrated into the optical waveguide (4).

12. A head mounted display comprising an image generator (1) for presenting an original image, and an imaging optical unit as claimed in any one of claims 1 to 11 for forming a virtual image of the original image presented on the image generator (1).

13. The head mounted display according to claim 12, wherein: Its configuration is smart glasses.

14. A method for improving the imaging quality of an imaging optical unit when transmitting one or more color channels each having a spectral maximum and a spectral bandwidth, wherein: The one or more color channels are transmitted by the light-guiding arrangement (3) of the imaging optical unit, characterized in that the spectral bandwidth of the one or more color channels is reduced during the transmission of the one or more color channels by the light-guiding arrangement (3), and the distortions in the images present at the wavelengths of these spectral maxima are compensated by the opposite distortions of the original image at the wavelengths of these spectral maxima, which distortions are generated during the transmission of the corresponding color channels, the original image being presented on the display and serving as the basis for imaging.

15. The method according to claim 14, characterized in that At least one first color channel and one second color channel are transmitted, the color channels having respective different spectral maxima and respective spectral bandwidths, wherein the spectral bandwidths of the first color channel and the second color channel are reduced during transmission of the first color channel and the second color channel by the light guide arrangement (3).

Images