Projector or display including a scanning light source and a pixelated array

Abstract

The invention relates to an imaging unit, preferably comprising a light source (1) for generating an illumination radiation (2) and a light-modulating pixel array (4) for generating an image by pixel-wise modulation of the illumination radiation (2) incident on the pixel array (4). The imaging unit is characterized in that the illumination radiation (2), when it impinges on the light-modulating pixel array (4), has a smaller lateral extent than the pixel array (4) and is guided by a scanning unit (3) over the pixel array (4) to generate an image. By combining the scanning process of the illumination radiation (2) over the light-modulating pixel array (4), the speckle signatures of the scanning unit (3) and the pixel array (4) are superimposed or combined to generate a pixel. Advantageously, the visible speckle pattern in the resulting image can be significantly reduced.

Description

[Technical field]

[0001] The invention preferably relates to an image generating unit having a light source for generating illumination radiation and a light-modulating pixel array for generating an image by pixel-by-pixel modulation of the illumination radiation incident on the pixel array. The image generating unit is characterized in that the illumination radiation, when incident on the light-modulating pixel array, has a smaller lateral extent than the pixel array and is guided by a scanning unit over the pixel array to generate the image. By combining the scanning process of the illumination radiation over the light-modulating pixel array, the speckle signatures of the scanning unit and the pixel array are superimposed or combined to generate an image point. Advantageously, the visible speckle pattern in the resulting image can be significantly reduced in this way.

[0002] The present invention relates to the field of illumination systems, in particular to the reduction of speckle and interference patterns in displays or projectors illuminated by coherent light sources, especially lasers. [Background technology]

[0003] The use of lasers to replace white light sources such as xenon arc lamps leads to many advantages in imaging: in particular, lasers provide higher color saturation, higher performance, improved efficiency and contrast.

[0004] Lasers have also proven to be an advantageous illumination source for applications involving head-up displays (HUDs). HUDs are used, for example, to display information in an imaginary plane in front of the windshield of a car. A car occupant or car driver can read the information without having to look down at the dashboard.

[0005] When coherent light sources such as lasers are used in projectors or displays, an undesirable interference phenomenon, the so-called speckle, can occur. Speckle patterns are image grainy interference phenomena that can be observed especially with sufficiently coherent illumination of optically rough object surfaces.

[0006] When laser light is incident on a rough surface, such as a projection screen, it is reflected at various angles, causing the coherent laser light to spatially interfere randomly. The resulting interference of the coherent light radiation produces constructive and destructive interference. To the human eye, this image defect appears as a visible speckle or speckle pattern.

[0007] The inhomogeneity of the illuminated rough surface can be considered as scattering centers, from which spherical waves of different phases emanate, which interfere in the far field. A spatial structure of randomly distributed intensity minima and maxima is generated. As three-dimensional interference phenomena, there are longitudinal and transverse speckles, which depend on the respective longitudinal and transverse coherences. Transverse speckles are more important at longer distances, because the individual spherical wave components can be simplified as plane waves.

[0008] Speckle is therefore caused by local phase differences within the aperture of an optical system, which inevitably arise due to the surface roughness of individual surfaces within the optical system or the roughness of the projection screen. The speckle pattern is therefore spatially fixed and characteristic for the optical path through the system.

[0009] In the prior art, there are various approaches to reduce the adverse effect that speckle patterns have on image quality.

[0010] In U.S. Patent No. 5,272,473, an image generation system using a coherent light source is proposed, in which a display screen is coupled to a transducer for generating surface acoustic waves to reduce the occurrence of speckle. However, this implementation is complex and additionally cannot be ported to any desired display or projection mechanism.

[0011] US Patent No. 8,262,235 B2 discloses a laser projector including an oscillator, in which at least one optical element of the optical projection system oscillates periodically along the optical axis of the light. The oscillator element in the laser projector is intended to reduce the speckle pattern on the screen to a degree that it becomes invisible to the naked eye. However, variations in the oscillation along the optical axis may degrade image quality.

[0012] US Patent No. 9,541,760 B2 discloses a head-up display for an automobile, which includes a laser and a scanning system, by which an image to be displayed in the field of view of the automobile driver is generated point by point. To avoid unwanted brightness differences, the laser is selected so that the laser point on the projection surface is very small, smaller than the resolution of the human eye even after magnification of the image displayed in the virtual image plane.

[0013] From US Pat. Nos. 4,035,068 and 5,313,479 it is known to use a moving diffuser for speckle reduction, using local phase modulation to average the speckle pattern over the observer / detector integration time and reduce its visibility.

[0014] To reduce observable speckle patterns in an image, WO 97 / 02507 proposes averaging between multiple uncorrelated fields by rotating the speckle field between the object point and the image point in a laser projector around the optical axis.

[0015] US 2008 / 0304128 A1 relates to a laser projection system in which an expanded laser beam is directed to a two-dimensional light modulator, e.g. an LCD panel, which modulates the expanded laser beam pixel by pixel to generate an image on a projection surface. To reduce the visibility of speckle in the projected image, an angle-dependent scan is imprinted on the expanded laser beam. For this purpose, a movable mirror is provided, the surface of which is imaged onto the input of a multimode waveguide, so that the laser beam at the input of the waveguide has a different angle, which leads to averaging the speckle pattern when it is expanded onto the LCD panel and projected onto a projection screen.

[0016] EP 3267236 A1 discloses a projector including an image processing unit and an optical scanner, in which a laser beam is guided in two directions on a surface to be scanned by a MEMS mirror. On the surface to be scanned there are one or more photodetectors, which are arranged to measure the incident laser radiation in the detection area. The measurement signals of the photodetectors can be transmitted to a control unit and used to adjust and / or control the light source of the MEMS mirror. This makes it possible to compensate for variations in the scanning amplitude of the MEMS mirror, for example due to temperature changes.

[0017] The scanning surface is a light-transmitting element, preferably glass. The image drawn on the scanning surface is preferably projected onto a projection screen behind it. The image is preferably generated based on image data in an image processing unit by modulating the driver of the light source. In order to reduce the speckle pattern, the scanning surface is designed in a preferred embodiment as an array of microlenses, so that interference between the light fields of different microlenses and thus the generation of speckles is avoided. Improvements are needed with respect to prior art approaches. In particular, other approaches to reducing speckle patterns are complex to implement, which may at the same time lead to a decrease in image quality. It would therefore be desirable to provide an apparatus that allows for effective speckle reduction by simple means, without affecting image quality. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] U.S. Patent No. 5,272,473 [Patent Document 2] U.S. Patent No. 8,262,235B2 [Patent Document 3] U.S. Patent No. 9,541,760B2 [Patent Document 4] U.S. Pat. No. 4,035,068 [Patent Document 5] U.S. Pat. No. 5,313,479 [Patent Document 6] International Publication No. 97 / 02507 Brochure [Patent Document 7] US Patent Application Publication No. 2008 / 0304128A1 [Patent Document 8] European Patent Application Publication No. 3267236A1 Summary of the Invention [Problem to be solved by the invention]

[0019] The object of the present invention is to provide an image generating unit that does not have the drawbacks of the prior art. In particular, it was an object of the present invention to provide an image generating unit that allows an effective reduction of the speckle pattern by simple and advanced means, while at the same time ensuring an excellent image quality. [Means for solving the problem]

[0020] This object is achieved by the features of the independent claims. Advantageous configurations of the invention are set forth in the dependent claims.

[0021] In a preferred embodiment, the invention relates to an image generating unit having a light source for generating illumination radiation and a light-modulating pixel array for generating an image by pixel-by-pixel modulation of illumination radiation incident on the pixel array, the illumination radiation having a smaller lateral extent than the pixel array when incident on the light-modulating pixel array and being guided by a scanning unit over the pixel array to generate the image, reducing the visibility of speckle patterns in the generated image.

[0022] This advantageously takes advantage of the fact that during generation of the image points, the speckle patterns resulting from the scanning unit and the light modulating pixel array are superimposed and therefore represent a high frequency speckle pattern, which is preferably not visible in the generated image.

[0023] The imaging unit according to the invention advantageously makes it possible to reduce, using simple measures, the speckle patterns visible in the display or projection plane without compromising the image quality.

[0024] According to the present invention, this takes advantage of the fact that both the scanning unit and the light-modulating pixel array have characteristic speckle signatures for different scanning positions or pixel states. In particular, each pixel of the light-modulating pixel array has a specific speckle signature, which depends on the surface condition and / or the control state (e.g., the crystal orientation in the case of an LCD (liquid crystal display)). Similarly, the speckle generated by the scanning unit also differs with the scanning position. In the case of a mirror-based scanning unit, the speckle pattern generated depends not only on the position of the laser beam on the mirror surface, but also on the difference in the light emission angle, which means that the speckle pattern in the light beam changes with the scanning position.

[0025] By combining the scanning process of the light beam over the pixel array, the speckle signatures of the scanning unit and the pixel array are superimposed or combined to generate an image point. Figures 2a)-d) show this as an example. The illumination beam guided by the scanning unit is generated by the scanning unit while sweeping a pixel of the light-modulating pixel array, and the speckle pattern that differs depending on the scanning position is superimposed with the speckle pattern characteristic of each pixel. The resulting image point is advantageously characterized by an averaged speckle pattern, which has a higher spatial frequency and is not perceptible or only perceptible to a lower extent by the observer.

[0026] Reduction in the visibility of the speckle pattern in the generated image is therefore preferably achieved by guiding the illuminating radiation as it sweeps over the pixels of the light-modulating pixel array such that a speckle pattern that differs depending on the scanning position is superimposed on the speckle pattern characteristic of each pixel, the speckle pattern being generated by the scanning unit.

[0027] The image generating unit according to the invention thus advantageously utilizes the inherent variations of the components to generate high quality images without annoying brightness or interference patterns. The light source itself may have high coherence, which is desirable for example for holographic applications, and annoying interference patterns (speckle) are not noticeable. Recognizable speckle patterns are already substantially reduced, so there is no need to reduce the coherence of the light beam, redirect, (de)focus or rotate the illumination beam, or guide it through a microphone lens array. Instead, the speckle is reduced by the image generating scanning process itself on the pixel array as described above, and image quality is not reduced.

[0028] In this respect, the invention represents a departure from known technical approaches: when using light-modulating pixel arrays, it is common in the prior art to illuminate these with an extended illumination beam that is as uniform as possible. Images are generated by pixel-by-pixel modulation of the extended illumination beam, which illuminates the entire pixel array as uniformly as possible.

[0029] According to the invention, it is instead desirable that the illumination radiation, when incident on the light-modulating pixel array, has a smaller lateral extent than the pixel array. Preferably, the illumination radiation, when incident on the pixel array, may have a lateral extent, for example, that is one fifth, one tenth, one hundredth or even less than the lateral extent of the pixel array. This results in the generation (and superposition) of multiple speckle patterns during the process of scanning the illumination radiation on the individual pixels, thereby generating image points. With regard to the illumination radiation, it is therefore preferably guided in focus to the pixel array in the form of a beam. The terms illumination radiation, illumination beam or beam are preferably used synonymously. Optical components such as lenses can collimate or focus the radiation accordingly.

[0030] Speckle reduction can be advantageously achieved for a variety of light sources.

[0031] In a preferred embodiment, the illumination radiation is coherent radiation and / or the light source is a laser. Coherence preferably refers to a property of light waves that results in a fixed phase relationship between two wave trains. As a result of the fixed phase relationship between two wave trains, a spatially stable interference pattern can be generated. In holographic applications, coherent illumination radiation is desirable, because otherwise the intensity and phase of the wave field cannot be reconstructed. A drawback of coherent radiation is the generation of unwanted interference patterns, i.e. speckle patterns. Coherence can also preferably be understood as the ability to interfere.

[0032] Concerning coherence, a distinction can be made between temporal coherence and spatial coherence: spatial coherence preferably describes the degree of fixed phase relationship between the wave-trains perpendicular to the direction of propagation, e.g. obtained for parallel light beams; temporal coherence preferably describes the degree of fixed phase relationship between the wave-trains along the direction of propagation, e.g. obtained for narrowband, preferably monochromatic light beams.

[0033] Coherence length preferably refers to the maximum path length difference or flight time difference that two light beams have from a starting point, such that a stable (spatially and temporally) interference pattern appears during their superposition. Coherence time preferably refers to the time required for light to travel the coherence length.

[0034] Lasers can have coherence lengths in the micrometer, meter and even kilometer ranges. A typical range for using lasers as light sources in image generating units is, for example, 1 m to 100 m, which on the one hand makes them very suitable for holographic imaging, but on the other hand can lead to unwanted (laser) speckle patterns.

[0035] In a particularly preferred embodiment, the light source is therefore a laser, which is particularly preferably a narrow-band, preferably monochromatic laser with a preferred wavelength in the visible range (preferably 400 nm to 780 nm).

[0036] For the purposes of the present invention, laser preferably refers to a light source emitting laser radiation, non-exhaustive examples include a solid-state laser, preferably a semiconductor laser or a laser diode, a gas laser or a dye laser.

[0037] Other light sources, preferably coherent light sources, may also be used if desired. Narrowband light sources, preferably monochromatic light sources including light emitting diodes (LEDs), are preferred, optionally in combination with a monochromator. Compared to lasers, LEDs have a shorter coherence length, most often in the millimeter or micrometer range.

[0038] In a preferred embodiment, the image generating unit comprises two or more light sources, preferably two or more monochromatic lasers and / or a polychromatic light source with illumination radiation in two or more wavelength ranges. The illumination radiation emitted by the two or more light sources is preferably guided along a common optical axis over the light-modulating pixel array by the same scanning unit. However, it is also possible to guide the two or more light sources via separate scanning units.

[0039] For colour imaging, for example, it may be preferable to provide illumination radiation in the red wavelength range (preferably 630 nm to 700 nm), the green wavelength range (preferably 500 nm to 560 nm) and the blue wavelength range (preferably 450 nm to 475 nm).

[0040] Particularly preferably, a laser system is provided for this purpose which has three monochromatic lasers or one polychromatic laser, each with a laser emission in the red, green or blue (RGB) range.

[0041] To control components of the image generating unit, such as the light modulating pixel array and / or the scanning unit, the image generating unit preferably comprises a control unit.

[0042] The control unit is preferably adapted to output and / or receive electrical control signals to and from the components for this purpose. Without being limited thereto, the control unit may include, for example, a microprocessor, a microcomputer, an integrated circuit (IC), an ASIC (Application Specific Integrated Circuit), a programmable logic circuit (PLD), a field programmable gate array (FPGA), a programmable logic controller and / or other electronic circuit elements, such as digital-to-analog converters, analog-to-digital converters, memories and / or (signal) amplifiers.

[0043] The skilled person will understand that the preferred method steps for image generation disclosed with respect to the image generation unit may preferably be executed by the control unit. Preferably, corresponding software and / or firmware can be installed for this purpose in the control unit or in an external data processing unit connected to the control unit.

[0044] The illumination radiation or light beam is preferably guided by a scanning unit over the pixel array.

[0045] Preferably, the scanning unit (or a control unit connected thereto) is configured to guide the illumination radiation line-by-line or column-by-column across the pixel array. The scanning frequency of the scanning unit preferably refers to the frequency with which the scanning unit scans across the pixel array or the frequency with which the illumination radiation sweeps over one and the same pixel. Thus, a scanning frequency of 25 Hz preferably means that the scanning unit scans across the pixel array 25 times per second, or preferably sweeps over a particular pixel 25 times per second when scanning line-by-line or column-by-column.

[0046] In a preferred embodiment, the scanning frequency is higher than 20 Hz, preferably higher than or equal to 25 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz.

[0047] The scanning unit can be any of a variety of systems.

[0048] In a preferred embodiment, the scanning unit includes one or more scanning mirrors, which are preferably tiltable about one or more axes. For example, the scanning unit may include a first scanning mirror, tiltable about a first axis to guide the illumination radiation in a first direction (e.g., horizontal) on the pixel, and a second scanning mirror, tiltable about a second axis to guide the illumination radiation in a second direction (e.g., vertical) on the pixel. Preferably, the scanning mirrors may be galvanometer mirrors (e.g., with gimbal suspension) or microelectromechanical mirrors (MEMS). The scanning unit may use individual scanning mirrors (tilting in at least two axes) or a combination of two or more scanning mirrors.

[0049] In another embodiment, the scanning unit includes one or more lenses and / or lens arrays, which allow controllable movement of the illumination beam on the pixel array. For this purpose, at least one of the lenses may be of a translatable and / or rotatable design. Similarly, the scanning unit may have prisms and / or wedges as beam splitting elements.

[0050] In another embodiment, the scanning unit includes one or more diffractive optical elements, which allow for controllable movement of the illumination radiation over the pixel array. A scanning unit including a diffractive optical element formed as two diffractive Fresnel lenses with offset and opposite refractive powers is described in Bawart et al. (Bawart et al., Dynamic beam-steering by a pair of rotating diffractive elements, Optics Communications 460 (2020) 125071).

[0051] Other scanning systems are conceivable - for example the use of an acousto-optical deflector (AOD) may be preferred - and of course different technologies can also be combined.

[0052] Preferably, the light-modulating pixel array (or a control unit connected thereto) is configured to modulate the illumination radiation incident on the pixel array on a pixel-by-pixel basis. The modulation is preferably an intensity modulation and / or a phase modulation of the illumination radiation. The modulation is preferably performed on a pixel-by-pixel basis such that each pixel of the light-modulating pixel array is controllable to set a modulation state, i.e. a defined intensity modulation and / or phase modulation for the pixel area. The pixel array is preferably a two-dimensional surface type light modulator.

[0053] In a preferred embodiment, the pixel array comprises a plurality of pixels, preferably 100, 200, 500, 1000, 5000, 10,000, 50,000, 100,000, 500,000, 1,000,000 or more pixels.

[0054] Preferably, the pixels are arranged in a plane or surface that is preferably perpendicular to the optical axis along which the illumination radiation substantially propagates.

[0055] The terms substantially, approximately, about, approximately, etc. preferably indicate an error range of less than ±20%, preferably less than ±10%, particularly preferably less than ±5% and especially less than ±1%, always including the exact value. Preferably, "similar" indicates a magnitude that is approximately the same. "Partially" preferably indicates at least 5%, particularly preferably at least 10%, especially at least 20% or at least 40%.

[0056] The pixels are preferably arranged in the pixel array in the form of a matrix, with a line-by-line or column-by-column arrangement of pixels being particularly preferred, resulting in a pixel array that is, for example, rectangular in shape with horizontal and vertical extent, as well as other arrangements of the pixels in the pixel array, for example concentric circles, being conceivable.

[0057] The pixels may preferably have a rectangular, square or diamond shape, although other two- or three-dimensional shapes are conceivable, such as circles, ellipses, triangles, polygons, etc.

[0058] The array frequency of a pixel array preferably refers to the frequency at which the pixel array can change the state of all pixels of the pixel array to generate an image or the frequency at which the state of each pixel of the pixel array can be changed to generate an image. The states of the pixels of the pixel array can preferably be changed simultaneously. It may also be preferred to change the states of the pixels of a line and / or column of the pixel array simultaneously or to change the states of individual pixels sequentially. In the first case, the array frequency corresponds to the frequency at which the states of all pixels are controlled simultaneously, while in the latter two cases it corresponds to the frequency at which the states of the pixels of the same line / column are changed to generate an image or the frequency at which the states of individual pixels are changed.

[0059] In a preferred embodiment, the array frequency is greater than 20 Hz, preferably greater than or equal to 25 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz.

[0060] For the purposes of the present invention, refresh rate preferably refers to the frequency at which one image per second can be generated by an image generating unit.

[0061] The refresh rate preferably corresponds to the minimum of the scan frequency and the array frequency, the scan frequency preferably being equal to an (integer) multiple of the array frequency and / or the array frequency preferably being equal to an (integer) multiple of the scan frequency.

[0062] The generation of an image by an image generating unit is described below by way of a non-limiting example in which the scanning frequency is equal to the array frequency.

[0063] For example, for the generation of an image, it may be arranged that the state of all pixels of the pixel array is changed simultaneously at an array frequency of 30 Hz. The scanning unit likewise guides the illumination radiation over all the pixels of the pixel array at a scanning frequency of 30 Hz. This means that the scanning unit scans the entire pixel array at a frequency of 30 Hz or the illumination radiation sweeps one and the same pixel accordingly at a frequency of 30 Hz. The state of each pixel that the illumination radiation sweeps over at a frequency of 30 Hz also changes at the array frequency of 30 Hz. Thus, the image points of the generated image are generated or defined at a refresh rate of 30 Hz. The image points are preferably generated over a period of time during the scanning process while the illumination radiation illuminates or sweeps over the corresponding pixel of the pixel array. In each new scanning process, a modified image point may be generated or defined according to any change in the pixel state on the pixel array. If the refresh rate is high enough, as in this case, the limited integration time of the eye will result in the successively generated image points being perceived as a continuous image.

[0064] Such image generation by combination of a scanning unit and a pixel array represents a development from known approaches of the prior art, where, for example, a light-modulating pixel array is illuminated with an extended substantially uniform illumination radiation. In these cases, the refresh rate is specified by the array frequency of the pixel array. If the pixels of the pixel array change their state with a frequency of 30 Hz, then the corresponding image is generated at 30 Hz as well. In the case of an extended substantially uniform illumination radiation, each pixel is permanently illuminated.

[0065] The introduction according to the present invention of an additional scanning unit, with which each pixel is not permanently illuminated, but with which illumination radiation is guided over the pixel array in a repetitive scanning process, is not self-evident to a person skilled in the art and appears on the surface to be redundant.

[0066] However, as explained in the introduction, according to the present invention, it is recognized that by performing a scanning process on the pixel array to generate an image point, the speckle signatures of the scanning unit and the pixel array are superimposed or combined. While the illumination beam guided by the scanning unit sweeps over a pixel of the light-modulating pixel array, the speckle pattern resulting from the scanning unit and different depending on the scanning position is superimposed with the speckle pattern characteristic of the respective pixel. The resulting image point is advantageously characterized by an averaged speckle pattern, which has a higher spatial frequency and is not perceptible or only perceptible to a lower extent by the observer. According to the present invention, different light-modulating pixel arrays can also be used.

[0067] In a preferred embodiment, the light-modulating pixel array is a liquid crystal display (LCD) and / or a micromatrix, preferably a micromirror array, such as a digital micromirror device (DMD). Other spatial light modulators (SLMs) may also be used.

[0068] A large number of liquid crystal displays are known in the prior art that may be used in the present invention.

[0069] In general, liquid crystal displays are based on the fact that liquid crystals can affect the direction of polarization of light depending on an applied voltage. By pixel-by-pixel modulation of the crystal orientation, polarized illumination radiation can thus be made to be transmitted or absorbed pixel by pixel, generating an image. For example, the polarized light can be rotated by 90 degrees in one state of the liquid crystal, but not in the other state. To produce an LCD in an absorbing or transmitting state, polarizers can be provided on each side of the liquid crystal such that their polarization angles are offset by 90 degrees.

[0070] For example, the liquid crystal display may include transparent electrodes attached to the inner surfaces of the two substrates in different display modes, e.g., a twisted nematic (TN) display mode in which the positive (+) dielectric isotropy of the liquid crystal molecules is arranged parallel to the substrates and twisted at an angle difference of 90 degrees between the substrates, or a super twisted nematic (STN) display mode in which the liquid crystal molecules are arranged similarly to the TN display mode, but twisted at an angle difference of 180 to 270 degrees between the substrates. Other display types, e.g., triple super twisted nematic, are also contemplated. A number of different liquid crystal displays may be used in accordance with the present invention.

[0071] The micromirror array is preferably a microelectromechanical system (MEMS) including a plurality of micromirrors for dynamic modulation of light. In a (tilt) mirror matrix or micromirror array, preferably a DMD, pixels are formed by individual (micro)mirrors, which can preferably be deflected individually. The individual micromirrors of the (tilt) mirror matrix can preferably be electrostatically actuated, in particular switched between at least two (tilt) states, preferably one state diverting the illumination radiation to an image point on the image to be generated and the other state diverting the illumination radiation outside the image to be generated, for example to an absorbing plate.

[0072] DMDs can have different configurations. For example, the mirror can be connected to an underlying yoke, which itself is connected to a support post attached to the underlying substrate via two thin, mechanically flexible torsion hinges. An electrostatic field generated between the underlying memory cell (e.g., SRAM), the yoke, and the mirror can induce a positive or negative tilt direction.

[0073] Advantageously, the inherent variation in speckle signature of the scanning unit and pixel array as specified as preferred leads to a significant reduction in speckle. One preferred parameter for reducing speckle depending on the application is also the lateral extent of the illumination beam on the pixel array.

[0074] In preferred embodiments, the illumination radiation, when incident on the pixel array, has a (maximum) lateral extent that is one-fifth, one-tenth, one-hundredth or less than the (minimum) lateral extent of the pixel array.

[0075] In preferred embodiments, the illumination radiation has a (maximum) lateral extent when incident on the pixel array of less than 50, 30, 20, 10, 5, 4, 3, 2 pixels or 1 pixel. It may also be preferred that the maximum lateral extent of the illumination radiation when incident on the pixel array is, for example, only 0.8, 0.5, 0.2 or less of the size of a pixel. Similarly, it may be preferred that the maximum lateral extent of the incident radiation when incident on the pixel array is more than 1 pixel or more than 2, 3, 4, 5, 10 pixels or more.

[0076] In a preferred embodiment, the maximum lateral extent of the illumination radiation as it is incident on the pixel array may be between 0.2 and 50 times the size of one pixel.

[0077] With regard to the illumination radiation, it is preferred that it is guided to the pixel array in a focused state in the form of a beam. The lateral extent of the illumination radiation upon incidence on the pixel array is preferably given by the full width at half maximum (FWHM) of the light intensity. The lateral extent of the illumination radiation upon incidence on the pixel array therefore preferably corresponds to the spot size (FHMW) of the illumination radiation on the pixel array.

[0078] The lateral extent of the pixel array preferably refers to the smallest extent along the plane of the areal pixel array (measured at the centroid of the area). In the case of a square pixel array, the smallest lateral extent preferably corresponds to the length of the square. In the case of a rectangular shape of the pixel array, the smallest lateral extent preferably corresponds to the shorter of the two lengths of the rectangle. In the case of a circular pixel array, the lateral extent is preferably given by the diameter.

[0079] The above-mentioned preferred dimensions show particularly good results in terms of reducing speckle patterns in the generated patterns. On the one hand, the magnitude of the incident illumination radiation is small enough to ensure that for the generation of an image point (corresponding to a pixel of the pixel array), multiple speckle signatures (resulting from different scanning positions of the scanning system) are superimposed with the speckle signature of each pixel. On the other hand, the magnitude of the incident illumination radiation is not so small that the speckle signatures of the scanning system and the pixel array are not effectively averaged.

[0080] Those skilled in the art will appreciate that optical components ensure that the illumination radiation has a desired beam profile upon incidence on the pixel array.

[0081] In a preferred embodiment, one or more lenses and / or a lens array are present in front of the pixel array in the beam path to set the lateral extent of the illumination radiation upon incidence on the pixel array, preferably to ensure a smaller spot size of the illumination radiation on the pixel array.

[0082] In a preferred embodiment, one or more lenses are in the beam path between the scanning unit and the pixel array, which ensures that the illumination radiation is guided to the pixel array regardless of the point of incidence on the pixel array at a constant angle of incidence. The one or more lenses may preferably be diffractive, refractive or Fresnel lenses. In a preferred embodiment, the one or more lenses may be positioned such that the scanning unit is at the object-side focus of the lens (see FIG. 11). The distance between the scanning unit and the one or more lenses may also be varied to set a desired radiation pattern.

[0083] The inherent variation of speckle signatures of commercially available scanning units and pixel arrays already advantageously leads to a significant reduction in recognizable speckle structures or patterns in the generated image. For the purposes of the present invention, the term speckle signature preferably characterizes the properties of the components of the image generating unit that generate a characteristic speckle pattern in the generated image. As explained in the introduction, speckle patterns are image grainy interference phenomena that can be observed especially with sufficiently coherent illumination of optically rough object surfaces. To generate an image point, the multiple speckle signatures of the scanning system (resulting from the difference in scanning position) can advantageously be superimposed with the speckle signature of each pixel (depending on its state value).

[0084] To further increase speckle reduction, it may be preferable to introduce an additional phase change for the illumination radiation by the scanning unit and / or pixel array.

[0085] In a preferred embodiment, the image generation unit is configured to impart an additional phase change to the illumination radiation by the pixel array and / or the scanning unit, which can increase the variation of the speckle signature of the pixel array and / or the scanning unit.

[0086] To increase the variation of the speckle signature of the pixel array and / or the scanning unit, different approaches can be envisaged.

[0087] In a preferred embodiment the image generating unit is configured to additionally modulate the pixel states for each generated image, preferably the modulation frequency of the pixel states being two, four or more times higher than the refresh rate of the image generating unit. The expression image generating unit is configured preferably means that a control unit comprised in the image generating unit is configured to perform the aforementioned method steps (here modulation of pixel states), e.g. corresponding software and / or firmware being installed for this purpose in the control unit and / or in an external data processing device connected thereto.

[0088] Similar to amplitude modulation, the state of a pixel can be changed multiple times, for example with respect to a light source, during which the eye synthesizes an image. Preferably, the modulation frequency of the pixel state should be so high that the eye cannot distinguish between the individual images. Preferably, the pixel changes its state multiple times (for example 2, 4, 6 or more times) within the desired refresh rate. Provided that the refresh rate or the frequency of state changes is high enough, the pixel therefore changes its state multiple times within the integration time of the eye. The state perceived per image preferably corresponds to the average value of all of the pixel states within the refresh rate. As an example, this is shown in FIG. 3, where in the illustrated embodiment, the pixel state changes its state four times within the integration time of the eye or within the desired refresh rate (t_int).

[0089] In a liquid crystal display, for example, a temporal sequence of different phase or amplitude values ​​can be manifested for a pixel to implement a modulation frequency of the pixel state, so that only when integrated in time over the refresh rate does the desired phase or amplitude value for the generated image result.

[0090] The array frequency corresponds in a preferred embodiment to an integer multiple of the refresh rate, which may be 2, 4, 6 or more times, causing pixel states to change during the generation of an image point.

[0091] The scanning frequency should preferably correspond to or represent an integer multiple of the modulation frequency of the pixel states.

[0092] For example, at an array frequency of 120 Hz and a scanning frequency of 120 Hz, the refresh rate can be reduced to 60 Hz, provided that each pixel has two different states per generated image, and for four different states the refresh rate is reduced to 30 Hz.

[0093] In another preferred embodiment, the image generating unit is configured to additionally modulate the scanning unit for a phase change of the illumination radiation, preferably the modulation frequency of the scanning unit is 2, 4, 6 or more times higher than the refresh rate of the image generating unit, and / or preferably one or more components of the scanning unit are excited to vibrate by an actuator.

[0094] For scanning units, a similar additive speckle reduction effect can be achieved if different phase values ​​are additively imprinted onto the illumination radiation faster than the eye can resolve.

[0095] Preferably, one or more components of the scanning unit can be excited to vibrate by an actuator for this purpose. Preferably, the actuator for this purpose is mechanically coupled to at least one component of the scanning unit and is configured to vibrate the component. The actuator can be, for example, an electrostatic, piezoelectric, electromagnetic and / or thermal actuator. Preferably, the actuator also exists as a MEMS actuator and can therefore be extremely compact. Corresponding actuators are known in the art, for example piezoelectric or micromechanical modulators. For example, an oscillating crystal can also be used as a frequency transmitter for the actuator or can function as an actuator itself.

[0096] For example, in the case of a scanning system including one or more scanning mirrors, the mirror surface of the scanning mirror may be excited to vibrate by one or more actuators. The vibration excitation by the actuators may occur in the mirror plane (see FIG. 4) and / or perpendicular thereto (see FIG. 5). Similarly, lenses, wedges, prisms or other components of a preferred scanning unit may be excited to vibrate.

[0097] Advantageously, mechanical vibration of the components of the scanning unit leads to an additional variation or modulation of the speckle signature for a specific scanning position (point of incidence of the illumination radiation on the pixel array). In case of vibration excitation of the scanning mirror or lens, the surface and thus the microscopic roughness of the surface vibrates at an additional mechanical modulation frequency, so that the speckle pattern or speckle signature on the pixel array changes at that modulation frequency even at a constant scanning position.

[0098] The additional modulation frequency of the scanning unit is preferably higher or lower than the scanning frequency of the scanning unit or the array frequency of the pixel array. Preferably, the additional modulation frequency of the scanning unit (e.g. the vibration frequency of the components of the scanning unit) should be more preferably 2, 4, 6, 8, 10 times higher or more than the refresh rate.

[0099] In another preferred embodiment, the image generating unit further comprises one or more diffusers in the beam path between the light source and the light-modulating pixel array, preferably between the scanning unit and the light-modulating pixel array.

[0100] The diffuser is an optical element that preferably adds an additional random or stochastic phase to the illumination beam. Preferably, the diffuser has multiple randomly distributed scattering centers, at which the light beam is scattered in different directions.

[0101] As shown in Fig. 8, the diffuser thus preferably mixes the individual beams of possibly collimated illumination radiation that are incident on the diffuser at different points of incidence. As a result, the coherence length of the illumination radiation can be further reduced. The diffuser can be designed as an optical element with a random phase or as one or more lens arrays. Preferably, the diffuser can also be such that its radiation pattern varies depending on the lateral position on the diffuser. This allows the radiation pattern of the entire system to be modulated, for example to generate a larger or smaller eyebox.

[0102] In a preferred embodiment, the diffuser is selected from the group comprising a lens array, a refractive and / or a diffractive diffuser.

[0103] Diffusers can cause surface and / or volume scattering. Diffusers can be designed as reflective or transmissive optical elements.

[0104] In the case of surface scattering, the illumination radiation is preferably scattered at the surface of the diffuser, which surface is preferably treated for that purpose. For example, a plate made of a transparent material (e.g., glass) can be mechanically, chemically and / or optically treated to act as a diffuser (see U.S. Pat. No. 4,035,068, in particular for providing a glass diffusing plate by polishing and etching the surface). The desired diffusion effect can also be specified by microstructuring the surface of the transparent material.

[0105] The transmissive diffusing element may also be preferably designed to provide volume scattering, preferably with a substantially transparent material surrounding scattering centers, e.g. transparent and / or opaque particles, through which the illumination radiation is phase-modulated and / or amplitude-modulated. In the case of volume scattering, it is preferable to use a thin layer diffuser, so that speckle pattern reduction can be achieved as described above, without significant degradation in performance.

[0106] The diffusion angle is the scattering power of the diffuser and thus the degree of mixing of the individual beams. In a preferred embodiment, the scattering angle of the one or more diffusers is between 0.5° and 35°, preferably between 1° and 20°, particularly preferably between 1° and 10°.

[0107] In a particularly preferred embodiment, the image generating unit comprises two or more diffusers, which are preferably arranged successively at a spatial distance in the beam path, which leads to a further improved reduction of the speckle and / or interference patterns.

[0108] As shown in Fig. 8, it is advantageously utilized that the illumination radiation, which is initially scattered by the first diffuser, is already incident on the second diffuser at several different points of incidence. Thereby, several speckle patterns are superimposed simultaneously. The number of superimposed beams or speckle patterns on the pixel array (and in the image plane) is several times larger than when using one diffuser. The arrangement of the diffusers with a spatial distance in succession along the optical axis therefore leads to an enhancement of the superimposition of the individual beams. If the spatial frequency of the superimposed speckle patterns is high enough, they cannot be resolved by the eye and therefore do not adversely affect image quality.

[0109] In a preferred embodiment, the diffusion angle of the first and / or second diffuser is 0.5° to 35°, preferably 1° to 20°, particularly preferably 1° to 10°. The spatial distance between the first and second diffusers is preferably 0.5 mm to 100 mm, preferably 1 mm to 50 mm.

[0110] The image generation unit can be designed as a display and a projector.

[0111] In a preferred embodiment, the image generating unit is formed as a display, and the light-modulating pixel array forms a display screen and / or the image generated by the light-modulating pixel array is projected onto a (semi-)transparent display screen. In a preferred embodiment, the image generated by the pixel array can therefore be directly viewed in transmitted light (see FIG. 10) or the image generated by the pixel array is imaged onto a transparent or semi-transparent display screen, which can be viewed in transmitted light.

[0112] In a preferred embodiment, the light-generating unit is designed as a projector and the image generated by the light-modulating pixel array is projected onto a reflective, preferably diffusely reflective, projection screen.

[0113] In a preferred embodiment, the image generating unit is used in a head-up display (HUD). The HUD may include a volume holographic optical unit, which is a diffraction grating structure that exhibits a strong wavelength dependence (dispersion). As a result, the observation angle of the HUD varies with wavelength, and as a result, the HUD is blurred in the case of broadband illumination. An image generating unit for such a HUD should therefore have a spectral line that is as narrow as possible. Advantageously, narrow-band, preferably monochromatic illumination radiation can be provided using the image generating unit according to the invention, and the associated coherence does not cause adverse interference hardening or speckle patterns.

[0114] Various possibilities are envisaged for the arrangement of the image generating unit including the scanning unit, the light-modulating pixel array and other possible optical components for shaping and / or guiding the illumination radiation.

[0115] In a preferred embodiment, the image generating unit comprises a substrate body that is transparent to illumination radiation and has a bonding surface, through which the illumination radiation in the transparent substrate body is directed towards a rear surface on which a redirecting element is present, the redirecting element being formed such that the incident illumination radiation is redirected towards a front surface of the substrate body, through which the illumination radiation exits onto the light-modulating pixel array.

[0116] The embodiment proves to be particularly compact. In particular, the space taken up by the image generating unit perpendicular to the light-modulating pixel array can be significantly reduced. Preferably, the mounting space perpendicular to the pixel array is predefined by the distance between the rear and front faces of the substantially transparent substrate body, which can preferably be kept very small compared to the lateral extent (i.e., for example, height and / or width) of the pixel array. In a preferred embodiment, the distance between the front and rear faces of the transparent substrate body can be 5 times, 10 times, 50 times or less than the maximum lateral extent (i.e., for example, height and / or width) of the pixel array.

[0117] The rear and / or front surface of the transparent substrate body may be formed as a flat surface. For example, the transparent substrate body may exist as a plane-parallel plate or a cube in basic form. However, the front and / or rear surface may also be curved.

[0118] As a basic shape, the transparent substrate body preferably has the shape of a cube with a rear and a front face arranged parallel to each other. Preferably, the thickness of the cube, i.e. the distance between the rear and the front face, is preferably significantly smaller than the height and / or width of the rear and / or front face, which is preferably adjusted to the dimensions of the pixel. For example, the thickness of the cube can be 1 / 5, 1 / 10, 1 / 50 or less than its height and / or width. The substrate body is preferably substantially transparent with respect to the wavelength of the illumination radiation.

[0119] Preferably, the substrate body comprises a material which is preferably an optical plastic selected from the group comprising polymethylmethacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP), cycloolefin copolymer (COC) and / or an optical glass preferably selected from the group comprising borosilicate glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and / or P-BK7.

[0120] The image generating unit is preferably configured to diverge the illumination radiation generated by the light source, preferably in the form of a beam as described above, onto the binding surface by the scanning unit and guide it within the substrate body towards the direction of the redirecting element.

[0121] The binding surface may preferably have a shape that ensures that the illumination radiation is as free as possible from divergence and / or aberration when entering the transparent substrate body, for example it may be preferred that the binding surface has a concave shape, which ensures that the illumination radiation guided by the scanning unit enters the substrate body at a substantially perpendicular angle with respect to the binding surface for different scanning positions (see FIG. 12).

[0122] Within the transparent material of the substrate body, illumination radiation is incident on a redirecting element, which may preferably be applied directly to the rear surface of the substrate body. The redirecting element directs the illumination radiation towards the opposite front surface of the preferably transparent substrate body. The light radiation exits the material through the front surface and is incident on the pixel array.

[0123] In a preferred embodiment, the redirecting element is a redirecting hologram, which is preferably formed as a volume hologram, a reflection and / or a transmission hologram. The redirecting element may also preferably be formed by a microstructured diffractive element and / or a (structured) mirror surface.

[0124] In the case of a diffractive direction-changing element, e.g. a direction-changing hologram, not only the zero-order undiffracted light of the illumination radiation but also light of the illumination radiation that is diffracted into diffraction orders other than the one desired in the direction of direction-changing may propagate as interference light within the transparent substrate body.

[0125] For example, the diffractive direction-changing element is configured to guide the nth order illumination radiation towards the pixel array, and in that sense, the interference light preferably refers not only to the zeroth order undiffracted light of the illumination radiation, but also to diffraction orders different from the nth order diffraction.

[0126] In a preferred embodiment, the image generating unit may be configured to interfere with the light from the diffractive redirecting element and at least a portion may be guided to the pixel array. Advantageously, the light may be guided by the interfered light to further points of incidence on the pixel array, further reducing the visible speckle pattern by additional superposition.

[0127] In a preferred embodiment, the image generating unit may also be configured to interfere with the light from the diffractive redirecting element to exit the surface of the substrate body without entering the pixel array. For example, the scanning angle region of the scanning system may be specified for this purpose to ensure that the interfering light exits outside the area of ​​the pixel array. Similarly, it may be preferred that the coupling surface is designed such that the illumination radiation is incident on the redirecting element at the same angle of incidence, regardless of the scanning position. For this purpose, it may be preferred to use, for example, freeform optical units, biconic lenses, rotationally symmetric lenses and / or refractive or diffractive elements. Furthermore, the rear surface of the transparent substrate body, on which the redirecting element is attached, may also be adapted to direct the interfering light away from the pixel array, for example by a concave shape (see FIG. 15).

[0128] Preferably, one or more diffusers can also be incorporated into the image generating unit of the above compact design to further reduce the visibility of speckle pattern.One or more diffusers can preferably be installed between the scanning unit and the transparent substrate body, between the transparent substrate body and the pixel array, between the light source and the scanning unit or between the direction conversion element and the transparent substrate body.

[0129] The invention is explained in more detail below by means of examples and figures, without however being limited thereto. [Brief description of the drawings]

[0130] [Figure 1] 1 shows a schematic diagram of a preferred embodiment of an image generation unit according to the present invention; [Diagram 2] 1 shows a schematic diagram of a) the pixel array and b) the speckle signature of the scanning unit and their superposition with respect to c) the scanning position and d) the image point. [Diagram 3] FIG. 13 shows a schematic diagram of increasing the variance of the speckle signature of a pixel array by additional modulation of pixel states per generated image. [Figure 4] 13 shows a schematic diagram of increasing the variation of the speckle signature of a scanning unit by exciting the scanning mirror to oscillate along the mirror plane. [Diagram 5] 13 shows a schematic diagram of the increase in the variation of the speckle signature of a scanning unit by exciting the scanning mirror to oscillate perpendicular to the mirror plane. [Figure 6] 1 shows a schematic diagram of a preferred embodiment of an image generating unit having a diffuser in the beam path. [Figure 7] FIG. 2 shows a schematic diagram of a preferred embodiment of an image generating unit having two diffusers in the beam path. [Figure 8] FIG. 1 shows a schematic diagram of overlapping of multiple beams by using two diffusers in the beam path. [Figure 9]FIG. 2 shows a schematic diagram of a preferred embodiment of an image generating unit having a lens to ensure a constant angle of incidence of the illumination radiation on the pixel array. [Figure 10] 1 shows a schematic diagram of a preferred embodiment of an image generating unit designed as a display. [Figure 11] FIG. 2 shows a schematic diagram of a preferred embodiment of an image generation unit designed as a projector. [Figure 12] 1 shows a schematic diagram of a preferred embodiment of an image generating unit with reduced mounting space perpendicular to the pixel array. [Figure 13] 1 shows a schematic diagram of a preferred embodiment of an image generating unit with reduced mounting space perpendicular to the pixel array, in which coherent light is guided to the pixel array. [Figure 14] 1 shows a schematic diagram of a preferred embodiment of an image generating unit with reduced mounting space perpendicular to the pixel array, in which the incidence of interfering light on the pixel array is avoided by specifying the scan angle. [Figure 15] FIG. 1 shows a schematic diagram of a preferred embodiment of an image generating unit with reduced mounting space perpendicular to the pixel array, which is avoided by shaping the steering element. [Figure 16] FIG. 2 shows a schematic diagram of a preferred embodiment of an image generating unit with reduced mounting space perpendicular to the pixel array, which is avoided by the design of the coupling surfaces. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0131] FIG. 1 shows a schematic diagram of a preferred embodiment of an image generation unit according to the invention.

[0132] The image generating unit preferably comprises at least one light source 1 for generating illumination radiation 2 which is guided on an optical axis as a beam. By means of a scanning unit 3, the illumination radiation 2 is guided over a light-modulating pixel array 4 to generate an image. The light source 1 may be a system of several, preferably monochromatic lasers, which are guided on a common optical axis by further optical components. The diameter of the beam of illumination radiation 2 on incidence on the pixel array 4 may be larger or smaller than the size of one pixel, but smaller than the entire pixel array 4.

[0133] To reduce the speckle pattern, the image generating unit according to the invention exploits the fact that both the scanning unit 3 and the light-modulating pixel array 4 have characteristic speckle signatures for different scanning positions or pixel states.

[0134] Advantageously, the speckle signatures of the scanning unit 3 and pixel array 4 are superimposed or combined during the image point generation of the scanning process, resulting in a reduction of visible or discernible speckle patterns in the generated image.

[0135] FIG. 2 shows the speckle signatures of the pixel array 4 and the scanning unit 3 and their superpositions in a schematic way. FIG. 2a) shows the speckle signature of a pixel of the light-modulating pixel array 4. The speckle signature of a pixel may depend, for example, on the surface condition and / or the control condition (e.g., the crystal orientation of an LCD display). Dx indicates the size of the pixel in the scanning direction. FIG. 2b) shows the speckle signature of the scanning unit 3 at a specific scanning position (dx). In the case of a scanning unit 3 using a mirror, the speckle signature may depend, for example, on the surface condition of the mirror surface 5.

[0136] Alternatively, the speckle signature of a pixel array (FIG. 2a) or a scanning unit (FIG. 2b) is characterized by significant minima and maxima, which can be perceived by an observer as brightness differences or specks in the generated image points or images.

[0137] FIG. 2c) shows the superposition of the speckle signature of the scanning unit 3 at a particular scanning position with the speckle signature of the pixel array 4. This already leads to a higher spatial frequency of the speckle pattern and therefore a lower visibility. A particularly strong reduction of the speckle pattern is achieved in that when one pixel is swept over one and the same image point, multiple speckle patterns (depending on the scanning position) are generated, which are superimposed with the speckle signature of the pixel.

[0138] In a stepwise scanning process, the number of superimposed speckle patterns is equal to the number of scanning steps. In the case of analogue movement, the number of speckle patterns is infinite, with small variations between individual speckle patterns. With a sufficient scanning frequency, the human eye cannot recognize these individual patterns. All speckle patterns over a period of time are summed up, which cannot be distinguished by the eye. Figure 2d) shows an example of the summation of all speckle patterns occurring in the range of -Dx ≦ dx ≦ Dx, when the step size is Dx / 80. The contrast of the speckle pattern (i.e. the distance between the minimum and maximum of the intensity distribution) is clearly reduced, thereby achieving a significant reduction in the recognizable speckle patterns.

[0139] The inherent variation in the speckle signatures of commercially available scanning units and pixel arrays is usually already sufficient for significant speckle reduction. To further increase this, additional phase variations can be introduced through both the scanning unit 3 and the pixel array 4.

[0140] FIG. 3 illustrates diagrammatically the increased variance of the speckle signature of a pixel array 4 due to the additional modulation of pixel states for each generated image.

[0141] For example, similar to amplitude modulation in a light source, the state of one pixel can be changed several times while the eye adds up the images: for this, the modulation frequency must be high enough so that the eye cannot distinguish the individual images.

[0142] As shown in Fig. 3a), preferably one pixel can change its state four times within the integration time of the eye or within the desired refresh rate (t_int). The recognized state corresponds to the average value of all states within t_int (see Fig. 3b), and the corresponding speckle patterns are advantageously superimposed or averaged within the integration time.

[0143] 4 and 5 show schematic diagrams of an exemplary embodiment for increasing the variation of the speckle signature of the scanning unit 3 by exciting the scanning mirror 5 to oscillate along the mirror plane 6 (FIG. 4) or perpendicular to the mirror plane 6 (FIG. 5) by an actuator 7. The oscillation can be induced, for example, by a piezoelectric or micromechanical modulator or a quartz crystal. Preferably, the speckle signature of the scanning unit 3 is changed at high frequency by the actuator, and the modulation frequency of the scanning unit 3 is preferably significantly higher than the refresh rate.

[0144] Figure 4 shows a scanning mirror 5 with gimbal suspension, which is oscillated along the mirror plane 6 by an actuator with a frequency transmitter 7. Figure 5 shows a scanning mirror 5 in gimbal suspension, which is oscillated perpendicular to the mirror plane 6 by an actuator with a frequency transmitter 7.

[0145] Additionally, additional elements that add a speckle signature can be introduced in the beam path, preferably between the scanning unit 3 and the pixel array 4. For example, a diffuser is preferred, which increases the speckle fluctuations during the scanning process.

[0146] 6 shows a schematic diagram of a preferred embodiment of an image generating unit with a diffuser 8 in the beam path. The diffuser 8 can be designed, for example, as an optical element or lens array with a random phase. The diffuser 8 preferably causes the individual beams of illumination radiation 2 incident on the diffuser 8 at different points of incidence to be scattered and mixed. Thereby, the coherence length of the illumination radiation 2 is further shortened and the visibility of speckle patterns in the generated image is reduced.

[0147] 7 shows a schematic diagram of a preferred embodiment of an image generating unit with two diffusers 8 in the beam path. The two diffusers 8 are arranged successively with a spatial distance along the propagation direction in the beam path. With two diffusers, an even greater improvement in the speckle and / or interference pattern reduction can be achieved.

[0148] FIG. 8 illustrates diagrammatically the superposition of multiple beams of illumination radiation 2 by using two diffusers 8 in the beam path.

[0149] The illumination radiation 2 is scattered at the first diffuser 8 and is already incident at several different points of incidence on the second diffuser 8 where it is further scattered, whereby several speckle patterns are simultaneously superimposed. The number of superimposed beams 2 or speckle patterns on the pixel array 4 (and in the image plane) is many times higher than with one diffuser 8.

[0150] This is particularly evident when comparing the number of superimposed beams 2 or speckle patterns on the second diffuser 8 and on the pixel array 4. If the spatial frequency of the speckle patterns is high enough, they cannot be resolved by the eye. In addition, radiation beams 2 are superimposed which are laterally further apart from each other than in the case of one diffuser 8. This reduces the spatial coherence of the light source. If the coherence length of the light source is short enough, no discernible speckle patterns arise. The expansion of the beams 2 is shown in Figures 7 and 8 and preferably corresponds to the diffusion angle.

[0151] FIG. 9 shows a schematic diagram of a preferred embodiment of an image generating unit having a lens 9 to ensure a constant angle of incidence of the illumination radiation 2 on the pixel array 4 .

[0152] The lens 9 is preferably a refractive, diffractive or Fresnel lens. Preferably, the lens 9 is positioned between the scanning unit 3 and the pixel array 4 as shown, and is configured such that all beams 2 have the same angle of incidence on the pixel array 4, regardless of their spatial position (see FIG. 9 for two exemplary scanning angles and beam profiles). To this end, for example, the scanning unit 3 may be placed at the object-side focus of the lens 9. This distance can be varied to change the radiation pattern of the entire system.

[0153] The image generation unit may be used as a display or a projector.

[0154] Figure 10 shows diagrammatically a preferred embodiment of an image generating unit designed as a display. For use as a display, the pixel array 4 can serve as a display screen 10 and can either be viewed directly (as shown) or the pixel array 4 can be projected onto a (semi-)transparent display screen 10, which can then be viewed in transmitted light (not shown).

[0155] 11 shows a schematic representation of a preferred embodiment of an image generating unit designed as a projector. To be designed as a projector, the pixel array 4 is projected onto a reflective, preferably diffusely reflective, projection screen 11.

[0156] FIG. 12 shows diagrammatically a preferred embodiment of an image generating unit with reduced mounting space perpendicular to the pixel array 4 .

[0157] For this purpose, the image generating unit comprises a substrate body 14 which is transparent for the illumination radiation 2 and has a coupling surface 12, via which the illumination radiation 2 in the transparent substrate body 14 is guided to a rear face 15, on which a redirecting element 13 is present. The redirecting element 13 is designed such that the incident illumination radiation 2 is redirected in the direction of a front face 16 of the substrate body 14, through which the illumination radiation 2 emerges onto the light-modulating pixel array 4.

[0158] The substrate body 14 is preferably of low profile design with respect to the height and width of the pixel array 4 and may have a cubic basic shape with a specially shaped coupling surface 12 on at least one surface. In order to reduce divergence or aberrations, the coupling surface 12 may be concave such that the illumination radiation 2 guided by the scanning unit 3 is incident at a substantially normal angle of incidence on the substrate body 14 at different scanning positions.

[0159] The redirecting element 13 can be, for example, a volume hologram, a microstructured diffractive element or a (structured) mirror surface. In the case of a diffractive redirecting element (e.g. a volume hologram), not only the zeroth order undiffracted light but also light diffracted into diffraction orders other than the desired one can propagate as interference light 17 in the transparent substrate body 14.

[0160] FIG. 13 shows diagrammatically a preferred embodiment of an image generating unit, in which the coherent light 17 is at least partially guided to a pixel array 4 .

[0161] This allows light to be directed to multiple points on the pixel array 4 simultaneously, thus further reducing visible speckle.

[0162] 14 to 16 show schematic diagrams of preferred embodiments of an image generating unit according to the invention, in which incidence of interfering light 17 on a pixel array 17 is avoided.

[0163] In FIG. 14, the scanning angle of the scanning unit 3 is specified so that the interference light 17 does not exit from the front surface 16 to the pixel array 4 but exits from the bottom surface of the substrate body 14 .

[0164] In FIG. 15, the rear surface 15 of the transparent substrate body 14 on which the direction conversion element 13 is attached is configured to guide the interference light 17 away from the pixel array 4.

[0165] 16 the coupling surface 12 is designed such that all beams of illumination radiation 2 from the scanning unit 3 are incident at the same angle on the redirecting element 13. For example, a freeform optical unit, a biconic lens or a rotationally symmetric lens can be used for this purpose.

[0166] It should be noted that various alternatives of the above-mentioned embodiments of the invention can be used to implement the invention and arrive at the solution according to the invention. The image generating unit according to the invention is therefore not limited in its embodiments to the above-mentioned preferred embodiment. Rather, many design variants are conceivable that may deviate from the shown solution. The object of the claims is to define the scope of protection of the invention. The scope of protection of the claims is intended to cover the image generating unit according to the invention and its equivalent embodiments. [Explanation of symbols]

[0167] 1 light source 2. Illumination Radiation 3 Scanning Unit 4. Light Modulating Pixel Array 5 Scanning mirror 6 Mirror Plane 7 Actuator 8 Diffuser 9 Lenses 10 Display Screen 11 Projection Screen 12 Bonding surface 13 Directional change element 14 Transparent substrate body 15 Rear side of the board 16 Front of the board 17 Interferometric light

Claims

1. 1. An image generating unit comprising a light source (1) for generating illumination radiation (2) and a light-modulating pixel array (4) for generating an image by pixel-by-pixel modulation of the illumination radiation (2) incident on the pixel array (4), characterized in that the illumination radiation (2) when incident on the light-modulating pixel array (4) has a smaller lateral extent than the pixel array (4) and is guided by a scanning unit (3) over the pixel array (4) for the generation of the image to reduce the visibility of speckle patterns in the generated image.

2. 2. An image generating unit according to claim 1, characterized in that the illumination radiation (2) is coherent radiation and / or the light source (1) is a laser.

3. 2. An image generating unit according to claim 1, characterized in that it comprises two or more light sources (1), preferably two or more monochromatic lasers.

4. 2. An image generating unit according to claim 1, characterized in that the scanning unit (3) comprises one or more scanning mirrors (5), lenses, prisms, wedges and / or diffractive optical elements (DOE).

5. 2. An image generating unit according to claim 1, characterized in that the light-modulating pixel array (4) is selected from the group comprising a spatial light modulator (SLM), a liquid crystal display (LCD) and / or a micromirror array.

6. 2. The image generating unit of claim 1, wherein the illumination radiation (2), when incident on the pixel array (4), has a lateral extent that is one-fifth, one-tenth, one-hundredth or less than that of the pixel array (4), and / or the illumination radiation (2), when incident on the pixel array (4), has a lateral extent that is less than 50, 30, 20, 10, 5, 4, 3, 2 or 1 pixel.

7. 2. An image generating unit according to claim 1, characterized in that the scanning frequency of the scanning unit (3) and / or the array frequency of the pixel array (4) is at least 20 Hz, preferably at least 25 Hz, 30 Hz, 40 Hz, 50 Hz, 60 Hz or higher.

8. 2. The image generating unit according to claim 1, characterized in that it is configured to cause an additional phase change of the illumination radiation (2) by the pixel array (4) and / or the scanning unit (3) in order to increase the variation of the speckle signature of the pixel array (4) and / or the scanning unit (3).

9. 2. The image generating unit according to claim 1, configured to additionally modulate pixel states for each generated image in order to increase the variation of the speckle signature of the pixel array (4), preferably wherein the modulation frequency of the pixel states is 2, 4, 6 times or higher than the refresh rate of the image generating unit.

10. 2. The image generating unit of claim 1, further comprising: a scanning unit (3) configured to additionally modulate the scanning unit (3) due to a phase change of the illumination radiation (2) in order to increase the variation of the speckle signature of the scanning unit (3); wherein the modulation frequency of the scanning unit (3) is 2, 4, 6 or more times higher than the refresh rate of the image generating unit; and / or preferably, one or more components of the scanning unit (3) are excited to vibrate by an actuator (7).

11. 2. The image generating unit according to claim 1, further comprising one or more diffusers (8) in the beam path between the light source (1) and the light-modulating pixel array (4), preferably in the beam path between the scanning unit (3) and the light-modulating pixel array (4).

12. 2. An image generating unit according to claim 1, characterized in that it comprises two or more diffusers (8) arranged successively in the beam path at a spatial distance.

13. 2. The image generating unit according to claim 1, characterized in that it is designed as a display, and the light-modulating pixel array (4) forms a display screen (11) and / or the image generated by the light-modulating pixel array (4) is projected onto a (semi-)transparent display screen (11).

14. 2. An image generating unit according to claim 1, characterized in that it is designed as a projector, and the light-modulating pixel array (4) is projected onto a reflective projection screen (11).

15. 2. The image generating unit of claim 1, comprising a substrate body (14) that is transparent to the illumination radiation (2) and has a bonding surface (12), through which the illumination radiation (2) in the transparent substrate body (14) is guided to a rear surface (15) on which a redirecting element (13) is present, the redirecting element (13) being designed to redirect the incident illumination radiation (2) towards a front surface (16) of the substrate body (14), through which the illumination radiation (2) emerges onto the light-modulating pixel array (4).

16. An image generating unit as described in claim 6, characterized in that the lateral range when the illumination radiation (2) is incident on the light-modulating pixel array (4) is given by the full width at half maximum (FWHM) of the light intensity of the illumination radiation (2) on the light-modulating pixel array (4).

Images