Methods and devices for reducing the speckle effect

Abstract

A method for projecting an image into a viewer's field of view, comprising the following steps: Guiding (705) a first light beam, which has first image information for a first pixel of the image, through an arrangement of at least two switchable lenses (201; 401) to a first position, assigned to the first pixel, of a projection surface (101) located in the field of view using a movable deflecting mirror (825) located between the two switchable lenses (201; 401) and the projection surface (101); guiding (705), after the first light beam, a second light beam having a second item of image information for a second pixel through the arrangement of the at least two switchable lenses (201; 401) to a second position of the projection surface (101) associated with the second pixel using the movable deflecting mirror (825); guiding (705), after the second light beam, a further first light beam, which has the first image information for the first pixel, through the arrangement of the at least two switchable lenses (201; 401) to the first position of the projection surface (101) assigned to the first pixel using the movable deflecting mirror (825); characterized in that a switching (701) of the switchable first lens (201) between a first curvature state and a second curvature state and a switching (703) of the switchable second lens (401) between a further first curvature state and a further second curvature state is carried out synchronized with the switching of the first lens (201) between the guiding of the first light beam and the guiding of the further first light beam, wherein the curvature states of the lenses (201; 401) are selected such that a light beam (103) is emitted in collimated form from the second lens (401) when the light beam (103) strikes the first lens (201) arranged in front of the second lens (401) with respect to the beam path in collimated form.

Description

State of the art

[0001] The present invention relates to a method and a device for reducing the speckle effect and to a method and a device for projecting an image into a field of view of a viewer, for example in order to be able to project a speckle-reduced image in the flying spot method.

[0002] Speckles are grainy interference phenomena that can be observed when optically rough object surfaces are illuminated with coherent light. Such speckles or spots can be perceived as disturbing by the observer.

[0003] US 2010 / 0165297 A1 discloses a laser projector in which a shift of a display position of a two-dimensional light modulation element and an optical system is performed synchronously with each other, so that the display positions of the images in a display plane are substantially identical to each other. This sufficiently removes speckle noise.

[0004] US 2009 / 0168010 A1 discloses an electro-optical reading device in which the working range and beam cross-section for reading characters are adjusted by applying voltages to electrodes in one or more liquid crystal lenses, thereby changing the refractive index. Disclosure of the invention

[0005] Against this background, the present invention presents a method and a device for reducing the speckle effect, as well as a method and a device for projecting an image into a viewer's field of view, according to the main claims. Advantageous embodiments emerge from the respective subclaims and the following description.

[0006] By using an arrangement of at least two lenses arranged one after the other in the path of a light beam and adjustable in terms of their curvature, a speckle effect can be reduced, which occurs, for example, when the light beam hits a surface with a certain roughness. Such an arrangement can be used, for example, in conjunction with a head-up display.

[0007] A method for reducing the speckle effect for a light beam striking a surface comprises the following steps: Switching a switchable first lens arranged in a beam path of the light beam between a first curvature state and a second curvature state; and Switching a switchable second lens arranged in the beam path of the light beam between a further first curvature state and a further second curvature state, synchronized with the switching of the first lens.

[0008] The light beam can be a focused light beam, for example from a laser. The surface can be a projection surface. Such a projection surface can have a radiation pattern that is as directional as possible. The surface can therefore be understood as a "screen" with potentially directional radiation patterns. The speckle effect can be caused by the surface onto which the light beam hits having a certain roughness. The speckle effect can lead to undesirable patterns within a light spot or light field projected onto the surface by the light beam. The first lens and the second lens can be arranged one after the other in the beam path of the light beam.The light beam can hit the first lens, be refracted by the interfaces of the first lens and emitted towards the second lens, hit the second lens, be refracted by the interfaces of the second lens and emitted towards the surface or another optical element. The first curvature state of the first lens can correspond to a first curvature or first focal length of the first lens. The second curvature state of the first lens can correspond to a second curvature or second focal length of the first lens. The first curvature and the second curvature can differ in terms of their radius of curvature or their direction of curvature. Thus, the first lens can be switched between two focal lengths. Accordingly, the further first curvature state of the second lens can correspond to a first curvature or first focal length of the second lens.The further second curvature state of the second lens can correspond to a second curvature or second focal length of the second lens. Thus, the second lens can be switched between two focal lengths. The first curvature state of the first lens can be the same as the further second curvature state of the second lens. Alternatively, the first curvature state of the first lens can differ from the further second curvature state of the second lens. The first curvature state and the further first curvature state can be coordinated with one another. The second curvature state and the further second curvature state can also be coordinated with one another. As a result, a parameter of the light beam emitted by the arrangement of lenses can be maintained regardless of the set curvature states of the lenses. The parameter can, for example, relate to a bundling of the light beam.The first lens and the second lens can be identical. Alternatively, the first lens and the second lens can be different, for example, they can differ in their material. The lenses can each be held in a curvature state or converted into a curvature state by applying a control signal. A curvature state of the first lens can be switched simultaneously with a curvature state of the second lens. For example, the lenses can each be switched alternately between at least two adjustable curvature states. Switching between two curvature states causes a change in the speckle effect. Such successive changes can be used to reduce the effect of the speckle effect that is visible to an observer.

[0009] According to one embodiment, the method may further comprise a step of switching a switchable further lens arranged in the beam path of the light beam between yet another first curvature state and yet another second curvature state, synchronized with the switching of the first lens and the second lens. Thus, two, three, or more switchable lenses can be used to reduce the speckle effect.

[0010] In the step of switching the second lens, the second lens can be switched so that the second lens has the further first curvature state when the first lens has the first curvature state, and the second lens has the further second curvature state when the first lens has the second curvature state. The first curvature state and the further second curvature state can represent a concave curvature, and the second curvature state and the further first curvature state can represent a convex curvature of the lenses. In the arrangement of lenses, one of the lenses can assume the function of a converging lens and the other of the lenses can assume the function of a diverging lens. The functions of the lenses can be swapped each time the lenses are switched. In this way, an originally parallel bundle of light rays that strikes the arrangement of lenses can leave the arrangement of lenses again as a parallel bundle of light rays.

[0011] Thus, the curvature states of the lenses can be selected such that the light beam is emitted in a collimated form from the second lens when the light beam impinges in a collimated form on the first lens, which is arranged in front of the second lens with respect to the beam path. Such an arrangement is suitable, for example, for use in a projector with a flying spot method.

[0012] Advantageously, the switching steps between the first curvature state and the second curvature state, as well as between the further first curvature state and the further second curvature state, can be performed within a time period of less than 20 ns. In this way, at least two, but typically significantly more, changes in the speckle pattern can be generated within the averaging time of the human eye. In other words, at least two images or pixels with the same image information can be generated, but which display different speckle pattern characteristics. The at least two images or pixels appear superimposed to the human eye, so that the speckle patterns can compensate for each other.

[0013] According to one embodiment, the first lens and the second lens can each be embodied as a liquid lens. A liquid lens can be constructed from two different liquids. By applying a control signal, a curvature at a transition surface between the two different liquids can be changed. Thus, a focal length of the liquid lens can be changed. The curvature of a liquid lens can be changed very easily, quickly, and reversibly. Furthermore, a liquid lens with very small dimensions can be realized.

[0014] In the step of switching the first lens, a control voltage of the first lens can be switched from a first voltage value to a second voltage value in order to switch the first lens from the first curvature state to the second curvature state. Correspondingly, in the step of switching the second lens, a further control voltage of the second lens can be switched from a further first voltage value to a further second voltage value in order to switch the second lens from the further first curvature state to the further second curvature state. Corresponding control voltages can be provided, for example, by a control device for controlling the arrangement of the lenses. By using electrical voltages, the switching of the lenses can be carried out very easily.

[0015] According to one embodiment, the method may comprise a step of switching the first lens between the second curvature state and a third curvature state, and a step of switching the second lens between the further second curvature state and a further third curvature state, synchronized with the switching of the first lens between the second curvature state and the third curvature state. Thus, lenses with more than two coordinated curvature states can be used.

[0016] A method for projecting an image into a viewer's field of view comprises the following steps: Guiding a light beam containing image information for a pixel of the image through an arrangement of at least two switchable lenses onto a projection surface located in the field of view, wherein a first of the at least two switchable lenses is switchable between a first curvature state and a second curvature state, and a second of the at least two switchable lenses is switchable between a further first curvature state and a further second curvature state synchronized with the first lens; and

[0017] Performing the steps of a said method for reducing the speckle effect for a light beam incident on a surface in order to reduce the speckle effect of the pixel.

[0018] This process is suitable for projecting a speckle-reduced image using the flying spot method. Multiple optical elements, such as mirrors or additional lenses, can be used to direct the light beam. Depending on the diameter of the light beam, the light beam can contain image information for a single light spot or for a specific area of ​​the projection surface. The light beam can be generated, for example, by an imager of a field-of-view display. The field-of-view display can be a laser-based projector.

[0019] In the method for projecting an image into a viewer's field of view, in the guiding step, a first light beam containing first image information for a first pixel can be guided through the arrangement of the at least two switchable lenses to a first position on the projection surface assigned to the first pixel. After the first light beam, a second light beam containing second image information for a second pixel can be guided through the arrangement of the at least two switchable lenses to a second position on the projection surface assigned to the second pixel. After the second light beam, a further first light beam containing the first image information for the first pixel can be guided through the arrangement of the at least two switchable lenses to the first position on the projection surface assigned to the first pixel.The assignment of the light beam to the image positions can be implemented, for example, by at least one mirror located behind the lenses. This can be done according to a so-called "flying spot" method. This step can be performed between the transmission of the first light beam and the transmission of the second first light beam. In this way, the speckle effect of one and the same light spot projected at different times can be changed by switching the lenses.

[0020] A device for reducing the speckle effect for a light beam striking a surface has the following features: a device for switching a switchable first lens arranged in a beam path of the light beam between a first curvature state and a second curvature state; and a device for switching a switchable second lens arranged in the beam path of the light beam between a further first curvature state and a further second curvature state, synchronized with the switching of the first lens.

[0021] For example, the device may be configured to provide a first control signal for switching the first lens to the first lens and a second control signal for switching the second lens to the second lens.

[0022] In this case, a device can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The device can have an interface, which can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the device. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0023] A device for projecting an image into a viewer's field of view has the following features: an arrangement of at least two switchable lenses, wherein a first of the at least two switchable lenses is switchable between a first curvature state and a second curvature state and a second of the at least two switchable lenses is switchable between a further first curvature state and a further second curvature state synchronized with the first lens; a device for guiding a light beam containing image information for a pixel of the image through the arrangement of at least two switchable lenses onto a projection surface located in the field of view; and a speckle reducing device for a light beam incident on a surface to reduce the speckle effect of the pixel.

[0024] The device is suitable for projecting a speckle-reduced image using the flying spot method. The projection device can represent a field-of-view display or part of a field-of-view display. The projection device can be used, for example, in a vehicle or in a stationary facility, for example, within a building. The at least two lenses can be arranged one behind the other with respect to a beam path of the light beam, so that the light beam first passes through one of the lenses and then the other. The lenses can have the same optical axis.

[0025] Also advantageous is a computer program product with program code that can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory, or an optical memory and is used to carry out the method according to one of the embodiments described above, when the program code is executed on a computer or device. Thus, the steps of the method defined in the program code can be implemented by devices of the computer or device.

[0026] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a representation of the speckle effect; Fig. 2 shows a lens in a first curvature state according to an embodiment of the present invention; Fig. 3 shows a lens in a second curvature state according to an embodiment of the present invention; Fig. 4 shows an arrangement of lenses according to an embodiment of the present invention; Fig. 5 is a schematic representation of an arrangement of lenses in a first state of curvature according to an embodiment of the present invention; Fig. 6 is a schematic representation of an arrangement of lenses in a second curvature state according to an embodiment of the present invention; Fig. 7 is a flowchart of a method according to an embodiment of the present invention; Fig. 8 is a block diagram of a field of view display; Fig. 9 is a block diagram of a head-up display according to an embodiment of the present invention; Fig. 10 is an illustration of the speckle effect according to an embodiment of the present invention; Fig. 11 is an illustration of the speckle effect according to an embodiment of the present invention; Fig. 12 is an illustration of the speckle effect according to an embodiment of the present invention; Fig. 13 is an illustration of a first curvature state of a first lens according to an embodiment of the present invention; Fig. 14 is an illustration of a first curvature state of a second lens according to an embodiment of the present invention; Fig. 15 is a diagram illustrating a control signal for driving a lens according to an embodiment of the present invention; Fig. 16 is a diagram illustrating pixel diameters of a light beam according to an embodiment of the present invention; and Fig. 17 a comparison of pixel diameters and beam diameters according to an embodiment of the present invention.

[0027] In the following description of preferred embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0028] Fig. Figure 1 shows a representation of the speckle effect. It depicts a projection surface 101 exhibiting roughness or granularity, which is illuminated with coherent light 103 from a laser. Spherical wave reflections from scattering centers on the projection surface 101 are detected by an observer's eye 105.

[0029] Such a projection surface 101 can be used, for example, in a field-of-view display in the form of a laser-based projection device. A laser-based projection device generates mutual interference of wavefronts of different phases with the projection surface 101, for example in the form of a screen. This leads to speckle intensity distributions due to screen surface granularities, as shown in Fig. 1. Speckles appear when coherent light 103 is scattered by the surface 101 used as a screen, which has these granularities. The observer's eye 105, which has a finite aperture, will see small areas exhibiting different light intensities.

[0030] Head-up displays (HUDs), also called field-of-view displays, present driving information in the driver's field of vision. Such HUD devices consist of an array of an image sensor and one or more optical components, such as lenses and / or mirrors.

[0031] In the case of a laser-based imager, the image is projected onto a surface 101, which exhibits varying roughness depending on the material used to create it, as well as its own optical properties. The image displayed on the projection surface 101 is then collected by the various optical elements and reflected onto the windshield of a vehicle or onto an inclined combiner. This allows the driver to perceive an enlarged virtual image of the imager, hovering in front of them at a predetermined distance. The optical setup is optimized for a given starting position of the driver's head.

[0032] Due to the coherent light emitted by the laser, the reflected light exhibits a random distribution of narrow spots with varying intensities, called speckles. These speckles are visible to an observer at a specific position and degrade image quality by creating small, visible fields of random fluctuations in light intensity.

[0033] To determine the image quality in relation to the speckle effect, a simplified formula is used to determine the speckle contrast, i.e. a contrast change within a predetermined range: C=σI〈I〉∞135N

[0034] The speckle contrast C is defined as the ratio of the standard deviation σl of the intensity deviations and the average intensity 〈I〉.

[0035] Furthermore, the contrast depends inversely on the square root of the number of modes N of the light field. Different modes can be realized, for example, by using polarization variations, wavelength variations, or spatial propagation variations of the light field. To minimize contrast and thus improve image quality, a large number of modes is required.

[0036] Fig. Figure 2 shows a switchable lens 201 in a first curvature state according to an embodiment of the present invention. According to this embodiment, this is a liquid lens. In the first curvature state, the lens 201 has a first focal length of at least two adjustable focal lengths.

[0037] The lens 201 has an optical axis 202. The lens 201 has two opposing windows 210, 211, between which a layer of a first liquid 213, here water, and a layer of a second liquid 214, here oil, are arranged adjacent to one another. A boundary between the liquids 213, 214 has a curvature. The curvature of this curvature can be adjusted by applying a control voltage provided by a control unit 215 to two electrodes 216, 217 of the lens 201. The electrodes 216, 217 are made of metal and are electrically insulated from one another by an insulation 218. The control voltage creates an electrostatic pressure 219 in the area of ​​the electrode 217, which can influence the curvature. A change in the curvature can cause a change in the focal length of the lens 201.

[0038] Light 103 entering the lens 201 through the window 210 is refracted at the curvature of the interface between the liquids 213, 214. In the Fig. In the curvature state shown in Figure 2, the interface is bulged toward the second liquid 214. As a result, the light beam 103 is focused toward a focal point of the lens 201 located behind the lens 201 with respect to the beam path of the light beam 103. The lens 201 thus acts as a converging lens.

[0039] Fig. 3 shows the Fig. 2 in a second curvature state according to an embodiment of the present invention. In the second curvature state, the lens 201 has a second focal length of at least two adjustable focal lengths.

[0040] The boundary between the liquids 213, 214 now points in relation to the Fig. 2. The curvature state of this opposite curvature can be adjusted by applying an additional control voltage provided by a control unit 215 or, according to this embodiment, by applying no control voltage to the two electrodes 216, 217 of the lens 201.

[0041] Light 103 entering the lens 201 through the window 210 is refracted at the curvature of the interface between the fluids 213, 214. In the Fig. In the curvature state shown in Figure 3, the interface is bulged toward the first liquid 213. This widens the light beam 103. The lens 201 thus acts as a scattering lens.

[0042] Based on the Fig. 2 and Fig. Figure 3 illustrates the operation of a single liquid lens. By controlling the electrical voltage applied to the liquid lens, the curvature of the inner surface can be adjusted, thus modifying its optical performance. By changing the voltage of the liquid lens 201, the curvature of the inner surface of the liquid lens 201 changes. This leads to a change in the optical performance of the lens 201.

[0043] Two of the Fig. 2 and Fig. The lenses 201 shown in Figure 3 can be arranged one behind the other and operated in synchronized relation to each other in mutually different curvature states. The optical axes of the lenses 201 can correspond to each other. Such a lens arrangement comprising at least two lenses 201 can create a liquid lens telescope. A method for speckle reduction for laser projectors can be implemented based on such a liquid lens telescope.

[0044] A corresponding optical arrangement for speckle reduction consists of two liquid lenses that can be inserted into the light path of a beam emitted by the laser, thereby significantly reducing the speckle effect. The speckle is reduced without altering the color or sharpness of the projected image. In the case of an imager that uses different laser beams for color images, the optical arrangement for speckle reduction can be inserted after each laser beam or after the optical component that partially or globally sums the emitted beams of the different laser colors.

[0045] Advantageously, a compact optic, for example, with a diameter of approximately 3 mm, can be used to implement such an approach. The optic can be easily integrated at different positions in the beam path of the optical arrangement. A controlled output beam can be achieved without disruptive light scattering. Electronically variable control is possible without additional mechanical movement. Very high speckle reduction can be achieved. This approach is suitable for general applications for optical devices based on laser projection.

[0046] According to one embodiment, the said method for speckle reduction is based on a pair of liquid lenses constructed in a Galileo telescope-like arrangement.

[0047] Fig. Figure 4 shows an arrangement of two switchable lenses 201, 401 arranged in a beam path of light beams 103 according to an embodiment of the present invention. The lenses 201, 401 can each be a lens as shown in Fig. 2 and Fig. 3. In the Fig. In the illustration shown in Figure 4, light rays 103 propagate from left to right, i.e. first through the first lens 201 and then through the second lens 401.

[0048] When the first lens 201 is in the Fig. 2 and the second lens 401 is in the first curvature state shown in Fig. 3, a diameter of the bundled incident light rays 103 is reduced by the lenses 201, 401, so that a bundle of light rays 403a leaving the second lens 401 has a smaller diameter than the bundle of light rays incident into the first lens 201.

[0049] If, however, the first lens 201 is in the Fig. 3 and the second lens 401 is in the state shown in Fig. 2, i.e. the curvature states of the lenses 201, 401 are swapped, a diameter of the bundled incident light rays 103 is increased by the lenses 201, 401, so that a bundle of light rays 403b leaving the second lens 401 has a larger diameter than the bundle of light rays incident into the first lens 201.

[0050] According to one embodiment, Fig. 4 a liquid lens telescope with a set of two liquid lenses 201, 401. Simultaneous control of the voltage of the liquid lenses 201, 401 results in the two maximum telescope modes shown in Fig. 4 and result in the different light beams 403a, 403b. In the two maximum modes, the first lens 201 is adjusted from a convex to a concave lens and vice versa for the second lens 401. The response time for the transition from the first to the second mode for a single lens 201, 401 and thus for the telescope is approximately 15 ms. An optical arrangement of the liquid lens telescope for despeckle removal is shown. In this implementation, the two liquid lenses 201, 401 are spaced 2 mm apart. The two maximum modes of the light field 403a, 403b achieved by the maximum telescope configurations are shown by the lines.

[0051] The lens voltages of lenses 201, 401 are controlled such that the outgoing beam 403a, 403b remains focused. Between the two modes, the curvatures of lenses 201, 401 are changed so that the beam 403a, 403b, for example, of a laser, remains focused throughout. Changing the telescope results in a change in the length of the optical path of laser beam 103 and thus in a change in the phase of laser beam 103 over time. Since this modulation is performed in a time shorter than the averaging time of the human eye of approximately 20 ms, resulting in a large number of modes N, a reduction in speckle contrast can be achieved according to the aforementioned formula (1).

[0052] Nevertheless, the modulation results in a modulation of the collimated beam waist. This change limits the modulation depth of the two liquid lenses 201, 401. This is arranged so that the beam size changes of beam 103 result in a constant, non-disturbing average beam size observed by the human eye.

[0053] Fig. Figure 5 shows a schematic representation of an arrangement of two switchable lenses 201, 401 according to an embodiment of the present invention. A corresponding arrangement is shown in Fig. 4. The first lens 201 is in a state of curvature, as can be seen, for example, from Fig. 2. The second lens 401 is in a state of curvature as described, for example, by Fig. 3. The individual light rays of the light beam 103 incident on the lens arrangement consisting of the two lenses 201, 401 run parallel. The light enters the first lens 201 from the left and exits the second lens 401 to the right. Likewise, the light rays of the light beam 403a emitted by the lens arrangement run parallel to each other. The emitted light beam 403a has a smaller beam diameter than the incident light beam 103.

[0054] Fig. 6 shows a schematic representation of the Fig. 5 of two switchable lenses 201, 401 according to an embodiment of the present invention. The first lens 201 is in a state of curvature, as can be seen, for example, from Fig. 3. The second lens 401 is in a state of curvature, as can be seen, for example, from Fig. 2. In relation to the Fig. In the state shown in Figure 5, the curvature states of the lenses 201, 401 have been reversed. The individual light rays of the light beam 103 incident on the lens arrangement consisting of the two lenses 201, 401 run parallel. Likewise, the light rays of the light beam 403b emitted by the lens arrangement run parallel to each other. The emitted light beam 403b has a larger beam diameter than the incident light beam 103.

[0055] According to one embodiment, the Fig. 5 and Fig. 6 the two maximum configurations of the Fig. 4. The telescope is operated by the Fig. 5 shown to the one in Fig. 6, and vice versa, at a frequency of approximately 67 Hz to achieve the averaging of the images transmitted by the light beam 103 for the human eye. By following the beams 103 from left to right, different spatial positions on an optical surface following the second lens 401, for example, a projection surface in the case of a HUD system, are determined for the Fig. 5 and the Fig. 6 is achieved. Ultimately, this difference in spatial arrangement results in a despeckle effect. The described approach can be used in laser projector-based despeckle applications.

[0056] Fig. Figure 7 shows a flowchart of a method for reducing the speckle effect for a light beam incident on a surface according to an embodiment of the present invention. This can be a light beam that, after passing through a first and a second switchable lens, as described, for example, with reference to Fig. 4, hits a projection surface, as can be seen, for example, from Fig. 1 is shown.

[0057] To reduce the speckle effect, in a step 701, the switchable first lens arranged in the beam path of the light beam is switched between a first curvature state and a second curvature state. Synchronized with this, in a step 703, the switchable second lens arranged in the beam path of the light beam is switched between a further first curvature state and a further second curvature state.

[0058] For example, the first curvature state of the first lens and the further second curvature state of the second lens can be determined by Fig. 2. Accordingly, the second curvature state of the first lens and the further first curvature state of the second lens can correspond to the state shown in Fig. 3 shown condition.

[0059] Depending on the embodiment, an actual switching of the lenses can be performed in steps 701, 703 or suitable control signals for switching the lenses can be generated and provided at suitable interfaces to the lenses.

[0060] According to one embodiment, steps 701, 703 can be used for a method for projecting an image into a viewer's field of view. For this purpose, in a step 705, a light beam containing image information for a pixel of the image can be directed through an arrangement of the two switchable lenses onto a projection surface located in the field of view. Steps 701, 703, 705 can be repeated so that, due to the switched lenses, the light beam has different speckle patterns upon impacting the projection surface, which leads to a reduction in the speckle effect perceived by the viewer.

[0061] Fig. Figure 8 shows a block diagram of a field-of-view display. It shows the structure of a field-of-view display in the form of a laser projection system. A red laser 821, a green laser 822, and a blue laser 823 generate light beams that are guided via deflection mirrors 825 into a beam path of a light beam 103, which is directed line by line onto a projection surface 101 via a movable deflection mirror 825.

[0062] A video signal is received via a video input from a device 827 for video and signal processing. Device 827 is in reciprocal signal exchange with a device 829, which implements signal generation and a control loop, as well as with a laser driver 831 for controlling the lasers 821, 822, 823. Device 829 is configured to output a signal to a driver 833 of the deflection mirror 825 and to receive a signal from a position sensor 835 of the deflection mirror 825.

[0063] A power supply 837 is also shown. The field-of-view display is configured to project image information received via the video input onto the projection surface 101.

[0064] In a laser projection system according to the “flying spot” method, as described in an embodiment in Fig. As shown in Figure 8, the light from a red laser diode 821, the light from a green laser diode 822, and the light from a blue laser diode 823 (monochromatic embodiments are also possible) are combined by a beam combining element, e.g., a dichroic mirror. This beam 103 strikes one or two micromechanical mirrors 825, which deflect the laser beam 103 in two axes onto a projection surface 101. The image is written line by line, like an electron beam tube.

[0065] Using liquid lenses, such as those shown in the Fig. 2 to 7, a despeckling method with liquid lenses for laser projectors can be realized using the flying spot method.

[0066] Fig. Figure 9 shows a block diagram of a visual field display according to an embodiment of the present invention. This may be a visual field display as described in Fig. 8. The field of view display has a laser source 920 that emits a light beam 103, which, according to this exemplary embodiment, is directed onto a projection surface 101 via an arrangement of two liquid lenses 201, 401 in the form of a liquid lens telescope onto a movable deflecting mirror 825 in the form of a micromirror. A control unit 930 is designed to control both the laser source 920 and the liquid lenses 201, 401, as well as the deflecting mirror 825. In particular, the control unit 930 is designed to switch the liquid lenses 201, 401 jointly between at least two possible curvature states.

[0067] According to one embodiment, Fig. Figure 9 is a schematic representation of an implementation of a liquid lens telescope despeckling method in a flying-spot projector setup. The collimated output beam 103 of the laser 920 passes through the liquid lens pair 201, 401 and is reflected by micromirror 825 onto the projection surface 101, where the desired image is formed.

[0068] A control unit 930 controls the laser 920 and the micromirror 825 as well as the liquid lens telescope.

[0069] According to this embodiment, the light striking the deflection mirror 825 is collimated, i.e., focused. This is achieved by a telescope consisting of two liquid lenses 201, 401. The light 103 remains collimated after leaving the liquid lenses 201, 401 and can then be used, for example, in the flying-spot method with the micro-mirror 825 for speckle-reduced image generation. The control of the two liquid lenses 201, 401 is synchronized to maintain the property of the collimated output beam. In the embodiment shown, the light 103 and the mirror 825 carry the information about the image and do not serve for illumination. Application in a field of view display in the form of a head-up display is therefore easy to implement.

[0070] Especially within certain temperature limits, the approach shown is suitable for application in laser projectors, for example for flying-spot HUDs in the automotive sector.

[0071] The Fig. The method and arrangement described in Figures 2 to 7 can be used for speckle reduction in laser-based projectors. For this purpose, several liquid lenses 201, 401 are used, which lead to different speckle images by changing the optical path, as shown for example in the Fig. 10 to 12. This approach can be applied to laser-based projectors that operate according to the flying-spot principle.

[0072] Unlike imaging projectors, flying spot projectors have a temporal regime that must be considered in the proposed speckle reduction solution. Furthermore, such projectors have certain requirements regarding the beam size at different distances, which must not be compromised by the use of additional liquid lenses.

[0073] Advantageously, the described method can also be applied to speckle reduction for projectors using the flying spot method. Since flying spot projectors inherently require a spatially coherent light source 920, lasers are used for this purpose. These, in turn, exhibit significant speckle, which can be reduced using the described approach.

[0074] From the formula for calculating the speckle contrast (C = speckle contrast, 〈I〉 = mean intensity, σ I= standard deviation of intensity, N = number of statistically independent speckle images) C=σI〈I〉∞1N It can be seen that the speckle contrast depends on the number N of independent speckle images. In order to achieve speckle reduction at a specific location within the image on the projection surface 101, different, ideally independent, speckle patterns must be generated at this location, usually called a picture element or pixel. Due to the scanning image construction, a pixel is illuminated only once for approximately 40-50 ns within the refresh rate, which is usually approximately 60 Hz, corresponding to approximately 16 ms per image. Since it is not possible to change the liquid lenses 201, 401 within this short time, as this would require frequencies greater than 20 MHz, a change in the liquid lenses 201, 401 is achieved at the same pixel in the subsequent image. Assuming an integration time of the eye of approximately 67 ms, a maximum of four images can be integrated at a refresh rate of 60 Hz. A maximum speckle reduction of a factor of two is possible (see Eq. 1).To achieve this, the liquid lenses 201 and 401 generate four independent speckle images at the four times within the 67 ms at which the same pixel is projected. This condition is met for all pixels.

[0075] To test this possibility, simulations can be performed for flying-spot systems. These simulations calculate the speckle pattern of a pixel as seen by a detector, such as a camera or an eye.

[0076] The Fig. Figures 10 to 12 show exemplary speckle effects, which are noticeable as different speckle patterns 1030, 1031, 1032 in a pixel. The pixel can, for example, be a Fig. 9 shown projection surface. The different speckle patterns 1030, 1031, 1032 can be achieved by different settings of the curvature states of the switchable lenses through which the light beam representing the pixel is guided. For the speckle pattern 1030, the lenses can, for example, be in a first state, for the speckle pattern 1031 in a second state, and for the speckle pattern 1032 in a third state. For example, in the Fig. 10, a first lens is in a first curvature state and a second lens is in a further first curvature state, wherein the first lens in the first curvature state can function, for example, as a diverging lens and the second lens in the further first curvature state can function, for example, as a converging lens.

[0077] The Fig. The results shown in Figures 10 to 12 show that it is possible to generate different speckle images 1030, 1031, 1032 with such a system with different states of the liquid lenses.

[0078] Shown is a speckle pattern 1030, 1031, 1032 of a pixel in different states of the two liquid lenses used.

[0079] To generate the Fig. 10, the lenses used are set to the parameters R1 = -7.45 mm, R2 = 9.03 mm, d1 = 400 µm, d2 = 240 µm, n1 = 1.33 and n2 = 2.2.

[0080] To generate the Fig. 11, the parameters R1 = -11.27 mm, R2 = 27.81 mm, d1 = 350 µm, d2 = 290 µm, n1 = 1.33 and n2 = 2.2 are used.

[0081] To generate the Fig. 12, the parameters R1 = -4.72 mm, R2 = 7.72 mm, d1 = 410 µm, d2 = 230 µm, n1 = 1.33 and n2 = 2.2 are used.

[0082] The respective parameters in the representations of the Fig. 13 and Fig. 14 is shown.

[0083] Fig. Figure 13 shows a representation of the curvature of a first switchable lens 201 of an arrangement of two switchable lenses, by means of which, for example, the lens used to generate the Fig. 10 to 12 shown light points. Shown are the light beams used in connection with the Fig. 10 to 12 mentioned parameters.

[0084] Fig. Figure 14 shows a representation of the curvature of a second switchable lens 401 of an arrangement of two switchable lenses, by means of which, for example, the lens used to generate the Fig. 10 to 12 shown light points. Shown are the light beams used in connection with the Fig. 10 to 12 mentioned parameters.

[0085] For speckle reduction in projector applications, such as those used in Fig. As shown in Figure 9, the frequency of the liquid lenses is sensibly selected depending on the projector's refresh rate. According to the manufacturer's specifications, the time between the two extreme positions of the liquid lenses 201 and 401 is, for example, 15 ms (~67 Hz). This value, like the maximum difference in optical power at the extreme positions, can be adjusted, including by using different liquid lens materials.

[0086] Fig. 15 shows a representation of a control signal 1540 for controlling a lens according to an embodiment of the present invention. This can, for example, be the Fig. This could be the lens shown in Figure 13. The ordinate represents time in milliseconds, and the abscissa represents the values ​​of the control signal, in this case a voltage applied to a liquid lens in volts.

[0087] This diagram shows the temporal sequence of image projection in laser projectors using a liquid lens telescope. A control signal 940 in the form of a triangular voltage for controlling one of the liquid lenses is shown as a function of time. The image of the projector, as shown, for example, in Fig. 9, is constructed here with a frequency of 60 Hz, which represents a range 1541, 1542. The liquid lens settings for a constant pixel are shown as points 1545. These settings vary over a period of 67 ms, which corresponds to the averaging time of the eye, resulting in different speckle images, as shown, for example, in the Fig. 10 to 12 are shown.

[0088] In Fig. Figure 15 illustrates the temporal progression of a liquid lens in a telescope in a projector. A linear voltage change is applied to the liquid lens. According to the manufacturer's specifications, the optical power also changes linearly for each lens. It is shown that in a period of 67 ms, the averaging time of the eye, four different voltages are present, represented by points 1545, resulting in the generation of four speckle images. As described above, this represents a reduction in speckle contrast by a factor of 2.

[0089] To achieve a speckle reduction by a factor of 2, i.e., 4 independent speckle images, the liquid lens must be selected to ensure that the above-mentioned maximum difference in optical power is sufficiently large. Furthermore, when selecting the frequency for controlling the liquid lens, it is important to ensure that the Fig. 15 is realized for all pixels. A lower control frequency is also possible, which Fig. 15 can be concluded. Therefore, liquid lenses are predestined for such an application.

[0090] At higher refresh rates above 60 Hz, a speckle reduction of more than 2 can be achieved. However, if the two liquid lenses are varied between their two extreme positions at a frequency of 60 Hz, no speckle reduction is achieved.

[0091] In another embodiment, the liquid lens drive voltage can be modified, for example, by frequency modulation or phase shifts to generate as many speckle images as possible for all pixels.

[0092] Fig. Figure 16 shows a representation of pixel diameters 1651, 1652, 1653, 1654 of a light beam according to an embodiment of the present invention. The abscissa represents a distance in millimeters, and the ordinate represents the pixel diameter in millimeters. The pixel diameters are shown for various resolutions, with a horizontal optical angle of 48°, of which 40.1° are utilized.

[0093] The pixel diameter curve 1651 is assigned an HD1080 resolution (1920 x 1080). The pixel diameter curve 1652 is assigned an HD720 resolution (1280 x 720). The pixel diameter curve 1653 is assigned a PAL resolution (1024 x 576). The pixel diameter curve 1654 is assigned a WVGA resolution (854 x 480).

[0094] Fig. Figure 17 shows a comparison of pixel diameter 1761 and beam diameter 1763 according to one embodiment of the present invention. The abscissa represents a distance in millimeters, and the ordinate represents the pixel diameter or beam diameter in millimeters.

[0095] With scanning laser projection systems, a further difficulty arises: the beam diameter must be adapted to the pixel diameter. This must be true for all distances at which images with acceptable image quality are to be projected. The pixel diameter depends on the resolution of the projector and the projection distance, as shown in Fig. 16. Since the beam diameter is determined by the profile of the laser beam (Gaussian beam), optimal adaptation can only be achieved in a limited distance range, as shown in Fig. 17 is shown, where it would be the range between 500mm and 1500mm.

[0096] The liquid lenses change the diameter of the Gaussian beam, as is also the case with the different size of the spot in the Fig.10 to 12. To ensure good image quality, this size change is ensured within certain tolerances. This can be achieved by appropriately positioning the liquid lenses, possibly even using more than two liquid lenses. Furthermore, it is possible to provide one or more translational lens displacement options, i.e., in the direction of the optical axis.

[0097] The exemplary embodiments described and shown in the figures are selected only as examples. Different exemplary embodiments can be combined with one another in their entirety or with regard to individual features. An exemplary embodiment can also be supplemented by features of another exemplary embodiment. Furthermore, method steps according to the invention can be repeated and performed in a different order than the one described.

Claims

[1] A method for projecting an image into a field of view of a viewer, comprising the following steps: Guiding (705) a first light beam, which has first image information for a first pixel of the image, through an arrangement of at least two switchable lenses (201; 401) to a first position, assigned to the first pixel, of a projection surface (101) located in the field of view using a movable deflecting mirror (825) located between the two switchable lenses (201; 401) and the projection surface (101); guiding (705), after the first light beam, a second light beam having a second item of image information for a second pixel through the arrangement of the at least two switchable lenses (201; 401) to a second position of the projection surface (101) associated with the second pixel using the movable deflecting mirror (825); guiding (705), after the second light beam, a further first light beam, which has the first image information for the first pixel, through the arrangement of the at least two switchable lenses (201; 401) to the first position of the projection surface (101) assigned to the first pixel using the movable deflecting mirror (825); characterized by , that a switching (701) of the switchable first lens (201) between a first curvature state and a second curvature state and a switching (703) of the switchable second lens (401) between a further first curvature state and a further second curvature state is carried out synchronized with the switching of the first lens (201) between the guiding of the first light beam and the guiding of the further first light beam, wherein the curvature states of the lenses (201; 401) are selected such that a light beam (103) is emitted in collimated form from the second lens (401) when the light beam (103) strikes the first lens (201) arranged in front of the second lens (401) with respect to the beam path in collimated form. [2] The method according to claim 1, wherein in the step of switching (703) the second lens (401), the second lens (401) is switched such that the second lens (401) has the further first curvature state when the first lens (201) has the first curvature state and the second lens (401) has the further second curvature state when the first lens (201) has the second curvature state, wherein the first curvature state and the further second curvature state represent a concave curvature and the second curvature state and the further first curvature state represent a convex curvature of the lenses (201; 401). [3] Method according to one of the preceding claims, wherein in the switching steps (701, 703) switching takes place between the first curvature state and the second curvature state and between the further first curvature state and the further second curvature state within a time period of less than 20 ns. [4] Method according to one of the preceding claims, wherein the first lens (201) and the second lens (401) are each designed as a liquid lens. [5] Method according to one of the preceding claims, wherein in the step of switching (701) the first lens (201) a control voltage (1540) of the first lens (201) is switched from a first voltage value to a second voltage value in order to switch the first lens (201) from the first curvature state to the second curvature state and in the step of switching (703) the second lens (401) a further control voltage of the second lens (401) is switched from a further first voltage value to a further second voltage value in order to switch the second lens (401) from the further first curvature state to the further second curvature state. [6] Method according to one of the preceding claims, comprising a step of switching (701) the first lens (201) between the second curvature state and a third curvature state and a step of switching (703) the second lens (401) between the further second curvature state and a further third curvature state, synchronized with the switching of the first lens (201) between the second curvature state and the third curvature state. [7] Device for projecting an image into a field of view of a viewer, the device having the following features: a laser source (920) for emitting a light beam (103); an arrangement of at least two switchable lenses (201; 401), wherein a first of the at least two switchable lenses (201; 401) is switchable between a first curvature state and a second curvature state, and a second of the at least two switchable lenses (201; 401) is switchable between a further first curvature state and a further second curvature state in synchronization with the first lens (201); a movable deflecting mirror (825) for directing the light beam (103), which has image information for a pixel of the image, to a position assigned to the pixel of a projection surface (101) located in the field of view, wherein the movable deflecting mirror (825) is located between the two switchable lenses (201; 401) and the projection surface (101); and a control unit (930) for controlling the laser source (920), the two switchable lenses (201; 401) and the movable deflecting mirror (825), wherein the control unit (930) is designed to carry out the steps of a method according to one of claims 1 to 6.

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