Optical device

Abstract

The present disclosure relates to an optical device (1) for providing illumination to an area (2), comprising:-a despeckle device (3) configured for dynamically and continuously changing the beam path and / or phase of a light beam incident on the despeckle device (3); -a multi-beam optical element (4) configured for emitting at least two light beams (5) towards the despeckle device when optically coupled into the multi-beam optical element (4); wherein each of the at least two light beams (5) is emitted by the multi-beam optical element (4) from a position (6) different from the position (6) at which the multi-beam optical element (4) emits a respective other of the at least two light beams (5); wherein the at least two light beams (5) are emitted such that each of the at least two light beams (5) at least partially overlaps at least one other of the at least two light beams (5) at the region (2) to be illuminated.

Description

Technical Field

[0001] The present disclosure relates to an optical device for providing area illumination. In particular, the present invention relates to an optical element for providing flooding illumination, for example for augmented reality (AR) or virtual reality (VR) applications. Background Art

[0002] Such devices are crucial for providing display illumination in, for example, augmented reality (AR) or virtual reality (VR) devices. These applications require bright, energy-efficient and compact lighting devices. In particular, they should have a low etendue, because light emitted in the case of excessive etendue may be lost, thus having a negative impact on brightness and energy efficiency. For example, in augmented reality (AR) applications, the limiting factor is the input pupil of the combiner waveguide (e.g., 3x3mm and 30° acceptance angle); all light with an etendue greater than this value and emitted will be lost. If LEDs are used for illumination, their size needs to be small to achieve a low etendue. If the size is limited, the LEDs can only reach a certain brightness, because as the current density increases, the efficiency decreases. Therefore, there are fundamental limitations on how much light can be provided by LED-based lighting devices that should achieve a low etendue. In addition, the light emitted by LEDs usually has to be collimated first with a mirror or lens structure, and then the three-color light is superimposed and mixed to achieve uniform illumination. This limits the compactness of such lighting devices.

[0003] In addition, the illumination required for, for example, an LCOS projector is collimated, which means that the light rays should propagate at a small opening angle. LEDs emit light at an opening angle of 180°, which makes it optically challenging to collect all the emitted light and use it for LCOS illumination. In addition, LED light is non-polarized, which means that 50% of the light is lost, because polarized light is necessary for LCOS illumination.

[0004] An alternative approach is to use a light source with an inherently low etendue, such as a laser light source. However, laser illumination has the disadvantage of coherence artefacts (also known as speckle). To reduce speckle, static speckle reduction devices have been proposed. For example, US11275482B2 mentions top-hat microlenses, holographic elements or gratings. In addition, speckle reduction devices that can be switched between discrete states have been proposed, for example, see WO2020 / 219092A1. However, static devices or devices that can only enter a limited number of discrete states cannot significantly or sufficiently reduce speckle.

[0005] US2014 / 0055755A1 discloses an image projector that includes a laser light source for emitting light and a diffuser screen coupled to a planar vibrator. A dichroic combiner cube combines the light beams from red, blue, and green laser diodes into a combined single light beam. The diffuser screen is positioned to receive the single light beam and phase-modulate it. The purpose of this is to eliminate the observed speckle pattern. Due to the limited frame rate and exposure time of the human eye (e.g., about 20 milliseconds), if enough speckle patterns can be generated within a short period of time, they will eventually reach an average level. However, the method described in US2014 / 0055755A1 does not sufficiently reduce the speckle, especially not to the extent that it is invisible to the human eye, which requires a speckle contrast of less than 5%.

[0006] In addition, WO2012 / 136970A1 discloses a device for reducing laser speckle, US2010 / 007852A1 discloses a laser-illuminated micromirror projector, EP3599541A1 discloses an optical waveguide light emitter and a touch screen, and EP3926233A1 discloses an optical device having primary and secondary fan-out waveguides and a bus waveguide. Summary of the Invention

[0007] The object of the present disclosure is to avoid or mitigate at least one drawback of the prior art. Specifically, the object of the present invention is to provide an optical device for providing area illumination with reduced speckle contrast, especially when using a coherent light source.

[0008] This is achieved by an optical device for providing area illumination, which includes: - A speckle reduction device configured to dynamically and continuously change the light beam path and / or phase of the light beam incident on the speckle reduction device; - A multi-beam optical element configured to emit at least two light beams to the speckle reduction device when light is coupled to the multi-beam optical element; wherein the emission position of each of the at least two light beams emitted by the multi-beam optical element is different (i.e., there is an offset) from the emission position of the corresponding other light beam among the at least two light beams emitted by the multi-beam optical element; wherein the at least two light beams are emitted in such a way that each of the at least two light beams at least partially overlaps with at least another one of the at least two light beams in the area to be illuminated.

[0009] When light is coupled into the multi-beam optical element, it emits at least two beams of light from different positions towards the speckle reduction device. The speckle reduction device dynamically and continuously changes the beam paths and / or phases of these beams. After being manipulated by the speckle reduction device, the at least two beams of light illuminate the area such that each of the at least two beams of light overlaps at least partially with another beam. Thus, the beams of light propagating along different beam paths to the speckle reduction element will illuminate the area and overlap at least partially on the area. As long as the beam pairs overlap, speckles will be formed by the interference between the at least two beams of light. Since they propagate along different beam paths to the speckle reduction device, the at least two beams of light shown are particularly likely to undergo changes that vary differently over time. Since the beams of light in the at least two beams of light illuminating a specific point in the illuminated area propagate along different beam paths to the speckle reduction device, the points in the area are particularly likely to be illuminated by beams of light whose optical paths and / or phases have been changed, and the optical paths and / or phases change at least temporarily differently over time. Therefore, the variation of the generated speckle pattern may be further increased, resulting in a further reduction in speckle contrast. Optionally, the active area of the speckle reduction device may correspond to the active area of the display element. The speckle contrast ratio of N beams of light is proportional to 1 / sqrt(N). Therefore, using the multiple discrete states mentioned in the context of the above prior art can only limitedly reduce the speckle contrast ratio. On the contrary, dynamically and continuously changing the beam path or phase of the beam (substantially corresponding to an uncountable set of beams) can significantly reduce the speckle contrast, and the speckle contrast can be further improved by using at least two beams of light (emitted from different positions).

[0010] In the case of dynamically and continuously changing the beam path and / or phase of the incident beam, it should be understood that the change of the beam path and / or phase varies over time, and the set of achievable changes is an uncountable set. In particular, the change varies with any minute change over time (for example, the changing parameter can be differentiable over time). Specifically, changing the beam path includes changing the direction and / or angle and / or optical path length of the corresponding beam.

[0011] Specifically, the multi-beam optical element is configured to emit at least a first beam and a second beam towards the speckle reduction device when light is coupled into the multi-beam optical element.

[0012] Among them, the multi-beam optical element emits the first beam from a first position, and the first position is offset relative to the second position from which the multi-beam optical element emits the second beam.

[0013] Among them, the first beam and the second beam are emitted in such a way that the first beam overlaps at least partially with the second beam at the area to be illuminated.

[0014] Optionally, the area to be illuminated includes a plurality of areas that together constitute the area to be illuminated, and each area is illuminated by at least two of the at least two light beams. Optionally, the at least two light beams are emitted such that each of the at least two light beams at least partially overlaps with at least another one of the at least two light beams in the area to be illuminated and at least partially (optionally completely) does not overlap with the at least another one of the at least two light beams at the speckle reduction device. Optionally, the speckle reduction device changes the beam path and / or phase of the light beams incident on the speckle reduction device from different directions and / or at different positions of the speckle reduction device in different ways for at least a period of time. Optionally, the speckle reduction device changes the beam path and / or phase of the light beams incident on the speckle reduction device from various directions and / or at various positions of the speckle reduction device with arbitrarily small but non-zero alterations for at least a period of time, where the direction and / or position differ by an arbitrarily small and non-zero amount of change. Optionally, the speckle reduction device causes the beam paths and / or phases of the light beams incident on the speckle reduction device from each adjacent direction and / or at each adjacent position on the speckle reduction device to change by different amounts for at least a period of time. Optionally, the speckle reduction device includes a surface on which the light beams are incident, and the light beams incident on different but adjacent surface areas experience a non-zero amount of change in at least a period of time.

[0015] Optionally, the multi-beam optical element includes at least one input end for light and / or at least one output end for each of the at least two light beams. Optionally, each of the at least two light beams propagates in the multi-beam optical element along a well-defined optical path. This can improve the étendue. Optionally, the multi-beam optical element is configured such that more than one light beam of each color enters the speckle reduction device. The light propagates from the speckle reduction device to the area to be illuminated. The number of light beams included in the at least two light beams is optionally at least 10, further optionally at least 100, and further optionally at least 1000.

[0016] Optionally, the optical device further includes a diffuser disposed in the beam paths of at least two of the beams emitted by the multi-beam optical element when coupling light into the multi-beam optical element. The diffuser hides the beam grid (formed by the at least two beams emitted by the multi-beam optical element from different positions) from the view of the observer and prevents the observer from focusing on the emission points of the at least two beams. The diffuser is preferably a small-angle diffuser so that the light spread is not affected too much. Preferably, the diffuser increases the beam divergence angle by less than 15°, more preferably less than 10°, and even more preferably less than 5°. Optionally, the multi-beam optical element is configured to emit the at least two beams such that each of the at least two beams (already) at least partially overlaps with at least another one of the at least two beams at the diffuser (in particular, on the surface of the diffuser). The diffuser may include the area to be illuminated. The diffuser may be arranged such that each of the at least two beams passes through the diffuser twice.

[0017] Optionally, the diffuser is disposed in the beam paths of at least two of the beams emitted by the multi-beam optical element when coupling light into the multi-beam optical element, and is optically located between the speckle-reducing device and the multi-beam optical element. In this way, the diffuser can be further away from the position where the multi-beam optical element emits the at least two beams, making it easier to hide the beam grid from the view of the observer (i.e., a lower angular diffusion is required, which is beneficial for the light spread). Optionally, the diffuser (alternatively or equally) is disposed in the optical path of the at least two beams and is optically located between the speckle-reducing device and the area to be illuminated.

[0018] Depending on the image to be displayed by the display device, some pixels may need to be black and do not need to be illuminated. In addition, for example, the image content displayed, such as the image content displayed in AR glasses, is usually sparse, which means that only a small fraction of the pixels are active at any given time. For self-emitting displays, this can reduce power consumption because only the active pixels consume energy. For displays that use (combined) front / back illumination for the entire display element (such as LCOS or LCD), the illumination usually has to be always on, regardless of the image content, which results in unnecessary high power consumption. Another object of the present disclosure is to provide an optical device for providing area illumination, wherein the power consumption can be reduced and / or the achievable contrast ratio can be increased when sub-regions of an area do not need to be always illuminated.

[0019] This is achieved as follows: Optionally, the multi-beam optical element is configured to couple light from a first external light source and a second external light source into the multi-beam optical element such that the light coupled into the multi-beam optical element from the first external light source provides a first subset of the at least two beams emitted by the multi-beam optical element, and the light coupled into the multi-beam optical element from the second external light source provides a second subset of the at least two beams different from the first subset.

[0020] Wherein, the first subset illuminates a first sub-region of the region to be illuminated, and the second subset illuminates a second sub-region of the region to be illuminated, wherein the first sub-region and the second sub-region at least partially do not overlap. In this way, these sub-regions can be (at least partially) illuminated by different external light sources, such that when it is not necessary to illuminate the corresponding sub-region, one of the external light sources can be turned off or its power can be reduced, thereby achieving dynamic beam steering. Optionally, this function can be applied to other external light sources. That is, optionally, the multi-beam optical element is configured to couple light from a plurality of external light sources into the multi-beam optical element such that the light coupled into the multi-beam optical element from each of the plurality of external light sources provides a corresponding subset of the at least two beams emitted by the multi-beam optical element, wherein these subsets are different from each other.

[0021] Wherein each subset illuminates a corresponding sub-region of the region to be illuminated, and each subset at least partially does not overlap with other subsets. Preferably, the plurality of external light sources are at least 9 (for example, a 3x3 grid). This allows the use of a larger number of external light sources to illuminate the region, thereby achieving better brightness.

[0022] As an alternative or in addition, local dimming / dynamic beam control can also be achieved for a single external light source. Optionally, the multi-beam optical element is configured to couple light from a plurality (at least one) of external light sources into the multi-beam optical element such that the light coupled into the multi-beam optical element from each of the plurality of external light sources provides a plurality of subsets of the at least two beams emitted by the multi-beam optical element, wherein the subsets belonging to each of the plurality of external light sources are different from each other, and the multi-beam optical element is configured to selectively reduce the power of one, more or all of the subsets belonging to each of the plurality of external light sources. Optionally, each subset illuminates a corresponding sub-region of the region to be illuminated, and each subset does not overlap with other subsets belonging to each of the plurality of external light sources.

[0023] Optionally, the multi-beam optical element includes: - a bus waveguide for receiving the light coupled into the multi-beam optical element; - At least two fan-out waveguides associated with a bus waveguide, wherein each of the at least two fan-out waveguides associated with the bus waveguide is arranged to provide one of the at least two light beams emitted by the multi-beam optical element. For each of the at least two fan-out waveguides associated with the bus waveguide, a fan-out optical coupler is provided for coupling light from the bus waveguide into the corresponding one of the at least two fan-out waveguides associated with the bus waveguide. In this way, light can be conveniently distributed to provide the at least two light beams emitted by the multi-beam optical element. Optionally, the number of fan-out waveguides associated with the bus waveguide is at least ten. Optionally, at least one fan-out type optical coupler includes an adjustment structure for adjusting the proportion of light coupled from the bus waveguide into the corresponding fan-out type waveguide. Optionally, as the adjustment structure, an interference structure is provided, wherein a part of the bus waveguide forms the first arm of the interference structure, and a part of the fan-out waveguide forms the second arm of the interference structure. The first arm and / or the second arm includes a phase shifter. This achieves dynamic beam control.

[0024] Optionally, the bus waveguide is a first bus waveguide. Wherein, the multi-beam optical element further includes: - A second bus waveguide for receiving light coupled into the multi-beam optical element; - At least two fan-out waveguides associated with the second bus waveguide, wherein each of the at least two fan-out waveguides associated with the second bus waveguide is arranged to provide one of the at least two light beams to be emitted by the multi-beam optical element; for each of the at least two fan-out waveguides associated with the second bus waveguide, a fan-out optical coupler is provided for coupling light from the second bus waveguide into the corresponding one of the at least two fan-out waveguides associated with the second bus waveguide. In this way, it is beneficial to the distribution of light. For example, the bus waveguides can extend side by side with each other for at least a section. In this way, it is beneficial to the distribution of light. For example, the bus waveguides can extend side by side with each other for at least a section.

[0025] Optionally, the multi-beam optical element includes: - A plurality of additional bus waveguides for receiving light coupled into the multi-beam optical element; - At least two fan-out waveguides, each associated with one of the plurality of additional bus waveguides, wherein each of the at least two fan-out waveguides associated with each of the plurality of additional bus waveguides is arranged to provide one of the at least two light beams emitted by the multi-beam optical element; wherein, for each of the at least two fan-out waveguides associated with each of the plurality of additional bus waveguides, a fan-out optical coupler is provided for coupling light from a corresponding one of the plurality of additional bus waveguides into a corresponding one of the at least two fan-out waveguides associated with the corresponding one of the plurality of additional bus waveguides. The number of the additional bus waveguides is preferably greater than 10.

[0026] Optionally, each of the (first) bus waveguide, the second bus waveguide, and / or the plurality of additional bus waveguides is coupled to a light source.

[0027] Optionally, the multi-beam optical element further comprises: - A main waveguide for receiving light coupled into the multi-beam optical element; - A first bus optical coupler for coupling light from the main waveguide into the first bus waveguide; - A second bus optical coupler for coupling light from the main waveguide or the first bus waveguide into the secondary bus waveguide. This allows light from a single waveguide (or a small number of waveguides) to be easily distributed to a larger number of bus waveguides and thus to the respective fan-out waveguides. This distribution can occur directly from the main waveguide to all bus waveguides; or from the main waveguide to the first bus waveguide, then from the first bus waveguide to the second bus waveguide, then from the second bus waveguide to other waveguides, and so on; or in a different configuration. The main waveguide may also have the characteristics of a bus waveguide, that is, optionally, the multi-beam optical element further comprises at least two fan-out waveguides associated with the main waveguide, wherein each of the at least two fan-out waveguides associated with the main waveguide is arranged to provide one of the at least two light beams emitted by the multi-beam optical element, and wherein, for each of the at least two fan-out waveguides associated with the main waveguide, a fan-out optical coupler is provided for coupling light from the main waveguide into a corresponding one of the at least two fan-out waveguides associated with the main waveguide. Optionally, the light source is coupled to the main waveguide.

[0028] Optionally, the first bus optical coupler includes an adjustment structure for adjusting the proportion of light coupled from the main waveguide into the first bus waveguide.

[0029] Optionally, as an adjustment structure, an interference structure is provided, wherein a part of the main waveguide forms a first arm of the interference structure, and a part of the first bus waveguide forms a second arm of the interference structure, and wherein the first arm and / or the second arm includes a phase shifter. In this way, the power of the light beam emitted by the fan-out waveguide associated with the first bus waveguide can be adjusted. This allows for dynamic beam control, i.e., guiding light to the areas where light is needed in the multi-beam optical element and saving power when the sub-areas illuminated by the fan-out waveguide associated with the first bus waveguide do not require (full) illumination. The interference structure optionally includes a Mach-Zehnder interference structure. Further optionally, the second bus optical coupler includes an adjustment structure for adjusting the proportion of the light coupled from the main waveguide or the first bus waveguide to the second bus waveguide. Preferably, the sub-areas illuminated by the light beam provided by the first bus waveguide and the sub-areas illuminated by the light beam provided by the second bus waveguide are at least partially non-overlapping.

[0030] Optionally, the multi-beam optical element further includes: - a first bus set, configured to receive light from a first external light source, the first bus set including a bus waveguide and the at least two fan-out waveguides associated with the bus waveguide; and - a second bus set, configured to receive light from a second external light source different from the first external light source, the second bus set including: - the bus waveguide of the second bus set; - at least two fan-out waveguides associated with the bus waveguide of the second bus set, wherein each of the at least two fan-out waveguides associated with the bus waveguide of the second bus set is arranged to provide one of the at least two light beams emitted by the multi-beam optical element; wherein, for each of the at least two fan-out waveguides associated with the bus waveguide of the second bus set, a fan-out optical coupler is provided for coupling the light from the bus waveguide of the second bus set to the corresponding one of the at least two fan-out waveguides associated with the bus waveguide of the second bus set. Different bus sets can be used, for example, to illuminate an area with different colors, especially in the field-sequential color mode, i.e., the color information is transmitted in a sequential and continuous manner with a single color, and these colors are fused by the human visual system into a color image. Optionally, the device includes a first external light source and a second external light source. Optionally, the first external light source and the second external light source are configured to emit light of different wavelengths, especially light of different colors. Optionally, the sub-areas illuminated by the light beams emitted by the second bus set and the sub-areas illuminated by the light beams emitted by the first bus set are substantially overlapping. Optionally, the optical device includes a third bus set having the same characteristics as the second bus set, for example, for a third color. Optionally, each bus set includes additional bus waveguides.

[0031] Optionally, the multi-beam optical element further includes a transparent substrate. Optionally, the bus waveguide is at least partially disposed in the transparent substrate, and the at least two fan-out waveguides are disposed in the transparent substrate. Optionally, the bus waveguide and the at least two fan-out waveguides are disposed in the transparent substrate by femtosecond laser direct writing. Optionally, one, some, or all of the other waveguides mentioned in the present disclosure are also at least partially disposed in the transparent substrate, in particular the second bus waveguide and its associated fan-out waveguides, additional bus waveguides and their associated fan-out waveguides, and / or the main waveguide. Optionally, the substrate has a boundary surface, and the fan-out waveguides (associated with the (first) bus waveguide, the second bus waveguide, and / or the additional bus waveguide) are bent towards the boundary surface of the transparent substrate.

[0032] Optionally, the transparent substrate includes glass, in particular borosilicate glass, such as aluminoborosilicate glass or alkaline earth metal borosilicate glass type. Optionally, the substrate contains Corning EAGLE XG (R), which is an alkaline earth metal borosilicate glass type with a refractive index of about ca. 1.5 (in the visible light range). Optionally, the transparent substrate has a refractive index of 1.5 in the visible light range, for example 1.5185 at 450 nm, 1.5134 at 520 nm, and / or 1.5080 at 638 nm.

[0033] Femtosecond laser direct writing (FDLW, also commonly referred to as femtosecond laser direct engraving) optionally includes one or more of the following steps: - Providing a substrate that includes a transparent dielectric material and / or includes glass, ceramic, polymer, and / or crystal material; - Using multi-photon (i.e., more than 2 photons) absorption of photons having energy below the bandgap of the substrate material, and / or where the pulses are femtosecond pulses with low to medium frequency, such as between 20 kHz and 10 MHz, optionally between 80 kHz and 5 MHz, in particular between 100 kHz and 2 MHz, and even more specifically between 500 kHz and 1.5 MHz, and / or where the pulses have a medium pulse width, such as between 40 fs and 2 ps, optionally between 100 fs and 1 ps, in particular between 200 fs and 400 fs.

[0034] Another laser writing technique that can be used to provide waveguides in a transparent substrate is 2PP (two-photon polymerization) laser writing, which can include two-photon lithography or multi-photon lithography. Compared with femtosecond laser direct writing, it can include one or more of the following steps or characteristics:

[0035] - Using femtosecond pulses with generally high frequency, such as 80 MHz, and a pulse width less than 100 fs; - Two-photon absorption is a third-order process with respect to the third-order susceptibility and a second-order process with respect to the light intensity; - Provide a special resist (photosensitive material) that is highly transparent to photons of wavelength λ but highly absorptive to photons of wavelength λ / 2.

[0036] Optionally, the multi-beam optical element further includes a main waveguide, an associated bus waveguide, and an associated fan-out waveguide. In this way, a larger number of light sources can be used to illuminate the area, thus achieving higher brightness.

[0037] Optionally, the multi-beam optical element (especially the transparent substrate) includes an optical structure, and the fan-out waveguides (associated with the (first) bus waveguide, the second bus waveguide, and / or the additional bus waveguide) are bent towards the side interface such that they direct the light beams emitted from the fan-out waveguides to the optical structure. Optionally, the optical structure includes a reflective interface for reflecting the light beams directed to the optical structure by the fan-out waveguides. Specifically (if the optical structure is provided outside the transparent substrate), the reflective interface reflects the light beams emitted by the fan-out waveguides towards the transparent substrate, especially towards the side interface of the substrate. Optionally or additionally, the optical structure includes a transmissive interface (different from the side interface of the substrate) that is arranged such that the light beams directed to the optical structure are emitted from the transmissive interface.

[0038] Optionally, the optical structure includes an optical redirecting element for each fan-out waveguide (associated with the (first) bus waveguide, the second bus waveguide, and / or the additional bus waveguide), the optical redirecting element being associated with the corresponding fan-out waveguide, wherein each fan-out waveguide is configured to emit a light beam to the corresponding optical redirecting element. Optionally, each optical redirecting element directs the light beam emitted to the optical redirecting element by the corresponding fan-out waveguide to a speckle reduction device. The optical redirecting element can also shape the corresponding light beam. Specifically, the optical redirecting element is configured to collimate the light beam. The optical redirecting element can reduce the divergence angle (e.g., less than 1°), it can keep the divergence angle unchanged, or it can increase the divergence angle (e.g., increase to greater than 20°). Optionally, the optical redirecting element includes a lens for collimating the corresponding light beam.

[0039] Optionally, the transparent substrate is arranged such that the light beams emitted by the multi-beam optical element after the light is coupled into the multi-beam optical element pass through the transparent substrate after interacting with the speckle-reducing device. This allows for a particularly compact size. The at least two light beams may pass through the transparent substrate non-parallel to the at least two light beams emitted by the multi-beam optical element. Optionally, the optical device is arranged such that the light beam passes through the optical structure such that the light beam avoids the optical redirecting element, and / or such that the path of the light beam is not changed by the optical redirecting element, and / or such that the path of the light beam is deflected by less than 10°, optionally less than 5°. Optionally, the multi-beam optical element includes, for each of the at least two light beams reflected by the speckle-reducing element, an optical deflection element that is configured to direct the corresponding light beam to the area to be illuminated and / or to deflect the light beam such that its light beam path is substantially perpendicular to the boundary surface of the transparent substrate or the surface of the transparent substrate opposite the boundary surface. Optionally, each optical redirecting element is combined with the optical deflection element; that is, each optical redirecting element is configured to (also) adjust the path of the corresponding light beam after reflection from the speckle-reducing device.

[0040] Optionally, the speckle-reducing device includes: a mirror that is configured to reflect the at least two light beams emitted by the multi-beam optical element when the light is coupled into the multi-beam optical element; and a deflection device that is configured to provide a continuous change in the position of the mirror surface points. In this way, the light beam path and / or the angle of the light beam incident on the speckle-reducing device can be changed dynamically and continuously. Optionally, at least during a certain period of time, the positions of at least some of the mirror surface points will experience different changes. Optionally, the deflection device is configured to continuously (especially periodically, i.e., one-sided back and forth) change the position of the mirror surface points. Optionally, the deflection element causes the mirror to move or vibrate, especially at least partially in a direction parallel to the optical axis of the light beam incident on the mirror.

[0041] The speckle-reducing device may include a plurality of independent (especially tiled) speckle-reducing elements, where each speckle-reducing element is arranged to reduce the speckle of a subset of the at least plurality of light beams. For example, each speckle-reducing element may include a mirror and a deflection device.

[0042] Optionally, the deflection device is configured to continuously (especially periodically, i.e., one-sided back and forth) tilt the mirror. In this way, the deflection device continuously changes the angle of the light beam (and to some extent the optical path length). Optionally, the speckle-reducing device includes a MEMS tilt mirror, that is, optionally, the mirror and the deflection device form a MEMS tilt mirror.

[0043] Optionally, the deflection device is configured to induce surface waves on the surface of the mirror (i.e., the surface on which the at least two light beams are incident). Optionally, the deflection device includes a Dyoptyka mirror. Optionally, the mirror is deformable.

[0044] Optionally, the deflection device is configured to deform the surface of the mirror to achieve various patterns, in particular various non-flat regions. Specifically, the deflection device is configured to vibrate the surface of the mirror, optionally such that a plurality of surface deformations are formed over time. Specifically, the deflection device is configured to induce surface waves on the surface of the mirror such that the beam path and / or phase of the light beam reflected from the mirror changes dynamically and continuously. Specifically, the deflection device is configured to induce surface waves on the surface of the mirror such that the speckle pattern formed by the light beam reflected from the mirror in the area to be illuminated changes dynamically and continuously. Optionally, the deflection device includes a deformable mirror system for changing the optical path of the light beam over time, wherein the deformable mirror system includes:

[0045] - A deformable thin plate or film coated with a coating for reflecting light beams, in particular light of a predetermined wavelength; - Actuator means arranged to move the thin plate or film so that its surface shape is continuously elastically deformed; and - A control system arranged to control the actuator to cause the thin plate or film to perform a series of movements and / or surface shape deformations, thereby changing the speckle pattern formed by the light beam reflected from the thin plate or film in the area to be illuminated (in particular within a time period less than the predetermined time resolution of the illumination sensor) to reduce the speckle contrast ratio.

[0046] Optionally, the optical device is a backlight device or a frontlight device. Optionally, the optical device includes at least one laser light source for providing light coupled into a multi-beam optical element, in particular for coupling light into a main waveguide, a (first) bus waveguide, and / or a second bus waveguide. Optionally, the optical device includes an external light source mentioned in the present disclosure, preferably a laser light source. The coherence length of the laser light source is optionally less than 2 mm, further optionally less than 500 microns. A lower coherence length is advantageous because the ability of the at least two light beams to interfere with each other is lower. The coherence length of the at least two light beams is optionally less than 2 mm, further optionally less than 500 microns. The coupling of the laser (diode) to the waveguide can be achieved, for example, through a microlens (e.g., bonded to the face of a transparent substrate) or through a tapered waveguide.

[0047] Optionally, the optical device is a display device or a projection device. Optionally, the optical device includes a display element, optionally a reflective or transmissive display element, specifically an LCOS panel, an LCD panel, or a DLP panel, wherein at least two light beams emitted when light is coupled into the multi-beam optical element propagate to the display element, and wherein the display element includes an area to be illuminated. Optionally, the display element includes a plurality of pixel elements (specifically for changing the polarization of incident light according to an image to be displayed), and each of the at least two light beams illuminates more than one pixel element among the plurality of pixel elements (i.e., there is flood illumination). Optionally, each of the plurality of pixel elements is illuminated by more than one of the at least two light beams.

[0048] Optionally, the optical device includes a polarization beam splitter that is arranged to pass or block light beams emitted from the display element according to the current pixel state of the display element. Optionally, the polarization beam splitter is also disposed in the path of at least two light beams emitted by the multi-beam optical element, between the multi-beam optical element and the speckle reduction device. That is, optionally, the polarization beam splitter directs the at least two light beams emitted by the multi-beam optical element to the speckle reduction device.

[0049] The fan-out optical coupler is optionally a directional coupler and / or couples through an evanescent field. The (first and / or second) bus optical coupler is optionally a directional coupler and / or couples through an evanescent field. The (first and / or second) bus waveguide, fan-out waveguide, and / or main waveguide are optionally SiN waveguides.

[0050] The emitted light beams, propagating light beams, etc. mentioned in this disclosure refer to the emitted light beams, propagating light beams, etc. when light is coupled into the optical device (especially the multi-beam optical element) (i.e., during use). Description of the Drawings

[0051] As an example, this disclosure will be further explained in conjunction with some embodiments shown in the drawings. However, these embodiments should not be regarded as a limitation to this disclosure.

[0052] Figure 1 An exemplary embodiment of an optical device for providing area illumination is schematically shown, especially an AR projector.

[0053] Figure 2 Another exemplary embodiment of an optical device for providing area illumination is schematically shown, especially an AR projector.

[0054] Figure 3 A first exemplary embodiment of a multi-beam optical element is schematically shown.

[0055] Figure 4 Schematically shows a second exemplary embodiment of a multi-beam optical element.

[0056] Figure 5 Schematically shows a third exemplary embodiment of a multi-beam optical element.

[0057] Figure 6 Schematically shows a fourth exemplary embodiment of a multi-beam optical element in a top view.

[0058] Figure 7 Schematically shows a fourth exemplary embodiment of a multi-beam optical element in a side view.

[0059] Figure 8 Schematically shows yet another exemplary embodiment of an optical device for providing area illumination (especially for VR applications).

[0060] Figure 9a Shows a Zemax diagram of yet another exemplary embodiment of the optical device.

[0061] Figure 9b Shows Figure 9a a detailed view of.

[0062] Figure 9c Shows Figure 9b a detailed view of.

[0063] Figure 9d Shows Figure 9a the incoherent irradiance of the far field of the shown figure.

[0064] Figure 10a Shows an image generated by an AR projector projecting with a single laser beam without speckle reduction.

[0065] Figure 10b Shows an image generated by an AR projector projecting with a single laser beam and with speckle reduction by a MEMS mirror.

[0066] Figure 10c Shows an image generated by an AR projector projecting with multiple laser beams without speckle reduction.

[0067] Figure 10d Shows an image generated by an AR projector projecting with multiple laser beams with speckle reduction by a MEMS mirror.

[0068] Figure 11a Shows an image generated by an AR projector projecting with a single laser beam without speckle reduction.

[0069] Figure 11bShows an image generated by an AR projector using a single laser beam projection processed by a MEMS mirror for speckle removal.

[0070] Figure 11c Shows an image generated by an AR projector using multiple laser beam projections without speckle removal.

[0071] Figure 11d Shows an image generated by an AR projector using multiple laser beam projections processed by a MEMS mirror for speckle removal. Detailed Description

[0072] Figure 1 Schematically shows an exemplary embodiment of an optical device 1 for illuminating region 2. The optical device includes a despeckling device 3 configured to dynamically and continuously change the beam path and / or phase of the light beam incident on the despeckling device 3. The optical device 1 further includes a multi-beam optical element 4 configured to emit at least two light beams 5 towards the speckle device when light is coupled into the multi-beam optical element 4. The light can be coupled into the multi-beam optical element 4, for example, at the bottom of the element in Figure 1 Each of the at least two light beams 5 is emitted from a position 6 that is different from the position 6 from which the multi-beam optical element 4 emits the corresponding other light beams of the at least two light beams 5. The at least two light beams 5 are emitted in such a way that each of the at least two light beams 5 at least partially overlaps with at least another light beam 5 of the at least two light beams 5 at the region 2 to be illuminated. (The light beams 5 are only schematically drawn and their beam divergence angles are not shown.)

[0073] Since the at least two light beams 5 propagate along different beam paths to the despeckling device, the despeckling device 3 will at least partially perform different beam path and / or phase changes on the at least two light beams 5. Therefore, the variation of the generated speckle pattern will increase, resulting in a decrease in speckle contrast.

[0074] The present invention further includes a diffuser 7 disposed in the beam paths of the at least two light beams 5 emitted by the multi-beam optical element 4 when light is coupled into the multi-beam optical element 4. The function of the diffuser 7 is to hide the beam pattern of the at least two light beams 5 emitted by the multi-beam optical element 4 from the viewer. In this embodiment, the diffuser 7 is disposed in the beam paths of the at least two light beams 5 emitted by the multi-beam optical element 4 when light is coupled into the multi-beam optical element 4 and is optically located between the despeckling device 3 and the multi-beam optical element 4.

[0075] The speckle reduction device 3 includes a mirror 18 for reflecting at least two light beams 5 emitted by the multi-beam optical element 4 when coupling light into the multi-beam optical element 4. In addition, the speckle reduction device 3 further includes a deflection device 22 for continuously changing the position of points on the surface of the mirror 18. For example, the deflection device 22 may include a MEMS, such as a tilting device, configured to continuously tilt the mirror 18. For example, the continuous tilting may be periodic actuation within a range of less than 2° at a frequency of about 100 Hz, which can be achieved by a MEMS with a diameter of 5 mm. The deflection device 22 may be (alternatively or additionally) configured to induce surface waves on the surface 23 of the mirror 18.

[0076] In this embodiment, the multi-beam optical element 4 includes a transparent substrate 17. To achieve a compact layout, at least two light beams 5 emitted by the multi-beam optical element 4 are reflected by the shown speckle reduction element 3 along the direction of the multi-beam optical element 4 and pass through the transparent substrate 17 of the multi-beam optical element 4.

[0077] In addition, in this embodiment, the optical device 1 is a projection device (e.g., an AR projector) and includes a display element 20, specifically a reflective display element, such as an LCOS panel. At least two light beams 5 emitted by the multi-beam optical element 4 after coupling light into the multi-beam optical element 4 propagate to the display element 20, which includes an area 2 to be illuminated. A polarization beam splitter 21 is provided, which is arranged to allow or block the light beam emitted from the display element 21 according to the current pixel state of the display element 21. The light beam transmitted through the polarization beam splitter 21 is propagated to the projector lens 24, which projects an image onto a (transparent) screen (not shown). Therefore, in this embodiment, the optical device 1 can be used as an AR device.

[0078] Figure 2 Another embodiment of the optical device 1 is schematically shown. This embodiment is similar to Figure 1 the embodiment shown, so only the differences are explained, and features corresponding to Figure 1 the features shown use the same reference numerals.

[0079] In this embodiment, the polarization beam splitter 21 is placed between the multi-beam optical element 4 and the speckle reduction device 3. That is, at least two light beams 5 emitted by the multi-beam optical device 4 pass through the polarization beam splitter 21 and the diffuser 7. Compared with Figure 1Different from the embodiment, a quarter-wave plate 31 is provided in the path of the at least two light beams 5 between the diffuser 7 and the speckle reduction device 3. The quarter-wave plate 31 ensures that the polarization of the at least two light beams 5 is rotated, so that the at least two light beams 5 (after being reflected at the mirror 18 and passing through the quarter-wave plate 31 and the diffuser 7 again) are reflected to the display element 20 at the polarization beam splitter 21. Depending on the pixel state of the display element 20, the light beam then passes through the polarization beam splitter 21 and propagates to the projection lens 24, or does not pass through the polarization beam splitter 21 and propagates to the projection lens 24.

[0080] Therefore, in this embodiment, the at least two light beams 5 do not pass through the transparent substrate 17 after interacting with the speckle reduction device 3.

[0081] Figure 3 A first exemplary embodiment of the multi-beam optical element 4 is schematically shown, which includes a transparent substrate 17. The multi-beam optical element 4 includes a bus waveguide 10 for receiving light coupled into the multi-beam optical element 4. Figure 3 A laser light source 19 is also shown for coupling light into the multi-beam optical element 4, particularly into the bus waveguide 10. The multi-beam optical element 4 has at least two fan-out waveguides associated with the bus waveguide 10. For each of the at least two fan-out waveguides 11 associated with the bus waveguide 10, a fan-out optical coupler 12 is provided for coupling light from the bus waveguide 10 into the corresponding one of the at least two fan-out waveguides 11 associated with the bus waveguide 10. Therefore, the light from the laser source 19 is distributed to the at least two fan-out waveguides 11.

[0082] The bus waveguide 10 and the at least two fan-out waveguides 11 are provided in the transparent substrate 17. The substrate has a boundary surface 25, and the at least two fan-out waveguides 11 associated with the bus waveguide 10 are bent towards the boundary surface 25 of the transparent substrate 17. The multi-beam optical element 4 further includes an optical structure 26. The optical structure includes an optical redirecting element 27 for each of the at least two fan-out waveguides 11 shown associated with the bus waveguide 10, wherein each of the at least two fan-out waveguides is configured to emit a corresponding light beam at the corresponding optical redirecting element 27. Each optical redirecting element 27 includes a reflective interface 28 that reflects the corresponding light beam emitted by the corresponding fan-out waveguide 11 back into the transparent substrate 17, so that the at least two light beams 5 are emitted from the transparent substrate 17 at its surface opposite to the boundary surface 26 (substantially perpendicular in this embodiment).

[0083] In summary, each of the at least two fan-out waveguides 11 associated with the shown bus waveguide 10 is arranged to provide one of the at least two light beams 5 through the shown optical redirecting element 27, and the shown multi-beam optical element 4 emits each of the at least two light beams 5 from a position 6 that is different from the position 6 from which the shown multi-beam optical element 4 emits the corresponding other one of the at least two light beams 5.

[0084] Figure 4 A second exemplary embodiment of the multi-beam optical element 4 is schematically shown. This second embodiment is similar to the first embodiment, and thus only the differences will be explained, and features corresponding to those of the first embodiment above will be given the same reference numerals as used in the context of the first embodiment.

[0085] Compared with the first embodiment, in this embodiment, the reflective interface 28 of each optical redirecting element 27 does not reflect the light beam back through the substrate 17. Instead, each optical redirecting element 27 includes a transmissive interface 29, and the reflective interface 28 of the corresponding optical redirecting element 27 guides the corresponding light beam 5 to the transmissive interface 29, at which the corresponding light beam 5 exits from the multi-beam optical element 4. Thus, the light beam 2 is emitted on the side of the side interface 25 of the substrate 17. Similarly, different light beams 5 are emitted from different positions 6.

[0086] Figure 3 and Figure 4 the multi-beam optical element 4 shown in Figure 1 the shown optical device 1 can be used, for example. In this case, a feasible method is to emit the light beam 6 slightly obliquely (i.e., the angle with respect to the side interface 25 deviates from 90°), and / or to place the speckle-reducing device 3 (in particular, the mirror 18) obliquely so that the light beam 6 reflected from the speckle-reducing device 3 (in particular, the mirror 3) avoids the reflective interface 28.

[0087] Figure 5 A third exemplary embodiment of the multi-beam optical element 4 is schematically shown. Features corresponding to those of the first embodiment above are given the same reference numerals as used in the context of the first embodiment.

[0088] The multi-beam optical element 4 is configured to receive light from a first external light source 8a, a second external light source 8b, and additional external light sources (also as Figure 5The light (as shown) is optically coupled into the multi-beam optical element 4. The light from each (first, second, and additional) external light source 8a, 8b is optically coupled into the main waveguide 13. From each (first, second, and additional) main waveguide 13, the light is optically coupled from the corresponding main waveguide 13 into the first bus waveguide 10a via the first bus optical coupler 14a, into the second bus waveguide 10b via the second bus optical coupler 14b, and into additional bus waveguides via additional bus optical couplers. Associated with each (first, second, and additional) bus waveguide 10a, 10b are at least two fan-out waveguides 11, 11a, 11b, which are associated with the corresponding bus waveguides 10a, 10b. Each of the at least two fan-out waveguides 11, 11a, 11b associated with the corresponding bus waveguides 10a, 10b is arranged to provide one of the at least two light beams 5, wherein for each of the at least two fan-out waveguides 11, 11a, 11b associated with the corresponding bus waveguides 10a, 10b, a fan-out optical coupler 12 is provided for optically coupling the light from the bus waveguide 10 into the corresponding one of the at least two fan-out waveguides 11, 11a, 11b associated with the corresponding bus waveguides 10a, 10b. In summary, each of the at least two light beams 5 is emitted by the fan-out waveguide 11 such that each of the at least two light beams 5 is emitted from a different position 6. The fan-out waveguide 11 can be formed in the manner described in Figure 3 and Figure 4 and can be associated with the optical redirecting element 27.

[0089] Additional external light sources, additional main waveguides, and associated bus waveguides and fan-out waveguides are not labeled with reference numerals but are shown in the figure. It should also be noted that crossovers between different waveguides are avoided along the Z-axis (perpendicular to the plane of the drawing).

[0090] It is advantageous if the light optically coupled into the multi-beam optical element 4 from the first external light source 8a provides a first subset 9a of the at least two light beams 5 emitted by the multi-beam optical element 4, and the light optically coupled into the multi-beam optical element 4 from the second external light source 8b provides a second subset 9b (different from the first subset 9a) of the at least two light beams 5. The first subset 9a illuminates a first sub-region of the region to be illuminated 2, and the second subset 9b illuminates a second sub-region of the region to be illuminated 2, wherein the first sub-region and the second sub-region are at least partially non-overlapping. Thus, when the illumination of the corresponding sub-region is not required or needs to be reduced, the power of the first or second external light source 8a, 8b can be reduced.

[0091] In this embodiment, the four external light sources on the left can provide a first color, the four external light sources in the middle can provide a second color, and the four external light sources on the right can provide a third color, especially when using the optical device in a field sequential mode.

[0092] Figure 6 A top view of a fourth exemplary embodiment of the multi-beam optical element 4 is schematically shown. Figure 7 A side view of the same embodiment is shown. Features corresponding to those of the third embodiment above are given the same reference numerals as used in the context of the third embodiment.

[0093] The fourth embodiment is similar to the third embodiment, and thus only its differences are explained. In this embodiment, the number of external light sources is reduced. For example, one external light source can be provided for each color.

[0094] In the fourth embodiment, light is coupled from the main waveguide 13 to the first bus waveguide 10a via the first bus optical coupler 14a, and from the first bus waveguide 10a to the second bus waveguide 10b via the second bus optical coupler 14b. The first bus optical coupler 14a includes an adjustment structure 15 for adjusting the proportion of light coupled from the main waveguide 13 to the first bus waveguide 10a. In addition, the second bus optical coupler 14a includes an adjustment structure 15 for adjusting the proportion of light coupled from the first bus waveguide 10a to the second bus waveguide 10b. As the adjustment structure 15 of the first bus optical coupler 14a, an interference structure is provided, where a part of the main waveguide 13 forms the first arm of the interference structure, and a part of the first bus waveguide 10a forms the second arm of the interference structure, where the first arm and / or the second arm includes a phase shifter. Other adjustment structures can be formed in a similar manner. These adjustment structures can adjust the power transmitted to each fan-out waveguide 11, thereby achieving dynamic beam control of each external light source.

[0095] The waveguide connected to the second external light source 8b and another external light source has the same features as the waveguide connected to the first external light source 8a.

[0096] In addition, the multi-beam optical element 4 includes a first bus set 16a configured to receive light from a first external light source 8a. The first bus set 16a includes a bus waveguide 10 and the at least two fan-out waveguides 11 associated with the bus waveguide 10. The multi-beam optical element 4 further includes a second bus set 16b configured to receive light from a second external light source 8b different from the first external light source 8a. The second bus set 16 includes a bus waveguide 10' of the second bus set 16b and at least two fan-out waveguides 11' associated with the bus waveguide 10' of the second bus set 16b. Each of the at least two fan-out waveguides 11' associated with the bus waveguide 10' of the second bus set 16b is arranged to provide one of the at least two light beams 5 to be emitted by the multi-beam optical element 4. For each of the at least two fan-out waveguides 11' associated with the bus waveguide 10' of the second bus set 16b, a fan-out optical coupler is provided for coupling light from the bus waveguide 10' of the second bus set 16b into the corresponding one of the at least two fan-out waveguides 11' associated with the bus waveguide 10' of the second bus set 16b. Different bus sets 16a, 16b can be used, for example, to illuminate the area 2 in different colors, especially in the field-sequential color mode.

[0097] In the fourth embodiment, additional bus waveguides (connected to additional fan-out waveguides) are distributed from the main waveguide 13, the first bus waveguide 10a, and the second bus waveguide 10b.

[0098] From Figure 7 It can be seen that these waveguides are also scattered on the Z-axis to avoid crossing between different waveguides.

[0099] Figure 8 Another exemplary embodiment of the optical device 1 is schematically shown. This embodiment provides backlighting, for example, for VR applications. The optical device 1 includes Figure 4A multi-beam optical element 4 similar to that of the second embodiment shown; however, at least two beams 5 are emitted obliquely with respect to the boundary surface 25 of the substrate 17. The at least two beams 5 are emitted to the speckle reduction device 3, which, in this embodiment, includes a mirror 18 for reflecting the at least two beams 5 emitted by the multi-beam optical element 4 and a deflection device (not shown) for providing a continuous change in the position of the surface points of the mirror 18. Since VR applications require larger display elements, in this case, preferably, the deflection device is configured to induce surface waves on the surface of the mirror 18. The mirror 18 reflects the beam 5 back and through the transparent substrate 17, avoiding the reflection interface 28. In this case, the diffuser 7 is provided between the side of the substrate 17 opposite to the boundary surface 25 and the display element 20. That is, the diffuser 7 is provided in the beam path of the beam 7 and is optically located after the speckle reduction device 3, and the beam 5 passes through the diffuser after passing through the substrate 17 for the second time.

[0100] The optical device 1 of this embodiment is preferably a display device, and the display element 20 is a transmissive display element, such as an LCD panel.

[0101] Figure 9a A Zemax diagram showing another exemplary embodiment of the optical device 1, which includes a multi-beam optical element 4 and a speckle reduction device 3. Features corresponding to the above features are denoted by the same reference numerals as above. The multi-beam optical element 4 includes a transparent substrate 17. The multi-beam optical element 4 includes an optical structure 26. Multiple beams are guided in the transparent substrate 17 to the optical structure 26, where only the last part of the beams in the transparent substrate 17 is shown. The beams can be guided to the optical structure 26, for example, Figure 3 and Figure 4 as shown, by a curved waveguide. In this case, the beams can have different colors.

[0102] From Figure 9b (showing a detailed view of the optical structure 26), it can be seen more clearly that the optical structure 26 includes a light redirection element 27 for each beam, such that each beam 6 is emitted from a different position 5.

[0103] From Figure 9c (showing a detailed view of one light redirection element 27), it can be seen more clearly that each light redirection element 7 includes a reflection interface 28 for reflecting the beam and a transmission interface 29. The reflection interface 28 reflects the corresponding beam and guides the beam to the transmission interface 29, from which the beam is emitted. The light redirection feature 27 also includes a lens 30, particularly a microlens, for collimating the corresponding beam 6. The beam 5 is emitted from the multi-beam optical element 4 obliquely (i.e., deviated from the vertical) with respect to the boundary surface 25 of the transparent substrate 17.

[0104] At least two light beams 5 emitted by the multi-beam optical element 4 are incident on the speckle-removing device 3 (in particular, the mirror 18) at an inclined angle and are reflected back to the multi-beam optical element 4 by the speckle-removing device 3. Each light beam 5 is deflected by a corresponding optical redirecting element 27 such that the corresponding light beam 5 is perpendicular to the boundary surface 25 while avoiding the corresponding lens 30. Then, the light beam 5 passes through the transparent substrate 17. Figure 9d The incoherent irradiance of the far field of the light beam 5 is shown.

[0105] This embodiment of the multi-beam optical element 4 can be implemented, for example, in Figure 1 the embodiment of

[0106] Figure 10a The image generated by the AR projector using a single laser beam without speckle removal is shown. Figure 10b The image generated by the AR projector using a single laser beam projected and subjected to speckle removal by a MEMS mirror is shown. Figure 10c The image generated by the AR projector using multiple laser beams projected without speckle removal is shown. Figure 10d The image generated by the AR projector using multiple laser beams projected and subjected to speckle removal by a MEMS mirror is shown. In addition, Figures 10c - 10d It is a color projection, where the image has been converted to a grayscale image for the use of this disclosure.

[0107] By comparing Figure 10a and Figure 10b it can be seen that using a MEMS mirror for speckle removal can provide a better (i.e., lower) speckle contrast ratio. However, even when using a MEMS mirror for speckle removal, if only a single laser beam is used, the speckles are still visible (see Figure 10b ). Only by using more than one laser beam and a speckle-removing device can the speckle contrast ratio be sufficiently reduced (see Figure 10d ).

[0108] Figure 10c and Figure 10d A large number of light beams are used (the multi-beam optical element 4 is similar to that shown in Figure 4 ). The speckle contrast ratio is proportional to the number of light beams used. Therefore, using at least two light beams emitted from different positions has an advantage over using a single light beam.

[0109] Figure 11a The image generated by the AR projector using a single laser beam without speckle elimination is shown. Figure 11b The image generated by the AR projector using a single laser beam and subjected to speckle elimination by a MEMS mirror is shown. Figure 11c The image generated by the AR projector using multiple lasers without speckle elimination is shown.Figure 11d Shows an image generated by an AR projector using multiple laser beams, which is subjected to speckle elimination processing by a MEMS mirror. In addition, Figures 11c to 11d Is a color projection, where the image has been converted to grayscale for the purpose of this disclosure.

[0110] Figures 11a to 11d Is Figures 10a to 10d A cropped version of. The conclusions drawn in the context of Figures 10a to 10d Also apply to these figures.

Claims

1. An optical device (1) for illuminating a region (2), comprising: - A speckle reduction device (3) configured to dynamically and continuously change the beam path and / or phase of a light beam incident on the speckle reduction device (3); - A multi-beam optical element (4) configured to emit at least two light beams (5) to the speckle reduction device when light is coupled into the multi-beam optical element (4); wherein each of the at least two light beams (5) is emitted by the multi-beam optical element (4) from a position (6) different from the position (6) from which the multi-beam optical element (4) emits the corresponding other light beam(s) among the at least two light beams (5); wherein the at least two light beams (5) are emitted such that each of the at least two light beams (5) at least partially overlaps with at least another one of the at least two light beams (5) at the region (2) to be illuminated.

2. The optical device according to claim 1, further comprising a diffuser (7) disposed in the optical path of the at least two light beams (5) emitted by the multi-beam optical element (4) when light is coupled into the multi-beam optical element (4).

3. The optical device according to claim 2, wherein, The diffuser (7) is disposed in the beam path of the at least two light beams (5) emitted by the multi-beam optical element (4) when light is coupled into the multi-beam optical element (4), and is optically located between the speckle reduction device (3) and the multi-beam optical element (4).

4. The optical device according to any one of the preceding claims, Among them, The multi-beam optical element (4) is configured to couple light from a first external light source (8a) and a second external light source (8b) into the multi-beam optical element (4), such that the light coupled from the first external light source (8a) into the multi-beam optical element (4) provides a first subset (9a) of the at least two light beams (5) emitted by the multi-beam optical element (4), and the light coupled from the second external light source (8b) into the multi-beam optical element (4) provides a second subset (9b) of the at least two light beams (5) different from the first subset (9a), wherein the first subset (9a) illuminates a first sub-region of the region (2) to be illuminated, and the second subset (9b) illuminates a second sub-region of the region (2) to be illuminated, wherein the first sub-region and the second sub-region at least partially do not overlap.

5. The optical device according to any one of the preceding claims, wherein, The multi-beam optical element (4) comprises: - A bus waveguide (10) for receiving light coupled into the multi-beam optical element (4); - At least two fan-out waveguides (11) associated with the bus waveguide (10), wherein each of the at least two fan-out waveguides (11) associated with the bus waveguide (10) is arranged to provide one of the at least two light beams (5) to be emitted by the multi-beam optical element (4); wherein, for each of the at least two fan-out waveguides (11) associated with the bus waveguide (10), a fan-out optical coupler (12) is provided for coupling light from the bus waveguide (10) into the corresponding one of the at least two fan-out waveguides (11) associated with the bus waveguide (10).

6. The optical device according to claim 5, wherein, The bus waveguide (10) is a first bus waveguide (10a), wherein the multi-beam optical element (4) further comprises: - A second bus waveguide (10b) for receiving light coupled into the multi-beam optical element (4); - At least two fan-out waveguides (11b) associated with the second bus waveguide (10b), wherein each of the at least two fan-out waveguides (11b) associated with the second bus waveguide (10b) is arranged to provide one of the at least two light beams (5) to be emitted by the multi-beam optical element (4); wherein, for each of the at least two fan-out waveguides (11b) associated with the second bus waveguide (10b), a fan-out optical coupler (12) is provided for coupling light from the second bus waveguide (10b) into the corresponding one of the at least two fan-out waveguides (11b) associated with the second bus waveguide (10b).

7. The optical device according to claim 6, wherein The multi-beam optical element (4) further comprises: - A main waveguide (13) for receiving light coupled into the multi-beam optical element (4); - A first bus optical coupler (14a) for coupling light from the main waveguide (13) into the first bus waveguide (10a); - A second bus optical coupler (14b) for coupling light from the main waveguide (13) or the first bus waveguide (10a) into the second bus waveguide (10b).

8. The optical device according to claim 7, wherein, The first bus optical coupler (14a) includes an adjustment structure (15) for adjusting the proportion of light coupled from the main waveguide (13) into the first bus waveguide (10a), wherein, optionally, as the adjustment structure (15), an interference structure is provided, wherein a part of the main waveguide (13) forms the first arm of the interference structure, and a part of the first bus waveguide (10a) forms the second arm of the interference structure, wherein the first arm and / or the second arm includes a phase shifter.

9. The optical device according to any one of claims 5 to 8, wherein, The multi-beam optical element (4) further comprises: - A first bus group (16a) configured to receive light from a first external light source (8a), the first bus group (16a) including the bus waveguide (10) and the at least two fan-out waveguides (11) associated with the bus waveguide (10); and - A second bus group (16b) configured to receive light from a second external light source (8b) different from the first external light source (8a), including: - A bus waveguide (10') of the second bus group (16b); - At least two fan-out waveguides (11') associated with the bus waveguide (10') of the second bus group (16b), wherein each of the at least two fan-out waveguides (11') associated with the bus waveguide (10') of the second bus group (16b) is arranged to provide one of the at least two light beams (5) to be emitted by the multi-beam optical element (4), and for each of the at least two fan-out waveguides (11') associated with the bus waveguide (10') of the second bus group (16b), a fan-out optical coupler is provided for coupling light from the bus waveguide (10') of the second bus group (16b) into the corresponding one of the at least two fan-out waveguides (11') associated with the bus waveguide (10') of the second bus group (16b).

10. The optical device according to any one of claims 5 to 9, wherein, The multi-beam optical element (4) further includes a transparent substrate (17), wherein the bus waveguide (10) is at least partially disposed in the transparent substrate (17), and the at least two fan-out waveguides (11) are disposed in the transparent substrate (17), wherein the bus waveguide (10) and the at least two fan-out waveguides (11) are optionally disposed in the transparent substrate (17) by femtosecond laser direct writing, and the transparent substrate (17) is arranged such that the light beam (5) emitted by the multi-beam optical element (4) when light is coupled into the multi-beam optical element (4) passes through the transparent substrate (17) after interacting with the speckle reduction device (3).

11. The optical device according to any one of the preceding claims, wherein, The speckle reduction device (3) includes: a mirror (18) for reflecting the at least two light beams (5) emitted by the multi-beam optical element (4) when light is coupled into the multi-beam optical element (4); and a deflection device for continuously changing the position of the surface points of the mirror (18).

12. The optical device according to claim 11, wherein, The deflection device is configured to continuously tilt the mirror (18).

13. The optical device according to any one of claims 11 or 12, wherein, The deflection device is configured to induce surface waves on the surface of the mirror (18).

14. The optical device according to any one of the preceding claims, in particular a backlight device or a frontlight device, comprising: A laser light source for providing light coupled into the multi-beam optical element (4).

15. The optical device according to any one of the preceding claims, in particular a display device or a projection device, comprises a display element (20), optionally a reflective or transmissive display element, in particular an LCOS panel, an LCD panel or a DLP panel, wherein, The at least two light beams (5) emitted by the multi-beam optical element (4) when light is coupled into the multi-beam optical element (4) propagate to the display element (20), wherein the display element (20) includes the area (2) to be illuminated, and optionally a polarization beam splitter (21) is provided, which is arranged to pass or block the light beam emitted from the display element (21) according to the current pixel state of the display element (21).

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