Light steering system, method for producing an illumination field of steered polarized light, and hybrid projector using the same

Abstract

A light steering system, a method for producing an illumination field of steered polarized light, a hybrid projector using the same as well as a method for producing images using said hybrid projector are disclosed. A light steering system (60) comprises a number of optical elements, namely at least a light steering device (62), a polarizing beam splitter (64), a polarization rotator (66), and one or more mirrors (68, 70, 72). The light steering device (62) is arranged for modulating and directing an incident light beam (58) containing light in two orthogonal polarization states onto the polarizing beam splitter (64). The polarizing beam splitter (64) is arranged for receiving the modulated and directed light from the light steering device and splitting the light beam (58) into a transmitted beam (58t) having a first polarization and a reflected beam (58r) having a second polarization different from said first polarization. The polarization rotator (66) is arranged for rotating the polarization of one of the reflected beam (58r) and the transmitted beam (58t) to correspond to the polarization of the respective other beam. The one or more mirrors (68, 70, 72) are arranged for reflecting and directing the transmitted beam (58t) or the reflected beam (58r) or both beams such that a) one of the beams is reflected zero times and the other beam is reflected an uneven number of times or b) one of the beams is reflected an even number of times and the other beam is reflected an uneven number of times, and such that both beams converge and meet in an image plane.

Description

[0001] LIGHT STEERING SYSTEM, METHOD FOR PRODUCING AN ILLUMINATION FIELD OF STEERED POLARIZED LIGHT, AND HYBRID PROJECTOR USING THE SAME

[0002] TECHNICAL FIELD

[0003] The present invention relates to a light steering system, a method for producing an illumination field of steered polarized light, and and a hybrid projector using the same. The invention also relates to a method for producing images using said hybrid projector.

[0004] TECHNICAL BACKGROUND

[0005] In recent years, light steering has become a highly important technology for producing realistic-looking images. Real images often have a high peak luminance and high dynamic range. Hybrid projectors such as the one shown in WO 2017 059537 A1 allow producing realistic-looking images by employing at least one baselight engine and at least one highlight engine for providing illumination fields in registration at an entry of an imaging engine, which imaging engine uses the light distributed in the illumination fields to produce the actual image on a screen.

[0006] In use, the baselight engine and the highline engine are connected to one or more light sources, which can be a common source for both engine or separate sources for each engine, and which may produce white light or light of different colors. The baselight engine produces a substantially uniform illumination field, whereas the highlight engine can, as needed, produce an illumination field in which one or more distinct areas are much brighter than others. To do this, the highlight engine comprises at least one light steering system typically comprising a number of optical elements such as in particular at least one light steering device such as e.g. a phase light modulator, which can produce a beam of steered light, i.e. which allows to steer light from a light source to one or more areas in the illumination field as needed. As used herein, a beam of light has a certain spatial extension orthogonal to its propagation direction, in contrast to a single light ray, whose spatial extension can be neglected. The illumination field of steered light can then be used by the imaging element to create a realistic looking image with very bright regions. Likewise, light can be steered away from certain areas in the illumination field, which allows producing darker regions in the image. This way, the total light budget is used more efficiently, a higher peak in brightness can be achieved, and the black level is lower, resulting in a higher contrast and a higher dynamic range. If a phase light modulator is used as the light steering device, it can phase modulate the incoming light so that there is constructive interference in some areas and destructive interference in others.

[0007] Some hybrid projectors employ separate baselight and highlight engines for producing illumination fields of different colors, typically red, green and blue, which are then combined in a color engine. Other hybrid projectors produce illumination fields of different colors by using different colors in a time sequential manner. In any case, the light from the baselight engine, the so-called the baselight, and the light from the highlight engine, the so-called the highlight, must be combined prior to entering the imaging engine.

[0008] A common approach to combine baselight and highlight is polarization combination: The baselight and the highlight are orthogonally polarized with respect to each other, e.g. one being s-polarized and the other p-polarized, and both are combined by means of a polarized beams combiner, which is basically a polarizing beam splitter used reversely.

[0009] While some light steering devices work best with polarized light, others like in particular newer generation phase modulators based on microelectromechanical systems (MEMS) technology work with both polarized or unpolarized light. Some modulators for high power system are hermetically sealed in glass that in use can become birefringent due to heating and the thus induced mechanical stress. Hence, even if polarized light is used as a source light for producing highlight, the highlight might at least not fully be polarized.

[0010] However, for some applications like in particular the combination of baselight and highlight via a polarized beams combiner, it is preferable or even necessary to generate a polarized beam of steered light even if unpolarized light is used as a source of a light steering system. One obvious solution to this problem would be to use a polarizer on the the steered light beam, i.e. downstream of the light steering device, but this would, depending on the polarization state of the steered light which in some cases is not predictable, block at least some if not even most of the steered light and make a corresponding system less efficient.

[0011] US 2004 / 0240057 A1 discloses a polarization recuperation system for LCD imagers, in which a beam of unpolarized light from a source is directed under an angle of 45° onto a polarizing beam splitter that transmits a part of the light with a first polarization and reflects the other part of the light with a second polarization orthogonal to the first polarization onto a wave plate. The wave plate rotates the polarization of the reflected beam so that it corresponds to the polarization of the transmitted beam, and the reflected beam is then directed via a mirror so that it runs parallel to the transmitted beam.

[0012] While a polarization recuperation system as shown in US 2004 / 0240057 A1 is useful for LCD imagers, it cannot be simply employed in light steering systems of the aforementioned kind as two parallel light beams would not illuminate the same entry area of an imaging engine, thus reducing or even eliminating the intended effect. Also, the optical path lengths of the two beams must be substantially identical in case of steered light, as each beam produces an illumination field at a certain distance that can be considered as an "image", and it would not be possible, after splitting the beam, to have that image in focus at two different distances.

[0013] In addition to the polarization recuperation system discussed above, other prior art documents address various aspects of light steering and polarization handling in projection systems, but they also present limitations when applied to light steering systems of the kind described herein.

[0014] WO 2022 / 069727 A1 discloses a light steering system with a polarizing beam splitter, a polarization rotator, and mirrors. While it describes splitting an unpolarized light beam into two polarized beams, rotating the polarization of one beam, and then recombining them, it does not address the challenge of efficiently modulating light containing both orthogonal polarization states before beam splitting occurs. WO 2023 / 186324 A1 describes a hybrid projector system with baselight and highlight engines, using light steering for producing illumination fields. Although it discusses various optical arrangements for combining different color channels, it does not specifically address the efficient handling of unpolarized or mixed polarization light in the light steering process.

[0015] US 2021 / 168340 A1 discloses a projection system with a light steering device, polarizing beam splitter, and polarization rotator. However, it uses separate light sources for different polarization states and does not describe a method for efficiently handling light containing both polarization states in a single light path before beam splitting. Moreover, the LCoS-based phase modulator in US 2021 / 168340 A1 typically only phase-modulates one polarization direction, effectively acting as a mirror for the orthogonal polarization direction, resulting in zero modulation or steering capabilities for that polarization. In contrast, our invention efficiently modulates and steers both polarization states simultaneously

[0016] US 5,748,379 A describes an optical system using polarization to separate and recombine light paths. While it discusses path length compensation, it does not address the challenges associated with modulating light containing both polarization states in a light steering system.

[0017] US 2022 / 191440 A1 relates to projection systems and discusses various optical arrangements. However, it does not specifically address the efficient modulation and steering of light containing both orthogonal polarization states in a single optical path before polarization splitting.

[0018] These prior art documents, while addressing various aspects of light steering and polarization handling, do not fully solve the problem of efficiently modulating and steering light containing both orthogonal polarization states before polarization splitting occurs in a manner that maintains equal optical path lengths and ensures proper focusing of the resulting illumination fields. DISCLOSURE OF THE INVENTION

[0019] In view of the aforementioned restrictions, the invention aims at solving the problem of producing an illumination field of steered polarized light with high energy efficiency.

[0020] The problem is solved by a light steering system according to claim 1 , a method for producing an illumination field of steered polarized light according to claim 23, a hybrid projector according to claim 18 and a method for producing images according to claim 37. Advantageous embodiments are defined in the dependent claims.

[0021] The invention ensures that upon polarizing a beam of steered light basically no steered light is lost, allowing to produce and use e.g. a highlight illumination field with high energy efficiency and thus in an environmentally friendly manner.

[0022] The invention also facilitates using unpolarized light as source light for all light steering devices that work well with such light, as in such cases it is no longer necessary to use polarized light to be able to combine the steered light with baselight. The invention facilitates to double the amount of laser diodes of a specific wavelength used for illuminating a light steering device, by combining two types of orthogonally polarized beams with a polarization beam combiner, without doubling the final beam size or the final beam etendue of the combined light beam. As a consequence, the power of the light steering system can be substantially increased, without enlarging the minimum illumination spot size. According to one embodiment, a light steering system comprises a number of optical elements, namely at least a light steering device, a polarizing beam splitter, a polarization rotator, and one or more mirrors, wherein the light steering device is arranged for modulating and directing an incident light beam onto the polarizing beam splitter, the polarizing beam splitter is arranged for splitting the light beam into a transmitted beam having a first polarization and a reflected beam having a second polarization different from said first polarization, the polarization rotator is arranged for rotating the polarization of one of the reflected beam and the transmitted beam to correspond to the polarization of the respective other beam, the one or more mirrors are arranged for reflecting and directing one of the transmitted beam and the reflected beam or both beams such that such that a) one of the beams is reflected zero times and the other beam is reflected an uneven number of times or b) one of the beams is reflected an even number of times and the other beam is reflected an uneven number of times, and such that both beams converge and meet in an image plane. This advantageously not only allows to use basically all steered light in the image plane, but also ensures that the reflected and the transmitted beams have the same orientations, i.e. they are not mirrored with respect to each other. Put in other words: while by definition the reflected beam has already been reflected a first time, the total number of reflections (including the first) each beams experiences must either be a) uneven or b) even including zero (the transmitted beam might not be reflected at all, which, however, is not the preferred set-up as will be explained below). As used herein, the term "image plane" denotes the plane where the converging steered beams meet. It is a virtual plane and the light beams pass through that plane. Accordingly, the term "converging" relates to the fact that the beams, seen along their propagation path, are not parallel but converge towards each other before they meet in the image plane. They may diverge afterwards, which however may be handled with respective relay optics as will be explained later. The image plane may also be the entry of an image entry, so that the light may be directly used for producing images.

[0023] The illumination field of polarized steered light thus produced in the image plane can be regarded as an intermediate image, in particular as a first intermediate image as depending on the further processing of the light beam more than one intermediate images might be created.

[0024] The light steering device in the present invention, particularly when implemented as a phase light modulator, is capable of modulating both orthogonal polarization states of the incident light beam indiscriminately. This means that the device applies the same phase modulation to the entire incident beam, regardless of the polarization state of its constituent light. As a result, when the modulated beam is subsequently split by the polarizing beam splitter, both the transmitted and reflected beams have undergone identical phase modulation. This characteristic ensures that the steered light patterns formed by both beams are substantially identical, which is crucial for maintaining the integrity and quality of the final illumination field. In a preferred embodiment, the light steering device comprises separate phase modulators for different colors, each modulator arranged to modulate both orthogonal polarization states indiscriminately for its respective color. This configuration allows for efficient handling of multiple color channels while maintaining the ability to modulate both polarization states simultaneously for each color. By using separate modulators for different colors, the system can optimize the steering and modulation for each wavelength independently, potentially improving overall color management and image quality. Additionally, this arrangement allows for different steering distances for each color, which can be advantageous given that the optimal steering distance may vary with wavelength as described in the formula of claim 10 (formerly claim 9). This approach combines the benefits of color-specific optimization with the efficiency of handling both polarization states in a single device for each color, resulting in a versatile and high-performance light steering system.

[0025] Additionally or alternatively, the light steering device may be a single light steering device that modulates both polarization states indiscriminately. This offers several advantages. Firstly, it allows for a more compact and cost-effective system design, as only one modulation device is needed instead of separate devices for each polarization state. Secondly, it simplifies the control and synchronization of the light steering process, as the same modulation pattern can be applied to the entire incident beam. Lastly, this approach ensures that any variations or imperfections in the modulation process affect both polarization states equally, helping to maintain consistency in the final illumination field. This polarization-agnostic modulation is particularly beneficial in systems using unpolarized or mixed polarization light sources, as it eliminates the need for pre-polarization of the incident light or separate handling of different polarization states. It also facilitates the efficient use of the entire light budget from the source, regardless of its polarization characteristics.

[0026] Additionally or alternatively, the light steering device may be a microelectromechanical systems (MEMS) based phase modulator. Such MEMS- based modulators are particularly well-suited for this application due to their ability to modulate light regardless of its polarization state. The pixels or elements of these MEMS devices can be controlled to create the desired phase pattern across the entire incident beam, affecting both orthogonal polarization states equally. Additionally or alternatively, the polarizing beam splitter and the one or more mirrors may be arranged such that the reflected beam and the transmitted beam each form an illumination field on the image plane, the illumination fields overlapping each other and being substantially identically in size and light distribution. The illumination fields are usually of rectangular shape and may already have the same aspect ratio and in some cases even the same size as an entry into an imaging engine, which uses the highlight. Typically, the illumination fields will be re-imaged by some relay optics that can optionally also perform some additional optical transformations like making the beams telecentric, adding some diffusors (one or more, static or dynamic) to reduce speckle whilst filling the available optical etendue, magnifying the beam size so that it gets a same size as the beam at the exit of a light rod in the baseline path that can be used as homogenizing element in that baseline path, for both beams at the entry of the combining element that combines the highlight and baseline beam (also using a same minimum f-number). Preferably, the illumination fields are spatially relatively slowly varying, because of having “minimum size” features called Point Spread Functions that take a significant part of the illuminated area, i.e. having a diameter of e.g. 5 - 20 % of the illuminating outer beam size dimensions. This allows to have some distortion discrepancies between the two beams with the same light distribution as a result of the difference in incident angle.

[0027] In these cases, the illumination field of polarized steered light in said image plane would be the first intermediate image and its image by said relay optics would be a second intermediate image.

[0028] Additionally or alternatively, the polarizing beam splitter and the one or more mirrors may be arranged such that the transmitted beam and the reflected beam converge towards the image plane forming an angle with each other not exceeding 20°, preferably less than 15°, and more preferably less than 10°. As typical image engines accept incoming beams inside of a cone with half angle up to 15° or more, this arrangement ensures that a combination of a transmitted beam and a reflected beam with two distinct angular fields will be fully accepted by the optical system. The difference in incidence angle of the transmitted beam and the reflected beam on the image plane may cause different local optical distortions and local optical defocusing effects in the two beams with the same steered light pattern. A person skilled in the art understands that with the convergence kept lower than 20°, more preferred 15°, even more preferred 10°, these local variations between the two steered beams remain at least one order of magnitude lower than the general extent of the minimum light steered spot size (also known as Point Spread Function, or PSF for short), so that these variations are not substantially changing the illumination profile of the light steering system.

[0029] Additionally or alternatively, the polarization beam splitter and the one or more mirrors may be arranged such that the reflected and that transmitted beam are each directed from different directions onto the image plane under a non-zero incidence angle, said incidence angles being substantially identical. With such arrangement, the local distortions (i.e. keystone distortions) and local defocusing effects caused by the oblique incidence of each beam on the image plane, are understood to become more symmetrical and balanced out against each other (partly selfcompensating), so that local variations on the steered illumination profile become even more reduced.

[0030] Additionally or alternatively, the polarizing beam splitter and the one or more mirrors may be arranged such that the optical paths of the reflected beam to the center point of the beam spot in the image plane and of the transmitted beam to the center point of the beam spot in the image plane have substantially the same optical length. This advantageously ensures that the illumination fields from the reflected and the transmitted beam can be in focus. In order to do so, the optical path of the reflected beam may comprise optical elements, in particular at least one glass plate, for compensating a focus shift of the transmitted beam.

[0031] Additionally or alternatively, the polarization rotator may be one of a Faraday rotator, a prism rotator and a birefringent rotator, in particular a quarter-wave plate or a halfwave plate. The person skilled in the art may thus advantageously choose a rotator best suited for the respective use case.

[0032] Additionally or alternatively, the light steering device may be a phase light modulator, in particular a microelectromechanical device. This type of light steering device has turned out to be particularly useful when the respective light steering system shall be used for high quality projectors, in particular high dynamic range hybrid projectors for cinemas and the like. If the light steering device is a phase light modulator comprising a plurality of pixels and having a pixel pitch, i.e. a center-to-center distance between adjacent pixel (which may be micromirrors), the minimum optical path length dmin between the phase light modulator and the image plane across the polarizing beam splitter and along either one of the paths of the transmitted beam and the reflected beam may advantageously be set to dmin = img_size I tan(sin’1( / pp), wherein img_size is the greatest dimension of the illumination fields to be formed in the image plane, is the wavelength of the incident light beam, and pp is the pixel pitch.

[0033] Additionally or alternatively, the light steering system may comprise further optical elements arranged in or after the image plane, for example elements to magnify the illumination fields formed in the image plane and optionally to also restore telecentricity by imaging the light steering device at infinity. In other words, with such optical elements a relay optic can be formed that re-images a first intermediate image onto a second intermediate image for example to have the desired size to be combined with the baselight. The further optical elements may also comprise one or more diffusers for despeckling and laser safety purposes (if, as will be in most cases done, the light sources are lasers). One can for example use a single diffuser in the plane of the second intermediate image, or a combination of two diffusers, one in or close to the plane of the first intermediate image and one in the plane of the second intermediate image. Using at least two diffusers adds to laser safety in case one of the diffusers breaks.

[0034] Additionally or alternatively, the light steering system may comprise three separate arrangements of a light steering device, a polarizing beam splitter and one or more mirrors arranged for steering light beams, each of said separate arrangements adapted for directing light of one of three different colors towards the image plane. In such embodiment, the light steering system may further comprise at least one light combining element arranged for combining and directing light beams of different colors onto the image plane. Such at least one light combining element may be a dichroic prism, a dichroic mirror, or a combination of dichroic mirrors. In an alternative preferred embodiment, the light steering system comprises one polarizing beam splitter and three separate light steering devices arranged with two dichroic mirrors to direct light of three different colors along at least partially overlapping light paths onto the polarizing beam splitter. In yet another alternative preferred embodiment the light steering system comprises one light steering device, one polarizing beam splitter and an optical path length compensation arrangement of one or more mirrors and dichroic mirrors arranged between the light steering device and the polarizing beam splitter to allow simultaneously steering light of at least two different wavelengths. Each of these embodiments allows using highly efficient laser light sources of different colors to produce illuminations fields of steered polarized light as desired.

[0035] A hybrid projector according to the invention comprises in one embodiment a baselight engine and a highlight engine, the baselight engine arranged for producing a first illumination field in an illumination plane, the highlight engine arranged for producing a second illumination field overlapping the first illumination field in the illumination plane, wherein said highlight engine comprises at least one light steering system as described above. Such hybrid projector allows to produce very realistic images with high dynamic range.

[0036] In a preferred embodiment, the at least one light steering system of the hybrid projector is arranged such that the image plane is in said illumination plane. This allows a very compact design of the projector with only a few optical parts. However, in most cases the image plane will be arranged upstream of said illumination plane.

[0037] Additionally or alternatively, the hybrid projector may comprise three separate arrangements of a baselight engine and a highlight engine, each arrangement arranged for producing overlapping first and second illumination fields of one three different colors, and further comprises a light combining element arranged for combining the first and second illumination fields of said three separate arrangements.

[0038] A method for producing an illumination field of steered polarized light according to one embodiment comprises the steps of directing a light beam onto a light steering device, modulating the light beam with the light steering device to obtain a light beam of steered light and directing the light onto a polarizing beam splitter, splitting the light beam with the polarizing beam splitter into a transmitted beam having a first polarization and a reflected beam having a second polarization different from said first polarization, rotating the polarization of one of the reflected beam and the transmitted beam to correspond to the polarization of the respective other beam, reflecting one of the transmitted beam and the reflected beam or both beams such that a) one of the beams is reflected zero times and the other beam is reflected an uneven number of times or b) one of the beams is reflected an even number of times and the other beam is reflected an uneven number of times, and directing the beams such that both beams meet in an image plane.

[0039] In a preferred embodiment, modulating the light beam comprises using separate phase modulators for different colors, each modulator arranged to modulate both orthogonal polarization states indiscriminately for its respective color. This approach in the method allows for precise control over each color channel while maintaining the efficiency of handling both polarization states simultaneously. By modulating each color separately, the method can adapt to the specific requirements of different wavelengths, such as varying steering distances or phase modulation patterns. This can lead to improved color fidelity and more accurate light steering across the entire visible spectrum. Furthermore, this method maintains the advantage of efficient polarization handling for each color, potentially reducing light loss and improving overall system efficiency. The ability to independently optimize the modulation for each color while still handling both polarization states can result in a more flexible and adaptable light steering process, suitable for a wide range of high-performance projection and illumination applications.

[0040] Additionally or alternatively, the reflected beam and the transmitted beam may each form an illumination field on the image plane, the illumination fields overlapping each other and being substantially identically in size and light distribution. In yet another preferred embodiment, the transmitted beam and the reflected beam converge towards the image plane forming an angle with each other not exceeding 20°, preferably less than 15°, and more preferably less than 10°.

[0041] Additionally or alternatively, the reflected beam and the transmitted beam may each be directed from different directions onto the image plane under a non-zero illumination angle, said illumination angles being substantially identical. Said different directions are preferably in the same plane with a normal of the image plane.

[0042] Additionally or alternatively, the reflected beam and transmitted beam may be directed to the image plane such that the length of their optical paths to the center point of the beam spot in the image plane is substantially the same.

[0043] Additionally or alternatively, modulating the light beam may comprise modulating the phase of light rays forming said light beam, in particular by using a microelectromechanical device.

[0044] Additionally or alternatively, the beams may be directed through optical elements arranged in or after the image plane, such as in particular elements to magnify the illumination fields formed in the image plane and optionally to also restore telecentricity by imaging the light steering device at infinity and / or one or more diffusers for despeckling and laser safety purposes.

[0045] Additionally or alternatively, the method may comprise directing light of three different colors towards the image plane via three separate arrangements of a light steering device, a polarizing beam splitter and one or more mirrors arranged for steering the light beams, each of said separate arrangements adapted for of one of three different colors. The light beams of the different colors may be combined via at least one combining element. Alternatively, light of three different colors is directed via three separate light steering devices, one for each of the three colors, and at least two dichroic mirrors along at least partially overlapping light paths onto the polarizing beam splitter. Alternatively, light of three different wavelengths is simultaneously directed via one light steering device, one polarizing beam splitter and an optical path length compensation arrangement of one or more mirrors and dichroic mirrors arranged between the light steering device and the polarizing beam splitter towards said image plane. Alternatively, light of three different wavelengths is directed via one light steering device and one polarizing beam splitter towards said image plane in a time sequential manner.

[0046] According to one embodiment, a method for producing images comprises producing a first illumination field in an illumination plane, producing a second illumination field overlapping the first illumination field in the illumination plane, wherein one of said illumination fields is a baselight illumination field and the other is an illumination field of steered polarized light produced with a method as described above. With such method, very realistic images having a high dynamic range can be produced.

[0047] In a preferred embodiment, the baselight illumination field is temporarily modulated to generate a uniform illumination field with dynamically changing intensity level, for instance depending on the image content. If an image does not require a lot of medium brightness areas, the highlight illumination can be fully used to create the highlights, so that the baseline illumination can be reduced causing the black zones in the image to become darker and the general contrast in the image to increase.

[0048] Further details and advantages of the invention will become apparent from the following purely exemplary and non-limiting detailed description in conjunction with the drawings.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Fig. 1 is a schematic diagram for explaining the fundamental principle of light steering.

[0051] Fig. 2 is a schematic diagram showing some of the main components of a hybrid projector including a light steering system.

[0052] Fig. 3 is a schematic perspective diagram showing the propagation of a light beam in a light steering system according to a first embodiment. Fig. 4 is a schematic diagram showing the optical path of a single light ray in a light steering system according to Fig. 3.

[0053] Fig. 5 is a schematic diagram showing the optical path of light rays in a light steering system according to a second embodiment.

[0054] Fig. 6 is a schematic diagram showing the optical path of light rays in a light steering system according to a third embodiment.

[0055] Fig. 7 is a schematic diagram showing the optical path of light rays in a light steering system according to a fourth embodiment.

[0056] DETAILED DESCRIPTION

[0057] An "imager" is any device that is operable to impart a desired image (an image may be any pattern) to a beam of light. A spatial light modulator (SLM) may be used as an imager. For example, in a cinema projector an imager may be used to modulate light incident from one or more light sources according to image data to project images according to the image data onto a screen.

[0058] An "engine" denotes an apparatus for outputting light. An imaging engine comprises at least one imager and has at least one entry for light such as the combined light of a baselight engine and a highlight engine.

[0059] A "light steering device" is a device for creating a desired even or uneven light field at a certain distance by locally manipulating the main propagation direction of light at it is input.

[0060] A "spatial light modulator" or "SLM" is a device that operates to apply different alterations to a property of light at different locations. Typically, a SLM comprises an array of controllable elements or "pixels" that are individually operable to alter a property of light at a corresponding pixel location. Properties of light that may be altered by a SLM include amplitude (light intensity), polarization and phase. A SLM may modulate light that is transmitted through the SLM (e.g. light is incident on one face of the SLM and modulated light is emitted from another opposing face of the SLM).

[0061] A "spatial amplitude modulator" or "SAM" means a type of SLM that is operable to controllably alter amplitude of light when it reaches the screen. Non-limiting examples of SAMs are liquid crystal panels (also called LCDs), liquid crystal on silicon (LCoS) devices and digital mirror devices ("DMDs"). A DMD has two operational states: the "ON" state, in which light is sent to the projection lens and the screen, and the "OFF" state, in which light is sent to a light dump. The amplitude modulation happens by temporal modulation and rapid switching between the ON and OFF state.

[0062] A "phase light modulator" or "PLM" (also known as "spatial phase modulator" or "SPM") is a type of SLM that is operable to controllably alter the phase of light. Nonlimiting examples of PLMs are LCoS devices and the already mentioned MEMS devices.

[0063] A spatial amplitude modulator is typically made of an array of pixels that traditionally reflect or transmit an incoming light beam whilst modulating, for each pixel independently, its amplitude. A phase light modulator has a very similar structure, but instead of modulating the amplitude of the beam it adds some phase value at each pixel. As such, a phase light modulator can be considered as a 2D pixelated programmable diffraction grating able to produce, at some distance, some non- uniform illumination pattern. The light can be distributed within the desired pattern, as an example for instance resulting in a localized highlight within the illumination field. PLM devices are usually of the reflective type, although some transmissive configurations have been reported in the literature.

[0064] An SLM may modulate light that is reflected from one face of the SLM (e.g. light is incident on one face of the SLM and modulated light is emitted from the same face of the SLM).

[0065] Some SLMs operate only to modulate light amplitude. Some SLMs operate to modulate light phase. Some SLMs operate to modulate both light amplitude and light phase. Operation of some SLMs may be dynamically controlled in real time to modulate light amplitude only, modulate light phase only or modulate both light phase and light amplitude.

[0066] The "f-number" is a dimensionless number that can be used to characterize an optical system, f-number is a ratio of a focal length of the optical system to a diameter of an entrance pupil of the optical system.

[0067] The term "highlight" in reference to a projected light field (which may include an image) denotes a bright spot or area. Highlights may include the brightest points in a light field.

[0068] A "highlight beam" as used herein includes a beam of light that has the capability to produce a non-uniform light field which includes one or more highlights at a target area. The target area may for example be a screen or image plane onto which the highlight beam is incident. The target of the highlight beam can of course also be an imager (such as a SAM) that is then illuminated by this highlight beam and provides a full and highly detailed image that is projected on a screen. The highlight beam may include areas having higher illumination intensities and areas having lower illumination intensities. A highlight beam may for example result from light steering. The highlight beam can also be dynamic: the location and intensity of the highlights may change continuously together with a dynamic image, (like in a movie for a movie projector).

[0069] The term "modulate" means to vary a property of something. Light can be modulated temporally and / or spatially. Example properties of light that may be modulated include amplitude (brightness or intensity), phase and polarization state. Spatial modulation of light can be achieved by selectively modulating light at spatial locations (e.g. pixels) and / or by steering light. Light steering involves steering light that would otherwise illuminate some spatial locations to other spatial locations. Light steering may be achieved dynamically, for example, using variable lenses, variable mirrors and / or phase modulators (e.g. PLMs). A phase pattern applied by a PLM may direct incident light to selected regions in an image plane. Interference between different parts of the directed light may result in some locations in the image plane having more light (i.e. constructive interference) and / or some locations in the image plane having less light (i.e. destructive interference). As a result of such interference, the phase pattern applied by the PLM may effectively steer or direct incident light away from certain regions in the image plane and / or steer or direct the incident light so that light is concentrated in certain regions in the image plane.

[0070] The "numerical aperture" or "NA" for an optical system is a dimensionless number that provides a measure of the range of angles of incoming light that can pass through the optical system. NA is given by the product of the index of refraction of the medium through which incoming light arrives at the optical system and the sine of the maximum angle (also called half-angle) of light rays that will pass through the optical system relative to an optical axis of the optical system.

[0071] The "acceptance angle" for an optical system is a solid angle for which light rays entering the optical system with directions lying within in the solid angle will pass through the optical system. Solid angle may be measured in steradians.

[0072] The "etendue" is a number that characterizes how "spread out" light is in area and angle. From the point of view of an optical system, the etendue may be defined as the area of an entrance pupil of the optical system times the acceptance angle (as defined herein) of the optical system.

[0073] In the drawings, similar or identical elements of different embodiments are provided with the same reference numbers, and a repetition of the description of such elements has been avoided as far as possible. In order to avoid overloading the drawings, not all elements are provided with reference numbers whenever it is obvious, which element is shown. Also, a person skilled in the art understands that in addition to the elements shown in the drawings further elements may be used for example in the optical paths of reflected and / or transmitted beams of Figs. 3 - 7, such as e.g. a glass plate for compensating a focus shift of the transmitted beam.

[0074] The term "light steering" denotes the operation of guiding light towards specific areas and this is realized with a light steering device such as e.g. a phase light modulator. Fig. 1 shows the general principle of light steering using an PLM 10 having a phase grating. In Fig. 1A, the phase grating on PLM 10 is "turned off" in a sense that all pixels are set in a mode that they add the same phase modulation to the incoming light. It thus forms a "constant phase grating" over the whole pixel array of the PLM 10 and the PLM is in a so-called "mirror mode".

[0075] In Fig. 1B, the phase grating on PLM 10 is "turned on" and controlled such that its single controllable elements produce a desired pattern schematically indicated in Fig. 1 B by concentric ellipses. An incident light beam 12 is now modulated by PLM 10, and the reflected light beam is a steered light beam 14.

[0076] Controlling light steering devices like PLM 10 as such is well known in the art and done automatically based on data of the desired image respectively the desired light distribution using corresponding computational hardware. A person skilled in the art hence understands that devices and systems including projectors as disclosed herein always comprise such hardware respectively are in use connected to such hardware including respective electric power sources although such elements are not shown in the drawings.

[0077] Fig. 2 is a schematic diagram showing some of the main components of a hybrid projector 20, which in this embodiment comprises an imaging engine 22 with three DMDs 24 for modulating light of three different colors and inputting this light into a projection part 26 comprising at least a lens for creating and projecting an image for example onto a cinema screen. In the schematic diagram, some light beams are represented by the gray beams.

[0078] In this embodiment, the imaging engine 22 comprises a total internal reflection prism 28, TIR prism for short, and a trichroic prism 30, also known as "Philips prism", for distributing light of three different colors onto the respective DMDs 24.

[0079] Hybrid projector 20 further comprises a baselight engine 32 and a highlight engine 34, each producing light that is combined in unit 36 comprising a polarized beam combiner 38 and some relay optics 40.

[0080] In use, baselight engine 32 produces via some integration optics 42 a typically rectangular baselight illumination field of polarized light, schematically indicated by 44, using light from one or, typically three light source(s) 46 such as e.g. lasers of three different colors. Using the same or a separate light source(s) 48, highlight engine 34 produces a typically also rectangular highlight illumination field, schematically indicated by 50, of steered and polarized light, which illumination field can be regarded as a second intermediate image as explained above.

[0081] The polarization state of the light from the highlight engine 34 is orthogonal to that coming from the baselight engine 32 so that the light from both engines can be combined using the polarized beam combiner 38. To do this, the light from light source 48 is steered via light steering engine 52 comprising in particular a light steering system according to the invention to produce a first illumination field, schematically indicated by 54, of steered and polarized light, which illumination field can be regarded as a first intermediate image, which is then processed by some relay optics 56 to produce illumination field 50. By modulating the light source 48, i.e. red, green and blue lasers forming "the" light source, the homogenized light beam fluctuate over time depending on how much baseline light is required for the final content.

[0082] Illumination fields 44 and 50 are combined in unit 36 and inputted into the TIR prism 28, where the incoming light is reflected into the trichroic prism 30. In the shown embodiment, trichroic prism 30 is set up to distribute red, green and blue light onto respective DM Ds 24, where it is modulated and reflected back into the trichroic prism 30, from which it passes through TIR prism 28 into the projection part 26. In some embodiments, no relay optics 56 are used and instead illumination field 54 is combined with illumination field 44. In the shown embodiment, light sources 46 and 48 may each comprise separate lasers for outputting green, red and blue light that are used in a time sequential manner. However, in other embodiments a hybrid projector may comprising three separate arrangements of a baselight engine and a highlight engine, each arrangement arranged for producing overlapping first and second illumination fields of one of three different colors, which arrangements can be used simultaneously.

[0083] Fig. 3 is a schematic perspective diagram showing the propagation of an unpolarized light beam 58 in a light steering system 60 according to a first embodiment. Fig. 4 is a schematic diagram showing the optical path of a single light ray in a light steering system according to Fig. 3. Similar to Fig. 4, Figs. 5, 6, and 7 are schematic diagrams showing the optical path of light rays in light steering systems according to a second, a third embodiment and a fourth embodiment.

[0084] The light steering system of Figs. 3 and 4 comprises a light steering device 62, a polarizing beam splitter 64, a polarization rotator 66, and mirrors 68, 70 and 72.

[0085] The light steering device 62 is arranged for modulating and directing an incident light beam 58 onto the polarizing beam splitter 64, which splits the light beam 58 into a transmitted beam 58t having a first polarization, e.g. a p-polarization, and a reflected beam 58r having a second polarization different from said first polarization, e.g. an s-polarization.

[0086] The polarization rotator 66 is arranged for rotating the polarization of one of the reflected beam and the transmitted beam to correspond to the polarization of the respective other beam. In the shown embodiment, the polarization rotator 66 is arranged in the path of the transmitted beam 58t. If beam 58t is p-polarized before entering the polarization rotator 66, it will become s-polarized after polarization rotator 66. Thus, both beams 58r and 58t end up having the same polarization and can thus easily be combined with other light e.g. via a polarized beam combiner like the one shown at 38 in Fig. 2. In the shown embodiment, the polarization rotator 66 is a half-wave plate, but other polarization rotators may of course be used such as e.g. a Faraday rotator, a prism rotator, or a quarter-wave plate.

[0087] In the shown embodiment, two mirrors 68 and 70 are arranged in the path of the transmitted beam 58t, and one mirror is arranged in the path of the reflected beam 58r. As the reflected beam 58r is reflected once by polarizing beam splitter 64 and once by mirror 72, the total number of reflections the reflected beam 58r including the one at beam splitter undergoes is even, like the number of reflections the transmitted beam 58t undergoes, and the images represented by both beams are not mirrored with respect to each other.

[0088] The polarizing beam splitter 64 and the mirrors 68, 70 and 72 are arranged such that the reflected beam 58r and the transmitted beam 58t converge under an angle a (Fig. 4) and meet in an image plane 74. Each beam 58r and 58t forms an illumination field on the image plane 74, which illumination fields overlap each other and are substantially identically in size and light distribution, creating a first illumination field, like the one indicated by 54 in Fig. 2, of steered and polarized light, which illumination field can be regarded as a first intermediate image. Note that the quadrangle in the perspective drawing (Fig. 3) and the line in the two-dimensional drawing (Fig. 4) indicating the image plane 74 are virtual and not indicating real elements, although elements such as a diffusor may be positioned there. Polarizing beam splitter 64, polarization rotator 66 and the mirrors 68, 70 and 72 form a polarization recuperation unit (PRU for short) 76 that apart from the light steering system 60 shown in Figs. 3 and 4 can be employed in many different light steering systems and configurations like the ones shown in Figs. 5, 6 and 7.

[0089] As best shown in Fig. 4, the reflected beam 58r and the transmitted beam 58t are each directed from different directions onto the image plane 74 under a non-zero illumination angle of approximately a / 2, said illumination angles being substantially identical and in the same plane with a normal of the image plane 74. The polarizing beam splitter 64 and the mirrors 68, 70 and 72 are arranged such that the angle a, under which the transmitted beam 58t and the reflected beam 58r converge towards the image plane 74, does not exceed 20° and is preferably less than 15°, and more preferably less than 10°. Furthermore, the polarizing beam splitter 64 and the mirrors 68, 70 and 72 are arranged such that the optical path lengths of the reflected beam 58r to the center point of the beam spot in the image plane 74 and of the transmitted beam 58t to the center point of the beam spot in the image plane 74 are substantially the same. This will be explained in more detail below. To achieve this, the optical path of the reflected beam 58r may comprise optical elements, in particular at least one glass plate (not shown).

[0090] As previously stated, the optical path lengths, OPLs in following, of the reflected beam 58r and the transmitted beam 58t are substantially equal. Generally, some conditions in this respect should be met. If:

[0091] L1 denotes the OPL from the light steering device 62 to the polarizing beam splitter 64, L2 denotes the OPL of the reflected beam 58r from the polarizing beam splitter 64 to the mirror 72,

[0092] L3 denotes the OPL of the reflected beam 58r from the mirror 72 to the first intermediate image plane 74,

[0093] L4 denotes the OPL of the transmitted beam 58t from the polarizing beam splitter 64 to the mirror 68,

[0094] L5 denotes the OPL of the transmitted beam 58t from the mirror 68 to the mirror 70,

[0095] L6 denotes the OPL of the transmitted beam 58t from the mirror 70 to the first intermediate image plane 74,

[0096] L7 denotes the OPL of a focus shift of the transmitted beam 58t introduced by the polarizing beam splitter 64 in the transmitted beam 58t, and

[0097] L8 denotes the OPL of a focus shift of the transmitted beam 58t introduced by the polarization rotator 66, then

[0098] L1 + L2 + L3 = SD, where SD represents the steering distance and L1 + L4 + L5 + L6 = SD + L7 + L8. Small asymmetries between the paths of the transmitted beam 58t and the reflected beam 58r compensated by one or more glass plate(s) into the path of the reflected beam. The exact values of L4 and L5 may be easily determined by using known optical optimization algorithms.

[0099] OPLs L3 and L6 should be long enough for the two beams 58r and 58t to separate completely.

[0100] When the light steering device 62 is a PLM, the steering distance SD should not be shorter than the minimum distance needed to fully separate the different diffraction orders of steered light generated by the periodic structure of the PLM at the location of image plane 74. However, it is technically possible to choose a distance which shorter than this minimum distance but in that case orders other than the "main" diffraction order having substantial light intensity, will still land in the target area (because they are not separated far enough yet over that short distance) and thus create "ghost" highlights at non-desired locations in the (active) image area.

[0101] The smaller the separation angle a, the longer the optical path lengths L3 and L6 will need to be. The separation angle a is preferably kept as small as possible. Since the beams 58r and 58t each reach the first intermediate image plane 74 at an angle, substantially equal to a / 2, the images are tilted accordingly and may hence be slightly out of focus and may also be slightly distorted (they will be slightly trapezoidal). As these image imperfections are opposite for one image compared to the other, a perfect match of both images is not possible, but will be better if a is kept small.

[0102] OPL L1 should be large enough to avoid interference between polarizing beam splitter 64 and the incoming beam, i.e. the unpolarized light beam from the light steering device 62. As a person skilled in the art understands, other configurations are possible with for example the provision of additional folding mirrors in each optical path.

[0103] The light steering system 60 can be used in a hybrid projector, for example a hybrid projector according to Fig. 2, for performing light steering in a time sequential manner in particular with red, blue and green light.

[0104] Fig. 5 shows a light steering system 80 comprising three PRUs 76, 76', 76" that can be used for simultaneously steering light of three different colors, typically a beam 58 of red light, a beam 58' of green light and a beam 58" of blue light, towards the same intermediate image plane 74. To do this, for each incident light beam 58, 58’, 58" of a different color a separate light steering device 62, 62’, 62" is used, and two dichroic mirrors 82 and 84 are employed to align the respective light paths of the polarized steered reflected and transmitted light beams towards image plane 74.

[0105] The steering distance of the different colored light beams 58, 58’ and 58" are determined according to their respective wavelengths. Typically, red, blue and green light is used, and the steering distance for blue is the longest and the steering distance for red is the shortest.

[0106] Fig. 6 shows an embodiment of a light steering system 90, in which one PRU 76 is used together with three separate light steering devices 62, 62’ and 62" arranged with one mirror 92 and two dichroic mirrors 94 and 96 for steering light beams 58, 58’ and 58" of three different colors along the same path in the PRU 76 for arriving at the image plane 74. Typically, light beam 58 will be red light, light beam 58’ will be green light and light beam 58" will be blue light. Again, the steering distances increase from red over green to blue light. Mirror 92 is a standard mirror, while mirrors 94 and 96 are dichroic mirrors reflecting green light and transmitting red light (mirror 94) respectively reflecting blue light and transmitting red and green light (mirror 96).

[0107] Fig. 7 shows an embodiment of a light steering system 100 comprising one PRU 76 only one light steering device 62 and a light path compensation arrangement of four dichroic mirrors 102, 104, 106 and 108 and two standard mirrors 110 and 112. This arrangement allows for a very compact light steering system. Again, the steering path lengths increase proportionally inverse to the wavelengths of the respective incident light on the light steering device 62. If, as usual, red, green and blue light is used for creating an image, mirrors 102 and 106 will reflect green and blue light, but let red light pass. Mirrors 104 and 108 will reflect green light and let blue light pass, and mirrors 110 and 112 are standard mirrors.

[0108] To configure an optical assembly positioned in a beam path of at least one unpolarized light beam for providing a substantially polarized light beam to an intermediate image plane through light steering, the unpolarized light beam deflected into a first polarized light beam and a second polarized light beam, the optical assembly including a light steering device, a polarizing beam splitter, a polarization rotator, and a plurality of mirrors, a method can be used, which comprises: determining a number of the plurality of mirrors used for reflecting the first polarized light beam and the second polarized light beam according to a number of reflections for the first polarized light beam and the second polarized light beam; determining optical path lengths of the a light steering device, the polarizing beam splitter, the polarization rotator, and the plurality of mirrors; calculating placement angles of the a light steering device, the polarizing beam splitter, the polarization rotator, and the plurality of mirrors; and optimizing, using an optical optimization algorithm, the location and the angle of the plurality of mirrors in the optical path of the second polarization light beam. Such method may take into the thickness of the polarization dependent deflection element and the polarization rotator. The light steering systems described above facilitate a method for producing an illumination field of steered polarized light, comprising the steps of directing a light beam onto a light steering device, modulating the light beam with the light steering device to obtain a light beam of steered light and directing the light beam onto a polarizing beam splitter, splitting the light beam with the polarizing beam splitter into a transmitted beam having a first polarization and a reflected beam having a second polarization different from said first polarization, rotating the polarization of one of the reflected beam and the transmitted beam to correspond to the polarization of the respective other beam, reflecting one of the transmitted beam and the reflected beam or both beams such that either a) one of the beams is reflected zero times and the other beam is reflected an uneven number of times or b) one of the beams is reflected an even number of times and the other beam is reflected an uneven number of times, and directing the beams such that both beams meet in an image plane. This method in turn facilitates producing images and comprises producing a first illumination field in an illumination plane, and producing a second illumination field overlapping the first illumination field in the illumination plane, wherein one of said illumination fields is a baselight illumination field and the other is an illumination field of steered polarized light produced with the method.

[0109] Within the scope of the invention as defined in the claims, many alterations to the above described examples can be made, for example relating to the number and arrangements of additional optical elements in the light steering system, such as elements for compensating any focus shift a beam transmitted through an element like a polarizing beam splitter or a polarization rotator may experience.

[0110] LIST OF REFERENCE NUMBERS

[0111] 10 Spatial Light Modulator (SLM)

[0112] 12 incident light beam

[0113] 14 steered light beam

[0114] 20 hybrid projector

[0115] 22 imaging engine

[0116] 24 digital mirror device (DMD)

[0117] 26 projection part

[0118] 28 total internal reflection (TIR) 30 trichroic prism

[0119] 32 baselight engine

[0120] 34 highlight engine

[0121] 36 unit combining baselight and highlight

[0122] 38 polarized beam combiner

[0123] 40 relay optics

[0124] 42 integration optics

[0125] 44 baselight illumination field

[0126] 46 light source

[0127] 48 light source

[0128] 50 highlight illumination field

[0129] 52 light steering system

[0130] 54 first illumination field

[0131] 56 relay optics , 58’, 58" light beam

[0132] 58r reflected beam

[0133] 58t transmitted beam

[0134] 60 light steering system , 62’, 62" light steering device

[0135] 64 polarizing beam splitter

[0136] 66 polarization rotator

[0137] 68 mirror

[0138] 70 mirror

[0139] 72 mirror , 76', 76" polarization recuperation unit (PRU)

[0140] 74 image plane

[0141] 80 light steering system

[0142] 82 dichroic mirror

[0143] 84 dichroic mirror

[0144] 90 light steering system

[0145] 92 mirror

[0146] 94 dichroic mirrors

[0147] 96 dichroic mirrors

[0148] 100 light steering system

[0149] 102 dichroic mirror dichroic mirror dichroic mirror dichroic mirror mirror mirror

Claims

CLAIMS1. Light steering system comprising a number of optical elements, namely at least a light steering device, a polarizing beam splitter, a polarization rotator, and one or more mirrors, the light steering device arranged for modulating and directing an incident light beam containing light in two orthogonal polarization states onto the polarizing beam splitter, the polarizing beam splitter, receiving the modulated and directed light from the light steering device, arranged for splitting the light beam into a transmitted beam having a first polarization and a reflected beam having a second polarization different from said first polarization, the polarization rotator arranged for rotating the polarization of one of the reflected beam and the transmitted beam to correspond to the polarization of the respective other beam, the one or more mirrors arranged for reflecting and directing one of the transmitted beam and the reflected beam or both beams such that a) one of the beams is reflected zero times and the other beam is reflected an uneven number of times or b) one of the beams is reflected an even number of times and the other beam is reflected an uneven number of times, and such that both beams converge and meet in an image plane.

2. The light steering system according to claim 1, wherein the light steering device comprises separate phase modulators for different colors, each modulator arranged to modulate both orthogonal polarization states indiscriminately for its respective color.

3. The light steering system according to claim 1 or 2, wherein the light steering device is a single light steering device that modulates both orthogonal polarization states indiscriminately.

4. The light steering system according to one of claims 1 to 3, wherein the polarizing beam splitter and the one or more mirrors are arranged such that the reflected beam and the transmitted beam each form an illumination field on the image plane, the illumination fields overlapping each other and being substantially identically in size and light distribution.

5. The light steering system according to one of claims 1 to 4, wherein the polarizing beam splitter and the one or more mirrors are arranged such that the transmitted beam and the reflected beam converge towards the image plane forming an angle with each other not exceeding 20°, preferably less than 15°, and more preferably less than 10°.

6. The light steering system according to one of claims 1 to 5, wherein the polarizing beam splitter and the one or more mirrors are arranged such that the transmitted beam and the reflected beam are each directed from different directions onto the image plane under a non-zero illumination angle, said illumination angles being substantially identical, said different directions preferably being in the same plane with a normal of the image plane.

7. The light steering system according to one of claims 1 to 6, wherein the polarizing beam splitter and the one or more mirrors are arranged such that the optical path lengths of the reflected beam to the center point of the beam spot in the image plane and of the transmitted beam to the center point of the beam spot in the image plane are substantially the same.

8. The light steering system according to claim 7, wherein the optical path of the reflected beam comprises optical elements, in particular at least one glass plate, for compensating a focus shift of the transmitted beam.

9. The light steering system according to one of claims 1 to 8, wherein the polarization rotator is a Faraday rotator, a prism rotator or a birefringent rotator, in particular a quarter-wave plate or a half-wave plate.

10. The light steering system according to one of claims 1 to 9, wherein the light steering device is a phase light moderator, in particular a microelectromechanical device.11 . The light steering system according to claim 10, said phase light modulator comprising a plurality of pixels and having pixel pitch, wherein the minimum optical path length dmin between the phase light modulator and the image plane across the polarizing beam splitter and along either one of the paths of the transmitted beam and the reflected beam is dmin = img_size I tan(sin'1( / pp), wherein img_size is the greatest dimension of the illumination fields to be formed in the image plane, is the wavelength of the incident light beam, and pp is the pixel pitch.

12. The light steering system according to one of claims 1 to 11 , further comprising optical elements arranged in or after the image plane, such as in particular optical elements to magnify the illumination fields formed in the image plane and / or to restore telecentricity and / or one or more diffusers for despeckling and laser safety purposes.

13. The light steering system according to one of claims 1 to 12, comprising three separate arrangements of a light steering device, a polarizing beam splitter and one or more mirrors arranged for steering light beams, each of said separate arrangements adapted for directing light of one of three different colors towards the image plane.

14. The light steering system according to claim 13, further comprising at least one light combining element arranged for combining and directing light beams of different colors onto the image plane.

15. The light steering system device according to claim 14, wherein the at least one light combining element is a dichroic prism, a dichroic mirror, or a combination of dichroic mirrors.

16. The light steering system according to one of claims 1 to 12, comprising one polarizing beam splitter and three separate light steering devices arranged with two dichroic mirrors to direct light of three different colors along at least partially overlapping light paths onto the polarizing beam splitter.

17. The light steering system according to one of claims 1 to 12, comprising one light steering device, one polarizing beam splitter and an optical path length compensation arrangement of one or more mirrors and dichroic mirrors arranged between the light steering device and the polarizing beam splitter to allow simultaneously steering light of at least two different wavelengths.

18. A hybrid projector comprising a baselight engine and a highlight engine, the baselight engine arranged for producing a first illumination field in an illumination plane, the highlight engine arranged for producing a second illumination field overlapping the first illumination field in the illumination plane, wherein said highlight engine comprises at least one light steering system according to claim 1.

19. The hybrid projector according to claim 18, wherein the at least one light steering system is arranged such that the image plane is in said illumination plane.

20. The hybrid projector according to claim 18, wherein the at least one light steering system is arranged such that the image plane is, seen in along the light path, before said illumination plane.

21. The hybrid projector according to claim 18, wherein the at least one light steering system is further configured according to one of claims 2 to 17.

22. The hybrid projector according to one of claims 18 to 21 , comprising three separate arrangements of a baselight engine and a highlight engine, each arrangement arranged for producing overlapping first and second illumination fields of one three different colors, further comprising a light combining element arranged for combining the first and second illumination fields of said three separate arrangements.

23. A method for producing an illumination field of steered polarized light, comprising the steps of directing a light beam containing light in two orthogonal polarization states onto a light steering device, modulating the light beam with the light steering device to obtain a light beam of steered light and directing the light onto a polarizing beam splitter, receiving the modulated and directed light from the light steering device at the polarizing beam splitter, splitting the light beam with the polarizing beam splitter into a transmitted beam having a first polarization and a reflected beam having a second polarization different from said first polarization, rotating the polarization of one of the reflected beam and the transmitted beam to correspond to the polarization of the respective other beam, reflecting one of the transmitted beam and the reflected beam or both beams such that a) one of the beams is reflected zero times and the other beam is reflected an uneven number of times or b) one of the beams is reflected an even number of times and the other beam is reflected an uneven number of times, and directing the beams such that both beams meet in an image plane.

24. The method according to claim 23, wherein modulating the light beam comprises using separate phase modulators for different colors, each modulator arranged to modulate both orthogonal polarization states indiscriminately for its respective color.

25. The method according to claim 23 or 24, wherein the light steering device is a single light steering device that modulates both orthogonal polarization states indiscriminately.

26. The method according to one of claims 23 to 25, wherein the reflected beam and the transmitted beam each form an illumination field on the image plane, the illumination fields overlapping each other and being substantially identically in size and light distribution.

27. The method according to one of claims 23 to 26, wherein the reflected beam and the transmitted beam converge towards the image plane forming an angle with each other not exceeding 20°, preferably less than 15°, and more preferably less than 10°.

28. The method according to one of claims 23 to 27, wherein the reflected beam and the transmitted beam are each directed from different directions onto the image plane under a non-zero illumination angle, said illumination angles being substantially identical, said different directions preferably being in the same plane with a normal of the image plane.

29. The method according to one of claims 23 to 28, wherein the reflected beam and transmitted beam are directed to the image plane such that the optical path lengths of their light paths to the center point of the beam spot in the image plane are substantially the same.

30. The method according to one of claims 23 to 29, wherein modulating the light beam comprises modulating the phase of light rays forming said light beam, in particular by using a microelectromechanical device.

31. The method according to one of claims 23 to 30, further comprising directing the beams through optical elements arranged in or after the image plane, such as in particular optical elements to magnify the illumination fields formed in the image plane and / or to restore telecentricity, and / or one or more diffusers for despeckling and laser safety purposes.

32. The method according to one of claims 23 to 31 , comprising directing light of three different colors towards the image plane via three separate arrangements of a light steering device, a polarizing beam splitter and one or more mirrors arranged for steering the light beams, each of said separate arrangements adapted for of one of three different colors.

33. The method according to claim 32, further comprising combining the light beams of the different colors via at least one combining element.

34. The method according to one of claims 23 to 33, comprising directing light of three different colors via three separate light steering devices, one for each of the three colors, and at least two dichroic mirrors along at least partially overlapping light paths onto the polarizing beam splitter.

35. The method according to one of claims 23 to 34, comprising simultaneously directing light of at least two different wavelengths via one light steering device, one polarizing beam splitter and an optical path length compensation arrangement of one or more mirrors and dichroic mirrors arranged between the light steering device and the polarizing beam splitter towards said image plane.

36. The method according to one of claims 23 to 34, comprising directing light of three different wavelengths via one light steering device and one polarizing beam splitter towards said image plane in a time sequential manner.

37. A method for producing images, comprising producing a first illumination field in an illumination plane, producing a second illumination field overlapping the first illumination field in the illumination plane, wherein one of said illumination fields is a baselight illumination field and the other is an illumination field of steered polarized light produced with a method according to one of claim 23 to 36.

38. The method according to claim 37, further comprising temporarily modulating the baselight illumination field to generate a uniform illumination field.

Images