Patent Description:
It is known to project an image by illuminating a spatial light modulator, such as a liquid crystal display (LCD), liquid crystal on silicon (LCOS) modulator or a digital micromirror device of a digital light processing (DLP) system, and collimating the modulated image for output to an eye of a user. Such projectors are often used in near eye displays, where the projected image is typically introduced into a light guide along which the image propagates by internal reflection until being coupled out to the eye of the user, typically by partially-reflective surfaces or by diffractive elements, which may contribute to expansion of the effective optical aperture from which the image is projected towards the eye.

Near eye displays typically include two major modules: a light-guide optical element ("LOE" or "waveguide") and an image projector, sometimes referred to as a "projecting optical device" or "POD". The entrance pupil into the waveguide dictates the exit pupil required from the projector. The exit pupil of the projector is therefore located at some distance forward from its optics. The optical coupling arrangement of light from the projector into the waveguide determines this distance.

<FIG> shows an existing diagonal approach where a projector 12A transmits image light through a prism <NUM> into a waveguide <NUM>. In this configuration the optical distance between projector 12A and waveguide entrance pupil is relatively short.

<FIG> shows perpendicular approach to couple light into waveguide. In this figure projector 12B is shown to transmit the chief ray 16A. The light ray is reflected from mirror surface <NUM> at such angle that it is trapped by total internal reflection (TIR) within waveguide <NUM>.

In both <FIG>, a critical point (actually, an edge extending into the page of the drawing) <NUM> determines the entrance pupil into the waveguide, at least in the width dimension as illustrated. It is apparent that the optical path from the projector to this entrance pupil is shorter in <FIG> than in <FIG>.

The optical apertures of the waveguides are actually defined in two dimensions. In particularly preferred implementations, two dimensions of aperture expansion are performed between the projector exit pupil and the observer's eye. This may be achieved by using an independent waveguide for a first dimension of expansion, as exemplified by the waveguide of <FIG> (corresponding to <FIG> of <CIT>), where an entrance pupil to the waveguide <NUM> is defined by two edges <NUM> and <NUM>. These edges are not necessarily on the same plane. <FIG> shows a "1D" or slab-type waveguide <NUM> performing 2D aperture expansion by use of two sets of included partially-reflecting surfaces. In this case, waveguide edges <NUM> determine one side of the entrance pupil (marked area) while the edge on the other dimension <NUM> is not uniquely defined (schematically shown as arrow <NUM>), allowing the entrance pupil in this dimension to vary along the waveguide plane.

<CIT> discloses a scanning type display device includes a light source that includes multiple rows and columns of light emitters. The display device also includes a rotatable mirror that projects light to different areas of an image field as the mirror rotates. There can be a redundant number to light emitters in the light source to increase the brightness of the pixels in the image field. A data driver may replicate and shift data values among light emitters of the same columns. The light emitters may operate in conjunction with the mirror in a synchronized manner.

The present invention is an image projector according to the appended claims.

The present invention is an image projector.

The principles and operation of image projectors according to the present invention may be better understood with reference to the drawings and the accompanying description.

By way of introduction, the present invention relates to image projectors with various arrangements employing a tilt-mirror assembly with an illumination system as part of the image generating subsystem. The subject matter described herein can be conceptually subdivided into a number of different aspects of the invention which each stands alone in its own right, but which are most preferably used to advantage in various combinations. All combinations of the various aspects of the invention discussed below should be considered within the scope of the invention, except where specifically indicated to be incompatible.

Referring now to the drawings, <FIG> illustrates schematically an image projector according to a first aspect of the present invention, for projecting a collimated image via an exit stop <NUM>. The image passes through an image plane <NUM> where an image is generated by a spatial light modulator (SLM) providing a two dimensional array of pixel elements, each of the pixel elements being controllable to modulate a property, typically polarization, of light transmitted or reflected by the pixel element. An example of a transmitted light SLM is a liquid crystal display (LCD), while an example of a reflective SLM is a liquid crystal on silicon (LCOS) device or a digital light processing (DLP) device. The schematic representation here illustrates progression along an optical path from left to right, but it will be appreciated that this optical path can be folded at various reflective elements, including at LCOS <NUM>, as will be exemplified in examples below. A collimating arrangement <NUM> of at least one optical element is configured to collimate illumination from the image plane (e.g., spatial light modulator) to generate a collimated image directed to exit stop <NUM>, for injection into an input stop of a light-guide optical element (waveguide).

The image projector also includes an illumination arrangement delivering illumination from an illumination stop <NUM>, and illumination optics <NUM> deployed in the optical path between illumination stop <NUM> and image plane <NUM>. Preferably, in order to achieve high optical efficiency, illumination optics <NUM> and collimating arrangement <NUM> are configured such that an image of illumination stop <NUM> falls substantially on exit stop <NUM>. This achieves "pupil imaging", ensuring that illumination rays directed from illumination stop <NUM> towards the SLM are efficiently directed towards the exit stop <NUM>.

Light can be delivered to entrance stop <NUM> from any suitable light source <NUM>, and can be concentrated by any suitable components, whether optical imaging components (lenses, mirrors) or non-imaging (light-pipe, diffusers) components. After illumination stop <NUM>, only imaging optical components are used, so that "pupil-imaging" is achieved. Exit stop <NUM> is preferably the entrance into a light-guide optical element, such as those illustrated in <FIG>, <FIG>, that relays the image to the observer (not shown). In a case of perfect pupil imaging, any light ray passing through stop <NUM> and falling on illumination optics <NUM> will reach exit stop <NUM> (subject to image modulation) and enter the waveguide, thereby achieving maximal illumination efficiency. Practically, much of the advantage of this aspect of the invention can be achieved by having the image of the illumination stop falling "substantially" on exit stop <NUM>, taken here to mean that at least half of the rays exiting illumination stop <NUM> and reaching illumination optics <NUM>, and more preferably at least <NUM> percent, fall on exit stop <NUM>.

The image passing through exit stop <NUM> to an LOE must be collimated, i.e., where every point in the image is represented by a set of parallel rays that fill stop <NUM> uniformly. Image formation can be achieved using three main alternatives, wherein the third alternative is in accordance with the invention.

<FIG> shows architecture equivalent to <FIG> only with larger distance between exit pupil <NUM> and first lens <NUM>, more suitable for implementing certain optical designs, such as the perpendicular coupling in of <FIG>. The larger distance between <NUM> and <NUM> dictates use of a larger lens <NUM>, and also shifts the pupil image plane <NUM> closer to image plane <NUM>. As a result, space limitations typically dictate placing lens <NUM> adjacent to illumination stop <NUM>, and typically prior to the illumination stop along the optical path.

In the examples given below, reference will be made to an LCOS spatial light modulator, but it should be noted that this is a non-limiting example of a spatial light modulator, and that variant implementations employing other types of spatial light modulator may readily be implemented by a person having ordinary skill in the art on the basis of the description herein.

<FIG> shows an architecture equivalent to <FIG> based on two PBS (Polarizing Beam Splitters). Light source <NUM> transmits light onto PBS 40a, to lens <NUM> and onto scanning reflecting mirror <NUM>. Hereafter, throughout this document, it is taken as a given that a quarter wave-plate is used after PBS reflection and before PBS transmission, and vice versa, as is known in the art, but this detail will be omitted for simplicity of presentation. The light reflects from mirror <NUM> and is transmitted through PBS 40a, reflected by mirror <NUM> (which may be a plane mirror as shown or may have optical power), reflected by PBS 40a and by PBS 40b so as to be directed onto LCOS imaging matrix <NUM>. From the LCOS, the light pass through PBS 40b onto lens <NUM>, back to PBS 40b and onto exit pupil <NUM> that is also the entrance pupil to the waveguide.

<FIG> shows only part of the rays that are focused on scanning mirror <NUM> and focus once again by the optics on pupil <NUM>. This way the scanning mirror at image of exit pupil can perform scanning while maintaining illumination into pupil <NUM>.

<FIG> shows a single point in image field that is focused on LCOS <NUM> and also being focused also in source plane <NUM>. This way scanner <NUM> can scan illumination spot from <NUM> into LCOS <NUM>. In preferred embodiment, if a single spot source is used (such as a laser) then a diffuser is placed in the optical path multiple pixels are illuminated on LCOS. Alternatively, the LCOS can be replaced by a reflecting lens (flat or curved) and laser maintained focused by imaging optics all the optical path without diffusers or other non-imaging components.

It is apparent that in configuration of <FIG> the distance between image plane <NUM> and the pupil image <NUM> is relatively large (as a result of a relatively short distance between pupil <NUM> and lens <NUM>) therefore this configuration is more appropriate for diagonal coupling as described in <FIG>.

In <FIG>, the exit pupil <NUM> is further away from lens <NUM> therefore the scanning mirror <NUM> placed at shorter optical path from the image at <NUM> relative to the configuration in <FIG>. As shown in <FIG>, here exit pupil <NUM> is refocused to plane <NUM> without an additional optical path through PBS 40a. This configuration is equivalent to the one shown in <FIG> and useful when implementing the coupling arrangement shown in <FIG>.

<FIG> show scanning of mirror <NUM> so light source <NUM> illuminates different angular points of the field as exiting pupil <NUM> or as illuminating LCOS <NUM>.

As previously mentioned, it is also possible to place a static mirror at <NUM> (without any spatial light modulator) and use a focused beam from a small-spot illumination source (e.g., laser beam, S-LED, edge-emitting diode or the like) for which the focused illumination spot at the focal plane is no larger than dimensions of a pixel of the image to achieve efficient image generation by scanning only.

<FIG> show an optical arrangement of a projector with perpendicular coupling as described in <FIG>. <FIG> shows a side view and <FIG> shows a bottom view. In this case, waveguide <NUM> has an entrance pupil defined by <NUM>. The coupling orientation of reflecting mirror <NUM> is perpendicular to the orientation of the projector PBS, so that it is better seen in the bottom view of <FIG>.

According to the principles set out thus far for preferred implementations, the entrance pupil <NUM> of the waveguide (shown as light rays focus 166C) would be imaged onto scanning mirror <NUM> (as was illustrated in <FIG> and <FIG>). However, if the scanner scans only in one dimension and the scanning axis is as shown by the dashed line in <FIG>, then the pupil imaging requirement can be relaxed, provided that a suitable waveguide configuration is chosen. In this example, the image of the pupil is at 166D (not on mirror <NUM>). In this case, the scanning will cause the exit pupil from the projector to travel along arrow <NUM> (<FIG>). This type of pupil movement along the waveguide does not degrade coupling efficiency, so long as the waveguide includes two-dimensional pupil expansion.

In certain embodiments of the present invention, such as will be described in more detail below, it may be desirable to perform two-dimensional scanning of the illumination across the image plane, typically in a raster pattern, where a first, more rapid, scanning direction is referred to as the primary scanning direction, and a direction perpendicular to the primary scanning direction is referred to as a secondary scanning direction. Although two-axis scanning can be performed using a single mirror, in many cases, lower costs and improved reliability can be achieved by employing two separate scanning mirrors, each with its own actuator, each providing tilt about a single axis. Where two single axis scanners are used, it is impossible to place these two axis mirrors in a single plane that is the image of the exit pupil. According to an aspect of the present invention, each single axis scanning mirror can be placed substantially at a plane containing an image of the effective waveguide pupil for the corresponding axis. These distinct locations for the waveguide pupil for two different axes are exemplified in <FIG> as edges <NUM> and <NUM>, and in <FIG> as dimensions <NUM> and <NUM>.

<FIG> shows an exemplary system with two tilt-mirror assemblies including two distinct mirrors <NUM>, <NUM>, each with its own actuator as part of a driver (not shown). The light originates from source <NUM>, is reflected onto first scanning mirror <NUM> then second scanning mirror <NUM>. The light then continues to LCOS (or mirror) <NUM> and collimating lens <NUM>, before being projected into the waveguide (not shown) where it impinges on folding mirror <NUM> and then waveguide entrance <NUM>. This system is a further example of a system having two effectively distinct entrance apertures to the waveguide: the entrance pupil in the dimension in which the illumination is guided within the waveguide is delimited by waveguide aperture <NUM> (corresponding to edge <NUM> of <FIG>) while the pupil stop in the transverse dimension (perpendicular to the drawing plane) may be designed to lie at folding mirror <NUM> (although other locations are also possible).

<FIG> illustrates that a point on folding mirror <NUM> is imaged to scanning mirror <NUM>. It follows that the scanning axis of scanning mirror <NUM> should be horizontal to the page (shown by dot-dash line). <FIG> illustrates that a point on pupil plane <NUM> is imaged onto scanning mirror <NUM>. It follows that scanning mirror <NUM> should be implemented with a rotation axis perpendicular to drawing plane.

As an alternative to the approach of <FIG>, according to another aspect of the present invention, two-axis scanning can advantageously be achieved by twice imaging of the exit pupil <NUM> on both separated mirrors. <FIG> shows schematically how first pupil image 42V (vertical scanner) is reimaged onto another pupil image <NUM> (horizontal scanner).

<FIG> show optical arrangement including double pupil imaging where a point source <NUM> is scanning the image without spatial image modulator. <FIG> shows point from exit pupil <NUM> is imaged onto first vertical scanning mirror 42V and being reimaged onto horizontal scanning mirror <NUM>. Figure <NUM> shows that point source is collimated at exit pupil <NUM>. This architecture can be used to advantage when scanning with a single laser or other single-pixel illumination source modulated to generate an image. Alternatively, it may be used to advantage with various multi-source illumination schemes, and is particularly suited to the various "spaced sources" illumination schemes described below.

Up to this point, a number of novel optical arrangements have been presented to provide capabilities of scanned illumination, either as a primary image generation mechanism or for use in combination with a spatial light modulator. Presented below are a number of particular implementations which are facilitated by, and can advantageously be implemented using, one or more of the above optical arrangements.

By way of introduction, <FIG> is a block diagram illustrating the main components of an image projector, generally designated <NUM>, for projecting a collimated image via an exit stop for injection into an input stop of a light-guide optical element (waveguide entrance <NUM>). The collimated image is a representation of a digital image with a certain desired field of view, as provided to the system as an image input <NUM>. In general terms, image projector <NUM> includes an illumination arrangement <NUM> which includes a plurality of illumination sources <NUM>, numbered here as sources <NUM>, <NUM>. n (although certain implementations may have only two illumination sources). The types of illumination sources <NUM> used, and the relative deployment of those sources, will be discussed in detail below in the context of each application. A scanning arrangement <NUM> includes at least one tilt-mirror assembly <NUM> that has a mirror <NUM> and a driver <NUM> for driving tilt motion of the mirror <NUM>. The tilt-mirror assembly may be implemented using a range of commercially available products well known in the art. Where two-axis scanning is required, either a two-axis tilt-mirror assembly may be used, also as commercially available, or a single axis tilt-mirror assembly <NUM> may be used as a primary scanning mechanism, supplemented by a secondary tilt-mirror assembly <NUM> with its own mirror <NUM> and driver <NUM>.

Various aspects of the present invention also employ a spatial light modulator (SLM) <NUM> having individually controlled pixel elements in a pixel array <NUM> driven by suitable driver circuitry <NUM>, all as is well known in the art. The SLM may employ any suitable technology, such as for example LCD for transmission configurations or an LCOS or a DLP device for reflective configurations. In each case, the SLM is in itself typically a standard commercially available product.

A controller <NUM>, typically including one or more processors <NUM> and at least one data storage device <NUM>, is provided in electronic connection with spatial light modulator <NUM> (if present), tilt-mirror assembly driver(s) <NUM> (and <NUM> if present) and the illumination arrangement <NUM>. Controller <NUM> may be implemented using dedicated circuitry, general purpose processors operating under suitable software, or any other combination of hardware, firmware and/or software, as is known in the art. Furthermore, the structure and functions of controller <NUM> may be subdivided between two or more physical subsystems, and some of its functions may be performed by remote devices and/or dynamically allocated resources of a virtual machine or otherwise defined "cloud" computer.

The optical relationships between the various components are defined by an optical arrangement <NUM> including a plurality of optical elements (typically including collimating optics and illumination optics based on any combination of reflective and/or refractive lenses, mirrors, beam splitters, quarter wave-plates, and transparent blocks defining surfaces for maintaining components in optical alignment. Examples of suitable optical arrangements for implementing various aspects of the present invention may be found in the designs of <FIG>, as described above.

In general, the various elements of optical arrangement <NUM> are deployed so as to direct illumination from plurality of illumination sources <NUM> towards mirror <NUM> (and <NUM> if present), to direct the illumination reflected from the mirror(s) towards the SLM <NUM>, and to collimate illumination from SLM <NUM> to generate a collimated image directed to the exit stop and the waveguide entrance.

Although the present invention may be implemented using solely refractive optical components and free-space optics, it is considered preferable in many cases to employ implementations without an air gap in the optical path between the illumination optics and the exit stop, and most preferably, from the illumination stop to the exit stop. At least some if not all elements with optical power are preferably implemented as reflective lenses. The optical path of the devices described herein typically includes certain components, such as laser light sources and scanning mirror components, which inherently include some internal air space. Even here, however, the components are preferably encapsulated components which can be integrated with the rest of the optical system without any "inter-component air gaps", i.e., where there are no air gaps other than internal spaces within encapsulated components. The use of an architecture without inter-component air gaps helps to ensure minimal performance degradation over time due to environmental changes or penetration of dirt into the system.

Various implementations of the present invention as described herein employ a plurality of independently controllable (i.e., intensity modulated) illumination sources which each scan across an SLM while instantaneously illuminating a plurality of pixel elements. In other words, illumination from each of the illumination sources generates a patch of illumination illuminating a plurality of the pixel elements of the spatial light modulator, and the intensity of illumination of each patch is varied as the scanning arrangement moves the illumination pattern across the SLM. The resulting sequential illumination of different regions of the two-dimensional pixel array allows savings in illumination power in various ways. Firstly, in regions where no image content is required, the illumination source need not be actuated, thereby saving significant power. An example of such an application is an augmented reality application where much of the display area is left inactive, to allow an undisturbed review of the real world, and only selected regions of the display are actuated to provide the augmented reality content.

In other situations, even where a region of the display is active, it may still be possible to save display power in accordance with a local maximum required display intensity. Specifically, according to a further aspect of certain implementations of the present invention, the display controller is configured to: (a) determine a maximum required intensity of a pixel of the digital image in a part of the digital image corresponding to each of the regions of the two-dimensional array; (b) determine a reduced illumination level for at least one of the regions sufficient to generate the corresponding maximum required intensity within the regions; (c) generate a modified pixel intensity map for pixels within the at least one region for generating a required projected image intensity based on the reduced illumination level; and (d) actuate the illumination arrangement to illuminate at least one region with the reduced illumination level while the pixel elements within the at least one region are actuated according to the modified pixel intensity map.

This feature is illustrated here with reference to a one-dimensional scanning pattern, but can equally be implemented for more complex illumination scanning patterns. <FIG> illustrates a simple pattern <NUM> (for illustrative purposes) corresponding to an input image for display over a field of view <NUM>. The input image has variable image intensity over field of view <NUM>. The darker image here portrays higher intensity. This image is for a single color and three such images generate every frame for all colors. The dashed lines are for ease of reference to features between the different representations of the Figure. Parenthetically, whenever reference is made herein to a "field of view", this refers interchangeably to the span of angles (angular field of view) spanned by pixels of the image in the collimated image at the projector exit pupil and to the spatial field of view at the image plane (e.g., LCOS surface).

If the LCOS were to be scanned with a beam at constant maximum intensity, this image as illustrated in pattern <NUM> would be loaded as is, and scanning with the maximum intensity beam would generate the desired output image. As an alternative, according to an aspect of the present invention, graph <NUM> illustrates a "maximum required intensity" for each column of figure <NUM>. This pattern is then used to set a corresponding profile of laser intensity as the illuminating pattern (here assumed to be a line spanning a dimension perpendicular to the primary scanning direction) scans across the LCOS. In a region for which the illumination intensity is reduced, less attenuation is required from the LCOS <NUM>. Image <NUM> shows the resulting illumination intensity across the LCOS. At beginning of scan (covering area 905a of the array) there is no laser illumination. For area 905b, an intermediate intensity is used, corresponding to a "reduced illumination level". Area 905c is illuminated with maximal intensity and at the final section (area 905d) requires no illumination.

Image <NUM> corresponds to a modified pixel intensity map such that the product of the modified pixel intensity of <NUM> and the illumination level for a given column (or more generally, illumination region) from <NUM> will generate the desired output image intensity <NUM>. Thus, the image <NUM> (the actual image loaded to the LCOS) is generated by dividing the required image <NUM> by the illumination image <NUM>.

In practice, each illumination region typically covers a number of columns in the scanning direction simultaneously and, as a result, the illumination image <NUM> will typically be smooth with gradual transitions, even if the illumination output is driven by a step function, as the overall intensity of illumination for each column will be the integral of the illumination as the illumination line passes. The calculation of the loaded image <NUM> as the desired output image <NUM> divided by the illumination level <NUM> remains valid. In each case, controller <NUM> drives the spatial light modulator <NUM> in coordination with modulation of an intensity of each of the illumination sources <NUM> synchronously with the tilt motion of the mirror <NUM> to generate a reproduction of the digital image.

In certain implementations of the present invention, the plurality of illumination sources <NUM> include at least one group of individually controlled illumination sources generating a substantially continuous illumination pattern spanning at least part, and in some cases the entirety, of a dimension of the field of view perpendicular to the primary scanning-direction dimension of the field of view. This reduces the required repetition frequency and/or scanning motion speed required by the scanning arrangement.

<FIG> shows an architecture where the light from source (for example <NUM> or <NUM>) is distributed as a line or other oblong shape <NUM> as imaged across LCOS active area <NUM> (<NUM> or <NUM>). This line distribution can be generated by an elliptical diffuser placed along the optical path before or near the scanning mirror. It can also be generated by imaging the emitting output facet of a laser onto the LCOS, or by a combination of the above.

Here and in other examples, illumination source <NUM> is most preferably a laser, and is collimated by suitable optics onto scanning mirror <NUM>, preferably implemented as a high-speed mirror (typically using MEMS technology). Non-collimated illumination may also be used, as long as the SLM is properly illuminated. It is preferable that the spot size is large enough to cover a relatively large number of pixels at any instant, typically at least <NUM>, preferably at least <NUM>, and in some preferred cases at least <NUM> pixels or in excess of <NUM>,<NUM> pixels (e.g., 100x100 pixels or larger), thereby reducing scanning speed requirements. The shape of the illuminating spot can be modified, for example, by the shape of the emitter beam from source <NUM>, optical properties of the source collimation optics, deployment of a diffuser on the scanning mirror and/or deployment of a diffuser in the illumination path. Where diffusers are used, the diffuser is preferably a structured diffuser with a specifically chosen angular distribution of the output light, such as those commercially available from RPC Photonics (NY, USA).

In contrast to the single source illustrated in <FIG> illustrate more preferred implementations in which at least one group of individually controlled illumination sources generating a substantially continuous illumination pattern spanning at least part, and in some cases the entirety, of a dimension of the field of view perpendicular to the primary scanning-direction dimension of the field of view. In this case, the scanning motion is preferably such that the illumination patch from each individual illumination source does not scan over the entire image field of view, but that the plurality of illumination sources (for any given color) together with the scanning motion ensure that the entire active area of the SLM <NUM> is covered (for each color).

<FIG> shows the illumination distribution of an array of lasers <NUM> (in this case three lasers placed in a line at source plane <NUM> or <NUM>) where every laser illuminates a strip or patch that is individually only part of a dimension of the LCOS, but together span an entirety of one dimension of the LCOS. This allows the use of simple one-axis scanning by tilt-mirror assembly <NUM> to cover the entire active area of the SLM. Each strip or patch illuminates multiple pixels of the LCOS simultaneously. The intensity of each laser is modulated according to the maximum image intensity required in the corresponding strip or patch, and the intensity of the LCOS pixels are modulated in order to provide the desired pixel intensity scaled according to the illumination intensity, as explained above with reference to <FIG>. Thus, if the maximum pixel intensity within the region corresponding to a certain laser at a certain position is <NUM>% of the maximum intensity, the corresponding laser is preferably actuated at <NUM>% intensity, while LCOS pixels with <NUM>% intensity will be actuated at <NUM>% (maximum) intensity and pixels requiring <NUM>% intensity output will be actuated at <NUM>% intensity. If in the neighboring region there is a pixel requiring <NUM>% intensity, the corresponding laser is preferably actuated at <NUM>% intensity, and any pixel in that region requiring <NUM> intensity will be actuated at <NUM>% brightness level.

The same principles can be applied with slightly more complex calculations where a continuous scanning action is used, and the overall pixel intensity depends on the integral of the illumination intensity for the period the laser illumination pattern is passing across a given pixel as well as the pixel intensity setting. As previously described, a rectangular or elliptical diffuser (or circular as shown) can be used to generate the illumination pattern for each laser, but with lower angular divergence than that of <FIG>.

If mechanical limitations prevent placing the lasers side-by-side then a staggered configuration may be used, as shown schematically in <FIG>. A staggered configuration is also possible if different arrays are needed for the different colors (e.g., R, G and B). In this case, the linear scanning motion should be long enough to ensure that each illumination region scans across the entire active area of the LCOS.

<FIG> shows schematically that the staggered configuration can also be used for 2D scanning thereby enabling reduced scanning speed of the second axis of the scanner.

The scanner can be activated in step-and-illuminate mode if the image of the illuminating source covers a substantial area of the LCOS.

Here a laser refers to a high brightness source. For example, a bright LED with small divergence (such as an S-LED or edge-emitting LED) can also be used.

As an addition, or alternative, to the contiguously grouped illumination patterns described above, according to another aspect of the present invention, certain implementations of the present invention employ illumination sources that are spaced apart to reduce the angular extent of a scanning motion which is required to span a field of view of the image to be projected. Specifically, by using spaced-apart illumination sources, the tilt motion of tilt-mirror assembly <NUM> can be reduced such that illumination from each of the illumination sources scans across only part of one dimension of the field of view while illumination from the plurality of illumination sources together scans across the entirety of the one dimension.

By way of introduction to this feature, and for the purpose of facilitating an understanding of the invention without in any way limiting the invention to any specific theoretical basis, the scanning mirrors of the projector must typically preserve the etendue (product of angular and spatial size) of the system. For example if the entrance pupil to the waveguide is <NUM> and the angular field of the image injected is <NUM> degrees then the etendue will be:<MAT>.

The scanning mirror must fulfill this parameter by having the product of size and angular tilt having same value. For example, a mirror having aperture of <NUM> must have an optical scan angle of:<MAT>.

However, in many cases it is difficult to obtain large aperture and large angular scan at same component. According to an aspect of the present invention, spaced sources are used to segment the image field, thereby reducing etendue requirements of the scanning mirror. This configuration is applicable for illuminating an image generating matrix (LCOS) as previously described or for laser point scan of the image, where modulation of scanned laser point illumination is the sole image generation mechanism. <FIG> shows architecture similar to <FIG> in which laser sources 630A, 631A and 632A are equivalent laser sources individually modulated while surface <NUM> is a reflecting mirror (or lens) without an SLM. This way the lasers beams are collimated when exiting pupil <NUM> into the waveguide. Scanners <NUM> and <NUM> are positioned at appropriate pupil image locations (as explained above with reference to <FIG>) and have appropriate size.

The equivalent laser sources illuminate points 630B-632B (respectively) in different sub-fields of the image field <NUM> as shown in <FIG>. The points in the field 630B, 631B and 632B are the angular illumination points (size as small as possible and defines image sharpness) within aperture <NUM> as generated by the corresponding lasers. These spots are scanned across the field as shown schematically by curved line arrows. The arrangement of <NUM>×<NUM> lasers illumination separates the image field <NUM> to three (in this example) smaller sub-fields associated with every laser show as dashed rectangle. Consequently, the required angular scanning amplitude of mirror <NUM> (the primary high-speed scanner) is reduced by a factor of <NUM> to: <NUM>/<NUM>=<NUM> degrees of optical deflection (side to side). During the scan, every laser is modulated individually in order to generate the appropriate part of the image being scanned by the specific laser.

In <FIG>, a 3x2 arrangement is shown, so that the horizontal angular image scanning (by mirror <NUM>) is again divided by <NUM> while the vertical scanning by mirror <NUM> is divided by two.

<FIG> shows the color sources to be angularly separated. Here the color lasers 637R, <NUM> and 637B are separated (for example by spatial location in plane <NUM>). The scanning mirrors scan the illumination angler points across the image simultaneously for all sub-fields and colors.

The multiple separated lasers in <FIG> are each responsible for providing only a subsection of the overall image brightness, and can therefore provide a higher brightness display output without exceeding eye-safety levels.

In a system with direct laser illumination (no LCOS), the placement of lasers at <NUM> can be on a curved profile according to field curvature of the optics. Specifically, every laser may advantageously be placed at an average focal distance of its assigned sub-field. This way a substantial part of the field curvature can be compensated for.

Although suitable for implementing a direct-scanning image generation mechanism, this aspect of the invention is not limited to such applications, and can also be used to advantage according to the principles described above, where each illumination source illuminates a group (plurality) of pixels of a SLM located at plane <NUM>. In this case, each of the aforementioned spaced-apart illumination sources is advantageously part of a group of illumination sources that cooperate to generate a substantially continuous illumination pattern spanning at least part of the field of view perpendicular to the primary scanning-direction dimension of the field of view.

Turning now to <FIG>, there is illustrated a further aspect of the present invention according to which a tilt-mirror assembly is used to switch between illumination sources of different colors. Specifically, the plurality of illumination sources <NUM> here include illumination sources of different colors, and the controller <NUM> drives the scanning arrangement driver <NUM> to displace mirror <NUM> between at least a first position, in which the spatial light modulator <NUM> is fully illuminated by a first of the illumination sources, and a second position, in which the spatial light modulator is fully illuminated by a second of the illumination sources, thereby switching between colors of illumination. Controller <NUM> also actuates the spatial light modulator <NUM> synchronously with switching between colors of illumination to generate corresponding content of the digital image for each of the colors of illumination. This eliminates the need to employ a light-pipe or diffuser to mix illumination sources of different colors.

<FIG> shows a first position of a scanning mirror <NUM>. In this position, the center LED <NUM> is imaged onto the LCOS <NUM>. <FIG> shows the footprint of the LCOS <NUM> on the center LED <NUM>, preferably providing full frame illumination by LED <NUM>.

<FIG> shows scanning mirror <NUM> tilted in a second position. In this state, LED <NUM> (for example having a different color) is activated and imaged onto the LCOS <NUM> as shown by the footprint <NUM> in FIG. This illumination switch is synchronized with loading of the corresponding color separation image onto the LCOS. A fast sequence of illumination switch between different color LEDs and appropriate image loading generates a perceived full color image.

Optionally, the LED configuration can also include a white LED (not shown) in addition to the three RGB LEDs.

Part or all of the LEDs <NUM>, <NUM> and <NUM> can be replaced with a matrix of a single color mini-LEDs thereby achieving sequential selective illumination per color. In this case, the appropriate illumination pattern is loaded to the illumination matrix in sync with loading to the LCOS.

Part or all of the LEDs <NUM>, <NUM> and <NUM> can be replaced with a laser illuminated diffuser, thereby achieving more collimated illumination (less loss) while the mirror <NUM> vibrates slightly during each laser illumination to eliminate speckles.

Claim 1:
An image projector for projecting a collimated image via an exit stop (<NUM>) for injection into an input stop of a light-guide optical element, said collimated image being a representation of a digital image with a field of view, the image projector comprising:
(a) an illumination arrangement (<NUM>) comprising a plurality of illumination sources (<NUM>);
(b) a tilt-mirror assembly (<NUM>) comprising a mirror (<NUM>) and a driver (<NUM>) for driving tilt motion of said mirror (<NUM>);
(c) a controller (<NUM>) in electronic connection with said driver (<NUM>) and said illumination arrangement (<NUM>); and
(d) an optical arrangement (<NUM>) comprising a plurality of optical elements deployed to:
(i) direct illumination from said plurality of illumination sources towards said mirror;
(ii) direct the illumination reflected from said mirror towards an image plane; and
wherein said controller (<NUM>) modulates an intensity of each of said illumination sources (<NUM>) synchronously with said tilt motion of said mirror (<NUM>) according to the content of the digital image, and
said plurality of illumination sources (<NUM>) are spaced apart and said tilt motion is such that illumination from each of said illumination sources (<NUM>) scans across only part of one dimension of the field of view while illumination from the plurality of illumination sources (<NUM>) together scans across the entirety of the one dimension
characterized in that
the optical arrangement (<NUM>) further comprises an optical element deployed to collimate illumination from said image plane to generate a collimated image directed to said exit stop (<NUM>), and in that
the image projector further comprises a spatial light modulator (<NUM>) deployed at said image plane, and wherein said optical arrangement (<NUM>) is configured to generate a patch of illumination from each of said illumination sources (<NUM>) illumination a plurality of pixel elements of said spatial light modulator (<NUM>), said spatial light modulator (<NUM>) being driven by said controller (<NUM>) in coordination with said illumination arrangement (<NUM>) to generate a reproduction of the digital image.