Patent Description:
Scanning mirror-based light projection systems are known in the field of illumination systems. <CIT> discloses an example of such a system, in which the light source is a laser type light source. A scanning mirror rotatable around two orthogonal axes is actuated and receives a light signal from a primary light source to project an image on to a phosphorous element. The light radiated by the primary light source, or more specifically its luminous intensity, for example, can be modulated to project a desired image on to the phosphorous element. The phosphorous element is then arranged to perform a wavelength conversion of the light signal received from the primary light source. Consequently the phosphorous element, acting as a secondary light source, re-emits light, which when combined with the light from the primary light source produce useful white light in various directions. In this kind of system a very high overall energy efficiency can be obtained, as the wavelength conversion performed by the phosphorous element is more energy efficient than the electrical-to-optical conversion of the laser light source. According to <CIT>, instead of using one scanning mirror rotatable around two orthogonal axes, it possible to use two mirrors instead, each movable around one axis, where the two axes are mutually orthogonal.

<FIG> shows a simplified cross-sectional view of an illumination system comprising a light source <NUM>, such as a laser light source <NUM>, and a scanning mirror assembly <NUM>, which comprises a movable plate <NUM> arranged to be rotated about axis <NUM> in this example. The movable plate comprises a mirror and is connected to a frame <NUM> by two support arms (not shown), aligned on both sides of the plate along the same axis <NUM>. In <FIG>, the light emitted by the light source <NUM> is denoted by A, while the light reflected by the mirror is denoted by B. In order to save space, and in order to obtain a reflected image free of deformations, the light source should preferably be placed directly above the mirror so that the light beam A forms an angle of incidence at the mirror surface which is close to <NUM> degrees with respect to the centre point of the mirror when at rest. However, in this position the light source would obstruct the reflected light, thereby creating an occluded or non-illuminated spot behind the light source. In order to avoid this occlusion problem, a free passage to the reflected light directly above the mirror centre point can be guaranteed by arranging the light source slightly offset from a position directly above the centre point of the mirror, as shown in <FIG>. However, the light source still obstructs some of the reflected light in the position as shown in <FIG>. Furthermore, the arrangement of <FIG> is also not optimal in terms of use of space.

<FIG> shows a similar arrangement as in <FIG>, but in this case the light source is still further offset with respect to the centre position. Now the light source no longer obstructs the reflected signals, but the configuration has the disadvantage that it takes up even more space than the configuration of <FIG>, and the resulting or reflected image becomes clearly deformed due to the large angle of incidence of the light A striking the surface of the mirror. It is also to be noted that the current manufacturing processes of the above type illumination systems are not optimal. For instance, the angled configuration of <FIG> requires a very high precision in the alignment of various components, such as the light source and the scanning mirror assembly. This naturally increases the complexity of the manufacturing process.

<CIT> discloses a vehicle headlight having an array of moveable mirrors to control the distribution of light. European patent application <CIT> refers to a light collection system for a projection system, in which a projected light beam has a uniform arc image size throughout the width of the light beam. <CIT> describes an adaptive lighting system for an automotive vehicle with a wavelength conversion device for receiving light radiation from a primary source and re-emitting white light radiation.

According to the invention, there is provided an illumination system according to claim <NUM>.

This may provide a more compact illumination system since the light source is located in front of the scanning mirror assembly and thus the length of the light path from the light source to the reflective surface and onwards to an output aperture of the system can be minimised. The shadow or occlusion effect caused by the obstruction of the reflected light by the light source is mitigated by means of the optical element, which is placed so that it directs the reflected light into the occlusion region. Thus, this arrangement at least partially overcomes the known problem that if the light is reflected back towards the light source, the light source occludes the reflected light.

According to an embodiment, the first optical element is located at least partly beyond the light source with respect to the reflective surface.

According to another embodiment, the first optical element comprises a lens, a wavelength conversion element or a diffractive grating.

According to the claimed invention, the light source is located on a first axis extending from a mid-point of the reflective surface and substantially orthogonal to the reflective surface when at rest and not subjected to a rotational displacement.

According to another embodiment, the cross-sectional shape of the first optical element is plano-convex, biconvex, plano-concave, biconcave, cylindrical, spherical or aspherical.

According to another embodiment, the first optical element comprises an array of lenses.

According to another embodiment, the system further comprises a support element between the light source and the first optical element and arranged to support the light source and the first optical element in their relative locations with respect to the axis of rotation of the reflective surface.

According to another embodiment, the system further comprises a second optical element for shaping the light emitted by the light source before the light reaches the reflective surface.

According to another embodiment, the first optical element comprises a lens and the system further comprises a wavelength conversion element.

According to another embodiment, the wavelength conversion element is located between the first optical element and the scanning mirror assembly.

According to another embodiment, the wavelength conversion element is located beyond the light source with respect to the reflective surface.

According to another embodiment, the light source is separated from the reflective surface by a distance equal to half the focal length of the first optical element.

Other features and advantages of the invention will become apparent from the following description of a non-limiting exemplary embodiment, with reference to the appended drawings, in which:.

An embodiment of the present invention will now be described in detail with reference to the attached figures. Identical or corresponding functional and structural elements which appear in the different drawings are assigned the same reference numerals.

<FIG> is a schematic cross-sectional view illustrating an exemplary illumination or lighting system or device according to an embodiment of the present invention. This arrangement may be used for example in photographic flash applications or in 3D sensing solutions used for example in gesture sensing applications and/or three dimensional mapping of an object or the environment. <FIG> shows a light source <NUM>. Various types of light sources and packaging may be used; light source <NUM> may be for example an edge emitting laser diode, a vertical-cavity surface-emitting laser (VCSEL), a light emitting diode (LED), a resonant-cavity LED, a micro-LED or an array of such light sources. The light source may be a monochromatic laser light source. If the illumination system is used for smart flash applications, then the light emitted is typically either an ultraviolet (UV) or near-UV light, with a wavelength of <NUM> to <NUM> once re-emitted by a wavelength conversion element as part of the system, or a visible light, obtained for example by use of three light sources (i.e. red, green and blue) that could generate a white beam or other colour beams once combined with each other. However, for other applications other wavelengths may be used, from UV light through visible light to infra-red light. The light source <NUM> typically emits non-collimated light, i.e. light whose rays are not parallel. As can be seen in <FIG>, the light source is located in front of a scanning mirror system <NUM>, and more specifically in front of a mirror which is formed on a movable plate <NUM>. In this example the scanning mirror system is a MEMS (Micro-Electro-Mechanical System) scanning mirror. The movable plate <NUM> is arranged to be rotated about axis <NUM>. The movable plate <NUM> is connected to a frame <NUM> by two support arms (not shown), aligned on both sides of the plate along the same axis <NUM>. In this example, the mirror rotates about one axis, but it could also rotate about two mutually orthogonal axes. The advantage of a scanning system is that a real image can be projected, allowing the brightness of the projected image to be locally controlled (for example at the pixel level), so that the resulting projected and reflected light beam can have local brightness adjustments and/or a control of the contrast level between non-illuminated and illuminated pixels.

The scanning system <NUM> is arranged to deflect the light following various kinds of patterns, such as a Lissajous pattern or a raster pattern (interlaced or non-interlaced). Within the raster pattern projection, the image can also be displayed during the so-called fly-back scanning pattern (in a typical raster scan display, the MEMS mirror displays the image only in one sweep of the mirror or mirror axis controlling the image refresh rate (i.e. the mirror axis actuated outside of its resonant frequency once using a 2D MEMS mirror, which has the movable plate <NUM> that rotates about two mutually orthogonal axes), however in the fly-back option, the same or another pattern may be displayed on the other sweep of the mirror) or other patterns could be used, in which the direction of the scanning pattern can be switched (vertical scanning instead of horizontal scanning, for example, whereby the image is formed as vertical lines instead of from left to right, or vice-versa), or where the screen is scanned using any kind of space filling curve, for example Peano, Hilbert, or other fractal or L-system curves.

The scanning mirror system <NUM> may be actuated using magnetic, electrostatic, thermal, piezo-electric, hydraulic, pneumatic, chemical or acoustic means, for example. If the plate <NUM> is actuated magnetically, then the bottom and/or side parts of the scanning mirror system may comprise a magnet <NUM> for generating a magnetic field to move the plate comprising the mirror. In this example the light source is located in front of the mirror on an imaginary line drawn from the centre point of the mirror when at rest (rest position is the one shown in <FIG>), or at a so-called neutral position, and having a <NUM> degree angle with respect to the mirror surface. Thus, the mirror has a light-source-facing side and a plate-facing side.

In this example, there is also shown an optical element <NUM>, referred to in this text as the second optical element. The second optical element is optional and its purpose is to do some beam shaping, for example modifying the footprint profile of the beam and/or making the light diverging, or focusing, or collimating the light beam A emitted by the light source before it reaches the mirror. For instance, without the second optical element <NUM> it is possible that the light beam would have an elliptical footprint profile in the plane of the mirror surface. However, the second optical element <NUM> can be configured to change the footprint of the light beam, and make it for instance circular. The second optical element may simply be a lens, for example, whose form is selected depending on the kind of beam-forming desired.

Another optical element <NUM>, referred to in this text as the first optical element, is provided on a support or substrate <NUM>. In this example the first optical element <NUM> and the support are placed behind the light source <NUM> (when viewed from the plate <NUM>). The first optical element may comprise a lens, a microlens array or a wavelength conversion element such as a phosphorous element, or a combination of the above elements. The first optical element may also or alternatively comprise a diffractive grating. The first optical element may be of glass or transparent plastic. The purpose of the first optical element <NUM> is to change the direction of propagation of the light B reflected from the mirror, and thereby to at least partly redirect the reflected light into an occluded region which is caused by the presence of the light source itself. As a result of this redirection of the reflected light by the first optical element <NUM>, a sensor <NUM> (e.g. a person's eye) placed behind the first optical element at the position shown in <FIG> detects the image pattern of the reflected light as though the sensor had not been occluded by the light source, or at least the effect of obstruction is greatly reduced compared to a situation in which no first optical element <NUM> is present. In this manner, by placing the optics behind the light source, and by carefully designing the optics to compensate for the occlusion, the negative effects of the light obstruction caused by the light source <NUM> can be considerably reduced or even substantially removed.

This architecture also enables the manufacturing process, and the miniaturisation of such an optical system to be considerably simplified. Furthermore, because the light source is placed directly above or in front of the mirror, any resulting image projected by the mirror is less affected by deformations. If the first optical element comprises a lens, then the reflected light would retain at least some of it its optical characteristics as it passes through the lens. For instance, if the light beam reaching the first optical element is coherent, then also the redirected light beam would be coherent. The characteristics regarding the direction of the beam and the shape of the beam may be modified, on purpose, by the lens.

In the illustrated example, the first optical element comprises a plano-convex lens, arranged to converge the light beams passing through it, and in particular to provide greater convergence adjacent to the region where occlusion of the reflected light B occurs. However, other forms are also possible, depending on the implementation details. Examples of various optical element shapes which could also be used are biconvex, plano-concave (diverging the passing light beams), biconcave, meniscus, cylindrical, spherical or aspherical. The lens may also be a Fresnel lens which has the advantage of being thinner than a spherical, aspherical or cylindrical lens, thereby enabling even smaller illumination systems. The first optical element could also be an array of lenses or a phosphorous element having a flat or bumpy surface or a combination of a lens or microlens array with a phosphorous element placed either on top of the lens or microlens array or in between the element <NUM> and the lens or microlens array.

If the illumination system illustrated in <FIG> is used for distance measurement (3D mapping) applications, then the first optical element may comprise a lens or an array of lenses, and there may be no need for a wavelength conversion element. However, if the illumination system is used for smart flash applications, then system preferably comprises a wavelength conversion element. In this case, the optical element <NUM> could comprise the wavelength conversion element. Alternatively, the first optical element may comprise a lens, and a separate wavelength conversion element could be provided as a separate element. This wavelength conversion element may be placed for example between the support <NUM> and the first optical element <NUM>, or the wavelength conversion element may be placed on the further side of the first optical element <NUM> (as viewed from the plate <NUM>). The wavelength conversion element may be in direct contact with the first optical element, or it may be placed at a predetermined distance from the first optical element. The possibilities for optically modifying the light beam may be maximised by placing the wavelength conversion element at a distance from the first optical element. The wavelength conversion element may comprise a phosphor film, or a plate on which a preferably continuous and homogeneous layer of phosphor has been deposited. Each point on the wavelength conversion element receiving the light beam A from the scanning system, typically monochromatic, absorbs the light power and then re-emits a light B of one or more different wavelengths. The resulting combined light can be considered as "white", since it contains a plurality of wavelengths between about <NUM> and <NUM>, i.e. in the visible light spectrum.

If the scanning mirror reflective surface is placed at a distance equal to half the lens focal length (j/<NUM>) from the lens <NUM>, or more precisely if the sum distance from the lens to the mirror plus the distance form the mirror to the light source emission point is equal to the focal length of the lens, then the resulting light beam may become collimated by the lens. This has the advantage that the projected light may substantially retain its shape and intensity profile over multiple projection distances. Alternatively, if the lens is placed closer or further away than f/<NUM> from the reflective surface of the mirror, the resulting projected light will be diverging, thereby enabling the illumination system to cover a larger illumination area.

Next the manufacturing process, which is not part of the claimed invention, of the above illumination system is explained with reference to the flow chart of <FIG> and <FIG>. In step <NUM> a first substrate <NUM> (<FIG>), also referred to as a light source substrate, and a second substrate <NUM> (<FIG>), also referred to as a mirror substrate, are provided or manufactured. The light source substrate <NUM> is transparent and may be a wafer and typically made of glass, plastic or silicon (if an infra-red laser is used). The mirror substrate <NUM> may be a wafer made of silicon or glass or electronics printed circuit board (PCB) and for example made of FR4 material (woven fiberglass cloth with an epoxy binder). In step <NUM> electrical contact elements <NUM> are provided on the substrates as shown in <FIG>. These contacts <NUM> may for example be conductive indium tin oxide (ITO) or tin-doped indium oxide layers. Such contacts are nearly transparent. When it comes to the light source substrate <NUM>, this transparency property has the advantage that obstructions to the light passing through the substrate can be minimised. These contacts may be simply metallic contact elements. The contacts may be deposited on the surface of the substrates and then patterned. As can be seen, in the illustrated example, the contact elements may be provided as pairs, however other arrangements are possible, and the number of the contacts depends on the wirings required in the fabrication process. For simplicity, the illustrated example is shown with only four contact pairs in two rows on the light source substrate, while eight contact pairs in two rows are provided on the mirror substrate. However, it is to be noted that in practical implementations each substrate may contain tens, hundreds or thousands or more of contacts. Contact pads <NUM> may also be provided on the reverse side of the substrate. In step <NUM> holes or vias <NUM> may also be provided in the substrate to enable connections from one side of the substrate to the other. The holes, or vias, could be present in the substrates before the formation of the contact elements on the substrates.

In step <NUM>, various components, such as the light sources <NUM> and the scanning mirror systems <NUM>, including the required connection wires <NUM>, are provided or formed on the respective substrates as shown in <FIG>. This can be accomplished by placing the components by pick-and-place by using standard pick-and-place machines, for example. In this example, light sensors <NUM> are also provided or formed on the mirror substrate <NUM> so that a light sensor is provided for every scanning mirror system, and these elements are provided in an alternating sequence on the mirror substrate <NUM>. This step may also include adding the connection wires <NUM> and connecting the wires to the respective components by soldering for example. In step <NUM>, an optical element substrate <NUM> is deposited on the light source substrate <NUM> on the same side as the contact pads <NUM>, as shown in <FIG>. In step <NUM> a master substrate <NUM>, a mask or a mould, is patterned with a pattern which is inverted or opposite to the desired form of the first optical elements, as illustrated in <FIG>. The master substrate may be of a glass, polymer, silicon or metal such as copper or nickel material, for example. In step <NUM> the optical element substrate is patterned by using the master substrate <NUM> to generate the desired first optical elements <NUM> on the light source substrate surface as shown in <FIG>. The patterning operations may be done for example by hot embossing, stamping and/or by applying pressure jointly with or separately to the final curing, or hardening, of the optical element curing done by thermal or UV curing in the case of the optical element made of respectively thermally curable material, or UV curable material such as UV curable polymer, or a mix of both.

In step <NUM> a spacer element <NUM> is provided on the mirror substrate <NUM>, as shown in <FIG>. This may be accomplished by deposition and patterning of polymer material, for instance, or by using a complete spacer wafer having through holes. The spacer <NUM> preferably has non-transparent surfaces to avoid any parasitic light beam emitted by the light source <NUM> and reflected by the scanning system <NUM> to illuminate the light sensor <NUM>. For example the spacer may be made of silicon or non-transparent, or opaque, plastic or polymer material or non-transparent, or opaque, glass. In step <NUM> the light source substrate <NUM> is stacked on the mirror substrate <NUM> so that the light source substrate is supported by the spacers, as shown in <FIG>. In step <NUM> the stacked substrates are diced or cut to form finalised complete system modules. In this example, each final module comprises one illumination system module next to a sensor module. In another arrangement, the module could be composed of one illumination system module and multiple sensor modules. This may be done, for example, in order to create redundancy in the sensed light as two or more sensors would be able to sense the light reflected by the illuminated object and then an algorithm may be able to compare the obtained information and then enable stronger system redundancy and therefore robustness. The same module may be used in a way compatible with stereovision and/or triangulation, where the distance information is derived by computing the light information detected by two sensors, placed at different locations. This kind of complete module may be used for distance measurements and is thus suitable for 3D sensing, for instance. If such modules are used for photographic flash applications, then the sensor module may be arranged to measure ambient light, for instance. Alternatively, depending on the specific application, the sensor module may not be needed at all. By including many (typically hundreds or more) light sources, scanning mirror assemblies and optical elements together with other required components provided on the two substrates, more of the manufacturing process can be carried out during substrate-level assembly, instead of relying on individual parts assembly steps.

The above described exemplary manufacturing process may be adapted in various ways. For example, the order of the above steps may be changed. For instance, the spacer may be provided on the mirror substrate before providing the necessary components on that substrate, or at the same time as the other components. It would be also possible to provide the spacer on the light source substrate instead of providing it on the mirror substrate.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention being not limited to the disclosed embodiment. Other embodiments and variants are understood, and can be achieved by those skilled in the art when carrying out the claimed invention defined by the appended claims.

Claim 1:
An illumination system comprising:
a first substrate (<NUM>) and a second substrate (<NUM>);
a scanning mirror assembly (<NUM>) provided on the second substrate (<NUM>), the scanning mirror assembly (<NUM>)comprising a reflective surface (<NUM>), the reflective surface (<NUM>) to be rotationally displaced around at least one rotation axis (<NUM>);
a light source (<NUM>) provided on the first substrate (<NUM>), the light source (<NUM>) being arranged to emit non-collimated light towards the reflective surface (<NUM>), and the light source (<NUM>) being located to occlude a region of the light (B) reflected from the reflective surface (<NUM>), wherein the light source (<NUM>) is disposed on a first axis extending substantially orthogonally to the reflective surface (<NUM>) from a mid-point of the reflective surface (<NUM>) when the reflective surface (<NUM>) is not subjected to a rotational displacement;
a first optical element (<NUM>) provided on the first substrate (<NUM>) for changing a propagation direction of the reflected light (B) to illuminate at least a portion of the occluded region; and
a spacer element for retaining the first and second substrates (<NUM>, <NUM>) at a predetermined separation distance from one another,
wherein the first and second substrates (<NUM>, <NUM>) are stacked.