Illumination assembly

Abstract

The invention describes an illumination assembly (1) of a portable device (2), comprising an array (11) of semiconductor emitters (11E) and an imaging lens (10) arranged above the emitter array (11) and adapted to direct the light from each emitter (11E) into a corresponding region (11Eimage) of a target area (T); characterized in that the imaging lens (10) comprises a surface pattern (10S) adapted to shape the light from adjacent emitters (11E) such that the corresponding imaged emitter regions (11Eimage) overlap at the target area (T). The invention further describes a method of manufacturing such an illumination assembly (1), and a portable device (2) comprising such an illumination assembly (1).

Description

[0001] Illumination assembly

[0002] FIELD OF THE INVENTION

[0003] The invention describes an illumination assembly, a method of manufacturing such an illumination assembly, and a portable device comprising such an illumination assembly.

[0004] BACKGROUND OF THE INVENTION

[0005] An array of individually addressable semiconductor emitters such as LEDs can be used to provide selective illumination for a target area. Selective regions of the target area can be illuminated by actuating the corresponding element of the emitter array. When all elements of the emitter array are active, the entire target area is illuminated. The array can comprise very small discrete emitters (e.g. micro-LEDs) mounted on a backplane or substrate, for example. Alternatively, the emitter array can be made from a single section of wafer, with gaps or patterned insulation to separate the individual emitters (referred to as a "segmented emitter"). A suitable optical element such as an imaging lens can project the light from each emitter into a corresponding region of the target area. An emitter array in combination with an imaging lens can be used as a flash for a digital camera arrangement of a mobile device such as a smartphone. The individually addressable emitters of the flash can be switched on or off to control the amount of light that is cast onto different regions of the target area, whereby the active emitters can be driven with different current densities as appropriate. In this way, the target area (here, any objects, in the scene to be photographed, which will be illuminated by the flash can be selectively illuminated according to the current density distribution, i.e. proportionally to the applied current. An emitter array may also be used in an optical projection system for display illumination in an augmented reality or virtual reality application, for example.

[0006] In addition to providing selective illumination in the visible spectrum, a similar kind of emitter may find use in various other applications. For example, an array of individually addressable infrared emitters can be deployed in a time-of-flight application; an array of individually addressable ultraviolet emitters can be deployed in an industrial UV curing application; etc.

[0007] Regardless of the application in which it is used, it is generally desirable to provide an emitter array in which the individual array elements are optically separate so that crosstalk between adjacent emitters is avoided. In this way, stray light from an active emitter is prevented from passing laterally into an adjacent inactive emitter, and the corresponding regions of the target area or scene will be illuminated with the desired high level of contrast. Optical separation of adjacent array elements can be done in various ways as will be known to the skilled person.

[0008] However, any measures to achieve optical separation can result in visible artefacts in the target area when adjacent array elements are active. For example, the illumination pattern projected into the target area can exhibit a darker "line" between regions illuminated by a pair of adjacent active emitters. In the case of a camera flash, such artefacts may even be noticeable in the resulting image. One approach to avoiding such undesirable lines of lower brightness in the projected illumination pattern might be to arrange discrete emitters closer together to further reduce the physical separation in between, but this can be difficult to achieve because of various constraints such as PCB tolerance, placement tolerance, solder process tolerance etc. For example, emitter dies with an area of 0.5 mm2may require a minimum spacing in the order of 50 pm. In the case of a monolithic die with electrically separate individual segments, the spacing between adjacent emitters can be as small as 8 pm, but even such a narrow separation width can be noticeable as a darker "gap" in the target area when adjacent regions are illuminated by corresponding adjacent emitters.

[0009] A further problem associated with a segmented emitter is that the light around the border of an illuminated region in the target area can have a colour that is noticeably different from the light in the illuminated region. Such artefacts may result from differences in the light propagation through epitaxial layers of a die and through any wavelength conversion layers (optical cross-talk). For example, blue pump light can be converted to white light by means of a suitable phosphor conversion layers applied over each LED, and stray light from the emission area of an active emitter can pass through the conversion layers of an adjacent inactive emitter, resulting in yellowish light.

[0010] A target area illuminated by such a segmented emitter array can therefore comprise primarily white light with discernible yellowish patches. Local colour inhomogeneity in the target area may also result from aggregation of phosphor particles in any wavelength conversion layer of the segmented array.

[0011] Another problem observed when using separate red, green and blue emitters arises from the different luminance profiles, which can result in an uneven appearance of the imaged region.

[0012] Therefore, it is an object of the invention to provide a way of overcoming the problems known from the prior art.

[0013] SUMMARY OF THE INVENTION

[0014] The object of the invention is achieved by the claimed illumination assembly for a portable device, by the claimed method of manufacturing such an illumination assembly, and by a portable device comprising such an illumination assembly.

[0015] In the context of the invention, it shall be understood that the dimensions of the illumination assembly are very small, allowing it to be deployed in a compact portable device application such as a camera phone flash, an augmented reality headset, etc. It may be assumed that the diameter of the imaging lens is very small, for example 1.5 mm - 5 mm (depending on the application), and a correspondingly small thickness of 0.8 mm - 2.5 mm respectively.

[0016] According to the invention, the illumination assembly comprises an array of semiconductor emitters, and an imaging lens arranged above the emitter array and adapted to direct or disperse the light from each emitter of the array into a corresponding target area region, whereby each emitter is associated with a specific region of the target area. The inventive illumination assembly is characterized in that the imaging lens comprises a surface pattern adapted to direct a portion of the light from each emitter beyond the boundary of the target area region of that emitter, i.e. light from neighbouring emitters will overlap in the target area, effectively preventing the separation width between those emitters from being imaged as a darker line in the target area. The arrangement of emitter array and patterned lens is referred to herein as a "patterned assembly". The illumination assembly can comprise any number of such patterned assemblies. Equally, the illumination assembly can comprise further "nonpatterned assemblies", i.e. combinations of emitter arrays and non-patterned lenses. In an embodiment with two or more assemblies, an optical element can be provided to combine the light exiting the lenses and to direct the combined light at the target area.

[0017] The array can comprise any number of emitters in a square or rectangular configuration, for example a 3 x 3 array, a 3 x 4 array, an 8 x 8 array, etc. The emitter array may have equal row heights and column widths, i.e. the emitters may all have the same size. Alternatively, the row heights and / or column widths can differ, and the emitters are not all of equal size. The aspect ratio of the array generally corresponds to the aspect ratio of the individual emitters. The emitters can be top-emitting LEDs, for example, or any suitable semiconductor light-emitting device for the intended application. The lens effectively disperses the light from the emitter area onto the target area, whereby the shape of the target area is generally defined by the shape of the emitter array, i.e. the target area has the same aspect ratio as the emitter array.

[0018] The inventive illumination assembly overcomes the problem of the imaged gaps as described above. While the lens primarily behaves in the conventional manner to project the light from each emitter into the corresponding target area, the surface pattern alters the manner in which the light is projected, and has the effect of preventing the separation width (between any two adjacent active emitters) from being imaged as a darker "gap" in the target area.

[0019] The invention is based on the insight that a suitable surface pattern on the imaging lens can mix light from any two neighbouring emitters by an amount that is just sufficient to "join" or "blend" the corresponding illuminated regions in the target area, but without directing light from one emitter into the target area region of an adjacent emitter. When two or more adjacent emitters are active, the light projected into the target area will therefore exhibit a favourably uninterrupted light pattern, i.e. any two adjacent illuminated regions in the target area will not be separated perceptibly by a darker "dividing line" or imaged gap, i.e. the illumination will appear homogenous to the viewer. A further advantage of the inventive illumination assembly is that it can be realised essentially without any significant additional cost, since it is straightforward to add the surface pattern to the lens surface, for example when the lens itself is being formed.

[0020] Another advantage of the inventive illumination assembly, particularly when used with a segmented emitter, is that the surface pattern can essentially eliminate colour inhomogeneity around the border of an illuminated region in the target area, since the surface pattern mixes light from the outer edges of an emission area with light from within that emission area. In this way, the light arriving at the corresponding region of the target area is favourably homogenous. The surface pattern also ensures that local colour inhomogeneities, which would otherwise arise from an uneven distribution of phosphor particles in a conversion layer, are effectively evened out.

[0021] According to the invention, the method of manufacturing such an illumination assembly comprises the steps of arranging a plurality of emitters in the form of an array; forming an imaging lens to direct the light from each emitter into a corresponding region of the target area, and forming a surface pattern on the imaging lens to direct a portion of the light from each emitter beyond the boundary of the target area region of that emitter.

[0022] The dependent claims and the following description disclose particularly advantageous embodiments and features of the invention. Features of the embodiments may be combined as appropriate. Features described in the context of one claim category can apply equally to another claim category.

[0023] In the following, it may be assumed that the emitter array comprises top-emitting LEDs. Depending on the intended application, the surface area of an emitter can be in the order of 0.06 - 1.0 mm2with a total array size of up to 5 mm2(e.g. for a camera-phone flash application) or even smaller, for example in the order of 0.04 - 0.005 mm2with a total array size of up to 0.36 mm2(e.g. for an AR / VR application) . As indicated above, an emitter array can be made from discrete LEDs, or can be a "segmented emitter" made from a single semiconductor die in which the individual emitters are separated using any appropriate technology. In the following, it may be assumed that the separation width between any two adjacent emitters is at most 50 pm.

[0024] The imaging lens can be of any suitable type, for example a Fresnel lens, a catadioptric lens, etc. As explained above, the imaging lens can be very small and can have a correspondingly small thickness. In the following, the imaging lens may be assumed to have an essentially biconvex shape that refracts the light from the emitter array in such a way as to create a larger "image" of the array at a distance removed from the lens. The lens essentially determines the "field of view" illuminated by the assembly, and may be shaped according to the field of view of a camera for which the illumination assembly is used as a flash. The lens can be made from any suitable material and can be manufactured in any suitable manner. For example, the imaging lens can be made of an epoxy resin or a transparent thermoplastic such as polymethyl methacrylate, polycarbonate etc., and can be manufactured using any suitable technique, for example injection moulding.

[0025] The surface pattern can be formed on the "entrance face" and / or on the "exit face" of the lens of a patterned assembly. In some applications, the exit face of the lens, i.e. the side of the lens that is oriented outward (towards the target area), may be exposed to the environment and may therefore be more vulnerable to damage. Therefore, the surface pattern in such applications is preferably formed on the "entrance face" of the lens, i.e. the side of the lens that is oriented towards the emitter array. In other applications, it may be desirable to provide a pattern on both sides of a lens, i.e. on the entrance face and also on the exit face of the lens. For example, in an RGB application using separate arrays of red-emitting, green-emitting and blue-emitting LEDs, each array is placed under its own imaging lens. In such an application, the red-emitting array is part of a patterned assembly, and a surface pattern may be formed on the entry and exit faces of the "red" imaging lens. In possible embodiment of the invention, the green-emitting and blue-emitting arrays are part of non-patterned assemblies and the surfaces of the respective imaging lenses are smooth. Such a configuration can be sufficient to equalize the luminance profiles of the different-coloured emitters. In a further preferred embodiment of the invention, the green-emitting array and / or the blue-emitting array are part of patterned assemblies, i.e. the light entry face and / or the light exit face of the "green" imaging lens and / or the "blue" imaging lens comprises a surface pattern. In other words, for a multi-colour application, each lens can be patterned according to the colour of the light emitted by the respective emitter array. For each emitter colour, the surface pattern(s) of the respective lens can be chosen accordingly, for example the amplitude and pitch of a sinusoidal surface pattern can be different for each imaging lens, and the parameters of each surface pattern is tailored to the respective colour. An advantage of such a configuration is that the surface patterns of the lenses can be formed to eliminate any imaged dark gaps in the imaged emitters, as well as correcting for differences in the luminance profiles of the different-coloured emitters.

[0026] The inventive illumination assembly can be used in a variety of applications involving a portable (i.e. mobile or handheld) device, for example in an augmented reality (AR) or virtual reality (VR) application to illuminate a "microdisplay" such as an LCOS (liquid crystal on silicon) display incorporated in an AR / VR headset. Equally, the inventive illumination assembly can be used in a flash arrangement of a handheld device such as a smartphone or "camera phone". For example, a camera phone can comprise a number of cameras (each with an image sensor and a lens to determine its field of view); a flash arrangement comprising an instance of the inventive illumination assembly; and a controller for actuating the emitters as appropriate when the camera arrangement is being used to capture an image of the target area or scene.

[0027] An emitter array can be mounted on a substrate with electrical connections to a suitable driver (for example, the emitters can be mounted on a CMOS driver), so that each emitter can be driven independently of the others as required. Each imaging lens of a patterned or non-patterned assembly is arranged over the respective emitter array. In a preferred embodiment, an imaging lens is formed with a flange about its perimeter so that it can be mounted in a housing (for example the rear of a camera phone) that has a corresponding annular aperture. The housing can have an annular chamfer shaped according to the field of view of the emitter array. The surface pattern may be formed in a number of ways. Any surface pattern that achieves the desired objective - namely to eliminate the imaged gap between any two adjacent emitters without altering the aspect ratio of the imaged array - can be used. In a particularly preferred embodiment of the invention, the surface pattern has the form of sinusoidal "ripples" or "waves", with suitable dimensions. The peak height or amplitude of each wave or ridge is preferably very small, and the peak-to-peak distance or pitch is also preferably very small. In the case of a lens with a diameter in the order of a few millimetres, as may be used in a flash application of a camera-phone, the surface pattern has a pitch of at most 1000 pm, more preferably at most 200 pm, and the amplitude of the surface pattern is preferably at most 50 pm, more preferably at most 10 pm. In the case of a very small lens with a diameter in the order of 1.5 mm, as may be used in an AR / VR headset application, the surface pattern can have a pitch of in the range of 60 pm to 200 pm, and an amplitude of up to 5 pm.

[0028] Surface pattern parameters such as pitch and amplitude may be chosen under consideration of relevant lens parameters such as diameter and may also be chosen under consideration of the separation width between emitters. In a particularly preferred embodiment of the invention, the surface pattern is rotationally symmetric, i.e. the microscopically small sinusoidal wave pattern is in the form of concentric rings or ridges separated by grooves or channels. Alternatively, a rotationally symmetric prismatic surface pattern may be formed on the lens surface. Here, instead of a sinusoidal wave, the pattern may have the form of a sawtooth wave.

[0029] Instead of a concentric arrangement of ridges and channels, the surface pattern can comprise an arrangement of many isolated protrusions or "outdentations", for example a multitude of microscopically small rounded or angular "beads" on the surface of the lens. Equally, the surface pattern can comprise an arrangement of rounded or angular indentations, depressions or pits in the surface of the lens. Such a surface pattern can also be rotationally symmetric, for example thousands of microscopically small indentions and / or outdentations arranged in an essentially rotationally symmetric configuration. Equally, an arrangement of rounded and / or angular indentations and / or outdentations can be formed with a random distribution. In a further preferred embodiment of the invention, the surface pattern is a holographic pattern, which may for example be embossed as a relief pattern onto the lens using an electroforming or electrodeposition technique on the moulding tool. In a further embodiment of the invention, the pattern formed on the surface of the lens can be a diffuse pattern, created for example by an electrical discharge machining technique. Regardless of the type of surface pattern, any relevant parameters that define the pattern can depend on the shape and size of the very small lens, and can also depend on the separation width between emitters.

[0030] The surface pattern can be made from the same material as the lens, and can be manufactured using any technique that is suitable for such a small lens. Conventional machining techniques, as used for example in the manufacture of significantly larger automotive front lighting lenses, cannot be deployed. Instead, in a preferred embodiment of the invention, a rotationally symmetric sinusoidal pattern with the very small desired dimensions can be obtained by preparing a corresponding mould using a highly-accurate diamond turning process, and subsequently forming the lens along with the surface pattern using an injection moulding technique. A surface pattern comprising isolated depressions or concentric grooves can be formed using a technique such as five-axis diamond turning to prepare the mould, but high quality milling or drilling procedures may be used if these can provide the desired surface smoothness. A diffuse surface pattern may also be obtained by treating the tool or mould using an electrical discharge machining ("spark erosion") procedure.

[0031] Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 shows an exemplary embodiment of the inventive illumination assembly;

[0034] Figure 2 shows a plan view of the imaging lens of the illumination assembly of Figure 1;

[0035] Figure 3 shows a cross-section through a prior art illumination assembly;

[0036] Figure 4 compares a prior art illumination assembly and the illumination assembly of Figure 1;

[0037] Figure 5 shows a further cross-section through the illumination assembly of Figure 1;

[0038] Figure 6 illustrates the underlying principle of the illumination assembly of Figure 5;

[0039] Figures 7 - 9 show a further embodiment of the invention;

[0040] Figure 10 illustrate the effect of the patterned assembly in an embodiment as shown in Figures 7 - 9;

[0041] Figure 11 and Figure 12 each show a portable device equipped with an embodiment of the inventive illumination assembly.

[0042] Figure 13 shows alternative surface patterns for the lens of the inventive illumination assembly.

[0043] In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

[0044] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] Figure 1 shows an exemplary embodiment of the inventive illumination assembly 1, in cross-section. In this case, the illumination assembly 1 is incorporated in a mobile device such as a camera phone, and comprises a single patterned assembly 10, 11. The diagram shows an emitter array 11 of individually addressable emitters 1 IE mounted on a substrate 12. The emitter array 11 is arranged underneath an imaging lens 10 which defines the field of view of the emitter array 11. Here, the imaging lens 10 has an essentially bi-convex form, and the underside 101 or light entry face 101 of the lens 10 comprises a surface pattern 10S. The enlarged view shows that the surface pattern 10S is essentially sinusoidal, i.e. with the form of a sine wave. The sinusoidal surface pattern can be modulated, i.e. it can have a varying amplitude, for example the amplitude can decrease gradually from a maximum near the lens centre to a minimum near the lens perimeter. Figure 2 shows a plan view of the underside 101 of the lens 10 (as "seen" from the emitter array), showing that the rotationally symmetric surface pattern 10S has the form of concentric ripples.

[0046] The surface pattern 10S can be microscopically small. For example, the lens 10 of Figures 1 - 2 may have a diameter in the order of 5 mm and a thickness of about 2.5 mm, and the amplitude 10A and pitch 10P of the surface pattern 10S can be up to 5 pm and 160 pm respectively.

[0047] Figure 3 shows a cross-section through a prior art illumination assembly. Here also, a 3 x 3 emitter array is arranged underneath a biconvex imaging lens 70, which has an unmodified light entry surface. Light rays from the emitters 1 IE are refracted by the lens 10 and imaged at the target area T. Since adjacent emitters 1 IE are separated by gaps 11G from which no light originates, these "dark lines" are also imaged at the target area T, which shows corresponding imaged gaps Gimage between the imaged emitters 7Eimage. As explained above, scattering or other effects at the edge of an emitter 1 IE can alter the colour of the light, so that the light at the border of an illuminated target region 7Eimagecan have a colour that is noticeably different from the colour within the illuminated target region 7Eimage.

[0048] Figure 4 compares a conventional illumination assembly (top row) and the inventive illumination assembly (bottom row), in each case for a 3 x 3 emitter array positioned below an imaging lens. In order to demonstrate the effect of the emitter array, the target area is a simple flat surface. To illuminate a target area with a specific aspect ratio, for example a conventional aspect ratio of 4:3 used in a camera flash application, the emitter array will have the same overall aspect ratio. The shapes and relative sizes of the emitters are repeated in the target area. The conventional illumination assembly uses a plain biconvex lens; the inventive illumination assembly uses a similar lens, modified with a surface pattern 10S as shown in Figures 1 - 2. The upper left image 41 and lower left image 43 show the illumination distribution when only the central emitter is active. The lower left image 43 demonstrates that the modified lens 10 of the illumination assembly 1 steers or refracts the light from an emitter in a manner similar to the lens of the conventional assembly, i.e. the lens directs the light from each emitter at a specific region of the target area, while the surface pattern spreads the light in such a way that colour and / or brightness inhomogeneities are essentially blended out and no longer appear in the illuminated target area 430.

[0049] The upper right image 42 and lower right image 44 show the illumination distribution when all nine emitters are active. In the upper right image, the imaged emitter regions 420 are separated by darker imaged gaps 421 (appearing as two dark rows and two dark columns). The lower right image 44 demonstrates that the surface pattern 10S on the modified lens 10 of the illumination assembly 1 spreads the light from the emitters in such a way that the gaps between emitters are not imaged, so that the resulting illumination distribution is uniform and does not exhibit any dark regions between the nine imaged emitter regions 440.

[0050] Although this cannot be shown in a monochrome diagram, the surface pattern also has the effect of eliminating colour inhomogeneities, for example colour inhomogeneities arising from optical cross-talk and / or an uneven distribution of phosphor particles in the wavelength conversion layer(s).

[0051] Figure 5 shows a further cross-section through the illumination assembly 1 of Figure 1, and shows exemplary light rays to illustrate the principle of operation. Light rays from the emitters 1 IE are refracted by the lens 10 and spread, so that the imaged emitters Eimage overlap in the indicated regions 5, so that the light from adjacent emitters forms an uninterrupted illuminated region at the target area T.

[0052] Figure 6 illustrates the underlying principle of the illumination assembly of Figure 5. The diagram shows the emitter array 11 and the biconvex imaging lens 10. Exemplary rays from active emitters 1 IE show how the light is "mixed" or directed by the imaging lens 10 and its surface pattern 10S. As can be seen on the left, light (represented by exemplary light rays 61, 62) from adjacent active emitters 1 IE is mixed in such a way as to avoid the gap G being imaged in the target area. As can be seen on the right, light from the edge of an emitter (represented by exemplary light ray 63) is mixed with light from further inside the emitter area (represented by exemplary light ray 64) to ensure colour homogeneity of the light in the illuminated target region Eimage.

[0053] Figures 7 - 9 illustrate a further exemplary embodiment of the inventive illumination assembly 1. In this case, the illumination assembly 1 is intended for use in a device such as an augmented reality headset as shown in Figure 12, and comprises a red- emitting array 11R, a blue-emitting array 1 IB and a green-emitting array 11G. Each array is an 8 x 8 array of emitters.

[0054] The emitter arrays 11R, 11G, 1 IB can be mounted close together on a common substrate or printed circuit board for connection to driver circuitry, as indicated in Figure 7. Each emitter array 11R, 11G, 1 IB is arranged underneath its respective imaging lens 10R, 10G, 10B. Here, each imaging lens 10R, 10G, 10B has an essentially bi-convex form as shown in Figure 8, and the lenses are very similar in shape. The device may be assumed to comprise a means of combining the light from the lenses 10R, 10G, 10B (for example an arrangement of dichroic beam splitters) and directing the combined light at the target area. The target area will therefore comprise 8 x 8 regions which can be illuminated as desired by activating the respective emitters of the emitter arrays HR, 11 G, 11B.

[0055] Various configurations are possible: for example, only the red-emitting array 11R may be part of a patterned assembly 10R, 11R, while the green and blue arrays can each be part of a non-patterned assembly. In an alternative realisation, the lens for the red- emitting array HR can comprise a surface pattern on its entry face and also its exit face, while the lenses for the blue-emitting and green-emitting arrays are patterned only on their entry faces. Equally, the green-emitting array 11G and / or the blue-emitting array 1 IB can be part of a patterned assembly, with a lens having a surface pattern on its entry face or its exit face.

[0056] Figure 8A shows a possible arrangement for the emitter arrays. Here, a red emitter array 11R (i.e. an array of emitters that emit red light), a green-emitting array 11G (i.e. an array of emitters that emit green light) and a blue-emitting array 1 IB (i.e. an array of emitters that emit blue light) are arranged side by side. Their lenses 10R, 1OG, 1OB are arranged accordingly.

[0057] Figure 8B shows a further possible arrangement for the emitter arrays. Here, a greenemitting array 11G and a blue-emitting array 1 IB are arranged side by side, and a red emitter array 11R is arranged perpendicular to the other two arrays 11G, 1 IB. Their lenses 10R, 10G, 10B are arranged accordingly. The light exiting the lenses 10R, 10G, 10B is combined using dichroic beam splitters 24, each designed to transmit red light and to reflect blue / green light.

[0058] Figure 9 shows an outline of the imaging lens 10R of the red-emitting array overlaid on an outline of the imaging lens 10G of the green-emitting array HR (i.e. an array of emitters that emit green light). Both surfaces (light entry surface 101 and light exit surface 102) of the "red" imaging lens 10R (drawn using the thicker line) are patterned with a concentric sinusoidal or ripple pattern as shown in the enlarged portions, while the "green" imaging lens (drawn using the thinner line) is not patterned. The surface pattern 10S can be microscopically small. For example, each lens 10R, 10G, 10B of the illumination assembly of Figures 7 - 9 may have a diameter in the order of 1.5 mm and a thickness of about 1 mm, and the amplitude and pitch of the surface pattern 10S on the light exit surface 102 of the "red" imaging lens 10R can be 5 pm and 80 pm respectively, while the amplitude and pitch of the surface pattern 10S on the light entry surface 101 of the "red" imaging lens 10R can be 5 pm and 80 pm respectively.

[0059] Figure 10 illustrates the effect of the patterned assembly 10R, 11R in the embodiment of Figures 7 - 9. The upper part of the diagram shows four sets of intensity profiles P11, P12, P13, P14 (each indicating the red-emitter light intensity Pred by the solid line; a green-emitter light intensity Pgreen by the dashed line; and the blue-emitter light intensity Pbiue by the dotted line) for the four pixels in the topmost row of the upper-left quadrant of the target area. A similar set of intensity profiles (i.e. with similar amplitudes) may be assumed for the other three rows of that quadrant; and the following explanation applies equally to the other three quadrants.

[0060] The lower part of the diagram also shows equivalent intensity profiles NP11 - NP14 for a prior art emitter-lens configuration (here also, the diagram indicates the red-emitter light intensity NPred by the solid line; the green-emitter light intensity NPgreen by the dashed line; and the blue-emitter light intensity NPbiue by the dotted line). In the prior art configuration, none of the lenses has a patterned entry face or exit face, and as a result the intensity profile of the red light has a more "rectangular" shape compared to the "Gaussian" shape of the intensity profiles of the blue and green light. These profile shape differences as indicated in the diagram result in an uneven distribution of light over the target area, which can be perceived by the viewer as colour shadows.

[0061] The comparison shows that the effect of the patterned assembly 10R, 11R is to adjust the intensity profile of the red light so that it very closely matches the intensity profiles of the green and red light. From the user's point of view, the benefit of the inventive illumination assembly is that the imaged colours appear favourably homogenous, and the intensity of light over the target area appears favourably uniform. Particularly in the case of a device such as an augmented reality headset, the use of a patterned assembly can contribute significantly to user comfort by presenting clear RGB images without colour shadows or borders.

[0062] Figure 11 shows a portable device 2 equipped with an embodiment of the inventive illumination assembly 1. Here, the device is a camera phone 2 which is equipped with several cameras 20 and a flash 21. The flash 21 comprises the inventive illumination assembly 1 of Figure 1, with the lens 10 mounted in the housing 23 of the camera phone 2. With the emitter array 11 of the patterned assembly 10, 11, the flash 21 can illuminate a target area that is typically at most a few metres away from the camera. As indicated, the camera phone 2 has a controller 22 for controlling the image sensors of the cameras 20 and the emitters 1 IE of the illumination assembly 1.

[0063] Figure 12 shows another type of portable device 2 equipped with an embodiment of the inventive illumination assembly 1 as explained in Figures 7 - 10. Here, the device is an AR headset 25, incorporating a micro-display 26 that is illuminated by an embodiment of the illumination assembly 1, and various optics for shaping the light, for example beam-splitters, a projection lens, etc. These components are arranged in the headset frame as indicated in this exemplary embodiment (equally, the components could be arranged in the bridge of the headset frame; in a larger AR / VR visor, the components can be arranged above the wearer's eyes). In contrast to the camera phone application of Figure 11, the target area T is even closer to the illumination assembly 1, which can be used to project small images from the display 26 into the lower part of the right-hand glass of the headset. The diagram shows exemplary icons being projected into the user's field of view. Equally, video sequences generated by a navigation app or similar can be projected into the user's field of view.

[0064] Figure 13 shows alternative surface patterns IOS that may be applied to an imaging lens, for example to the imaging lens 10 of Figure 1. In the upper part of the diagram, the convex shape of the underside 101 of a lens 10 is augmented by a rotationally symmetric prismatic surface pattern 10S. Here, the surface pattern 10S can be regarded as concentric rings of tightly-packed small prisms, and the prisms can be formed by appropriately shaped angular outdentations 10S2 (protrusions) or angular indentations 10S3. Equally, the surface pattern 10S can comprise continuous concentric prisms.

[0065] In the lower part of the diagram, the underside 101 of a biconvex lens 10 is augmented by a surface pattern 10S comprising rounded protrusions 10S2 or flat "bumps" 102 arranged in a dense or closely-packed configuration. Equally, the surface pattern 10S can be defined as an arrangement of inversely- shaped indentations 10S3.

[0066] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0067] For the sake of clarity, it is to be understood that the use of "a" or "an" throughout this application does not exclude a plurality, and "comprising" does not exclude other steps or elements. Reference signs illumination assembly imaging lens 10, 10R, 10G, 10B surface pattern IOS amplitude 10A pitch 10P light entry face 101 light exit face 102 protrusion 10S2 indentation 10S3 emitter array 11, HR, 11G, 11B emitter HE gap 11G substrate 12 device 2 camera arrangement 20 flash arrangement 21 controller 22 housing 23 dichroic beam splitter 24 headset 25 micro-display 26 image 41 - 44 imaged emitter 410, 420 imaged gap 421 imaged emitter 430, 440 target area T imaged gap Gimage imaged emitter Eimage illuminated overlap 5 light ray 61 - 64 prior art assembly 7 imaging lens 70 imaged emitter 7Eimage light intensity Pred, Pgreen, Pblue, NPred, NPgreen, NPblue luminance profile Pl 1, P12, P13, P14; NP11, NP12, NP13, NP14

Claims

CLAIMS1. An illumination assembly (1) for a portable device (2), comprising an array (11, 11R) of semiconductor emitters (1 IE); an imaging lens (10, 10R) arranged above the emitter array (11, 11R) and adapted to direct the light from each emitter (1 IE) into a corresponding region (1 lEimage) of a target area (T); characterized in that the imaging lens (10, 10R) comprises a surface pattern (10S) adapted to shape the light from adjacent emitters (1 IE) such that the corresponding imaged emitter regions (1 lEimage) overlap at the target area (T).

2. An illumination assembly according to the preceding claim, wherein the surface pattern (10S) is a sinusoidal pattern.

3. An illumination assembly according to any of the preceding claims, wherein the surface pattern (10S) is rotationally symmetric.

4. An illumination assembly according to any of the preceding claims, wherein the surface pattern (10S) has a pitch (1 OP) in the range of 60 pm to 1.0 mm.

5. An illumination assembly according to any of the preceding claims, wherein the surface pattern (10S) has a maximum amplitude (10A) in the range of 5 pm to 0.1 mm.

6. An illumination assembly according to any of the preceding claims, wherein the array is a red emitter array (HR), and wherein the illumination assembly (1) further comprises a blue emitter array (1 IB) and an imaging lens (10B) arranged above the blue emitter array (1 IB); and a green emitter array (11G) and an imaging lens (10G) arranged above the green emitter array (11G).

7. An illumination assembly according to the preceding claim, further comprising a surface pattern (10S) on the light exit face (102) of the imaging lens (10R) of the redemitter array (HR).

8. An illumination assembly according to claim 6 or claim 7, wherein the one or more surface patterns (IOS) on the imaging lens (10R) of the red emitter array (11R) are formed to equalize the light intensity (Pred) of the red emitter array (11R) to the light intensities (Pgreen, Pbiue) of the blue emitter array (1 IB) and the green emitter array (11G).

9. An illumination assembly according to any of the preceding claims, wherein the surface area of an emitter (1 IE) is in the range 0.004 - 1.0 mm2.

10. An illumination assembly according to any of the preceding claims, wherein adjacent emitters (1 IE) of an emitter array (11, HR, 11G, 1 IB) are separated by a gap in the order of 8 pm.

11. An illumination assembly according to any of the preceding claims, wherein an imaging lens (10, 10R, 10G, 10B) is made from a transparent thermoplastic material and / or wherein an imaging lens (10, 10R, 10G, 10B) is formed by injection moulding.

12. A method of manufacturing an illumination assembly (1) according to any of claims 1 to 11, which method comprises the steps of arranging a plurality of emitters (1 IE) in the form of an array (11, 11R); providing an imaging lens (10, 10R) to direct the light from the emitter array (11, 11R) into a target area (T); and forming a surface pattern (10S) on the imaging lens (10, 10R) to shape the light from adjacent emitters (1 IE) such that the corresponding imaged emitter regions (1 lEimage) overlap at the target area (T).

13. A method according to the preceding claim, wherein the array is a red emitter array (11R), and wherein the method further comprises steps of arranging a blue emitter array (1 IB) and a green emitter array (11G) adjacent to the red emitter array (HR); and arranging an imaging lens (10B) above the blue emitter array (1 IB) and arranging an imaging lens (10G) above the green emitter array (11G).

14. A method according to the preceding claim, comprising a step of arranging a colour combiner (24) above the imaging lenses (10R, 10G, 10B).

15. A portable device (2) comprising an illumination assembly (1) according to any of claims 1 to 11.

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