WO2013175232A2

WO2013175232A2 - Media exposure device

Info

Publication number: WO2013175232A2
Application number: PCT/GB2013/051381
Authority: WO
Inventors: Trevor Elworthy
Original assignee: Lumejet Holdings Limited
Priority date: 2012-05-24
Filing date: 2013-05-24
Publication date: 2013-11-28
Also published as: GB201309415D0; GB2504199A; GB201209142D0; WO2013175232A3

Abstract

This invention relates to a media exposure device for directly exposing a photographic print medium to radiation emitted from the device. The media exposure device comprises a plurality of radiating members (12), each radiating member including a set of radiating elements (26), the radiating elements (26) in the set being spaced in a predetermined pattern; each radiating member (12) being fixed in relation to at least one other radiating member (12) such that corresponding sets of radiating elements (26) of each of the radiating members (12) form a continuous set of radiating elements (26) in a predetermined alignment, and radiation modification means for modifying and emitting from the device radiation originally emitted by the radiating elements, the radiation emitted by the device being focused onto the print medium by the modification means at a distance which is within a particular range of distances from the device thereby to expose the print medium. A media exposure system and method, and method of manufacturing the same are also disclosed.

Description

MEDIA EXPOSURE DEVICE

This invention relates to a media exposure device, a media exposure system and a method of constructing a media exposure device. This invention also relates to a method of operating a media exposure device or media exposure system.

Optical media exposure devices typically operate in accordance with a moving head, moving media principle, similar to a scanning inkjet. This has the advantage of using a controllable number of 'macro' Light Emitting Diodes (hereinafter "LEDs") which are commercially available at low prices, which can be packaged using conventional wire bonding technologies and can be thermally managed.

The technology can be easily extended for larger or faster applications by a redesign of the head transport mechanism (to expose longer swathes), adding additional memory in the print buffers (to expose wider swathes), or adding more heads (to increase the speed of the exposure).

However, a moving head will always have certain physical limits to exposure speed, governed by the mass and inertia of the payload. More heads may be added, to increase the effective swathe width per pass, but this increases mass. It is therefore necessary to either reduce the speed of exposure or to increase the width of the exposure device to allow for longer acceleration and deceleration periods.

A media exposure device operating in accordance with a moving head moving media principle is thus not suitable for certain applications, for example where printing speed is critical, a smaller packaging volume is required, or smaller exposure sizes are required.

The present invention aims to alleviate at least some of these problems. According to one aspect of the present invention, there is provided a media exposure device for exposing a medium, the media exposure device comprising a plurality of radiating members each defining opposing edges which are complementary to one another; each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; each radiating member being fixed in abutment with at least one other radiating member along each of their respective complementary edges such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment.

The terms medium / media, as used herein, refer to any media that may be optically exposed so that an image, pattern or mark can then be generated on the media. An illustrative example of such media is photographic paper. It should also be remembered that where the term 'printing' or other related terms are used, it is not intended to refer to the deposition of inks and such like onto media. In general terms, 'printing' in the context of the present application is the exposure of print media with light and/or radiation, and (optionally) the treatment of that media to yield an image, pattern or mark.

According to another aspect of the invention, there is provided a media exposure device for directly exposing a photographic print medium to radiation emitted from the device, the media exposure device comprising: a plurality of radiating members, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; each radiating member being fixed in relation to at least one other radiating member such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment, and radiation modification means for modifying and emitting from the device radiation originally emitted by the radiating elements, the radiation emitted by the device being focused onto the print medium by the modification means at a distance which is within a particular range of distances from the device thereby to expose the print medium. Preferably, the radiation modification means includes at least one lens, each lens being disposed in an arrangement wherein radiation emitted by one or more of the radiating elements is emitted from the device by the lens.

Preferably, the radiation modification means comprises a microlens array. Preferably, the radiation modification means comprises a macrolens array.

Preferably, the radiation modification means comprises a telecentric lens.

Preferably, the radiation modification means includes a tapered bundle of optic fibres of a predetermined length, each fibre having substantially the same orientation and substantially the same tapered profile, the tapered bundle thereby defining a planar wide end and a planar narrow end and being disposed in an arrangement wherein the planar wide end is adjacent the radiating elements. Preferably, the radiation modification means comprises a telecentric lens and a bundle of optic fibres aligned with the telecentric lens.

Preferably, the continuous set of radiating elements is operable to cause a swathe to be exposed on the medium through the controlled emission of radiation from the radiating elements.

Preferably, the photographic print medium is silver-halide based photosensitive paper.

Preferably, the sets of radiating elements are in the form of a plurality of rows of radiating elements which are parallel to one another.

Preferably, successive rows are offset relative to one another.

Preferably, the radiating elements are in the form of micro LEDs with a pixel size between 1 pm and 150pm, preferably 60pm, and more preferably 63.5 pm. Preferably, the micro LEDs are provided on semiconductor solid state dies.

Preferably, the solid state dies are in the form of flip-chips. Preferably, the micro LEDs are formed of GaN (Gallium Nitride) and/or GaAIN (Gallium Aluminium Nitride) such that they are adapted to emit light preferably in at least three primary colours preferably to match the spectral response of colour sensitive silver halide paper. Preferably, the radiating elements are in the form of organic LEDs with a pixel size between 1 pm and 150pm, preferably 60pm, and more preferably 63.5 pm.

Preferably, the radiating elements are each in the form of a plurality of micro LEDs arranged to form a cluster.

Preferably, the cluster is substantially circular.

Preferably, reflectors are provided to reflect light towards the photographic print medium, and preferably where the reflectors are fabricated in GaN or GaAIN.

Preferably, the reflectors are parabolic.

Preferably, the media exposure device includes a mounting structure to which the radiating members are fixed.

Preferably, the mounting structure is in the form of a silicon substrate.

Preferably, each radiating member is fixed to said mounting structure via solder bumps. Preferably, sets of solder bumps are locatable on said mounting structure such that adjacent radiating members are located in abutment with one another. Preferably, solder bump location sites are provided on the mounting structure.

Preferably, the media exposure device comprises a support structure including a plurality of conduits for the passage of cooling fluid.

Preferably, the plurality of conduits are provided by a sintered block.

Preferably, the sintered block is formed of copper.

Preferably, the media exposure device comprises at least one Peltier device for cooling the support structure.

Preferably, the radiating members each define opposing edges which are complementary to one another, each radiating member being fixed in abutment with at least one other radiating member along each of their respective complementary edges.

Preferably, each radiating member includes one or more further sets of radiating elements, and wherein the corresponding sets of radiating elements of each of the radiating members form continuous sets of radiating elements in a predetermined alignment.

Preferably, each radiating member is offset in relation to at least one adjacent radiating member in a direction transverse to the direction of alignment.

Preferably, each radiating member has a substantially planar parallelogrammatic shape in which the edges are diagonal to the orientation of the aligned radiating elements.

Preferably, the radiating elements are equally spaced apart, and preferably the spacing between radiating elements in each set being the same as the spacing between radiating elements on either side of the abutment between the neighbouring radiating members. According to a further aspect of the invention, there is media exposure device for directly exposing a medium to radiation emitted from the device, the media exposure device comprising: a plurality of radiating members, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; each radiating member being fixed in relation to at least one other radiating member such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment, and wherein the media exposure device includes a mounting structure to which the radiating members are fixed, each radiating member being fixed to said mounting structure via at least one solder bump, wherein solder bump location sites are provided on the mounting structure such that at least one set of solder bumps is locatable on said mounting structure such that adjacent radiating members are located in abutment with one another.

Preferably, the radiating elements are each in the form of a plurality of (micro) LEDs arranged to form a cluster.

According to yet a further aspect of the invention there is provided a media exposure device for directly exposing a medium to radiation emitted from the device, the media exposure device comprising: a plurality of radiating members, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; each radiating member being fixed in relation to at least one other radiating member such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment, and wherein the radiating elements are each in the form of a plurality of (micro) LEDs arranged to form a cluster, the cluster preferably being substantially circular. According to a further aspect of the invention, there is provided a media exposure system for exposing a medium, the media exposure system comprising a plurality of media exposure devices each in the form of a media exposure device as herein described.

Preferably, the media exposure devices are disposed adjacent one another transverse to the direction of movement of the medium through the system.

Preferably, the media exposure system includes: at least one red light media exposure device in which the radiating elements emit radiation including radiation in the red portion of the visible electromagnetic spectrum; at least one blue light media exposure device in which the radiating elements emit radiation in the blue portion of the visible electromagnetic spectrum; and at least one green light media exposure device in which the radiating elements emit radiation in the green portion of the visible electromagnetic spectrum. According to a further aspect of the invention, there is provided a media exposure device for directly exposing a photographic print medium, the media exposure device comprising: one or more sets of organic light emitting diodes; and a substrate on which the organic light emitting diodes are fixed; each set of organic light emitting diodes being disposed in a configuration wherein they are operable to cause a swathe to be exposed on the medium through the controlled emission of radiation from the organic light emitting diodes.

Preferably, the one or more sets of organic light emitting diodes are arranged as offset rows.

Preferably, the substrate on which the organic light emitting diodes are deposited is a glass substrate.

Preferably, the media exposure device comprises a plurality of glass substrates in the form of radiating members, each defining opposing edges which are complementary to one another; each radiating member being fixed in abutment with at least one other radiating member along each of their respective complementary edges such that corresponding sets of organic light emitting diodes of each of the radiating members form a continuous set of organic light emitting diodes in a predetermined alignment. Preferably, each radiating member has a substantially planar parallelogrammatic shape in which the edges which abut adjacent radiating members are diagonal to the orientation of the aligned radiating elements.

Preferably, the organic light emitting diodes are equally spaced apart, and preferably the spacing between organic light emitting diodes in each set being the same as the spacing between organic light emitting diodes on either side of the abutment between the neighbouring radiating members.

Preferably, at least one of the sets of organic light emitting diodes emit radiation including radiation in the red portion of the visible electromagnetic spectrum; at least one of the sets of organic light emitting diodes emit radiation including radiation in the blue portion of the visible electromagnetic spectrum; and at least one of the sets of organic light emitting diodes emit radiation including radiation in the green portion of the visible electromagnetic spectrum.

Preferably, the media exposure device includes radiation modification means for modifying and emitting from the device radiation originally emitted by the radiating elements. Preferably, the radiation modification means includes a tapered bundle of optic fibres of a predetermined length, each fibre having substantially the same orientation and substantially the same tapered profile, the tapered bundle thereby defining a planar wide end and a planar narrow end and being disposed in an arrangement wherein the planar wide end is adjacent the radiating elements.

Preferably, the radiation modification means includes at least one lens, each lens being disposed in an arrangement wherein radiation emitted by one or more of the radiating elements is emitted from the device by the lens, the radiation emitted by the device being focused by the lens at a distance which is within a particular range of distances from the device.

Preferably, the radiation modification means comprises a macrolens array.

Preferably, the radiation modification means comprises a telecentric lens. Preferably, the radiation modification means comprises a telecentric lens and a bundle of optic fibres aligned with the telecentric lens.

Preferably, the radiation modification means comprises a microlens array. According to another aspect of the invention, there is provided a method of printing onto a photosensitive medium using a media exposure device or system as herein described, the method comprising exposing the medium to a swathe of radiation emitted from the device or system, and causing relative movement between the medium and the device so as to expose successive adjacent portions of the medium to further swathes of radiation emitted from the device or system.

Preferably, the medium is colour photographic paper such as silver halide paper.

Preferably, the radiating elements are arranged to form rows of printable pixels, and exposing the medium to a swathe of radiation comprises addressing the elements in each row by first addressing every Nth element in each row, and subsequently addressing every N+1th element in the row, and preferably where the method comprises addressing all the elements in each Nth radiating member, and subsequently addressing all the elements in every N+1th radiating member.

According to a further aspect of the invention, there is provided a method of constructing a media exposure device, comprising: providing a plurality of radiating members each defining opposing edges which are complementary to one another, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; providing a mounting structure to which said radiating members are to be fixed; placing the radiating members on said mounting structure in abutment with another other along each of their respective complementary edges such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment; and fixing said radiating members to the mounting structure.

Preferably, the method further comprises fixing the radiating members to said mounting structure via solder bumps.

Preferably, the method further comprises depositing sets of solder bumps on said mounting structure corresponding to each radiating member such that adjacent radiating members can be located in abutment with one another.

Preferably, the method further comprises lithographically etching solder bump location sites on to the mounting structure in a prior step.

Preferably, the solder bump location sites are etched onto the mounting structure in a predefined arrangement so that adjacent radiating members are aligned in abutment with one another. Preferably, the method further comprises lithographically etching solder bump location sites on to the radiating elements.

Preferably, the solder bump location sites are etched onto the radiating elements in a predefined arrangement so that adjacent radiating members are aligned in abutment with one another. Preferably, the radiating members are fixed to said mounting structure by the melting and subsequent re-solidification of said solder bumps.

The invention extends to any novel aspects or features described and/or illustrated herein.

Further features of the invention are characterised by the other independent and dependent claims. The invention extends to methods and/or apparatus substantially as herein described with reference to the accompanying drawings.

Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features disclosed in the description, and (where appropriate) the claims and drawings in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. The present invention will now be described, purely by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows a schematic view of a media exposure device in accordance with the invention;

Figure 2A shows a schematic view of mounted micro LED dies of the media exposure device of Figure 1 in plan view with a microlens array removed; Figure 2B shows an enlarged view of a portion of the media exposure device of Figure 2A;

Figure 2C is an enlarged view of a radiating element of the device of Figure 1 according to one example;

Figure 2D is a schematic view of mounted micro LED dies according to another example;

Figure 2E is a schematic view of mounted micro LED dies according to a further example;

Figure 2F is a schematic view of another example of mounted LED dies according to the invention;

Figure 2G is a schematic view showing the arrangement of the micro LEDs of Figures 2D, 2E or 2F;

Figure 3 shows a plan view of a microlens array of the media exposure device of Figure 1 ; Figure 4 shows a schematic view of micro LEDs and a telecentric lens of a media exposure device in accordance with the invention; Figure 5 shows a schematic view of micro LEDs, a telecentric lens and an optic fibre bundle of a media exposure device in accordance with the invention; Figure 6A shows a schematic view of a media exposure system in accordance with the invention;

Figure 6B shows a schematic view of a media exposure system in accordance with another example;

Figure 7 shows a schematic view of the media exposure system of Figure 6 in plan view with the microlens arrays removed;

Figure 8 shows a glass substrate with organic LEDs mounted thereon of a media exposure device in accordance with the invention;

Figure 9 shows a schematic view of the media exposure device of Figure 1 showing one example of the placement of solder bumps; and Figure 10 shows a flowchart of a method of constructing a media exposure device in accordance with the invention.

With reference to Figures 1 to 3 of the drawings, a schematic view of a media exposure device for exposing a medium in accordance with the invention is designated, generally, by the reference numeral 10. The media exposure device 10 includes, broadly, a plurality of radiating members in the form of micro LED semiconductor dies 12, radiation modification means in the form of a microlens array 14, a mounting structure in the form of a silicon microbench 16, a printed circuit assembly 20 and control circuitry 21. Each micro LED die 12 includes two sets 22, 24 of aligned radiating elements in the form of micro LEDs 26, each of which acts as an emitter to produce a spot of light or pixel of the image to be formed. The micro LEDs produce high intensity, quasi-collimated light directly from the surface of the die 12. The two sets 22, 24, configured as offset rows, allow for Gaussian overlap of the radiation emitted from two LEDs onto an exposed spot, thus reducing the effects of 'microbanding', where certain areas are either under- or over-exposed. In other examples, there may be more than two rows, indeed a two- dimensional array could be constructed to further alleviate the problem of microbanding, and to increase the exposure level attainable at a particular spot. Further, each micro LED die 12 has a substantially planar parallelogrammatic shape, consequently defining a pair of opposing complementary angled edges. More particularly, each micro LED die 12 is in the form of a flip chip having the micro LEDs 26, tracking 27 and connectors or wire bonds 28 disposed on a major side of the micro LED die 12. Utilising flip chip LEDs is advantageous over traditional top-emission LEDs as they typically provide better current spreading higher light extraction efficiency, better thermal dissipation capability and better optical coupling to further optical components such as lenses. The tracking 27 and wire bonds 28 electrically connect the LEDs 26 to the printed circuit assembly 20 via the silicon microbench 16. The dies 12 are physically attached via their opposing major side to the silicon microbench 16 by means of solder bumps 46 (see Figures 1 and 6) which also ensure correct alignment of the dies 12 as is described in more detail below. The control circuitry may optionally be optically printed, for example using an exposure device according to this invention.

This produces an addressable and controllable micro array for emitting radiation with minimal cross talk between the individually addressable pixels of the array. The array may for example be at least about 308mm wide.

Figure 2B shows an enlarged view of an intersection between two LED dies 12. The alignment of neighbouring dies 12 ensures that the distance A between LEDs next to one another on the same die is the same as the distance B between LEDs next to one another, but on different dies 12. The angled dicing of the dies 12 allows for easier alignment in the 'x' and y directions. Further details relating to this alignment are provided below with reference to Figures 9 and 10. Each LED die 12 is shown to have 10 LEDs 26 in each row 22, 24 for clarity; in a preferred embodiment there are 128 LEDs 26 in each row 22, 24. In other embodiments, and depending on the desired printing quality and/or speed, there may be more or less LEDs 26 in each row 22, 24. In the example shown in Figure 2A the LEDs are offset so that the LEDs on the edge of a row are 5 diagonal to the angle of dicing. In an alternative example (see Figure 2E) the offset LEDs are aligned so that they are parallel to the angle of dicing.

Figure 2C shows an enlarged view of a single micro LED 26. In a preferred example, each radiating element in the form of a micro LED 26 is formed of a cluster of separate

10 smaller micro LEDs 25. In the example shown in Figure 2C, 9 LEDs 25 each with a spot size D of about 19 microns clustered together to form a source of light with a diameter C of about 60 microns, and in one preferable embodiment 63.5pm, are shown. The micro LEDs of each cluster are connected in parallel so as to act as a single emitter or pixel. Alternatively the cluster may be formed of a different number of micro LEDs, for example

15 19.

This arrangement may produce a brighter highly focussed beam, for example with an emission angle of about plus or minus 30 degrees. In one example, parabolic reflectors (not shown) are provided for each of the micro LEDs in the cluster to increase the 20 effective power output and reduce the emission (cone) angle to plus or minus 30 degrees. The parabolic reflectors may be fabricated in the GaN (Gallium Nitride) and/or GaAIN (Gallium Aluminium Nitride) substrate of the micro LEDs or micro LED cluster, for example, the reflectors may be etched into the semiconductor material of the substrate.

25 The silicon microbench 16 includes a stable substrate with accurately plotted sets of solder pads 29 provided thereon. The configuration of the solder pads 29 corresponds to the configuration of the wire bonds 28 of the LED dies. Each micro LED 26 is electrically connected to the silicon microbench 16 by soldering the wire bond 28 of each micro LED 26 to a corresponding solder pad 29 of the silicon microbench 16. The silicon

30 microbench 16 is mounted on the printed circuit assembly 20. The control circuitry 21 (which typically includes a Field-Programmable Gate Array (FPGA)), in one example, is mounted on the side of the printed circuit assembly 20 opposite to the side of the printed circuit assembly on which the silicon microbench 16 is mounted.

In one example, the micro LED dies 12 are aligned end-to-end and in abutment with one another to form a bar 30 of micro LED dies. The micro LED dies 12 at the opposing ends of the bar 30 are each fixed in abutment along one of its angled edges with an adjacent micro LED die. The micro LED dies intermediate the micro LED dies 12 at the opposing ends of the bar are each fixed along both of its angled edges in abutment with one each of different adjacent micro LED dies. The micro LED dies 12 are fixed in a configuration wherein corresponding sets 22, 24 of the micro LEDs 26 of adjacent micro LED dies are aligned with one another thereby forming rows 32, 34 of aligned micro LEDs. The alignment is accurate to micron tolerances such that the micro LEDs of each row are aligned with precise continuity of pitch. The rows of micro LEDs 32, 34 are offset relative to one another. Each of the micro LEDs is fabricated in its die in Gallium Nitride (Green and Blue) or Gallium Aluminium Nitride (Red). The micro LEDs have a pixel size of 60 pm to expose the medium at 60pm spot sizes. The LEDs are spaced by 120 pm centre- to-centre, thus a gap of 60 m is provided between LEDs. This gap is maintained for neighbouring LEDs which are on different dies 12, as described in more detail below. In the example illustrated in Figure 2A, the bar 30 is made up of three micro LED dies 12. In other examples, the number of dies 12 is tailored to suit the width of the medium that is to be exposed, for example, many more dies 12 may be provided so that the bar 30 spans the entire width of the medium to be printed.

The rows 32, 34 of micro LEDs 26 of the bar 30 are disposed in a configuration wherein they can emit radiation towards the medium. Each of the micro LEDs of the bar is individually controllable. The micro LEDs of each row are operable to emit radiation in a controlled fashion thereby to expose a swathe of the medium.

The microlens array 14 is mounted adjacent to the micro LED dies 12 in an arrangement wherein each lens of the microlens array is aligned with a particular micro LED. ln use, each of the rows 32, 34 of micro LEDs 26 are operable to cause a swathe to be exposed on the medium through the controlled emission of radiation from the micro LEDs of the row. Radiation emitted by each micro LED is emitted from the media exposure device 10 from a point located along an outwardly facing surface of the lens of 5 the microlens array 14 which is aligned with the micro LED. Each lens focuses the radiation of its corresponding LED at a distance which is within a particular range of distances from the device. The offset of the respective rows of micro LEDs relative to one another allows for a contiguous image to be exposed on the medium as perceived by the eye. Suitable media include thermally or optically activated substrates including

10 paper products such as colour photographic paper, for example silver halide (AgX) paper. Such media can be directly exposed to the radiation emitted by the device in order to achieve direct printing onto the media. The wavelength(s) of light emitted by the device correspond to the spectral response of the medium it is adapted to expose. For example, these may be three primary colours (red, green and blue) to match the spectral

15 response of colour-negative papers, such as silver halide-based paper. Alternatively, other wavelengths, spot sizes and powers may be used e.g. ultraviolet and/or infrared for other photonic applications.

An alternative arrangement is shown in Figure 2D. In this example, each micro LED die 20 12 comprises four rows 38, 40, 42, 44 of micro LEDs or LED clusters 26, forming an array of emitters and thereby pixels on the medium to be printed. As described above each row is offset from the adjacent row so as to give a consistent pitch between pixels. This staggered arrangement may produce a pitch for example of about 254 microns, which produces a print resolution of 400 dpi. The distance between each of the LEDs in a 25 row may be about 127 microns, for example. (Note this is not generally shown to scale in the drawings.) One example of the placement of the LEDs is shown in Figure 2G where the scale is shown. In this example, each micro LED is 63.5 microns wide and each micro LED is horizontally separated by 63.5 microns from neighbouring micro LEDs on the same diagonal row. This prevents horizontal gaps in coverage which would otherwise 30 cause 'banding' of the printed medium. It will be appreciated that more or fewer rows of LEDs may be used. Light output from such an arrangement is about 1 mW, corresponding to a power density of approximately 9W/cm².

The dies 12 are mounted in pairs onto each silicon microbench bar 37-1 , 37-2, 37-3. The microbenches may then be mounted to a printed circuit assembly 35 in an offset relation in staggered rows. For example, two rows may be provided, with the bars positioned in an alternating pattern so as to produce a consistent pitch across the width of the device. This arrangement allows control circuitry 36-1 , 36-2, 36-3 such as FGPAs or ASICs to be mounted inbetween each adjacent bar in each row of bars. Thus the control circuitry may be provided close to each pair of dies.

Referring to Figure 2E, the bars 37 carrying each pair of dies may alternatively be mounted simply adjacent one another and aligned for consistent pitch as described above with reference to Figure 2A. Optionally, the control circuitry 36 may be provided on the silicon bar 37 itself on one side of the pair of dies, as shown in Figure 2F. It is important to note that the spacing between adjacent LEDs 26 on neighbouring dies 12 or bars 37 are the same as the spacing between adjacent LEDs 26 on the same die 12, as illustrated in Figure 2B.

As an example, each die may suitably be about 4mm in length, and about 2mm wide, such that the bar containing a pair of dies is about 8mm in length. Each chip thus, in this example, contains 64 emitters consisting of four rows of 16 emitters. Thus a print head of about 308mm illuminated length will require 38 such bars.

The LEDs or pixels of the device may be addressed in such a way that alternate dies or pairs of dies are addressed in sequence, followed by the remaining alternate sequence. Thus the first, third, fifth chips (and so on until the end of the bar) are addressed and then the remaining even-numbered chips are addressed in that order, so as to complete a swathe or printing before moving the media to print the next swathe. This may have advantages in terms of power and heating considerations. Alternatively, a similar method where three, four or n iterations (or 'ripples') are performed, where each iteration ('ripple') consists of every, third, fourth or n^th chip being addressed simultaneously. A higher number of iterations may result in slower printing, but afford greater advantages with regard to power and heating considerations. Such a method of addressing the elements of the exposure device can be applied to any of the examples described herein, for example, those shown in Figures 2A, 2D, 2E or an array of elements as shown in Figure 2F.

With reference to Figure 4 of the drawings, another example of a media exposure device in accordance with the invention is designated, generally by the reference numeral 100. The media exposure device 100 differs from the media exposure device 10 described hereinabove in that the radiation modification means comprises one telecentric lens 136.

In use, radiation emitted by each micro LED 126 is emitted from the media exposure device 100 from a point located along an outwardly facing surface of the telecentric lens 136. The telecentric lens focuses radiation emitted by the micro LEDs at a distance which is within a particular range of distances from the device.

With reference to Figure 5 of the drawings, another example of a media exposure device in accordance with the invention is designated, generally, by the reference numeral 200. The media exposure device 200 differs from the media exposure device 10 described hereinabove in that the radiation modification means comprises a telecentric lens 236 and a bundle of optic fibres 238 aligned with the telecentric lens.

In use, radiation emitted by each micro LED 226 is emitted from the media exposure device from a point located at the end of the optic fibre bundle 238. The radiation of the micro LED is emitted by the telecentric lens 236 and then conducted by the optic fibre bundle 238. The optic fibre bundle then focuses the radiation emitted by the micro LED at a distance which is within a particular range of distances from the device. An end of the optic fibre bundle focuses the radiation emitted by the micro LEDs as equidistantly spaced beams of radiation which are in alignment at a distance from the device which is within a particular range of distances from the device. ln a further example (not shown) of a media exposure device in accordance with the invention, the media exposure device differs from the media exposure device described hereinabove in that the radiation modification means comprises of a tapered bundle of optic fibres. The fibres are of a predetermined length. The tapered bundle defines a wide end and a narrow end and is disposed in an arrangement wherein the points are defined along the narrow end of the tapered bundle.

In use, radiation emitted by each micro LED propagates from the wide end to the narrow end of the tapered bundle. Radiation emitting from the narrow end of the tapered bundle is focused at a distance from the media exposure device.

In yet a further example (not shown) of a media exposure device in accordance with one aspect of the invention, the media exposure device differs from the media exposure device described hereinabove in that the radiation modification means comprises a macrolens array (e.g. a FOCAL lens as provided by Nippon Glass). Each lens of the macrolens array is disposed in an arrangement wherein the radiation emitted by a group of micro LEDs is focused by it at a distance which is within a particular range of distances from the device. The applicant envisages that the use of micro LEDs together with one of a telecentric lens, a telecentric lens and a corresponding optic fibre bundle, a tapered bundle of optic fibres or a macrolens array will allow for the printing or patterning of smaller (sub-10pm) surface area spot sizes as are required for patterning of Thin-film Transistors and other electronic components, conductor tracks etc. in flexible substrates.

It will be appreciated that the radiating elements may be constituted by a plurality of any one of Organic Light Emitting Diodes (OLEDs), fibre coupled laser diodes, edge emitting lasers or other radiating elements, provided that the required resolution of surface area spots can be achieved.

It will be further appreciated that the specific application of the media exposure device 10 and the medium that is to be exposed will determine the number, size, wavelengths and powers of the micro LEDs as well as the size of the micro LED dies.

With reference to Figure 6 and 7 of the drawings, a media exposure system for exposing a medium in accordance with the invention is designated, generally, by the reference numeral 300. The media exposure system includes, broadly, a red light media exposure device 340, a blue light media exposure device 342 and a green light media exposure device 344. For example, light may be emitted at about 700nm (red), 525nm (green), and 460nm (blue) for producing colour printing or in colour negative printing applications.

The red light media exposure device 340 is the example 10 of a media exposure device in accordance with the invention. The micro LEDs of the red light media exposure device 340 emit radiation which is situated predominantly in the red portion of the visible electromagnetic spectrum.

The blue light media exposure device 342 is the example 10 of a media exposure device in accordance with the invention. The micro LEDs of the blue light media exposure device 342 emit radiation which is situated predominantly in the blue portion of the visible electromagnetic spectrum.

The green light media exposure device 344 is the example 10 of a media exposure device in accordance with the invention. The micro LEDs of the green light media exposure device 344 emit radiation which is situated predominantly in the green portion of the visible electromagnetic spectrum.

The features of the red light, blue light and green light media exposures devices 340, 342, 344 are designated by reference numerals corresponding to the reference numerals of the example 10 of a media exposure device described hereinabove. The red light, blue light and green light media exposure devices 340, 342, 344 are disposed adjacent to one another transverse to the direction of movement of the medium through the media exposure system 300.

In use, each row of micro LEDs of the red, blue and green media exposure devices 340, 342, 344 is operated to cause a swathe to be exposed on the medium through the 5 controlled emission of radiation from the micro LEDs of the row.

More particularly, as the medium passes relative to the device, the same surface area spot of the medium is exposed by a red micro LED of the red light media exposure device 340, then by a blue micro LED of the green light media exposure device 342 and 10 then by a blue micro LED of the green light media exposure device 344. The power of the radiation emitted by the red, blue and green micro LEDs and the length of time each micro LED is turned on is controlled in order to expose each surface area spot as required.

15 The radiating devices 340, 342 and 344 are affixed to a printed circuit assembly 320, preferably by a conductive epoxy, which holds the radiating devices 340, 342, 344 in place. The printed circuit assembly 320 comprises components such as control circuitry 321 (for example FGPAs) which are shown on the underneath side of the system 300 in Figure 7. The control circuitry 321 is electrically connected to the radiating devices 340,

20 342, 344 via tracks (not shown) which may be on the top and/or bottom of the system 300 as shown in Figure 7. The printed circuit assembly 320 is affixed to a macrobench 330 which holds all the aforementioned elements in place.

The system 300 depicted in Figure 6 shares many of the same components and layout 25 as that shown in Figure 1 , such as microlens 314, dies 312, microbench 316, printed circuit assembly 320 and control circuitry 321. The system 300 comprises multiple control circuitry components 321 , mounted on or comprised within the printed circuit assembly 320. Moreover it will be appreciated that the various structures described above in relation to Figures 1 to 6, in particular concerning various alternative arrangements of 30 lenses, microlenses, telecentric lenses and optical fibres, and in relation to alternative arrangements of the LED dies either in pairs or in staggered rows including alternative arrangements of the control circuitry may equally be applied to each of the red, green and blue arrays of LED emitters; for example, the arrays shown in Figure 2E or 2D or an array of emitters as shown in Figure 2F, could form the radiating devices 340, 342, 344 of Figure 7.

5

The silicon acts as a heat sink for the LEDs and control circuitry, and are preferably designed with good thermal conductivity. For example a thermal layer 17 is sandwiched between the control circuitry 321 , printed circuit assembly 320 and the macrobench 330. In one example, cooling fins 23 are provided beneath the macrobench 330 to aid the 10 radiation of heat away from the system 300. Other passive or active cooling means, along with temperature sensors may be provided to ensure accurate temperature control of the system 300. The printed circuit assembly may additionally have a large number of vias.

15 In an alternative arrangement shown in Figure 6B, the macrobench 330 includes a heat dissipating structure for example in the form of a honeycomb arrangement 333, which may conveniently be formed of sintered copper. Such a structure forms a heat sink, and may additionally contain cooling fluid. Thus for example, water may be pumped through the interior of the macrobench through the heat sink to conduct heat away from the

20 device. The device may also or alternatively include Peltier devices 322 provided across the macrobench 330.

With reference to Figure 8 of the drawings, a media exposure device for exposing a medium in accordance with the invention is designated, generally, by the reference 25 numeral 400.

The media exposure device 400 includes a first set 410 and a second set 412 of Organic Light Emitting Diodes (hereinafter "OLEDs") which emit radiation predominantly situated in the red portion of the visible electromagnetic spectrum. The media exposure device 30 400 also includes a first set 414 and a second set 416 of OLEDs which emit radiation predominantly situated in the blue portion of the visible electromagnetic spectrum. The media exposure device 400 further includes a first set 418 and a second set 420 of OLEDs which emit radiation predominantly situated in the green portion of the visible electromagnetic spectrum. The OLEDs are vapour phase deposited on a substrate in the form of a glass plate 422. The OLEDs of each of the sets of OLEDs are aligned with one another. The first and second sets of OLEDs of each colour are offset relative to one another, thereby allowing, in use, for a contiguous image without microbanding to be exposed on the medium as perceived by the eye.

In one example, bus tracks 424, one each corresponding to the first and second sets of OLEDs of each colour are fixed to the glass plate 422 and connected to the corresponding OLEDs. Figure 8 shows such a structure schematically, but in reality the tracking and drive circuitry is more complicated than this, as is known in the art.

The OLEDs of each set of OLEDs can be driven to emit radiation whose timing and power is controlled via the bus track corresponding to the sets of OLEDs of that colour.

The media exposure device 400 includes radiation modification means in the form of a microlens array (not shown) which is mounted adjacent to the glass plate 422 in an arrangement wherein each lens of the microlens array is aligned with a particular OLED.

In use, each set of OLEDs is operated to cause a swathe to be exposed on the medium through the controlled emission of radiation from the OLEDs of the set.

More particularly, as the medium passes relative to the device, the same surface area spot of the medium is exposed by a red OLED, then by a blue OLED and then by a green OLED. The power and the timing of the radiation emitted by the red, blue and green OLEDs is controlled via the bus tracks to expose each surface area spot as required. Radiation emitted by each OLED is emitted from a point located along an outwardly facing surface of the lens of the microlens array (not shown) which is aligned with the OLED. Each lens focuses the radiation of its corresponding OLED at a distance which is within a particular range of distances from the device.

In another example (not shown) of a media exposure device in accordance with the invention, the media exposure device differs from the media exposure device 400 in that the mounting structure comprises a plurality of glass plates. Corresponding subsets of OLEDs deposited on each glass plate together constitute each set of OLEDs. The glass plates are aligned end to end and in abutment with one another in a configuration wherein the subsets of OLEDs are aligned with one another to form the sets of OLEDs. The bus tracks run across the glass plates.

In each one of other examples (not shown) of a media exposure device in accordance with the invention, the media exposure device differs from the media exposure device 400 in that the radiation modification means comprises one of a telecentric lens, a telecentric lens and an optic fibre bundle aligned with the telecentric lens, a tapered bundle of optic fibres or a macrolens array. Said radiation modification means is as described for the examples 100, 200 and the relevant not shown examples, respectively, of a media exposure device described hereinabove. Figure 9 shows one example of the placement of solder bumps 46, at sites 502 on the device 10 shown in Figure 1. Figure 9 shows the top side of the device 10, but omits many of the details shown in previous Figures for clarity. The sites 502 are lithographically etched onto the microbench 16 in positions corresponding to the desired location of the four corners of each micro LED die 12. Accurate placement and alignment of the sites 502 can be achieved as lithographic etching can produce very precise small scale markings. A ball of solder is then deposited onto each site 502. The exact amount of solder deposited on each site can also be very precisely controlled. The solder bump 46 naturally rests onto the etched site as a ridge, furrow, textured area or dip has been formed, guiding the bump 46 into the correct location. Each die 12 is placed onto the silicon microbench 16 and fixed into place as is described in more detail below and in relation to Figure 10. The accuracy of placement and size on each solder bump 46 thus corrects for the inaccuracy resulting from the robotic placement of the dies 12, as the solder bumps 46 guide the dies 12 into their respective intended positions. The above description of the placement of solder bumps 46 applies to the positioning of the dies 12 of all of the examples of Figures 2A, 2D, 2E and 2F.

In a preferred embodiment, solder bump sites 502 are etched into both the top side of the microbench 16 and the corresponding underside of the dies 12.

Solder bump sites 502 may be, for example, in the form of a ridge, furrow, textured area or concave dip, so that the solder bumps 46 naturally fall into the correct location when deposited (whilst molten). Such shapes may be present on the LED dies 12 or the silicon microbench, or both.

With reference to Figures 1 to 3 and Figure 10 of the drawings, a method of constructing the media exposure device 10 is designated, generally, by the reference numeral 500.

A plurality of radiating members in the form of the micro LED dies 12 are provided (Block 510). Further, a mounting structure in the form of the silicon microbench 16 having mounting formations in the form of solder bumps 46 deposited on the sites 502 (Figure 9), is provided (Block 512). Also, radiation modification means in the form of the microlens array 14 is provided (Block 514).

The micro LED dies 12 are placed (Block 516) end-to-end and in abutment with one another to form a bar 30 of micro LED dies 12 above the silicon microbench 16 on the solder bumps 46.

More specifically, each micro LED die 12 is placed on the solder bumps 46 and above the silicon microbench 16 in a position wherein solder bump sites of the micro LED die are in register with the corresponding sites 502 of the silicon microbench. The micro LED dies at the opposing ends of the bar are each placed in abutment along one of its angled edges with an adjacent micro LED die. The micro LED dies intermediate the micro LED dies at the opposing ends of the bar are each placed along both of its angled edges in abutment with one each of different adjacent micro LED dies. Further, the micro LED dies 12 are placed such that the corresponding sets 22, 24 of the micro LEDs 26 of adjacent LED dies are aligned (Block 518) with one another, thereby to form rows 32, 34 5 of aligned micro LEDs.

The solder bumps 46 are melted by radiant heating localised to the pads 502. The surface tension of the molten solder bumps 46 acts to pull the dies 12 into alignment in the x and y directions (angle and pitch), and the accurately controlled volume of solder 10 ensures accurate height alignment. Other ways of heating the solder bumps 46 are possible, such as contact heating or resistive heating.

The flowing and subsequent solidification (Block 520) of the solder bumps 46 between the solder bump sites of the micro LED dies 12 and the corresponding solder bump sites

15 502 of silicon microbench 16, fixes the micro LED dies to the silicon microbench 16. The complementary edges of the abutting micro LED dies 12 constrain the movement of the abutting micro LED dies on the molten solder bumps 46, thereby facilitating said alignment of the micro LEDs 26 of adjacent LED dies. Each micro LED die 12 settles to its final position, relative to adjacent micro LEDs, by the surface tension of the molten

20 solder bumps 46.

The microlens array 14 is fixed (Block 522) adjacent the bar 30 of micro LED dies 12 in an arrangement wherein each lens of the microlens array is aligned with a particular micro LED. Subsequent bars 30 are then arranged next to one another and affixed to a 25 macrobench 330 to form an RBG light emitting system as shown in Figure 6.

Pairs of dies 12 may be mounted on respective bars by use of robotic positioning in association with solder bump alignment as described above. Thus the dies may be positioned on the bars robotically into the required position. The precise placement of 30 solder bumps then serves to adjust the position to reduce or eliminate any small misalignment such that the dies are precisely aligned. It is envisaged that the method of constructing a media exposure device will allow for the fixing of micro LED dies at micron accuracy. It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

Claims:

1. A media exposure device for directly exposing a photographic print medium to radiation emitted from the device, the media exposure device comprising: a plurality of radiating members, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; each radiating member being fixed in relation to at least one other radiating member such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment, and radiation modification means for modifying and emitting from the device radiation originally emitted by the radiating elements, the radiation emitted by the device being focused onto the print medium by the modification means at a distance which is within a particular range of distances from the device thereby to expose the print medium.

2. A media exposure device according to Claim 1 , wherein the radiation modification means includes at least one lens, each lens being disposed in an arrangement wherein radiation emitted by one or more of the radiating elements is emitted from the device by the lens.

3. A media exposure device according to Claim 1 or 2, wherein the radiation modification means comprises a microlens array.

4. A media exposure device according to Claim 1 , 2 or 3, wherein the radiation modification means comprises a macrolens array.

5. A media exposure device according to any preceding claim, wherein the radiation modification means comprises a telecentric lens.

6. A media exposure device according to any preceding claim, wherein the radiation 5 modification means includes a tapered bundle of optic fibres of a predetermined length, each fibre having substantially the same orientation and substantially the same tapered profile, the tapered bundle thereby defining a planar wide end and a planar narrow end and being disposed in an arrangement wherein the planar wide end is adjacent the radiating elements.

10

7. A media exposure device according to any preceding claim, wherein the radiation modification means comprises a telecentric lens and a bundle of optic fibres aligned with the telecentric lens.

15 8. A media exposure device according to any preceding claim, wherein the continuous set of radiating elements is operable to cause a swathe to be exposed on the medium through the controlled emission of radiation from the radiating elements.

20 9. A media exposure device according to any preceding claim wherein the photographic print medium is silver-halide based photosensitive paper.

10. A media exposure device according to any preceding claim, wherein the sets of radiating elements are in the form of a plurality of rows of radiating elements which

25 are parallel to one another.

1 1. A media exposure device according to Claim 10, wherein successive rows are offset relative to one another.

30 12. A media exposure device according to any one of the preceding claims wherein the radiating elements are in the form of micro LEDs with a pixel size between 1 m and 150pm, preferably 60 m, and more preferably 63.5 pm.

13. A media exposure device according to Claim 12, wherein the micro LEDs are provided on solid state dies.

5

14. A media exposure device according to Claim 13 wherein the solid state dies are in the form of flip-chips.

15. A media exposure device according to Claim 13 or 14 wherein the micro LEDs 10 are formed of GaN (Gallium Nitride) and/or GaAIN (Gallium Aluminium Nitride) such that they are adapted to emit light preferably in at least three primary colours preferably to match the spectral response of colour sensitive silver halide paper.

16. A media exposure device according to any one of Claims 1 to 1 1 wherein the 15 radiating elements are in the form of organic LEDs with a pixel size between 1 pm and 150pm, preferably 60pm, and more preferably 63.5 pm.

17. A media exposure device according to any preceding claim, wherein the radiating elements are each in the form of a plurality of micro LEDs arranged to form a

20 cluster.

18. A media exposure device according to Claim 17, in which the cluster is substantially circular.

25 19. A media exposure device according to Claim 17 or 18 wherein reflectors are provided to reflect light towards the photographic print medium, and preferably where the reflectors are fabricated in GaN or GaAIN.

20. A media exposure device according to Claim 19 wherein the reflectors are 30 parabolic.

21. A media exposure device according to any one of the preceding claims, wherein the media exposure device includes a mounting structure to which the radiating members are fixed.

5 22. A media exposure device according to Claim 21 , wherein the mounting structure is in the form of a silicon substrate.

23. A media exposure device according to Claim 22, wherein each radiating member is fixed to said mounting structure via solder bumps.

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24. A media exposure device according to Claim 23, wherein sets of solder bumps are locatable on said mounting structure such that adjacent radiating members are located in abutment with one another.

15 25. A media exposure device according to Claim 23 or 24, wherein solder bump location sites are provided on the mounting structure.

26. A media exposure device according to any of Claims 21 to 25, comprising a support structure including a plurality of conduits for the passage of cooling fluid.

20

27. A media exposure device according to Claim 26 wherein the plurality of conduits are provided by a sintered block.

28. A media exposure device according to Claim 27 wherein the sintered block is 25 formed of copper.

29. A media exposure device according to any of Claims 21 to 28, comprising at least one Peltier device for cooling the support structure.

30 30. A media exposure device according to any of the preceding claims, wherein the radiating members each define opposing edges which are complementary to one another, each radiating member being fixed in abutment with at least one other radiating member along each of their respective complementary edges.

31. A media exposure device according to any one of the preceding claims, wherein 5 each radiating member includes one or more further sets of radiating elements, and wherein the corresponding sets of radiating elements of each of the radiating members form continuous sets of radiating elements in a predetermined alignment.

10 32. A media exposure device according to any one of Claims 1 to 29, wherein each radiating member is offset in relation to at least one adjacent radiating member in a direction transverse to the direction of alignment.

33. A media exposure device according to any preceding claim, wherein each 15 radiating member has a substantially planar parallelogrammatic shape in which the edges are diagonal to the orientation of the aligned radiating elements.

34. A media exposure device according to any of the preceding claims, wherein the radiating elements are equally spaced apart, and preferably the spacing between

20 radiating elements in each set being the same as the spacing between radiating elements on either side of the abutment between the neighbouring radiating members.

35. A media exposure device for directly exposing a medium to radiation emitted from 25 the device, the media exposure device comprising: a plurality of radiating members, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern;

30

each radiating member being fixed in relation to at least one other radiating member such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined alignment, and

5 wherein the media exposure device includes a mounting structure to which the radiating members are fixed, each radiating member being fixed to said mounting structure via at least one solder bump, wherein solder bump location sites are provided on the mounting structure such that at least one set of solder bumps is locatable on said mounting structure such that adjacent radiating members are 10 located in abutment with one another.

36. A media exposure device as claimed in Claim 35, wherein the radiating elements are each in the form of a plurality of LEDs arranged to form a cluster.

15 37. A media exposure device for directly exposing a medium to radiation emitted from the device, the media exposure device comprising: a plurality of radiating members, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a 20 predetermined pattern; each radiating member being fixed in relation to at least one other radiating member such that corresponding sets of radiating elements of each of the radiating members form a continuous set of radiating elements in a predetermined 25 alignment, and wherein the radiating elements are each in the form of a plurality of LEDs arranged to form a cluster, the cluster preferably being substantially circular.

30 38. A media exposure system for exposing a medium, the media exposure system comprising a plurality of media exposure devices each in the form of a media exposure device according to any of the preceding claims.

A media exposure system according to Claim 38, wherein the media exposure devices are disposed adjacent one another transverse to the direction of movement of the medium through the system.

A media exposure system according to Claim 38 or 39, wherein the media exposure devices include: at least one red light media exposure device in which the radiating elements emit radiation including radiation in the red portion of the visible electromagnetic spectrum; at least one blue light media exposure device in which the radiating elements emit radiation in the blue portion of the visible electromagnetic spectrum; and at least one green light media exposure device in which the radiating elements emit radiation in the green portion of the visible electromagnetic spectrum.

A media exposure device for directly exposing a photographic print medium, the media exposure device comprising: one or more sets of organic light emitting diodes; and a substrate on which the organic light emitting diodes are fixed; each set of organic light emitting diodes being disposed in a configuration wherein they are operable to cause a swathe to be exposed on the medium through the controlled emission of radiation from the organic light emitting diodes.

42. A media exposure device according to Claim 41 , wherein the one or more sets of organic light emitting diodes are arranged as offset rows.

43. A media exposure device according to Claim 41 or 42, wherein the substrate on 5 which the organic light emitting diodes are deposited is a glass substrate.

44. A media exposure device according to any of Claims 41 to 43, comprising a plurality of glass substrates in the form of radiating members, each defining opposing edges which are complementary to one another; each radiating member

10 being fixed in abutment with at least one other radiating member along each of their respective complementary edges such that corresponding sets of organic light emitting diodes of each of the radiating members form a continuous set of organic light emitting diodes in a predetermined alignment.

15 45. A media exposure device according to Claim 44, wherein each radiating member has a substantially planar parallelogrammatic shape in which the edges which abut adjacent radiating members are diagonal to the orientation of the aligned radiating elements.

20 46. A media exposure device according to Claim 44 or 45, wherein the organic light emitting diodes are equally spaced apart, and preferably the spacing between organic light emitting diodes in each set being the same as the spacing between organic light emitting diodes on either side of the abutment between the neighbouring radiating members.

25

47. A media exposure device according to any of Claims 41 to 46, wherein at least one of the sets of organic light emitting diodes emit radiation including radiation in the red portion of the visible electromagnetic spectrum;

30

at least one of the sets of organic light emitting diodes emit radiation including radiation in the blue portion of the visible electromagnetic spectrum; and at least one of the sets of organic light emitting diodes emit radiation including radiation in the green portion of the visible electromagnetic spectrum.

5

48. A media exposure device according to any of Claims 41 to 47, including radiation modification means for modifying and emitting from the device radiation originally emitted by the radiating elements.

10 49. A media exposure device according to Claim 48, wherein the radiation modification means includes a tapered bundle of optic fibres of a predetermined length, each fibre having substantially the same orientation and substantially the same tapered profile, the tapered bundle thereby defining a planar wide end and a planar narrow end and being disposed in an arrangement wherein the planar

15 wide end is adjacent the radiating elements.

50. A media exposure device according to Claim 48, wherein the radiation modification means includes at least one lens, each lens being disposed in an arrangement wherein radiation emitted by one or more of the radiating elements is

20 emitted from the device by the lens, the radiation emitted by the device being focused by the lens at a distance which is within a particular range of distances from the device.

51. A media exposure device according to Claim 50, wherein the radiation 25 modification means comprises a macrolens array.

52. A media exposure device according to Claim 50, wherein the radiation modification means comprises a telecentric lens.

30 53. A media exposure device according to Claim 50, wherein the radiation modification means comprises a telecentric lens and a bundle of optic fibres aligned with the telecentric lens.

A media exposure device according to Claim 50, wherein the radiation modification means comprises a microlens array.

A method of printing onto a photosensitive medium using a media exposure device or system according to any preceding claim, the method comprising exposing the medium to a swathe of radiation emitted from the device or system, and causing relative movement between the medium and the device so as to expose successive adjacent portions of the medium to further swathes of radiation emitted from the device or system.

A method of printing according to Claim 55, in which the medium is colour photographic paper such as silver halide paper.

A method of printing according to Claim 55 or 56, in which the radiating elements are arranged to form rows of printable pixels, and exposing the medium to a swathe of radiation comprises addressing the elements in each row by first addressing every Nth element in each row, and subsequently addressing every N+1th element in the row, and preferably where the method comprises addressing all the elements in each Nth radiating member, and subsequently addressing all the elements in every N+1th radiating member.

A method of constructing a media exposure device, comprising: providing a plurality of radiating members each defining opposing edges which are complementary to one another, each radiating member including a set of radiating elements, the radiating elements in the set being spaced in a predetermined pattern; providing a mounting structure to which said radiating members are to be fixed; placing the radiating members on said mounting structure in abutment with another other along each of their respective complementary edges such that corresponding sets of radiating elements of each of the radiating members form a 5 continuous set of radiating elements in a predetermined alignment; and fixing said radiating members to the mounting structure.

59. A method according to Claim 58, further comprising fixing the radiating members 10 to said mounting structure via solder bumps.

60. A method according to Claim 59, further comprising depositing sets of solder bumps on said mounting structure corresponding to each radiating member such that adjacent radiating members can be located in abutment with one another.

15

61. A method according to Claim 59 or 60, further comprising lithographically etching solder bump location sites on to the mounting structure in a prior step.

62. A method according to Claim 61 wherein the solder bump location sites are 20 etched onto the mounting structure in a predefined arrangement so that adjacent radiating members are aligned in abutment with one another.

63. A method according to any of Claims 59 to 62, further comprising lithographically etching solder bump location sites on to the radiating elements.

25

64. A method according to Claim 63 wherein the solder bump location sites are etched onto the radiating elements in a predefined arrangement so that adjacent radiating members are aligned in abutment with one another.

30 65. A method according to any of Claims 59 to 64 wherein the radiating members are fixed to said mounting structure by the melting and subsequent re-solidification of said solder bumps.

66. A method substantially as herein described and/or as illustrated with reference to the accompanying diagrammatic drawings.

67. A system substantially as herein described and/or as illustrated with reference to the accompanying diagrammatic drawings.

68. A media exposure device substantially as herein described and/or as illustrated with reference to the accompanying diagrammatic drawings.