WO2012172365A1

WO2012172365A1 - A radiation source

Info

Publication number: WO2012172365A1
Application number: PCT/GB2012/051385
Authority: WO
Inventors: John Cridland; Lee Holloway; Tristan Phillips
Original assignee: Datalase Limited
Priority date: 2011-06-15
Filing date: 2012-06-15
Publication date: 2012-12-20
Also published as: GB201110026D0

Abstract

A substrate marking apparatus (100) comprises: a plurality of radiation sources (101) operable to emit radiation (113); and a guiding means. The guiding means comprises a primary array (104) comprising a plurality of elements; and a controllabie optical system (102) comprising a plurality of controllable optical pathways disposed between the radiation sources (101) and the primary array (104) which are operable to guide the radiation emitted by each of the radiation sources (101) to one or more elements in the primary array (101). The system can be configured so that each element is connectable to two or more of the radiation sources (101). In turn, each of the elements of the primary array (104) is operable to guide radiation onto a substrate (not shown). The apparatus (100) further comprises: a monitoring means (110) operable to monitor each of the radiation sources, determine whether or not they are operational, and output a signal (111) indicative thereof; and a processing means (112) which is operable to receive the signal (111) from the monitoring means (110) and in response thereto is further operable to control: the emission of radiation from the radiation sources (101) and the configuration of optical pathways in the optical system (102). In the event of a failure of one of the radiation sources (101), the apparatus (100) can automatically correct for the failed radiation source and ensure that an image is produced with no gaps.

Description

A radiation source

The present invention relates to an apparatus which is operable to irradiate a region of a substrate using a plurality of radiation sources. In particular, it relates to such an apparatus with redundancy so that the effect of one radiation source failing on the output of the array is at least limited.

Electronic and optical imaging systems, such as those used for graphic art. inkless printing, code and marking applications often use multiple laser sources whose outputs are arranged as an array. Such systems are described, for example, in US patent numbers 5812179 and 5168288, which describe individually addressable laser diode devices coupled to optical fibres which are subsequently terminated into a linear array of fibres. In turn, such a linear array can be imaged onto a medium as desired or required. Individually addressable monolithic laser diode arrays are also used in the laser industry for applications such as computer to plate, and general laser imaging applications. One limitation of using diode arrays or individual sources coupled to an optical fibre array is that if one of the sources fails there will be a gap in the printed region.

In the case of individually addressable laser diode devices which are coupled to an array via optical fibres, a failed laser source can be replaced by breaking the fibre and reconnecting a new diode to the optical array using some form of splice. In the case of monolithic array the problem is more complicated and one solution has been described in US2003/0210861. This teaches the use of two laser diode arrays wherein the output of each diode is connected to an optical fibre. Some of the optical fibres are connected to an array and some of the optical fibres are not connected to the array and are therefore redundant. In the event of a failure of one of the diodes which is connected to the array one of the redundant diodes can be used to replace it by disconnecting the optical fibre associated with the failed source and connecting the redundant optical fibre. Whilst both of the above mentioned approaches provide a solution, disadvantageously, manual or mechanical intervention is required to replace the failed source.

It is therefore an object of the present invention to provide a solution that at least partially overcomes or alleviates the above problems.

According to a first aspect of the present invention there is provided an apparatus suitable for irradiating a region of a substrate comprising: a plurality of radiation sources operable to emit radiation; a monitoring means operable to monitor each of the radiation sources, determine whether or not they are operational, and output a signal indicative thereof; a guiding means operable to guide the radiation emitted by each of the radiation sources onto a region of a substrate; and a processing means which is operable to receive the signal from the monitoring means and in response thereto, in the event that one of the radiation sources fails, is further operable to control the emission of radiation from another of the radiation sources and to control the guiding means so as to guide said radiation so that it irradiates substantially the same area of the substrate as the failed radiation source would have irradiated.

With such an apparatus a subset of the radiation sources may be used to irradiate substantially the entire region of the substrate. In the event that one of these radiation sources fails, the processing means and guiding means can ensure that another radiation source irradiates the area of the substrate that the failed radiation source would have irradiated is still irradiated. Therefore, the apparatus can ensure that there are substantially no gaps in the irradiated region.

Advantageously, the process of replacing a failed source with a redundant source is substantially automatic and does not require manual or mechanical intervention. Advantageously, this may not require the system to be powered down before the failed source can be replaced.

The guiding means may comprise a primary array comprising a plurality of elements each of which is operable to guide radiation onto the substrate. The profile of the primary array projected onto the substrate may substantially match the region of the substrate to be irradiated. Each element of the array is preferably connectable to at least one radiation source.

The primary array may be a one dimensional or a two dimensional array as is required and/or desired.

Each radiation source may be operable to irradiate more than one area within the region of the substrate.

The number of radiation sources may be greater than the number of elements in the primary array. The plurality of radiation sources may comprise a plurality of primary radiation sources and one or more secondary radiation sources. The apparatus may comprise one primary radiation source for each element of the primary array. The number of secondary radiation sources may be chosen having regard to the mean time to failure for each radiation source, and the required life of the apparatus and the cost of each source. Each primary radiation source may be operable to irradiate a different area within the region of the substrate. Each secondary radiation source may be operable to irradiate substantially the same area within the region of the substrate as one or more of the primary radiation sources. Preferably, the apparatus comprises fewer secondary radiation sources than primary radiation sources.

The guiding means may comprise a controllable optical system. The controllable optical system may comprise a plurality of controllable optical pathways. The controllable optical pathways may be disposed between the radiation sources and the substrate. The controllable optical pathways may be operable to guide the radiation emitted by at least some of the radiation sources to one or more elements in the primary array.

The controllable optical system may comprise any or all of the following as is desired and/or required: electro-optical; acousto-optical; magneto-optical; electrically activated mechanical; and micro-mechanical mechanisms.

The controllable optical system may comprise a plurality of optical switches. The optical switches may comprise multi-way switches with a single output port and a plurality of input ports or vice versa. The configuration of the controllable optical system may be altered by controlling the optical switches.

The controllable optical system may be configurable so that each element in the primary array is connectable to two or more radiation sources. Furthermore, in the event of a failed radiation source, the controllable optical system can preferably be reconfigured so that the radiation from another radiation source can be guided to that element or to its corresponding secondary position.

The number of secondary radiation sources may be chosen having regard to the number of optical switches in the optical pathways.

The guiding means may be operable to guide the radiation emitted by each radiation source to one or more elements of the primary array. With such an embodiment, in the event that one of the radiation sources fails, the processing means can effectively cause radiation from another of the radiation sources to be guided to the element in the primary array which was connected to the failed radiation source.

In one embodiment of the present invention the apparatus comprises a linear array of individually addressable radiation sources. This embodiment is particularly appropriate for monolithic laser diode arrays but may also be used for fibre coupled arrangements. Each individually addressable radiation source may comprise a laser diode. The apparatus may comprise a laser diode bar. Preferably, there is provided one individually addressable radiation sources for each element in the primary array, The optical system may comprise a plurality of units. Each unit may be operable to guide radiation from a first point on an input side of the optical system to a second point on an output side of the optical system. Preferably, there is provided one unit for each individually addressable radiation source and the radiation emitted by each individually addressable radiation source is incident upon the first point of its corresponding unit

Each unit may have a corresponding element in the primary array. Preferably, the second point of each unit can be chosen to be aligned with either: its corresponding element; or to one of the elements adjacent to its corresponding element.

The units of the optical system may comprise e!ectro-optic beam dispiacers and/or rotatable or pop up micro-mirrors with reflection coatings on both sides.

Preferably, when all of the individual radiation sources are functioning correctly each of the units in the optical system transmits the radiation emitted by its corresponding radiation source to a second point which is aligned with its corresponding element.

Preferably, when one of the radiation sources fails: each of the units to a first side of the unit corresponding to the failed source transmits the radiation emitted by their corresponding radiation source to a second point which is aligned with its corresponding element; and each of the units to the other side of the unit that corresponds to the failed source transmits the radiation emitted by their corresponding radiation source to a second point which is aligned with the element which is adjacent to its corresponding element and closer to the unit corresponding to the failed source. With such an arrangement all of the radiation sources to one side of the failed diode are effectively shifted along by one position in the array. This compensates for the failed radiation source and results in an array which does not have any gaps, however, the array is reduced in size by one element.

Preferably, when two of the radiation sources fail: units to a first side of the unit that corresponds to the first failed source route the radiation emitted by their corresponding radiation source to a second point which is aligned with the element which is adjacent to its corresponding element and closer to the unit corresponding to the first failed source; each of the units in between the unit that corresponds to the first failed source and the unit that corresponds to the second failed source transmits the radiation emitted by their corresponding radiation source to a second point which is aligned with its corresponding element; and each of the units to a second side of the unit that corresponds to the second failed source routes the radiation emitted by their corresponding radiation source to a second point which is aligned with the element which is adjacent to its corresponding element and closer to the unit corresponding to the second failed source. Therefore, the arrangement is operable to compensate for both of the failed radiation sources and results in an array which does not have any gaps, however, the array is reduced in size by two elements.

In another embodiment of the present invention, the optical system comprises: one primary radiation source and one primary optical switch for each element in the primary array and at least one secondary radiation source. Preferably, the output port of each primary optical switch is connected to its corresponding primary array element and one input port of each primary optical switch is connected to its corresponding primary radiation source. At least one other input port of each of the primary optical switches is connected to secondary source. The connections between the secondary sources and the primary optical switches may comprise a cascade of optical switches. Preferably, the number of optical switches in the cascade is less than four so that losses are minimised. The number of cascaded optical switches may depend on the number of radiation sources per primary source and the number of input ports per switch. Upon the detection of a failed primary source the processing means may be operable to control a secondary source to emit radiation and to control the configuration of optical switches so that the output of said secondary source is routed to the primary switch to which the failed primary source is connected.

A broad or narrow band optical amplifier may be employed between each primary optical switch and its corresponding primary array element. The optical amplifiers may be operable to compensate for losses in the optical system. Advantageously, by positioning the optical amplifiers at the output of the optical system the optical system can operate with lower laser power and the laser power can be boosted to any desired level before leaving the optical system. Preferably, the optical amplifiers comprise optica] fibre amplifiers.

The connections between different parts of the optica! system may comprise optical fibres. This includes the connections between: the primary sources and the primary switches; the secondary sources and the primary switches; the primary switches and the optical amplifiers; and the optical amplifiers and the elements of the primary array. The preferred router / optical switch technologies include: magneto- optic technology (for example Agiltron); electro-optical; acousto-optical; micro electro-mechanical systems (MEMS); micro electro optical mechanical systems (MEOMS); photonic crystal light deflectors; and coherent beam combining.

The optical system may be wavelength dependent. The wavelength dependent optical system may be operable to route a particular input to a particular output based on its operating wavelength. For such embodiments, the apparatus may comprise: a plurality of primary radiation sources each of which is operable to emit a different wavelength of radiation; a secondary radiation source; and a wavelength shifter which is operable to shift the wavelength of the radiation emitted by the secondary radiation source to any wavelength within a predefined operating band. In the event that one of the primary radiation sources fails then the secondary radiation source is activated and its operating frequency is shifted to correspond to the wavelength of the primary source. The output of the wavelength shifter may be passed through a broad band optical amplifier in order to compensate for any reduction in power which results from the wavelength conversion.

In other embodiments of the present invention, the guiding means may comprise a conveying means for moving a substrate relative to the apparatus and an optical guide. The optical guide may be operable to guide the radiation emitted by each secondary radiation source to one or more secondary positions. The conveying means may be operable to move the substrate relative to the apparatus so that the secondary position is aligned with substantially the same area of the substrate as would have been irradiated by one or more of the primary radiation sources before the substrate was moved. With such an arrangement in the event that one of the primary radiation sources fails a secondary source can be activated and its output directed to the secondary position corresponding to the element that is connected to the failed primary radiation source. Therefore, the region of the substrate can be irradiated in two steps: (i) all of the operational primary radiation sources are used to irradiate a first part of the predefined region; (ii) the conveying means is used to move the substrate relative to the apparatus so that the remainder of the region can be irradiated by secondary radiation sources.

The optical guide may be operable to guide the radiation emitted by the secondary radiation sources to one or more of the secondary positions.

Preferably, there is a secondary position corresponding to each element in the primary array. Each secondary position may be a fixed distance and direction from its corresponding element. In such embodiments, the apparatus may further comprise a storage means to store the relationship between each secondary position and its corresponding element.

In a particularly preferred embodiment, the secondary positions are the positions which the elements of the primary array would be mapped onto if the entire primary array was translated by a fixed distance and direction. Advantageously, in the case of a plurality of failed primary radiation sources, this allows the regions of the substrate corresponding to all failed primary sources to be irradiated substantially simultaneously after translating the substrate once by said fixed distance and in the opposite direction to said direction. Preferably, the direction is substantially parallel or anti-parallel to the direction of any relative motion between the apparatus and any substrate it is desired to irradiate. Advantageously, in applications where the substrate moves relative to the apparatus (for example inkless printing), no additional relative movement of the substrate and apparatus is necessary. A fixed predetermined region of the substrate can be irradiated by activating the secondary radiation sources a fixed time after the primary radiation sources, said time being the time taken for the substrate to move by the fixed distance. Preferably, for embodiments wherein the primary array is a linear array, the direction is substantially perpendicular to the primary array.

The apparatus may comprise a secondary array of elements which are operable to guide radiation onto the substrate. Preferably, the secondary array comprises the same number of elements as the primary array. Preferably, the size and shape of the secondary array substantially matches that of the primary array. The secondary array of elements may be parallel to but displaced relative to the primary array of elements so that each element in the secondary array is adjacent to one element in the primary array. The secondary positions may correspond to the elements of the secondary array.

Rather than a secondary array, the apparatus may comprise one or more movable elements that are operable to guide radiation onto the substrate. Preferably, the movable elements are disposed adjacent to the primary array and are operable to move through a plurality of positions, in a direction substantially parallel to the array, so that they can be disposed in one of a range of secondary positions each of which is adjacent to one of the elements of the primary array.

The apparatus may be suitable for use in the field of inkless printing. For such embodiments, the substrate may be moved relative to the apparatus so that several regions of the substrate, each substantially the same size and shape, can be irradiated sequentially so as to effect a colour change of the substrate. The substrate may comprise a layer of di acetylene material.

In order that the invention can be more clearly understood embodiments thereof are now described further below, by way of example, with reference to the accompanying drawings, of which:

Figure 1 is a schematic view of an embodiment of an apparatus according to the present invention;

Figure 2 shows a first exemplary embodiment of an apparatus according to the present invention;

Figures 3a-3c show a second exemplary embodiment of an apparatus according to the present invention; and

Figure 4 shows embodiment of an apparatus according to the present invention which comprises a wavelength dependent optical system.

Figure 5 shows a third exemplary embodiment of an apparatus according to the present invention;

Figure 6 shows a fourth exemplary embodiment of an apparatus according to the present invention; Figure 1 shows a schematic view of an apparatus 100 according to the present invention. The apparatus comprises: a plurality of radiation sources 101 operable to emit radiation 1 13; and a guiding means. The guiding means comprises a primary array 104 comprising a plurality of elements; and a controllable optical system 102 comprising a plurality of controllable optical pathways disposed between the radiation sources and the primary array which are operable to guide the radiation emitted by each of the radiation sources to one or more elements in the primary array and wherein the system can be configured so that each element is connectable to two or more of the radiation sources. In turn, each of the elements of the primary array is operable to guide radiation onto a substrate (not shown).

The apparatus 100 further comprises: a monitoring means 1 10 operable to monitor each of the radiation sources, determine whether or not they are operational, and output a signal 1 11 indicative thereof; and a processing means 1 12 which is operable to receive the signal 11 1 from the monitoring means 1 10 and in response thereto is further operable to control: the emission of radiation from the radiation sources 101 and the configuration of optical pathways in the optical system 102.

Referring to figure 2, a first exemplary embodiment of an apparatus 200 according to the present invention is shown.

The apparatus 200 comprises a plurality of radiation sources 201, 203 which are operable to emit radiation and a primary array 204 comprising a plurality of elements 205. In the example shown, the apparatus comprises four primary sources 201 , one secondary source 203 and four array elements 205. However, as will be obvious to one skilled in the art the number of primary sources 201 , the number of secondary sources 203, the ratio of the number of primary sources 201 to the number of secondary sources 203 and the number of array elements 205 may be altered as desired and/or required. Each of the radiation sources 201 , 203 may comprise a diode or fibre laser.

The apparatus further comprises a controllable optical system 202 comprising a plurality of controllable optical pathways disposed between the radiation sources 201, 203 and the array 204 which are operable guide the radiation emitted, by each of the radiation sources 201, 203 to one or more elements 205 in the array 204.

The optical system comprises a plurality of optical switches 202a, 202b, 202c. Although two way switches are shown, as will be obvious to one skilled in the art, additionally or alternatively multi-way switches with more ports may be used. The configuration of the optical system 202 can be altered by controlling the optical switches 202a, 202b, 202c and each element 205 is connectable to two or more of the radiation sources 201, 203.

The output from each primary source 201 is connected to one input port of one of four primary optical switches 202a. The output port of each of these primary optical switches 202a is connected to one of the elements 205. Optionally, a broad or narrow band optical amplifier 206 may be employed between each primary optical switch 202a and its corresponding element 205. The optical amplifiers 206 may be operable to compensate for losses in the optical system 202. Advantageously, by positioning the optical amplifiers 206 at the output of the optical system 202 the optical switches 202a, 202b, 202c can operate with lower laser power and the laser power can be boosted to any desired level before leaving the optical system 202. Preferably, the optical amplifier 206 may comprise an optical fibre amplifier. The other input port of each of the primary optical switches 202a is connected to a secondary source 203 via a cascade of optical switches 202b, 202c, This connection may comprise any number of cascaded optical switches 202b, 202c although it is preferred that the number be less than four so as to minimise losses. The number of cascaded optical switches may depend on the number of secondary sources 203 per primary source 201 and the number of input ports per switch.

The apparatus also comprises: a monitoring means (not shown) which is operable to monitor each of the radiation sources and determine whether or not they are operational; and a processing means (not shown) which is operable to control: the emission of radiation from the radiation sources 201, 203 and the configuration of the optical switches 202a, 202b, 202c in the optical system 202. Upon the detection of a failed primary source 201 the processing means is operable to control the secondary source 203 to emit radiation and the configuration of optical switches 202b, 202c so that the output of the secondary source 203 is routed to the primary switch 202a connected to the failed primary source 201.

The connections between different parts of the optical system 202 (indicated by solid arrows) may be by optical fibres. This includes the connections between: the primary sources 201 and the primary switches 202a; the secondary sources 203 and switches 202c; switches 202b and primary switch 202a; primary switch 202a and optical amplifiers 206; and optical amplifiers 206 and elements 205. The preferred router / optical switch technologies include: magneto-optic technology (for example Agiltron); electro-optical; acousto-optical; micro electro-mechanical systems (MEMS); micro electro optical mechanical systems (MEOMS); photonic crystal light deflectors; and coherent beam combining. Turning to figures 3a - 3c, a second embodiment 300 according to the present invention is shown. This embodiment 300 is particularly appropriate for monolithic laser diode arrays but may also be used for fibre coupled arrangements. The apparatus comprises a laser diode bar 301 and an optical system 302. The laser diode bar 301 comprises a linear array of individually addressable radiation sources, each of which is operable to emit radiation. Each individually addressable radiation source may comprise a laser diode. The optical system 302, which will be discussed further below, comprises a plurality of units, each of which corresponds to one of the individually addressable radiation sources. Each unit is operable to guide the radiation emitted by its corresponding radiation source from a first point on an input side 303 to a second point on an output side 304. The second point may correspond to a point directly opposite the first point or, alternatively, the second point may correspond to a point which is displaced relative to the first point a distance which is substantially equal to the separation of individually addressable radiation sources.

As can be seen in figure 3a, when all of the individual radiation sources are functioning correctly each of units the in optical system 302 transmits the radiation emitted by its corresponding radiation source from a first point on an input side 303 to a second point on an output side 304, which corresponds to a point directly opposite the first point.

The apparatus 300 also comprises: a monitoring means (not shown) which is operable to monitor each of the radiation sources and determine whether or not they are operational; and a processing means (not shown) which is operable to control: the emission of radiation from the radiation sources and the optical system 302. Figure 3b shows the same arrangement wherein one of the radiation sources 305 has failed, as indicated by an X. This is detected by the monitoring means and, in turn, the processing means controls the units in the optical system 302. Each of the units to the right of the unit that corresponds to the failed source 305 transmit the radiation emitted by their corresponding radiation source from a first point to a second point, which corresponds to a point directly opposite the first point as before. However, each of the units to the left of the unit that corresponds to the failed source 305 transmits the radiation emitted by their corresponding radiation source from a first point to a second point which is displaced to the right relative to the first point by a distance which is substantially equal to the separation of individually addressable radiation sources. That is, all of the radiation sources to the left of the failed source

305 are effectively shifted to the right by one position in the array. This compensates for the failed radiation source 305 and results in an array which does not have any gaps, however, the array is reduced in size by one element.

Figure 3c shows the same arrangement 300 wherein another radiation source

306 has failed. The second failed source 306 is located to the right of the first failed source 305. Once again this is detected by the monitoring means and, in turn, the processing means controls the units in the optical system 302 as described below.

Each of the units to the left of the unit that corresponds to the first failed source 305 shifts the radiation emitted by their corresponding radiation source to the right by one position; each of the units in between the unit that corresponds to the first failed source 305 and the unit that corresponds to the second failed source 306 transmits the radiation emitted by their corresponding radiation source to a second point directly opposite the first point; and each of the units to the right of the unit that corresponds to the second failed source 306 shifts the radiation emitted by their corresponding radiation source to the left by one position. Therefore the arrangement 300 compensates for both of the failed radiation sources 305, 306 and results in an array which does not have any gaps, however, the array is reduced in size by two elements.

This arrangement 300 could be implemented with electro-optic beam displacer or rotatable or pop up micro-mirrors with reflection coatings on both sides.

Referring to Figure 4 an arrangement 400 is shown which differs from the embodiment 200 of figure 2 in that it employs a wavelength dependent optical system 402. The apparatus comprises three laser sources 401 a, 401 b, 401c each of which is operable to emit slightly different wavelengths of radiation, preferably around 1500nm in the near infra-red (NIR). Each of the laser sources 401a, 401 b, 401c is connected to a wavelength dependent multiplexer 402 which is operable to route a particular input to a particular output based on its operating wavelength. The output for the optical system 402 is connected to an array 404.

The apparatus 400 further comprises a secondary laser diode 403, which is operable to emit radiation, and a wavelength shifter 405 which is operable to shift the wavelength of the emitted radiation to any wavelength within a predefined operating band. In the event that one of the laser diodes 401a, 401 b, 401 c fails then the secondary laser diode 403 is activated and its operating frequency is shifted to correspond to the wavelength of the failed laser diodes. The output of the wavelength shifter 405 is passed through a broad band optical amplifier 406 in order to compensate for any reduction in power which results from the wavelength conversion. As with the embodiment 200 of figure 2, broad band optical amplifiers 406 may also be employed to compensate for losses in the optical system 402. Moreover, positioning the optical amplifiers 406 at the output to the optical system 402 allows the optical system to operate at a lower laser power whilst the laser power is boosted to levels required at the output to the optical system.

Referring to figure 5, a third exemplary embodiment 500 is shown. The apparatus comprises a number, n, of primary optical sources 501 each of which is coupled to one of elements of a primary array 502. Each of the elements of the primary array 502 is operable to guide radiation onto a substrate (not shown). The primary array is preferably a linear array. The apparatus further comprises a number, m, of secondary sources 504 where m<n. The secondary sources 504 are connected via a second optical system 505, 512 to a secondary array 503. The secondary array 503 comprises the same number of elements as the primary array 502 and is disposed parallel thereto so that each element of the secondary array 503 is adjacent to an element of the primary array 502.

In the event that a primary source 501 fails, there will be a gap in the primary array and the monitoring means (not shown) will output a signal indicating this. One of the secondary sources 504 will be activated by the processing means (not shown) and a secondary optical system 505 is configured such that the radiation from the secondary source 504 is directed to the element in the secondary emitter array 503 which is adjacent to the element in the primary array 502 that is connected to the failed primary source 501.

Such an apparatus may be used to irradiate a substrate by moving the substrate relative to the apparatus 500 through the path of the primary and secondary arrays 502, 503. The displacement in the position of the imaged dots on the moving substrate caused by the physical separation between the primary and secondary arrays 502, 503 is compensated for by adjusting the timing of the emission from the secondary source 504 so that the image produced aligns with appropriate row of imaged dots produced by the primary array 502.

The number of secondary sources 504 required may depend on the number of cascaded optical switches in each optical pathway 505, 512 of the secondary optical system. The number of secondary sources 504 should be less than or equal to nl 4 and preferably less than or equal to n/8 and more preferably less than or equal to n/16. The secondary optical system 505 may incorporate or uti!ise any of the technologies mentioned above.

A fourth exemplary embodiment 600 of the present invention is shown in figure 6. The apparatus 600 comprises: a plurality of primary sources 601 connected to primary emitter array 602; and one or more secondary sources 604 connected to one or more moveable, secondary emitter elements 603, The apparatus may comprise one or more movable secondary elements 603 arranged on one or more planes substantially parallel to the primary array 602. Each movable secondary emitter element 603 is configured to be translatable substantially parallel to the primary emitter array 602 so that it may be disposed adjacent to any of the elements of the primary array 602.

In the event of a failure of one of the primary emitters 601 , there will be a gap in the primary array 602 and the monitoring means (not shown) will output a signal indicating this. The processing means (not shown) will cause a secondary source 604 to be activated and routed to one of the moveable, secondary elements 603. Said moveable, secondary element 603 is translated so as to be adjacent to the element of the primary array 602 that is connected to the failed primary source 601. In the event of a further primary source 601 failure, a second secondary emitter 604 is activated and guided to a second movable secondary element 603 which is translated to be adjacent to the element of the primary array 602 that is connected to the second failed primary source 601.

The position of the imaged dot on a moving substrate created by any secondary emitter 604 via a movable secondary element can be arranged to be coincident with the appropriate row of dots produced by the primary emitter array by adjustment of the timing of the emission of radiation from the secondary source or sources so as to compensate for the displacement between the secondary and primary emitters in the direction of substrate motion.

It is of course to be understood that the invention is not to be restricted to the details of the above embodiments which have been described by way of example only.

Claims

1. An apparatus suitable for irradiating a region of a substrate comprising: a plurality of radiation sources operable to emit radiation; a monitoring means operable to monitor each of the radiation sources, determine whether or not they are operational, and output a signal indicative thereof; a guiding means operable to guide the radiation emitted by each of the radiation sources onto a region of a substrate; and a processing means which is operable to receive the signal from the monitoring means and in response thereto, in the event that one of the radiation sources fails, is further operable to control the emission of radiation from another of the radiation sources and to control the guiding means so as to guide said radiation so that it irradiates substantially the same area of the substrate as the failed radiation source would have irradiated, wherein the guiding means comprises a primary array, said primary array comprising a plurality of elements each of which is operable to guide radiation onto the substrate and wherein the number of radiation sources is greater than the number of elements in the primary array.

2. An apparatus as claimed in claim 1 wherein the profile of the primary array projected onto the substrate substantially matches the region of the substrate to be irradiated.

3. An apparatus as claimed in claim 1 or claim 2 wherein each element of the primary array is connectable to at least two radiation sources.

4. An apparatus as claimed in any preceding claim wherein the plurality of radiation sources comprises a plurality of primary radiation sources and one or more secondary radiation sources.

5. An apparatus as claimed in claim 4 wherein there is provided one primary radiation source for each element of the primary array.

6. An apparatus as claimed in claim 4 or claim 5 wherein the number of secondary radiation sources is chosen having regard to the mean time to failure for each radiation source, and the required life of the apparatus and the cost of each source.

7. An apparatus as claimed in any one of claims 4 to 6 wherein each primary radiation source is operable to irradiate a different area within the region of the substrate.

8. An apparatus as claimed in any one of claims 4 to 7 wherein each secondary radiation source is operable to irradiate substantially the same area within the region of the substrate as one or more of the primary radiation sources.

9. An apparatus as claimed in any one of claims 4 to 8 wherein the apparatus comprises fewer secondary radiation sources than primary radiation sources.

10. An apparatus as claimed in any preceding claim wherein the guiding means comprises a controllable optical system comprising a plurality of controllable optical pathways disposed between the radiation sources and the substrate.

11. An apparatus as claimed in claim 10 wherein the controllable optical system comprises any or all of the following: electro-optical; acousto-optical; magneto -optical; electrically activated mechanical; and micro-mechanical mechanisms.

12, An apparatus as claimed in any one of claims 10 to 1 1 wherein the controllable optical system is configurable so that each element in the primary array can be connected to two or more radiation sources.

13. An apparatus as claimed in any preceding claim wherein the guiding means is operable to guide the radiation emitted by each of the radiation sources to one or more elements of the primary array.

14. An apparatus as claimed in any one of claims 10 to 13 wherein the optical system comprises a plurality of units and wherein each unit is operable to guide radiation from a first point on an input side of the optical system to a second point on an output side of the optical system.

15. An apparatus as claimed in claim 14 when dependent directly or indirectly upon claim 4 wherein there is provided one unit for each primary radiation source and the radiation emitted by each primary radiation source is incident upon the first point of its corresponding unit.

16. An apparatus as claimed in claim 14 or claim 15 wherein each unit has a corresponding element in the primary array.

17. An apparatus as claimed in any one of claims 10 to 16 wherein the controllable optical system comprises a plurality of optical switches and wherein the configuration of the controllable optical system may be altered by controlling the optical switches.

18. An apparatus as claimed in claim 17 when dependent either directly or indirectly upon claim 4 wherein the optical system comprises one primary optical switch for each element in the primary array and wherein upon the detection of a failed primary source the processing means is operable to control a secondary source to emit radiation and to control the configuration of optical switches so that the output of said secondary source is routed to the primary switch to which the failed primary source is connected.

19. An apparatus as claimed in claim 18 wherein the output port of each primary optical switch is connected to its corresponding primary array element; one input port of each primary optical switch is connected to a corresponding primary radiation source; and at least one other input port of each of the primary optical switches is connected to a secondary radiation source.

20. An apparatus as claimed in claim 19 wherein the connections between the secondary radiation sources and the primary optical switches comprise cascades of optical switches.

21. An apparatus as claimed in any one of claims 18 to 20 wherein the optical system comprises one or more broad or narrow band optical amplifiers.

22. An apparatus as claimed in any one of claims 18 to 21 wherein the connections between different parts of the optical system comprise optical fibres.

23. An apparatus as claimed in any one of claims 10 to 22 wherein the optical system is wavelength dependent and is operable to route a particular input to a particular output based on its operating wavelength.

24. An apparatus as claimed in 23 wherein the apparatus comprises: a plurality of primary radiation sources each of which is operable to emit a different wavelength of radiation; a secondary radiation source; and a wavelength shifter which is operable to shift the wavelength of the radiation emitted by the secondary radiation source to any wavelength within a predefined operating band.

25. An apparatus as claimed in any one of claims 4 to 24 wherein the guiding means comprises a conveying means which is operable to move a substrate relative to the apparatus and an optical guide and wherein: the optical guide is operable to guide the radiation emitted by each secondary radiation source to one or more secondary positions; and the conveying means is operable to move the substrate relative to the apparatus so that the secondary position is aligned with substantially the same area of the substrate as would have been irradiated by one or more of the primary radiation sources before the substrate was moved.

26. An apparatus as claimed in claim 25 wherein the optical guide is operable to guide the radiation emitted by the secondary radiation sources to one or more of the secondary positions.

27. An apparatus as claimed in claim 25 or claim 26 wherein there is a secondary position corresponding to each element in the primary array which is a fixed distance and direction from its corresponding element.

28. An apparatus as claimed in claim 27 wherein the apparatus further comprises a storage means to store the relationship between each secondary position and its corresponding primary array element.

29. An apparatus as claimed in claim 27 or claim 28 wherein the secondary positions are the positions which the elements of the primary array would be mapped onto if the entire primary array was translated by a fixed distance and direction.

30. An apparatus as claimed in claim 29 wherein the fixed direction is substantially parallel or anti-parallel to the direction of any relative motion between the apparatus and any substrate it is desired to irradiate.

31. An apparatus as claimed in claim 29 or claim 30 wherein the fixed direction is substantially perpendicular to the primary array.

32. An apparatus as claimed in any one of claims 25 to 31 wherein the optical guide comprises a secondary array of elements which are operable to guide radiation onto the substrate and the secondary positions correspond to the elements of the secondary array.

33. An apparatus as claimed in claim 32 wherein the secondary array comprises the same number of elements as the primary array and the size and shape of the secondary array substantially matches that of the primary array.

34. An apparatus as claimed in claim 33 wherein the secondary array of elements is parallel to but displaced relative to the primary array of elements so that each element in the secondary array is adjacent to one element in the primary array.

35. An apparatus as claimed in any one of claims 25 to 31 wherein the optical guide comprises one or more movable elements that are operable to guide radiation onto the substrate and which are disposed adjacent to the primary array and are operable to move through a plurality of positions, in a direction substantially parallel to the primary array, so that they can be disposed in one of a range of secondary positions each of which is adjacent to one of the elements of the primary array.

36. An apparatus as claimed in in any preceding claim wherein in the event that one of the radiation sources fails, the guiding means continues to guide radiation from each functioning radiation source so that it irradiates substantially the same area of the substrate as it did prior to failure of the failed radiation source.

37. An apparatus as claimed in any preceding claim wherein the apparatus is suitable for use in the field of inkless printing.

38. An apparatus as claimed in any preceding claim wherein the substrate comprises a layer of diacetylene material.