WO1998045645A1

WO1998045645A1 - Illumination apparatus and a method of providing illumination

Info

Publication number: WO1998045645A1
Application number: PCT/GB1998/001043
Authority: WO
Inventors: Allan John Davie; Cameron Rae; Douglas Alexander
Original assignee: Lifor Limited
Priority date: 1997-04-10
Filing date: 1998-04-09
Publication date: 1998-10-15
Also published as: GB9707312D0; AU6930798A

Abstract

A method and apparatus for providing illumination are described which is based on a laser source (10) and a side emitting fibre optic cable (12). The laser light source (10) is coupled to the side emitting fibre optic cable (12), the laser light source being of sufficient power to illuminate the cable (12) throughout its length. In a preferred arrangement the illumination apparatus consists of a solid-state laser light (10) source which is energised via a mains supply with a rechargeable battery (16), and which is coupled to a length of side emitting fibre optic cable (12) such that the illumination system is portable and provides a length of illuminated side emitting fibre optic cable (26) several times the length obtained by prior art systems using metal halide illumination. The apparatus includes an arrangement for detecting if the cable is cut and for disconnecting the laser beam to the cable. Embodiments of the invention are described. Thus, this apparatus can be used to provide emergency lighting in stairwells, cinemas, offices, homes, aircraft and the like.

Description

m tional pp cation o

PCT/GB 98/01043

A. CLASSIFICATION OF SUBJECT MATTER

IPC 6 F21V8/00 G02B6/42 H01S3/096

According to International Patent Classιfιcatιon(IPC) or to both national classification and IPC

B. FIELDS SEARCHED

Minimum documentation searched (classification system followed by classification symbols)

I PC 6 F21V G02B HOIS

Documentation searched other than minimumdocumentation to the extent that such documents are included in the fields searched

Electronic data base consulted during the international search (name of data base and, where practical, search terms used)

C. DOCUMENTS CONSIDERED TO BE RELEVANT

Category ° Citation of document, with indication, where appropnate, of the relevant passages Relevant to claim No

DE 43 26 525 A (BRIDGESTONE CORP.) 10 1 , 4 , 18

February 1994 see the whol e document 2,3,5-9 10

DE 296 01 992 U (C. OELLER) 1 August 1996 2,3 see the whol e document

P ,Y PATENT ABSTRACTS OF JAPAN 2,3 vol. 097, no. 010, 31 October 1997

& JP 09 168242 A (HITACHI), 24 June 1997, see abstract

US 5 617 497 A (B.M.KINGSTONE) 1 April 5

1997 see abstract; figures 1-4 23

-/--

Further documents are listed in the continuation of box C Patent family members are listed in annex

° Special categories of cited documents

T" later document published after the international filing date

"A" document defining the general state of the art which is not or priority date and not in conflict with the application but considered to be of particular relevance cited to understand the principle or theory underlying the invention

Ε" earlier document but published on or after the international "X" document of particular relevance, the claimed invention filing date cannot be considered novel or cannot be considered to

1" document which may throw doubts on pπorrty claιm(s) or involve an inventive step when the document is taken alone which is cited to establish the publicationdate of another "Y" document of particular relevance, the claimed invention citation or other special reason (as specified) cannot be considered to involve an inventive step when the

O" document refernng to an oral disclosure, use, exhibition or document is combined with one or more other such docuother means ments, such combination being obvious to a person skilled

"P" document published prior to the international filing date but in the art later than the priority date claimed '&" document member of the same patent family

Date of the actual completion of theinternational search Date of mailing of the international search report

15 July 1998 21/07/1998

Name and mailing address of the ISA Authonzed officer

European Patent Office, P B 5818 Patentlaan 2 NL - 2280 HV Ri|swi|k Tel (+31-70) 340-2040, Tx 31 651 epo nl, Fax (+31-70) 340-3016 Mal i c , K

Form PCT/ISA210 (second sheet) (July 1992) n iona pp ica on o

PCT/GB 98/01043

C.(Contιnuatιon) DOCUMENTS CONSIDERED TO BE RELEVANT

Category ° Citation of document, with indioation.where appropnate, of the relevant passages Relevant to claim No

WO 94 06044 A (HOBART LASER PRODUCTS) 17 6-9

March 1994 see the whol e document

FR 2 689649 A (BRIDGESTONE) 8 October 1,4,18

1993 see the whol e document 10

Form PCT/ISA210 (continuation of second sheet) (July 1992) n t ona pp ca on o

Information on patent family members

PCT/GB 98/01043

Patent document Publication Patent family Publication cited in search report date member(s) date

DE 4326525 10-02-1994 P 6060294 A 04-03-1994 JP 6068705 A 11-03-1994 JP 6073715 A 15-03-1994

DE 29601992 U 01-08-1996 NONE US 5617497 A 01-04-1997 US 5617496 A 01-04-1997 US 5333228 A 26-07-1994 AU 686172 B 05-02-1998 AU 6954094 A 20-12-1994 CA 2162138 A 08-12-1994 EP 0700530 A 13-03-1996 JP 8510847 T 12-11-1996 O 9428451 A 08-12-1994

WO 9406044 17-03-1994 US 5463710 A 31-10-1995 AU 4855993 A 29-03-1994

FR 2689649 08-10-1993 JP 5288948 A 05-11-1993

JP 5313015 A 26-11-1993

JP 5313016 A 26-11-1993

JP 6075120 A 18-03-1994

DE 4311359 A 14-10-1993

US 5333227 A 26-07-1994

Form PCT/ISA/210 (patent family annex) (July 1992) - 1 -

ILLUMINATION APPARATUS AND A METHOD OF PROVIDING ILLUMINATION

The present invention relates to illumination apparatus and to a method of providing illumination. Particularly, but not exclusively, the invention relates to such an apparatus and method for use in emergency lighting situations or for use in low-light environments. Side emitting fibre optic cables are well known and have been used to provide light emission over a distributed length. In practice, this length is up to about 35 metres and the light source used to provide illumination is usually a metal halide lamp with an output of about 100 . Such side emitting fibre optic cables appear to be evenly illuminated along their length and they have found application for use in advertising and mainly novelty or entertainment applications. The requirement of a 100 light source and a maximum length of about 35 metres has restricted application of such side emitting fibre optic cables to certain environments and especially to those with a mains power supply. Attempts have been made to increase the useful length by increasing the light output of the light source but this places increased demands on the electrical power supply and adds complexity.

There is a requirement for providing illumination by such side emitting fibre optic cable in a number of different applications, such as hazardous environments and other low- light situations, for example in stairwells, subsea applications and the like. It has hitherto not been possible to use such cables because of the limitation in length available and in the type of power supply required to be coupled to the apparatus to energise the cable to provide sufficient illumination.

It is an object of the present invention to provide an improved illumination apparatus and a method of providing illumination which obviates or mitigates the - 2 - aforementioned problems.

This is achieved by coupling a laser light source to a side emitting fibre optic cable, the laser light source being of sufficient power to illuminate the cable throughout its length. The laser light source is capable of being energised by a battery such that the illumination system is portable and provides a length of illuminated side emitting fibre optic cable several times the length obtained by prior art systems using metal halide illumination.

In a preferred arrangement the illumination apparatus consists of a solid-state laser light source which is energised via a mains supply with a rechargeable battery, and which is coupled to a length of side emitting fibre optic cable. The laser can be coupled either to the mains power supply or, alternatively, in the event of power failure, coupled to the rechargeable battery to provide sufficient power to excite the laser to illuminate the cable. Thus, this apparatus can be used to provide emergency lighting in stairwells, cinemas, offices, homes, aircraft and the like.

In addition, the length of illuminated cable can be made several orders of magnitude greater than with the prior art systems by providing optical coupling, in parallel, from the same laser light source to different sections of concatenated side emitting fibre optic cables. This results in much greater possibility of applications than has hitherto been possible with such side emitting fibre optic cables. A safety fibre runs in parallel with the cable or optical coupling cable and doubles back to a switch in the supply housing so that if the cable is cut, the cut is detected and the laser light source to the cable is cut-off by moving a shutter across the laser beam or by disabling the laser driven power supply.

According to a first aspect of the present invention there is provided illumination apparatus comprising a - 3 - laser light source, a power supply for the laser light source and a side emitting fibre optic cable coupled to the laser light source, the light source laser being of sufficient power such that when energised the side emitting cable is illuminated along its length.

The laser power supply can be a mains power supply or battery power supply. The power supply can include a rechargeable battery such that in the event of mains power failure, the rechargeable battery continues to energise the laser for a predetermined time. The power supply can include a relay system such that the battery energises the laser only in the event of a mains failure . The laser may be any type of laser but preferably is a solid-state laser which is, in turn, excited by a semi- conductor diode-laser.

The side emitting fibre optic cable comprises a plurality of side emitting fibre optic cables bundled and twisted together and encased in a transparent plastic jacket. The end of the fibre optic cable is aligned to receive the laser beam when the laser is energised. It will be understood that the illumination apparatus includes optical coupling means to couple the output of the laser light source to the end of the side emitting fibre optic cable, the optical coupling means being arranged so as to cause the beam to expand or contract to match the diameter of the side emitting fibre optic cable to maximise efficient light coupling. The optical coupling means is preferably a lens.

According to another aspect of the present invention, there is provided illumination apparatus for illuminating side emitting fibre optic cable over a relatively long distance, said fibre optic cable comprising at least two fibre optic cable sections coupled by optical coupling means, said apparatus comprising a laser light source, a power supply for said laser light source, a first fibre optic cable section coupled to said light source, said first fibre optic - 4 - cable section having a first set of side emitting optical fibres, and a first low-loss optical fibre located in parallel with side emitting fibres, said optical coupling means disposed between the first and second fibre optic cable sections and being optically coupled to said first low-loss optical fibre, at a first end proximal to said laser light source, and to low-loss optical fibres and side emitting optical fibres in said second cable section, at a second end distal to said laser light source so that laser light from said first low-loss optical fibre is coupled to side emitting optical fibres and low-loss optical fibres in a second section to cause said second and subsequent sections to illuminate in the same way as said first section. This can be achieved by using a single fibre optic cable which has a structure such that a plurality of side emitting optical fibres are located on the periphery of the cable with a low-loss optic fibre located in the core, said coupling means at the end of a feeder section of said cable is coupled to the core only and feeds light from the core to both low-loss optical fibre and to the peripheral side emitting optical fibre in subsequent receiving sections of cable. In this way, lengths of cable can be concatenated together via optical coupling means, such that the effective length of illuminated cable is greatly in excess of a single piece of cable (for example, 300 metres) and may be several kilometres in length.

An alternative way of achieving an increase in effective length is to provide a side emitting fibre optic cable in parallel with a separate low-loss single fibre optical cable and, after a predetermined length, to provide a coupling lens which takes light from the low- loss cable and feeds it to a subsequent length of side emitting fibre optic cable. The low- loss fibre runs in parallel with each subsequent length of side emitting optical cable and continually feeds light, via a series - 5 - of optical lengths, to subsequent lengths of side emitting fibre optic cable to provide appropriate illumination .

With this arrangement it will be appreciated that in a long length of cable, selected sections of the cable can be illuminated, all of the sections of the cable being coupled to a low-loss optical fibre with appropriate coupling means interfacing with side emitting fibre optic cables to provide illumination over a particular length of cable. There are two types of coupling means; one can pass light as described above, the other can pass light between the low-loss optical fibres only so that some sections of cable may be illuminated and others dark. This would allow manufacture of one cable structure.

According to a further aspect of the present invention, there is provided a method of illuminating a side emitting fibre optic cable, said method comprising the steps of, coupling a laser light source to said fibre optic cable and energising said laser to provide sufficient power throughout its length to illuminate the cable.

Conveniently, the method includes the step of providing illumination over a substantial length of cable by coupling a first side emitting fibre optic cable to a laser source, coupling a first low- loss fibre optic cable to the same laser source, energising the side emitting cable and said low- loss cable in parallel from the same laser source and coupling light from the low-loss cable to at least one subsequent length or side emitting fibre optic cable to provide illumination of an increased length of cable.

In accordance with yet a further aspect of the invention, there is provided a fibre optic cable for use with laser light source for providing illumination over the length of the cable, the cable comprising a plurality of side emitting optical fibres disposed on the periphery - 6 - of the cable over its length, and a low-loss optical fibre in parallel with the side emitting fibres. Preferably, the low-loss fibre is located centrally in the fibre optic cable. Conveniently, said fibre optic cable is coupled by optical coupling elements which receive light from the low- loss optical fibre and which couple the light to the central core and side emitting optical fibres of a subsequent length of cable . In combination with each of the embodiments and aspects of the invention described above, an optical steering element is inserted between the laser and the fibre optic cable for controlling the access of laser light to the selected edge emitting optical fibres in the cable so that the fibres are illuminated sequentially, in one direction, providing the effect of light travelling along the cable in one direction in a stepwise motion. This effect can be used to provide an indication of direction in particular situations, for example in emergencies and the like. The light steering element may comprise a movably mounted mirror but is preferably fixedly mounted. Any suitable component which has light steering properties may be used but is preferably a electro-optic or an acousto-optic deflector whereby light is steered from one fibre within the cable to the next by using a varying d.c. field or radio frequency signal respectively.

Alternatively, the steering element is provided by an optical shutter in the form of a liquid crystal display panel disposed between the laser and the end of the fibre optic cable, the liquid crystal display panel having liquid crystal elements controllable to allow transmission of the laser light from the laser through the panel to selected fibres. In a further alternative arrangement the optical shutter may be provided by a mechanical shutter.

Preferably, the apparatus includes an internal - 7 - electrical supply which is conveniently a rechargeable battery.

These and other aspects of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:

Fig. la is a schematic illustration of illumination apparatus in accordance with a first embodiment of the present invention;

Fig. lb is an enlarged cross section of a fibre optic cable for use with the laser illumination apparatus of Fig. la;

Fig. lc is a circuit diagram of a control circuit for controlling light from the laser to the fibre optic cable ; Fig. 2 depicts an alternative embodiment of illumination apparatus for use as a portable illumination system;

Fig. 3a depicts an alternative embodiment of illumination apparatus for use in providing illumination over a relatively long distance;

Fig. 3b is an enlarged part of Fig. 3a and depicts a preferred form of fibre optic cable for providing illumination over a relatively long distance;

Fig. 4a is a diagrammatic view of an optical coupling means for use with the cable shown in Fig. 3b; Fig. 4b is a diagrammatic view of an alternative optical coupling means for use with the cable shown in Fig. 3b;

Fig. 5 depicts an embodiment of illumination apparatus for use as a mains failure safety illuminated guideline ;

Figs. 6a, b depict a cross-sectional and perspective view, respectively, of an alternative construction of fibre optic cable for use in providing illumination over relatively long distances; and

Figs. 7a, b are diagrammatic views of laser illumination apparatus in accordance with a further - 8 - embodiment of the invention coupled to energise a fibre optic cable via a controllable optical coupling means provided by a liquid crystal display element with Fig. 7b being an enlarged view of part of Fig. 7a. Reference is first made to Fig. 1 of the drawings which depicts a preferred embodiment of illumination apparatus in accordance with the present invention. It will be seen that the apparatus consists of a light source generally indicated by reference numeral 10 and a side emitting fibre optic cable 12. The light source 10 consists of a semi-conductor diode-laser pumped solid- state laser (dpssl) which is a neodymium yttrium orthovanadate (Nd:YV0₄) laser with intra-cavity frequency doubling to produce light at a wavelength of 532 nanometres (nm) . The laser 10 produces a laser beam 11 lmm in diameter which exits the laser at a light power of up to 20 milliwatts (mW) . The laser 10 is connected to a constant current diode-laser driver 14 which provides up to 1 Amp (A) of current at a voltage of 6V (the actual current level being used in this case being 850 milliAmps) . The diode- laser driver has a 12V power supply at a current rating of up to 1.2A which is provided by a rechargeable sealed lead-acid battery (National Panasonic) 16 rated at 12V and up to 6A maximum supply current. The battery is recharged by an open- frame linear power supply 18 set to 13.6V output which is used as an uninterruptible power source. The open-frame linear power supply consists of a step-down transformer, bridge rectifier, capacitive smoothing circuit, voltage current regulator with thermal protection (ER325; RS

Components) and its power supply input is 220-240V a.c. main voltage .

A plano-concave lens 20 with a focal length of 100mm (negative) is disposed between the output of the laser 10 and the fibre optic cable 12 and causes the laser beam 11 to diverge or increase in size to match the size of the end 22 of the side emitting fibre optic cable 12. In - 9 - this case the lens 20 causes the beam to diverge to match the 7mm diameter of the end 22 of the side emitting fibre optic cable 12 to optimise coupling between the laser and the cable . The fibre optic cable 12 is about 150 metres long and is best illustrated by reference to Fig. lb which is a cross-sectional view through the cable 12. It will be seen that fibre optic cable 12 consists of a bundle of high-loss optical fibres 1mm in diameter, generally indicated by reference numeral 24 all contained in a transparent sheath 27. The fibres 24 are twisted or rifled along the entire length of the cable 12 in accordance with fibre optic cable manufacturing techniques. The high- loss optical fibres 24 emit light along their length so that, when the laser beam is fed to the end 22 of the fibre optic cable, the entire length of the cable is illuminated and glows at the wavelength colour (green) . A 50μm low-loss fibre cable 26 (Optical Cable Corporation, U.S.A.) runs in parallel with cable 12 over its length and doubles back to the laser supply into a transition switch 29 to provide a safety cut-out, as best seen in Fig. lc . The switch 29 has an output 29a and is coupled either to a solenoid 31 which has an output which is connected to a shutter 33 movable across the laser beam 11 or connected directly to an input of the laser driver 14 where it is arranged to disconnect power to the laser. If the cable 12 and 50μm cable 26 are cut, the photo-transistor 29b (SFH 309) in switch 29 senses a reduction in light and switches off. Current is supplied via 150KΩ resistor to turn transistor 29c (BC 109) ON and the output of the transistor drops. This change causes the solenoid 31 to move shutter 33 into the path of beam 11, thus preventing laser light from being transmitted down cable 12, thus providing a failsafe arrangement. The switch output 29a can also cause the laser driver 14 to switch off power to the laser 10. An alternative form of cable construction is - 10 - illustrated by reference to Fig. 3b where the cable 13 consists of a number of fibre optic cable lengths or sections 13a, 13b, 13c etc. each about 150 metres in length which are coupled together by optical coupling means 28 (as shown in Fig. 3a) and where the cable construction includes a low-loss optic cable 26 to transport light to distant cable sections so as to extend the operating length of illuminated cable, as will be later described in detail. In this case it is necessary for both the central low-loss core fibre 26a and peripheral side emitting fibres 24a to be energised simultaneously by the laser 10. As with the arrangement shown in Fig. lb, a 50μm cable 26 is also coupled to cable lengths 13a, 13b, 13c for the same safety reason. However, the cable 26 is coupled in parallel until the last optical coupling means 28 whereupon it is doubled back to switch 29 because if the central low-loss fibre 26a is cut at any position along its length the laser beam into fibre 26a is prevented by the shutter 33 or by switching off the laser driver 14 as described above.

Fig. 3a shows the assembly; the beam 11 from the laser 10 is split by a beamsplitter 45 and coupled by a lens 47 into the low-loss fibre optic cable 26, then transmitted some distance along the cable before being injected into the composite optical cable 13 by the optical coupling means 28. Simultaneously, some light is transmitted through the beamsplitter 45 and made to diverge by lens 20 to fill the peripheral side emitting fibres 24 at face 22. The reason for this is that illumination tends to diminish after about 150 metres because of intrinsic decay and, accordingly, in order to extend the effective length of illuminated cable, it is necessary to couple light from the central low- loss core fibre 26 to the peripheral fibres 24 of subsequent lengths of cable 13b, 13c etc. This is achieved by using optical coupling means 28 as best seen in Figs. 4a and 4b of the drawings. - 11 -

With reference to Fig. 4a, where only a single subsequent section of cable 13b is to be appended, a coupling means as illustrated may be used. The optical coupling element 28 is secured to the remote end 32 of the first section 13a of the cable. Light from the low- loss core fibre 26 diverges from face 32 to a larger area on a second face 38 of the subsequent cable section 13b, so as to encompass the peripheral side emitting fibres 24b of the second section 13b, this second section 13b also being secured to the optical coupling element 28. In this way the subsequent section of fibre optic cable is illuminated. Where a second and further subsequent cable sections are to be illuminated 13b, c etc., the optical coupling element shown in Fig. 4b is used because it is necessary to couple light from a preceding cable section into both the central low-loss core fibre 26b, c etc. and peripheral side emitting fibres 24b, c etc.

Referring to Fig. 4b, the remote end 32 of a preceding section of cable 13a is secured to the coupling element 28b and the low-loss fibre cable 26a terminated in a fibre bulkhead connector and collimator 70. Light from the low-loss fibre 26a is split by the beamsplitter 72 and coupled by a lens 74 into the subsequent low- loss fibre optic cable 26b. Simultaneously, light is transmitted by the beamsplitter 72 and made to diverge by the lens element 76 to fill the peripheral side-emitting fibres in the composite cable section 13b and so illuminate this section. This is repeated throughout the length of the cable 13 with the result that the entire length of cable is illuminated.

It will be appreciated that the illumination apparatus described above has a variety of applications, for example as a safety guideline in darkened areas, such as stairwells, cinemas and subsea applications. In a stairwell, for example, the laser is actuated as par_t of an emergency lighting situation using the circuit as shown in Fig. 5. This circuit is similar to that shown - 12 - in Fig. 1 except it includes a double-pole relay 39 which is normally held open by the electrical supply, and which isolates the internal battery 16 from the laser-diode driver 14. Upon external power supply failure, the relay contacts close, allowing the battery 16 to energise driver 14 to allow the laser to operate and illuminate the cable 12. Thus, this embodiment provides a self- contained unit such that, in the event of power failure, the re-chargeable battery 16 supplies power to the laser 10 which, in turn, illuminates the cable 12 to provide a safety illuminated guideline within the stairwell or the like. Similarly, with such a portable unit the laser illuminatable guideline could be used in hazardous environments, for example pot -holing, mines and the like as well as in subsea applications. The safety cut-out cable 26 and switch 29 operate as described with reference to Figs, la, lb.

In addition, it will be understood that sections of optical fibre cable may be laid in a variety of environments and left with appropriate free ends with coupling elements such that, in the event there is a need for illuminating a path in the environment, such as, for example, mines, tunnels and the like, a laser unit is coupled to the fibre optic cable and energised to provide illumination. This provides a flexible illumination system and such fibre cables can be readily installed along with other utility cables, such as electrical power and communication cables. Such applications are also in large power plants or any similar environment where there is a large amount of corridors, tunnels and the like, to assist in providing guidance and direction in the event of power failure.

Reference is now made to Figs. 6a, b of the accompanying drawings showing a fibre optic cable 40 which has an alternative structure to that shown in Fig. 3b. In this case, as best seen in Fig. 6a, cable 40 comprises two fibre optic cables 41,42 coupled together - 13 - in parallel and with reference to Fig. 6b each cable section 40a, 40b is formed of cable sections 41a, 42a; 41b, 42b etc., and, as with the first embodiment, subsequent sections 40a, 40b of cable are connected by an optical coupling element 28b, as best seen in Fig. 4b. Cable 41 is an edge emitting cable formed of edge emitting optical fibres 24 (Fig. lb) and cable 42 is a low-loss optic fibre. In this case, the side emitting fibre optic cable 41 is separate from the low-loss fibre optic cable 42 and both of these cables are energised simultaneously by the laser 10. Fig. 3a again shows an assembly for this type of cable structure. The safety feature is also provided by cable 26, switch 29, solenoid 31 and shutter 33 or laser driver 29 as described with reference to Figs. 3a and 3b.

However, as described above, after about 150 metres intrinsic decay means there is insufficient optical power available to provide satisfactory illumination and therefore light travelling through the low- loss fibre optic 42a, 42b etc. is coupled into subsequent sections

41b, 41c etc. of edge emitting fibre optic cable 41. This is achieved using the optical coupling 28b as shown in Fig. 4b. In this way, laser light is coupled through the serially connected low-loss and high-loss cables in parallel to provide a long length of cable 40 similar to that shown in Fig. 3a. This cable may also be several kilometres in length. The side emitting fibre optic cable 41 as shown in Figs. 6a and 6b is manufactured by similar technology to the cable shown in Figs. 3a and 3b, but without the central core. The low-loss fibre optic cable 42 coupled in parallel to the edge emitting cable 41 is a standard fibre optic cable and both of these cables may be encased in a single transparent plastic jacket 57 as with the cable shown in Fig. 3b to simultaneously protect the cable and allow light to escape .

Reference is now made to Figs. 7a, b of the drawings - 14 - in which the apparatus has a laser light source 10, driver 14 and battery 16 similar to that shown in Figs. la and 2, except that an optical shutter 54 is disposed between the laser light source 10 and the end 22 of the fibre optic cable 12. This optical shutter is provided by a liquid crystal display panel 56 which is controllable via a programmable unit, generally indicated by reference numeral 58, which, in turn, is coupled to the battery 16. The programmable unit 58 controls various liquid crystal cells 60 in the display to operate each cell between an optically transmissive mode, shown by broken lines 62, and an optically opaque mode, as shown by solid lines 64. As best seen in Fig 7b, in the optically transmissive mode, light from the laser 10 passes through the targeted liquid crystal display cell 62 to be received by the appropriate optical fibre 24 aligned with that particular liquid crystal display cell. In this arrangement, the cells in the liquid crystal display panel 56 are energised by unit 58 to operate so that the cells 60 open and close sequentially in a circular path (shown by the arrow in the clockwise direction) . This has the effect of allowing the laser beam to be received sequentially by each aligned fibre 24 in the cable 12 in a stepwise manner, for example a clockwise (or anti-clockwise) direction. Thus, the laser illuminates each fibre at a different time, the timing of illumination being set by programming in the unit 58. The perception of illumination of the cable 12 by a user is that a light beam appears to run along the fibre in one direction at very high speed. This feature can be used to guide people to follow a particular path in a dark environment, for example in a stairwell, cinema, tunnel or the like. It will be understood that the liquid crystal panel is fixedly mounted and is compact and robust and requires minimal electrical power to operate and is therefore suitable, in particular, with the portable embodiment shown in Fig. 2. A 50μm safety

Claims

- 15 - fibre 26 and the aforementioned components are also present in this arrangement.It will be appreciated that an alternative arrangement to that shown in Figs. 7a, b is implemented by an alternative embodiment of the invention (not shown in detail) . In such a case there are at least three different sets of cables within a particular side emitting fibre optic cable. In this case, light is steered, from the same light source, from one cable set within the fibre optic cable to the next cable set. It will be appreciated that another alternative arrangement to that shown in Figs. 7a, b is implemented by an alternative embodiment of the invention (not shown in detail) . In such a case the apparatus further comprises a beam steering element whereby light from the laser may be steered selectively toward a particular side emitting fibre optic. The light steering element may be a movably mounted mirror or an acousto-optic deflector or an electro-optic deflector, the latter two controllable by the application of a radio frequency (rf) signal or direct current (d.c.) electric field respectively. These techniques have a similar effect to the liquid crystal shutter panel described above with reference to Figs. 7a, 7b and this arrangement is also robust and compact.It will be appreciated that various modifications may be made to the embodiments hereinbefore described without departing from the scope of the invention. For example, other laser light sources could be implemented for providing different colours of illumination, such as a red semi-conductor diode-laser light at 635 nm. In addition, it will be appreciated that a red and a green laser may be combined in a single unit to provide dual energisation of the same or different fibres which may be coupled to the laser light sources using appropriate optical couplers. This may be used for situations where guidance is required between a source and different - 16 - destinations , one particular colour of illumination denoting a first destination and a second colour denoting a different destination to avoid ambiguity or confusion. Such lasers could be combined in a single portable unit or a hand-held unit which could be readily coupled to cables already in place or cables to be provided with the unit. The portable unit may use a non-rechargeable battery and laser driver. The safety fibres may be provided by other than a 50μm fibre. It may be omitted from arrangements where safety is not believed to be an issue .As mentioned above, it will be appreciated that the embodiments of the illumination apparatus in accordance with the present invention may be used in a variety of different environments. One such environment is subsea work where a sea diver uses such an illuminated cable to follow guidance from a remote vehicle or a diving bell in pitch black conditions to a wellhead or pipeline or the like requiring inspection and/or workover. Advantages of the present invention include: light emission is produced over a distributed length of side emitting fibre optic cable from a device which is robust, longer lived and more energy efficient than visually similar devices; the optical coupling arrangement allows longer use of side emitting fibre optic cable lengths than with prior art systems, and the use of optical coupling arrangements of different lengths of cable allows illumination of such cable up to several kilometres in length. The invention has application in a number of environments because of its versatility, for example, use in emergency lighting situations, in light guiding applications for stairwells, cinemas, aircraft, subsea uses and the like or where a long length of cable is desired and the use of a mains power source is often not possible. In addition, the fibre optic cables can be manufactured separately and installed for subsequent connection to a laser source further providing an - 17 - increased flexibility for security and guidance when the situation demands it.The invention uses conventional electronics and is easily serviceable and/or repairable, if required, and overcomes the limitations of the prior art arrangements which limit their flexibility and application. CLAIMS

1. Illumination apparatus comprising a laser light source, a power supply for the laser light source and a side emitting fibre optic cable coupled to the laser light source, the light laser source being of sufficient power such that when energised the side emitting cable is illuminated along its length.

2. Apparatus as claimed in claim 1 wherein the power supply includes a rechargeable battery such that in the event of mains power failure, the rechargeable battery continues to energise the laser for a predetermined time.

3. Apparatus as claimed in claim 1 wherein the power supply is a mains power supply which includes a relay system such that the battery energises the laser only in the event of a mains failure.

4. Apparatus as claimed in any preceding claim wherein the laser light source is a solid state laser which is, in turn, excited by a semiconductor diode-laser.

5. Apparatus as claimed in any preceding claim wherein the side emitting fibre optic cable comprises a plurality of side emitting fibre optic cables bundled and twisted together and encased in a transparent plastic jacket.

6. Apparatus as claimed in any preceding claim including optical coupling means to couple the output of the laser light source to the end of the side emitting fibre optic cable, the optical coupling means being arranged so as to cause the beam to expand or contract to match the diameter of the side emitting fibre optic cable to maximise efficient light coupling.

7. Apparatus as claimed in any preceding claim wherein said apparatus includes a fibre disposed in parallel with - 19 - said fibre optic cable for also receiving said laser light, said fibre being coupled back to said laser or to said laser supply via a light sensing means and a laser control means whereby if the fibre optic and said fibre are cut, said light sensing means detects a change and interrupts the supply of laser energy to said cable.

8. Apparatus as claimed in claim 7 wherein said light sensing means is coupled to a movable shutter which is moved to obstruct the laser beam in response to the cable and fibre being cut.

9. Apparatus as claimed in claim 7 wherein said light sensing means is coupled to said laser power supply for switching off said power supply in response to the cable and fibre being cut.

10. Illumination apparatus for illuminating side emitting fibre optic cable over a relatively long distance, said fibre optic cable comprising at least two fibre optic cable sections coupled by optical coupling means, said apparatus comprising a laser light source, a power supply for said laser light source, a first fibre optic cable section coupled to said light source, said first fibre optic cable section having a first set of side emitting optical fibres, and a first low-loss optical fibre located in parallel with side emitting fibres, said optical coupling means disposed between the first and second fibre optic cable sections and being optically coupled to said first low-loss optical fibre, at a first end proximal to said laser light source, and to low-loss optical fibres and side emitting optical fibres in said second cable section, at a second end distal to said laser light source so that laser light from said first low-loss optical fibre is coupled to side emitting optical fibres and low-loss optical fibres in a second section to cause said second and subsequent - 20 - sections to illuminate in the same way as said first section.

11. Apparatus as claimed in claim 10 wherein said fibre optic cable has a structure such that a plurality of side emitting optical fibres are located on the periphery of the cable with a low-loss optic fibre located in the core, said coupling means at the end of a feeder section of said cable being coupled to the core to feed light from the core to both low-loss optical fibre and to the peripheral side emitting optical fibre in subsequent receiving sections of cable such that lengths of cable can be concatenated together via optical coupling means, such that the effective length of illuminated cable is greatly in excess of a single piece of cable.

12. Apparatus as claimed in claim 10 wherein said fibre optic cable has a structure in which a side emitting fibre optic cable is disposed in parallel with a separate low-loss single fibre optical cable and, after a predetermined length, is coupled to an optical coupling lens which takes light from the low-loss cable and feeds it to a subsequent length of side emitting fibre optic cable to provide an effective increase in cable length, the low-loss fibre running in parallel.

13. Apparatus as claimed in claim 12 wherein the low- loss fibre runs in parallel with each subsequent length of side emitting optical cable and continually feeds light, via a series of optical couplers, to subsequent lengths of side emitting fibre optic cable to provide appropriate illumination.

14. Apparatus as claimed in any preceding claim wherein an optical steering element is inserted between the laser and the fibre optic cable for controlling the access of laser light to the selected edge emitting optical fibres