GB2190513A

GB2190513A - Optical fibre switching devices

Info

Publication number: GB2190513A
Application number: GB08608086A
Authority: GB
Inventors: John Clive Challans; Matthew Norman Albert Lee
Original assignee: Plessey Co Ltd; Acorn Computers Ltd
Current assignee: Plessey Co Ltd; Broadcom UK Ltd Great Britain
Priority date: 1986-04-02
Filing date: 1986-04-02
Publication date: 1987-11-18
Also published as: WO1987006014A1; GB8608086D0; EP0277144A1

Abstract

An optical switching device comprising a housing (2) having means for receiving three or more optical fibres, an electrically operable means (44) for moving an optical path changing device (36, 38) between different positions for switching optical coupling paths selectively between pairs of the optical fibers. A cable (16) carries at least one of the optical fibers and electrically conducting member, electrical coupling means being provided between the cable and the electrically operable means so that when there is no power in the electrically conducting member the or each optical fiber within the cable is optically decoupled from the other optical fibers within the housing. A local area network incorporating the optical switching devices is also provided.

Description

SPECIFICATION Improvements in and relating to optical switching devices The present invention relates to an optical switching device and more particularly to an optical switching device for use in coupling a terminal station to an optical fibre bus in an optical communication network.

According to the present invention there is provided an optical switching device comprising a housing having means four receiving three or more optical fibres, each fibre being associated with a lens for either collimating a light beam or for converging a collimated light beam, electrically operable means moving an optical path changing device between different positions for switching optical coupling paths selectively between the optical fibres, a cable carrying at least one of the optical fibres and an electrically conducting member, electrical coupling means being provided between the cable and the electrically operable means so that when there is no power in the electrically conducting memberthe or each optical fibre within the cable is optically decoupled from the other optical fibres within the housing.

In a preferred embodiment means are provided by which the cable is easily attachable to and detachable from the housing. In a preferred embodimentthe housing is provided with a socket for receiving one end ofthe cable.

In different embodiments of the present invention the optical path changing device may comprise one or more prisms, one or more mirrors or combinations thereof.

The electrically operable means may be mechanically coupled to the optical path changing device to cause sliding, rotation or swinging of the optical path changing device for switching optical coupling paths selectively between pairs ofthe optical fibres. In a preferred embodiment the electrically operable means is a solenoid the core of which is mechanically coupled to a mechanism for moving the optical path changing device.

In a preferred embodiment the optical path changing device is mounted on an arm pivotally mounted within the housing, the electrically operable means being mechanically coupled to the arm to move the arm into a first position when the electrically operable means is energised and spring biassing means being provided to move the arm into a second position when the electrically operable means is de-energised.

The present invention also provides an optical communication network comprising an optical fibre bus coupled by means of optical switching devices to a plurality ofterminal stations at spaced locations along the length ofthe optical fibre bus, each optical switching device comprising a housing having means for receiving three or more optical fibres, each fibre being associated with a lens for either collimating a light beam orforconverging a collimated light beam, electrically operable means for moving an optical path changing device between different positions for switching optical coupling paths selectively between pairs of the optical fibres, a cable carrying at least one of the optical fibres and an electrically conducting member, electrical coupling means being provided between the cable and the electrically operable means so that when there is no power in the electrically conducting member the or each optical fibre within the cable is optically decoupled from the other optical fibres within the housing.

The present invention will be described further, by way of example, with reference to the accompanying drawings in which Figure lisa sectional view of an optical switching device according to one embodiment of the present invention; Figure2 is a sectional view of the optical switching device of Figure 1 viewed from the direction A in Figure 1; and, Figure 3 illustrates an optical communication network coupled by means of the optical switching device of Figures 1 and 2 to spaced terminal stations around the periphery of the communication network.

Referring to Figures 1 and 2 an optical switching device comprises a substantially oblong housing 2 four side walls of which are designated by numerals 4,6,8and 10.

Two optical cables 13 and 15, the end portions of which protrude through the side walls 4 and 6, each carry a respective optical fibre 12 and 14. The optical cables 13,15 and their associated optical fibres 12,14 are held in axial alignment with one another by a pair of retaining members 5,7 and by the provision of two aligned elongated holes 17, 19 defined within the housing 2 for receiving the ends of the optical cables 13and 15.

A cable 16 extending from a terminal station has its end formed as a plug 18forengagementwithin a complementary socket assembly 20 located and fixed within the housing 2 immediately adjacent a portion ofthe side wall 10. The plug 18 is retained after insertion within the socket assembly 20 by means of a spring biased portion 22 of the plug 18.

The plug 18 is detachable from the socket assembly 20 by depressing the portion 22 towards the central axis through the plug 18 thereby enabling removal of the plug 18 from the socket assembly 20 and from the housing 2.

The cable 16 carries two optical fibres 24,26 the ends of which terminate within the plug 18. The ends of the optical fibres 24,26 are associated with respective lenses 28,30. Each lens 28,30 forms part of a respective expanded beam connector and may serveforeither collimating a light beam emerging from the optical fibre end orforconverging and focussing a collimated light beam onto the optical fibre end. Similarly the optical fibres 12 and 14 are associated with respective lenses 32 and 34. Each lens 32, 34forms partofa respective expanded beam connector and may also serve to produce either a collimated light beam orto converge a collimated light beam.

An optical path changing device in the form of a pair of spaced, inclined mirrors 36 and 38 are mounted on an arm 40, the arm 40 being pivotally mounted at one end about a pivot axis 42 defined within the housing 2. Within the housing 2 adjacent the arm 40 is located a solenoid 44 having a fixed housing 45 and an inner core 46 one end of which engages a side surface of the arm 40. The arm 40 is also provided with an extension 48 to which is attached one end of a return spring 56.

A power source for energising the coils ofthe solenoid 44 is provided at the terminal station, the electrical power being fed to the coils via an electrical conductor carried bythecable 16, a spring contact 50 and two wires (not shown).

Iftheterminal station is not active, i.e. is not switched on orthere is a malfunction, power is no longertransmitted to the coils of the solenoid which become de-energised. When the coils of the solenoid are de-energised the tension within the return spring 56 exerted on the extension 48 results in rotation of the arm 40 in a clockwise direction aboutthe pivot axis 42, the arm 40 compressing a resilient spacing material 52 sandwiched between the side surface of the arm 40 and the housing 45 ofthe solenoid. The fixed housing 45 prevents further clockwise rotation ofthe arm 40, and the arm 40 adopts an inclined orientation as shown in Figure 2.The inclined mirrors 36 and 38 are therefore rotated away from the gap defined between the lenses 32 and 34 enabling lightto pass directly between the lenses 32 and 34 and thereby optically coupling the end ofthe optical fibres 12 and 14.

The energisation ofthe coils causes the inner core 46 of the solenoid to move in a direction towards the arm 40, abutting the side surface of the arm 40 exerting a force thereon and forcing the arm 40to pivot against the bias of the spring 56 in an anticlockwise direction aboutthe pivot point 42 until it reaches a vertical orientation as shown in Figure 2.

When the arm 40 is in its vertical orientation the mirrors 36 and 38 adopt a position within the gap defined between the lenses 32 and 34. The mirror 36 reflects the collimated light beam emerging from the lens 32 towards the lens 28 which focuses the light beam onto the end ofthe optical fibre 24.Similarly light emerging from the optical fibre 26 is collimated bythe lens 30, reflected through 90" by the mirror38 and is focused by the lens 34 onto the end ofthe opticalfibre 14. In this way light signals can be received by and transmitted from the terminal station andthere is provided a fail safe system whereby should the terminal station become inactive, the mirrors 36 and 38 will be rotated away from the gap between the lenses 32 and 34thereby enabling lightto pass directly along an optical path between the two lenses 32 and 34.

In different embodiments ofthe present invention the optical path changing device may comprise one or more prisms, one or more mirrors/or combinationsthereof.

Whereas the electricallyoperable means is described above as a solenoid it will be appreciated that other electrically operable means, such as an electric machine, may be provided. The electrically operable means is mechanically coupled to the optical path changing device and in various embodiments this coupling may give rise to sliding, rotation or swinging of the optical path changing device for switching optical coupling paths selectively between pairs ofthe optical fibres.

Figure 3 illustrates an optical communication ring network having fourterminal stations TA, TB, TC and TD spaced around its periphery, each oftheterminal stations being associated with its respective optical switching device A, B, C and D. The optical switching devices, A, B, C and Dare like that described above with reference to Figures 1 and 2 but maytakethe form of any embodiment within the scope of the present invention. Each of the terminal stations TA, TB, TC and TD has a d.c. power source, a light transmitter such as a light emitting diode or laser and a light receiver such as a photodiode.

It will be appreciated that any number of optical switching devices may be installed in the ring of optical fibre in dependence on current and future requirements. Thus at a later date, terminal stations can be plugged into the fibre optic ring network without disturbing the operation of any active terminal station services.

In one embodiment of the present invention power is only supplied to the solenoid in the optical switching device when the associated terminal station is switched on and the light transmitter is working. Thus, in a fail-safe situation the optical path changing device moves out of the main light beam passing around the ring network thereby preventing the failure of one terminal station from stopping the entire system.

Claims

1. An optical switching device comprising a housing having means for receiving three or more optical fibres, each fibre being associated with a lens foreithercollimating a light beam or for converging a collimated light beam, electrically operable means for moving an optical path changing device between different positions for switching optical coupling paths selectively between the optical fibres, a cable carrying at least one of the optical fibres and an electrically conducting member, electrical coupling means being provided between the cable and the electrically operable means so that when there is no power in the electrically conducting member the or each optical fibre within the cable is optically decoupled from the other optical fibres within the housing.

2. An optical switching device as claimed in claim 1 wherein the cable is easily attachable to or detachablefromthe housing.

3. An optical switching device as claimed in claim 2 wherein the housing is provided with a socketfor receiving one end of the cable.

4. An optical switching device as claimed in any one of claims 1 to 3 in which the electrically operable means is mechanically coupled to the optical path changing device to cause sliding, rotation or swinging of the optical path changing device for switching optical coupling paths selectively between pairs ofthe optical fibres.

5. An optical switching device as claimed in any one of claims 1 to 4 in which the optical path changing device comprises one or more prisms.

6. An optical switching device as claimed in any one of claims 1 to Sin which the optical path changing device comprises one or more mirrors.

7. An optical switching device as claimed in any one of claims 1 to 6 in which the lense for either collimating a light beam orforconverging a light beam forms part of a respective expanded beam connector.

8. An optical switching device as claimed in any one of claims 1 to 7 in which the optical path changing device is mounted on an arm pivotally mounted within the housing, the electrically operable means being mechanicallycoupledtothe arm to move the arm into a first position when the electrically operable means is energised and spring biassing means being provided to move the arm into a second position when the electrically operable means is de-energised.

9. An optical communication network comprising an optical fibre bus coupled by means of optical switching devices to a plurality ofterminal stations at spaced locations along the length ofthe optical fibre bus, each optical switching device comprising a housing having means for receiving three or more optical fibres, each fibre being associated with a lens for either collimating a light beam orforconverging a collimated light beam, electrically operable means for moving an optical path changing device between different pairs ofthe optical fibres, a cable carrying at least one ofthe optical fibres and an electrically conducting member, electrical coupling means being provided between the cable and the electrically operable means so that when there is no power in the electrically conducting member, the or each optical fibre within the cable is optically decoupled from the other optical fibres within the housing.

10. An optical communication network as claimed in claim 9 the optical switching devices being as claimed in any one of claims 1 to 8.

11. An optical communication network substantially as hereinbefore described with reference to Figure 3 ofthe accompanying drawings.

12. An optical switching device substantially as hereinbefore described with reference to Figures 1 and 2 ofthe accompanying drawings.