GB1581614A - Fibre optic switch device - Google Patents

Description

(54) FIBRE OPTIC SWITCH DEVICE (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company, of 190 Strand, London W.C.2, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical switches and in particular to a fibre optic switch of the magnetic reed type.

A major problem in the construction of fibre optic systems, e.g. telecommunication or control systems, is the provision of devices for switching light betwen fibres.

Switch devices at present in use are generally expensive to manufacture and often require factory fitment to the fibres prior to installation. Furthermore, it is a difficult problem to provide a switch which will operate reliably for a large number of switching operations such as is necessary in a telecommunications exchange.

According to the invention there is pro- vided an optical switch arrangement,-including two or more rigidly mounted tutu lar reeds at least one of which is made of a magnetic material and each of which contains an optical fibre threaded therethrough, the contact end of each reed being cut away so as to partly expose the respective optical fibre end, the reeds being so constructed and disposed with respect to one another that, when their contact ends are brought into mutual contact, their respective fibres are brought into optical alignment.

Embodiments of the invention will now be described with reference to the accompanying drawing in which: Fig. 1 shows the contact arrangement of a fibre optic reed switch, Fig. 2 shows one of the reed assemblies of the contact arrangement of Fig. 1, and Figs. 3 and 4 show the contact arrangement of a fibre optic reed changeover switch.

Referring to Figs. 1 and 2, the switch includes a pair of tubular reeds 11 made of a magnetic material and rigidly mounted, e.g. in a glass or other non-magnetic envelope (not shown). The contact end of each reed is cut to provide a hollow hemicylindrical portion 12 extending frpm the reed end and defined by shoulder 13.

Each reed is threaded by a snugly fitting optical fibre 14, which may be of the plastics clad silica type, the end of each fibre being cut and polished perpendicular to its longitudinal axis. Each fibre is arranged with its end in a plane midway along the hemicylindrical portion and is secured in place, e.g. with a small quantity of an adhesive.

The fibres 14 and the reeds 11 are so arranged that, when the reed ends are attracted together by the application of a magnetic field, each fibre end fits snugly in the unfilled hemicylindrical channel portion 16 in the end of each reed thus prc- viding a butt joint between the two fibres.

The nature of the arrangement also ensures that the fibres are in optical alignment when coupled in this way. In some applications a small quantity of refractive index matching fluid may be placed on the fibre ends to reduce coupling losses.

Fig. 3 shows an alternative arrangement in which a changeover action is provided.

In this arrangement an input fibre 21 may be coupled to either of two output fibres 22 or 23. As before, the input fibre 21 is threaded through and secured in a tubular magnetic reed 24. The contact end of the reed 24 is cut away to provide two forwardly extending fingers 25 with the fibre 21 held therebetween, the fibre end extending part way along the fingers.

The stationary contact reed 26 of the changeover arrangement is provided by a tube of non-magnetic material containing fibre 22 and whose free end is cut away, as shown in Fig. 3, to form a mating surface with the end of the reed 24. The fibre 22 mounted in the reed 26 is disposed with its c lt and polished end flush with the shoulder 27 part way along the cut-away portion of the reed. The third contact reed 28 of the switch arrangement is similar in construction to the reed 26, but is made of a low remanance magnetic material.

The three reeds are rigidly mounted, e.g.

in a glass envelope, as shown in Fig. 4 with the contact end of changeover reed 24 in mating abutment with the contact end of the stationary reed 26 and adjacent the contact end of the third reed 28. Application of a magnetic field to the reeds causes the changeover reed 24 to disengage the non-magnetic reed 26, the magnetic reeds 24 and 28 deflecting into mutual contact. As before, the open channels 29 and 30 in the ends of the reeds 26 and 28 engage the fibre 21 to ensure axial alignment when an optical contact is effected.

The switch devices described herein may be operated either by a surrounding solenoid as in a conventional electrical reed contact unit, or by an adjacent movable magnet. The switches may advantageously be employed in the construction of a fibre optic telecommunication exchange but may also be employed in other fibre optic switching applications. Thus they may also be employed in the construction of fibre connected instrumentation particularly in those environments where the introduction of an electrical device would be hazardous.

In some applications only one of the reeds of the arrangement of Figs. 1 and 2 may be magnetic so as to provide a normally closed contact arrangement, the magnetic reed being drawn away from the nonmagnetic reed by the application of a magnetic field.

WHAT WE CLAIM IS:- 1. An optical switch arrangement, including two or more rigidly mounted tubu- lar reeds at least one of which is made of a magnetic material and each of which contains an optical fibre threaded therethrough, the contact end of each reed being cut away so as to partly expose the respective optical fibre end, the reeds being so constructed and disposed with respect to one another that, when their contact ends are brought into mutual contact, their respective fibres are brought into optical alignment.

2. A switch arrangement as claimed in claim 1, and which includes three reeds one of which is non-magnetic so as to provide a changeover action.

3. A switch arrangement as claimed in claim 1 or 2, and in which the reeds are mounted in a non-magnetic envelope.

4. An optical switch arrangement substantially as described herein with reference to Figs. 1 and 2 or to Figs. 3 and 4 of the accompanying drawings.

5. A telecommunication exchange provided with a plurality of switch devices as claimed in any one of the preceding claims; 6. A method of selectively coupling pairs of optical fibres substantially as described herein with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. switch arrangement is similar in construction to the reed 26, but is made of a low remanance magnetic material. The three reeds are rigidly mounted, e.g. in a glass envelope, as shown in Fig. 4 with the contact end of changeover reed 24 in mating abutment with the contact end of the stationary reed 26 and adjacent the contact end of the third reed 28. Application of a magnetic field to the reeds causes the changeover reed 24 to disengage the non-magnetic reed 26, the magnetic reeds 24 and 28 deflecting into mutual contact. As before, the open channels 29 and 30 in the ends of the reeds 26 and 28 engage the fibre 21 to ensure axial alignment when an optical contact is effected. The switch devices described herein may be operated either by a surrounding solenoid as in a conventional electrical reed contact unit, or by an adjacent movable magnet. The switches may advantageously be employed in the construction of a fibre optic telecommunication exchange but may also be employed in other fibre optic switching applications. Thus they may also be employed in the construction of fibre connected instrumentation particularly in those environments where the introduction of an electrical device would be hazardous. In some applications only one of the reeds of the arrangement of Figs. 1 and 2 may be magnetic so as to provide a normally closed contact arrangement, the magnetic reed being drawn away from the nonmagnetic reed by the application of a magnetic field. WHAT WE CLAIM IS:-

1. An optical switch arrangement, including two or more rigidly mounted tubu- lar reeds at least one of which is made of a magnetic material and each of which contains an optical fibre threaded therethrough, the contact end of each reed being cut away so as to partly expose the respective optical fibre end, the reeds being so constructed and disposed with respect to one another that, when their contact ends are brought into mutual contact, their respective fibres are brought into optical alignment.

2. A switch arrangement as claimed in claim 1, and which includes three reeds one of which is non-magnetic so as to provide a changeover action.

3. A switch arrangement as claimed in claim 1 or 2, and in which the reeds are mounted in a non-magnetic envelope.

4. An optical switch arrangement substantially as described herein with reference to Figs. 1 and 2 or to Figs. 3 and 4 of the accompanying drawings.

5. A telecommunication exchange provided with a plurality of switch devices as claimed in any one of the preceding claims;

6. A method of selectively coupling pairs of optical fibres substantially as described herein with reference to the accompanying drawings.