GB2224129A - Optical matrix - Google Patents

Abstract

An optical matrix switch comprising a single crystal silicon slice (8) having a plurality of mutually orthogonal V-grooves (10, 12) etched into its surface using a conventional silicon photolithographic technique, the silicon being crystallographically orientated such that, as a result of the cubic structure of the silicon, the resulting V-grooves are precisely at 90 DEG to each other, with the sides of each V precisely at 54.74 DEG to the surface of the silicon. The mutually orthogonal V-grooves (10, 12) serve as guides for a plurality of cylindrical fibre optic terminations (16) so that light signals can be routed from one selected fibre optic (14) to another by the location of a light reflecting means, also formed as an etched silicon crystal with a mirror or pentaprism, at the intersection of the grooves (10, 12) associated with those particular fibre optics. <IMAGE>

Description

DESCRIPTION OPTICAL MATRIX.

The present invention is concerned with optical switching systems and in particular with an optical matrix for use in switching fibre optic signals.

Fibre optic communication systems offer considerable advantages over conventional electronic systems, primarily because of the replacement of bulky copper cables with lightweight optical fibres which can carry substantially more information.

In particular, fibre optic cables are increasingly used in communication networks where, typically, several hundred computer terminals need to be linked to several hundred data transmitters and receivers, such as the ports of a mainframe computer.

In conventional systems, interconnections within the networks are effected using plugs and sockets so that equipment can be physically disconnected and the networks reconfigured as requirements for information within the network change.

To facilitate the constant plugging and unplugging of cables and cross patching between equipment, matrix switches are used, typically as shown in U.K. Patent 1,081,171. In these, a matrix or cross hatch of bus bars is used with the bus bars sandwiched between layers of insulation so that alternate planes contain bus bars in the X and Y directions. Insertion of a plug at any co-ordinate (X,Y) then allows the routing of any X-input to any Y-output.

By the use of several layers of bus bars, multi-level signals can be conveniently switched with one plug designed to selectively short only adjacent X and Y bus bars.

Fibre optic networks also need to be reconfigured in much the same way as conventional electronic networks and the object of the present invention is to provide a fibre optic matrix switch whereby a fibre optical signal can be routed by the selection of a particular matrix co-ordinate.

In its broadest aspect, the essence of the present invention is to use a plurality of intersecting V-grooves etched into the surface of a slice of single crystal silicon which has been crystallographically orientated so that preferred crystal planes are exposed by the etch using a conventional silicon photolithographic technique.

Such V-grooves are crystallographically accurate and in particular the crystal orientation of the silicon can be chosen so that the sides of the V are precisely at 54.74 to the surface of the silicon and so that the intersecting V-grooves are precisely at 90 one to another.

Thus, in accordance with one embodiment of the present invention, there is provided an optical matrix switch comprising a single crystal silicon slice having a plurality of mutually orthogonal V-grooves etched into its surface using a conventional silicon photolithographic technique, the silicon being crystallographically orientated such that, as a result of the cubic structure of the silicon, the resulting V-grooves are precisely at 900 to each other, with the sides of each V precisely at 54.740 to the surface of the silicon, the mutually orthogonal V-grooves serving as guides for a plurality of cylindrical fibre optic terminations so that light signals can be routed from one selected fibre optic to another by the location of a light reflecting means at the intersection of the grooves associated with those particular fibre optics.

The light reflecting means, such as a mirror or pentaprism, can be mounted on, or be part of, a structure whose configuration matches the intersecting grooves. Advantageously, this is achieved in that said structure is formed by an etched single silicon crystal which is the male counterpart of the intersecting V-grooves, whereby alignment of the reflecting means to the silicon base is crystallographically precise.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig.l is a perspective view, on an enlarged scale, of one embodiment of an optical matrix in accordance with the present invention; Fig.2 is a plan view of the matrix of Fig.l to a smaller scale; Fig.3 illustrates diagrammatically the operation of the matrix of Figs. 1 and 2; Fig.4 is a section on line B-B in Fig.2; Fig.4a is an enlarged detail of one of the V-grooves of the matrix of Fig.2; Fig.5 is a perspective view of a second embodiment of an optical matrix in accordance with the invention; Fig.6 illustrates the construction of one possible means for mounting the fibre optic and its lens in the matrix; Fig.7 is an inverted plan view of one embodiment of a reflection device;; Fig.8 is an end view of the reflection device of Fig.7; Fig.9 is a side view of the reflecting device of Fig.7; Fig.10 is an inverted plan view of a second embodiment of a reflecting device; Fig.ll is a side view of the device of Fig.9; Fig.12 is a plan view of a further embodiment of an optical matrix in accordance with the present invention; and Fig.13 is a section on A-A in Fig.12.

Fig.l of the drawings shows a slice 8 of single crystal silicon formed photolighographically with two sets of mutually orthogonal intersecting V-grooves 10a-10f, 12a-12f. The cubic structure of single crystal silicon is such that, by choosing the correct orientation of the silicon during etching, the two sets-of V-grooves 10,12 will be precisely at 900 to one another. Furthermore, the angle made by the sides of each V with the surface of the silicon can be arranged to be precisely 54.74 , as illustrated in Figs. 4 and 4a. Since, in such a structure the angle of the grooves will always be 54.743, this provides a constant, accurate seating for receiving a fibre optic termination as described hereinafter.

Optical lenses are available which comprise a cylinder of graded index fibre optic, the optical properties of the cylindrical lens so formed being essentially similar to that of a conventional optical lens. Cylindrical, so-called GRIN lenses are particularly convenient for focussing and collimating light from the ends of optical.fibres because the fibre can be positioned on the precise axis of the lens by arranging for one end of the cylindrical lens to be held in a metal bush, an extension to which carries a small hole to take the fibre and position it axially on the circular face of the cylindrical lens, as shown in Fig.6.

Having arranged for the optical fibres to be terminated with a cylindrical lens in the aforegoing or similar manner, the cylindrical lenses themselves can then be positioned very accurately in the V-grooves in the silicon. Fig.l shows, by way of a simple example, two optical fibres 14a,14b positioned in the matrix as X-inputs and two optical fibres 16a,16b positioned as Y-outputs. The fibres 14a,14b, 16a,16b have respective cylindrical lenses illustrated diagrammatically at 18a,1 & , 20a,20b.

In order then to enable a light signal from any X input to be routed to any Y output (or vice versa), a reflecting means, such as a mirror or prism, can be accurately positioned and aligned at any appropriate intersection of the grooves, as illustrated in principle in Fig.3. Thus, for example, to route a signal from fibre 14b to fibre 16a, a light reflecting means would be positioned at the intersection of grooves 12d and lOc.

Advantageously, the reflecting means can be, or can be mounted on, etched silicon crystal which is the male counterpart of the intersecting V-grooves, so that alignment of the reflecting means to the silicon base 8 is crystallographically precise and referenced to the axis of the cylindrical lens of the input fibre optic and thus to the collimated light beam which is directed therefrom.

Figs. 7, 8 and 9 illustrate diagrammatically the principle on which one embodiment of such a reflecting means can be configured. This embodiment employs a 45v prism 22, acting as the light reflector itself, which is mounted on an elongate guide 24 whose cross-sectional configuration is a truncated male counterpart to the V-section grooves 10,12 so that it can slide along any such groove 10,12 in which it is placed. In this case, provision can be made (not shown) for detenting the reflecting means at a chosen intersection to hold it accurately in position. Also, the guide member 24 should be arranged so that it does not interfere with other light beams in the matrix.

Figs.10 and 11 show another possible embodiment of a reflecting means comprising a reflector 26 having a reflecting surface 28 which is formed with, or mounted on, a support formed with mutually orthogonal guide portions 30a,30b whose cross-sectional configuration forms a male counterpart to that of the intersection of two V-grooves on the base 8. In this case the reflecting means is adapted to be moved in the Z-direction for insertion into the selected V-groove intersection. It can be spring-loaded into position if required. When positioned on the base at a selected intersection, the face 28 of the reflector 26 lies precisely at 459 to the input and output lens axes.

In order to enable the physical configuration to be optimised, the V-grooves can be arranged to be truncated so that a thinner silicon slice 8 can be used.

Also, in order that the reflecting means can be positioned to receive all of the collimated light beam from the input fibre optic, the inner region of the matrix can be etched with deeper truncated V-grooves, with the cylindrical lenses positioned in the narrower V-grooves located for this purpose at the X-input and Y-output edges of the matrix, as shown in Fig.5.

The Y-output cylindrical lenses which receive the signal from the reflecting means can advantageously be of a larger aperture than the X-input lenses so that they can more effectively receive all of the light signals.

Figs.12 and 13 illustrate a still further embodiment in the form of a 2x2 array having lens input and output aligning grooves 30a,30b, 32a,32b formed in the surface 34 of a single crystal silicon slice. Much larger, truncated grooves 36a,36b, 38a,38b follow the aligning grooves 30a,30b, 32a,32b for slidably receiving a carriage 40 of complementary cross-section which carries a reflector in the form of a pentaprism 42. Fig.13 also shows how the pentaprism is aligned with the optical axis of an input GRIN lens 44 of an input fibre optic.

By virtue of the invention described herein, it is possible to achieve accurate alignment of the fibre optics in a matrix switch so as to minimise any reduction or distortion of the light signal being switched.

It will be appreciated that the invention is not restricted to the details of the particular embodiments described herein. Thus, for example, the overall shape of the silicon base need not be circular; any number of V-grooves can be provided, with a corresponding chosen number of input and output fibre optics; the method of terminating the fibre optics need not be as shown in Fig.6, provided that some form of cylindrical outer guide is present on the fìvre-optics of diameter suitable to seat in the V-grooves; and other means may be used to locate the light reflecting means at a selected intersection of the V-grooves and to provide positional adjustability therefor.

Claims (6)

1. An optical matrix switch comprising a single crystal silicon slice having a plurality of mutually orthogonal V-grooves etched into its surface using a conventional silicon photolithographic technique, the silicon being crystallographically oriented such that, as a result of the cubic structure of the silicon, the resulting V-grooves are precisely at 909 to each other, with the sides of each V precisely at 54.74 to the surface of the silicon, the mutually orthogonal V-grooves serving as guides for a plurality of cylindrical fibre optic terminations so that light signals can be routed from one selected fibre optic to another by the location of a light reflecting means at the intersection of the grooves associated with those particular fibre optics.

2. An optical matrix switch as claimed in claim 1, wherein the light reflecting means is mounted on or is part of a structure whose configuration matches the intersecting grooves.

3. An optical matrix switch as claimed in claim 2, wherein said structure is formed by an etched single silicon crystal which is the male counterpart of the intersecting V-grooves, whereby alignment of the reflecting means to the silicon base is crystallographically precise.

4. An optical matrix switch as claimed in claim 2 or 3, wherein the light reflecting means is a mirror or a pentaprism.

5. An optical matrix switch as claimed in any of claims 1 to 4, wherein each said cylindrical fibre optic termination comprises a cylindrical GRIN lens, one end of which is mounted in a metal bush, an extension to which carries a small hole to take an optical fibre and position it axially on the circular face of the cylindrical lens.

6. An optical matrix switch substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.