WO1988005995A2

WO1988005995A2 - An optical switching arrangement

Info

Publication number: WO1988005995A2
Application number: PCT/GB1988/000078
Authority: WO
Inventors: Peter John Duthie
Original assignee: Plessey Overseas Limited
Priority date: 1987-02-10
Filing date: 1988-02-10
Publication date: 1988-08-25
Also published as: GB8802997D0; GB8702997D0; GB2201313A

Abstract

An optical switching arrangement of interleaved switch elements in which a reflective surface is used to increase the effective substrate length by reflecting incident light into another waveguide for further switching operations.

Description

AN OPTICAL SWITCHING ARRANGEMENT

The present invention relates to an optical switching arrangement and more particularly but not exclusively to an optical switching arrangement in the so called "cross-bar" switch format.

Broad-band optical signal switching arrays are being developed which can, for example, be formed by directional coupler electro- optic switches. A good array will have a large number of input and output channels and will be easy to interface to optical fibres.

Integrated optic switch dimensions and interconnect topologies are governed by considerations of the optical interaction lengths along with waveguide and electrode widths, typically at an order of 2f //m. Such waveguides can neither have large angle bends or small radius curves in order avoid scatter and attenuation losses. Thus, switches have a high aspect ratio and are constructed as switch arrays .

The size of switch arrays possible is thus limited by the length of the substrate. For example, for an n x n crossbar switch, then 2n- 1 switches are required in succession. Thus for a 3" substrate with 5mm switch elements, the largest possible size is 8 x 8.

Previous methods of increasing packing density have involved reducing element size but this has the undesirable consequence of increasing device operating voltages and increasing optical attenuation through small radius curves.

According to the present invention there is provided an optical switching arrangement for switching light signals between input ports and output ports coupled to a common substrate comprising an array of guide wave optical switches interconnected by a plurality of optical paths, the switches being selectively operable to couple different pairs of optical - paths together to define input and output channels in mutually respective planes of the switching arrangement, and a reflective means being provided for optically coupling the input channels to the output channels whereby available optical path lengths in the substrate are substantially increased.

Preferably, there is at least one optical switch in the input channel of the arrangement. The reflective surface may be a continuous suface or independent reflective elements.

The optical switches may be directional coupler electro-optic switches with the switches in the input channels interleaved with those in the output channels.

Additionally, a method of switching light signals comprising directing the light signals through an array of guided wave optical switches arranged in a plurality of optical paths by selectively operating said optical switches to assign an input channel for the light signals to a reflective surface, the reflective surface reflecting the light signals into an assigned output channel parallel with the respective input channel such that the available optical path length is substantially increased.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying figure 1 wherein a typical arrangement according to the present invention is illustrated. In our invention the effective substrate length is increased by employing reflectors at the end of the substrate to reflect the light into another waveguide for further switching operations. An arrangement to achieve such a reflection can be achieved by two waveguides aligned at appropriate angles to a reflective edge, e.g. a reflective 3dB coupler with separated waveguide input and output parts.

Construction of the above structure does however require quite stringent fabrication in regard to construction tolerances and the preferred structure would be to a reflective coupler arrangement where the length of the coupler is (n + 1/2) lc where n is an integer and lc is the coupling length.

Figure 1 illustrates a typical arrangement according to the present invention wherein optical switches 5 (after the reflection against reflective surface 1 ) are interleaved with those before the reflection. This results in a compact configuration. The arrangement shown in figure 1 is a non-blocking reflecting 8 x 8 switch array.

Light signals enter the array through eight input channels or ports 3 represented by solid lines. The signals are rearranged and distributed by switches 5 before reflection at surface 1 back along output channels 7 represented by dashed lines. In the course of exiting along channels 7 the signals are again rearranged and distributed by switches 5. The switches 5 comprise a central waveguide element and peripherally located electrodes which, when suitably stimulated, actuate the waveguide element to allow passage of the light signals. Input and output ports 9 can be connected to fibres in a single fibre array. Ordinarily, optimisation of alignment requires precise manipulation of three axial components thus the manipulation of only two axial components in the present arrangement will be much simpler.

It will be appreciated by a man skilled in the art that the principle of reflection can be carried to two or more reflections, by appropriate patterning of edge metallisation and disposition of connecting waveguides.

Light signals may be switched in an arrangement according to the present invention by operating the optical switches to designate respective input and output channels for the lights signals to and from the reflective surface.

Claims

1. An -optical switching arrangement for switching light signals between input ports and output ports coupled to a common substrate comprising an array of guide wave optical switches interconnected by a plurality of optical paths, the switches being selectively operable to couple different pairs of optical paths together to define input and output channels in mutually respective planes of the switching arrangement, and a reflective means being provided for optically coupling the input channels to the output channels whereby available optical path lengths in the substrate are substantially increased.

2. An optical switching arrangement as claimed in claim 1 wherein there is at least one optical switch in the input channel.

3. An optical switching arrangement as claimed in claim 1 or 2 wherein the reflective means is a continuous reflective surface for all coupled input and output channels.

4. An optical switching arrangement as claimed in claim 1 or 2 wherein the reflective means comprises independent reflective surfaces between each input and output channel.

5. An optical switch arrangement as claimed in any preceding claim wherein the optical switches are directional coupler electro- optic switches.

6. An optical switching arrangement as claimed in any proceeding claim wherein the reflective means is a reflective 3bB coupler with separated waveguide input and output ports.

7. An optical switch arrangement as claimed in any preceding claim wherein the optical switches in the input channel are interleaved with the optical switches of the output channel.

8. An optical switch arrangement as claimed in any preceding claim wherein the input and output channels are connected to external optical fibre by a single fibre-array.

9. A method of switching light signals comprising directing the light signals through an array of guided wave optical switches arranged in a plurality of optical paths by selectively operating said optical switches to assign an input channel for the light signals to a reflective surface, the reflective surface reflecting the light signals into an assigned output channel parallel with the respective input channel such that the available optical path length is substantially increased.

10. A telecommunication system using light signaling wherein said light signals are switched by an optical switching arrangement substantially as hereinbefore described.

11. An optical switching arrangement substantially as hereinbefore described with reference to the accompanying drawing.

12. A method of switching light signals substantially as hereinbefore described with reference to the accompanying drawing.