GB2270224A - Networks of self-routing optical switches - Google Patents

Abstract

Each Self Routing Optical Switch comprises a non-linear crystal 1, 5, 6, 7 and associated half-mirrors 2, 3, 4, 8, 9, 10, 11, 12, 13, 14, 15, 16. The network consists of arrays of Self Routing Optical Switches connected in layers where each layer has a different set of mirror spacings to enable non ambiguous coding of the destination address. Routing to a particular node is performed by modulating the input light with an autocorrelation function whose period is arranged to coincide with the round trip time delay between the non linear crystal and the Semi-reflecting mirror to which routing is required. A further requirement is that the modulation does not cause ambiguity by having a period equal to a round trip time in a different layer. <IMAGE>

Description

Networks for SROI This application describes how Self Routing Optical Interconnects (SROI's), which are described in Patent Applications 9201122.0, 9203603.7 and 9212102.9, can be interconnected to produce large switching networks which could be used for example for optical communications systems, optical computers and optical neural networks where a large number of input and output nodes are required.

In previous patent applications (9201122.0, 9203603.7 and 9212102.9) a Self Routing Optical Interconnect has been described which consists of a non-linear material surrounded by an array or Semi-reflecting Mirrors (SRM's) with different spacings between the Non Linear Crystal (NLC) and each Semireflecting Mirror (SRM). An input beam incident on the non linear crystal (NLC) can be directed to a specified output Semi-reflecting mirror (SRM) by varying the autocorrelation function of the input beam.

A network is shown in Figure 1. This consists of arrays of Self Routing Optical Interconnects connected in Layers where each layer has a different set of mirror spacings to enable non ambiguous coding of the destination address.

This will be illustrated by way of example as shown in figure 1.

This system will be described by starting at point A where for convenience this will be classed the input however any node can be both an input and an output.

NLC1 (1) is surrounded by an array of N semireflecting mirrors (2,3,4) (N is 3 in this example but could be any number) where the spacing between NLC 1 (1) and SRM1 (2) , SRM2 (3), SRM3 (4), is between L1 and L3. At each of these semireflecting mirrors (2,3,4) there is another Self Routing Optical Interconnect (SROI) which consists of non linear crystals (5,6,7) each of which is surrounded by another set of N mirrors (8,9,19 and 11,12,13 and 14,15,16) with spacing between L4 and L6. The distances L1 to L3 do not overlap with the distances L4 to L6.Routing to a particular node is performed by setting peaks in the autocorrelation function where the time delay between peaks in the autocorrelation function is arranged to coincide with the round trip time delay between a non linear crystal and the Semi-reflecting mirror to which routing is required (described in earlier patent applications (9201122.0, 9203603.7 and 9212102.9). A further requirement is that the delays between any peaks do not cause ambiguity by being equal to a round trip time in a different group.

Power throughput can be increased by performing the routing through one SROI in one polarisation state where the semireflecting mirror (SRM) lets the orthogonal polarisation through without any reflection and then the next switch works in an orthogonal polarisation.

Polarisation rotators and isolators may need to be positioned within the network to reduce the effect of multiple reflected beams. Polarisation rotators can also be used to rotate the polarisation if the autocorrelation function is varied by polarisation switching.

The system shown in Figure 1 is a two layer structure where M is the number of layers and N is the number of semireflecting mirrors surrounding each non linear crystal. The number of nodes can be further expanded by using more layers and/or by increasing the number of semireflecting mirrors surrounding each non linear crystal. The number of nodes is therefore equal to NM. If for example 105 nodes are required a five layer structure would be used where each Self Routing Optical Interconnect (SROI) would have 10 outputs/inputs.

By using this technique only N*M autocorrelation codes are required to access NM addresses.

If input and output nodes are placed at every semireflecting mirror (SRM) then this would increase the number of nodes.

It may well be possible to remove the semireflecting mirror (SRM) in front of each NLC where the NLC acts as the SRM itself by producing a phase conjugate mirror. However the self routing optical interconnect would probably take more time to switch.

Non linear crystal, NLC, here means any material where an optical property for example the refractive index, permittivity, permeability, loss or propagation velocity vary linearly or non linearly with the intensity of the Electric or magnetic field of the electromagnetic wave.

The coding of the destination address is performed by varying the Autocorrelation function.

AUTO-CORRELATION FUNCTION: The autocorrelation function can be varied by modulating a reference optical signal using amplitude modulation and phase modulation and frequency modulation or polarisation modulation where the data would be encoded within this signal where the modulation could be any combination of amplitude modulation and phase modulation and frequency modulation or polarisation modulation.

The optical input signal to the NLC could therefore consist for example of a train of pulses or of pseudo random codes or pulsed codes such as for example Golay codes or of any coded data or of a superposition of the signal with a delayed version of itself or of the superposition of two or a number of delayed versions of the same signal where the input signal could also be a modulated.

The auto correlation function can be varied in any way by for example varying the pulse code rate or by varying the delay between the superposition of the signal with a delayed version of itself where the variation of the auto correlation function can be implemented in any way such as by optoelectronic modulation of the light source using electro-optic crystals and Bragg cells or electronically by switching the laser on or off or by electronic tuning of the phase, frequency, phase or polarisation or by mechanical or electromechanical means. These variations of the autocorrelation function could be in the form of amplitude, phase, frequency or polarisation modulation of a reference optical signal.

It would also be possible to have a separate header which contains the destination information which is followed by the data stream thereby separating the data from the header.

The signal will therefore only be routed to the mirrors where the reflected signals are phase coherent within the crystal with the incident input beam where it is usually required that the width of the spike in the autocorrelation function is less than the differential differences between the mirrors and the width of the NLC.

A single Beam could be sent to multiple destinations either by producing an autocorrelation function which correlates for a number of SRM's or by having the spacing between the SRM's to the crystal to be the same for a number of SRM's.

All figures are schematic in format and therefore do not show the true directions.

The SROI networks could be made use bulk optical components, waveguide components, fibre components or any combinations thereof.

To obtain multiple channels through the same nodes these structures can be stacked.

A Surface Self Routing Optical Interconnect is shown in Figure 2 and consists of a semiconductor layer (6) overlaid with a non linear optical material (7).

An input optical beam is incident at A and split into two paths using a beam splitter (2). These two beams are directed onto the semiconductor using mirrors (3,4) where the interference between the two optical beams produces a periodic space charge field in the semiconductor. To obtain a space charge field it is necessary for the electron and hole mobilities (and hence diffusion coefficients) in the semiconductor to be different. Some light is scattered from the semiconductor and non linear crystal. This light when incident on the selected semireflecting mirror (8,9) light is reflected back to the semiconductor (6). This returning light sets up a new periodic grating of space charge field in the semiconductor (6) by interfering with one of the input optical beams, from mirrors (3 or 4).This new space charge field produces a new optical grating in the non linear material which builds up in a characteristic time to route significant amounts of optical power to the selected semireflecting mirror. Routing to a particular Semireflecting mirror (8 or 9) is performed by setting peaks in the autocorrelation function of the optical signal where the time delay between peaks in the autocorrelation function is arranged to coincide with the round trip time delay between the non linear material and the Semi-reflecting mirror to which routing is required (described in earlier patent applications (9201122.0, 9203603.7 and 9212102.9). The number of semireflecting mirrors is two in this instance but could be any number.

The interconnect shown in Figure 2 may be simplified to the system shown in Figure 3. Here only one optical input beam is required and the other input optical beam is produced by placing a mirror at B as shown in Figure 3.

Where semiconductor is referred to this can include any material which absorbs light to produce electron hole pairs.

Non linear material here means any material where an optical property for example the refractive index, permittivity, permeability, loss or propagation velocity vary linearly or non linearly with the intensity of the Electric or magnetic field of the electromagnetic wave. Non linear optical materials therefore also include semiconductors.

Multilayer stacked structures consisting of a large number of interleaved non linear materials and semiconductors could be used to enhance the diffraction efficiency. These include multiple quantum well and superlattice structures.

Claims (13)

1. A network comprising arrays of Self Routing Optical Interconnects connected in Layers where each layer has a different set of mirror spacings to enable non ambiguous coding of the destination address, means for varying coding on the optical input beam which incorporates the destination address where this coding enables unique addressing of specified destinations, means for ensuring unique addressing between layers, means for providing destination addressing using very few address codes, means for modulating the data on the optical input beam.

2. A network as described in claim 1 in which each layer has a different range of delays between the non linear material and the semi-reflecting mirrors thus enabling the coding of a large number of destinations using only a few codes.

3. A network as described in claim 1 in which the coding could be arranged to enable to send the optical beam to more than one destination at the same time.

4. A network as described in claim 1 in which the spacing between the semi-reflecting mirrors and the non linear materials could be arranged to enable the optical beam to be sent to more than one destination at the same time.

5. A network as described in claim 1 in which the switches and or networks could be made using bulk optical components, optical waveguide components, fibre components or any combination thereof.

6. A network as described in claim 1 in which the self routing optical interconnects are based on reflections from surface or multilayer structures.

7. A network as described in claim 1 in which polarisation rotators and or isolators are incorporated to reduce the effect of multiple reflected beams.

8. A network as described in claim 1 in which polarisation rotators are used to rotate the polarisation if the autocorrelation function is varied by polarisation switching.

9. A network as described in claim 1 in which the number of destinations per layer and the number of layers can be set to any number.

10. A network as described in claim 1 in which input and output nodes are placed at every semireflecting mirror (SRM) thus increasing the number of nodes.

11. A network as described in claim 1 in which input and output nodes are placed at selected semireflecting mirrors (SRM).

12. A network as described in claim 1 in which these networks can be stacked to obtain multiple channels through the same nodes.

13. An all optical Self routing network substantially as described with reference to the accompanying drawings.