GB2263371A

GB2263371A - Self routing optical switch

Info

Publication number: GB2263371A
Application number: GB9201122A
Authority: GB
Inventors: Jeremy Kenneth Arthur Everard
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-01-20
Filing date: 1992-01-20
Publication date: 1993-07-21
Anticipated expiration: 2012-01-20
Also published as: GB2263371B; GB9201122D0

Abstract

A self routing optical switch consists of a non linear material 1 surrounded by an array of reflecting or semi-reflecting mirrors or surfaces 3, 4, or 5. These reflecting surfaces reflect some light from the non linear material back to the non linear material. An optical signal beam or optical data packet incident on the non linear material is routed to a selected reflecting surface by including the destination address in the optical signal in the form of the autocorrelation function of the optical signal. The destination is selected by arranging for the round trip propagation time between the non linear material and the semi-reflecting surface to be equal to the time delay between any two peaks in the autocorrelation function. The address and hence autocorrelation function can be changed by varying any combination of the amplitude. phase, frequency or polarisation of the optical signal. This routing information could be in a header or in the data itself and could be removed afterwards if required. This system has the capability to route most of the input signal down the wanted route. <IMAGE>

Description

Specification SELF ROUTING OPTICAL INTERCONNECTS In opto-electronic communications and computing networks there is a requirement to route the signals to specified destinations. For Optical data signals this is usually performed by converting the optical signal to an electrical signal, performing the switching to a designated link electronically and then reconversion to an optical signal for final transmission.

This invention relates to self Routing optical interconnects where an optical signal beam or optical data packet is routed to a destination using an all optical switch where the destination is defined within the optical signal by the autocorrelation function of the optical signal. This routing information could be in a header or in the data itself and could be removed afterwards if required. This system has the capability to route most of the input signal down the wanted route.

If we take the system shown in Figure 1 which contains a non linear optical crystal (1) which hereafter we will call NLC which could be any type of non linear crystal, for example a photo-refractive crystal, and a semi-reflecting mirror or beam splitter (2) where one of the reflecting surfaces is pointing towards the NLC and apply an optical input signal with a long coherence length and of sufficient power along path AB it will be found that some light will scatter from the crystal in all directions and some of this light will be incident on the mirror and reflected back to the crystal. This reflected light if coherent with the input beam will set up a non linear interference grating of refractive index in the crystal which will build up to ensure that a significant amount of the light will eventually travel along the path ABC.

According to the present invention, which is called a self routing optical interconnect hereafter called an SROI, there is provided a non linear optical crystal hereafter called an NLC surrounded by an array of semi-reflecting mirrors hereafter called SRM's. The spacing and hence propagatiori time delay between each SRM and the NLC is different. Initially an input optical signal incident on the NLC is scattered in all directions where this scattered light is reflected back from the SRM's and is re-incident on the NLC. Note that the SRM's are orientated to re-direct the scattered light back onto the NLC. The light reflected from the SRM's when it is phase coherent with the input optical beam produces a grating of refractive index in the NLC such that after a time a significant proportion of the input beam is deflected to a specified SRM.The specified SRM is defined by making the repeat time of the autocorelation function of the input optical beam equal to the round trip propagation time between the specified SRM and the NLC. The optical input signal will therefore only be routed to the specified SRM which satisfies the condition that the reflected signals from the specified SRM are phase coherent within the NLC with the optical input beam. In summary therefore the signal route is set by aranging for the auto correlation function repeat time, T, of the optical input signal to be equal to the round trip time between one of the SRM's and the NLC.

Specified embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 2 shows an embodiment using bulk optics which illustrates the general principles of the SROI.

Figure 3 shows a bi-directional system Figure 4 illustrates an implementation using optical fibres and bulk optics.

Figure 5 illustrates the use of the self routing optical interconnect, SROI, to couple all or most of the modes from a multimode fibre into a single mode fibre.

Figure 6. shows the initial experimental embodiment used to demonstrate the operation of this Self Routing Optical Interconnect hereafter called an SROI.

Figure 2 shows an embodiment using bulk optics where for example only 3 SRM's are used however any number could be used and they could be in three dimensions if required.

In the SROI, which is shown in Figure 2 there is a non linear crystal (NLC) (1) surrounded by an array of semi-reflecting mirrors (SRM's), (3,4,5) where in this example only 3 SRM's are used where any number could be used in practice where the spacing between each SRM and the NLC is different where by setting the repeat time of the autocorrelation function or the time between peaks of the autocorrelation function of the input signal to a defined time T it is possible to set which SRM the signal routes to by aranging for the autocorrelation function repeat time T to be equal to the round trip time between one of the SRM's and the NLC.The signal will therefore only be routed to the SRM where the reflected signals are phase coherent within the NLC with the incident input beam where the output signal which could be 6 or 7 or 8 is the signal transmitted through the SRM's.

It is usually required therefore that the width of the peak in the autocorrelation function in terms of time is less than the difference in round trip propagation time between one SRM and the NLC and another SRM and 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 arranging for the spacing between the SRM's to the crystal to be the same for a number of SRM's.

Also in this embodiment there is a defined input AB and three outputs. In fact the SROI can be bi-directional and can handle multiple inputs and multiple outputs at the same time as shown in figure 3 where each input can also be an output and each output can also be an input and therefore for such a system there would be a SRM on every port (5,9,10,11) including one SRM (5) on what was defined as the input port (AB) in figure 2. Therefore a multiway system is shown in Figure 3 with different propagation delays hereafter called PD's between each SRM (5,9,10,11) and the NLC (1). The system shown in figure 3 as well as being bi-directional is also reciprocal where if reciprocity needs to be avoided then a system which is non reciprocal can be built by having separate inputs and outputs for each port and thereby using a system such as that shown in figure 2 for every input.Therefore every input has a separate NLC.

Where input is refered to this usually means the position where the optical signal is incident on the NLC from an outside source and is designated AB Therefore each input could have a different NLC or operate in different parts of the same NLC where for each port there is now both an output and an input where if required the input and output parts of each port could be combined in a directional coupler.

Figure 4 shows an embodiment using bulk optics and fibre optics in which there is again an input signal AB however the input signal is incident on the NLC (1) where there are three outputs in this example where any number could be used where these outputs consist of a lens (23), fibre (24), and in fibre SRM (25), and of a lens (26), fibre (27), and in fibre SRM (28), and of a lens (29), fibre (30), and in fibre SRM (31), where the propagation times between the NLC (1) and the SRM's (25,28,31) are different and the autocorrelation function of the input signals sets which output is selected by making the repeat time of the autocorrelation function equal to the spacing between the NLC (1) and the SRM's (25,28,31). It should be noted here that the SRMs are inside the fibre where this is to ensure that the grating in the NLC (1) launches most of the light into the actual fibre required where attention needs to be taken to avoid spurious reflections which have the same delay as an input autocorrelation function repeat time. Note also that this system can also be bidirectional if required and therefore there is an SRM on the line AB combined with fibre 21 and lens 20.

For optimum performance the orientation of the crystal is also important.

The optimum coupling of the optical signals to the NLC is critical where the size of the waist and interaction length of the optical beam should be adjusted to obtain optimum performance.

These SROI's can be operated using LASER's.

These SROI's could be used with LED's or superluminescent lasers if the crystals can be made sensitive enough.

When ever the term input is used this can also often be used as an output as well where it is termed input to ease the description of the SROI.

Non linear crystal, NLC, here means any material where an optical property for example the refactive 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.

This SROI system could be used to convert the output of a multimode fibre to a single mode fibre as shown in Figure 5 where here the incident beam comes from a multimode optical fibre (40) via a lens (41) and is incident on the NLC (1) and the NLC (1) produces gratings for each mode to direct all of the modes with phase coherence into the single mode fibre (43) via lens (42) where the fibre contains an SRM (44) which could be an in fibre discontinuity (44)or grating (44) or semireflecting mirror (44) where because all the modes of the multimode fibre experience the same position and reflectivity from the SRM(44) they would all be coupled into the single fibre. If required some of the mides could also be coupled into other fibres 46 and 49 with associated lenses 45,48 where the outputs are 51,52 and 53.

Crosstalk between the modes may be a problem although to cancel the delay between different modes different parts of the NLC would automatically be used where to reduce the problems the interaction length could be increased by varying the waist size of the optical beam and the size and shape of the crystal.

The SROI shown in Figure 5 could therefore be used to correct for modal dispersion in multimode optical fibres.

The experimental system first used to demonstrate operation of the SROI is shown in Figure 6. Here the optical input signal (60) from a laser goes into a Michelson interferometer consisting of Mirror (62), Mirror 63 and beam splitter 61 where the signal going along AB into the NLC (1) consist of hte input signal 60 superimposed with a delayed version of the input signal where the delay is equal to 2*L1 - 2 *L2. By varying L1 and L2 the output signal would go through SRM 64 if L1 -L2 = L3 and through SRM 66 if L1-L2 = L4. This system was therefore used to demonstrate a working SROI.

Techniques for varying the autocorrelation function are described later.

All these systems have the ability to self adjust and compenste for aging and microphony as long as these effects are slower than the grating set up time.

Additional Information Where the repeat time of the autocorrelation is defined this could also mean the repeat time between any individual peaks on the autocorrelation function as the complete autocorrelation function could include may peaks before the function repeats.

Enhancements 1. The SRM could be made by polishing flats on the NLC itself to produce the semireflecting mirrors actually on the crystal thereby making the whole switch within the crystal. The surface of the crystal could also be polished in a continuously curved surface allowing the direction of propagation to be fully variable. These surfaces could also be coated to vary the reflectivity.

2. The non linear crystal could also contain a fixed grating which initially scatters a small amount of light only towards the mirrors thus enhancing the speed of response as the light is no longer scattered in all directions.

3 Where one non linear crystal is used many could be used in a staggered formation.

4 Optically Amplifying gain blocks could be included in between the SRM's and the NLC and also within the NLC to increase signal power levels and speed of response. Optical amplifiers could also be used outside the SRM's.

5. Another method to produce a pre-grating would be send a priming signal into the NLC every so often such as a CW signal, a signal with many peaks in the autocorrelation function or a signal which regularly switches between the different routes.

6. Electrical techniques such as applying RF or DC voltages across the NLC can sometimes be used to enhance the speed of response especially for photorefractive NLC's.

7. Make SRM mirrors frequency selective such that routing could be performed by changing the input frequency as well as the auto correlation function.

8. Further improvements may be obtained by using a separate pump laser incident on the NLC to enhance the speed of response and reduce the input power required in the data beam. This extra beam could be phase or frequency locked to the input beam if required. Intemal self pumping can also be used.

9. Use glass blocks of variable thickness to vary the delay while keeping mirror spacings constant. The glass blocks could be anti-reflection coated to reduce spurious reflections 10. High peak powers could be used to set up the gratings in the NLC and lower powers used to maintain gratings.

11. The same crystal could be used to route many different independent signals simultaneously and in both directions where the crosstalk could be further reduced by tilting the SRM's to use slightly different parts of the NLC for each interconnect.

12. Different colours of LASER light can be used simultaneously where for example one colour could be used to set up the switch direction and the other to carry the data. Further by orienting the direction of many input beams one beam could set the direction for the other beam.

13 Both analogue and digital Optical Logic functions can be produced for example AND, NOT where the decision could either be in the form of propagation direction of the output based on a decision on one or many input beams or in the amplitude, phase, Polarisation or autocorrelation function of the transmitted beam where it can therefore be used for both analogue and digital computers.

14. The NLC could be placed inside an optical resonator to enhance the field intensity inside the NLC and hence improve the speed of response but the resonator would need to be switched out when data transmission is required as the resonator would corrupt the data.

The light beam could be focussed inside the NLC using optics to obtain the optimum beam waiste and interaction length.

15. The communications can be in three dimension and bi-directional between any ports of the self routing optical interconnect where port means any input or output channel.

16. These systems have the capability to route multiple channels down a single multimode optical fibre where each channel is a different mode with different propagation distances.

17. These routing systems could be used as optical scanners by varying the repeat time of the autocorrelation function with time and using a curved SRM where the spacing between the SRM and the NLC varies with angle.

18. A scanning Michelson Interferometer using bulk or fibre optics can be used to vary the autocorrelation function of the input beam by effectively superimposing the input beam with a delayed version of itself. This can be used to select different output SRM's and to produce a scanning beams if the distance between the SRM and the NLC varies with angle.

19. The peaks in autocorrelation function need not be the same height and therefore different power levels can be sent along different routes for certain types of non linear crystal.

20. The scattering can be increased by material choice NLC orientation and shape choice and by having a fixed low level grating to produce scattering in discrete directions thereby improving the grating set-up time.

21. These techniques could be used to implement variable optical interconnects between points on integrated circuits and points on different integrated circuits where for example on chip lasers are used and a layer of non-linear material is placed above or inside the integrated circuit.

22. A fibre optic system could be built by placing a NLC directly against a number of fibres or by using a multiway fibre coupler with a non linear core at the coupler interfaces where each fibre has an SRM at different distances from the non linear section.

23. The NLC could be used in two modes such that bulk or surface non linear gratings are produced where this is dependent on the optical properties of the NLC such as absorption and transmission coefficients.

use surface grating on material where NLC could be for example GaAs or InP or any non linear material.

24. The speed of response can be further improved by launching seeding beams from each port to the NLC.

25. Fibre delay lines can be use to interconnect the SRM and the NLC.

26. multiple outputs could be produced from the same input, at the same time, by having multiple peaks in the auto correlation function.

27. These systems could be made using combinations of bulk, fibre or waveguide configurations.

28. These techniques could be used for any electromagnetic wave systems such as electronic systems operating at RF and microwave frequencies where the NLC is a non linear medium where its electrical properties vary with the Electric and or magnetic field of the electromagntic wave and the inputs or outputs are in free space or any wave guiding stucture and the SRM's are implemented electrically using for example shunt or series inductors, capacitors, stubs or filters. These techniques could also be used for any type of wave propagation system.

29. Switch reflectivity of SRM's to a high reflectance initially to enhance switching time and then to low reflectance to enhance the transmitted power.

30. Make the SRM a non linear crystal such that it operates as a phase conjugate mirror.

31. The NLC could consist of a Multiple Quantum Well device where a lateral field can be used to considerably vary the recombination time.

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 autocorrelation 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 autocorrelation 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 elctoronic 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.

Another proposed scheme is shown in Figure 7.

Here the light is incident at A and split into three paths. Path B is the loss modulation path where the rep rate of the code burst, pseudorandom code or coherence repeat distance produces an enhanced intensity at one of the points L1 to L4 thus setting up the lowest loss at this point. Beam splitters are also included at these points to allow some of the light to be transmitted. A new beam between the photo-refractive materials then evolves along the lowest loss route due to scattering and four wave mixing such that photo-refractive grating mirrors are formed which eventually direct the beam along the lowest loss path. In a final system the beam splitters would be switched to complete transmit once the path was set up. They would then be switched back when the gratings started to significantly dissappear.

Photo-refractive Materials can be used as the NLC if required These materials require both photo-conductive and non linear electro optic effects (ie variation of refractive index with space charge field) simultaneously.

Unfortunately semiconductors have the correct photo-conductive properties but have small non linear electro-optic coefficients whereas Ferro-electric materials have large electro-optic effects but low mobility. Multi structure materials will therefore be considered If two optical signals are interfered on or within a material an optical field in the form of a periodic grating is set up. This in turn generates electron hole pairs in the high optical field region. These carriers then tend to diffuse to the dark regions. However as the electron mobility is far greater than the hole mobility and holes are often trapped a large negative charge distribution tends to occur in the dark region which sets up a space charge field with a spatial phase shift of s/2 due to the integrating effect off Gauss's law. This is in fact necessary for the power exchange processes required.

It has been shown that the effect of diffusion can be increased (and mimicked) by applying a large DC external drift field, however this field also modifies the s/2 phase shift of the grating. If an AC field of period much longer than the carrier recombination time is applied the electrons effectively experience only a DC field during the carrier recombination time but experience an AC field during the grating set up time. This is described in reference 3.

Claims

SELF ROUTING OPTICAL INTERCONNECTS 1. A self routing switch comprising a non linear material surrounded by an array of reflecting or semi-reflecting mirrors or surfaces which reflect some light from the non linear material back to the non linear material, means for launching the optical signal into the non linear material, means for varying the address information in the optical signal or signals by varying the auto-correlation function of the optical signal.
2. A self routing switch as claimed in claim 1 in which the reflecting or semireflecting surfaces could be reflecting surfaces and beam splitters.
3. A self routing switch as claimed in claim 1 which can be used to route any form of input wave.
4. A self routing switch as claimed in claim 1 which is used as a multimode to single mode convertor.
5. A self routing switch as claimed in claim 1 which is used as a multimode to single mode convertor so as to input the multimodes of a multimode fibre into a single mode fibre thereby offering cancellation of modal dispersion in a multimode optical fibre.
6. A self routing switch as claimed in claim 1 surrounded by a array of mirrors each a different distance away from the non linear material whereby the destination address is selected by setting the repeat times between any peaks in the autocorrelation function to be equal to the round trip time between the reflecting surface and the non linear material.
7. A self routing switch as claimed in claim 1 and claim 6 surrounded by a array of mirrors some the same distance away from the non linear material and some a different distance away from the non linear material
8. A self routing switch as claimed in claim 1 in which the semi-reflecting mirrors or surfaces are frequency selective allowing frequency coding of the input signal.
9. A self routing switch as claimed in claim 1 in which the address is stored in the auto-correlation function of the optical signal where the autocorrelation function can be varied by modulating a reference optical signal using amplitude modulation or phase modulation or frequency modulation or polarisation modulation or any combination thereof.
10. A self routing switch as claimed in claim 1 in which the optical input signal consists of a train of pulses or of pseudo random codes or pulsed codes such as 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.
11. A self routing switch as claimed in claim 1 in which the autocorrelation 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. The variation of the auto correlation function can be implemented in any way such as by opto-electronic 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.
12. A self routing switch as claimed in claim 1 in which the destination address is in the data or in a header.
13. A self routing switch as claimed in claim 1 which is made using bulk optics
14. A self routing switch as claimed in claim 1 which is made in optical waveguides.
15. A self routing switch as claimed in claim 1 which is made in optical fibres.
16. A self routing switch as claimed in claim 1 which is made using any combination of bulk optics, waveguides or fibres.
17. A self routing switch as claimed in claim 1 wherein the semireflecting mirrors or surfaces could be made by polishing flats on the non linear material itself.
18. A self routing switch as claimed in claim 1 wherein the semireflecting mirrors or surfaces are curved surfaces allowing the direction of propagation to be fully variable. These surfaces could also be coated to vary the reflectivity.
19. A self routing switch as claimed in claim 1 wherein the non linear material could also contain a fixed grating which initially scatters a small amount of light only towards the mirrors thereby enhancing the speed of response.
20. A self routing switch as claimed in claim 1 where many non linear materials could be used in a staggered formation.
21. A self routing switch as claimed in claim 1 wherein optically amplifying gain blocks could be included in between the semi reflecting mirrors or surfaces and the non linear materials and also within the non linear materials to increase signal power levels and speed of response.
22. A self routing switch as claimed in claim 1 wherein optical amplifiers could also be used outside the semireflecting surfaces.
23. A self routing switch as claimed in claim 1 wherein a pre-grating would be produced by sending a priming signal into the non linear material.
24. A self routing switch as claimed in claim 1 wherein RF or DC voltages are applied across the non linear material to enhance switching performance.
25. A self routing switch as claimed in claim 1 wherein the semireflecting mirrors or surfaces could be frequency selective such that routing could be performed by changing the input frequency as well as the autocorrelation function.
26. A self routing switch as claimed in claim 1 wherein a separate pump laser is incident on the non linear material which could be phase or frequency locked to the input beam if required to reduce signal power requirements.
27. A self routing switch as claimed in claim 1 wherein glass blocks of variable thickness are used to vary the delay while keeping mirror spacings constant where the glass blocks could be anti-reflection coated to reduce spurious reflections
28. A self routing switch as claimed in claim 1 wherein high peak powers could be used to set up the gratings in the non linear material and lower powers used to maintain gratings.
29. A self routing switch as claimed in claim 1 wherein the same crystal could be used to route many different independent signals simultaneously and in both directions where the crosstalk could be further reduced by tilting the semi-reflecting surfaces to use slightly different parts of the non linear material for each interconnect.
30. A self routing switch as claimed in claim 1 in which different colours of LASER light can be used simultaneously where one colour could be used to set up the switch direction and the other to carry the data.
31. A self routing switch as claimed in claim 1 wherein one beam could set the direction for the other beam.
32. A self routing switch as claimed in claim 1 wherein analogue and digital Optical Logic functions can be produced.
33. A self routing switch as claimed in claim 1 wherein the non linear material could be placed inside an optical resonator to enhance the field intensity inside the non linear material and hence improve the speed of response but the resonator would need to be switched out when data transmission is required as the resonator would corrupt the data.
34. A self routing switch as claimed in claim 1 wherein the the light beam could be focussed inside the non linear material using optics to obtain the optimum beam waist and interaction length.
35. A self routing switch as claimed in claim 1 wherein the communications can be in three dimensions and bidirectional between any ports of the self routing optical interconnect where port means any input or output channel.
36. A self routing switch as claimed in claim 1 wherein these systems have the capability to route multiple channels down a single multimode optical fibre where each channel is a different mode with different propagation distances.
37. A self routing switch as claimed in claim 1 wherein these routing systems could be used as optical scanners by varying the repeat time of the autocorrelation function with time and using a curved semireflecting surface where the spacing between the semi reflecting surface and the non linear material varies with angle.
38. A self routing switch as claimed in claim 1 wherein a scanning Michelson Interferometer using bulk or fibre optics can be used to vary the autocorrelation function (address information) of the input beam.
39. A self routing switch as claimed in claim 1 wherein the peaks in autocorrelation function need not be the same height and therefore different power levels can be sent along different routes.
40. A self routing switch as claimed in claim 1 wherein the scattering can be increased by material choice, non linear material orientation and shape and by having a fixed low level grating to produce scattering in discrete directions thereby improving the grating set-up time.
41. A self routing switch as claimed in claim 1 wherein these switches would be used to implement variable optical interconnects between points on integrated circuits and points on different integrated circuits where for example on chip lasers are used and a layer of non-linear material is placed above or inside the integrated circuit.
42. A self routing switch as claimed in claim 1 wherein a fibre optic system could be built by placing a non linear material directly against a number of fibres or by using a multi-way fibre coupler with a non linear core at the coupler interfaces where each fibre has an semireflecting surface at different distances from the non linear section.
43. A self routing switch as claimed in claim 1 in which the non linear material could be used in two modes such that bulk or surface non linear gratings are produced where this is dependent on the optical properties of the non linear material such as absorption and transmission coefficients.
44. A self routing switch as claimed in claim 1 which uses surface or bulk gratings on materials where the non linear material could be for example Gallium Arsenide or Indium Phosphide or any non linear material.
45. A self routing switch as claimed in claim 1 in which the speed of response can be further improved by launching seeding beams from each port to the non linear material.
46. A self routing switch as claimed in claim 1 in which fibre delay lines can be use to interconnect the semireflecting mirrors and the non linear material.
47. A self routing switch as claimed in claim 1 in which multiple outputs could be produced from the same input, at the same time, by having multiple peaks in the autocorrelation function.
48. A self routing switch as claimed in claim 1 wherein these switches could be used for any electromagnetic wave systems.
49. A self routing switch as claimed in claim 1 wherein these techniques could also be used for any type of wave propagation system.
50. A self routing switch as claimed in claim 1 wherein the semireflecting mirrors or surfaces have reflectivity switched to a high reflectance initially to enhance switching time and then to low reflectance to enhance the transmitted power.
51. A self routing switch as claimed in claim 1 in which the reflecting surfaces are also a non linear material such that they operate as a phase conjugate mirror.
52. A self routing switch as claimed in claim 1 in which the non linear material could consist of a Multiple Quantum Well device where an Electric or magnetic field can be used to considerably vary the recombination time if required.
53. A self routing switch as claimed in claim 1 wherein the switches can be connected in networks of switches to enable communication between a very large number of nodes.
54. A self routing interconnecting switch substantially as described herein with reference to the diagrams