WO2002052313A1

WO2002052313A1 - Tuning of optical devices

Info

Publication number: WO2002052313A1
Application number: PCT/AU2001/001622
Authority: WO
Inventors: Dmitrii Yu Stepanov
Original assignee: Redfern Optical Components Pty Ltd
Current assignee: Redfern Optical Components Pty Ltd
Priority date: 2000-12-22
Filing date: 2001-12-17
Publication date: 2002-07-04
Anticipated expiration: 2003-06-22
Also published as: AUPR230200A0

Abstract

A method of tuning an optical device incorporated in a waveguide structure, the method comprising the step of effecting localised heating to manipulate optical properties of the optical device, wherein the localised heating is effected contactless.

Description

Tuning of optical devices

Field of the invention

The present invention relates broadly to a method of tuning an optical device, to an apparatus for tuning an optical device, and to a tunable optical device.

Background of the invention

There is a general need for provision of tunable optical devices to e.g. facilitate the provision of more versatile and more complex optical processing devices.

A number of mechanically tunable optical devices have been proposed. However, typically it has been found that the mechanical tuning of optical devices can suffer from limited accuracy and the fact that it is often cumbersome to automate the tunability.

Another group of tunable optical devices proposed utilise a form of temperature tuning of e.g. grating structures in a waveguide. In such devices a current is being sent through a conductive layer on e.g. an optical fibre, whereby the optical fibre and the grating structure incorporated therein are being heated resistively.

In the proposed tunable devices, one difficulty is to provide temperature profiles along the waveguide device, to facilitate a more versatile and complex tunability. This is because of the inherent difficulty of creating suitably configured/shaped resistive coating layers, together with the appropriate electric connections.

Summary of the invention

In accordance with a first aspect of the present invention there is provided a method of tuning an optical device incorporated in a waveguide structure, the method comprising the step of effecting localised heating to manipulate optical properties of the optical device, wherein the localised heating is effected contactless.

Accordingly, the present invention can provide a method of localised tuning an optical device, which does not require physical electronic connections to be made, thereby enabling greater freedom in the design of temperature profile for tuning optical devices. The step of effecting the localised heating may be conducted in a manner such that a temperature profile is created along the optical device, for distributed tuning of the optical device.

The step of effecting the localised heating may comprise inducing currents in a surface layer of the waveguide structure for effecting contactless resistive localised heating. Alternatively, the step of effecting the localised heating may comprise absorbing light energy in the surface layer for effecting the localised heating through energy conversion into heat. The step of effecting the localised heating may further or alternatively comprise absorbing kinetic energy of particles directed onto the surface layer for effecting the localised heating through energy conversion into heat. The particles may comprise one or more of the group of electrons, photons, and ions.

In one embodiment the step of inducing the currents comprises directing an electron beam onto a surface layer of the waveguide structure, whereby localised currents are induced for effecting the localised heating. The method may further comprise the step of scanning the electron-beam across the surface to effect induction of a temperature profile along the optical device for distributed tuning of the optical device.

The steps of scanning the electron beam and/or absorbing kinetic energy of particles may be implemented utilising a cathode-ray tube (CRT) unit placed in the vicinity of the surface area.

In another embodiment, the step of inducing the currents comprises controlling a gas- discharge in the vicinity of the surface layer of the waveguide structure. The method may further comprise the step of controlling a plurality of localised gas-discharges in the vicinity of a surface area of the waveguide to effect induction of a temperature profile in the surface layer for distributed tuning of the optical device. The step of controlling the plurality of gas-discharges may be implemented utilising a plasma screen placed in the vicinity of the surface area.

Preferably, the surface layer of the waveguide structure comprises a resistive coating.

In one embodiment, the step of absorbing the light energy comprises directing a light beam onto the surface layer of the waveguide structure. The light beam may be provided through a laser source or a light emitting diode (LED). The method may further comprise the step of scanning the light beam across the surface to effect absorption of the light energy in a manner such as to create a temperature profile along the optical device for distributed tuning of the optical device. The step of scanning the light beam may be implemented utilising a dynamic optical circuit or through mechanical scanning of a light source providing the light beam.

In one embodiment, the method comprises utilising an LED array located in the vicinity of the surface layer of the waveguide structure and controlling the emission of light from the LED array in a manner such as to effect a temperature profile along the optical device for distributed tuning of the optical device.

Preferably, the surface layer of the waveguide structure comprises an absorptive coating. The optical device may comprise one or more of the group of a grating structure, a coupler, an arrayed waveguide, and a Mach-Zehnder interferometer.

The waveguide structure may comprise a planar waveguide or an optical fibre.

The method may further comprise the step of controlled removal of heat from the waveguide structure.

In accordance with a second aspect of the present invention there is provided an apparatus for tuning an optical device incorporated in a waveguide structure, the apparatus comprising means for effecting contactless localised heating to manipulate optical properties of the optical device and means for positioning the waveguide structure and the means for contactless localised heating relative to one another.

The means for effecting the contactless localised heating may be arranged, in use, to create a temperature profile along the optical device, for distributed tuning of the optical device.

The means for effecting the contactless localised heating may comprise means for inducing currents in a surface layer of the waveguide structure for effecting contactless resistive localised heating. Alternatively, the means for effecting the localised heating may comprise means for emitting light and for directing the light onto the surface for absorption of the light energy for effecting the localised contactless heating through energy conversion into heat. The means for effecting the localised heating may further or alternatively comprise means for imparting kinetic energy to particles directed onto the surface layer for effecting the localised heating through energy conversion into heat. The particles may comprise one or more of the electrons, photons, and ions. In one embodiment, the means for inducing the currents comprises an electron beam arranged, in use, to be directed onto a surface layer of the waveguide structure. The means for inducing the currents may further comprise means for scanning the electron-beam across the surface to effect, in use, induction of a temperature profile in the surface layer for distributed tuning of the optical device.

The means for inducing the currents and/or the means for imparting kinetic energy may comprise a CRT unit.

In another embodiment, the means for inducing the currents comprises means for controlling a gas-discharge in the vicinity of the surface layer of the waveguide structure. The means for inducing the currents may comprise means for controlling a plurality of localised gas- discharges in the vicinity of a surface area of the waveguide to effect induction of a temperature profile in the surface layer for distributed tuning of the optical device. The means for inducing the currents may comprise a plasma screen.

The means for emitting the light may comprise a laser source or an LED. The means for emitting the light may be arranged to be capable of scanning a light beam across the surface to effect absorption of the light energy in a manner such as to create a temperature profile along the optical device for distributed tuning of the optical device. The means for emitting the light may comprise a dynamic optical circuit or a means for scanning the light beam across the surface.

Alternatively, the means for emitting the light may comprise an LED array arranged in a manner such that emission of light from the LED array is controllable to effect a temperature profile along the optical device for distributed tuning of the optical device.

The apparatus may further comprise means for controlled removal of heat from the waveguide structure. Accordingly, e.g. temperature focusing can be effected to improve spatial resolution of the localised heating/tuning, and/or removal of excess heat generated within the waveguide structure.

In accordance with a third aspect of the present invention there is provided a tunable optical device comprising a waveguide structure, a waveguide device incorporated in the waveguide structure and means for effecting contactless localised heating to manipulate optical properties of the waveguide device. The means for effecting the contactless localised heating may be arranged, in use, to create a temperature profile along the waveguide device, for distributed tuning of the waveguide device.

The means for effecting the contactless localised heating may comprise means for inducing currents in a surface layer of the waveguide structure for effecting contactless resistive localised heating. Alternatively, the means for effecting the localised heating may comprise means for emitting light and for directing the light onto the surface for absorption of light energy for effecting the localised contactless heating through energy conversion into heat. The means for effecting the localised heating may further or alternatively comprise means for imparting kinetic energy to particles directed on the surface layer for effecting the localised heating through energy conversion into heat. The particles may comprise one or more of the electrons, photons, and ions.

In one embodiment, the means for inducing the currents comprises an electron beam arranged, in use, to be directed onto a surface layer of the waveguide structure. The means for inducing the currents may further comprise means for scanning the electron-beam across the surface to effect, in use, induction of a temperature profile in the surface layer for distributed tuning of the waveguide device.

In another embodiment, the means for inducing the currents comprises means for controlling a gas-discharge in the vicinity of the surface layer of the waveguide structure. The means for inducing the currents may comprise means for controlling a plurality of localised gas- discharges in the vicinity of a surface area of the waveguide to effect induction of a temperature profile in the surface layer for distributed tuning of the waveguide device. The means for inducing the currents may comprise a plasma screen.

The means for emitting the light may comprise a laser source or an LED. The means for emitting the light may be arranged to be capable of scanning a light beam across the surface to effect absorption of the light energy in a manner such as to create a temperature profile along the optical device for distributed tuning of the waveguide device. The means for emitting the light may comprise a dynamic optical circuit or a means for scanning the light beam across the surface. Alternatively, the means for emitting the light may comprise an LED array arranged in a manner such that emission of light from the LED array is controllable to effect a temperature profile along the optical device for distributed tuning of the waveguide device.

Preferably, the surface layer of the waveguide structure comprises a resistive coating. For the alternative embodiment, the surface layer of the waveguide structure comprises an absorptive coating.

The waveguide device may comprise one or more of the group of a grating structure, a coupler, an arrayed waveguide, and a Mach-Zehnder Interferometer.

The waveguide structure may comprise a planar waveguide or an optical fibre.

Preferred forms of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 shows a schematic diagram of a tunable optical device structure embodying the present invention.

Figures 2 A, B and C shows a schematic diagrams illustrating the construction of another tunable optical device structure embodying the present invention.

Figure 3 shows a schematic diagram of another tunable optical device structure embodying the present invention.

Figure 4 shows a schematic diagram of another tunable optical device structure embodying the present invention.

Detailed description of the embodiments

In Figure 1, an optical device structure 10 comprises a planar waveguide structure 12, which consists of a waveguide layer 14 embedded in a cladding material 16. Optical connectors 18, 20 are provided on either side of the waveguide layer 14, for connecting the optical device structure 10 between two external waveguides (not shown). The optical device structure 10 further comprises a CRT unit 22 incorporated within a housing 24 of the optical device structure 10. The CRT unit 22 comprises deflection plates e.g. 26 to effect scanning of an electron-beam 28 originating from an electron source of the CRT unit 22.

The optical device structure 10 further comprises a control unit 30 to control the scanning of the electron-beam 28.

Through suitable control of the scanning of the electron-beam 28 by way of the control unit 30, a temperature profile can be created in the optical waveguide layer 14. As a result, the spectral response of a grating structure 34 within the waveguide layout 14 can be shaped in a complex manner.

It will be appreciated by a person skilled in the art that in addition to inducing localised currents, kinetic energy of the electrons can also be converted to heat within the waveguide layer 14. This can contribute to creating the temperature profile for distributed tuning of the grating structure 34. It will further be appreciated by the person skilled in art that in alternative embodiments of the present invention, thus conversion of kinetic energy of particles directed onto the surface of a waveguide structure into heat can be utilised to effect localised tuning of an optical device incorporated in the waveguide structure as the major or only mechanism.

Figure 2 shows an exemplary construction process of an optical device structure embodying the present invention.

Turning initially to Figure 2 A, a small, preferably flat screen CRT unit 100 forms one of the components of the optical device structure to be constructed. In a first step, the front screen 102 is removed through cutting.

In its place, a suitably dimensioned planar waveguide device plate 104 will be mounted. Figure 2B shows a top view of the planar waveguide device plate 104. The device structure 104 comprises e.g. a plurality of waveguides 106, which are configured in a coupler arrangement.

Coupling regions e.g. 108 between two adjacent waveguides e.g. 106, and 110 are coated with metal layers e.g. 112.

In use, the electron beam of the CRT unit 100 (see figure 2 A) can be scanned across the metal layers e.g. 112 to effect contactless localised heating of the various coupling regions e.g. 108 for localised tuning of the coupling conditions. As shown in Figure 2C, the planar optical device plate 104 is mounted onto the body of the CRT unit 100 utilising a suitable solder glass, 105 and the resulting optical device 114 is then evacuated through appropriate means (e.g. by utilising a sealable pump out tube, not shown). The planar optical device plate 104 also comprises a Peltier element 116 for controlled removal of heat. As the Peltier element 116 is located underneath the planar waveguide structure, temperature focusing can be effected to improve spatial resolution of the localised heating/tuning.

The control of the deflector plates (not shown) and acceleration voltages for the electron beam of the CRT unit 100 as well as of the Peltier element 116 is performed by a control unit 118.

It will be appreciated by a person skilled in the art that the controlled removal of heat may be implemented in other ways e.g. by providing cooling channels between the planar optical waveguides.

Optical contacting of the waveguides e.g. 106 can be effected in various known ways, including through provision of suitable optical connectors (not shown) on the waveguide device plate 104.

Turning now to Figure 3, in another optical device structure 50 a plurality of optical fibres 52 are mounted within a casing 54 of the optical device structure 50. The optical device structure 50 further comprises a plasma screen 53 positioned closely above the plurality of optical fibres 52. The display surface 56 of the plasma screen 53 is facing the plurality of optical fibres 52. The optical device structure 50 further comprises a control unit 58 for controlling the plasma screen 53.

Each of the optical fibres 52 comprises a grating structure 60.

The optical device structure 50 further comprises a plurality of optical connectors 62 for connecting external optical fibres to the optical device structure 50.

The spacing between the display surface 56 and the plurality of optical fibres 52 is chosen such that electric currents are being induced in resistive coatings 64 of the optical fibres 52 as a result of the gas discharges occurring in the plasma display 53. The resistive coatings 64 may be formed from a suitable metal, such as e.g. chromium. Through suitable control of the plasma display 53 by way of the control unit 58, different temperature profiles can thus be created in the optical fibres 52 along their respective gratings 60. This allows individual tuning of the optical properties of the grating structure 60 of each optical fibre 52. The temperature profile created in each optical fibre 52 may be identical or may differ between the fibres 52.

Turning now to Figure 4, in an alternative embodiment, in an optical device structure 200 a plurality of optical fibres 202 are mounted within a case 204. The optical device structure 200 further comprises an LED array plate 205 positioned closely above the plurality of optical fibres 202. The emitting surface 206 of the LED array plate 205 is facing the plurality of optical fibres 202. The optical device structure 200 further comprises a control unit 208 for controlling the LED array plate 205.

Each of the optical fibres 202 comprises a grating structure 210.

The optical device structure 200 further comprises a plurality of optical connectors 212 for connecting external optical fibres to the optical device structure 200.

The spacing between the emitting surface 206 of the LED array plate 205 and the plurality of optical fibres 202 is selected such that the emitted photon energy is absorbed in absorptive coatings 214 of the optical fibres 202 for conversion into heat to create a temperature profile along the grating structures 210 for effecting distributed tuning.

Through suitable control of the LED array plate 205 by way of the control unit 208, different temperature profiles can be created depending on tuning requirements.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in these specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are therefore, to be considered in all respects to be illustrative and not restrictive.

For example, it will be appreciated that the present invention is not limited to any particular tunable optical device structure, but is applicable to any optical device structure in which timing of the optical properties can be effected through localised heating. Other devices to which the present invention is applicable include e.g. Mach-Zehnder interferometers or arrayed waveguides (AWG). In the claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the feature specified may be associated with further features in various embodiments of the invention.

Claims

1. A method of tuning an optical device incorporated in a waveguide structure, the method comprising the step of effecting localised heating to manipulate optical properties of the optical device, wherein the localised heating is effected contactless.

2. A method as claimed in claim 1, wherein the contactless localised heating is conducted in a manner such that a temperature profile along the optical device is created, for distributed tuning of the optical device.

3. A method as claimed in claims 1 or 2, wherein the step of effecting the localised heating comprises inducing currents in a surface layer of the waveguide structure for effecting contactless resistive localised heating.

4. A method as claimed in claims 1 or 2, wherein the step of effecting the localised heating may comprise absorbing light energy in the surface layer for effecting the localised heating through energy conversion into heat.

5. A method as claimed in any one of claims 1 to 4, wherein the step of effecting the localised heating comprises absorbing kinetic energy of particles directed onto the surface layer for effecting the localised heating through energy conversion into heat.

6. A method as claimed in claim 3, wherein the step of inducing the currents comprises directing an electron beam onto a surface layer of the waveguide structure, whereby localised currents are induced for effecting the contactless resistive localised heating.

7. A method as claimed in claim 6, wherein the method further comprises the step of scanning the electron-beam across the surface to effect induction of a temperature profile along the optical device for distributed tuning of the optical device.

8. A method as claimed in claims 5 or 7, wherein the steps of scanning the electron beam and/or absorbing kinetic energy of particles directed onto the surface layer is implemented utilising a CRT unit placed in the vicinity of the surface area.

9. A method as claimed in claim 3, wherein the step of inducing the currents comprises controlling a gas-discharge in the vicinity of the surface layer of the waveguide structure.

10. A method as claimed in claim 9, wherein the method further comprises the step of controlling a plurality of localised gas-discharges in the vicinity of a surface area of the waveguide to effect induction of a temperature profile in the surface layer for distributed tuning of the optical device.

11. A method as claimed in claim 10, wherein the step of controlling the plurality of gas-discharges is implemented utilising a plasma screen placed in the vicinity of the surface area.

12. A method as claimed in any one of claims 3 or 6 to 11, wherein the surface layer of the waveguide structure comprises a resistive coating.

13. A method as claimed in claim 4, wherein the step of absorbing light energy comprises directing a light beam onto the surface layer of the waveguide structure.

14. A method as claimed in claim 13, wherein the light beam is provided through a laser source or a light emitting diode (LED).

15. A method as claimed in claim 14, wherein the method further comprises the step of scanning the light beam across the surface to effect absorption of the light energy in a manner such as to create a temperature profile along the optical device for distributed tuning of the optical device.

16. A method as claimed in claim 15, wherein the step of scanning the light beam is implemented utilising a dynamic optical circuit or through mechanical scanning of a light source providing the light beam.

17. A method as claimed in claim 4, wherein the method comprises utilising an LED array located in the vicinity of the surface layer of the waveguide structure and controlling the emission of light from the LED array in a manner such as to create a temperature profile along the optical device for distributed tuning of the optical device.

18. A method as claimed in any one of claims 4, 5 or 13 to 17, wherein the surface layer of the waveguide structure comprises an absorptive coating.

19. A method as claimed in any one of the preceding claims, wherein the optical device comprises one or more of the group of a grating structure, a coupler, an arrayed waveguide or a Mach-Zehnder interferometer.

20. A method as claimed in any one of the preceding claims, wherein the waveguide structure comprises a planar waveguide or an optical fibre.

21. A method as claimed in any one of the preceding claims, wherein the method further comprises the step of controlled removal of heat from the waveguide structure.

22. An apparatus for tuning an optical device incorporated in a waveguide structure, the apparatus comprising means for effecting contactless localised heating to manipulate optical properties of the optical device and means for positioning the waveguide structure and the means for effecting contactless localised heating relative to one another.

23. An apparatus as claimed in claim 22, wherein the means for effecting the contactless localised heating is arranged in a manner such that it is capable of creating a temperature profile along the optical device for distributed tuning of the optical device.

24. An apparatus as claimed in claims 22 or 23, wherein the means for effecting the contactless localised heating comprises means for inducing currents in a surface layer of the waveguide structure for effecting contactless resistive localised heating.

25. An apparatus as claimed in claims 22 or 23, wherein the means for effecting the contactless localised heating comprises means for emitting light directed onto the surface layer for effecting the localised heating through energy conversion into heat.

26. An apparatus as claimed in any one of claims 22 to 25, wherein the means for effecting the contactless localised heating comprises means for imparting kinetic energy to particles directed onto the surface layer for effecting the localised heating through energy conversion into heat.

27. An apparatus as claimed in claim 24, wherein the means for inducing the currents comprises an electron beam arranged, in use, to be directed onto a surface layer of the waveguide structure.

28. An apparatus as claimed in claim 27, wherein the means for inducing the currents further comprises means for scanning the electron-beam across the surface to effect, in use, induction of a temperature profile in the surface layer for distributed tuning of the optical device.

29. An apparatus as claimed in claims 26 or 28, wherein the means for inducing the currents and/or means for imparting kinetic energy to particles directed onto the surface layer comprises a CRT unit.

30. An apparatus as claimed in claim 24, wherein the means for inducing the currents comprises means for controlling a gas-discharge in the vicinity of the surface layer of the waveguide structure.

31. An apparatus as claimed in claim 30, wherein the means for inducing the cuoents comprises means for controlling a plurality of localised gas-discharges in the vicinity of a surface area of the waveguide to effect induction of a temperature profile in the surface layer for distributed tuning of the optical device.

32. An apparatus as claimed in claim 31 , wherein the means for inducing the currents comprises a plasma screen.

33. An apparatus as claimed in claim 25, wherein the means for emitting the light comprises a laser source or an LED.

34. An apparatus as claimed in claim 32, wherein the means for emitting the light is arranged to be capable of scanning a light beam across the surface to effect absorption of the light energy in a manner such as to create a temperature profile along the optical device for distributed tunning of the optical device.

35. An apparatus as claimed in claim 34, wherein the means for emitting the light comprises a dynamic optical circuit or a means for scanning the light beam across the surface.

36. An apparatus as claimed in claim 25, wherein the means for emitting the light comprises an LED array arranged in a manner such that emission of light from the LED array is controllable to create a temperature profile along the optical device for distributed tuning of the optical device.

37. An apparatus as claimed in any one of claims 22 to 36, wherein the apparatus further comprises means for controlled removal of heat from the waveguide structure.

38. A tunable optical device comprising:

- a waveguide structure,

- a waveguide device incorporated in the waveguide structure and - means for effecting contactless localised heating to manipulate optical properties of the waveguide device.

39. A device as claimed in claim 38, wherein the means for effecting the contactless localised heating is arranged, in use, to create a temperature profile along the waveguide device for distributed tuning of the waveguide device.

40. A device as claimed in claims 38 or 39, wherein the means for effecting the contactless localised heating comprises means for inducing currents in a surface layer of the waveguide structure for effecting contactless resistive localised heating.

41. A device as claimed in claims 38 or 39, wherein the means for effecting the localised heating comprises means for emitting light and for directing the light onto the surface for absorption of light energy for effecting the localised contactless heating through energy conversion into heat.

42. A device as claimed in any one of claims 38 to 41, wherein the means for effecting the contactless localised heating comprises means imparting kinetic energy to particles directed onto a surface layer of the waveguide structure for effecting localised heating.

43. A device as claimed in claim 40, wherein the means for inducing the currents comprises an electron beam arranged, in use, to be directed onto a surface layer of the waveguide structure.

44. A device as claimed in claim 43, wherein the means for inducing the currents further comprises means for scanning the electron-beam across the surface to effect, in use, induction of a temperature profile in the surface layer for distributed tuning of the waveguide device.

45. A device as claimed in claims 42 to 44, wherein the means for inducing the currents and/or means for imparting kinetic energy to particles directed onto the surface layer comprises a CRT unit.

46. A device as claimed in claim 40, wherein the means for inducing the currents comprises means for controlling a gas-discharge in the vicinity of the surface layer of the waveguide structure.

47. A device as claimed in claim 46, wherein the means for inducing the currents comprises means for controlling a plurality of localised gas-discharges in the vicinity of a surface area of the waveguide to effect induction of a temperature profile in the surface layer for distributed tuning of the waveguide device.

48. A device as claimed in claim 47, wherein the means for inducing the currents comprises a plasma screen.

49. A device as claimed in claim 41, wherein the means for emitting the light comprises a laser source or an LED.

50. A device as claimed in claim 49, wherein the means for emitting the light is arranged to be capable of scanning a light beam across the surface to effect absorption of the light energy in a manner such as to create a temperature profile along the optical device for distributed tunning of the waveguide device.

51. A device as claimed in claim 50, wherein the means for emitting the light comprises a dynamic optical circuit or a means for scanning the light beam across the surface.

52. A device as claimed in claim 41, wherein the means for emitting the light comprises an LED array arranged in a manner such that emission of light from the LED array is controllable to create a temperature profile of the optical device for distributed tuning of the optical device.

53. A device as claimed in any one of claims 40 or 43 to 48, wherein the surface layer of the waveguide structure comprises a resistive coating.

54. A device as claimed in any one of claims 41, 42 or 49 to 52, wherein the surface layer of the waveguide structure comprises an absorptive coating.

55. A device as claimed in any one of claims 38 to 54, wherein the device further comprises means for controlled removal of heat from the waveguide structure.

56. A device as claimed in any one of claims 38 to 55, wherein the waveguide device comprises one or more of the group of a grating structure, a coupler, a Mach-Zehnder interferometer or an arrayed waveguide.

57. A device as claimed in any one of claims 38 to 56, wherein the waveguide structure comprises a planar waveguide or an optical fibre.