Controlled phase delay between beams for writing bragg gratings

• US 20030124438A1
• Filed: 01/09/2003
• Published: 07/03/2003
• Est. Priority Date: 05/29/1998
• Status: Active Grant

• Current Assignee: University of Sydney
• Original Assignee: University of Sydney
• Inventors: Sceats, Mark, Stepanov, Dmitrii
• Granted Patent: US 7,018,745 B2
• Time in Patent Office: Days
• US Class Current: 430/2
• CPC Class Codes: G02B 2006/02157 Grating written during drawing of the fibre
• CPC Class Codes: G02B 5/1857 using exposure or etching means, e.g. holography, photolithography, exposure to electron or ion beams
• CPC Class Codes: G02B 6/02133 using beam interference
• CPC Class Codes: G02B 6/02138 based on illuminating a phase mask
• CPC Class Codes: G02B 6/02152 involving moving the fibre or a manufacturing element, stretching of the fibre G02B6/02147 takes precedence
• CPC Class Codes: G03H 1/0476 Holographic printer G03H1/268 takes precedence
• CPC Class Codes: G03H 2001/0482 Interference based printer
• CPC Class Codes: Y10S 430/146 Laser beam

Abstract

A method of writing an extended grating structure in a photosensitive waveguide comprising the steps of utilising at least two overlapping beams of light to form an interference pattern, moving the waveguide through said overlapping beams, simultaneously controlling a relative phase delay between the beams utilising a phase modulator, thereby controlling the positions of maxima within said interference pattern to move at approximately the same velocity as the photosensitive waveguide, wherein the phase modulator does not comprise a mechanical means for effecting the phase modulation, and modifying the relative phase delay between the beams during the writing of the grating structure, whereby a deliberate detuning of the velocity of the positions of maxima within said interference pattern and the velocity of the photosensitive waveguide is utilised to vary a period of the written grating structure in the photosensitive waveguide.

Claims

1. A method of writing an extended grating structure in a photosensitive waveguide comprising:

utilising at least two overlapping beams of light to form an interference pattern,

moving the waveguide through said overlapping beams,

simultaneously controlling a relative phase delay between the beams utilising a phase modulator, thereby controlling the positions of maxima within said interference pattern to move at approximately the same velocity as the photosensitive waveguide, wherein the phase modulator does not comprise a mechanical means for effecting the phase modulation, and

modifying the relative phase delay between the beams during the writing of the grating structure, whereby a deliberate detuning of the velocity of the positions of maxima within said interference pattern and the velocity of the photosensitive waveguide is utilised to vary a period of the written grating structure in the photosensitive waveguide.

2. A method as claimed in claim 1, wherein the at least two overlapping beams are formed by the splitting of a single coherent beam of light.

3. A method as claimed in claim 2, wherein the steps of controlling and modifying of the relative phase delay is performed before the splitting of the single coherent beam.

4. A method as claimed in claim 2, wherein the steps of controlling and modifying of the relative phase delay is performed after the splitting of the single coherent beam.

5. A method as claimed in claim 2, wherein the steps of controlling and modifying of the relative phase delay is performed prior to the splitting of the single coherent beam.

6. A method as claimed in claim 1, wherein said modulator comprises one or more of a group comprising an electro-optic phase modulator, a magneto-optic phase modulator, a frequency shifter, an acousto-optic frequency shifter, a controllable optical retarder, and an optical delay line.

7. A method as claimed in claim 2, wherein the method further comprises, after the splitting of the single coherent beam, the step of reflecting said beams at a series of reflection elements for effecting the overlapping of the beams to form the interference pattern.

8. A method as claimed in claim 1, further comprising utilising a feedback loop in controlling and modifying of the phase delay to improve the noise properties of the grating structure.

9. A method as claimed in claim 8, wherein the feedback loop comprises an opto-electronic feedback loop.

10. A method as claimed in claim 1, wherein the grating structure comprises a chirped grating and/or an apodized grating.

11. A method as claimed in claim 1, wherein the grating structure has one or more of a group comprising a predetermined strength profile, a predetermined period profile, and a predetermined phase profile.

12. A method as claimed in claim 1, wherein the two beams have substantially orthogonal polarization states and wherein the modulator modulates the relative phase delay between the polarization states and wherein the method further comprises the step of aligning the polarization states of the beams subsequent to modulating the relative phase delay for forming the interference pattern.

13. A method as claimed in claim 12, wherein the two beams having the substantially orthogonal polarization states initially from a single beam of light, and a polarization splitter element is utilised to separate the two beams from each other.

14. A method as claimed in claim 13, wherein the modulator modulates the relative phase delay between the polarisation states in the single beam.

15. A device for writing an extended grating structure in a photosensitive waveguide comprising:

an interferometer arranged to form an interference pattern utilising at least two overlapping beams of light; and

a phase modulator for controlling a relative phase delay between the beams whereby, in use, the positions of maxima within said interference pattern are controlled to move at approximately the same velocity as the photosensitive waveguide moving through said overlapping beams,

wherein the phase modulator does not comprise a mechanical means for effecting the phase modulation, and

wherein the phase modulator is arranged, in use, to modify the relative phase delay between the beams during the writing of the grating structure, whereby a deliberate detuning of the velocity of the positions of maxima within said interference pattern and the velocity of the photosensitive waveguide is utilised to vary a period of the written grating structure in the photosensitive waveguide.

16. A device as claimed in claim 15, wherein the device comprises a beam splitter element for splitting of a single coherent beam of light into said at least two overlapping beams.

17. A device as claimed in claims 16, wherein the device is arranged, in use, such that the controlling and modifying of the relative phase delay is performed before the splitting of the single coherent beam.

18. A device as claimed in claim 16, wherein the device is arranged, in use, such that the controlling and modifying of the relative phase delay is performed after the splitting of the single coherent beam.

19. A device as claimed in claim 16, wherein the device is arranged, in use, such that the controlling and modifying of the relative phase delay is performed prior to the splitting of the single coherent beam.

20. A device as claimed in claim 15, wherein said modulator comprises one or more of a group comprising an electro-optic phase modulator, a magneto-optic phase modulator, a frequency shifter, an acousto-optic frequency shifter, a controllable optical retarder, and an optical delay line.

21. A device as claimed in claim 15, wherein the device further comprises a series of optical reflection elements for effecting the overlapping of the beams to form the interference pattern.

22. A device as claimed in claim 15, further comprising a feedback unit for facilitating the controlling and modifying of the phase delay to improve the noise properties of the grating structure.

23. A device as claimed in claim 22, wherein the feedback unit comprises an opto-electronic feedback loop.

24. A device as claimed in claim 15, wherein the two beams have substantially orthogonal polarization states and the modulator is arranged, in use, to modulate the relative phase delay between the polarization states and wherein the device further comprises a polarisation manipulation element for aligning the polarization states of the beams subsequent to modulating the relative phase delay for forming the interference pattern.

25. A device as claimed in claim 24, wherein the two beams having the substantially orthogonal polarization states initially from a single beam of light, and the device compresses a polarization splitter element for separating the two beams from each other.

26. A device as claimed in claim 25, wherein the modulator is arranged, in use, to modulate the relative phase delay between the polarisation states in the single beam.