Optical fiber laser
A method of fabricating a distributed feedback optical fiber laser, comprises the step of exposing an optical fiber ( 20 ) to a transverse light beam ( 30 ) to form a grating structure in a section of the optical fiber, the writing light beam being polarized in a direction not parallel to the axis of the section ( 10 ) of optical fiber ( 20 ).
1. A method of fabricating an optical fiber laser, the method comprising:
repeatedly exposing an optical fiber to a transverse writing light beam to form a DFB grating structure in a section of the optical fiber, the writing light beam being polarized in a direction not parallel to the axis of the section of the optical fiber so that the induced grating structure has a different grating strength for two orthogonal polarization modes of the optical fiber; and
moving at least one of the optical fiber and the writing light beam between each exposure;
wherein the grating structure has a discrete phase shift which is substantially identical for the two orthogonal polarization modes and the grating structure is formed without introducing a phase shift by post processing of the orating structure.
2. A method according to claim 1 , in which the writing light beam is polarized in a direction substantially perpendicular to the axis of the section of the optical fiber.
3. A method according to claim 1 , in which the writing light beam is an ultraviolet beam.
4. A method according to claim 3 , in which the ultraviolet beam has a wavelength of about 244 nanometers.
5. A method according to claim 1 , in which the optical fiber section is doped with at least one amplifying dopant.
6. A method according to claim 5 , in which the optical fiber section is doped with at least one rare earth element.
7. A method according to claim 6 , in which the optical fiber section is doped with erbium and ytterbium.
8. A method according to claim 1 , wherein the optical fiber laser is stressed to provide substantially single polarization operation.
9. A method according to claim 1 , wherein the optical fiber laser is stressed to provide dual polarization operation.
10. A method according to claim 1 , wherein the grating structure is written as a Moire phase shifted structure to provide lasing operation at two wavelengths having one polarization.
11. A method according to claim 1 , wherein the grating structure is written as first and second overlaying DFB grating structures to provide lasing operation at two wavelengths having one polarization.
12. A method according to claim 1 , wherein the movement is carried out such that at least a majority of grating lines from the grating structure are generated by exposure to different respective regions of the writing light beam.
13. A method of fabricating an optical fiber laser, the method consisting of the step of repeatedly exposing an optical fiber to a transverse writing light beam to form a plural grating structures in different sections of the optical fiber, the writing light beam being polarized in a direction not parallel to the axis of the section of the optical fiber so that the induced grating structure has a different grating strength for two orthogonal polarization modes of the optical fiber, the grating structure having a discrete phase shift which is substantially identical for the two orthogonal polarization modes and the grating structure is formed without introducing a phase shift by post processing of the grating structure.
14. A method according to claim 13 , in which the writing light beam is polarized in a direction substantially perpendicular to the axis of the section of the optical fiber.
15. A method according to claim 13 , in which the writing light beam is an ultraviolet beam.
16. A method according to claim 15 , in which the ultraviolet beam has a wavelength of about 244 nanometers.
17. A method according to claim 13 , in which the optical fiber section is doped with at least one amplifying dopant.
18. A method according to claim 17 , in which the optical fiber section is doped with at least one rare earth element.
19. A method according to claim 18 , in which the optical fiber section is doped with erbium and ytterbium.
20. A method according to claim 13 , wherein the optical fiber laser is stressed to provide substantially single polarization operation.
21. A method according to claim 13 , wherein the optical fiber laser is stressed to provide dual polarization operation.
22. A method according to claim 13 , wherein the grating structure is written as a Moire phase shifted structure to provide lasing operation at two wavelengths having one polarization.
23. A method according to claim 13 , wherein the grating structure is written as first and second overlaying DFB grating structures to provide lasing operation at two wavelengths having one polarization.
24. A method according to claim 13 , wherein the grating structure is a DFB grating structure.
25. A method according to claim 13 , wherein the grating structure is formed without tuning of the discrete phase shift.