FBG production system

• US 6,816,649 B2
• Filed: 06/28/2002
• Issued: 11/09/2004
• Est. Priority Date: 06/29/2001
• Status: Active Grant

• Current Assignee: Optopland AS
• Original Assignee: Optoplan AS (Nokia Corporation)
• Inventors: Rønnekleiv, Erlend
• Primary Examiner(s): Bruce, David V.
• Assistant Examiner(s): Artman, Thomas R
• Application Number:
  US10/184,057
• Publication Number:
  US 20030007732A1
• Time in Patent Office: 865 Days
• Field of Search: 385/37, 385/137
• US Class Current: 385/37
• CPC Class Codes: G02B 6/02133 using beam interference
• CPC Class Codes: G02B 6/02152 involving moving the fibre or a manufacturing element, stretching of the fibre G02B6/02147 takes precedence

Abstract

An optical waveguide Bragg grating fabrication apparatus (1) comprises a light source (2) providing ultra-violet (UV) light and optical means (4,5A-B,6A-B,7A-B,9) for adapting the light beam to form an interference pattern in a photosensitive optical waveguide (8). The interference pattern has a spatial intensity modulation along the length of the optical waveguide and thus providing an optical grating in the waveguide in the form of a refractive index modulation.

The optical means comprises a movable non-uniform diffractive mask (4) for dividing the optical beam in at least two beams (12A-B) and optical elements for collecting two or more of the light beams to interfere on the optical waveguide.

The optical means comprises position control means for controlling the position of at least one mirror or lens.

Corresponding methods and the use of a super-periodic diffractive mask in such fabrication are described.

Claims

1. An apparatus for fabricating an optical waveguide Bragg grating comprising:

a light source for providing a beam of ultra violet (UV) light;

optical means for adapting the light beam to form an interference pattern in a photo sensitive optical waveguide, the interference pattern having a spatial intensity modulation along a length of the optical waveguide and thus providing an optical grating in the waveguide in the optical form of a refractive index modulation,

wherein the optical means comprises

a first position control means and a waveguide holder assembly comprising a second position control means for setting the position of the optical waveguide,

a movable non-uniform diffractive mask for dividing the optical beam into at least two beams, wherein the diffractive mask comprises one or more sections with different super-periodic patterns having repeated segments of arbitrarily modulated periodic index variation, each segment forming one period of the super-periodic pattern, and

optical elements for collecting two or more of the light beams to interfere on the optical waveguide.

2. The apparatus of claim 1, wherein the arbitrarily modulated periodic index variation comprises a chirped mask pattern.

3. The apparatus of claim 2, wherein the arbitrarily modulated periodic index variation comprises a continuously or step-wise chirped mask pattern.

4. An apparatus for fabricating an optical waveguide Bragg grating comprising:

a light source for providing a beam of ultra violet (UV) light;

optical means for adapting the light beam to form an interference pattern in a photo sensitive optical waveguide, the interference pattern having a spatial intensity modulation along a length of the optical waveguide and thus providing an optical grating in the waveguide in the form of a refractive index modulation,

wherein the optical means comprises

a first position control means and a waveguide holder assembly comprising a second position control means for setting the position of the optical waveguide,

a movable non-uniform diffractive mask for dividing the optical beam into at least two beams, and

Fresnel lenses for collecting two or more of the light beams to interfere on the optical waveguide.

5. An apparatus for fabricating an optical waveguide Bragg grating comprising:

a light source for providing a beam of ultra violet (UV) light;

optical means for adapting the light beam to form an Interference pattern in a photo sensitive optical waveguide, the interference pattern having a spatial intensity modulation along the length of the optical waveguide and thus providing an optical grating in the waveguide in the form of a refractive index modulation,

wherein the optical means comprises

a first position control means and a waveguide holder assembly comprising a second position control means for setting the position of the optical waveguide,

a movable non-uniform diffractive mask for dividing the optical beam into at least two beams, wherein the diffractive mask comprises one or more sections with different super-periodic patterns having repeated segments of arbitrarily modulated periodic index variation, each segment forming one period of the super-periodic pattern, and

an arrangement of curved mirrors for collecting two or more of the light beams to interfere on the optical waveguide.

6. A method of fabricating an optical waveguide grating comprising:

providing a beam of light using an ultraviolet (UV) light source;

directing the UV beam through optical means for providing an interference pattern in a photosensitive optical waveguide;

altering and determining the position of at least part of the optical means relative to the UV beams using a first position control means;

altering and determining the position of an optical waveguide holder assembly using a second position control means, the optical waveguide holder assembly comprising the at least one optical waveguide; and

controlling the position of a non-uniform diffractive mask being part of the optical means, thereby controlling which area of the mask is exposed to the UV beam, and thus yielding an interference pattern in the waveguide corresponding to that part of the diffractive mask which is exposed to the UV beam, wherein

the interference pattern on the waveguide is held stable relative to the waveguide during a movement of the waveguide over a distance by continuously controlling the position of one or more lenses, mirrors or glass prisms and/or the angle of one or more mirrors, and

the position of the one or more tenses, mirrors or glass prisms and/or the angle of one or more mirrors is rapidly reset at intervals in order to limit the maximum displacement of the envelope of the interference pattern to only one or a limited number of Bragg periods between each reset operation.

7. A method of fabricating an optical waveguide grating comprising:

providing a beam of light using an ultraviolet (UV) light source;

directing the UV beam through optical means for providing an interference pattern in a photosensitive optical waveguide;

altering and determining the position of at least part of the optical means relative to the UV beams using a first position control means;

altering and determining the position of an optical waveguide holder assembly using a second position control means, the optical waveguide holder assembly comprising the at least one optical waveguide; and

controlling the position of a non-uniform super-periodic diffractive mask being part of the optical means, thereby controlling which area of the mask is exposed to the UV beam, and thus yielding an interference pattern in the waveguide corresponding to that part of the diffractive mask which is exposed to the UV beam.

8. The method of claim 7, wherein a reset operation is executed one or more times, the reset operation comprising moving the super-periodic diffractive mask one or more super-periods, Λ

_P.

9. A method of forming a grating profile having a desired length and a desired period, phase, and amplitude distribution along the grating profile in a photo-sensitive optical waveguide, comprising:

illuminating a portion of a non-uniform phase mask with an ultraviolet (UV) beam smaller in dimension than a total length of the non-uniform phase mask resulting in an interference pattern region smaller in dimension than the desired length of the grating profile;

moving the optical waveguide through the interference pattern region; and

moving the non-uniform phase mask to maintain illumination of a region of the non-uniform phase mask having a grating period that is appropriate for maintaining a period of the interference pattern region sufficiently close to the desired period of the grating profile in a region of the optical waveguide being exposed.

10. The method of claim 9, wherein the non-uniform phase mask is not moved during exposure of the desired grating length.

11. The method of claim 10 further comprising:

moving the non-uniform phase mask; and

forming another grating profile in the optical waveguide using the non-uniform phase mask.

12. The method of claim 9, further comprising adjusting a phase and visibility of total UV exposure of the optical waveguide via track end reset operations.

13. The method of claim 12, wherein adjusting the phase and visibility of the total UV exposure of the optical waveguide via track and reset operations comprises superimposing a patterned motion on at least one at movement of the optical waveguide or movement of the phase mask.

14. The method of claim 9, wherein:

illuminating the portion of the non-uniform phase mask with the UV beam results in a plurality of beams; and

the method further comprises collecting at least two out of the plurality of beams with one or more optical collection elements that are smaller in dimension than a total length of the non-uniform phase mask resulting in an interference pattern region smaller in dimension then the desired length of the grating profile.

15. The method of claim 14, further comprising moving the optical collection elements to adjust a phase and visibility of the total UV exposure of the optical waveguide.

16. The method of claim 14, further comprising moving the optical collection elements to achieve the desired period, phase, and amplitude distribution along the grating profile.

17. A method of writing a grating profile, having a desired length and a desired period, phase, and amplitude distribution along the grating profile, in a photo-sensitive optical waveguide, comprising:

illuminating a non-uniform phase mask with an ultraviolet (UV) beam resulting in a plurality of light beams;

collecting at least two of the light beams with optical elements to form an interference pattern region;

moving the optical waveguide through the interference pattern region;

moving the non-uniform phase mask to maintain illumination of a portion of the non-uniform phase mask having a grating period that is appropriate for generating an interference spot on the optical waveguide having a period sufficiently close to the desired period of the grating profile being written; and

moving the optical elements in a defined pattern versus time to adjust the phase of the interference pattern region, wherein the defined pattern is chosen to compensate for movement of both the optical waveguide and the non-uniform phase mask.

18. The method of claim 17, wherein different grating profiles are formed in different regions of the optical waveguide without changing the non-uniform phase mask.

19. The method of claim 17, wherein the grating profile covers a Bragg wavelength bandwidth of at least 60 nm.

20. The method of claim 17, wherein non-uniformities in the grating are formed in a different direction than non-uniformities in the non-uniform phase mask.

21. The method of claim 17, wherein moving the optical elements in a defined pattern adjusts a phase and visibility of total UV exposure of the optical waveguide via track and reset operations.

22. An apparatus for forming a grating profile, having a desired length and a desired period, phase, and amplitude distribution along the grating profile, in a photo-sensitive optical waveguide, comprising:

a light source;

a non-uniform mask;

a mask holding assembly capable of holding and moving the non-uniform mask while the non-uniform mask is illuminated by the light source;

an optical collection holding assembly capable of holding and moving optical collection elements used to collect at least two light beams generated by illuminating the non-uniform mask with the light source to form an interference pattern region; and

an optical waveguide holding assembly capable of holding and moving the optical waveguide through the non-uniform interference pattern region.

23. The apparatus of claim 22, wherein the optical collection elements comprise a plurality of mirrors.

24. The apparatus of claim 22, wherein the optical collection elements comprise one or more lenses.

25. The apparatus of claim 22, wherein the optical collection assembly is movable in a defined pattern versus time to adjust a phase of the interference pattern region, wherein the defined pattern is chosen to compensate for movement of both the optical waveguide and the non-uniform mask to achieve the desired phase and amplitude distribution of the total exposed grating profile.