Index matched grating inscription

Patent metadata

Field	Value
Publication number	US-9568670-B2
Application number	US-201414185443-A
Country	US
Kind code	B2
Filing date	Feb 20, 2014
Priority date	Feb 21, 2013
Publication date	Feb 14, 2017
Grant date	Feb 14, 2017

Abstract

The disclosed embodiments provide systems and methods for mitigating lensing and scattering as an optical fiber is being inscribed with a grating. The disclosed systems and methods mitigate the lensing phenomenon by surrounding an optical fiber with an index-matching material that is held in a vessel with an integrated interferometer (e.g., phase mask, etc.). The index-matching material has a refractive index that is sufficient to reduce intensity variations of the actinic radiation within the optical fiber. Some embodiments of the system include different vessels for holding the index-matching material, with the vessel having an interferometer integrated into the vessel. These vessels permit the optical fiber to be surrounded by the index-matching material while the gratings are written to the optical fiber.

First claim

What is claimed is:

1. An optical fiber, comprising:
an outer diameter (R fiber );
a fiber index of refraction (n fiber );
an offset core following a helical trajectory along an axial direction along the optical fiber, the offset core being offset from a center of the optical fiber by R offset ;
gratings written on the offset core, the gratings being written with the optical fiber being surrounded by an index-matching material, the index-matching material having an index of refraction (n surround ), the gratings having a maximum grating strength, the gratings having a minimum gratings strength, a ratio of the minimum grating strength to the maximum grating strength being:

1
-

ρ
⁡

(

η
-
1

)

1
+

ρ
⁡

(

η
-
1

)

,

where η=n fiber /n surround , ρ<1/η, and ρ=R offset /R fiber .

2. The optical fiber of claim 1 , the grating being longer than one (1) centimeter (cm).

3. The optical fiber of claim 1 , the grating being longer than fifteen (15) centimeters (cm).

4. The optical fiber of claim 1 , the grating being longer than one (1) meter (m).

5. The optical fiber of claim 1 , further comprising cores, the cores comprising the offset core, each of the cores following a helical trajectory along the axial direction, the helical trajectory having a twist period.

6. The optical fiber of claim 5 , the cores comprising gratings, the cores having less than approximately two (2) decibels (dB) of variation in index modulation throughout the twist period.

7. The optical fiber of claim 5 , the cores comprising gratings, the gratings having substantially the same index modulation.

8. The optical fiber of claim 1 , the fiber index of refraction comprising a core index of refraction.

9. The optical fiber of claim 1 , the fiber index of refraction comprising a cladding index of refraction.

10. The optical fiber of claim 1 , the fiber index of refraction comprising a coating index of refraction.

11. The optical fiber of claim 1 , the fiber index of refraction comprising a combination of a core index of refraction, a cladding index of refraction, and a coating index of refraction.

12. The optical fiber of claim 1 , the fiber index of refraction being one selected from the group consisting of:
a core index of refraction;
a cladding index of refraction;
a coating index of refraction;
a combination of a core index of refraction and a cladding index of refraction;
a combination of a cladding index of refraction and a coating index of refraction; and
a combination of a core index of refraction, a cladding index of refraction, and a coating index of refraction.

13. An optical fiber, comprising:
an outer radius (R fiber );
a core that is offset from a center of the optical fiber by more than approximately forty (40) percent (%) of R fiber , the core following a helical trajectory along an axial direction along the optical fiber, the helical trajectory having a twist period; and
a grating inscribed on the core, the grating being longer than approximately twenty (20) centimeters, the grating having a strength variation that is less than approximately three (3) decibels (dB) through the twist period.

14. An optical fiber, comprising:
a core that is offset from a center of the optical fiber by a distance that is greater than R max =1/η, where η=n fiber /n surround , where n fiber is a fiber index of refraction and n surround is an index of refraction of an index-matching material surrounding the core, the core following a helical trajectory along an axial direction of the optical fiber, the helical trajectory having a twist period; and
gratings inscribed on the core, the gratings having substantially uniform strength throughout the twist period.

15. The optical fiber of claim 14 , the grating having a grating strength variation that is less than approximately ten (10) decibels (dB) throughout the twist period.

Assignees

• Ofs Fitel Llc

Inventors

• Feder Kenneth S
• Westbrook Paul S

Classifications

• G02B2006/0209

  Helical, chiral gratings · CPC title

• G02B6/02123

  characterised by the method of manufacture of the grating (photolithography G03F7/0005) · CPC title

• G02B6/021

  characterised by the core or cladding or coating, e.g. materials, radial refractive index profiles, cladding shape · CPC title

• G02B6/02042 Primary

  Multicore optical fibres · CPC title

• G02B6/02095 Primary

  Long period gratings, i.e. transmission gratings coupling light between core and cladding modes · CPC title