On-fiber tunable bragg gratings for DWDM applications

• US 20070258673A1
• Filed: 05/08/2006
• Published: 11/08/2007
• Est. Priority Date: 05/08/2006
• Status: Active Grant

• Current Assignee: Photonics On-Fiber Devices, Inc.
• Original Assignee: Photonics On-Fiber Devices, Inc.
• Inventors: El-Sherif, Mahmoud
• Granted Patent: US 8,805,136 B2
• Time in Patent Office: Days
• US Class Current: 385/10
• CPC Class Codes: G02B 6/02066 Gratings having a surface relief structure, e.g. repetitive variation in diameter of core or cladding
• CPC Class Codes: G02B 6/02195 characterised by means for tuning the grating
• CPC Class Codes: G02F 2201/307 Reflective grating, i.e. Bragg grating

Abstract

A method and apparatus for tunable on-fiber Bragg gratings for DWDM and other applications on a small section of the core of single mode communication of an optical fiber. The method comprises etching most of the cladding on a small section of the fiber; coating the etched portion with a metallic electrode material and then with a layer of an electrooptic material; coating the electrooptic material with a photoresist; producing the Bragg grating pattern using a holographic process or on-axis interferometry; dissolving the non-exposed photoresist,; etching the grating pattern into the electrooptic material, and coating the Bragg gratings with a metallic material constructing the outer electrode. The presence of an electric signal on the electrodes will change the optical properties of the electrooptic material, as well as the diffraction/reflection properties of the Bragg gratings.

Claims

1. A method of producing a tunable Bragg grating pattern in an optical fiber having a cladding layer and a core layer, comprising the steps of:

etching a section of said cladding layer to produce modified section having a thin cladding layer;

coating said modified section with a metallic material to form an inner electrode;

coating said inner electrode with an electrooptic material;

coating said electrooptic material with a photoresist and forming a Bragg grating pattern within said photoresist by UV exposure and development;

copying said Bragg grating pattern onto the electrooptic material by etching said photoresist, and thereafter etching said Bragg grating pattern into said electrooptic material;

forming an outer electrode on said electroptic material; and

enclosing said section with outer packaging material.

2. The method of claim 1, wherein said photoresist is a liquid photoresist and said photoresist material is exposed to an interference pattern formed by reflecting a beam of a laser on a reflecting surface placed perpendicular to the direction of the optical fiber axis and the direction of the laser beam to thereby expose said photoresist to an on-axis interference pattern, said exposed photoresist thereafter being developed to reproduce said interference pattern on said modified section prior to said etching of said Bragg grating pattern.

3. The method of claim 2, wherein said photoresist is exposed and developed simultaneously to form said Bragg grating pattern, said exposure being done using holographic or interference techniques.

4. The method of claim 1, wherein said optical fiber is selected from single mode and multimode optical fibers.

5. The method of claim 1, wherein said modified section is from about 100-200 micrometers to about 2-3 millimeters.

6. The method of claim 1, wherein said photoresist is exposed to a Chrip interference pattern producing Chirp Bragg gratings in said photoresist layer.

7. The method of claim 1, which further includes means for applying an external electric signal to said inner and outer electrodes to permit tuning the wavelength of said Bragg grating in said modified section of said optical fiber.

8. The method of claim 1, which further includes the step of writing a polarization independent Bragg grating pattern into a different section of the fiber having a partially etched cladding, said Bragg grating being formed before the modified section is coated with said inner electrode, said electooptic material, said outer electrode, and said outer packaging material.

9. The method of claim 8, wherein cladding is reduced in said different section of said optical fiber to a thickness of about 2-3 microns.

10. Apparatus having a tunable Bragg grating pattern in an optical fiber having a cladding layer having a Bragg grating pattern therein and a core layer, in which the index of refraction of the cladding is changeable, said apparatus being formed by:

etching a section of said cladding layer to produce modified section having a thin cladding layer;

coating said modified section with a metallic material to form an inner electrode;

coating said inner electrode with an electrooptic material;

coating said electrooptic material with a photoresist and forming a Bragg grating pattern within said photoresist by UV exposure and development;

copying said Bragg grating pattern onto said electooptic material by etching said photoresist, and thereafter etching said Bragg grating pattern into said electrooptic material;

forming an outer electrode on said electrooptic material; and

enclosing said section with outer packaging material.

11. The apparatus of claim 10, wherein said photoresist is a liquid photoresist and said photoresist material is exposed to an interference pattern formed by reflecting a beam of a laser on a reflecting surface placed perpendicular to the direction of the optical fiber axis and the direction of the laser beam to thereby expose said photoresist to an on-axis interference pattern, said exposed photoresist thereafter being developed to reproduce said interference pattern on said modified section prior to said etching of said Bragg grating pattern.

12. The apparatus of claim 10, wherein said Bragg gratings are constructed to diffract the light propagating within said fiber core at the Bragg wavelength and not diffract all other wavelengths to function as a wavelength division de-multiplexer.

13. The apparatus of claim 12, wherein said Bragg gratings are constructed for coupling an incident light into said fiber core at the Bragg wavelength to function as a wavelength division multiplexer.

14. The apparatus of claim 13, wherein said modified section of said optical fiber is mounted on a photonics chip for said signal multiplexing or demultiplexing.

15. The apparatus of claim 10, wherein said Bragg gratings are constructed to reflect light in said fiber core at the Bragg wavelength to function as an optical filter.

16. The apparatus of claim 10, wherein said fiber is connected to a bi-directional coupler for said signals coupling and filters applications.

17. The apparatus of claim 10, wherein a photoresist is exposed to a Chrip interference pattern producing Chip Bragg gratings in said photoresist layer, wherein said Chip Bragg gratings function as a device selected from the group consisting of multiplexer, de-multiplexer, coupler and optical filter,

18. The apparatus of claim 10, which further includes means for applying an external electric signal to said inner and outer electrodes to permit tuning the wavelength of said Bragg grating in said modified section of said optical fiber.

19. The apparatus of claim 10, which further includes a polarization independent Bragg grating pattern written into a different section of the fiber having a partially etched cladding, said Bragg grating being formed before the modified section is coated with said inner electrode, said electrooptic material, said outer electrode, and said outer packaging material.

20. The apparatus of claim 19, wherein cladding is reduced in said different section of said optical fiber to a thickness of about 2-3 microns