Planar-waveguide Bragg gratings in curved waveguides

• US 8,731,350 B1
• Filed: 09/11/2012
• Issued: 05/20/2014
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Jacobs, Everett W., Adleman, James R., Lin, Chunyan, Rodgers, John Scott
• Primary Examiner(s): Ullah, Akm Enayet
• Application Number:
  US13/609,294
• Time in Patent Office: 616 Days
• Field of Search: 385 34- 39147, 385/10, 385/129, 359/341.1, 359/346, 359/337, 359/885, 359/337.21
• US Class Current: 385/37
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/136 by etching

Abstract

A method for forming planar-waveguide Bragg grating in a curved waveguide comprises: forming a long chirped planar-waveguide Bragg grating in an Archimedes'"'"' spiral such that a long length of the waveguide can fit in a small chip area where the grating is formed in the curved waveguide; using periodic width modulation to form the planar-waveguide Bragg grating on the curved waveguide, and where the formation of the periodic width modulation occurs during the etching of the waveguide core; using rectangular width modulation to create Bragg gratings with a higher order than 1^st order to allow a larger grating period and larger modulation depth, using waveguide width tapering while keeping the width modulation period constant to introduce chirp to the planar-waveguide Bragg grating where the index of refraction is a function of waveguide width, by applying a specific width tapering to create a desired arbitrary chirp profile.

Claims

1. A method for forming planar-waveguide Bragg grating in a curved waveguide comprising:

forming a long chirped planar-waveguide Bragg grating in an Archimedes'"'"' spiral such that a long length of the waveguide can fit in a small chip area for single mask photolithography fabrication where the grating is formed in the curved waveguide;

using periodic width modulation to form the planar-waveguide Bragg grating on the curved with modulation periods equal to R_inΛ

/(R_in+W/2) and R_outΛ

/(R_out−

W/2) for the inner and outer edge of the curve waveguide, where R_in and R_out are the inner and outer radius, Λ

is modulation period for Bragg condition, and W is the width of the waveguide and where the formation of the periodic width modulation occurs during the etching of the waveguide core;

using rectangular width modulation to create Bragg gratings with a higher order than 1^st order to allow a larger grating period and larger modulation depth, and therefore relax fabrication requirements;

using waveguide width tapering while keeping the width modulation period constant to introduce chirp to the planar-waveguide Bragg grating where the index of refraction is a function of waveguide width, by applying a specific width tapering such that desired arbitrary chirp profile can be created for the planar-waveguide Bragg grating.

2. The method of claim 1 wherein the higher order is 3^rd order.

3. The method of claim 1 wherein the higher order is 5^th order.

4. The method of claim 1 wherein the grating is fabricated in low loss silica waveguide platform.

5. A method for forming planar-waveguide Bragg grating in a curved waveguide comprising:

forming a long chirped planar-waveguide Bragg grating in an Archimedes'"'"' spiral such that a long length of the waveguide can fit in a small chip area for single mask photolithography fabrication where the grating is formed in the curved waveguide and fabricated in low loss waveguide platform;

using periodic width modulation or periodic cladding modulation to form the planar-waveguide Bragg grating on the curved waveguide where the formation of the periodic width modulation or periodic cladding modulation occurs during the same fabrication step as the etching of the waveguide core and where the modulation period is R_inΛ

/(R_in+W/2) and R_outΛ

/(R_out−

W/2) for the inner and outer edge of the curve waveguide, where R_in and R_out are the inner and outer radius, Λ

is modulation period for Bragg condition, and W is the width of the waveguide;

using rectangular width modulation to create higher order Bragg gratings instead of 1^st order sinusoidal width modulation where higher order (such as 3rd &

5^th) gratings allows larger grating period and larger modulation depth, and therefore relaxed fabrication requirements;

using rectangular width modulation with duty cycle not equal to 50% to optimize the grating reflectivity;

using waveguide width tapering while keeping the width modulation period constant to introduce chirp to the planar-waveguide Bragg grating where the index of refraction is a function of waveguide width;

using a specific width tapering such that a desired arbitrary chirp profile is realized for the planar-waveguide Bragg grating; and

using a specific width tapering such that a linear chirp is realized for the planar-waveguide Bragg grating.

6. A planar-waveguide Bragg grating in a curved waveguide comprising:

a long chirp planar-waveguide Bragg grating formed in an Archimedes'"'"' spiral such that a long length of the waveguide can fit in a small chip area for single mask photolithography fabrication where the grating is formed in the curved waveguide and fabricated in low loss silica waveguide platform;

the planar-waveguide Bragg gratings formed using periodic width modulation with modulation periods equal to R_inΛ

/(R_in+W/2) and R_outΛ

/(R_out−

W/2) for the inner and outer edge of the curve waveguide, where R_in and R_out are the inner and outer radius, Λ

is modulation period for Bragg condition, and W is the width of the waveguide and where the formation of the periodic width modulation occurs during the etching of the waveguide core;

the Bragg grating having higher order Bragg gratings created using rectangular width modulation where the higher order gratings allows larger grating period and larger modulation depth, and therefore relax fabrication requirements;

the Bragg grating formed using width tapering while keeping the width modulation period constant to introduce chirp to the planar-waveguide Bragg grating where the index of refraction is a function of waveguide width, by applying a specific width tapering such that desired arbitrary chirp profile can be created for the planar-waveguide Bragg grating.