Patent ID: 8731350

Claim:
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 in Λ/(R in +W/2) and R out Λ/(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.