Vernier-tuned distributed bragg reflector laser

An optical device, comprising:

• a first distributed Bragg reflector (DBR) grating comprising a first plurality of repeat units, wherein the first plurality of repeat units each comprise a plurality of phase grating elements and a plurality of pi phase shifts, wherein:
• a number of phase grating elements is substantially the same in each of the plurality of repeat units of the first DBR grating, and
• a number or a location of the plurality of pi phase shifts is substantially the same in each of the plurality of repeat units of the first DBR grating;
• and
• a second DBR grating comprising a second plurality of repeat units, wherein the second plurality of repeat units each comprise a plurality of phase grating elements and a plurality of pi phase shifts, wherein:
• a number of phase grating elements is substantially the same in each of the plurality of repeat units of the second DBR grating,
• a number or a location of the plurality of pi phase shifts is substantially the same in each of the plurality of repeat units of the second DBR grating, and
• the number of the plurality of pi phase shifts in each of the first plurality of repeat units of the first DBR grating is different from the number of the plurality of pi phase shifts in each of the second plurality of repeat units of the second DBR grating.

A method, comprising:

• generating light by a gain section of a wavelength tunable semiconductor laser;
• reflecting the light by a first mirror comprising a first integer number of repeat units, wherein each of the first integer number of repeat units comprises a plurality of phase grating elements with a first plurality of pi phase shifts distributed among the plurality of phase grating elements;
• and
• outputting a first portion of the light and reflecting a second portion of the light by a second mirror comprising a second integer number of repeat units, wherein each of the second integer number of repeat units comprises a plurality of phase grating elements with a second plurality of pi phase shifts distributed among the plurality of phase grating elements,
• wherein the first plurality of pi phase shifts and the second plurality of pi phase shifts differ by one phase shift per repeat unit.