External cavity lasing and on-chip self-injection locking based on cascaded grating structures

A laser device comprising:

• a gain chip configured to emit a beam of light;
• and
• a photonics chip optically coupled to the gain chip, the photonics chip comprising:
• a waveguide platform including an input waveguide, which is optically coupled to the gain chip, the input waveguide in optical communication with a cascaded arrangement of waveguide grating structures on the waveguide platform, the waveguide grating structures comprising:
• a first waveguide grating structure configured to produce a single resonance frequency within a stopband;
• and
• a second waveguide grating structure in optical communication with the first waveguide grating structure, the second waveguide grating structure configured to diffract a narrowband resonance, overlapping with the stopband of the first waveguide grating structure, back toward the gain chip, while passing any light outside of the stopband of the first waveguide grating structure out of the waveguide platform;
• wherein the first and second waveguide grating structures cooperate to yield a single resonance frequency of the light that feeds back into the gain chip to produce a self-injection lock for the laser device.