Hertz-level-linewidth semiconductor laser via injection locking to an ultra-high Q silicon nitride microresonator

A conventional semiconductor DFB laser is self-injection-locked to a CMOS-foundry- fabricated ultra-high Q silicon nitride microresonator, suppressing high-offset frequency noise to 0.2 Hz2 Hz-1 and yielding instantaneous linewidth of 1.2 Hz.