Narrow Linewidth Semiconductor Lasers from Visible to Infrared Wavelengths

We review recent breakthroughs of narrow-linewidth semiconductor lasers over broad wavelength range, including record-low fundamental linewidth below 40 mHz by self-injection-locking at infrared, the first fully integrated narrow-linewidth laser below silicon's bandgap wavelength, and an ultra-low loss platform for narrow-linewidth lasers at blue and violet.