Narrow-linewidth diode laser using a fiber-optic ring resonator.

Experimental results of linewidth reduction in AlGaAs diode lasers with frequency-selective Rayleigh scattering from a fiber-optic ring resonator are presented. The intermediate-frequency signal produced by two such lasers is shown to have less than a 100-Hz intermediate-frequency linewidth. Self-homodyning measurements indicate an estimated laser linewidth of 0.6 Hz. Observing the intermediate-frequency beat signal and a Fabry-Perot interferometer, we demonstrate frequency mode stability and tuning. This tuning allowed us to lock a heterodyne optical phase-locked loop successfully. The narrow-linewidth ring laser also produced a stimulated Brillouin scattering wave.