Heterodyne optical phase-locked loop by confocal Fabry-Periot cavity coupled AlGaAs lasers

Two external confocal Fabry-Perot cavity-coupled 0.83- mu m AlGaAs lasers phase-locked to one another by a heterodyne optical phase-locked loop are discussed. The phase error under phase-locking conditions was measured using the square root of the Allan variance. The result confirmed that the heterodyne signal was a full replica of the spectrum of the reference RF signal within the loop bandwidth. The estimated phase-error variance was 0.02 rad/sup 2/, i.e. approximately=8.1 degrees .>