Phase noise study of laser diodes with external optical feedback for digital coherent communications

We evaluated external optical feedback effect for TDA-CSG-DR tunable laser by real-time phase variation measurements. The phase variation slower than feedback delay was significantly reduced without imperiling laser stability, and the noise level obtained for 50-100 MHz was ~17 kHz
²
/kHz as calculated results for an equivalent Fabry-Perot laser well explaining.