InP-Based Passive Ring-Resonator-Coupled Lasers

Design of passive ring-coupled lasers based on InGaAsP waveguides is investigated using beam propagation method. Mode coupling, propagation loss due to bending, and scattering loss from waveguide sidewall roughness are taken into account. By compromising threshold gain, linewidth and side-mode suppression ratio (SMSR), suitable waveguide width and coupling strength are determined for different ring sizes. Using a ring with radius ranging from 20 to 200 (mu)m, it is possible to design passive ring-coupled lasers with threshold gain less than 60/cm and 80/cm for waveguide sidewall roughness 5 and 10 nm, respectively, SMSR larger than 50 dB, and linewidth in the range of ~3-500 kHz.