Investigation on high speed directly modulated microcircular lasers

High speed modulation characteristics are investigated for microcircular lasers connected with an output waveguide theoretically and experimentally. The injection current profile and carrier spatial hole-burning and diffusion are accounted in the rate equation model by radially dividing the microcircular resonator into two regions under the approximation of uniform carrier densities. The numerical results indicate that wide mode field pattern in radial direction has merit for high speed modulation, which is expected for coupled modes in circular microlasers connected with an output waveguide. Small signal response curves and large signal modulation responses are investigated for a 15-μmradius microlaser connected with a 2 μm wide output waveguide. The highest resonance frequencies of 7.2, 5.9 and 3.9 GHz are obtained at the temperatures of 287, 298 and 312 K from the small signal response curves, and clear eye diagrams at 12.5Gbit/s with an extinction ratio of 6.1 dB are observed for the microlaser at biasing current of 38 mA and the temperature of 287 K.