Lasing Mode Hysteresis Characteristics in Semiconductor Ring Lasers

Wavelength and directional hysteresis due to increasing and decreasing current and temperature have been investigated. Measurements indicate that lasing direction hysteresis associated with changes in injection current can be attributed to the resulting shift in the linear gain peak which is due to the change in device temperature. Interaction between the linear gain spectrum and the asymmetric nonlinear gain spectrum results in contrasting behavior for increasing and decreasing temperature and current. The phenomena are modeled using a nonlinear time domain model including the carrier density pulsation (CDP), carrier heating (CH) and spectral hole burning (SHB) effects. The numerically reproduced hysteresis loop is in close agreement to the experimental observation. Our work further shows that mode hops to longer wavelength non lasing modes are quicker than those to shorter wavelength lasing modes due to the lack of four wave mixing (FWM) mode coupling in the non-lasing mode. The same model can be used to study the dynamics during switching of lasing directions triggered by other means, such as optical injection.