Abstract

Integrated semiconductor ring lasers with an output waveguide have been produced.¹ They have attracted considerable attention because high-quality mirrors are not needed, the output termination has little influence on oscillation conditions, and the small dimensions make the longitudinal mode spacing increase so that single-mode operation is possible. A rib waveguide configuration was used to maximize light confinement and to minimize bending loss in the small cavity (Fig. 1). However, the temperature increases within the ring-laser structure are expected to be excessive as the heat source is more concentrated and the heat generated is difficult to dissipate because of the extremely small dimensions. A thermal model of the ring-laser device has been developed. Laser-device substrate and lasing rib were considered separately in this cylindrical symmetry model. For simplicity, no convection or radiation has been taken into account, and all the heat was assumed to transfer to the heat sink, which is forced down to an adjustable temperature, e.g., 20°C. The temperature distribution within the ring-laser structure has been calculated by using a finite-difference technique² and plotted by using a Ghost 80 computer plot package (Fig. 2). The thermal resistance for the whole laser device has also been calculated (Fig. 3). All modeling was done on an IBM 3090 computer with a vector facility. The resulting temperature profiles agree with IR imaging thermal measurement results fairly well.³ The temperature gradient is strongest just beneath the rib, and the distribution is the same for an increase in input power or in heat-sink temperature. Only the temperature corresponding to each isotherm increases.

© 1990 Optical Society of America