Research on transient thermal behavior of semiconductor lasers under pulse current excitation by thermoreflection technique

Abstract

We measured the response of the facet temperature of the semiconductor laser to a single pulse current with a magnitude of microseconds by using transient thermoreflection method, and then calculated the thermal time constants of the laser. The thermoreflection technique measures the reflectivity of facet which is affected by temperature in real time and thus only measures the thermal parameter. In addition, we select the falling edge of the pulse current where current and light dissipate immediately during the heat decline as the starting point for the study of the thermal response. Therefore, the electro-optical-thermal characteristics of the laser are decoupled in the measurement process. The transient thermal response is formulated as a second-order exponential function of time. The two time constants, i.e τ1 and τ2, represent thermal conductivity performance of laser chip and device package, respectively. We studied the transient thermal behavior of the laser under unsteady state based on the evolution trends of the thermal time constants with amplitude and width of the pulse current. When the pulse is narrow, the heat of the device is concentrated in the active region, even if the current amplitude is relatively large; With the increase of pulse width, the heat generated in the active region diffuses outward to other layers of the chip and heat sink. We also observed the mechanical deformation of the facet in the active region which results from heat accumulation, and the heat generation is related to light intensity.