Temperature dependence of electroabsorption dynamics in an InAs quantum dot saturable absorber at 1.3μm

This paper investigated absorption recovery in a 5-layer, p-i-n InAs quantum dot modulator that was 1.1 mm long and having a 6 µm ridge waveguide. The change in transmission of a weak probe optical pulse, induced by an intense pump pulse, has been measured as a function of time delay. The 250 fs pump and probe pulses are degenerate in wavelength with the transition at 1.3 µm of the QD ground state and so the temporal absorption dynamics could be mapped out. This measurement was performed with an increasing device temperature in order to assist in the removal of photogenerated carriers. For a test two-section QD mode-locked laser having a pulse repetition rate of 21 GHz, we have also observed that the pulse durations decreased significantly as the temperature was increased up to 70°C. At constant current and reverse bias values, the pulse durations were obtained over the temperature range of the pump-probe measurements. These data support the view that a reduction of the absorber recovery time plays the most important role in the shortening mechanism for the mode-locked pulses produced by this laser. Furthermore, these results also demonstrate the potential for higher repetition rate mode-locked QD lasers that can be resilient to temperature effects.