A new concept of an ultra fast pulse picker for fs- and ps-pulses from GHz pulse-trains with semiconductor tapered elements

In this paper, we present a new concept for an ultra fast pulse picker, consisting of a tapered diode amplifier and a high-speed high-current transistor switch. The transistor switch is realized using a GaN high-electron mobility transistor (HEMT), which offers low parasitic capacitances und high current capabilities together with high switching speed. Moreover, the SiC transistor substrate gives rise to an excellent thermal conductivity thus allowing for high duty cycles. The tapered diode amplifier (TDA), on the other hand, consists of a 2000mum long ridge waveguide section (RW) and a 2000mum long tapered section (TP) with a tapered angle of 4deg for the wavelength range 900-950nm. The RW section is driven by the transistor switch with short current pulses, which modulate the transparency properties. Thus, if the RW section is transparent, an injected optical pulse can pass and is amplified in the tapered section, otherwise all optical pulses will be absorbed.