Generation of high power gain-switched pulses from a two-section ridge-waveguide laser diode with a laterally tapered energy-storage section

The achievable pulse energy of a gain-switched single-section laser is mainly limited by the amplitude and abruptness of the initial carrier overshoot and by the nonlinear gain compression factor /spl epsiv/. To obtained the shortest pulsewidth and the highest peak power, a gain-switched laser diode is usually biased below threshold. One possible way to increase the pulse energy is to add an energy storage element to a gain-switched device. This can be implemented by using a multi-section structure. In this paper, we report generation of gain-switched picosecond laser pulses with energies above 20 pJ and peak powers around 1 W from a simple two-section ridge-waveguide laser. The proposed device consists of a straight modulator section, an etched gap for electrical isolation, and a tapered gain section as the energy storage element. The modulator section maintains a relatively small area which allows a large and fast carrier overshoot to be excited by high-speed electrical pulse modulation. It also acts as a spatial filter for lateral mode selection. In the tapered gain section, the lateral mode is allowed to expand along the tapered structure, which increases the energy storage capacity and improves the energy extraction efficiency. We fabricated the proposed two-section ridge-waveguide lasers from a GaAs/AlGaAs GRINSCH double quantum well wafer grown by MBE.