Semiconductor Diode Laser Mode-Locking by a Waveguide Array

We demonstrate theoretically that robust mode-locking can be achieved in an edge-emitting semiconductor diode laser with a waveguide array architecture. The waveguide array provides an ideal saturable absorption mechanism for initial start-up from noise, as well as pulse shaping and stabilization. One element in the waveguide array is forward-biased to generate gain, while nonlinear coupling to the other elements results in an effective saturable absorber. This new approach can be integrated directly with standard edge-emitting designs.

I. Introduction

Mode-locked lasers are the primary source of ultrashort optical pulses, with durations ranging from picoseconds down to a few femtoseconds. These ultrashort pulses find a wide range of uses, including time resolved spectroscopy [1], multiphoton imaging [2], high-field physics [3] and laser machining [4]. In addition, mode-locked lasers do not produce isolated pulses, but phase coherent trains of them, enabling the field of femtosecond frequency combs [5]. The most successful mode-locked laser technologies are based on solid-state gain media, such as Ti:sapphire, or fiber lasers using rare-earth dopants such as erbium or ytterbium. In both cases, the gain medium is pumped by a diode laser, either directly in the case of a fiber laser or indirectly for Ti:sapphire.