Optimized InAs/AlGaAs Quantum Dot semiconductor optical amplifier tapered geometry for enhanced beam quality and optical gain

Quantum Dot (QD) based semiconductor optical amplifiers (SOA) have attracted the spotlight of attention due to the ability to operate efficiently in multi-GHz rates [1]. Furthermore, flared geometry was proposed as an elegant design solution to overcome gain saturation, unfortunately at the expense of low beam quality. In this paper a novel tapered SOA design (G-structure) is proposed and it is experimentally compared in terms of gain and single mode fiber coupling, to an optimized conventional tapered SOA (A-structure). The novel design exhibits increased fiber coupling efficiency by a factor of 5, whereas it also exhibits increased gain for all tested currents (1982mA/mm² to 4850mA/mm²). Although, our design was utilized recently to elevate the peak power of a QD mode-locked laser to the record level of 30W [2], the details of the SOA have not yet been presented.