On-chip gain elements for integrated photonics

The design of gain chips for hybrid integration with photonic integrated circuits (PICs) is studied and highlights the benefits of incorporating at least one reflector in the III-V gain material. Quantum dot (QD)-based gain chips with a multi-mode interference (MMI) reflector (MMIR) offer fabrication simplicity and good performance in the O-band. The inclusion of an MMIR in a ridge waveguide (RWG) laser reduces the threshold current by 87% (6 mA vs 46 mA for 1 mm length) and leads to higher slope efficiency, indicating over 90% mirror reflectivity, as compared to Fabry-Perot structures. Both 1- and 2-port designs will simplify alignment of active and passive waveguides for hybrid integration and are strong candidates for large-scale PIC applications.