Effects of Two-photon Absorption and Non-linear Index in InP-based Passive Waveguides on Integrated Extended Cavity Semiconductor Lasers

Integrated indium phosphide (InP) based semiconductor laser systems with extended cavities can be realized using photonic integration technologies that combine optical amplifiers with devices based on passive ridge waveguides with a quaternary InGaAsP waveguide core [1] or pure InP nanophotonic waveguides (IMOS technology) [2]. Extended cavities can be utilized for lasers with tunable filters or mode locked lasers (MLL) with long cavities and fine-tuning elements [3]. In these passive waveguide sections two-photon absorption (TPA) can occur, which in turn gives rise to free carrier absorption (FCA) from high energy carriers and a change in refractive index. In addition to that the refractive index of the material is intensity dependent. Observations in MLLs with intra-cavity phase modulators [3] and of linewidths of the modes that are much wider than those reported for extended cavity MLLs using silicon waveguides [4], may be due to TPA generated carriers.