Theory and observation on non-linear effects limiting the coherence properties of high-Q hybrid Si/III-V lasers

Hybrid Si/III-V is a promising platform for semiconductor narrow-linewidth lasers, since light can be e ciently stored in low loss silicon and ampli ed in III-V materials. The introduction of a high-Q cavity in silicon as an integral part of the laser's resonator leads to major reduction of the laser linewidth. However, the large intra-cavity eld intensity resulting from the high-Q operation gives rise to non-linear e ects. We present a theoretical model based on non-linear rate equations to study the e ect of two-photon absorption and induced free-carrier absorption in silicon on the laser's performance. The predictions from this model are compared to the experimental results obtained from narrow-linewidth lasers fabricated by us. It is shown to have an e ect on the linearity of the L-I curve, and to reduce the achievable Schawlow-Townes linewidth.