Flip-chip-integrated silicon nitride ECL at 640nm with relaxed alignment tolerances

We present work towards a visible wavelength tuneable external cavity laser (ECL) on a silicon nitride platform working around 640 nm. A ring resonator Vernier structure on the photonic integrated circuit (PIC) provides delayed feedback with spectral filtering and tuning. Gain is provided by a reflective semiconductor optical amplifier (SOA) grown on a GaAs substrate and integrated by pick-and-place flip-chip assembly. In a novel coupling scheme, the 1-dB in-plane placement tolerance is relaxed by a multi-mode edge-coupler to +/- 2.6 mu m in the direction parallel to the SOA edge and to displacements up to 3.5 mu m from the PIC interface along the SOA's optical axis. Pedestals defined in the PIC guarantee vertical alignment.