Spot-size conversion and near-circular far-field profile for efficient laser-fiber coupling

When a photonic integrated circuit (PIC), incorporating active devices, producing a small and noncircular spot-size is directly butt-coupled to single mode fiber (SMF) with a larger and circular spot-size, use of this arrangement can cause typically a 10 dB (or 90% power) loss. In this presentation, an approach of using two non-identical but phased matched uniform coupled waveguides is considered, to achieve the necessary spot-size conversion where such a system can be easily fabricated by using standard techniques