Enabling light coupling between nanowires and low refractive index contrast optical waveguides towards scalable quantum circuits

A primary constraint in the major photonic integration platform of Silica-on-Silicon, especially when combined with fabrication approaches like Direct Laser Writing is the optical waveguides' low refractive index contrast, leading thus to limitations for efficient coupling with currently available state-of-the-art single photon emitters such as semiconductor nanowires with quantum dots (NWQD). We propose and demonstrate a novel approach to drastically enhance the light coupling between silica based Laser-written channel waveguides and NWQDs, by incorporating an optical microsphere in their intermediate space. It is demonstrated that the induced photonic nanojet action of a suitably designed microsphere illuminated by the NWQD, excites efficiently the channel waveguide's modes and can enable light coupling to a degree even above 50%. The proposed method is reasonably robust to imperfections and misalignments and could be implemented by current state-of-the-art micro/nano patterning techniques. It is anticipated that the practical implementation of the method will allow the integration of multiple quantum emitters in silica based hybrid integrated circuits thus enabling their scalability towards for quantum computing and sensing applications.
QC 20240530