Coupling strategies for integrated photonics: advances and opportunities

Integrated photonics is envisioned as a key enabler for numerous emerging applications, including high-speed communications, ultra-fast optical computing, and quantum information processing. These applications call upon efficient connection between the sub-micrometric planar photonic waveguides and standard optical fibers (SMF-28). Fiber-to-chip optical interfacing has always been recognized as an issue of fundamental importance in the field of integrated photonics, particularly by imposing a critical constraint on the power budget for the chip-scale photonic systems. Hence the direct fiber-chip connection is vastly inefficient with position-restricted accessibility, the key challenge for light coupling involves several factors. This includes geometrical and material discrepancies, different mode field diameters of SMF-28 fibers and photonic waveguides, on-chip design flexibility, and fast optical testing, preferably utilizing available die-level or wafer-scale accessories. In this work, we report on our recent progress in the development of efficient fiber-to-chip optical interfaces based on compact surface grating couplers. We present and discuss prospective design approaches and experimental results for grating-coupled devices implemented on surging silicon (Si) and silicon nitride (SiN) waveguide platforms, supporting advanced photonic integration with coupling efficiencies approaching -1 dB level.