Subwavelength Surface Gratings for Ultra-Efficient Fiber-to-Photonic-IC Coupling

There has been significant efforts to reduce the size, weight, and power (SWaP) of various quantum subsystems (700-900 nm) through the use of photonic ICs (PICs). A key challenge is efficient coupling of light between PICs and off-chip components. While coupling losses on the order of 1dB are achievable in telecom, losses at shorter wavelengths relevant for quantum sensing are much less efficient. It is desired to have robust PIC-to-fiber high-power connections that are labor and power efficient. Existing solutions are labor-intensive and involve inefficient coupling, especially at the shorter wavelengths where diameters of fiber cores are just a few microns. To address the above challenges, IFOS proposes an innovative solution based on judicious selection of refractive indices of PIC waveguide claddings to create an asymmetric PIC, together with metamaterial-basedÝsubwavelength gratings (SWG) to prevent downward diffraction of light that occurs in conventional surface-grating couplers, which limits coupling to <50%. The proposed innovation creates a highly directional coupling to off-chip components, enabling close to 100% coupling efficiency. The approach is scalable to multi-fiber-to-PIC coupling. It can be fully automated using established production techniques. Phase I will focus on modeling and simulation to prepare suitable designs for fabrication in Phase II.Ý