Diffractive and Subwavelength Grating Couplers for Microphotonic Waveguides

We review our advances in diffractive and subwavelength grating coupler structures for microphotonic waveguides. We present a subwavelength grating fiber-chip edge coupler with a loss as low as 0.9 dB and with minimal wavelength dependence over a broad wavelength range exceeding 200 nm. We also present fiber-to-chip surface grating couplers based on subwavelength effective medium. The effective medium refractive index is engineered to control …