Fiber-to-Chip Spot-Size Converter for Coupling to Silicon Waveguides in the O-Band

A fiber-to-chip spot size converter (SSC), fully compatible with silicon-on-insulator technology and optimized for efficient coupling in the O-band, is proposed, designed, and experimentally demonstrated. The SSC is based on a parabolic inverted taper structure in between two lateral air trenches. The proposed air trenches only require one extra etch step after the silica cladding deposition and allow improving the optical confinement and therefore minimize the coupling losses. An optical bandwidth of 60 nm across the O-band and coupling losses as low as 2 dB at the wavelength of 1310 nm have been experimentally demonstrated.