CMOS compatible integration of Si/SiO2 multilayer GRIN lens optical mode size converter to Si wire waveguide.

We present a CMOS compatible mass manufacturable, compact Si/SiO(2) multilayer GRIN lens mode size converter from standard single mode fiber to 300 nm-thick Si waveguide. The fiber-to-GRIN lens coupling loss is 2.6 ± 0.3 dB (coupling efficiency: 51~60%) with optimized focal length of 11.6~11.8 µm and Si/SiO(2) multilayer thickness of 7.4 µm.

Ultra-compact multilayer Si/SiO(2) GRIN lens mode-size converter for coupling single-mode fiber to Si-wire waveguide.

We report on the fabrication and experimental demonstration of optical mode size transformation between standard single-mode fiber and 0.26 µm-thick Si-waveguide by 12 µm-thick Si/SiO(2) multilayer on-chip GRIN lens of lengths 16 µm or 24 µm butt-joint to 10 µm-wide terminated Si-waveguide. The overall coupling loss of the coupler was measured to be 3.45 dB in which the Fresnel reflection loss is estimated to be 2dB at the GRIN-lens/air interface. The on-chip integrated GRIN lens opens up the feasibility of a low cost passive aligned fiber-pigtailed electronic-photonics integrated circuits platform.