Compact silicon diffractive components for integrated optics

The area of integrated optical circuits has been undergoing rapid development and gaining a great deal of applications in fiber communications and optical interconnections. These applications bring a significant challenge to optical circuits such as increased circuit density and further miniaturized devices. Compact and high performance optical components are in great demand. This paper present our proposal to use Si based compact diffractive components for coupling, splitting, and reflection in integrated optical circuits. First, a novel subwavelength grating, binary blazed grating (BBG), is used as a high efficient vertical coupler from single mode fiber to Si waveguide. By using the strong polarization dependence of the BBG coupler, a polarization beam splitter (PBS) is proposed to split the polarizations of input light from fiber into two waveguides separately, during the coupling process. The coupling length is merely 14 μm. The extinction ratio is better than 20 dB for both polarizations over a 40 nm wavelength range and the coupling efficiencies for two polarizations are 58% and 50%, respectively. Second, a broadband and high efficient mirror based on the BBG is designed and fabricated. Up to 96% reflectivity over a wavelength rang of 1.2~1.7um was achieved both theoretically and experimentally. Finally, a nanoscale pillar waveguide is proposed as an ultra small nanotaper for mode conversion between fiber and submicron waveguide. It has been demonstrated that a 13 μm long taper is able to convert a mode size of 4 μm into 1 μm with an efficiency of 85%.