Advances in silicon nanophotonics

Silicon has long been established as an ideal material for passive integrated optical circuitry due to its high refractive index, with corresponding strong optical confinement ability, and its low-cost CMOS-compatible manufacturability. However, the inversion symmetry of the silicon crystal lattice has been an obstacle for a simple realization of electro-optic modulators, and its indirect band gap has prevented the realization of efficient silicon light emitting diodes and lasers.

Still, significant progress has been made in the past few years. Electro-optic modulators based on the free carrier plasma effect have been tested up to 40 Gbit/s, and hybrid evanescent silicon lasers have been realized both in the form of distributed feed-back lasers and micro-disk lasers. For enhancing the impact of silicon photonics in future ultrafast and energy-efficient all-optical signal processing, e.g. in high-bit-rate optical communication circuits and networks, it is vital that the nonlinear optical effects of silicon are being strongly enhanced.

This can among others be achieved in photonic-crystal slow-light waveguides and in nano-engineered photonic-wires (Fig. 1). In this talk I shall present some recent advances in this direction. The efficient coupling of light between optical fibers and the planar silicon devices and circuits is of crucial importance.

Both end-coupling (Fig. 1) and grating-coupling solutions will be discussed along with polarization issues. A new scheme for a hybrid III-V/silicon laser will also be discussed briefly.