Compact grating couplers between optical fibers and Silicon-on-Insulator photonic wire waveguides with 69% coupling efficiency

We present efficient, compact and broadband grating couplers in Silicon-on-Insulator, for coupling between single mode fiber and nanophotonic waveguides. By adding a gold bottom mirror, the coupling efficiency is increased to 69%.

1. Introduction

High refractive index contrast materials are very well suited for ultra-dense photonic integrated circuits. An example of such a material is Silicon-on-Insulator (SOI), for which a lot of photonic-wire based components have been demonstrated [1]. Because of the large confinement, components can be very compact. However, the coupling with the outside world (optical fiber) remains an important problem, and shrinking the size of components makes the situation even worse. The reason is the huge mismatch between the fiber mode and the nanophotonic waveguide mode.