Abstract

Ultra-small waveguides like photonic crystal waveguides promise to offer a base for high-density
integration of optical functions on one chip by decreasing their footprints. As a consequence the
number of optical connections on a chip will increase and perhaps different functions will require
different types of waveguides, e.g. photonic crystal waveguides for certain non-linear functions and
photonic wires for other functions. Also the interface between ultra-small waveguides and an optical
fiber needs to be optimized. A vertical fiber coupler can already couple light from a fiber into a
broad planar waveguide [1] but the following coupling into ultra-small waveguides remains to be
solved. Nowadays, adiabatic tapers are used as spot-size converters but easily reach lengths of a few
hundred microns. It is believed that couplers could become drastically shorter by applying reflection,
interference and wavelength-scale structures in their designs. Different designs are investigated in a
two-dimensional way, using eigenmode expansion, namely the tool CAMFR[2]. A first, the in-plane
grating coupler, has a grating etched in the side-wall of a small waveguide and bends the light in an
orthogonal broad waveguide. In the second design, a cascade of resonators of decreasing size, passes
the light between ridge waveguides of different widths. The interference taper, a last design, is made
out of different waveguide sections, which vary in length and width, and successfully connects two
different waveguides[3]. The parameters of this design are determined using optimization routines
like simulated annealing or genetic algorithms. The different simulations will be discussed, the
validity of the 2-D approximation and the first steps towards realization of these components.

Related Research Topics

• Compact spot-size converters (2000-2005)

Related Projects

• IST: PICCO (Photonic Integrated Circuits using photonic Crystal Optics)