3D and 2D Silicon Photonic Crystals for Microphotonic Integrated Circuits

Silicon microphotonics might offer high density integration of individual optical components on a single chip. Possible utilization of current CMOS fab lines for their fabrication might also result in further chip-scale integration of optical and electrical circuitry, thus opening a way for mass production of dense optoelectronic integrated circuits. Silicon photonic crystals can provide the extreme confinement of light at diffraction limit and are viewed as a possible way to manipulate light signals in a minituarized optical circuits.

In the first part of my talk I will review efforts on fabrication of a 3D photonic crystals by self-assembly approach employing colloidal microspheres. The existence of the omnidirectional photonic band gap (PBG) at telecom wavelength is explored in silicon inverted opals, which are obtained by combining planar self-assembly of colloidal spheres with silicon deposition techniques. Using optical spectroscopy with high spatial resolution we show that defect densities in our silicon photonic crystals are sufficiently low that the PBG survives. In addition, we demonstrate that the structure can be subsequently patterned for a desired device application with straightforward post-growth processing. Thus, while retaining the simplicity of natural-assembly, this approach provides PBG crystals that reclaim the advantages of more conventional nanofabrication.

In the second part of my talk I will cover recent results obtained within a microphotonic project at IBM. The appoach we adopted is based on leveraging the CMOS microfab line and is based on two-dimensional slab-type SOI photonic crystals. In this system the light is confined in the silicon slab by total internal reflection (TIR), while waveguiding within a slab plane is dictated by photonic crystal made of periodic array of holes etched through the slab. This particular system has attracted much attention recently due to relative simplicity of fabrication steps and anticipated small penalty in radiation losses. We first address the problem of radiation losses in 2D SOI photonic crystals by quantitative measurements of transmission spectra for various designs of photonic crystal waveguides. We compare then these resutls with losses obtained on a usual TIR ridge waveguides of different width. Next we show the way to effectively couple the light from the fiber to high index microphotonic circuits and photonic crystals by proper design of mode converter and butt-coupler.