The project is a consortium based activity involving researchers from the UK institutions of the
Universities of Surrey, St. Andrews, Leeds, Warwick, and Southampton, as well as the commercial
research institution QinetiQ. The aims of the project are to progress the state of the art in Silicon
Photonics, in the areas of waveguides, modulators, couplers, detectors, Raman processes, and integration
with electronics. Thus the field is vast, and impossible to cover comprehensively in one project, nor
indeed in one paper. The programme is run on a truly collaborative basis, with members from each
institution running one or more work packages within the project, each co-ordinating work from their
own plus other institutions. To date, the most well developed work has emerged from the activity on basic
waveguides and their characteristics, the modulator activity, optical filters, and work on Raman
Amplifiers. This work will be the main focus of this paper, but an attempt will be made to update the
audience on the remaining activities within the project. By the nature of the project, much of the work is
medium term, and hence some activities are not expected to yield viable results until at least next year,
hence the concentration on some activities rather than all activities at this stage.
Previously we have reported the effects of silicon ion irradiation on free carrier lifetime and propagation loss in silicon
rib waveguides, and simulated net Raman gain based on experimental results. We further extend this work by reporting
the effects of thermally treating a silicon irradiated sample with a higher dose and energy than previously reported,
which produced a poor trade-off between free carrier lifetime and excess optical absorption prior to thermal treatment.
Excess losses greater than 80dB/cm were recorded prior to annealing. After thermal treatment, the sample demonstrated
characteristics of excess loss and free carrier lifetime recorded previously in much lower energy and dose silicon ion
irradiated samples, suggesting that thermally treating samples could enhance the trade-off between free carrier lifetime
and excess loss introduced to the rib waveguides. Raman gain simulations based on the new experimental data are
reported and show an increase in net gain over previously reported data, suggesting that higher dose, shallow silicon ion
implantation is the most efficient way of optimising the trade-off between lifetime reduction and excess optical
absorption in silicon rib waveguides, a proposal in our earlier work. The effects of thermally treating low temperature
oxide clad waveguides with respect to free carrier lifetime are also reported. Results show that thermally treating a low
temperature oxide clad waveguide can vary the intrinsic lifetime. The results of this investigation as well as a discussion
into the possible origin of the lifetime change are given.
Silicon Photonics is a field that has seen rapid growth and dramatic changes in the past 5 years. According to the MIT
Communications Technology Roadmap , which aims to establish a common architecture platform across market
sectors with a potential $20B in annual revenue, silicon photonics is among the top ten emerging technologies. This has
in part been a consequence of the recent involvement of large semiconductor companies around the world, particularly in
the USA. Significant investment in the technology has also followed in Japan, Korea, and in the European Union. Low
cost is a key driver, so it is imperative to pursue technologies that are mass-producible.
Therefore, Silicon Photonics continues to progress at a rapid rate. This paper will describe some of the work of the
Silicon Photonics Group at the University of Surrey in the UK. The work is concerned with the sequential development
of a series of components for silicon photonic optical circuits, and some of the components are discussed here. In
particular the paper will present work on optical waveguides, optical filters, modulators, and lifetime modification of
carriers generated by two photon absorption, to improve the performance of Raman amplifiers in silicon.
We investigate the effects of silicon ion irradiation on free carrier lifetime and propagation loss in silicon rib
waveguides, and thus its ability to reduce the density of two-photon-absorption (TPA) generated free carriers, an
undesired effect of the Raman process in crystalline silicon. Our experimental results show that free carrier lifetime can
be reduced significantly by silicon ion implantation. Associated excess optical absorption from the implanted silicon ions
can be kept low if irradiation energy and dose are correctly chosen. Simulations of Raman amplification in silicon rib
waveguides suggest that net gain can be achieved in certain cases without the need for an integrated diode in reverse bias
to sweep out the photo-generated free carriers.