D. Dimitropoulos

Influence of nonlinear absorption on Raman amplification in Silicon waveguides

We model the TPA-induced free carrier absorption effect in silicon Raman amplifiers and quantify the conditions under which net gain may be obtained. The achievable Raman gain strongly depends on the free carrier lifetime, propagation loss, and on the effective Raman gain coefficient, through pump-induced broadening.

Anti-Stokes Raman conversion in silicon waveguides

The first observation of parametric down-conversion in silicon is reported. Conversion from 1542.3nm to 1328.8nm is achieved using a CW pump laser at 1427 nm. The conversion occurs via Coherent Anti-Stokes Raman Scattering (CARS) in which two pump photons and one Stokes photon couple through a zone-center optical phonon to an anti-Stokes photon. The maximum measured Stokes/anti-Stokes power conversion efficiency is 1x10-5. The value depends on the effective pump power, the Stimulated Raman Scattering (SRS) coefficient of bulk silicon, and waveguide dispersion. It is shown that the power conversion efficiency is a strong function of phase mismatch inside the waveguide.

Lifetime of photogenerated carriers in silicon-on-insulator rib waveguides

The lifetime of photogenerated carriers in silicon-on-insulator rib waveguides is studied in connection with the optical loss they produce via nonlinear absorption. We present an analytical model as well as two-dimensional numerical simulation of carrier transport to elucidate the dependence of the carrier density on the geometrical features of the waveguide. The results suggest that effective carrier lifetimes of ⩽1ns can be obtained in submicron waveguides resulting in negligible nonlinear absorption. It is also shown that the lifetime and, hence, carrier density can be further reduced by application of a reverse bias pn junction.

Wavelength conversion in silicon using Raman induced four-wave mixing

Conversion of digital- and analog-modulated optical signals from the 1550nm band to the 1300nm band is demonstrated in silicon waveguides. The conversion is based on parametric Stokes to anti-Stokes coupling using the Raman susceptibility of silicon.

Limitations of active carrier removal in silicon Raman amplifiers and lasers

The lifetime of two-photon generated carriers has been established as the critical parameter that determines the performance of silicon Raman lasers and amplifiers since it determines the optical loss. Here, we investigate the intensity dependence of the carrier lifetime in the case where the carriers are swept out by means of a p‐n junction. Numerical simulations show that at sufficiently high pump intensities, the generated carriers screen the applied electric field and therefore result in a higher lifetime and hence a lower net Raman gain. We also quantify the electrical power dissipation necessary to maintain low optical losses.

Coupled-mode theory of the Raman effect in silicon-on-insulator waveguides

Coupled-mode theory is used to calculate Raman gain and spontaneous efficiency in silicon waveguides with cross-sectional areas ranging from 0.16 to 16 microm2. We find a monotonic increase in the Raman gain as the waveguide cross section decreases for the range of dimensions considered. It is also found that mode coupling between the Stokes modes is insignificant, and thus polarization multiplexing is possible. The results also demonstrate that for submicrometer waveguide dimensions the Einstein relation between spontaneous efficiency and stimulated gain no longer holds.

Silicon Raman amplifiers, lasers, and their applications

This paper presents recent breakthroughs and applications of Raman based silicon photonics such as silicon Raman amplifiers and lasers. These lasers would extend the wavelength range of III-V laser to mid-IR where important applications such as laser medicine, biochemical sensing, and free space optical communication await the emergence of a practical and low cost laser.

Wavelength conversion and light amplification in silicon waveguides

This study demonstrates wavelength conversion and intrinsic Raman amplification. This work shows that phase matching is required to achieve high conversion efficiencies. In addition, reduction of waveguide cross section, while maintaining low propagation loss, is highly desirable for both wavelength conversion and optical amplification. The resulting increase in light intensity enhances the Raman interaction and the reduction in free carrier lifetime diminishes the two-photon absorption-induced free carrier losses.

Observation of stimulated Raman amplification in silicon waveguides

This paper demonstrates the use of stimulated Raman scattering (SRS) in silicon to create optical amplification in SOI waveguides. Advantages of this approach include its tunability and the fact that it does not necessitate special impurities or nanostructures. Moreover, SRS is also a candidate for realization of lasers on silicon.

Noise and Information Capacity in Silicon Nanophotonics

Modern computing and data storage systems increasingly rely on parallel architectures. The necessity for high-bandwidth data links has made optical communication a critical constituent of modern information systems and silicon the leading platform for creating the necessary optical components. While silicon is arguably the most extensively studied material in history, one of its most important attributes, i.e., an analysis of its capacity to carry optical information, has not been reported. The calculation of the information capacity of silicon is complicated by nonlinear losses, which are phenomena that emerge in optical nanowires as a result of the concentration of optical power in a small geometry. While nonlinear loss in silicon is well known, noise and fluctuations that arise from it have never been considered. Here, we report fluctuations that arise from two-photon absorption, plasma effect, cross-phase modulation, and four-wave mixing and investigate their role in limiting the information capacity of silicon. We show that these fluctuations become significant and limit the capacity well before nonlinear processes affect optical transmission. We present closed-form analytical expressions that quantify the capacity and provide an intuitive understanding of the underlying physics.