Inverse Raman Scattering in Silicon

TL;DR

This paper demonstrates inverse Raman scattering in silicon, showing how free carriers enable significant optical attenuation, which can be used for chip-scale optical devices like multiplexers and switches.

Contribution

It is the first demonstration of inverse Raman scattering in silicon, highlighting the role of free carriers in facilitating this nonlinear process.

Findings

Achieved >15 dB attenuation with 4 GW/cm^2 pump intensity

Free carriers delay coherent anti-Stokes Raman scattering

Silicon-based IRS enables potential optical switching applications

Abstract

Stimulated Raman scattering is a well-known nonlinear process that can be harnessed to produce optical gain in a wide variety of media. This effect has been used to produce the first silicon-based lasers and high-gain amplifiers. Interestingly, the Raman effect can also produce intensity-dependent nonlinear loss through a corollary process known as inverse Raman scattering (IRS). Here, we demonstrate IRS in silicon--a process that is substantially modified by the presence of optically-generated free carriers--achieving attenuation levels >15 dB with a pump intensity of 4 GW/cm^2. Ironically, we find that free-carrier absorption, the detrimental effect that suppresses other nonlinear effects in silicon, actually facilitates IRS by delaying the onset of contamination from coherent anti-Stokes Raman scattering. The carriers allow significant IRS attenuation over a wide intensity range. Silicon-based IRS could be used to produce chip-scale wavelength-division multiplexers, optical signal inverters, and fast optical switches.