Nonlinear Absorption and Raman Scattering in Silicon-on-Insulator Optical Waveguides

Abstract

We study the nonlinearities in silicon-on-insulator (SOI) optical waveguides, which include two-photon absorption (TPA), free-carrier absorption, and spontaneous and stimulated Raman scattering (SRS). We show experimentally that free carriers generated by TPA in the SOI waveguides produce large optical loss at room temperature. The experimental results confirmed the presence of relative optical signal amplification from SRS, but it was found that net gain was hardly achieved because the stimulated Raman gain was less than the induced loss from TPA-generated free carriers at room temperature with continuous-wave pumping source in a SOI rib waveguide. We also experimentally investigated the temperature dependence of Raman scattering in the SOI waveguide and observed the Raman gain to be greater than TPA-generated free-carrier absorption loss at 77 K.

Nonlinear optical phenomena in silicon waveguides: modeling and applications

“…In general, both Ω R and Γ R are sensitive to temperature [37,108,109]. As an example, Ω R /2π decreases by ∼40 GHz, while Γ R /π increases by ∼ 10 GHz, if temperature increases by 50 • C. The parameter g in Eq.…”

“…Detailed numerical simulations show that this blue shift is caused by a free-carrier-induced chirp (FCC) that affects pulse dynamics on a different time scale [9,14,[20][21][22]25]. Equation (37) can be used to describe pulse propagation inside SOI waveguides under quite general conditions. For simplifying the following discussion, we do not consider the polarization effects by assuming that the input pulse is polarized along the fundamental TE or TM mode of the waveguide.…”

“…Equation (37) shows that both the electronic nonlinearity and free carriers would induce nonlinear phase shifts and extra losses on the pulse. Here we provide a simple analytical approach to estimate their relative magnitudes.…”

“…The interplay among various dispersive and nonlinear effects leads to many interesting features [8-25, 88, 89] that provide new functionalities on the one hand [90-100], but may become obstacles in some cases on the other [25,32,33,[35][36][37]39,[65][66][67][68]89]. Therefore, it is important to have a unified theoretical platform that not only can be used for understanding the underlying physics but also provides guidance toward new and useful applications.…”

New CMOS-compatible platforms based on silicon nitride and Hydex for nonlinear optics

“…That issue is the fact that bulk crystalline silicon suffers from high nonlinear absorption due to two-photon absorption (TPA) [23,43] in all telecommunications bands at wavelengths shorter than about 2000 nm. While the effect of TPA generated free carriers can be mitigated by the use of p-i-n junctions to sweep out carriers [44], for example, silicon's intrinsic nonlinear figure of merit (FOM = n 2 /β λ, where β is the TPA coefficient and  the wavelength) is only 0.3 near 1550 nm [45 -47].…”