Impact of nonlinear loss on stimulated Brillouin scattering

Abstract

We study the impact of two-photon absorption (2PA) and fifth-order nonlinear loss such as 2PAinduced free-carrier absorption in semiconductors on the performance of Stimulated Brillouin Scattering devices. We formulate the equations of motion including effective loss coefficients, whose explicit expressions are provided for numerical evaluation in any waveguide geometry. We find that 2PA results in a monotonic, algebraic relationship between amplification, waveguide length and pump power, whereas fifth-order losses lead to a non-monotonic relationship. We define a figure of merit for materials and waveguide designs in the presence of fifth-order losses. From this, we determine the optimal waveguide length for the case of 2PA alone and upper bounds for the total Stokes amplification for the case of 2PA as well as fifth-order losses. The analysis is performed analytically using a small-signal approximation and is compared to numerical solutions of the full nonlinear modal equations.

Large Brillouin amplification in silicon

“…Short free carrier lifetimes, combined with a reduced two-photon absorption coefficient, result in 15-times lower nonlinear losses than the nanowire systems analyzed in Ref. [30]. Together these properties yield an unprecedented Brillouin gain figure of merit of F = 5.2 [30].…”

“…[30]. Together these properties yield an unprecedented Brillouin gain figure of merit of F = 5.2 [30]. Hence, this unique hybrid photonic-phononic waveguide design represents a significant advance over prior silicon nanowire waveguide systems.…”

“…Hence, this unique hybrid photonic-phononic waveguide design represents a significant advance over prior silicon nanowire waveguide systems. Moreover, this improved figure of merit suggests significant opportunity for high-efficiency Brillouin amplification and cascaded energy transfer [30].…”

“…Even with superb dimensional control, amplification diminishes with longer interaction lengths [28], highlighting the problem of dimensionally induced inhomogenous broadening [29]. Careful theoretical analyses by Wolff et al, suggest that large net amplification is fundamentally challenging to achieve in silicon nanowires at near-IR wavelengths due to nonlinear absorption [30].In this paper, we report large Brillouin amplification in silicon through an alternative device paradigm; using a new all-silicon membrane structure (Fig. 1) that permits independent design of photonic and phononic modes, we demonstrate net amplification at remarkably low (< 5 mW) pump powers, and record-high Brillouin *These authors contributed equally to this work.…”

“…Even with superb dimensional control, amplification diminishes with longer interaction lengths [28], highlighting the problem of dimensionally induced inhomogenous broadening [29]. Careful theoretical analyses by Wolff et al, suggest that large net amplification is fundamentally challenging to achieve in silicon nanowires at near-IR wavelengths due to nonlinear absorption [30].…”