Resonant, broadband, and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Abstract

Using a hydrodynamic approach, we examine bulk- and surface-induced second- and third-harmonic generationfrom semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrateresonant, broadband, and highly efficient optical frequency conversion: contrary to conventional wisdom, weshow that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where non-linear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately500MW/cm2peak power density, we predictthird-harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UVor visible wavelength, including the range of negative dielectric constant. We also predict surface second-harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass; bistable behaviorof the signals as a result of a reshaped resonance; and the onset of fifth-order nonlinear effects. These remarkablefindings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase lock-ing, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest thatneither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metalsfrom the list of useful or practical nonlinear materials in any spectral range.