Mid-infrared optical parametric amplifier using silicon nanophotonic waveguides

All-optical signal processing is an approach used to dramatically decrease power consumption and speed up the performance of next-generation optical telecommunications networks1-3. Nonlinear optical effects such as four-wave mixing and parametric gain have been explored to realize all-optical functions in glass fibres. An alternative approach is to use nanoscale engineering of silicon waveguides to enhance optical nonlinearities by up to five orders of magnitude, enabling integrated chip-scale all-optical signal processing. Four-wave mixing within silicon nanophotonic waveguides has been used to demonstrate telecom-band (λ ≈ 1,550 nm) all-optical functions including wavelength conversion6-9, signal regeneration and tunable optical delay11. Despite these important advances, strong two-photon absorption12 of the telecom-band pump presents a fundamental obstacle, limiting parametric gain to values of several decibels13. Here, we demonstrate a silicon nanophotonic optical parametric amplifier exhibiting broadband gain as high as 25.4 dB, using a mid-infrared pump near one-half the bandgap energy (E ≈ 0.55 eV, λ ≈2,200 nm), where parasitic two-photon absorption-related absorption vanishes12,14,15. This gain is high enough to compensate all insertion losses, resulting in 13-dB net off-chip amplification, using only an ultra-compact 4-mm silicon chip. Furthermore, engineering of higher-order waveguide dispersion16 can potentially enable mid-infrared-pumped silicon parametric oscillators 17-19 and amplifiers for telecom-band optical signals. © 2010 Macmillan Publishers Limited. All rights reserved.