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 networks(1-3). Nonlinear optical effects such as four-wave mixing and parametric gain have been explored to realize all-optical functions in glass fibres(4). An alternative approach is to use nanoscale engineering of silicon waveguides to enhance optical nonlinearities by up to five orders of magnitude(5), enabling integrated chip-scale all-optical signal processing. Four-wave mixing within silicon nanophotonic waveguides has been used to demonstrate telecom-band (lambda approximate to 1,550 nm) all-optical functions including wavelength conversion(6-9), signal regeneration(10) and tunable optical delay(11). Despite these important advances, strong two-photon absorption(12) of the telecom-band pump presents a fundamental obstacle, limiting parametric gain to values of several decibels(13). 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 approximate to 0.55 eV, lambda approximate to 2,200 nm), where parasitic two-photon absorption-related absorption vanishes(12,14,15). 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 dispersion(16) can potentially enable mid-infrared-pumped silicon parametric oscillators(17-19) and amplifiers for telecom-band optical signals.