Observation of soliton compression in silicon photonic crystals.

Solitons are nonlinear waves present in diverse physical systems including plasmas, water surfaces and optics. In silicon, the presence of two photon absorption and accompanying free carriers strongly perturb the canonical dynamics of optical solitons. Here we report the first experimental demonstration of soliton-effect pulse compression of picosecond pulses in silicon, despite two photon absorption and free carriers. Here we achieve compression of 3.7 ps pulses to 1.6 ps with <10 pJ energy. We demonstrate a ~1-ps free-carrier-induced pulse acceleration and show that picosecond input pulses are critical to these observations. These experiments are enabled by a dispersion-engineered slow-light photonic crystal waveguide and an ultra-sensitive frequency-resolved electrical gating technique to detect the ultralow energies in the nanostructured device. Strong agreement with a nonlinear Schrödinger model confirms the measurements. These results further our understanding of nonlinear waves in silicon and open the way to soliton-based functionalities in complementary metal-oxide-semiconductor-compatible platforms.

Pulse evolution and phase-sensitive amplification in silicon waveguides.

We provide an analytic solution for pulse propagation and phase-sensitive amplification in silicon waveguides in the regime of strong two-photon absorption (TPA) and significant free-carrier effects. Our analytic results clearly explain why and how the TPA and free carriers affect the signal gain. These observations are confirmed with numerical modelling and experimental results.

Slow-light dispersion engineering of photonic crystal waveguides using selective microfluidic infiltration.

We experimentally demonstrate dispersion engineering of slow light photonic crystal (PhC) waveguides using selective infiltration of the first two rows of air holes with high index ionic liquids. The infiltrated PhC waveguide exhibits a dispersion window of 3 nm with a nearly constant group velocity of ~c/80 that depends on the liquid physical properties. We investigate how the effective refractive index changes in time due to the dynamics of the liquids in the holes. This demonstration highlights the versatility, flexibility, and tunability offered by optofluidics in PhC circuits.

All-optical XOR logic gate for 40Gb/s DPSK signals via FWM in a silicon nanowire.

We demonstrate an all-optical XOR logic function for 40Gb/s differential phase-shift keyed (DPSK) data signals in the C-band, based on four-wave mixing (FWM) in a silicon nanowire. Error-free operation with a system penalty of ~3.0dB and ~4.3dB at 10⁻9 BER is achieved.

Ultracompact all-optical XOR logic gate in a slow-light silicon photonic crystal waveguide.

We demonstrate an ultracompact, chip-based, all-optical exclusive-OR (XOR) logic gate via slow-light enhanced four-wave mixing (FWM) in a silicon photonic crystal waveguide (PhCWG). We achieve error-free operation (<10⁻9) for 40 Gbit/s differential phase-shift keying (DPSK) signals with a 2.8 dB power penalty. Slowing the light to vg = c/32 enables a FWM conversion efficiency, η, of -30 dB for a 396 µm device. The nonlinear FWM process is enhanced by 20 dB compared to a relatively fast mode of vg = c/5. The XOR operation requires ≈ 41 mW, corresponding to a switching energy of 1 pJ/bit. We compare the slow-light PhCWG device performance with experimentally demonstrated XOR DPSK logic gates in other platforms and discuss scaling the device operation to higher bit-rates. The ultracompact structure suggests the potential for device integration.