We demonstrate all-optical modulation based on ultrafast optical carrier injection in a GaAs photonic crystal cavity using a degenerate pump-probe technique. The observations agree well with a coupled-mode model incorporating all relevant nonlinearities. The low switching energy (∼120 fJ), small energy absorption (∼10 fJ), fast on-off response (∼15 ps), limited only by carrier lifetime, and a minimum 10 dB modulation depth suggest practical all-optical switching applications at high repetition rates.

We demonstrate experimentally that the fiber to fiber total insertion loss into a single-mode waveguide in a suspended photonic crystal membrane can be reduced to less than 10 dB (input, output, and propagation) without introducing any supplementary processing step (e.g., polymer deposition and etching). This is achieved through a suitable design of the waveguide end-facets minimizing the impedance mismatch and thereby the residual reflectance at the waveguide ends.

We have established a new material, indium gallium phosphide, lattice matched to gallium arsenide, for two-dimensional photonic crystals at 1.55 μm. We have demonstrated single-mode cavities with intrinsic Q-factor larger than one million and achieved very large self-phase-modulation coefficient 1.1×103 W1 m−1 in line-defect waveguides. Importantly, the material band gap is such that two-photon absorption, Eg>2ℏω, is completely suppressed at this important telecommunications wavelength.

We haves realized and measured a GaAs nanocavity in a slab photonic crystal based on the design by Kuramochi et al. [Appl. Phys. Lett. 88, 041112 (2006)]. We measure a quality factor Q=700,000, which proves that ultrahigh Q nanocavities are also feasible in GaAs. We show that owing to larger two-photon absorption in GaAs nonlinearities appear at the microwatt level and will be more functional in gallium arsenide than in silicon nanocavities.

We investigate the nonlinear response of photonic crystal waveguides with suppressed two-photon absorption. A moderate decrease of the group velocity (approximately c/6 to c/15, a factor of 2.5) results in a dramatic (x 30) enhancement of three-photon absorption well beyond the expected scaling, proportional, variant 1/v3g. This non-trivial scaling of the effective nonlinear coefficients results from pulse compression, which further enhances the optical field beyond that of purely slow-group velocity interactions. These observations are enabled in mm-long slow-light photonic crystal waveguides owing to the strong anomalous group-velocity dispersion and positive chirp. Our numerical physical model matches measurements remarkably.

We investigate the nonlinear response of GaAs-based photonic crystal cavities at time scales which are much faster than the typical thermal relaxation rate in photonic devices. We demonstrate a strong interplay between thermal and carrier induced nonlinear effects. We have introduced a dynamical model entailing two thermal relaxation constants which is in very good agreement with experiments. These results will be very important for Photonic Crystal-based nonlinear devices intended to deal with practical high repetition rate optical signals.

Nonlinear propagation experiments in GaAs photonic crystal waveguides (PCW) were performed, which exhibit a large enhancement of third order nonlinearities, due to light propagation in a slow mode regime, such as two-photon absorption (TPA), optical Kerr effect and refractive index changes due to free-carriers generated by TPA. A theoretical model has been established that shows a very good quantitative agreement with experimental data and demonstrates the important role that the group velocity plays. These observations give a strong insight into the use of PCWs for optical switching devices.

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