Integrated all‐optical switch with 10 ps time resolution enabled by ALD

Abstract

The potential of GaAs‐based photonic crystals for fast all‐optical switching in the telecom spectral range is exploited by controlling the surface recombination and, thereby, the carrier relaxation dynamics. The structure is entirely coated with a layer of aluminium oxide using atomic layer deposition. This results in a carrier lifetime of about 10 ps, as determined by spectrally resolved pump–probe measurements. We show that the nonlinear response of the resonator is optimized when it is excited with a few‐picoseconds pulse. This dynamics is perfectly captured by our model accounting for the carrier diffusion with an impulse response function. Moreover, the suppression of photo‐induced oxidation is revealed to be crucial to demonstrate all‐optical operation at GHz rates with average coupled pump power of 0.5 mW (hence 100 fJ/bit). The switching window is 12 ps wide (1/e), as resolved by homodyne pump–probe measurements. The devices respond to a sequence of closely spaced pump pulses demonstrating a gating window close to 10 ps, with a contrast as high as 7 dB.

In‐Plane Photonic Crystal Devices using Fano Resonances

“…Bulk recombination, due to radiative and Auger recombination, is a slow process with characteristic time scales spanning from tens to several hundreds of nanoseconds . An important carrier relaxation process in PhC structures, owing to their large surface area to volume ratio, is the surface recombination . At the surface of a semiconductor the atomic lattice is abruptly interrupted.…”

“…This results in dangling bonds, i.e., unpaired outer‐shell electrons, which introduce surface states that can trap charge carriers enhancing electron‐hole recombination . The effective carrier lifetime, τ eff , can then be written as where τ rec is the bulk recombination rate, S is the surface recombination velocity, and L is the maximum distance to the top or bottom surface of the photonic crystal. For PhC membrane structures, , where h is the PhC membrane thickness.…”

“…However, if the recovery time is significantly shorter than the modulating signal, the build‐up of carrier density in the cavity region is reduced, which lowers the refractive index changes and diminishes the effect of the modulation. Due to this, GaAs‐based PhC nanocavities need to be coated with a few nanometer‐thick layer of alumina using atomic layer deposition (ALD) in order to achieve larger modulation . The situation is different for InP with much lower surface recombination velocity of around .…”

“…A Lorentzian structure composed of two identical H0 cavities, which are coupled to each other forming a photonic molecule, and connected to input and output waveguides based on GaAs material is shown in Figure c . Similar to other Lorentzian structures, light transmission from the input port to the output port is only possible via the photonic molecule.…”

“…Similar to other Lorentzian structures, light transmission from the input port to the output port is only possible via the photonic molecule. The coupling between the two cavities results in the splitting of the resonance into two peaks that are separated by 10 nm, c.f. Figure c (right).…”