We have studied a GaAs-AlAs planar microcavity with a resonance near 1300 nm in the telecom range by ultrafast pump-probe reflectivity. By the judicious choice of pump frequency, we observe a ultimate fast and reversible decrease of the resonance frequency by more than half a linewidth due to the instantaneous electronic Kerr effect. The switch-on and switch-off of the cavity is only limited by the cavity storage time of τ cav = 0.3ps and not by intrinsic material parameters. Our results pave the way to supra-THz switching rates for on-chip data modulation and real-time cavity quantum electrodynamics.Switches are widely applied and necessary ingredients in modulation and computing schemes 1 . The recent progress on photonic integrated circuits 2,3 promises to overtake boundaries set by conventional switching technology. To do so, ultrafast switching of photonic cavities is crucial as it allows the capture or release on demand of photons 4-6 , which is relevant to on-chip communication with light as information carrier 7 , and to high-speed miniature lasers 8 . Ultrafast switching would also permit the quantum electrodynamical manipulation of coupled cavity-emitter systems 9 in real-time. Switching the optical properties of photonic nanostructures is achieved by changing the refractive index of the constituent materials. To date, however, the switching speed has been limited by material properties 11-14 , but not by optical considerations. To achieve ultimate fast switching of a cavity two challenges arise. Firstly, both the switch-on and switch-off times τ on and τ of f must be shorter than all other relevant time scales for the system, i.e., the cavity storage time in photon capture/release experiments τ cav , or the vacuum Rabi period τ Rabi for a strongly coupled emitter-cavity system 10 . Secondly, the refractive index change must be large enough to switch the cavity resonance by at least half a linewidth.Here, we demonstrate the ultimate fast switching of the resonance of a planar cavity in the well-known GaAs/AlAs system in the telecom wavelength range. We exploit the instantaneously fast electronic Kerr effect by the judicious tuning of the pump and probe frequencies relative to the semiconductor bandgap. We observe that the speed of the switching is then only limited by the dynamics of the light in our cavity (τ cav = 0.3 ps), but not by the intrinsic material parameters.Instantaneous on-and off-switching with vanishing τ on and τ of f is feasible with the well-known nonlinear rea) Electronic mail: g.ctistis@utwente.nl b) Electronic mail: W.L.Vos@tnw.utwente.nl fractive index from nonlinear optics 15 . Physically the electronic Kerr effect is the fastest Kerr phenomenon on account of the small electron mass. In many practical situations, however, non-degenerate two-photon absorption overwhelms any instantaneous effect and therefore also the dispersive electronic Kerr effect 13,15 . In order to avoid two-photon absorption and to access the electronic Kerr switching regime, we designed our experiment to op...

We have repeatedly and reproducibly switched a GaAs-AlAs planar microcavity operating in the "original" telecom band by exploiting the virtually instantaneous electronic Kerr effect. We achieve repetition times as fast as 300 fs, thereby breaking the terahertz modulation barrier. The rate of the switching in our experiments is only determined by optics and not by material-related relaxation. Our results offer opportunities for fundamental studies of cavity quantum electrodynamics and optical information processing in the subpicosecond time scale.

Abstract:We describe novel optical switching schemes operating at femtosecond time scales by employing free carrier (FC) excitation. Such unprecedented switching times are made possible by spatially patterning the density of the excited FCs. In the first realization, we rely on diffusion, i.e., on the nonlocality of the FC nonlinear response of the semiconductor, to erase the initial FC pattern and, thereby, eliminate the reflectivity of the system. In the second realization, we erase the FC pattern by launching a second pump pulse at a controlled delay. We discuss the advantages and limitations of the proposed approaches and demonstrate their potential applicability for switching ultrashort pulses propagating in silicon waveguides. We show switching efficiencies of up to 50% for 100 fs pump pulses, which is an unusually high level of efficiency for such a short interaction time, a result of the use of the strong FC nonlinearity. Due to limitations of saturation and pattern effects, these schemes can be employed for switching applications that require femtosecond features but standard repetition rates. Such applications include switching of ultrashort pulses, femtosecond spectroscopy (gating), time-reversal of short pulses for aberration compensation, and many more. This approach is also the starting point for ultrafast amplitude modulations and a new route toward the spatio-temporal shaping of short optical pulses.

We perform spatially dependent tuning of a GaInP photonic crystal cavity using a continuous wave violet laser. Local tuning is obtained by laser heating of the photonic crystal membrane. The cavity resonance shift is measured for different pump positions and for two ambient gases: He and N 2 . We find that the width of the temperature profile induced in the membrane depends strongly on the thermal conductivity of the ambient gas. For He gas a narrow spatial width of the temperature profile of 2.8 µm is predicted and verified in experiment.Photonic crystal (PhC) cavities are widely studied because of their fascinating applications 1-3 . Arrays of PhC cavities can form coupled resonator optical waveguides (CROW), which are very promising for slow light applications 4 and the study of light localization 5 . Various fabrication imperfections can cause a disorder in a CROW structure which leads to a detuning of cavities from the intended resonance and reduces the waveguide throughput and bandwidth. Tuning each cavity independently can restore cavities in resonance and counteract the disorder. There is a variety of methods to change the refractive index of a PhC cavity, including free-carrier injection 6 , the nonlinear Kerr effect 7 , thermal effects 8,9 , oxidation 10-12 and chemical processes 13 . Of these methods, thermal tuning through local laser heating is easy, reversible and can give a steady-state control of the resonance properties of the system. However due to the diffusion of heat in the PhC membrane thermal control of one cavity will affect the neighbor cavities. The width of the temperature profile is determined by the sample material and the surrounding media. Therefore one can expect that by carefully selecting the sample material and ambient medium one can control the width of the temperature profile.In this work we use the semiconductor alloy Ga 0.51 In 0.49 P as a sample material and two gases, nitrogen and helium, as a surrounding media. Ga 0.51 In 0.49 P has a thermal conductivity 14 of 4.9 W/(m·K) which is quite small in comparison to other semiconductor materials 15 . The thermal conductivity of gases is often assumed to be negligible compared to semiconductors, such as Si. However, the effect of the gas on the width of the thermal profile depends strongly on the ratio of the thermal conductivity of the gas and the semiconductor. Helium has a high thermal conductivity 16 of 0.153 W/(m·K), which is more than 6 times higher than of a) s.sokolov@utwente.nl; http://cops.nano-cops.com nitrogen 16 (0.024 W/(m·K)) and only 32 times smaller that that of Ga 0.51 In 0.49 P. Therefore the combination of Ga 0.51 In 0.49 P and He should have a high thermal exchange efficiency and small width of the temperature profile in comparison with other materials. To investigate the width of the temperature profile in PhC membranes we measured the response of the resonance of a H0-type cavity to a spatially scanned continuous wave (CW) heating laser focused on the membrane. pump 405 nm SLM (b) L1 IR camera CW IR laser ...