Alex Hartsuiker

Ultimate fast optical switching of a planar microcavity in the telecom wavelength range

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 an ultimate fast and reversible decrease in 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 τcav = 0.3 ps and not by intrinsic material parameters. Our results pave the way to supraterahertz switching rates for on-chip data modulation and real-time cavity quantum electrodynamics.

Non-exponential spontaneous emission dynamics for emitters in a time-dependent optical cavity

We have theoretically studied the effect of deterministic temporal control of spontaneous emission in a dynamic optical microcavity. We propose a new paradigm in light emission: we envision an ensemble of two-level emitters in an environment where the local density of optical states is modified on a time scale shorter than the decay time. A rate equation model is developed for the excited state population of two-level emitters in a time-dependent environment in the weak coupling regime in quantum electrodynamics. As a realistic experimental system, we consider emitters in a semiconductor microcavity that is switched by free-carrier excitation. We demonstrate that a short temporal increase of the radiative decay rate depletes the excited state and drastically increases the emission intensity during the switch time. The resulting time-dependent spontaneous emission shows a distribution of photon arrival times that strongly deviates from the usual exponential decay: A deterministic burst of photons is spontaneously emitted during the switch event.

Observation of a stronger-than-adiabatic change of light trapped in an ultrafast switched GaAs-AlAs microcavity

We study the time-resolved reflectivity spectrum of a switched planar GaAs-AlAs microcavity. Between 5 and 40 ps after the switching (pump) pulse, we observe a strong excess probe reflectivity and a change of the frequency of light trapped in the cavity up to 5 linewidths away from the cavity resonance. This frequency change does not adiabatically follow the fast-changing cavity resonance. The frequency change is attributed to an accumulated phase change due to the time-dependent refractive index. An analytical model predicts dynamics in qualitative agreement with the experiments, and points to crucial parameters that control future applications.

Optical characterization and selective addressing of the resonant modes of a micropillar cavity with a white light beam

We have performed white light reflectivity measurements on GaAs/AlAs micropillar cavities with diameters ranging from 1 μm up to 20 μm. We are able to resolve the spatial field distribution of each cavity mode in real space by scanning a small-sized beam across the top facet of each micropillar. We spectrally resolve distinct transverse-optical cavity modes in reflectivity. Using this procedure we can selectively address a single mode in the multimode micropillar cavity. Calculations for the coupling efficiency of a small-diameter beam to each mode are in very good agreement with our reflectivity measurements

Observation of sub-Bragg diffraction of waves in crystals

We investigate the diffraction conditions and associated formation of stop gaps for waves in crystals with different Bravais lattices. We identify a prominent stop gap in high-symmetry directions that occurs at a frequency below the ubiquitous first-order Bragg condition. This sub-Bragg-diffraction condition is demonstrated by reflectance spectroscopy on two-dimensional photonic crystals with a centered rectangular lattice, revealing prominent diffraction peaks for both the sub-Bragg and first-order Bragg conditions. These results have implications for wave propagation in 2 of the 5 two-dimensional Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as centered rectangular, triangular, hexagonal, and body-centered cubic.

Ultimate fast optical switching of a semiconductor photonic microcavity

We present ultrafast pump-probe reflectivity measurements on semiconductor microcavities with a resonance at telecom wavelengths. We observe an ultimate fast red shift and recovery of the cavity resonance due to the instantaneous electronic Kerr effect.

Experimental observation of sub-Bragg frequency gaps in photonic crystals

Photonic crystals control light propagation at a fundamental level [1]. Photonic crystals are ordered composite materials with a spatially varying dielectric constant that has a periodicity of the order of the wavelength of light. Frequency gaps emerge for which light cannot propagate inside such structure due to Bragg diffraction. These frequency gaps appear in experiments as stopbands. We have investigated stopbands in directions of high symmetry for two-dimensional photonic crystals. Surprisingly, we find a stopband below the first order Bragg condition. This result is valid not only for photonic crystals, but for wave propagation in periodic media in general. This has implications for crystallography, scattering of phonons and band gap formation.

Instantaneous switching of photonic cavity structure by electronic Kerr nonlinearity

We present time-resolved reflectivity spectra of optically switched GaAs/AlAs photonic structures. We show for the first time instantaneous tuning of the optical properties, using a surprisingly large electronic Kerr effects at femtosecond times.

Spatially resolved modes in GaAs/AlAs micropillar resonators

We present broadband reflectivity measurements on micropillars, resolving distinct modes inside the cavity resonance. We observe that the spectral mode position and spacing strongly depend on both pillar diameter and illumination position.

What is the real quality factor of an ultrafast planar photonic microcavity

We perform ultrafast time resolved autocorrelation measurements of a microcavity to deduce the quality factor. This value agrees well with transfer matrix calculations, but is higher than found from spectroscopic measurements.