ABSTRACT
We measure fast carrier decay rates (6 ps) in GaAs photonic crystal cavities with resonances near the GaAs bandgap energy at room temperature using a pump-probe measurement. Carriers generated via photoexcitation using an above-band femtosecond pulse cause a substantial blue-shift of three time the cavity linewidth for the cavity peak. The experimental results are compared to theoretical models based on free carrier effects near the GaAs band edge. The probe transmission is modified by nearly 30% for an estimated above-band pump energy of 4.2 fJ absorbed in the GaAs slab.
ABSTRACT
We demonstrate fast nonlinear optical switching between two laser pulses with as few as 140 photons of pulse energy by utilizing strong coupling between a single quantum dot (QD) and a photonic crystal cavity. The cavity-QD coupling is modified by a detuned pump pulse, resulting in a modulation of the scattered and transmitted amplitude of a time synchronized probe pulse that is resonant with the QD. The temporal switching response is measured to be as fast as 120 ps, demonstrating the ability to perform optical switching on picosecond timescales.
ABSTRACT
PbS quantum dots are promising active emitters for use with high-quality Si nanophotonic devices in the telecommunications-band. Measurements of low quantum dot densities are limited both because of low fluorescence levels and the challenges of single photon detection at these wavelengths. Here, we report on methods using a fiber taper waveguide to efficiently extract PbS quantum dot photoluminescence. Temperature dependent ensemble measurements reveal an increase in emitted photons concomitant with an increase in excited-state lifetime from 58.9 ns at 293 K to 657 ns at 40 K. Measurements are also performed on quantum dots on high-Q (>10(5)) microdisks using cavity-resonant, pulsed excitation.
Subject(s)
Equipment Failure Analysis/instrumentation , Equipment Failure Analysis/methods , Lead/chemistry , Quantum Dots , Selenium Compounds/chemistry , Spectrometry, Fluorescence/instrumentation , Cold Temperature , Equipment DesignABSTRACT
We demonstrate a reversibly tunable photonic crystal quantum dot laser using a photochromic thin film. The laser is composed of a photonic crystal cavity with a bare cavity Q as high as 4500 coupled to a high density ensemble of indium arsenide quantum dots. By depositing a thin layer of photochromic material on the photonic crystal cavities, the laser can be optically tuned smoothly and reversibly over a wavelength range of 2.68 nm. Lasing is observed at temperatures as high as 80 K in the 900-1000 nm near-infrared wavelength range. The spontaneous emission coupling factor is measured to be as high as ß=0.41, indicating that the laser operates in the high-ß regime.
ABSTRACT
We present evidence of cavity quantum electrodynamics from a sparse density of strongly quantum-confined Pb-chalcogenide nanocrystals (between 1 and 10) approaching single-dot levels on moderately high-Q mesoscopic silicon optical cavities. Operating at important near-infrared (1500-nm) wavelengths, large enhancements are observed from devices and strong modifications of the QD emission are achieved. Saturation spectroscopy of coupled QDs is observed at 77K, highlighting the modified nanocrystal dynamics for quantum information processing.
Subject(s)
Chalcogens/chemistry , Lab-On-A-Chip Devices , Lead/chemistry , Models, Chemical , Quantum Dots , Spectrum Analysis/methods , Cold Temperature , Colloids/chemistry , Computer SimulationABSTRACT
We present the first time-resolved cryogenic observations of Forster energy transfer in large, monodisperse lead sulfide quantum dots with ground-state transitions near 1.5 microm (0.8 eV), in environments from 160 K to room temperature. The observed temperature-dependent dipole-dipole transfer rate occurs in the range of (30-50 ns) (-1), measured with our confocal single-photon counting setup at 1.5 microm wavelengths. By temperature-tuning the dots, 94% efficiency of resonant energy transfer can be achieved for donor dots. The resonant transfer rates match well with proposed theoretical models.
ABSTRACT
A long-lived photonic state is observed in measurements of microwave transmission through a helical stack of anisotropic overhead transparencies with various twist defects in the center of the structure. Once account is taken of absorption and of the angular spread of the source, computer simulations of transmission through a polarized localized state are in agreement with measurements. Unlike for isotropic one-dimensional bandgaps, the intensity of the localized mode is not modulated in space on a wavelength scale.
