We investigated the behavior of a Raman silicon laser based on a photonic-crystal nanocavity while it was irradiated with electrostatic charges from a static-electricity generator. Laser oscillation stopped after a few seconds of a weak irradiation and the time needed for the recovery of laser oscillation increased with irradiation time. We measured the resonance spectra of the nanocavity modes during irradiation. It indicates that such a lasing interruption can be caused by wavelength shifts of the nanocavity modes and absorption losses due to the electrostatic charges on the nanocavity surface. These results are useful for the sensing of electrostatic charges.
Modulation of the Purcell effect by controlling both the Q-factor and detuning in a quantum-dot-nanocavity coupled
system was investigated. The Q-factor and detunings are controlled independently by using a nanocavity, a waveguide
and a reflector formed in a two-dimensional photonic crystal slab, in combination with a newly developed nitrogen
adsorption/desorption technique that enables local control of the refractive index. We investigated analytically and
experimentally how the density of states of cavity mode is modulated, and we experimentally clarified how the emission
of a quantum dot on resonance with a cavity is modulated. We observed that the emission of a quantum dot via a cavity
mode was increased by 3.3 times when the Q-factor was changed from 3,500 to 6,900 while keeping the detuning fixed.
The dependence of the Purcell effect on the Q-factor was directly observed.
High-quality (Q) factor photonic-crystal nanocavities are currently the focus of much interest because they can strongly
confine photons in a tiny space. Nanocavities with ultrahigh Q factors of up to 2,500,000 and modal volumes of a cubic
wavelength have been realized. If the Q factor could be dynamically controlled within the lifetime of a photon,
significant advances would be expected in areas of physics and engineering such as the slowing and/or stopping of light
and quantum-information processing. Here, we review the demonstration of dynamic control of the Q factor, by
constructing a system composed of a nanocavity, a waveguide with nonlinear optical response and a photonic-crystal
heterointerface mirror. The Q factor of the nanocavity was successfully changed from 3,800 to 22,000 within
picoseconds.
An Organic light-emitting diode (OLED) is very promising device for a flat panel display and an illumination applications due to the possibility of very thin and flexible structures, large area emission, high brightness and low power consumption. To realize a high efficiency is one of the most important issues for these applications. Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) structures, which are expected to realize the versatile control of light. We fabricate two-dimensional PC structures in the organic and indium-tin-oxide anode layers in which most of the light is confined. This results in light extraction from the waveguide mode. Improvements of 20 and 130% are observed in the spectrally-integrated intensity and the peak intensity, respectively, in comparison with samples without PCs. As the thickness of the organic layer is reduced, lower operating voltages are found to maintain the light-extraction efficiency. We can expect further improvement in the overall efficiency by optimizing this structure.
High Q and ultra-small photonic nanocavity operating at optical communication wavelength is developed using a silicon-based two-dimensional photonic-crystal slab. The cavity is designed based on the concept that light should be confined gently in order to be confined strongly, which means that the envelope function of the cavity electric field profile should be gently varying but remain spatially localized. Structure of a cavity is adjusted to fit the envelope to a Gaussian function that fulfill the two conditions, and a Q factor more than 45,000 and a modal volume of 0.07 μm3 are successfully realized.
Two optical functional devices based on 2D photonic crystal are investigated. First of all, add-drop filtering devices based on single defects in 2D photonic crystal slabs are characterized. After describing basic characteristics of channel-drop function, we show the improvement of device characteristics through defect engineering. We also demonstrate the channel-add function of the device. Next, we describe a 2D large-area surface-emitting laser exhibiting single-longitudinal and single-lateral mode oscillation with narrow divergence angle based on the 2D coupling effect of lightwave in 2D photonic crystals. A method of controlling the polarization mode by changing the shape of the unit cell is also presented. These results indicate that 2D photonic crystals are useful for the realization of novel optical functional devices.
A picosecond modulation of interband (IB) resonant light (approximately 800 nm) by intersubband (ISB) resonant light (approximately 7 micrometers ) in n-doped GaAs/AlGaAs quantum wells is demonstrated. Two-color pump-probe measurements are carried out by using ultrashort (approximately 120 fs) ISB (pump) and IB (probe) light pulses at room temperature. Ultrafast modulation (FWHM approximately 1.3 ps) of the IB light is clearly observed with a low pump pulse energy of about 4 fJ/micrometers 2. The observed modulation depth is approximately 8.5% which corresponds to the absorption coefficient change of as large as approximately 1000 cm-1. The modulation depth decreases when the pump pulse wavelength is detuned from the ISB absorption peak. The modulation dependence on the ISB light pulse energy is also measured. The carrier relaxation mechanism in high and low excitation conditions is discussed by employing a numerical simulation of the relaxation process of electron-- longitudinal optical phonon systems. The results indicate that the utilization of the intersubband transition is promising for the ultrashort all-optical modulation and switching.
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