353 research outputs found
Low-Threshold Surface-Passivated Photonic Crystal Nanocavity Laser
The efficiency and operating range of a photonic crystal laser is improved by
passivating the InGaAs quantum well (QW) gain medium and GaAs membrane using an
(NH4)S treatment. The passivated laser shows a four-fold reduction in
nonradiative surface recombination rate, resulting in a four-fold reduction in
lasing threshold. A three-level carrier dynamics model explains the results and
shows that lasing threshold is as much determined by surface recombination
losses as by the cavity quality factor (Q). Surface passivation therefore
appears crucial in operating such lasers under practical conditions.Comment: 3 pages, 2 figure
Time-resolved lasing action from single and coupled photonic crystal nanocavity array lasers emitting in the telecom-band
We measure the lasing dynamics of single and coupled photonic crystal
nanocavity array lasers fabricated in the indium gallium arsenide phosphide
material system. Under short optical excitation, single cavity lasers produce
pulses as fast as 11 ps (FWHM), while coupled cavity lasers show significantly
longer lasing duration which is not explained by a simple rate equations model.
A Finite Difference Time Domain simulation including carrier gain and diffusion
suggests that asynchronous lasing across the nanocavity array extends the
laser's pulse duration.Comment: 4 pages, 4 figure
Terahertz Room-Temperature Photonic Crystal Nanocavity Laser
We describe an efficient surface-passivated photonic crystal nanocavity
laser, demonstrating room-temperature operation with 3-ps total pulse duration
(detector response limited) and low-temperature operation with
ultra-low-threshold near 9uW.Comment: 6 pages, 3 figure
Photoluminescence measurements of quantum-dot-containing semiconductor microdisk resonators using optical fiber taper waveguides
Fiber taper waveguides are used to improve the efficiency of room temperature
photoluminescence measurements of AlGaAs microdisk resonant cavities with
embedded self-assembled InAs quantum dots. As a near-field collection optic,
the fiber taper improves the collection efficiency from microdisk lasers by a
factor of ~ 15-100 times in comparison to conventional normal incidence
free-space collection techniques. In addition, the fiber taper can serve as a
efficient means for pumping these devices, and initial measurements employing
fiber pumping and collection are presented. Implications of this work towards
chip-based cavity quantum electrodynamics experiments are discussed.Comment: 10 pages, 7 figure
Tailoring Chirp in Spin-Lasers
The usefulness of semiconductor lasers is often limited by the undesired
frequency modulation, or chirp, a direct consequence of the intensity
modulation and carrier dependence of the refractive index in the gain medium.
In spin-lasers, realized by injecting, optically or electrically,
spin-polarized carriers, we elucidate paths to tailoring chirp. We provide a
generalized expression for chirp in spin-lasers and introduce modulation
schemes that could simultaneously eliminate chirp and enhance the bandwidth, as
compared to the conventional (spin-unpolarized) lasers.Comment: 4 pages, 3 figure
Electron-Hole Generation and Recombination Rates for Coulomb Scattering in Graphene
We calculate electron-hole generation and recombination rates for Coulomb
scattering (Auger recombination and impact ionization) in Graphene. The
conduction and valence band dispersion relation in Graphene together with
energy and momentum conservation requirements restrict the phase space for
Coulomb scattering so that electron-hole recombination times can be much longer
than 1 ps for electron-hole densities smaller than cm.Comment: 13 pages, 7 figure
Scaling of losses with size and wavelength in nanoplasmonics and metamaterials
We show that, for the resonant metal-dielectric structures with
sub-wavelength confinement of light in all three dimensions, the loss cannot be
reduced significantly below the loss of the metal itself unless one operates in
the far IR and THz regions of the spectrum or below. Such high losses cannot be
compensated by introducing gain due to Purcell-induced shortening of
recombination times. The only way low loss optical metamaterials can be
engineered is with as yet unknown low loss materials with negative
permittivity.Comment: Submitted to AP
Voltage-controlled wavelength conversion by terahertz electro-optic modulation in double quantum wells
An undoped double quantum well (DQW) was driven with a terahertz (THz)
electric field of frequency \omega_{THz} polarized in the growth direction,
while simultaneously illuminated with a near-infrared (NIR) laser at frequency
\omega_{NIR}. The intensity of NIR upconverted sidebands
\omega_{sideband}=\omega_{NIR} + \omega_{THz} was maximized when a dc voltage
applied in the growth direction tuned the excitonic states into resonance with
both the THz and NIR fields. There was no detectable upconversion far from
resonance. The results demonstrate the possibility of using gated DQW devices
for all-optical wavelength shifting between optical communication channels
separated by up to a few THz.Comment: 3 pages, 6 figures. Figures 5 and 6 are JPEG files, figures/fig5.jpg
and fig6.jp
Optical loss and lasing characteristics of high-quality-factor AlGaAs microdisk resonators with embedded quantum dots
Optical characterization of AlGaAs microdisk resonant cavities with a quantum
dot active region is presented. Direct passive measurement of the optical loss
within AlGaAs microdisk resonant structures embedded with InAs/InGaAs
dots-in-a-well (DWELL) is performed using an optical-fiber-based probing
technique at a wavelength (lambda~1400 nm) that is red-detuned from the dot
emission wavelength (lambda~1200 nm). Measurements in the 1400 nm wavelength
band on microdisks of diameter D = 4.5 microns show that these structures
support modes with cold-cavity quality factors as high as 360,000.
DWELL-containing microdisks are then studied through optical pumping at room
temperature. Pulsed lasing at lambda ~ 1200 nm is seen for cavities containing
a single layer of InAs dots, with threshold values of ~ 17 microWatts,
approaching the estimated material transparency level. Room-temperature
continuous wave operation is also observed.Comment: 4 pages, 3 figure
Lasing from a circular Bragg nanocavity with an ultra-small modal volume
We demonstrate single-mode lasing at telecommunication wavelengths from a
circular nanocavity employing a radial Bragg reflector. Ultra-small modal
volume and Sub milliwatt pump threshold level are observed for lasers with
InGaAsP quantum well active membrane. The electromagnetic field is shown to be
tightly confined within the 300nm central pillar of the cavity. The quality
factors of the resonator modal fields are estimated to be on the order of a few
thousands.Comment: 3 pages, 4 figures Submitted to AP
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