1,301 research outputs found
Microwave-induced nonequilibrium temperature in a suspended carbon nanotube
Antenna-coupled suspended single carbon nanotubes exposed to 108 GHz
microwave radiation are shown to be selectively heated with respect to their
metal contacts. This leads to an increase in the conductance as well as to the
development of a power-dependent DC voltage. The increased conductance stems
from the temperature dependence of tunneling into a one-dimensional electron
system. The DC voltage is interpreted as a thermovoltage, due to the increased
temperature of the electron liquid compared to the equilibrium temperature in
the leads
Critical-Current Reduction in Thin Superconducting Wires Due to Current Crowding
We demonstrate experimentally that the critical current in superconducting
NbTiN wires is dependent on their geometrical shape, due to current-crowding
effects. Geometric patterns such as 90 degree corners and sudden expansions of
wire width are shown to result in the reduction of critical currents. The
results are relevant for single-photon detectors as well as parametric
amplifiers
Low loss, high contrast optical waveguides based on CMOS compatible LPCVD processing
A new class of integrated optical waveguide structures is presented, based on low cost CMOS compatible LPCVD processing. This technology allows for medium and high index contrast waveguides with very low channel attenuation. The geometry is basically formed by a rectangular cross-section silicon nitride filled with and encapsulated by silicon dioxide . The birefringence and minimal bend radius of the waveguide is completely controlled by the geometry of the waveguide layer structures. Experiments on typical geometries will be presented, showing excellent characteristics (channel attenuation ≤0.06 dB/cm, IL ≤0.6 dB, PDL ≤0.2 dB, Bg «1 x , bend radius ≤500 μm)
Probing thermalization and dynamics of high-energy quasiparticles in a superconducting nanowire by scanning critical current microscopy
Besides its fundamental interest, understanding the dynamics of pair breaking
in superconducting nanostructures is a central issue to optimize the
performances of superconducting devices such as qubits or photon detectors.
However, despite substantial research efforts, these dynamics are still not
well understood as this requires experiments in which quasiparticles are
injected in a controlled fashion. Until now, such experiments have employed
solid-state tunnel junctions with a fixed tunnel barrier. Here we use instead a
cryogenic scanning tunnelling microscope to tune independently the energy and
the rate of quasiparticle injection through, respectively, the bias voltage and
the tunnelling current. For high energy quasiparticles, we observe the
reduction of the critical current of a nanowire and show it is mainly
controlled by the injected power and, marginally, by the injection rate. Our
results prove a thermal mechanism for the reduction of the critical current and
unveil the rapid dynamics of the generated hot spot.Comment: 25 pages, 14 figure
On-chip integrated amplifiers and lasers utilizing rare-earth-ion activation
This contribution reviews our recent results on rare-earth-ion-doped integrated amplifiers and lasers. We have concentrated our efforts on complex-doped polymers, amorphous Al2O3, and crystalline potassium double tungstates
25 kHz narrow spectral bandwidth of a wavelength tunable diode laser with a short waveguide-based external cavity
We report on the spectral properties of a diode laser with a tunable external
cavity in integrated optics. Even though the external cavity is short compared
to other small-bandwidth external cavity lasers, the spectral bandwidth of this
tunable laser is as small as 25 kHz (FWHM), at a side-mode suppression ratio
(SMSR) of 50 dB. Our laser is also able to access preset wavelengths in as
little as 200 us and able to tune over the full telecom C-band (1530 nm - 1565
nm).Comment: 8 pages, 7 figure
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