190 research outputs found
Bond orbital description of the strain induced second order optical susceptibility in silicon
We develop a theoretical model, relying on the well established sp3
bond-orbital theory, to describe the strain-induced in
tetrahedrally coordinated centrosymmetric covalent crystals, like silicon. With
this approach we are able to describe every component of the
tensor in terms of a linear combination of strain gradients and only two
parameters and which can be estimated theoretically. The
resulting formula can be applied to the simulation of the strain distribution
of a practical strained silicon device, providing an extraordinary tool for
optimization of its optical nonlinear effects. By doing that, we were able not
only to confirm the main valid claims known about in strained
silicon, but also estimate the order of magnitude of the generated
in that device
Optical Gain in Carbon Nanotubes
Semiconducting single-wall carbon nanotubes (s-SWNTs) have proved to be
promising material for nanophotonics and optoelectronics. Due to the
possibility of tuning their direct band gap and controlling excitonic
recombinations in the near-infrared wavelength range, s-SWNT can be used as
efficient light emitters. We report the first experimental demonstration of
room temperature intrinsic optical gain as high as 190 cm-1 at a wavelength of
1.3 {\mu}m in a thin film doped with s-SWNT. These results constitute a
significant milestone toward the development of laser sources based on carbon
nanotubes for future high performance integrated circuits.Comment: 4 figure
Wideband tunable microwave signal generation in a silicon-based optoelectronic oscillator
Si photonics has an immense potential for the development of compact and
low-loss opto-electronic oscillators (OEO), with applications in radar and
wireless communications. However, current Si OEO have shown a limited
performance. Si OEO relying on direct conversion of intensity modulated signals
into the microwave domain yield a limited tunability. Wider tunability has been
shown by indirect phase-modulation to intensity-modulation conversion,
requiring precise control of the phase-modulation. Here, we propose a new
approach enabling Si OEOs with wide tunability and direct intensity-modulation
to microwave conversion. The microwave signal is created by the beating between
an optical source and single sideband modulation signal, selected by an
add-drop ring resonator working as an optical bandpass filter. The tunability
is achieved by changing the wavelength spacing between the optical source and
resonance peak of the resonator. Based on this concept, we experimentally
demonstrate microwave signal generation between 6 GHz and 18 GHz, the widest
range for a Si-based OEO. Moreover, preliminary results indicate that the
proposed Si OEO provides precise refractive index monitoring, with a
sensitivity of 94350 GHz RIU and a potential limit of detection of only 10-8
RIU, opening a new route for the implementation of high-performance Si photonic
sensors
Polarization and wavelength agnostic nanophotonic beam splitter
High-performance optical beam splitters are of fundamental importance for the
development of advanced silicon photonics integrated circuits. However, due to
the high refractive index contrast of the silicon-on-insulator platform, state
of the art Si splitters are hampered by trade-offs in bandwidth, polarization
dependence and sensitivity to fabrication errors. Here, we present a new
strategy that exploits modal engineering in slotted waveguides to overcome
these limitations, enabling ultra-wideband polarization-insensitive optical
power splitters, with relaxed fabrication tolerances. The proposed splitter
relies on a single-mode slot waveguide which is transformed into two strip
waveguides by a symmetric taper, yielding equal power splitting. Based on this
concept, we experimentally demonstrate -30.5 dB polarization-independent
transmission in an unprecedented 390 nm bandwidth (1260 - 1650 nm), even in the
presence of waveguide width deviations as large as 25 nm
Optical microcavity with semiconducting single-wall carbon nanotubes
We report studies of optical Fabry-Perot microcavities based on
semiconducting single-wall carbon nanotubes with a quality factor of 160. We
experimentally demonstrate a huge photoluminescence signal enhancement by a
factor of 30 in comparison with the identical film and by a factor of 180 if
compared with a thin film containing non-purified (8,7) nanotubes. Futhermore,
the spectral full-width at half-maximum of the photo-induced emission is
reduced down to 8 nm with very good directivity at a wavelength of about 1.3
m. Such results prove the great potential of carbon nanotubes for photonic
applications
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