5 research outputs found
Inverted loss engineering in functional material covered waveguides
Optical waveguides, covered with thin films, which transmittance can be
controlled by external action, are widely used in various applications from
optical modulators to saturable absorbers. It is natural to suggest that the
waveguide losses will be proportional to the covering material absorption. We
demonstrate that under certain conditions this simple assumption fails.
Instead, we observe the reduction of the film material absorption can lead to
an increase in the waveguide propagation losses. For this, we use a side
polished fiber covered with a single-walled carbon nanotube thin film whose
absorption is attenuated either due to saturable absorption or electrochemical
gating. For the films thicker than 50 nm, we observe saturable absorption to
turn into light induced absorption with nonmonotonic dependence on the incident
power. With a numerical simulation and analytical approach, we identify that
this nontrivial behavior comes from mode reshaping and predict required
parameters for its observation.Comment: 7 pages, 3 figure
Polynomial unconstrained binary optimisation inspired by optical simulation
We propose an algorithm inspired by optical coherent Ising machines to solve
the problem of polynomial unconstrained binary optimisation (PUBO). We
benchmark the proposed algorithm against existing PUBO algorithms on the
extended Sherrington-Kirkpatrick model and random third-degree polynomial
pseudo-Boolean functions, and observe its superior performance. We also address
instances of practically relevant computational problems such as protein
folding and electronic structure calculations with problem sizes not accessible
to existing quantum annealing devices. In particular, we successfully find the
lowest-energy conformation of lattice protein molecules containing up to eleven
amino-acids. The application of our algorithm to quantum chemistry sheds light
on the shortcomings of approximating the electronic structure problem by a PUBO
problem, which, in turn, puts into question the applicability of quantum
annealers in this context.Comment: 10 pages, 6 figure
Optimization of laser stabilization via self-injection locking to a whispering-gallery-mode microresonator: experimental study
Self-injection locking of a diode laser to a high-quality-factor
microresonator is widely used for frequency stabilization and linewidth
narrowing. We constructed several microresonator-based laser sources with
measured instantaneous linewidths of 1 Hz and used them for investigation and
implementation of the self-injection locking effect. We studied analytically
and experimentally the dependence of the stabilization coefficient on tunable
parameters such as locking phase and coupling rate. It was shown that precise
control of the locking phase allows fine tuning of the generated frequency from
the stabilized laser diode. We also showed that it is possible for such laser
sources to realize fast continuous and linear frequency modulation by injection
current tuning inside the self-injection locking regime. We conceptually
demonstrate coherent frequency-modulated continuous wave LIDAR over a distance
of 10 km using such a microresonator-stabilized laser diode in the
frequency-chirping regime and measure velocities as low as sub-micrometer per
second in the unmodulated case. These results could be of interest for
cutting-edge technology applications such as space debris monitoring and
long-range object classification, high resolution spectroscopy and others
Single-walled carbon nanotube membranes as non-reflective substrates for nanophotonic applications
We demonstrate that single-walled carbon nanotube (SWCNT) membranes can be successfully utilized as nanometer-thick substrates for enhanced visualization and facilitated study of individual nanoparticles. As model objects, we transfer optically resonant 200 nm silicon nanoparticles onto pristine and ethanol-densified SWCNT membranes by the femtosecond laser printing method. We image nanoparticles by scanning electron and bright-field optical microscopy, and characterize by linear and Raman scattering spectroscopy. The use of a pristine SWCNT membrane allows to achieve an order-of-magnitude enhancement of the optical contrast of the nanoparticle bright field image over the results shown in the case of the glass substrate use. The observed optical contrast enhancement is in agreement with the spectrophotometric measurements showing an extremely low specular reflectance of the pristine membrane (≤0.1%). Owing to the high transparency, negligibly small reflectance and thickness, SWCNT membranes offer a variety ofperspective applications in nanophotonics, bioimaging and synchrotron radiation studies.Peer reviewe