170 research outputs found
Self-injection-locked magnetron as an active ring resonator side coupled to a waveguide with a delayed feedback loop
The theoretical analysis and numerical simulations of the magnetron operation
with a feedback loop were performed assuming that the delay of the
electromagnetic wave propagating in the loop is constant whereas the phase of
the complex feedback reflection coefficient is varied. Results of simulations
showed that by a proper adjustment of values of the time delay and phase of
reflection coefficient that determines phase matching between the waves in the
resonator and feedback loop, one can increase the magnetron's output power
significantly without any other additional measures.Comment: 12 pages, 4 figure
Anomalous time delays and quantum weak measurements in optical micro-resonators
We study inelastic resonant scattering of a Gaussian wave packet with the
parameters close to a zero of the complex scattering coefficient. We
demonstrate, both theoretically and experimentally, that such near-zero
scattering can result in anomalously-large time delays and frequency shifts of
the scattered wave packet. Furthermore, we reveal a close analogy of these
anomalous shifts with the spatial and angular Goos-H\"anchen optical beam
shifts, which are amplified via quantum weak measurements. However, in contrast
to other beam-shift and weak-measurement systems, we deal with a
one-dimensional scalar wave without any intrinsic degrees of freedom. It is the
non-Hermitian nature of the system that produces its rich and non-trivial
behaviour. Our results are generic for any scattering problem, either quantum
or classical. As an example, we consider the transmission of an optical pulse
through a nano-fiber with a side-coupled toroidal micro-resonator. The zero of
the transmission coefficient corresponds to the critical coupling conditions.
Experimental measurements of the time delays near the critical-coupling
parameters verify our weak-measurement theory and demonstrate amplification of
the time delay from the typical inverse resonator linewidth scale to the pulse
duration scale.Comment: 14 pages, 5 figure
Transverse Shifts in Paraxial Spinoptics
The paraxial approximation of a classical spinning photon is shown to yield
an "exotic particle" in the plane transverse to the propagation. The previously
proposed and observed position shift between media with different refractive
indices is modified when the interface is curved, and there also appears a
novel, momentum [direction] shift. The laws of thin lenses are modified
accordingly.Comment: 3 pages, no figures. One detail clarified, some misprints corrected
and references adde
Coupling and Level Repulsion in the Localized Regime: From Isolated to Quasi-Extended Modes
We study the interaction of Anderson localized states in an open 1D random
system by varying the internal structure of the sample. As the frequencies of
two states come close, they are transformed into multiply-peaked quasi-extended
modes. Level repulsion is observed experimentally and explained within a model
of coupled resonators. The spectral and spatial evolution of the coupled modes
is described in terms of the coupling coefficient and Q-factors of resonators.Comment: 4 pages, 6 figure
Anderson localization in metamaterials and other complex media
We review some recent (mostly ours) results on the Anderson localization of
light and electron waves in complex disordered systems, including: (i)
left-handed metamaterials, (ii) magneto-active optical structures, (iii)
graphene superlattices, and (iv) nonlinear dielectric media. First, we
demonstrate that left-handed metamaterials can significantly suppress
localization of light and lead to an anomalously enhanced transmission. This
suppression is essential at the long-wavelength limit in the case of normal
incidence, at specific angles of oblique incidence (Brewster anomaly), and in
the vicinity of the zero-epsilon or zero-mu frequencies for dispersive
metamaterials. Remarkably, in disordered samples comprised of alternating
normal and left-handed metamaterials, the reciprocal Lyapunov exponent and
reciprocal transmittance increment can differ from each other. Second, we study
magneto-active multilayered structures, which exhibit nonreciprocal
localization of light depending on the direction of propagation and on the
polarization. At resonant frequencies or realizations, such nonreciprocity
results in effectively unidirectional transport of light. Third, we discuss the
analogy between the wave propagation through multilayered samples with
metamaterials and the charge transport in graphene, which enables a simple
physical explanation of unusual conductive properties of disordered graphene
superlatices. We predict disorder-induced resonances of the transmission
coefficient at oblique incidence of the Dirac quasiparticles. Finally, we
demonstrate that an interplay of nonlinearity and disorder in dielectric media
can lead to bistability of individual localized states excited inside the
medium at resonant frequencies. This results in nonreciprocity of the wave
transmission and unidirectional transport of light.Comment: 37 pages, 30 figures, Review pape
Resonant Plasmon-Soliton Interaction
We describe an effective resonant interaction between two localized wave
modes of different nature: a plasmon-polariton at a metal surface and a
self-focusing beam (spatial soliton) in a non-linear dielectric medium.
Propagating in the same direction, they represent an exotic coupled-waveguide
system, where the resonant interaction is controlled by the soliton amplitude.
This non-linear system manifests hybridized plasmon-soliton eigenmodes, mutual
conversion, and non-adiabatic switching, which offer exciting opportunities for
manipulation of plasmons via spatial solitons.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
Nonreciprocal Anderson Localization in Magneto-Optical Random Structures
We study, both analytically and numerically, disorder-induced localization of
light in random layered structures with magnetooptical materials. The Anderson
localization in such structures demonstrates nonreciprocal features in the
averaged localization length and individual transmission resonances. We employ
short-wavelength approximation where the localization effects are strong, and
consider both the Faraday and Voigt magnetooptical geometries. In the Faraday
geometry, the transmission is strongly nonreciprocal for the circularly
polarized waves, whereas in the Voigt geometry, the nonreciprocity is much
weaker, and it may appear only for the individual transmission resonances of
the TM-polarized waves.Comment: 8 pages, 6 figure
Spatio-temporal vortex beams and angular momentum
We present a space-time generalization of the known spatial (monochromatic)
wave vortex beams carrying intrinsic orbital angular momentum (OAM) along the
propagation direction. Generic spatio-temporal vortex beams are polychromatic
and can carry intrinsic OAM at an arbitrary angle to the mean momentum.
Applying either (i) a transverse wave-vector shift or (ii) a Lorentz boost to a
monochromatic Bessel beam, we construct a family of either (i) time-diffracting
or (ii) non-diffracting spatio-temporal Bessel beams, which are exact solutions
of the Klein-Gordon wave equations. The proposed spatio-temporal OAM states are
able to describe either photon or electron vortex states (both relativistic and
nonrelativistic), and can find applications in particle collisions, optics of
moving media, quantum communications, and astrophysics.Comment: 9 pages, 6 figures, to appear in Phys. Rev.
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