140 research outputs found
Photon spin-to-orbital angular momentum conversion via an electrically tunable -plate
Exploiting electro-optic effects in liquid crystals, we achieved real-time
control of the retardation of liquid- crystal-based -plates through an
externally applied voltage. The newly conceived electro-optic -plates can be
operated as electrically driven converters of photon spin into orbital angular
momentum, enabling a variation of the orbital angular momentum probabilities of
the output photons over a time scale of milliseconds.Comment: 4 pages, 5 figures, submitte
Efficient generation and control of different order orbital angular momentum states for communication links
We present a novel optical device to encode and decode two bits of
information into different Orbital Angular Momentum (OAM) states of a paraxial
optical beam. Our device generates the four angular momentum states of order
and by Spin-To-Orbital angular momentum Conversion (STOC) in a
triangular optical loop arrangement. The switching among the four OAM states is
obtained by changing the polarization state of the circulating beam by two
quarter wave plates and the two-bit information is transferred to the beam OAM
exploiting a single -plate. The polarization of the exit beam is left free
for additional one bit of information. The transmission bandwidth of the device
may be as large as several megahertz if electro-optical switches are used to
change the beam polarization. This may be particularly useful in communication
system based on light OAM.Comment: 5 pages, 5 figures, 1 table. Submitte
Universal unitary gate for single-photon spinorbit four-dimensional states
The recently demonstrated possibility of entangling opposite values of the
orbital angular momentum (OAM) of a photon with its spin enables the
realization of nontrivial one-photon spinorbit four-dimensional states for
quantum information purposes. Hitherto, however, an optical device able to
perform arbitrary unitary transformations on such spinorbit photon states has
not been proposed yet. In this work we show how to realize such a ``universal
unitary gate'' device, based only on existing optical technology, and describe
its operation. Besides the quantum information field, the proposed device may
find applications wherever an efficient and convenient manipulation of the
combined OAM and spin of light is required.Comment: 7 pages, 2 figure
Polarization-controlled evolution of light transverse modes and associated Pancharatnam geometric phase in orbital angular momentum
We present an easy, efficient and fast method to generate arbitrary linear
combinations of light orbital angular momentum eigenstates
starting from a linearly polarized TEM laser beam. The method exploits
the spin-to-orbital angular momentum conversion capability of a
liquid-crystal-based -plate and a Dove prism inserted in a Sagnac polarizing
interferometer. The nominal generation efficiency is 100\%, being limited only
by reflection and scattering losses in the optical components. When closed
paths are followed on the polarization Poincar\'{e} sphere of the input beam,
the associated Pancharatnam geometric phase is transferred unchanged to the
orbital angular momentum state of the output beam.Comment: 5 pages and 5 figure
Efficient generation and sorting of orbital angular momentum eigenmodes of light by thermally tuned q-plates
We present methods for generating and for sorting specific orbital angular
momentum (OAM) eigenmodes of a light beam with high efficiency, using a liquid
crystal birefringent plate with unit topological charge, known as \qo{q-plate}.
The generation efficiency has been optimized by tuning the optical retardation
of the q-plate with temperature. The measured OAM eigenmodes
generation efficiency from an input TEM beam was of 97%. Mode sorting of
the two input OAM eigenmodes was achieved with an efficiency of 81%
and an extinction-ratio (or cross-talk) larger than 4.5:1.Comment: 4 pages, 3 Figures and 1 table. Submitte
Geometric-Phase Waveplates for Free-Form Dark Hollow Beams
We demonstrate the possibility of creating optical beams with phase singularities engraved into exotic intensity landscapes imitating the shapes of a large variety of diverse plane curves. To achieve this aim, we have developed a method for directly encoding the geometric properties of a selected curve into a single azimuthal phase factor without passing through indirect encryption methods involving lengthy numerical procedures. The outcome is utilized to mold the optic axis distribution of a liquid-crystal-based inhomogeneous waveplate. The latter is finally used to sculpt the wavefront of an input optical gaussian beam via the Pancharatnam-Berry phase
Guiding light via geometric phases
Known methods for transverse confinement and guidance of light can be grouped
into a few basic mechanisms, the most common being metallic reflection, total
internal reflection and photonic-bandgap (or Bragg) reflection. All of them
essentially rely on changes of the refractive index, that is on scalar
properties of light. Recently, processes based on "geometric Berry phases",
such as manipulation of polarization states or deflection of spinning-light
rays, have attracted considerable interest in the contexts of singular optics
and structured light. Here, we disclose a new approach to light waveguiding,
using geometric Berry phases and exploiting polarization states and their
handling. This can be realized in structured three-dimensional anisotropic
media, in which the optic axis lies orthogonal to the propagation direction and
is modulated along it and across the transverse plane, so that the refractive
index remains constant but a phase distortion can be imposed on a beam. In
addition to a complete theoretical analysis with numerical simulations, we
present a proof-of-principle experimental demonstration of this effect in a
discrete element implementation of a geometric phase waveguide. The mechanism
we introduce shows that spin-orbit optical interactions can play an important
role in integrated optics and paves the way to an entire new class of photonic
systems that exploit the vectorial nature of light.Comment: Publication supported by European Union (EU) within Horizon 2020 -
ERC-Advanced Grant PHOSPhOR, grant no. 694683. This is the final
peer-reviewed manuscript as accepted for publication (including methods and
supplementary information
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