156 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
Measuring the complex orbital angular momentum spectrum and spatial mode decomposition of structured light beams
Light beams carrying orbital angular momentum are key resources in modern
photonics. In many applications, the ability of measuring the complex spectrum
of structured light beams in terms of these fundamental modes is crucial. Here
we propose and experimentally validate a simple method that achieves this goal
by digital analysis of the interference pattern formed by the light beam and a
reference field. Our approach allows one to characterize the beam radial
distribution also, hence retrieving the entire information contained in the
optical field. Setup simplicity and reduced number of measurements could make
this approach practical and convenient for the characterization of structured
light fields.Comment: 8 pages (including Methods and References), 6 figure
Tuning optical cavities by Möbius topology
The resonance wavelengths of optical Möbius strip microcavities can be continuously tuned via geometric phase manipulation by changing the thickness-to-width ratio of the strip
Spatially dependent electromagnetically induced transparency
Recent years have seen vast progress in the generation and detection of
structured light, with potential applications in high capacity optical data
storage and continuous variable quantum technologies. Here we measure the
transmission of structured light through cold rubidium atoms and observe
regions of electromagnetically induced transparency (EIT). We use q-plates to
generate a probe beam with azimuthally varying phase and polarisation
structure, and its right and left circular polarisation components provide the
probe and control of an EIT transition. We observe an azimuthal modulation of
the absorption profile that is dictated by the phase and polarisation structure
of the probe laser. Conventional EIT systems do not exhibit phase sensitivity.
We show, however, that a weak transverse magnetic field closes the EIT
transitions, thereby generating phase dependent dark states which in turn lead
to phase dependent transparency, in agreement with our measurements.Comment: 5 Pages, 5 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
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