791 research outputs found
Frequency division multiplexing for interferometric planar Doppler velocimetry
A new method of acquiring simultaneously the signal and reference channels used for interferometric
planar Doppler velocimetry is proposed and demonstrated. The technique uses frequency division multiplexing
(FDM) to facilitate the capture of the requisite images on a single camera, and is suitable for
time-averaged flow measurements. Furthermore, the approach has the potential to be expanded to allow
the multiplexing of additional measurement channels for multicomponent velocity measurement. The
use of FDM for interferometric referencing is demonstrated experimentally with measurements
of a single velocity component of a seeded axisymmetric air jet. The expansion of the technique to
include multiple velocity components was then investigated theoretically and experimentally to
account for bandwidth, crosstalk, and dynamic range limitations. The technique offers reduced
camera noise, automatic background light suppression, and crosstalk levels of typically <10%.
Furthermore, as this crosstalk is dependent upon the channel modulations applied, it can be corrected for in postprocessing
Boundary effects in finite size plasmonic crystals: Focusing and routing of plasmonic beams for optical communications
Plasmonic crystals, which consist of periodic arrangements of surface features at a metal-dielectric interface, allow the manipulation of optical information in the form of surface plasmon polaritons. Here we investigate the excitation and propagation of plasmonic beams in and around finite size plasmonic crystals at telecom wavelengths, highlighting the effects of the crystal boundary shape and illumination conditions. Significant differences in broad plasmonic beam generation by crystals of different shapes are demonstrated, while for narrow beams, the propagation onto the smooth metal film is less sensitive to the crystal boundary shape. We show that by controlling the boundary shape, the size and the excitation beam parameters, directional control of propagating plasmonic modes and associated beam parameters such as angular beam splitting, focusing power and beam width can be efficiently achieved. This provides a promising route for robust and alignment-independent integration of plasmonic crystals with optical communication components
Experimental demonstration of RGB LED-based optical camera communications
Red, green, and blue (RGB) light-emitting diodes (LEDs) are widely used in everyday illumination, particularly where color-changing lighting is required. On the other hand, digital cameras with color filter arrays over image sensors have been also extensively integrated in smart devices. Therefore, optical camera communications (OCC) using RGB LEDs and color cameras is a promising candidate for cost-effective parallel visible light communications (VLC). In this paper, a single RGB LED-based OCC system utilizing a combination of undersampled phase-shift on off keying (UPSOOK), wavelength-division multiplexing (WDM), and multiple-input multiple-output (MIMO) techniques is designed, which offers higher space efficiency (3 bits/Hz/LED), long-distance, and nonflickering VLC data transmission. A proof-of-concept test bed is developed to assess the bit-error-rate performance of the proposed OCC system. The experimental results show that the proposed system using a single commercially available RGB LED and a standard 50-frame/s camera is able to achieve a data rate of 150 bits/s over a range of up to 60 m
Non-paraxial design and fabrication of a compact OAM sorter in the telecom infrared
A novel optical device is designed and fabricated in order to overcome the
limits of the traditional sorter based on log-pol optical transformation for
the demultiplexing of optical beams carrying orbital angular momentum (OAM).
The proposed configuration simplifies the alignment procedure and significantly
improves the compactness and miniaturization level of the optical architecture.
Since the device requires to operate beyond the paraxial approximation, a
rigorous formulation of transformation optics in the non-paraxial regime has
been developed and applied. The sample has been fabricated as 256-level
phase-only diffractive optics with high-resolution electron-beam lithography,
and tested for the demultiplexing of OAM beams at the telecom wavelength of
1310 nm. The designed sorter can find promising applications in next-generation
optical platforms for mode-division multiplexing based on OAM modes both for
free-space and multi-mode fiber transmission.Comment: 12 pages, 8 figure
Test of mode-division multiplexing and demultiplexing in free-space with diffractive transformation optics
open5openGIANLUCA RUFFATO, 1; FILIPPO ROMANATO, ; 1Department of Physics and Astronomy ‘G. Galilei’, University of Padova; 2Laboratory for Nanofabrication of Nanodevices, c.so Stati Uniti 4GIANLUCA RUFFATO, 1; Romanato, Filippo; Ruffato, Gianluca; Astronomy ‘. G. Galilei’, University of Padova; 2Laboratory for Nanofabrication of Nanodevices, c. so Stati Uniti
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