181 research outputs found
High-Base Optical Signal Proccessing
Optical signal processing is a promising technique to enable fast data information processing in the optical domain. Traditional optical signal processing functions pay more attention to binary modulation formats (i.e., binary numbers) with single-bit information contained in one symbol. The ever-growing data traffic has propelled great success in high-speed optical signal transmission by using advanced multilevel modulation formats (i.e., high-base numbers), which encode multiple-bit information in one symbol with resultant enhanced transmission capacity and efficient spectrum usage. A valuable challenge would be to perform various optical signal processing functions for multilevel modulation formats, i.e., high-base optical signal processing. In this chapter, we review recent research works on high-base optical signal processing for multilevel modulation formats by exploiting degenerate and nondegenerate four-wave mixing in highly nonlinear fibers or silicon photonic devices. Grooming high-base optical signal processing functions including high-base wavelength conversion, high-base data exchange, high-base optical computing, and high-base optical coding/decoding are demonstrated. High-base optical signal processing may facilitate advanced data management and superior network performance
Sorting photons by radial quantum number
The Laguerre-Gaussian (LG) modes constitute a complete basis set for
representing the transverse structure of a {paraxial} photon field in free
space. Earlier workers have shown how to construct a device for sorting a
photon according to its azimuthal LG mode index, which describes the orbital
angular momentum (OAM) carried by the field. In this paper we propose and
demonstrate a mode sorter based on the fractional Fourier transform (FRFT) to
efficiently decompose the optical field according to its radial profile. We
experimentally characterize the performance of our implementation by separating
individual radial modes as well as superposition states. The reported scheme
can, in principle, achieve unit efficiency and thus can be suitable for
applications that involve quantum states of light. This approach can be readily
combined with existing OAM mode sorters to provide a complete characterization
of the transverse profile of the optical field
Novel Insights into Orbital Angular Momentum Beams: From Fundamentals, Devices to Applications
It is well-known by now that the angular momentum carried by elementary particles can be categorized as spin angular momentum (SAM) and orbital angular momentum (OAM). In the early 1900s, Poynting recognized that a particle, such as a photon, can carry SAM, which has only two possible states, i.e., clockwise and anticlockwise circular polarization states. However, only fairly recently, in 1992, Allen et al. discovered that photons with helical phase fronts can carry OAM, which has infinite orthogonal states. In the past two decades, the OAM-carrying beam, due to its unique features, has gained increasing interest from many different research communities, including physics, chemistry, and engineering. Its twisted phase front and intensity distribution have enabled a variety of applications, such as micromanipulation, laser beam machining, nonlinear matter interactions, imaging, sensing, quantum cryptography and classical communications. This book aims to explore novel insights of OAM beams. It focuses on state-of-the-art advances in fundamental theories, devices and applications, as well as future perspectives of OAM beams
Demonstration of a 280-Gbit/s free-space SDM communications link utilizing plane-wave spatial multiplexing
We demonstrate a 280-Gbit/s free-space SDM
communications link incorporating a set of independent
tilted truncated plane-waves, each generated by a single
mode fiber placed at the back-focal plane of a spherical
lens. Each of the 7 tilted plane-wave channels are
encoded with a 40-Gbit/s 16-QAM signal. Our approach
comprises two identical linear fiber-arrays placed
approximately 5 m apart. As each fiber array is placed at
the back-focal-plane of a spherical lens, each fiber array
is effectively placed in a conjugate image plane of the
other. A channel crosstalk less than 26 dB is shown, with
a bit-error-rate below the FEC threshold of 3.8 × 10−3
Using all transverse degrees of freedom in quantum communications based on a generic mode sorter
The dimension of the state space for information encoding offered by the
transverse structure of light is usually limited by the finite size of
apertures. The widely used orbital angular momentum (OAM) number of
Laguerre-Gaussian (LG) modes in free-space communications cannot achieve the
theoretical maximum transmission capacity unless the radial degree of freedom
is multiplexed into the protocol. While the methodology to sort the radial
quantum number has been developed, the application of radial modes in quantum
communications requires an additional ability to efficiently measure the
superposition of LG modes in the mutually unbiased basis. Here we develop and
implement a generic mode sorter that is capable of sorting the superposition of
LG modes through the use of a mode converter. As a consequence, we demonstrate
an 8-dimensional quantum key distribution experiment involving all three
transverse degrees of freedom: spin, azimuthal, and radial quantum numbers of
photons. Our protocol presents an important step towards the goal of reaching
the capacity limit of a free-space link and can be useful to other applications
that involve spatial modes of photons
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