13,355 research outputs found
An accurate envelope equation for light propagation in photonic nanowires: new nonlinear effects
We derive a new unidirectional evolution equation for photonic nanowires made
of silica. Contrary to previous approaches, our formulation simultaneously
takes into account both the vector nature of the electromagnetic field and the
full variations of the effective modal profiles with wavelength. This leads to
the discovery of new, previously unexplored nonlinear effects which have the
potential to affect soliton propagation considerably. We specialize our
theoretical considerations to the case of perfectly circular silica strands in
air, and we support our analysis with detailed numerical simulations.Comment: 5 figures. The normalization of the fields is now more appropriate
(orthonormal). Figure concerning dispersion of gamma0 has been eliminated.
New figures for nonlinear coefficients and pulse propagation for the
corrected envelope functio
Linear and nonlinear photonic Jackiw-Rebbi states in waveguide arrays
We study analytically and numerically the optical analogue of the
Jackiw-Rebbi states in quantum field theory. These solutions exist at the
interface of two binary waveguide arrays which are described by two Dirac
equations with opposite sign masses. We show that these special states are
topologically robust not only in the linear regime, but also in nonlinear
regimes (with both focusing and de-focusing nonlinearity). We also reveal that
one can generate the Jackiw-Rebbi states starting from Dirac solitons.Comment: 4 pages, 3 figure
Diffractive resonant radiation emitted by spatial solitons in waveguide arrays
We study analytically and numerically the diffractive resonant radiation emitted by spatial solitons, which is generated in waveguide arrays with Kerr nonlinearity. The phase matching condition between solitons and radiation is derived and studied for the first time and agrees well with direct pulse propagation simulations. The folded dispersion due to the Brillouin zone leads to a peculiar anomalous soliton recoil that we describe in detail. DOI: 10.1103/PhysRevLett.110.11390
Mimicking the nonlinear dynamics of optical fibers with waveguide arrays: towards a spatiotemporal supercontinuum generation
We numerically demonstrate the formation of the spatiotemporal version of the
so-called diffractive resonant radiation generated in waveguide arrays with
Kerr nonlinearity when a long pulse is launched into the system. The phase
matching condition for the diffractive resonant radiation that we have found
earlier for CW beams also works well in the spatiotemporal case. By introducing
a linear potential, one can introduce a continuous shift of the central
wavenumber of a linear pulse, whereas in the nonlinear case one can demonstrate
that the soliton self-wavenumber shift can be compensated by the emission of
diffractive resonant radiation, in a very similar fashion as it is done in
optical fibers. This work paves the way for designing unique optical devices
that generate spectrally broad supercontinua with a controllable directionality
by taking advantage of the combined physics of optical fibers and waveguide
arrays.Comment: arXiv admin note: substantial text overlap with arXiv:1210.520
Dynamic Radio Cooperation for Downlink Cloud-RANs with Computing Resource Sharing
A novel dynamic radio-cooperation strategy is proposed for Cloud Radio Access
Networks (C-RANs) consisting of multiple Remote Radio Heads (RRHs) connected to
a central Virtual Base Station (VBS) pool. In particular, the key capabilities
of C-RANs in computing-resource sharing and real-time communication among the
VBSs are leveraged to design a joint dynamic radio clustering and cooperative
beamforming scheme that maximizes the downlink weighted sum-rate system utility
(WSRSU). Due to the combinatorial nature of the radio clustering process and
the non-convexity of the cooperative beamforming design, the underlying
optimization problem is NP-hard, and is extremely difficult to solve for a
large network. Our approach aims for a suboptimal solution by transforming the
original problem into a Mixed-Integer Second-Order Cone Program (MI-SOCP),
which can be solved efficiently using a proposed iterative algorithm. Numerical
simulation results show that our low-complexity algorithm provides
close-to-optimal performance in terms of WSRSU while significantly
outperforming conventional radio clustering and beamforming schemes.
Additionally, the results also demonstrate the significant improvement in
computing-resource utilization of C-RANs over traditional RANs with distributed
computing resources.Comment: 9 pages, 6 figures, accepted to IEEE MASS 201
Understanding the Computational Requirements of Virtualized Baseband Units using a Programmable Cloud Radio Access Network Testbed
Cloud Radio Access Network (C-RAN) is emerging as a transformative
architecture for the next generation of mobile cellular networks. In C-RAN, the
Baseband Unit (BBU) is decoupled from the Base Station (BS) and consolidated in
a centralized processing center. While the potential benefits of C-RAN have
been studied extensively from the theoretical perspective, there are only a few
works that address the system implementation issues and characterize the
computational requirements of the virtualized BBU. In this paper, a
programmable C-RAN testbed is presented where the BBU is virtualized using the
OpenAirInterface (OAI) software platform, and the eNodeB and User Equipment
(UEs) are implemented using USRP boards. Extensive experiments have been
performed in a FDD downlink LTE emulation system to characterize the
performance and computing resource consumption of the BBU under various
conditions. It is shown that the processing time and CPU utilization of the BBU
increase with the channel resources and with the Modulation and Coding Scheme
(MCS) index, and that the CPU utilization percentage can be well approximated
as a linear increasing function of the maximum downlink data rate. These
results provide real-world insights into the characteristics of the BBU in
terms of computing resource and power consumption, which may serve as inputs
for the design of efficient resource-provisioning and allocation strategies in
C-RAN systems.Comment: In Proceedings of the IEEE International Conference on Autonomic
Computing (ICAC), July 201
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