867 research outputs found
All-optical pulse reshaping and retiming systems incorporating pulse shaping fiber Bragg grating
This paper demonstrates two optical pulse retiming and reshaping systems incorporating superstructured fiber Bragg gratings (SSFBGs) as pulse shaping elements. A rectangular switching window is implemented to avoid conversion of the timing jitter on the original data pulses into pulse amplitude noise at the output of a nonlinear optical switch. In a first configuration, the rectangular pulse generator is used at the (low power) data input to a nonlinear optical loop mirror (NOLM) to perform retiming of an incident noisy data signal using a clean local clock signal to control the switch. In a second configuration, the authors further amplify the data signal and use it to switch a (low power) clean local clock signal. The S-shaped nonlinear characteristic of the NOLM results in this instance in a reduction of both timing and amplitude jitter on the data signal. The underlying technologies required for the implementation of this technique are such that an upgrade of the scheme for the regeneration of ultrahigh bit rate signals at data rates in excess of 320 Gb/s should be achievable
Quadrature decomposition of optical fields using two orthogonal phase sensitive amplifiers
We propose a new technique to optically process coherent signals by simultaneously extracting their two (I and Q) quadrature components into two orthogonal polarizations at the same frequency. Two possible implementations are demonstrated
Phase sensitive amplifiers for regeneration of phase encoded optical signal formats
We discuss the application of phase sensitive fiber optical parametric devices for the regenerative processing of high baud rate optical signals. We present recent advances in phase-sensitive amplification technology and its application to the regeneration of phase-encoded signals. By combining four wave mixing based parametric effects in highly nonlinear optical fibers and injection locking assisted synchronisation of multiple coherent lasers, we demonstrate how it possible to derive phase regeneration in signals with more than two levels of phase encoding
Efficient binary phase quantizer based on phase sensitive four wave mixing
We experimentally demonstrate an efficient binary phase quantizer operating at low pump powers. Phase-sensitive operation is obtained by polarization mixing the phase-locked signal/idler pair in a degenerate dual-pump vector parametric amplifier
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On reconciling macro and micro energy transport forecasts for strategic decision making in the tanker industry
We propose the use of hierarchical structures for forecasting freight earnings. Hierarchical time series approaches are applied in the dry-bulk and tanker markets to identify the most suitable strategy for forecasting freight rates. We argue that decision making for shipping practitioners should be based on forecasts of freight earnings at different hierarchical levels. In other words, different strategic shipping decisions such as operations management, choice of freight charter contract and type of investment should be matched with the appropriate level of forecasts of freight earnings that are aggregated at different macro-levels: operating route, vessel size and type of trade
Novel polarization-assisted phase sensitive optical signal processor requiring low nonlinear phase shifts
We demonstrate a new scheme to achieve binary step-like phase response and high phase-sensitive extinction ratio at low powers. Phase-sensitive operation is achieved by polarization filtering phase-locked signal/idler in a degenerate dual-pump vector parametric amplifier
Signal regeneration techniques for advanced modulation formats
We review recent results on all-optical regeneration of phase encoded signals based on phase sensitive amplification achieved by avoiding phase-to-amplitude conversion in order to facilitate the regeneration of amplitude/phase encoded (QAM) signals
Ricci flows and expansion in axion-dilaton cosmology
We study renormalization-group flows by deforming a class of conformal
sigma-models. We consider overall scale factor perturbation of Einstein spaces
as well as more general anisotropic deformations of three-spheres. At leading
order in alpha, renormalization-group equations turn out to be Ricci flows. In
the three-sphere background, the latter is the Halphen system, which is exactly
solvable in terms of modular forms. We also analyze time-dependent deformations
of these systems supplemented with an extra time coordinate and time-dependent
dilaton. In some regimes time evolution is identified with
renormalization-group flow and time coordinate can appear as Liouville field.
The resulting space-time interpretation is that of a homogeneous isotropic
Friedmann-Robertson-Walker universe in axion-dilaton cosmology. We find as
general behaviour the superposition of a big-bang (polynomial) expansion with a
finite number of oscillations at early times. Any initial anisotropy disappears
during the evolution.Comment: 22 page
G3-homogeneous gravitational instantons
We provide an exhaustive classification of self-dual four-dimensional
gravitational instantons foliated with three-dimensional homogeneous spaces,
i.e. homogeneous self-dual metrics on four-dimensional Euclidean spaces
admitting a Bianchi simply transitive isometry group. The classification
pattern is based on the algebra homomorphisms relating the Bianchi group and
the duality group SO(3). New and general solutions are found for Bianchi III.Comment: 24 pages, few correction
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