Quantifying the influence of crosstalk-crosstalk beat noise in optical DPSK systems

In-band crosstalk, due to multiple interferers, is one of the most severe physical impairments in optical transparent networks. Differential phase-shift keying (DPSK) has been identified as an attractive modulation scheme to be used in such environments due to its robustness to in-band crosstalk. At the output of the receiver photodiode, which is assumed to behave as a square law device, the in-band crosstalk interferes with the signal, resulting in the signal-crosstalk beat noise and the crosstalk-crosstalk beat noise. Usually this last noise contribution is neglected, but in this paper the impact of the crosstalk-crosstalk beating terms is considered and quantified. It is concluded that these terms have a growing influence as the optical signal-to-noise ratio (OSNR) value increases.info:eu-repo/semantics/acceptedVersio

Theoretical Insights into the Impact of Coherent and Incoherent Crosstalk on Optical DPSK Signals

WOS:000283247600001 (Nº de Acesso Web of Science)“Prémio Científico ISCTE-IUL 2011”This paper provides new theoretical insights into the properties of direct detection differential phase-shift keying (DPSK) signals impaired by coherent and incoherent crosstalk. Coherent crosstalk is due to multiple replicas originated while a data signal is routed through an optical network, whereas the source of incoherent crosstalk resides on the interference from other DPSK signals. A special emphasize has been put on modeling the multipath coherent crosstalk, with analytical expressions being derived and presented for both the moment generating function of the decision variable and the average error probability. A rigorous analysis, capable of dealing with arbitrary filtering, is also presented, which is used afterwards to assess the accuracy of the analytical formulas. A detailed comparison with incoherent crosstalk is also performed. Using also an exact treatment for this type of crosstalk it is shown that for low OSNR penalties the coherent crosstalk leads, in some circumstances, to slightly worse results than the incoherent one, but this situation is reversed when the total crosstalk level and the number of interferers increase

Implications of in-band crosstalk on DQPSK Signals in ROADM-based metropolitan optical networks

Metropolitan optical networks can be designed to transport a multitude of signals with different bit rates and modulations formats. In this way, in-band crosstalk signals, originated from imperfect isolation inside ROADM (Reconfigurable Optical Add and Drop Multiplexer)-based optical nodes, will potentially have a different modulation format than the primary signal. In this paper, the origin of in-band crosstalk in a typical ROADM is analysed and its impact on differential quadrature phase-shift keying (DQPSK) signals is assessed through an analytical formalism based on the moment generating function (MGF) of the receiver decision variable. Various scenarios are analysed including the case of multiple interfering terms with different modulation formats, namely the on-off keying (OOK). It is concluded that the OOK interferer is more detrimental than the DQPSK interferer for DQPSK systems, or than the differential phase-shift keying (DPSK) interferer for DPSK systems.info:eu-repo/semantics/publishedVersio

Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field

The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic model, with a magnetic field applied in the easy plane, is studied using the self-consistent harmonic approximation. We found a linear dependence of the transition temperature as a function of the field for large values of the field. Our results are in agreement with experimental data for the spin-1 honeycomb compound BaNi_2V_2O_3Comment: 3 page

Assessing land-ocean connectivity via Submarine Groundwater Discharge (SGD) in the Ria Formosa Lagoon (Portugal): combining radon measurements and stable isotope hydrology

Natural radioactive tracer-based assessments of basin-scale Submarine Groundwater Discharge (SGD) are well developed, but because of the different modes in which SGD takes place and the wide range of spatial and temporal scales under which the flow and discharge mechanisms involved occur, quantifying SGD while discriminating its source functions remains a major challenge. Yet, correctly identifying both the fluid source and composition is critical: when multiple sources of the tracer of interest are present, failure to adequately discriminate between them will lead to inaccurate attribution and the resulting uncertainties will affect the reliability of SGD solute loading estimates. This lack of reliability then extends to the closure of local biogeochemical budgets, confusing measures aiming to mitigate pollution. Here, we report a multi-tracer study to identify the sources of SGD, distinguish its component parts and elucidate the mechanisms of their dispersion throughout the Ria Formosa – a seasonally hypersaline lagoon in Portugal. We combine radon budgets that determine the total SGD (meteoric + recirculated seawater) in the system with stable isotopes in water (2H, 18O), to specifically identify SGD source functions and characterize active hydrological pathways in the catchment. Using this approach, SGD in the Ria Formosa could be separated into a net water input and another involving no net water transfer, i.e. originating in seawater recirculation through permeable sediments. The former SGD mode is present occasionally on a multiannual timescale, while the latter is a permanent feature of the system. In the absence of meteoric SGD inputs, seawater recirculation through beach sediments occurs at a rate of ~ 1.4 × 106 m3 day−1, implying the entire tidal-averaged volume of the lagoon is filtered through local sandy sediments within 100 days, or about 3.5 times a year, driving an estimated nitrogen (N) load of ~ 350 t N yr−1 into the system as NO3−. Land-borne SGD could add a further ~ 61 t N yr−1 to the lagoon. The former source is autochthonous, continuous and responsible for a large fraction (59 %) of the estimated total N inputs into the system via non-point sources, while the latter is an occasional allochthonous source, so more difficult to predict, but capable of driving new production in the system