Polarization converters based on ring-resonator phase-shifters

In this letter, novel devices based on ring-resonator phase-shifters are proposed for the realization of efficient polarization converters with periodical spectral response. The main spectral properties of several architectures, including parallel-coupled and directly coupled ring-resonators, are analytically investigated and conditions for complete polarization rotation are derived. The exploitation as polarization interleavers and polarization splitters/combiners is also briefly discussed.     

Semiconductor Laser in Distributed Optical Feedback Regime

Wireless Personal Communications - In this work, we first analyse the behaviour of semiconductor laser in the presence of weak-to-moderate feedback from a single (lumped) and double external cavity...     

Induction of cytochrome P-450 and catalase activity in Saccharomyces cerevisiae by UV and X-ray irradiation. Possible role for cytochrome P-450 in cell protection against oxidative damage

Cytochrome P-450 was induced both in the diploid wild-type D7 strain and in two isogenic DNA-repair-deficient strains (rad3 and rad56) of Saccharomyces cerevisiae following UV- and X-irradiation. The induction occurred only in logarithmic growth phase cells and it was transient showing a peak 3 h after irradiation. The maximal amount of cytochrome P-450 was directly proportional to the radiation dose applied. Under the same experimental conditions an increase of the catalase activity was also observed, suggesting that activated oxygen species produced by irradiation might be implicated in the induction of both enzymes. The sensitivity to H2O2 of cells containing high cytochrome P-450 levels was enhanced when this enzyme was specifically inhibited by tetrahydrofuran and metyrapone. This supports the hypothesis that cytochrome P-450, as well as catalase, might be involved in cell protection against oxidative damage.     

Equivalent circuit of Bragg gratings and its application to Fabry-Pérot cavities

An equivalent circuit of both uniform and apodized symmetrical Bragg gratings is proposed, consisting of an ideal partially reflecting mirror placed between two wavelength-dependent uniform propagating sections. The model is simple, exact, and valid for every wavelength; it can be combined with other port-based models and is of great aid in the analysis and design of devices containing two or more Bragg gratings. As an application, the synthesis of dispersive Bragg gratings based Fabry-Pérot cavities is demonstrated. The conditions under which a Bragg-grating-based Fabry-Pérot cavity behaves exactly as an ideal dispersive Fabry-Pérot cavity are discussed. Experimental results that confirm the theoretical spectral response calculated by using the equivalent circuit are reported.     

Competitiveness of stationary planar low concentration photovoltaic modules using silicon cells: A focus on concentrating optics

The economical competitiveness of stationary Low Concentration Photovoltaic (LCPV) modules is evaluated, starting from detailed expressions of the Levelized Cost of Energy (LCoE). For trackless LCPV to be competitive with standard modules, the key approach is to maximize the performance of concentrating optics in terms of yearly averaged effective optical power ratio. To express this a novel parameter named P_ro,eff is introduced and its contribution to the expression of LCoE for LCPV modules is discussed. By comparing the LCoEs of standard and LCPV modules, threshold conditions for P_ro,eff and for the relative unitary cost of concentrating optics C_r are found, in dependence on the geometrical concentration gain G and as a function of other sensitive design parameters.Aiming at the maximization of P_ro,eff, the novel design of a modified prism-coupled compound parabolic stationary concentrator is introduced, as a trackless LCPV solution compatible with standard flat panel size, weight and installation infrastructures. It provides geometrical concentration gain G = 5, an acceptance angle of 24° and P_ro,eff = 81%, using a reflective primary concentrator and high refractive index dielectric for the secondary optics. A first experimental validation of the approach is given by a proof-of-concept prototype, implemented in commercially available polymethylmethacrylate, suitable for quasi-stationary installations requiring seasonal adjustment.     

Differential Polarization Delay in Coupled-Resonator Optical Waveguides

An integrated device capable of dynamically controlling the differential delay between two orthogonally polarized data channels is presented. The polarization-selective delay is induced by exploiting waveguide birefringence in a ring-resonator coupled resonator optical waveguide. A prototype realized in silicon-oxynitride technology is employed to manage the differential delay between two polarization-division-multiplexed channels modulated up to 10 Gb/s over several bit-slots. Reconfiguration is achieved by thermo-optic effect with 1-ps delay accuracy. Back-to-back and propagated bit-error-rate measurements show minor deterioration of the signal with negligible polarization crosstalk.