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Abstract:We propose and experimentally demonstrate that, contrary to what was thought up to now, an efficient BB84 operation is feasible using the double phase modulator (PM-PM) configuration in frequency-coded quantum key distribution systems without dispersion compensation. This is achieved by exploiting the chromatic dispersion provided by the fiber linking Alice and Bob. Thus, we refer to this system as dispersion supported or as the DS BB84 PM-PM configuration.

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The state of the art for calibration of photovoltaic reference devices has been reviewed recently. In the global sunlight method the total irradiance is measured by a pyrheliometer and a shaded pyranometer while the device is held at 25 °C. The method is supposed to have high repeatability even if the spectral irradiance is not measured, provided that the atmospheric conditions are selected carefully. Here we investigate seasonal variation of this method by calculating the spectral mismatch for crystalline silicon reference solar cells for spectra measured at air mass of 1.5 and the defined reference spectral irradiance. A seasonal variation is found with negligible mismatch for certain periods but significant deviations for other periods. Based on this a modified global sunlight method using global natural sunlight for the calibration of photovoltaic reference devices is proposed, using measured spectral irradiance and applying mismatch correction.

Quantum wells offer advantages in conventional bulk tandem solar cells since they allow the independent tailoring of the absorption edge of either cell with no lattice mismatch and subsequent relaxation. We describe progress in the band gap engineering of InGaP/GaAs solar cells using strain balanced quantum wells and present a tandem quantum well structure which has achieved 30.6% efficiency under 54 suns AM1.5g. This is a record for photovoltaic nanostructured devices. We predict realistic efficiencies of 34% under 600suns, AM1.5d low AOD for optimized devices. Finally, the possibility and potential gains of introducing quantum wells into both cells of an InGaP/GaAs device are discussed.

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