A real-time polarization control system employing two non-orthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results on the wavelength multiplexing setup show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel.

We demonstrate an active polarization drift compensation scheme for optical fibres employed in a quantum key distribution experiment with polarization encoded qubits. The quantum signals are wavelength multiplexed in one fibre along with two classical optical side channels that provide the control information for the polarization compensation scheme. This setup allows us to continuously track any polarization change without the need to interrupt the key exchange. The results obtained show that fast polarization rotations of the order of 40 π rad/s are effectively compensated. We demonstrate that our setup allows continuous quantum key distribution even in a fibre stressed by random polarization fluctuations. Our results pave the way for Bell-state measurements using only linear optics with parties separated by long distance optical fibres.

a combination of radiated susceptibility plus conducted susceptibility. Sensors with cables of ECG equipments are so sensitive and open to be distorted. These induced current is then driving through electronics by conduction mechanisms. CONCLUSIONSABSTRACT: We experimentally demonstrate the compatibility of wavelength multiplexed active polarization stabilization for quantum communication in an optical fiber carrying telecom traffic. One of the feedback control channels contains a 9.953 Gb/s datastream generated from a BER meter. We verify the ability to transmit single-photons in the two opposite directions of a 23-km optical fiber spool, while maintaining their state of polarization stable and a classical BER in the feedback channel error-free, during 6 h of continuous operation.ABSTRACT: This letter deals with a GaAs monolithic microwave integrated circuit (MMIC) Doherty power amplifier (DPA) for X-band systems. To the best of authors' knowledge, it represents the first DPA realization in the X-band frequency range. Experimental results showed a 30-dBm saturated output power and a drain efficiency greater than 53% at 9.5 GHz. Moreover, in the 6-dB power back-off (from 18 to 24 dBm input power), an amplitude modulation (AM/AM) distortion lower than 1 dB is also demonstrated with an average efficiency greater than 50%.

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