G. Vilela de Faria

Full polarization control for fiber optical quantum communication systems using polarization encoding

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.

Experimental polarization encoded quantum key distribution over optical fibres with real-time continuous birefringence compensation

In this paper 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 set-up 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??rad?s?1 are effectively compensated for. We demonstrate that our set-up 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.

Scattering Effects on QKD Employing Simultaneous Classical and Quantum Channels in Telecom Optical Fibers in the C‐band

Almost all Quantum Key Distribution experiments in optical fibers performed so far have used the so called “dark fibers,” which are exclusively used as the quantum channel. As quantum communications make its way towards commercial applications, there is a clear advantage in using fibers with simultaneous classical signals, via wavelength multiplexing, for that purpose. We show what is the noise impact of transmitting classical optical signals alongside a quantum channel for a fixed fiber length.

Fully powered-over-fibre remote antenna unit

In order to achieve a reliable ROF system with centralized wavelength operation, it is essential to provide enough power for remote antenna unit without the need of copper wires or any kind of batteries. Moreover, to ensure a high quality full-duplex communication when heterodyne generation is employed to obtain the microwave signal, a carefully choice of the laser sources is very important. Despite no wires or batteries and no laser stability control were used, error free transmission was obtained in an original scheme.

Feasibility of Centralized Passive Optical Network Monitoring Using Passive Optical Network-Tuned Optical Time-Domain Reflectometry

Abstract The increasing deployment of passive optical networks implies an equally increasing need for automatic monitoring systems. This article evaluates the feasibility of obtaining reliable information on fault position and loss by direct inspection of the optical time-domain reflectometry trace and via measurements of end-fiber reflectivity devices. Detailed calculations considering parameters often neglected, such as non-uniformity of splitters, fiber bending losses, as well as different Rayleigh backscattering factors and fiber attenuation coefficients, will be provided and experimentally verified. The limits and reliability of automated solutions for optical time-domain reflectometry passive optical network monitoring will be discussed.

Feasibility of centralized PON monitoring using PON-tuned OTDR

The increasing deployment of passive optical networks (PON) implies in an equally increasing need for automatic monitoring systems. Cost-effective solutions employing an optical time domain reflectometry (OTDR) system in the optical line terminal (OLT) have already been proposed, and “PON-tuned” OTDRs are already commercially available. Despite the claims from manufacturers and previous proposals in the literature, precise and reliable fault detection and localization are still unsolved problems for the telecom operators. In this paper, we evaluate the feasibility of obtaining reliable information on fault position and loss by direct inspection of the OTDR trace and via measurements of end-fiber reflectivity devices. Detailed calculations considering usually neglected parameters such as non-uniformity of splitters, fiber bending losses as well as different Rayleigh backscattering factors and fiber attenuation coefficients will be provided and experimentally verified. The limits and reliability of automated solutions for OTDR PON monitoring will be discussed.

Comparative analysis of interferometric measurements of PMD on optical fibers

Polarization modes dispersion (PMD) is one of the major factors that impose restrictions in the speed of optical communication links and some efforts must be done in order to properly quantify this effect. In this way we develop studies on the behavior of such a phenomenon, critical when light is transmitted through long optical fibers. The focus in this paper is to discuss the different behavior of PMD over different wavelengths ranges. Results indicate that PMD value varies, depending on the spectral region covered by the optical source. Measurements were performed using the interferometric method on three different types of optical fiber with three broadband optical sources covering the infrared spectral bands O, S, C and L. The evaluation of mean PMD is also discussed in the metrology concepts.

Dynamic PMD compensation at 43Gb/s for NRZ-ASK transmission

We report experimental PMD compensation in an ASK-NRZ transmission system at 43Gb/s. One- and two-section optical delay lines were evaluated. A large improvement in PMD robustness was achieved.

Optical coherence tomography applied to a human tissue cancer investigation

In recent years optical coherence tomography has been used as a characterization tool of biological tissues with a ten-fold improvement in resolution when compared to ultra-sound. In this paper we present time-domain optical coherence tomography measurements of ex-vivo human samples of stomach tissue with and without neoplasia. Intra-tissue depth of 400 µm with axial resolution of 8 µm was achieved.

Fast broadband swept source for optical coherence tomography

A fast broadband swept source for optical coherence tomography at 1,300 nm is presented. Axial resolutions as high as 3 µm were achieved over a measuring range up to 0.5 mm.