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Red blood cells (RBCs) stored in hypothermic environments for the purpose of transfusion have been documented to undergo structural and functional changes over time. One sign of the so-called RBC storage lesion is irreversible damage to the cell membrane. Consequently, RBCs undergo a morphological transformation from regular, deformable biconcave discocytes to rigid spheroechinocytes. The spherically shaped RBCs lack the deformability to efficiently enter microvasculature, thereby reducing the capacity of RBCs to oxygenate tissue. Blood banks currently rely on microscope techniques that include fixing, staining and cell counting in order to morphologically characterize RBC samples; these methods are labor intensive and highly subjective. This study presents a novel, high-throughput RBC morphology characterization technique using image flow cytometry (IFC). An image segmentation template was developed to process 100,000 images acquired from the IFC system and output the relative spheroechinocyte percentage. The technique was applied on samples extracted from two blood bags to monitor the morphological changes of the RBCs during in vitro hypothermic storage. The study found that, for a given sample of RBCs, the IFC method was twice as fast in data acquisition, and analyzed 250-350 times more RBCs than the conventional method. Over the lifespan of the blood bags, the mean spheroechinocyte population increased by 37%. Future work will focus on expanding the template to segregate RBC images into more subpopulations for the validation of the IFC method against conventional techniques; the expanded template will aid in establishing quantitative links between spheroechinocyte increase and other RBC storage lesion characteristics.

We investigate theoretically the spontaneous four-wave mixing (FWM) process that occurs in optical waveguides, as a source of quantum correlated photon-pairs. We consider that the waveguide used to implement the spontaneous FWM process presents a high value of nonlinear parameter, γ = 93.4 W-1m-1, and a non-negligible value of loss coefficient, α = 133.3 dB/m. Moreover, the theoretical model also consider the Raman scattering that inevitably accompanies the FWM process, and generates time-uncorrelated (noise) photon pairs. We use the coincident-to-accidental ratio (CAR) as a figure of merit of the photon pair source, and we were able to observe a CAR of the order of 65 in a high loss regime. After, we use the time-correlated photon pairs generated by the spontaneous FWM process to implement a heralded single photon source at waveguide output. In this scenario, the detection of one photon of the pair heralds the presence of the other photon. The quality of the source was studied by the evaluation of the second order coherence function for one photon of the pair conditioned by the detection of its twin photon. We observe that the presence of a high loss coefficient tends to improve the quality of the photon source, when compared with the lossless regime, even considering the Raman noise photons. We obtain a value for the conditional second order coherence function of the order of 0.11 in absence of loss, and a value of 0.03 for a loss coefficient of 133.3 dB/m.

In this paper, the implementations of clock and carrier recovery in digital domain are analyzed. Hardware implementation details, resources estimation and real-time results are presented. Analog-to-Digital Converters (ADC), operating at 1.25Gsa/s, and a Virtex-6 Field-Programmable Gate Array (FPGA), have been used, allowing the implementation of a real-time Quadrature Phase Shift Keying (QPSK) system operating at 1.25Gb/s. The real-time mode operation is successfully demonstrated over 80 km of Standard Single Mode Fiber (SSMF).

We present a calculation of the required number of bits to be received in a system of communications in order to achieve a given level of confidence. The calculation assumes a binomial distribution function for the errors. The function is numerically evaluated and the results are compared with the ones obtained from Poissonian and Gaussian approximations. The performance in terms of the signal-to-noise ratio is also studied. We conclude that for higher number of errors in detection the use of approximations allows faster and more efficient calculations, without loss of accuracy.

We perform a thorough performance and complexity analysis of a recently proposed Volterra series nonlinear equalizer (VSNE) for digital post-compensation of nonlinear fiber impairments in high-speed and long-haul coherent optical communication systems. Using a maximum absolute value selection criteria, we implement a pruning strategy for the matrix-based VSNE and compare its performance/complexity with the symmetric VSNE (symVSNE) and simpli ed VSNE (simVSNE) algorithms. The theoretical analysis is supported by simulation results obtained for a single-channel 224 Gb/s PM-16QAM transmission system with a signal propagation distance of 1920 km.

The tunable mode conversion between symmetric and antisymmetric optical modes induced by acoustic flexural waves in optical microwires is proposed. The acoustic frequency dictates the resonant coupling between the optical modes, and consequently, the modes in which the mode conversion occurs. On the other hand, the efficiency of the mode conversion can be controlled by the acoustic wave amplitude. Moreover, symmetric modes can also be excited by a double resonant coupling between a symmetric and an antisymetric mode, and further between the antisymmetric mode excited and another symmetric mode, leading to a mode conversion between symmetric modes.

We show how to generate, encode, transmit and detect single photons. By using single photons we can address two of the more challenging problems that communication engineers face nowadays: capacity and security. Indeed, by decreasing the number of photons used to encode each bit, we can efficiently explore the full capacity to carry information of optical fibers, and we can guarantee privacy at the physical layer. We present results for single and entangled photon generation. We encode information in the photons polarization and after transmission we retrieve that information. We discuss the impact of fiber birefringence on the photons polarization.

We developed a system to investigate resonant nonlinear optical interactions in acetylene molecules, confined in a hollow-core photonic crystal fiber (HC-PCF), using light injection through a low-loss splice from one end of the fiber, allowing us to work at low power. Electromagnetically induced transparency (EIT) was observed in the 1500 nm telecommunications window.

In classical cryptography, the bit commitment scheme is one of the most important primitives. We review the state of the art of bit commitment protocols, emphasizing its main achievements and applications. Next, we present a practical quantum bit commitment scheme, whose security relies on current technological limitations, such as the lack of long-term stable quantum memories. We demonstrate the feasibility of our practical quantum bit commitment protocol and that it can be securely implemented with nowadays technology.

In this paper we present an experimental characterization of a highly nonlinear silica fiber. It includes the determination of the fiber effective nonlinear parameter using the nonlinear four-wave mixing process. From the experimental results, a value γ = 10.6 W −1 km −1 has been obtained for the nonlinear parameter in the co-polarized case, which was reduced to γ = 9.4 W −1 km −1 in the case of a decorrelated state of polarization between pump and signal waves. A threshold power of 17.8mW was found for the stimulated Brillouin scattering process. A Raman gain curve extending over a frequency range of 25 THz, with a peak value shifted by 13.1 THz from the pump frequency, was also measured.

The all-optical control of light parameters such as intensity profile, power, phase, modes, wavelength, and state of polarization is viewed as a cornerstone for the feasibility of future high-speed fiber-optic communication networks. In particular, the ability to repolarize light with an almost unitary efficiency represents a huge advantage over the standard polarizers that waste 50% of the unpolarized light. In this paper, we show how to obtain a nonlinear lossless repolarization of light in low-birefringence optical fibers. A characterization of the stimulated Raman scattering based polarization pulling process is also presented, with particular focus on the optimization of several parameters such as fiber length, polarization mode dispersion coefficient, correlation length, and signal and auxiliar pump power regimes. Finally, we compare the co-propagating and counter-propagating signal and pump schemes, presenting the main advantages and disadvantages of each scenario and its suitability for particular applications.

In this paper we present results from the study of optical signal regeneration using Mamyshev type regenerator. We have performed the simulations and experimental characterization of regenerator by obtaining it`s transfer function and output optical signal to noise ratio measurements for two different filters - fixed and a tunable optical filter. Investigated regenerator setup consists of a high power erbium doped fiber amplifier, highly nonlinear fiber and a single stage optical filtering. Signal used for regeneration was an on-off keying return to zero code 40 Gbps pulse sequence. To find out optimum filter pass-band shift from signal`s central wavelength the regenerator`s transfer function was measured. Results show that highest output signal to noise ratio improvement for the fixed filter is at 0.6nm shift and amplifier output power set to 63 mW. While the tunable filter shift is 0.7nm at the 100 mW power level.

We present a low-loss fusion splicing of a non-linear photonic-crystal fiber (NL-PCF) with a single-mode fiber (SMF), helped by an intermediate fiber, using a electric-arc splicer. We also analysed the splice loss between SMF and intermediate fiber, as a function of the electrical discharge duration, to achieve a low-loss transition between SMF and intermediate fiber, through a thermally expanded core splice (TEC). The NL-PCF has a external cladding diameter of 105 μm , a core diameter of 1.7 μm and mode-field diameter (MFD) of 1.5 μm . We also performed mechanical strength tests to verify the robustness of the splice joints obtained.

Optical regeneration is a key technology for next generation high-speed optical networks. All-optical regeneration can increase the reach of transmission systems without expensive optical-to-electrical signal conversion. Among various regeneration schemes, the Mamyshev regenerator attracted particular attention due to its simplicity and robustness. In this paper, we report an all-optical regeneration of a 40 Gbit/s return-to-zero signals. The regenerator proposed is based on the standard Mamyshev regenerator, which the temporal intensity profile and the average power are recovered. This device allows regenerating the signal without wavelength shift, decreasing the complexity and cost when compared with others 2-R regenerators reported. The input signal is first spectrally broadened, by self-phase modulation, after passing through a highly nonlinear fiber. Afterwards, the signal is amplified by a bidirectional erbium doped fiber amplifier, and offset spectral backscattering sliced by a fiber Bragg grating. In the second stage, the signal is spectral broadening and filtered recovering the input wavelength. The transfer function for the regenerator proposed is measured, and the all-optical regeneration is assessed by means of bit-error-rate measurements as well as real-time observation of the signal.

The rapid increase on the information sharing around the world, leads to an utmost requirement for capacity and bandwidth. However, the need for security in the transmission and storage of information is also of major importance. The use of quantum technologies provides a practical solution for secure communications systems. Quantum key distribution (QKD) was the first practical application of quantum mechanics, and nowadays it is the most developed one. In order to share secret keys between two parties can be used several methods of encoding. Due to its simplicity, the encoding into polarization is one of the most used. However, when we use optical fibers as transmission channels, the polarization suffers random rotations that may change the state of polarization (SOP) of the light initially sent to the fiber to a new one at the output. Thus, in order to enable real-time communication using this encoding method it is required the use of a dynamic control system. We describe a scheme of transmission of quantum information, which is based in the polarization encoding, and that allows to share secret keys through optical fibers without interruption. The dynamic polarization control system used in such scheme is described, both theoretically and experimentally. Their advantages and limitations for the use in quantum communications are presented and discussed.

Single photon sources are fundamental elements for quantum information science, mainly for quantum key distribution (QKD) applications. Nevertheless, on-demand single photon sources are difficult to obtain, and their implementation in a practical application, such as QKD, demands further developments. A different approach to a single photon source is based on the generation of quantum correlated photon-pairs. In that case, the detection of one photon of the pair heralds the presence of the second photon. In this work, we present a heralded single photon source based on the spontaneous four-wave mixing (FWM) process in optical fibers. We characterize theoretically the heralded photon source by means of the conditional second-order coherence function, g c (2) , with g c (2) = 0 for a perfect single photon source. We observe the nonclassical nature of the source, with g c (2) ≪ 1 far below the classical limit. Our results also show that the Raman scattering in general degrades the quality of the source, due to the generation of uncorrelated photons. However, our findings show that in some frequency regimes we are able to observe a g c (2) ≈ 10 −3 . Moreover, our analysis shows that the propagation of the photons in a standard single mode fiber (SSMF) does not change significantly the value of g c (2) , for distances of L < 25/α, with α the loss coefficient of the SSMF. This results can help to guide the development of single photon sources for quantum information applications.

The supercontinum generation has been achieved mainly by two different approaches, namely, with femtosecond intense pulses or using a continuous wave laser or larger pulses centered on the anomalous dispersion region. In order to improve temporal coherence, it has been suggested the introduction of a pulse seed or the propagation of both a large pulse pump and a small weaker continuous wave to control the soliton fission. Here we propose supercontinuum generation using a hybrid input, we pump with a continuous laser and copropagate a picosecond signal. We compare the bandwidth of the supercontinuum using only the continuous pump or the hybrid setup. Simulations of the generalized Schrodinger equation, using an adequate input-noise model to reproduce the spectrum of the continuous signal, are performed in order to investigate the supercontinuum generation in the optical communication window under different dispersion regimes.

Quantum communications can provide almost perfect security through the use of quantum laws to detect any possible leak of information. We discuss critical issues in the implementation of quantum communication systems over installed optical fibers. We use stimulated four-wave mixing to generate single photons inside optical fibers, and by tuning the separation between the pump and the signal we adjust the average number of photons per pulse. We report measurements of the source statistics and show that it goes from a thermal to Poisson distribution with the increase of the pump power. We generate entangled photons pairs through spontaneous four-wave mixing. We report results for different type of fibers to approach the maximum value of the Bell inequality. We model the impact of polarization rotation, attenuation and Raman scattering and present optimum configurations to increase the degree of entanglement. We encode information in the photons polarization and assess the use of wavelength and time division multiplexing based control systems to compensate for the random rotation of the polarization during transmission. We show that time division multiplexing systems provide a more robust solution considering the values of PMD of nowadays installed fibers. We evaluate the impact on the quantum channel of co-propagating classical channels, and present guidelines for adding quantum channels to installed WDM optical communication systems without strongly penalizing the performance of the quantum channel. We discuss the process of retrieving information from the photons polarization. We identify the major impairments that limit the speed and distance of the quantum channel. Finally, we model theoretically the QBER and present results of an experimental performance assessment of the system quality through QBER measurements.

A single-photon source based on the stimulated four-wave mixing (SFWM) process in optical fibers is presented. At the output of the source, the state of polarization (SOP) of the photons can be adjusted in order to obtain any linear polarization. A theoretical model to describe the average photon counts recorded in the avalanche photodiodes (APDs) is presented. The experimental results show an accurate detection of two non-orthogonal linear SOPs after propagation through a 60 km quantum channel, and good agreement with theory. This source, operating in a low power regime, can be used for quantum key distribution (QKD) using polarization-encoding in quantum communications.

In this work we develop an analysis of polarization control schemes suitable for quantum key distribution systems. Both time division multiplexing and wavelength division multiplexing based schemes are considered. A model for the optimization of the temporal separation between reference pulses and polarization encoded photons is presented. The model accounts for the reference pulse shape, the single photon detector gate width, and the respective temporal separation between them. The theoretical results are validated through experimental measurements. These results can be used to optimize the performance of polarization control schemes and therefore to optimize the polarization encoded quantum key distribution systems.

We propose the use of modal engineered tapered optical fibers for single photon interferometry experiments. Tapered optical fibers (TOF) can be designed to function as tunable Mach-Zehnder (MZ) type modal single photon interferometer. The MZ design criteria of tunability, visibility, and wavelength range are inherently interconnected in TOF's, which makes the design complex. Moreover, novel TOF related design criteria, like loss minimization, have to be taken into account. Design guidelines can be based on a semi-analytical approach assuming multiple two mode beat equations for different mode power amplitudes. Linearization permits to obtain a set of simple and robust analytical relations that correlate the TOF design parameter with the TOF and MZI optical properties. By focusing on the tunability, we have demonstrated a device that permits to be tuned between local minima and maxima.

We present the cost impact of establishing new links in mesh optical networks. The analysis is based on an analytical study for quickly calculate the transmission and bandwidth management systems costs. Results show that each network has a mean nodal degree that minimizes the total cost. information. The aims of the present study consist in evaluating the impact of the number of links on network costs and to gain a deeper insight into the network dimensioning issue. To accomplish this, in this paper we focused on five elements: optical line terminals, optical transponders, optical amplifiers, optical and electrical bandwidth management. The quantities of these elements provide enough information to account for transmission costs (CTRANS) and bandwidth management costs (CBWM ). Furthermore, allow us to analyze the impact of each element over the total cost (CT ) in function of the mean nodal degree. The optical fiber cable is part of the transmission system. Since there exist a vast amount of already installed dark fibers, the operators can only light up the required fibers and equip them with transponders, amplifiers and regenerators. Thus, we assume fiber cost as an operational cost, and it is not considered in the CAPEX.

A technique for the extraction of laser rate equation parameters to be used in the simulation of high-speed optical telecommunication systems is described. The simulation using the extracted parameters exhibits good agreement with the experimental results, even for a large current modulation and soliton pulses. A model, which represents the parasite effect introduced by the mount fixture, was built. The model presented here is ready to use in the simulation of high-speed lightwave systems.

This paper summarizes the research activities of the optical communications group at University of Aveiro and Institute of Telecommunications-Aveiro pole. Several activities like clock recovery systems, both electrical and all optical, electrical equalizers for very high bit rate DST systems, post-detection filters for multigigabit optical receivers, soliton systems, simulation work on WDM, DST, EDFA and short pulse generation for high bit rate systems are presented.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.