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We study quantum correlations and discord in a bipartite continuous variable hybrid system formed by linear combinations of coherent states $|\alpha\rangle$ and single photon added coherent states (SPACS) of the form $|\psi\rangle_{\text{dp(pa)}}= \mathcal{N}/\sqrt{2} (\hat{a}^\dagger |\alpha\rangle_a |\alpha\rangle_b \pm \hat{b}^\dagger |\alpha\rangle_a |\alpha\rangle_b)$. We stablish a relationship between the quantum discord with a local observable (the quadrature variance for one sub-system) under the influence of scattering and phase fluctuation noise. For the pure states the quantum correlations are characterized by means of measurement induced disturbance (MID) with simultaneous quadrature measurements. In a scenario where homodyne conditional measurements are available we show that the MID provides an easy way to select optimal phases to obtain information of the maximal correlations in the channels. The quantum correlations of these entangled states with channel losses are quantitatively characterized with the quantum discord (QD) with a displaced qubit projector. We observe that as scattering increases, QD decreases monotonically. At the same time for the state $|\psi\rangle_{\text{dp}}$, QD is more resistant to high phase fluctuations when the average photon number $n_0$ is bigger than zero, but if phase fluctuations are low, QD is more resistant if $n_0=0$. For the dp model with scattering, we obtain an analytical expression of the QD as a function of the observable quadrature variance in a local sub-system. This relation allows us to have a way to obtain the degree of QD in the channel by just measuring a local property observable such as the quadrature variance. For the other model this relation still exists but is explored numerically. This relation is an important result that allows to identify quantum processing capabilities in terms of just local observables., Comment: 27 pages, 14 figures

We present a nondestructive method that allows the spectral birefringence characterization of single-mode erbium-doped fibers within the amplification band. Using the same optical set up and the predicted polarization eigenmodes, the quality of the results has been verified. The results obtained for three commercial erbium-doped fibers with different erbium concentrations are shown. For two of them, the values measured for the elliptical birefringence shift, for different signal wavelengths, from having a dominant circular component to exhibit a dominant linear component.

Few research institutions from Mexico work together to finalize the integration of a technological demonstration microsatellite called Satex, aiming the launching of the first ever fully designed and manufactured domestic space vehicle. The project is based on technical knowledge gained in previous space experiences, particularly in developing GASCAN automatic experiments for NASA's space shuttle, and in some support obtained from the local team which assembled the Mexico-OSCAR-30 microsatellites. Satex includes three autonomous payloads and a power subsystem, each one with a local microcomputer to provide intelligent and dedicated control. It also contains a flight computer (FC) with a pair of full redundancies. This enables the remote maintenance of processing boards from the ground station. A fourth communications payload depends on the flight computer for control purposes. A fifth payload was decided to be developed for the satellite. It adds value to the available on-board computers and extends the opportunity for a developing country to learn and to generate domestic space technology. Its aim is to provide automatic maintenance capabilities for the most critical on-board computer in order to achieve continuous satellite operations. This paper presents the virtual computer architecture specially developed to provide maintenance capabilities to the flight computer. The architecture is periodically implemented by software with a small amount of physical processors (FC processors) and virtual redundancies (payload processors) to emulate a hybrid redundancy computer. Communications among processors are accomplished over a fault-tolerant LAN. This allows a versatile operating behavior in terms of data communication as well as in terms of distributed fault tolerance. Obtained results, payload validation and reliability results are also presented.

We present a simple method for the localization of a loss region for a fiber-optic alarm-condition sensor based on the measurement of transmitted and Rayleigh backscattered power. Bending the sensing fiber affects both the transmitted and backscattered power of unmodulated continuous-wave light that is launched into the fiber. The position of the loss region is determined from unique relationships between normalized transmitted and backscattered powers for different locations of the disturbance along the test fiber. The localization of a strong disturbance with an estimated accuracy of few meters along a few km-length single-mode test fiber was demonstrated.

In this paper we present simple interferometric technique for thin film testing with GaAs:Cr adaptive photodetectors based on the effect of the non-steady-state photoelectromotive force. The technique needs no special vibroinsulation and automatically adjusts and keeps the operation point of the interferometer. Two different interferometric schemes with GaAs:Cr adaptive photodetectors are reported. A modified Mach-Zehnder interferometer with adaptive photodetector is used for the measurement of piezoelectric coefficient of the thin film. A two-beam polarization interferometer with adaptive photodetector is used for the measurement of effective differential Pockels coefficient r e = r 33 -(n 0 /ne) 3 r 13 . It is shown that two-beam polarization technique allows measurement of the Pockels coefficient of thin film with a strong Fabry-Perot effect that usually presents in ferroelectric thin film. Strong hysteresis effect with a slightly asymmetric form of the hysteresis loop was observed at the dependence of d 33 and r e coefficients of the PZT thin film versus DC electric field. The values of d 33 and r e are in agreement with known data.

The relative insensitivity of erbium doped fiber amplifiers to the state of polarization of the input signal is considered as an advantage when these devices are used within communication networks. On the other hand, in order to use them in combination with interferometric optical fiber sensor, they should be able to maintain the input polarization state. In this work we presented the results obtained for the performance characterization of an EDFA built with a helically wound monomode erbium fiber. The use of a regular winding allows the control of the evolution of the state of polarization of the optical signal to be amplified. We include results of the geometrical and birefringence characterization of two helices built with tow different commercial erbium fibers. The amplification of polarized signals has been evaluated for the C band. It presents a high gain for small as well as for saturated signals. In regard with the noise due to the amplified spontaneous emission, it was evaluated also for small as well as for saturated signals. The values we measured are below the theoretical predictions based on typical EDFAs built with an irregularly wound erbium fiber.

The volution of the state of polarization along an out-of- plane trajectory has been widely studied for monomode optical fibers. To demonstrate the validity of our proposal we compare the results predicted by our model with experimental result obtained for helically wound optical fibers and the conoscopic patterns obtained for GRIN lenses when oblique illumination is used.

In this work we apply a simple, non-destructive method we developed for the birefringence characterization of helically wound passive fibers to monomode erbium-doped optical fibers. This method is based on the Jones matrix model developed by JN Ross for helically wound optical fibers. In the case of passive fibers Ross model is correct if the polarization evolution of light is measured with respect o an input local reference frame defined by the helix geometry; but in order to use a fixed reference frame it is necessary to consider the rotation of the plane of polarization introduced by parallel transport along the fiber. The use of Poincare's method and Mueller calculus simplifies the physical interpretation of the results. The birefringence properties of two helically wound erbium fibers are tested in the neighborhood of the amplification band showing that in this case the spectral response has a much stronger variation than in the case of passive step- index monomode fibers. Despite the topological contribution due to the parallel transport of the reference frame, with method where presented provides an easy way to measure the total linear retardation induced by the fiber curvature and the total circular retardation indued by the fiber torsion. Experimental results obtained for two commercial EDF are presented.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In a helically wound single-mode fiber the mode degeneracy is lifted by the geometric form and the photo-elastic effect. Fiber bending induces linear birefringence' and the presence of torsion is responsible for circular birefringence.2 Considering the geometrical properties of a helix and using Jones calculus, it has been shown3 that a helically wound fiber can be described as the combination of two distributed homogeneous retarders: a linear retarder and a circular retarder. Since linear and circular retardation can be easily followed on the Poincare sphere, we use Mueller calculus to describe the polarization optics of helical fiber structures.4 Because of the strong absorption and the subsequent emission that active fibers present within the amplification band, the signal becomes depolarized and it is not possible to characterize the birefringence properties of active fibers at these wavelengths. In this work, the birefringence performance of active fibers is evaluated in the neighborhood of the amplification band, using signals with a high signal to noise ratio at the active fiber output. We present the birefringence characterization of a helically wound erbium fiber. This helical fiber structure was built with a commercial fiber. Since the birefringence parameters we measured agree with the values predicted by the theoretical model, we propose that we can make use of this model to design the helix structure and, to select the input polarization states of the pump and the signal that can be used to control the polarization evolution of the amplified signal as it propagates along the fiber.

The polarization optical properties of single mode fibers are important in those applications based on the use of coherent polarized light, such as fiber optic interferometric sensors and coherent communication systems. Various birefringence mechanisms and combinations of them have been developed to control the polarization evolution of light along the fiber. Since 1977 when A.Papp and H.Harms1 suggested the application of helical core fibers for this purpose, their polarization properties have been studied by several authors.24 In I 984 J.N. Ross2 showed that helically wound monomode fibers behave as the combination of a distributed linear retarder and a distributed circular retarder. Since linear and circular retardation can be easily followed on the Poincare sphere, this representation of polarized light results adequate for helical fibers. In this work the non-destructive evaluation of the equivalent optical activity and the equivalent linear retardation of a fiber helix are performed using the trajectory described on the Poincare sphere when the orientation of the linearly polarized light at the input rotates 360°. The results we obtain are compared with the values determined for the linear and circular retardation using Ross model and an input circular or linear polarization. We present preliminary results obtained for the birefringence characterization of two helically wound fibers built with .-l4m and —27m of a telecommunications fiber ( I 550nm).

The polarization dependent performance of EDFA has been explained in terms of polarization hole burning, considering that the erbium sites in the silica matrix preserve its random nature. Although typical EDFAs are built with an erbium fiber longer than 10 m (hence the active fiber is necessarily wound) the influence of the bending has not been included in the investigation of this effect. To verify the relevance of bending induced birefringence, a helically- wound active fiber has been used to build an EDFA. The characterization of this helically-wound optical amplifier has shown that the polarization dependent performance was enhanced. The stronger link between the states of polarization of the signal wave, the pump wave and the active fiber birefringence axes was used to show that a selective excitation of the erbium ions by a polarized pump and a selective de-excitation of those ions by a polarized signal are the origin of the polarization dependent performance of EDFAs.

The development of a new fiber Bragg grating multiplexing technique is reported. The technique is based on a twin Bragg grating sensor configuration and exploits a combination of wavelength- and frequency-domain multiplexing. We demonstrate that very weak Bragg gratings with reflexivity of approximately 0.5 percent or less can be efficiently used by this technique. Experimental results presented in the paper and theoretical estimates indicate that the interrogation of more than 100-element serial array sensor system is feasible.