Influence of cardiac hemodynamic variables on retinal vessel density measurement on optical coherence tomography angiography in patients with myocardial infarction.

INTRODUCTION: Quantitative measurements of retinal microvasculature by optical coherence tomography angiography (OCT-A) have been used to assess cardiovascular risk profile. However, to date, there are no studies focusing on OCT-A imaging in the setting of the altered hemodynamic status found in high-risk cardiovascular patients. METHODS: To determine the potential association between retinal vascular density on OCT-A and a comprehensive battery of hemodynamic variables in patients with myocardial infarction (MI) using data from the acute phase and at 3 months follow-up after cardiac rehabilitation. This prospective longitudinal study included patients who presented with MI in the cardiology intensive care unit at Dijon University Hospital. Main outcomes and measurements were retinal vessel density on OCT-A, hemodynamic status based on left ventricular ejection fraction (LVEF), and indexed cardiac output during the acute phase of myocardial infarction and at 3 months follow-up. RESULTS: Overall, 30 patients were included in this pilot study. The median (IQR) age was 64 years (55-71) with 87% men. At admission, the mean (SD) LVEF was 53% (11), and the mean indexed cardiac output was 2.70 (0.83) L/min/m2. On OCT-A, the mean inner retinal vascular density was 19.09 (2.80) mm-1. No significant association was found between retinal vascular density and hemodynamic variables. CONCLUSION: We found no significant association between retinal vascular density on OCT-A and hemodynamic variables in the acute phase of a myocardial infarction or after 3 months of cardiac rehabilitation. Therefore, OCT-A findings do not seem to be influenced by the hemodynamic changes associated with myocardial infarction.

Temporal spying and concealing process in fibre-optic data transmission systems through polarization bypass.

Recent research has been focused on the ability to manipulate a light beam in such a way to hide, namely to cloak, an event over a finite time or localization in space. The main idea is to create a hole or a gap in the spatial or time domain so as to allow for an object or data to be kept hidden for a while and then to be restored. By enlarging the field of applications of this concept to telecommunications, researchers have recently reported the possibility to hide transmitted data in an optical fibre. Here we report the first experimental demonstration of perpetual temporal spying and blinding process of optical data in fibre-optic transmission line based on polarization bypass. We successfully characterize the performance of our system by alternatively copying and then concealing 100% of a 10-Gb s(-1) transmitted signal.

A universal optical all-fiber Omnipolarizer.

Wherever the polarization properties of a light beam are of concern, polarizers and polarizing beamsplitters (PBS) are indispensable devices in linear-, nonlinear- and quantum-optical schemes. By the very nature of their operation principle, transformation of incoming unpolarized or partially polarized beams through these devices introduces large intensity variations in the fully polarized outcoming beam(s). Such intensity fluctuations are often detrimental, particularly when light is post-processed by nonlinear crystals or other polarization-sensitive optic elements. Here we demonstrate the unexpected capability of light to self-organize its own state-of-polarization, upon propagation in optical fibers, into universal and environmentally robust states, namely right and left circular polarizations. We experimentally validate a novel polarizing device - the Omnipolarizer, which is understood as a nonlinear dual-mode polarizing optical element capable of operating in two modes - as a digital PBS and as an ideal polarizer. Switching between the two modes of operation requires changing beam's intensity.

Demonstration of polarization pulling using a fiber-optic parametric amplifier.

We report the observation of all-optical polarization pulling of an initially polarization-scrambled signal using parametric amplification in a highly nonlinear optical fiber. Broadband polarization pulling has been achieved both for the signal and idler waves with up to 25 dB gain using the strong polarization sensitivity of parametric amplifiers. We further derive the probability distribution function for the final polarization state, assuming a randomly polarized initial state, and we show that it agrees well with the experiments.

All-optical nonlinear processing of both polarization state and intensity profile for 40 Gbit/s regeneration applications.

In this paper, we report all-optical regeneration of the state of polarization of a 40-Gbit/s return-to-zero telecommunication signal as well as its temporal intensity profile and average power thanks to an easy-to-implement, all-fibered device. In particular, we experimentally demonstrate that it is possible to obtain simultaneously polarization stabilization and intensity profile regeneration of a degraded light beam thanks to the combined effects of counterpropagating four-wave mixing, self-phase modulation and normal chromatic dispersion taking place in a single segment of optical fiber. All-optical regeneration is confirmed by means of polarization and bit-error-rate measurements as well as real-time observation of the 40 Gbit/s telecommunication signal.

Observation of light-by-light polarization control and stabilization in optical fibre for telecommunication applications.

In many photonics applications, especially in optical fibre based systems, the state of polarization of light remains so far an elusive uncontrolled variable, which can dramatically affect the performances of that systems and which one would like to control as finely as possible. Here, we experimentally demonstrate light-by-light polarization control via a nonlinear effect occurring in single mode optical fibre. We observe a polarization attraction and stabilization of a 10 Gbit/s optical telecommunication signal around 1550 nm. We also validate the potentiality of the device to annihilate very fast nanosecond polarization bursts. This result confirms yet another fascinating possibility to all-optical control the light properties in optical fibre.

Polarization attraction using counter-propagating waves in optical fiber at telecommunication wavelengths.

In this work, we report the experimental observation of a polarization attraction process which can occur in optical fibers at telecommunication wavelengths. More precisely, we have numerically and experimentally shown that a polarization attractor, based on the injection of two counter-propagating waves around 1.55microm into a 2-m long high nonlinear fiber, can transform any input polarization state into a unique well-defined output polarization state.

Experimental investigation of Brillouin and Raman scattering in a 2SG sulfide glass microstructured chalcogenide fiber.

In this work, we investigate the Brillouin and Raman scattering properties of a Ge15Sb20S65 chalcogenide glass microstructured single mode fiber around 1.55 microm. Through a fair comparison between a 2-m long chalcogenide fiber and a 7.9-km long classical single mode silica fiber, we have found a Brillouin and Raman gain coefficients 100 and 180 larger than fused silica, respectively.

All-optical extinction-ratio enhancement of a 160 GHz pulse train by a saturable-absorber vertical microcavity.

A vertical-access passive all-optical gate has been used to improve the extinction ratio of a 160 GHz pico-second pulse train at 1555 nm. An extinction ratio enhancement of 6 dB is observed within an 8 nm bandwidth. Such a device is a promising candidate for low-cost all optical reamplication and reshaping (2R) regeneration at 160 Gbits/s.

Frequency tunable polarization and intermodal modulation instability in high birefringence holey fiber.

We present an experimental analysis of polarization and intermodal noise-seeded parametric amplification, in which dispersion is phase matched by group velocity mismatch between either polarization or spatial modes in birefringent holey fiber with elliptical core composed of a triple defect. By injecting quasi-CW intense linearly polarized pump pulses either parallel or at 45 degrees with respect to the fiber polarization axes, we observed the simultaneous generation of polarization or intermodal modulation instability sidebands. Furthermore, by shifting the pump wavelength from 532 to 625 nm, we observed a shift of polarization sidebands from 3 to 8 THz, whereas intermodal sidebands shifted from 33 to 63 THz. These observations are in excellent agreement with the experimental characterization and theoretical estimates of phase and group velocities for the respective fiber modes.

Incoherent modulation instability in instantaneous nonlinear Kerr media.

We demonstrate theoretically and experimentally in an optical fiber system that partially temporally incoherent light exhibits modulational instability during its propagation in an instantaneous response nonlinear medium. We show that the modulation frequency and gain are substantially increased with respect to the corresponding values of coherent modulational instability.

Regenerative 40 Gbit/s wavelength converter based on similariton generation.

We present an all-optical regeneration technique based on spectral filtering of self-similar parabolic pulses (similaritons). In particular, we demonstrate numerically and experimentally that ghost pulses, which occur in the zero bit slots of telecommunication pulse trains, can be effectively suppressed. These results are obtained with a 40 Gbit/s pulse train.

Spectral broadening of a partially coherent CW laser beam in single-mode optical fibers.

The nonlinear propagation of a partially coherent continuous-wave laser beam in single-mode optical fibers is investigated both theoretically and experimentally, with a special attention to the zero-dispersion wavelength region where modulation instability is expected. Broadband asymmetric spectral broadening is reported experimentally and found in fairly good agreement with a numerical Schrödinger simulation including a phase-diffusion model for the partially coherent beam. This model shows in addition that the underlying spectral broadening mechanism relies not only on modulation instability but also on the generation of high-order soliton-like pulses and dispersive waves. The coherence degradation which results from these ultrafast phenomena is confirmed by autocorrelation measurement.

Experimental demonstration of 160-GHz densely dispersion-managed soliton transmission in a single channel over 896 km of commercial fibers.

We experimentally demonstrate the first 160-GHz densely dispersion-managed soliton transmission in a single channel at 1550 nm over nearly 900 km using commercially available non-zero dispersionshifted fibers. This performance has been achieved by using a 16 km-long recirculating loop configuration and an appropriate design of the dispersion map.

Generation of a 160-GHz transform-limited pedestal-free pulse train through multiwave mixing compression of a dual-frequency beat signal.

We report the experimental generation of a 160-GHz picosecond pulse train at 1550 nm, using multiple four-wave mixing temporal compression of an initial dual-frequency beat signal in the anomalous-dispersion regime of a nonzero dispersion-shifted fiber. Complete intensity and phase characterizations of the pulse train were carried out by means of a frequency-resolved optical gating technique, showing that 1.27-ps transform-limited pedestal-free Gaussian pulses were generated.

Bragg modulational instability induced by a dynamic grating in an optical fiber.

By means of a dynamic Bragg grating obtained through cross-phase modulation with a beating wave in a highly birefringent fiber, we perform a detailed experimental study of Bragg modulational instability.

Sources of the eutrophication problems associated with toxic algae: an overview.

Blooms of cyanobacteria (toxic blue-green algae) can produce health and environmental hazards in water, including water used for drinking or recreational purposes. How, why, and when these blooms are produced, as well as how to deal with them, are questions whose answers are vital to the safeguarding of public health in regions where the algae occur. The blooms are linked to eutrophication of water, and this paper discusses the eutrophication problems, their nature, and their relevance to the production of cyanobacteria. Nutrient limitations on algal productivity are considered, as is the involvement of the atmosphere, the storage of nutrients in soils, and the influence of anthropogenic activity.

Generation of optical domain-wall structures from modulational instability in a bimodal fiber.

We study experimentally modulational instability in a normally dispersive bimodal fiber under modal group-velocity-matching conditions. In the strong pump depletion regime, higher order sideband harmonics detected in the output spectra as well as autocorrelation measurements reveal the formation of subpicosecond domain-wall structures. Across these temporal structures the electromagnetic field distribution switches abruptly between the two transverse modes of the fiber. These structures are reminiscent of the so-called domain-wall soliton. Our results constitute therefore an experimental indication of the existence of this fundamental soliton.

Generation and characterization of 0.6-THz polarization domain-wall trains in an ultralow-birefringence spun fiber.

Polarization domain-wall (PDW) trains have been generated at a repetition rate of 0.6 THz in an ultralow-birefringence spun optical fiber and measured by use of an adapted frequency-resolved optical gating technique. Characterization of the intensity and the phase of the PDW train shows complete switching between adjacent domains of counterrotating circular polarizations and directly confirms predictions based on numerical simulations of the incoherently coupled nonlinear Schrödinger equations.

Influence of parametric four-wave mixing effects on stimulated Raman scattering in bimodal optical fibers.

We analyze stimulated Raman scattering in normally dispersive bimodal fibers under single-frequency pumping conditions. Experiments show that whenever the interacting nonlinear waves propagate in the LP(01) and LP(11) modes, a parametric four-wave mixing enters unavoidably into play in the wave-coupling behavior, which causes qualitatively different phenomena compared with the ordinary process of Raman scattering, such as the parametric suppression of the first-order Raman Stokes radiation.