Vinicius N. H. Silva

A New Triangulation-Like Technique for the Evaluation of the Refractive Index Structure Constant

A light beam propagating through the atmosphere has its amplitude, phase, and propagation direction changed along the optical path due to atmospheric turbulence. This effect is caused by the randomness of the air refractive index and depends on the local temperature, pressure, and humidity. The physical parameter that quantifies the turbulence strength is well known in the literature as the refractive index structure constant (Cn2). In this paper, a simple and low-cost technique based on a triangulation-like method to measure the Cn2 is presented for the first time to the best knowledge of the authors. Through a novel device comprised of three photodetectors in a triangle-shaped array placed on the receiver plane, it is possible, after power measurements and applying a developed mathematical model, to obtain precisely the position of the beam spot. Therefore, calculates the Cn2 and evaluates the atmospheric turbulence strength. Furthermore, the technique is useful to check the suitability of a free-space optical (FSO) link in a specific geographic region by monitoring the local turbulence. Also, the device will be useful to improve the deployment and maintenance of FSO systems.

(C_{n}^{2})

Snapshot Mueller matrix polarimetry was performed for static and dynamic analyses of surface-stabilised ferroelectric liquid crystal cells under an electric field. A strong correlation between the static (at fixed voltage) and dynamic (upon field reversal) polarimetric properties and the texture of ferroelectric liquid crystal cells was established. The birefringence properties were different between a rooftop/zigzag-textured cell and a stripe-textured cell. The trajectory of the optic axis, plotted over the transition between two addressed states, was analysed for each cell. The shape of the trajectories could be explained by a reversible motion of the smectic layers while switching.

in Free-Space Optical Links

In this paper, we discuss various technical options to implement 3D dual-view systems, from four frames generated by two triggered or non-triggered 3D projectors. Such a technique offers 3D free-viewpoint capabilities for two viewers. We compare two different technical implementations based on transmissive video projection and reflective silver screen, combining two different 3D encoding techniques: polarization and time multiplexing. The main objective is to analyze and mitigate the ghosting effects, as a function of the technical, modal and frame pairing choices with respect, first to the image optical quality and second to prevent visual fatigue. We suggest some solutions to reduce the impact of the physical ghosting and frame unbalance. These solutions will be expanded in a second paper.

Correlation between static and dynamic polarimetric properties and the texture of surface-stabilised ferroelectric liquid crystal cells

The full-optical set-up snap-shot Mueller matrix polarimeter (SMMP) is used to measure the channelled spectrum Iλ(λ) related to a twisted ferroelectric liquid crystal (TwFLC) studied here with this technique. The samples were preliminarily exposed to a high-amplitude/low-frequency rectangular voltage before all the optical measurements. This voltage applied permits one to work in the specific stripe regime. From the channelled spectrum recorded Iλ(λ), the different Mueller matrix (MM) can be obtained: the depolarization matrix, the retardance matrix and the diattenuation matrix. Several scalar polarimetric parameters are extracted from these MM, and especially αR(t), R(t) and R(t). These relevant scalar coefficients, calculated from the retardance matrix, are used to determine the three hysteresis loops αR(V), R(V) and R(V). We define ψ as the difference of angle between the two rubbing directions of the two symmetrical (top and bottom) substrates and we examine how the hysteresis loops obtained are modified with the value of the geometrical externally controllable parameter ψ, for angles between ψ = 0° and ψ = 90°. The key characteristics of the hysteresis loops and the evolution of these key values with ψ are detailed.

Ghosting Impingements in 3D Dual-View Projection Systems

Experimental results are presented related to the dynamic behaviour of Polymer Stabilized Ferro-electric Liquid Crystal (PSFLC) samples under external applied electric field, using Snap-shot Mueller Matrix Polarimetry (SMMP) and Mueller Matrix (MM) formalism. Different polarimetric coefficients are simultaneously extracted from each channeled spectrum measured with this full-optical SMMP technique. The impact of the concentration of polymer present into the liquid crystal cell on this dynamic behaviour is studied, permitting a direct and quick characterisation of the material. The results obtained for PSFLC are compared with those already measured for pure Surface Stabilized Ferro-electric Liquid Crystal (SSFLC) samples, which correspond to a 0% concentration in polymer.Graphical abstract

Experimental study of the dynamic behaviour of twisted ferroelectric liquid crystal samples using snap-shot Mueller matrix polarimetry

In this paper we demonstrate the development of an adjustable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators that squeezes a defined pieces of an Hi-Bi fiber. Using this device, the first and second order PMD (SOPMD) can be reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators and for the study of several polarizations phenomena that can represent impairments to the high data transmission networks. This emulator was used to perform an analysis of the correlation between the PMD and SOPMD under different climate chamber temperature.

Impact of the concentration in polymer on the dynamic behavior of Polymer Stabilized Ferroelectric Liquid Crystal using Snap-shot Mueller Matrix Polarimetry

We describe a simple and inexpensive inline optical power monitor (OPMo) for polymer optical fibre (POF) links that are transmitting visible light carriers. The OPMo is non-invasive in the sense that it does not tap any guided light from the fibre core; rather, it collects and detects the spontaneous side-scattered light. Indeed, the OPMo indicates whether a POF transmission link has dark or live status and measures the average optical power level of the propagating signals without disconnecting the fibre link. This paper demonstrates the proof-of-principle of the device for one wavelength at a time, selected from a set of previously calibrated wavelength channels which have been found in the 45 dB dynamic range, with 50 dBm sensitivity or insensitivity by the use or non-use of a mode scrambler. Our findings are very promising milestones for further OPMo development towards the marketplace.

PMD Emulator based on PZTs attached to pieces of an Hi-Bi fiber

This paper discloses an Analogiser able to carry out digital to analogue conversion of the optically digitised Radio-over-Fibre signals. The Analogiser comprises many interconnected optical circuits based on the Sagnac interferometric rings with an inserted semiconductor optical amplifier. Numerical simulation results are shown for 2.5 GHz sampling rate and 4-bit resolution. The designed circuits are compact, thus enabling optical integration and require optical peak power control in the ~mW range.

Non-disturbing optical power monitor for links in the visible spectrum using a polymer optical fibre

This paper describes the conception, design and numerical simulations of an electromagnetic-receiver & optical-modulator based on a solely semiconductor optical amplifier (SOA) and a fibre-optic Sagnac loop incorporating a SOA both without bias current. Only the interferometric device was able to detect weak high-frequency RF carriers from hundred pW to hundreds nW power delivering an output with 37% optical offset in the 0.3-10.0 GHz frequency range. Even though the adopted SOA model presents around 1 ns gain recovery time, RF carriers up to 30 GHz frequency were received/modulated because a full gain recovery was not needed.

Design of an Analogiser for optically digitised Radio-over-Fibre signals

This paper describes the conception, design and numerical simulations of a temporal filter able to suppress unmodulated optical carrier. It is based on a fibre-optic Sagnac loop incorporating a semiconductor optical amplifier (SOA) presenting around 1 ns gain recovery time. Numerical simulations using the VPI Transmission Maker™ platform were carried out regarding a large optical offset with 5 Gb/s binary digital stream or 2.5 GHz sinusoidal (analogue) buried signals.