Maria Thereza M. Rocco Giraldi

Strain and Temperature Discrimination Using High-Birefringence Erbium-Doped Fiber Loop Mirror With High Pump Power Laser

This work presents a method to tune the sensitivity of the sensor in a highly birefringent erbium-doped fiber loop mirror (FLM) when it is pumped. This concept was used for simultaneous measurement of strain and temperature. The FLM is sequentially pumped and unpumped by a high pump laser at 980 nm to change the erbium-doped fiber properties. The sensing head changes its sensitivity when subjected to strain and/or temperature variations due to thermal effects originated by the pump laser.

Numerical simulations and experimental results of a hybrid EDFA-Raman amplifier

In this work numerical simulated and experimental results are obtained for a hybrid EDFA-Raman amplifier. Rigorous numerical models of both EDFA and Raman amplifiers are implemented and validated with experimental measurements. Results of ripple smaller than 1 dB are obtained for the hybrid amplifier gain, in 40 nm of bandwidth. The numerical model permits to achieve optimal design and to predict flat amplifier gain using genetic algorithm.

Interferometric optical fiber inclinometer with dynamic FBG based interrogation

The development of an interferometric optical fiber inclinometer is described in this paper. A weak tapered region is induced in a standard single mode fiber in the vicinity of the cleaved fiber tip, using a standard fusion splicer. In this situation an in-fiber Michelson interferometer is constructed that is sensitive to curvature applied in the tapered region. It is shown that depending on the angular range, fringe visibility and/or peak position depend strongly on the applied curvature enabling low cost dielectric inclinometer to be setup that is suitable for high voltage applications. It is presented an analysis of the sensor response by means of experimental measurements and manipulation of these experimental data through computational simulations. The results coming from the numerical simulations indicate a good performance of the sensor within range of angular variation between 3 and 6 degrees and 10 and 14 degrees. A low cost strategy to interrogate the response of sensor using electrically modulated fiber Bragg gratings, a photodetector and frequency analysis is described. The results presented by this electric interrogation technique show a good sensitivity in the range 3.5 to 5.5 degrees.

Fiber Loop Mirror Sensors Interrogated and Multiplexed by OTDR

In this paper, two techniques for interrogation and multiplexing of fiber loop mirror (FLM) intensity sensors based on optical time domain reflectometer (OTDR) are proposed. These configurations enable series and parallel FLM sensor interrogation. A fiber taper characterized as a displacement sensor was used as the intensity sensor. The OTDR parameters were optimized in order to obtain the best results. The optimized parameters were 100-ns pulse width and 10-dB input signal attenuation which permitted to attain ~18 dB dynamic range in the operating wavelength of 1550 nm. The results show a linear behavior for both configurations with similar slope, -15.3 dB/mm, in the normalized displacement range of 0.2 to 0.7 mm. It was also achieved a displacement resolution of 0.027 and 0.093 mm, for the series and parallel configurations, respectively. Sensors multiplexing are demonstrated for both configurations and the systems do not present crosstalk. Based on the experimental results, the best configuration is the parallel one. The proposed approach is a viable alternative for multiplexing and interrogation of remote fiber sensors.

Ag-nanowire metamaterials: spectral reflectance analysis and homogenization models

In this work, we address a study of the spectral reflectance of silver nanowire metamaterials in the visible and near-infrared regions. To this end, several samples were fabricated with different fill-ratios and lattice constants, and their respective optical responses characterized in terms of these parameters. We perform a direct comparison between the collected experimental data with the values predicted by different analytical homogenization models to provide a better understanding of the effective optical behavior of this kind of metamaterials.

Performance analysis of a 2D double hard-limited OCDMA system over FSO link under strong turbulence for defense applications

This work analyses the performance of a complete two-dimensional Optical Code Division Multiple Access system over Free Space Optics link under strong atmospheric turbulence. The system feasibility and performance is demonstrated through simulation with the commercial tool OptiSystem, from Optiwave, Inc. If a necessary component was not present in the software or its model did not correspond to the expectations, the desired device was created and programmed using the software MatLab. With the presented proposal, multiple users could share a single optical wireless channel, transmitting coded information for defense mobile applications. A usual optical sequence, called Prime Code, is used for both wavelength-hopping and time-spreading. The effects of variable distance, strong turbulence and different divergence angles are considered in terms of Bit Error Rate.

Analysis of the resonant layer effect in multilayer nanostructured optical waveguides

Abstract. The resonant layer effect (RLE) is investigated for a multilayer structure with iron nanoinclusions. The RLE tuning and strength are analyzed as a function of nanoinclusion filling factor and resonant, cladding and guiding layers thicknesses. Crossing, splitting, and quasidegeneration of modes in the structure dispersion diagram are discussed, along with its relation to the RL effect detuning and structure-coupling regime. For the range of parameters considered, multiple resonances are tunable in the multilayer structure. Optimized RLE TE and TM polarizers are proposed for operation at 1550 nm based on modal loss and field confinement calculations. For the TE-pass polarizer, a 201.1-dB rejection ratio and 3.85-dB/cm insertion loss are obtained, while for the TM-pass polarizer, a 95.6-dB rejection ratio and 4.41-dB/cm insertion loss are achieved.

Curvature and Vibration Sensing Based on Core Diameter Mismatch Structures

Core diameter mismatch structures are proposed and experimentally investigated for curvature and vibration sensing. Two configurations are suggested, one approach uses a structure formed by splicing an uncoated short section of multimode fiber between two standard single-mode fibers (SMFs) single-mode-multimode-single-mode (SMS), combined to a fiber optical mirror at its end, and the other approach uses a structure made by splicing a section of SMF between two multimode fibers (SMSMS). In the curvature analysis, the proposed SMS sensor generates the destructive interference patterns when it is bent, varying only the attenuation of the optical signal without wavelength shifts. The SMSMS vibration sensor proved to be suitable to monitor very low frequencies such as 0.1 Hz. The configuration of the proposed sensors presents several interesting features, such as easy fabrication, low cost, high efficiency, and high sensitivity. These advantages make such sensors very useful in a wide range of applications, for instance, structural health monitoring.

Characterisation of all-optical wavelength conversion by cross-gain modulation of ASE on a SOA

Broadband all-optical wavelength conversion at 1550 nm is attained by means of cross-gain modulation of the whole ASE spectrum of a SOA. In this technique, the pump wavelength is converted into any other wavelength with no need of probe light sources using the spectrum slicing method. The conversion is demonstrated here for ultra short input pulses that allow precise characterisation of the devices time response. Results to the conversion efficiency are also presented.

Fiber ring laser optimization as an optical source for WDM transmission systems

This work presents the results of the study on the longitudinal modes behavior in an erbium doped fiber ring laser that uses two optical fibers--one mechanic and another electric. The operation of both filters is combined to cover the whole spectral range corresponding to the erbium fluorescence. The influence of the cavity length, host matrix and combination of two optical filters on the mode suppression and performance of the laser is discussed. We obtained the match conditions for operation of the optical filters which better improve the laser performance. An estimate of the relative intensity noise due to the introduction of the laser in a communication system is also presented.