Fabry-Perot Cavity Optimization for Absolute Strain Sensing Using Finite Element Analysis.

The finite element method (FEM) was used to investigate the optical-mechanical behavior of a Fabry-Perot Interferometer (FPI) composed of a capillary segment spliced between two sections of standard optical fiber. The developed FEM model was validated by comparing it with theory and with previously published experimental data. The model was then used to show that the absolute strain on the host substrate is usually smaller than the strain measurement obtained with the sensor. Finally, the FEM model was used to propose a cavity geometry that can be produced with repeatability and that yields the correct absolute strain experienced by the host substrate, without requiring previous strain calibration.

In-fiber Fabry-Perot interferometer for strain and magnetic field sensing.

In this paper we discuss the results obtained with an in-fiber Fabry-Perot interferometer (FPI) used in strain and magnetic field (or force) sensing. The intrinsic FPI was constructed by splicing a small section of a capillary optical fiber between two pieces of standard telecommunication fiber. The sensor was built by attaching the FPI to a magnetostrictive alloy in one configuration and also by attaching the FPI to a small magnet in another. Our sensors were found to be over 4 times more sensitive to magnetic fields and around 10 times less sensitive to temperature when compared to sensors constructed with Fiber Bragg Grating (FBG).

Dengue immunoassay with an LSPR fiber optic sensor.

Dengue fever is a viral disease that affects millions of people worldwide. Specific tests for dengue are not usually performed due to high costs, complicated procedures and, in some cases, long time to yield a result. For widespread use of specific tests to be possible, fast, reliable and fairly simple methods are needed. In this paper, we present a new dengue diagnostic method for the acute phase of the infection. The method proposed uses an all-optical fiber sensor based on Localized Surface Plasmon Resonance (LSPR) and specular reflection from gold nanoparticles (AuNPs). Dengue anti-NS1 antibody was immobilized on AuNPs deposited on the endface of a standard multimode fiber (62.5 µm/125 µm). The sensor is able to detect NS1 antigen at different concentrations, with limit of quantification estimated to be 0.074 µg/ml = 1.54 nM. These results indicate that the sensor could potentially be used for dengue diagnosis in the acute phase of the infection.

Gold nanoparticles on the surface of soda-lime glass: morphological, linear and nonlinear optical characterization.

Materials presenting high optical nonlinearity, such as materials containing metal nanoparticles (NPs), can be used in various applications in photonics. This motivated the research presented in this paper, where morphological, linear and nonlinear optical characteristics of gold NPs on the surface of bulk soda-lime glass substrates were investigated as a function of nanoparticle height. The NPs were obtained by annealing gold (Au) thin films previously deposited on the substrates. Pixel intensity histogram fitting on Atomic Force Microscopy (AFM) images was performed to obtain the thickness of the deposited film. Image analysis was employed to obtain the statistical distribution of the average height of the NPs. In addition, absorbance spectra of the samples before and after annealing were measured. Finally, the nonlinear refractive index (n2) and the nonlinear absorption index (α2) at 800 nm were obtained before and after annealing by using the thermally managed eclipse Z-scan (TM-EZ) technique with a Ti:Sapphire laser (150 fs pulses). Results show that both n2 and α2 at this wavelength change signs after the annealing and that the samples presented a high nonlinear refractive index.

Measurement of depletion region width in poled silica.

The width of the depletion region in fused-silica samples thermally poled during various periods of time is investigated experimentally with four previously reported characterization techniques in an attempt to unify their findings. Although all measurements give a similar width of the depletion region, it is shown that the determination of the profile of chi(2) is also required for a good estimate of the nonlinearity induced by poling.