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.

Nonlinear refractive index of electric field aligned gold nanorods suspended in index matching oil measured with a Hartmann-Shack wavefront aberrometer.

The capability to dynamically control the nonlinear refractive index of plasmonic suspensions may enable innovative nonlinear sensing and signaling nanotechnologies. Here, we experimentally determine the effective nonlinear refractive index for gold nanorods suspended in an index matching oil aligned using electric fields, demonstrating an approach to modulate the nonlinear optical properties of the suspension. The nonlinear optical experiments were carried out using a Hartmann-Shack wavefront aberrometer in a collimated beam configuration with a high repetition rate femtosecond laser. The suspensions were probed at 800 nm, overlapping with the long-axis absorption peak of the nanorods. We find that the effective nonlinear refractive index of the gold nanorods suspension depends linearly on the orientational order parameter, S, which can be understood by a thermally induced nonlinear response. We also show the magnitude of the nonlinear response can be varied by ∼ 60%.

Prenatal alcohol exposure reduces mandibular calcium and phosphorus concentrations in newborn rats.

Previous studies suggest that prenatal alcohol exposure affects fetal bone development, including bone quality. This study evaluated the chemical composition of mandibles from newborn rats after maternal 20% alcohol consumption before and throughout gestation. Nine rats were initially distributed into three groups: an Alcohol group, Pair-fed group, and Control group. The groups were fed prespecified diets for 8 weeks before and the 3 weeks during pregnancy. At age 5 days, eight newborns from each group were euthanized (total, n = 24). Using energy dispersive spectrometry, we evaluated samples of mandibles from newborns to identify changes in bone mineralization, specifically Ca and P concentrations. Ca and P concentrations were lower in the Alcohol group than in the Control and Pair-fed groups (P = 0.003 and P = 0.001, respectively). In summary, alcohol exposure before and throughout gestation reduces mandibular Ca and P concentrations in newborn rats. (J Oral Sci 58, 439-444, 2016).

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).

Optical creation and erasure of the linear electrooptical effect in silica fiber.

We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (~108 V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (~0.06 pm/V) is limited by the field applied during poling (1.2 × 108 V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated.

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.

Poling-assisted fabrication of plasmonic nanocomposite devices in glass.

We report on the fabrication and optical properties of large-scale plasmonic nanocomposite metamaterial directly within glass matrix by thermal electric-field poling of glass. The achieved structure exhibits an enhanced backscattering (see Figure), which has strong dependence on the exposure of the surface to different organic vapors and can be used for development of new sensing platforms.

Hydrostatic pressure sensing with high birefringence photonic crystal fibers.

The effect of hydrostatic pressure on the waveguiding properties of high birefringence photonic crystal fibers (HiBi PCF) is evaluated both numerically and experimentally. A fiber design presenting form birefringence induced by two enlarged holes in the innermost ring defining the fiber core is investigated. Numerical results show that modal sensitivity to the applied pressure depends on the diameters of the holes, and can be tailored by independently varying the sizes of the large or small holes. Numerical and experimental results are compared showing excellent agreement. A hydrostatic pressure sensor is proposed and demonstrated using an in-fiber modal interferometer where the two orthogonally polarized modes of a HiBi PCF generate fringes over the optical spectrum of a broad band source. From the analysis of experimental results, it is concluded that, in principle, an operating limit of 92 MPa in pressure could be achieved with 0.0003% of full scale resolution.

All-fiber devices based on photonic crystal fibers with integrated electrodes.

A special kind of microstructured optical fiber is proposed and fabricated in which, in addition to the holey region (solid core and silica-air cladding), two large holes exist for electrode insertion. Either Bi-Sn or Au- Sn alloys were selectively inserted into the large holes forming two parallel, continuous and homogeneous internal electrodes. We demonstrate the production of a monolithic device and its use to externally control some of the guidance properties (e.g. polarization) of the fiber.

Low loss photonic components in high index bismuth borate glass by femtosecond laser direct writing.

Single mode, low loss waveguides were fabricated in high index bismuth borate glass by femtosecond laser direct writing. A specific set of writing parameters leading to waveguides perfectly mode matched to standard single-mode fibers at 1.55 microm with an overall insertion loss of approximately 1 dB and with propagation loss below 0.2 dB/cm was identified. Photonic components such as Y-splitters and directional couplers were also demonstrated. A close agreement between their performances and theoretical predictions based upon the characterization of the waveguide properties is shown. Finally, the nonlinear refractive index of the waveguides has been measured to be 6.6 x 10(-15) cm(2)/W by analyzing self-phase modulation of the propagating femtosecond laser pulse at the wavelength of 1.46 microm. Broadening of the transmitted light source as large as 500 nm was demonstrated through a waveguide with the length of 1.8 cm.

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.