Francisco Villuendas

New in-line optical-fibre sensor based on surface plasmon excitation

Abstract A new ‘in-line’ fibre-optic sensor based on the excitation of surface plasmons in a thin metal film deposited in the polished cladding of the fibre is presented. Optical-power transmission characteristics of the device, for TM-polar- ized light, have been both experimentally and theoretically investigated. The obtained results show the feasibility of practical designs with in-line fibre-optic configuration for a large range of optical sensor applications.

Single-mode, optical-fiber sensors and tunable wavelength filters based on the resonant excitation of metal-clad modes

The resonant excitation of metal-clad modes, including fundamental and higher-order modes, in a multilayer structure deposited on the polished cladding of a single-mode optical fiber is theoretically analyzed and experimentally demonstrated. The excitation of metal-clad modes is shown as a resonant power transfer from the fiber to the metal-clad mode that takes place for an external refractive-index value such that the effective index of the metal-clad mode reaches the cladding level. The observed attenuation on the TM polarization provides a suitable transducing mechanism for refractive-index sensor devices as well as the principle for developing tunable wavelength-polarized filters with a wide range of optical performance characteristics.

High resolution light intensity spectrum analyzer (LISA) based on Brillouin optical filter

A high-resolution light intensity spectrum analyzer technique to derive the RF modulation spectrum of optical signals is presented and experimentally confirmed. It uses the XPM nonlinear effect in a dispersion shifted fiber to obtain the light intensity spectrum, and a Brillouin optical filtering method to implement the high resolution spectrometric analysis. Measured RF spectra of PRBS modulated optical signals at 2.5 Gb/s and 10 Gb/s are presented and compared with their corresponding ones obtained in the electrical detection domain to confirm the capabilities of the method.Influence of fiber electrostriction effect is measured and analyzed.

Analysis of leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides

Power leakage properties and guiding conditions of rib antiresonant reflecting optical waveguides (rib-ARROW) have been theoretically and experimentally studied as a function of wavelength and polarization of the light for different geometrical and optical parameters that characterize the rib-ARROW structure. Obtained results show that rib-ARROWs can only be fabricated with low losses in a wavelength range when determined rib configurations are adopted. Furthermore, these waveguides exhibit a polarization sensitivity that largely depends on the core-substrate refractive index difference. Together with the experimental results, theoretical calculations from different modeling methods are also presented and discussed.

p-type conduction in sputtered indium oxide films

We report p-type conductivity in intrinsic indium oxide (IO) films deposited by magnetron sputtering on fused quartz substrates under oxygen-rich ambient. Highly oriented (111) films were studied by x-ray diffraction, optical absorption, and Hall effect measurements. We fabricated p-n homojunctions on these films.

All in fiber optical frequency metrology by selective Brillouin amplification of single peak in an optical comb.

Suitable use of stimulated Brillouin amplification (SBA) effect for selective single peak amplification in an optical frequency comb is demonstrated to provide high accuracy in optical frequency metrology. A pump wave generated by a tunable laser source (TLS) is used to stimulate SBA of such optical comb along an optical fiber and selectively amplify only one single peak of the comb. Nature of SBA preserves both linewidth and absolute wavelength position of the selected comb peak. All of these features result in a simple, robust and compact all in fiber system. Relative optical frequency accuracy in the order of Hz is confirmed.

Vortex configuration flow cell based on low-temperature cofired ceramics as a compact chemiluminescence microsystem.

The integration of optical detection methods in continuous flow microsystems can highly extend their range of application, as long as some negative effects derived from their scaling down can be minimized. Downsizing affects to a greater extent the sensitivity of systems based on absorbance measurements than the sensitivity of those based on emission ones. However, a careful design of the instrumental setup is needed to maintain the analytical features in both cases. In this work, we present the construction and evaluation of a simple miniaturized optical system, which integrates a novel flow cell configuration to carry out chemiluminescence (CL) measurements using a simple photodiode. It consists of a micromixer based on a vortex structure, which has been constructed by means of the low-temperature cofired ceramics (LTCC) technology. This mixer not only efficiently promotes the CL reaction due to the generated high turbulence but also allows the detection to be carried out in the same area, avoiding intensity signal losses. As a demonstration, a flow injection system has been designed and optimized for the detection of cobalt(II) in water samples. It shows a linear response between 2 and 20 microM with a correlation of r > 0.993, a limit of detection of 1.1 microM, a repeatability of RSD = 12.4%, and an analysis time of 17 s. These results demonstrate the suitability of the proposal to the determination of compounds involved in CL reactions by means of an easily constructed versatile device based on low-cost instrumentation.

Analysis of optochemical absorbance sensors based on bidimensional planar ARROW microoptics

Abstract A new approach for developing absorbance optochemical sensors is presented in this paper. It is based on a planar microoptic circuit where an optochemically active membrane, which responds selectively to a compound, is deposited in the device, yielding a part of the guiding planar structure. Light is propagated through the membrane, which changes its spectral absorption properties and controls the selectivity of the measurements by means of several immobilised compounds. This way, high sensitivity of the device can be easily obtained due to relatively long light paths through the membrane, and low response times can be achieved as the analyte diffusion occurs perpendicularly to the light path and through a thin membrane. Experimental results on measurements of the concentration of a specific ion in solution using the fabricated sensors are also presented.

Brillouin induced self-heterodyne technique for narrow line width measurement

A novel technique is introduced for jitter-insensitive sub-KHz resolution linewidth characterization technique in ultra-narrow lasers for optical communication applications. The technique is based on self-heterodyne detection induced by Stimulated Brillouin Scattering (SBS). Non linear SBS drives the heterodyne mixing through optical frequency locking of a narrow tunable laser source and the signal under test, which is modulated in the low frequency range. Due to SBS nature, jitter variations in the optical frequency do not affect the correlation spectra measured with resolution figures up to 300 Hz, without the need for optical delay line as in conventional homodyne correlation techniques.

Subpicometer wavelength accuracy with gain-switched laser diode in high-resolution optical spectrometry

We present a method to generate an optical reference comb signal with subpicometer wavelength accuracy. XPM nonlinear effect in a fiber is used to get an optical frequency comb signal, free of frequency chirp and wavelength instabilities, from a pulsed gain-switched laser diode. Principles of such comb generation are presented as well as the application of this comb as a ruler to measure frequency differences in high resolution optical spectrum measurements. To confirm this method, Brillouin filtering optical spectrometric technique is used to characterize a modulated optical source. Typical resolution of this technique allows 0.08 pm wavelength accuracy.