C. M. S. Vicente

Multi-objective genetic algorithm applied to spectroscopic ellipsometry of organic-inorganic hybrid planar waveguides

The applicably of multi-objective optimization to ellipsometric data analysis is presented and a method to handle complex ellipsometric problems such as multi sample or multi angle analysis using multi-objective optimization is described. The performance of a multi-objective genetic algorithm (MOGA) is tested against a single objective common genetic algorithm (CGA). The procedure is applied to the characterization (refractive index and thickness) of planar waveguides intended for the production of optical components prepared sol-gel derived organic-inorganic hybrids, so-called di-ureasils, modified with zirconium tetrapropoxide, Zr(OPr(n))(4) deposited on silica on silicon substrates. The results show that for the same initial conditions, MOGA performs better than the CGA, showing a higher success rate in the task of finding the best final solution.

Simple measurement of surface free energy using a web cam

In this paper we describe a simple and pedagogical experiment to measure surface free energy (SFE), which is a mainstream subject to teach undergraduate and graduate level Physics science. Beyond this, the advantage of this work relies on the simplicity of the materials used, namely non-harmful and low cost products such as water, glycerol, ethylene glycol and propanol, offering a useful pedagogical opportunity to discuss basic but relevant concepts regarding surface science phenomena. As example, contact angle measurements were used to estimate SFE and the wetting behavior of distinct solid surfaces such as glass and polytetrafluoroethylene (PTFE, Teflon®).

Fabrication of low-cost thermo-optic variable wave plate based on waveguides patterned on di-ureasil hybrids

An integrated variable wave plate device based on a thermo-optic (TO) effect was fabricated by patterning a waveguide channel through direct UV laser writing on the surface of sol-gel derived organic-inorganic hybrid (di-ureasil) films. The di-ureasil layer is stable up to 250 °C and has a high TO coefficient calculated as -(4.9 ± 0.5) × 10(-4) °C(-1) at 1550 nm. The waveguide temperature was tuned, inducing optical phase retardation between the transverse electric and transverse magnetic modes, resulting in a controllable wave plate. A maximum phase retardation of 77 ° was achieved for a waveguide induced temperature increase of 5 °C above room temperature, with a power consumption of 0.4 W. The thermal linear retardation coefficient was calculated to be 19 ± 1 °/ °C.

Determination of Refractive Index Contrast and Surface Contraction in Waveguide Channels Using Multiobjective Genetic Algorithm Applied to Spectroscopic Ellipsometry

The application of spectroscopic ellipsometry for the characterization of UV-patterned channel waveguides to obtain the refractive index contrast and surface deformation profile is presented. Thin films were prepared with organic-inorganic di-ureasils hybrids modified with zirconium tetra-propoxide deposited in silica on silicon substrates. The channel waveguides were produced by direct writing using UV laser radiation. The refractive index contrast and the surface ablation induced by the UV optical signal were estimated by ellipsometry being 4.5 × 10-3 and 30.5 nm, respectively. The deepness of the surface ablation due to the UV exposition was also estimated by atomic force microscopy measurements that pointed out a value of 31.0 ± 1.0 nm, concordant with the ellipsometric calculations. The near-field intensity technique was used as a support for contextualizing the proposed ellipsometry method for the characterization of refractive index profiles. The estimated refractive index contrast (2.0 × 10-3) is in a good agreement with the refractive index contrast derived from ellipsometry.

Organic-inorganic hybrids for the new generation of optical networks

Organic-inorganic hybrids were tailored as transparent monoliths and as planar waveguides deposited on borosilicate substrates by the spin coating technique. Laser direct writing process was used to create monomode Y-splitters. The Y-splitter structures were designed and optimized for a coupling ratio of 50 % using a beam propagation method (BPM) software.. The potential of these optical structures based on di-ureasil hybrids to be used as optical filters operating in the C+L telecommunication windows will be evaluated.

Integrated Optical Mach-Zehnder Interferometer Based on Organic-Inorganic Hybrids for Photonics-on-a-Chip Biosensing Applications

The development of portable low-cost integrated optics-based biosensors for photonics-on-a-chip devices for real-time diagnosis are of great interest, offering significant advantages over current analytical methods. We report the fabrication and characterization of an optical sensor based on a Mach-Zehnder interferometer to monitor the growing concentration of bacteria in a liquid medium. The device pattern was imprinted on transparent self-patternable organic-inorganic di-ureasil hybrid films by direct UV-laser, reducing the complexity and cost production compared with lithographic techniques or three-dimensional (3D) patterning using femtosecond lasers. The sensor performance was evaluated using, as an illustrative example, E. coli cell growth in an aqueous medium. The measured sensitivity (2 × 10−4 RIU) and limit of detection (LOD = 2 × 10−4) are among the best values known for low-refractive index contrast sensors. Furthermore, the di-ureasil hybrid used to produce this biosensor has additional advantages, such as mechanical flexibility, thermal stability, and low insertion losses due to fiber-device refractive index mismatch (~1.49). Therefore, the proposed sensor constitutes a direct, compact, fast, and cost-effective solution for monitoring the concentration of lived-cells.

Flexible 90° hybrid coupler for coherent optical systems based on organic-inorganic hybrids

The next generation of optical networks requires the development of optical technology that supports high bandwidth, such as the coherent systems. The coherent detection allows the in-phase and quadrature components of a QPSK signal to be extracted as a result of the interference with a local oscillator. An integrated optics flexible 90° hybrid coupler device based on a single organic-inorganic di-ureasil hybrid layer was fabricated using direct UV-laser writing. The demodulator exhibits a single input - multiple output port transfer function depending on the optical signal phase. This example demonstrates that di-ureasils are potential low-cost solutions for the fabrication of polarization controlling devices.

Polarization state control using thermo-optic effect in organic-inorganic hybrids waveguides

In this work, we report an integrated tunable wave-plate based on thermo-optic (TO) effect on a waveguide patterned by direct UV laser writing on films of organic-inorganic hybrid materials. The temperature of the waveguide was tuned inducing phase retardation between transverse electric and transverse magnetic modes. The TO coefficient of the planar waveguide is (-4.9±0.3)×10-4°C-1 at 1550 nm. A maximum phase retardation of 77° was achieved for a temperature variation of 5 oC, with a power consumption of 435 mW. The transformations of the state of polarization between linear and circular were visualized on the Poincaré sphere.

Thermo-optic variable attenuator/waveplate based on waveguides patterned on organic-inorganic hybrids

This work reports a variable attenuator/waveplate based on thermo-optic (TO) effect induced on a waveguide patterned by direct UV-laser writing on films of organic-inorganic di-ureasil hybrids. The waveguide temperature was tuned inducing phase retardation between the transverse electric (TE) and transverse magnetic (TM) modes, resulting in a controllable waveplate. Furthermore, the waveguide TO actuation allows obtaining a variable optical attenuator. The relevant properties, such as attenuation, polarization dependence of the thermal actuation and power consumption will be presented in the NIR (1550 nm). The required electrical power and temperature variation to attain the optical signal extinction and the retardation phase of π/2 were estimated.

Optical haar transform for 2D processing and compression

In this paper we present integrated schemes for parallel data processing based on optical transforms. The design of an all-optical system for 2D data processing is presented and supported by simulation results based on the Haar wavelet transform and further compression.