Javier Sánchez-Mondragón

Data fitting on a spherical shell

We present in this paper a data fitting method that analyzes a spherical shell that uses the near orthogonality of the Spherical Harmonics Ylm(Θ,Φ) within a discrete data collected on a spherical shell to obtain the best rms fit. This is obtained through the generation of an orthogonal basis from the spherical harmonics Ylm(Θ,Φ) on a discrete and often irregular data set on a spherical shell.

Polysilicon thermal micro-actuators for heat scavenging and power conversion

This paper describes the design and experimental characterization of two optimized thermal actuators devised to operate by means of scavenging heat from the environment. Different from the traditional MEMS thermal actuator that relies on electric current to generate heat by Joule effect, the devices herein presented have been optimized to absorb external heat and convert it into mechanical displacement and force. The behavior of vertical and horizontal microactuators fabricated in a standard surface micro-machining process (PolyMUMPs) demonstrates the viability of exploiting heat from the surrounding medium to realize batteryless microsystems. Analytical and finite element models are provided in support of the design. Results show that fairly large and useful displacements can be achieved at commonly available operating temperatures.

Spectral narrowing due to linear coupling in two-core fibers

We develop for the first time, to the best of our knowledge, a comprehensive theory to describe the nonlinear propagation of picosecond pulses through symmetric two-core fibers (TCFs). Considering the elementary TCF switching process, we derive an exact analytical expression for the nonlinear phase shift of a picosecond pulse of arbitrary shape and chirp. Applying our results to an unchirped Gaussian input pulse, we demonstrate spectral narrowing in the propagation of the pulse through a TCF. Our results show that the linear coupling induces that spectral narrowing. The amount of narrowing of the pulse spectra depends on the peak power of the input pulse.

Background illumination regularization on interferograms

Abstract. A method for background illumination regularization, which requires only one image and a single-stage correction, is presented. The method yields in the exact computation of the background illumination and the local visibility of the fringes from the envelopes of the intensity distribution. The approach is clear, elegant, and easy to implement. The results of the method are compared with another recent approximation, proving itself competitive enough.

Digital-Optical Experimental Set up for in vitro Cell Tracking Based on Cross Correlation Technique

An automatic cell tracking system based in the NCC technique is proposed. Image operations were performance by a FPGA while Fourier transforms were done by an optical correlator. The time consuming was reduced about 70%.

Temperature sensing based on optical transmission in a LiBr heat pump

A new technique, based on Optical Methods, has been tested for the evaluation of the lithium bromide (LiBr) concentration, a corrosive substance frequently used in heat pumps. Those solutions have large oxidizing capabilities. This technique avoids the direct contact between the electrodes and the LiBr aqueous solution within a thermodynamic absorption cycle. The viability of this technique in a potential commercial device, resides on its capability to detect working fluid concentrations within a temperature range from 25 °C up to 70 °C, those limiting temperature values correspond to the operating wavelengths of 1.33 μm and 1.55 μm, respectively. Our system determines the correlation among the signal and temperature data, for various concentrations, between 49 and 58 mass percentages. This function of two variables is represented as a surface with the transmittance, concentration and temperature as parameters and wavelength as reference. We discuss the adequate parameters characterization used in this technique.

Chirping on a nonlinear finite stack

The chirping of a pulse propagating on a nonlinear media is nowadays a rather well studied phenomena and we are aware that requires an appreciable propagation length to develop. A nonlinear stack of finite dimension, does not have those dimensions. Therefore, chirping in this media is a rather new feature that deserves to be studied at considerable length given the greater importance that those structures have in photonics. We present a nonlinear analysis of a finite stack, nonlinear at each media and compare it with its analytically solvable linear case. The pulse propagation is discussed, in particular we demonstrate intensity dependence of the chirp as a distinctive nonlinear signature. We show two additional nonlinear characteristics: the nonlinear switching and the bistability.

Superheterodyne amplification of sub millimeter electromagnetic waves in nGaAs film

Superheterodyne amplification of sub-millimeter electromagnetic waves in GaAs due to negative differential mobility is analyzed. The nonlinearity arises from the current and the magnetic field of the electromagnetic waves. The case of interaction of two traveling counter-propagating electromagnetic waves and the following space charge wave in an n-GaAs film placed onto an i-GaAs substrate is considered The case of 2D electron gas is also analyzed. The simulation of this nonlinear interaction shows a certain increment of the amplification.

Photonic crystal slab with layered elements

Abstract We introduce the simulation of a photonic crystal slab with a square lattice, whose basis elements are layered cylinders of an averaged refractive index . We compare it with a similar photonic crystal with a basis of the same size and a refractive index matching to the average of the layered ones. Even when this is such a simple system with internal structure, we have found an interesting phenomenology: an increase in band gaps, flattening of the bands, degeneracy nodes, etc. We also introduce additional methods to fine tuning the design and analyze the inclusion of a plain cylinder defect within the slab.

Ultrafast Spectroscopy Used to Generate and Detect Longitudinal Acoustic Phonons in High Quality Silicon on Glass Sample

We show the experimental generation and detection, as well as theoretical studies, of unusual coherent acoustic phonons on a high quality silicon-on-glass sample. We suggest a photonic crystal based on the studied sample.