J. Escobedo-Alatorre

Design and fabrication of a MEMS thermal actuator for 3D optical switching applications

This paper presents a novel thermally-actuated vertical micromirror for optical communications. Fabricated in a standard surface micromachining process, this micromirror can achieve low insertion loss (< 1 dB) and is capable of operating at CMOS-compatible voltage levels. It has a measured maximum power consumption of only 50-mW and a switching speed in the order of 16 ms with 5-V drive.

Complex dispersion relation of 1D dielectric photonic crystal with thin metallic layers

We have carried out the analytical and numerical analysis of metallic insets embedded in a dielectric photonic crystal (DPC). The corresponding one-dimensional metallo-dielectric photonic crystal (MDPC) is studied in relation to the substratum DPC. We describe the complex MDPC dispersion relation curves and the transmission coefficient at the different propagation regimens trough the finite stack. While in the DPC, the band gap argument corresponds to undefined complex solutions of a real dispersion relation, in a MDPC corresponds to a definite complex solution, function of the metal thickness; and analytic continuation of the dispersion curve on the imaginary K plane. The metal absorption is described by the Drude model, and as a result of the absorption in the inset metallic films, complex Bloch vectors are produced for all frequencies as evanescent waves that differ from the straightforward metal absorption.

Superheterodyne amplification of sub-millimeter electromagnetic waves in an n-GaAs film

A superheterodyne amplification of sub-millimeter electromagnetic waves in GaAs due to the negative differential mobility is analyzed. The nonlinearity arises from the modulation of concentration, due to a space charge wave, and from the ponderomotive force, due to electromagnetic waves. The case of resonant interaction of two traveling counter propagating electromagnetic waves and the space charge wave in a thin n-GaAs film placed into a dielectric waveguide is considered. The case of 2D electron gas is also analyzed. The simulation of this nonlinear interaction shows a certain increment of the amplification.

Amplification of space charge waves in n-InN films of THz range

The instability of space charge waves (SCW) of THz range due to the negative differential conductivity (NDC) in n-InN films of submicron thicknesses is investigated theoretically. The influence of the nonlocal dependence of the average electron velocity on the electron energy is considered. The momentum and energy relaxation frequencies are calculated. The influence of the nonlocality on NDC decreases the absolute value of its real part. The nonlocality is essential at the frequencies f ≥ 250 GHz, and the amplification is possible up till the frequencies f ≤ 800 GHz. The increments in n-InN films are 10 times higher than in n-GaN ones, but the frequency range is mainly determined by smaller energy relaxation frequencies in n-InN.

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.

A semi-spherical irradiance profiles meter used as a quality control device

The design of a semi-spherical irradiance profile detector (SD) is shown. With this device, we obtain the distribution of illumination due to punctual sources in the visible range. This meter can be also used as quality control device for lamps and bulbs. We are interested in the distribution of the irradiance, instead of the total irradiance over a complete region, which is the information given by spherical meters, such as the Ulbrich spheres. The obtained discrete profiles corresponds to the irradiance, as equivalent to the voltage intensity detected in semispherical detector basic sensor. These voltage values permit us to obtain the corresponding profile to each source and give as the capability to chose the better sources for specifics tasks.

Low Cost Prototype of an Outdoor Dual Patch Antenna Array for the Openly TV Frequency Ranges in Mexico

The interest in this area is because of the fact that the openly TV is one of the most important communication media in our country. From information supplied in 2009 in the National Survey over availability and use of Technologies, it reveals that the 72.8% of the population uses the services of the openly TV (Instituto Nacional de Estadistica, Geografia e Informatica [INEGI], 2009). A TV can be found in almost all homes of the country, but only 13.6% correspond to digital technology, while only a half of homes with a digital TV requires signal payment. The availability of TVs in Mexican homes in 2010 remained without severe changes (INEGI, 2010).

Rectangular prototype to determine the irradiance pattern produced by directive sources

In order to determine the irradiance profile of a directive source on a plane XY, we present an arrangement of geometry similar to conventional scanners. It is formed by two vertical bases of a mobile rail. On this rail, a photodetector is located, making it able to move from right to left, covering a mesh of 14x15 detection points. The XY movements of the setup are determined by servo motors, which determine the resolution, but considering the interest of researchers in this area, and the feasibility to use a table XY for the scanning, we implement its use as a part of this meter. The detector is located at the corner of the mobile section. The height of the light source under test is located at the central part of the described area. The utilization of only one photo-detector was decided with the purpose of a higher homogeneity of the irradiance measurements. The detector must have high stability and low noise. The resolution XY is determined by the movements on the axes of a length determined by the DSPIC programming. The use of this device instead of commercial hardware for data acquisition contributes to the low costs of the prototype. It was realized all the necessary tests for the generation of reliable information, establishing the time needed to achieve the stability of the system, as well as the levels of noise due to the presence of the detector and of the electronic elements. This prototype has a very simple geometry and relatively low cost. It constitutes a good option to determine the irradiance profile of directive sources.

Nonlinear properties of the omniguide fiber

Annular Photonic structures, which occur on bulk and fibers, are Bragg structures that share both Bragg resonances and waveguiding. They are related to Photonic crystals because of their large enough refraction difference indexes (n2 - n1) that makes unavoidable to consider in full the reflected wave, well beyond the approximations required for analytical gap solitons. Effectively, their confining capabilities are or primary importance, however, the potential of those structures are substantial and deserves to be further explored. Waveguiding occurs where the structure is homogenous, and may be handled on well known methods. Nonlinear propagation has been observed on solid core Bragg fibers and the soliton distribution on a nonlinear circular and annular region have been described. Linear Photonic annular structures, such as resonators, have been studied by A. Yariv as well as on omniguide fibers. The propagation along the direction where the material is inhomogenous, and that correspond to the beam profile, is a complex task and it is the objective of this paper.

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.