Inigo Salinas

BESOI-based integrated optical silicon accelerometer

The design, simulation, fabrication and characterization of a new integrated optical accelerometer is presented in this paper. The reduction of fabrication, packaging and thermomechanical stresses are considered by keeping the weak mechanical parts free of stresses. The mechanical sensor consists on a quad beam structure with one single mass. In addition, there are two waveguides on the frame of the chip self-aligned to one on the mass of the accelerometer. Four lateral beams increase the mechanical sensitivity and allow the flat displacement of the optical waveguides on the mass. The working principle is based on the variation of the output light intensity versus the acceleration due to the misalignment of the waveguides. The devices have been optimized by the finite-element method to obtain a mechanical sensitivity of 1 /spl mu/m/g. The fabrication technology is based on BESOI wafers combining bulk an surface micromachining. Moreover, machined glass wafers with cavities are bonded to the silicon wafer for packaging and damping control. Special packaging considerations as dicing, polishing and alignment are also presented. Optical measurements at 633 nm shown an optical sensitivity of 2.3 dB/g for negative and 1.7 dB/g for positive acceleration. This difference in the sensitivity has been demonstrated as a consequence of the passivation layer located over the core of the waveguides.

Measurement of the linewidth enhancement factor in DFB lasers using a high-resolution optical spectrum analyzer

Linewidth enhancement factor (also know as chirp parameter is calculated for two distributed feedback lasers using the linewidth asymptotic behavior predicted by Schawles-Townes and Henry. A high-resolution optical spectrum analyzer (BOSA) is used to measure power and linewidth. Comparison with widely accepted network analyzer method is performed with very good agreement.

Stimulated Brillouin scattering gain profile characterization by interaction between two narrow-linewidth optical sources

We report on results from the characterization of Stimulated Brillouin Scattering (SBS) spectra for standard single-mode fiber produced by the interaction between two counter-propagating tunable laser sources (TLS) using one as the probe signal to measure and the other as the pump, sweeping a wide span around the signal. Assuming TLS linewidth negligible against SBS gain bandwidth, we measure SBS spectrum for a wide range of pump and probe signal power levels and study the evolution of relevant SBS parameters such as linewidth and gain profile. High signal to noise ratio measurements allows analyzing the evolution of the SBS gain profile from Lorentzian to Gaussian as predicted by current theory of SBS and the use of SBS response for filtering applications.

Low-cost, digital lock-in module with external reference for coating glass transmission/reflection spectrophotometer

A versatile, low-cost, digital signal processor (DSP) based lock-in module with external reference is described. This module is used to implement an industrial spectrophotometer for measuring spectral transmission and reflection of automotive and architectonic coating glasses over the ultraviolet, visible and near-infrared wavelength range. The light beams are modulated with an optical chopper. A digital phase-locked loop (DPLL) is used to lock the lock-in to the chop frequency. The lock-in rejects the ambient radiation and permits the spectrophotometer to work in the presence of ambient light. The algorithm that implements the dual lock-in and the DPLL in the DSP56002 evaluation module from Motorola is described. The use of a DSP allows implementation of the lock-in and DPLL by software, which gives flexibility and programmability to the system. Lock-in module cost, under 300 euro, is an important parameter taking into account that two modules are used in the system. Besides, the algorithms implemented in this DSP can be directly implemented in the latest DSP generations. The DPLL performance and the spectrophotometer are characterized. Capture and lock DPLL ranges have been measured and checked to be greater than the chop frequency drifts. The lock-in measured frequency response shows that the lock-in performs as theoretically predicted.

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.

Infrared Thermometry System for Temperature Measurement in Induction Heating Appliances

The theoretical analysis and design of an infrared (IR) thermometry system for temperature measurement in domestic induction hobs is presented together with the results of its implementation. The system includes an InGaAs PIN photodiode and a preamplifier which detects the IR radiation emitted from the bottom of the cookware and the glass-ceramic top. The analysis includes an algorithm to discount the contribution of the glass-ceramic material from the total signal. The proposed system has been designed for frying temperature measurements (140 ^°C-180 ^°C) and tested in the cooking range from 120 ^°C to 200 ^°C for cookware made of different materials. Finally, the measurement temperature errors were around 20 ^°C for almost any emissivity of the cookware.

Simple estimation of transition losses in bends of wide optical waveguides by a ray tracing method

Numerical simulation methods based on modal theory are not suitable for wide waveguides where the number of guided modes increases greatly. A simple ray tracing method for treating this situations is proposed, and its results are validated with experimental measurements of fabricated waveguides. The important agreement between theory and experiments makes this method an easy way to design bent waveguides with transitions between sections with different curvature.

Characterization and passivation effects of an optical accelerometer based on antiresonant waveguides

An optical accelerometer based on antiresonant reflecting optical waveguides is presented. The design consists on a quad beam structure where two waveguides are placed on the frame of the accelerometer, while a third is placed over the proof mass. When an acceleration is applied, a misalignment between the three waveguides is immediate, causing a reduction in the output power. If the passivation layer is not considered, simulations predict a nearly symmetrical behavior for positive and negative accelerations, with an optical sensitivity of 2.3 dB/g. Experimental and simulation confirm that passivation modes produce a reduction in the optical sensitivity for positive acceleration values, resulting in an asymmetrical response of the accelerometer.

Dual-wavelength measurement system for absorbance chemical sensing

A novel compact dual-wavelength measurement system for absorbance chemical sensing incorporating digital lock-in amplifiers is reported. Its main innovation is the introduction of a reference wavelength to correct the possible non-specific optical changes of the system. The performance of the instrumentation has been tested on a laboratory setup and with integrated optical absorbance sensors.

Absorbance-Based Integrated Optical Sensors

Optochemical sensors have had a huge expansion and in recent years interesting sorts of optical sensor have been developed which make use of the integrated circuit microelectronic technology and the optical technological advances achieved in the telecommunications industry. These devices are based on optical fibers, planar waveguides or the combination of both supports as light-guiding structures and offer an enhanced performance thanks to a miniaturized size, a feasible mass production at low cost, the possibility to measure at large distances and the capability of reaching places hard to access for the in situ monitoring of environmental or medical parameters. In this chapter, we provide an overall view of integrated chemical sensors based on absorbance measurements, describing their main characteristics, advantages and drawbacks. In order to focus on these types of devices, first of all, a brief classification is given, in terms of the interaction mechanisms and the reactive phases or membranes that are involved in the response, and the radiation transmission medium. Next, different waveguide configurations are briefly described because of to the relevancy of these structures as the main constituent of integrated optodes and, finally, some absorbance-based integrated sensors are detailed.