Robust and low-cost interrogation technique for integrated photonic biochemical sensors based on Mach-Zehnder interferometers

We describe and experimentally demonstrate a measuring technique for Mach-Zehnder interferometer (MZI) based integrated photonic biochemical sensors. Our technique is based on the direct measurement of phase changes between the arms of the MZI, achieved by signal modulation on one of the arms of the interferometer together with pseudoheterodyne detection, and it allows us to avoid the use of costly equipment such as tunable light sources or spectrum analyzers. The obtained output signal is intrinsically independent of wavelength, power variations, and global thermal variations, making it extremely robust and adequate for use in real conditions. Using a silicon-on-insulator MZI, we demonstrate the real-time monitoring of refractive index variations and achieve a detection limit of 4.1 × 10−6 refractive index units (RIU)

Very sensitive porous silicon NO2 sensor

We report a nitrogen dioxide sensor suitable for environmental control, based on the change in conductivity of a single meso-porous silicon (PS) layer with about 80% porosity. We present the characterization of the sensor in the presence of low concentrations of NO2 in dry air and study the influence of humidity on sensor behaviour. The sensor shows a sensitivity to 12 ppb of NO2 in dry air and a good response to 50 ppb in humid air. © 2003 Elsevier Science B.V. All rights reserved

Porous silicon free-standing coupled microcavities

Porous silicon free-standing coupled microcavities were grown by an electrochemical attack. The natural drift of the layer thickness and porosity was successfully compensated by changing the etching parameters in a controlled way. Potential applications for CMC structures with controlled optical parameters could be channel filtering within optical telecommunication devices

Free-standing porous silicon single and multiple optical cavities

The porous silicon free-standing microcavity structures, with different layer designs, were fabricated. The single microcavities were found to show transmission resonances in the wavelength region of 1.55μm with quality factors of upto 3380. The incident angle dependent measurements were also reported where transmission peak blueshift and splitting of transverse electric and transverse magnetic polarized modes due to porous silicon birefringence were observed

Broken symmetry in photonic crystals: Resonant Zener tunneling of light waves

We report on the observation of Zener tunnelling of light waves in spectral and timeresolved transmission measurements, performed on an optical superlattice of porous silicon with broken translational symmetry. © 2006 Optical Society of America

Role of microstructure and layer thickness in porous silicon conductometric gas sensors

The electrical injection in porous silicon fabricated with heavily doped p-type silicon is very sensitive to NO 2. The known effect is an injection increase associated to NO 2. We show experimentally a strong correlation between two structural properties and the sensitivity of electrical injection to NO 2. The first property is the microstructure, i.e. the pore morphology at nm scale. A structure with straight, elongated pores shows large sensitivity, as opposed to a branching structure. The second property is the layer thickness, which determines the sign of the effect of NO 2. If the thickness is sufficiently low - of the order of few Urn - the injection in presence of NO 2 decreases, instead of increasing. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Silicon nanoclusters containing nitrogen and sensitization of erbium luminescence in SiOx:Er

Silicon-rich silica samples doped with erbium were grown by PECVD and characterized by photoluminescence, time-resolved photoluminescence and Fourier transform infrared spectroscopy. We observe that upon increased silicon content, the absorption spectrum reveals the formation of a SiN bond. This indicates the possible incorporation of nitrogen from the precursor NO gas into the Si nanoclusters. The highest erbium photoluminescence is obtained for the sample with the highest silicon content and its decay characteristics are nearly single exponential with a time constant of 5 ms. In addition to erbium emission, a visible luminescence peak at about 550 nm is observed. This shows multi-exponential decay kinetics with decay times of the order of 10 ns. We propose that this emission is due to small Si nanoclusters covered by a SiN shell. From the measurements, we study a mechanism to explain the erbium excitation in this material

Waveguiding, absorption and emission properties of dye-impregnated oxidized porous silicon

The waveguiding, absorption and emission properties of oxidised porous silicon waveguides when impregnated with Nile Blue have been studied. We present m-line measurements before and after the impregnation showing that the effective indices of the modes remain the same. When performing guided luminescence experiments, a structured emission band is measured. Using the refractive index profile extracted from m-line measurements it has been possible to simulate the emission lineshape assuming the observation of an interference pattern formed across the waveguide. We demonstrate that these oscillations appear because in the first hundreds of nanometers the dye concentration is several orders of magnitude higher than in the rest of the sample. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA

Interferometric method for monitoring electrochemical etching of thin films

In this work we present a method for monitoring the optical parameters of a film during its etching process. Optical interferometry of two laser beams with different angles of incidence is observed to measure the index of refraction profile and the etch rate evolution simultaneously. With this technique we have measured the inhomogeneity in the etch process of porous silicon layers, which is an essential issue to make good quality optical microcavities or photonic crystals with this material. In addition, by sweeping a range of currents we are able to fully characterize the etch rate and the porosity vs. current density in one single sample, without the need of independent measurements