We present the theoretical and the experimental implementation of an all-optical phase modulation system in integrated Mach-Zehnder Interferometers to solve the drawbacks related to the periodic nature of the interferometric signal. Sensor phase is tuned by modulating the emission wavelength of low-cost commercial laser diodes by changing their output power. FFT deconvolution of the signal allows for direct phase readout, immune to sensitivity variations and to light intensity fluctuations. This simple phase modulation scheme increases the signal-to-noise ratio of the measurements in one order of magnitude, rendering in a sensor with a detection limit of 1.9·10⁻⁷ RIU. The viability of the all-optical modulation approach is demonstrated with an immunoassay detection as a biosensing proof of concept.
There is still the need for a compact and cost-effective solution for efficient light in-coupling in integrated waveguides employed in photonic biosensors, especially when these waveguides are of submicron dimensions and operate at visible wavelengths. The employment of a vertically stacked taper with a larger input area is proposed to meet this need. The design of the taper is divided into two stages: in the first stage, light is guided downwards by two vertically stacked tapers; in the second stage, an inverted taper directly confines the light inside the waveguide. The design parameters are optimized using commercial software, obtaining a total theoretical light coupling efficiency of 72.25%. The taper is manufactured using SU-8 polymer as the main material, employing standard photolithography techniques at wafer level. After characterization, the results show the practicality of the taper when coupling light from macrometric sources to nanometric waveguides, obtaining an experimental coupling efficiency of 55%. With this vertical taper, a compact, easy-to-couple and cost-effective solution is achieved for waveguide-based biosensors operating at visible wavelengths, opening the way for a truly portable point-of-care biosensor for low-cost and label-free diagnostics.
It is shown that the whole spectrum of dimensions and entropies which characterize a strange attractor can be computed by an extension of the Grassberger Procaccia method. A measure of algorithmic complexity is introduced which characterizes pattern formation in space and time.
We present an optical characterization of the effect of reactive ion beam etching on InP using a plasma of CH 4 /H 2 /N 2 generated by electron cyclotron resonance discharges. We have studied both semi-insulating (Fe-doped) and n + -type material (Sn-doped). Raman scattering and photoreflectance have been used to study the evolution of the lattice disruption and the surface electric field as a function of the ion beam voltage, which was varied in the range from 100 V to 600 V. Results indicate that the optimum etching conditions are obtained for an ion beam voltage of about 300 V due to the better relationship between disturbance of the crystal lattice and the etch rate.
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