Modeling and design of a spiral-shaped Mach-Zehnder interferometric sensor for refractive index sensing of watery solutions

The modeling and design of a spiral-shaped Mach-Zehnder Interferometric sensor (sMZI sensor) for refractive index sensing of watery solutions is presented. The goal of the running project is to realise a multi-sensing array by placing multiple sMZIs in series to form a sensing branch, and to place several sensing branches in parallel. In such an arrangment it is possible to use a single light source for several sensors. Each sensor will contain an electro-optical modulator, which makes it possible to separately interrogate and accurately read-out each sensor in the same sensing branch. One of the novelties in this project is the spiral-shaped layout of the MZI, which has several advantages: a long sensor window length can be placed in a compact sensor chip: within an area of 1 × 1 cm2 lengths of several tens of cm are feasible. Another advantage of the spiral shape is that if both MZI branches are identical (except for the sensor layer) the sensor should be very insensitive to fluctuations in temperature and even to temperature gradients across the chip. Beside robustness, the spiral shape also allows cascading of several sensors. A parametrised sMZI has been designed such that the position, slope, and curvature are continuous. The sensors can each be coated with e.g. a specific immunolayer to be able to detect changes in concentration of viri, bacteria or enzymes. In this project, technology is being developed for the immobilisation and photolithographical patterning of such immunolayers, which should result in a demonstrator to monitor the ripening process of cheese by measuring changes in the concentration of several different enzymes involved in this process

Micromachined two dimensional resistor arrays for determination of gas parameters

A resistive sensor array is presented for two dimensional temperature distribution measurements in a micromachined flow channel. This allows simultaneous measurement of flow velocity and fluid parameters, like thermal conductivity, diffusion coefficient and viscosity. More general advantages of measuring temperature distributions are the inherent compensation of heat losses to the support and the insensitivity to variations in the temperature coefficient of resistance

Fabrication of microcantilever-based IO grated waveguide sensors for detection of nano-displacements

We propose a novel and highly sensitive integrated read-out scheme, capable of detecting sub-nanometre deflections of a cantilever in close proximity to a grated waveguide structure. A very compact and stable sensor element can be realized by monolithically integrating a microcantilever structure with the grated waveguide (GWG), using conventional layer deposition and sacrificial layer etching techniques. The platform integrating a high quality GWG and a low initial bending cantilever has been fabricated and characterized

Si₃N₄ grated waveguide optical cavity based sensors for bulk-index concentration, label-free protein, and mechano-optical gas sensing

A grated waveguide (GWG), which is a waveguide with a finite-length grated section, acts as an optical resonator, showing sharp fringes in the transmission spectrum near the stop-band edges of the grating. These oscillations are due to Fabry-Perot resonances of Bloch modes propagating in the cavity defined by the grated section. Small changes in the environment of the GWG, which disturb the evanescent field of the GWG resonant modes, lead to a shift of its transmission spectrum. This effect can be exploited for sensing applications by detection of a bulk refractive index change or nanodisplacements of a cantilever suspended above the GWG. Here we present 3 applications: (1) a concentration sensor, based on the bulk index change of the GWG top cladding; (2) label-free protein sensing (PepN enzyme - the major Suc-LLVY-AMC-hydrolyzing enzyme in Escherichia coli), where the GWG spectral shift is due to the antibody-antigen interaction and growth of an ad-layer on it; and (3) gas sensing, where the GWG detects stress-induced deflections of a doubly-clamped microcantilever (microbridge) with a Pd top layer due to H2 gas absorption by the Pd receptor layer. Gratings were defined on Si3N4 waveguides using laser interference lithography. To demonstrate (1) concentration sensing, we filled a cuvette on the surface of the sensor with a phosphate buffered saline solution of 1 wt% (PBS1x). Evaporation of water from the open cuvette continuously changes the concentration, hence the bulk index, which is measured as a spectral shift of the sensor. Changes of the refractive index down to 2×10-5 RIU and concentration changes down to 0.01 wt% can be resolved, which is comparable with the resolution of ultrasonic sensors. For (2) protein sensing, it was found that the spectral shift of a peak in response to the antibody-antigen binding reaction changes with time t approximately according to an exponential function, with time constant 770 s. The reaction saturates after ~35 minutes. The total shift was approximately 342 pm, corresponding to the growth of an ad-layer of ~2 nm. The sensitivity of a micro-bridge device for (3) gas sensing was rather low due to the relatively large gap g of ~700 nm between the bridge and the GWG. During the H2 absorption process, the shift depends almost linearly on time, which is partly due to the initially rapid change of the gap size, g. The H2 desorption takes place at approximately half the rate of the absorption process

Mechanical tuning of optical race-track ring resonators

This paper presents the fabrication and mechanical characterization of electrostatically actuated micro bimorphs integrated with race-track ring resonators, for optical tuning applications. The bimorphs, having an upward deflection in the off-state, are integrated by surface micromachining techniques with race-track ring resonators fabricated on Silicon On Insulator (SOI) wafers. Using electrostatic actuation, these bimorphs are pulled into the evanescent field of the ring resonator thereby modulating the propagation properties. Pull-in voltages of the bimorphs have been measured statically and the effect of electrostatic spring softening (ESS) on the resonance frequency has been measured dynamically. The resonance wavelength of the optical ring resonator could be tuned by 50 pm by applying an 8.5 V DC voltage to a 40 μm long bimorph, bringing it into close proximity of the ring resonator waveguide. To the best of our knowledge, this is the first experimental demonstration of tuning of race track ring resonators by integrated, electrostatically actuated bimorphs.\ud \u