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Quartz enhanced photo acoustic spectroscopy (QEPAS) has gained a growing interest in recent years for gas sensing technology because of the high sensitivity provided by sharp resonant tuning forks (QTFs) exploited as piezoelectric sound wave detectors; and the modularity, compactness, and robustness of the sensors. The currently used experimental configurations of the QEPAS sensors still rely on free space optics, which are potentially subject to misalignment and require a relatively high space occupation. Here we propose the modelling and the design of a QEPAS sensor with the laser source and optical components for beam delivery bonded together and semi-integrated with the tuning fork. In particular, we propose a configuration in which an optical resonator placed between the prongs of the QTF is coupled with the laser source through a waveguide (OMRSI-QEPAS). For this setup design, COMSOL simulations provided pressure values of the acoustic wavefront comparable with the standard on-beam configuration employing acoustic resonator tubes. Therefore, the design here proposed aims to package the opto-acoustic core of a QEPAS sensor in a single module of few cubic centimeters to definitively address the misalignment issues and pave the way to a further level of miniaturization, integration and deployment for application like mobile and on-drone sensing. [ABSTRACT FROM AUTHOR]

Third order grating filters fabricated in small Silicon-on-Insulator rib waveguides are demonstrated. Variations in grating etch depth and duty cycle are considered, and a maximum experimental reflection of 42% is demonstrated for gratings of 1500 µm in length, with a grating period of approximately 689 nm and an etch depth of 200 nm. Agreement with modeling is shown to be good.

A fiberoptic architecture based on a ring resonator (RR) including a typical long period grating (LPG) was investigated. The interactions between the fundamental core mode (LP01 or HE11) coupled to the RR and the cladding mode (LP08), excited into the cavity by means of the LPG, allow a peculiar spectral response characterized by two splitting resonances to be achieved. The new LPGRR architecture is investigated theoretically and a mathematical modelling based on the transfer matrix method (TMM) is proposed. The theoretical results are compared with the experiments measured by an open-loop LPG, while the performance of the relative LPGRR was estimated by a theoretical parametric analysis. Finally, an overview of the possible LPGRR sensing applications is provided by investigating the features of a strain sensor operating in different environmental conditions. [ABSTRACT FROM AUTHOR]

The influence of Germanium-on-Silicon waveguide geometries on single-mode and multimode operations as well as on zero birefringence conditions has been deeply investigated in the mid infrared spectrum. The design equations to estimate the single mode conditions have been carried out and interpolated by exponential functions. Moreover, the group velocity dispersion and third-order dispersion have been investigated in the range 3-6 μm as a function of various waveguide geometries. Finally, nonlinear properties, for instance the modal Raman gain, have been investigated, comparing with Silicon-on-Insulator waveguides. The set of results identifies accurate guidelines for the design of these optical waveguides for several applications. [ABSTRACT FROM PUBLISHER]

In this paper, a spectroscopic sensor formed by a silicon-on-insulator waveguiding Bragg grating ring resonator working in linear and non-linear regime is proposed. In linear regime, the device shows a spectral response characterized by a photonic band gap (PBG). Very close to the band gap edges, the resonant structure exhibits split modes having a splitting magnitude equal to the PBG spectral extension, whose characteristics can be exploited to obtain a RI optical sensor almost insensitive to the fabrication tolerances and environmental perturbations. When the device operates in nonlinear regime, exactly in the spectral region showing the split resonant modes, the RI sensing performance is strongly improved with respect to the linear regime. This improvement, demonstrated by taking into account all the non-linear effects excited in the integrated silicon structure (i.e., Two Photon Absorption (TPA), TPA-induced Free Carrier Absorption, plasma dispersion, Self-Phase-Modulation and Cross-Phase-Modulation effects as induced by Kerr nonlinearity) as well as the deleterious thermal and stress effects, allows enhancing the performance of the RI split mode resonant sensors, while achieving good immunity to the fabrication tolerances and environmental perturbations. The improvement in terms of sensor resolution can be at least one order of magnitude, still without using optimal parameters. [ABSTRACT FROM AUTHOR]

In this paper, the investigation and detailed modeling of a cascaded Raman laser, operating in the midwave infrared region, is described. The device is based on silicon-on-insulator optical waveguides and a coupled resonant microcavity. Theoretical results are compared with recent experiments, demonstrating a very good agreement. Design criteria are derived for cascaded Raman lasers working as continuous wave light sources to simultaneously sense two types of gases, namely C2H6 and CO2, at a moderate power level of 130 mW. [ABSTRACT FROM AUTHOR]

A guided-wave chemical sensor for the detection of environmental pollutants or biochemical substances has been designed. The sensor is based on an asymmetric directional coupler employing slot optical waveguides. The use of a nanometer guiding structure where optical mode is confined in a low-index region permits a very compact sensor (device area about 1200 μm²) to be realized, having the minimum detectable refractive index change as low as 10-5. Silicon-on-Insulator technology has been assumed in sensor design and a very accurate modelling procedure based on Finite Element Method and Coupled Mode Theory has been pointed out. Sensor design and optimization have allowed a very good trade-off between device length and sensitivity. Expected device sensitivity to glucose concentration change in an aqueous solution is of the order of 0.1 g/L. [ABSTRACT FROM AUTHOR]

We propose and analyze three Si-based room-temperature strip-guided "manufacturable" integrated quantum photonic chem/bio sensor chips operating at wavelengths of 1550 nm, 1330 nm, and 640 nm, respectively. We propose design rules that will achieve super-sensitivity (above the classical limit) by means of mixing between states of coherent light and single-mode squeezed-light. The silicon-on-insulator (SOI), silicon-on-sapphire (SOS), and silicon nitride-on-SiO2-on Si (SiN) platforms have been investigated. Each chip is comprised of photonic building blocks: a race-track resonator, a pump filter, an integrated Mach-Zehnder interferometric chem/bio sensor, and a photonic circuit to perform parity measurements, where our homodyne measurement circuit avoids the use of single-photon-counting detectors and utilizes instead conventional photodetectors. A combination of super-sensitivity with super-resolution is predicted for all three platforms to be used for chem/bio sensing applications. [ABSTRACT FROM AUTHOR]