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In conclusion, the papers collected in this Special Issue summarize significant advances in the field of optical sensors, with specific contributions in sensor technology and applications of fiber Bragg gratings, resonators and spectroscopy. The performance of this integrated sensor is demonstrated using glucose solutions (0.05-0.3 g/mL) and the sensor response is shown to be dynamic and reversible. The refractive index sensor exhibits a linear response in the refractive index range of 1.333-1.358 RIU (refractive index unit), with a sensitivity of 32.4 RIU SP -1 sp and a resolution of 2 × 10 SP -3 sp RIU at the refractive index of water. Today, optical sensors are the subject of a very significant number of studies and applications. [Extracted from the article]

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]

This paper presents results of numerical modeling of a modified design of an optical sensor based on segmented periodic silicon oxynitride (SiON) grating evanescently coupled with silicon wire. This segmented grating works as a leaky waveguide, which filters input power from a broadband optical source and radiates it as an outcoming optical beam with both a small wavelength band and a small beam divergence. The radiation angle strongly depends on the refractive index of the grating environment and provides sensor interrogation by measuring the far field pattern in the focal plane of the lens, which is placed near the sensor element. The device concept was verified by direct numerical modeling through the finite difference time domain (FDTD) method and provided moderate intrinsic limit of detection (iLOD) ~ 0.004 RIU with a possible iLOD ~ 0.001 RIU for 10 mm-long structures. [ABSTRACT FROM AUTHOR]

In this paper the numerical modeling of periodic structures for implementation of a novel type of photonic sensors by using the 3D finite difference time domain (FDTD) method is presented. The sensing is based on the optical phenomena occurring in the segmented grating which is placed on the thin silica buffer over the silicon wire waveguide in the silicon‐on‐insulator (SOI) structure. This design provides the effective resonance interaction of the guided wave with the virtual leaky wave supported by the segmented grating evanescently coupled with the silicon wire. The dropping wavelength of this interaction is strongly dependent on the grating environment and it provides a strong refractometricsensitivity (Sn > 420 nm RIU−1) and surface sensitivity Sh > 0.17, evaluated in the case of water. The modeling proves that the effect of abnormal blocking due to virtual leaky wave could be the base for the design of optical sensors with extremely high sensitivity. 3D FDTD modeling is used to investigate the sensing properties in water of segmented gratings of SU‐8 polymer having period 1.4 µm and evanescently coupled with an underlying silicon wire. Sensor shows homogeneous sensitivity Sn = ∂λ/∂n > −420 nm‐1 and surface sensitivity Sh = ∂λ/∂h > 0.17. Its sensitivities are compatible with those of slot or subwavelength structures but using four times larger feature sizes. [ABSTRACT FROM AUTHOR]

Fibre Bragg grating (FBG) strain sensors are not only a very well-established research field, but they are also acquiring a bigger market share due to their sensitivity and low costs. In this paper we review FBG strain sensors with high focus on the underlying physical principles, the interrogation, and the read-out techniques. Particular emphasis is given to recent advances in highly-performing, single head FBG, a category FBG strain sensors belong to. Different sensing schemes are described, including FBG strain sensors based on mode splitting. Their operation principle and performance are reported and compared with the conventional architectures. In conclusion, some advanced applications and key sectors the global fibre-optic strain sensors market are envisaged, as well as the main market players acting in this field. [ABSTRACT FROM AUTHOR]

An accurate design of an innovative fiber optic temperature sensor is developed. The sensor is based on a cascade of three microstructured optical fibers (MOFs). In the first one a suitable cascade of long period gratings is designed into the core. A single mode intermediate and a rare-earth activated Fabry-Perot optical cavity are the other two sensor MOF sections. An exhaustive theoretic feasibility investigation is performed employing computer code. The complete set-up for temperature monitoring can be obtained by utilizing only a low cost pump diode laser at 980 nm wavelength and a commercial optical power detector. The simulated sensitivity S = 315.1 μW/°C and the operation range ΔT = 100 °C is good enough for actual applications. [ABSTRACT FROM AUTHOR]

This paper discusses the physical nature and the numerical modeling of a novel approach of periodic structures for applications as photonic sensors. The sensing is based on the high sensitivity to the cover index change of the notch wavelength. This sensitivity is due to the effect of abnormal blocking of the guided wave propagating along the silicon wire with periodic strips overhead it through the silica buffer. The structure sensing is numerically modeled by 2D and 3D finite difference time domain (FDTD) method, taking into account the waveguide dispersion. The modeling of the long structures (more than 1000 strips) is accomplished by the 2D method of lines (MoL) with a maximal implementation of the analytical feature of the method. It is proved that the effect of abnormal blocking could be used for the construction of novel types of optical sensors. [ABSTRACT FROM AUTHOR]