130,570 research outputs found
Fiber Optic Sensing with Lossy Mode Resonances: Applications and Perspectives
No full textThis review focuses on the recent advances in lossy more resonance (LMR) fiber optic sensors. LMR sensors present many interesting features also in comparison with surface plasmon resonance (SPR), the most widespread resonance-based sensing platform. Two key parameters determine the performance of LMR sensors: geometrical configuration and material supporting the LMR. After reviewing those aspects and some fundamentals of the theory, the review focuses on the sensing mechanisms, mainly based on refractometry, and their possible applications. Many examples from the literature are reported ranging from electric field to pressure sensors and from gas detection to biosensors. Such vibrant activity on LMR sensors confirms the potentiality of this technology making it a very promising platform for sensor development
All-optical electric field sensor in domain inverted LiNbO3 for harsh environment
No full textOptical high-voltage sensors have outstanding advantages in terms of isolation and immunity to electromagnetic interference. So far, several configurations have been proposed, mostly based on integrated Mach-Zehnder interferometers [1] or polarization/phase rotation in piezo-electric crystal [2]. While the first scheme requires initial electrical bias to compensate for the phase mismatch between the two arms, the second one requires interrogation or phase noise reduction systems that are expensive to implement. Near cut-off optical waveguide devices have been already reported in LiNbO3. In particular, the use of waveguides at cut-off was proposed for modulation in the field of optical communications [3,4] and sensing [5]. We present a novel integrated optical high voltage sensor based on a Z-cut LiNbO3 which operates without any metallic parts. The proposed device is sketched in Fig. 1 (left). An annealed proton exchange (APE) waveguide near cut-off is fabricated in Z-cut LiNbO3 and centered in a domain inverted region. The application of an external electric field parallel to the z axis of the device produces a refractive index change n between positive and negative domains given by ne 3r33E, where E is the intensity of the external electric field along the z-axis, ne=2.14 and r 33=30.8 pm/V are the refractive index and the electro-optic coefficient along the z-axis, respectively. As a consequence the optical mode will broaden so that, after a sufficient propagation length, a loss is produced due to a mode-profile mismatch of the guided modes between active and passive regions
Ray and wave instabilities in twisted graded-index optical fibers
No full textWe study ray and wave propagation in an elliptical graded-index optical fiber or lens with a twisted axis and show analytically the existence of an instability for both ray trajectories and beam moments in a finite range of axis twist rate embedded within the spatial frequencies of periodically focused rays for the untwisted fiber. By considering the paraxial ray equations and the paraxial wave dynamics in a rotating frame that follows the fiber axis twist, we reduce the dynamical problem of ray trajectories to the classical Blackburn’s pendulum, which shows a dynamical instability, corresponding to classical diverging trajectories, due to the competing effects of confining potential, Coriolis force, and centrifugal force. A closed set of linear evolution equations for gener- alized beam moments are also derived from the paraxial wave equation in the rotating reference frame, revealing the existence of a dynamical moment instability in addition to the trajectory instability. A detailed analysis of beam propagation is presented in case of a Gaussian beam, and different dynamical regimes are discussed
High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers
No full textIn recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated
Prescription of vitamin D among Swiss pediatricians.
No full textThe traditional recommendation that Swiss children receive vitamin D during the first year of life was recently extended to the second and third year of life and during winter for older children. The aim of the study was to identify how Swiss pediatricians prescribe vitamin D. Between December 2016 and March 2017, 795 (52%) of 1530 invited Swiss board-certified pediatricians answered a closed-ended questionnaire. Respondents routinely prescribe vitamin D supplements in infants ≤ 1 year of age, but infrequently in children ≥ 3 years of age. Only a minority of them prescribe vitamin D in children with conditions that predispose to poor vitamin D status. Oily vitamin D preparations are the most popular and are usually prescribed in a once-a-day regimen. In situations like intake of drugs interfering with vitamin D metabolism, intestinal malabsorption, and diabetes mellitus, Swiss pediatricians often seek the advice of a subspecialist. In cases with clinical suspicion of poor vitamin D status, the diagnosis is confirmed by the determination of 25-hydroxyvitamin D.Conclusion: Few pediatricians prescribe a vitamin D supplementation in children ≥ 3 years of age. Collaboration between policymakers and health care professionals is required to fill the gap between guidelines and clinical practice. What is Known: • In Switzerland, vitamin D supplementation is recommended during the first, second, and third year of life as well as during winter for older children. • Both alcoholic and oily preparations are currently available. What is New: • Swiss pediatricians routinely prescribe vitamin D in infants ≤ 1 year of age, but infrequently in children ≥ 3 years of age. • Oily vitamin D preparations are the most popular and are usually prescribed in a once-a-day regimen
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