Fiber Optic Sensing with Lossy Mode Resonances: Applications and Perspectives

This 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

Self-Supervised Intrinsic Image Decomposition

Intrinsic decomposition from a single image is a highly challenging task, due to its inherent ambiguity and the scarcity of training data. In contrast to traditional fully supervised learning approaches, in this paper we propose learning intrinsic image decomposition by explaining the input image. Our model, the Rendered Intrinsics Network (RIN), joins together an image decomposition pipeline, which predicts reflectance, shape, and lighting conditions given a single image, with a recombination function, a learned shading model used to recompose the original input based off of intrinsic image predictions. Our network can then use unsupervised reconstruction error as an additional signal to improve its intermediate representations. This allows large-scale unlabeled data to be useful during training, and also enables transferring learned knowledge to images of unseen object categories, lighting conditions, and shapes. Extensive experiments demonstrate that our method performs well on both intrinsic image decomposition and knowledge transfer.Comment: NIPS 2017 camera-ready version, project page: http://rin.csail.mit.edu

High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers

In 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

Optical Quality Resorbable Calcium-Phosphate Glasses for Biophotonic Applications

Recently developed calcium-phosphate glass formulations are proposed in this chapter as a new class of materials for biomedical optics and photonics. The glasses have been designed and carefully prepared in our laboratory to be dissolvable in biological fluids while being optically transparent, mechanically reliable both in dry and humid environments, and suitable for both preform extrusion and fiber drawing. Optical fibers have been drawn from these glasses using our custom-made induction heated drawing tower and showed attenuation loss values from one to two orders of magnitude lower than the counterpart polymeric-based bioresorbable devices reported in literature. In addition, the optical fibers have been implanted in living rats for several weeks and no clinical signs of any adverse effect have been found. Results on the inscription and characterization of different types of fiber Bragg grating-based optical filters will be also shown, together with the demonstration of the suitability of the above-mentioned bioresorbable optical fibers for time-domain diffuse optical spectroscopy

Optimizing gold nanoparticle size and shape for the fabrication of sers substrates by means of the langmuir–blodgett technique

The Langmuir–Blodgett technique, in which a layer of nanoparticles is spread at the water/air interface and further transferred onto a solid support, is a versatile approach for the preparation of SERS substrates with a controllable arrangement of hotspots. In a previous work, we demonstrated that fine-tuning the lateral packing and subsequent seed growth of 10 nm gold nanoparticles led to a quasi-resonant enhanced in the SERS signal of a test analyte. Here, we explore further enhancements by modifying the size and shape of the spread gold nanoparticles in order to take advantage of the inherent interparticle repulsion mechanisms present at the interface. We show that the size of the used nanoparticles is also a determinant factor, which cannot be compensated by the subsequent electroless growth. We also show that, although the seeded growth leads to rough hotspots, the sensitivity can be optimized by self-assembling urchin-shaped nanoparticles, with a roughness that is fine-tuned a priori. Our results suggest an intriguing correlation between surface homogeneity and SERS signal enhancement, indicating that regular substrates will have the optimal performance

Toward the fabrication of extruded microstructured bioresorbable phosphate glass optical fibers

The steps toward the fabrication of directly extruded microstructured fiber preforms made of a bioresorbable phosphate glass are herein presented, analyzing the features of the process from the glass synthesis to the manufacturing of the fiber. The realization of these fibers leverages on three main pillars: an optically transparent bioresorbable glass, its extrusion into a preform, and the fiber drawing. The glass has been designed and carefully prepared in our laboratory to be dissolvable in a biological fluid while being optically transparent and suitable for both preform extrusion and fiber drawing. To support the production of an optimized die for the preform extrusion, a simplified laminar flow model simulation has been employed. This model is intended as a tool for a fast and reliable way to catch the complex behavior of glass flow during each extrusion and can be regarded as an effective design guide for the dies to fulfill the specific needs for preform fabrication. After die optimization, extrusion of a capillary was realized, and a stacking of extruded tubes was drawn to produce a microstructured optical fiber made of bioresorbable phosphate glass

Perturbed geodesics on the moduli space of flat connections and Yang-Mills theory

If we consider the moduli space of flat connections of a non trivial principal SO(3)-bundle over a surface, then we can define a map from the set of perturbed closed geodesics, below a given energy level, into families of perturbed Yang-Mills connections depending on a small parameter. In this paper we show that this map is a bijection and maps perturbed geodesics into perturbed Yang-Mills connections with the same Morse index.Comment: 58 pages, 3 figure

Multifunctional bioresorbable phosphate glass optical fibers for theranostics

We report on the design and development of microstructured phosphate glass optical fibers for minimally invasive diagnosis and therapy. We discuss preliminary results of fiber drawing and characterization

Calcium-phosphate glass-based bioresorbable fibre optics for light and drug delivery

Calcium-phosphate glasses (CPGs) are commonly used as scaffolds in tissue engineering. A novel formulation of optically transparent CPG has been recently developed to be used as an optical fibre for biomedical implantable devices. Its purpose is to combine the bioresorbability of CPGs with optical features, thus extending the applications of bioresorbable sensors for in-body monitoring or diagnostics. Modifications of the glass composition or post-treatments on the fibres can tailor the dissolution time and the interaction of the glass with different stimuli as well as with specific cells. The tested glasses both in bulk and fibre shapes showed good strength (from 200 to 350 MPa) with values that are lower than standard silica glass and much higher than common bioresorbable polymers. CPG fibres were also implanted in living rats for several weeks and no clinical signs of any adverse effect have been found. We will present our latest results on these subjects starting from the characterisation of the CPGs by means of dissolution tests, in-vitro, and ex-vivo experiments