The Experts below are selected from a list of 283329 Experts worldwide ranked by ideXlab platform
Mario Martinelli - One of the best experts on this subject based on the ideXlab platform.
-
Backscattering in silicon photonic waveguides and circuits
Proceedings of SPIE, 2011Co-Authors: Francesco Morichetti, Antonio Canciamilla, Carlo Ferrari, Mario Martinelli, Andrea MelloniAbstract:The effects of roughness induced Backscattering in optical waveguides and circuit realized on a silicon-on-insulator platform are investigated. A systematic experimental investigation on low-loss silicon nanowires, with a sidewall roughness rms around 1-2 nm, is presented, showing that a few hundreds of micrometers long waveguide exhibits a Backscattering level that can hinder its exploitation in many applications. The effect is typically stronger for TE polarization and is significantly enhanced inside optical cavities, such as microring resonators, where Backscattering is coherently enhanced according to the square of the finesse of the resonator and can modify dramatically the spectral response of the resonators, even at moderate quality factors. We found general relationships relating Backscattering to the geometric and optical parameters of the waveguides, to polarization rotation effects, and to coupling with higher-order modes. On the basis of these results, design rules to mitigate Backscattering effects are proposed. The main statistical properties of roughness induced Backscattering were also experimentally derived, these results enabling an accurate modeling of realistic waveguides and the evaluation of the Backscattering impact in integrated devices and circuits.
-
coherent Backscattering in optical microring resonators
Applied Physics Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Mario Martinelli, Antonio Samarelli, R M De La Rue, M Sorel, Andrea MelloniAbstract:The effects of Backscattering induced by waveguide sidewall roughness in integrated ring resonators (RRs) are experimentally observed. We demonstrate that coherent Backscattering, originated by multiple round trips in the RR, increases with the square of the effective group index of the cavity and can dramatically affect the behavior of integrated RRs even at moderate quality factors of 104. From our results Backscattering emerges as one of the most severe limiting factors on the performance of RRs fabricated with state-of-the-art silicon-on-insulator nanowaveguides.
-
roughness induced Backscattering in optical silicon waveguides
Physical Review Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Carlo Ferrari, Andrea Melloni, M Torregiani, Mario MartinelliAbstract:We report on the direct observation of Backscattering induced by sidewall roughness in high-index-contrast optical waveguides based on total internal reflection. Our results demonstrate that Backscattering is one of the most severe limiting factors in state-of-the art silicon on insulator nanowires employed in densely integrated photonics. We also derive the general relationship between Backscattering and geometrical and optical parameters of the waveguide. Further, the role of roughness in polarization rotation and coupling with higher-order modes is pointed out.
Andrea Melloni - One of the best experts on this subject based on the ideXlab platform.
-
Backscattering in silicon photonic waveguides and circuits
Proceedings of SPIE, 2011Co-Authors: Francesco Morichetti, Antonio Canciamilla, Carlo Ferrari, Mario Martinelli, Andrea MelloniAbstract:The effects of roughness induced Backscattering in optical waveguides and circuit realized on a silicon-on-insulator platform are investigated. A systematic experimental investigation on low-loss silicon nanowires, with a sidewall roughness rms around 1-2 nm, is presented, showing that a few hundreds of micrometers long waveguide exhibits a Backscattering level that can hinder its exploitation in many applications. The effect is typically stronger for TE polarization and is significantly enhanced inside optical cavities, such as microring resonators, where Backscattering is coherently enhanced according to the square of the finesse of the resonator and can modify dramatically the spectral response of the resonators, even at moderate quality factors. We found general relationships relating Backscattering to the geometric and optical parameters of the waveguides, to polarization rotation effects, and to coupling with higher-order modes. On the basis of these results, design rules to mitigate Backscattering effects are proposed. The main statistical properties of roughness induced Backscattering were also experimentally derived, these results enabling an accurate modeling of realistic waveguides and the evaluation of the Backscattering impact in integrated devices and circuits.
-
Statistics of Backscattering in optical waveguides
Optics Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Andrea MelloniAbstract:The statistics of Backscattering induced by sidewall roughness in dielectric optical waveguides is experimentally investigated. We demonstrate that waveguide Backscattering is a wavelength-dependent random process, whose statistics follows the rules of single scattering systems, independently of shape, size, and refractive index contrast of the waveguide, and of the light polarization state. The intensity of Backscattering is distributed according to an exponential probability density function, and its mean delay corresponds to a reflection at half the effective length of the waveguide.
-
coherent Backscattering in optical microring resonators
Applied Physics Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Mario Martinelli, Antonio Samarelli, R M De La Rue, M Sorel, Andrea MelloniAbstract:The effects of Backscattering induced by waveguide sidewall roughness in integrated ring resonators (RRs) are experimentally observed. We demonstrate that coherent Backscattering, originated by multiple round trips in the RR, increases with the square of the effective group index of the cavity and can dramatically affect the behavior of integrated RRs even at moderate quality factors of 104. From our results Backscattering emerges as one of the most severe limiting factors on the performance of RRs fabricated with state-of-the-art silicon-on-insulator nanowaveguides.
-
roughness induced Backscattering in optical silicon waveguides
Physical Review Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Carlo Ferrari, Andrea Melloni, M Torregiani, Mario MartinelliAbstract:We report on the direct observation of Backscattering induced by sidewall roughness in high-index-contrast optical waveguides based on total internal reflection. Our results demonstrate that Backscattering is one of the most severe limiting factors in state-of-the art silicon on insulator nanowires employed in densely integrated photonics. We also derive the general relationship between Backscattering and geometrical and optical parameters of the waveguide. Further, the role of roughness in polarization rotation and coupling with higher-order modes is pointed out.
Francesco Morichetti - One of the best experts on this subject based on the ideXlab platform.
-
Backscattering in silicon photonic waveguides and circuits
Proceedings of SPIE, 2011Co-Authors: Francesco Morichetti, Antonio Canciamilla, Carlo Ferrari, Mario Martinelli, Andrea MelloniAbstract:The effects of roughness induced Backscattering in optical waveguides and circuit realized on a silicon-on-insulator platform are investigated. A systematic experimental investigation on low-loss silicon nanowires, with a sidewall roughness rms around 1-2 nm, is presented, showing that a few hundreds of micrometers long waveguide exhibits a Backscattering level that can hinder its exploitation in many applications. The effect is typically stronger for TE polarization and is significantly enhanced inside optical cavities, such as microring resonators, where Backscattering is coherently enhanced according to the square of the finesse of the resonator and can modify dramatically the spectral response of the resonators, even at moderate quality factors. We found general relationships relating Backscattering to the geometric and optical parameters of the waveguides, to polarization rotation effects, and to coupling with higher-order modes. On the basis of these results, design rules to mitigate Backscattering effects are proposed. The main statistical properties of roughness induced Backscattering were also experimentally derived, these results enabling an accurate modeling of realistic waveguides and the evaluation of the Backscattering impact in integrated devices and circuits.
-
Statistics of Backscattering in optical waveguides
Optics Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Andrea MelloniAbstract:The statistics of Backscattering induced by sidewall roughness in dielectric optical waveguides is experimentally investigated. We demonstrate that waveguide Backscattering is a wavelength-dependent random process, whose statistics follows the rules of single scattering systems, independently of shape, size, and refractive index contrast of the waveguide, and of the light polarization state. The intensity of Backscattering is distributed according to an exponential probability density function, and its mean delay corresponds to a reflection at half the effective length of the waveguide.
-
coherent Backscattering in optical microring resonators
Applied Physics Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Mario Martinelli, Antonio Samarelli, R M De La Rue, M Sorel, Andrea MelloniAbstract:The effects of Backscattering induced by waveguide sidewall roughness in integrated ring resonators (RRs) are experimentally observed. We demonstrate that coherent Backscattering, originated by multiple round trips in the RR, increases with the square of the effective group index of the cavity and can dramatically affect the behavior of integrated RRs even at moderate quality factors of 104. From our results Backscattering emerges as one of the most severe limiting factors on the performance of RRs fabricated with state-of-the-art silicon-on-insulator nanowaveguides.
-
roughness induced Backscattering in optical silicon waveguides
Physical Review Letters, 2010Co-Authors: Francesco Morichetti, Antonio Canciamilla, Carlo Ferrari, Andrea Melloni, M Torregiani, Mario MartinelliAbstract:We report on the direct observation of Backscattering induced by sidewall roughness in high-index-contrast optical waveguides based on total internal reflection. Our results demonstrate that Backscattering is one of the most severe limiting factors in state-of-the art silicon on insulator nanowires employed in densely integrated photonics. We also derive the general relationship between Backscattering and geometrical and optical parameters of the waveguide. Further, the role of roughness in polarization rotation and coupling with higher-order modes is pointed out.
Emmanuel Boss - One of the best experts on this subject based on the ideXlab platform.
-
The open-ocean missing Backscattering is in the structural complexity of particles
Nature Communications, 2018Co-Authors: Emanuele Organelli, Emmanuel Boss, Giorgio Dall’olmo, Robert Brewin, Glen Tarran, Annick BricaudAbstract:Marine microscopic particles profoundly impact global biogeochemical cycles, but our understanding of their dynamics is hindered by lack of observations. To fill this gap, optical Backscattering measured by satellite sensors and in-situ autonomous platforms can be exploited. Unfortunately, these observations remain critically limited by an incomplete mechanistic understanding of what particles generate the Backscattering signal. To achieve this understanding, optical models are employed. The simplest of these models—the homogeneous sphere—severely underestimates the measured Backscattering and the missing signal has been attributed to submicron particles. This issue is known as the missing Backscattering enigma. Here we show that a slightly more complex optical model—the coated sphere—can predict the measured Backscattering and suggests that most of the signal comes from particles >1 µm. These findings were confirmed by independent size-fractionation experiments. Our results demonstrate that the structural complexity of particles is critical to understand open-ocean Backscattering and contribute to solving the enigma.
-
the role of seawater constituents in light Backscattering in the ocean
Progress in Oceanography, 2004Co-Authors: Dariusz Stramski, Emmanuel Boss, Darek Bogucki, Kenneth J VossAbstract:The significance of light Backscattering in the ocean is wide ranging, especially in optical remote sensing. However, the complexity of natural seawater as an optical medium often obscures the measured optical signals to the point that our present-day interpretation and detailed understanding of major sources of Backscattering and its variability in the ocean are uncertain and controversial. Here we review the roles played by various seawater constituents in light Backscattering and we address a question of missing Backscattering. Historically, this question has resulted from a hypothesis that under non-bloom conditions in the open ocean, phytoplankton make a significantly smaller contribution to the particulate Backscattering coefficient than to the particulate (total) scattering coefficient. By discussing the Backscattering properties and potential contributions of the various water constituents (colloids, bacteria, phytoplankton, biogenic detritus, minerogenic particles, bubbles), we show that due to substantial variability in water composition, different types of constituents can explain the missing Backscattering. Under typical non-bloom conditions in the open ocean, the small-sized non-living particles appear to be the most important because of their high abundance relative to other particle types. These particles are believed to be primarily of organic origin but an important role of minerogenic particles cannot be excluded. Still, in the very clear ocean water the Backscattering by water molecules themselves can contribute as much as 80% to the total Backscattering coefficient in the blue spectral region. The general scenario of the dominance of molecules and small-sized particles can, however, be readily perturbed due to changes in local conditions. For example, bubbles entrained by breaking waves can intermittently dominate the Backscattering at shallow depths below the sea surface, the calcifying phytoplankton (coccolithophores) producing calcite scales of high refractive index can dominate if present in sufficient concentration, and other plankton species can dominate during blooms. The role of
-
particulate Backscattering ratio at leo 15 and its use to study particle composition and distribution
Journal of Geophysical Research, 2004Co-Authors: Emmanuel Boss, W S Pegau, M E Lee, Michael S Twardowski, Eugeny B Shybanov, G K Korotaev, F BaratangeAbstract:[1] Particulate scattering and Backscattering are two quantities that have traditionally been used to quantify in situ particulate concentration. The ratio of the Backscattering by particles to total scattering by particles (the particulate Backscattering ratio) is weakly dependent on concentration and therefore provides us with information on the characteristics of the particulate material, such as the index of refraction. The index of refraction is an indicator of the bulk particulate composition, as inorganic minerals have high indices of refraction relative to oceanic organic particles such as phytoplankton and detrital material that typically have a high water content. We use measurements collected near the Rutgers University Long-term Ecosystem Observatory in 15 m of water in the Mid-Atlantic Bight to examine application of the Backscattering ratio. Using four different instruments, the HOBILabs Hydroscat-6, the WETLabs ac-9 and EcoVSF, and a prototype VSF meter, three estimates of the ratio of the particulate Backscattering ratio were obtained and found to compare well. This is remarkable because these are new instruments with large differences in design and calibration. The Backscattering ratio is used to map different types of particles in the nearshore region, suggesting that it may act as a tracer of water movement. We find a significant relationship between the Backscattering ratio and the ratio of chlorophyll to beam attenuation. This implies that these more traditional measurements may be used to identify when phytoplankton or inorganic particles dominate. In addition, it provides an independent confirmation of the link between the Backscattering ratio and the bulk composition of particles.
-
relationship of light scattering at an angle in the backward direction to the Backscattering coefficient
Applied Optics, 2001Co-Authors: Emmanuel Boss, Scott W PegauAbstract:We revisit the problem of computing the Backscattering coefficient based on the measurement of scattering at one angle in the back direction. Our approach uses theory and new observations of the volume scattering function (VSF) to evaluate the choice of angle used to estimate bb. We add to previous studies by explicitly treating the molecular Backscattering of water (bbw) and its contribution to the VSF shape and to bb. We find that there are two reasons for the tight correlation between observed scattering near 120° and the Backscattering coefficient reported by Oishi [Appl. Opt.29, 4658, (1990)], namely, that (1) the shape of the VSF of particles (normalized to the Backscattering) does not vary much near that angle for particle assemblages of differing optical properties and size, and (2) the ratio of the VSF to the Backscattering is not sensitive to the contribution by water near this angle. We provide a method to correct for the water contribution to Backscattering when single-angle measurements are used in the back direction (for angles spanning from near 90° to 160°) that should provide improved estimates of the Backscattering coefficient.
Vadim Backman - One of the best experts on this subject based on the ideXlab platform.
-
experimental confirmation at visible light wavelengths of the Backscattering enhancement phenomenon of the photonic nanojet
Optics Express, 2011Co-Authors: Seungmoo Yang, Allen Taflove, Vadim BackmanAbstract:We report what we believe is the first experimental confirmation at visible light wavelengths of the Backscattering enhancement phenomenon of the photonic nanojet. A specially designed sample stage consisting of a multilayered sandwich of glass, solid polydimethylsiloxane (PDMS), and liquid PDMS, permitted the precise positioning of a gold nanoparticle of diameter between 50 and 100 nm within the nanojet emitted by a 4.4 μm diameter BaTiO3 microsphere embedded within the PDMS. We determined that, when the gold nanoparticle is optimally positioned within the nanojet, the Backscattering of the microsphere can greatly increase: for example, by 3:1 (200%) for the 50 nm gold nanoparticle. The increased Backscattering is strongly dependent upon the illumination wavelength and the numerical aperture of the imaging system, and occurs for nonresonant illuminations of the isolated microsphere. Low objective numerical apertures of approximately 0.075 yield the maximum observed increases in Backscattering. The measured data agree well with numerical calculations incorporating Mie-based theory and Fourier optics.
-
experimental confirmation of Backscattering enhancement induced by a photonic jet
Applied Physics Letters, 2006Co-Authors: Alexander Heifetz, Allen Taflove, Kevin Huang, Alan V Sahakian, Vadim BackmanAbstract:The authors report experimental confirmation of Backscattering enhancement induced by a photonic jet emerging from a dielectric sphere, a phenomenon recently predicted by theoretical solutions of Maxwell’s equations. To permit relatively straightforward laboratory measurements at microwave frequencies rather than visible light, they appropriately scaled the original conceptual dimensions of the dielectric microsphere and its adjacent perturbing nanoparticle (located within the microsphere’s photonic jet). Their experiments verified the existence of enhanced position-dependent Backscattering perturbations by the adjacent particle. Their measured Backscattering perturbations agreed well with prior theory and with additional finite-difference time-domain computational models of the complete microwave test geometry.
-
risk stratification of colon carcinogenesis through enhanced Backscattering spectroscopy analysis of the uninvolved colonic mucosa
Clinical Cancer Research, 2006Co-Authors: Ramesh K Wali, Vladimir Turzhitsky, Michael J Goldberg, Jonathan Horwitz, Vadim BackmanAbstract:Introduction: Our group has been interested in applying advances in biomedical optics to colo- rectal cancer risk stratification.Through a recent technological breakthrough, we have been able to harness information from enhanced Backscattering spectroscopy, an optics phenomenon that allows quantitative, depth-selective analysis of the epithelial microscale/nanoscale architecture. In the present study, we investigated the ability of enhanced Backscattering analysis of the preneoplastic mucosa to predict risk of colon carcinogenesis. Methods: Enhanced Backscattering analysis was done on intestinal mucosa at preneoplastic time points from two experimental models of colorectal cancer: the azoxymethane-treated rat and the multiple intestinal neoplasia (MIN) mouse. Data were analyzed using two previously validated spectral markers: spectral slope and principle components.We then did a pilot study on mucosal biopsies from 63 subjects undergoing screening colonoscopy. Results: In the azoxymethane-treated rat, when compared with saline-treated controls, signifi- cant changes in the enhanced Backscattering markers were observed as early as 2 weeks after azoxymethane treatment (before the development of aberrant crypt foci and adenomas). Enhanced Backscattering markers continued to progress over time in a manner consonant with future neoplasia. These data were replicated in the preneoplastic MIN mouse mucosa. In humans, spectral slopes in the endoscopically normal cecum, midtransverse colon, and rectum were markedly reduced in patients harboring adenomas when compared with those who were neo- plasia free. Conclusions: We show, for the first time, that enhanced Backscattering analysis of an aliquot of uninvolved mucosa has the potential for predicting neoplastic risk throughout the colon in both experimental colorectal cancer models and humans.
-
Elastic Backscattering spectroscopic microscopy
Frontiers in Optics, 2005Co-Authors: Xu Li, Vadim BackmanAbstract:We present elastic Backscattering spectroscopic microscopy that allows simultaneous acquisition of sub-micron-resolution images and Backscattering spectra at each pixel. It enables detection of highly localized scattering features within a single micro-particle and densely packed scatterers.
-
optical analysis of nanoparticles via enhanced Backscattering facilitated by 3 d photonic nanojets
Optics Express, 2005Co-Authors: Xu Li, Allen Taflove, Zhigang Chen, Vadim BackmanAbstract:We report the phenomenon of ultra-enhanced Backscattering of visible light by nanoparticles facilitated by the 3-D photonic nanojet – a sub-diffraction light beam appearing at the shadow side of a plane-wave-illuminated dielectric microsphere. Our rigorous numerical simulations show that Backscattering intensity of nanoparticles can be enhanced up to eight orders of magnitude when locating in the nanojet. As a result, the enhanced Backscattering from a nanoparticle with diameter on the order of 10 nm is well above the background signal generated by the dielectric microsphere itself. We also report that nanojet-enhanced Backscattering is extremely sensitive to the size of the nanoparticle, permitting in principle resolving sub-nanometer size differences using visible light. Finally, we show how the position of a nanoparticle could be determined with subdiffractional accuracy by recording the angular distribution of the backscattered light. These properties of photonic nanojets promise to make this phenomenon a useful tool for optically detecting, differentiating, and sorting nanoparticles.