Multimaterial optical coatings are a promising viable option to meet the challenging requirements (in terms of transmittance, absorbance, and thermal noise) of next-generation gravitational wave ...detector mirrors. In this paper we focus on ternary coatings consisting of quarter-wavelength-thick layers, where a third material (H^{′}) is added to the two presently in use, namely, silica (L) and titania-doped tantala (H), featuring higher dielectric contrast (against silica) and lower thermal noise (compared with titania-doped tantala), but higher optical losses. We seek the optimal material sequences, featuring minimal thermal (Brownian) noise under prescribed transmittance and absorbance constraints, by exhaustive simulation over all possible configurations, for different values of the optical density and extinction coefficient of the third material, including the case of amorphous silicon and silicon nitride operating at ambient and cryogenic temperatures. In all cases studied, the optimal designs consist of a stack of (H^{′}|L) doublets topped by a stack of (H|L) doublets, confirming previous heuristic assumptions, and the achievable coating noise power spectral density reduction factor ranges from ∼0.5 at 290 K down to ∼0.1 at 20 K. The robustness of the found optimal designs against layer thickness deposition errors and uncertainties and/or fluctuations in the optical losses of the third material is also investigated. Possible margins for further thermal noise reduction by layer thickness optimization, and strategies to implement it, are discussed.
A triadic Cantor fractal multi-layer is a stack of two different dielectric materials whose thicknesses are determined according to the triadic Cantor fractal scheme. When inserted in a rectangular ...waveguide, the spectral response of a triadic Cantor multi-layer can be tailored to feature a narrow single transmission peak in the waveguide single-mode frequency range, with a low insertion loss and a high rejection level of forbidden frequencies. The experimental characterization of alumina-polystyrene and plexiglass-polystyrene Cantor multi-layers inserted in a WR90 waveguide (Hewlett-Packard, USA) matches thoroughly with the results of the theoretical modeling and demonstrates that triadic Cantor multi-layers can be used to realize feasible narrow-band microwave filters.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this paper, a novel solution for signal conditioning, fiber illumination, and measurement is proposed for an optical fiber sensor based on a modified cladding sensing element. The presented ...technique has properties of compactness and low cost, due to the use of very common optoelectronic components, and flexibility, since it could be employed for different kinds of optical fiber sensors. In particular, a prototype has been realized and characterized for the measurement of liquid temperature.
Variational analysis of matched-clad optical fibers Chiadini, F.; Panariello, G.; Scaglione, A.
Journal of lightwave technology,
2003-Jan., 2003, 2003-01-00, 20030101, Letnik:
21, Številka:
1
Journal Article
Recenzirano
A variational analysis of weakly guiding optical fibers is described. A series expansion of Laguerre-Gauss functions and a modified Bessel function have been used to describe the field in the fiber ...core and in the uniform cladding, respectively. A numerical procedure optimizing the field parameters (the expansion coefficients, the Gaussian spot-size and the normalized transverse propagation constant) has been developed which allowed highly accurate field representations to be obtained through few-term expansions. Low-order LP modes have been analyzed for refractive index profiles with a power-law variation in the core for which reference solutions (either exact or approximate) are available. A modified profile exhibiting a high index ring around the core has also been analyzed. For power-law profiles, the results are in excellent agreement with the reference solutions and show that the proposed variational analysis also appears to be appropriate for determining the field at wavelengths near to cutoff. Moreover, the comparison with other field representations which use series expansions, shows that our solution needs a noticeably lower number of terms. The analysis of the modified profile, for which only numerical solutions are available, highlights that the developed method provides very accurate field representations.
The coating design for mirrors used in interferometric detectors of gravitational waves currently consists of stacks of two alternating dielectric materials with different refractive indexes. In ...order to explore the performance limits of such coatings, we have formulated and solved the design problem as a multiobjective optimization problem consisting in the minimization of both coating transmittance and thermal noise. An algorithm of global optimization (Borg MOEA) has been used without any a priori assumption on the number and thicknesses of the layers in the coating. The algorithm yields a Pareto tradeoff boundary exhibiting a continuous, decreasing and non convex (bump-like) profile, bounded from below by an exponential curve which can be written in explicit closed form in the transmittance-noise plane. The lower bound curve has the same expression of the relation between transmittance and noise for the quarter wavelength design where the noise coefficient of the high refractive index material assumes a smaller equivalent value. An application of this result allowing to reduce the computational burden of the search procedure is reported and discussed.
•Solution of the design optimization problem of two-materials coatings for Gravitational Wave detectors.•Pareto front computation by (state of art) multi-objective optimizations algorithm (Borg MOEA).•Analytic expression bounding the Pareto fronts.•Noise reduction in realistic Gravitational Waves detectors.
A reflectometric fiber-optic temperature sensor was manufactured and characterized. The sensing probe is obtained by replacing the cladding with a temperature sensitive liquid on a short length of ...fiber. Its reduced dimensions make it suitable for monitoring applications whenever a high spatial resolution is required. A numerical modeling of the sensor, based on a ray-tracing technique, was carried out. The metrological performance of the first prototype seems to be very interesting in terms of accuracy and, above all, response time. A system for multipoint temperature measurements is also described.
Multifrequency numerical simulations of the light-coupling efficiency of a prismatic bioinspired compound lens (BCL) of silicon atop a thick silicon substrate were carried out within the framework of ...geometrical optics. Comparison was made with untextured and groove-textured silicon substrates as well as with untextured silicon substrates with a double-layer anti-reflection (DLAR) coating. Taking into account the broadband nature and the sea-level spectral irradiance of the insolation flux, and averaging over all admissible directions and both linear polarization states of the incident light, we found that the light-coupling efficiency can be almost doubled with respect to the untextured silicon substrate and enhanced by about a third with respect to a DLAR-coated untextured silicon substrate, by adopting a DLAR-coated silicon BCL.
We characterize both the ordinary and extraordinary refractive indexes of columnar thin films (CTFs) as Gaussian functions of the vapor incidence angle. This simple model is compared to the one ...available in literature for three different materials, resulting in low relative errors. The Gaussian model can be easily used to design Bragg multilayers made of CTFs.
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