Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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Optical preamplification has been used in a fiber-optic distributed temperature sensor based on spontaneous Brillouin scattering and the use of direct detection, resulting in improved signal-to-noise ratios. The fiber-based optical preamplifier system comprises a three-port circulator, an erbium doped fiber amplifier with a small-signal gain of 27 dB, and a fiber Bragg grating with 47 GHz bandwidth. An improvement of 17 dB in the optical signal-to-noise ratio for the Brillouin signal is demonstrated in a 23 km sensor. The limit to the signal-to-noise ratio is attributed to spontaneous-spontaneous beat noise generated at the photodetector by amplified spontaneous emission from the optical amplifier.
The authors report a spontaneous Brillouin-based distributed temperature sensing (DTS) system using a short pulse width laser source at 1.5μm, which permits measurements down to an accuracy of 35cm spatial resolution. This DTS system has been demonstrated utilising conventional single-mode silica fibers for a range of 1km from a single-ended source, and a temperature resolution of 43°C was achieved.
We demonstrate a low-loss, long-range, single-ended distributed optical fiber sensor to measure both temperature and strain simultaneously and unambiguously. By using the Landau-Placzek ratio and cascaded Mach-Zehnder interferometric filters, we measure both the intensity and the frequency changes in the Brillouin backscattered signal. Strain and temperature measurements can then be independently resolved. A temperature resolution of 4°C, a strain resolution of 290 με, and a spatial resolution of 10 m have been achieved for a sensing length of 15 km.
The technical evolution in the field of optical fibre sensors is reviewed with particular reference to high temperature measurements. Optimisation of fibre composition and system design to fully realise the potential of these sensors has led to the substantial advances in both distributed and point sensor systems. Distributed sensing techniques based on Rayleigh, Raman and Brillouin scattering with their dependences on strain and temperature are examined. The use of spontaneous Brillouin scattering is demonstrated to achieve both short and long range temperature sensing with high spatial and temperature sensitivities. Simultaneous distributed strain and temperature sensing is also demonstrated by measuring both the Brillouin intensity and frequency shift. Remote sensing for applications in volcanic areas and deep borehole monitoring is...
Broadband monolithic acousto-optic tunable filters that combine a piezoelectric transducer array and an acousto-optic interaction medium in a single crystal have been investigated. A linearly chirped acoustic superlattice with an optical tuning range of λ = 1.3-1.6 μm was formed by domain inversion in LiNbO3. X-propagating longitudinal acoustic waves are excited in a crossed-field scheme by a rf Ey field applied to the superlattice and couple collinearly propagating e- and o-polarized optical modes. At λ = 1.319 μm and λ = 1.55 μm the spectral bandwidths (FWHM) were 1.54 and 2.3 nm, respectively. A relative conversion efficiency of 43%/W and a maximum conversion efficiency of 51% were measured at 1.319 μm.
Self-guided waves (spatial solitons) that can be excited in quadratic nonlinear media have been extensively studied for their potential applications in ultra-fast all-optical processing. We have previously reported the use of solitary waves collision in a KTP crystal to experimentally demonstrate all-optical switching of infrared picosecond pulses. Up to now, the intensity required to obtain self-trapping of a beam remained at a high level. This has been due to the lack of nonlinear crystals which combine the attributes of a large nonlinearity and phase-matching capability at experimentally convenient wavelengths. The availability of Periodically Poled Lithium Niobate can circumvent this difficulty. Two-dimensional spatial solitary waves in PPLN have been predicted theoretically and simulated numerically. In this communication we will ...
We report the first operation of a planar dielectric tapered waveguide laser. The waveguide lasers are fabricated by potassium ion-exchange in Nd3+-doped BK7 glass, and consist of a single-mode channel waveguide of a few microns width followed by a linear taper up to a broad region with a width of ~180μm. A slope efficiency of 42% is found in both the tapers and standard channel waveguides fabricated on the same substrate, indicating similar internal losses and hence the low-loss nature of the tapered beam expansion. The output from either end of the tapered structure is found to be near to diffraction-limited.
Colloidal gold spheres of radius 10 nm are reported to move forward in water, under the influence of radiation pressure forces, due to the evanescent field at the surface of an optical channel waveguide. The velocity is linearly dependent upon the optical power in the waveguide, acquiring a maximum velocity of 4 μm/s for modal power of 500 mW in the TM polarization at a wavelength of λ = 1.047 μm.
A thin film containing the complexing agent 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol deposited on the surface of an ITO electrode has been used as a colorimetric sensor for lead. The sensor is based on a new electrochemically assisted solvent extraction method. When an anodic potential was applied to the thin-film sensing layer, lead ions were extracted from aqueous solution into the film resulting in an increase of absorbance at 550 nm. The magnitude of the absorbance change was linearly dependent on the concentration of lead in the range 0-5 ppm with an estimated limit of detection for a simple spectrophotometric method better than 250 ppb. The sensor was reset for a fresh measurement by applying a cathodic potential. The prospects for using this electroassisted extraction method in conjunction with optical waveguide evanesce...
