Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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26 records were found.
In recent years, near-field microscopy has been utilized for assessing the properties of optical wave-guides at an increasing rate. Here, a Scanning Near-field Optical Microscope (SNOM) has been designed and constructed in order to expand this work into an analysis of the optical and structural properties of fibre Bragg gratings, which are used throughout the optical fibre telecommunications network. By imaging the evanescent fields of Bragg gratings, a characterization technique has been developed which has enabled the acquisition of sub-wavelength information about the optical field distribution within a fibre grating and its refractive index structure. Six separate fibre grating samples have been examined, demonstrating the feasibility of the developed scanning technique to become a useful characterization tool. In particular, the s...
Near-field scanning optical microscopy (NSOM) can provide direct information about the electric fields inside optoelectronic devices with subwavelength resolution. This letter describes direct, wavelength-resolved measurements of the amplitude and phase of the standing waves within a fiber Bragg grating, using a heterodyne interference variant of NSOM that works at telecommunications wavelengths. The amplitudes of forward- and backward-going components of the standing wave can be measured separately, and the position shift of the standing wave antinodes as the wavelength varies across the stop band is imaged directly. ©2003 American Institute of Physics.
A technologically important use of the free-space interference patterns formed by phase gratings is in the creation of the refractive-index variation along optical fiber Bragg gratings. The patterns can be imaged directly by use of a tapered optical fiber tip, which acts as a local probe of the optical field. We present measurements of these patterns under varying conditions and compare them with theoretical predictions. In discussing the results within the context of fiber grating manufacture, we also demonstrate the effects of incident-beam misalignment and wave-front curvature.
Thermal poling of silica glass modified by femtosecond laser irradiation has been demonstrated. Evidence of second-order nonlinearity modulation between the treated and non-treated regions has been observed. The technique was used for χ(2) grating fabrication.
Directly written photonic structures created within silica by a femtosecond Ti:Sapphire laser are observed to strongly reflect light only in a direction along the polarization axis of the writing laser, indicating highly anisotropic microstructuring.
We demonstrate the fabrication of maskless large diameter Fresnel zone plates embedded deep inside silica glass substrates, using direct write techniques employing femtosecond laser pulses. High quality focussing properties are achieved.
Periodic structures are directly written into the core of single-mode optical fibers with a femtosecond laser enabling control over the exiting light. The diffracting beams retain their original mode profile offering new device possibilities.
In recent years, the use of a focused femtosecond laser to directly write structures deep within transparent media has attracted much attention due to its ability to write in three-dimensions [1]. By utilizing an amplified Ti:sapphire laser (pulse duration 150fs, repetition rate 250kHz, λ=850nm), we have developed a novel technique that enables us to write grating structures within the bulk of an optical fiber through its cleaved face, allowing control over light subsequently exiting the fiber. Fig 1(a) shows a microscope image of an embedded diffraction grating having a 5μm pitch and buried 25 μm below a fiber's cleaved face. Fig 1(b) displays a far-field pattern created by a single-mode fiber which has a two-dimensional grating written 5μm below its cleaved face. The controllability of the power and direction of diffracting orders of...
Recently, the use of a focused femtosecond laser to directly write devices into the bulk of glass has become increasingly prevalent [1]. The physical damage created by such lasers, especially in the high power regime has been identified to display anisotropic properties such as anomalous anisotropic light scattering [2] and uniaxial birefringence [3]. So far, the microscopic processes underlying such anisotropies remain unclear. By writing embedded structures with a Ti:sapphire laser (repetition rate 250kHz pulse duration 150fs, λ=850nm, and beam width ~1.5μm), we have identified a further anisotropic property in silica - strong reflection from the modified region occurring only along the direction of polarization of the writing laser. Our analysis suggests that this effect is also the primary cause of all previously reported anisotrop...
Supercontinuum has been generated at long wavelengths in a tapered bismuth silicate fibre. Simulations predict the zero-dispersion wavelength for a range of taper diameters.
