Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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210 records were found.
Glass dominates modern optical technologies. Nonlinear optical processes, such as second-harmonic generation and parametric frequency conversion, are technological very attractive and require a second-order optical nonlinearity - a χ gratings. Moreover in the experiments on electric-field second harmonic generation in optical fibres the first evidence of phase dependent modulation of a total cross-section of ionization due to quantum interference (coherent photoconductivity) in solid state materials has been obtained.
Optical glass-fibres and waveguides dominate optical communications. The development of linear electrooptic modulators/switches and parametric frequency converters directly integrated into optical glass waveguide structures technologically is very attractive. However such components require u second-order nonlinearity - a chi (2), which is normally absent in glass owing to its inversion symmetry. Thus, when self-organised frequency doubling was first discovered wide-ranging studies ensued into the mechanism and properties of this unexpected phenomenon. The mystery of photoinduced chi (2) gratings was finally solved on the basis of a new physical phenomenon - the coherent photogalvanic effect, consisting in quantum interference, which excites a phase dependent current (coherent photocurrent). Coherent photocurrent induces quasi-phase ma...
Electric field poling of silica glass provides the prospect of efficient second-order nonlinear interactions in optical fibres. Recent advances in quasi-phase-matched second harmonic generation in electric field poled silica fibres are reviewed
When glass fibres were first proposed for optical communications in the late 1960's, one attractive selling point was their extreme insensitivity (if not complete immunity) to electromagnetic interference, which - in addition to a much larger bandwidth - gave them considerable advantages over co-axial cable. Early research concentrated on reducing the optical absorption to the lowest possible levels, eventually achieving values <0.1 dB/km in the main communications windows at 1.3 and 1.5µm. At this point there seemed no reason to suppose that germanium doped silica glass of extremely high purity should be anything other than an almost perfect optical transmission medium. Ambitious, however, to extend the capabilities of optical fibres, researchers went on to study whether more complex functions such as amplification, modulation, wavele...
D-shape silica fibres have been periodically poled at elevated temperature by applying high voltage via a patterned electrode deposited on the plane side. The resulting nonlinear grating of 25µm period, uniform over the whole 1.8cm length, has been used for quasi-phase-matched second harmonic generation. With a mode-locked laser as fundamental source blue powers up to ~76µW have been generated at ~422nm with an average conversion efficiency of ~0.22%.
A strong electrostatic field applied to glass is spatially modulated by intense light at frequencies omega and 2 omega. The phenomenon is explained in terms of photoconductivity being dependent on the relative phase of the light fields at different frequencies
Glass, e.g. silica glass, is one of the dominant materials in information technology because of its low fabrication cost compared to crystalline materials, and its superior optical properties such as high transparency and high optical damage threshold. However inversion symmetry of the glass matrix ensures the absence of optical effects based on second-order nonlinearity such as linear electrooptic effect and parametric frequency conversion. The ability to modulate a material's refractive index with an applied field, as in the electrooptic or piezoelectric effect, is necessary for making optical switches and electric field sensors. Frequency conversion of coherent radiation through parametric processes, such as second harmonic and sum or difference frequency generation, is also desirable to produce a large range of wavelength from fibr...
Recent advances in silica fibres exhibiting second-order optical nonlinearities as a result of both self-induced and thermal poling processes are reported. Efficient second-harmonic generation in silica fibre subjected to a strong electrostatic field via internal electrodes was observed. Spatial periodic modulation of the applied electric field, responsible for the second-harmonic signal, arises from the interaction of the intense light at fundamental and doubled frequencies with glass, which has its inversion symmetry broken by the applied field. The process could represent the first evidence of coherent photoconductivity in glass - conductivity being dependent on the relative phase of the light fields at different frequencies. Moreover, D-shaped silica fibres have been periodically poled at elevated temperature by applying high volta...
Periodic patterning of the second-order nonlinearity chi microstructures in lithium niobate, in glass and in glass fibres
