Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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174 records were found.
The 'holey fibre' (HF) is a new class of optical fibre which has a cladding formed by a number of air holes which run along the length of the fibre. Typical HFs are shown in Figures 1 and 2. These fibres can be made from a single material, and guidance is provided by the difference in effective indices between the core and the 'holey' cladding. The microstructured transverse profile opens up a diverse range of novel optical properties, many of which are not possible in more conventional fibre structures. For example, HFs can have anomalous waveguide dispersion at visible wavelengths and be single-mode, which is impossible in conventional fibers.
The combination of wavelength-scale features and geometric flexibility offered by microstructured or holey optical fibres (HFs) leads to a significantly broader range of optical properties than is possible in conventional optical fibres (see the examples in Figure 1). These properties include single-mode guidance at all wavelengths, novel dispersion properties including broadband dispersion flattening and anomalous dispersion at visible wavelengths, mode size tailoring over three orders of magnitude, and many more. The optical properties of holey fibres are determined by the size, shape and locations of the air holes that define the cladding region. HFs can be made either from a single material (eg pure silica) or can be doped, which allows active fibre devices to be made.
Progress in this rapidly emerging technology will be review...
Over the past century, the development of communications technology has had a dramatic impact on our way of life. It is now possible to phone people almost anywhere in the world, the one mobile phone can work in every continent, and researchers in Antarctica have ready access to EMAIL services! Historians of the future looking back on the late 20th/early 21st century will probably use the word "globalization" to describe this time.
In this chapter, I will present an overview of the concepts and technology used in modern communications systems. These systems rely on fundamental principles such as light scattering, optical excitation of electrons and superposition of waves, and it is necessary to draw on physical principles ranging from ray optics through to quantum optics.
The story begins with a brief chronological description o...
The development of core-clad silica glass optical fibers has revolutionized communications systems over the past 30 years. These 'conventional' optical fibers have also made a significant impact in areas as diverse as sensing, medical imaging, laser welding and machining, and the realization of new classes of lasers and amplifiers. All of these advances have been enabled by one key factor: the reduction of the fiber loss. Reducing loss was a topic of intensive research and development for two decades, and dramatic improvements in the transmission of silica-based fibers in the 1.5 micron telecommunications window were achieved as a result. The widely used Coming SMF-28 fiber has a loss of less than 0.2 dB/km at 1550nm.
In the early 1970s, when the fabrication processes for the manufacture of core-clad preforms had not yet reached matu...
We show that illuminating bulk Nd-doped Bk7 glass at 488 nm induces a decrease in refractive index of order 10-4. Using this index change we experimentally demonstrate that it is possible to use self-writing to enhance the divergence of a Gaussian beam.Here simulations with a Laguerre-Gaussian ‘donut’ writing beam show that a depressed-index ‘pipe’ structure can be created.We demonstrate that these complex waveguide structures can subsequently be used to guide light of different wavelengths.
A waveguide can be self-written by a beam of light propagating in a photosensitive material. We report the first observation of self-writing effects in bulk chalcogenide glass and investigate the influences of different writing beam sizes and powers. We observe increases in refractive index of 2.5×10-4 due to illumination at 1047 nm in Ce-doped Ga-La-S. Simulations of the self-writing process show a good agreement with the experimental results. This verifies our numerical model and allows the dynamics of this process to be explored. Using this knowledge, we predict the experimental parameters and conditions required to write waveguides, tapers, and ultimately complex three-dimensional (3-D) structures
Microstructured or holey optical fibres are a novel class of fibres that have attracted much interest recently because they can be tailored to have properties (dispersion, nonlinearity, mode size) very different from conventional fibres. These structures can consist exclusively of air holes arranged around a solid core region in a uniform background. Since such fibres do not have any raised index regions, they cannot support true bound modes. They can, however, possess leaky modes where the light is trapped within a region surrounded by air holes. Such modes suffer confinement losses due to energy leakage between and through the holes. The confinement loss is given by the imaginary part of the complex effective mode index n eff. Existing basis function expansion (Galerkin) techniques (using plane waves [1] or Hermite-Gaussians [2]) giv...
Microstructured optical fibres (MOFs) are all-silica fibres that guide light by means of an arrangement of air-holes that run down the entire fibre length. In the kind of MOFs here considered, also named holey fibres (HFs), guidance arises from average-index effects: the holes form the cladding region around the solid core. The modes of such fibres are leaky because the core refractive index is the same as the index beyond the (finite) cladding region. HFs with a core diameter of the scale of an optical wavelength and large holes have been fabricated, resulting in the smallest effective area ever measured in a fibre at 1550 nm [1]. Such small effective areas make these fibres attractive for nonlinear applications. The cladding of a HF is usually comprised of hexagonally-packed rings of holes, and when the hole-to-hole spacing (Λ) is of...
A waveguide can be self-written by a beam of light in a photosensitive material. We report here the first observations of self-written tapers in bulk chalcogenide glass.
We use numerical simulations to predict the first complex self-written structure in a bulk material. A depressed-index "pipe" structure, which guides light like a channel, is created using a Laguerre-Gaussian "donut" beam.
