2007光纤技术.pdf

光纤通信与高压中应用 光纤通信与高压中应用 Information Capacity The usual rate for new systems is 2.4 Gbps or even 10 Gbps. By sending many (“wavelength division multiplexed”) channels on a single fibre capacity to carry about 30 million uncompressed telephone calls No Electrical Connection protected from high voltages because of the danger to people touching the wire. No Electromagnetic Interference optical communication has so few errors. Cables may be located near water or power lines without risk to people or equipment. Distances between Regenerators the repeater spacing is typically 40 kilometres,Some recently installed systems have spacings of up to 120 kilometres This compares with 12 km for the previous coaxial cable electrical technology. some limitations: Joining Cables“fusion splicing”. Bending Cables Optics for Transmission Only:no available optical amplifier. Gamma Radiation:cause glass to discolor Electrical Fields:Very high-voltage electrical fields also affect some glasses tends to emit light and discolor. fibre communication cables wrapped around high-voltage electrical cables on transmission towers, only of 30 000 volts or below Light as an Electromagnetic Wave Naming Modes Transverse Electric (TE) Modes Transverse Magnetic (TM) Modes Transverse ElectroMagnetic (TEM) Modes:both the electric and magnetic fields are perpendicular to the z- direction. the only mode of a single- mode fibre. Helical (Skew) Modes (HE and EH) Hard Polymer (plastic) Clad (silica) Fibre (HPCF) Transmitting Light on a Fibre Fibre Refractive Index Profiles Transmission through a Sheet of Glass Snells law. critical angle critical angle At the critical angle we