1,720,965 research outputs found
Group velocity of dielectric waveguide modes
Full text linkThe group velocity and dispersion of surface-wave nodes propagating along a circular dielectric rod are computed and presented graphically in normalised form. The group velocity as each mode approaches the cutoff frequency is calculated approximately
Bandwidths of single-mode and multimode optical fibre
No full textAn analysis is given of the effect of carrier spectral width on bandwidth of optical fibre transmission lines and a simple generalized expression is deduced relating carrier bandspread and maximum permissible pulse rate. It is shown that for the case of a semiconductor laser carrier source the bandwidth of a multimode fibre can be made to approach that expected from single-mode and graded-index fibres
Limiting bandwidth of a glass-fibre transmission line
No full textThe effect of natural dispersion on the bandwidth of a glass-fibre transmission line is analysed. It is shown that, if typical optical glasses are used, the limiting pulse rate, in both cladded fibres and those having a parabolic radial variation of refractive index, is not likely to exceed 10 Gbit/s over a distance of 10 km. The effect of the optical breakdown strength of the glass is also considered
Communicating with light
No full textToday's communications systems are fast becoming overloaded. By using light instead of microwaves or telephone wires an enormously enlarged bandwidth may provide more than enough capacity in the 1980s and beyond
Pulse propagation along optical fibres
No full textMode-locked helium-neon lasers have been used to propagate pulses of ~1 ns duration along multimode cladded glass fibres. Any pulse spreading due to dispersion in a 33 m length of fibre is less than 0.5 ns which is the limit of resolution of the measuring equipment. This result indicates that a pulse transmission rate of at least 33 MHz may be possible over a distance of 1 km
A photometer to measure light scattering in optical glass
No full textA photometer is described for the measurement of light-scattering in high-quality, optical bulk glass. The photometer operates continuously over the wavelength range 0.5 to 1 µm and can measure scattering coefficients down to a level of 5 x 10-7 /cm. A photon counting technique is used for light measurement and calibration is by reflection of the incident beam from on ideal diffusing screen. Measurements with high-purity benzene are in good agreement with computed and previous experimental values. Results of scattering from two samples of optical glass are given
Measurement of attenuation in low-loss optical glass
No full textAn improved spectrophotometer for measuring the bulk attenuation of optical quality bulk glass over the wavelength range 500 to 1000 nm is described. It is capable of measuring loss coefficients equivalent to an attenuation of a few dB/km. Results obtained with lead flint and barium crown glasses are described
Fibre-optical communications. Final report on Ministry of Technology Contract PD/40/049/AT
No full textThe work described in this final report has been carried out under the terms of Contract PD/40/049/AT from May 1968 to September 1970. It formed part of a programme to develop a restricted-bandwidth, optical communications link using glass fibres, carried out jointly with S.R.D.E., Christchurch. The parts of the programme assigned to the Quantum Electronics Research Group in the Department of Electronics, University of Southampton, were as follows:a) Measurement of optical absorption and scattering losses in high-purity bulk glass; b) Development of equipment for pulling suitable cladded glass fibres from bulk glass;c) Assessment of the quality of fibres so produced.The necessary apparatus for the measurements in (a) has been designed and built, and measurements have been made and are still in progress. Fibre-drawing equipment has been designed and built, and fibres produced and assessed; meanwhile, modifications to the drawing apparatus are being made in the light of the quality of the initially-produced fibres. Some theoretical work on mode propagation in fibres was carried out in the early stages of the Contract, and is described in the first report on the Contract and elsewhere [1]
Accurate tuning of a laser mode-locking device
No full textTwo simple methods are described for accurately tuning a mode-locking device for a laser. The first is suitable for an acoustic diffraction cell and involves a simple measurement of the diffracted light. The second can be used with any type of active mode locking and requires only a photodiode and a simple low-frequency spectrum analyser
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