Limiting bandwidth of a glass-fibre transmission line

The 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

Group velocity of dielectric waveguide modes

The 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

Pulse propagation along optical fibres

Mode-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

Accurate tuning of a laser mode-locking device

Two 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

Bandwidths of single-mode and multimode optical fibre

An 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

Communicating with light

Today'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

Measurement of attenuation in low-loss optical glass

An 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