Baseband characteristics of long-wavelength l.e.d. systems

As multimode fibres improve, the transfer characteristics of l.e.d.-based systems become dominated by chromatic effects. We derive a simple formula describing the baseband transfer function and verify it by comparative laser and l.e.d. dispersion measurements.     

Effect of chromatic dispersion on pulses of arbitrary coherence

Chromatic signal distortion in fibre waveguides depends on the coherence of the optical carrier. The theory derived here covers carriers of arbitrary coherence and arbitrary dispersion characteristics. It gives simple estimates for the available signal bandwidth.     

Dispersion in a low-loss multimode fibre measured at three wavelengths

Short pulses from mode-locked lasers (neodynium/yttrium-iron-garnet and krypton) were used to measure mode and material dispersion in 20 m of a multimode fibre at 1060, 647 and 568 nm. Uniform illumination of the cone of acceptance at the input caused a 200 ps pulse to broaden to 400 ps.     

L.E.D. design for fibre systems

An analysis of the interaction of optical modes with the active region of an L.e.d. leads to simple design recommendations both for front- and edge-emitting structures. If used in conjunction with mode transformers, both diodes could provide more than I mW of optical power for multimode-fibre transmission.     

Profile dispersion in multimode fibres: measurement and analysis

An electronically scanned interference microscope has been used to measure the refractive-index profile and its dispersion in optical fibres. From these measurements, we find that the power-law profile that best equalises modal delays in GeO2-S1O2 fibres should have an exponent that varies between 1.9 and 2.5 in the wavelength range from 0.5 to 1.1 ?m and is close to 2 at 0.9 ?m.     

System experiments using 1.3 ?m LEDs

An experimental LED/PIN system is described that operates at 274 Mbit/s over 7.5 km or at 44.7 Mbit/s over 23.3 km without repeaters. These results are compared with repeater spans calculated for various loss and bandwidth conditions.     

Self-pulsing GaAs laser for fiber-dispersion measurements

Internal self-pulsing of commercially available GaAs lasers produces pulses as short as 100 ps. The simplicity and versatility of such devices make them very useful for fiber-dispersion studies. We describe pulse-transmission measurements in 178 m of a liquid-core fiber and explain the considerable pulse broadening (11 ns at the pulse base) in terms of mode delay and mode mixing.