Abstract

In order to fulfil the demand for increasingly sophisticated and bandwidth intensive services, telecommunications operators will require flexible optical transmission networks which will operate at higher data rates than those installed to date. At present, the maximum data capacity of installed optical systems is limited by the bandwidth of the electronics in the terminal and repeater equipment (currently around 2.5Gbit/s). Optical wavelength [1] or time [2] division multiplexing techniques may be used to access data rates substantially over 10Gbit/s, offering a substantial increase in capacity. Both multiplexing techniques could be used in conjunction with switching in either the wavelength or time domains to allow increased network flexibility through, for example, the drop-and-insert function. Discrete erbium-doped fibre amplification is an excellent method of compensating for the loss of the transmission link, providing bit-rate independent amplification. However, the regenerative function of conventional opto-electronic repeaters is no longer available in fibre amplifiers: linear dispersion of the optical pulses now becomes a major system constraint. The availability of fibre amplifiers with excellent performance in the 1550nm window restricts the signal wavelength of optically multiplexed systems to this wavelength range, implying the use of dispersion-shifted transmission fibre. The operation of wavelength division multiplexed transmission with more than a few channels over fibre with low dispersion can lead to significant system penalties due to four wave mixing, even over fibre spans of less than 100km [3]. An alternative approach to ultra-high speed transmission is to use time division multiplexing, requiring a transmitter configuration based on short (≈ps) optical pulses. In this instance, nonlinear optical pulse compression in the transmission fibre may be used to advantage to significantly reduce (or even balance completely [4]) the linear dispersion of the optical pulses, permitting transmission well beyond the usual dispersion limit.

© 1991 Optical Society of America