M.C. Brain

Erbium-doped fiber amplifier cascade for multichannel coherent optical transmission

The requirements and practicalities of amplifier cascades for multichannel coherent transmission are discussed. A four-amplifier cascade which maintains an overall noise figure of less than 13 dB across a 20-nm optical bandwidth for total input powers up to -10 dBm is described. A potential capacity of 100 wavelength division multiplexing channels is demonstrated in a 300-km 622-Mb/s DPSK (differential phase shift keying) coherent transmission experiment. >

Progress towards the field deployment of coherent optical fiber systems

A description is given of the first demonstration of a coherent optical transmission system deployed in an operational network. The miniaturized external cavity laser and the automated endless polarization control scheme which made it possible to mount this demonstration are described in detail, together with specific system results. A discussion is presented of the possible field deployment of other coherent system options, based on FSK modulation of DFB and DBR lasers, and polarisation diversity reception. The considerable potential afforded by coherent techniques for meeting future network requirements is highlighted. The demonstrated advantages of greater power budget and wavelength selectivity, combined with the use of optical amplifier multiwavelength repeaters, make coherent techniques particularly relevant to the growing demand for greater transmission capacity, transparency, and network flexibility. An increasingly urgent need for robust coherent optical technology can thus be anticipated, for wideband transmission and passive routing, for both telecommunications and computer networks of the near future. >

Optical receivers for lightwave communication systems

As long-wavelength optical telecommunications systems are now being installed in countries throughout the world, this is an opportune time to review the successful developments in detectors and receivers for this application. We given prominence to receivers using p-i-n and avalanche photodiodes, describing in some detail the principles of their operation as well as the details of their development. However, we also consider bipolar phototransistors, photoconductive detectors, and the receiver requirements for coherent optical systems, concluding with a broad comparison of the Various receiver designs.

Laser diode pumped Er/sup 3+/-doped fiber amplifier in a 565 Mbit/s DPSK coherent transmission experiment

A laser-diode-pumped erbium-doped fiber amplifier, exhibiting 9-dB gain, has been operated as an in-line optical repeater in a 565-Mb/s coherent optical communications system. A sensitivity penalty of 0.4 dB was observed when the amplifier was positioned 35 dB away from the receiver, thus indicating a system improvement of 8.6 dB. By progressively reducing the coupling loss between amplifier and receiver, the noise figure of the contradirectionally pumped amplifier was calculated to be 5.4 dB, a value which is consistent with simple noise theory.<<ETX>>

Transparency in optical amplifier repeaters

Transmission links with optical amplifier repeaters are potentially transparent to system upgrades such as increased bit rate or the addition of wavelength division multiplexed (WDM) channels. The potential ease of upgrade in the capacity of an optically amplified transmission link, from a single channel to one hundred channels, is demonstrated in a 300 km 622 Mb/s coherent transmission experiment. The authors consider the limitations imposed by amplifier noise and discuss the degree of transparency that can be achieved with currently available optical amplifiers.<<ETX>>

Recent Progress In Coherent Systems Research At British Telecom

This paper reviews recent technological progress on coherent systems. Both devices and system developments are described, though the accent is placed on systems applications. Subjects investigated recently include stabilisation and modulation of LEC lasers, optical amplifiers, FSK based systems and phase modulation in amplifiers.

Field demonstration of coherent WDM with a fibre amplifier repeater, for transparent optical network applications

A series of field experiments performed with two-wavelength transmissions at 622 Mb/s over 200-km of installed single-mode fiber using a diode-pumped erbium-doped fiber amplifier repeater are described. Both differential phase-shift keying (DPSK) modulation and frequency-shift keying (FSK) modulation were employed, along with two implementations of automated endless polarization control. In a further field experiment, a power budget of 64 dB was demonstrated in the form of repeaterless DPSK transmission at 622 Mb/s over 264 km of installed fiber. The use of such a large power budget to accommodate the sharing of power between many wavelength channels and the accumulation of spontaneous emission noise through cascaded optical amplifier repeaters is discussed.<<ETX>>