D.M. Spirit’s research while affiliated with University of East London and other places

The recently-installed UK—Channel Islands No 7 cable system is a 132 km unrepeatered, twelve optical fibre, 140 Mbit/s system. In February the cable was used for a series of tests to demonstrate new transmission and receiver equipment developed at British Telecom Research Laboratories (BTRL). The paper describes first the use of erbium fibre power amplifiers to achieve two-way transmission over the system at 2.488 Gbit/s, and then the testing of a novel semi-ruggedised laser PIN receiver.

The paper presents optical duobinary signalling as an alternative to the binary format for improved transmission performance in dispersion-limited systems and summarises results achieved from both experimental and theoretical investigations. The potential advantages of duobinary transmission for dispersion accommodation in high capacity systems are demonstrated in both laboratory experiments and installed optical fibres. Unrepeatered transmission at 10 Gbit/s without dispersion compensation was achieved with penalties of only 1.5 dB after 120 km and 2.5 dB after 138 km. Initial indications of the influence of self-phase modulation (SPM) and stimulated Brillouin scattering (SBS) on duobinary transmission are also presented. Two channel, 2×10 Gbit/s wavelength division multiplex (WDM) operation with mixed binary and duobinary transmission was demonstrated in a field trial. This is the world's first demonstration of using both duobinary and binary signallings at a total capacity of 20 Gbit/s over installed fibre. The investigations show that duobinary signalling should become an important transmission format for future wideband networks where system performance is primarily dispersion dominated

We have demonstrated that not only can travelling wave semiconductor laser amplifer-nonlinear optical loop mirrors (TWSLA-NOLMs) be driven by clock signals to provide remarkable performance as optical demultiplexers, but by taking due care over the carrier density evolution, a true two port optical AND gate may be produced. Given that the output may be carried on either the incoming or the locally generated wavelength, wavelength conversion is easily obtained, and in data driven operation, a regenerative function is also obtained, certainly for data rates of up to 40 Gbit/s

Optical time division multiplexing (OTDM) is an attractive alternative to wavelength division multiplexing for future high capacity all optical networks. In order to provide a low cost evolution strategy to upgrade a network, it is imperative that any techniques exploit existing fibre plant. Several techniques have been proposed to overcome the chromatic dispersion inherent in installed fibre. We report two studies of dispersion compensation as an enabling technology for 40 Gbit/s OTDM system and network applications on standard fibre. In addition to removing the need for dispersion shifted fibre at 1.5 μm, the techniques adopted have been chosen to maximise the repeater spacing above those currently installed in transmission networks. Specifically the reported distance bit rate products of 3.2 Tbit/s.km unrepeatered and 8.1 Tbit/s.km with a single repeater represent world record performance for single channel systems. The first technique, optical dispersion compensation (using dispersion compensating fibre), has recently attracted significant interest by virtue of its straight-forward approach to the fundamental problem. That is, the link dispersion is directly negated by a length of fibre of almost exactly opposite total dispersion. Results are presented for an 80 km unrepeatered link. The second technique, mid span spectral inversion, requires little in the way of additional optics in the signal path, and certainly no modifications to standard terminal equipment

Soliton communications technology has become a promising candidate for the next generation of high speed long-haul optical transmission systems, mainly due to the rapid development of discrete erbium-doped fibre amplifiers (EDFA). However, the requirement that the amplifier spacing must be much smaller than the soliton period may make the amplifier spacing impratically small for line rates above 50 Gbit/s. It is still difficult to control the fibre dispersion zero to within a fraction of a nanometre during fabrication, and thus the yield of useful fibre will be low. One solution to this problem is to use distributed erbium-doped fibre (DEDF) as the transmission line, in which the fibre loss is continuously compensated for by the erbium gain, and a nearly lossless transmission line can be realised, removing the constraint on the soliton period. We present our experimental results of 10 GHz and 80 GHz soliton transmission over 60 km Corning DEDF, which, to our knowledge, represents the highest repetition rate soliton transmission through DEDF reported to date

The use of semiconductor amplifiers in high speed communications systems is reviewed. Processing of signals at 10 Gb/s in a 40-Gb/s OTDM network is demonstrated using nonlinear loop mirror configurations, and mode locked ring lasers. Particular attention is paid to the role of carrier density modulation, long believed to be a detrimental effect, and its useful exploitation

The authors discuss the performance of a low-timing-jitter, diode-driven, Nd:YLF pumped 5 ps, 30-40 GHz soliton source based on beat-signal conversion in a dispersion-decreasing fibre. In addition, the first experimental demonstration is reported of long-distance (205 km) propagation of such pulse streams in an amplified transmission line incorporating three amplifiers at 50 km amplifier spacing

Citation E. M. Kimber, X. Gu, S. J. Pycock, B. L. Patel, D. M. Spirit, J. Wakefield, A. D. Ellis, and C. J. Anderson, "Unrepeatered 2 x 10-Gbit/s narrow-band WDM field technology demonstration over 120 km of installed step-index fiber," in Optical Fiber Communications Conference, Vol. 8 of 1995 OSA Technical Digest Series (Optical Society of America, 1995), paper TuC4. http://www.opticsinfobase.org/abstract.cfm?URI=OFC-1995-TuC4

The first field demonstration using optical duobinary signalling at 10 Gbit/s over installed fibres is reported. Transmission over 138 km of standard fibre is demonstrated without repeaters or dispersion compensation and with a penalty of only 2.5 dB. This technique significantly increases the bit rate distance product without changing any specifications of the existing fibre network. The influence of fibre nonlinearity on system performance is also investigated

Dispersion compensation by mid-span spectral inversion has been used to achieve the transmission of 10 Gbit/s signals from a directly modulated DFB over 200 km dispersive fibre. The spectral inversion is provided by nondegenerate four-wave mixing in a semiconductor optical amplifier