Abstract

The sliding-frequency guiding filters dramatically reduce timing and amplitude jitter in long-distance soliton data transmission [1,2]. They also reduce the soliton pair interaction, so the soliton pulses can be packed closer together. The sliding filters effectively remove dispersive wave radiation from imperfect input pulses, which permits the soliton data transmission using even NRZ sources [3]. The technique of sliding- frequency guiding filters has enabled extremely robust, error-free soliton data transmission at single channel rates of 10 to 20 Gbit/s, over distances often approaching the circumference of the earth [2,4]. Guiding-frequency filters provide additional benefits when used in WDM systems. One of these benefits is the equalization of relative signal amplitudes of WDM channels. Depending on the soliton energy, solitons experience different loss when pass through the guiding filters: the higher the soliton energy the higher the loss. As a result, the guiding filters equalize relative signal amplitudes of WDM channels, automatically compensating for the unflatness of the amplifiers’ gain spectrum. We demonstrate this effect of WDM channel energy self-equalization in soliton transmission experiments with sliding-frequency filters. Filters can also reduce or eliminate residual defects of WDM. Soliton transmission using frequency guiding filters has enabled 40 Gbit/s, in the form of an 8 × 5 Gbit/s WDM transmission over 9600 km [5]. One would like to extend the filtered soliton transmission to many WDM channels at 10 Gbit/s each. Increased bit rate per channel leads to the increased number of soliton collisions. Increased bit rate per channel also requires shorter pulses, which as a rule increases the residual effects from each soliton collision. At the same time, the allowable timing jitter for error-free propagation at higher bit rate per channel is less. All these factors require a very careful design of multi-channel WDM system with 10 Gbit/s per channel, taking into account many different factors. In particular, we will discuss the following points which were recently discovered in our experiments and theoretical analysis.

© 1995 Optical Society of America