We demonstrate polarization-independent and highly-efficient optical fiber wavelength converters in a 10 Gb/s NRZ transmission system. They are based on synchronous phase or frequency modulations of the two orthogonally polarized pump lights, and can suppress not only the stimulated Brillouin scattering (SBS) but also the spread of the converted spectrum without modulating the signal light.

Soliton transmission control has already proved to be an outstanding technique and enable a soliton to be transmit over one million kilometers. This technique is not only applicable to vast distances but also to shorter distances where the amplifier spacing is greater than that of conventional systems. A combination of time and frequency domain control eliminates the noise accumulation and timing jitter caused by soliton interaction and the Gordon-Haus effect, that are the main impediments to extending the transmission distance. In this paper we describe soliton control techniques applied over an astronomical transmission distance of 180,000,000 km, and to a terrestrial system with a large amplifier spacing of up to 100km. We also report the possibility of realizing a sub-tera bit/s soliton transmission system operating over more than 5,000 km in which the soliton self-frequency shift is controlled with the soliton control technique.

Optical soliton transmissions at 10 and 20Gbit/s over 1000km with the use of erbium-doped fiber amplifiers are described in detail. For the 10Gbit/s experiment, a bit error rate (BER) of below 110-13 was obtained with 220-1 pseudorandom patterns and the power penalty was less than 0.1dB. In the 20Gbit/s experiment optical multiplexing and demultiplexing techniques were used and a BER of below 110-12 was obtained with 223-1 pseudorandom patterns under a penalty-free condition. A new technique for sending soliton pulses over ultralong distances is presented which incorporates synchronous shaping and retiming using a high speed optical modulator. Some experimental results over 1 million km at 7.210Gbit/s are described. This technique enables us to overcome the Gordon-Haus limit, the accumulation of amplified spontaneous emission (ASE), and the effect of interaction forces between adjacent solitons. It is also shown by computer runs and a simple analysis that a one hundred million km soliton transmission is possible by means of soliton transmission controls in the time and frequency domains. This means that limit-free transmission is possible.