Recent advances in developing nonlinear optical techniques for processing serial digital information at high speed are reviewed. The field has been transformed by the advent of semiconductor nonlinear devices capable of operation at 100 gigabits per second and higher, well beyond the current speed limits of commercial electronics. These devices are expected to become important in future high-capacity communications networks by allowing digital regeneration and other processing functions to be performed on data signals “on the fly” in the optical domain.

In this paper, we experimentally demonstrate the benefit of polarization insensitive dual-band optical phase conjugation for up to ten 400 Gb/s optical super-channels using a Raman amplified transmission link with a realistic span length of 75 km. We demonstrate that the resultant increase in transmission distance may be predicted analytically if the detrimental impacts of power asymmetry and polarization mode dispersion are taken into account.

We demonstrate that a distributed Raman amplification scheme based on random distributed feedback (DFB) fiber laser enables bidirectional second-order Raman pumping without increasing relative intensity noise (RIN) of the signal. This extends the reach of 10 × 116 Gb/s DP-QPSK WDM transmission up to 7915 km, compared with conventional Raman amplification schemes. Moreover, this scheme gives the longest maximum transmission distance among all the Raman amplification schemes presented in this paper, whilst maintaining relatively uniform and symmetric signal power distribution, and is also adjustable in order to be highly compatible with different nonlinearity compensation techniques, including mid-link optical phase conjugation (OPC) and nonlinear Fourier transform (NFT).

We demonstrate that a combination of Raman laser based amplification and optical phase conjugation enables transmission beyond the nonlinear-Shannon limit. We show nonlinear compensation of 7×114Gbit/s DP-QPSK channels, increasing system reach by 30%.

80 Gbit/s all-optical regenerative wavelength conversion is demonstrated using a data driven interferometric switch incorporating a semiconductor optical amplifier. Error free operation is achieved for 2³¹ – 1 pattern lengths with switching powers of only 200 fJ. Furthermore, the interferometer is insensitive to the polarisation state of the driving data signal.

Nonlinear Fourier transform (NFT) and eigenvalue communication with the use of nonlinear signal spectrum (both discrete and continuous) have been recently discussed as promising transmission methods to combat fiber nonlinearity impairments. In this paper, for the first time, we demonstrate the generation, detection, and transmission performance over transoceanic distances of 10 Gbd nonlinear inverse synthesis-based signal (4 Gb/s line rate), in which the transmitted information is encoded directly onto the continuous part of the signal nonlinear spectrum. By applying effective digital signal processing techniques, a reach of 7344 km was achieved with a bit error rate (2.1 × 10 ^-2 ) below the 20% FEC threshold. This represents an improvement by a factor of ~12 in data capacity × distance product compared with other previously demonstrated NFT-based systems, showing a significant advance in the active research area of NFT-based communication systems.