Optical phase-modulated systems: numerical estimation and experimental measurement of phase jitter

Abstract

The objective of the proposed research is to investigate new and more efficient techniques in numerical evaluation and experimental measurement of phase jitter impact on more general communication systems including dispersion management, filtering, and spectral inversion schemes. There has recently been a renewed effort to develop coherent optical communication systems. In particular, differential phase-shift keying (DPSK), which does not require a local oscillator to perform decoding, has focused the attention and is perceived to be the promising candidate for future optical communication systems updates. This motivates us to exploit DPSK in wavelength-division multiplexed systems. First, modulation formats based on phase show an increased robustness to nonlinear impairments such as cross-phase modulation (XPM) and nonlinear polarization rotation, primarily because the time-dependence of optical power is deterministic and periodic. Second, coherent formats allow a higher spectral efficiency since both in-phase and quadrature dimensions of the signal space are available to encode information. Optical phase is also used in intensity-modulated direct detection systems as an extra degree of freedom, for example to provide better resistance to intrachannel four-wave mixing (FWM), or to increase spectral efficiency in duobinary modulation. Finally, phase modulation outperforms its intensity counterpart in terms of sensitivity since a 3 dB improvement can be achieved when balanced detection is used. Nevertheless, DPSK-based formats show a different behavior to noise accumulated along the propagation. Noise-induced power fluctuations are converted into phase fluctuations by the Kerr effect and become a penalty source which limits the transmission system reach. In this context, there have been intense research activities for evaluating phase uncertainties but the previous studies assume an analytically determined pulse shape and a constant-dispersion optical link which is far from reflecting the actual and future structures of transmission lines.