Abstract
In optical communications, sphere shaping is used to limit the energy of lightwaves to within a certain value over a period. This minimizes the energy required to contain information, allowing the rate of information transmission to approach the theoretical limit if the transmission medium is linear. In optical fiber, however, the sphere shaping induces Kerr nonlinearity in a peculiar way that makes analysis of transmission performance difficult, potentially lowering the communications capacity. In this article, we show how the impact of sphere shaping on Kerr nonlinearity varies with the chromatic dispersion and the structure of shaped lightwaves in time and frequency, and give insights into why the structure matters. As a practical consequence, by optimally controlling the structure of lightwaves in time and frequency, it is experimentally demonstrated that the information rate can be increased by up to 25% in low-dispersion channels on a 2824-km dispersion-managed wavelength-division multiplexed optical fiber link.
Shaping Lightwaves in Time and Frequency for Optical Fiber Communication