The production and exchange of information drive much§of today's economy. This information exchange takes§place more and more at a global level, so it becomes§crucial to be able to transmit ever larger amounts of§information over very long optical-fibre transmission§links. At the same time, the sobering up after the§burst of the dot-com bubble in 2000-2001 has made§cost a major consideration in any upgrading solution.§This translates into the need for modulation§techniques that allow for the transmission of high§bit rates over large distances at minimum cost. This§book presents three phase-modulation techniques that§allow the upgrade of existing transmission links to§higher bit rates using cost-effective On-Off keying§and direct detection. This is achieved thanks to the§suppression of intra-channel non-linear effects, such§as IFWM which become a major impairment for bit rates§of 40 Gb/s and above. The techniques are examined§analytically, tested in numerical simulations, and§verified in transmission experiments.