Quaternary optical transmission system combining phase and polarization-shift keying

A new optical transmission scheme which combines polarization-shift keying and differential phase-shift keying on the same optical carrier is proposed. Simulations carried out show a considerable tolerance toward different physical impairments, such as polarization-mode dispersion, nonlinear effects, and chromatic dispersion. When compared to other multilevel modulation formats, it shows the advantage of reusing the carrier power, thus, sensitivity is improved.