Effects of phase modulation and filtering on NRZ and RZ signals

We investigate the process by which phase modulation and filtering interact to compress optical pulses at the transmitter and during propagation. The paper has two parts. (1) An appropriate combination of phase modulation and filtering can convert an NRZ signal to RZ at the transmitter. Closed form expressions for the modulation index and filter bandwidth that not only compress pulses at the transmitter but do so maximally, with a specific resulting time-bandwidth product, are obtained for the case of Gaussian shaped pulses and filters. (2) Phase modulation and filtering can also be applied to RZ pulses so as to improve the propagation characteristics. Analytical formulas and numerical simulations are used to compare maximum eye openings corresponding to various phase modulation formats.