Relation Between Vestigial Sideband Filtering and pi/2 Progressive Phase-Shift

We show that a Gaussian-shaped vestigial sideband-(VSB) return-to-zero on-off keying (RZ-OOK) optical signal is essentially an RZ-OOK signal with pi/2 progressive phase-shift (PPS). The reduced inter symbol interference (ISI) of the VSB signal can be explained as a distinctive interference effect. We experimentally demonstrate a method to generate an effective 40-Gb/s VSB signal without relying on detuning of an optical filter.