Proposal and simulation investigation of optical format conversion between quaternary amplitude-shift keying signals based on cascaded modulators

We propose a simple and novel format conversion scheme based on a polarization modulator (PolM) and a zero-chirp intensity modulator (IM) to perform NRZ to RZ conversion for quaternary amplitude-shift keying (4-ASK) signals. Simulation shows that the scheme is capable of realizing format conversion from 20-Gbit/s NRZ-4-ASK signal to RZ-4-ASK signal with tunable pulse-width for 4-level intensity modulation format. The converted signals can transmit over a dispersion-managed fiber link from 200 km to 300 km confirming the high quality conversion.

► We propose a novel format converter for 4-ASK signal based on modulators.
► NRZ-4-ASK to RZ-4-ASK with tunable pulse-width can be achieved by control the drive to the modulator.
► Transmission comparison performed to evaluate the conversion performance.