All-Optical Modulation Format Conversion From QPSK to Symbol Rate Doubled BPSK Using FWM and Pulse Width Compression

Conversion between multilevel modulation formats is one of the key functions for flexible networking aimed at high spectral efficiency in optical fiber transmission. The authors previously proposed an all-optical conversion system from quadrature phase shift keying signal to simultaneous two binary phase shift keying (BPSK) signals by using four-wave mixing and interference. Since the converted BPSK signals are spatially separated, there is an issue that they cannot be transmitted at the same time through a single fiber core when redirected to the same destination. In this paper, therefore, we consider to solve the issue by converting to a symbol rate doubled single BPSK signal using a pulse width compression technique. Numerical simulation reveals that the location of the pulse width compressor affects the system performances evaluated by bit error rate and constellation diagram.