The optical modulation conversion of a quadrature phase-shift keying (QPSK) signal to two binary phase-shift keying (BPSK) signals is theoretically realized in a phase-sensitive amplification (PSA) conversion system. We propose a multi-slot silicon-carbon nanotube/polydimethylsiloxane hybrid waveguide to achieve high nonlinearity of 108 W -1 m -1 for improving PSA performance. Constellation diagrams, error vector magnitude, and bit error rate (BER) are used to investigate and measure the performance of the output. The results show that the converted BPSK signal has more than a 10 dB higher signal-to-noise ratio than the QPSK signal with a BER threshold of 10-3. Furthermore, the system has great potential for hierarchical modulation of advanced format signals and long-distance transmission.