Fig. 1. Principle of the format conversion from a Pol-MUX QPSK signal to Pol-MUX BPSK signals based on phase-doubled FWM in a silicon waveguide. (a) Phase-doubled FWMs with polarization-angled pumps, and (b) phase change between the QPSK signal and the BPSK idler via the phase-doubled FWM process.

Fig. 2. Experimental setup of the two-channel format conversion from Pol-MUX QPSK to Pol-MUX BPSK signals based on phase-doubled FWM in a silicon waveguide.

Fig. 3. Measured optical spectrum of the FWM processes for two-channel format conversion at the end of the silicon waveguide.

Fig. 4. Measured eye diagrams of the Pol-MUX QPSK signal: (a) SX, and (b) SY. Format-converted Pol-MUX BPSK signals on idlers I1 and I2: (c) I1X, (d) I1Y, (e) I2X, and (f) I2Y (20 ps/div).

Fig. 5. Measured constellation diagrams of the Pol-MUX QPSK signal on signal S and the two-channel format-converted Pol-MUX BPSK signals on idlers I1 and I2: (a) SX, (b) SY, (c) I1X, (d) I1Y, (e) I2X, and (f) I2Y.

Fig. 6. Measured BERs as functions of the OSNR for the incident BTB signals and the two-channel format-converted idlers.