Multiple optical carrier generation using frequency mixing in damage resistant multiple QPM device.

We devised a method for the measurement of the phase-matching curve of multiple quasi-phase-matched (QPM) LiNbO₃ waveguide under conditions of high-power second-harmonic generation. The data obtained revealed that the phase-matching condition can be preserved due to the high damage resistance of the directly bonded LiNbO₃ waveguide. Based on this evaluation, we tried to generate multiple optical carriers using multi-stage frequency mixing in the multiple QPM device. The multiple optical carriers have mutual phase correlation, which is suitable for coherent wavelength division multiplexing (WDM) transmission. We also demonstrated 20 Gb/s quadrature phase shift keying (QPSK) signal generation using multiple optical carriers in order to ensure signal quality.