Properties of power dependence on low-crosstalk waveband conversion with an apodized multiperiod-QPM LiNbO₃ device

Quasi-phase-matched (QPM) LiNbO₃ devices having a multiperiod-periodically-poled structure, which we call multiperiod-QPM LiNbO₃ devices, are capable of shifting the idler waveband during waveband conversion via cascaded difference-frequency generation (cascaded DFG). However, these multiperiod-QPM devices have a problem that they produce extra ripples between QPM peaks in the phase-matching curve. These ripples cause crosstalk between wavebands arising from sum-frequency generation (SFG) between the signal and idler wavebands and subsequent DFG between the SFG wavelength and the signal waveband. To decrease the size of the ripples and thus that of the crosstalk, an apodized multiperiod-QPM device is developed. In demonstrating waveband conversion for low crosstalk with this device, we measure the dependence of the idler power, the crosstalk power, and their ratio on the signal power. This measurement shows that it agrees well with theoretical prediction and that the obtained feature of crosstalk reduction is kept even for decreased signal power.