Bandwidth enhancement in difference frequency generation (DFG) has been investigated using domain-shifted quasi-phase-matching (QPM) structure of electrically poled ferroelectric crystals. The exact periodic QPM condition is relaxed by extending the periodic structure to a more flexible domain-shifted structure. The dependence of bandwidth enhancement and flatness on the positions and number of shifted domains are systematically studied for optimum output efficiency. The results presented here are useful for the fabrication of wide-bandwidth wavelength conversion devices based on the DFG process.
In this paper, for the first time, we present a theoretical investigation of optimization and stabilization of wavelength conversion bandwidth based on a counter-propagating configuration, which correspond to second-order wavelength conversion architectures with propagation directions of signal and idler beams being opposite. Optimized example for two-, four-, six- and ten-segment chirp gratings are given, respectively. The stabilization of signal bandwidth can be realized by adjusting the pump wavelength. The numerical results show that the counter-propagating difference frequency generation (CDFG)-based wavelength converter with chirped modulation is an excellent candidate for wavelength division multiplexed (WDM) application.