Broadband wavelength converter based on segmented quasi-phase matched grating

Broadband wavelength converters based on difference frequency generation (DFG), single-pass and double-pass cascaded second harmonic generation and difference frequency generation (SHG+DFG), single-pass and double-pass cascaded sum and difference frequency generation (SFG+DFG) are fulfilled by utilizing segmented grating structure in lithium niobate waveguide. Under the small-signal approximation, the effects of the waveguide length and the response flatness on DFG-based wavelength conversion are investigated by use of matrix operator, and then a feasible scheme to enhance the bandwidth and stability of signal and pump wave is proposed. For single-pass/double-pass SHG+DFG wavelength conversion scheme and single-pass/double-pass SFG+DFG wavelength conversion scheme, the effect of segmented grating structure on conversion bandwidth is studied theoretically and numerically, the results show that the signal conversion bandwidth can be broadened by optimizing the aperiodic grating. Moreover, the influence of "balance condition" on double-pass SFG+DFG-based wavelength conversion is analyzed, one can achieve enhanced conversion efficiency and conversion bandwidth by adjusting the power and wavelengths of pump sources according to the "balance condition". In the end, a reasonable suggestion is presented to achieve broadband wavelength conversion under different requirements.