摘要： We have theoretically demonstrated the efficient generation of nearly flattop ultra-broadband response in a periodic quasi-phase matching (QPM) device using a single phase shifter (PS) domain. The flat broadband response is generated using optical parametric generation (OPG) with a QPM device of grating period Λ = 27 μm. The choice of grating period and pump source depends on the group velocities of signal and idler wavelengths to match close to the degeneracy point. We have identified the location of phase shifter domain, which generates a nearly flattop OPG gain bandwidth of ?λ = 1.41 μm. The variations in broadband response are studied when the location and width of phase shifter domains are altered. When compared to a periodic device, the phase shifter domain included QPM structure exhibits higher tolerance to temperature in retaining the smoothness of the broadband response. Furthermore, we have generated the same ultra-broadband response by introducing multiple phase shifter domains at suitable locations in a periodic QPM device.