Generation of Nearly Flattop Ultrabroadband Response in a QPM Device Using Phase Shifter

We have theoretically demonstrated the efficient generation of nearly flattop ultrabroadband response in a periodic quasiphase matching (QPM) device using a single phase shifter 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 Δλ = 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 ultrabroadband response by introducing multiple phase shifter domains at suitable locations in a periodic QPM device.