Broadband second-harmonic generation in APPLN with group-velocity matching

In this paper, we present a method to increase the acceptance bandwidth of second harmonic generation (SHG) with 5  mol% MgO-doped aperiodically poled lithium niobate (APPLN) when the conditions of quasi-phase-matching and group-velocity matching are satisfied simultaneously. The APPLN, with a length of 10 mm, has 3333 uniform domains, with the polarization directions of each domain optimized by a genetic algorithm, to obtain the profile of nonlinear coefficients in the communication band. By adjusting the positions and quantities of the fundamental wavelengths appropriately, the evolution of bandwidths is investigated theoretically. The simulation results show that the acceptance bandwidth of SHG is approximately 243.3 nm for type-I (o+o→e) interaction around the wavelength of zero-group-velocity dispersion in crystal, which is enhanced by 4.5 times that of periodic structures.