A second-harmonic generation nonlinear frequency converter includes a nonlinear optical crystal. The nonlinear optical crystal includes a plurality of sections. The sections connect to each other in sequence, and each section has a phase different from others. Each of the phases includes a positive domain and a negative domain. Each of the sections includes a plurality of quasi-phase-matching structures. The quasi-phase-matching structures connect to each other in sequence and have the same phase in one section.