Broadband Second Harmonic Generation using Fixed-Period Periodically Poled Lithium Niobate

Periodically poled lithium niobate (PPLN) is a widely used nonlinear optical device for second harmonic generation (SHG). Despite its wide adoption in commercial systems, its bandwidth for SHG is fundamentally limited by the quasi-phase matching condition. This can be overcome by aperiodic or chirped PPLN structures; however, such devices are typically custom-fabricated and not readily available commercially. In this study, we investigate an alternative approach to achieving broadband SHG by using a standard PPLN crystal containing multiple fixed poling periods. Broadband operation is realized by angle tuning the crystal relative to input beam in free-space. The effect of angle tuning is examined over a range of incident angles, and an 1.6x enhancement in SHG bandwidth is demonstrated. These results suggest a practical and efficient strategy for broadband SHG using standard PPLN devices.