The broadband response of second harmonic generation(SHG)is experimentally observed in a two-dimensional(2D)quasi-random quasi-phase-matching(QPM)structure.A nonlinear conversion efficiency of more than 50%is obtained.Due to the line-type distribution of the reciprocal vector,the second harmonic wave(SHW)covering a broad frequency band is efficiently radiated in the shape of one single spot or three spots instead of a stripe.This is believed to be favorable for its practical application and paves the way for the use of ultrahigh-bandwidth light sources and devices in modern optical technologies.
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