Photorefractive damage of LiNbO3 quasiphase matched wavelength converters

Photorefractive damage (PRD) of LiNbO3 quasiphase matched (QPM) wavelength converters is studied by a novel two-beam method, in which the second-harmonic generation (SHG) tuning curve of a broadband probe beam is monitored. The QPM condition and wavelength conversion efficiency, which are characterized by the peak wavelength and peak intensity of the SHG tuning curve respectively, are investigated in detail with respect to the irradiation power and irradiation time. It is found that the QPM condition and wavelength conversion efficiency change markedly even for low irradiation powers (<20 mW), indicating that the PRD effect is non-negligible in LiNbO3 QPM wavelength converters intended for practical applications.