Study of Photorefractive Effects in Periodically-Poled Lithium Niobate

摘要

The objective of this DURIP-97 program was to facilitate investigation of photo-refractive effects in periodically poled lithium niobate (PPLN). Performance limitations due to photo-refractivity were studied using photo-thermal common-path interferometry (PCI) to determine if photo-refractive damage sensitivity is dependent on grating duty cycle. The PCI technique operates in a 'pump-probe' configuration, and is sensitive to both linear optical absorption at the ppm/cm level and photo-refraction. Bulk and waveguide frequency doubling PPLN modules having a range of grating pitches were fabricated by Corporation. In the bulk PPLN devices, optimum performance was found in modules with a nominal duty cycle close to the 50% value predicted by assuming that photo-refraction in lithium niobate is caused by photo-galvanic charge separation and that the alternating ferroelectric domain polarity due to the grating acts to 'short-circuit' any charge build-up. Similar optimum performance is expected from waveguide harmonic conversion devices which have 40-50% duty cycles.