Development of high efficiency waveguided green SHG device

摘要

Development on shorter wavelength laser light source for next generation displays or high density DVD recorders has been the latest and hottest topic at many R&D centers in the world. One of the technologies to realize a short wavelength light source is SHG (Second Harmonic Generation) from longer wavelength lasers using non-linear optical crystals. In this paper, we report on the high efficiency waveguided green SHG devices based on Periodically Poled Magnesium Oxide doped lithium Niobate (PPMgLN). SHG from periodically poled crystal, generated by Quasi-Phase Matching, is a promising technology, because of the wideband harmonic wavelength ranging from ultraviolet to infrared and high conversion efficiency. Research on LN as a periodically poled crystal, has been very popular, regardless of such inadequacy as the weakness against photo-refractive damages. Therefore high temperature operation has been must for the LN crystals. On the other hand, MgO doped LN crystal has good endurance against photo-refractive damage, and PPMgLN shows high conversion performances without heating the crystal. Green SHG devices in this report were manufactured from this MgO doped LN crystal with the optical waveguides fabricated on the +z surface by proton exchange process to attain higher conversion efficiency than the bulk crystals. Dimensions of the device is 10 mm (L) × 5 mm (W) × 0.3 mm (t). Poled domain grating period is 6.9 micro-meter and domain duty cycle is 56.9%. Using 1064 nm Nd:YAG laser of 50 mW as an incident light source, we confirmed the strong green light emission of 4.1 mW as the converted second harmonic light from the other end of the device at room temperature.