Second-harmonic generation in waveguide structures

Abstract

Optical waveguides offer potentially significant advantages to bulk crystals for efficient second harmonic generation from relatively low power sources because the fundamental optical beam can be tightly confined over long interaction lengths. However, since channel waveguides must be used to achieve this confinement, phase matching becomes a severe problem. Because the channel orientation is predefined, birefringence angle tuning, which is commonly used with bulk crystals, cannot be used and temperature tuning, when it can be used, usually requires precise temperature control. Also, since the effective propagation constants depend on guide geometry, the waveguide dimensions must be tightly controlled over the entire optical path length. Although guided second harmonic generation has been observed in uniform channel waveguides using both LiNbO3 and KTiOPO4 normalized conversion efficiencies have not exceeded about 5%/W-cm2 and considerable sample-to-sample variation in efficiency and/or phase matching temperature is common.