Second harmonic generation for the analysis of lithium niobate substrates and boules

Abstract

The nonlinear optical properties of thin (1 mm) lithium niobate integrated optical substrates and much thicker (∼8cm) boules can be obtained from the interference between the free and bound second harmonic waves (Maker fringes). The harmonic power is affected by the homogeneity of the plate, and this provides us with a method of quality control. We use a Q switched Nd: YAG laser to generate the harmonic power and the equipment is computer controlled. Fringe patterns that deviate appreciably from those expected for homogeneous plates indicate substrates that may not function properly in devices. In addition, the method can be used to analyze lithium niobate boules to ascertain if they are potentially useful for substrates.