Observation of noncritically phase-matched second-harmonic generation in an optical waveguide

Abstract

Experimental observation of noncritically phase‐matched second‐harmonic generation in a liquid/TiO₂/quartz waveguide is reported. The phase‐match condition, approximately independent of waveguide thickness, was achieved by tuning the liquid refractive index. Nonlinear interaction occurs in the quartz between the fundamental (1.06 μm) TE₀ mode and the harmonic (0.53 μm) TM₀ mode. Mode effective indices were measured versus liquid index to determine the phase‐match point. Coherence lengths greater than 3.5 mm were achieved, but propagation lengths were limited to 4 mm by losses due to surface scattering. These losses arise from waveguide design requirements of noncritical phase matching, not experimental film quality. Conversion efficiency was approximately 0.01%.