Enhanced Phase-Matched Second-Harmonic Generation in a Ferroelectric Liquid Crystal Waveguide

Abstract

A binary mixture of crosslinkable ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The liquid crystal was aligned in layers parallel to the glass plates (homeotropic) in a sandwich geometry and then the arrangement was permanently fixed by photopolymerization which yielded a polar network possessing a high thermal and mechanical stability. The linear and nonlinear optical properties have been measured and all four independent components of the nonlinear susceptibility tensor d have been determined. The off-resonant d-coefficients are remarkably high and comparable to those of the best known inorganic materials. Phase-matching was achieved by taking advantage of the modal dispersion of the waveguide. A reversal of sign of χ(2) at the nodal plane of the electric field distribution of the first-order mode was needed to maximize the overlap integral between the fundamental and the second-harmonic (SH) light. In samples with χ(2) inversion the SH signal was 1000 larger that in samples without χ(2) inversion.