Nonlinear optical properties of a channel waveguide produced with crosslinkable ferroelectric liquid crystals

Abstract

A binary mixture of ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The FLCs possess two important functionalities: a chromophore with a high hyperpolarizability β and photoreactive groups. The smectic liquid crystal is aligned in layers parallel to the glass plates in a sandwich geometry. This alignment offers several advantages, such as that moderate electric fields are sufficient to achieve a high degree of polar order. The arrangement was then permanently fixed by photopolymerization which yielded a polar network possessing a high thermal and mechanical stability which did not show any sign of degradation within the monitored period of several months. 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. The alignment led to an inherent channel waveguide for p-polarized light without additional preparation steps. The photopolymerization did not induce scattering sites in the waveguide and the normalized losses were less than 2 dB/cm. The material offers a great potential for the design of nonlinear optical devices such as frequency doublers of low-power laser diodes.PACS. 61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order -42.65.

Phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide

“…Various aspects of the preparation process as well as some nonlinear optical properties are described in a recently submitted publication. 19 In this contribution we focus on the problem of phase matching in waveguide geometry and demonstrate that true phasematching is possible to achieve.…”

“…19 A linear and nonlinear optical characterization is presented in Ref. 19 ͑absorption, scattering losses, secondorder reduced nonlinear optical susceptibilities͒. According to the prevailing symmetry, second-harmonic generation can only occur for transverse electric TE -TE 2 and TM -TE 2 modes.…”

“…Without any additional preparation step this arrangement is also a channel waveguide for tranverse magnetic ͑TM͒ modes. 19 A linear and nonlinear optical characterization is presented in Ref. 19 ͑absorption, scattering losses, secondorder reduced nonlinear optical susceptibilities͒.…”

“…The mixture of A1b and A2c balances the tradeoff between a high polarization on one hand and the field strength required for a manipulation of the helix on the other hand. 19 Even a moderate electric field strength is sufficient to obtain a highly ordered structure and no aligning layers are required. The achieved polar order of the monomeric FLC system is then permanently fixed by photopolymerization leading to a mechanically and thermally stable PP network.…”

“…To overcome these problems the FLCs are further functionalized with photoreactive groups. Subsequent photopolymerization leads to the formation of stable polymer net- works [15][16][17][18][19] where the polar order is frozen (pyroelectric polymer, PP). Various aspects of the preparation process as well as some nonlinear optical properties are described in a recently submitted publication [19].…”