Organic crystal isopropyl-4-acetylphenylurea and waveguide second-harmonic generation

A new organic crystal isopropyl-4-acetylphenylurea (IAPU) was identified as a promising candidate for blue second-harmonic generation (SHG). The nonlinear optical d coefficient obtained is d₂₂ = 30.5 pm/V at the fundamental wavelength 1064 nm, and the crystal's transmitting range is 380-1400 nm. Thin, single crystalline films fabricated on the glass substrate are useful for waveguide-device applications. For the improvement of SHG efficiency and the relaxation of phase-matching conditions, the concept of thickness-noncritical phase matching (TNCPM) in a four-layer waveguide is proposed. Modal dispersion calculations for the various four-layer structures suggested the possibility of TNCPM from the TE₀^ω mode to TE₁^2ω mode and from the TE₀^ω mode to the TE₂^2ω mode by adjustment of the refractive indices of the two guiding layers.