Nonlinear properties of poled-polymer films: SHG and electro-optic measurements

Lock-In Free ATR Detections of Organic Thin Film Pockels Effects within and beyond Nyquist

“…More importantly, none of the above is applicable to the ATR measurements for the unpoled films, which gave no modulation-induced reflectivity change (Figures l and S1). Also, we have never observed an inversion point on any of the modulation curves, or the plots of ∂ R /∂ N eff versus N eff , from the lowest 0–1 modes of ATR spectra for the poled films. − It is commonly considered as evidence of a negligible piezoelectric effect or other electromechanical effects. These studies verify that new LIA-free ATR measurements in this study can be reliably applied to analyze the predominant Pockels effect of highly active poled OEO films at low frequencies.…”

“…To understand the origin of large modulation signals near the mode dip beyond the Nyquist sampling theorem, we took a second look at the Taylor expansion of modulated reflectivity in the ATR spectra and carried out the corresponding data analysis. From Morichére and Dumont et al, the Taylor expansion of Δ R as a function of angular change Δθ to the first order and second order gives normalΔ R prefix= prefix− normalΔ θ ∂ R ∂ θ + 1 2 ∂ 2 R ∂ θ 2 false[ normalΔ θ false] 2 where θ is the internal unitless angle or the θ in degree from the export data of Metricon 2010/M multiplied by 2π/360. , Also, the ATR measurement gives normalΔ n = normalΔ θ ∂ N eff ∂ θ = normalΔ θ ∂ ( n p r i s m sin ⁡ θ ) ∂ θ = n normalp normalr normali normals normalm normalΔ θ 0.25em cos nobreak0em0.25em⁡ θ …”

“…According to Park’s calculation, all of the ∂ N /∂ n terms are approaching 1.0 for multimode waveguides, which were confirmed by our independent analysis by COMSOL Multiphysics . It is noteworthy that the first term in eq has been neglected previously in analyzing the TM-mode modulation signals in ATR measurement. ,,,− ,, Such analyses were reported by Dumont and Park, respectively, but have received little recognition in the past. ,, As shown in Figure , in the TE-mode, the electric field E s of s -polarized light can only induce the polarization in the plane of the surface of thin films. However, in the TM-mode, the E p of p -polarized light can induce polarization with a vector component that is in the plane of the surface and a vector component that is perpendicular to the surface, leading to the expression of the first and second terms in eq , respectively.…”

“…The theory and instrumentation of the ATR technique by prism coupler have been well established to characterize the optical properties of thin film optical waveguides, including the anisotropic index of refraction, the thickness, and the propagation loss. ,, The ATR method in the Otto configuration is suitable for thin film EO detections due to its high sensibility for measuring small changes of refractive indices and high tolerance for repetitive tests of many thin film samples (Figure ). − ,,, In this configuration, a poled EO thin film sandwiched between a top gold electrode and an indium–tin oxide (ITO)-coated glass substrate is pressed against the bottom of the high-index prism.…”

“…where R TE and R TM are the ATR spectra with the changes of effective refractive indices N eff s for s-and N eff p for p-polarized waves, n TE and n TM are the anisotropic indices of refraction, and Δn TE and Δn TM are the Pockels effect-induced change in refractive indices, respectively, in the TE and TM polarizations. 29,30 In eqs 1 and 2, all of the parameters are measurable or can be derived from the ATR spectra, and under the applied modulation field of E mod , the Δn TE and Δn TM are given by…”