Methodological analysis for the electrooptic coefficient and birefringence of BaTiO₃ crystal films with complementary polarization modulations

Abstract

BaTiO3 crystal films, possessing advanced electrooptic (EO) properties, have spurred a broad interest in research and development of EO modulators for fiber-optic communications. However, the EO coefficient is still at uncontrollable and unoriented states despite it playing a crucial role in developing applicable industrial devices. In this work, accurate measurements of the EO coefficient r 51 and birefringence b e o of BaTiO3 crystal films are implemented with a theorem-based theoretical model, an embedded waveguide/electrode device configuration and a complementary modulation of both the linear and ellipse polarizations. Then, with two state-of-the-art device samples on different crystal films, the final average values of the r 51 and b e o are 410 ± 8 pm V−1 and −0.0208 ± 0.0003 for Sample-1 and 624 ± 31 pm V−1 and −0.0138 ± 0.0015 for Sample-2, respectively. Furthermore, a theoretical model for analyzing the measurement accuracies of r 51 and b e o is proposed and the accuracy dependences on the two key variables, drive voltage and optic–electric interaction efficiency, are investigated. Finally, the limitations to the measurement accuracy of this methodology are discussed, including the effect of temperature on the measurement accuracy of r 51 .

Lowering The Bit‐Energy of Electro‐Optic Modulators Via Polarization‐Phase Modulation in Thin‐Film BaTiO3 Ferroelectric Crystal Waveguide

“…To this end, we create two MZI EO intensity modulators based on thin‐film BaTiO 3 crystal waveguide with two device samples having different EO coefficient $${r}_{{\mathrm{51}}}$$, namely $${r}_{{\mathrm{51}}}$$ = 628 pm V −1 for Sample‐1 and 429 pm V −1 for Sample‐2, for comparison. [ 32 ] The corresponding $${b}_{eo}$$ values of the Sample‐1 and Sample‐2 are −0.0107 and −0.0215, respectively. In order to systematically simulate the performance of the BaTiO 3 thin film MZI‐type intensity EO modulators, certain parameters are set as follows: the initial optical phase difference between the two arms of the MZI structure is 0, the thickness of the BaTiO 3 film T f is 0.45 µm, the width of the rib‐waveguide W is 4 µm, the height of the rib‐waveguide H is 0.1 µm, the electrode embedded depth $${S}_z$$ is 0.1 µm, and the four electrode gaps of $${G}_x$$= 5, 6, 7, and 8 µm are considered.…”

“…[30] In our previous works, we have introduced the accurate methodology for the electro-optical coefficient and manifested the intrinsic dependence of the EO effect on the initial state of crystal film/environment temperature. [31][32][33] Very recently, we discussed the highly efficient EO modulation method-phase-polarization modulation (PPM) for the thin-film caxis BaTiO 3 waveguide-based modulator and also demonstrated the crucial role of the PPM scheme in increasing the slope of optical phase transfer function of an MZI type intensity EO modulator. [34] In this work, we first analyze the dynamic-polarization interference process of a thin-film BaTiO 3 waveguide-based MZI type EO intensity modulator mechanism under the PPM mechanism, investigate the intrinsic relationships between the slope of optical phase transfer function and the electric-to-optical signal energy transition efficiency and clarifies the principle of PPM mechanism to reduce the half-wave voltage (V 𝜋 ).…”

“…[ 30 ] In our previous works, we have introduced the accurate methodology for the electro‐optical coefficient and manifested the intrinsic dependence of the EO effect on the initial state of crystal film/environment temperature. [ 31–33 ] Very recently, we discussed the highly efficient EO modulation method‐phase‐polarization modulation (PPM) for the thin‐film c‐axis BaTiO 3 waveguide‐based modulator and also demonstrated the crucial role of the PPM scheme in increasing the slope of optical phase transfer function of an MZI type intensity EO modulator. [ 34 ]…”