Theoretical Feasibility Demonstration for Over 100 GHz Electro-Optic Modulators With c-Axis Grown BaTiO 3 Crystal Thin-Films

Single-channel 100 GHz and higher bandwidth external optical modulators are dramatically demanded to realize the aggregate carrier data rate of 100 Tb/s per optic-fiber in next-generation optical networks, but the current technologies used in industrial systems have never shown any feasibility to reach such high-speed operations. In this study, the feasible potential of ultrahigh bandwidths higher than 100 GHz are theoretically demonstrated for waveguide electro-optic (EO) modulators with c-axis-oriented BaTiO₃ crystal thin-films. As the three dominant factors of determining the bandwidths of EO modulators, the interaction length L, the absolute refractive difference of light-wave and microwave |N_m-N_o| determining the velocity mismatch, and the microwave loss coefficient are investigated to realize the ultrahigh bandwidths of over 100 GHz, where L is a weight factor of both the velocity mismatch and the microwave loss. Thus, in this process, the nonlinear EO modulation effects are taken into account to determine the L values with respect to the values of EO coefficient r₅₁ under a given half-wave voltage V_π. Then, the optimal tradeoff conditions for the over 100 GHz bandwidths are obtained with the consistent relations among the interaction length, the optical loss, the electrode gap, and the overlap integral of optical and electrical fields, the refractive index difference between the optical guidedmode and the microwave. As a result, for an industrial acceptable V_π of 5.0 V and a feasible absolute birefringence b_eo of 0.005, at the EO coefficient r₅₁ values of over 550 pm/V an optimal device in both optical rib waveguide and microwave electrode dimensions shows the illustrative results of over 100 GHz bandwidth in the believable simulations albeit both the velocity mismatch and the microwave loss are taken into account in simulations under a microwave impedance matching, which are all reachable in the real c-axis BaTiO3 crystal thin-film.