Absorption loss and Kerr nonlinearity in barium titanate waveguides

TL;DR

This study measures the optical absorption loss and Kerr nonlinearity of barium titanate waveguides, demonstrating their potential for high-efficiency integrated photonic devices leveraging both Pockels and Kerr effects.

Contribution

It provides the first precise measurement of BaTiO$_3$'s absorption loss and Kerr nonlinear index at telecom wavelengths, highlighting its suitability for advanced photonic applications.

Findings

Absorption loss of BaTiO$_3$ waveguides is approximately 10.9 dB/m, below scattering losses.

BaTiO$_3$ exhibits a large Kerr nonlinear index of about 1.8×10$^{-18}$ m$^2$/W.

Results suggest potential for highly efficient integrated photonic circuits using BaTiO$_3$.

Abstract

Because of its exceptionally large Pockels coefficient, barium titanate (BaTiO$_3$) is a promising material for various photonic applications at both room and cryogenic temperatures, including electro-optic modulation, frequency comb generation, and microwave-optical transduction. These applications rely on devices with low optical loss to achieve high efficiency. Material absorption sets a lower limit to optical loss and is thus a crucial property to determine, particularly for integrated photonic devices. Using cavity-enhanced photothermal spectroscopy, we measure the absorption loss of BaTiO$_3$ ridge waveguides at wavelengths near 1550~nm to be $\alpha_{\mathrm{abs}} = 10.9$~{\raisebox{0.5ex}{\tiny$^{+5.8}_{-0.4}$}} dB~m$^{-1}$, well below the propagation losses due to other sources, such as scattering. We simultaneously determine that BaTiO$_3$ has a large Kerr nonlinear refractive index of $n_{\mathrm{2,BaTiO_3}}$ = 1.8 {\raisebox{0.5ex}{\tiny$^{+0.3}_{-0.3}$}} $\times$ 10$^{-18}$ m$^2$ W$^{-1}$. Considering these results, photonic integrated circuits utilizing BaTiO$_3$ have the potential to achieve significantly higher efficiency than demonstrated to date and are especially interesting for applications exploiting the combination of Pockels and Kerr effects.