High-efficiency slow-light modulator on thin-film lithium tantalate operating at high optical power

Integrated electro-optic (EO) modulators are essential interfaces between electrical and optical signals, but maintaining high modulation efficiency and broadband EO response under high optical power remains challenging. Here, we demonstrate a thin-film lithium tantalate (TFLT) Mach-Zehnder modulator combining 1-mm-long one-dimensional topological slow-light waveguides with capacitively loaded T-shaped traveling-wave electrodes. The device achieves a minimum V_π of 3 V at 1560.408 nm, corresponding to a V_πL of 0.3 V·cm. At 1550, 1558.957, 1559.798, 1560.11, and 1560.408 nm, the extracted V_πL values remain consistent at 0 and 35 dBm off-chip input, with the latter corresponding to an estimated on-chip optical power of ~27 dBm (~500 mW). Multi-wavelength EO S₂₁ measurements show no 3-dB roll-off within the 67 GHz measurement range, with the broadband response preserved under high optical power. The device supports 75 Gb/s OOK and 80/100 Gb/s PAM4 transmission, which remain achievable under the high-power condition. These results demonstrate a high-efficiency, broadband TFLT slow-light modulator operating at high optical power.