Ultrahigh-Efficiency Dual-Band Thin-Film Lithium Niobate Modulator Incorporating Low-k Underfill for 390 Gbit s−1 PAM8 Transmission

Abstract

High-performance electro-optic (EO) modulators are critical components in modern telecommunication networks and intra-datacenter interconnects. Low driving voltage, wide EO bandwidth, compact device size, and multi-band operation capability are essential for various application scenarios, particularly energy-efficient high-speed data transmission. However, it is challenging to meet all these requirements simultaneously. Here, a high-performance dual-band thin-film lithium niobate EO modulator with a low dielectric constant (low-k) underfill is demonstrated to achieve overall performance improvement. The low-k material helps reduce the RF loss of the modulator and achieve perfect velocity matching with a narrow electrode gap to overcome the voltage-bandwidth limitation, extending EO bandwidth and enhancing modulation efficiency simultaneously. The fabricated 7-mm-long modulator exhibits a low half-wave voltage V_π of 1.9 V in the C-band and 1.54 V in the O-band, featuring a low half-wave voltage-length product of 1.33 and 1.08 V·cm, respectively. Meanwhile, the novel design yields an ultrawide extrapolated 3 dB EO bandwidth of 220 GHz (218 GHz) in the C-band (O-band). High-speed data transmission in both C- and O-bands using the same device has been demonstrated for the first time by PAM8 with data rates up to 390 Gbit s⁻¹, achieving a record-low energy consumption of 0.69 fJ bit⁻¹ for next-generation cost-effective ultrahigh-speed optical communications.