A zero-power biasing approach for Mach–Zehnder modulators using phase-change materials

High-performance and energy-efficient optical modulators are indispensable for the development of next-generation high-speed optical interconnects. Thin-film lithium niobate (TFLN) has emerged as a leading platform owing to its large Pockels coefficient and broad optical transparency. Despite the outstanding performance of lithium niobate electro-optic (EO) modulators, a bias method is typically required to set the Mach–Zehnder modulators (MZMs) to the operating point. Conventional bias schemes, whether based on EO or thermo-optic (TO) approaches, consume static power to sustain the bias. In this work, we integrate the low-loss phase-change material (PCM) Sb2Se3 into the phase-shifting section of a TFLN MZM, enabling precise nonvolatile phase calibration and zero-power biasing. Laser-induced crystallization is employed to program the PCM phase state for bias adjustment, and replacing the TO heaters further simplifies chip layout. In addition, the high-speed performance of the PCM-biased modulator has been verified, with 120 Gbps on–off keying and 160 Gbps four-level pulse amplitude modulation successfully demonstrated. The proposed PCM-biased strategy shows great potential and offers a scalable and energy-efficient solution for bias establishment in advanced TFLN modulators.