Microvolt-Level Suppression of DC Electrical Crosstalk Between InP Electro-Optic Phase Modulators

Electro-optic phase modulators tune the phase of light by modulating the refractive index in response to an applied voltage, making them essential in photonic integrated circuits. In current indium phosphide technology, they share a p-doped layer with waveguides, creating a resistive electrical path that causes crosstalk between modulators. To address this issue, our study presents the first quantitative multi-chip characterization of a previously proposed shorted element, which suppresses DC electrical crosstalk. We also propose and experimentally confirm an equivalent-circuit model for it, demonstrating that it preserves the modulators’ forward-diode characteristics. Our results show that a 30-micrometer element is sufficient to reduce voltage crosstalk to the microvolt measurement floor, representing a five-order-of-magnitude improvement over a 50-micrometer isolation section, hence offering a practical design rule. In summary, this work clarifies the electrical behavior and proves the capabilities of the shorted element, thereby improving modulator control and enabling greater integration density.