High‐Isolation Electro‐Optic Isolator Based on an Ultra‐Compact Double‐Pass Thin‐Film Lithium Niobate Modulator

Thin‐film lithium niobate (TFLN) has emerged as one of the leading platforms for integrated photonics. On‐chip optical isolators are indispensable for achieving fully integrated and advanced photonic systems. However, prior demonstrations either suffer from long modulation lengths despite high microwave drive power, or fall short due to the necessity of dual microwave inputs, fundamentally limiting device compactness and practical feasibility. Here, we demonstrate a compact TFLN‐based electro‐optic (EO) isolator utilizing a novel double‐pass Mach–Zehnder modulator (DBP‐MZM) architecture. By leveraging both and modes to double the optical–microwave interaction, the fabricated device achieves a comparable isolation ratio and power consumption to state‐of‐the‐art EO isolators on TFLN while reducing the footprint. It exhibits an ultra‐low half‐wave voltage–length product of , a compact modulation length of , and a maximum optical isolation of with a drive power of at , while a high isolation ratio exceeding is achieved across the C‐band. This approach paves the way for compact and high‐isolation non‐reciprocal photonic systems on the TFLN platform.