Ultra‐Wideband Phase‐Tunable Millimeter‐Wave Photonic Down‐Converter in Lithium Niobate on Insulator

Down‐converters are critical components in modern wireless communication and radar systems, enabling the translation of high‐frequency signals to a lower intermediate frequency (IF). Photonic‐assisted radio frequency (RF) down‐converters offer remarkable advantages over their electronic counterparts, including wide bandwidth, simple architecture, and immunity to electromagnetic interference. However, due to the bandwidth limitations of existing electro‐optic modulators, integrated photonic down‐converters face significant challenges in achieving efficient conversion at high frequencies, especially in the millimeter‐wave (mmWave) band. Here, a photonic mmWave down‐converter with record‐breaking operating bandwidth is demonstrated on a lithium niobate on insulator (LNOI) platform. The device achieves broadband down‐conversion across 20–81 GHz, generating IF signals up to 20 GHz. Additionally, the system enables precise optical‐domain phase control of the IF signal. A maximum phase shift of 164° can be achieved when a 67 GHz RF signal is converted to a 0.1 GHz IF signal. This work offers a promising approach to high‐performance mmWave signal processing and paves the way for next‐generation mmWave receivers.