Microwave Electromagnetic Field Sensor on Thin-Film Lithium Niobate Using Photonic Down-Conversion Detection

We integrate a bow-tie antenna on a thin-film lithium niobate (TFLN) phase modulator to form an electromagnetic E-field sensor. The fiber-coupled TFLN chip is probed by a two-tone optical local oscillator generated using an external phase modulator, which after appropriate filtering allows the system to act as a photonic down-converter. The system is compatible with the use of balanced detection, enabling an improved signal-to-noise ratio. We demonstrate the down-conversion of a 28.3 GHz free-space microwave signal to 100 MHz with a sensitivity of 2 mV/m/√Hz. The current sensitivity limitation stems from the relatively high (25 dB) insertion loss of the packaged device, which is not inherent to the design. The technology can be directly scaled to much higher frequencies and is attractive for remote detection of microwave electromagnetic signals.