Thin-film lithium niobate terahertz differential field detectors with a bandwidth reaching 3 terahertz

Broadband and sensitive detection of terahertz (THz) radiation is critical for advances in fields like telecommunications, spectroscopy, and quantum physics. We present a compact and high-performance THz field detector based on resonant THz antennas printed along near-infrared waveguides on thin-film lithium-niobate. These antennas were shown to have their peak response between 250 GHz to 1 THz, depending on their geometry, while the non-resonant nature of the interaction enables THz detection to be achieved up to 3 THz. We show that combining two such antennas in an integrated Mach Zehnder interferometer allows for a measurement of the discrete time derivative of the THz waveform, while using a single antenna measures the instantaneous derivative of the field. Using this approach, we have achieved a noise equivalent intra-cavity field as low as 1.9 Vm^-1 for an integration time of 100 ms, corresponding to a single-shot noise-equivalent field of 4.6 kV m¹, using a pulsed laser operating at 1575 nm with 76 μW average power. Our device would enable the next generation of compact detectors for applications in spectroscopy and quantum optics.