Direct Integration of MoTe ₂ Onto Thin‐Film Lithium Niobate Grating Couplers for On‐Chip Photodetection

Abstract The inherent inability of thin‐film lithium niobate (TFLN) to perform photodetection poses a significant challenge for fully integrated photonic circuits with this highly promising next‐generation photonic material. While some 2D material photodetectors (PDs) have been integrated onto TFLN waveguides using transfer methods and exhibit excellent performance, the direct integration of 2D materials onto the crucial interface of grating couplers remains unexplored. This work demonstrates the first successful integration of a MoTe ₂ photodetector directly onto TFLN grating couplers and leverages the unique advantages of grating integration that enable in situ light detection immediately after diffraction. The fabricated MoTe ₂ PD still exhibits a relatively low dark current under different bias voltages (≈0.04 nA at 0 V, ≈35 nA at 1.0 V), attributed to the unique properties of MoTe ₂ , and achieves a highest responsivity of 6.5 mA W ⁻¹ at 1.0 V bias. This work validates grating couplers as a feasible integration site for 2D material PDs on TFLN, offering enhanced mechanical compatibility with promising potential for increased polarization sensitivity and streamlined packaging potential. It establishes a promising route toward compact, monolithic, and multi‐functional TFLN photonic receivers, moving beyond the limitations of both flip‐chip assembly and waveguide‐restricted 2D material integration.