The thin film lithium niobate platform has shown its potential to support high-performance active and passive integrated photonic devices. Yet, due to the transparency of lithium niobate, it is not suitable for building a photodetector monolithically for conventional communication wavelengths. In this work, we demonstrate a high-speed photodetector on the thin film lithium niobate platform using hybrid integration of two-dimensional materials, i.e., black phosphorus. The black phosphorus and lithium niobate hybrid waveguide exhibit a high absorption coefficient of 1.56 dB/µm. The constructed metal-semiconductor-metal photodetector also presents a high responsivity of 2.64 A/W (at an input optical power of 25.1 µW). The 3-dB bandwidth of the device is as high as 1.97 GHz.

Black phosphorus gives several advantages and complementarities over other two-dimensional materials. It has drawn extensive interest owing to its relatively high carrier mobility, wide tunable bandgap, and in-plane anisotropy in recent years. This manuscript briefly reviews the structure and physical properties of black phosphorus and targets on black phosphorus for photonic integrated circuits. Some of the applications are discussed including photodetection, optical modulation, light emission, and polarization conversion. Corresponding recent progresses, associated challenges, and future potentials are covered.

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