Waveguide‐Integrated Two‐Dimensional Material Photodetectors in Thin‐Film Lithium Niobate

Abstract

Thin‐film lithium niobate on insulator (LNOI) is a promising platform for optical communications, microwave photonics, and quantum technologies. While many high‐performance devices like electro‐optic modulators and frequency comb sources have been achieved on LNOI platform, it remains challenging to realize photodetectors (PDs) on LNOI platform using simple and low‐cost fabrication techniques. 2D materials are excellent candidates to achieve photodetection since they feature strong light‐matter interaction, excellent mechanical flexibility, and potential large‐scale complementary metal–oxide–semiconductor‐compatible fabrication. Herein, this demand is addressed using an LNOI‐2D material platform, and two types of high‐performance LNOI waveguide‐integrated 2D material PDs, namely graphene and tellurium (Te), are addressed. Specifically, the LNOI‐graphene PDs feature broadband operations at telecom and visible wavelengths, high normalized photocurrent‐to‐dark current ratios up to 3 × 106 W−1, and large 3‐dB photoelectric bandwidths of ≈40 GHz, simultaneously. The LNOI‐Te PDs on the other hand provide ultrahigh responsivities of 7 A W−1 under 0.5 V bias for telecom signals while supporting GHz frequency responses. The results show that the versatile properties of 2D materials and their excellent compatibility with LNOI waveguides could provide important low‐cost solutions for system operating point monitoring and high‐speed photoelectric conversion in future LNOI photonic integrated circuits.