In the context of the continuous development of high-speed optical communication, on-chip optical information processing is regarded as the core of next-generation computing architectures. Integrated photonics, as the cornerstone of this transformation, will strongly drive the advent of the all-optical computing era. Among various photonic integration platforms, lithium niobate (LiNbO₃, LN) is hailed as the "optical silicon" due to its unique nonlinear optical properties. However, traditional LN waveguides are limited by low refractive index contrast, weak optical field confinement, and large device size, making it difficult to achieve high integration and limiting further applications. The emergence of Lithium Niobate on Insulator (LNOI) technology has broken this bottleneck, achieving a technological innovation from bulk LN materials to Thin-Film Lithium Niobate (TFLN) structures. As a result, TFLN has garnered significant attention in current research on integrated photonics and integrated nonlinear photonics.
As a core component for converting optical signals to electrical signals, photodetectors play a key role in integrated photonic applications. However, the inherent weak optical absorption of LN makes it difficult to achieve detection. Although recent reports have proposed feasible solutions to this problem through ion doping and heterogeneous integration, the full integration of high-performance detectors in TFLN still faces many challenges.
The research group of Prof. Feng Chen from Shandong University review recent advances and perspectives of TFLN-based detectors. The article outlines several physical mechanisms involved in achieving photodetection with TFLN, elaborates on the implementation schemes of TFLN-based photodetectors based on free-space light incidence and waveguide transmission modes, and provides an in-depth discussion of the technical characteristics of TFLN-based single-photon detectors and pyroelectric detectors. Finally, by comparing the advantages and limitations of different technical approaches, the article prospects the developmental challenges and research prospects of TFLN-based detectors.
Heterogeneous Integration Strategy
As a key path to overcoming the inherent limitations of LN materials, the heterogeneous integration strategy primarily involves integrating TFLN with functional material systems such as III-V semiconductors (e.g., InGaAs/InP), silicon-based materials, and two-dimensional materials (e.g., Graphene, TMDs). This effectively addresses the weak absorption issue in the visible to near-infrared bands caused by its wide bandgap. By combining LN's excellent pyroelectric and ferroelectric properties with the efficient light absorption and carrier transport capabilities of heterogeneous materials, this strategy has successfully achieved a performance leap in multifunctional photodetectors. In 2022, Marko Lončar's team, by heterogeneously integrating an InGaAs/InP structure on a TFLN platform, developed a high-speed photodiode with a bandwidth of up to 80 GHz. This achievement still holds the record for the highest bandwidth among photodiodes on extrinsic substrates via heterogeneous integration.
Material Modification Strategy
Although the heterogeneous integration strategy can effectively expand the spectral response range and improve the responsivity of TFLN photodetectors, its complex fabrication process, interfacial stability issues, and challenges in compatibility with CMOS technology still hinder further development. In contrast, direct material modification techniques, by tuning the intrinsic properties of LN, open a new path for realizing structurally compact and performance-stable monolithically integrated detectors. Currently, this strategy primarily employs the following four types of methods: (1) Ferroelectric Domain Engineering; (2) Ion Doping Control; (3) Ion Beam Modification Technology; (4) Acoustic Resonator Structure Design.
These direct modification strategies effectively expand the photodetection mechanisms and application scope of lithium niobate materials while preserving their inherent advantages, providing new ideas for developing highly integrated, low-power on-chip detection systems.
Conclusion:
Heterogeneous integration and direct material modification have formed two complementary technological pathways: The former heterogeneously integrates TFLN with functional materials like III-V semiconductors, silicon, or 2D materials, preserving LN's excellent waveguide, electro-optic modulation, and ferroelectric properties while leveraging the high absorption and efficient carrier transport of heterogeneous materials to broaden the spectral response. The latter achieves localized control of material properties through methods such as ion implantation, defect engineering, and nanoparticle modification, enhancing integration density and mechanical stability while reducing interfacial defects.
In the future, TFLN detectors will continue to evolve toward ultrafast response, low power consumption, and multifunctional integration. Key challenges such as optical loss control, process scalability, and CMOS compatibility still need to be addressed. The introduction of advanced micro-nano fabrication technologies like electron-beam lithography and wafer-level bonding, combined with AI-assisted inverse design and hybrid integration strategies, will effectively enhance device performance and production yield. Future research could further explore metasurface-based optical field manipulation, novel heterogeneous integration schemes, and optoelectronic co-packaging technologies to fully realize the application potential of the thin-film lithium niobate platform in communications, computing, sensing, and quantum technologies.
About the research group:
Feng Chen is currently a Distinguished Professor at the School of Physics, Shandong University, China. His research interests encompass integrated photonics, lasers, nonlinear optics, 2D materials, plasmonic nanoparticles, topological photonics, ion beams, and ultrafast laser writing. He has authored one book, five book chapters, and published over 400 papers in peer-reviewed journals, which have garnered more than 11,000 citations. He also holds 10 patents. Since 2014, he has been recognized as one of the Most Cited Chinese Researchers by Elsevier China for ten consecutive years (2014-2024).
Feng Chen is a Fellow of the Institute of Physics (IOP UK), SPIE, and Optica (formerly OSA), as well as a senior member of the Chinese Optical Society (COS). He has served as an Associate Editor for Optical Engineering (2010-2022), an Editorial Board Member for Scientific Reports (since 2015), the Executive Editor-in-Chief of Chinese Optics Letters (since 2021), and an Editorial Board Member for Physics (since 2020).
Xiaoli Sun received degrees of Ph.D (2020) at Shandong University, China. Her Ph.D work focused on ultrafast laser generation and third-order nonlinear optical effect. After, she researched on ion beam modification for photonic devices at Shandong University, China, as a Postdoctoral Research Fellow. In 2024, she was appointed Professor of Optics at Shandong University supported by the "Qilu Young Scholars Program" of Shandong University. She has more than 50 papers published in peer-reviewed journals such as ACS Nano, Advanced Functional Materials, Laser Photonics Reviews, Small, Advanced Optical Materials, and Applied Physics Letters.
Read the full Article here: https://www.oejournal.org/oes/article/doi/10.29026/oes.2025.250028
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