Topology is a branch of mathematics concerned with global properties of geometric structures or parameter spaces that remain unchanged during continuous deformations. Applying topological theory to photonics, known as, topological photonics, has become a significant principle and method in the field, attracting considerable attention for its novel light field manipulation capabilities. As an emerging research field, topological photonics originates from the concept of topological insulators in condensed matter physics. By introducing topology, integrated photonic systems acquire new properties, including unidirectional edge states and robustness against impurities or defects. These properties endow topological photonic devices with great potential for applications in optical communications, quantum computing, and high-precision sensing.

This paper reviews the research progress in integrated topological photonic devices for on-chip information processing. Initially, it delves into the basic theory of topological photonics, detailing the design principles of one- and two-dimensional topological photonic devices and their applications in on-chip optical information processing. These applications include waveguides, couplers, splitters, mode-order converters, electro-optical modulators, lasers, optical switches, logic gates, and filters. Each device exhibits unique features and advantages based on different topological phases or mechanisms, such as Zak phase (Fig. 1), Floquet phase (Fig. 1), topological pumping mechanism (Fig. 2), quantum Hall phase (Fig. 3), quantum spin Hall phase (Fig. 4), and quantum valley Hall phase (Fig. 5). In addition, we explore topological photonic devices in emerging fields, including non-Hermitian systems (Fig. 6), synthetic dimensions (Fig. 7), nonlinear optics (Fig. 8), and bound states in the continuum (Fig. 9). Examples such as non-Hermitian topological lasers and synthetic dimension microloop modulators illustrate the expansion of topological photonics applications and the realization of new functionalities in practical systems.

Integrated topological photonic devices hold substantial potential for on-chip optical information processing, enabling both the speed and quality of information processing while improving system robustness and reliability. With continued advancements in topological photonics theory and related technologies, we can expect the development of more topological photonic devices with innovative functions, enabling complex optical path control and high-efficiency optical signal processing. Further research in topological photonics will likely bridge connections with other fields such as quantum information science and nanotechnology, driving revolutionary advancements in information technology.