Research progress in integrated optics for optical coherence tomography

Optical coherence tomography (OCT) is a noninvasive biomedical imaging technique that exploits the back-reflection and scattering properties of tissue without the need for exogenous contrast agents. It enables high-resolution, in situ visualization of tissue microstructures and pathological features, without requiring specimen removal or processing. OCT offers cross-sectional and three-dimensional imaging of biological tissues with micron-level resolution and millimeter-scale depths. When integrated with an endoscope, OCT becomes a powerful and versatile imaging tool in the medical field. However, conventional OCT systems face several limitations, including a bulky system volume of approximately 1 m³, high costs of around 100,000, operational complexity, limited portability, and the need for precise optical alignment, which demands substantial manpower and time. To overcome these challenges, integrated optics has emerged as a promising solution. In recent years, significant advances have been made in developing OCT systems based on integrated photonics. All the integrated-optics devices, such as light sources, isolators, couplers, circulators, detectors, and active optical components, can be exploited for endoscopic and non-endoscopic OCT systems and enable more compact designs and implementations. This review provides a comprehensive overview of these advancements. We first summarize the fundamental principles and imaging properties of OCT, along with the design and functionality of OCT endoscopic probes. We then examine the recent progress in on-chip OCT systems, focusing on system optimization and the implementation of integrated photonic technologies. Finally, we discuss the current challenges, including the full integration of optical components onto a single chip, and explore prospects of integrated-optics based OCT endoscopy, particularly the integration of AI-powered intelligent diagnostics to enhance real-time clinical decision-making and expand the applications of OCT in personalized medicine.