Compact Spectral Imaging: A Review of Miniaturized and Integrated Systems

The push for portable and cost‐effective spectral imaging has accelerated the transition from traditional bulky instruments to compact, integrated systems. This review outlines recent advancements in compact spectral imaging systems (SIS) and their applications in environmental monitoring, precision agriculture, and medical diagnostics. It examines four major design trends: Do‐It‐Yourself (DIY) approaches, freeform optics, integrated filter‐on‐chip technologies, and metasurface‐based solutions. DIY systems have made spectral imaging more accessible by offering customizable, low‐cost platforms for researchers and hobbyists. Freeform optics enhance miniaturization by merging multiple optical functions into a single, non‐axisymmetric surface, thereby reducing size and complexity. Filter‐on‐chip designs, where spectral filters are fabricated directly on imaging detectors, further shrink device dimensions while retaining high spectral resolution and sensitivity. Metasurface‐based designs leverage ultrathin, nanostructured materials to enable advanced functionalities, such as tunable spectral and polarization responses, in extremely compact formats. Together, these innovations not only fulfill practical requirements across diverse fields but also extend the potential of spectral imaging into new and challenging application domains. This review aims to provide an in‐depth understanding of these trends, their applications, and the future direction of miniaturized and compact spectral imaging technology.