Design of an infrared/laser dual-band common-aperture optical system based on harmonic diffraction

Current mature designs for multi-band common-aperture systems predominantly employ catadioptric configurations with a beam-splitting secondary mirror or dual-channel transmissive structures. However, catadioptric systems suffer from limitations such as a narrow field of view, significant central obscuration, and alignment complexity, while transmissive systems require elaborate compensation mechanisms to correct astigmatism induced by the axial deviation from parallel-plate beam splitters. To address these challenges, this paper presents a large-aperture, wide-field-of-view transmissive infrared-laser dual-band optical system based on harmonic diffraction. The system shares a front group of two lenses for both infrared and laser channels, with a 45° beam splitter directing light into separate paths. A harmonic diffractive surface is introduced in the infrared channel to correct astigmatism caused by the beam splitter, achieving high-quality imaging over an 8.3^∘×7^∘ field of view with a total length of less than 108 mm under a 52 mm aperture. The laser channel, comprising three lenses, ensures concentrated and uniform spot energy distribution. Passive athermalization is implemented to maintain consistent performance across a temperature range of -40^∘C to 60°C. The system demonstrates compact size, lightweight construction, and stable performance, offering a valuable reference for advanced multi-mode detection systems.