Design of a dual-band dual-mode optical system for visible and near-infrared spectrums

In response to the application requirements for long-distance detection, identification, and ranging of a near-space UAV platform, this paper designs a common-aperture visible and near-infrared dual-band dual-mode optical system. By utilizing imaging in both the near-infrared and visible light bands, it ensures the richness of information obtained during the daytimes and takes advantage of the near-infrared's ability to penetrate fog and detect weak light for imaging, while also integrating a laser ranging function. The front end of the optical system adopts a common-aperture catadioptric structure, and the rear end uses a beam splitter to divide the optical path into a transmitted and reflected branch. The transmitted optical path is designed based on an InGaAs detector array of 1280×1024 (5μm), with a working wavelength of 0.4μm to 1.7μm. The focal length of the transmitted light path is 650mm, and the F-number is 4, which is used for detection and identification of long-distance targets. The reflected optical path is the laser reception optical path, with a working wavelength of 1.535μm, used to achieve long-distance laser ranging. Compared with parallel plate beam splitting, the use of a cube beamsplitter in this system eliminates the prerequisite for parallel incident light, thereby streamlining the optical path and contributing to the overall compactness and lightweight nature of the system. The optical system has achieved passive heat dissipation in the temperature range of minus 70 degrees Celsius to 65 degrees Celsius. The system's Modulation Transfer Function (MTF) remains impressively close to the diffraction limit across this entire temperature spectrum. The weight of the optical system is 565g, and the external dimensions are 235mm. While meeting the stringent performance requirements of long-distance laser ranging and dual-band detection, the advantages of miniaturization, lightweight, and integration technology are evident.