Optical design of a monolithic compressed folding imaging lens for infrared/laser dual-band

In order to realize the miniaturization of the dual-band system, the monolithic compressed folding imaging lens (CFIL) is designed for infrared/laser dual-band in this paper. The relationship among the back focal length, field of view, pupil diameter, and central obscuration of the CFIL are derived. The design method of the dual-band CFIL is given, and the stray light of the CFIL can be suppressed by the double-layer hood structure. According to the design method of the CFIL, the infrared/laser dual-band can be applied by a monolithic optical element. The design results show that the minimum MTF for all fields of view in the infrared band is greater than 0.125 at 42lp/mm, the spot uniformity in the laser band is greater than 90%, and the total system length is only 0.305 times the focal length. After tolerance analysis, the MTF of CFIL is greater than 0.1, and the spot diagram is less than 880µm. The working temperature of the system is -20∼50°C, and the compensation distance is given. After stray light optimization, The point source transmittance (PST) value in the infrared band is reduced by 2 to 4 orders of magnitude, and the PST value in the laser band is reduced by 1 to 5 orders of magnitude. Compared with the traditional coaxial reflective system, the infrared/laser dual-band CFIL has only one lens, and the optical structure is compact. It provides a new idea for the integration and miniaturization of the multi-band system.