Design Of Dual-band Shared-aperture Co-zoom Optical System

Dual-band continuous zoom optical system incorporates characteristics of dual band system (e.g. round-the-clock detection; accurate and comprehensive access to target information) with advantages of continuous zoom system (e.g. wide detection range, fast search, and continuous observation on target). Therefore, dual-band continuous zoom system has soon become a worldwide research hotspot. However, most of the existing visible light/infrared dual band zoom systems consist of two separate systems with large system volume and complex structure of reconnaissance equipment. In addition, due to changes of external environment, such as target obscured, smoke interference, alternation of day and night, after changing light path, there is a need to search target and adjust focal length again before observing target for the second time, which results in long change process and slow system response. Furthermore, the target may be lost in the condition that the target tracked and observed moves fast.For the above problems, this design is made to obtain continuous zoom at the same time for dual bands (visible light/mid-IR) in the same optical path, with a zoom ratio of10×An analysis is made to identify the difference between visible plus mid-IR light focal length and zoom ratio during the zoom process, and the change law of the difference. Combined with2-group and3-group zoom theories and derived the conditions for compensating zoom ratio difference, a method is analyzed to directly compensate zoom ratio difference. With this method, focal length and zoom ratio for the visible/mid-infrared light at any zoom location are the same. The total volume of less than290mm×45mm. In the entire zoom process, the max difference in focal length of visible light and mi-infrared is less than0.02mm. The transfer function value is above0.5for visible light at the spatial frequency of801p/mm, and the transfer function value is above0.45for mid-IR at the spatial frequency of20lp/mm. The image quality meets design requirements after realizing optical system’s athermalization under the temperature of-40℃～60℃. Compared with ordinary dual-band zoom system, the system has the advantages of small size, light weight, high timeliness and fast response, and realize synchronous observation, synchronous tracking and synchronous measurement on the target with dual band.