Aperture sharing between low-background infrared sensors and ladar sensors

The sharing of a common aperture for both ladar pulse transmission and reception; and passive sensor surveillance, acquisition, and tracking, presents many unique challenges. Performance assessments based on fielded optical systems of this type are few. Our particular application (the BMDO Advanced Sensor Technology Program-ASTP for enhanced theater missile defense capability) calls for the sharing of common optics between a MWIR and LWIR, relatively low-background passive sensor, and a ladar for which the operational wavelength has not been selected. This paper describes the advantages and technical challenges associated with our shared optics application, reviews the state of the art in this area, and derives constraints on system designs. Briefly, we find that the shared aperture approach enjoys the obvious advantages of reduced size and weight, and simplifies handover of targets from the passive sensor to the ladar sensor. These advantages must be traded against potential passive sensor performance degradation in the areas of reduced duty cycle, increased noise floor, and reduced sensitivity.