Optical concepts for dual band infrared continuous zoom lenses

Dual band focal plane arrays enable the simultaneous imaging of the MWIR and LWIR onto the same detector. Each spectral band is read out independently providing a separable MWIR and LWIR image. The development of this technology has necessitated the further development of dual band optics. Although reflective solutions simplify the need for color correction, multiple field of view reflective optics do not package nearly as well as refractive or catadioptric solutions. Dual band optical systems require that both bands focus at the same image plane at the same time. The challenge lies with the very broad spectral band of 3.5 - 11.0 microns, the different partial dispersions between the MWIR and LWIR, and the need to minimize the number of lenses to maximize transmission. This paper looks at the development of refractive and catadioptric concepts for designing continuous zoom lenses for dual band detectors.