Optical Design Study and Prototyping
December 1, 2015
12:54 pm
Optical Design Study and Prototyping of a Dual-Field Zoom lens imaging in the 1-5 micron infrared waveband
ABSTRACT
Optical systems can provide simultaneous imaging in several spectral bands and thus be much more useful. A new and current generation of focal plane arrays is allowing detection in more than one spectral region. The design of a refractive imaging lens for such detectors requires correcting chromatic aberrations over the wider range of wavelengths. However, the fewer available refracting materials, the material properties that change between the spectral bands, and the system transmission requirements make the design of such lenses particularly challenging.
We present a dual-field zoom lens designed for a cooled detector sensing across short-wave infrared (SWIR) and midwave infrared (MWIR) spectral bands (continuous imaging for 1-5 μm). This zoom lens has a 75 mm focal length in the wide mode and a 250mm focal length in the narrow mode, and operates at f/4.7 in both discrete zoom positions. The lens is actively compensated to work in thermal environments from -20°C to +60°C. We discuss the optical design methodology, review the selection of materials and coatings for the optical elements, and analyze the transmission of the lens and optical performance. A prototype system has been manufactured and assembled. We validate our design with experimental data.
1. INTRODUCTION
Modern electro-optical systems for intelligence, surveillance and reconnaissance (ISR) applications are required to produce the highest quality images under a variety of different environmental conditions. Most systems feature zoom lenses along with additional system components such as laser designators and laser range finders, for example Simultaneous imaging in several spectral bands is often required for efficient operation…
