Hybrid Lens Implemented Usine An afocal Microlens Telescope

Abstract

Large arrays of smart pixels place demands on optical systems which are difficult to satisfy: low f-numbers are required since small (typically 10pm) detectors and transmitters are used to minimize capacitance and response time, large field of view is simultaneously necessary. One approach is to use microlens arrays. However, this necessitates the use of large chip areas. Hybrid lenses (figure 1) have been proposed for use with dilute arrays (low fill-factor) of smart pixels[l]. They combine the large field of view of slow, conventional lenses with the small spot size that can be achieved using fast microlenses. The pitch between the windows of the smart pixel (typically <100pm) is equal to the microlens pitch. An f75 lens was designed which images over a *So field angle and produces spots with 99% of the energy coupled into a 15pm spot. This spot is imaged by an afocal telescope composed of t73 and t7l microlens doublets. The first doublet collimates the light and the second, faster microlens doublet focuses the light into a small spot. The hybrid lens creates an array of small spots over a large field (7" diagonal). These hybrid lenses will be used to interconnect two S-SEED arrays. S-SEEDS comprise two 5pm windows which are separated by 20pm. Imaging two spots with each microlens requires that they be used off-axis. The use of an afocal telescope allows off-axis operation whereas the microlenses-only approach does not. The doublets work at infinite conjugates.