Enhancement of form factor and light collection in computational imaging systems through wavefront coding techniques.

摘要

The bulky form factor of traditional optical sensors limits their utility for certain applications. Flat multiplex imaging sensor architectures face the light gathering challenges inherent with small collection apertures. This research presents a wavefront coding approach towards enlarging the apertures of multiplex imagers while maintaining the distance from the lens to the detector array. Wavefront coding techniques permit optical sensors to attain an extended depth of field by modulating the phase of incoming light waves and enabling imaging even in the presence of considerable misfocus. The proposed approach exploits this ability of such computational optical sensors to operate over a large range of misfocus values, thereby permitting the capture of images at working distances shorter than its focal length.; The core of this body of work lies in the mathematical analyses of the exact spatial frequency responses of various wavefront coding systems whose results are applicable over all misfocus values. Such a methodology allows the prediction of the spatial and angular resolutions of these wavefront coding systems for any specified value of misfocus. This research also facilitates the system design of flat form factor imagers through wavefront coding while throwing light on the trade-offs involved and limitations encountered during the design process.; Comprehensive spatial frequency analyses are conducted for two phase modulation elements, namely the cubic and the odd-symmetric quadratic phase masks, and exact mathematical expressions of their optical transfer functions are derived. The results obtained are used to quantify the spatial filtering effect of misfocus and the available bandwidth of these systems for a given operating condition. Criteria for form factor enhancement are assessed and trade-offs encountered in the design process are evaluated. Applicability of wavefront coding techniques to form factor enhancement of computational imaging systems is illustrated through simulated imaging results and design examples. The groundwork is laid for the mathematical derivation of higher order phase masks that are good candidates for wavefront coding applications.