Areas of Expertise (7)
Synthetic-Aperture and Pupil-Plane Active Imaging Systems
Imaging with Sparse and Segmented-Aperture Systems
James R. Fienup is the Robert E. Hopkins Professor of Optics at the Institute of Optics. His research area is imaging science, including phase retrieval, unconventional imaging, image reconstruction, wavefront sensing, imaging with sparse and segmented-aperture systems, and synthetic-aperture and pupil-plane active imaging systems.
Stanford University: PhD, Applied Physics 1975
Stanford University: MS, Applied Physics 1972
Selected Articles (2)
Phase Retrieval Algorithms: A ComparisionApplied Optics
Iterative algorithms for phase retrieval from intensity data are compared to gradient search methods. Both the problem of phase retrieval from two intensity measurements (in electron microscopy or wave front sensing) and the problem of phase retrieval from a single intensity measurement plus a non-negativity constraint (in astronomy) are considered, with emphasis on the latter. It is shown that both the error-reduction algorithm for the problem of a single intensity measurement and the Gerchberg-Saxton algorithm for the problem of two intensity measurements converge. The error-reduction algorithm is also shown to be closely related to the steepest-descent method. Other algorithms, including the input–output algorithm and the conjugate-gradient method, are shown to converge in practice much faster than the error-reduction algorithm.
Direct-detection synthetic-aperture coherent imaging by phase retrievalSPIE
This paper describes a way to synthesize a larger coherent aperture from smaller apertures combined with motion, when only intensities are measured. It relies on collecting intensity patterns in two planes for each aperture, for example, the aperture plane and an image plane, and using a phase-retrieval algorithm to reconstruct the optical field in the aperture plane. As the sensor moves forward, a larger two-dimensional aperture is synthesized, allowing a much finer resolution image to be reconstructed. An algorithm to correct for the relative pointing (tip and tilt phases) and piston errors between different apertures and at different times is needed to phase up the synthetic aperture. Results of simulations, including the effects of speckle, are shown, and practical considerations are evaluated.