Registering large caustic distortions for high dynamic range diffuser wavefront sensing

Gregory N. McKay; Faisal Mahmood; Nicholas J. Durr

doi:10.1117/12.2509765

20 February 2019 Registering large caustic distortions for high dynamic range diffuser wavefront sensing

Gregory N. McKay, Faisal Mahmood, Nicholas J. Durr

Proceedings Volume 10886, Adaptive Optics and Wavefront Control for Biological Systems V; 108860Y (2019) https://doi.org/10.1117/12.2509765
Event: SPIE BiOS, 2019, San Francisco, California, United States

Abstract

Wavefront sensing is typically accomplished with a Shack-Hartmann wavefront sensor (SHWS), where a CCD or CMOS is placed at the focal plane of a periodic, microfabricated lenslet array. Tracking the displacement of the resulting spots in the presence of an aberrated wavefront yields measurement of the relative wavefront introduced. A SHWS has a fundamental tradeoff between sensitivity and range, determined by the pitch and focal length of its lenslet array, such that the number of resolvable tilts is a constant. Recently, diffuser wavefront sensing (DWS) has been demonstrated by measuring the lateral shift of a coherent speckle pattern using the concept of the diffuser memory effect. Here we demonstrate that tracking distortions of the non-periodic caustic pattern produced by a holographic diffuser allows accurate autorefraction of a model eye with a number of resolvable tilts that extends beyond the fundamental limit of a SHWS. Using a multi-level Demon’s image registration algorithm, we are able to demonstrate that a DWS demonstrates a 2.5x increase in number of resolvable prescriptions as compared to a conventional SHWS while maintaining acceptable accuracy and repeatability for eyeglass prescriptions. We evaluate the performance of a DWS and SHWS in parallel with a coherent laser diode without (LD) and with a laser speckle reducer (LD+LSR), and an incoherent light-emitting diode (LED), demonstrating caustic-tracking is compatible with coherent and incoherent sources. Additionally, the DWS diffuser costs 40x less than a SHWS lenslet array, enabling affordable large-dynamic range autorefraction without moving parts.

Conference Presentation

Citation Download Citation

Gregory N. McKay, Faisal Mahmood, and Nicholas J. Durr "Registering large caustic distortions for high dynamic range diffuser wavefront sensing", Proc. SPIE 10886, Adaptive Optics and Wavefront Control for Biological Systems V, 108860Y (20 February 2019); https://doi.org/10.1117/12.2509765

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