Aperture-scanning Fourier ptychography for 3D refocusing and super-resolution macroscopic imaging

Abstract

Abstract:We report an imaging scheme, termed aperture-scanning Fourier ptychography, for 3D refocusing and super-resolution macroscopic imaging. The reported scheme scans an aperture at the Fourier plane of an optical system and acquires the corresponding intensity images of the object. The acquired images are then synthesized in the frequency domain to recover a high-resolution complex sample wavefront; no phase information is needed in the recovery process. We demonstrate two applications of the reported scheme. In the first example, we use an aperture-scanning Fourier ptychography platform to recover the complex hologram of extended objects. The recovered hologram is then digitally propagated into different planes along the optical axis to examine the 3D structure of the object. We also demonstrate a reconstruction resolution better than the detector pixel limit (i.e., pixel super-resolution). In the second example, we develop a camera-scanning Fourier ptychography platform for super-resolution macroscopic imaging. By simply scanning the camera over different positions, we bypass the diffraction limit of the photographic lens and recover a super-resolution image of an object placed at the far field. This platform's maximum achievable resolution is ultimately determined by the camera's traveling range, not the aperture size of the lens. The FP scheme reported in this work may find applications in 3D object tracking, synthetic aperture imaging, remote sensing, and optical/electron/X-ray microscopy.

Overlapped Fourier coding for optical aberration removal

“…The spatial coherence length of the illuminating beam must be as wide as the sample at the object plane (approximately 5 mm here). Likewise, the source's temporal coherence must follow the quasi-monochromatic condition in [35], although a spectral bandwidth full width half maximum of approximately 10 nm has been observed as sufficiently narrow [13,40]. Both conditions may be achieved with an LED placed sufficient far behind the sample.…”

“…Unlike in the related Fourier ptychographic microscope [3], the sample here may be thick, optically reflective, and under arbitrary quasi-coherent illumination. While the aperture scanning procedure in [13] also follows similar steps, OFC's SLM modulator requires certain algorithm modifications that we outline below.…”

“…So while OFC cannot extend an optical system's resolution beyond its aperture-defined cutoff, it can increase its SBP via removal of undesired aberrations and misalignments. This sets our goal as distinct from prior methods using aperture-based [13] and SLM amplitude modulation [14] to only acquire phase, without correcting for system aberrations. Although not used by the current OFC setup, phase-based modulation may also lead to accurate sample phase recovery [15][16][17].…”

Wide-field Fourier ptychographic microscopy using laser illumination source

“…There also have been numerous efforts in improving the Fourier ptychographic (FP) reconstruction by adopting more noise-robust algorithms [15][16][17][18]. Alternative FPM modalities involving aperture scanning instead of angular illuminations were demonstrated, which allowed for imaging the complex field of a thick specimen [19,20] and estimating optical aberrations [21]. Imaging a thick specimen with angular illuminations also became possible by employing the first Born approximation [22] or multislice coherent model [23].…”

Aperture scanning Fourier ptychographic microscopy

“…The thin-sample requirement can be circumvented by implementing FP with an alternate configuration, in which a scannable aperture is placed at the Fourier plane of the imaging system while the sample is illuminated with a single plane wave [7]. In this configuration, the 2D wavefront (light field scattered by the sample's 3D distribution) exiting the thick sample is modulated by the scannable aperture, captured at the imaging plane, and reconstructed by the conventional FP algorithm.…”