Increased space-bandwidth product in pixel super-resolved lensfree on-chip microscopy

Abstract

Pixel-size limitation of lensfree on-chip microscopy can be circumvented by utilizing pixel-super-resolution techniques to synthesize a smaller effective pixel, improving the resolution. Here we report that by using the two-dimensional pixel-function of an image sensor-array as an input to lensfree image reconstruction, pixel-super-resolution can improve the numerical aperture of the reconstructed image by ~3 fold compared to a raw lensfree image. This improvement was confirmed using two different sensor-arrays that significantly vary in their pixel-sizes, circuit architectures and digital/optical readout mechanisms, empirically pointing to roughly the same space-bandwidth improvement factor regardless of the sensor-array employed in our set-up. Furthermore, such a pixel-count increase also renders our on-chip microscope into a Giga-pixel imager, where an effective pixel count of ~1.6–2.5 billion can be obtained with different sensors. Finally, using an ultra-violet light-emitting-diode, this platform resolves 225 nm grating lines and can be useful for wide-field on-chip imaging of nano-scale objects, e.g., multi-walled-carbon-nanotubes.

Sparse superresolution phase retrieval from phase-coded noisy intensity patterns

“…One of the straightforward approaches to overcome the pixel size limitations is to use a sequence of laterally shifted holograms (e.g., see Refs. [29][30][31]. Compressed sensing (CS) or sparse imaging is a computational approach for the restoration of subsampled data based on a special mathematical modeling of u o .…”

Compact lensless phase imager

“…sample-camera distance < 900μm) [29,30] and other quantitative phase imaging techniques [31,32]. However, lensless phase imagers are mainly used to image biological samples like cells [4][5][6][7][8][9][10] which sizes are typically less than 20μm for which the phase can be correctly computed.…”

“…The images are then reconstructed numerically from the digital inline hologram [3]. This technique has been proposed with incoherent illumination [4][5][6][7][8][9][10] to create speckle free images; however, the compactness of the imager is then compromised since a rather large distance (several centimeters) is needed between the source and the sample to obtain enough spatial coherence. Other compact common-path interferometric methods have been investigated to obtain quantitative phase imaging based on lateral phase shifting [11,12].…”

“…Then, the amplitude and the phase are numerically reconstructed using all those holograms. This technique has been proposed with an optical fiber mounted on a rotational arm [7,19] or several light-emitting diodes (LEDs) coupled in a fiber-optic array [21]. In this system, the distance between the end of the fiber and the object has to be quite large (several cm) to obtain enough spatial coherence.…”

Digital micromirror device-based laser-illumination Fourier ptychographic microscopy

“…Increasing the SBP in a conventional microscope will inevitably lead to system design complexity that minimizes optical aberrations [1]. In recent years, several methods have been proposed to overcome this limitation, which include synthetic-aperture microscopy [2][3][4], lens-free imaging [5][6][7][8], montaging microscope images [9], multiscale gigapixel photography [10], and Fourier ptychographic microscopy (FPM) [11][12][13][14][15][16]. Among these methods, FPM has been developed as an effective approach to achieve imaging with both large FOV and high resolution.…”