Lensless quantitative phase imaging is of high interest for obtaining a large field of view (FOV), typically the size of the camera chip, to observe biological cell material with high contrast. It has the potential to be widely spread due to its inherent simplicity. However, the tradeoff is the added complexity due to the illumination. Current illumination systems are several centimeters away from the sample, use mechanics to obtain super resolution (i.e., smaller than the detector pixel size) or different illumination directions, and block the view to the sample. In this paper, we propose and demonstrate a side illumination system which reduces the height by an order of magnitude while providing an unobstructed view of the sample. We achieve this by shaping the illumination using multiplexed analog holograms that produce 9 illumination angles. We demonstrate experimentally imaging of phase samples with a FOV of ~17mm 2 .

HighlightsA side illumination system based on VCSELs which provides multiple angle illumination.The multiple angles are produced by diffraction of a multiplexed volume grating.The imager height is ten times smaller than the state of the art lensless imagers.The sample unobstructed view allows simultaneous imaging modalities (fluorescence..).We demonstrate quantitative imaging of phase objects with the proposed imager.

Current compact lensless holographic microscopes are based on either multiple angle in-line holograms, multiple wavelength illumination or a combination thereof. Complex computational algorithms are necessary to retrieve the phase image which slows down the visualization of the image. Here we propose a simple compact lensless transmission holographic microscope with an off-axis configuration which simplifies considerably the computational processing to visualize the phase images and opens the possibility of real time phase imaging using off the shelf smart phone processors and less than $3 worth of optics and detectors, suitable for broad educational dissemination. This is achieved using a side illumination and analog hologram gratings to shape the reference and signal illumination beams from one light source. We demonstrate experimentally imaging of cells with a field of view (FOV) of ~12mm, and a resolution of ~3.9μm.

We report on a method to increase the spatial resolution in a compact lensless microscope. A compact side illumination is fabricated to illuminate the sample with a collimated beam by diffraction from a volume phase grating. The wavelength of a semi-conductor laser source (vertical-cavity surface-emitting laser) is tuned with the injection current to alter the illumination direction by wavelength selective diffraction from the volume phase grating. The angle tuning is such that several subpixel shifted digital inline holograms are obtained. The stack of holograms is then processed in a pixel super-resolution reconstruction algorithm. The amplitude of the sample is reconstructed with subpixel resolution over a large field of view (FOV). The technique is demonstrated on a 1951 USAF test target. A resolution of ∼2.76 , over a FOV of ∼28, is demonstrated for a device of <2 height. The original pixel size was 5.2 μm demonstrating the subpixel resolution.

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