Miniature Fourier Ptychography Microscope using Raspberry Pi Camera and Hardware

We report a Fourier ptychography setup using a raspberry pi camera sensor and its lens in reversed configuration. In this work data acquisition was performed by means of a raspberry pi board which eliminates the requirement of a computer for data acquisition thus allowing a miniaturized system for remote data acquisition costing around £100

Next generation Fourier ptychographic microscopy: computational and experimental techniques

Fourier ptychography is a recently developed computational imaging technique, which enables gigapixel image reconstruction from multiple low-resolution measurements. The technique can be implemented on simple, low-quality microscopes to achieve unprecedented image quality by exchanging optical design complexity with computational complexity. While developments have been made, demonstrations typically use well-calibrated, highperformance microscopes. Therefore, the real world performance and true benefits of(lowcost) Fourier ptychography still need to be demonstrated in out-of-lab environments where unforeseen problems are not unlikely. In this thesis, I will demonstrate how to utilise Fourier ptychography in a fast, robust and cheap manner. Two experimental prototypes will be introduced, one of them being an ultra-low-cost 3D printed microscope capable of wide-field sub-micron resolution imaging. Another prototype was built to demonstrate high-speed gigapixel imaging, capable of 100-megapixel, 1µm resolution image capture in under 3 seconds. Novel image formation models and their refinements were developed to correct the incomplete conventional model. These include partial coherence of the illumination, deviation from the plane-wave assumption, and spatially varying aberrations. Lastly, Experimental work was also heavily supplemented by novel calibration and reconstruction algorithms. Theoretical work outlined in this thesis enables the use of tilted, off-axis optical components, alleviating typically assumed parallel plane optical geometry. Optical precision requirements can also be relaxed due to novel robust calibration algorithms. As a result, low-cost 3D printed microscopes can be used

Miniature Fourier Ptychographic Microscope Using Mobile Phone Camera Sensors

We report a Fourier ptychographic setup with sub-micron resolution costing around £100 using mobile phone camera sensors. Reconstruction algorithms were developed to overcome the Bayer pattern on these sensors and robust calibration methods have been developed to tackle alignment errors

Addressing phase-curvature in Fourier ptychography

In Fourier ptychography, multiple low resolution images are captured and subsequently combined computationally into a high-resolution, large-field of view micrograph. A theoretical image-formation model based on the assumption of plane-wave illumination from various directions is commonly used, to stitch together the captured information into a high synthetic aperture. The underlying far-field (Fraunhofer) diffraction assumption connects the source, sample, and pupil planes by Fourier transforms. While computationally simple, this assumption neglects phase-curvature due to non-planar illumination from point sources as well as phase-curvature from finite-conjugate microscopes (e.g., using a single-lens for image-formation). We describe a simple, efficient, and accurate extension of Fourier ptychography by embedding the effect of phase-curvature into the underlying forward model. With the improved forward model proposed here, quantitative phase reconstruction is possible even for wide fields-of-views and without the need of image segmentation. Lastly, the proposed method is computationally efficient, requiring only two multiplications: prior and following the reconstruction

Phase and amplitude imaging with quantum correlations through Fourier Ptychography

Extracting as much information as possible about an object when probing with a limited number of photons is an important goal with applications from biology and security to metrology. Imaging with a few photons is a challenging task as the detector noise and stray light are then predominant, which precludes the use of conventional imaging methods. Quantum correlations between photon pairs has been exploited in a so called ‘heralded imaging scheme’ to eliminate this problem. However these implementations have so-far been limited to intensity imaging and the crucial phase information is lost in these methods. In this work, we propose a novel quantum-correlation enabled Fourier Ptychography technique, to capture high-resolution amplitude and phase images with a few photons. This is enabled by the heralding of single photons combined with Fourier ptychographic reconstruction. We provide experimental validation and discuss the advantages of our technique that include the possibility of reaching a higher signal to noise ratio and non-scanning Fourier Ptychographic acquisition

Addressing phase-curvature in Fourier ptychography

In Fourier ptychography, multiple low resolution images are captured and subsequently combined computationally into a high-resolution, large-field of view micrograph. A theoretical image-formation model based on the assumption of plane-wave illumination from various directions is commonly used, to stitch together the captured information into a high synthetic aperture. The underlying far-field (Fraunhofer) diffraction assumption connects the source, sample, and pupil planes by Fourier transforms. While computationally simple, this assumption neglects phase-curvature due to non-planar illumination from point sources as well as phase-curvature from finite-conjugate microscopes (e.g., using a single-lens for image-formation). We describe a simple, efficient, and accurate extension of Fourier ptychography by embedding the effect of phase-curvature into the underlying forward model. With the improved forward model proposed here, quantitative phase reconstruction is possible even for wide fields-of-views and without the need of image segmentation. Lastly, the proposed method is computationally efficient, requiring only two multiplications: prior and following the reconstruction

High-speed multi-objective Fourier ptychographic microscopy

The ability of a microscope to rapidly acquire wide-field, high-resolution images is limited by both the optical performance of the microscope objective and the bandwidth of the detector. The use of multiple detectors can increase electronic-acquisition bandwidth, but the use of multiple parallel objectives is problematic since phase coherence is required across the multiple apertures. We report a new synthetic-aperture microscopy technique based on Fourier ptychography, where both the illumination and image-space numerical apertures are synthesized, using a spherical array of low-power microscope objectives that focus images onto mutually incoherent detectors. Phase coherence across apertures is achieved by capturing diffracted fields during angular illumination and using ptychographic reconstruction to synthesize wide-field, high-resolution, amplitude and phase images. Compared to conventional Fourier ptychography, the use of multiple objectives reduces image acquisition times by increasing the area for sampling the diffracted field. We demonstrate the proposed scaleable architecture with a nine-objective microscope that generates an 89-megapixel, 1.1 µm resolution image nine-times faster than can be achieved with a single-objective Fourier-ptychographic microscope. New calibration procedures and reconstruction algorithms enable the use of low-cost 3D-printed components for longitudinal biological sample imaging. Our technique offers a route to high-speed, gigapixel microscopy, for example, imaging the dynamics of large numbers of cells at scales ranging from sub-micron to centimetre, with an enhanced possibility to capture rare phenomena