We report an imaging method, termed Fourier ptychographic microscopy (FPM), which iteratively stitches together a
number of variably illuminated, low-resolution intensity images in Fourier space to produce a wide-field, high-resolution
complex sample image. By adopting a wavefront correction strategy, the FPM method can also correct for aberrations and
digitally extend a microscope’s depth of focus beyond the physical limitations of its optics. As a demonstration, we built a
microscope prototype with a resolution of 0.78 µm, a field of view of ∼120 mm^2 and a resolution-invariant depth of focus
of 0.3 mm (characterized at 632 nm). Gigapixel colour images of histology slides verify successful FPM operation. The
reported imaging procedure transforms the general challenge of high-throughput, high-resolution microscopy from one
that is coupled to the physical limitations of the system’s optics to one that is solvable through computation.

Wide-field, high-resolution Fourier ptychographic microscopy

Holography is one of the most attractive approaches for reconstructing optical images, due to its capability of recording both the amplitude and phase information on light scattered from objects. Recently, optical metasurfaces for manipulating the wavefront of light with well-controlled amplitude, phase, and polarization have been utilized to reproduce computer-generated holograms. However, the currently available metasurface holograms have only been designed to achieve limited colors and record either amplitude or phase information. This fact significantly limits the performance of metasurface holograms to reconstruct full-color images with low noise and high quality. Here, we report the design and realization of ultrathin plasmonic metasurface holograms made of subwavelength nanoslits for reconstructing both two- and three-dimensional full-color holographic images. The wavelength-multiplexed metasurface holograms with both amplitude and phase modulations at subwavelength scale can faithfully produce not...

Full-Color Plasmonic Metasurface Holograms

Monolithic semiconductor lasers capable of emitting over the full visible-colour spectrum have a wide range of important applications, such as solid-state lighting, full-colour displays, visible colour communications and multi-colour fluorescence sensing. The ultimate form of such a light source would be a monolithic white laser. However, realizing such a device has been challenging because of intrinsic difficulties in achieving epitaxial growth of the mismatched materials required for different colour emission. Here, we demonstrate a monolithic multi-segment semiconductor nanosheet based on a quaternary alloy of ZnCdSSe that simultaneously lases in the red, green and blue. This is made possible by a novel nanomaterial growth strategy that enables separate control of the composition, morphology and therefore bandgaps of the segments. Our nanolaser can be dynamically tuned to emit over the full visible-colour range, covering 70% more perceptible colours than the most commonly used illuminants.

A monolithic white laser

Digital holography (DH) has emerged as one of the most effective coherent imaging technologies. The technological developments of digital sensors and optical elements have made DH the primary approach in several research fields, from quantitative phase imaging to optical metrology and 3D display technologies, to name a few. Like many other digital imaging techniques, DH must cope with the issue of speckle artifacts, due to the coherent nature of the required light sources. Despite the complexity of the recently proposed de-speckling methods, many have not yet attained the required level of effectiveness. That is, a universal denoising strategy for completely suppressing holographic noise has not yet been established. Thus the removal of speckle noise from holographic images represents a bottleneck for the entire optics and photonics scientific community. This review article provides a broad discussion about the noise issue in DH, with the aim of covering the best-performing noise reduction approaches that have been proposed so far. Quantitative comparisons among these approaches will be presented.

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Strategies for reducing speckle noise in digital holography

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 (ie, 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

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

Theoretical analysis shows that, to improve the resolution and the range of the field of view of the reconstructed image in digital lensless Fourier transform holography, an effective solution is to increase the area and the pixel number of the recorded digital hologram. A new approach based on the synthetic aperture technique and use of linear CCD scanning is presented to obtain digital holographic images with high resolution and a wide field of view. By using a synthetic aperture technique and linear CCD scanning, we obtained digital lensless Fourier transform holograms with a large area of 3.5 cm×3.5 cm (5000×5000 pixels). The numerical reconstruction of a 4 mm object at a distance of 14 cm by use of a Rayleigh-Sommerfeld integral shows that a theoretically minimum resolvable distance of 2.57 μm can be achieved at a wavelength of 632.8 nm. The experimental results are consistent with the theoretical analysis.

High resolution digital holographic microscopy with a wide field of view based on a synthetic aperture technique and use of linear CCD scanning

The numerical recording and reconstruction of a color holographic image are achieved by using digital lensless Fourier transform holography. Firstly, for a color object, three monochromatic digital holograms with different wavelengths (red, green, blue) are recorded by a black-white CCD, respectively. Then the reconstructed monochromatic holographic images (red, green, blue) are adjusted to be same in size through padding digital holograms with zeros, and the corresponding digital color holographic image is acquired by accurately syncretizing the resized reconstructed monochromatic images. One of the advantages using lensless Fourier transform holography is that it can well assure the precise superposition of the reconstructed images. By applying median filtering technique and superposing the speckle fields with different distributions, the speckle noises are well suppressed and the quality of the digital color holographic image is greatly improved. This digital color holography with high quality of reconstruction effect would have potential applications on digital holographic display of color objects.

Recording and reconstruction of a color holographic image by using digital lensless Fourier transform holography

Phase aberration compensation of digital holographic microscopy based on least squares surface fitting

We report a real-time measurement method of the solution concentration variation during the growth of protein-lysozyme crystals based on digital holographic interferometry. A series of holograms containing the information of the solution concentration variation in the whole crystallization process is recorded by CCD. Based on the principle of double-exposure holographic interferometry and the relationship between the phase difference of the reconstructed object wave and the solution concentration, the solution concentration variation with time for arbitrary point in the solution can be obtained, and then the two-dimensional concentration distribution of the solution during crystallization process can also be figured out under the precondition which the refractive index is constant through the light propagation direction. The experimental results turns out that it is feasible to in situ, full-field and real-time monitor the crystal growth process by using this method.

Real-time monitoring of the solution concentration variation during the crystallization process of protein-lysozyme by using digital holographic interferometry

We present a novel method for dynamical measurement of the ternary diffusion by using digital holographic interferometry based on wavelength and angular multiplexing techniques. Two laser beams with different wavelengths (λ1=532 nm and λ2=473 nm) are used for the ternary diffusion measurement, and they are adjusted to make corresponding interference fringes in orthogonal directions on the CCD target. The orthogonal splitting of the fringes enables the spatial frequencies of each wavelength to be filtered separately in the Fourier spectrum of the hologram. Finally, they are reconstructed to obtain the molar concentration. This method is also suitable for two-phase diffusion measurement.

Hongzhen Jiang

Papers

High resolution digital holographic microscopy with a wide field of view based on a synthetic aperture technique and use of linear CCD scanning

Recording and reconstruction of a color holographic image by using digital lensless Fourier transform holography

Phase aberration compensation of digital holographic microscopy based on least squares surface fitting

Real-time monitoring of the solution concentration variation during the crystallization process of protein-lysozyme by using digital holographic interferometry

Digital holographic interferometry based on wavelength and angular multiplexing for measuring the ternary diffusion.