In this article, 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 mm2, and a resolution-invariant depth-of-focus of 0.3 mm (characterized at 632 nm). Gigapixel colour images of histology slides verify FPM’s successful 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.

Abstract:We present theoretical and experimental results which demonstrate the superior sensitivity of swept source (SS) and Fourier domain (FD) optical coherence tomography (OCT) techniques over the conventional time domain (TD) approach. We show that SS-and FD-OCT have equivalent expressions for system signal-to-noise ratio which result in a typical sensitivity advantage of 20-30dB over TD-OCT. Experimental verification is provided using two novel spectral discrimination (SD) OCT systems: a differential fiber-based 800nm FD-OCT system which employs deep-well photodiode arrays, and a differential 1300nm SS-OCT system based on a swept laser with an 87nm tuning range.

We describe devices in which optics and fluidics are used synergistically to synthesize novel functionalities. Fluidic replacement or modification leads to reconfigurable optical systems, whereas the implementation of optics through the microfluidic toolkit gives highly compact and integrated devices. We categorize optofluidics according to three broad categories of interactions: fluid-solid interfaces, purely fluidic interfaces and colloidal suspensions. We describe examples of optofluidic devices in each category.Optofluidics refers to a class of optical systems that are synthesized with fluids. Fluids have unique properties that cannot be found in solid equivalents, and these properties can be used to design novel devices. Examples of such properties include: the ability to change the optical property of the fluid medium within a device by simply replacing one fluid with another; the optically smooth interface between two immiscible fluids; and the ability of flowing streams of miscible fluids to create gradients in optical properties by diffusion. Most optical systems are currently made with solid materials such as glasses, metals and semiconductors, but there are cases in which it has been advantageous to use fluids. The oil-immersion microscope 1 , liquid mirrors for telescopes 2 , liquid-crystal displays 3 and electrowetting lenses 4 are good examples. Here we describe the various methods used to implement optofluidic devices with recently developed microfluidic technologies that allow accurate control of liquids on small spatial scales. Integration and reconfigurability are two major advantages associated with optofluidics. Whereas microfluidics has made it possible to integrate multiple fluidic tasks on a chip, most optical components, such as the light source, sensors, lenses and waveguides, remained off the chip. Optofluidic integration combines optics and microfluidics on the same chip by building the optics out of the same fluidic toolkit. The second advantage of optofluidics lies in the ease with which one can change the optical properties of the devices by manipulating fluids.Microfluidics is a burgeoning field with important applications in areas such as biotechnology, chemical synthesis and analytical chemistry. Many of these applications of microfluidics are discussed elsewhere in this issue, and for the purposes of this Review we emphasize only a few salient points. First, there is now an extensive body of literature on how the physical properties of fluids that are available only on small spatial scales can be exploited for device functionality [5][6][7] . Many of these effects can also be used to control optical properties. Second, technological advances in device fabrication have made it possible to build miniaturized devices with complex networks of channels, valves, pumps and other methods of fluidic encapsulation and manipulation 8 . This creates a powerful set of tools for fluidic control, and because the feature sizes in these systems are shrinking over time, they will inevitably appro...

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Fluorescence imaging is one of the most important research tools in biomedical sciences. However, scattering of light severely impedes imaging of thick biological samples beyond the ballistic regime. Here we directly show focusing and high-resolution fluorescence imaging deep inside biological tissues by digitally time-reversing ultrasound-tagged light with high optical gain (~5×105). We confirm the presence of a time-reversed optical focus along with a diffuse background—a corollary of partial phase conjugation—and develop an approach for dynamic background cancellation. To illustrate the potential of our method, we image complex fluorescent objects and tumour microtissues at an unprecedented depth of 2.5 mm in biological tissues at a lateral resolution of 36 μm×52 μm and an axial resolution of 657 μm. Our results set the stage for a range of deep-tissue imaging applications in biomedical research and medical diagnostics.