Holography has been recognized as a wavefront reconstruction method that helps generate three-dimensional (3D) images. However, its potential capability, which enables us to manipulate the complex-amplitude information of light, is not limited to 3D image construction, and holography is now utilized in a wide range of research and industrial fields. It actually provides many notable features useful in tools for observing and analyzing physical or optical phenomena, and in devices that create various optical fields as well as in systems that measure information on materials or light with non-contact manner and high precision. The advance of holography is also supported by improving the hardware’s performance, including spatial light modulators and image sensors, and by software based on developing information science. This special issue presents recent research topics in holography, including digital holography, computer-generated holograms, data storage, imaging, and microscopy applications.

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Developments of incoherent digital holography (IDH) with daily-use light are presented, and its prospective applications are discussed. Optical systems of IDH have become extremely compact, and the applications of IDH have been extended to various imaging techniques and apparatus. A theory of IDH for spatially and temporally incoherent light has been confirmed by various research studies. Directions of the developments and applications of IDH are discussed on the basis of research achievements.

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Electro-holography is one of the many three-dimensional display technologies, and has the potential to replay most physiologically natural images. Hence, it is expected to have widespread applications in various fields, including augmented reality (AR). Interactivity is essential in such systems, specifically in AR, because inconsistency between the displayed- and actual-image can cause feelings of unease. The extensive computational resources required for calculating computer-generated holograms, which is a digital medium for replaying three-dimensional images, is a major issue for practical electro-holography, and exacerbates the interactive applications. In this study, I provide a brief overview of the general issues faced during electro-holographic computation and the current solution for interactive systems, as well as my recent research.

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We provide a brief overview of tissue diagnosis using quantitative phase imaging that enables label-free tissue diagnosis using quantitative criteria. First, we introduce quantitative phase imaging methods and their properties. Next as one quantitative phase imaging method that is suitable for tissue diagnostic applications, we explain a procedure that obtains quantitative phase images using spatial light interference microscopy (SLIM). Next we calculate the procedure of feature maps that can be extracted from the quantitative phase images of tissue slices that are particularly useful for cancer diagnosis. Finally, we introduce some recent trends, especially examples of quantitative phase imaging and tissue diagnostic methods using artificial intelligence (AI) technologies.

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Real-time imaging technique for light pulse propagation plays an important role to clarify ultrafast phenomena occurring on femtosecond to picosecond time scales. Recently, there have been highly demanding for visualization of polarized light propagation to reveal the ultrafast behavior of laser material processing or a polarization-sensitive materials. We developed a technique for recording polarized light propagation by use of light-in-flight recording by holography. The imaging technique can record a motion picture that provides information about light pulse propagation and its polarization state. We demonstrated our proposed technique by recording the ultrashort light pulse propagation through a calcite crystal and adopted the behavior of a light pulse incident at Brewster’s angle.

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We report on two methods of designing the input signal images for controlling or exploiting crosstalk noise in holographic data storage systems. The first is a phase detection method using crosstalk noise. By placing phase-known pixels in the signal patterns, the signal phase can be extracted by a single image acquisition without requiring multi-step interferometric measurements. The other method suppresses and controls crosstalk noise in intensity-modulated multivalued signals. By appropriately designing the signal patterns, the intensity modulation owing to the interference with noise diffracted light can be significantly reduced. The signal detection error rates in these methods were evaluated using our holographic simulator, and the effectiveness of our proposed methods was discussed in terms of recording density.

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We introduce three-dimensional Stimulation and Imaging-based Functional Optical Microscopy (SIFOM) as a new optical microscopy to advance cell activity manipulation methods using optogenetics in neuroscience. SIFOM can freely illuminate neurons and other cells in three-dimensional space using computer-generated holograms. Therefore, SIFOM can be used to investigate the correlation between multiple cells or to change the cellular network. In addition, we introduced high-speed 3D fluorescence imaging to observe the activity of stimulated cells and their surrounding cells via fluorescence in order to investigate the cellular activity in response to light stimulation.

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