Self-interference holography is a common technique to record holograms of incoherently illuminated scenes. In this review, we survey the main milestones in the topic of self-interference incoherent digital holography from two main points of view. First, we review the prime architectures of optical hologram recorders over more than 50 years. Second, we discuss some of the key applications of these recorders in the field of imaging in general, and for 3D super-resolution imaging, fluorescence microscopy, partial aperture imaging, seeing through a scattering medium, and spectral imaging in particular. We summarize this overview with a general perspective on this research topic and its prospective directions.

Various multimodal imaging systems with different configurations and for different purposes have been recently developed because these systems enable one to analyze the functional and structural behaviors of a biological specimen at a single examination and, therefore, facilitate a better understanding of the behavior of molecular, cellular, and disease biology.^{1 – 9} The multimodal systems were developed for simultaneous fluorescence and quantitative phase imaging by incorporating the two-dimensional (2-D) epifluorescence microscopy with the diffraction phase microscopy by Park et al.¹ and with the Mach–Zehnder-type digital holographic microscopy (DHM) by Pavillon et al.² and Quan et al.³ A multimodal approach that incorporates confocal Raman, confocal reflectance, and quantitative phase microscopy⁴ has demonstrated the potential for retrieving the molecular specific and morphological information. Optical diffraction tomography (ODT) is another technique to reconstruct the three-dimensional (3-D) quantitative phase imaging from the recorded multiple 2-D holograms. This technique was exploited with the optofluidic rotation of suspended cells by Schürmann et al.⁵ to measure the 3-D correlated refractive index and fluorescence data for a quantitative interpretation of the nuclear refractive index. Further, a multimodal system was developed by integrating the ODT and 3-D structured illumination microscopy by Shin et al.⁶ for the measurement of 3-D refractive index and fluorescence distribution of live cells. The structured illumination microscopy-based multimodal system⁷ is demonstrated for 3-D subdiffraction multimodal imaging of both quantitative phase and fluorescence. Chowdhury et al.⁸ and Nygate et al.⁹ proposed the multimodal systems based on the principle of off-axis holographic multiplexing to obtain the quantitative phase and fluorescence imaging (FI) of the biological cells using a single camera. These systems,^8,9 owing to the use of single camera for recording both the phase hologram and the fluorescence image, are free from image registration issues.

The demand for single-shot and common-path holographic systems has become increasingly important in recent years, as such systems offer various advantages compared to their counterparts. Single-shot holographic systems, for example, reduce computational complexity as only a single hologram with the object information required to process, making them more suitable for the investigation of dynamic events; and common-path holographic systems are less vibration-sensitive, compact, inexpensive, and high in temporal phase stability. We have developed a single-shot common-path off-axis digital holographic setup based on a beam splitter and pinhole. In this paper, we present a concise review of the proposed digital holographic system for several applications, including the quantitative phase imaging to investigate the morphological and quantitative parameters, as a metrological tool for testing of micro-optics, industrial inspection and measurement, and sound field imaging and visualization.

Digital speckle pattern interferometry (DSPI) is widely used in many scientific and industrial applications. Besides its several advantages, one of the basic problems encountered in DSPI is the undesired speckle noise existing in the fringe pattern. In this paper, we demonstrate the performance of nonlocal means (NLM) and its related adaptive kernel-based filtering methods for speckle noise reduction in DSPI fringes. The NLM filter and its related kernel-based filters such as NLM-average, NLM-local polynomial regression, and NLM-shape adaptive patches are implemented first on simulated DSPI fringes, and their performances are quantified on the basis of peak signal-to-noise ratio (PSNR), mean square error (MSE), and quality index ($Q$). Further, their effectiveness and abilities in reducing speckle noise are compared with other speckle denoising methods. These filtering methods are then employed on experimental DSPI fringes. The obtained results reveal that these filtering methods have the ability to improve the PSNR and $Q$ of the DSPI fringes and provide better visual and quantitative results. It is also observed that the proposed filtering methods preserve the edge information of the DSPI fringes, which is evaluated on the basis of the edge preservation index of the resultant filtered images.