In this review, we introduce digital holographic techniques and recent progress in multidimensional sensing by using digital holography. Digital holography is an interferometric imaging technique that does not require an imaging lens and can be used to perform simultaneous imaging of multidimensional information, such as three-dimensional structure, dynamics, quantitative phase, multiple wavelengths and polarization state of light. The technique can also obtain a holographic image of nonlinear light and a three-dimensional image of incoherent light with a single-shot exposure. The holographic recording ability of this technique has enabled a variety of applications.

We propose a parallel two-step phase-shifting digital holography technique capable of instantaneous measurement of three-dimensional objects, with a view toward measurement of dynamically moving objects. The technique is based on phase-shifting interferometry. The proposed technique carries out the two-step phase-shifting method at one time and can be optically implemented by using a phase-shifting array device located in the reference beam. The array device has a periodic two-step phase distribution, and its configuration is simplified compared with that required for three-step and four-step parallel phase-shifting digital holographies. Therefore the optical system of the proposed technique is more suitable for the realization of a parallel phase-shifting digital holography system. We conduct both a numerical simulation and a preliminary experiment in the proposed technique. The results of the simulation and the experiment agree well with those of sequential phase-shifting digital holography, and results are superior to those obtained by conventional digital holography using the Fresnel transform alone. Thus the effectiveness of the proposed technique is verified.

Parallel phase-shifting digital holography can obtain three-dimensional information of a dynamically moving object with high accuracy by using space-division multiplexing of multiple holograms required for phase-shifting interferometry. We demonstrated high-speed parallel phase-shifting digital holography and obtained images of the phase variation of air caused by a compressed gas flow sprayed from a nozzle. In particular, we found the interesting phenomenon of periodic phase distributions. Reconstructed images were obtained at frame rates of 20,000 and 180,000 frames per second.

Digital holography (DH) is a promising technique for modern three-dimensional (3D) imaging. Coherent holography records the complex amplitude of a 3D object holographically, giving speckle noise upon reconstruction and presenting a serious drawback inherent in coherent optical systems. On the other hand, incoherent holography records the intensity distribution of the object, allowing a higher signal-to-noise ratio as compared to its coherent counterpart. Currently there are two incoherent digital holographic techniques: optical scanning holography (OSH) and Fresnel incoherent correlation holography (FINCH). In this review, we first explain the principles of OSH and FINCH. We then compare, to some extent, the differences between OSH and FINCH. Finally, some of the recent applications of the two incoherent holographic techniques are reviewed.

We propose parallel phase-shifting digital holographic microscopy (PPSDHM) which has the ability of three-dimensional (3-D) motion measurement using space-division multiplexing technique. By the PPSDHM, instantaneous information of both the 3-D structure and the phase distributions of specimens can be simultaneously acquired with a single-shot exposure. We constructed a parallel phase-shifting digital holographic microscope consisting of an optical interferometer and an image sensor on which micro polarizers are attached pixel by pixel. The validity of the PPSDHM was experimentally verified by demonstrating the single-shot 3-D imaging and phase-imaging ability of the constructed microscope.