*Proceeding Paper* **Incoherent Digital Holography for Multidimensional Motion Picture Imaging †**

**Tatsuki Tahara 1,\*, Yuichi Kozawa 2, Tomoya Nakamura 3, Atsushi Matsuda <sup>4</sup> and Tomoyoshi Shimobaba <sup>5</sup>**


**Abstract:** Incoherent digital holography (IDH) is a technique used to obtain a three-dimensional (3D) image of spatially incoherent light diffracted from an object as an incoherent hologram. Color holographic 3D motion picture imaging of daily-use light at the frame rate of a color polarization imaging camera can be achieved by the combination of IDH and single-shot phase-shifting interferometry. We show experimental results for color 3D motion picture imaging in this proceedings article.

**Keywords:** incoherent digital holography; 3D motion picture imaging; color 3D imaging

## **1. Introduction**

Incoherent digital holography (IDH) [1–14] is a three-dimensional (3D) image-sensing technique using interference of light and spatially incoherent light. Interference fringe images that contain 3D information about an object are obtained, even for spatially and temporally incoherent light, by generating two waves from an object wave and utilizing selfinterference. A digital hologram of the daily use of light can be obtained using IDH, and the applications of this technology to fluorescence microscopy [15–20] and 3D imaging [21–28] have been actively researched. Full-color holographic 3D imaging using IDH has been shown to be possible, even for sunlight [5,28].

IDH has the ability for simultaneous imaging of multidimensional information such as a 3D image, multiple wavelengths [18–20,29–31], a state of polarization, and a variety of types of light [32]. Holographic quantitative phase imagers can be constructed using a small light emitting diode (LED) [33,34]. High-speed image sensing and robustness against external vibrations are important factors when constructing a multidimensional IDH system. Single-shot IDH [8–14] performed using single-shot phase-shifting [35–37] has been proposed as an IDH technique capable of satisfying the factors at play. In most of this IDH technique, holographic 3D imaging can be carried out using single-shot exposure of a polarization image sensor and a single-path interferometer. In this publication, we briefly introduce these holography techniques and the multidimensional imaging possible with this IDH technique.

**Citation:** Tahara, T.; Kozawa, Y.; Nakamura, T.; Matsuda, A.; Shimobaba, T. Incoherent Digital Holography for Multidimensional Motion Picture Imaging. *Eng. Proc.* **2023**, *34*, 3. https://doi.org/ 10.3390/HMAM2-14153

Academic Editor: Vijayakumar Anand

Published: 13 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **2. Digital Holography Systems Adopting Single-Shot Phase-Shifting Interferometry for Multidimensional Motion Picture Imaging**

Figure 1 illustrates two types of single-shot single-path digital holography (DH) systems: a single-shot full-color IDH system with birefringent materials [27,28] and a single-shot DH system for quantitative phase imaging with LED light [34]. A single-path self-interference or self-reference interferometer is adopted to the IDH systems. In these IDH systems, two waves are generated from a wave diffracted from an object. Coherence length should be considered when obtaining a digital hologram of natural light because of its low temporal coherence. These single-path IDH systems are designed to generate an interference fringe image of temporally incoherent light with high visibility. Differences in optical path length between the two waves can be carefully adjusted using polarimetric optical elements. Figure 1a depicts how a full-color hologram of natural light is obtained with a single exposure of a color polarization image sensor and with single-shot phase shifting. The DH system shown in Figure 1b is based on self-reference interferometer and has improved the depth resolution of DH with an LED light in comparison to selfinterference IDH [33,34].

**Figure 1.** Single-shot single-path DH systems. (**a**) Single-shot full-color IDH system with birefringent materials [27,28]; (**b**) Self-reference DH system with a commonly used light source [34].

Figure 2 shows photographs of the constructed single-shot full-color IDH system and an example of experimental results obtained with the constructed IDH system. This IDH system can be used on a wood table to record a full-color hologram of objects illuminated by sunlight [27]. One study obtained a full-color holographic image from a single recorded hologram using the constructed IDH system and an RGB-LED, as shown in Figure 2b,c. Video-rate full-color holographic 3D motion picture imaging has also been experimentally demonstrated via the setup [28].

**Figure 2.** An optical implementation and an example of experimental results. (**a**) Constructed singleshot full-color IDH system with birefringent materials with a camera lens, termed "Holocamera"; (**b**) A recorded hologram with a holocamera; (**c**) the image reconstructed from (**a**).

#### **3. Conclusions**

We have briefly introduced a single-shot single-path IDH with which to perform multidimensional imaging. As another study remarked, the limitation of the measurement accuracy in interferometry and holography can be quantitatively evaluated based on the theory of quantum optics [38]. Algorithms and architectures for high-speed image reconstruction are also highly required for use in real-time measurement [39–41]. We will show experimental results for multidimensional holographic imaging of incoherent light, such as sunlight and LED light, in the presentation.

**Author Contributions:** All authors contributed equally. This manuscript was compiled by T.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was partially supported by Precursory Research for Embryonic Science and Technology (PRESTO) (JPMJPR16P8), Japan Society for the Promotion of Science (JSPS) (JP19H03202), The Cooperative Research Program of "Network Joint Research Center for Materials and Devices" (No. 20224020 and 20234030), and The Mitsubishi Foundation (202111007).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data is contained within the article.

**Acknowledgments:** We thank co-workers and co-authors of our articles related to IDH.

**Conflicts of Interest:** The authors declare no conflict of interests.

### **References**


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