Multiwavelength Digital Holography and Phase-Shifting Interferometry Selectively Extracting Wavelength Information: Phase-Division Multiplexing (PDM) of Wavelengths

In this chapter, we introduce multiwavelength digital holographic techniques and a novel multiwavelength imaging technique. General multiwavelength imaging systems adopt temporal division, spatial division, or space-division multiplexing to obtain wavelength information. Holographic techniques give us unique multiwavelength imaging systems, which utilize temporal or spatial frequency-division multiplexing. Conventional multiwavelength digital holography systems have been combined with one of the methods listed above. We have proposed phase-shifting interferometry selectively extracting wavelength information, characterized as a multiwavelength three-dimensional (3D) imaging technique based on holography and called phase-division multiplexing (PDM) of multiple wavelengths. In PDM, wavelength-multiplexed phase-shifted holograms are recorded, and multiwavelength information is separately extracted from the holograms in the space domain. Phase shifts are introduced for respective wavelengths to separate object waves with multiple wavelengths in the polar coordinate plane, and multiple object waves are selectively extracted by the signal processing based on phase-shifting interferometry. Additionally, the system of equations needed to obtain a multiwavelength 3D image is solved with less wavelength-multiplexed images using two-step phase-shifting interferometry-merged phase-division multiplexing (2π-PDM), which makes the best use of 2π ambiguity of the phase and two-step phase-shifting method. The PDM techniques are reviewed and color 3D imaging ability is described with numerical and experimental results

Wavelength-Selective Phase-Shifting Digital Holography: Color Three-Dimensional Imaging Ability in Relation to Bit Depth of Wavelength-Multiplexed Holograms

The quality of reconstructed images in relation to the bit depth of holograms formed by wavelength-selective phase-shifting digital holography was investigated. Wavelength-selective phase-shifting digital holography is a technique to obtain multiwavelength three-dimensional (3D) images with a full space-bandwidth product of an image sensor from wavelength-multiplexed phase-shifted holograms and has been proposed since 2013. The bit resolution required to obtain a multiwavelength holographic image was quantitatively and experimentally evaluated, and the relationship between wavelength resolution and dynamic range of an image sensor was numerically simulated. The results indicate that two-bit resolution per wavelength is required to conduct color 3D imaging