Multiple object recognition by digital holography with a wavelength-tuned laser diode

Abstract

Digital holography can record fully complex-amplitude information in a Fourier-transformed hologram between a reference and multiple-target objects. Complex amplitude of a hologram can be measured by using six-step phase-shifting interferometry with a wavelength-tuned laser diode in a Mach-Zehnder interferometer. The six-step algorithm is inherently insensitive to a laser-diode power change associated with its current variation. The correlation signal is periodically repeated by the sampled digital hologram and high-order harmonics are mixed up with the peaks corresponding to other orders. The artifact false signals can be diminished when the objects are equally dispersedly placed those separations are equal to the number of multiple objects. The experimental results are shown.