  Digital holography has applications in bio-imaging because it can
simultaneously obtain the amplitude and phase information of a microscopic
sample in a single shot, thus facilitating non-contact, noninvasive observation
of the 3D shape of transparent objects (phase objects, which can be mapped with
the phase information,) and moving objects. The combination of digital
holography and microscopy is called digital holographic microscopy (DHM). In
this study, we propose a smartphone-based DHM system for 3D imaging that is
compact, inexpensive, and capable of observing objects in real time; this
system includes an optical system comprising a 3D printer using commercially
available image sensors and semiconductor lasers; further, an Android-based
application is used to reconstruct the holograms acquired by this optical
system, thus outlining the amplitude and phase information of the observed
object. Also, by utilizing scalable diffraction calculation methods and
touchscreen interaction, we implemented zoom functionality through pinch-in
gestures. The study results showed that the DHM system successfully obtained
the amplitude and phase information of the observed object via the acquired
holograms in an almost real time manner. Thus, this study showed that it is
possible to construct a low cost and compact DHM system that includes a 3D
printer to construct the optical system and a smartphone application to
reconstruct the holograms. Furthermore, this smartphone-based DHM system's
ability to capture, reconstruct, and display holograms in real time
demonstrates its superiority and novelty over existing systems. This system is
also expected to contribute to biology fieldwork and pathological diagnosis in
remote areas.
