Parallel Phase-shifting Digital Holography System Research Articles

Dynamic phase measurement of a transparent object by parallel phase-shifting digital holography with dual polarization imaging cameras

Measurement of surface shape and refractive index for moving transparent objects is critical in various fields. A parallel phase-shifting digital holography system that can record and reconstruct the phase information of moving transparent objects using two high-resolution polarization imaging cameras was presented. In the developed system, two polarization imaging cameras with 3.45 µm pixel pitch passed through the object in different directions. These two polarization imaging cameras were controlled by LabVIEW and worked synchronously. The proposed system can obtain the object's integral phase distributions in different directions, which is more effective for measuring an asymmetric object. In the experiment, the resolution of the system was confirmed by using a transmission-type test target. Besides, the dynamic phase measurement of an irregularly shaped transparent object was completed to verify the proposed system's effectiveness.

Digital Holographic Microscopy Using a Spherical Reference Wave and Polarization Hologram

A reflective lensless on-axis digital holographic microscopic system with a spherical reference wave was developed and used to obtain a reconstructed image at several magnification levels. A polarization image camera (PIC) was used to suppress the direct current term and twin images of the on-axis digital holography (DH) microscope. The PIC was used in a parallel phase-shifting DH system without mechanical movement. Here, we show that the magnification can be adjusted by changing the ratio of the distance between the object and the PIC to that between the reference light and the PIC while maintaing a constant reconstruction distance.

A4-Sized Parallel Phase-Shifting Digital Holography System

An A4-sized parallel phase-shifting digital holography system was constructed and experimentally demonstrated. Parallel phase-shifting digital holography is a technique being capable of instantaneous recording of three-dimensional (3-D) image of moving object. Aiming at a 3-D motion picture measurement of moving object system that can be carried on sites where the measurement system is needed, we improved a previous portable parallel phase-shifting digital holography system. The size and weight of the improved portable system are 300 mm × 210 mm × 160 mm and 6 kg, respectively. Also, we experimentally recorded a series of holograms of a moving object and reconstructed motion pictures, which show the same event but are focused at each depth, from the holograms. Thus, the 3-D motion picture recording and reconstruction capability of the constructed system were successfully demonstrated. A 3-D motion picture at 10 frames/s was obtained by the system.

Construction of a portable parallel phase-shifting digital holography system

We propose a portable parallel phase-shifting digital holography system. Parallel phase-shifting digital holography is a technique capable of instantaneous and three-dimensional measurement of objects. This technique has been verified by an experiment on anti-vibration optical tables, but had not been realized as a system for practical use yet. Then, we designed a portable system of parallel phase-shifting digital holography for the purpose of practical use. The size and weight of the system are 450 mm (L)×250 mm (W)×200 mm (H) and less than 7 kg, respectively. We designed the configuration of the system in a way which can be easily changed to implement two types of parallel phase-shifting digital holographies. The system was constructed by the use of ready-made optical components. To confirm the validity of the system, the capability of the three-dimensional imaging free from the superimposition of the unwanted images, which was the problem accompanied with conventional in-line digital holography, with a single-shot exposure was successfully demonstrated.

Parallel two-step phase-shifting digital holography

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.