Takuhisa Numata

Phase-shifting digital holography with a phase difference between orthogonal polarizations

Phase-shifting digital holography with a phase difference between orthogonal polarizations is proposed. The use of orthogonal polarizations can make it possible to record two phase-shifted holograms simultaneously. By combining the holograms with the distributions of a reference wave and an object wave, the complex field of the objects wavefront can be obtained. Preliminary experimental results are shown to confirm the proposed method.

Polarization imaging of a 3D object by use of on-axis phase-shifting digital holography

A polarimetric imaging method of a 3D object by use of on-axis phase-shifting digital holography is presented. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. Experimental demonstration of a 3D polarimetric imaging is presented.

Image quality improvement of digital holography by superposition of reconstructed images obtained by multiple wavelengths

A method to improve the image quality of a digital holographic reconstructed image by means of speckle reduction is proposed. The size and position of the speckles are changed according to the wavelengths to record a digital hologram. By superposing reconstructed images with different wavelengths, the effect of speckle is reduced so that the image quality is improved. Optical experiments are given to confirm the proposed method.

Design of input phase mask for the space bandwidth of the optical encryption system

A method to design an input phase mask for double-random phase-encoding optical encryption is proposed. The input phase mask is iteratively designed so that the extent of the Fourier spectrum of the product of an input image and the input phase mask correspond to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved. We also discuss the number of phase levels of the designed input phase mask.

Design of Reference Pattern and Input Phase Mask for Coaxial Holographic Memory

Design methods of a reference pattern and an input phase mask for a coaxial holographic memory are described. By the proposed method, it is expected that the useless consumption of the dynamic range of a recording medium will decrease, and the light efficiency and the interference efficiency between the signal beam and the reference beam will be improved. A reference pattern and an input phase mask are designed by a simulated annealing. The performance of the proposed design method is confirmed by numerical simulations and optical experiments. Furthermore, the holographic memory system using both the designed reference pattern and the designed input phase mask is also confirmed by numerical simulations and optical experiments.

Profilometry and Reflectmetry Using Low-Coherent Digital Holography

The both profilemotry and reflectmetry of a 3-D object by use of digital holography with low coherent light source is proposed. For noise reduction, integration of digital holograms is introduced.

One-shot digital holography by use of polarization

The one-shot phase-shifting digital holography using phase difference of orthogonal polarizations is proposed. Using a CCD camera with pixelated polarizers, three images for phase analysis can be obtained simultaneously. The proposed method can be applied to a moving object, because a complex field of the wavefront of a 3D object can be obtained in a single exposure.

Speckles removal in digital holography using multiple wavelengths/distances from an object

The method to reduce speckles in a reconstructed image of a digital hologram is proposed. The size and position of the speckles are changed according to both the wavelengths to be recorded and the distances from the object the hologram. The superposition of the reconstructed images recorded with different wavelength/ distance holograms gives the image with reduced speckles

Optical encryption using an input phase mask designed for the space bandwidth of the optical system

The method to design an input phase mask for the double-random phase-encoding optical encryption is proposed. The input phase mask is designed so that the extend of the Fourier spectrum of the product of an input image and the input phase mask corresponds to the space bandwidth of the optical system. By using the designed input phase mask, we show that the bit-error rate is improved.

Improvement of viewing-zone angle and image quality of digital holograms

The method to improve of a viewing-zone angle and an image quality of a digital hologram is presented. A number of digital holograms of a central object are recorded from the position on the circumference. The holograms are used for a hologram synthesis to improve the image quality from whole viewing-zone angle. The synthesis is achieved by a correlation between a hologram and numerically propagated holograms. The large-sized synthesized digital hologram has a wide viewing-zone angle and less speckles. Some experimental results are shown to confirm the proposed method.