Toyohiko Yatagai

Three-dimensional imaging using computer-generated holograms synthesized from 3-D Fourier spectra

Computer-generated holograms(CGHs) synthesized from projection images of real existing objects are considered. A series of projection images are recorded both vertically and horizontally with an incoherent light source and a color CCD. According to the principles of computer tomography(CT), the 3-D Fourier spectrum is calculated from several projection images of objects and the Fresnel CGH is synthesized using a part of the 3-D Fourier spectrum. This method has following advantages. At first, no-blur reconstructed images in any direction are obtained owing to two-dimensionally scanning in recording. Secondarily, since not interference fringes but simple projection images of objects are recorded, a coherent light source is not necessary. Moreover, when a color CCD is used in recording, it is easily possible to record and reconstruct colorful objects. Finally, we demonstrate reconstruction of biological objects.

Analytic function expression of signal wave for data retrieve in holographic data storage (Conference Presentation)

Holographic data storage is a data storage with large data amount recorded by volume holography. Holography is well known as a method to record three-dimensional scenes. The principle is roughly established and major characteristics are well understood. In the case of three-dimensional scenes, some noises are acceptable because they are compensated by our brain. However, in the case of holographic data storage, the recording images are minute two-dimensional coded patterns so that the images are not robust for noises. Therefore, rigorous expressions of recording signal is required. In this study, the recording signal wave is expressed by Taylor expansion for small argument and asymptotic expansion for large argument. Then, the filling factor of pixels in a spatial light modulator (SLM), the size and the position shift of a rectangular aperture at a Fourier plane are considered. When the signal wave is ideally reconstructed, the signal wave at an image plane is captured by using an image sensor. Then, the signal wave is integrated by the area of pixels in the image sensor. In this study, the integral is analytically calculated whereas it is numerically calculated in general because the signal wave is expressed by analytic functions. Therefore, interpixel crosstalk is easily evaluated. In our previous study, high-density recording method of binary data pages is proposed by using four-step phase mask. The high-density recording characteristics are evaluated by analytic functions. When parameters such as the filling factor of pixels in a SLM and an image sensor and the size and the position shift of a rectangular aperture can be known, the analytic functions are obtained. Then, the analytic functions are expected for error corrections.

Experimental Verification of Lens-less Fourier Digital Holography based on Rayleigh-Sommerfeld Diffraction Integral

The principle of our proposed lens-less Fourier digital holography is experimentally verified by observing a test target. The reconstruction is performed by using a Fourier integral formula derived from Rayleigh-Sommerfeld diffraction integral and coordinate conversion.

Resonant enhansment modulators using electro-optical effect of poled polymers

Spatial light modulators (SLMs) play very important roles in optical computing, including of optical neural networks and optical image processing.