Hitoshi Ohzu

Hybrid holographic microscopy free of conjugate and zero-order images

The true image area that can be used for recording microscopic objects in hybrid holographic microscopy can be increased by elimination of the conjugate image and the zero-order image. We therefore added two shutters and one phase modulator to the electro-optical holographic recording system so that we could change the recording parameters and evaluate four methods of eliminating the conjugate image and the zero-order image. We found that the methods that use only the phase modulator require the recording of fewer holograms than do the methods that use the shutters and also provide reconstructed images that are less noisy.

Scale and rotation invariant real time optical correlator using computer generated hologram

Abstract Scale and rotation invariant optical correlation is performed with a combination of the In r - θ coordinate transformation and the conventional optical matched filtering. The mask for the In r - θ coordinate transformation is made of the computer generated hologram whose transmission function is derived by the ise of the stationary phase method. For the real time processing, a BSO incoherent-to-coherent device is placed on the coordinate transformed plane.

Hybrid holographic microscopy: visualization of three-dimensional object information by use of viewing angles

One of the attractive features of hybrid holographic microscopy, in which the hologram of a microscopic object recorded by an image sensor is numerically reconstructed with a computer, is that the three-dimensional (3-D) information of a recorded object is obtained. The 3-D information has often been extracted by means of changing the reconstruction distance in the numerical reconstruction process, but here we describe an alternative technique that allows for variable viewing angles. That is, the perspective from which the object is viewed can be varied. The approximation used enables use of the fast-Fourier-transform algorithm for numerical reconstruction even in the high-resolution case in which the Fresnel approximation is no longer valid. The resolution of the proposed technique is also discussed.

Human Visual Spatio-temporal Frequency Performance as a Function of Age

Deterioration of human spatial frequency contrast sensitivity with increasing age was measured, for both stationary and drifting gratings, by producing interference fringes directly on the subjects retinas. There were losses at high spatial frequency up to 40 years of age, and losses at all spatial frequencies thereafter. Older subjects exhibited better than expected performance for drifting low spatial frequency gratings. These results are consistent with the differential effects of aging on different populations of visual neurons.

Liquid-crystal active lens: a reconfigurable lens employing a phase modulator

The proposed active lens consists of a lens attached to a liquid-crystal two-dimensional phase modulator and it provides both a variable focal length and image processing capability. Since the lens has main refractive power and the phase modulator provides a small and variable power, the device features a large and variable power and a small F number. It can also perform convolution-based image processing in an incoherent imaging system, since its intensity point-spread function can be controlled by changing the modulators phase distribution. A prototype device varied its focal length from 0.23 m to 0.28 m and image-shifting, image-splitting and matched-filtering operations were experimentally demonstrated.

Reconfigurable lens with an electro-optical learning system.

An electro-optical system is proposed to control a reconfigurable lens that is a combination of a physical lens and a two-dimensional liquid-crystal phase modulator. The functions of an imaging system employing the reconfigurable lens can be controlled by a change in the phase distribution of the modulator. A computer changes the phase distribution and evaluates the image of an optical system. This process is iteratively performed on the basis of the simulated-annealing algorithm to optimize the phase distribution. We demonstrate control of a point-spread function and the correction of imaging properties degraded by defocusing or phase objects. The corrected imaging properties are even better than the original ones.

Measurement of the human factors of 3-D images on a large screen

Three dimensional displays using binocular disparity techniques are widely used. Binocular stereoscopic images can produce a mismatch of distance between plane of focus (accommodation) and plane of fixation (convergence) of the observe?s eyes. The viewing distance, i.e. plane of required focus, is generally greater when looking at a large screen than when look at a small display. In this study the fusional ranges of the binocular three dimensional image are compared when viewing a large screen (75inch,projection type TV display) at a distance of 350cm and when observing a small display (2linch CRT) at a distance of 100cm. We found that the fusional range was more extended on the larger screen than the smaller display. Accommodative responses were measured when looking at the 3D image. Accommodation does not remain in the plane of the display but changes to the stereoscopic distance of the 3D image fixated by the observer. The changes required when using a longer viewing distance were smaller than those measured with an a short viewing distance. These results suggest the longer viewing distance reduces an unnatural feeling of viewing 3D images due to the mismatch of distance between the planes of accommodation and convergence. Accommodation response time was measured after looking at stereoscopic 3D images. Far-to-near response time was longer than before viewing these images. The results showed that the viewing stereoscopic 3D images provided the observers visual system with different type of stimuli from these experienced in normal viewing.

Laser scanning microscope with a differential heterodyne optical probe.

A new laser scanning microscope system has been developed to observe the spatial distribution of light scattering particles or defects in a partially transparent object. The present microscope has an optical probe whose intensity is modulated by the interference effect between two crossed laser beams with slightly different frequencies. In this paper, a Zeeman laser combined with a simple polarizing optical system is used to produce two such coherent beams. Experimental results obtained by using a latex sphere and a microscale as the target show qualitatively that high image contrast is obtained by the present method even if some obscuring particles exist in front of the probe volume. Distributions of light scattering particles or defects in a LiNbO(3) and TGS single crystal can be visualized by a computer-controlled scan stage.

Evaluation of optical systems using the dynamic properties of laser-produced speckles

A lens-evaluation method based on the dynamic properties of laser-produced speckles is investigated and developed into a real-time modulation-transfer-function measuring system controlled by a microprocessor. One of the most important advantages of this method is the redundancy that permits rough adjustment of the lateral position of the light detecting point in the focal plane. Experimental results applied to a grin-rod lens as well as to an ordinary camera lens are obtained. For detection of the best focal position, the method of counting the zero-cross distribution along the optical axis is found to be effective.

The Application of Lasers in Ophthalmology and Vision Research

The potential use of dynamic speckles in accommodation or refractive measurements of the eye are discussed. The advantageous application of holographic techniques to eye research and some important results obtained are described. Studies of the modulation sensitivity function of the human visual pathway for both normal and abnormal vision are described which use laser interference, and its possible use in clinical ophthalmology is discussed.