Osamu Matoba

Advances in passive imaging elements with micromirror array

We have proposed a new passive imaging optics which consists of a grid array of micro roof mirrors working as dihedral corner reflectors. Although this element forms mirror-like images at opposite side of objects, the images are real. Because the imaging principle of the proposed element is based on accumulation of rays, the design of each light path makes many kinds of devices possible. So, we propose two variations of such a device. One device consists of an array of micro retroreflectors and a half mirror, and it can also form real mirror-like images. The advantage of this device is wide range of view, because the displacement of each retororeflector is not limited on a plane unlike the roof mirror grid array. The other consists of an array of long dihedral corner reflectors. Although this structure has been already known as a roof mirror array, it can be used for imaging. This device forms two heterogeneous images. One is real at the same side of an object, and the other is virtual at the opposite side. This is a conjugate imaging optics of a slit mirror array whose mirror surface is perpendicular to the device surface. The advantage of a roor mirror array is that the real image has horizontal parallax and can be seen in air naturally.

Iterative algorithm of phase determination in digital holography for real-time recording of real objects

We propose a numerical method to obtain complex amplitude distribution of a three-dimensional (3D) object from a digital hologram. The method consists of two processes. The first process is to measure simultaneously a hologram of the 3D object and an object intensity distribution by two image sensors. These intensity distributions give us the amplitude and absolute value of phase of the 3D object at the image sensor plane. The second process is the determination of phase distribution by a proposed iterative process based on the criterion that the reconstructed 3D object is in focus and its conjugate reconstruction is out of focus. Numerical and experimental results show the effectiveness of the proposed method.

Three-dimensional measurement and imaging based on multicameras randomly distributed on the circumference.

We present a three-dimensional (3D) measurement and imaging based on a multicamera system. In the presented system, projected images of 3D objects are taken by cameras located at random positions on a circumference, and then the 3D objects can be reconstructed numerically. We introduce an angle correction function to improve the quality of the reconstructed object. The angle correction function can correct the angle error caused by the position errors in the projected images due to the finite pixel size of the image sensor. The numerical results show that the point source was reconstructed successfully by introducing the angle correction function. We also demonstrate experiments: the two objects are located on a rotary stage controlled by a computer, the projected images are taken by a single camera, and by using 33 projected images, the two objects are reconstructed successfully.

Speckle-Shift Multiplexing along Axial Direction in Reflection-Type Holographic Memory

In reflection-type holographic memory, speckle-shift multiple recording along the axial direction of a storage medium is investigated experimentally and numerically. We record three data pages along the axial direction of an iron-doped lithium niobate medium with a thickness of 0.5 mm and an interval of the first null distance of shift selectivity, and each hologram was read out at the recording position. We also numerically evaluate the multiple recording along the axial direction. The numerical analysis supports the fact that the speckle size determines the three-dimensional recording interval. The numerical results are in qualitative agreement with the experimental results. We numerically examine the bit error rate as a function of the recording interval. The results show that multiplexing along the axial direction can increase the storage capacity.

Optical retrodirective tracking system approach using an array of phase conjugators for communication and power transmission

A new concept for a retrodirective tracking system applicable for communication and power transmission is proposed. In the proposed concept, the power transmitter utilizes a receivers pilot signal to obtain information about its direction by conjugating the signals phase inside a nonlinear medium. Power is therefore transmitted back to the receiver by the phase-conjugated signal beam. The power can be concentrated by an array of phase conjugators, which provides a large aperture so that the intensity can be increased on the receivers photovoltaic panels compared to a single element. Controlling the phase and the direction of the readout beams in the four-wave-mixing process provides control over the interference pattern, its position, and its size. A numerical analysis is given for the phase and spot size control, and measurements with two Co-doped Sr(x)Ba(1-x)Nb(2)O(6) (Co:SBN) crystals confirm the occurrence of interference that is achieved for the case of two beams.

A method for factorization by means of digital optical computing and image compression

A method to reduce computational costs of a factorization algorithm based on two dimensional pattern processing is presented. We develop logical operations to implement a factorization in the data compressed domain. In the method, firstly, two dimensional discrete images for data processing is compressed in accordance with the presented coding. Secondly, sequences of logical operations are executed in compression domain. Finally, desired results are obtained by extraction of the compressed data after the operations. An advantaged feature of the presented method is that computational costs can be decreased by the data compression rate.

Optical Security Card by Three‐dimensional Random Phase Distribution

An optical security card based on a three‐dimensional (3D) phase object is presented. This card enables us to develop a personal authentification system and secure data storage in a highly scattering medium. The authentification is implemented by the correlation between a speckle pattern of the 3D phase object and stored speckle patterns. For secure data storage, absorption distribution is involved in a scattering volume medium. Appropriate user can only reconstruct the absorption distribution by solving inverse problem. Experimental and numerical results are presented to show the effectiveness of the proposed system.

Design of Waveguide Array for Wide and Thin Coherent Illuminator

We have proposed a waveguide array device for a wide and thin coherent illuminator. The device is numerically analyzed by beam propagation method. In the numerical evaluation, 81 beam array is designed, but the intensity fluctuation is not small. We have to modify the waveguide structure along the propagation direction.

Interpage Crosstalk Noise in Reflection-type Holographic Memory System by Speckle Three-dimensional Shift Multiplexing

This paper investigates numerically interpage crosstalk noise in reflection-type holographic memory system by speckle three-dimensional shift multiplexing. The crosstalk noise is one of factors to limit storage capacity. Numerical evaluation showed that constant crosstalk noise was caused by illumination of a readout beam.

Characteristics of 3-D image reconstruction in a system based on multi vision data acquisition and holographic display

The characteristics of image quality on a three-dimensional (3D) imaging system based on multi-vision capturing and holographic display are analyzed numerically. We compare the longitudinal resolution in holographic reconstruction with accuracy of axial positions obtained with stereogram analysis.