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We measured the time variation of a received laser signal level during snowfall over a distance of 72 m. The signal level dropped sharply for up to 10 ms when a snowflake crossed the laser beam. The probability distribution of the variation due to snowfall was calculated by assuming it to be the linear superposition of the light diffracted by snowflakes.(More)
Recently, a number of high-speed optical clock generation technologies have been developed due to their potential useful applications in different fields. Here, we propose a new terahertz optical clock generation technique with tunable repetition rate and central wavelength. The proposed optical clock generator consists of an frequency comb light source and(More)
The educational system has gradually shifted from a face-to-face to an e-learning system, which has become prevalent in advanced countries with the advance of information technology, and connection of global networks. Accordingly, a growing demand is emerging for more reliable individual certification with technical precision in order to measure and record(More)
We implement a fully automatic fast face recognition system by using a 1000 frame/s optical parallel correlator designed and assembled by us. The operational speed for the 1:N (i.e., matching one image against N, where N refers to the number of images in the database) identification experiment (4000 face images) amounts to less than 1.5 s, including the(More)
Taking advantage of small aberrations, high efficiency, and compactness, we developed a new, to our knowledge, design procedure for a binary zone-plate array (BZPA) and applied it to a parallel joint transform correlator for the recognition of the human face. Pairs of reference and unknown images of faces are displayed on a liquid-crystal spatial light(More)
The binary zone plate (BZP) is a diffractive optical element whose wide-ranging development is expected to have a strong effect on fields such as optical communications and information processing. With the increasing demand for more-compact systems and devices the BZP needs to be efficient as well as small. It is well known that fabrication errors strongly(More)
A novel, to our knowledge, scheme for a parallel joint transform correlator system is demonstrated by the introduction of a five-channel zone-plate image multiplicator combined with photographic referencing and is applied to the recognition of Devanagari script. For considering the script's specific features, a partial image was obtained by means of(More)
The blurring effect in printing fine grating patterns on photoresist films can be minimized by using the Fourier image effect, which involves the image-forming nature of periodic patterns in the Fresnel region. Experiments using gratings having lattice constants of 3.8 mum and 10 mum are reported. The effectiveness of the Fourier image was confirmed by the(More)