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 preprocessing and postprocessing times. The binary real-only matched filter is devised for the sake of face recognition, and the system is optimized by the false-rejection rate (FRR) and the false-acceptance rate (FAR), according to 300 samples selected by the biometrics guideline. From trial 1:N identification experiments with the optical parallel correlator, we acquired low error rates of 2.6% FRR and 1.3% FAR. Facial images of people wearing thin glasses or heavy makeup that rendered identification difficult were identified with this system.
With the progress of information technology, the need for an accurate personal identification system based on biological characteristics is increasing the demand for this type of security technology instead of conventional systems using ID cards or pin numbers. Among other features, the face is the most familiar element and is less subject to psychological resistance. As a simple and compact recognition system satisfying the required performance, we implemented a hybrid system based on the optical recognition principle using a multi-level zone plate as a Fourier-transform lens and we report the preliminary results of their application to face recognition. In this paper, we present the design procedure and fabrication process for an improved version of a second-generation compact parallel correlator (named COPaC II), the size of which is 20 × 24 × 43 cm3 and weight 6 kg. As a result, we obtained a low error rate of 0% as the false match rate and 0.3% as the false non-match rate, thus the COPaC II significant identification security level is sufficiently stable. With the aim of further enhancing the throughput and robustness, we conducted performance tests where the system is used as a computer log-in device and as a pre-screening device for crime investigation. In both experiments, a high rate of successful recognition, such as 90% recognition and 94% rejection rate for log-in, was obtained. Experiments on twins to check the disguise recognition, and on the effects of changes in brightness and arbitrary size of images to test its robustness are also included.
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. The measured distributions could be reproduced by assuming reasonable snowflake size distributions. Furthermore, the probability distributions due to snowfall over a 1 km distance were calculated, and the expected bit errors during snowfall and the transmitted beam sizes were evaluated.
Faint Object Camera and Spectrograph (FOCAS) is a versatile common-use optical instrument for the 8.2m Subaru Telescope, offering imaging and spectroscopic observations. FOCAS employs grisms with resolving powers ranging from 280 to 8200 as dispersive optical elements. A grism is a direct-vision grating composed of a transmission grating and prism(s). FOCAS has five grisms with replica surface-relief gratings including an echelle-type grism, and eight grisms with volume-phase holographic (VPH) gratings. The size of these grisms is 110 mm×106 mm in aperture with a maximum thickness of 110 mm. We employ not only the dichromated gelatin, but also the hologram resin as a recording material for VPH gratings. We discuss the performance of these FOCAS grisms measured in the laboratory, and verify it by test observations, and show examples of astronomical spectroscopic observations.
The volume of information we handle is markedly increasing as a result of the change from text data to still and moving image files. In this paper, we propose and describe fabrication of a much higher speed search engine for image and video data using a holographic optical disc system. Preliminary correlation experiments using the holographic optical disc setup show an excellent performance as indicated by high correlation peaks and low error rates at a multiplexing pitch of 10 mm, and a rotational speed of 300 rpm. It is clear that the processing speed of our optical holographic calculation is markedly higher than the conventional digital signal processing architecture. This system can also be applied to various search engine systems.
A spatially divided beam splitter is designed, by which the laser diode light couples into multiple fibers using a cylindrical lens and a phase type linear zone plate array. Using skew ray tracing, the focusing characteristics of a spatially divided beam splitter are predicted. A three-section linear zone plate array with the linewidth changing from 1.1 to 2.05 microm was fabricated by holographic mask patterning and deep UV printing. In oblique incident conditions close to the Bragg angle, the diffraction efficiency reached 60%. By combining the linear zone plate array with a cylindrical lens, simultaneous focusing and separation of the laser output are achieved.
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 influence the characteristics of BZPs. To mitigate the influence of fabrication errors and obtain an efficient BZP with a high numerical aperture, we propose a design, called the hybrid-level BZP (HBZP), that combines zones with different numbers of phase levels. A method to correct the phase mismatch generated by such a combination is described. We furthermore discuss the optimum design of HBZPs in the presence of fabrication errors and report on its experimental evaluation.
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