Shin Yoshikado

Shift multiplexing for holographic storage system using fiber bundle referencing

We propose a shift multiplexing method for volume holographic storage using fiber bundle referencing. The reference beam is guided by a fiber bundle and multiplexing can be implemented by shifting the recording medium for a small distance. No sidelobe or period has been found and the signal-to-noise ratio is high. Multiple images are stored in a crystal with a spatial separation of 3 μm between successive holograms.

Nondiffracting narrow light beam with small atmospheric turbulence-influenced propagation

A narrow light beam that propagates in the atmosphere with less disturbance than conventional light beams is introduced. The operating method and features of the newly proposed long-range nondiffracting beam (LRNB) are briefly demonstrated. Some experimental results of the atmospheric propagation of this beam at a distance of 500 m are shown in comparison with a conventional collimated beam and a focused beam. The results and related analyses show that the LRNB is much less influenced by atmospheric turbulence than other beams and suggest that the LRNB can apply to many fields.

Airborne microwave rain-scatterometer /radiometer

Abstract An airborne microwave rain-scatterometer/radiometer system operated at 10 and 34-45 GHz was developed for the remote sensing of precipitation, especially rain, from an aeroplane. Airborne rain-scatterometers were developed as a first step for the development of the future spaceborne rain-scatterometer. Flight experiments of more than 30 hours were performed in co-operation with the ground-based C-band weather radar. The sensor system of the airborne microwave rain-scatterometer/radiometer, flight experiment in June 1981 cooperating with the ground-based weather radar, and results of data analyses are described.

Short-range verification experiment of a trial one-dimensional synthetic aperture infrared laser radar operated in the 10-µm band

A trial one-dimensional (1-D) synthetic aperture infrared laser radar (SAILR) system for imaging static objects, with two CO(2) lasers as a transmitter and a local oscillator for heterodyne detection, was constructed. It has a single receiving aperture mounted on a linearly movable stage with a length of 1 m and a position accuracy of 1 microm. In an indoor short-range experiment to confirm the fundamental functions of the system and demonstrate its unique imaging process we succeeded in obtaining 1-D synthetic aperture images of close specular point targets with theoretically expected resolution.

Incoherent-to-coherent conversion by use of the photorefractive fanning effect

A dynamic incoherent-to-coherent converter using the photorefractive fanning effect is demonstrated in a BaTiO(3):Ce crystal, and high-quality positive replicas of the incoherent image are obtained with a resolution of 32line pairs/mm. In this method the incoherent image-bearing beam modulates the transmission intensity of the coherent beam directly, and no readout beam is required. When the intensity ratio of the incoherent beam to the coherent beam is smaller than 5, the transmission intensity of the coherent beam increases almost linearly with increased intensity of the incoherent beam.

Feasibility study of synthetic aperture infrared laser radar techniques for imaging of static and moving objects

Techniques for two types of 10-mum band synthetic aperture infrared laser radar using a hypothetical reference point target (RPT) are presented. One is for imaging static objects with a single two-dimensional scanning aperture. Through the simple manipulation of a reference wave phase, a desired image can be obtained merely by the two-dimensional Fourier transformation of the correlator output between the intermediate frequency signals of the reference and object waves. The other, with a one-dimensional aperture array, is for moving objects that pass across the array direction without attitude change. We performed imaging by using a two-dimensional RPT correlation method. We demonstrate the capability of these methods for imaging and evaluate the necessary conditions for signal-to-noise ratio and random phase errors in signal reception through numerical simulations in terms of feasibility.

Mutually pumped phase conjugator with a rainbow configuration in BaTiO 3 :Ce crystal using nanosecond pulses

A new type of mutually pumped phase conjugator with a rainbow configuration has been demonstrated experimentally in cerium-doped barium titanate crystal that uses pulsed beams with a pulse width of 3.0 ns and a repetition rate of 40 Hz at a wavelength of 532 nm. The highest phase-conjugate reflectivity was ~24%. The dependence of the phase-conjugate reflectivity on the incident angle and distance, as well as the grating formation time for achieving 1 - e(-1) of equilibrium reflectivity, has been measured.

SIR-B Experiments in Japan: Sensor Calibration and Oil Pollution Detection Over Ocean

Preliminary results of the SIR-B experiments conducted in Japan are reported mainly on the sensor calibration and the oil pollution experiments. No significant result was obtained for the rice crop experiment which was carried out at the same time, mainly due to the late flight of SIR-B. The sensor calibration experiment was eventually reduced to only the evaluation of the imaging characteristics of SIR-B. However, a reasonable relation between the image count and RCS is found, and the resolution analysis by using the corner reflector images gives satisfactory results. A possible cause leading to what are rather overestimates of the resolution is pointed out to be the background clutter. A simulated oil slick area over sea was clearly detected on the SIR-B image, although the incident angle was not so appropriate for the purpose. This result demonstrates the capability of a space-borne synthetic aperture radar for effective surveillance of oil spills over high seas.

ONE-WAY IMAGE TRANSMISSION THROUGH A THICK DYNAMIC DISTORTER WITHOUT A REFERENCE BEAM

We demonstrated a method to perform one-way image transmission through a dynamic distorter without a reference beam. In this method, a photorefractive four-wave mixing configuration was used to pick up the reconstructed image from the image-bearing signal beam, which acted as an erase beam. The fluctuation period of the dynamic distorter must be much shorter than the response time of the nonlinear material. Reconstructed images with high-fidelity have been obtained. Because use of a reference beam is unnecessary this method is simpler and more effective.

Photorefractive low-pass temporal filter

Abstract We present a technique of photorefractive low-pass temporal filter. The performance of this filter is characterized and simulated by a resistance–capacitor (RC) filter circuit. An example of applying this filter to process a time-dependent fluctuation 2D image is also introduced.