Optical Pick Up head is dominant device in optical memory systems because it have much issues to develop and make production, and consequently owes large part of product cost. This paper discusses 4 development issues to the background of each epochs. The issues such as miniaturizing, making to accumulate, interchangebablity with former media, and higher density for larger memory capacity are also taken up, and the technology to solve these issues are examined. The paper also presents the proposals for the next generation products and briefly describes the optical Pick Up technologies expected in the future.

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We developed an integrated optical device for MiniDisc MO recording systems. The simple configuration and manufacturing process of the device were realized through developing ray-tracing and diffraction integral methods for crystals and employing a simple micro-prism of a birefringent crystal KTP (KTiOPO₄). We confirmed that an optical head using the device had adequate quality and reliability for practical use.

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Recent technological developments for CD and DVD optical heads are described. Optical heads play a key role in supporting optical disks, for which a large market has been formed. To evolve optical disks from playing only into recordable ones with a higher density and a larger capacity, high-power, high-resolution optical heads have been developed. The advent of a higher-performance optical head largely depends on the development of laser diode technology, as well as on the development of optical technology.

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780 nm-band AlGaAs and 650 nm-band AlGaInP laser diodes are monolithically integrated on a GaAs substrate as the light source in DVD/CD optical pickups. In order to reduce internal losses for improved characteristics and to ensure better flexibility of device design, real-refractive index-guided self-aligned (RISA) structure is employed for both 780 nm and 650 nm-band LDs. As a result, low noise characteristics due to self-sustained pulsation in the both wavelength bands have been achieved. A dual-wavelength laser with a high power ( > 100 mW) 780 nm-band LD has also been developed for recording of CD-R/RW disks.

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The total efficiency and the output energy of Nd:YAG laser under coaxial pumping with solar light have been calculated. The results of our work suggest that the total efficiency could be improved to 20 % from 10 % by using a collector structure with 10 cm in diameter of D-type aperture and 10m length. Excitation and laser output had been compared in good agreement with an experiment performed by C. G. Young.

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Cylindrical internal defects in carbon steel specimens were detected noncontactly and nondestructively from the measurements of ultrasonic diffraction signals using the laser ultrasonic technique. Laser beams used for both ultrasonic generation and detection have a 0.7-mm diameter. Spatial profiles of the diffracted ultrasonic amplitude were measured for the internal defects of 0.5 to 5.0 mm in diameter, which were in good agreement with the profiles calculated by using Cornu's spiral. This method can be useful for the noncontact detection of internal defects in metal, and is considered to be applicable to the noncontact sizing of the internal defects such as those in power plant components.

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