OSAKA—Matsushita Electric has developed a three-beam hologram unit containing a monolithic dual-wavelength laser to be used as an optical pickup for DVD-ROM (digital versatile disk read-only memory) players. The unit uses the three-beam method so that it can be used in a variety of optical-disk playback units. In addition, the seven components (not counting the object lens system) required for conventional two-wavelength optical pickups—two semiconductor lasers, a coupling prism, a beamsplitter, a three-beam grating, and two lenses—have all been integrated together, reducing the total package size to a thickness of 4.5 mm (see figure).
For the two-wavelength laser, indium gallium aluminum phosphide and gallium aluminum arsenide semiconductors are crystal-grown using a process that creates red and infrared read-guide laser structures. The resulting low-power laser emits in the red and infrared from a single chip. The low-noise photo-integrated circuit (a photosensor containing a photosensitive area and signal-processing integrated circuit in the same package) with 45° micromirrors can detect the two wavelengths of reflected light with different absorption coefficients at high sensitivity and speed.
Courtesy O plus E magazine, Tokyo