| 摘要 |
PURPOSE: To provide an optical head device composed of plural light sources of different wavelengths having the diameter of a light spot and light intensity suitable for recording/reproducing optical information on an optical information recording medium with high density. CONSTITUTION: The transmitted light beams from semiconductor lasers 11, 12 are made parallel beams by means of collimator lenses 13, 14, respectively, and both transmitted beams are adjusted so as to become parallel beams 10 whose optical axes are in coincidence. The parallel beams 10 are focused on the recording surface 19 of a recording medium 110 through a diffraction grating 17 having a shape shown by (b), a beam splitter 111 and an objective lens 18. A part of the reflected beam is made incident on a signal detecting system 112 through the beam splitter 111. The diffraction grating has the wavelength selectivity, the laser beam 11 is transmitted through it and the laser beam 12 is reflected by it. The former is utilized as a recording light source and the latter is utilized as a reproducing light source since it gives a light spot whose diameter is smaller than the diffraction limit value owing to the super- high resolution effect. |
