| 摘要 |
An art for reading information from an optical recording disk by means of a light beam emitted from a semiconductor laser, particularly an optical integrated circuit type apparatus which is improved to suppress fluctuation of the focal point of the beam caused by a change in the wavelength of the laser beam. The apparatus has a substrate, the semiconductor laser beam provided on one end of the substrate and an optical waveguide provided on one side of the substrate and capable of guiding the laser beam from the semiconductor laser. The apparatus further has a first diffraction grating provided on the waveguide and capable of diffracting the guided beam to the exterior of the waveguide and a second diffraction grating disposed at a position where it is capable of receiving the light beam diffracted by the first diffraction grating. According to this arrangement, when the wavelength of the laser beam is changed, the diffraction angle of the laser beam from the first diffraction grating is changed but this change does not cause substantial change in the diffraction angle of the second diffraction grating because the second diffraction grating diffracts the beam in such a direction as to cancel the above-mentioned change in the angle of diffraction of the laser beam from the first diffraction grating. In consequence, fluctuation of the diffraction angle of the laser beam irradiated by the second diffraction grating onto the recording surface of the optical recording disk is suppressed remarkably.
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