| 摘要 |
PURPOSE:To enable a semiconductor laser to oscillate in a plurality of wavelengths and to realize the reproduction of a high S/N, ratio a reduction in the size of the device and the speed up of the operation by a method wherein the laser; wherein the oscillation threshold values of wavelengths to be determined by a plurality of quantum well layers. which constitute an active layer and whole thicknesses are different from one another, are set at the same value; is used as a light source and this laser and an optical disc are arranged so as to constitute a resonator. CONSTITUTION:First, four layers of quantum well layers of a thickness of 50Angstrom are provided for one layer of a quantum well layer of a thickness of 80Angstrom , for example, whereby the gains of oscillation wavelengths of 830nm and 800nm, for example, can be roughly made equal. That is, by making a discrimination between the threshold gains of the oscillation wavelengths of 830nm and 800nm by an external structure and the like, a wavelength is selected and a laser can be actuated. On the other hand, as the loss of a resonator, which is constituted by the semiconductor laser 11 and an optical disc 14, is reduced by a wavelength having a high reflectivity, the laser oscillates in the oscillation wavelength of 800nm at a signal '0', oscillates in the oscillation wavelength of 830nm at a signal '1' and an oscillation light of the oscillation wavelengths of 800nm and 830nm is outputted from a rear 13 of the laser. The oscillation light is separated into a light of a wavelength of 800nm and a light of wavelength of 830nm by a half-mirror 15 and filters 16 and 17 and the lights are respectively detected by photodetectors 18 and 19. |
