| 摘要 |
PURPOSE:To obtain a small and sufficient signal-to-noise ratio by using a semiconductor laser having characteristics in which an optical output discontinuously changes with a threshold current, and the threshold current changes according to a coupling quantity with reflection returning light from the outside. CONSTITUTION:The semiconductor laser having the characteristics, in which the optical output discontinuously changes by a certain applied current and the threshold current to be the applied current changes according to the coupling quantity with the reflection returning light from the outside, is used. That is, the applied current-optical output characteristics of the semiconductor laser change according to the coupling quantity with the reflection returning light, and the optical output discontinuously changes at the threshold current. By detecting the change at the optical output of the semiconductor laser, and reproducing information recorded on an optical recording medium, the fluctuation of the optical output of the semiconductor laser becomes larger as the discontinuous quantity of the optical output at the threshold current becomes larger. Thus, the sufficient signal-to-noise ratio can be obtained. In addition, the above process can be executed without damaging an advantage that the size of the optical pickup device is small. |
