| 摘要 |
PURPOSE:To reduce both quantum noise being a problem with a large feedback luminous amount and modal contention noise appearing when a feedback light quantity is small by providing an application means for applying a deep pulse being a threshold current or below to a semiconductor laser decreasing the reflectance of the irradiated end face. CONSTITUTION:An AC generator 8 is connected to the semiconductor laser 1 via a capacitor, a photodetection diode 9 is connected to a drive circuit of the semiconductor laser 1 and also connected to a constant output circuit via a low-pass filter 10. Thus, a DC curren is applied from the constant output circuit 11 to the semiconductor laser 1 in response to the signal from the photodetection diode 9, an AC current from the AC generator 8 is superimposed thereon to drive the semiconductor laser 1. Since large feedback amount to the laser means that the luminous amount for reading a signal is decreased, the maximum feedback within the permissible range of the system is obtained and a 1/4 wavelength plate 5 is adjusted to obtain this value. |
