| 摘要 |
PURPOSE:To always minimize distortion in an output of a laser diode by applying feedback to a distortion correction circuit of the laser diode. CONSTITUTION:The transmitter is provided with an automatic power control circuit 6 dividing an output of a PIN diode 5 into two, using one output as an input signal and making output power of a laser diode 4 constant, a band pass filter(BPF) 7 receiving the other output of a PIN diode 5 and extracting a frequency component of an integral number (2 or over) of a frequency of a pilot signal, a detection circuit 8 detecting the frequency component, and a loop 12 through which an output of the detection circuit is fed back to a distortion correction circuit 2. In this case, an output of the band pass filter 7 represents nonlinear distortion itself of the laser diode 4 and the nonlinear distortion of the laser diode 4 is minimized when the output of the band pass filter is small. Since the linear distortion of the laser diode 4 is corrected by controlling the distortion correction circuit 2 so as to minimize the output of the detection circuit 8, the deterioration in the characteristic is prevented. |
