| 摘要 |
PURPOSE:To make a mean output and a signal output constant, and to prevent the lowering of S/N by controlling bias currents for a semiconductor laser and the gain of a mixed output signal of a signal to be transmitted and a pilot signal. CONSTITUTION:Signals transmitted from an input terminal 1 for signals to be transmitted from an output stabilizing system and pilot signals at predetermined frequency and a prescribed level are mixed by a mixer 2, and amplified by a gain variable amplifier 3. The mixed outputs are converted into current signals by a LD driving circuit 4, and optical outputs corresponding to input signals are generated from a semiconductor laser (LD) 11. The optical outputs are received by a light-receiving element 10, and amplified to fixed values by a DC amplifier 9, and a mean value is detected by a mean-value detecting circuit 13. The detected mean value and the reference voltage of a reference-voltage power supply 16 are compared by a comparison amplifier 12, and bias currents are fed to the LD11 from an LD bias-current supply circuit 14 in response to the results of the comparison. Pilot signals are extracted by a BPF8 from output signals from the element 10, a peak value is detected by a peak-value detecting circuit 7, and the levels of the pilot signals are inhibited by the amplifier 3. |
