| 摘要 |
PURPOSE:To preferably maintain the on to off ratio of the laser driving system even if a laser is deteriorated by superposing a pilot signal to a pulse signal and detecting the output to thereby control the pilot signal together with the pulse signal in response to the value of the pilot signal. CONSTITUTION:A pilot signal f0 as a sinusoidal wave signal of a frequency having twice the frequency of the bit rate of the pulse signal is generated from a pilot signal generator 10. Then, the pilot signal f0 is superposed to the pulse signal at a mixer 9, is then amplified by an amplifier 11 to generate a drive signal F so as to drive the semiconductor laser 2 under control. Subsequently, the part of the light output is branched by a divider 3, and is received by a photodetector 4 which detects the component of the pilot signal f0. The signal is thus amplified by the amplifier 17, and is compared with the output from a signal pulse space factor detector 12. On the other hand, when the semiconductor laser 2 is deteriorated so that the gradient of the output characteristic curve becomes low, the pilot signal from the photodetector 4 also becomes low. Then, the gain of the variable gain amplifier 11 is increased by the output from an operational amplifier 13 to drive the laser 2 so as to maintain the on to off ratio constantly. |
