| 摘要 |
PURPOSE:To improve the reception sensitivity of a light receiver by controlling signal amplitude currents which are applied to a luminous element by the output of an extraction circuit so as to keep the extinction ratio of a light signal outputted by the said luminous element constant. CONSTITUTION:The light output of an LD is partially input into a PD for monitor, and light output level signals outputted from an amplifier IC 5 are input into a pair of discrimination circuits IC 2 and IC 3 which are supplied with standard levels Ref.1 and Ref.2. The discrimination circuits IC 2 and IC 3 output rectangular waves shown by Fig.A-2, corresponding to each threshold. The shapes of these two output waves are taken for exclusive logical sum in an IC 6 and becomes the wave shapes shown by Fig.A-3. And these signal wave shapes are converted into direct currents shown by Fig.A-4 in an integration circuit C. If differential efficiency deteriorates and extinction ratio lowers, the peak level of light output signals lowers, and also the bottom level rises. And the voltage output of an IC 4 integrated changes as shown by Fig.B-4, so the base currents of a transistor Q3 rises, and the currents flowing in the transistor Q3 are made to increase, and the extinction ratio is improved corresponding to the characteristic fluctuation of a laser diode. |
