| 摘要 |
PURPOSE:To obtain a balanced light receiving circuit with high sensitivity over a wide range by equally forming three impedances to a coupler, the characteristic impedance to two transmission lines and the input impedance of a preamplifier. CONSTITUTION:The input impedances from ports 6-1, 6-2 and 6-3 of a coupler 6, the characteristic impedances of transmission lines 8-1 and 8-2 and the input impedance of a preamplifier 3 are equally formed. As a result, in the ports 6-1 and 6-3, the frequency band of a signal component from a photodetector 1-1 is made equal. The signal component from a photodetector 1-2 is made similar as well and the phase is staggered only by. Accordingly, when reversely biasing the photodetectors 1-1 and 1-2, the signal component is added and an amplitude is increased at the port 6-3. Thus, without degrading the frequency band, the balanced light receiving circuit can be obtained with the high sensitivity over the wide band. |
