| 摘要 |
<p>An analogue signal is applied to a transformer (3) with a centre tapped secondary winding. The positive and negative half waves pass through decoupling capacitors (4,5) to the bases of transistors with LED's (1,2) in their collector circuits. The LED's radiate light along separate fibres (6,7) in an optical monomode monofibre cable. At the receiving end of the cable the signals are received by avalanche photodiodes powered by identical and constant polarising currents. The detected signals are applied to a centre tapped primary winding on a transformer of which second drives an amplifier with a predetermined gain to provide the output signal. This signal is symmetrical and independent of optical losses on the two channels. The reduction in diode polarising current reduces transmitted noise of the Schottky type, the principle noise source in such an optical communication system.</p> |
