| 摘要 |
In a balanced optical receiver for heterodyne or homodyne reception, the input part contains two series-connected photodiodes, at whose connection point the difference between the two photocurrents is tapped. The advantage of the balanced receiver is that, in the amplified differential signal, the components of the composite signal comprising received light and local laser light are added to one another due to the 180@ phase shift, whereas the DC components of the photocurrents and unwanted AC components produced by the intensity noise of the local laser cancel each other out. This requires perfect balance in the optical paths and in the photodiode response, for which it is advisable to use avalanche photodiodes. For balancing purposes, it is proposed to generate a correction voltage from the DC component of the differential current signal which is added to one avalanche photodiode and is subtracted from the other avalanche photodiodes in order to produce an effective bias voltage. <IMAGE>
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