How to check the sensitivity of an optical module

Unstressed receiver sensitivity testing is performed by simply connecting the transmitter to the receiver via a variable optical attenuator. BER values are recorded against different receiver power values and are finally plotted against each other. In optical communication systems, sensitivity is a measure of how weak an input signal can get before the bit-error ratio (BER) exceeds some specified number. The standards body governing the application sets this specified BER. [pdf]