HFAN-03.0.0: Accurately Estimating Optical Receiver Sensitivity

Abstract: In optical communication systems, sensitivity is a measure of how weak an input signal can get beforethe bit-error ratio (BER) exceeds some specified number. The standards body governing the applicationsets this specified BER. For example, SONET specifies that the BER must be 10 -10 or better.Gigabit Ethernet and Fibre Channel specifications require a BER of 10 -12 or better. This BER is thefoundation for determining a receiver's sensitivity. In the design of an optical receiver, such as a smallform factor optical transceiver module, it is vital that the module be capable of converting and shaping theoptical signal while meeting or surpassing the maximum BER. Ultimately, the influence of noise on thesignal will determine the sensitivity of the system. The portion of the receiver that contributes the mostnoise is the optical-to-electrical conversion provided by the photodetector and the transimpedance amplifier (TIA). More often than not, designers will use a combination of simple estimation and \"rules ofthumb\" to predict performance and select components. This discussion presents a reliable method forestimating the receiver's sensitivity.