HFAN-03.0.0: Accurately Estimating Optical Receiver Sensitivity


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. 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 the foundation for determining a receiver's sensitivity. In the design of an optical receiver, such as a small form factor optical transceiver module, it is vital that the module be capable of converting and shaping the optical signal while meeting or surpassing the maximum BER. Ultimately, the influence of noise on the signal will determine the sensitivity of the system. The portion of the receiver that contributes the most noise 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 of thumb\" to predict performance and select components. This discussion presents a reliable method for estimating the receiver's sensitivity. Read full article.