An optical receiver is an electronic device that detects and converts optical signals into electrical signals. In this comprehensive guide, we will explore the world of optical receivers, their significance in optical communications, and the key. In an optical transmission system, one essential parameter in determining the system power budget is the optical receiver sensitivity, which is defined as the minimum average optical power for a given bit error rate (BER). The average optical power corresponding to a BER of 10 -9 is a measure of receiver sensitivity.