Low bit error rate of optical receiver

Receive sensitivity defines the minimum optical power required to maintain an acceptable bit error rate (BER ≤ 1E-12) at specific data rates. What Is BER? The bit error rate (BER) measures the data transmission precision within. 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). In essence, it measures how well a receiver can detect weak optical signals. For example, SONET specifies that the BER must be 10 -10 or better. [pdf]