What does RX optical power refer to?

• A. The transmitter optical power level.
• B. The light level at receiver measured in dBm; extremes cause errors.
• C. The loss in fiber due to attenuation.
• D. The noise figure of the receiver.

Answer: (B)

RX optical power is the light level arriving at the receiver input, measured in dBm. This power tells you what the receiver actually detects; it must be within the receiver’s usable range. If the RX power is too low, the signal-to-noise ratio degrades and errors increase; if it’s too high, the receiver can saturate or distort the signal. This is different from the transmitter optical power (light emitted by the transmitter) and from fiber attenuation (loss along the link), and it’s also not the receiver’s noise figure (which describes how much noise the receiver adds). In practice, staying within the specified RX power window ensures reliable decoding of the data.