Transmitter (Tx) output is characterized by average power (Pavg), extinction ratio (ER), and optical modulation amplitude (OMA). Pavg: Average of max and min signal powers. The total noise is a stochastic process composed of both additive noise components and multiplicative (nonadditive) noise. cal source by varying the current through the source. An optical source converts el ctrical energy (current) into optical energy (light). We'll cover everything from physical form factors to spectral characteristics, modulation formats. Optical modules are crucial for today's communication systems as they convert electrical signals into light signals for rapid data transfer.