An active device is a device that requires a source of energy for its operation. Active device has an output that is a function of present and past input signals. Examples of active device include controlled power supplies, transistors, LEDs, amplifiers, and transmitters. Commonly used in fiber optics to refer to the transmitter/transceiver and/or detector of the optical network, these devices can be known as either electro-optical or opto-electrical devices and consist of laser or LED diode transmitters, amplifiers, APD (avalanche photodiode) or PIN (positive intrinsic negative) diode detectors. These devices are responsible for converting both analog and digital signals to and from optical pulses transported over the optical fiber network.