An optical preamplifier is positioned just before the detector in a fiber-optic communication system to boost a weak incoming light signal. Among the various types of amplifiers, optical Booster Amplifier (BA), optical Line Amplifier (LA), and optical Pre-amplifier (PA) are each with unique. Booster (power) amplifiers: Boost power into transmission fiber, low NF, high Psat. In-line amplifiers: Periodically amplify signal due to fiber attenuation, high G, high Psat. An illustration of the effective gainis given below. Note the presence of a gain peak around 1530nm and a semi-flat gain. An optical amplifier is a device which receives some input signal light and generates an output signal with higher optical power. Typically, inputs and outputs are laser beams (very rarely other types of light beams), either propagating as Gaussian beams in free space or in a fiber.
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