Fiber optic amplifier

Optical fiber transmission of information has played a key role in increasing the capability of communication system to transmit information. Fiber optic communication utilizes optical transmitters, optical receivers and optical fiber, among other components, to transmit light signals through the fiber. A fiber optic amplifier is an optical device for amplifying a plurality of channels of signals so as to compensate for their loss when they propagate through an optical transmission line in an optical communication system. In general, a fiber optic amplifier comprises an optical fiber for amplification, doped with a rare-earth element, and a pumping light supply system for supplying pumping light to the optical fiber for amplification. The pumping light supply system usually includes a semiconductor laser and an optical coupler for guiding the pumping light into the optical fiber for amplification. In fiber-optics communication systems in practice today, repeaters are inserted in the transmission line at regular intervals to compensate for attenuation of the optical signal due to loss in the optical fiber. In a repeater, an optical signal is converted into an electrical signal by a photodiode and amplified by an electronic amplifier, and then converted into an optical signal to be delivered into the fiber-optic transmission line again. Erbium-doped amplifiers are made by doping a segment of the fiber with erbium and then exciting the erbium atoms to a high energy level through the introduction of pumping light. The energy is transferred gradually to signal light passing through the fiber segment during excitation, resulting in an amplification of the signal light upon exit from the amplifier. Fiber optic amplifiers can amplify signal light including one or more wavelengths within a predetermined wavelength band without converting them into electricity.