Optical amplifier "erbium-doped waveguide amplifier" ("EDWA") is an optical amplifier that uses a waveguide to boost an optical signal. Amplification is achieved by stimulated emission of photons from dopant ions in the doped fiber. The pump laser excites ions into a higher energy from where they can decay via stimulated emission of a photon at the signal wavelength back to a lower energy level. The excited ions can also decay spontaneously (spontaneous emission) or even through nonradiative processes involving interactions with phonons of the glass matrix. These last two decay mechanisms compete with stimulated emission reducing the efficiency of light amplification. The
Sound amplification by stimulated emission of radiation one quantum well to another neighbouring well it produces a phonon. External energy pumping (e.g. a light beam or voltage) can help to the excitation of an electron. Relaxation of an electron from one of the upper states may occur by emission of either a photon or a phonon. This is determined by the density of states of phonons and photons. Density of states is the number of states per volume unit in an interval of energy (E, E+dE) that are available to be occupied by electrons. Both phonons and photons are bosons and thus, they obey Bose–Einstein statistics. This