Lasers can be classified by pumping method, gain medium, operating method, output power, and output wavelength.
Fiber Optical Amplifier is a kind of optical amplifier using optical fiber as gain medium. Typically, the gain medium is fiber doped with rare earth ions, such as erbium (EDFA, Erbium-Doped Fiber Amplifier), neodymium, ytterbium (YDFA), praseodymium and thulium. These active dopants are pumped (provided with energy) by light from a laser, such as a fiber-coupled diode laser; in most cases, the pump light and the amplified signal light travel simultaneously in the fiber core.
Wavelength division multiplexing refers to a technology in which signals of different wavelengths are transmitted together and separated again. At most, it is used in optical fiber communication to transmit data in multiple channels with slightly different wavelengths. Using this method can greatly improve the transmission capacity of the optical fiber link, and the use efficiency can be improved by combining active devices such as optical fiber amplifiers. In addition to applications in telecommunications, wavelength division multiplexing can also be applied to the case where a single fiber controls multiple fiber optic sensors.
Ultrafast amplifiers are optical amplifiers used to amplify ultrashort pulses. Some ultrafast amplifiers are used to amplify high repetition rate pulse trains to get very high average power while the pulse energy is still at moderate levels, in other cases lower repetition rate pulses get more gain and get very high pulses energy and relatively large peak power. When these intense pulses are focused on some targets, very high light intensities are obtained, sometimes even greater than 1016 W/cm2.
Definition: The pump power when the laser oscillation threshold is reached. The pumping threshold power of the laser refers to the pumping power when the laser threshold is satisfied. At this time, the loss in the laser resonator is equal to the small-signal gain. Similar threshold powers exist in other light sources, such as Raman lasers and optical parametric oscillators.
Photodiode with internal signal amplification by avalanche process