Optical Fiber Amplifier

The first optical fiber amplifier, called an erbium-doped fiber amplifier (EDFA), was invented in the late 1980s. An optical fiber amplifier consists of a low single mode fiber made of silica glass. A coupling pump light generates length gain at both fiber ends or in between locations.

Optical fiber amplifiers are categorized, based upon different physical mechanisms, as follows:

• Doped fiber amplifiers (DFA): Use a doped optical fiber medium for boosting signals in a similar manner to fiber lasers. The signal requiring amplification, along with a pump laser, is multiplexed in a doped fiber medium and intersects with doping ions. Amplified spontaneous emission is the major reason behind the DFA noise. An ideal noise level for DFA is around 3 decibels. Practically, the noise figure is calculated at around 6 to 8 decibels.
• Semiconductor optical amplifiers: Use semiconductors to produce the gain medium in the laser. The analogous structure is made of laser diodes. The recent design of semiconductor optical amplifiers has added antireflective coatings and window regions to minimize the end face reflection.
• Raman amplifiers: Employ Raman amplification techniques to boost optical signals. The two types of Raman amplifiers are distributed, where the transmission fiber is used by multiplexing the pump wavelength along with the signal wavelength as the gain medium, and lumped, where short length and dedicated fibers are used for amplification. Nonlinear fiber is used to increase the intersection between the pump wavelength and the signal to reduce the fiber to the required length.
• Optical parametric amplifiers: Permit the amplification of weak signal impulses to a nonlinear optic medium. They use non-collinear interaction geometry for broader bandwidth amplifications.