EDFA is defined as an optical amplifier that doped by Er3+ ions and the gain is from stimulated emission process. Doped optical fiber Erbium is a process fouling optical fiber from the pure atoms of erbium so that the material result is called intrinsic material. The intrinsic material is a material that is not pure because it has been inserted by atoms of other elements. This process is called doping or impurity.
The fouling process is described as follows. Si atoms have four valence electrons in the outer shells. Er atoms are trivalent atom that have three electrons in its outer shell. If the Si atoms inserted by Er which serves as an acceptor then each atom will only form three covalent bonds with three valence electrons from the closest intrinsic Si atoms. Fourth nearest Si valence electrons of atoms with trivalent atom does not form a covalent bond.
Erbium is composed of atoms acceptor that will cause a hole in the Si that serves as majority carriers. Thus, there are only seven fouling valence electrons in each atom of trivalent valence electrons.
The light source that activates Erbium Dopped Fiber produce optical strengthening and pumping source is a semiconductor laser diode with a wavelength of 820 nm, 980 nm, and 1480 nm.
A coupling device designed to pass the energy of the optical wavelength that will be strengthened by pumping wavelength from the pumping source.
Used to prevent from the reflection of optical signals.
d. ErbiumDopped Fiber (EDF).
An active EDF is a major components where the optical signal gained. The structure of EDF is same as ordinary optical fiber, but the fiber core is doped an additional substance like erbium ions (Er3 +), called dopped substances. The dopped substances derived from the rare-earth elements or lanthanide elements.
The principle used by EDFA is using laser pump, the laser will pumped to the Er3+ dopped fiber optic and charges on the EDF will have a displacement of lower energy bands to higher energy band. The Optical signals passing through the Er3 + doped optical fiber with its photon energy will serve as a stimulus so that the charges on the EDF will release their energy and produce coherent emission resulting in strengthening optical signal.
Characteristic of EDFA
According to the type of optical signal amplified by EDFA, the amplifying characteristic is divided by 2 type such as Small Signal Gain and Large Signal Gain. The Small Signal Gain is suitable as repeater, while The Large Signal Gain will boost the power significantly.
The simpler method of erbium doped fiber can be characterized by using amplifier equation in terms of the erbium absorption coefficient α(λ), gain coefficient g*(γ), a fiber saturation parameter ζ and excess loss in the fiber from scattering and impurity absorption l(λ).
These easily measured parameters allow the fiber performance evaluation in 980 nm or 1480 nm pumped optical amplifiers. Conventional fiber measurement techniques are used to obtain these parameters, from which the amplifier performance can be calculated.
Saleh –Jopson Model
This model developed for estimation of the pump and signal power along the length of the EDF fiber. The Saleh-Jopson model valid for amplifiers with gain less than 20 dB, and gain saturation by ASE can be neglected.
This model compute the gain and noise figure at other wavelengths from a computation of the average inversion from a measured reference spectrum and cross section ratio.
Higher Erbium Concentration Model
The higher +3rEion concentration model require additional modeling terms which account for concentration quenching or ion-ion interaction and ESA.
The concentration of +3rEion increase in fiber leads to undesirable effect like cooperative up-conversion and pair induced quenching. The ion- ion interaction effects limits the concentration of erbium ions in silica matrix.
Signal or pump excited state absorption is possible in EDF due to presence of other energy levels in erbium energy levels. These other energy levels in erbium can absorb signal or pump photon to higher energy level. This effect can be depletes the population inversion and also gain.