) An erbium-doped fiber amplifier (EDFA) is a device that amplifies an optical fiber signal. It is used in the telecommunications field and in various types of research fields, In general, EDFA works on the principle of stimulating the emission of photons. With EDFA, an erbium-doped optical fiber at the core is pumped with light from laser diodes. This type of setup in telecom systems can help with fiber communications, for example, boosting the power of a data transmitter. An EDFA may also be used to maintain long spans of a passive fiber network and may also be used for some types of equipment testing. Pump lasers, known as pumping bands, insert dopants into the silica fiber, resulting in a gain, or amplification. EDFA amplification occurs as the pump laser excites the erbium ions, which then reach a higher energy level. Photons are emitted as erbium ion levels decrease, or decay. This decaying process creates an interaction between the phonons and the glass matrix, which are vibrating atomic elastic structures.
6) Dispersion in optical fibers In an optical medium, such as fiber, there are three types of dispersion, chromatic, modal, andmaterial Chromátic Dispersion Chromatic dispersion results from the spectral width of the emitter. The spectral width detemines the number of different wavelengths that are emitted from the LED or laser. The smaller the spectral width, the fewer the number of wavelengths that are emitted Modal Dis Modal dispersion deals with the path (mode) of each light ray. As mentioned above, most transmitters emit many different travel straight through the center of the fiber (axial mode) while others will repeatedly bounce off the cladding/core boundary to zigzag their way along the waveguide persion of modes. Some these rays Iaterial Dispersion Material dispersion is caused by the wavelength dependence of the refractive index on the fiber core material, while the waveguide dispersion occurs due to dependence of the mode propagation constant on the fiber parameters (core radius, and difference between refractive indexes in fiber core and fiber cladding) and signal wavelength.