WHY AMPLIFIERS ???o To amplify an optical signal with a conventional repeater works well for moderate-speed single wavelength operation.o Repeaters are expensive for high-speed multiple wavelength systems.o Thus optical amplifiers have been developed.o Optical amplifiers boost up the power level of multiple light wave signals.
ERBIUM-DOPED FIBER AMPLIFIERSo Active medium in an optical fiber amplifier consist 10 to 30 m length of optical fiber that has been lightly doped with a rare-earth element such as erbium(Er), thulium(Tm).o Fiber material can be silica or a tellurite glass.o silica doped with erbium is good for long telecommunication.o EDFA operates in the spectral band of 1530 to 1560 nm region that is c band or conventional band.
o Amplification mechanism:- a. Optical amplifier uses optical pumping. b. Pumping gives energy to electrons to reach the excited state. c. After reaching its excited state, the electron must release some energy and drop to the lower level. d. Here a signal photon can then trigger the excited electron into stimulated emission. And electron releases its remaining energy in the form of new photon.
ENERGY LEVEL DIAGRAM AND TRANSITION PROCESS OF Er3+ IONS IN SILICA
o EDFAs include the ability:- a. To pump the devices at several different wavelengths. b. Low coupling loss to the compatible-sized fiber transmission medium. c. Highly transparent to signal format and bit rate. d. Immune from interference effects( crosstalk and intermodulation distortion) when wavelength channels are injected simultaneously into amplifier.
GENERAL APPLICATIONS OF OPTICAL AMPLIFIERSo In line optical amplifiers:- a. In single mode link, the fiber dispersion may be small so that repeater can be eliminated. b. Instead of regeneration of signal, simple amplification can be done. c. It is used to increase the distance between regenerative repeaters.
o Preamplifier:- • Optical amplifier being used as a front-end preamplifier for an optical receiver. • A weak optical signal is amplified before photo-detection so that signal to noise ratio degradation due to noise can be suppressed in the receiver. • It provides a larger gain factor and bandwidth.o Power amplifier:- a. The device which can be placed after the transmitter to boost the transmitted power is called as power amplifier. b. This provides increase in distance depending on the amplifier gain and fiber loss.