Summary Note OPTICAL FIBER AMPLIFIRE FOR TELECOMMUNICATION SYSTEMS

#communications #y2021 #Electronics
Based on : Optical Fiber Amplifiers for Telecommunication Systems - Mareello Potenza, CSELT - Centro Studi E Laboratori Telecomunieazioni
Optical fiber amplifiers for telecommunication systems | IEEE Journals & Magazine | IEEE Xplore

Losses in Fiber Optics : The fiber optics uses near infrared signal to transmit the data. Transmission trough fiber optics has two main limitations, Attenuation: Due to partial transparency if glass. Dispersion: Causes distortion and broadening of the modulated pulse travelling trough the fiber. It is more difficult to indicate typical dispersion limit since it not depend only depression coefficients. But also with operating wave length, bit rate, optical source, etc..

Transmission Windows: Optical fiber transmission take place on specificd spectu=ral regoins are reffred as transmission windows. There are four transmission windows that currently using.2nd and 3rd transmission windows are use now days in fiber communication.

1st Window: using the wavelength around 850 nm =. Because of the high intrinsic fiber losses, this transmission window does not use in telecommunications except for a few limited applications such as LAN and computer interconnections. Source and detectors are made from low cost Galliumarsernide and silicon based technologies, Transmission distances are low.

 4th  Window: Using spectral range 2500 -2600nm. It has been anticipated in non-silicon fibers design specially for mid-infared transmission. But it has not been explored so far.

2nd Window: uses spectral range 1240 to 1340 nm. It has local minimum of attenuation as 0.35 dB/km at 1300 nm and localization of zero dispersion wavelength around 1310nm. Most installed systems operates under the that window and referred as 1st generation commercial products. They use in access networks such as FTTH/FTTB and narrowband services.

3rd Window:Uses spectural range from 1500nm to 1650nm.; Absoulte attenuation minimum of silica fiber 0.2 dB/km at 1550nm. Therefore this window most suitable for long distance transmission.

Optical Repeaters: Due to the attenuation and dispression, it need to install a suitable repeaters for regenerating, reshaping and retiming the signal along an optical link.(3R repeaters). They make neccary corrections at electroinc level.

Optical Amplifires: Optical amplification can  overcome attenuation limit, bit dispresiom constraints are still limit the maximum transmission span. Practical substitution of 3R repeaters with optical amplifres also increase the optical trasperency of the network. The operation of amplifier can be shown as this.

The amplifires can said as a laser without optical feedback. The active medium gained up the optical signal by obserbing external energy from pump. According to the technology, Optical amplifore can dicied into 3 categorize, known as active fiber, Semiconductoe and Raman fiber amplifiers.

The amplifires can said as a laser without optical feedback. The active medium gained up the optical signal by obserbing external energy from pump. According to the technology, Optical amplifore can dicied into 3 categorize, known as active fiber, Semiconductoe and Raman fiber amplifiers.

Optical Fiber Amplifires(OFAs)

Equipied with 2 optical isolators for eliminate back and reflections. Use erbium-doped active fiber. In this paper discuss about the OFA with 2 categories, Er3 dopped sillicom fiber amplifier, Non silican fiber amlifire. Also discuss about Raman Fiber amplifier.

Er3 dopped Sillicon Fiber

Specs: Gain bandwidth: 1520nm to 1570 nm (3rd window) ,small signal gain : 30+40dB for pump power 50-100 mW.

Output power from 13 dB to 20 dB.

Noises – SNR <3dB

Use 980-1480 Laser pump

Structure: some times use two active fiber in series for high gain

Uses: Losses of G.652 fibers in access networks. Compensate for propagational losses on long distance, high-bit rate networks, limit dispersion on a G.652 fiber multichannel amplification and for analig amplification such as cable TV.

Benefites: EDFAs show a flatter portion of the gain from 1540nm to 1565 nm.

Optimizing techniques of EDFA:
There are two adoption methods a gain and spectral control.Gain control techniqes

• Gain control by means of optoelectronic feedback loop
• All-optical control by means of laser emission
• Control through the use of a twincore active fiber

Spectrual Control Techniques:

• Optical filtering with photowritten grating filters
• Optical filtering with acousto-optic tunable filters
• Gain equalization using Mach-Zehnder interferometers
• Host glass selection

Non silica Fiber Amplification
Fluorizironate active fiber doped with suitable rare-earth element because to frabricate OFAs for operation acress the whole spectrum of fiber transmission.
For the 1st window: Thulim and Erbium in fluorozxonte fiber
For 2nd window: Prasedymium in cadmium fluoride glasses (Problm:Glass purity and non stability)
Neodymum (Problem: Serious harzard, low efficiency)

For 3rd window:

• Praseodymium doped fluoride fiber amplifore : Low efficiency, very small core size, High NA. Economic in nature.
• Master oscillator power amplifier
  Solve the main existence problems of PDFEA

Raman Fiber Amplifire

Raman effect is a kind of nonlinear interaction which takes place at high powers in an optical meduium. The major drawback is complicatioed design and the unavailability of the forect power sources for ramman generation because remarkable powers are required to attain the non linear threshold. The main advantage is raman amplification an obtained to second, thied and ecen beyond windows. So some countries are using supervisory techniques for telecommunication networks at wavelength higher than from 16000nm in order to not onterfare with service channels.