**1. Introduction**

Optical amplifiers are optical active components as a circuit enabling technology for optical communication networks. Together with telecommunication system and technology allowing the transmission of channels over the fiber, optical amplifiers have made it possible to transmit many data over distances from 100 km and up to transoceanic distances, providing the data capacity required for current and future communication networks. Optical amplifiers have important role in optical telecommunication and data information. They can be used as repeater circuit in long-distance optical fiber component and cables carrying the world's telecommunication links.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The main aim of this topic is to provide a description of optical amplifiers having a device that amplifies an optical signal, without the need to convert it to an electrical signal or source. This can be formed in visible or invisible electromagnetic spectral source such as light or a laser without an optical resonator, or one in which feedback from the cavity is suppressed. A fundamental optical communication link comprises a transmitter and receiver, with an optical fiber cable and connector which connect them. Even though signals propagating in fiber suffer far less energy in terms of absorption and other damped along the media, such conductor media still have a limit of about 140 km on the distance the signal wave can propagate before producing the disturbance like noise. Before going to the market, the optical amplifiers are necessary to regenerate the optical signals every 80–140 km [1] electronically in order to fulfill the transmission value over long distances. This process describes the receiving of the information signal, organizing and multiplying the amplification optically and electronically, and then retransmitting it over the next medium and segment of the circuit and link. It can be feasible if a single low optical signal is transmitted; it will travel fast and be unfeasible, transmitting in tens of high-capacity order of wavelength-division multiplexing (WDM) channel devices. This results in high-cost, power-hungry, and bulky regenerator port. Furthermore, the regeneration hardware and software depend upon bit-rate, protocol, channel numbers, and modulation which are set to each channel. Any upgrade to the link therefore will automatically require upgrades to the regenerator stations. On the other hand, an ideal amplifier is modeled and designed to amplify any input optical signal directly, no need to transform the signal first to an electronic one.

the effects that can limit the delivery and speed of data transmission. This effect is divided into linear effects and nonlinear effects. Linear effects include attenuation and dispersion, a distortion in the beam of light passing through the optical fiber core caused by different modes, wavelengths, and velocities, while nonlinear effects arise due to Kerr effect in the form of self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) and as the result of inelastic scattering including stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) [2]. These linear and nonlinear effects can damage information signals such as widespread light pulses, reduced bandwidth shortened, trans-

Optical Amplifiers for Next-Generation Telecommunication

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Optical amplifiers have several properties. First, it has a gain that the input optical signal is amplified and that is detected from the output port one. It is typically measured in the range of 5–35 dB. For instance if the gain is 10 dB, meaning the input signal is amplified by a factor of 10 subject to logarithm factor. It is also characterized by the supported input and output powers. Especially, the main specification of the amplifier is the maximum output power, which can be contributed and subjected to as saturated output power. There are two kinds of optical amplifiers. They are single and multichannel. The former is designed to amplify only one channel located within a specified band, such as the C-band (1528–1564 nm). This channel can usually deal with over a wide range of gains and require relatively low output power. In the latter channel, WDM amplifiers are designed to work out if any number of channels are input to the amplifier. The gain flatness is the properties of WDM amplifiers, the variation of the gain for different channels, as depicted in **Figure 2** (right side). When the gain is not flat, different WDM channels will have different gains, which can accumulate along a chain of amplifiers leading to a large mismatch between channels. To maintain flat gain, most low-end WDM amplifiers only support a single gain, or a relatively narrow gain range, supporting

**Figure 2.** Example input (green) and output (blue) spectrums of a single channel amplifier (left) and a WDM multichannel

mission distance, and limited bit-rate. All this is a communication disorder.

**2. Optical amplifier properties**

amplifier (right) [1].

There are different kinds of processes that can be applied to amplify electromagnetic signals corresponding to the major formation of amplifier optics. For doped fiber ones and bulk lasers, SOA, electron-hole interaction process and recombination will occur. For RA, its scattering of incoming electromagnetic signal with phonons in the lattice of the gain media will produce photons coherent with the incoming photons. Parameters of amplifiers use parametric amplification. **Figure 1** shows amplifier's gain medium causes amplification of incoming light. In semiconductor optical, the block diagram of an amplified signal was optically totally different from an electronic signal regeneration regime, in which channels are usually split, detected, amplified, cleaned electronically, retransmitted, and then recombined. This is a benefit of optical amplifier that can be used to all channels optically and transparently amplified together.

Optical transmission media greatly affect the performance of a communication system. Fiber optic is one of the transmission media that is capable of transmitting information with a large capacity, is high speed, and has low attenuation. Although optical fiber provides many advantages, there are also disadvantages that can disrupt the performance of the fiber optics,

**Figure 1.** An optical amplifier, all channels are optically, transparently amplified together.

the effects that can limit the delivery and speed of data transmission. This effect is divided into linear effects and nonlinear effects. Linear effects include attenuation and dispersion, a distortion in the beam of light passing through the optical fiber core caused by different modes, wavelengths, and velocities, while nonlinear effects arise due to Kerr effect in the form of self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) and as the result of inelastic scattering including stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) [2]. These linear and nonlinear effects can damage information signals such as widespread light pulses, reduced bandwidth shortened, transmission distance, and limited bit-rate. All this is a communication disorder.
