Extinction Ratio and the Fiber Optic Transmission Networks

In the fiber optic communication network for example,FTTH, EPON, NBN, OTN and so on, the most important components are fiber length between transmitter and receiver point. So, to make, cheap and meaningful communication through optical fiber it must be required to calculate how and what amount of signal is transmitted with the given length of the fiber. Finally, it is said that the optical fiber network have several limitations like extension ratio. So, it is necessary to investigate its affect on the performance of the Optical Network. This research is based on simulation by OptiSystem 0.17 on the basis of Dense wavelength division multiplex (DWDM) technology, Erbium Doped Fiber Amplifier (EDFA), dispersion Compensating Fiber (DCF) and single mode fiber of length 50–100 km

optical fiber networks of long distance minimized in the C-band and L-band (Addanki, Amiri, & Yupapin, 2018;Gorshe, 2009). Also, EDFA can simultaneously amplify the optical signal. So, it is used with WDM technology.
Furthermore, by the advent of InGaAsP semiconductor laser and optical backward propagation detection technique (Mateo, Zhu, & Li, 2008; SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS-Transmission media and optical systems characteristics -Optical fibre cables, (2016); Liptai, Dolník, Pavlík, Zbojovský, & Špes, 2017), the fiber channel operated near 1,300-nm wavelength and fiber loss became 1 dB/km. After, the 20 years continuous effort of scientist, in the optical fiber communication, it is observed that BL product increased generation to generation and in the decades of 2000s we entered in the fourth generation communication system with the bit rate160Gbs and repeater's spacing 35,000 km and operating wavelength range 1.53-1.5 μm (Liu, 2019). Optical Fiber in fifth Generation -While WDM system greatly improved the transmission capacities of the fiber with the simultaneously operating higher wavelength range by the use of Raman amplification techniques. Thus we can say that in this generation the signal spectral efficiency is improved (Bosternák & Róka, 2018;Smiesko & Uramova, 2012). And to remove the drawbacks of the direct detection, the coherent fiber optic system is introduced to do the coherent detection or phase detection of an optical signal of transmitter. It means coherent detector can detect any information carried by the phase and frequency of the transmitted signal. Also, the development of digital signal processing for high speed allows us the implementation of phase locking, frequency synchronization and control over polarization in electronic domain that is with the help of coherent detection system and digital signal processing both amplitude and phase information detected (Badraoui, Berceli, & Singh, 2017). Furthermore, due to the coherent detection all the optical parameters like amplitude, phase, frequency and polarization are available in the electrical domain so, it is helpful to design the advanced modulator. It is also proved that the optical modulator with semiconductor laser increases not only the operational performance but the stability in the optical signal throughout the communication, with the application of compensation technique of nonlinearity, the optical spectrum becomes 10 THz and per channel capacity approaches to 64 Tbps by 2022 (Addanki, Amiri, & Yupapin, 2018; Liu, 2019).
To improve the power efficiency of the optical fiber communication system, minimize the major drawbacks of the fiber channel like linear and nonlinear impairments (Gordon & Mollenauer, 1990;Batagelj, Janyani, & Tomažič, 2014). Actually, in the fiber optic transmission system, signal power can be improved by highly sensitive optical receiver for a noise limited transmission that is power loss can be compensated by amplifier. But the ultimate demand of this information era, higher bandwidth with highest possible data speed is compensated only and only by improving the power efficiency and spectral efficiency of the system (Addanki, Amiri, & Yupapin, 2018). Linearity of fiber: Due to the linear impairment (Ryu, 1991) of the optic fiber, the fiber behaves as the linear medium at the smaller optical power of transmission. To remove this impairment, Generally, we consider one by one of their types, as (1) Attenuation-it decreases the strength of signal in the fiber due to scattering, absorption and physical bending. Experimentally, it is observed that the attenuation can be compensated by the amplifier. (2) Chromatic dispersion-if the propagation speeds of different wavelengths are different and intersymbol interference takes place, then it indicates that the existence of chromatic dispersion due to the pulse spreading. Since the greater bit rate propagation for the long distance becomes possible by the use of DCF (dispersion Compensating Fiber) like LiNbO3 fiber. (3) Polarization mode dispersion-It is really most dominant linear effect for limiting the channel capacity by pulse broadening of the output signal of the system. It can be reduced by deterministic

Research Article
Vol. 12 No.6 (2021), 2244-2252 differential group delay method and birefringence of the fiber. (4) Cross-talk-it is most common in the dense WDM system due to the decreasing channel spacing and increasing data. It can be reduced by the use of R-Z format or by filter cascading or double polarization method. Nonlinearity of Fiber: -It is observed that due to higher power or bit rate of transmission, the optical fiber behaves as nonlinear medium (Ryu, 1991;Chraplyvy, 1990;Lyubomirsky et al., 2003) and concerned defects influence the performance of the technology of fiber optic transmission. To reduce the effect of them, they are considered as (1). Scattering Based: -when optic signal propagates at high bit rate then having scattering of signal through fiber that affects the energy of the signal pulse. Like SBS, SRS and so on (2) Refractive Index Based: -Like SPM, XPM that leads to the deformation of signal pulse due to the change in refractive index of the fiber with the wavelength of the signal (Ryu, 1992). As the second order susceptibility does not exist in the silica glass due to symmetricity of its molecules, so the all-nonlinear effects like nonlinear polarization in the optical fiber can be determined by third order susceptibility. When signal power in the optical fiber fluctuates due to the addition of noise of the amplifier leads the phase fluctuation, which degrades the performance by the devaluation of OSN ratio. After all it is said that the fiber nonlinearities exist as the signal becomes strong so it dominantly limits the upper boundary of the signal power. As the performance of optical fiber network evaluated in terms of quality factor and bit error rate then the role extinction ratio cannot be neglected because the slight change in extinction ratio indirectly affects the constancy and the minimal value of BER.

Simulation
Now with the basic components like EDFA, DCF (Dispersion Fiber) the DWDM technology based optical network with single mode fiber (50-100 km) prepared for simulation as given in the Figure 1.

Figure 1. Design of four channel DWDM Network with different extinction ratio
On the basis of OptiSystem programing software this four-channel DWDM system with EDFA amplifier and dispersion compensator is designed to eliminate the nonlinearity due to XPM by changing the input Optical Power density in the adjacent channels. In which EDFA output power is set at 10 dB and Optical Fiber behind the amplifier is of length 50-100 km.    Eye Diagram Analysis: -On the basis of Figure 4, It is observed that by increasing the extinction ratio and asymmetrical distribution of in input powers in this DWDM network, bit error rate becomes smaller with higher quality factor which is shown by the maximal eye opening in Figure 4. Whereas __________________________________________________________________________________ 2249 the distortion in the upper part of the eye pattern shows that high extinction ratio gives negative effect directly and indirectly on the components of the Networks.
In this simulation, all the parameters are kept constant with Low Extinction Ratio Also, it is crystal clear information that the highest possible quality factor attended at higher power of Extinction Ratio and vice-versa. At last, but not least, the small change in Extinction Ratio shows larger difference in the value of power required to make stable and lower bit error rate.

Conclusion:
The main aim of this research is to describe the effect of extinction ratio on the Optical Fiber network for the particular fiber length and this simulation proved that in the Optical Fiber, the highest quality factor attended for the higher value of extinction ratio as per the Tables 3 & 4. Also, each of the fiber optic network must have the specific range of ER that gives the better performance. Furthermore, it is required that to investigate and differentiate the direct and indirect effect of ER on the transmission of signal through the fiber network.