International Journal of Applied Engineering Research, ISSN 0973-4562 Vol.6 N0.18(2011),Pg 2983-88 © Research India Publication; http://www.ripublication.com/ijaer.htm Gain Non-Uniformity Correction of EDFA based WDM Systems Zahid Gulzar Khaki 1 , Gausia Qazi 2 , and Arshid Ahmad 3 Electronics & Communication Engineering Department, National Institute of Technology Srinagar (J&K) INDIA 190006 1 xahidkhaki@gmail.com 2 gausia.qazi@yahoo.com 3 arshid.sk@gmail.com Abstract—The invention of EDFA in late 1980s was one of the major events in the history of optical communication. It provided new life to the optical fiber transmission window centered at 1.55 μm and the consequent research into technologies that allow high bit-rate transmission over long distances. EDFA have a high gain, operating at low pump power and their performances are better in comparison with other similar amplifiers and optical devices. Also, the EDFA have a large bandwidth, a low noise figure and polarization insensitivity. However, in case of EDFA based WDM systems a serious problem of un-flattened gain spectrum is observed. This problem can be rectified using several methods. The methods like filter optimization, controlling the doped fiber length and pump power and an all-optical feedback loop in inline erbium- doped fiber amplifiers (EDFA's) are analyzed. Here the implementations for EDFA based WDM Transmission system using various topologies have been proposed and then multiple simulations were carried out to obtain proper Gain Flattening in the Transmission System. In addition to this a detailed analysis has been carried out to compare the Gain Flattening capabilities of various implemented topologies. The results obtained were in well accordance with the practical results. Keywords— EDFA, DWDM, WDM, WDMA Gain I INTRODUCTION Erbium-Doped Fiber Amplifier (EDFA): A device that boosts the signal in an optical fiber introduced in the late 1980s, the EDFA was the first successful optical amplifier [1, 2]. It was a major factor in the rapid development of fiber-optic networks in the 1990s, because it extended the distance between costly regenerators [3, 4]. This EDFA is designed for the Dense Wavelength Division Multiplexing (DWDM) applications. The device features excellent gain flatness but is not constant throughout the device operation, low noise figure and wide operating wavelength range. It also has good network control interface. II SETUP AND OPERATION PRINCIPLE OF EDFA Fig1 EDFA Setup A typical setup of a simple erbium-doped fiber amplifier (EDFA) is shown in Figure 4.1. Its core is the erbium-doped optical fiber, which is typically a single-mode fiber. In the shown case, the active fiber is “pumped” with light from two laser diodes (bidirectional pumping), although unidirectional pumping in the forward or backward direction (co-directional and counter-directional pumping) is also very common [5]. The pump light, which most often has a wavelength around 980 nm and sometimes around 1450 nm, excites the erbium ions (Er3+) into the 4I13/2 state (in the case of 980-nm pumping via 4I11/2), from where they can amplify light in the 1.5-μm wavelength region via stimulated emission back to the ground-state manifold 4I15/2. The setup shown also contains two “pig-tailed” (fiber-coupled) optical isolators. The isolator at the input prevents light originating from amplified spontaneous emission from disturbing any previous stages, whereas that at the output suppresses lasing (or possibly even destruction) if output light is reflected back to the amplifier [6]. Without isolators, fiber amplifiers can be sensitive to back reflections. Very high signal gains, as used, e.g., for the amplification of ultra short pulses to high energies, are usually realized with amplifier chains, consisting of several amplifier stages with additional optical elements (e.g. isolators, filters, or modulators) in between [7].