International Journal of Computer Applications (0975 – 8887) Volume 111 – No 8, February 2015 1 High Gain, Low NF EYDFA with Distributed Pumping Nupur Agarwal Research Scholar Department of Electronics & Communication Engineering Maulana Azad National Institute of Technology Bhopal, M.P. (India) Aditya Goel, Ph.D Professor Department of Electronics & Communication Engineering Maulana Azad National Institute of Technology Bhopal, M.P. (India) ABSTRACT Optical amplifiers are an indispensable part of today’s network and face increasingly stringent demands on their performance in terms of peak gain, noise figure, cost, compactness, etc with growing transmission rates, increasing link lengths, wavelength division multiplexing and the continual improvisation of technology. Erbium-Ytterbium co- doped fiber amplifier ( EYDFA ) an improvement of Erbium doped fiber amplifier (EDFA), helps overcome the limitation of increase in the concentration of excited erbium ions by countering the pairs quenching phenomenon. This paper investigates the role of optical pumping in dual stage single pass EYDFA and the strong dependence of gain on the pump power till a stage of saturation is reached is observed. Further, an amplifier with high gain of 40-46 dB at 1550nm with low noise figure is simulated for very short lengths of active fiber. General Terms Compact in-line amplifier, dual stage configuration, high gain, low noise figure, optical amplifier Keywords Distributed pumping, EYDFA 1. INTRODUCTION Consumer products like smartphones, tablets combined with multiple AirPlay devices are stimulating demand globally. Market research has accepted that these devices are further exposing existing bottlenecks in telecom networks. As a consequence there are further investments in fibre optic networks and fierce global competition on who delivers more, better, faster and cheaper. Thus, stringent demands are placed on the performance of these networks. Any incremental improvisation in technology helps in cost savings and performance improvement in a large scale. Optical amplifiers in particular erbium doped fiber amplifiers (EDFA) form an integral part of today’s optical network [1] as they are in general bit rate transparent and can amplify signals at different wavelengths simultaneously. The goal is to achieve maximum gain with acceptable noise figure thereby enabling high capacity repeaterless transmission [2-4]. The gain profile of an EDFA is a function of the Erbium concentration, length of the Erbium doped Fiber, Pump Power and Input Signal power amongst other variables [5,6]. EYDFA which is an advancement of EDFA, overcomes the limitation of increase in the concentration of excited erbium ions by countering the pairs quenching phenomenon [7] also shows similar correspondence. It is demonstrated here that optical pump power for an EYDFA is a variable which can influence the performance of an optical amplifier and lead to cost savings. 2. PRINCIPLE OF EYDFA A well known technique to minimize the effects of pair induced quenching is to co-dope fiber with Yb 3+ . sensitizer [8-9]. Ytterbium ions absorb most of the pump power, and subsequently transfer the absorbed energy to adjacent erbium ions through a cross relaxation mechanism. Figure 1: Energy Level for Er-Yb System The energy level for Er-Yb system is shown in Figure1. Depending on the pump wavelength, pump energy can be absorbed by both the Er ions in the 4 I 15/2 and by the Yb 3+ ions in the 2 F 7/2 ground levels. Ytterbium ions excited to the 2 F 5/2 level transfer their energy to neighboring Erbium ions in the 4 I 15/2 ground level, exciting them to the 4 I 11/2 pump level from where they rapidly relax to the metastable 4 I 13/2 level. Ytterbium ions absorb most of the pump power, and subsequently transfer the absorbed energy to adjacent erbium ions through a cross relaxation mechanism. Higher power levels can be achieved by increasing the available pump power as evident in the following simulations. Various configuration of EDFA/EYDFA [10-16] such as single stage, single stage double pass, conventional dual stage, dual stage with partial double pass, dual stage double pass, quadruple pass have been reported. Also, various combinations of hybrid amplifiers targeting higher broadband gain low noise figure are reported. Here this particular configuration leads to a gain of above 46 dbm at 1550 nm with noise figure in the range 3 to 4. The salient feature of the proposed setup is achieving high gain and low noise figure using smaller length of active fiber and a single pump laser i.e. a compact overall setup. For pumping, distributed pumping from single pump laser as reported in [17] has been employed. 3. SIMULATION SETUP The characteristics and design parameters for EDFA, the use of interstage elements, and various digital transmissions systems applications for multi-stage amplifiers have been reviewed [19]. The schematic layout of the proposed dual stage EYDFA is presented in Figure 2.