DESIGN AND CHARACTERIZATION OF HIGH PERFORMANCE C AND L BAND ERBIUM DOPED FIBER AMPLIFIERS (C,L-EDFAs) Ahmet Altuncu Arif Başgümüş Burçin Uzunca Ekim Haznedaroğlu e-mail: altuncu@dumlupinar.edu.tr e-mail: basgumus@dumlupinar.edu.tr e-mail: burcinuz@yahoo.com e-mail: ekimhaz@yahoo.com Dumlupınar University, Faculty of Engineering, Department of Electrical & Electronics Engineering, 43100, Tavşanlı Yolu 12.km, Kütahya, Turkey Key words: Erbium doped fiber, EDFA, fiber optical communications, WDM ABSTRACT The design and experimental characterization of high performance C and L band EDFAs pumped at 980 nm are presented. The spectral gain and noise figure performance of EDFAs analysed through simulations have shown strong dependence to EDF length. Highly optimized C and L band EDFAs are realised and experimentally characterized by gain and noise figure measurements. A small signal gain as high as 32.4 dB with a noise figure as low as 3.7 dB were obtained in our C band EDFA. In a L band EDFA, gain enhancement provided through C band signal injection is experimentally demonstrated. In this design, the backward ASE noise at the amplifier input is suppressed by an injected 1550 nm seed signal increasing PCE. This has resulted in a gain as high as 18.3 dB and a moderate noise figure of 7.1 dB obtained in our L band EDFA. I. INTRODUCTION Erbium doped fiber amplifiers which have been initially developed for optical signal amplification in the conventional band (C band, 1525-1565 nm)[1] are now being utilized to cover the long wavelength band (L-band, 1565-1620 nm) with an inherent flat gain spectrum [2]. A combined C and L bands offer a much wider transmission window for the dense WDM systems. The lower EDFA gain in L band relative to the C band can in principle be increased by using longer lengths and more heavily doped active fibers. Several different amplification methods have been proposed in order to improve the relatively low pump conversion efficiency (PCE) and thus enable a higher gain per unit fiber length in the L-band EDFA (L- EDFA). Specifically, a significant gain enhancement was achieved through external C-band (1550-1560 nm) seed signal injection [3-7], re-reflection of the unused backward ASE to amplifier using fiber reflectors [7], circulators [8] or fiber Bragg gratings [9], the use of external ASE sources as a secondary pump source [10], the use of signal double-pass configuration [11] and using 1540 nm band pumping [12]. In this paper, firstly, the fiber length dependence of the spectral gain and noise figure performance in C and L band EDFAs are analysed through the simulations. Then, a C band EDFA pumped forward at 980 nm with optimized gain and noise characteristics was constructed and its experimental characteristics are given. Finally, gain enhancement provided in an L-band EDFA pumped bidirectionally at 980 nm through C band signal injection is experimentally demonstrated. II. SIMULATION RESULTS The simulations are performed in order to analyse the length dependence of spectral gain and noise figure performance in C and L band EDFAs using Optiwave OptiAmplifer 4.0 simulation program. The important parameters of erbium doped fiber (Metro-12 EDF of Fibercore) used in both the simulations and the experiments are shown in Table 1. Table 1. Metro-12 EDF parameters. NA 0.21 Cutoff Wavelength 960 nm Ion Concentration 1.6e25 iyon/m 3 Core radius 1.75 µm Background Loss 8 dB/km @ 1310 nm Absorption Loss 10.46 dB/m @ 980 nm 17.70 dB/m @ 1530 nm Emission Loss 16.59 dB/m @ 1530 nm In the simulations, the total bidirectionally applied pump power was 2x150 mW and the signal input power was -30 dBm for each channel assuming 100 WDM channels in total from 1520 nm to 1635 nm. Figure 1 shows the gain spectrum of bidirectionally pumped EDFA with different fiber lengths varying from 5 m to 100 m. For short fiber lengths (5-10 m), the EDFA operates