Thulium Doped Fiber Amplifier (TDFA) for S-band WDM Systems Fady I. El-Nahal Department of Electrical Engineering Islamic University of Gaza Gaza, Gaza Strip, Palestine fnahal@iugaza.edu.ps Abdel Hakeim. M. Husein Physics Department Al-Aqsa University Gaza, Gaza Strip, Palestine Hakeim00@yahoo.com Abstract— A comprehensive numerical model based on solving rate equations of a thulium-doped silica-based fiber amplifier is evaluated. The pump power and thulium-doped fiber (TDF) length for single-pass Thulium-Doped Fiber Amplifiers (TDFA) are theoretically optimized to achieve the optimum Gain and Noise Figure (NF) at the center of S-band region. The 1064 nm pump is used to provide both ground-state and excited state absorptions for amplification in the S-band region. The theoretical result is in agreement with the published experimental result. Keywords-component; Thulium-Doped Fiber Amplifiers, Rate Equations, Gain, Noise Figure I. 1. Introduction The increase demands on the capacity of WDM transmission system now require newly developed transmission windows beyond the amplification bandwidth supported by erbium-doped fiber amplifiers (EDFA’s). Thulium-doped fiber amplifier (TDFA) provides high-power optical amplification in the S+ (1450–1480 nm) and S-bands (1480–1530 nm) [1-3], hence the TDFA is expected to complement C- (1530–1560 nm) and L-band (1560–1580 nm) amplification based on EDFAs in high-capacity dense wavelength division multiplexed (DWDM) systems [4, 5]. The additional bandwidth, modularity, inherent higher pumping efficiency, and lower nonlinear signal degradation (compared with alternatives such as S-band Raman amplification [6,7] offered by TDFA enables applications such as coarse wavelength-division multiplexing (CWDM) and fiber to the home (FTTH). The TDFA length and Pump power are the important parameters that determine the achievable gain and NF in TDFA [8]. In this paper, we detail the observation and modeling of TDFA where TDFA gain and NF are optimized by solving the rate equations. 2. Configuration of the TDFA The basic architecture used to model TDFA in the WDM system consists of 16 input signals (channels), an ideal multiplexer, a pump laser , pump coupler, Thulium-doped fiber (TDF), Optical spectrum analyzer and dual port WDM analyzer. The input of the system is 16 equalized wavelength multiplexed signals (channels) in the wavelength region of 80 nm (1450 nm-1530 nm) with 5 nm channels spacing. The power of each channel is -20 dBm. The pumping at 1064 nm is used to excite the doped atoms to a higher energy level. The TDF used is a glass based one with thulium density of 15.6×10 -24 m 2 , core radius is 1.3μm, doping radius is 1.3 μm and Numerical aperture (NA) is 0.3. The simulation done with maximum number of iterations is 150 and relative error is 5×10 -4 . 3. Theory of the TDFA The rate equations describe the interaction between signal, pump, and ASE light in the TDFA. The rate equations are used to analyze theoretically the populations in the energy levels of Tm 3+ ions under 1064 nm pump and signal power conditions. The absorption and stimulated emission cross sections define the absorption coefficient for pump light and gain coefficient for signal light [9]. The transition cross- sections of thulium are shown in Fig. 1 [8]. The transition cross-sections were calculated in fluoride based TDF [10]. The Judd–Ofelt analysis shows that the transition strengths obtained were consistent with those for silica. Figure 1. Absorption and emission cross-sections spectra of the fluoride- based TDFA. Open Journal of Applied Sciences Supplement：2012 world Congress on Engineering and Technology Copyright © 2012 SciRes. 5