1064 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 9, MAY 1, 2009 Design of Nonzero Dispersion Flattened Fiber Amplifier Optimized for S-Band Optical Communication Pramod RamdasraoWatekar and Won-Taek Han Abstract—We present a new design of dispersion flattened op- tical fiber for flat nonzero dispersion in the S-band region. The op- timized parameters of optical fiber are used to find the optimum concentration of Tm-ions in Tm-doped optical fiber, which is fur- ther analyzed for the gain and noise performance. It is found that about 5000 mW of pumping power at 1.064 m is required to ob- tain 15 dB gain at 1.47 m in the silica glass Tm-doped (dispersion flattened) optical fiber. Index Terms—Excited-state absorption, optical fiber amplifier, Tm-doped amplifier (TDFA). I. INTRODUCTION T O DATE, the C- and L-bands of optical communication (1.53–1.65 m) are used for the data transfer over op- tical fiber link. Apart from the low loss, a reason for the pop- ularity of these bands is the availability of erbium-doped op- tical fiber amplifiers operating in the C- and L-bands [1], [2]. However, an increase in the number of high-speed Internet users has made the C- and L-bands of optical communication almost fully utilized. Engineers are trying to use other bands of op- tical communication, such as 1.47 m centered band (S-band) and 800-nm centered band [3]–[10]. For the S-band operation, the Tm-doped optical fiber amplifiers are the promising can- didates because they operate around 1.47 m. Recently, suc- cessful realization of a thulium-doped amplifier (TDFA) oper- ating at 1.47 m has been reported by our group [5], [11] for silica glass fiber and by others for silica glass fiber [6]–[8] and telluride/fluoride fiber [9]–[12]. To mention a specific case, a gain of about 20 dB with 1 W pumping power at 1065 nm has been predicted in the Tm/Al-doped silica glass fiber amplifier [6]. With regards to high-speed optical fiber communication that utilizes wavelength-division multiplexing (WDM), it is neces- sary to: i) manage dispersion by having flat dispersion over the entire band; ii) allow a small value of dispersion to avoid the Manuscript received October 09, 2007; revised March 18, 2008. Current ver- sion published April 17, 2009. This work was supported in part by the Brain Korea-21 Information Technology Project, Ministry of Education and Human Resources Development, South Korea. P. R. Watekar is with the Department of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea (e-mail: pramod@gist.ac.kr; prwatekar@yahoo.com). W.-T. Han is with the Department of Information and Communications and the School of Photon Science and Technology, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea (e-mail: wthan@gist.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2008.923237 nonlinear issues like self-phase modulation, etc.; and iii) have an amplification in the band of optical communication. Ear- lier there were successful efforts to address these issues for C- and L-bands [13], and impressive work was also done for dis- persion management with or without combination of amplifiers [14]–[20]. Although there are no S-band specific fiber designs reported so far, broadband fiber designs have been already pro- posed [21], [22]. In a special kind of fiber, a negative disper- sion-flattened fiber for metropolitan networks (operating from O-band to L-band), which has dispersion value varying from 10 to 5 ps/nm-km, has been reported [21]. Such fiber has a finite negative dispersion that is large enough to be accumulated over a long distance, necessitating the dispersion management schemes to increase the cost of the optical fiber network. In an- other approach, a flat-field fiber with a small dispersion slope of 9 ps/km-nm and a dispersion-compensating fiber operating in the range of 1.48 to 1.61 m with dispersion of 6 ps/km-nm have been proposed [22], which are also susceptible to the prob- lems of accumulated dispersion if used in the long-haul optical fiber communication link. In the current communication, we propose a new design of optical fiber, which is optimized for near zero dispersion in the entire S/S+ band. Dispersion slope is far less (about 0.001 at 1.47 m), giving a flat dispersion operation. The nonlinearity is nearly same as that of single mode fiber (SMF) and a low bending loss. Using the designed values of nonzero dispersion flattened fiber (NZDFF); we theoretically optimize and analyze the performance of Tm-doped amplifier under dispersion man- aged profile. II. THEORY A. Optical Fiber The scalar wave equation for evolution of electrical field in the optical fiber is given as [23] (1) where is the electric field along fiber radius , is the prop- agation constant in the free space, is the refractive index profile of fiber, is the azimuthal mode number, and is the propagation constant. The resolution of mode present in the op- tical fiber and the effective index calculations are done using the direct integration of scalar wave equation with appropriate 0733-8724/$25.00 © 2009 IEEE Authorized licensed use limited to: IEEE Xplore. Downloaded on April 18, 2009 at 03:01 from IEEE Xplore. Restrictions apply.