Raman amplification in fiber optic networks using multiwavelength fiber laser pump module

ABSTRACT We present the design and construction of Raman fiber amplifie rs that can provide gain in C- and L- bands in optical communication networks. Using a 700mW single-wavelength pump at 1480nm, we have obtained on-off gain up to 16dB near 1584nm in 25km long Corning ® SMF28 fiber. In order to provide flat gain, spectrum slicing of a broadband Raman profile has been suggested to construct multi-wavelength pump module in the 1460-1510nm range. According to our simulation, a 6-wavelength pump module will amplify signals in the 1560-1615nm range, with 10dB on-off gain and 2.0dB gain-ripple. Using 5 pairs of fiber Bra gg gratings, one can easily realize this ga in-flattened Raman amplifier that is not only cost-effective but also has st able operation and optimized performance. Keywords: Optical amplifiers, Raman lasers, Software and m odeling in optics, Optical components and devices. 1 INTRODUCTION Distributed Raman amplification (DRA) is an enabling technology for long-haul and metropolitan-area broadband optical networks. In this technique, stimulated Raman scattering process in the transmission fiber itself is utilized to achieve gain over a bandwidth of ~ 40THz. In contrast to discrete or lumped Raman amplifiers located at various points/nodes in the light-path, DRA remains with the signal throughout the length of the optical link. Remote pumps distributed in the fiber optic network can provide gain on demand. While DRA offers various advantages by the ubiquitous presence in the transmission path, it also poses challenges such as gain-flattening in the broadband spectral regime. It has been shown that gain-flattening over wideband can be achieved using multiwavelength (multi- )pumping [1-3]. The gain-module can be constructed using pumps of either semiconductor laser diodes [3] or all Raman fiber lasers (RFLs) [4, 5]. The RFLs approach has several advantages, including stable operation at room temperature and wavelength tunability. RFL is also potentially cost-effective, therefore this approach has been used in our investigations presented in this paper. In order to realize multi- O pumps, spectral slicing technique has been proposed that is based on Raman fiber laser modules. Novel test amplifiers have been designed and simu lated with various pump parameters such as the number of RFLs pumps, their wavelengths, relative powers, and length of the transmission fi ber. The designs using 2- , 4- , and 6- RFL-pumps were simulated to demonstrate the effectiv eness of the technique and determine best performance. The results obtained using a 6- -pump module in the range 1460-1510nm, showed a superior gain-flattened amplification, inferred from the ratio of gain-ripple to the on-off gain [2]. We have designed various netw ork test topologies, which are simulated using commercially available software packages. For the real networks, however, longer span fiber (100-10,000km) and reconfigurable gain module are suggested [6]. Th e simulated design configuration uses RFL pumps with output optimized around 1480nm and maximum power of 700mW of the primary pump. We designed our 6- pump module by adding 5 pairs of fiber Bragg grati ngs (FBGs) to a RFL pump at 1480nm [2].