Research Of Spectrum Defragmentation And Its Performance Based On Four Wave Mixing Effect Of Highly Nonlinear Fiber

Since the 1990 s,optical fiber communication has made many breakthroughs in speed and capacity, with the continuous development of the optical fiber fabrication technology and network technology. Wavelength Division Multiplexing(WDM) is a significant technology on multiplication of communication capacity by multiplexing a number of optical carrier signals with different wavelengths onto a single optical fiber, however, the fixed WDM grid has a low spectral efficiency. On the other hand, OFDM elastic Networks with flexible spectrum allocation strategy, enable a high spectral efficiency. The OFDM technology is a frequency-division multiplexing scheme, where a large number of closely spaced orthogonal sub-carrier signals are used. There is no frequency separation between adjacent channel bandwidth, and thus it greatly improves the spectral efficiency. In OFDM flexible Networks system the allocation of spectrum resources are constantly released due to the accumulation of time caused by a lot of data requirements, there will be some free spectrum in the entire network. The idle spectrum not only wastes the spectrum resources, but also increases the network blocking probability. Therefore, Spectrum Defragmentation is playing an important role in the elastic optical networks. Research of spectrum defragmentation currently focused on the network algorithms and the transport layer. In the transport layer, the technology of wavelength conversion has a broad application prospect.In the paper, we investigated the improved wavelength conversion technology and its application in the spectrum defragmentation. The paper firstly discussed the issues of the current wavelength converters based on highly nonlinear fiber(HNLF), such as the lower Stimulated Brillouin Scattering(SBS) threshold wtih input pump power limitation and the high cost. Then, we proposed our developed HNLF-based wavelength converters with improved SBS threshold and lower cost by the cascading two-stage HNLFs scheme and the bi-directional scheme, respectively. Finally, we simulated an OFDM spectrum defragmentation system based on the aforementioned two kinds of schemes and achieved an organized spectrum with good performance.