Spectrum Defragmentation Technology For Orthogonal Frequency Division Multiplexing Signal

With the explosive growth in demand for information, optical fiber communication technology has been developed rapidly. A flex-grid optical network based on Orthogonal Frequency Division Multiplexing(OFDM) technique has been proposed, which increases the spectral efficiency, but simultaneously induces the spectral fragmentation. Therefore, the spectral defragmentation is indispensable. In this paper, the wavelength conversion technologies are utilized to realize the spectral defragmentation. The wavelength conversion is able to redistribute wavelengths, increase flexibility and the utilization of optical spectrum, scale the optical network. All optical wavelength conversion based on four wave mixing(FWM) of highly nonlinear fiber(HNLF), is transparent to various modulation format and data rates and good for the future all-optical network. OFDM technique has several advantages, such as improved spectrum utilization, strong anti-interference and large transmission capacity, which is a key technology of several wireless communication standards, and also widely studied in optical fiber communication.This paper focuses on the spectral defragmentation of coherent optical orthogonal frequency division multiplexing(CO-OFDM) signal, and the main contents are as follows: 1. Theoretically studying on the spectrum defragmentation of CO-OFDM signal based on all-optical wavelength conversion scheme. The CO-OFDM technique, combined with OFDM and optical coherent detection, has high spectrum efficiency, dispersion resistance and anti interference, but also improves the OSNR tolerance and PMD sensitivity in the receiver. The all-optical wavelength converter based on FWM effect of HNLF, has high conversion rate, wide conversion bandwidth. Moreover, the two-stage wavelength converter scheme can realize gapless conversion and eliminate phase conjugation.2. Simulation on the wavelength conversion characteristics and feasibility of spectral defragmentation of CO-OFDM signal. By utilizing the two-stage scheme, the CO-OFDM signals with spectral fragmentation can be relocated in order and realized the spectral defragmentation. The simulation results show that the two-stage wavelength converter provides a wide 30-nm conversion bandwidth in C-band with a high conversion efficiency of about-10 d B. Compared with the back-to-back CO-OFDM signals, the converted signals have less than 4.8d B power penalty at bit error ratio of 10-9. The gapless conversion based on the two-stage wavelength converter has been utilized to realize the spectral defragmentation.