WDM Lightwave Systems Employing Unequal-Spaced Channel-Allocation

• Main Authors: Keng-Duan Chang, 張耿端
• Other Authors: Guu-Chang Yang
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/06132367137391231320

碩士 === 國立中興大學 === 電機工程學系 === 88 === Wavelength-division multiplexing (WDM) technique is recently receiving substantial attention for fiber-optic communication systems. WDM, which allows information at various channels being transmitted in form of different wavelengths, achieves high data-rate transmission and hence fully exploits the vast bandwidth provided by optical fiber. To allow high-data rate transmission over long distances, dispersion-shifted fiber (DSF) is deployed to reduce the chromatic dispersion. However, the commercially available DSF increases the efficiency of four-wave mixing (FWM), resulting in system degradation. Among the optical nonlinearities, FWM is the most serious one to the WDM fiber-optic systems. Therefore, to analyze the performance of the system with the effects of FWM and other optical nonlinearities is important to the design of the WDM system. The efficiency of FWM depends on both channel spacing and fiber dispersion. FWM cannot be reduced by only increasing the channel spacing. Furthermore, wider channel separations result in the less number of channels in a fixed operating bandwidth. In this thesis, we develop two algorithms, using frequency difference triangles and frequency difference squares, that can systematically determine the total numbers of FWM signals falling onto the operating band and each channel, respectively, of unequal-spaced WDM systems. By knowing these two numbers, one can adjust the system parameters, such as minimum channel spacing, to keep a good balance on the adverse effects of FWM crosstalk and interchannel interference, or avoid the assignment of channels at locations with the most severe crosstalk. The order of computational complexity of the frequency difference square algorithm and direct computation method is compared. An upper bound on the total number of FWM signals falling onto the operating band of an unequal-spaced WDM system are also developed. Finally, the system degradations due to FWM crosstalk with four different kinds of modulation/demodulation schemes are analyzed.