Performance Enhancement of Arrayed Waveguide Grating-Based Optical Multiplexers/Demultiplexers in Dense Wavelength Division Multiplexing Optical Communication Systems

Abstract

The ever increasing rate of use of modern communication systems resulted in an increasing need for more transmission bandwidth. Optical communication using optical fiber is expected to overcome and meet the better part, if not all, of this need for more transmission capacity. Fiber optics have not only wide bandwidth but they also and by their nature provide for applying novel methods for the further extended utilization of their wide bandwidths. One such main method is Dense Wavelength Division Multiplexing (abbreviated as DWDM). DWDM increases the available transmission capacity of an optical fiber through simultaneous transmission on several slightly different wavelengths each carrying a separate channel of information on the same optical fiber. The most popular optical structure used for multiplexing and demultiplexing these DWDM numerous channels is called the Array Waveguide Grating (AWG). However the number of channels a DWDM system handles is affected by the level of channel crosstalk in such a manner that the lower the level of the crosstalk the higher will the number be of provided system channels. This thesis proposes a method whereby a MUX/DEMUX formed of cascaded AWG stages results in total channel crosstalk reduction which allows for more DWDM channel count. The thesis therefore describes the analysis and derivation of accumulated crosstalk in different setups of DWDM AWG-based multiblexers/demultiplexers. The cascading method used relies on the bandwidth optimization of the bandpass AWGs taking into account their center wavelength differences as a crosstalk reducing factor, and assuming the transmittance in linear units for each cascade stage, and that each stage has a Gaussian spectral response envelope. On the other hand the previously derived performance equations were transformed into Matlab programs. A WDM_Phasar simulation software package was also used for the different AWG units design and simulation giving results agreeing with those calculated by the Matlab programs. For the thesis, the results obtained demonstrate that AWG cascading method followed is capable of reducing accumulated channels crosstalk in DWDM systems allowing them to accommodate extra communication channels.