Basedontheelectromagneticfieldtheory,theopticalsignaltransmissioncharacteristicsininput/outputwaveguides,slabwaveguidesandarrayedwaveguidesofthearrayedwaveguidegrating(AWG)multi/demultiplexerareanalyzed.TherelationshipbetweenthephysicalparameterssuchasgeometrysizesandrelativerefractiveindexinAWGmulti/demultiplexerandtheopticalsignaltransmissioncharacteristicsarediscussed.ThistheoreticalstudycanbeusedforoptimizingthedesignandimprovingtheperformanceoftheAWGmulti/demultiplexer.