Asimplifiedmodalmethodtoexplaintheresonancephenomenoninguidedmoderesonance(GMR)gratingswithasymmetriccoatingsispresented.Theresonanceobservedisduetotheinteractionoftwopropagationmodesinsidethegrating.Thereflectivityspectraandelectricfielddistributionscalculatedfromthesimplifiedmodalmethodarecomparedusingrigorouscoupled-waveanalysis(RCWA).Theinfluencesofhigh-orderevanescentmodesontheresonancepeakareanalyzed.AmatrixFabry-Perot(FP)resonanceconditionisdevelopedtoevaluatetheresonancewavelength.AnexplanationfortheresonancephenomenonobservedbasedontheFPresonancephaseconditionisalsoproposedanddemonstrated.ThesimplifiedmethodprovidesclearphysicalinsightsintoGMRgratingsthatareusefulfortheanalysisofavarietyofotherresonancegratings.
