( n 1 2 − n 2 2 ) 1/2 MathType@MTEF@5@5@+=feaagCart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbbjxAHXgarqqtubsr4rNCHbGeaGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaqFn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpeWZqaaeqabiGaciGacaqadmaadaqaaqaaaOqaamaabmaabaGaamOBamaaDaaaleaacaaIXaaabaGaaGOmaaaakiabgkHiTiaad6gadaqhaaWcbaGaaGOmaaqaaiaaikdaaaaakiaawIcacaGLPaaadaahaaWcbeqaamaalyaabaGaaGymaaqaaiaaikdaaaaaaaaa@3EC0@
where n1 is the maximum refractive index of the core, and n2 is the refractive index of the innermost homogeneous cladding