Omnidirectional reflection by multilayer dielectric mirrors

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Abstract
Periodic structures reflect strongly at frequencies and angles of incidence corresponding to photonic bandgaps. It has recently been shown that for a suitable choice of high and low refractive indices nh and nℓ, a high-low dielectric multilayer can reflect strongly at all angles of incidence. An accurate and simple analytic approximation for the location of the band edges for the s and p polarizations is given. The region in the (nℓ,nh) plane where omnidirectional reflection occurs is determined. This region lies above a curve which has its minimum value of nh(≈2.247n1) at nℓ≈1.492n1, where n1 is the refractive index of the medium of incidence. The minimum occurs when the optical paths in the high and low refractive index layers are in the ratio 1.362 to 1.