Abstract
A simple analytic analysis of the ultra-high reflectivity feature of subwavelength dielectric gratings is developed. The phenomenon of ultra high reflectivity is explained to be a destructive interference effect between the two grating modes. Based on this phenomenon, a design algorithm for broadband grating mirrors is suggested.
Highlights
Subwavelegnth gratings are of interest for a wide range of integrated optoelectronic device applications, including lasers, filters, splitters, couplers, etc., because the elimination of nonzero diffraction orders increases coupling efficiency
Gratings were experimentally shown to have a promising application in vertical cavity surface emitting lasers (VCSELs), in which they were monolithically integrated as a replacement of conventional distributed Bragg reflectors (DBRs) [2,3], and as a means to increase tuning speed in a tunable VCSEL [4] and to provide polarization control [5,6,7]
Due to the inhomogeneous refractive index profile, and due to the fact that the wavelength is comparable to the grating periodicity, the existing rigorous framework for the electromagnetic analysis of such gratings [9,10,11] is fairly complex, which makes it difficult to develop simple intuitive explanations for phenomena such as ultra-high broadband reflectivity, in a manner that will allow to predict and design this extraordinary and unexpected feature of high contrast gratings (HCGs)
Summary
Subwavelegnth gratings are of interest for a wide range of integrated optoelectronic device applications, including lasers, filters, splitters, couplers, etc., because the elimination of nonzero diffraction orders increases coupling efficiency. We proposed and demonstrated subwavelength dielectric gratings with a high contrast of refractive indices, referred to as high contrast gratings (HCGs), having reflectivity higher than 99% over an extraordinarily broad wavelength range of ∆λ/λ~30% [1,2]. Such high reflectivity is unexpected, since a uniform slab layer made of the same dielectric material (refractive index of 2.8~3.5) can only reach reflectivity of up to ~70%. Special attention is paid to the multi-mode nature of such gratings, and to the very quick convergence of their modal representation
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