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Integrated photonics technology is set to revolutionize our access to powerful on-chip computing, nondestructive sensors and more. The major limitation of modern integrated photonics is losses that accompany the coupling of high index waveguides. For instance: Fresnel reflection on CMOS compatible Si waveguide interface is of 35% for the single facet and of 51% for both facets. These losses, of course, are minor in glass waveguides ( ~%4) [1, 2]. The light coupling from fiber into a planar waveguide with complicated shape is even lossier. The abrupt change in refractive index on the interface is in charge of disruptive reflection. To reduce the reflection, one can gradually change the refractive index at the interface. Here we propose to use metasurfaces which utilize the sub-diffraction properties of resonators [3, 4, 5]. First, we study the anti-reflection properties of the random structures on the facet of the waveguides [6]. In general, rough surfaces, as random process, can be defined mainly by two statistical functions: the height distribution and the autocorrelation function (ACF). Therefore, by tuning these two parameters we change the reflection properties of such a structure. Allowing an additional degree of freedom, anti-reflective random metasurfaces have numerous advantages. In addition, they can be easily manufactured on space compatible devices, high power lasers to list a few.
References:
[1] Alina Karabchevsky, James S Wilkinson, and Michalis N Zervas. Transmittance and surface intensity in 3d composite plasmonic waveguides. Optics express, 23(11):14407–14423, 2015.
[2] A Karabchevsky and AV Kavokin. Giant absorption of light by molecular vibrations on a chip. Scientific reports, 6, 2016.
[3] Shalin A. S. Optical Antireflection of a Medium by Nanostructural Layers // Progress in Electromagnetic Research B. 2011. V. 31. P. 45-66.
[4] Shalin A. S., Nikitov S. A. Approximate Model for Universal Broadband Antireflection Nano-Structure // Progress in Electromagnetic Research B. 2013. V. 47. P. 127-144.
[5] D. A. Baranov, P. A. Dmitriev, I. S. Mukhin, A. K. Samusev, P. A. Belov, C. R. Simovski and A. S. Shalin. Broadband antireflective coatings based on two-dimensional arrays of subwavelength nanopores // Appl. Phys. Lett. 106, 171913 (2015);
[6] JA Ogilvy. Wave scattering from rough surfaces. Reports on Progress in Physics, 50(12):1553, 1987.
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