Friday, April 24, 2015

DTU & ITMO present ultracompact all-dielectric refractive index sensors by ALD

A new type of ultracompact all-dielectric refractive index sensors with much lower losses compared to plasmonics-based sensors fabricated by ALD has been published recnetly by DTU - Technical University of Denmark and ITMO University St Petersburg. The presented results will be useful for ellipsometric characterization of multilayer stacks, as well as for a variety of sensing applications.

Nanotechweb reports: Surprising optical properties of ultra-thin dielectric multilayer films

Ultra-thin dielectric films could act as a new type of chemical sensor. This is thanks to a minute variation in layer thickness and ordering on the light reflection in a very narrow range of incident angles. Surprisingly, this new discovery reported in Nanotechnology has a high influence. The same sensitivity can be utilized for the in-situ monitoring of multilayer deposition and for the development of new high-precision models for ellipsometry.

 
Anomalous effective medium approximation breakdown in deeply subwavelength all-dielectric photonic multilayers FREE ARTICLE Focus on Nanophotonics

Andrei Andryieuski1, Andrei V Lavrinenko1 and Sergei V Zhukovsky1,2

1 DTU Fotonik, Technical University of Denmark, Ørsteds pl. 343, Kongens Lyngby, 2800 Denmark
2 ITMO University, Kronverkskiy pr. 49, St. Petersburg, 197101 Russia
Andrei Andryieuski et al 2015 Nanotechnology 26 184001
doi:10.1088/0957-4484/26/18/184001
 
We present a comprehensive analysis of the applicability of the effective medium approximation to deeply subwavelength (period all-dielectric multilayer structures. We demonstrate that even though the dispersion relations for such multilayers differ from the effective medium prediction only slightly, there can be regimes when an actual multilayer stack exhibits significantly different properties compared to its homogenized model. In particular, reflection near the critical angle is shown to strongly depend on even very small period variations, as well as on the choice of the multilayer termination. We identify the geometries for which the influence of the subwavelength features is maximized and demonstrate that the difference between the reflectance from the actual multilayer and the effective medium prediction can be as great as 0.98. The results of this analysis can be useful for high-precision multilayer ellipsometry and in sensing applications.

 

Figure 6 from Anomalous effective medium approximation breakdown in deeply subwavelength all-dielectric photonic multilayers (Andrei Andryieuski et al 2015 Nanotechnology 26)