Nanoplasmonics and surface enhanced spectroscopy

Sensitivity of the waveguide resonance grating-based sensors elements 
V.V. Fitio1, I.Y. Yaremchuk1, A.V. Bendziak1,  Y.V. Bobitski 1,2

1 Department of Photonics, Lviv Polytechnic National University,
C. Bandera str. 12, Lviv-71013, Ukraine 
E-mail: v.m.fitio@gmail.com
2 Faculty of Mathematics and Natural Science, University of Rzeszów, 
Rejtan’s str. 16b, Rzeszów-35-959, Poland
There is in necessary to measure the change in the refractive index of various solutions under the influence of various factors for the chemistry, biology, medicine and other areas of science and industries. It is proposed to detect changes in the refractive index by changing the resonance parameters of dielectric gratings, in which the waveguide resonance occurs [1]. The reflection coefficient of such grating can be equal to one under resonance conditions. When the refractive index of the researched medium changes then the resonance is disturbed and the reflection coefficient becomes significantly smaller than unit. Resonance can be resumed by changing the wavelength or angle of incidence.
The sensitivity is an important feature of such sensors. The average refractive index of the grating, the substrate refractive index, the difference between the average refractive index of the grating and the index of the researched medium are parameters of the structure which affect on the sensors element sensitivity. It should be noted that the average grating refractive index is determined by the refractive index of the researched medium and the refractive index of the dielectric, which forms the grating on the dielectric substrate. In order to obtain the waveguide effect, the average grating refractive index should be higher than the substrate and researched medium refractive indices. The strongest field is formed in the waveguide layer, that is, in the grating under resonance. Therefore, the filling factor of the grating affects the sensitivity of such sensors element. Moreover, the width of the test beam should be taken into account.

1.	Yaremchuk I., Tamulevičius T., Fitio V., Gražulevičiūte I., Bobitski Ya. and Tamulevičius S. Guide-mode resonance characteristics of periodic structure on base of diamond-like carbon film. // OpticsCommunications.- 2013, 301-302, 1–6.