Nanooptics and photonics

Liquid crystal controlled self-referenced SPR sensor
Yarmoshchuk Ye. S.
Faculty of Physics, Taras Shevchenko National University of Kyiv, 2 Acad. Glushkova Avenue, Kyiv-03022, Ukraine. 
E-mail: yevheniia_serhiivna@outlook.com

The multilayer optical system with the layer of the nematic liquid crystal (LC) was theoretically investigated. The system contains a thin dielectric grating and a thin metal (silver) film similar to the sensor in [1]. Such sensor shows two surface plasmon resonance (SPR) dips in the reflectance spectrum. The LC layer was added to the system because of its ability to reorient under applied field. Change of the system parameters when it is already fabricated can improve functional properties and application of the system.
The reflectance of the normally incident TM-polarized infrared light was calculated by using the finite elements method. Parameters of the grating and the silver film is the same as in [1] the film thickness is 40nm the grating thickness 175nm, the grating period 1μm. Different LC configurations were investigated. Reflectance shows two SPR dips and this system can be a sensor. In the case when the LC layer goes before grating the LC director rotation can change the dip depth. The twisted LC cell changes the light polarization and surface plasmon does not exist. When the LC layer is after grating and metal the director rotation can shift the referenced dip. The dip position can be controlled by the LC orientation and the most suitable for the case can be chosen. These results can be used for designing tunable sensors or other SPR based devices.

1.	Abutoama M., Abdulhalim I. Self-referenced biosensor based on thin dielectric grating combined with thin metal film // OPTICS EXPRESS. – 2015.-23, N 22.-P. 28667-28682.