ᐊ P2-5
Open Readings 2021 • P2-6
P2-7 ᐅ

REFRACTIVE INDEX SENSOR FOR LIQUIDS BASED ON DIFFRACTION EFFICIENCY MEASUREMENT

Tomas Klinavičius1, Mindaugas Juodėnas1, Andrius Žutautas1, 2, Tomas Tamulevičius1, 2

1 Institute of Materials Science, Kaunas University of Technology, Lithuania

2 Department of Physics, Kaunas University of Technology, Lithuania

[email protected]

The refractive index of a material is a dimensionless quantity that defines a ratio of phase velocity of light in a vacuum and that material [1]. Refractive index sensors of liquids are important for chemical analysis, and there are many different constructions of these sensors proposed [2-4]. However, these solutions tend to not be aimed at small samples of liquid.

In this work, we propose a design and working principle for a microfluidic refractive index sensor based on diffraction efficiency measurement. It works by measuring the changes of diffraction efficiency at some wavelength before and after liquid intake, as the change of the diffraction grating superstrate influences its diffraction efficiency. The change in diffraction efficiency is related to the refractive index of liquids by using the Rigorous Coupled Wave Analysis method [5] to model a diffraction grating under different conditions (refractive indexes of superstrate). Typical situation of diffraction efficiency dependence on grating height for different superstrates is depicted in Fig. 1.

Figure 1
Fig. 1. Concept of sensor working principle – light transmission changes from high (microfluidic filled with air) to low (microfluidic filled with water) at a certain grating height. In case of water, efficiencies of all wavelengths were identical

[1] E. Hetch, Optics, Pearson, ISBN 978-0-321-18878-6, (2016).

[2] T. Tamulevičius, et al. Refractive index sensor based on the diamond like carbon diffraction grating, Thin Solid Films 519, 4082-4086 (2011).

[3] T. Tamulevičius, et al. Numerical and experimental analysis of optical response of sub-wavelength period structure in carbonaceous film for refractive index sensing, Optics Express 22, 27462-27475 (2014).

[4] R. Selvas-Aguilar, et al., Noncontact Optical Fiber Sensor for Measuring the Refractive Index of Liquids, Journal of Sensors 2016, 1-6 (2016).

[5] M. G. Moharam, e al., Stable implementation of the rigorous coupled-wave analysis for surface-relief gratings: enhanced transmittance matrix approach, Journal of the Optical Society of America A 12, 1077-1086 (1995).