Refractive Index Measurement of Waveguides BY IMAGING ELLIPSOMETR

SAMPLE AND SETUP

The dispersive refractive index needs to be measured on 8 μm wide waveguides of LiNbO₃ . Additionally, the thickness of an SiO2 layer is to be determined on the waveguides and on clad region.

Psi map at 250 nm (Courtesy of Samuel Margueron, FEMTO-ST)

Imaging ellipsometry with the nanofilm_ep4 offers highest lateral ellipsometric resolution down to 1 μm. It combines the sub-nanometer sensitivity for thickness and precise spectral refractive index measurements of ellipsometry with the benefits of magnification and high lateral resolution of optical microscopy.

MEASUREMEN

Spectral micro mapping

Spectral micro-maps of Delta and Psi were recorded from 200 nm to 400 nm. Spectral Delta and Psi data were extracted for multiple regions (average of 30 pixel) on the waveguides and beside them. Dispersive refractive index and thickness of top SiO₂ layer are fitted, using the EP4 optical model sortware.

RESULT

- SiO₂ thickness on Core: 3 nm / on Clad: 113 nm
- Difference of dispersive refractive index of core and clad region clearly visible
- Good reproducibility of results between different regions of the same kind

APPLICATIONS

- Spectral refractive index measurements on micron sized waveguides (wavelength 190-2700 nm) with a difference between clad and core of down to 0.001
- Thin layers on micron sized structures
-Integrated photonics