Optical waveguides are largely used in photonic devices and systems, due to its low optical loss. The refractive index profile of optical waveguides is the key parameter as it determines the insertion losses and propagating modes. Based on its Quantitative Phase Imaging (QPI) technique, Phasics offers high-accuracy metrology instruments for refractive index measurement.


  • Adapted for waveguide dimensions down to limit of diffraction
  • Immediate Measurement thanks to single shot imaging
  • Non-destructive
  • Reproducible

Tool can be implemented to study and control in real time the inscription process of optical waveguides.


Accurate refractive index measurement is necessary for the development, the optimization and the quality monitoring of produced photonic devices.
As a non-destructive method, QPI gives a precise refractive index profile with sub nanometer precision of waveguides in semi-transparent sample such as glass.
The measurement is single shot and the information extraction is quasi immediate (only one profile plot on the waveguide image). The SID4-Imaging system is adapted for measurement on either optical fiber or laser written waveguide.


Refractive index measurements of waveguides created by using different decreasing fluencies in a glass sample. We can measure differences of Dn about 10-3.

Topography of microstructures on a glass substrate (Magnification)


Waveguide measurement with quantitative phase
Waveguide imaging can be done in two different configurations: in XY or in the orthogonal plane.

Waveguide imaging measurement

By knowing the mechanical size of the waveguide, we can retrieve refractive index values.
OPD = (nwaveguide – nsusbtrate) x mechanical thickness (nm)