Direct measurement of substrate refractive indices and determination of layer indices in slab-guiding structures

We present a new method for accurate and nondestructive measurement of the refractive indices of substrates and guiding layers in slab waveguides. This method is based on the excitation of leaky waves in substrates and guided waves in guiding layers owing to the etching of grating couplers on the top of structures. It is particularly applicable to high refractive-index materials and to in situ measurements near the energy band gap of semiconductor waveguides. We present results that were obtained for an InP substrate with an InGaAsP epitaxial layer with regard to their refractive indices and temperature coefficients.