DETERMINATION OF REFRACTIVE-INDEXES AND THICKNESSES OF SILICA DOUBLE-LAYER SLAB WAVE-GUIDES ON SILICON

The authors present a method which simultaneously determines the refra ctive indices and thicknesses of double layer silica films grown on si licon independent of the index difference between the two layers. It i s based on an earlier theory for double layers on high index substrate s and uses the propagating and radiating mode indices obtained from pr ism coupling measurements (e.g. at wavelengths of 876, 1304 or 1547 nm ). The method is useful for analysing single mode waveguides at low in frared wavelengths used in telecommunication applications. The theoret ical mode indices obtained from a proper approximation of the rigorous eigenvalue equation with initial assumptions on refractive indices an d thicknesses are compared with the measured mode indices, and, in an iterative fashion, the procedure is repeated with different parameters until the mode indices match. Good agreement is found between the res ults of single and double layers with about 20 mu m buffer and 7 mu m core layer thicknesses, respectively, with index difference in the ran ge 10(-3)-10(-2) using prism coupling and reflectometric measurements. Typical accuracies within the constraints of the measurement for the refractive indices and thicknesses are beyond 10(-4) and 0.2 mu m, res pectively.