Rg. Kaufman et al., MEASUREMENT OF THE REFRACTIVE-INDEX OF ALXGA1-XAS AND THE MODE INDEXES OF GUIDED MODES BY A GRATING COUPLING TECHNIQUE, Journal of applied physics, 75(12), 1994, pp. 8053-8054
We have determined the index of refraction of AlxGa-xAs over the wavel
ength range 0.76-1.15 mum, and the composition range 0 less-than-or-eq
ual-to x < 0.33, using a grating to couple light into waveguides. We f
ind the mode indices of multimode slab waveguides from the coupling an
gle and grating period, then calculate the bulk indices of the core an
d cladding materials by a root searching technique using the analytica
l formula for the effective index of a guided mode. The method gives t
he core index within +/-0.001, and the cladding index within +/-0.01.
We are in agreement with high precision index values for GaAs in the l
iterature, confirming the method. We are in substantial agreement with
literature values for AlGaAs but find a significant systematic differ
ence in the composition dependence. An analysis of measurement uncerta
inties shows that the determination of composition is the dominant var
iable.