Measurement of the refractive index of AlxGa1−xAs and the mode indices of guided modes by a grating coupling technique

Abstract

We have determined the index of refraction of AlxGa−xAs over the wavelength range 0.76–1.15 μm, and the composition range 0≤x<0.33, using a grating to couple light into waveguides. We find the mode indices of multimode slab waveguides from the coupling angle and grating period, then calculate the bulk indices of the core and cladding materials by a root searching technique using the analytical formula for the effective index of a guided mode. The method gives the 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 literature, confirming the method. We are in substantial agreement with literature values for AlGaAs but find a significant systematic difference in the composition dependence. An analysis of measurement uncertainties shows that the determination of composition is the dominant variable.

Dispersion and Modulation of the Linear Optical Properties of GaAs–AlAs Superlattice Waveguides Using Quantum-Well Intermixing

“…The quadrature sum of these two errors results in overall angle determination on the order of 2 10 degrees. Contrary to previous work where it is assumed that the surface normal is determined exactly [28], [29], we conclude that the error resulting from retro-reflection of the incident beam through an aperture is more significant than the measurement of the unreferenced coupling angle itself. This can be compared to the 2-deg.…”

Optical Properties

“…There have been several publications since 1993. They concern a(E) in the fundamental absorption edge [71], n(E) in the terahertzÀE 0 (E g ) region [72][73][74][75][76][77] and SE «(E) in the near-IR-UV region [78,79].…”