Mid-infrared characterization of refractive indices and propagation losses in GaSb/AlXGa1−XAsSb waveguides

We report experimental results on M-lines characterization of GaSb refractive index as a function of doping level and lattice mismatch in the range of 2.15–7.35 μm with an accuracy of 10−3. We apply the same procedure to quaternary AlxGa1−xAsSb alloys lattice-matched to GaSb to study the refractive index evolution with aluminum fraction and with wavelength. We compare our measurements to theory, and we establish new parameter values for the dispersion law of GaSb. These parameters are confirmed by the excellent agreement between the calculated curves and experimental measurements performed on quaternary alloys. Using these values of optical indices, we design a GaSb/AlGaAsSb ridge waveguide and characterize the losses using the Fabry-Perot method at 2 μm. Very low losses are demonstrated in the range of 1 dB/cm and below in a single mode waveguide structure.