PHASE MODULATION IN GAAS ALGAAS DOUBLE HETEROSTRUCTURES .2. EXPERIMENT

Phase modulation in GaAs/AlxGa1-xAs double heterostructures with different doping profiles is systematically investigated. Very good agreement between the experimental measurements and the theory developed in Part I of this paper is reported. By measuring the phase modulation for both transverse electric and transverse magnetic modes along the [110] and [11̄0] crystallographic directions, we are able to deduce accurate values for the linear electro-optic coefficient. Values of r41=-1. 68×10-10 cm/V at λ=1.15 μm and r41=-1. 72×10-10 at λ=1.09 μm are obtained with an estimated accuracy of ±5%. An accurate estimation of the carrier effect permits us to deduce the quadratic electro-optic coefficient for GaAs. The values are R11=-2.0×10-16 cm2/V2, R 12=-1.7×10-16 cm2/V2 at λ=1.15 μm, and R11=-2.9×10-16 cm 2/V2, R12=-2.4×10-16 cm 2/V2 at λ=1.09 μm with an estimated uncertainty of ±25% for all values. Contrast measurement of Fabry-Perot fringes enables us to evaluate the modulator losses. A value of 4.8 cm-1 is reported for a P-n doped modulator (n=6×1017 cm-3). Free-carrier absorption is shown to be the dominant loss process in high-quality structures.