Phase modulation in GaAs/AlGaAs double heterostructures. II. Experiment

Abstract

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, R12=−1.7×10−16 cm2/V2 at λ=1.15 μm, and R11=−2.9×10−16 cm2/V2, R12=−2.4×10−16 cm2/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.

All-optical space switches with gain and principally ideal extinction ratios

“…To compare the experiments with the theoretical curves, we had to relate the applied voltage with the phase shift induced in the phase shifters. Since the voltages applied to the phase shifters are small, we could linearly interpolate the induced phase shifts with the voltage scale [21]. It is worth noting that for fitting all four curves we used only one fitting parameter, namely the alpha-factor, and only one reference point (see Fig.…”

“…7. As the new switch has two gain mediums, we have to substitute (20) and (21) The terms with a containing an upper index and are replaced due to their definitions in full analogy. The restrictions (11) and (12) are still valid and must be adapted according to the substitution (20).…”