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 [11¯0] crystallographic directions, we are able to deduce accurate values for the linear electro‐optic coefficient. Values ofr41=−1.68×10−10cm/V at &lgr;=1.15 &mgr;m andr41=−1.72×10−10at &lgr;=1.09 &mgr;m 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 areR11=−2.0×10−16cm2/V2,R12=−1.7×10−16cm2/V2at &lgr;=1.15 &mgr;m, andR11=−2.9×10−16cm2/V2,R12=−2.4×10−16cm2/V2at &lgr;=1.09 &mgr;m 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−1is reported for aP‐ndoped modulator (n=6×1017cm−3). Free‐carrier absorption is shown to be the dominant loss process in high‐quality structures.