Static and dynamic two-wave mixing in GaAs

We studied the two-wave mixing anisotropic diffraction process in GaAs for demodulation of static and dynamic phase encoded signals. The static results quantitatively agreed with a previous theoretical model for cubic crystals. This model has been described explicitly for all beam polarizations and crystal rotation angles with respect to the plane of incidence. Dynamic phase modulation, in which the signal beam was phase modulated at frequency f(s) and the reference beam at f(r) = f(s) + Deltaf, produced a signal at Deltaf that was proportional to the difference between the static beam intensities with and without two-wave mixing under all conditions of polarization and crystal orientation studied. A significant dynamic output signal was produced even when only a shift in polarization but no energy transfer occurred as a result of the anisotropic two-wave mixing process. Therefore not only is the two-wave mixing gain important when the photorefractive effect is used for dynamic phase demodulation, but so are the polarization shifts occurring from the mixing process.