Electrooptic Bragg-diffraction modulators in GaAs/AlGaAs heterostructure waveguides

Reports theoretical and experimental results on electrooptic Bragg-diffraction modulators in GaAs/GaAlAs heterostructure waveguides. The devices utilize the linear electrooptic effect in periodic structures to facilitate spatial modulation of the refractive index in the waveguide. A numerical method was established to solve the waveguide equation and quantify the induced changes in the effective index of the waveguide as a result of reverse bias. The numerical calculation has established the guidelines for an optimum design of the modulator that operates in the Bragg regime. The measured diffraction efficiency of the single-grating Bragg modulator was as high as 90 percent at a driving voltage of 15 V. A device consisting of four such basic diffraction gratings was also fabricated and used to demonstrate the function of scalar addition. The highest bandwidth of the devices that have been measured exceeds 1 GHz. The planar waveguide Bragg modulators offer advantages including lower optical propagation loss, greater fabrication tolerance, and spatial separation between the diffracted and the undiffracted light beams