University of Rochester

John A Nees

Gerard A Mourou

Steven L Williamson

Todd A Jackson

An ultrafast traveling wave optical modulator capable of functioning at frequencies greater than 100 GHz having an optical waveguide parallel to a transmission line. The optical waveguide is in a substrate of electro-optic material (GaAs with GaAlAs layers forming the optical waveguide). The transmission line is a pair of coplanar electrodes on the substrate. A superstrate having an effective dielectric constant substantially equal to the square of the index of refraction of the substrate (a GaAs body in which the electric field on the line is substantially confined) eliminates the mismatch in velocity of propagation of the traveling electrical and optical signals thereby increasing the response time of the modulator so that it can function when the electrical modulating signal on the line exceeds 100 GHz in bandwidth.

Ultrafast optical modulator

A measurement system using electro-optic sampling and operative in the time domain characterizes devices over a bandwidth extending to upper microwave frequencies (e.g., 100 GHz). The device under test is mounted to or integrated on a substrate of electro-optic semiconductor material and is connected to transmisison and lines on the substrate. Sampling signals are electro-optically generated and propagate along the lines toward and away from the device under test, using a laser pulse beam incident on the substrate. The signals are electrically sampled by a laser pulse sampling beam which is responsive to the change in refractive index due to the signal at locations equidistant from the generation position. The waveform resulting from electro-optic sampling near the device under test corresponds to the sum of the signal incident upon the device and the signal reflected therefrom. The waveform resulting from electro-optic sampling at the location away from the device corresponds to the incident waveform. The waveforms are processed by subtracting the waveform corresponding to the incident signal from the waveform corresponding to the sum of the incident and reflected signal and Fourier transformed to derive the scattering parameters. The laser pulses are very short (in the picosecond or sub-picosecond range) and the transmission lines are uniform in their attenuation and dispersion characteristics, thereby enabling measurements to be made to extremely high microwave frequencies in the time domain and converted by Fourier transform to the frequency domain to determine the scattering parameters characterizing devices operative at such high frequencies.

Growing community of inventors

Rochester, NY, United States of America

John A Nees