Demonstration of the ultrafast response of 50-nm gate HEMTs using cw optical mixing techniques

Abstract

The high speed response of 50-nm gate AlInAs/GaInAs/InP pseudomorphic high electron mobility transistors (HEMTs) have been used in optical mixing experiments to generate difference frequencies to 211 GHz from two continuous wave laser beams. A 16 dB signal to noise ratio was achieved. To our knowledge, this is the highest frequency optical mixing ever obtained for three-terminal devices. A broadband three wave mixing technique was employed to detect the optically mixed signals at these high frequencies. This scheme involves the nonlinear interaction of the optically generated signal with a millimeter wave signal electrically injected at the gate. The resulting signal, downshifted to W band, was radiated into the waveguide input of an external millimeter wave receiver system. To demonstrate the wide tunability of our system a sweep of frequencies from 160 - 190 GHz was performed. The HEMTs exhibited a relatively flat response with signal to noise ratios of greater than 12 dB. Ultrafast response of the HEMTs as indicated by cw mixing results was also characterized in the time domain using a picosecond electro-optic sampling system. To illustrate the use of the HEMTs in optical millimeter wave systems, optically mixed signals at 97 GHz, both continuous wave and modulated, were radiated into free space using a horn antenna. Modulation was obtained by injecting a baseband signal into the gate of the HEMT. Electrical characterization of the devices yielded cut-off frequencies of 228 GHz and a maximum oscillation frequency of 124 GHz.