Electro-Optic Millimeter-Wave Sources and Receivers for THz Electronics

Emerging applications in the millimeter-wave (mmWave) bands for 6G and beyond require new source and receiver instruments for high-frequency circuit characterization. Synthesizing and measuring arbitrary waveforms for characterizing circuits’ time-domain, nonlinear harmonic, and intermodulation responses is especially important for optimizing energy efficiency and stability. Today’s digital-to-analog and analog-to-digital converters lack the bandwidth, precision, and programmability needed for new mmWave integrated circuits. Here, we study applications of optical frequency combs, photodiodes, and electro-optic materials to synthesis and network analysis on-wafer of mmWave arbitrary waveforms with >100 GHz instantaneous bandwidth.

To synthesize arbitrary waveforms, we generate an electro-optic frequency comb, apply fine amplitude and phase control to pairs of comb lines (beat notes), and demultiplex the beat notes to uni-traveling carrier photodiodes. We apply this to arbitrary waveform generation with 100 GHz of instantaneous bandwidth on a single photodiode. By connecting several photodiodes on-wafer to a frequency combiner covering DC to 1 THz, we will enable much greater amplitude and bandwidth.

To explore network analysis on-wafer, we demonstrate an electro-optic imaging system for measuring millimeter-wave propagation along a coplanar waveguide (CPW). A custom polarization-resolved microscope images small electro-optic effects due to millimeter-wave voltages between the signal and ground of the CPW. By sampling multiple positions along the CPW, the amplitude and phase of all tones (up to 500 GHz in the first experiment) at multiple mmWave reference planes can be measured simultaneously, revealing forward and backward traveling waves. Dual electro-optic frequency combs demonstrate time-domain waveform imaging on-wafer with >100 GHz of bandwidth. A second configuration demonstrates continuous wave electro-optic vector network analysis with 70 measurement planes on-wafer.

With electro-optic synthesis and network analysis, we will measure new electronics such as NIST’s ultrawideband comb generators and mixers, making use of instantaneous bandwidth and time-domain capabilities that cannot be achieved otherwise.