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November, 2004 EEEL Demonstrates Traceable Waveform Measurement up to 200 GHz |
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In a joint collaboration between the Electromagnetics and Optoelectronics Divisions of EEEL, Dylan Williams, Paul Hale, Tracy Clement, and Nita Morgan have demonstrated temporal waveform measurements, in a coplanar waveguide, that are calibrated and traceable to fundamental physical units. The calibrations, from 500 MHz to 200 GHz, enable the team to correct for the complex characteristic impedance and dispersion of the coplanar waveguide, impedance mismatches, and multiple reflections in the measurement system. Because they are calibrated, these measurements make it possible to calculate such quantities as the Thevenin and Norton equivalent circuits describing the electrical source, and can be used to calibrate future generations of temporal on-wafer measurement systems. This work will support future generations of high-speed components and test equipment that are necessary for 40 Gbit/s and faster fiber-optic communications systems that cannot be supported by present-day state-of-the-art oscilloscopes, whose bandwidths are limited by their coaxial connectors. The EEEL team used an electro-optic sampling system with roughly 10 THz bandwidth to sample high-speed electrical waveforms on a coplanar waveguide with ultrashort laser pulses via the electro-optic effect. They also combined conventional microwave vector network analysis with a novel, non-invasive, slotted-line impedance measurement technique that uses electro-optic sampling to perform impedance measurements. This technique was useable up to the frequency where the spectrum of the source reached the noise floor of the instrumentation, which, in this case, is about 200 GHz. The team quantified the uncertainty in the temporal measurement using a Monte-Carlo simulation that included both systematic and random sources of uncertainty from a measurement of a 5.96 ps pulse with a 95% confidence interval of only 0.21 ps. This time-domain uncertainty analysis is the first of its kind. Although electro-optic sampling has been used to measure high-speed electrical waveforms for many years, the EEEL measurements are the first mismatch-corrected waveform measurements (using any method) that include a full time-domain uncertainty analysis and are calibrated up to 200 GHz, a factor of four improvement over previous achievements elsewhere. Details of the procedure are described in D.F. Williams, P.D. Hale, T.S. Clement, and J.M. Morgan, "Calibrated 200 GHz Waveform Measurement," IEEE Trans. Microwave Theory and Tech., January, 2005.
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