Picosecond Electrical Wavefront Generation and Picosecond Optoelectronic Instrumentation

While electronic components have been demonstrated over narrow bandwidths at millimeterwave frequencies, electronic components for broadband and pulse applications have shown much poorer performance. This discrepancy in performance between pulse and narrowband circuits also applies to the related instrumentation. This thesis describes the development of picosecond electronic devices and the related instrumentation. Picosecond electrical wavefronts are generated by propagation on a GaAs monolithic nonlinear transmission line consisting of a high-impedance coplanar-waveguide transmission line periodically loaded by a series of Schottky contacts. The variation of wave velocity with voltage permits compression of the falltimes of step-functions propagating on these lines, with a minimum compressed falltime set by the diode and periodic-line cutoff frequencies. With appropriate design, the characteristic impedance can be set at 50 ohms, permitting low-reflection interfaces. With firstgeneration devices, compression of 20 picosecond edges to 7.8 ps has been attained, and 38 ps wavefronts have been compressed to 10 ps on a cascade of two devices. Recently, with second-generation devices, compression from 20 ps to 5 ps and from 30 ps to 7 ps has been achieved. Theory, fabrication, and evaluation of these devices is discussed. Direct electrooptic sampling is a noncontact test method for measuring the voltage waveforms at the internal nodes of GaAs integrated circuits. The technique exploits the electrooptic effect of the GaAs substrate to obtain a voltage-dependent polarization-modulation of a probe beam passing through the circuit substrate. Sampling techniques result in ∼ 100 GHz bandwidth. The factors determining system bandwidth and sensitivity are discussed, and measurement results are reviewed. To attain picosecond time resolution in electrooptic sampling, the timing fluctuations of the pulsed laser system must be reduced to significantly below 1 ps. Timing fluctuations in the 50 Hz–25 kHz frequency range are reduced from 1.2 ps to 0.24 ps by phase-locking the laser to a precision radio-frequency oscillator. Stabilizer design considerations are discussed.