Xiaohua Wu

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Electrical and Computer Engineering


Dr. David R. Conn


Electro-optic (E-O) sampling is capable of measuring internal node response of microwave and high speed devices and circuits with minimal invasiveness up to terahertz frequency range or in the picosecond domain. Unfortunately, the accuracy of E-O sampling is still not comparable to a conventional network analyzer due to lack of a generl calibration technique. Therefore, a general and systematic calibration technique is demanded for quantitative measurement using E-O sampling. In this thesis, a full wave time domain field analysis technique, called the Finite-Difference Time-Domain (FD-TD) method, has been applied to the external E-O sampling problem. Using this theoretical simulation model, field disturbances in external E-O sampling have been investigated, calibration method of external E-O sampling developed and the optimum probing design techniques suggested. Field disturbances, (i.e. invasiveness and distortion) in external E-O sampling have been examined quantitatively, for the first time, by means of field and wave simulation. The results suggest that probes introduce little invasiveness if they are removed from contact by a finite distance which depends on dimensions of the device being tested. The sampled signal distortion introduces considerable error at high frequencies or when sub-picosecond pulses are involved. The FD-TD method has been successfully, applied, for the first time, to external E-O sampling problem and combined with electro-optic tensor to yield electro-optic response in E-O sampling. The probe transfer function has been then derived to characterize probe specifications. It provides a practical means to quantitatively investigate the operational frequency limit of any given probe. A field based calibration technique has been developed to de-embed both invasiveness and distortion using the full wave field modeling and the probe transfer function which can be found by field simulation or measurement results. It has been found that each specific robe has an intrinsic transfer function primarily determined by probe dimensions and space between the probe face and the device being tested. The impact of different probe materials, different sampling beam positions, and different probe dimensions with respect to the device being tested (i.e. the electric field orientation) has been systematically evaluated for the first time. The results provide necessary information for engineers to properly design probes and system set-up in order to achieve optimum E-O sampling results. It has been shown that LiTaO₃ probes are favored over GaAs when the sensitivity is the major concern. In contrast, GaAs probes are preferred when the accuracy in high frequencies up to several hundred gigahertz is of primary interest. In addition, sampling near the leading edge of probes is preferred in external E-O sampling to minimize the distortion induced in the measured results. The research conducted in this thesis can be straightforwardly extended to direct and hybrid E-O sampling problems. Further research and development will lead this field based calibration technique in E-O sampling to more general devices such as microwaves monolithic circuits (MMICs).

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