Optoelectronic characterization of transmission lines and waveguides by terahertz time-domain spectroscopy

An overview is presented of an experimental search for an ultrawide-band transmission channel with low dispersion and loss. Such a terahertz (THz) interconnect will soon be required by the insatiable demand for higher speed devices and wider bandwidth communication, Starting with the early optoelectronic generation and detection of single-mode, subpicosecond electrical pulses on coplanar transmission lines, their complete characterization by THz time-domain spectroscopy (THz-TDS) is described. The consequent discovery of phase-coherent Cherenkov radiation in the form of an electromagnetic shock wave from these propagating electrical pulses is discussed together with its dominant role in the large measured propagation loss of these pulses. Various techniques to reduce this radiation are presented. The importance of dielectric materials characterization is explained and illustrated by THz-TDS measurements of high T-c substrates. Newly obtained THz waveguide results are presented and compared to the performance of coplanar transmission lines.