Generating millimeter and terahertz waves

Research on millimeter waves and/or terahertz waves, which cover the frequency range from 30 GHz to 10 THz, has lately increased since the nature of these electromagnetic waves is well suited to spectroscopic sensing as well as ultrabroadband wireless communications. One of the obstacles to developing applications of millimeter waves and terahertz waves is a lack of solid-sate signal sources, rather than detectors. In fact, the frequency band in this region is often referred to as the terahertz gap.