THz Detectors and Related Topics

Abstract

This chapter will provide an overview of various methods of detecting electromagnetic waves, with a focus on THz wave detection. The detection can be made exploiting several different mechanisms. First, various thermal effects caused by THz radiation can be used for detection. Called thermal detectors, this type of detectors include bolometers, pyroelectric detectors, thermopiles, and Golay cells. Second, the rectification of AC signals, often after conversion from electromagnetic waves by antenna, into DC voltage can be used for detection, as in the case for the square-law detectors. Third, there is the heterodyne technique, in which signal is down-converted by a mixer and then detected with a conventional low-frequency AC signal detector. This relaxes the operation frequency requirement for the detector at the back-end of the receiver chain. Historically, the first technique has been widely deployed over infrared detection, while the other two techniques prevailed over the microwave and lower frequency detection. THz wave detection, therefore, can be realized based on these approaches with a proper extension of the frequency range, downward or upward. Yet another detection method that has been dominating the optical band is detection with photodetectors. However, this method does not fit for THz detection since the photon energy corresponding to the THz spectrum is too small (a few meV) for practical detection, and hence will not be treated in this chapter. The rectification and heterodyne techniques can be implemented by either diodes or transistor circuits and will be discussed separately after describing the thermal detector in this chapter. Array detectors will be treated as an additional section.