Towards terahertz photonics

Abstract

Optical generation of THz signals provides an attractive altemative to traditional methods. Recent progress in the generation and detection of mm-wave lo THz modulated optical signals is described, including the important consideration of spectral purity. INTRODUCTIONSignals in the upper mm-wave and THz region are of interest for imaging, short range communication and spectroscopic applications [I]. This part of the spectrum has in the past been difficult to access due to the lack of compact, low-cost sources; most work using vacuum devices such as the carcinotron or for very low powers, point contact diode frequency multipliers. The high centre-frequency of optical sources operating in the 1,500 nm wavelength region, of about 200 THz, makes it relatively simple to generate optical fields modulated at THz frequencies, by heterodyning two or more optical sources, or by generating multi-mode output from a single source, using modebeating or mode-locking. At the same time innovative work on photo-detector design is enabling efficient detection of the modulated optical fields in the upper mm-wave region leading to prospects of a compact and efficient THz source capable of opening up a wide range of applications in this frequency range. This paper will describe recent progress in the generation and detection of mm-wave to THz modulated optical signals, including the important consideration of spectral purity.