Terahertz Technology—Emerging Trends and Application Viewpoints

Abstract A review of the emerging trends of development of terahertz (THz) technology for signal generation, detection, and sensing, system component design, time-domain spectroscopy, and application viewpoints for security, pharmaceuticals, and medical, including advanced communications, has been provided. Limitations of conventional RF, microwave, and millimeter-wave electronic techniques for THz signal generation have been discussed first, followed by signal generation with optical means and accelerator-based techniques have been given. The optical means use optical heterodyning of laser sources, quantum cascade laser, and other methods based on photoconductive material or electro-optic and other nonlinear crystals irradiated with femtosecond laser. In accelerator-based technique, free-electron laser system has been covered for both high-power and portable systems. THz signal detection/sensing based on both electrical and optical techniques and image reconstruction technique has also been discussed. Both quasioptical and waveguide-based approaches are used at THz frequency to realize THz system components like couplers, resonators, polarizers, filters, antennae, etc., and that has been briefly covered. During the last 2 decades, THz technology is in use for terahertz time-domain spectroscopy (THz-TDS) or T-ray imaging and various techniques for this have been discussed. Application of THz technology for security purposes like concealed weapon detection, standoff detection of explosives, and illegal drugs has been addressed, including the use of THz technology by pharmaceutical industry and early diagnosis of cancer by medical fraternity. Possibility of the use of THz technology for the future 6G mobile communications with Tbps (terabit per second) data rate and other advanced communication applications has also been briefly discussed. Finally, the recent trends of metamaterial-inspired THz component design for better sensor and other passive component performance have been included too.