The sixth generation of mobile communications (6G) is expected to offer low-latency, low-power, high-capacity, and large-scale communication services in the future. Terahertz communication, with its wide bandwidth, high speed, and low latency, is considered a key technological pathway for the 6G era. This article details the development routes for signal generation in THz communication systems signal reception technologies, signal transmission characteristics, and channel modeling. It also analyzes the progress and challenges in technological issues such as ultra-massive multiple-in multiple-out, intelligent reflecting surfaces, and critical THz devices. Furthermore, potential applications of THz communication in areas like short-range ultra-high-speed communication, space communication, micro-scale communication, and high secure communication fields are explored. Although there are some technical obstacles, as research progresses, the challenges associated with terahertz communication are expected to be gradually resolved. The advent of the 6G era is also anticipated to be not far off.

Temporal ghost imaging (TGI) enables the detection of high-speed temporal signals using low-speed detectors. Communication systems based on TGI technology can transmit high-frequency optical waveforms that exceed the bandwidth limitations of the system, while also providing high confidentiality and security. In recent years, numerous communication systems utilizing TGI technology have been proposed. This paper primarily discusses the principles and historical development of experimental setups for symmetric and asymmetric encryption communication systems based on TGI, as well as several methods for evaluating the quality of secure communication systems.