Dong Woo Park

Nondestructive THz imaging technology is a promising technology in several industrial applications such as process monitoring and quality control. To further popularize the application of this technique in the industry, we developed photonics-based devices such as a dual-mode laser, uni-travelling carrier photodiode, and Schottky-barrier diode that enable the realization of a compact, low-cost, multifunctional continuous wave (CW) THz system. To develop CW THz reflective imaging systems with these devices, a telecentric f-θ lens and novel two-dimensional (2D) beam scanner were developed. A high-speed, low-cost 2D reflector with a 4-sided polygon mirror, a brushless DC (BLDC) motor rotating at approximately 2,990 revolutions per minute (RPM) and a stepping motor was designed to ensure that a THz image sized 500 × 400 pixels could be scanned in approximately 2 s. However, it is difficult to maintain a constant speed in high-speed rotating BLDC motors. The measured maximum deviation is approximately 0.7%, which results in distorted images. To compensate for this distortion, a sync signal reflector was designed to monitor the real-time RPM of the BLDC motor. Using the novel 2D beam scanner and sync signal reflector, the distorted images could be corrected simply, enabling the development of a 2D THz reflective imaging system using a single emitter and detector; this system could exhibit a higher speed and was more cost effective than the existing system. Although further improvements to photonics-based THz technologies are necessary, we believe that these efforts will begin an era of THz technologies as a widely used industrial technique.

We presented terahertz (THz) generation and detection characteristics of an InGaAs epilayer with periodic InAlAs insertion layers (InGaAs-PIL). The peak-to-peak current signal (PPCS) from a THz transmitter with the InGaAs-PIL was three times higher than that of a simple InGaAs epilayer. Moreover, the detection properties of a THz receiver with the low-temperature grown (LT) InGaAs-PIL showed more than twenty-five times higher than that of the LT-InGaAs epilayer. The PPCS of the LT-InGaAs-PIL was significantly improved with increasing the periods of the InAlAs insertion layer.