Abstract
Terahertz (THz) imaging techniques have attracted significant attention and have developed rapidly in recent years. However, despite several advances, these techniques are still not mature, and their high cost and system complexity continue to limit their applications. In this article, the techniques for achieving a practical imaging system with a compact THz transceiver are addressed, while considering the limitations of the current technique. The aim is to provide a brief review of related topics, while also covering our recent progress, which can provide some general perspectives and contrasting approaches for realizing a practical THz imaging system. The continuous wave devices are mainly focused for their flexibility of balancing the imaging resolution and data acquisition time. The importance of transceiver integration is also discussed and illustrated by introducing a 600-GHz band micro-photonic interface for integrating a THz source and detector, with a single resonant tunneling diode as a transceiver. With regard to system issues, spatial sampling with mechanical beam-scanning is discussed as an intermediate approach for moving stage and array technology. The potential and limitations of this approach are evaluated, along with an elliptical reflector as an alternative to an f-theta lens owing to its low cost and simplicity. The combination of integrated devices, along with the mechanical beam-scanning, is also discussed for demonstrating our current concept of realizing a practical THz imaging system.
Highlights
In recent years, a variety of sensing applications in the terahertz (THz) band have attracted significant attention as these frequencies provide sub-millimeter-level resolution and good transparency to electrical insulators such as paper, glass, and polymers
In order to improving the THz imaging technique, many significant works have been proposed for summarizing the related topics from different angles such as imaging speed [7], high-resolution imaging [1], [10], THz array integration [8], [11], [12] and specific techniques [3], [6], [13], while this article mainly focuses on the techniques that will lead to a practical THz imaging system, which includes a compact transceiver and cost-effective spatial sampling method
The pulse-based imaging technique, which refers to THz time-domain spectroscopy (TDS), is mainstream for THz sensing/imaging applications [4], [5], [7], [13]
Summary
A variety of sensing applications in the terahertz (THz) band have attracted significant attention as these frequencies provide sub-millimeter-level resolution and good transparency to electrical insulators such as paper, glass, and polymers. Since a fixed transceiver pair yields only a single pixel, spatial sampling is another key issue for THz imaging systems; the methods used for spatial sampling significantly affect the size, data acquisition time, and cost of the system. Both beam-focusing with quasi-optic components and digital focusing techniques such as holography [27], [28] or synthetic aperture radar (SAR) [1], [29]–[31] can be applied to 2D and/or 3D imaging with sufficient spatial sampling. The last section provides a conclusion and prospects for terahertz imaging techniques for related applications
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