Terahertz (THz) waves remain one of the most underdeveloped regions of the electromagnetic spectrum, despite the great promise for potential applications in remote sensing, imaging, spectroscopy, and communications. THz waves carry unique molecular signatures that are not available in the rest of the electromagnetic spectrum. In particular, THz waves offer the opportunity for transformational advances in homeland security, such as applications in standoff detection and identification of concealed explosive targets. However, THz waves have proven very challenging to control due to a paucity of electromagnetic materials with an effective response at THz frequencies. This “THz gap” results in a great impediment for the development of functional THz optical components and systems. In view of these challenges, the objective of this research proposal is to develop new engineering capabilities in designing and manufacturing three-dimensional THz imaging lens that consisting spatially varying refractive index. Such a gradient index lens can be extremely powerful to control the flow of the THz wave, in contrast to the traditional lens made of homogenous materials. We have implement the transformation optics theory to design the spatial distribution of the refractive index in accomplishing the desired optical functionalities, such as invisibility cloaking, focusing, imaging, and waveguiding. We also have developed novel additive manufacturing capabilities, or so called 3D printing process, to fabricate the 3D gradient index THz lens following the theoretical design.

As shown in Figure 1a, a home-made projection microstereolithography system has been developed. The optical image formed at the lower surface of photo-curable polymer resin is used to determined the shape of cured solid layer. Thus, the design of the 3D THz lens can be sliced into a sequence of many crosssectional images. The direct fabrication of 3D THz lens can be accomplished by projecting the movie containing the sequence of the crosssectional images while simultaneously translating the substrate vertically. The fabricated semi-spherical THz lens with the radius of 4.27 mm is shown in Fig. 1b. The lens consists of fine features much smaller than the THz wavelength and thus, the THz wavelength will only “see” the averaged effect properties (Fig. c). Hence, it is possible to create the design of the gradient index lens by locally adjusting the size of 3D printed polymer wires (Fig. 1d).

The innovations obtained from this research represent a technological breakthrough, which will usher in a new generation of THz optical systems with greatly improved resolution, efficiency, and miniaturization to meet the needs of commercial and military applications. The proposed THz 3D Metamaterials concept and integrated research protocol can be further extended to the broad electromagnetic wave spectrum for stealth technology, advanced communication systems, medical imaging, and remote sensing. The developed design methodology can be easily scalable to other photonic spectrum ranges, and thus, make it broadly applicable to enable the design of new photonic components and devices with extraordinary performance. The new scalable 3D microfabrication technology will pave the way for future development of a variety of integrated devices and system with ultimate performance. 

Last Modified: 03/09/2016
Modified by: Cheng Sun