Integrated optics show potential for terahertz technology applications

Terahertz technology has potential application in the areas of safe medical imaging, nondestructive security screening, and communications. Currently, the bulky free-space optics and manual optical alignment required for this technology limit the viable scope of real-world applications.

Headland et al developed a compact integrated terahertz system based on free-propagating beams, as opposed to channel waveguides. In addition, the system requires no manual optical alignment.

Their concept involved combining an unpatterned silicon, dielectric slab wave guide with a half-Maxwell fisheye lens. The wave guide confined radiation to a narrow air gap.

The half-Maxwell lens, innately compact due to a focal length of half its diameter, served as a beam expander. The result was a 90% efficient collimator with a bandwidth greater than one octave.

The researchers produced two different prototype systems to successfully demonstrate the versatility of this concept – a distributed Bragg reflector-based broadband diplexer for terahertz communications and an attenuated total internal reflection-based terahertz liquid sensor.

“The integrated optics paradigm that we present essentially replaces free-space with a flat silicon slab that’s one-fifth of a millimeter thick,” said co-author Daniel Headland. “The terahertz waves can, therefore, be thought of as half-guided. They are free to propagate within the 2D plane of the flat slab, but they cannot leak out.”

The next challenge will be to develop techniques to generate, detect, and modulate terahertz waves now that the flow of power can be controlled in this integrated optical platform.

“All of these points will be the subject of future research effort,” said Headland.

Source: “Dielectric slot-coupled half-Maxwell fisheye lens as octave-bandwidth beam expander for terahertz-range applications,” by Daniel Headland, Andreas Kurt Klein, Masayuki Fujita, and Tadao Nagatsuma, APL Photonics (2021). The article can be accessed at https://doi.org/10.1063/5.0054251 .