Graphene-enabled coherent terahertz wave detection and thickness determination

TL;DR

This paper presents a graphene-based on-chip THz detector-interferometer with high phase sensitivity and sub-wavelength thickness measurement capability, promising advancements in spectroscopy, wireless communication, and industrial inspection.

Contribution

The work introduces a novel graphene-enabled integrated THz detector-interferometer with optical cavity and antenna, achieving high sensitivity and sub-10 nm thickness accuracy.

Findings

Achieved sub-wavelength film thickness measurement of ~5 μm.

Recorded high external responsivity of 73 mA/W at 89 GHz.

Demonstrated potential for 10 nm thickness accuracy in future applications.

Abstract

Coherent detection and interferometry in the terahertz (THz) regime are key capabilities that enable applications ranging from astronomy to non-destructive testing. Phase-sensitive THz detection is currently achieved using nonlinear crystals or external interferometers and photomixers. However, the former approach requires femtosecond pulsed radiation, and all approaches suffer from a large footprint and sensitive alignment. Here, we demonstrate a graphene-enabled, on-chip, integrated THz detector-interferometer with optical cavity and antenna, exhibiting high sensitivity to the phase of incident THz light. We exploit this by determining the thickness of thin films placed in front of the detector-interferometer, obtaining a strongly sub-wavelength thickness accuracy of $\sim$5 $\mu$m, while we predict that an accuracy of 10 nm is within reach. This is relevant for a range of industrial application domains, including automotive, construction, and health. The detector-interferometer moreover exhibits a record-high external responsivity - without any normalization to a diffraction-limited spot size - of 73 mA/W and a noise-equivalent power of 79 pW$~\rm{Hz}^{-1/2}$. This performance is due to enhanced absorption at the cavity mode around 89 GHz, in agreement with multi-physics simulations. These results pave the way to exploiting coherent wave detection in the THz regime with utility in spectroscopy, next-generation wireless communication, and beyond.