Abstract-On-chip Terahertz-Frequency Measurements of Liquids

Matthew Swithenbank, Andrew David Burnett, Christopher Russell, Lianhe H. Li, Alexander Giles Davies, Edmund H. Linfield, John E. Cunningham, and Christopher David Wood

Anal. Chem., Just Accepted Manuscript

DOI: 10.1021/acs.analchem.7b01235

Publication Date (Web): July 6, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.analchem.7b01235?journalCode=ancham

Terahertz-frequency-range measurements can offer potential insight into the picosecond dynamics, and therefore function, of many chemical systems. There is a need to develop technologies capable of performing such measurements in aqueous and polar environments, particularly when it is necessary to maintain the full functionality of biological samples. In this study, we present a proof-of-concept technology comprising an on-chip planar Goubau line, integrated with a microfluidic channel, which is capable of low-loss, terahertz-frequency-range spectroscopic measurements of liquids. We also introduce a mathematical model that accounts for changes in the electric field distribution around the waveguide, allowing accurate, frequency-dependent liquid parameters to be extracted. We demonstrate the sensitivity of this technique by measuring a homologous alcohol series across the 0.1-0.8 THz frequency range.

Abstract-Integrated Terahertz Graphene Modulator with 100% Modulation Depth

Guozhen Liang†, Xiaonan Hu†, Xuechao Yu†, Youde Shen‡, Lianhe H. Li§, Alexander Giles Davies§, Edmund H. Linfield§, Hou Kun Liang∥, Ying Zhang∥, Siu Fung Yu⊥, and Qi Jie Wang*†‡

†OPTIMUS, School of Electrical and Electronic Engineering, and ‡CDPT, School of Physical and Mathematical Sciences, The Photonics Institute, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

§ School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, U.K.

∥ Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075, Singapore

⊥ Department of Applied Physics, Hong Kong Polytechnic University, Kowloon, Hong Kong

ACS Photonics, Article ASAP

DOI: 10.1021/acsphotonics.5b00317

Publication Date (Web): October 19, 2015

Copyright © 2015 American Chemical Society

*E-mail: qjwang@ntu.edu.sg.

http://pubs.acs.org/doi/10.1021/acsphotonics.5b00317

Terahertz (THz) frequency technology has many potential applications in nondestructive imaging, spectroscopic sensing, and high-bit-rate free-space communications, with an optical modulator being a key component. However, it has proved challenging to achieve high-speed modulation with a high modulation depth across a broad bandwidth of THz frequencies. Here, we demonstrate that a monolithically integrated graphene modulator can efficiently modulate the light intensity of the THz radiation from a THz quantum cascade laser with a 100% modulation depth for certain region of the pumping current, as a result of the strongly enhanced interaction between the laser field and the graphene enabled by this integration scheme. Moreover, the small area of the resulting device in comparison to existing THz modulators enables a faster modulation speed, greater than 100 MHz, which can be further improved through optimized designs of the laser cavity and modulator architectures. Furthermore, as the graphene absorption spectrum is broadband in nature, our integration scheme can be readily scaled to other wavelength regions, such as the mid-infrared, and applied to a broad range of other optoelectronic devices.