Semiconductor-based plasmonic interferometers for ultrasensitive sensing in a terahertz regime

Abstract

A robust plasmonic semiconductor-based Mach-Zehnder interferometer (MZI), which consists of a semiconductor layer with a microslit flanked by two identical microgrooves, is proposed and investigated for the terahertz sensing. The microgrooves reflect the surface plasmon polariton waves toward the microslit, where they interfere with the transmitted terahertz wave. The interference pattern is determined by the permittivities of the sensing material and semiconductor (i.e., temperature dependent), making the structure useful for the refractive index (RI) and temperature detection. A quantitative theoretical model is also developed for performance prediction and validated with a finite element method. The numerical results show that the Mach-Zehnder interferometer sensor possesses an RI sensitivity as high as 140000 nm/RIU (or 0.42 THz/RIU) and a relative intensity sensitivity of 1200%RIU^-1. In addition, a temperature sensitivity of 1470 nm/K (or 4.7×10^-3 THz/K) is determined. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure. The proposed sensing scheme may pave the way for applications in terahertz sensing and integrated terahertz circuits.

High‐Performance Terahertz Sensing at Exceptional Points in a Bilayer Structure

“…This reflects the presence of a square root behavior with the induced perturbation. The results show that the sensitivity in our system reaches a maximum value of approximately 800 GHz RIU −1 µm −1 , which is an order of magnitude higher than the ones of the present THz biosensors from metamaterial, SSP, and ATR methods. This is also larger than the one required for the detection of monolayer biomolecule (250 GHz RIU −1 µm −1 ) as discussed in Section 1.…”

“…MM‐based biosensors, for example, have been demonstrated to yield sensitivities of about 50 GHz RIU −1 µm −1 by reducing the substrate thickness and selecting high‐Q resonance modes. Most recently, a SSP‐type sensor was reported having a frequency shift of 420 GHz RIU −1 as an upper space was filled with the medium . Considering that the decay length of THz wave is assumed to be approximately 10 µm, we estimate its sensitivity to be 42 GHz RIU −1 µm −1 , which is in the same level as the MM‐based sensors.…”

“…In the past decade, artificial structures, such as metamaterials (MMs) and periodic structures that sustain spoof surface plasmons (SSPs), ‒ have been developed to enhance the spectroscopic sensitivity. However, up until this point, the requisite sensitivity at THz frequencies has not been demonstrated.…”

Non-Hermitian Electromagnetic Metasurfaces at Exceptional Points (Invited Review)

“…This EP-sensor is evaluated via a sensitivity defined by eigenfrequency shift per micrometer in thickness and per refractive index unit (RIU). The sensitivity can reach 800 GHz RUI −1 um −1 in theory, which is an order of magnitude higher than conventional terahertz biosensors in Hermitian settings [81,82]. In addition to exceptional sensitivity based on intensity or resonant frequency changes, phase changes or polarization rotations can also be monitored for ultrasensitive sensing.…”

Semiconductor THz microsensors based on ultrahigh-contrast T-shape patterned interferometers

“…18,19) To overcome this spectroscopic issue, we recently studied two kinds of interferometers, which are based on the silicon-oninsulator and slit-groove structures. 20,21) Their interference pattern contrasts are relatively low due to unbalanced SPPs intensities on upper/lower InSb surfaces and insufficient SPPs scattering efficiency of grooves.…”