Sensitive and Robust Millimeter-Wave/Terahertz Photonic Crystal Chip for Biosensing Applications

Abstract

In recent years terahertz (THz) technology has attracted great interest in biosensing applications. Due to the interaction between analyte and electromagnetic (EM) field, a THz resonator is sensitive to changes in the refractive index of the analyte and can be used as a thin-film sensor for rapid pathogen diagnosis. To achieve high sensitivity and reliability, the sensor should have a high Q factor, a high field concentration at the site of the analyte, and the ability to compensate for temperature effects. However, conventional metamaterial methods have a low Q factor, which may lead to ambiguous detection and no attention has been paid to address the temperature effects. Here, we present a photonic crystal (PhC) based chip consisting of a reference channel and a sensing channel with two identical PhC slot resonators. The resonance difference between the resonators is temperature invariant and can be used for analyte detection. The dual-channel PhC chip has a Q factor of 5063 and a figure of merit of 3.1 /RIU/µm (RIU is refractive index unit), which are higher than that of metamaterial sensors. The chip is designed and simulated for the W band by 3D field simulations and is verified by measurements. Our results suggest that THz PhC resonators can provide high sensitivity and high resistance to environmental effects. We anticipate our work to be a starting point for future biosensing applications.INDEX TERMS High Q factor, photonic crystal resonator, temperature invariant, terahertz, thin-film sensing.

3D printed sub-terahertz photonic crystal for wireless passive biosensing

“…This has motivated the research of PhC biosensors in the terahertz (THz) frequency range, where PhCs have been studied for wireless communication and biosensing applications [20][21][22] . Further, in previous study we have been able to demonstrate, that a sub-THz PhC slot resonator, working as a surface sensor, has a very high FOM when compared to other THz sensors 23 .…”

“…where FWHM is the full width at half maximum of the resonance in the frequency domain, h a is the thickness of an equivalent thin-film related to the captured analyte, and Δn is the difference in RI of the analyte to air. The FOM can be improved by increasing electric field concentration at the site of the analyte and by increasing the Q-factor 23 . To enhance the field strength within the thin-film analyte, a slot is introduced in the middle of the resonator as shown in Fig.…”

“…The displacement of the holes and the width of the slot are optimized for maximum Q-factor by sweeping the structural dimensions. Further details of design processes can be found in our previous work 23 . In addition, the coupling losses depend on the number of hole rows between the waveguide and the resonator, the diameter of the holes, and the number of waveguides used for the coupling.…”

“…3a. Since the analyte layer is very thin compared to the wavelength, the resonance shifts are assumed to be reciprocally related to the RI of the analyte 23 . Next, h a is swept from 0.1 to 1 µm while n is held constant (n = 1.8) to investigate the sensitivity to the analyte as the thickness varies, as shown in Fig.…”

Acousto-optical coupling in two-dimensional air-slot phoxonic crystal heterostructure cavity

“…In 2017, MA et al [36] studied a two-dimensional phoxonic crystal structure with a slot, and theoretically proved that the structure with an air slot can effectively enhance the acousto-optic coupling effect. In 2020, ZHAO et al [37] proposed a dual channel photonic crystal with air slot, which proved theoretically and experimentally that the introduction of air slot is helpful to increase the optical quality factor.…”