Improvement of Terahertz Photoconductive Antenna using Optical Antenna Array of ZnO Nanorods

Abstract

An efficient terahertz (THz) photoconductive antenna (PCA), as a major constituent for the generation or detection of THz waves, plays an essential role in bridging microwave-to-photonic gaps. Here, we propose an impressive approach comprising the use of arrayed zinc oxide nanorods (ZnO NRs) as an optical nanoantenna over an anti-reflective layer (silicon nitride) in the antenna gap to boost the photocurrent and consequently the THz signal. The numerical approach applied in investigating the optical behavior of the structure, demonstrates a significant field enhancement within the LT-GaAs layer due to the optical antenna performing simultaneously as a concentrator and an antireflector which behaves as a graded-refractive index layer. ZnO NRs have been fabricated on the PCA gap using the hydrothermal method as a simple, low cost and production compatible fabrication method compared to other complex methods used for the optical nanoantennas. Compared to the conventional PCA with a traditional antireflection coating, the measured THz power by time domain spectroscopy (TDS) is increased more than 4 times on average over the 0.1–1.2 THz range.

Photoconductive Meta‐Antenna Enabling Terahertz Amplitude Spectrum Manipulation

“…It can be clearly seen that although different PCAs do have amplitude fluctuation, the range of the error is not sufficient to affect the conclusion: the band‐stop and band‐pass resonances at 0.34 and 0.54 THz are definitely present. Comparing with previous nanostructure‐assisted PCA which focuses on enhancing the overall THz power, [ 11–21 ] the proposed micron‐scale SRRs here achieve the manipulation of the spectral characteristics of PCA which is rarely been realized and discussed.…”

“…To enhance the performance of PCAs, researchers set their sights on the booming field of metamaterials which have the high design degree of freedom level and flexible manipulation capability. [ 7–9 ] A variety of metallic/dielectric nanostructures, such as gratings, [ 10–12 ] nanoislands, [ 13 ] hole arrays, [ 14 ] pillar arrays, [ 15–18 ] optical nanoantennas, [ 19 ] and interdigitated fingers, [ 20 ] have been integrated to PCAs to achieve outstanding characteristics. These nanostructures play positive roles primarily by altering the interaction of the femtosecond laser pulse and the substrate, thereby controlling the density and dynamics of the photogenerated carriers.…”

Metallic and dielectric metasurfaces in photoconductive terahertz devices: a review

“…Further improvement of the PCA performance was proposed by Bashirpour et al, 106 where they implemented an optical nanoantenna comprised of an array of dielectric ZnO nanorods to boost the local field and the optical absorption. This resulted in a twofold increase in the THz photocurrent and a fourfold enhancement in the emitted THz power compared with the conventional PCA without nanoantenna.…”

An Efficient Photomixer Based Slot Fed Terahertz Dielectric Resonator Antenna

“…It has been demonstrated earlier that an enhancement factor of 4 in the optical to THz conversion efficiency can be achieved by using plasmonic material as interdigital electrodes [ 22 ]. Additionally, more than 4 times of THz power has been achieved by using optical antenna array of ZnO nanorods [ 23 ]. Further, an enhancement factor of 25 in terahertz radiation has been demonstrated by utilizing transparent-conducting oxcides nanocylinders between photomixer electrodes [ 24 ].…”