Abstract
Progress in the terahertz (THz) region of the electromagnetic spectrum is undergoing major advances, with advanced THz sources and detectors being developed at a rapid pace. Yet, ultrafast THz communication is still to be realized, owing to the lack of practical and effective THz modulators. Here, we present a novel ultrafast active THz polarization modulator based on GaAs semiconductor nanowires arranged in a wire-grid configuration. We utilize an optical pump-terahertz probe spectroscopy system and vary the polarization of the optical pump beam to demonstrate ultrafast THz modulation with a switching time of less than 5 ps and a modulation depth of -8 dB. We achieve an extinction of over 13% and a dynamic range of -9 dB, comparable to microsecond-switchable graphene- and metamaterial-based THz modulators, and surpassing the performance of optically switchable carbon nanotube THz polarizers. We show a broad bandwidth for THz modulation between 0.1 and 4 THz. Thus, this work presents the first THz modulator which combines not only a large modulation depth but also a broad bandwidth and picosecond time resolution for THz intensity and phase modulation, making it an ideal candidate for ultrafast THz communication.
Highlights
Terahertz (THz) radiation, lying between the infrared and microwave regions of the electromagnetic spectrum, has historically been an elusive frequency range (0.1−10 THz) with THz technology in its infancy.[1]
Previous works have mainly focused on modulation of THz intensity, with early demonstrations based on twodimensional electron-gas (2DEG) structures,[31,32] birefringent liquid crystals,[33,34] and static THz polarizers.[35−38] Recently, THz modulation has been realized with metamaterials,[25,27,29,37,39−43] optical cavities,[44,45] graphene,[46−49] and carbon nanotubes,[28,50,51] each with their own merits and weaknesses
Docherty et al.[28] demonstrated an ultrafast switchable carbon nanotube THz polarizer, which could be optically controlled and was capable of polarization and intensity modulation of THz radiation with a time resolution on the order of 1 ps, it suffered from a low modulation depth of around −27 dB
Summary
Letter depth by utilizing the evanescent wave in a total internal reflection setup coupled with a conductive interface to enhance attenuation of THz radiation.[54]. We define the dynamic range as the relative difference in THz transmission when the pump is polarized at angles of 2θ = 90° and 2θ = 0° For this single-layer parylene-coated GaAs nanowire polarizer at the highest investigated fluence (280 μJ cm−2), the modulation depth was found to be −17.4 ± 0.1 dB corresponding to extinction of ∼1.82 ± 0.04%, and the dynamic range was determined as −18.8 ± 0.1 dB. These values already exceed values measured for carbon nanotube-based THz polarizers but are not yet ideal for THz modulation in high-speed communication systems.
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