Abstract
Programmable conductive patterns created by photoexcitation of semiconductor substrates using digital light processing (DLP) provides a versatile approach for spatial and temporal modulation of THz waves. The reconfigurable nature of the technology has great potential in implementing several promising THz applications, such as THz beam steering, THz imaging or THz remote sensing, in a simple, cost-effective manner. In this paper, we provide physical insight about how the semiconducting materials, substrate dimension, optical illumination wavelength and illumination size impact the performance of THz modulation, including modulation depth, modulation speed and spatial resolution. The analysis establishes design guidelines for the development of photo-induced THz modulation technology. Evolved from the theoretical analysis, a new mesa array technology composed by a matrix of sub-THz wavelength structures is introduced to maximize both spatial resolution and modulation depth for THz modulation with low-power photoexcitation by prohibiting the lateral diffusion of photogenerated carriers.
Highlights
Over the last decade, the terahertz region (300 GHz - 3000 GHz) of electromagnetic spectrum has become increasingly important in radio astronomy, spectroscopy, medical imaging and defense [1,2,3,4]
The results provide design guidelines to optimal modulation depth, speed and spatial resolution which are essential to achieve high-performance THz tunable components for advanced sensing and imaging
In conclusion, we theoretically analyzed a spectrum of physical effects on photo-induced THz wave modulation and provided the rationale for the choice of substrate material and thickness, illumination wavelength, area and power density, and THz frequency
Summary
The terahertz region (300 GHz - 3000 GHz) of electromagnetic spectrum has become increasingly important in radio astronomy, spectroscopy, medical imaging and defense [1,2,3,4]. THz modulation through photo-induced carriers on a semiconductor using Digital Light Processing (DLP) projector is considered as a high-performance, reconfigurable and cost-effective approach [11, 12] This technique takes the advantages of optically generated conductive patterns on semiconductor substrates (e.g., silicon) to manipulate the transmission of THz waves, allowing one to perform a variety of reconfigurable functions, including THz beam steering [13], polarization, focusing and THz resonators. The theoretical studies lead to a new design named mesa-array structure that utilizes a matrix of sub-THz wavelength structures to restrict lateral diffusion of carriers in semiconductor substrates, remarkably improving both spatial resolution of the photo-induced conductive patterns and the modulation depth of THz waves. The new concept is expected to significantly improve the performance of THz wave spatial modulation using low-power optical excitation
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