Abstract
The increasing development of terahertz (THz) technology has led to various potential applications in THz imaging, spectroscopy and communications. These devices capable of actively manipulating the amplitude, phase and frequency of THz waves are thus gaining numerous interests. All-optical silicon-based spatial terahertz modulators (STMs), as a simple, cost-effective, and reconfigurable technique, are standing the focus of research. Beginning with a fundamental concept of THz radiation, this paper systematically summarized the modulation mechanism and theoretical model for this kind of STM, reviewed the recent advancements in THz functional devices implemented by this optical method and yet, discussed the performance-improved measures with an emphasis on the reflection reduction. Despite that, there has been considerable progress in realizing high-performance STMs, and novel design is urgent to realize higher modulation rate and more functionality.
Highlights
Terahertz (THz) radiation situated between microwave and infrared regions of electromagnetic spectrum has become increasingly attractive for its extraordinary properties
THz image and near-field microscopy is mainly used for non-destructive inspection, medical diagnose as well as security detection
Where ( ) is the complex conductivity and ε0, τ, m and e are the permittivity of free space, scattering rate, electron mass and electron charge, respectively. ωp represents the plasma frequency, p Ne2 0m, a characteristic frequency below which the material acts “metallic” while above which it is transparent to optical radiation. This phenomenon indicates that semiconductors are suitable for all-optical modulation of THz waves: A high-reflectance region is temporarily formed onto the semiconductor when the laser is incident and the co-projected THz radiation on this area is modulated
Summary
Terahertz (THz) radiation situated between microwave and infrared regions of electromagnetic spectrum has become increasingly attractive for its extraordinary properties. Ωp represents the plasma frequency, p Ne2 0m , a characteristic frequency below which the material acts “metallic” while above which it is transparent to optical radiation This phenomenon indicates that semiconductors are suitable for all-optical modulation of THz waves: A high-reflectance region is temporarily formed onto the semiconductor when the laser is incident and the co-projected THz radiation on this area is modulated. Regular semiconductor materials, such as silicon (Si), gallium arsenide (GaAs) and germanium (Ge), have been resoundingly put to use in optical-controlled THz waves modulators [12,13,14,15,16,17,18,19].
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