Abstract
Abstract In the past ten years, terahertz technology has developed rapidly in wireless communications, spectroscopy, and imaging. Various functional devices have been developed, such as filters, absorbers, polarizers, mixers, and modulators. Among these, the terahertz phase modulation is a current research hotspot. It is the core technology to realize flexible control of the terahertz wavefront, beam scanning, focusing deflection. It is indispensable in terahertz wireless communication, high-resolution imaging, and radar systems. This review summarizes the research progress of terahertz phase modulators from the two major types: free space and guided wave integration. Among these, the free space terahertz phase modulator is realized by combining the tunable materials and artificial metasurfaces. Based on different types of tunable materials, the terahertz free space phase modulator combining the semiconductor, liquid crystal, phase change materials, graphene, and other two-dimensional materials are introduced, and the influence of different materials on the phase modulation performance is discussed and analyzed. The monolithic integration and waveguide embedding methods are introduced separately, and the characteristics of different forms of terahertz-guided wave phase modulation are also discussed. Finally, the development trends of terahertz phase modulators, possible new methods, and future application requirements are discussed.
Highlights
Hongxin Zeng and Sen Gong contributed to this work.Terahertz technology has shown significant development potential in data communications, radar detection, highresolution imaging, and other fields
The free space terahertz phase modulator is realized by combining the tunable materials and artificial metasurfaces
Yang et al compared the phase response of three thermotropic liquid crystals (5CB, E7, and BNHR) to terahertz waves under an externally weak magnetic field (30 mT), and the results proved that the BNHR liquid crystal has a larger phase modulation depth and requires a lower magnetic field
Summary
Hongxin Zeng and Sen Gong contributed to this work. Terahertz technology has shown significant development potential in data communications, radar detection, highresolution imaging, and other fields. The basic principle is to change the electromagnetic characteristics of the semiconductor materials, phase change materials, liquid crystal materials, graphene, or other materials These materials can be combined with a custom-designed metasurface to change the resonance characteristics of the meta-atoms, thereby realizing the modulation of terahertz waves [15,16,17,18,19]. This kind of FSPM can be divided into transmission type and reflection type, most often in a quasi-optical configuration.
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