Abstract
The reversible and multi-stimuli responsive insulator-metal transition of VO2, which enables dynamic modulation over the terahertz (THz) regime, has attracted plenty of attention for its potential applications in versatile active THz devices. Moreover, the investigation into the growth mechanism of VO2 films has led to improved film processing, more capable modulation and enhanced device compatibility into diverse THz applications. THz devices with VO2 as the key components exhibit remarkable response to external stimuli, which is not only applicable in THz modulators but also in rewritable optical memories by virtue of the intrinsic hysteresis behaviour of VO2. Depending on the predesigned device structure, the insulator-metal transition (IMT) of VO2 component can be controlled through thermal, electrical or optical methods. Recent research has paid special attention to the ultrafast modulation phenomenon observed in the photoinduced IMT, enabled by an intense femtosecond laser (fs laser) which supports “quasi-simultaneous” IMT within 1 ps. This progress report reviews the current state of the field, focusing on the material nature that gives rise to the modulation-allowed IMT for THz applications. An overview is presented of numerous IMT stimuli approaches with special emphasis on the underlying physical mechanisms. Subsequently, active manipulation of THz waves through pure VO2 film and VO2 hybrid metamaterials is surveyed, highlighting that VO2 can provide active modulation for a wide variety of applications. Finally, the common characteristics and future development directions of VO2-based tuneable THz devices are discussed.
Highlights
The terahertz (THz) wave, which is defined as the electromagnetic spectrum (0.1–10 THz) between microwave radiation and infrared light, has attracted increasing attention since the 1980s [1,2,3]
Promoted by the femtosecond laser, as well as the significantly improved THz generators and detectors, a couple of advanced THz technologies have been materialized, e.g., the well-matured terahertz time-domain spectroscopy (THz-TDs) that is capable of providing whole new insights into the material nature in the THz frequency range [4]
This review aims to provide a comprehensive survey of the recent advances in tuneable THz devices based on phase-change material VO2
Summary
The terahertz (THz) wave, which is defined as the electromagnetic spectrum (0.1–10 THz) between microwave radiation and infrared light, has attracted increasing attention since the 1980s [1,2,3]. Since the 2010s, extensive applications in THz regime based on VO2 have been demonstrated, such as amplitude modulators [23,24], tuneable absorbers [25], phase shifters [26], polarization converters [27,28,29], active frequency selective surfaces [30,31,32] and optical memory devices [33,34,35]. Ultrafast pump-probe techniques have been widely used to give insights into the structural and electrical dynamics of VO2 in time [49] This kind of research usually uses intense femtosecond pump laser to trigger the phase transition of VO2 , while a delayed pulse of either THz radiation, X-rays or electrons is utilized to probe the evolution of IMT or CPT [50,51,52,53,54,55,56,57]. The challenges and future perspectives of VO of 272based active THz devices are considered
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