Abstract
In the last couple of decades, terahertz (THz) technologies, which lie in the frequency gap between the infrared and microwaves, have been greatly enhanced and investigated due to possible opportunities in a plethora of THz applications, such as imaging, security, and wireless communications. Photonics has led the way to the generation, modulation, and detection of THz waves such as the photomixing technique. In tandem with these investigations, researchers have been exploring ways to use silicon photonics technologies for THz applications to leverage the cost-effective large-scale fabrication and integration opportunities that it would enable. Although silicon photonics has enabled the implementation of a large number of optical components for practical use, for THz integrated systems, we still face several challenges associated with high-quality hybrid silicon lasers, conversion efficiency, device integration, and fabrication. This paper provides an overview of recent progress in THz technologies based on silicon photonics or hybrid silicon photonics, including THz generation, detection, phase modulation, intensity modulation, and passive components. As silicon-based electronic and photonic circuits are further approaching THz frequencies, one single chip with electronics, photonics, and THz functions seems inevitable, resulting in the ultimate dream of a THz electronic–photonic integrated circuit.
Highlights
Terahertz (THz) radiation, which occupies the frequency gap between the infrared and microwaves, typically referred to as the frequencies between 0.1 THz and 10 THz, becomes increasingly important for many applications such as data communications, biology, medical sciences, sensing, and imaging [1,2,3]
We provide an overview of the silicon photonics or hybrid silicon photonics that has already been used in the THz applications
The switch-on time is a function of the laser pulse duration, and the switch-off time is mainly determined by the photoexcited carrier lifetime in the semiconductor substrate of the antenna; in addition to a short laser pulse duration, a short carrier lifetime is a vital property for ultrafast photoconductive switching. Another approach is to use the media with a large second-order nonlinear coefficient to generate THz pulses by nonlinear optical effects, such as gallium arsenide (GaAs) [23], zinc telluride (ZnTe) [24], diethylaminosulphur trifluoride (DAST) [13], and lithium niobate (LiNbO3 ) [25,26]
Summary
Terahertz (THz) radiation, which occupies the frequency gap between the infrared and microwaves, typically referred to as the frequencies between 0.1 THz and 10 THz, becomes increasingly important for many applications such as data communications, biology, medical sciences, sensing, and imaging [1,2,3]. Early photonics-based THz research has largely relied on the use of bulky equipment which is costly and requires high driving powers for efficient operation. Assembling all these components into useful products further reduces the reliability and mass-manufacturability of the device. Silicon photonics is compatible with industrial CMOS technologies, which enables high-volume production for a low cost per device [6,7] It provides high index contrast between the core and cladding of the waveguide, allowing large-scale and high-density integration.
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