Abstract
We study the possibility of analog signal processing for the upcoming terahertz (THz) high-bitrate communications using as an example the problem of dispersion compensation in the THz communication links. In particular, two Waveguide Bragg Grating devices (WBGs) operating in the transmission mode are detailed. WBGs are designed by introducing periodic corrugation onto the inner surface of the metalized tubes. The resultant devices operate in a single mode regime either in the vicinity of the modal cutoff or in the vicinity of a bandgap edge, featuring large negative group velocity dispersions (GVD). We fabricate the proposed WBGs using 3D stereolithography, and metallize them using wet chemistry. Optical properties of the fabricated WBGs are investigated both theoretically and experimentally. The results confirm single mode guidance, relatively high coupling efficiency, as well as large negative group velocity dispersions in the range of several -100's ps/(THz · cm) in the vicinity of 0.14THz. This makes the short sections of proposed WBGs suitable for compensating positive dispersion incurred in the THz wireless links or fiber-assisted THz interconnects for signals of several-GHz bandwidth. Finally, we comment on the challenges associated with the analog signal processing in the THz spectral range.
Highlights
With the demand of wider bandwidths and higher bit rates, using terahertz frequencies for wireless communications is experiencing a surge of attention in recent years
Various THz wireless communication systems with carrier frequencies as high as 0.6THz and transmission data rates of up to 100Gbit/s have been developed and investigated [1,2,3,4]. Applications of these THz communication systems are still limited due to inherent challenges posed by the free space propagation (FSP) modality, such as strong dependence on atmospheric conditions, rapid divergence of the THz beams especially at the lower carrier frequencies, as well as lineof-sight nature of the links
THz fiber size is typically comparable to the wavelength of light, enabling compact several-mm in diameter communication links with very small footprint and low signal leakage outside of the fibers, which is of special interest for the ultra-high bandwidth on-chip interconnects
Summary
With the demand of wider bandwidths and higher bit rates, using terahertz frequencies for wireless communications is experiencing a surge of attention in recent years. We aim at designing a waveguide-based dispersion compensator with the highest negative dispersion possible, while keeping its operational bandwidth large enough to support THz wireless communications (510GHz) This design approach leads to shorter devices, and, lower propagation losses are expected compared to devices with smaller GVDs. Being hollow and circularly symmetric, our waveguides are inherently suitable for operation with the free space beams. As roughness of the coated silver layer (~1μm) is deeply subwavelength (THz wavelength is ~1mm), only a small scattering loss is expected due to surface roughness, which we have confirmed experimentally by comparing transmission through Ag-coated tubes and polished copper tubes
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