Low-loss terahertz waveguide with InAs-graphene-SiC structure

We demonstrate a low-loss terahertz waveguide based on the InAs-graphene-SiC structure. By analyzing the terahertz waveguide proposed in this paper, we can obtain that it is the characteristic of a low transmission loss coefficient （αloss 0.55 dB/m） for fundamental mode （LP01） when the incident frequency is larger than 3.0 THz. The critical radii of the inside and outside cylinders have been found for the high-quality transmission. The large inside radius and the high transmission frequency result in a fiat transmission loss coefficient curve. As a strictly two-dimensional material, the double graphene surface rings perform better to improve the quality of transmission mode. These results provide a new idea for the research of the long-distance THz waveguide.

A High Performance Terahertz Waveguide Detector Based on a Low-Barrier Diode

A Schottky barrier diode with low-barrier is presented, based on which a terahertz waveguide detector working at 500-600 GHz is designed and fabricated. By using the InGaAs/InP material system, the feature of the low barrier is obtained which greatly improves the performance of the detector. The measured typical voltage responsivity is about 900 V/W at 50-560 OHz and is about 400 V/W at 560 600 GHz. The proposed broadband waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, moleeuIar spectroscopy and atmospheric remote sensing.

Progress in Terahertz Waveguides

This paper summarizes the recent progress in Terahertz(THz) waveguides. Many THz waveguides of various sorts have been presented and examined, including dielectric THz waveguides, metal THz waveguides, THz fiber and photonic crystal THz waveguides. Their advantages and limitations are stated, and the perspective of research on Terahertz waveguides is discussed.

Design and optimization of terahertz directional coupler based on hybrid-cladding hollow waveguide with low confinement loss

We propose a design and optimization for directional coupling in terahertz hybrid-cladding hollow waveguide. It is composed of two square hollow waveguides which touch each other and are surrounded by a metallic layer. By employing the finite element method, the coupling performance and loss property are numerically investigated. Numerical results indi- cate that this directional coupler with hybrid-cladding can realize ultra-narrow-band coupling; it provides a low confinement loss performance： the confinement loss can reach as low as 6.27 × 10-5 cm- 1. Moreover, the further analyses of configura- tion and performance show that confinement loss and frequency range shift for the low-confinement-loss frequency regime can be realized and optimized by appropriately tuning the thickness values of the metallic and dielectric layer. In addition, through the further analysis of coupling performance, the possibilities of realizing ultra-narrow-band couplings in different frequency ranges are demonstrated. It is a powerful candidate for high precision optical fiber sensing, and communication in terahertz splitting fields.

Realization of a broadband terahertz wavelength-selective coupling based on five-core fibers

We propose a novel kind of wavelength-selective coupling for the terahertz range based on solid five-core fiber （FCF）. The performances of coupling, propagation characteristics, and confinement loss properties are numerically investigated by using a full vector beam propagation method （BPM）. Simulation results show that it is possible to realize a broad- band wavelength-selective coupling. The coupling length can reach 1.913 cm, and the confinement loss is better than 1.965 ×10^-4 cm^-1. Furthermore, a parameter, the power difference, is defined, and it numerically demonstrates the working performance of the wavelength-selective coupler; that is, when the power difference is better than - 15 dB, the frequency located in the range of 0.76 THz-100 THz is separated relatively well from the frequency of 0.3 THz. Finally, the effect of the structural parameter on the working performance of the coupler is also investigated. We show that the performance optimization is possible by appropriately tuning the core diameter, and the tunabilities of frequency and bandwidth are possible by appropriately tuning the pitch. The wavelength-selective coupler is of potential application for optical fiber sensing and communication in terahertz wavelength division multiplexer fields.

Resonances Characteristics of Parallel Plate Waveguide Cavities

The influence of air gaps on the response of transmission for a transverse-electric mode parallel-plate waveguide（TE-PPWG） with a single cavity and double cavities has been studied experimentally. As the air gap is larger than the resonant wavelength of high order cavity mode in the single deep grooved waveguide, only the fundamental cavity mode can be excited and single resonance can be observed in the transmission spectrum. Based on above observations, a tunable multiband terahertz（THz）notch filter has been proposed and the variation of air gap has turned out to be an effective method to select the band number. Experimental data and simulated results verify this band number tunability. This mechanical control mechanism for electromagnetic induced transparency（EIT） will open a door to design the tunable THz devices.

Design and fabrication of a sub-millimeter multi-beam folded waveguide structure

A novel multi-beam folded waveguide(MBFW) circuit,which can enhance the output power and interaction efficiency of sub-terahertz(THz) traveling wave tube(TWT),is presented in the paper. Operating with fundamental mode and multiple electron beams means that a larger beam current can be used for a higher output power. The characteristics of the MBFW structure are analyzed and optimized. Compared with the single-beam folded waveguide(SBFW) TWT,the output power of the MBFW TWT increases from 3.64 W to 25.45 W at 140 GHz and its electronic efficiency increases from 1.06% to 7.4% under the conditions of an input peak power of 10 m W,a beam voltage of 9.55 k V and a current of 12 m A. The optimized MBFW structure can be successfully fabricated by micro milling,with dimension errors below expectation,and the measured transmission characteristics are in good agreement with the design.