Abstract-Design of terahertz reconfigurable devices by locally controlling topological phases of square gyro-electric rod arrays

L. Zhang, Sanshui Xiao,

Fig. 4 Normalized electric field distribution of the edge wave propagation. The wave is excited by a point source. Blue areas denote the metal wall and the obstacle. (a) Distribution of edge wave between the array with θ = 0° and a metal wall at 3.5 THz. (b) Transmission spectrum without and with material loss involved when the wave propagates a length of 30a along the edge. (c) Distribution of edge wave between upper sub array with θ = 0° and lower sub array with θ = 45°. (d) Distribution of edge wave along the interface with two right-angled bends.

https://www.osapublishing.org/ome/fulltext.cfm?uri=ome-9-2-544&id=403962

In topological photonics, there is a class of designing approaches that usually tunes topological phase from trivial to non-trivial in a magneto-optical photonic crystal by applying an external magnetic field to break time reversal symmetry. Here we theoretically realize topological phase transition by rotating square gyro-electric rods with broken time reversal symmetry. By calculating band structures and Chern numbers, in a simple square-lattice photonic crystal, we demonstrate the topological phase transition at a specific orientation angle of the rods. Based on the dependence of topological phase on the orientation angle, we propose several terahertz devices including an isolator, circulator and splitter in a 50x50 reconfigurable rod array by locally controlling topological phases of the rods. These results may have potential applications in producing reconfigurable terahertz topological devices.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Experimental demonstration of a terahertz extended interaction oscillator driven by a pseudospark-sourced sheet electron beam

G. X. Shu, L. Zhang,   H. Yin, J. P. Zhao,   A. D. R. Phelps, A. W. Cross, G. Liu, Y. Luo, Z. F. Qian,  W. He

http://aip.scitation.org/doi/abs/10.1063/1.5011102

We have recently proposed to combine the advantages of a pseudospark-sourced sheet electron beam (PS-SEB) with a planar slow wave structure to generate high power terahertz radiation. To verify this idea, experimental investigation of an extended interaction oscillator based on the PS-SEB has been conducted and presented. A PS-SEB of approximately 1.0 mm × 0.17 mm in size with 21.5 A peak current (1.26 × 104 A/cm2 beam current density) and 34.5 kV peak voltage was measured after propagating a distance of 10-mm without the need of an external focusing magnetic field. A radiation pulse of ∼35 ns in duration and an output power of over 10 W at a frequency of ∼0.2 THz were measured.

Abstract-Experimental demonstration of a terahertz extended interaction oscillator driven by a pseudospark-sourced sheet electron beam

Shu, G. X. and Zhang, L. and Yin, H. and Zhao, J. P. and Phelps, A. D. R. and Cross, A. W. and Liu, G. and Luo, Y. and Qiao, Z. F. and He, W

https://strathprints.strath.ac.uk/62943/

We have recently proposed to combine the advantages of a pseudospark-sourced sheet electron beam (PS-SEB) with a planar slow wave structure to generate high power terahertz radiation. To verify this idea, experimental investigation of an extended interaction oscillator based on the PS-SEB has been conducted and presented. A PS-SEB of approximately 1.0 mm×0.17 mm in size with 21.5 A peak current (1.26×104 A/cm2 beam current density) and 34.5 kV peak voltage was measured after propagating a distance of 10-mm without the need of an external focusing magnetic field. A radiation pulse of ~35 ns in duration, and output power of over 10 W at a frequency of ~0.2 THz was measured.

Abstract-Broadband Amplification of Low-Terahertz Signals Using Axis-Encircling Electrons in a Helically Corrugated Interaction Region

W. He, C. R. Donaldson, L. Zhang, K. Ronald, A. D. R. Phelps, and A. W. Cross

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.184801

Experimental results are presented of a broadband, high power, gyrotron traveling wave amplifier (gyro-TWA) operating in the (75–110)-GHz frequency band and based on a helically corrugated interaction region. The second harmonic cyclotron mode of a 55-keV, 1.5-A, axis-encircling electron beam is used to resonantly interact with a traveling ${\mathrm{TE}}_{21}$-like eigenwave achieving broadband amplification. The gyro-TWA demonstrates a 3-dB gain bandwidth of at least 5.5 GHz in the experimental measurement with 9 GHz predicted for a wideband drive source with a measured unsaturated output power of 3.4 kW and gain of 36–38 dB. The approach may allow a gyro-TWA to operate at 1 THz.

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Abstract-Broadband amplification of low-terahertz signals using axis-encircling electrons in a helically corrugated interaction region

W. He, C. R. Donaldson, L. Zhang, K. Ronald, A. D. R. Phelps,  A. W. Cross,

https://journals.aps.org/prl/accepted/aa075Y48Q3c13a6851270ff5428f8a399615110c3


Experimental results are presented of a broadband, high power, gyrotron traveling wave amplifier (gyro-TWA) operating in the 75-110 GHz frequency band and based on a helically corrugated interaction region (HCIR). The second harmonic cyclotron mode of a 55 keV, 1.2 A, axis-encircling electron beam generated from a cusp electron gun was used to resonantly interact with a traveling TE21-like eigenwave, existing in the HCIR, achieving broadband amplification based on the cyclotron resonance maser instability. The gyro-TWA was measured to generate a maximum power of 3.4 kW with an unsaturated gain of 36-38 dB in the driving frequency band of 91-96.5 GHz.

Abstract-Simulation of rectangular TE10 to circular TE11 terahertz mode converters

J. R. Garner,   L. Zhang,  C. R. Donaldson,  A. W. Cross,  A. D. R. Phelps,  W. He,

http://ieeexplore.ieee.org/document/7758520/

Two designs of fundamental mode rectangular to circular waveguide TE10 to TE11 mode converter are presented. The waveguide transitions are optimized for operation as an input coupler on a 372 GHz gyro-TWA for Dynamic Nuclear Polarization (DNP) enhancement of NMR imaging. A T-junction input coupler and a multiple hole directional coupler were optimized for operation between 360-384 GHz. The T-junction coupler and the multiple hole coupler exhibited bandwidths of 10% and 35% respectively with a high coupling factor of > -1 dB.

Abstract-High power wideband gyrotron backward wave oscillator operating towards the terahertz region

W. He, C. R. Donaldson, L. Zhang, K. Ronald, P. McElhinney, and A. W. Cross
http://prl.aps.org/accepted/fa07cYcdM9c12133c6286d9809d8d09987fde325b
Experimental results are presented of the first successful gyrotron backward wave oscillator (gyro-BWO) with continuous frequency tuning near the low terahertz region. A helically corrugated interaction region (HCIR) was used to allow efficient interaction over a wide frequency band at the second harmonic of the electron cyclotron frequency without parasitic output. The gyro-BWO generated a maximum output power of 12 kW when driven by a 40 kV, 1.5 A, annular-shaped large-orbit electron beam and achieved a frequency tuning band of 88-102.5 GHz by adjusting the cavity magnetic field. The performance of the gyro-BWO is consistent with 3D particle-in-cell (PIC) numerical simulations