Zongjun Shi

Properties of obliquely incident electromagnetic wave in one-dimensional magnetized plasma photonic crystals

Properties of obliquely incident electromagnetic wave in one-dimensional (1D) magnetized plasma photonic crystals (PPCs) are studied in this paper. Based on the continuous boundary condition of electromagnetic wave in 1D PPC, transfer matrix equation and dispersion equation of transverse magnetic polarization are deduced, and the properties of dispersion and transmission relation in terms of external magnetic field, collision frequency, and dielectric constant of dielectric and incident angles are investigated, respectively. Results show that gap location and gap width can be effectively controlled by adjusting external magnetic field as well as incident angle, and increasing collision frequency has little effect on gap width while larger dielectric constant of dielectric leads to more gaps.Properties of obliquely incident electromagnetic wave in one-dimensional (1D) magnetized plasma photonic crystals (PPCs) are studied in this paper. Based on the continuous boundary condition of electromagnetic wave in 1D PPC, transfer matrix equation and dispersion equation of transverse magnetic polarization are deduced, and the properties of dispersion and transmission relation in terms of external magnetic field, collision frequency, and dielectric constant of dielectric and incident angles are investigated, respectively. Results show that gap location and gap width can be effectively controlled by adjusting external magnetic field as well as incident angle, and increasing collision frequency has little effect on gap width while larger dielectric constant of dielectric leads to more gaps.

Dispersion properties of a 2D magnetized plasma metallic photonic crystal

This is a study on a 2D magnetized plasma-filled metal photonic crystal (PMPC). We analyze the dispersion relation of the magnetized PMPC by using the finite-difference time-domain method. Results show a cutoff frequency for the PMPC, and two flat bands and new forbidden band gaps appear due to the external magnetic field. Adjusting the external magnetic field can control the positions of the flat bands, cutoff frequency, and location and width of the local gap. These results provide theoretical basis for designing tunable photonic crystal devices.

Enhancements of Terahertz Radiation From a Grating Waveguide by Two-Stream Instability

An approach to the enhancement of terahertz radiation from a grating waveguide by two-stream instability (TSI) is presented in this paper. The grating waveguide composed of a planar metallic grating and an opposite plate is driven by two electron beams with a velocity separation. The dispersion equation is derived with the linearized fluid theory and solved numerically. Also, the numerical results show that a considerable enhancement of growth rate is possible at an optimized velocity separation. With the help of 2-D particle-in-cell simulations, the improvement of radiation performance induced by the TSI is demonstrated.

Defect mode properties of two-dimensional plasma-filled defective metallic photonic crystal

This paper studies the frequency and amplitude properties of a defect mode which is only in a plasma-filled metallic photonic crystal with defect layer. Results show that the frequency almost has no change and the amplitude declines gradually with the growth of the number of the layers. The frequency of the defect mode not only can be modulated by filling ratio but also can be tuned by plasma density without modifying the structure. The amplitude can be modified by plasma angular frequency as well. These characteristics provide a foundation to design tunable filters, high power millimeter devices.

Investigation of a 30-GHz Relativistic Diffraction Generator with a Coaxial Reflector

This paper studies a 30-GHz relativistic diffraction generator with a coaxial reflector. The high frequency system is a disk-loaded cylindrical overmoded slow-wave structure. In order to decrease the energy leaking out from the diode end and increase output power, a coaxial reflector is placed upstream at the slow-wave structure. The reflector is designed with a center frequency of 30 GHz. Simulations and experiments of the device have been carried out. The measured microwave power is over 300 MW, and the pulse duration is about 20 ns. The microwave output power can be enhanced by adding a reflector to the devices.

Bandgap extension of disordered one-dimensional metallic-dielectric photonic crystals

Photonic crystal (PC) with a photonic band gap (PBG) has attracted much attention since the initial predictions of Yablonovitch and John. This active research area has been extended to frequency-dependent metallic-dielectric PC (MDPC) theoretically and experimentally in Keskinen, M.J., et al, (2000). In this paper, the PBG properties are investigated by transform matrix method when disorder is introduced in the one-dimensional (1D) frequency-dependent MDPC.

Ka-band relativistic diffraction generator with a tapered coaxial Bragg reflector

A coaxial line with periodically tapered inner rode corrugated ripples is introduced to act as a distributed Bragg reflector to increase output microwave power of relativistic diffraction generator (RDG). The RDG device consists of an overmoded cross-section, two-sectional disk-loaded cylindrical slow-wave structure (SWS), and coaxial reflector is placed upstream at the first SWS section. The RDG device with tapered Bragg reflector is investigated by full three-dimensional Particle-in-Cell (PIC) simulations and experiments in this paper. The structural parameters of the reflector are optimized for favorable characteristic of mode selection and frequency response. It is found that oscillation modes varied at different magnetic field magnitude. The measured radiation power at 29∼31 GHz is over 300 MW for TM01 mode and over 700 MW for TM11 mode. Results show that the reflector has a great impact on performance of the device. Operating at proper conditions, the radiation power is remarkably enhanced.

Multiband terahertz reflective polarizer based on asymmetric L-shaped split-ring-resonators metasurface

In this article, a multiband reflective polarization converter (RPC) based on asymmetric L-shaped split-ring-resonators(ALSRR) metasurface is theoretically presented. The proposed RPC is able to efficiently convert a linearly polarized (LP) wave to its cross-polarized wave at the four resonant frequencies, besides, it can convert the LP wave to a circularly polarized(CP) wave at the other eight resonant frequencies with a high polarization conversion ratio(PCR). Furthermore, specific elucidation of the surface current distributions of the polarizer reveal the underlying physical mechanism of mutual electromagnetic couplings. The proposed novel polarizer takes favorable advantages of more operation frequency bands for both linear and circular polarization conversions, which indicating great potential applications in terahertz detectors, antennas, imaging and communication systems.

Ultra-wideband terahertz reflective polarization conversion based on anisotropic meta-mirror with interlaced-parallel-dipole metasurface

An ultra-wideband, high efficiency, and wide angle terahertz reflective polarization converter (RPC) using interlaced-parallel-dipole metamaterial (IPDMM) is theoretically demonstrated in this paper. Illuminated by linearly polarized (LP) wave, the proposed polarizer performances an excellent 90° linear polarized conversions at three resonance frequencies, and pure circularly polarized (CP) conversion at two resonance frequencies. Remarkably, due to the enhanced inductive-capacitive (LC) resonances by the IPDMM using double-parallel cut-wire particles, 99% ultra-broadband width of triple-band overlapping over 75% and 0.99 highest power conversion efficiency are obtained numerically. Furthermore, the excellent cross-polarization conversion sustains when the incidence is a CP wave. In addition, the proposed polarizer obtains 80% relevant bandwidth over 70% reflective polarization conversion power with incident angle up to 45°. The physical mechanism of the polarization conversion is elucidated by analysis of the surface current distributions of the polarizer. The merits of broadband, high efficiency and widely incident angles could benefit the potential applications in THz regime.

Output characteristics of a 0.14 THz dual sheet beam backward wave oscillator based on a hole-grating slow wave structure

A novel backward wave oscillator (BWO) based on a hole-grating slow wave structure is proposed as a dual sheet beam millimeter wave radiation source. In this paper, we focus on the output characteristics of a 0.14 THz hole-grating BWO. The output characteristics of the hole-grating BWO, the conventional single-beam grating BWO, and the dual-beam grating BWO are contrasted in detail. 3-D particle-in-cell results indicate that the hole-grating slow wave structure can help to increase the maximum output power as well as lower the operating current density. Meanwhile, the hole-grating BWO shows good insensitivity to the differences between two sheet electron beams. These characteristics make the hole-grating BWO feasible to be a stable millimeter wave radiation source with higher output power.