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An analytical model for plasmon modes in graphene-coated dielectric nanowire is presented. Plasmon modes could be classified by the azimuthal field distribution characterized by a phase factor exp(imφ) in the electromagnetic field expression and eigen equation of dispersion relation for plasmon modes is derived. The characteristic of plasmon modes could be tuned by changing nanowire radius, dielectric permittivity of nanowire and chemical potential of graphene. The proposed model provides a fast insight into the mode behavior of graphene-coated nanowire, which would be useful for applications based on graphene plasmonics in cylindrical waveguide.

We propose in this Letter a single-mode graphene-coated nanowire surface plasmon waveguide. The single-mode condition and modal cutoff wavelength of high order modes are derived from an analytic model and confirmed by numerical simulation. The mode number diagram of the proposed waveguide in the wavelength-radius space is also demonstrated. By changing the Fermi level of graphene, the performance of the proposed waveguide could be tuned flexibly, offering potential application in tunable nanophotonic devices.

We propose in this paper a dielectric-graphene-dielectric tunable infrared waveguide based on multilayer metamaterials with ultrahigh refractive indices. The waveguide modes with different orders are systematically analyzed with numerical simulations based on both multilayer structures and effective medium approach. The waveguide shows hyperbolic dispersion properties from mid-infrared to far-infrared wavelength, which means the modes with ultrahigh mode indices could be supported in the waveguide. Furthermore, the optical properties of the waveguide modes could be tuned by the biased voltages on graphene layers. The waveguide may have various promising applications in the quantum cascade lasers and bio-sensing.

An innovative strategy of introducing space charge traps to dielectric materials is developed by copolymerization of MMA with conjugated VK, which enables superior energy storage performance (Ue = 15.7 J cm−3 @ 750 MV m−1, η = 88%).

We present a method in this Letter to generate optical vortices with tunable orbital angular momentum (OAM) in optical fibers. The tunable OAM optical vortex is produced by combining different vector modes HE2,meven (HE2,modd) and TE_0,m (TM_0,m) when l=1 or combining HEl+1,meven (HEl+1,modd) and EHl-1,modd (EHl-1,meven) when l>1 with a π/2 phase shift. The vortex can be regarded as a result of overlapping two orthogonal optical vortex beams of equal helicity but opposite chirality with a π/2 phase shift. We have experimentally demonstrated the smooth variation of OAM from l=-1 to l=+1 by adjusting a polarizer at the output end of the fiber.

In automotive testing systems such as chassis dynamometers and engine dynamometers, effective and efficient control strategies are required to control the induction motor drives, so that fast torque response and low‐torque ripples can be obtained. The fast torque response can be obtained by using model predictive control (MPC) due to its high bandwidth over a wide‐speed range; and the torque ripple can be reduced by using open‐end winding induction motor (OEWIM). Since MPC can be current based or flux/torque based, and can be linear and non‐linear, it is necessary to evaluate the effectiveness of different MPC methods on the open‐end winding drives. In this study, linear and non‐linear current‐based MPC methods and flux/torque‐based MPC methods for OEWIM drive are derived and evaluated. The transient and steady‐state responses of MPC methods are compared through simulation and experiment. The results show that linear MPC methods require less computation time, and under the same sampling frequency, linear MPC methods provide lower current ripple and better zero‐sequence‐current suppression than non‐linear MPC methods. This study provides practical perception for MPC used on multi‐level converters and MPC used for unbalanced situations.

We explore terahertz (THz) orbital angular momentum (OAM) modes supported in multimode Kagome hollow-core fibers. Numerical models are adopted to characterize the effective indices and confinement losses of vector modes over 0.2-0.9 THz, where two low-loss transmission windows are observed. Linearly combining the vector modes, THz OAM states can be generated. Covering a broad bandwidth of 0.25 THz, the purity values of OAM modes are beyond 0.9. Using numerical simulations, the hollow-core THz fibers with one and two rings of Kagome structures are also comparably investigated. We reveal that the OAM purity is dependent upon the confinement performance of THz fiber.