Sub-wavelength focusing of cylindrical vector beams has attracted much attention because of its special properties. On this basis, an all-dielectric concave grating lens with negative refractive index is proposed in this paper. Through discussing the influence of equivalent negative refractive index (neff) and preset focal length on the focusing properties, the parameters of the structure is optimized. The results show that when neff is -1, the focal size is the smallest. A smaller preset focal length results in a smaller the transverse focal size. Furthermore, the effect of higher order diffracted light is also studied. It is found that, sub-focusing can be suppressed effectively by removing the structural part that supports the higher order diffraction. Finally, not only the focusing property is improved, but also the structure is simplified. This work provides a flexible and feasible method for the design of negative-index lens, and offers a reference for manipulating the focus of CVBs. Therefore, it provides a scheme for focusing artificial microstructure.
Hybrid plasmonic waveguides (HPWs) have attracted wide attention in recent years, because it makes a better compromise between the low loss of dielectric waveguide and the constraint capability of surface plasmonic waveguide. In this work, a hollow HPW with slat metal layer is analyzed to further reduce the loss and maintain constraint capability, then Bragg grating is designed and studied. By changing the waveguide width to further analyze the mode. The results show that normalized mode area is around 0.01, and propagation length (Lp) is up to 3500 μm, for TM polarized mode at operating wavelength of 1550 nm. For TE mode, Lp keeps millimeter level. Based on hollow HPW, Bragg grating is constructed by alternating the waveguides with different widths. Since the effective index of waveguide mode is quite sensitive to the change of the width and the trends of TM and TE modes are different from each other, Bragg gratings with different filtering characteristics and polarization properties can be designed by choosing combinations with different width. Simulations prove the validity of the design. HPW and Bragg structure proposed in this work would provide a reference for designing related photonic devices and have the potential applied value in the field of optical communication and integrated optics.
This work reports a graphene hyperbolic metamaterial hybrid plasmonic waveguides (GHMMHPW), and unlike traditional hybrid plasmonic waveguide (HPW), the GHMMHPW consists of a plasmonic cladding constructed by graphene hyperbolic metamaterial. Thanks to the particular structural arrangement, EM field can be localized and significantly enhanced in the low-index dielectric layer with nano-thickness. Thus, a superior performance is achieved. Meanwhile, electromagnetic parameters of graphene are tunable, and the mode properties also depend on the structural parameters, so the mode area and propagation distance can be optimized by adjusting these parameters flexibly. TM mode is supported in the GHMHPW, and improved performance is obtained. This study provides a novel and valuable reference for design of graphene plasmonic waveguides and prepares for the further development of micro-nano optics and integrated optoelectronic devices.
We theoretically investigate the characteristics of the multilayered hyperbolic metamaterial (HMM) composed of graphene and discuss the transmission properties from another angle of Fabry–Perot (F–P) resonance analysis. Dispersion characteristics of graphene-dielectric multilayered hyperbolic metamaterials (GDM HMMs) can be adjusted by changing the chemical potential of graphene. Transfer matrix method is improved to adapt the condition of large tangential vectors, and transmission properties are analyzed numerically. Calculated results indicate that dielectric material and graphene codetermine the dispersion properties of the HMMs, and the optical properties can be dynamically adjusted due to the introduction of graphene. Transmission spectra exhibit F–P resonance properties and discussions prove the validity of the F–P cavity theory. However, the transmission characteristics of GDM HMMs are different from the phenomena and laws of the traditional F–P cavity. Further analysis reveals that the mechanism originates from the contribution of graphene and high-k waves in HMMs. We present an innovative perspective for investigating and understanding transmission properties of GDM HMMs and provide references for design of HMMs and other related photonic devices.
Hybrid plasmonic waveguides (HPWs) have become a hot topic in nanophotonic due to their excellent optical field constraints and low propagation loss. Based on the polarization dependence of surface plasmon polariton (SPP) excitation the symmetry of cylindrical vector beams, a cylindrical hybrid plasmonic waveguide (CHPW) realizing limited propagation and two tapered hybrid plasmonic waveguides (THPWs) achieving nanofocusing are presented. CHPW supports radial polarization mode and well compensate mode propagation loss by adjusting the structural parameters of the waveguide. Splendid mode limitation and long transmission distance with low loss can be achieved simultaneously. On the basis of CHPW, the structure is tapered to realize nanofocusing. And periodic grooves are constructed on the metallic surface of the tapered hybrid plasmonic waveguide (THPW) to meet the phase matching condition and maximize the coupling of light energy from inside to outside. Meanwhile, the low index layer of THPW is replaced with two different index layers, which is broadened to gather more energy efficiently and the energy is converged on the apex of the waveguide to form the ultrahigh field enhancement, which is another optional way to improve the performance of THPW. The results offer vital reference value for designing and manufacture related photonic devices.
This work reports a graphene cylindrical hybrid plasmonic waveguide (GCHPW) consisting of a high-index dielectric core, a sandwiched low-index dielectric layer and a single layer graphene. Unlike traditional metallic cylindrical hybrid plasmonic waveguide (CHPW), GCHPW’s advance is that the nano-thickness light field can be significantly enhanced in the sandwiched low-index dielectric layer and the graphene interface, and a superior performance is achieved. Furthermore, the electromagnetic parameters of graphene is tunable, and the mode properties of the waveguide depend on the structural parameters, so the mode area and transmission distance can be flexibly optimized by adjusting these parameters. TM01 mode with radially polarized transverse component is supported in the novel GCHPW, and a more compact confinement of light field is achieved. Additionally, the GCHPW has a smaller size compared with the CHPW. This study provides a valuable reference for design of graphene plasmonic waveguides and offers a new way for the limited transmission of radially polarized light.
A conical hybrid plasmonic probe (CHPP) for ultrahigh field enhanced nanofocusing with lower loss is demonstrated. The CHPP consists of two different low-index dielectric layers sandwiched between a high-index conical core and a silver cladding. Properties of nanofocusing are analyzed by finite element method, under illumination of a radially polarized beam at a wavelength of 632.8 nm. The numerical results prove that, by introducing the additional lower-index layer, the whole low-index dielectric region is broadened to collect more energy efficiently, and the energy is converged on the apex of the CHPP to form the ultrahigh field enhancement. Compared with the traditional hybrid plasmonic probe, the optimized CHPP exhibits lower loss and higher field enhancement of 1771 times. The thickness and refractive index of the lower-index layer are discussed for optimizing the structure. The results indicate that the CHPP has a simple structure with excellent performance, which has important potential applications in relevant fields, particularly in nanotechnology of field enhancement. This work also provides a convenient way for designing and optimizing hybrid plasmonic structure.
Hybrid plasmonic waveguide (HPW) has received extensive attention recently due to its excellent performance of tight field confinement and low propagation loss. In this work, the transmission spectra of hybrid plasmonic waveguide Bragg gratings (HPWBGs) composed of two alternately arranged low refractive index dielectric materials are studied, combining the finite element method (FEM) and transfer matrix method (TMM). Meanwhile, by changing the width of the outermost layer of the waveguide, the influence on transmission spectra under different optical admittance matching conditions are discussed through admittance matching theory. Theoretical calculations and simulation results show that a specific thickness of the matching layer has a specific influence on the pass band or the forbidden band of a specific frequency range on the transmission spectrum. The transmission characteristics of the low-frequency or high-frequency pass band and the band gap can be optimized by adjusting the thickness of matching layer to obtain the admittance match or mismatch conditions. This result provides a good theoretical basis and design method for preparing photonic devices for requirements in different wavebands.
We demonstrate an ultra-narrow-band mode-selection method based on a hybrid-microsphere-cavity which consists of a coated silica microsphere. Optical field distribution and narrow-band transmission spectrum of the whispering gallery modes (WGM) are investigated by finite-difference time-domain method. WGM transmission spectra are measured for microsphere and tapered fibers with different diameters. A high refractive index layer coated on the microsphere-cavity make the Q factor increased, the transmission spectrum bandwidth compressed and the side-mode suppression ratio increased. Parameters of the hybrid-microsphere-cavity, namely, the coated shell thickness and its refractive index are optimized under different excitation light source as to investigate the whispering-gallery-modes’ transmission spectrum. The 3dB bandwidth of the proposed filter can be less than MHz which will have great potential for applications in all-optical sensing and communication systems.
A fiber-wireless sensor system based on a power-over-fiber technique is developed to offer a flexible, distributed sensing ability over a middle distance, especially under environments that are sensitive to electromagnetic interference. In this system, the optical energy of a high-power laser in the base station is transmitted via a fiber and then converted into electrical energy by a photovoltaic power converter (PPC) in the remote unit. This optically power-supplied remote unit operates as the coordinator in the wireless sensor network (WSN) and exchanges the sensing information with the base station via another fiber. In our demonstration system, the sensing information can be collected by a WSN 2 km away and be transmitted back. In order to improve the power supply ability of PPC, a maximum power point tracking technique is applied. More than 80% of PPC’s maximum output power can be obtained. Moreover, to reduce the power consumption of the remote unit and the sensor nodes, a simple and stable low-power communication protocol is designed.
The fine manipulations of cylindrical vector beams (CVBs) based on metallic microstructures, such as sub-wavelength
focusing, have entered many interdisciplinary areas, and the important applications have been found in many fields
including optical micromanipulation, super-resolution imaging, micro-machining and so on. But so far, the
sub-wavelength focusing of azimuthally polarized beams is encountered, since the manipulation mechanisms rely
heavily on the excitation of surface plasmon polaritons, which brings the polarization limitation. We theoretically
investigated the focusing behavior of CVBs in 1D metallic photonic crystals (MPCs). The simulation results show that a
1D MPC plano-concave lens can focus cylindrical vector beams into scale of sub-wavelength. The negative refraction at
the interface between the air and the 1D MPC is analyzed at the frequencies corresponding to the second photonic band,
which makes the 1D MPC has the ability to focus higher Fourier components of light beams. The cylindrical
plano-concave structure is constructed to focus the radially and azimuthally polarized beams simultaneously. The
behavior is demonstrated by Finite Element Method (FEM). The shape of focusing field can be tailored, by changing the
polarization ratio of the incident beams. In addition, the effective sub-wavelength focusing phenomenon can also be
realized in variety of wave ranges, by choosing the proper materials and adjusting the parameters. We believe that it’s the
first time to realize the simultaneous sub-wavelength focusing of radially and azimuthally polarized beams, the
application of which is quite promising in broad prospects.
The finite-difference time-domain (FDTD) method, which solves time-dependent Maxwell’s curl equations numerically,
has been proved to be a highly efficient technique for numerous applications in electromagnetic. Despite the simplicity
of the FDTD method, this technique suffers from serious limitations in case that substantial computer resource is
required to solve electromagnetic problems with medium or large computational dimensions, for example in high-index
optical devices. In our work, an efficient wavelet-based FDTD model has been implemented and extended in a parallel
computation environment, to analyze high-index optical devices. This model is based on Daubechies compactly
supported orthogonal wavelets and Deslauriers-Dubuc interpolating functions as biorthogonal wavelet bases, and thus is
a very efficient algorithm to solve differential equations numerically. This wavelet-based FDTD model is a
high-spatial-order FDTD indeed. Because of the highly linear numerical dispersion properties of this high-spatial-order
FDTD, the required discretization can be coarser than that required in the standard FDTD method. In our work, this
wavelet-based FDTD model achieved significant reduction in the number of cells, i.e. used memory. Also, as different
segments of the optical device can be computed simultaneously, there was a significant gain in computation time.
Substantially, we achieved speed-up factors higher than 30 in comparisons to using a single processor. Furthermore, the
efficiency of the parallelized computation such as the influence of the discretization and the load sharing between
different processors were analyzed. As a conclusion, this parallel-computing model is promising to analyze more
complicated optical devices with large dimensions.
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