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Register a new userWideband Bandpass Filters Based on Multipole Resonances of Spoof Localized Surface Plasmons
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We propose wideband bandpass filters based on multipole resonances of spoof localized surface plasmons (SLSPs). The resonance characteristics and geometric tunability of SLSPs are investigated under microstrip excitations. Strong coupling with interlayer microstrip lines is proposed to join discrete multipole resonances into a continuous and flat passband. The SLSP filters exhibit wide passbands in compact sizes and well-balanced shapes, while holding satisfactory spurious rejection bands, group delays, and geometric tunability. This work exposes the SLSPs application potential in filters as novel resonators.
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Advances in graphene plasmonics offer numerous opportunities for enabling the design and manufacture of a variety of nanoelectronics and other exciting optical devices. However, due to the limitation of material properties, its operating frequency cannot drop to the microwave range. In this work, a new concept of microwave equivalent graphene based on the ultrathin monolayer plasmonic metasurface is proposed and demonstrated. Based on this concept, elliptical and hyperbolic dispersion can be theoretically obtained by stacking the equivalent graphene metasurfaces periodically. As proofs of the concept and method, an elliptical and an all-metal hyperbolic metamaterial are designed and numerically demonstrated. As a specified realization of the method, a practical hyperbolic metamaterial is fabricated and experimentally investigated with its validity verified by the directional propagation and photonic spin Hall effect. Furthermore, to investigate the validity of the method under extreme parameter conditions, a proof-of-concept hyperlens is designed and fabricated, with its near-field resolution of 0.05$lambda$ experimentally verified. Based on the proposed concept, diverse optical graphene metamaterials such as focusing lens, dispersion-dependent directional couplers, and epsilon-near-zero materials can also be realized in the microwave regime.
Manipulation of spoof surface plasmons (SSPs) has recently intrigued enormous interest due to the capability of guiding waves with subwavelength footsteps. However, most of the previous studies, manifested for a single functionality, are not suitable for multifunctional integrated devices. Herein, a bifunctional Luneburg-fisheye lens is proposed based on a two-dimension metal pillar array. Firstly, by tuning the geometric dimension of the metal pillars in the array, its ability to precisely manipulate the excited SSPs along one direction is confirmed, achieving subwavelength focusing and imaging with the resolution up to 0.14 times the wavelength. Then, separately controlling the propagation of the SSPs along the orthotropic directions is further implemented, and the bifunctional Luneburg-fisheye lens is realized. The bifunctional lens is characterized as a Luneburg one along the x-axis, whereas in the y-axis, it presents the properties of a Maxwell fisheye lens. The experimental results almost immaculately match with the simulation ones. This bifunctional lens can validly reduce the system complexity and exert flexibility in multifunctional applications, while the proposed metal pillar-based design method broadens the application range of gradient refractive-index lens in the microwaves, terahertz, and even optical ranges.
We demonstrate advanced integrated photonic filters in silicon-on-insulator (SOI) nanowires implemented by cascaded Sagnac loop reflector (CSLR) resonators. We investigate mode splitting in these standing-wave (SW) resonators and demonstrate its use for engineering the spectral profile of on-chip photonic filters. By changing the reflectivity of the Sagnac loop reflectors (SLRs) and the phase shifts along the connecting waveguides, we tailor mode splitting in the CSLR resonators to achieve a wide range of filter shapes for diverse applications including enhanced light trapping, flat-top filtering, Q factor enhancement, and signal reshaping. We present the theoretical designs and compare the CSLR resonators with three, four, and eight SLRs fabricated in SOI. We achieve versatile filter shapes in the measured transmission spectra via diverse mode splitting that agree well with theory. This work confirms the effectiveness of using CSLR resonators as integrated multi-functional SW filters for flexible spectral engineering.
In this paper, a wideband and low-scattering metasurface in terahertz (THz) is introduced. The proposed coding metasurface is composed of four different graphene square patches in one layer, which has a distinct bias voltage. By optimizing the chemical potential of each patch, the reflection phase and amplitude of a designed element can be controlled in a real-time manner. The chemical potential optimizing approach is a promising method to develop metasurfaces, which can tune the reflection phase, magnitude, or polarization dynamically at different frequencies spectrum. Indeed, by adjusting the metasurface reflection profile, the suggested device can manipulate the reflected wave. Also, this metasurface can reduce reflection energy in the wide-band spectrum. The programmable surface disperses reflected power in various directions in a first frequency band and converts incident electromagnetic waves into heat at second frequency band. The obtained results demonstrate that more than 10 dB reflection reduction can be realized over 1.02 to 2.82 THz under both TE and TM polarized wave incidences. Due to the conformal properties of the graphene monolayer, the stealth feature of the metasurface is well preserved while wrapping around a metallic curved object. This optimization method has an excellent aptitude for phase, magnitude, and polarization control in various beamforming applications at the THz spectrum for high-resolution imaging and stealth technology.
This letter presents a dumbbell-shaped defected ground resonator and its application in the design of differential filters. The operation principle of the dumbbell-shaped resonator (DSR) coupled to differential microstrip lines is studied through a circuit model analysis. The proposed circuit model is validated through the comparison with the electromagnetic simulation results. It is shown that the bandpass configuration of microstripline- coupled DSR can be used to design higher order bandpass filters. The design procedure is explained by developing a thirdorder filter prototype. The designed filter shows more than 57 dB common mode rejection within the differential passband.
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