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Electromagnetic metasurfaces have been intensively used as ultra-compact and easy-to-integrate platforms for versatile wave manipulations from optical to terahertz (THz) and millimeter wave (MMW) ranges. In this paper, the less investigated effects of the interlayer coupling of multiple metasurfaces cascaded in parallel are intensively exploited and leveraged for scalable broadband spectral regulations. The hybridized resonant modes of cascaded metasurfaces with interlayer couplings are well interpreted and simply modeled by the transmission line lumped equivalent circuits, which are used in return to guide the design of the tunable spectral response. In particular, the interlayer gaps and other parameters of double or triple metasurfaces are deliberately leveraged to tune the inter-couplings for as-required spectral properties, i.e., the bandwidth scaling and central frequency shift. As a proof of concept, the scalable broadband transmissive spectra are demonstrated in the millimeter wave (MMW) range by cascading multilayers of metasurfaces sandwiched together in parallel with low-loss dielectrics (Rogers 3003). Finally, both the numerical and experimental results confirm the effectiveness of our cascaded model of multiple metasurfaces for broadband spectral tuning from a narrow band centered at 50 GHz to a broadened range of 40 similar to 55 GHz with ideal side steepness, respectively.

Plasmonic metasurfaces act as appealing platforms for flexible and accurate wave regulation, but their functionalities in wavefront or spectral tuning are settled upon manufactured. So the ability to dynamically tailor the amplitude, phase or polarization is highly desirable for many scenarios of micro & nano photonics and the integrated optoelectronics. Here, one type of plasmonic metasurface devices for active wavefront control is demonstrated in the mid-infrared regime. Fundamentally, the switchable and tunable lensing is exemplified by phase change of refractive index and the generalized Snell's law as well as the Pancharatnam-Berry phase. As a proof of concept, the metal-insulator (MI) and metal-insulator-metal (MIM) architectures are employed with the phase change medium and an optimized energy conversion efficiency of cross polarization. In a wide spectral range between 2.8 mu m and 3.8 mu m, the reflective beam focuses with a cross-polarization efficiency of 80% in the amorphous state, but defocuses in the crystalline state with zero cross-polarization, i.e. the 'on' and 'off' states of the metalens. Further, both device architectures show tunable focal length from 4.4 mu m to 4.8 mu m (MI) and 3.4 mu m and 3.6 mu m (MIM) respectively upon switching between the two states. As a result, our scheme potentially paves a way to flexibly construct the active photonic devices for the reconfigurable wavefront engineering in integrated optoelectronics, i.e. beam switch, tunable steering and lensing, etc.

Plasmonic metasurfaces act as appealing platforms for flexible and accurate wave regulation, but their functionalities in wavefront or spectral tuning are settled upon manufactured. So the ability to dynamically tailor the amplitude, phase or polarization is highly desirable for many scenarios of micro & nano photonics and the integrated optoelectronics. Here, one type of plasmonic metasurface devices for active wavefront control is demonstrated in the mid-infrared regime. Fundamentally, the switchable and tunable lensing is exemplified by phase change of refractive index and the generalized Snell's law as well as the Pancharatnam-Berry phase. As a proof of concept, the metal-insulator (MI) and metal-insulator-metal (MIM) architectures are employed with the phase change medium and an optimized energy conversion efficiency of cross polarization. In a wide spectral range between 2.8 mu m and 3.8 mu m, the reflective beam focuses with a cross-polarization efficiency of 80% in the amorphous state, but defocuses in the crystalline state with zero cross-polarization, i.e. the 'on' and 'off' states of the metalens. Further, both device architectures show tunable focal length from 4.4 mu m to 4.8 mu m (MI) and 3.4 mu m and 3.6 mu m (MIM) respectively upon switching between the two states. As a result, our scheme potentially paves a way to flexibly construct the active photonic devices for the reconfigurable wavefront engineering in integrated optoelectronics, i.e. beam switch, tunable steering and lensing, etc.

Plasmonic metasurfaces act as appealing platforms for flexible and accurate wave regulation, but their functionalities in wavefront or spectral tuning are settled upon manufactured. So the ability to dynamically tailor the amplitude, phase or polarization is highly desirable for many scenarios of micro & nano photonics and the integrated optoelectronics. Here, one type of plasmonic metasurface devices for active wavefront control is demonstrated in the mid-infrared regime. Fundamentally, the switchable and tunable lensing is exemplified by phase change of refractive index and the generalized Snell's law as well as the Pancharatnam-Berry phase. As a proof of concept, the metal-insulator (MI) and metal-insulator-metal (MIM) architectures are employed with the phase change medium and an optimized energy conversion efficiency of cross polarization. In a wide spectral range between 2.8 mu m and 3.8 mu m, the reflective beam focuses with a cross-polarization efficiency of 80% in the amorphous state, but defocuses in the crystalline state with zero cross-polarization, i.e. the 'on' and 'off' states of the metalens. Further, both device architectures show tunable focal length from 4.4 mu m to 4.8 mu m (MI) and 3.4 mu m and 3.6 mu m (MIM) respectively upon switching between the two states. As a result, our scheme potentially paves a way to flexibly construct the active photonic devices for the reconfigurable wavefront engineering in integrated optoelectronics, i.e. beam switch, tunable steering and lensing, etc.