Yi Zhao

In this work, we propose a design method of the narrow passband filter with a high Q-factor based on a Fano resonance. A single-layer metallic frequency selective surface (FSS) with a simple structure is first designed according to this idea, but the result is not satisfying since the filter transmittance will significantly decrease with the increase of the Q-factor due to the presence of an inherent ohmic damping. Further, to improve the design, a ceramic-based FSS filter based on the similar mechanism is proposed, and the requirements of the ultrahigh Q-factors can be met owing to the high permittivity and low loss tangent of microwave ceramics. The design strategy proposed in this paper may have a promising potential in modern wireless communication and related fields.

In this paper, we proposed a triple layer structure consisting of the bottom silver layer, thin silicon oxide space layer, and ultrathin semiconductor silicon film with nano hole array achieving three absorption peaks with narrow band. The absorption spectrum can be easily controlled by adjusting the structural parameters including the radius and period of the nano hole array, and the maximal absorption can reach 99.0% and the narrowest full width of half maximum can reach about 6.5 nm in theory. We also clarified the physical mechanism of the proposed structure in details by finite-difference time-domain simulation, in which the three narrow band perfect adsorption peaks can be attributed to electric dipole resonance, magnetic dipole resonance and plasmonic resonance respectively. At the same time, we used a low-cost nanosphere lithography method to fabricate the proposed nano hole array in large area. In experiment, the absorption peak of the proposed triple layer structure can reach up to 98.3% and the narrowest full width of half maximum can reach up to about 10.1 nm. The highest quality factor Q can reach up to 98.4. This work can open a new avenue for high-quality factor narrow band perfect absorption using ultrathin semiconductor film and benefit for many fields such as infrared sensors, plasmonic filters, and hyperspectral imaging.

An all-silicon long-wavelength infrared (LWIR) achromatic metalens based on deep silicon etching is designed in this paper. With a fixed aperture size, the value range of the equivalent optical thickness of the non-dispersive meta-atoms constructing the achromatic metalens determines the minimum f-number. The fabrication characteristic with high aspect ratio of deep silicon etching amplifies the difference value of optical thickness between different meta-atoms by increasing the propagation distance of the propagation mode, which ensures a small f-number to obtain a better imaging resolution. A 280-µm-diameter silicon achromatic metalens with a f-number of 1 and the average focusing efficiency of 27.66% has been designed and simulated to validate the feasibility of this strategy. The simulation results show that the maximum focal length deviation percentage from the target value between the wavelength of 8.6 and 11.4 µm is 1.61%. This achromatic metalens design is expected to play a role in the field of LWIR integrated optical system.

An ultrathin layer of deep-red phosphorescent emitter tris(1-phenylisoquinoline) iridium (III) (Ir(piq)₃) is inserted within different positions of the electron blocking layer fac-tris (1-phenylpyrazolato-N,C^2′)-iridium(III) (Ir(ppz)₃) to distinguish the contribution of the emission from the triplet exciton energy transfer/diffusion from the adjacent blue phosphorescent emitter and the trap-assisted recombination from the narrow band-gap emitter itself. The charge trapping effect of the narrow band-gap deep-red emitter which forms a quantum-well-like structure also plays a role in shaping the electroluminescent characteristics of multi-color organic light-emitting diodes. By accurately controlling the position of the ultrathin sensing layer, it is considerably easy to balance the white emission which is quite challenging for full-color devices with multiple emission zones. There is nearly no energy transfer detectable if 7 nm thick Ir(ppz)₃ is inserted between the blue phosphorescent emitter and the ultrathin red emitter.