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Transmission of nanopillars with different tapering angles plotted against (a) the bottom radius (b) the volume.
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Despite the widespread interest in the metalens technology, few works show the errors during fabrication and analyze how they influence the focusing performance. In this work, we proposed a reflective metalens design and carry out a fundamental study on how a mild tapering angle (<6) of the nanopillars would influence the performance of a reflectiv...
Contexts in source publication
Context 1
... At normal incidence (í µí¼=0 o ), the focusing efficiency is 66%, which drops dramatically to 46% as the tapering angle increases to 6 o . The same trend is observed for other incident angles from 10 o to 30 o . The monotonic drop of the focusing efficiency with the increase of the tapering angle can be explained by the transmission curve in Fig. 4(a). With a small bottom radius (<95 nm), the transmission is almost 1. But it drops to almost 0 at the resonant wavelength. The contrast of transmission between different tapering angles is clear when it is plotted against the volume in Fig. 4(b). The FWHM of the transmission curve increases as a result of the tapering angle. The ...
Context 2
... efficiency with the increase of the tapering angle can be explained by the transmission curve in Fig. 4(a). With a small bottom radius (<95 nm), the transmission is almost 1. But it drops to almost 0 at the resonant wavelength. The contrast of transmission between different tapering angles is clear when it is plotted against the volume in Fig. 4(b). The FWHM of the transmission curve increases as a result of the tapering angle. The transmission is much lower at the same volume for the tapered structures due to the low Q factor of the resonance. Therefore, the tapered structure increases R1 shown in Fig. 1(b), which results in compromised focusing efficiency. To shed more light on ...
Context 3
... At normal incidence (í µí¼=0 o ), the focusing efficiency is 66%, which drops dramatically to 46% as the tapering angle increases to 6 o . The same trend is observed for other incident angles from 10 o to 30 o . The monotonic drop of the focusing efficiency with the increase of the tapering angle can be explained by the transmission curve in Fig. 4(a). With a small bottom radius (<95 nm), the transmission is almost 1. But it drops to almost 0 at the resonant wavelength. The contrast of transmission between different tapering angles is clear when it is plotted against the volume in Fig. 4(b). The FWHM of the transmission curve increases as a result of the tapering angle. The ...
Context 4
... efficiency with the increase of the tapering angle can be explained by the transmission curve in Fig. 4(a). With a small bottom radius (<95 nm), the transmission is almost 1. But it drops to almost 0 at the resonant wavelength. The contrast of transmission between different tapering angles is clear when it is plotted against the volume in Fig. 4(b). The FWHM of the transmission curve increases as a result of the tapering angle. The transmission is much lower at the same volume for the tapered structures due to the low Q factor of the resonance. Therefore, the tapered structure increases R1 shown in Fig. 1(b), which results in compromised focusing efficiency. To shed more light on ...
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Citations
... Despite significant advancements in design theory enabling the creation of highly efficient metalenses, the introduction of fabrication errors during manufacturing has often led to final device performances falling short of expectations [23][24][25][26][27]. In recent years, some researchers have delved into the effects of sidewall tilting, lateral dimension variation, and process defects of structural units on the performance of metalenses [28,29]. They have discovered that sidewall tilting leads to the proximity of neighboring structures, resulting in stronger structural resonance, which affects the efficiency of the metalens. ...
... This conclusion can be confirmed by comparing Figure 4c,d. Figure 4b shows that when a = 155 nm and the height of the nanobricks has a negative deviation, there is no expected phase shift theoretically, mainly because the appearance of Fabry-Pérot resonance alleviates the phase shift caused by the waveguide mode [28,50]. Specifically, the side length a affects the shape and size of the nanobricks, which in turn affects the effective refractive index of the structural unit. ...
Metalenses, as a new type of planar optical device with flexible design, play an important role in miniaturized and integrated optical devices. Propagation phase-based metalenses, known for their low loss and extensive design flexibility, are widely utilized in optical imaging and optical communication. However, fabrication errors introduced by thin-film deposition and etching processes inevitably result in variations in the height of the metalens structure, leading to the fabricated devices not performing as expected. Here, we introduce a reflective TiO2 metalens based on the propagation phase. Then, the relationship between the height variation and the performance of the metalens is explored by using the maximum phase error. Our results reveal that the height error of the unit structure affects the phase rather than the amplitude. The focusing efficiency of our metalens exhibits robustness to structural variations, with only a 5% decrease in focusing efficiency when the height varies within ±8% of the range. The contents discussed in this paper provide theoretical guidance for the unit design of the propagation phase-based metalens and the determination of its allowable fabrication error range, which is of great significance for low-cost and high-efficiency manufacturing.
... At P = 350 nm, the resonance almost vanishes and the absorption falls below 10%. It is worth noticing that such strong variation of the resonance depth is inherently related to the intrinsic losses included in the model, for such behavior was not observed in previous studies where intrinsic losses were neglected [46,47]. By further increasing the pitch, the absorption and the transmittance dip increase again, reaching almost zero transmittance at P = 380 nm. ...
We present an optical metasurface with symmetrical individual elements sustaining Fano resonances with high Q-factors. This study combines plane-wave illumination and modal analysis to investigate the resonant behavior that results in a suppression of the forward scattering, and we investigate the role of the lattice constant on the excited multipoles and on the spectral position and Q-factor of the Fano resonances, revealing the nonlocal nature of the resonances. The results show that the intrinsic losses play a crucial role in modulating the resonance amplitude in specific conditions and that the optical behavior of the device is extremely sensitive to the pitch of the metasurface. The findings highlight the importance of near-neighbor interactions to achieve high Q resonances and offer an important tool for the design of spectrally tunable metasurfaces using simple geometries.
... The full suppression of the forward scattering observed in the transmission spectra and the extremely high Q-factor of the Fano resonances can be understood by looking at the interplay between high order electric and magnetic multipole resonances that satisfies the generalized Kerker condition [33,34]. A recent paper clarified the role of multipole resonances when arrays of nanopillars are considered by performing a multipole expansion analysis on the scattered field [35]. Here, Fig. 2(b) and (c) show the electric field distribution across the xy plane at z = h/2 (b) and across the xz plane at y = P/2. ...
We report on the optical behaviour of a nanostructured diamond surface on a glass substrate. The numerical model reveals that a simple geometrical pattern sustains Fano-like resonances with a Q-factor as high as 3.5 · 10⁵ that can be excited by plane waves impinging normally on the surface. We show that the geometrical parameters of the nanopillars affect both the resonant frequency and the line shape. The nanostructured surface can be straightforwardly used as a refractive index sensor with high sensitivity and linearity. Our findings show that diamond-based meta-surfaces are a valuable nanophotonic platform to control light propagation at the nanoscale, enabling large field enhancement within the nanoresonators that can foster both linear and nonlinear effects.
... These issues can be overcome using dielectric materials to replace metallic nano-antennae, improving the focusing efficiency of the reflected beam [20,21]. However, most recently proposed reflective metalenses suffer from high mirror losses because the mirror structure absorbs a significant portion of the incident beam, reducing the focusing efficiency [22,23]. ...
... However, we are able to get decent focusing performance despite the tapering angle. The effect of the sidewall tapering angle on the metalens phase response and performance is discussed in detail in our previous publication [23]. Second, the resolution limit of the imaging system is used to characterize the proposed metalens. ...
Metalenses are one of the most promising metasurface applications. However, all-dielectric reflective metalenses are rarely studied, especially regarding their off-axis focusing performance. After experimentally studying the material optical properties in this work, we propose reflective metalens based on titanium dioxide (TiO2) and silicon dioxide (SiO2), which operate at a visible wavelength of 0.633 µm. Unlike conventional reflective metalenses based on metallic mirrors, the proposed device was designed based on a modified parabolic phase profile and was integrated onto a dielectric distributed Bragg reflector periodic structure to achieve high reflectivity with five dielectric pairs. The focusing efficiency characteristics of the metalens were experimentally studied for beam angles of incidence between 0 ∘ and 30 ∘ . The results reveal that the focusing efficiency for the modified metalens design remains higher than 54%, which is higher than 50%, making it promising for photonic miniaturization and integration.
... Figure 4(d) shows the electric field vector and magnetic field strength in the x − z section. The multistage expansion of the scattering field of nanopillars was primarily composed of four multistage contributions: the magnetic dipole (MD), electric dipole (ED), electric quadrupole (EQ), and magnetic quadrupole (MQ) [49]. It was observed that the nanotube without a cone angle comprised three rotation cycles. ...
Metalenses exhibit excellent performance as a new type of optical element; mid-infrared devices based on metalenses are advantageous to numerous applications in biomedical, military and industrial fields. The demand for large-area and high-efficiency mid-infrared metalenses has increased in recent years. However, the current processing methods for metalens production introduce different types of processing errors. Therefore, qualitative analyses of various errors that may exist in the processing of metalenses should be performed. In this study, we use the finite-difference time-domain calculation method and introduce various typical errors into a transmission phase-based mid-infrared metalens for simulation and analysis. The simulation results show that the defects caused by these processes affect focusing efficiency, and that some defects affect the quality of light. Subsequently, we prepare a metalens within the allowable error range and test its optical performances. The experiment confirms the excellent imaging performance of our metalens. Our study can help manufacturers identify defects to improve manufacturing processes, thereby enabling the incorporation of metalenses in industrial applications.
