Abstract:The microlens arrays (MLAs) are widely utilized for various applications. However, when the lens size and the spacing between two adjacent microlenses are of the length scale of the working wavelength, the diffraction effect plays a vital role in the final focusing performance. We suggest a kind of broadband metallic planar microlenses, based on which the ultra-compact microlens arrays are also constructed. The focusing coupling effect revealing for such devices is then investigated in detail by using the fini… Show more
“…Besides, the peak intensity values are uniformly distributed at the array plane, which is a great aspect of these metalens arrays. On the other hand, remarkably, no significant fringing effect exists on the achieved focal spots, which is another superior characteristic of this study comparing to the results of previously reported metallic planar microlens arrays [48], which clearly suffer from plasmonic coupling effects. This also simplifies the accurate control over the focusing performance of metalenses in an array.…”
Section: The Effect Of the Metalens Array Sizesupporting
The microlens arrays have been widely used for different optoelectronic applications. The demand for compact optical devices necessitates the deployment of even smaller microlens arrays; however, as the spacing between individual lens reduces and the lens diameter approaches to the length scale of the incident wavelength of light, the diffraction starts playing a critical role and produces a significant impact on the final focusing properties of the optical field. In this paper, we analyze the focusing characteristics of alldielectric ultra-compact metasurface lens arrays for efficient optical device applications, constructed by a kind of broadband planar lenses composed of subwavelength nanoscatterers. By using the 3D finite-difference time-domain (FDTD) method, the focusing and diffraction-based crosstalk effects caused by the changing physical spacing between adjacent metalenses, the diameter of microlenses, the operating wavelength, and the array size are rigorously investigated. Analysis of the achieved results show that a larger spacing, a larger lens size, a shorter wavelength can lead to a weaker focusing crosstalk effect. Moreover, the crosstalk effect does not have a significant dependence on the array overall size. This research study may provide an important technological reference to design an array of all-dielectric planar metasurface lenses with a well-controlled focusing performance and pave the way further toward application of metasurface lens arrays in compact optical sensing, coupling and detecting system designs.
“…Besides, the peak intensity values are uniformly distributed at the array plane, which is a great aspect of these metalens arrays. On the other hand, remarkably, no significant fringing effect exists on the achieved focal spots, which is another superior characteristic of this study comparing to the results of previously reported metallic planar microlens arrays [48], which clearly suffer from plasmonic coupling effects. This also simplifies the accurate control over the focusing performance of metalenses in an array.…”
Section: The Effect Of the Metalens Array Sizesupporting
The microlens arrays have been widely used for different optoelectronic applications. The demand for compact optical devices necessitates the deployment of even smaller microlens arrays; however, as the spacing between individual lens reduces and the lens diameter approaches to the length scale of the incident wavelength of light, the diffraction starts playing a critical role and produces a significant impact on the final focusing properties of the optical field. In this paper, we analyze the focusing characteristics of alldielectric ultra-compact metasurface lens arrays for efficient optical device applications, constructed by a kind of broadband planar lenses composed of subwavelength nanoscatterers. By using the 3D finite-difference time-domain (FDTD) method, the focusing and diffraction-based crosstalk effects caused by the changing physical spacing between adjacent metalenses, the diameter of microlenses, the operating wavelength, and the array size are rigorously investigated. Analysis of the achieved results show that a larger spacing, a larger lens size, a shorter wavelength can lead to a weaker focusing crosstalk effect. Moreover, the crosstalk effect does not have a significant dependence on the array overall size. This research study may provide an important technological reference to design an array of all-dielectric planar metasurface lenses with a well-controlled focusing performance and pave the way further toward application of metasurface lens arrays in compact optical sensing, coupling and detecting system designs.
“…The focal spots under the white light illumination have the similar lateral dimensions as those under a single wavelength, while the broadband focal length is approximately the average of the focal lengths at the SP-enhanced wavelengths. In addition, the focusing coupling effect in microlens array which we had analyzed in our previous research [37] emerges in the obtained focusing patterns as the regions C, D, and E flagged in Fig. 8 (b1) and (b2).Fig.…”
A novel low-cost, batch-fabrication method combining the spin-coating nanosphere lithography (NSL) with the conventional photolithographic technique is demonstrated to efficiently produce the metallic planar microlenses and their arrays. The developed microlenses are composed of subwavelength nanoholes and can focus light effectively in the entire visible spectrum, with the foci sizes close to the Rayleigh diffraction limit. By changing the spacing and diameter of nanoholes, the focusing efficiency can be tuned. Although the random defects commonly exist during the self-assembly of nanospheres, the main focusing performance, e.g., focal length, depth of focus (DOF), and full-width at half-maximum (FWHM), keeps almost invariable. This research provides a cheap way to realize the integrated nanophotonic devices on the wafer level.
“…The reported plasmonic lenses are based on slits [17,18], and less attention has been dedicated to the utilization of hole array. Few broadband spectrum lenses for the visible range based on nanohole array have recently been proposed [19][20][21], but they suffer from low transmittance, polarization sensitivity, and large size. In the meantime, plasmonics tapers by using grating-coupled SPPs made nanofocusing feasible [22,23].…”
A novel nanohole cluster configuration that consists of nine holes with gradually decreasing sizes and interspace distances for light focusing purposes in a plasmonic regime is proposed. The hole size and separation are correlated with each other by introducing a scaling factor (k). A similar arrangement has already been investigated in nanoparticle cases. For some values of k, the light propagating through the holes extraordinarily transmit, constructively interfere and strongly localize at a point under the metallic layer. The physics behind the focusing is attributed to the optical diffraction and surface plasmon effects. A numerical approach is used to illustrate the focusing features. The results show that the best focusing features occur when the largest hole size is in the order of incident light wavelength and scaling factor is between 0.35 and 0.45. The calculated enhancement factor of the light intensity at focal point is approximately 2.6. Notably, the proposed structure scales down the plasmonic lens size. The fabrication process is in accordance with typical fabrication techniques used in plasmonic chips integration.
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