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 finite-difference time-domain (FDTD) method, with the emphasis on the changing spacing between adjacent microlenses, the working wavelength, the diameter of microlenses, and the array size. The results show that a larger spacing, a larger lens size, a shorter wavelength, or a smaller array scale can lead to a weaker focusing coupling effect. This research provides an important technological reference to design an array of metallic planar microlenses with the well-controlled focusing performance.
Highlights
The microlens arrays (MLAs), as a kind of very important optical elements, are widely used in various fields, such as charge-coupled devices (CCDs) [1], displays [2, 3], LED lighting [4], solar concentrators [5], and photolithography [6]
To the best of our knowledge, it has not been discussed in any other publications on the metallic planar microlenses, and we find that this effect plays a vital role when the diameter of microlenses and the periodicity are in the length scale of the wavelength, which is rarely concerned for the conventional MLAs as their diameters are usually of hundreds of microns
The periodicity of nanoholes reveals an insignificant influence on the focal length, depth of focus (DOF), and full-width at half-maximum (FWHM) of the focal spot
Summary
The microlens arrays (MLAs), as a kind of very important optical elements, are widely used in various fields, such as charge-coupled devices (CCDs) [1], displays [2, 3], LED lighting [4], solar concentrators [5], and photolithography [6]. As an important category of plasmonic devices, plasmonic lenses based on thin metallic films were developed [15,16,17,18,19,20,21], being an alternative to the conventional dielectric-based refractive lenses These nanostructured plasmonic lenses enable subwavelength focusing and allow all-optical or Recently, the Odom research group reported a new type of metallic planar microlenses [22], the so-called patch structures consisting of a finite-sized nanohole array. These “patches” can focus the broadband white light with a little chromatic divergence.
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