Abstract
Controlling and manipulating the propagation of surface plasmons has become a field of intense research given their potential in a wide range of applications, such as plasmonic circuits, optical trapping, sensors, and lensing. In this communication, we exploit classical optics techniques to design and evaluate the performance of plasmonic lenses with meniscus-like geometries. To do this, we use an adapted lens maker equation that incorporates the effective medium concepts of surface plasmons polaritons travelling in dielectric-metal and dielectric-dielectric-metal configurations. The design process for such plasmonic meniscus lenses is detailed and two different plasmonic focusing structures are evaluated: a plasmonic lens with a quasi-planar output surface and a plasmonic meniscus lens having a convex-concave input–output surface, respectively. The structures are designed to have an effective focal length of 2λ0 at the visible wavelength of 633 nm. A performance comparison of the two plasmonic lenses is shown, demonstrating improvements to the power enhancement, with a 22% and 16.5% increase when using 2D (ideal) or 3D (realistic plasmonic) meniscus designs, respectively, compared to the power enhancement obtained with convex-planar lenses. It is also shown that the depth of focus of the focal spot presents a 19.8% decrease when using meniscus lenses in 2D and a 34.3% decrease when using the proposed 3D plasmonic meniscus designs. The broadband response of a plasmonic meniscus lens (550–750 nm wavelength range) is also studied along with the influence of potential fabrication errors on the generated effective focal length. The proposed plasmonic lenses could be exploited as alternative focusing devices for surface plasmons polaritons in applications such as sensing.
Highlights
Controlling and manipulating the propagation of surface plasmons has become a field of intense research given their potential in a wide range of applications, such as plasmonic circuits, optical trapping, sensors, and lensing
We focus the attention on plasmonic meniscus lenses as they have the potential to achieve improved focusing performances, as it has been demonstrated for designs working at microwave/millimeter-wave frequencies[35]
As the plasmonics lenses are designed using the lens maker equation their focusing performance is compared with two-dimensional (2D) lenses illuminated with a plane wave, on we will refer to these ideal lenses as 2D lenses
Summary
Controlling and manipulating the propagation of surface plasmons has become a field of intense research given their potential in a wide range of applications, such as plasmonic circuits, optical trapping, sensors, and lensing. The field of lenses has benefited greatly from the research of plasmonics and the manipulation of SPPs where different techniques have been proposed to design focusing devices, such as metalenses for free-space focusing[16], the excitation of photonic nanojets from cuboid and cylinder s tructures[5,17,18], as well as broadband achromatic lenses for SPP focusing[3,19], among others In this context, the design of SPP-based focusing devices can be carried out by borrowing and applying classical and transformation optics techniques to plasmonic structures[4,20,21]. We explore if this improvement extends to plasmonic analogues by implementing meniscus profiles as alternative geometries to more commonly used designs such as convex-planar or biconvex focusing structures
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