Corrugation-assisted metal-coated angled fiber facet for wavelength-dependent off-axis directional beaming

Abstract

We propose a fiber-optic-plasmonic hybrid device that is based on a corrugation-assisted metal-coated angled fiber facet (CA-MCAFF) for wavelength-dependent off-axis directional beaming (WODB). The device breaks into two key structures: One is the MCAFF structure, which is a modified Kretschmann configuration implemented onto a fiber platform, thereby being able to generate a unidirectional surface plasmon with dramatically enhanced properties in terms of non-confined diffracted radiation loss and operational bandwidth. The other is the periodic corrugation structure put on the MCAFF, thereby enabling WODB functionality out of the whole structures. The corrugated metal surface out-couples the surface plasmon mode to free-space optical radiation into a direction that varies with the wavelength of the optical radiation with excellent linearity. We perform extensive numerical investigations based on the finite-element-method and analyze the out-coupling efficiency (OCE_out) and spectral bandwidth (SB_out) of the proposed device for various designs and conditions. We determine the seven structural parameters of the device via taking sequential optimization steps. We deduce two optimal conditions particularly for the fiber-facet angle, in terms of the averaged OCE_out or the SB_out in the whole visible wavelength range (400 - 700 nm), which eventually leads to OCE_out = 30.4% and SB_out = 230 nm or to OCE_out = 24.5% and SB_out = 245 nm, respectively. These results suggest substantial enhancements in both OCE_out and SB_out, in comparison with the performance properties of a typical nano-slit-based device having a similar type of WODB functionality. The proposed CA-MCAFF is a simple, compact and efficient WODB device that is fully compatible with the state-of-the-art optical fiber technology.

Numerical and Experimental Study on Multi-Focal Metallic Fresnel Zone Plates Designed by the Phase Selection Rule via Virtual Point Sources

“…Fresnel zone plates (FZPs) or metallic Fresnel zone plates (MFZPs) have received considerable attention in recent years as an efficient focusing element for flat optical applications [1][2][3][4][5]. They can be used not only as a replacement for conventional focusing lenses, but also as optical elements with exquisite properties by implementing various novel patterns onto the metallic annular slit structure, such as multi-focal, multi-chromatic, and super-oscillatory lenses [6][7][8][9][10].…”

Plasmonics on Optical Fiber Platforms

“…Recently, the author has introduced a novel SPP coupling scheme in the optical fiber platform that is based on a metal-coated angled fiber facet (MCAFF) different from the aforementioned conventional schemes [10]. In fact, this scheme exploited the so-called Kretschmann configuration on the optical fiber platform, because the angle fiber facet can play exactly the same role as a prism to the optical mode guided in the core of the fiber [10,37].…”

“…In general, optical-fiber-based SPP generation has mostly been done based on nanoslit structures [4,6,9,38]. However, its coupling efficiency tends to be considerably low by the following factors: the generation of NCDL, the excitation of multidirectional SPPs, and the reflection of the incident light by aperture [10] as illustrated in Figure 7(a). In fact, such issues can be overcome if the Kretschmann configuration [37] is directly exploited on an angled optical fiber facet as illustrated in Figure 7(b).…”

“…In fact, the Kretschmann's prism coupling configuration should still be valid for an angled fiber facet, because it can be regarded as a prism to the optical mode guided in the core of the fiber [10,37]. Subsequently, an MCAFF can excite SPPs along the dielectric-metal interface as long as the following phase-matching condition is satisfied [10]:…”

“…Second, the author investigates fiberized plasmonic Fresnel zone plates for super-variable focusing with incident wavelength and for selective focusing with incident polarization [9]. Third, the author investigates novel metal-coated angled optical fiber facets for a versatile optical-to-SPP mode converter, which provide high efficiency, unidirectionality, and perfect compatibility with fiberized light sources [10]. The detailed investigation and discussion with numerical and experimental demonstrations are given in the following sections.…”