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We demonstrated silicon-on-insulator (SOI)-based high-efficiency metalenses at telecommunication wavelengths that are integrable with a standard 220 nm-thick silicon photonic chip. A negative electron-beam resist (ma-N) was placed on top of the Si nanodisk, providing vertical symmetry to realize high efficiency. A metasurface with a Si/ma-N disk array was numerically investigated to design a metalens that showed that a Si/ma-N metalens could focus the incident beam six times stronger than a Si metalens without ma-N. Metalenses with a thick ma-N layer have been experimentally demonstrated to focus the beam strongly at the focal point and have a long depth of field at telecommunication wavelengths. A short focal length of 10 μm with a wavelength-scale spot diameter of approximately 2.5 μm was realized at 1530 nm. This miniaturized high-efficiency metalens with a short focal length can provide a platform for ultrasensitive sensors on silicon photonic IC.

Coupling characteristics between a single mode fiber (SMF) and a waveguide embedded in a glass chip via a graded index fiber (GIF) tip are investigated at a wavelength of 976 nm. The GIF tips comprise a coreless fiber section and a GIF section. A depressed cladding waveguide in a ZBLAN glass chip with a core diameter of 35 μm is coupled with GIF tips that have a range of coreless fiber and GIF lengths. An experimental coupling efficiency as high as 88% is obtained while a numerical simulation predicts 92.9% for the same GIF tip configuration. Since it is measured in the presence of Fresnel reflection, it can be further improved by anti-reflection coating. Additionally, it is demonstrated that a gap can be introduced between the chip waveguide and the GIF tip while maintaining the high coupling efficiency, thus allowing a thin planar optical component to be inserted. The results presented here will enable miniaturization and simplification of photonic chips with integrated waveguides by replacing bulk coupling lenses with integrated optical fibers.

A readily configurable and scalable 2 µm laser source with multi-channel/wavelength fiber output could be advantageous to 2 µm applications such as spectral-beam combination or fiber communications. We report the first experimental realization and characterization of a two-channel holmium-doped zirconium fluoride glass waveguide array laser pumped by a single thulium fiber laser at 1945 nm. Specific laser wavelengths are selected by fiber Bragg gratings (2076.7 nm and 2074.4 nm), and single channel powers of >100 mW are achieved. Design and assembly details, and considerations for future improvements are discussed, including the potential extension to and beyond a 12 channel source. Refereed/Peer-reviewed

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Growing interest in devices based on layered van der Waals (vdW) materials is motivating the development of new nanofabrication methods. Hexagonal boron nitride (hBN) is one of the most promising materials for studies of quantum photonics and phonon polaritonics. A promising nanofabrication process used to fabricate several hBN photonic devices using a hybrid reactive ion etching (RIE) and electron beam-induced etching (EBIE) technique is reported in detail here. The shortcomings and benefits of RIE and EBIE are highlighted and the utility of the hybrid approach for the fabrication of suspended and supported device structures with nanoscale features and highly vertical sidewalls are demonstrated. Functionality of the fabricated devices is proven by measurements of high-quality cavity optical modes (Q ≈ 1500). This nanofabrication approach constitutes an advance toward an integrated, monolithic quantum photonics platform based on hBN and other layered vdW materials.

Copyright © 2018 American Chemical Society. The effects of Fano resonance on the optical chirality of planar plasmonic nanodevices in the visible wavelength range are experimentally observed and theoretically explained. The nanodevice consists of a nanodisk at the center with surrounding six gold nanorods with an orientation angle to exhibit optical chirality under dark-field illumination. The chiral response induced by the gold nanorods is affected by the presence of the nanodisk with different diameters which causes Fano resonance of different coupling strength. An intriguing change to the opposite selection preference of different handedness of the circularly polarized light has been clearly observed experimentally. This change of the preference is understood based on the coupled localized surface plasmon model. Moreover, electrostatic analysis and the time-dependent simulations provide a further understanding of the phenomenon. The observed and understood effects of Fano resonance on optical chirality enables effective manipulation of chiral characteristics of planar subwavelength nanodevices.

We consider periodic arrangements of metal nanostructures and study the effect of periodicity on the localized surface plasmon resonance of the structures within an electrostatic eigenmode approximation. We show that within this limit the collective surface plasmon resonances of the periodic structures can be expressed in terms of superpositions of the eigenmodes of uncoupled nanostructures that exhibit a standing-wave character delocalized across the entire periodic structure. The formalism derived successfully enables the design and accounts for the observation of plasmonic edge states in periodic structures. Refereed/Peer-reviewed

We suggest a plasmonic nanodevice for performing the second-order spatial derivative of light fields. The device consists of five gold nanorods arranged to evanescently couple to each other so that emit cross-polarized output proportional to the second-order differentiation of the incident wave. A theoretical model based on the electrostatic eigenmode analysis is derived and numerical simulations using the finite-difference time-domain methods are provided as supporting evidence. It is shown in both the analytic and numerical methods that the proposed plasmonic circuit performs second-order differentiation of the phase of the incident light field in transmission mode with a subwavelength planar resolution. The resolution of 0.29 lambda(-1) is numerically demonstrated for a 20 nm thick circuit at the wavelength of 700 nm. The suggested plasmonic device has potential application in miniaturized systems for all-optical computation. Refereed/Peer-reviewed

We investigated surface-roughness-dependent optical loss in a plasmonic cavity consisting of a semiconductor nanodisk/silver nanopan structure. Numerical simulations show that the quality factors of plasmonic resonant modes significantly depend on the surface roughness of the dielectric-metal interface in the cavity structure. In the transverse-magnetic-like whispering-gallery plasmonic mode excited in a structure with disk diameter of 1000 nm, the total quality factor decreased from 260 to 130 with increasing root-mean-square (rms) surface roughness from 0 to 5 nm. This quantitative theoretical study shows that the smooth metal surface plays a critical role in high-performance plasmonic devices. Refereed/Peer-reviewed

The authors introduce frequency selective beam splitters for surface plasmon polaritons (SPPs) in a metal-insulator-metal (MIM) structure. In the splitters, a part of SPPs keeps propagating straight along the initial direction, while the other part is split into the arm attached at right angle. The splitting ratio can be controlled by varying the width and the electric permittivity of the dielectric layer in the MIM, and by varying the width of the attached arm. (C) 2011 Elsevier B.V. All rights reserved. Refereed/Peer-reviewed

We report the geometric dependences of metal-coated silicon nanowire (Si NW) plasmonic waveguides on their propagation lengths and mode areas. We examined Si NWs with four different cross-sectional shapes. Numerical simulations showed that propagation lengths and mode areas are highly dependent on the cross-sectional geometries of Si NWs. In particular, the TM-like mode in a hexagonal-shaped Si NW plasmonic waveguide without an air void has the longest propagation length of 18 : 20 mu m, which is 4.7 times larger than that of the TM-like mode in a circular-shaped Si NW plasmonic waveguide. This study can be a useful guide for the design and application of metal-coated Si NW plasmonic waveguides. Korea Government (MSIP)2009-0081565 Refereed/Peer-reviewed

Using finite-difference time-domain simulations it is shown that a metal-insulator-metal (MIM) ring with a narrow gap exhibits plasmonic stop bands (PLSBs) in a similar way that a microstrip ring with a narrow gap exhibits photonic stop bands. A narrow gap created in the middle of the upper half of a regular MIM ring causes plasmonic fields to experience multiple reflections at the discontinuity introduced by the gap, which results in the formation of PLSBs. The PLSBs appear as transmission dips around the resonant frequencies of the isolated MIM ring with the narrow gap. The centre frequency and the range of PLSBs are shown to be controllable by varying the width of the narrow gap. The proposed design for a MIM ring in which PLSBs exist is expected to reduce the size of the plasmonic devices.