RESUMEN
A defect structure is proposed for enhancing the coupling efficiency of vertically incident circularly polarized light in a topological waveguide. In the topological edge-state waveguide based on triangle lattices of hexagons consisting of six nanoholes respecting C6v symmetry in a silicon optical circuit, the vertical coupling rate is improved by removing the nanoholes from one hexagonal cell near the line. The coupling efficiency was evaluated with and without the defect structure. The introduced defect structure operates suitably for focused beams of left- and right-handed circularly polarized light, enhancing the optical communication wavelength bandwidth by up to 10â dB.
RESUMEN
In this study, we developed a photonic band microscope based on hyperspectral Fourier image spectroscopy. The developed device constructs an infrared photonic band structure from Fourier images for various wavelength obtained by hyperspectral imaging, which make it possible to speedily measure the dispersion characteristics of photonic nanostructures. By applying the developed device to typical photonic crystals and topological photonic crystals, we succeeded in obtaining band structures in good agreement with the theoretical prediction calculated by the finite element method. This device facilitates the evaluation of physical properties in various photonic nanostructures, and is expected to further promote related fields.
RESUMEN
We propose a method for selectively propagating optical vortex modes with specific charge numbers in a photonic integrated circuit (PIC) by using a topological photonic system. Specifically, by performing appropriate band tuning in two photonic structures that comprise a topological waveguide, one specific electromagnetic mode at the Γ point of a band diagram can be excited. Based on theoretical analysis, we successfully propagated optical vortex modes with specific charge numbers over a wide range in the C band in the proposed topological waveguide. The proposed method could be useful in controlling optical vortex signals at the chip level in future orbital angular momentum multiplexing technologies.
RESUMEN
In this study, we propose a defect structure that enhances the vertical coupling efficiency of circularly polarized light incident on topological waveguides consisting of triangle nanoholes with C6v symmetry arranged in honeycomb lattice. The defect structure was formed by removing triangle nanoholes from a certain hexagonal unit cell around the topological waveguide. As a result of comparing the coupling efficiency with and without the defect structure through three-dimensional finite-difference time-domain analysis, significant improvement in the vertical coupling efficiency was observed over the entire telecom C band (4460%@1530 nm). In addition, it was also found that the wavelength showing maximum coupling efficiency can be controlled over the entire C band by changing the arrangement of the dielectric around the defect structure.
RESUMEN
Replacing part of a conventional optical circuit with a topological photonic system allows for various controls of optical vortices in the optical circuit. As an underlying technology for this, in this study, we have realized a topological converter that provides high coupling efficiency between a normal silicon wire waveguide and a topological edge waveguide. After expanding the waveguide width while maintaining single-mode transmission from the Si wire waveguide, the waveguides are gradually narrowed from both sides by using a structure in which nanoholes with C6 symmetry are arranged in a honeycomb lattice. On the basis of the analysis using the three-dimensional finite-difference time-domain method, we actually fabricated a device in which a Si wire waveguide and a topological edge waveguide were connected via the proposed topological converter and evaluated its transmission characteristics. The resulting coupling efficiency between the Si wire waveguide and the topological edge waveguide through the converter was -4.49â dB/taper, and the coupling efficiency was improved by 5.12â dB/taper compared to the case where the Si wire waveguide and the topological edge waveguide were connected directly.
RESUMEN
A metamaterial is an artificial material designed to control the electric permittivity and magnetic permeability freely beyond naturally existing values. A promising application is a slow-light device realized using a combination of optical waveguides and metamaterials. This paper proposes a method to dynamically control the slow-light effect in a metamaterial-loaded Si waveguide. In this method, the slow-light effect (i.e., group index) is controlled by changing the phase of the control light incident on the device from a direction opposite to that of the signal light. The group index of the device could be continuously controlled from 63.6 to 4.2 at a wavelength of 1.55â µm.
RESUMEN
Infrared refractive index is an indispensable parameter for various fields including infrared photonics. To date, critical-angle refractometers, V-block refractometers, and spectroscopic ellipsometry have been commonly used to measure the refractive index. Although every method has an accuracy of four decimal places for the refractive index, a measurable wavelength region is limited up to about 2 µm. In this study, we demonstrated a metamaterial infrared refractometer for determining broadband complex refractive index. Using the device, a broadband (40-120 THz; wavelength 2.5-7.5â µm) and high-precision(< 5 ×10-3) complex refractive index of polymethyl methacrylate was measured for the first time.
RESUMEN
We demonstrated a novel slow-light Si-wire waveguide combined with metamaterials, which can be easily integrated with other Si photonics devices. The slow-light effect can be produced simply by placing metamaterials at an appropriate position on a Si-wire waveguide. It was confirmed that the large group index of more than 40 could be obtained because of a steep and discontinuous change of dispersion relation near the resonance frequency of metamaterials.