Diameter is one of the most fundamental and important parameters that characterize the optical properties of a tapered fiber, so it is necessary to accurately measure its diameter. In this study, we proposed a method for measuring the diameter in the sub-1 µm diameter region of a tapered fiber by measuring the spatial period of the standing wave formed by counter-propagating light waves incident from its both sides. We used a scanning near-field optical microscopy (SNOM) probe fabricated from an optical fiber to measure the standing wave intensity distribution along the tapered fiber axial direction and its spatial period, from which the tapered fiber diameter can be estimated.
The significant development of terahertz wave technology requires precise measurement of terahertz optical devices such as diffractive gratings with micrometer-scale periodicity. We propose a new measurement method for fast, robust and precise shape measurement of micro-periodic structures, which can be regarded as a scan-less version of the deflectometry. Whereas the deflectometry demands the scanning of the beam spot in order to collect the tilt angle information from various different position on the sample surface, the proposed method simultaneously obtains it from a single diffraction image, then reconstructs the sample shape based on a light reflection model called ray reflection model. In comparison to the interferometry, the proposed method is principally robust to the mechanical vibration because the diffraction image is hardly affected by the displacement of the sample. The limitation of the proposed method is also discussed, and the mathematical expression of the constraint conditions required for the shape reconstruction is clarified. The numerical experiment based on the electromagnetic simulation with rigorous coupled-wave analysis (RCWA) demonstrates the possible accuracy on the order of 10 nm and the effectiveness of the use of the incoherent light. The physical experiment is also conducted by the constructed optical system, and the fundamental validity of the measurement result of the proposed method is confirmed.
Tapered fibers with a diameter of sub-micrometer to several micrometer show various optical characteristics, and the diameter is the most important parameter. To guarantee their functions, it is necessary to measure the fiber diameter with high precision during manufacturing. In this research, we propose an in-process measurement method of the diameter of sub-micro-optical fiber. The proposed technique is based on analyzing optically scattered light generated by standing wave illumination. First, we show the scattering characteristics of sub-microfibers using numerical simulation based on finite element method (FEM). From the result of simulation, it was revealed that the optical fiber of 100 nm in diameter can be evaluated with the standing wave illumination.
KEYWORDS: Finite-difference time-domain method, Super resolution, Near field, Near field optics, Microscopy, Waveguides, Reflection, Reconstruction algorithms, Diffraction, Light scattering
The optical-based super-resolution, non-invasive method is preferred for the inspection of surfaces with massive
microstructures widely applied in functional surfaces. The Structured Illumination Microscopy (SIM) uses standing-wave
illumination to reach optical super-resolution. Recently, coherent SIM is being studied. It can obtain both the super-resolved
intensity distribution and the phase and amplitude distribution from the sample surface. By analysis of the phase-depth
dependency, the depth measurement for microgroove structures with coherent SIM is expected. FDTD analysis is applied
for observing the near-field response of microgroove narrower than the diffraction limit under the standing-wave
illumination. The near-field phase shows depth dependency in this analysis.
As represented by "Lab on a Tip" using microchannels, the miniaturization of manufacturing and inspection processes attracts widespread interest. Therefore, many micro-tool fabrication techniques using optical tweezers have been reported. Most reported methods focus on assembling trapped microbeads, and it was necessary to have a photocurable resin phase and surface modification process to assemble solid beads. However, because many procedures such as dispersion of microbeads and removal from the resin solution were required, flexible one-step fabrication is difficult with previous methods. This study proposed a direct adhesion and assembly of the photocurable resin droplets dispersed in the aqueous solution. Since the photocurable droplets work as both base material and an adhesive, a flexible one-step fabrication of micro-tools can be achieved. It was experimentally found that the morphology of emulsion droplets in contact significantly affects the adhesion. Generally, oil-in-water emulsion droplets are stabilized by a surfactant, and adhesion between droplets can be disturbed by a surfactant bilayer. By controlling the contact angle between the droplets, the optically trapped droplets successfully adhered together with photopolymerization. Furthermore, combining the various diameter and materials of emulsion droplets using microfluidic channels, more functional and complex microtools can be expected.
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