Characterization of optical waveguides with near - field scanning optical microscope
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Abstract:
광 도파로를 따라 전파하는 빛의 특성을 측정하기 위해 근접장 주사 광학현미경(Near-field scanning optical microscope, NSOM)으로 광 도파로의 표면에 형성된 에바네슨트 파 evanescent wave)의 분포를 측정하였다. 사용된 NSOM은 photon scanning tunneling microscope방식으로 본 연구의 목적에 적합하도록 직접 제작한 것이다. 광원 파장 1550㎚에서 단일 모드 다중 모드 채널형 광 도파로에 대해 도파로 표면에 형성된 에바네슨트 파의 분포를 측정하였으며, 3차원 빔전파방법(Beam Propagation Method)으로 계산된 수치 해석 결과와 두 모드 간의 간섭 형상을 직접적으로 확인할 수 있었다. The propagation characteristic of an optical waveguide was investigated by measuring with a near-field scanning optical microscope (NSOM) the evanescent field formed at the neighbor of its core-cladding interface. For this purpose, the NSOM system was developed specially as a form of Photon scanning tunneling microscope. The evanescent field distributions of several channel waveguides were measured at the wavelength of 1550 ㎚, and the usefulness of the system was verified by comparing experimental results with simulation results. In particular, the interference phenomena of the guided modes during their propagation along a multimode channel waveguide could be observed directly from the measured evanescent field distribution.Keywords:
Cladding (metalworking)
Near-field optics
Waveguide
To overcome the diffraction limit, a laser irradiating cantilevered scanning near-field optical microscopy (SNOM) probe has been used in near-field optical nanopatterning. In this paper, the mechanism of nanopatterning on noble metal nano-films by this technique is investigated by the finite element method. It is proposed that the main mechanism of this phenomenon is the melt and reshaping of the nano-film under the SNOM tip. The melt is caused by the surface plasmon polariton-assisted enhancement and restriction within the SNOM tip aperture. The impacts of the gap g between the tip and substrate and the polarization of the laser are further analyzed.
Near-field optics
Nanophotonics
Scanning Probe Microscopy
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A scanning near-field optical microscope (SNOM) combined with a scanning tunneling microscope (STM) is used to investigate nanoscopic optical phenomena both in the near-field region and in the proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture, on which metal-coating is performed to obtain a half-transparent conducting tip. A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field standing on the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance con-trol is carried out under constant current condition in order to separate the optical properties from surface topography. λ/100 optical resolution and the identical channel transport both for electrons and photons are achieved.
Near-field optics
Aperture (computer memory)
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The most important part of a scanning near-field optical microscope (SNOM) is an optical probe that is scanned along the object at a very small distance. The probe tip is usually the tapered end of an optical monomode fiber. In various types of SNOM tips with and without metal coating are: utilized. In the aperture SNOM (a-SNOM) the tip is overcoated by a metal except for a small aperture at the apex. In the photon scanning tunneling microscope (PSTM) the bare quartz tip is used to detect the evanescent field near the sample.
Near-field optics
Aperture (computer memory)
Scanning Probe Microscopy
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In this work we use an approach that allows a determination of the spatial distribution of the electromagnetic field in the near-field region of the near field scanning optical microscope (NSOM) probe. We studied a MBE grown sample, which contains a 9 nm AlAs layer embedded in a GaAs matrix. The optical contrast arises from the difference in the index of refraction of the two materials. Topography related contrast is avoided by studying a freshly cleaved surface. With the NSOM working in emission mode the reflected light was collected in the far field.
Near-field optics
Aperture (computer memory)
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Scanning near-field optical microscope (SNOM) is hybridized with a scanning tunneling microscope (STM) to investigate nanoscopic optical phenomena in both the near-field region and its proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture (<100 nm), where the metal is coated on the aperture to obtain a half-transparent conducting tip after the fabrication of an “aperture probe.” A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field at the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance control is carried out under the constant-current condition in order to separate the optical properties from surface topography. An optical resolution of λ/ 100 and identical channel transport for both electrons and photons are achieved. The intensity changes, as a function of the gap distance, are also measured in the far-field and the near-field regions and the proximity.
Near-field optics
Aperture (computer memory)
Scanning Probe Microscopy
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Optics with resolution within the wavelength - scanning near-field optical microscopy - is highly important science field nowadays. Main parameters of the SNOM - resolution, contrast, energetic efficiency are defined by optical probes characteristics: aperture size or curvature radius of the sharp, geometry, material, etc. Fabrication and testing of optical probes in nanometric scale of size are described in the paper. For fabrication of near-field probes the laser many-steps drawing and chemical etching of single- and multimode optical fibers is realized. Investigation of far- field light distribution and theoretical reconstruction of near field carried out the testing of probes.
Near-field optics
Radius of curvature
Aperture (computer memory)
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We have developed a polyvalent reflection-mode apertureless scanning near-field optical microscope (SNOM) from a commercial scanning probe microscope (SPM). After having explained our motivations, we describe the instrument precisely, by specifying how we have integrated optical elements to the initial SPM, by taking advantage of its characteristics, and without modifying its initial functions. The instrument allows five different reflection-mode SNOM configurations and enables polarization studies. Three types of SNOM probes can be used: dielectric, semiconducting, and metallic probes. The latter are homemade probes whose successful use, as probes for atomic force microscopy, by the commercial SPM has been experimentally demonstrated. Using silicon–nitride (dielectric) probes, one of the five configurations has been experimentally tested with two samples. The first sample is made of nanometric aluminum dots on a glass substrate and the second sample is the output front facet of a laser diode. The preliminary SNOM images of the latter reveal pure optical contrasts.
Scanning Probe Microscopy
Near-field optics
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Based on theory and method of the near-field optics, optical resolution of near-field scanning optical microscopy (NSOM) is beyond the classical optical diffraction limit and down to tens of nanometer or even less. In this paper, a collection mode NSOM is built to detect and analyze local near-field distribution. The output optical field of a standard 1μm×1μm scale 2D grating has been detected. This NSOM system can also be used to study local near-field distribution of the focused spot of solid immerging lens (SIL) and the result can be directly used to evaluate SIL and compared with the calculation of its theoretical model and as a result, to improve the theoretical model.
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Near-field optics
Numerical aperture
Scanning Probe Microscopy
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While conventional optical microscopes have a resolution limit set by the diffraction to a size given by about half the wavelength of light, a near-field scanning optical microscope (NSOM) surpasses this resolution limit and achieves sub-wavelength resolution. A NSOM probe allows us to achieve higher resolution out of optical microscopy by squeezing it through an optical fiber tip (or narrow aperture) since the light is confined only to an area in the order of the size of the fiber tip. However, making a fine aperture is not easy work. The use of a reflection-mode NSOM detecting the second harmonic reflection signals was tried to examine the feasibility study of resolution enhancement.
Near-field optics
Reflection
Aperture (computer memory)
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