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Frequency domain analysis for micro-fiber based super-resolution imaging system. (a) The proposed model of wave vector shift. Using the sample itself as sub-diffractive gratings, the evanescent waves can be converted back to propagation mode so that the details beyond the diffractive limit can be discerned. (b) Ideal optical transition function (OTF) for a diffractive order of 1. In this wave vector band ( ), “one-to-one” wave vector conversion can be realized. k Λ < k Λ_max will result in a higher order of diffraction, while it is impossible to convert the frequency back to the propagation mode if k Λ > k Λ_min.
Scheme of micro-fiber based super-resolution imaging system. (a)The 3D structure of experimental system. The sizes of sample patterns and micro-fiber are exaggerated while the objective lens above is intentionally neglected. (b) The relative positions of micro-fiber, sample, and focal plane of objective lens in vertical direction (z direction). (c)–(e) The images of the sample obtained in the experiment. A clear phenomenon cannot be observed unless the focal plane is (e) below the sample's surface, while (c)above or (d) at the sample surface will result in chaotic images. MF, micro-fiber; TT, taper transition.
Super-resolution images of line pairs and FWHM analysis. The images of line pairs generated by using (a) scanning electron microscopy (SEM), (b) optical microscopy, and (c) our method. The intervals between the lines are 208 nm, 151 nm, 126 nm, and 75 nm (from left to right), respectively. (d) The intensity distribution of cross-section along the arrow direction shown in (c). M 2 and Mf are the geometric and spatial frequency magnification factors of micro-fiber. In this image, M 2 = 1.0 and Mf = 2.1, respectively.
Micro-fiber based Super-resolution images of complex patterns. (a) Micro-fiber based imaging of 150-nm-diameter dots spaced 150 nm apart. (b) Micro-fiber based imaging of “H” structure. The line width of the letter is approximately 100 nm. (c) A commercial Blu-ray Disk chip imaged with a micro-fiber. The typical track pitch of a Blu-ray Disk27 is not greater than 300 nm, and the land width is 200 nm and the groove width is 100 nm. (d) Micro-fiber based imaging of 150 nm-150 nm gratings. (e) Micro-fiber based imaging of 150-nm-width line pairs separated by 100 nm. Except the pattern of (c), all samples are fabricated by a focus ion beam (FIB). (a) and (b) Etched on a Si substrate, (d) fabricated on ITO glass, and (e) the sample prepared on silica.
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