5 results
Search Results
Now showing 1 - 5 of 5
- ItemSymmetry breaking-induced magnetic Fano resonances in densely packed arrays of symmetric nanotrimers(Berlin : Nature Publishing, 2019) Wang, Ning; Zeisberger, Matthias; Hübner, Uwe; Giannini, Vincenzo; Schmidt, Markus A.Due to unique properties and great design flexibilities, Fano resonances represent one of the most promising optical features mediated by metallic nanostructures, while the excitation of some Fano modes is impossible due to symmetry reasons. The aim of this work is to show that dense lattice arrangements can have a profound impact on the optical properties of nanostructures and, in particular, can enable the excitation of otherwise dark modes. Here, we demonstrate this concept using the example of rectangular arrays of symmetric trimers packed so densely that the coupling between neighbouring unit cells imposes a symmetry break, enabling the excitation of magnetic Fano resonances. We found that in experiments as well as in simulations, electric and magnetic Fano resonances can be simultaneously formed in cases where the inter-trimer distances are sufficiently small. By analysing the transition from an isolated trimer mode into a regime of strong near-field coupling, we show that by modifying the rectangular unit cell lengths due to the symmetry mismatch between lattice and trimer, two types of Fano resonances can be found, especially magnetic Fano resonances with loop-type magnetic field distributions within the centre of each trimer, which can be either enhanced or suppressed. In addition, the influence of the refractive index environment was measured, showing sensitivity values of approximately 300 nm/RIU. Our work provides fundamental insights into the interaction of the lattice and nanostructure response and paves the way towards the observation of novel optical excitations.
- ItemPhotonic candle – focusing light using nano-bore optical fibers(Washington D.C. : Optical Society of America, 2018) Schneidewind, Henrik; Zeisberger, Matthias; Plidschun, Malte; Weidlich, Stefan; Schmidt, Markus A.Focusing light represents one of the fundamental optical functionalities that is used in a countless number of situations. Here we introduce the concept of nano-bore optical fiber mediated light focusing that allows to efficiently focus light at micrometer distance from the fiber end face. Since the focusing effect is provided by the fundamental fiber mode, device implementation is extremely straightforward since no post-processing or nano-structuring is necessary. Far-field measurements on implemented fibers, simulations, and a dual-Gaussian beam toy model confirm the validity of the concept. Due to its unique properties such as strong light localization, a close to 100% implementation success rate, extremely high reproducibility, and its compatibility with current fiber circuitry, the concept will find application in numerous areas that demand to focus at remote distances.
- ItemUnderstanding Dispersion of Revolver-Type Anti-Resonant Hollow Core Fibers(Basel : MDPI, 2018) Zeisberger, Matthias; Hartung, Alexander; Schmidt, Markus A.Here, we analyze the dispersion behavior of revolver-type anti-resonant hollow core fibers, revealing that the chromatic dispersion of this type of fiber geometry is dominated by the resonances of the glass annuluses, whereas the actual arrangement of the anti-resonant microstructure has a minor impact. Based on these findings, we show that the dispersion behavior of the fundamental core mode can be approximated by that of a tube-type fiber, allowing us to derive analytic expressions for phase index, group-velocity dispersion and zero-dispersion wavelength. The resulting equations and simulations reveal that the emergence of zero group velocity dispersion in anti-resonant fibers is fundamentally associated with the adjacent annulus resonance which can be adjusted mainly via the glass thickness of the anti-resonant elements. Due to their generality and the straightforward applicability, our findings will find application in all fields addressing controlling and engineering of pulse dispersion in anti-resonant hollow core fibers.
- ItemAnalytic model for the complex effective index of the leaky modes of tube-type anti-resonant hollow core fibers(Berlin : Nature Pulishing, 2017) Zeisberger, Matthias; Schmidt, Markus A.Due to their promising applications, hollow-core fibers, in particular, their anti-resonant versions, have recently attracted the attention of the photonics community. Here, we introduce a model that approximates, using the reflection of a wave on a single planar film, modal guidance in tube-type anti-resonant waveguides whose core diameters are large compared to the wavelength. The model yields analytic expressions for the real and imaginary parts of the complex effective index of the leaky modes supported, and is valid in all practically relevant situations, excellently matching all the important dispersion and loss parameters. Essential principles such as the fourth power dependence of the modal loss on the core radius at all wavelengths and the geometry-independent transition refractive index, below which modal discrimination favors the fundamental mode are discussed. As application examples, we use our model for understanding higher-order mode suppression in revolver-type fibers and for uncovering the tuning capabilities associated with nonlinear pulse propagation.
- ItemNanotrimer enhanced optical fiber tips implemented by electron beam lithography(Washington D.C. : Optical Society of America, 2018) Wang, Ning; Zeisberger, Matthias; Hübner, Uwe; Schmidt, Markus A.Here we present a novel fabrication approach that allows for the implementation of sophisticated planar nanostructures with deep subwavelength dimensions on fiber end faces by electron beam lithography. Specifically, we planarize the end faces of fiber bundles such that they are compatible with planar nanostructuring technology, with the result that fibers can be treated in the same way as typical wafers, opening up the entire field of nanotechnology for fiber optics. To demonstrate our approach, we have implemented densely-packed arrays of gold nanotrimers on the end face of 50 cm long standard single mode fibers, showing asymmetrical resonance lineshapes that arise due to the interplay of diffractive coupling of the individual timer response at infrared wavelengths that overlap with the single mode regime of typical telecommunication fibers. Refractive index sensing experiments suggest sensitivities of about 390 nm/RIU, representing the state-of-the-art for such a device type. Due to its unique capability of making optical fibers compatible with planar nanostructuring technology, we anticipate our approach to be applied in numerous fields including bioanalytics, telecommunications, nonlinear photonics, optical trapping and beam shaping.