@article{21932, abstract = {{Gaussian-beam-like bundles of semi-guided waves propagating in a dielectric slab can excite modes with high-order optical angular momentum supported by a circular fiber. We consider a multimode step-index fiber with a high-index coating, where the waves in the slab are evanescently coupled to the modes of the fiber. Conditions for effective resonant interaction are identified. Based on a hybrid analytical–numerical coupled mode model, our simulations predict that substantial fractions of the input power can be focused into waves with specific orbital angular momentum, of excellent purity, with a clear distinction between degenerate modes with opposite vorticity.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguides}}, number = {{5}}, pages = {{1717}}, title = {{{Resonant evanescent excitation of guided waves with high-order optical angular momentum}}}, doi = {{10.1364/josab.422731}}, volume = {{38}}, year = {{2021}}, } @article{20189, abstract = {{A dielectric step-index optical fiber with tube-like profile is considered, being positioned with a small gap on top of a dielectric slab waveguide. We propose a 2.5-D hybrid analytical/numerical coupled mode model for the evanescent excitation of the tube through semi-guided waves propagating in the slab at oblique angles. The model combines the directional polarized modes supported by the slab with analytic solutions for the TE-, TM-, and orbital-angular-momentum (OAM) modes of the tube-shaped fiber. Implementational details of the scheme are discussed, complemented by finite-element simulations for verification purposes. Our results include configurations with resonant in-fiber excitation of OAM modes with large orbital angular momentum and strong field enhancement.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{0306-8919}}, journal = {{Optical and Quantum Electronics}}, keywords = {{tet_topic_waveguides}}, title = {{{Hybrid coupled mode modelling of the evanescent excitation of a dielectric tube by semi-guided waves at oblique angles}}}, doi = {{10.1007/s11082-020-02595-z}}, volume = {{52}}, year = {{2020}}, } @article{20372, abstract = {{A stepwise angular spectrum method (SASM) for curved interfaces is presented to calculate the wave propagation in planar lens-like integrated optical structures based on photonic slab waveguides. The method is derived and illustrated for an effective 2D setup first and then for 3D slab waveguide lenses. We employ slab waveguides of different thicknesses connected by curved surfaces to realize a lens-like structure. To simulate the wave propagation in 3D including reflection and scattering losses, the stepwise angular spectrum method is combined with full vectorial finite element computations for subproblems with lower complexity. Our SASM results show excellent agreement with rigorous numerical simulations of the full structures with a substantially lower computational effort and can be utilized for the simulation-based design and optimization of complex and large scale setups.}}, author = {{Ebers, Lena and Hammer, Manfred and Förstner, Jens}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_waveguides}}, number = {{24}}, pages = {{36361}}, title = {{{Light diffraction in slab waveguide lenses simulated with the stepwise angular spectrum method}}}, doi = {{10.1364/oe.409612}}, volume = {{28}}, year = {{2020}}, } @article{12908, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, issn = {{0740-3224}}, journal = {{Journal of the Optical Society of America B}}, keywords = {{tet_topic_waveguides}}, pages = {{2395}}, title = {{{Oblique quasi-lossless excitation of a thin silicon slab waveguide: a guided-wave variant of an anti-reflection coating}}}, doi = {{10.1364/josab.36.002395}}, volume = {{36}}, year = {{2019}}, } @article{14990, abstract = {{We investigate optical microresonators consisting of either one or two coupled rectangular strips between upper and lower slab waveguides. The cavities are evanescently excited under oblique angles by thin-film guided, in-plane unguided waves supported by one of the slab waveguides. Beyond a specific incidence angle, losses are fully suppressed. The interaction between the guided mode of the cavity-strip and the incoming slab modes leads to resonant behavior for specific incidence angles and gaps. For a single cavity, at resonance, the input power is equally split among each of the four output ports, while for two cavities an add-drop filter can be realized that, at resonance, routes the incoming power completely to the forward drop waveguide via the cavity. For both applications, the strength of the interaction is controlled by the gaps between cavities and waveguides.}}, author = {{Ebers, Lena and Hammer, Manfred and Berkemeier, Manuel B. and Menzel, Alexander and Förstner, Jens}}, issn = {{2578-7519}}, journal = {{OSA Continuum}}, keywords = {{tet_topic_waveguides}}, pages = {{3288}}, title = {{{Coupled microstrip-cavities under oblique incidence of semi-guided waves: a lossless integrated optical add-drop filter}}}, doi = {{10.1364/osac.2.003288}}, volume = {{2}}, year = {{2019}}, } @misc{7720, abstract = {{Die Erfindung betrifft einen optischen Übergang zwischen zwei optischen Schichtwellenleitern. Dazu ist eine Anordnung vorgesehen aus einem ersten optischen Schichtwellenleiter (2) und einem zweiten optischen Schichtwellenleiter (3), wobei der erste optische Schichtwellenleiter (2) und der zweite optische Schichtwellenleiter (3) voneinander verschiedene über ihre jeweilige Länge konstante Dicken (d, r) aufweisen, der erste optische Schichtwellenleiter (2) mit dem zweiten optischen Schichtwellenleiter (3) mittels einer optischen Schichtwellenleiterstruktur (4) verbunden ist, die über ihre gesamte Länge (w) eine Dicke (h) aufweist, die zwischen der Dicke (d) des ersten optischen Schichtwellenleiters (2) und der Dicke (r) des zweiten optischen Schichtwellenleiters (3) liegt. Erfindungsgemäß ist die Dicke (h) der optischen Schichtwellenleiterstruktur (4) über die gesamte Länge (w) der optischen Schichtwellenleiterstruktur (4) konstant. Damit wird eine Möglichkeit für einen effizienten und mit geringen Verlusten behafteten Übergang zwischen zwei optischen Schichtwellenleitern mit unterschiedlicher Dicke bereitgestellt. }}, author = {{Hammer, Manfred and Förstner, Jens and Ebers, Lena}}, keywords = {{tet_topic_waveguides}}, pages = {{9}}, title = {{{Optical transition between two optical waveguides layer and method for transmitting light}}}, year = {{2019}}, } @article{8634, abstract = {{A rectangular dielectric strip at some distance above an optical slab waveguide is being considered, for evanescent excitation of the strip through the semi-guided waves supported by the slab, at specific oblique angles. The 2.5-D configuration shows resonant transmission properties with respect to variations of the angle of incidence, or of the excitation frequency, respectively. The strength of the interaction can be controlled by the gap between strip and slab. For increasing distance, our simulations predict resonant states with unit extremal reflectance of an angular or spectral width that tends to zero, i.e. resonances with a Q-factor that tends to infinity, while the resonance position approaches the level of the guided mode of the strip. This exceptionally simple system realizes what might be termed a “bound state coupled to the continuum”.}}, author = {{Hammer, Manfred and Ebers, Lena and Förstner, Jens}}, journal = {{Optics Express}}, keywords = {{tet_topic_waveguides}}, number = {{7}}, pages = {{8}}, title = {{{Oblique evanescent excitation of a dielectric strip: A model resonator with an open optical cavity of unlimited Q}}}, doi = {{10.1364/OE.27.009313}}, volume = {{27}}, year = {{2019}}, } @inproceedings{4579, abstract = {{Semi-guided waves confined in dielectric slab waveguides are being considered for oblique angles of propagation. If the waves encounter a linear discontinuity of (mostly) arbitrary shape and extension, a variant of Snell's law applies, separately for each pair of incoming and outgoing modes. Depending on the effective indices involved, and on the angle of incidence, power transfer to specific outgoing waves can be allowed or forbidden. In particular, critical angles of incidence can be identified, beyond which any power transfer to non-guided waves is forbidden, i.e. all radiative losses are suppressed. In that case the input power is carried away from the discontinuity exclusively by reflected semi-guided waves in the input slab, or by semi-guided waves that are transmitted into other outgoing slab waveguides. Vectorial equations on a 2-D cross sectional domain apply. These are formally identical to the equations that govern the eigenmodes of 3-D channel waveguides. Here, however, these need to be solved not as an eigenvalue problem, but as an inhomogeneous problem with a right-hand-side that is given by the incoming semi-guided wave, and subject to transparent boundary conditions. The equations resemble a standard 2-D Helmholtz problem, with an effective permittivity in place of the actual relative permittivity. Depending on the properties of the incoming wave, including the angle of incidence, this effective permittivity can become locally negative, causing the suppression of propagating outgoing waves. A series of high-contrast example configurations are discussed, where these effects lead to - in some respects - quite surprising transmission characteristics.}}, author = {{Hammer, Manfred and Ebers, Lena and Hildebrandt, Andre and Alhaddad, Samer and Förstner, Jens}}, booktitle = {{2018 IEEE 17th International Conference on Mathematical Methods in Electromagnetic Theory (MMET)}}, isbn = {{9781538654385}}, keywords = {{tet_topic_waveguides}}, publisher = {{IEEE}}, title = {{{Oblique Semi-Guided Waves: 2-D Integrated Photonics with Negative Effective Permittivity}}}, doi = {{10.1109/mmet.2018.8460455}}, year = {{2018}}, }