TY - JOUR AB - High-contrast slab waveguide Bragg gratings with 1D periodicity are investigated. For specific oblique excitation by semi-guided waves at sufficiently high angles of incidence, the idealized structures do not exhibit any radiative losses, such that reflectance and transmittance for the single port mode add strictly up to one. We consider a series of symmetric, fully and partly etched finite gratings, for parameters found in integrated silicon photonics. These can act as spectral filters with a reasonably flattop response. Apodization can lead to more box shaped reflectance and transmittance spectra. Together with a narrowband Fabry–Perot filter, these configurations are characterized by reflection bands, or transmittance peaks, with widths that span three orders of magnitude. AU - Hammer, Manfred AU - Farheen, Henna AU - Förstner, Jens ID - 43245 IS - 4 JF - Journal of the Optical Society of America B KW - tet_topic_waveguide SN - 0740-3224 TI - How to suppress radiative losses in high-contrast integrated Bragg gratings VL - 40 ER - TY - CONF AB - Resonant evanescent coupling can be utilized to selectively excite orbital angular momentum (OAM) modes of high angular order supported by a thin circular dielectric rod. Our 2.5-D hybrid-analytical coupled mode model combines the vectorial fields associated with the fundamental TE- and TM-modes of a standard silicon photonics slab waveguide, propagating at oblique angles with respect to the rod axis, and the hybrid modes supported by the rod. One observes an efficient resonant interaction in cases where the common axial wavenumber of the waves in the slab matches the propagation constant of one or more modes of the rod. For certain modes of high angular order, the incident wave is able to transfer its directionality to the field in the fiber, exciting effectively only one of a pair of degenerate OAM modes AU - Hammer, Manfred AU - Ebers, Lena AU - Förstner, Jens ED - Andrews, David L. ED - Galvez, Enrique J. ED - Rubinsztein-Dunlop, Halina ID - 30387 KW - tet_topic_waveguide T2 - Complex Light and Optical Forces XVI TI - Resonant evanescent excitation of OAM modes in a high-contrast circular step-index fiber ER - TY - THES AB - In dieser Arbeit wird die elektromagnetische Wellenausbreitung in integrierten optischen Wellenleitern mit Hilfe von halb analytischen und numerischen Simulationsmethoden untersucht. Im ersten Teil werden 2-D Si/SiO2-Wellenleiterkonfigurationen mit hohem Brechungsindexkontrast betrachtet. Die Strukturen werden mit halb geführten Wellen unter schrägen Ausbreitungswinkeln angeregt. Dadurch kann die Leistungsübertragung zu bestimmten ausgehenden Moden unterdrückt werden, wodurch vollständig verlustfreie Systeme entstehen. Zusätzlich dient die Anregung mit einem seitlich begrenzten, einfallenden Wellenbündel aus halb geführten Wellen dazu, praktisch relevantere 3-D Konfigurationen zu realisieren. Darüber hinaus wird eine schrittweise Winkelspektrum-Methode vorgestellt, die es ermöglicht, in Kombination mit voll vektoriellen 2-D Finite-Elemente-Lösungen für Teilprobleme mit geringerer Komplexität, die Wellenausbreitung in planaren, linsenförmigen Wellenleitern numerisch in drei Raumrichtungen zu berechnen. Im zweiten Teil dieser Arbeit wird die Ausbreitung in Wellenleiterstrukturen aus Lithiumniobat untersucht, welche für quantenoptische Effekte genutzt werden. Zur Detektion einzelner Photonen werden supraleitende Nanodrähte auf eindiffundierten Lithiumniobat Wellenleitern mit zusätzlicher Taperschicht aus Silizium betrachtet. Um die Wellenausbreitung in diesen 3-D Wellenleitern zu beschreiben, wird eine einseitig gerichtete Finite-Elemente „Modal Matching“ Methode eingeführt. Abschließend werden Rippenwellenleiter aus Lithiumniobat analysiert, die auf Siliziumdioxid Plattformen aufgebracht sind. Der Schwerpunkt liegt hier auf dem nichtlinearen „Parametric Down-Conversion“ Prozess, der für die Erzeugung verschränkter Photonen verwendet wird. AU - Ebers, Lena ID - 30722 KW - tet_topic_waveguide TI - Semi-guided waves in integrated optical waveguide structures ER - TY - JOUR AB - Here we demonstrate a new, to the best of our knowledge, type of 3-dB coupler that has an ultra-broadband operational range from 1300 to 1600 nm with low fabrication sensitivity. The overall device size is 800 µm including in/out S-bend waveguides. The coupler is an asymmetric non-uniform directional coupler that consists of two tapered waveguides. One of the coupler arms is shifted by 100 µm in the propagation direction, which results in a more wavelength-insensitive 3-dB response compared to a standard (not shifted) coupler. Moreover, compared to a long adiabatic coupler, we achieved a similar wavelength response at a 16-times-smaller device length. The couplers were fabricated using the silicon nitride platform of Lionix International. We also experimentally demonstrated an optical switch that is made by using two of these couplers in a Mach–Zehnder interferometer configuration. According to experimental results, this optical switch exhibits –10 dB of extinction ratio over the 1500–1600 nm wavelength range. Our results indicate that this new type of coupler holds great promise for various applications, including optical imaging, telecommunications, and reconfigurable photonic processors where compact, fabrication-tolerant, and wavelength-insensitive couplers are essential. AU - Nikbakht, Hamed AU - Khoshmehr, Mohammad Talebi AU - van Someren, Bob AU - Teichrib, Dieter AU - Hammer, Manfred AU - Förstner, Jens AU - Akca, B. Imran ID - 35128 IS - 2 JF - Optics Letters KW - tet_topic_waveguide SN - 0146-9592 TI - Asymmetric, non-uniform 3-dB directional coupler with 300-nm bandwidth and a small footprint VL - 48 ER - TY - JOUR AB - Lithium niobate on insulator (LNOI) has a great potential for photonic integrated circuits, providing substantial versatility in design of various integrated components. To properly use these components in the implementation of different quantum protocols, photons with different properties are required. In this paper, we theoretically demonstrate a flexible source of correlated photons built on the LNOI waveguide of a special geometry. This source is based on the parametric down-conversion (PDC) process, in which the signal and idler photons are generated at the telecom wavelength and have different spatial profiles and polarizations, but the same group velocities. Distinguishability in polarizations and spatial profiles facilitates the routing and manipulating individual photons, while the equality of their group velocities leads to the absence of temporal walk-off between photons. We show how the spectral properties of the generated photons and the number of their frequency modes can be controlled depending on the pump characteristics and the waveguide length. Finally, we discuss special regimes, in which narrowband light with strong frequency correlations and polarization-entangled Bell states are generated at the telecom wavelength. AU - Ebers, Lena AU - Ferreri, Alessandro AU - Hammer, Manfred AU - Albert, Maximilian AU - Meier, Cedrik AU - Förstner, Jens AU - Sharapova, Polina R. ID - 30210 JF - Journal of Physics: Photonics KW - tet_topic_waveguide SN - 2515-7647 TI - Flexible source of correlated photons based on LNOI rib waveguides VL - 4 ER - TY - CONF AB - Online solvers for a series of standard 1-D or 2-D problems in integrated optics will be discussed. Implemented on the basis of HTML/JavaScript/SVG with core routines compiled from well tested C++-sources, the quasi-analytical algorithms require a computational load that can be handled easily even by current mobile devices. So far the series covers the 1-D guided modes of dielectric multilayer slab waveguides and the oblique plane wave reflection from these, the modes of rectangular channel waveguides (in an approximation of effective indices), bend modes of curved multilayer slabs, whispering-gallery resonances (“Quasi-Normal-Modes”) supported by circular dielectric cavities, the hybrid modes of circular multi-step-index optical fibers, bound and leaky modes of 1-D complex multilayers, including plasmonic surface modes, and, with restrictions, quite general rectangular scattering problems in 2-D. AU - Hammer, Manfred ED - García-Blanco, Sonia M. ED - Cheben, Pavel ID - 30389 KW - tet_topic_waveguide T2 - Integrated Optics: Devices, Materials, and Technologies XXVI TI - Small-scale online simulations in guided-wave photonics ER - TY - JOUR AB - We show that narrow trenches in a high-contrast silicon-photonics slab can act as lossless power dividers for semi-guided waves. Reflectance and transmittance can be easily configured by selecting the trench width. At sufficiently high angles of incidence, the devices are lossless, apart from material attenuation and scattering due to surface roughness. We numerically simulate a series of devices within the full 0-to-1-range of splitting ratios, for semi-guided plane wave incidence as well as for excitation by focused Gaussian wave bundles. Straightforward cascading of the trenches leads to concepts for 1×M-power dividers and a polarization beam splitter. AU - Hammer, Manfred AU - Ebers, Lena AU - Förstner, Jens ID - 28196 IS - 12 JF - OSA Continuum KW - tet_topic_waveguide SN - 2578-7519 TI - Configurable lossless broadband beam splitters for semi-guided waves in integrated silicon photonics VL - 4 ER - TY - CONF AB - We fabricate silicon tapers to increase the mode overlap of superconducting detectors on Ti:LiNbO3 waveguides. Mode images show a reduction in mode size from 6 µm to 2 µm FWHM, agreeing with beam propagation simulations. AU - Protte, Maximilian AU - Ebers, Lena AU - Hammer, Manfred AU - Höpker, Jan Philipp AU - Albert, Maximilian AU - Quiring, Viktor AU - Meier, Cedrik AU - Förstner, Jens AU - Silberhorn, Christine AU - Bartley, Tim ID - 21719 KW - tet_topic_waveguide SN - 9781943580811 T2 - OSA Quantum 2.0 Conference TI - Towards Semiconductor-Superconductor-Crystal Hybrid Integration for Quantum Photonics ER - TY - JOUR AB - Oblique propagation of semi-guided waves across slab waveguide structures with bent corners is investigated. A critical angle can be defined beyond which all radiation losses are suppressed. Additionally an increase of the curvature radius of the bends also leads to low-loss configurations for incidence angles below that critical angle. A combination of two bent corner systems represents a step-like structure, behaving like a Fabry-Perot interferometer, with two partial reflectors separated by the vertical height between the horizontal slabs. We numerically analyse typical high-index-contrast Si/SiO2 structures for their reflectance and transmittance properties. When increasing the curvature radius the resonant effect becomes less relevant such that full transmittance is reached with less critical conditions on the vertical distance or the incidence angle. For practical interest 3-D problems are considered, where the structures are excited by the fundamental mode of a wide, shallow rib waveguide. High transmittance levels can be observed also for these 3-D configurations depending on the width of the rib. AU - Ebers, Lena AU - Hammer, Manfred AU - Förstner, Jens ID - 3740 IS - 14 JF - Optics Express KW - tet_topic_waveguide TI - Oblique incidence of semi-guided planar waves on slab waveguide steps: effects of rounded edges VL - 26 ER - TY - CHAP AB - Frequently, optical integrated circuits combine elements (waveguide channels, cavities), the simulation of which is well established through mature numerical eigenproblem solvers. It remains to predict the interaction of these modes. We address this task by a general, “Hybrid” variant (HCMT) of Coupled Mode Theory. Using methods from finite-element numerics, the properties of a circuit are approximated by superpositions of eigen-solutions for its constituents, leading to quantitative, computationally cheap, and easily interpretable models. AU - Hammer, Manfred ED - Agrawal, Arti ID - 3743 KW - tet_topic_waveguide KW - tet_topic_numerics SN - 978-3-319-55438-9 T2 - Recent Trends in Computational Photonics TI - Guided Wave Interaction in Photonic Integrated Circuits — A Hybrid Analytical/Numerical Approach to Coupled Mode Theory VL - 204 ER - TY - JOUR AB - The 3D implementation of a hybrid analytical/numerical variant of the coupled-mode theory is discussed. Eigenmodes of the constituting dielectric channels are computed numerically. The frequency-domain coupled-mode models then combine these into fully vectorial approximations for the optical electromagnetic fields of the composite structure. Following a discretization of amplitude functions by 1D finite elements, pro- cedures from the realm of finite-element numerics are applied to establish systems of linear equations for the then- discrete modal amplitudes. Examples substantiate the functioning of the technique and allow for some numerical assessment. The full 3D simulations are highly efficient in memory consumption, moderately demanding in com- putational time, and, in regimes of low radiative losses, sufficiently accurate for practical design. Our results include the perturbation of guided modes by changes of the refractive indices, the interaction of waves in parallel, horizontally or vertically coupled straight waveguides, and a series of crossings of potentially overlapping channels with fairly arbitrary relative positions and orientations. AU - Hammer, Manfred AU - Alhaddad, Samer AU - Förstner, Jens ID - 3828 IS - 3 JF - Journal of the Optical Society of America B KW - tet_topic_waveguide KW - tet_topic_numerics SN - 0740-3224 TI - Hybrid coupled-mode modeling in 3D: perturbed and coupled channels, and waveguide crossings VL - 34 ER - TY - JOUR AB - The modal properties of curved dielectric slab waveguides are investigated. We consider quasi-confined, attenuated modes that propagate at oblique angles with respect to the axis through the center of curvature. Our analytical model describes the transition from scalar 2-D TE/TM bend modes to lossless spiral waves at near-axis propagation angles, with a continuum of vectorial attenuated spiral modes in between. Modal solutions are characterized in terms of directional wavenumbers and attenuation constants. Examples for vectorial mode profiles illustrate the effects of oblique wave propagation along the curved slab segments. For the regime of lossless spiral waves, the relation with the guided modes of corresponding dielectric tubes is demonstrated. AU - Ebers, Lena AU - Hammer, Manfred AU - Förstner, Jens ID - 3830 IS - 4 JF - Optical and Quantum Electronics KW - tet_topic_waveguide SN - 0306-8919 TI - Spiral modes supported by circular dielectric tubes and tube segments VL - 49 ER - TY - CONF AU - Hildebrandt, Andre AU - Alhaddad, Samer AU - Hammer, Manfred AU - Förstner, Jens ED - Broquin, Jean-Emmanuel ED - Nunzi Conti, Gualtiero ID - 3543 KW - tet_topic_waveguide T2 - Integrated Optics: Devices, Materials, and Technologies XX TI - Oblique incidence of semi-guided waves on step-like folds in planar dielectric slabs: Lossless vertical interconnects in 3D integrated photonic circuits ER - TY - CONF AB - Typical optical integrated circuits combine elements, like straight and curved waveguides, or cavities, the simulation and design of which is well established through numerical eigenproblem-solvers. It remains to predict the interaction of these modes. We address this task by a ”Hybrid” variant (HCMT) of Coupled Mode Theory. Using methods from finite-element numerics, the optical properties of a circuit are approximated by superpositions of eigen-solutions for its constituents, leading to quantitative, low-dimensional, and interpretable models in the frequency domain. Spectral scans are complemented by the direct computation of supermode properties (spectral positions and linewidths, coupling-induced phase shifts). This contribution outlines the theoretical background, and discusses briefly limitations and implementational details, with the help of an example of a 2-D coupled-resonator-optical-waveguide configuration. AU - Hammer, Manfred ED - Broquin, Jean-Emmanuel ED - Nunzi Conti, Gualtiero ID - 3934 IS - 9750 KW - tet_topic_waveguide KW - tet_topic_numerics T2 - Integrated Optics: Devices, Materials, and Technologies XX TI - Wave interaction in photonic integrated circuits: Hybrid analytical / numerical coupled mode modeling ER - TY - JOUR AB - The device principle of a prism-based on-chip spectrometer for TE polarization is introduced. The spectrometer exploits the modal dispersion in planar waveguides in a layout with slab regions having two different thicknesses of the guiding layer. The set-up uses parabolic mirrors, for the collimation of light of the input waveguide and focusing of the light to the receiver waveguides, which relies on total internal reflection at the interface between two such regions. These regions are connected adiabatically to prevent unwanted mode conversion and loss at the edges of the prism. The structure can be fabricated with two wet etching steps. The paper presents basic theory and a general approach for device optimization. The latter is illustrated with a numerical example assuming SiON technology. AU - Civitci, F. AU - Hammer, Manfred AU - Hoekstra, H.J.W.M. ID - 3845 JF - Optics Communications KW - tet_topic_waveguide SN - 0030-4018 TI - Planar prism spectrometer based on adiabatically connected waveguiding slabs VL - 365 ER - TY - JOUR AB - Sheets of slab waveguides with sharp corners are investigated. By means of rigorous numerical experiments, we look at oblique incidence of semi-guided plane waves. Radiation losses vanish beyond a certain critical angle of incidence. One can thus realize lossless propagation through 90-degree corner configurations, where the remaining guided waves are still subject to pronounced reflection and polarization conversion. A system of two corners can be viewed as a structure akin to a Fabry-Perot-interferometer. By adjusting the distance between the two partial reflectors, here the 90-degree corners, one identifies step-like configurations that transmit the semi-guided plane waves without radiation losses, and virtually without reflections. Simulations of semi-guided beams with in-plane wide Gaussian profiles show that the effect survives in a true 3-D framework. AU - Hammer, Manfred AU - Hildebrandt, Andre AU - Förstner, Jens ID - 3847 IS - 3 JF - Journal of Lightwave Technology KW - tet_topic_waveguide SN - 0733-8724 TI - Full Resonant Transmission of Semiguided Planar Waves Through Slab Waveguide Steps at Oblique Incidence VL - 34 ER - TY - JOUR AB - We show how to optically connect guiding layers at different elevations in a 3-D integrated photonic circuit. Transfer of optical power carried by planar, semi-guided waves is possible without reflections or radiation losses, and over large vertical distances. This functionality is realized through simple step-like folds of high-contrast dielectric slab waveguides, in combination with oblique wave incidence, and fulfilling a resonance condition. Radiation losses vanish, and polarization conversion is suppressed for TE wave incidence beyond certain critical angles. This can be understood by fundamental arguments resting on a version of Snell’s law. The two 90° corners of a step act as identical partial reflectors in a Fabry–Perot-like resonator setup. By selecting the step height, i.e., the distance between the reflectors, one realizes resonant states with full transmission. Rigorous quasi-analytical simulations for typical silicon/silica parameters demonstrate the functioning. Combinations of several step junctions can lead to other types of optical on-chip connects, e.g., U-turn- or bridge-like configurations. AU - Hammer, Manfred AU - Hildebrandt, Andre AU - Förstner, Jens ID - 3894 IS - 16 JF - Optics Letters KW - tet_topic_waveguide SN - 0146-9592 TI - How planar optical waves can be made to climb dielectric steps VL - 40 ER - TY - JOUR AB - The incidenceofthin-film-guided, in-planeunguidedwavesatobliqueanglesonstraightdiscontinuities of dielectricslabwaveguides,anearlyproblemofintegratedoptics,isbeingre-considered.The3-D frequencydomainMaxwellequationsreducetoaparametrizedinhomogeneousvectorialproblemona 2-D computationaldomain,withtransparent-influx boundaryconditions.Weproposearigorousvec- torial solverbasedonsimultaneousexpansionsintopolarizedlocalslabeigenmodesalongthetwo orthogonal crosssectioncoordinates(quadridirectionaleigenmodepropagationQUEP).Thequasi-ana- lytical schemeisapplicabletoconfigurations with — in principle — arbitrary crosssectiongeometries. Examples forahigh-contrastfacetofanasymmetricslabwaveguide,forthelateralexcitationofa channel waveguide,andforastepdiscontinuitybetweenslabwaveguidesofdifferentthicknessesare discussed. AU - Hammer, Manfred ID - 3890 JF - Optics Communications KW - tet_topic_waveguide KW - tet_topic_numerics SN - 0030-4018 TI - Oblique incidence of semi-guided waves on rectangular slab waveguide discontinuities: A vectorial QUEP solver VL - 338 ER - TY - JOUR AB - The relevance of our definition for sensitivity in refractometric sensing, being the relative change in the transmittance of a certain output channel of an optical device over the change in the refractive index of the probed material, is discussed. It is compared to one based on spectral shift per refractive index unit change. Further, there is discussion on how group delay and sensitivity are interrelated and can be converted into each other and which physical quantities are relevant for high sensitivity. As a by-product of the theory presented, a general expression relating group delay and the ratio of the time-averaged optical energy and the input power is presented. AU - Hoekstra, Hugo J. W. M. AU - Hammer, Manfred ID - 3937 IS - 7 JF - Journal of the Optical Society of America B KW - tet_topic_waveguide SN - 0740-3224 TI - General relation for group delay and the relevance of group delay for refractometric sensing VL - 31 ER -