Topology-optimized and dispersion-tailored photonic crystal slow-light devices

Lars Hagedorn Frandsen, Andrei Lavrinenko, Peter Ingo Borel, Jacob Fage-Pedersen, Anders Harpøth, Ole Sigmund, Jacob S. Jensen, Martin Kristensen, Amélie Têtu, Tapio Niemi

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

Abstract

Within the last few years, photonic crystal waveguides (PhCWs) with low propagation losses and exotic dispersion properties have been realized and, presently, there is a strong movement towards the deployment of such structures in integrated circuits. Effective passive components such as bends, splitters, and multiplexers are a necessity in optical circuits. However, the designing of such components in the PhC platform has been a great challenge, as they often constitute severe discontinuities in the PhCW and introduce high losses. Presently, the designing of PhCW components mostly rely on an Edisonian design approach combining physical arguments and experimental/numerical verifications. Further optimizations are typically done in an iterative trial-and-error procedure in order to improve a chosen performance measure of the PhCW component. Such an approach is very time-consuming and does not guarantee optimal solutions. The systematic design method based on topology optimization [1] allows creation of improved PhCW components with previously unseen low transmission losses, high operational bandwidths,and/or with wavelength selective functionalities. The method was originally developed for structural optimization problems, but has recently been extended to a range of other design problems. The method is based on repeated finite element analyses where the distribution of material in a given design area is iteratively modified in order to improve a chosen performance measure. The resulting designs are inherently free from geometrical restrictions such as the number of holes, hole shapes etc., thereby allowing the large potentials of PhC components [2] to be exploited to hitherto unseen levels. The intricate confinement of light in a PhCW and its resulting dispersion properties offer sophisticated possibilities for realizing complex nanophotonic circuits. Potentially,PhCWs may facilitate delay lines for package synchronization, dispersion compensation, and enhanced light-matter interactions in nanophotonic circuits by exploiting slow-light phenomena. The practical utilization of ultra-slow light reaching group velocities below ~c0/200 in PhCWs may be limited due to an inherent small bandwidth, impedance mismatch, intensified loss mechanisms at scattering centres, and extreme dispersive pulse broadening. However, the dispersion properties of PhCWs can be altered via knowledge of the field distribution for the target mode and through a simple structural tuning of the waveguide geometry [3]. In this way, it is possible to realize a silicon-on-insulator PhCW with semi-slow light having a group velocity in the range ~(c0/15 – c0/100); vanishing, positive, or negative group velocity dispersion (GVD); and low-loss propagation in a practical ~5-15 nm bandwidth. Such simple PhCW component may find widespread use in passive integrated circuits. The talk will present examples of topology-optimized PhCW components for broadband use and for narrowband use in the slow-light regime of PhCWs and exemplify how the dispersion properties of PhCWs can be tailored for use in passive components.
Original languageEnglish
Title of host publicationProceedings of APOC 2007
Publication date2007
Pages6781-116
Publication statusPublished - 2007
Event2007 Asia-Pacific Optical Communications - Wuhan, China
Duration: 1 Nov 20075 Nov 2007

Conference

Conference2007 Asia-Pacific Optical Communications
CountryChina
CityWuhan
Period01/11/200705/11/2007

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