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  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  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 . 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.
|Title of host publication||Proceedings of APOC 2007|
|Publication status||Published - 2007|
|Event||2007 Asia-Pacific Optical Communications - Wuhan, China|
Duration: 1 Nov 2007 → 5 Nov 2007
|Conference||2007 Asia-Pacific Optical Communications|
|Period||01/11/2007 → 05/11/2007|