Effect of hole-shape irregularities on photonic crystal waveguides

Degenerate band edge resonances in periodic silicon ridge waveguides

We experimentally demonstrate degenerate band edge resonances in periodic Si ridge waveguides that are compatible with carrier injection modulation for active electro-optical devices. The resonant cavities are designed using a combination of the plane-wave expansion method and the finite difference time domain technique. Measured and simulated quality factors of the first band edge resonances scale to the fifth power of the number of periods. Quality factor scaling is determined to be limited by fabrication imperfections. Compared to resonators based on a regular transmission band edge, degenerate band edge devices can achieve significantly larger quality factors in the same number of periods. Applications include compact electro-optical switches, modulators, and sensors that benefit from high-quality factors and large distributed electric fields.

Automated optimization of photonic crystal slab cavities

Thanks to their high quality factor, combined to the smallest modal volume, defect-cavities in photonic crystal slabs represent a promising, versatile tool for fundamental studies and applications in photonics. In paricular, the L3, H0, and H1 defects are the most popular and widespread cavity designs, due to their compactness, simplicity, and small mode volume. For these cavities, the current best optimal designs still result in Q-values of a few times 10(5) only, namely one order of magnitude below the bound set by fabrication imperfections and material absorption in silicon. Here, we use a genetic algorithm to find a global maximum of the quality factor of these designs, by varying the positions of few neighbouring holes. We consistently find Q-values above one million - one order of magnitude higher than previous designs. Furthermore, we study the effect of disorder on the optimal designs and conclude that a similar improvement is also expected experimentally in state-of-the-art systems.

Modeling and optimization of photonic crystal devices based on transformation optics method

In this paper, we propose a method for designing Photonic Crystal (PhC) devices that consist of dielectric rods with varying size. In the proposed design method, PhC devices are modeled with the Transformation Optics (TO) approach, and then they are optimized using the gradient method. By applying the TO technique, the original device model is transformed into an equivalent model that consists of uniform and fixed-sized rods, with parameterized permittivity and permeability distributions. Therefore, mesh refinement around small rods can be avoided, and PhC devices can be simulated more efficiently. In addition, gradient of the optimization object function is calculated with the Adjoint-Variable Method (AVM), which is very efficient for optimizing devices subject to multiple design variables. The proposed method opens up a new avenue to design and optimize a variety of photonic devices for optical computing and information processing.

Statistics of the disorder-induced losses of high-Q photonic crystal cavities

We analyze and compare the effect of fabrication disorder on the quality factor of six well-known high-index photonic crystal cavity designs. The theoretical quality factors for the different nominal structures span more than three orders of magnitude, ranging from 5.4 × 10(4) to 7.5 × 10(7), and the defect responsible for confining light is introduced in a different way for each structure. Nevertheless, among the different designs we observe similar behavior of the statistics of the disorder-induced light losses. In particular, we show that for high enough disorder, such that the quality factor is mainly determined by the disorder-induced losses, the measured quality factors differ marginally - not only on average as commonly acknowledged, but also in their full statistical distributions. This notably shows that optimizing the theoretical quality factor brings little practical improvement if its value is already much larger than what is typically measured, and if this is the case, there is no way to choose an alternative design more robust to disorder.