Wide-band Low-dispersion Low-losses Slow Light In Photonic Crystal Waveguides

Slow light is a new topic starting recent twenty years, and reveived more and more attention from all over the world. For a long time in the history, light was believed to be the material that travels at the fastest speed in the universe, and its speed was believed to be impossible to change. With the development of modern nano-technology and integrated optics, particularly the development of silicon photonics, people have observed slow down of the light speed in the atomic vapor under the absolute zero, the semiconductor quantum wells, micro-ring arrays, photonic crystal waveguides. Compared with other methods, photonic crystal waveguides provide slow light with the lagest bandwidth, the smallest losses, the smallest device size and working at room temperature, thus is considered most promising approach. Supported by the National Basic Research Program of China and National Natural Science Foundation of China , the design and fabrication of wide-band, low-dispersion, low-losses slow light in photonic crystal waveguide are systematically studied in this thesis, and the figure of merit of slow light has been improved. A number of achievements are obtained as follows:(1) We design a novel kind of photonic crystal waveguides with shift of the two bordering lines based on silicon on insulator (SOI) structure. The new proposed waveguides can present unconventional U type group index curve, thus called U-dispersion waveguides. The U-dispersion waveguides do not add any additional difficulty to the fabrication. Furthermore, this U-dispersion waveguide can provide extremely large bandwidth (> 40nm) the very low dispersion (<2nm.ps) or very low speed of light (the speed of light is slowed down to 200 times to its original value). More importantly, the modeling and simulation show a continuous change in the shift value can lead to the continuous vary of the light speed, achieving a static tunable slow light.(2) We summarized the current researches on slow light in photonic crystal waveguides. We compared various structures reported in the literature, analysing the advantages and disadvantages of their slow light properties. After these studies, we found that slow light quality factor -- "delay-bandwidth product" of most of the reported structures are less than 0.3 (normalized value), very few structures can have "delay-bandwidth product" more than 0.3. However, with the increase of "delay-bandwidth product", the slow light effect was significantly reduced (light speed increased). That is, before the proposed structure, the slow light quality factor is inversely proportional to the slow light effects, mutual restraint.(3)We systematicly analysis the relationship between the structural parameters and the final "delay-bandwidth product". Our results show that two geometrical parameters having dominaint effect on "delay-bandwidth product" in photonic crystal waveguide. We proposed an effective optimize method to increase the "delay-bandwidth product" while maintaining the same slow light speed. We have taken the U-dispersion waveguide as an example, successfully improve the "delay-bandwidth product" from 0.15 to 0.35, while the group velocity remained at c/90 unchanged. Slow light quality factor was increased by 130%, while the slow light effect was not reduced. This optimization method is also applicable to other reported slow light photonic crystal waveguide structures.(4)We have modeled 4 kinds of process-induced disorder in real fabrication. we first time pointed out the vital region in photonic crystal waveguide which has dominated effect for the optical losses. Our conclusion has guide effect for the future silicon photonics fabrication.