Propagation loss in slow light photonic crystal waveguides

Photonic crystals;Optical wave guides;Light--Transmission;Light--Speed;Nonlinear optics

Schulz, Sebastian Andreas ; Krauss, Thomas F. ; Krauss, Thomas F.

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Photonic crystals;    Optical wave guides;    Light--Transmission;    Light--Speed;    Nonlinear optics;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/2837/SebastianSchulzPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

Thefieldofnanophotonicsisamajorresearchtopic,asitofferspotentialsolutionstoimportant challenges, such as the creation of low power, high bandwidth interconnects oroptical sensors.Within this field, resonant structures and slow light waveguides are usedto improve device performance further. Photonic crystals are of particular interest, as theyallow the fabrication of a wide variety of structures, including high Q-factor cavities andslow light waveguides.The high scattering loss of photonic crystal waveguides, caused by fabrication disorder,however, has so far proven to be the limiting factor for device applications. In this thesis, Ipresent a detailed study of propagation loss in slow light photonic crystal waveguides.I examine the dependence of propagation loss on the group index, and on disorder, inmore depth than previous work by other authors. I present a detailed study of the relativeimportance of different components of the propagation loss, as well as a calculation methodfor the average device properties.A new calculation method is introduced to study different device designs and to show thatphotonic crystal waveguide propagation loss can be reduced by device design alone.These“loss engineered” waveguides have been used to demonstrate the lowest loss photonic crystalbased delay line (35 dB/ns) with further improvements being predicted (< 20 dB/ns).Novelfabricationtechniqueswereinvestigated,withtheaimofreducingfabricationdisorder.Initial results showed the feasibility of a silicon anneal in a nitrogen atmosphere,however poor process control led to repeatability issues.The use of a slow-fast-slow light interface allowed for the fabrication of waveguides spanning multiple writefields of the electron-beam lithography tool, overcoming the problem ofstitching errors.The slow-fast-slow light interfaces were combined with loss engineering waveguide designs, to achieve an order of magnitude reduction in the propagation loss compared to a W1waveguide, with values as low as 130 dB/cm being achieved for a group index around 60.