Photonic crystals in biology - NanoTR-VI

U NeslihanPPPPoster Session, Thursday, June 17Theme F686 - N112313 Dimensional L Shaped Photonic Crystal Waveguide111EtiUP P*, H. Sami SözüerP PP and Zebih ÇetinPPAbstract- We present theoretical studies on waveguide bends in a combination of 1 dimensional and 2 dimensional photonic crystal slab.In this work, we give a method to bend light on L shaped photonic crystal waveguide slabs with little loss.1The discovery of the photonic crystal waveguides (PCWs),which allow only certain electromagnetic wave modes topropagate inside the structure, has opened up new ways ofcontrolling light propagation in optical integrated circuitdesigns. By using photonic crystal slab waveguides, whichare 1 dimensional or 2 dimensional periodic structures with afinite thickness in the vertical direction, it is possible tofabricate light guiding optical materials by total internalreflection [1], that confines light to the slab, and bend themwith little loss by photonic crystal assistance.With conventional dielectric waveguides which dependentirely on total internal reflection, there is a problem inguiding light while turning through sharp edges and tightcurves because the angle of the incidence is too high for totalinternal reflection, resulting in most of the electromagneticfield being radiated out and lost.To cope with this problem, a 2 dimensional line defectwaveguide can be used [2-8]. The problem with 2dimensional line defect waveguides is that even smalldefects during manufacturing can greatly increaseattenuation, thus limiting their usefulness to guide light overlong distances. To overcome this difficulty, Notomi proposedusing a 1 dimensional slab waveguide which is not periodicin the direction of propagation, to reduce dispersion andattenuation [3]. But still in an optical circuit, one would wantto bend light through a 90 angle due to the confinedgeometry.In this work, we make use of the best of both worlds,namely, we use 1D slab waveguide of Notomi for the straightsections and a 2D slab waveguide for containig the light atthe corners. By this way, the wave would travel with littleloss through the straight sections, turns through sharp cornerwith little bending loss as well, reentering the 1D waveguideregion to travel for another long straight segment as shown infigure [1].Figure 2. 2D perfect square photonic crystal slab. There is a bandgap between 0.2 and 0.4 . The gray areas are unlocalized radiationmodes.Figure 3. Dispersion relations for 2D and 1D waveguides. The bigcrosses are localized TE-like modes of the 1DWG, while the big fullcircles are those of the 2D LDWG. The small dots show unlocalizedmodes. Matched modes for the two types of waveguides overlap,indicating good impedance matching between the 1D and 2Dwaveguides.Then choosing the proper defect size at 2D and 1Dstructes we created our waveguides and succeed to matchtheir modes as shown figure [3]. Thus, theoretically it ispossible to bend light in L shaped waveguide. It remains tobe seen actually what percentage of the light passes throughthe bend by FDTD calculations in the time domain.*Corresponding author: 2Tneslihaneti@iyte.edu.tr2TFigure 1. Photonic crystal waveguide slab, which is a periodicstructure with a finite thickness in vertical z-direction and combines1D and 2D slab waveguides.We used the data in [7] since preliminary evidenceshowed that it is possible to bend light by 90 degrees almostwithout loss, but with the difference that in our proposedstructure we studied the more realistic photonic crystalwaveguide slab which is finite in the z-direction. Firstly wefound the band diagram for the 2D perfect pc slab, shownin figure [2].[1]2TKrauss TF, DeLaRue RM, Brand S, "Two-dimensional photonicbandgapstructures operating at near infrared wavelengths"NATURE 383 pp. 699-702, (1996)[2] A. Mekis, J. C. Chen, I. Kurland, S. Fan, P. R. Villeneuve, and J.D. Joannopoulos, Phys. Rev. Lett. 77, 3787-3790 (1996).[3] H. Taniyama and M. Natomi and Y. Yoshhikuni, Phys. Rev.B.71, 153-103 (2005).[4] A. Chutinan and S. Noda Phys. Rev.B.62, 4488-4492 (2000).[5] S. G. Jhonson, S. Fan, P. R. Villeneuve, and J. D. Joannopoulos,Phys. Rev.B.60, 5751-5758 (1999)[6] Natalia Malkova, Sungwon Kim, and Venkatraman Gopalan,Appl Phys. Let. Vol 83, Number 8 (2003)6th Nanoscience and Nanotechnology Conference, zmir, 2010 639