Third Day Poster Session, 17 June 2010 - NanoTR-VI

U Neslihan
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Poster Session, Thursday, June 17
Theme F686 - N1123
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3 Dimensional L Shaped Photonic Crystal Waveguide
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EtiUP P*, H. Sami SözüerP PP and Zebih ÇetinP
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Abstract- 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.
1
The discovery of the photonic crystal waveguides (PCWs),
which allow only certain electromagnetic wave modes to
propagate inside the structure, has opened up new ways of
controlling light propagation in optical integrated circuit
designs. By using photonic crystal slab waveguides, which
are 1 dimensional or 2 dimensional periodic structures with a
finite thickness in the vertical direction, it is possible to
fabricate light guiding optical materials by total internal
reflection [1], that confines light to the slab, and bend them
with little loss by photonic crystal assistance.
With conventional dielectric waveguides which depend
entirely on total internal reflection, there is a problem in
guiding light while turning through sharp edges and tight
curves because the angle of the incidence is too high for total
internal reflection, resulting in most of the electromagnetic
field being radiated out and lost.
To cope with this problem, a 2 dimensional line defect
waveguide can be used [2-8]. The problem with 2
dimensional line defect waveguides is that even small
defects during manufacturing can greatly increase
attenuation, thus limiting their usefulness to guide light over
long distances. To overcome this difficulty, Notomi proposed
using a 1 dimensional slab waveguide which is not periodic
in the direction of propagation, to reduce dispersion and
attenuation [3]. But still in an optical circuit, one would want
to bend light through a 90 angle due to the confined
geometry.
In this work, we make use of the best of both worlds,
namely, we use 1D slab waveguide of Notomi for the straight
sections and a 2D slab waveguide for containig the light at
the corners. By this way, the wave would travel with little
loss through the straight sections, turns through sharp corner
with little bending loss as well, reentering the 1D waveguide
region to travel for another long straight segment as shown in
figure [1].
Figure 2. 2D perfect square photonic crystal slab. There is a band
gap between 0.2 and 0.4 . The gray areas are unlocalized radiation
modes.
Figure 3. Dispersion relations for 2D and 1D waveguides. The big
crosses are localized TE-like modes of the 1DWG, while the big full
circles are those of the 2D LDWG. The small dots show unlocalized
modes. Matched modes for the two types of waveguides overlap,
indicating good impedance matching between the 1D and 2D
waveguides.
Then choosing the proper defect size at 2D and 1D
structes we created our waveguides and succeed to match
their modes as shown figure [3]. Thus, theoretically it is
possible to bend light in L shaped waveguide. It remains to
be seen actually what percentage of the light passes through
the bend by FDTD calculations in the time domain.
*Corresponding author: 2Tneslihaneti@iyte.edu.tr2T
Figure 1. Photonic crystal waveguide slab, which is a periodic
structure with a finite thickness in vertical z-direction and combines
1D and 2D slab waveguides.
We used the data in [7] since preliminary evidence
showed that it is possible to bend light by 90 degrees almost
without loss, but with the difference that in our proposed
structure we studied the more realistic photonic crystal
waveguide slab which is finite in the z-direction. Firstly we
found the band diagram for the 2D perfect pc slab, shown
in figure [2].
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structures operating at near infrared wavelengths"
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6th Nanoscience and Nanotechnology Conference, zmir, 2010 639