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Broadband photonic crystal waveguide 60° bend obtained utilizing topology optimization

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Abstract

Topology optimization has been used to design a 60° bend in a single-mode planar photonic crystal waveguide. The design has been realized in a silicon-on-insulator material and we demonstrate a record-breaking 200nm transmission bandwidth with an average bend loss of 0.43±0.27 dB for the TE polarization. The experimental results agree well with 3D finite-difference-time-domain simulations.

©2004 Optical Society of America

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Figures (5)

Fig. 1.
Fig. 1. Schematics of photonic crystal waveguides containing two consecutive 60° bends. Left: Generic bend configuration. The red areas illustrate the chosen design domains in the topology optimization procedure. Right: Topology-optimized bends. The green areas highlight the optimized structures showing that a non-trivial smoothening has been applied to the bend.
Fig. 2.
Fig. 2. Scanning electron micrographs of fabricated photonic crystal waveguides containing two consecutive 60° bends. The pitch of the triangular lattice is Λ≈400nm with hole diameter D≈275nm. Left: Waveguide with generic. Right: Waveguide with topology-optimized bends. The number, shape and size of the holes at each bend are designed using topology optimization. The contrast and brightness of the images have been changed for clarity.
Fig. 3.
Fig. 3. Steady-state magnetic field distribution for the fundamental PBG mode simulated using 2D FDTD. The mode is incident from the bottom-left part of the waveguide. Left: Mode profile through the generic bends. Right: Mode profile through the topology-optimized bends.
Fig. 4.
Fig. 4. Measured loss per bend for the un-optimized 60° bends (red) and the topology-optimized 60° bends (green). Both spectra have been normalized to the transmission through straight PhCWs of the same length to eliminate the coupling and the propagation loss in straight waveguides. Dotted line marks a bend loss of 1dB.
Fig. 5.
Fig. 5. Experimental bend loss (green) compared to 3D FDTD calculated bend loss (blue). The 3D FDTD curve has been shifted 1.2% in absolute wavelength.
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