Optimization of a 60° waveguide bend in InP-based 2D planar photonic crystals
We present a novel design for a W1 (one missing row of holes) waveguide 60° bend implemented in a substratetype InP/ InGaAsP/ InP planar photonic crystal based on a triangular array of air holes. The bend has been designed to provide high transmission over a large bandwidth. The investigated design improvement relies only on displacing holes while avoiding changing individual holes diameter in the interest of better process control (homogenous hole depth). Two-dimensional (2D) finite-element simulations were used to increase the relative transmission bandwidth from 18% to 40% of the photonic bandgap for unoptimized and optimized 60° bends, respectively. The 2D results were verified by means of rigorous three-dimensional (3D) finite-difference time-domain (FDTD) simulations. We show that excellent agreement between 2D and 3D simulations can be obtained, provided a small effective-index shift of −0.024 (−0.74%) and an imaginary loss parameter (ϵ˝ =0.014) is introduced in the 2D simulations. To demonstrate the applicability of our improved design, the bend was fabricated and measured using the endfire technique. A bending loss of 3 dB is obtained for the optimized W1 waveguide bend compared to more than 8 dB in the unoptimized case.
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