Bend Coupling Through Near-Zero GVD Slow Light Photonic Crystal Waveguides

Slow light propagation through photonic crystal (PhC) slab devices has great potential to reduce the size and power consumption of silicon photonic optical circuits. Most commonly, slow light routing through photonic crystals is achieved by using W1 waveguide bends operating near their cutoff frequencies. Unfortunately, this leads to optical pulse distortion due the high group velocity dispersion (GVD) associated with these designs. In this letter, however, we study the coupling between slow light waveguides optimized for near-zero GVD and 60° PhC bends. Using numerical methods and the temporal coupled mode theory, we assess the performance of single bends coupled to input/output waveguides, and S-bends composed of two cascaded bends. In this latter, we observe that the bend-waveguide quality factor has great impact over transmission and dispersion. We propose a novel 60° PhC bend design for routing optical modes while maintained reduced dispersion. This is achieved over a -3 dB bandwidth of around 50 nm in devices with slowdown factor up to 40. We show that this 60° PhC bend has good stability under changes in S-bend length and fabrication induced disorder. These results can lead to great improvements in the design of monolithically integrated modulators, switches, (de)multiplexers, and filters based on photonic crystals, as well as on the routing of long optical buffers and delay lines.