Design-analysis of Silicon based Photonic crystal waveguide for On-chip Slow Light Applications

Abstract

Line-defect photonic crystal waveguides which is different from conventional dielectric waveguides such as optical fiber are receiving considerable attention. Our proposed waveguide structure is based on silicon photonics. Different optical components can be connected with each other using proposed silicon waveguide to establish very fast communication between circuit boards, between chips on a board, or even within single chips. A low-loss and flat dispersion line-defect photonic crystal waveguide is proposed based on triangular lattice of two dimensional photonic crystals. Our main aim was to achieve flat band slow light in silicon in a photonic crystal waveguide with large delay bandwidth product and low GVD by shifting the positions of rows which are adjacent to the waveguiding region. We propose two design approaches to design flat dispersion line defect waveguide with low loss. In first set of approach, lattice constant value remains constant throughout all proposed structures and in second set of approach, it is varied. A delaybandwidth product (NDBP) with acceptably small group velocity dispersion in photonic crystal waveguide is achieved. We proposed three structures by shifting the first two rows of holes adjacent to the waveguide. Larger group index values of 36.16, 44.9 and 53.95 over flat bandwidth of 15.7, 13.66 and 9.9 nm along with NDBP values of 0.351, 0.38 and 0.329 are obtained. NDBP value is further improved by taking different lattice constant values for all three structures and higher group indices 36.60, 46.52 and 54.58 over flat bandwidth of 18.82, 14.05 and 11.19 nm are reported. GVD parameter is also found to be low for all the structures. The reported results can be useful in realizing flat band slow light in silicon with improved waveguiding characteristics. To further test the practical applicability of our waveguide the buffering capacity is calculated which is found to be as high as 140 bits. Both the approaches are better from fabrication point of view as controlling the radius of holes at nano-metre scale brings fabrication challenges. Generation of slow light is a promising solution for buffering and time-domain processing of optical signals and also offers the possibility for spatial compression of optical energy and the enhancement of linear and nonlinear optical effects.