• B.M. Cowan, M.C. Lin, B.T. Schwartz
  Tech-X, Boulder, Colorado
• R.L. Byer, C. McGuinness
  Stanford University, Stanford, California
• E.R. Colby, R.J. England, R.J. Noble, J.E. Spencer
  SLAC, Menlo Park, California

Photonic crystal waveguides are promising candidates for laser-driven accelerator structures because of their ability to confine a speed-of-light mode in an all-dielectric structure. Because of the difference between the group velocity of the waveguide mode and the particle bunch velocity, fields must be coupled into the accelerating waveguide at frequent intervals. Therefore efficient, compact couplers are critical to overall accelerator efficiency. We present designs and simulations of high-efficiency coupling to the accelerating mode in a three-dimensional photonic crystal waveguide from a waveguide adjoining it at 90 degrees. We discuss details of the computation, including an optimization routine to modify the geometric parameters of the coupler for maximum efficiency, the resulting transmission, and estimates of the fabrication tolerance for these devices. We include some background on the accelerator structure and photonic crystal-based optical acceleration in general.