  We propose an on-chip optical power delivery system for dielectric laser
accelerators based on a fractal 'tree-branch' dielectric waveguide network.
This system replaces experimentally demanding free-space manipulations of the
driving laser beam with chip-integrated techniques based on precise
nano-fabrication, enabling access to orders of magnitude increases in the
interaction length and total energy gain for these miniature accelerators.
Based on computational modeling, in the relativistic regime, our laser delivery
system is estimated to provide 21 keV of energy gain over an acceleration
length of 192 um with a single laser input, corresponding to a 108 MV/m
acceleration gradient. The system may achieve 1 MeV of energy gain over a
distance less than 1 cm by sequentially illuminating 49 identical structures.
These findings are verified by detailed numerical simulation and modeling of
the subcomponents and we provide a discussion of the main constraints,
challenges, and relevant parameters in regards to on-chip laser coupling for
dielectric laser accelerators.
