  Three dimensional waveguides within the bulk of diamond are manufactured
using ultrafast laser fabrication. High intensities within the focal volume of
the laser cause breakdown of the diamond into a graphitic phase leading to a
stress induced refractive index change in neighboring regions. Type II
waveguiding is thus enabled between two adjacent graphitic tracks, but
supporting just a single polarization state. We show that adaptive aberration
correction during the laser processing allows the controlled fabrication of
more complex structures beneath the surface of the diamond which can be used
for 3D waveguide splitters and Type III waveguides which support both
polarizations.
