  An all-diamond photonic circuit was implemented by integrating a diamond
microsphere with a femtosecond-laser-written bulk diamond waveguide. The near
surface waveguide was fabricated by exploiting the Type II fabrication method
to achieve stress-induced waveguiding. Transverse electrically and transverse
magnetically polarized light from a tunable laser operating in the
near-infrared region was injected into the diamond waveguide, which when
coupled to the diamond microsphere showed whispering-gallery modes with a
spacing of 0.33 nm and high-quality factors of 105. By carefully engineering
these high-quality factor resonances, and further exploiting the properties of
existing nitrogen-vacancy centers in diamond microspheres and diamond
waveguides in such configurations, it should be possible to realize filtering,
sensing and nonlinear optical applications in integrated diamond photonics.
