Low-Loss Millimeter-Length Waveguides and Grating Couplers in Single-Crystal Diamond

We report on the design, fabrication, and characterization of millimeter-length strip waveguides with monolithic grating couplers in commercially available synthetic single-crystal diamond. To minimize the device footprint and the influence of the wafer wedge of the single-crystal diamond thin plate, we adopt a curled waveguide layout. The devices are fabricated using electron-beam lithography and reactive-ion etching. To improve the e-beam patterning accuracy of the grating etch masks, we apply proximity-effect compensation on the gratings and tapers. The linear characterization results indicate a waveguide attenuation of 6.5 dB/mm and a grating transmission of -6.3 dB in the fiber-optic communication C band. These results demonstrate the feasibility of fabricating long waveguides and integrated grating couplers in single-crystal diamond. Our research findings would be beneficial for further exploring quantum and nonlinear optics in integrated single-crystal diamond devices.