Polycrystalline diamond photonic waveguides realized by femtosecond laser lithography

In recent years, the perception of diamond has changed from it being a pure gemstone to a universal high-tech material. In the field of photonics, an increased interest is emerging due to its outstanding optical properties, such as its high refractive index, a spectrally wide transmission window, and high Raman coefficient. Furthermore, the capability to host color defects for room temperature single photon generation makes diamond an attractive platform for quantum photonics. Known as nature's hardest material, the fabrication and handling of crystalline diamond for integrated optics remains challenging. Here, we report on the fabrication of three-dimensional Type III depressed cladding waveguides in polycrystalline diamond substrates by direct laser writing. Single mode waveguiding is demonstrated in the near-infrared telecommunication C-band. We believe that this enables the fabrication of three-dimensional large-scale photonic circuits, which are essential for advanced classical and quantum diamond photonics.