Telecommunication-wavelength two-dimensional photonic crystal cavities in a thin single-crystal diamond membrane

We demonstrate two-dimensional photonic crystal cavities operating at telecommunication wavelengths in a single-crystal diamond membrane. We use a high-optical-quality and thin (∼300 nm) diamond membrane, supported by a polycrystalline diamond frame, to realize fully suspended two-dimensional photonic crystal cavities with a high theoretical quality factor of ∼8 × 106 and a relatively small mode volume of ∼2(λ/n)3. The cavities are fabricated in the membrane using electron-beam lithography and vertical dry etching. We observe cavity resonances over a wide wavelength range spanning the telecommunication O- and S-bands (1360-1470 nm) with Q factors of up to ∼1800. Our method paves the way for on-chip diamond nanophotonic applications in the telecommunication-wavelength range.