Diamond etalons for DWDM applications are available from Element Six. Fabricated from synthetic single-crystal CVD diamond that exhibits high thermal conductivity, they are insensitive to case temperature variations. They are unbreakable and unscratchable and have a high refractive index that allows uncoated usage. The etalons cover the C- and the L-bands. Specifications include flatness of λ/20 at 633 nm, typical parallelism of 5 arc sec, absolute thickness of ±0.25 µm and insertion loss of 0.15 dB.