Transmission which utilizes Dense Wavelength Division Multiplexing (DWDM) is in practice limited to the 1550 nm window (C band) nowadays due to commercial availability of erbium-doped fiber amplifiers. However, the demand for bandwidth is constantly growing and DWDM transmission in the 1300 nm window (O band) will soon be necessary. Fibrain introduces tunable narrowband filters for DWDM applications in the O band. Their central wavelength can be chosen in the 1293-1297 nm range. More technical details are available here.