Long wavelength transmission in HC-PBGFs. (A) Normalised transmission of ~5 m lengths of HC-PBGFs illustrating the possibility of scaling the operating wavelength of these fibres much deeper in the mid-IR than is possible using conventional silica fibres . (B) Low loss, wide bandwidth HC-PBGF designed for operation in the predicted region of minimum loss around 2 µm. Also shown is the output of a Thulium-doped amplifier with amplified data channel. The extent of the amplified stimulated emission (in blue) illustrates the gain bandwidth of the Thulium amplifier and the excellent match with the transmission bandwidth of the HC-PBGF .