Disclosed herein are systems and methods related to use of hollow core photonic crystal fibers. A system includes a tube and a collimating lens configured in a first end of the tube, wherein a single mode fiber is coupled to a first end of the collimating lens. A second lens is supported by a structure at a second end of the tube, the second lens receiving a first signal from a second end of the collimating lens and outputting a second signal that is coupled into a first end of a hollow core photonic crystal fiber. A first gas tube is configured to introduce gas through the structure into a chamber and a sealant seals at least one of the collimating lens and the structure within the tube. An output signal is received at a detector that catches the entire beam to suppress multiple-mode beating noise.