Abstract: An optical fiber hermetic feed-through for polarization maintaining fibre has, contained within a hollow metallic plug, a ceramic ferrule that is a concentricity providing sliding fit around the fiber and serves to hold the fiber centered in an aperture in the end wall of the plug. The fiber is secured with adhesive in the bore of the ferrule which is similarly secured within the plug. An hermetic seal between plug and fiber is provided by a soft solder fillet whose short length and circular symmetry minimises the stress applied to the fibre by the freezing of the solder and thereby minimises the degradation of the polarisation maintaining properties of the fibre.