Method of hermetically sealing a fiber optic light guide in a metallic feedthrough sleeve with glass solder and hermetically sealed feedthrough device made thereby

A method for hermetically sealing a fiber optic light guide in a metallic feedthrough sleeve by means of glass solder, said fiber optic light guide comprising a longitudinally extending glass fiber (2) provided with at least one protective layer or coating (3, 4), said method comprising the steps of:

• a) preparing a feedthrough sleeve (5) consisting of a metallic material, said metallic material comprising an Invar alloy;
• b) removing said at least one protective layer (3, 4) from the fiber optic light guide (1) to expose said glass fiber (2);
• c) preparing two half-cylinder-shaped pressed parts made (7) from a low-melting composite-glass solder with thermal expansion properties adapted to said metallic material of the feedthrough sleeve (5), the half-cylinder-shaped pressed parts (7) each having a respective axial groove (7a) with a corresponding cross-section adapted to a diameter of the exposed glass fiber (2);
• d) assembling both half-cylinder-shaped pressed parts (7) together with the exposed glass fiber (2) inserted in the grooves (7a) of the half-cylinder-shaped pressed parts;
• and
• e) melting the half-cylinder-shaped pressed parts (7) together with each other and with the glass fiber (2) and the feedthrough sleeve (5) by local heating.