Method of producing infrared image guide

A method of producing an image guide for transmitting infrared rays which comprises:

• a. inserting a glass rod into a first thermally shrinkable synthetic resin tube to form a first assembly,
• b. heating said first assembly under vacuum to produce a preform in which said first synthetic resin tube is adhered to the surface of said glass rod,
• c. drawing the preform of step b.,
• d. inserting a plurality of drawn preforms of step c. preforms into a second thermally shrinkable synthetic resin tube to form a second assembly, where the glass rods consist of fluoride glass rods and chacogenide glass rods,
• e. heating said second assembly to produce a bundled preform, in which a plurality of said preforms of step c. are formed in a bundle, by the thermal shrinkage of said second synthetic resin tube, and
• f. drawing said bundled preform while heating to produce an infrared image guide having said first and second synthetic resin tubes as cladding and a plurality of glass cores within said cladding
• and wherein said first and second thermally shrinkable resin tubes are made of the same material and have substantially the same softening point as said glass rods whereby said resin tubes melt together.