Abstract: A bundle of optical fibers each covered by an acid-soluble borosilicate glass is treated with an acid solution, with an alkali solution, and then with an acid solution to completely remove the acid-soluble glass from the middle portion between the end portions of the optical fiber bundle. A plastic material is charged into the interstices among the fibers at the boundary portions between the middle portion and the end portions. These interstices are free of any insoluble residue of the acid-soluble glass. A reinforcement is formed around the periphery of at least a part of the boundary portions by covering the periphery with a flexible plastic material or by winding a linear member around the periphery.

Abstract: An acid-soluble glass used in manufacture of a flexible fiber optic bundle and a process for manufacturing a flexible fiber optic bundle using the glass. The glass has a composition expressed by mol percent comprising more than 15.0% and less than 41.0% of SiO.sub.2, more than 29.0% and less than 54.0% of B.sub.2 O.sub.3, more than 6.0% and less than 23.0% of BaO, and more than 5.0% and less than 19.0% of at least one alkali metal oxide selected from the group consisting of Na.sub.2 O, K.sub.2 O and Li.sub.2 O, the total amount of SiO.sub.2, B.sub.2 O.sub.3 and BaO being more than 71.0% and less than 80.0%.

Abstract: An acid-soluble glass for use in making a flexible optical fiber bundle, which comprises the following composition:20.0 mol %<SiO.sub.2 <48.0 mol %25.0 mol %<B.sub.2 O.sub.3 <50.0 mol %5.0 mol %.ltoreq.BaO.ltoreq.6.0 mol %7.0 mol %<Na.sub.2 O, K.sub.2 O, or Li.sub.2 O, or total of the two or more thereof<18.0 mol %71.0 mol %<SiO.sub.2 +B.sub.2 O.sub.3 +BaO<80.0 mol %7.4 mol %<ZnO<12.0 mol %1.8 mol %<Al.sub.2 O.sub.3 <7 mol %The acid-soluble glass exhibits a high solubility in an acid, a high resistance to water, and a high viscosity at the fiber-forming temperature.

Abstract: A number of three-layer optical fibers each having a core a cladding and an overcoating layer of acid-soluble glass material are bonded together by means of an adhesive which can be removed by applying heat. The bonded optical fibers are heated and stretched to obtain a solid optical fiber bundle. The solid optical fiber bundle is brought into contact with an acid to elute (leach away) the overcoating layer of the acid-soluble glass material.

Abstract: An image transmitting optical fiber bundle has at an end of it a field stop for defining the size of image viewed thereby. The field stop is sandwiched between a pair of transparent thin plastic films. The pair of films which sandwiches the field stop is fixed to an end of the optical fiber bundle. A face plate is further fixed on the pair of films on the end face of the fiber bundle. Since the surfaces adhered are all flat, the formation of bubbles in the adhesive is easily precluded.

Abstract: A holographic lens which functions to converge light passing therethrough is located on a plane equivalent to the focal plane of a taking lens of a reflex camera. An image of the object is formed on the holographic lens and viewed in enlarged scale through an eyepiece. The light passing through the holographic lens is converged to the eyepiece so that a uniformly bright image of the object formed on the holographic lens may be viewed through the eyepiece.