Method and apparatus for producing an optical fiber preform

In a method of forming a porous glass preform comprising the steps of

• providing an elongated cylindrical core member,
• rotating said core member,
• longitudinally moving said core member,
• directing a first stream of glass particles toward a lateral surface of said core member to build up a first coating of given thickness thereon,
• continuously reciprocating said stream of particulate material with respect to a portion of the length of said core member to deposit and build up in the region of reciprocation movement of said stream a coating of thickness which tapers from said given thickness to zero thickness,
• the improvement comprising the step of directing said stream perpendicular to the longitudinal axis of said core member during its reciprocating movement except during that time in which said stream is at or near the end of its path of reciprocation when the axis of said stream becomes oriented in a direction other than perpendicular to said longitudinal axis.

Apparatus for forming an elongated porous glass preform comprising

• means for supporting a mandrel,
• means for rotating said mandrel,
• means for longitudinally moving said mandrel in a first direction,
• means for initially directing a stream of glass particles onto said mandrel to form an initial portion of a porous preform and for thereafter directing said stream of glass particles onto the end portion of said porous preform to continously form said end portion, and
• means for continously ocillating said means for directing in an arcuate path about said end portion so that said stream of glass particles is directed at the end portion of said preform at an angle with respect to the longitudinal axis of said preform, said angle continously varying with respect to time.

In an apparatus for forming a porous glass preform comprising

• means for supporting an elongated cylindrical core member,
• means for rotating said core member,
• means for longitudinally moving said core member in a first direction,
• source means for directing a first stream of glass particles toward a lateral surface of core member to build up a coating thereon, and
• means for reciprocatingly moving said source means with respect to a portion of the length of said core member, thereby forming on said core member a coating tapering from said given thickness of said coating tapering from said given thickness to zero thickness in the region in which said reciprocating motion of said source means takes place,
• the improvement comprising
• means for rotating said source means about an axis which is perpendicular to a plane which passes through said source means and which contains the axis of said cylindrical core member so that said source means can direct said stream toward said lateral surface at different angles with respect to the axis of said core member.