Method for manufacturing a preform for a multi-core optical fiber and method for manufacturing multi-core optical fibers

A method for manufacturing a preform for a multicore fiber, comprising:

• (a) stacking (S1) a plurality of core rods and a plurality of silica-based filler rods in a tube, forming a stack of rods;
• (b) collapsing the tube around the stack of rods, forming a collapsed stack;
• (c) depositing a layer of silica around the collapsed stack thereby forming the preform for the multicore fiber having an initial circularity;
• and
• (d) after step (c), removing at least part of the deposited layer of silica thereby increasing circularity and diameter stability of the preform for the multicore fiber along its length when compared with the initial circularity of the preform for multicore fiber formed in step (c), wherein depositing (S3) a layer of silica around the collapsed stack is achieved using a process comprising at least one of:
• a plasma vapor deposition process;
• an Outside Vapor Deposition (OVD) process;
• or
• sleeving the collapsed stack with a silica glass tube, and
• wherein, prior to depositing a layer of silica around the collapsed stack, further comprising a step for set-up of the collapsed stack on a lathe, comprising:
• placing two horizontally aligned handle rods within mandrels of the lathe;
• placing the collapsed stack on vertically adjustable positioning wheel supports such that each vertically adjustable wheel support is closer to one end of the collapsed stack than to another end;
• aligning a first end of the collapsed stack with a first handle rod;
• rotating the collapsed stack at a rotation speed of 15 to 16 rpm around an axis of rotation aligned with the central axis of said handle rods
• heating the first end of the collapsed stack in contact with the first handle rod with an O2/H2 burner until a welding point temperature limit is reached;
• vertically adjusting positioning wheels of the vertically adjustable positioning wheel supports until the collapsed stack is centered on said axis of rotation, and
• stopping the heating.