Provided is an optical fiber glass preform in which a starting rod and a dummy glass are hardly separated from each other, and a method for manufacturing the glass preform. In the optical fiber glass preform, the dummy glass is fitted into one end of the starting rod, and a part of the dummy glass and the starting rod are surrounded by a clad glass. In the manufacturing method, at the time of connecting the starting rod and the dummy glass, a shape is adjusted in such a manner that an iron is brought into contact with a connection portion and is moved from a starting rod side toward a dummy glass side with appliance of a load.

An automated large outside diameter preform tipping process. A zone of the preform is heated inside a furnace and softened. The preform tip is shaped and the process is controlled by the movement of the glass above and below the heating zone and by sensing the weight of the lower part of the preform, which in effect is a measure of the viscosity of the softened material. Once the correct viscosity is reached, the bottom holder is moved away from the top holder with a non-linear, accelerated velocity profile (derived from the FEM simulation of glass flow) which is precisely programmed and controlled so that the preform tip is optimally shaped (usually short and sharp tipped) with minimum waste and waveguide distortion when drawn into a fiber. The same concept of the non-linear, accelerated velocity profile can also be applied to other tipping processes such as horizontal preform tipping processes.

Provided is an optical fiber glass preform in which a starting rod and a dummy glass are hardly separated from each other, and a method for manufacturing the glass preform. In the optical fiber glass preform, the dummy glass is fitted into one end of the starting rod, and a part of the dummy glass and the starting rod are surrounded by a clad glass. In the manufacturing method, at the time of connecting the starting rod and the dummy glass, a shape is adjusted in such a manner that an iron is brought into contact with a connection portion and is moved from a starting rod side toward a dummy glass side with appliance of a load.

The application provides a method for automatically processing a conical tip of an optical fiber preform, including: step 10: suspending an optical fiber preform requiring conical tip processing on a suspension component, where the optical fiber preform moves downward vertically along with the suspension component; step 20: arranging a furnace body below the suspension component, where a preset depth is set inside the furnace body, and after the optical fiber preform moves to the preset depth inside the furnace body, the furnace body is heated; step 30: arranging an automatic cutting component below the furnace body, where a preset temperature is set inside the furnace body, after a temperature inside the furnace body reaches the preset temperature, a bottom of the furnace body is opened to make the optical fiber preform melt to form a conical tip, and the automatic cutting component cuts the molten conical tip.

An optical fiber preform includes: a columnar portion having an approximately constant radius of r; and a taper portion located adjacent to the columnar portion in a lengthwise direction and having a radius decreasing along the lengthwise direction. The taper portion includes: a first taper portion including a portion having a radius varying between 0.9r and 0.6r; and a second taper portion including a portion having a radius varying between 0.4r and 0.15r. A diameter of the first taper portion in the portion having the radius varying between 0.9r and 0.6r decreases so as to form a maximum angle θ1 between 40 degrees and 60 degrees with respect to the columnar portion, a diameter of the second taper portion in the portion having the radius varying between 0.4r and 0.15r decreases so as to form an average angle θ2 between 5 degrees and 30 degrees with respect to a central axis in the lengthwise direction, and a volume of the taper portion is smaller than or equal to 45% of a volume of a column having a same outer diameter as a maximum outer diameter of the taper portion and having a same length as the taper portion.

Provided is an optical fiber glass preform in which a starting rod and a dummy glass are hardly separated from each other, and a method for manufacturing the glass preform. In the optical fiber glass preform, the dummy glass is fitted into one end of the starting rod, and a part of the dummy glass and the starting rod are surrounded by a clad glass. In the manufacturing method, at the time of connecting the starting rod and the dummy glass, a shape is adjusted in such a manner that an iron is brought into contact with a connection portion and is moved from a starting rod side toward a dummy glass side with appliance of a load.

A multi-core optical fiber preform includes: a rod-shaped main cladding body having one or more main inner holes; main core rods inserted into the one or more main inner holes; and a tip continuously-installed portion disposed at one end of the rod-shaped main cladding body and including a glass rod having no core rod or having one core rod.

In a method of forming a conical shape on a glass rod including an effective portion and an ineffective portion adjoining the effective portion to form a conical shape in the effective portion by simultaneously heating a boundary and the vicinity of the boundary between the effective portion and the ineffective portion and pulling an end of the ineffective portion, the temperature of a heater is raised and a heating target on the glass rod is simultaneously moved from the ineffective portion to the boundary.

A method for manufacturing a multicore optical fiber includes a step of forming ring-shaped closed-end holes to axially extend from a first end toward a second end of a glass rod; a step of heating bottom parts of the ring-shaped closed-end holes and softening center rods surrounded by the ring-shaped closed-end holes; a step of pulling out the center rods toward a side of the first end, forming columnar closed-end holes from the ring-shaped closed-end holes, and treating the glass rod as a cladding material; a connecting step of connecting a supporting pipe to the first end; an inserting step of inserting core rods into the columnar closed-end holes after the connecting step; and a drawing step of drawing the cladding material and the core rods while heating a portion near the second end and integrating the cladding material and the core rods after the inserting step.

An optical fiber preform production method includes: inserting at least one glass rod into at least one through-hole that penetrates a cladding glass body that is a cladding of an optical fiber; integrating a dummy rod by either integrating a solid dummy silica rod with a first end of the cladding glass body by heating the first end to close a first opening of the through-hole that opens in the first end, or forming a base end seal that closes the first opening in the first end and integrating the solid dummy silica rod with the base end; and closing a second opening of the through-hole that opens in a second end of the cladding glass body by heating and deforming the second end.