JPS58120529A - Method and apparatus for manufacturing optical fiber retaining circularly polarized light - Google Patents

Abstract

PURPOSE:To obtain an optical fiber having high circularly polarized light retentivity by drawing molten glass from an elliptical hole while twisting the glass and by coating the resulting core glass with clad glass. CONSTITUTION:The 1st crucible 1 for molten core glass 4 is put in the 2nd crucible 2 for molten clad glass 5 so that the central axis of the elliptical hole of the crucible 1 is allowed to coincide with that of the circular hole of the crucible 2 and that the crucible 1 is rotated around the central axis of the crucible 2. Heaters 3 are placed at the outside of the crucibles 1, 2, and core glass 4 in the crucible 1 and clad glass 5 in the crucible 2 are melted with the heaters 3. The molten core glass 4 in the crucible 1 flows out of the bottom elliptical hole while being twisted around the axial line of the crucible 1 by the rotation of the crucible 1, and it is coated with the molten clad glass 5 in the crucible 2 and drawn from the bottom circular hole of the crucible 2 to form an optical fiber 6 retaining circularly polarized light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polarization-preserving optical fiber used in optical communications, optical sensors, etc., and particularly relates to a method for manufacturing a polarization-preserving optical fiber that preserves circularly polarized light, and a method for manufacturing a fiber used to carry out this manufacturing method. Regarding equipment.

Optical fibers that transmit light while preserving polarization are promising optical transmission lines for use in optical heterodynes, fiber gyros, pressure sensors, and the like. Polarization-maintaining optical fibers that have been developed in the past are divided into optical fibers that preserve linearly polarized light and optical fibers that preserve circularly polarized light, and their manufacturing methods are also different. The manufacturing method for linearly polarized, light-preserving optical fibers involves depositing glass films corresponding to the core and cladding on the inner wall of a quartz tube, heating them to form an optical fiber base material, and then forming the optical fiber base material. In this method, both sides are polished and then heated and stretched to obtain an optical fiber. In this case, the softening point temperature of the clad glass deposited on the inner wall of the quartz tube is selected to be lower than the softening point of the quartz glass used in the quartz tube and the core glass deposited on the inner wall of the quartz tube.

When this polished original fiber base material on the inner surface is heated and stretched, the quartz glass part polished with both mEii becomes circular in the cross section perpendicular to the central axis by applying a force of 1 ml at the beginning of ML. The inner peripheral shape is hardened into an elliptical shape, then the core glass is hardened into a circular shape due to surface tension, and finally the cladding glass is hardened, resulting in an optical fiber with an elliptical cladding. In this optical fiber, since the cross section of the cladding is elliptical, the pressure on the core of the cladding differs depending on the major and minor axis directions within the cross section of the cladding, causing birefringence in the core, which increases the propagation within the optical fiber. The effect of eliminating the regression of the fundamental mode and preserving only linearly polarized light with polarization planes in the major and minor axis directions within the cross section of the cladding! Motsu. However, optical fibers that preserve linearly polarized light using this conventional method preserve only linearly polarized light with polarization planes in the long and short axis directions within the cross section of the cladding, and when connecting optical fibers, it is necessary to It is necessary to match the long sleeve and short axes within each. However, when actually matching the long and short axes in the cladding cross section of an optical fiber, light is incident on the optical fiber, and the polarization of the light propagated through the connection point is 11. : Requires complicated operation of adjusting while measuring Vt.

A method for manufacturing an optical fiber that preserves circularly polarized light is to deposit glass films corresponding to the core and cladding on the inner wall of a quartz tube, heat it to make it solid, and then twist the heated and stretched optical fiber. Optical fibers with a core with a perfect circular cross section have the effect of preserving circularly polarized light because the propagation constant is constant in any direction within the core cross section, but in general, manufacturing of optical fibers with a core with a perfect circular cross section is is extremely difficult.

However, it is known that when an optical fiber is twisted to give a twist to the core of the optical fiber, the core of the optical fiber behaves isometrically as a perfectly circular core. In this way, in a circularly polarized optical fiber, the core behaves as a perfectly circular core, so there is no need to align the long and short axes in the clad cross section of the optical fibers when connecting the optical fibers.

However, since this optical fiber can only be twisted to the extent that it does not break, the effect of preserving circular polarization is small.

Therefore, an object of the present invention is to provide a method for manufacturing an optical fiber having high circular polarization preservation.

Another object of the present invention is to provide an apparatus for manufacturing a source fiber with a high circular polarization preservation effect.

The method for manufacturing a circularly polarized light preserving optical fiber of the present invention includes a method of placing molten glass in a crucible having an elliptical hole on the J& plane, and pulling out the molten glass from the elliptical hole while applying a twist to obtain a core glass; This method includes the step of covering the core glass with a clad glass having a lower refractive index than the core glass.

Embodiments of the present invention will be described below with reference to the drawings.

The drawing is a schematic illustration of a circular polarization preserving optical fiber manufacturing apparatus used to carry out the method of the present invention. In this example,
A first crucible 1 having an oval hole in the center of the bottom and a second crucible 2 which is larger but also having a circular hole in the center of the bottom are arranged in combination, and molten glass is injected into each of the crucibles. One piece is constructed so that it can be pulled out from the hole.
ilJ] As shown in the figure, the first crucible l containing the molten core glass 4 is placed in the second crucible 2 containing the molten cladding glass 5, so that the central axis of the elliptical hole of the first crucible l and iJ2 The first crucible 1 is arranged such that the central axis of the circular hole of the crucible 2 coincides with the central axis of the crucible 2, and the first crucible 1 is held so as to be rotated about the central axis with respect to the second crucible 2. Note that the position of the bottom oval hole of the crucible 1 of SL is slightly inside (above) the position of the circular hole of the second crucible 2.A heating body 3 is placed outside of these crucibles 1 and 2, and this The core glass 4 and clad glass 5 in each crucible are melted by the heating element 3.The molten core glass 4 in the first crucible is twisted around its axis by the rotation of the crucible i[1, and the bottom of the crucible is twisted. It flows out from the elliptical hole, and is pulled out from the bottom circular hole of the crucible 2 of 's2 while its periphery is covered with the molten clad glass 5 in the second crucible 2 to become a circular polarization preserving optical fiber 6.

In this example, the composition of the core glass 4 is: 13t3mo 1% 8i01, 4moJ%GeO
,,10moj% P2O3, clad crow 5
The composition is 90mol*g1%.

The optical fiber 6 is drawn out at a speed of 1 m/min while rotating the first crucible 1 at 200 revolutions/min. The circularly polarized light preserving optical fiber thus obtained was twisted 200 times/40 times, whereas the original circularly polarized light preserving fiber manufactured by adding twist in the conventional method had a maximum twist of about 40 times/... can be increased, thereby significantly increasing its circular polarization preservation.

Note that the compositions of the core glass and cladding glass are not limited to those in the above embodiments, and the number of revolutions of the first crucible or the drawing speed of the optical fiber are not limited to the one mentioned above.

[Brief explanation of the drawing]

The drawing is a schematic diagram of a circular polarization preserving optical fiber manufacturing apparatus according to an embodiment of the present invention. 1...first crucible, 2...second crucible, 3...
- Heating body, 4... Molten core glass, 5... Melted clad glass, 6... - Optical fiber. Agent Patent Attorney Toshiyoshi Somekawa

Claims (2)

[Claims] (1) A step of drawing molten glass through an elliptical hole and twisting it to form a core glass, and a step of covering the core glass with clad glass having a lower refractive index than the core glass. A method for manufacturing a circular polarization preserving optical fiber. (2) Has an oval hole at the bottom and inserts the molten core glass.
1 crucible, and a second crucible having a circular hole at the bottom and containing the molten clad glass, the first crucible having an elliptical hole whose center axis is the center of the second crucible's circular hole. positioned within the second crucible so as to coincide with the axis and the second
An apparatus for manufacturing a circularly polarized light preserving optical fiber, characterized in that the optical fiber is held in a crucible so as to be rotatable around its central axis.