JP3866725B2 - Manufacturing method of plastic holey fiber - Google Patents

Description

The present invention relates to a manufacturing method for a plastic holey fiber with a plurality of pores penetrating the interior of the core near the clad in the axial direction of the core.

  Optical fibers that enable high-capacity and high-speed communication are indispensable for the construction of optical communication networks. However, in recent and future optical communication networks, optical signals have become faster and information has increased. In addition, an optical fiber called a photonic crystal optical fiber (PCF) is attracting attention as a new optical fiber that satisfies this requirement.

  This PCF has a photonic structure, which is a periodic structure of refractive index, in the clad covering the core. Specifically, by providing a space of a honeycomb structure like a honeycomb in the clad portion, light is forbidden. A photonic band gap (PBG) that is a band is generated (see, for example, Non-Patent Document 1).

  In addition, there is a hollow core PCF having such a PBG structure as a waveguide principle (see, for example, Non-Patent Document 2). This hollow core PCF has the possibility of an ultra-low loss fiber in which Rayleigh scattering, which is a main factor of loss, is extremely small because there is no quartz medium in the core through which light propagates. As a PCF having a hollow core, for example, Patent Document 1 discloses that a reduction in loss of about 0.01 dB / km can be expected.

  However, in these conventional PCFs, if there is a slight structural fluctuation in the PBG structure, the light propagation condition cannot be maintained, and so-called structural loss is generated. Therefore, it is necessary to precisely configure the PBG structure. There are still many issues remaining for practical use.

  On the other hand, although it does not have a complete PBG structure like the PCF described above recently, the clad is placed in the clad near the core of the conventional optical fiber having a relative refractive index difference due to the difference in glass composition. An optical fiber called a so-called holey fiber, in which a plurality of holes penetrating in the axial direction are formed, has been proposed. The holey fiber has characteristics that could not be obtained in the past by lowering the effective refractive index of the clad and expanding the relative refractive index difference between the core and the clad by these holes.

  As such a holey fiber, for example, Non-Patent Document 3 describes a holey fiber in which four holes are formed in a clad near the core of a fiber having a structure of a normal single mode fiber. This holey fiber realizes a fiber having zero dispersion and single mode operation in the 0.8 μm wave band by expanding the effective relative refractive index difference between the core and the clad.

  By the way, such a conventional holey fiber is made of quartz glass, and is manufactured by subjecting a quartz glass rod (preform) before spinning to mechanical punching and spinning it to a predetermined fiber diameter. . On the other hand, plastic holey fibers made of plastic (resin) have been proposed for the purpose of reducing manufacturing costs and improving flexibility.

  In addition, there exists patent document 2 as prior art document information relevant to invention of this application.

Japanese Patent No. 3072842 JP 2002-98852 A Knight et al., “Photonic band gap guidance in optical fiber”, Science 282, 1476, 1998. Cregan et al., “Single-Mode Photonic Band Gap Guidance of Light in Air,” Science 285, 1537, 1999. Hasegawa, “Nobel Hall-Assisted Light Guide Fiber 1 Large and Anomalous Dispersion and Low Loss Billow (1 year, 1st, 1st, 1st, 1st, 5th

  However, in the conventional holey fiber, since a plurality of holes are formed linearly along the longitudinal direction of the fiber, it is difficult to make a complete symmetrical structure with respect to the fiber center (core) in terms of processing accuracy. As a result, the refractive index is biased and the polarization mode dispersion (PMD) characteristic is deteriorated.

Therefore, an object of the present invention is to provide a method for producing a low-cost plastic holey fiber having excellent PMD characteristics.

The present invention has been devised to achieve the above object, and the invention of claim 1 includes a core, a clad covering the outer periphery of the core, and a plurality of voids penetrating in the axial direction through the clad near the core. In a method of manufacturing a plastic holey fiber having holes, when extruding a core resin from a core extrusion nozzle and extruding a cladding resin from a clad extrusion nozzle provided so as to cover the core extrusion nozzle, and performing composite extrusion molding A plurality of pins for forming the plurality of holes are attached to the tip of the core extrusion nozzle in advance, and the core extrusion nozzle or the clad extrusion nozzle is rotated at a predetermined speed, simultaneously with the composite extrusion molding. A method for producing a plastic holey fiber in which the plurality of holes are continuously formed in a spiral around the axis of the core A.

  As is apparent from the above description, according to the present invention, the following excellent effects are exhibited.

  (1) PMD characteristics can be greatly improved by providing a spiral structure in which a plurality of holes in a plastic holey fiber are formed in a spiral shape around the axis of the core.

  (2) Manufacturing of a spiral structure of a hole that is difficult to realize with a holey fiber made of quartz glass can be easily performed with a plastic holey fiber, and a high-quality holey fiber can be obtained at a lower cost.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 (a) shows a cross-sectional view of a plastic holey fiber according to a preferred embodiment of the present invention, and FIG. 1 (b) shows a structural diagram thereof.

  As shown in FIG. 1A and FIG. 1B, a plastic holey fiber 1 according to the present invention includes a core 2 disposed in the center, a clad 3 covering the outer periphery of the core 2, and a vicinity of the core 2. It is composed of eight holes 4 that penetrate the clad 3 in the axial direction and a jacket 5 that covers the outer periphery of the clad 3, and the eight holes 4 are spirally formed around the axis of the core 2 at a predetermined pitch. Is formed.

  Each of the holes 4 has a circular cross section. When viewed in the cross section of the fiber 1, the holes 4 are arranged concentrically and at equal intervals in the clad 3 that is spaced a predetermined distance from the center of the core 2. In the present embodiment, each hole 4 has a diameter φh of 30 μm.

  The core 2 is made of, for example, polymethyl methacrylate as a core resin excellent in optical characteristics such as transparency, and has a circular cross section and a rod shape as a whole. The clad 3 is made of, for example, a fluorine-based resin as a clad resin in order to make the refractive index smaller than that of the core 2, and the cross section is formed in a ring shape and the whole is cylindrical except for the holes 4. The jacket 5 is formed in a ring shape in cross section and in a cylindrical shape as a whole. In the present embodiment, the diameter φa of the core 2 is 0.2 mm, the outer diameter φb of the cladding 3 is 1 mm, and the outer diameter φ of the jacket 5 is 2 mm.

  Next, a fiber manufacturing apparatus for manufacturing the plastic holey fiber 1 will be described.

  As shown in FIG. 2, the fiber manufacturing apparatus 21 according to the present invention is operated simultaneously with a core forming member 22a that extrudes a core resin a to form a core, and the core forming member 22a, and is disposed on the outer periphery of the core. A clad forming member 22b that extrudes the resin b to form a clad, and a winder 23 that draws and winds the core forming member 22a and the fiber preform 1p from the clad forming member 22b at a predetermined drawing speed. Yes.

  The core forming member 22a feeds the core resin a from the core resin tank 24a downward by a screw 26a rotated by a motor 25a, and pushes it downward from a core extrusion nozzle 27a provided below the screw 26a.

  Similarly, the clad forming member 22b is provided so that the clad resin b from the clad resin tank 24b is sent to the right by the screw 26b rotated by the motor 25b and covers the lower part of the core extrusion nozzle 27a to the right of the screw 26b. Then, it is pushed downward from the clad extrusion nozzle 27b which is fixed.

  As shown in FIG. 3, a detachable pin 31 that protrudes downward from the tip position of the nozzle 27a to the tip position of the nozzle 27b is concentrically arranged at the tip t spaced from the center of the core extrusion nozzle 27a. 8 are arranged at regular intervals and fixed. Although not shown in detail, the core extruding nozzle 27a is provided by a motor so as to be rotatable in a direction indicated by an arrow R at a predetermined speed with the center as a rotation axis A.

  A method for manufacturing the plastic holey fiber 1 will be described.

  First, the core resin a is extruded downward from the core extrusion nozzle 27a of the core forming member 22a of the device 21, and the clad extrusion resin b is extruded downward from the clad extrusion nozzle 27b of the cladding forming member 22b. The composite extrusion molding is performed.

  At the same time, the core extrusion nozzle 27a is rotated, and the pin 31 attached and fixed to the tip thereof is rotated together with the core extrusion nozzle 27a. Then, simultaneously with the composite extrusion molding of the core 2 and the clad 3, a plurality of holes 4 are continuously formed in a spiral around the axis of the core 2 in the clad 3 in the vicinity of the core 2, and the clad extrusion nozzle 27b The fiber preform 1p is sent downward from the tip. When this fiber preform 1p is drawn and wound by a winder 23 provided below the clad extrusion nozzle 27b and further covered with a jacket 5 in a separate process, FIG. 1 (a) and FIG. 1 (b) The plastic holey fiber 1 shown in FIG.

  As described above, the plastic holey fiber 1 according to the present invention has a long helical structure in which a plurality of holes 4 penetrating through the cladding 3 in the vicinity of the core 2 are formed in a spiral shape around the axis of the core 2. When viewed from the entire length of the fiber 1, the plurality of holes 4 have a substantially complete symmetrical structure with respect to the center (core 2) of the fiber 1, so that no refractive index deviation occurs and PMD characteristics can be greatly improved. .

  Moreover, according to the manufacturing method which concerns on this invention, the helical structure of the void | hole 4 can be easily formed by rotating the core extrusion nozzle 27a. The spiral pitch of the holes 4 can be easily changed by appropriately setting the rotation speed of the core extrusion nozzle 27a and the drawing speed of the winder 23. Further, the number and arrangement of the holes 4 can be easily changed by changing the number and arrangement of the pins 31 attached and fixed to the tip of the nozzle 27a.

  Therefore, it is possible to easily manufacture the spiral structure of the air holes 4 that is difficult to realize with a holey fiber made of quartz glass, and it is possible to easily perform the manufacturing with a plastic holey fiber. High quality holey fiber can be obtained at low cost.

  In the above embodiment, the example in which the eight holes 4 are formed in the clad 3 in the vicinity of the core 2 has been described. However, the present invention is not limited to the number and arrangement of the holes 4, but the holes 4 and the core 2. The distance between them is not particularly limited.

  In addition, the example in which the core extrusion nozzle 27a is rotatably provided and the clad extrusion nozzle 27b is fixed has been described. However, the clad extrusion nozzle 27b may be rotatably provided and the core extrusion nozzle 27a may be fixed. That is, one nozzle may be provided so as to be rotatable relative to the other nozzle.

FIG. 1A is a transverse sectional view showing a preferred embodiment of the present invention, and FIG. It is the schematic of the fiber manufacturing apparatus which concerns on this invention. It is an expanded sectional view of the A section of FIG.

Explanation of symbols

1 Plastic holey fiber 2 Core 3 Clad 4 Hole

Claims (1)

In a method for producing a plastic holey fiber comprising a core, a clad covering the outer periphery of the core, and a plurality of holes penetrating in the axial direction in the clad near the core, while extruding the core resin from the core extrusion nozzle, When extruding a clad resin from a clad extrusion nozzle provided so as to cover the core extrusion nozzle and performing composite extrusion molding, a plurality of pins for forming the plurality of holes are previously attached to the tip of the core extrusion nozzle. The core extrusion nozzle or the clad extrusion nozzle is rotated at a predetermined speed, and the plurality of holes are continuously formed in a spiral around the axis of the core simultaneously with the composite extrusion molding. Manufacturing method of plastic holey fiber.

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