JP2556350B2 - Method for manufacturing NA conversion optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention comprises a core having a refractive index changed in the longitudinal direction.
It relates to the manufacturing method of NA conversion type optical fiber.
Provided is one having a length of about several hundred cm, which is suitable for coupling with the optical component, the optical waveguide, and the fiber.

(Prior Art) As a manufacturing method of this kind of optical fiber, SiCl ₄ as a main raw material gas and GeCl ₄ as a dopant gas are supplied into an oxyhydrogen flame to be flame-hydrolyzed and SiO containing Ge as a dopant. _{(2) When} fine glass particles are generated and deposited as a porous glass preform on the tip of a rod-shaped rod, the refractive index changes in the lengthwise direction by changing the amount of GeCl ₄ as a dopant gas at predetermined time intervals. The porous glass preform was prepared, and this preform was made into transparent glass and then drawn to obtain an NA conversion fiber whose refractive index changed in the length direction.

(Problems to be solved by the invention) However, in such a method, the change in NA is at the preform stage, and if the fiber is drawn by drawing it, the refractive index difference is changed by 0.3 to 1% in the length direction. For 1
I needed a length of about 0km, so I could not get a short one.

(Means for Solving the Problem) From the above viewpoints, the present invention provides an optical fiber preform in which a glass for cladding having a softening temperature lower than that of the glass for core is formed, and draws this. The drawing is performed while changing the tension in a predetermined cycle. As a means for changing the drawing tension, specifically, for example, changing the drawing temperature while keeping the drawing speed constant.

(Operation) Generally, the refractive index of the medium changes with stress, and the composition is such that the cladding is much lower than the softening temperature of the core, and the drawing temperature is equal to or around the softening temperature of the core. When the wire is drawn at a temperature, the clad glass is completely softened and all the tension is applied to the core. When the clad is cooled with the stress applied to the core, the stress of the core remains. As a result, the core remains in its tensioned state and its refractive index decreases. When the drawing temperature is higher than the softening temperatures of both the core and the clad, no stress is applied to the core and the refractive index does not change. Thus, if a fiber is drawn at a temperature at which stress is applied to the core and stress is not applied to the clad, a fiber whose refractive index changes according to the length method can be obtained.

Incidentally, a preform made of pure silica as the core material and F-doped silica as the clad material (Δ = 0.7%) was prepared, and the relationship between the drawing temperature and the relative refractive index difference Δ of the core / clad was examined. It was like a graph. As is clear from this graph, the relative refractive index difference between the core and the clad increases as the drawing temperature increases, and Δ changes by 0.2% with respect to a change of 100 ° C.

(Example) FIG. 1 is a schematic view of an apparatus used in the method of the present invention. In the figure, reference numeral 1 denotes a core-clad type optical fiber preform that is rotatably and vertically movable, and the softening temperature of the core is higher than that of the clad. 2 is a heat source for the fiber of the preform by irradiating the lower end of the preform 1, CO ₂ lasers 3, CO ₂
It is composed of an AO converter 4 for controlling the optical power of the laser 3, a collimator lens 5, and a focusing lens 6. 7 is a capstan for drawing the proform 1 onto the fiber 10, 8 is a pot containing a thermosetting resin or an ultraviolet curable resin for coating the fiber 10, and 9 is a resin coated on the fiber 10. This is a device for curing the resin and is composed of a resistance heating furnace, an ultraviolet lamp, and the like. Reference numeral 11 is a bobbin for winding the fiber 10. In the above configuration, a GeO ₂ -doped quartz rod (Δ = 1.0%) made by the VAD method as Preform 1 was jacketed with Pyrex glass, and the core rod diameter was 1 mm and the cladding outer diameter was 12.5.
The lower end of the preform 1 having a size of mm was irradiated with a CO ₂ laser 3 and was taken up by a capstan 7 at a drawing speed of 1 m / min and wound on a bobbin 8. At that time, the converter 4 was operated to change the drawing temperature to 2200 to 1900 ° C. in a 10-minute cycle (converted to a drawing tension, 1 g to 20 g in a 10-minute cycle). An ultraviolet curable resin was put in the pot 8 and an ultraviolet lamp was used as the curing device 9. The fiber thus obtained has a core diameter
10 μm, clad diameter 125 μm, coating thickness 37.5 μm, change in refractive index in the length direction is 0.3-1 in 10 m cycle as shown in FIG.
It was a 0% change. When this fiber was cut every 10 m and used as a pigtail for a semiconductor laser, the coupling efficiency was about 55%, which was excellent.

(Effect) As described above, the present invention forms a preform having a glass layer for cladding having a softening temperature lower than the softening temperature of the core on the glass rod for core into a fiber while changing the drawing tension. Therefore, it is possible to obtain a fiber in which the stress is applied to the core, and thus a fiber in which the refractive index of the core periodically changes in the length direction can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus used in the method of the present invention, FIG. 2 is a graph showing a relative refractive index difference in the length direction of a fiber obtained by the method of the present invention, and FIG. 3 is a ratio with respect to a drawing temperature. It is a graph which shows a refractive index difference. In the figure, 1: optical fiber preform, 3: CO ₂ laser, 4: AO converter.

Claims (1)

(57) [Claims] 1. An NA conversion, wherein an optical fiber preform having a glass for cladding having a softening temperature lower than that of the glass for core is formed on the outside of the core glass while changing the drawing tension at a predetermined cycle. Optical fiber manufacturing method.