JPH01298037A - Production of na-conversion optical fiber - Google Patents

Abstract

PURPOSE:To easily obtain the title NA-conversion optical fiber wherein the refractive index of the core is periodically changed in the longitudinal direction by forming a clad glass having the softening temp. lower than that of a core glass on the outside of the core glass, and drawing the glasses while changing the drawing tension at a specified cycle. CONSTITUTION:The clad glass having the softening temp. lower than that of the core glass is formed on the outside of the core glass to form an optical fiber preform. The preform is then drawn while changing the drawing tension at a specified cycle to obtain an NA-conversion optical fiber. As the means for changing the drawing tension, the drawing temp. is changed, for example, while fixing the drawing rate. Since the low-softening-temperature glass is used as the clad glass, all the stress during the drawing is exerted on the core, and an optical fiber wherein the refractive index of the core is periodically changed in the longitudinal direction can be obtained.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention is based on
Concerning the manufacturing method of A conversion type optical fiber, different N
A length of approximately several hundred cm is provided, which is suitable for coupling with the optical components of A, optical waveguides, and fibers.

(Prior art) As a manufacturing method for this type of optical fiber, 5iC14 as a main raw material gas and GeC1n as a dopant gas are supplied into an oxyhydrogen flame and flame hydrolyzed to produce SiO□ glass containing Ge as a dopant. Porous glass whose refractive index changes in the length direction by changing the amount of GeCl4 as a dopant gas at predetermined intervals when fine particles are generated and deposited as a porous glass preform at the tip of a rod. A glass preform was made, and this preform was made into transparent glass and then drawn to obtain an NA conversion type fiber whose refractive index changes in the length direction.

(Problem to be solved by the invention) However, in such a method, the NA changes at the preform stage, and when the fiber is drawn after that, the refractive index difference in the length direction is 0.3 to 1%. In order to change the length, a length of about 10 km was required, and it was not possible to obtain a shorter length.

[Means for Solving the Problems] In view of the above, the present invention provides an optical fiber preform in which a cladding glass having a softening temperature lower than that of the core glass is formed on the outside of the core glass, and this is drawn. The wire is drawn while changing the tension at a predetermined period. Specifically, as a means for changing the drawing tension, for example, changing the drawing temperature while keeping the drawing speed constant is mentioned.

(Function) Generally, the refractive index of the medium changes depending on stress, so the composition of the cladding is made to be considerably lower than the softening temperature of the core, and the drawing temperature is set to be equal to or around the softening temperature of the core. When drawn at a temperature of '', Talarad glass is completely softened and all the tension is applied to the core. If the cladding cools while stress is still applied to the core, the stress in the core remains. As a result, the core remains in tension and its refractive index decreases. If the drawing temperature is higher than the softening temperature of both the core and cladding, no stress will be applied to the core, so the refractive index will not change.Thus, if the drawing is done at a temperature where no stress is applied to the core and no stress is applied to the cladding, the refraction of the core will change. A fiber is obtained whose modulus varies along the length.

By the way, we prepared a preform whose core material was pure silica and whose cladding material was F-doped silica (Δ=0.7%), and investigated the relationship between the drawing temperature and the relative refractive index difference Δ between the core and cladding, as shown in Figure 3. As shown in the graph shown in ().As is clear from this graph, as the drawing temperature increases, the relative refractive index difference between the core and cladding increases, and at 100℃
It can be seen that Δ changes by 0.2% with respect to the change in .

(Example) FIG. 1 is a schematic diagram of an apparatus used in the method of this invention. In the figure, l is a core-clad optical fiber preform supported rotatably and vertically, and the softening temperature of the core is higher than that of the clad. 2 is a heat source for irradiating the lower end of the preform 1 to make the preform into a fiber; CO□ laser 3;
02 AO converter 4 for controlling the optical power of the laser 3
, collimator lens5. 67, which consists of the focusing lens 6, is a capstan for drawing the preform l into the fiber 10; 8 is a thermosetting resin for coating the fiber IO; a pot containing an ultraviolet curable resin; 9 11 is a device for curing the resin coated on the fiber 10 and includes a resistance heating furnace, an ultraviolet lamp, etc. 11 is a bobbin for winding the fiber 10. In the above configuration, the preform 1 is VA
A GeO□ doped quartz rod (Δ=1.%) made by method D was jacketed with Pyrex glass, and CO2 was placed at the lower end of preform I with a core rod diameter of 1 ++on and a cladding outer diameter of 12.5 mm. The wire was irradiated with a laser 3, and drawn by a capstan 7 at a drawing speed of 1 m/min, and wound onto a bobbin 8. At that time, the converter 4 was operated to change the drawing temperature from 2200 to 1900° C. in 10 minutes (converted to drawing tension, 1 g to 20 g in 10 minutes). Note that the bot 8 contained an ultraviolet curing resin, and the curing device 9 used an ultraviolet lamp. The fiber thus obtained had a core diameter of 1 μm and a cladding diameter of 125 μm.
m, coating thickness 37.5 μm, refractive index change in length direction is second
As shown in the figure, it changed by 0.3 to 1.0% in a 10 m period. When this fiber was cut into sections of 10 m and used as a pigtail for a semiconductor laser, the coupling efficiency was approximately 55%, which was excellent.

(Effects) - As described above, in this invention, a preform in which a glass layer for crazing having a softening temperature lower than that of the core is provided on a glass rod for a core is made into a fiber while changing the drawing tension. Because of this, it is possible to obtain a fiber in which the core remains under stress, and thus a fiber in which the refractive index of the core changes periodically in the length direction can be obtained.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the apparatus used in the method of this invention, Figure 2 is a graph showing the relative refractive index difference in the longitudinal direction of the fiber obtained by the method of this invention, and Figure 3 is the ratio to drawing temperature. It is a graph showing a refractive index difference. In the figure, 1: optical fiber preform, 3: CO□
Laser, 4: AO converter. Fig. 1 Fig. 2 Tree length Ugly Fig. 3 Drawing line Temperature (°C)

Claims (1)

[Claims] A method for manufacturing a NA conversion optical fiber, comprising drawing an optical fiber preform in which a cladding glass having a softening temperature lower than that of the core glass is formed on the outside of the core glass, while changing the drawing tension at a predetermined period. .