JPH0281004A - Optical fiber and its manufacturing method - Google Patents

Abstract

PURPOSE:To obviate remaining of internal stress at the time of forming a fiber and to obtain the low-loss fiber by providing 1st and 2nd clads which are successively increased in softening temp. to the outer side of a core essentially consisting of quartz glass. CONSTITUTION:A quartz glass rod 1 for the core doped with germanium is rotated at 40rpm and prescribed amts. of SiCl4 and Ar, H2, O2 are supplied by a quadruple-tube burner 2 to deposit a fine SiO2 glass particle layer 4 on the rod by a flame 3. This layer is vitrified to transparent glass in an atmo sphere furnace kept at the max. high temp. of 1,620 deg.C to form the 1st clad higher in the softening temp. than the core. The SiO2 glass articles are again deposited thereon and are put into a quartz muffle tube 5. The conditions are slightly changed and the 2nd clad having the higher softening temp. than the softening temp. of the 1st clad is formed. Remaining of the stress in the fiber is obviated if this rod is drawn to make the fiber.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an optical fiber and a method for manufacturing the same, and in particular relates to a low-loss optical fiber. For external attachment, there is a method in which a core clad type base material is manufactured by a method, and this is drawn to form a fiber.

(Problems to be Solved by the Invention) However, in recent years, as the loss of optical fibers has been reduced, even extremely small causes of loss have become problematic. One of them is the problem of residual stress depending on the drawing method in the fiber.

For example, if there are parts of the fiber with different softening temperatures, the parts with higher softening temperatures will be pulled out of the drawing furnace and solidified first. However, the portion where the softening temperature is low still has a low viscosity. As a result, tensile stress during wire drawing is applied only to the portions where the softening temperature is high, resulting in elastic strain.

Other parts of the fiber also solidify as the fiber runs for a while, but the parts that have undergone elastic strain first and have a high softening temperature cannot relax the stress immediately because of the viscosity of the part that solidified later. A significant portion of the stress will remain. Another type of residual stress is caused by a mismatch in thermal expansion coefficients.

In other words, even if the softening temperature of all parts of the fiber is the same, if the coefficient of thermal expansion of a particular part is larger than that of other parts, the softening temperature of the fiber will change from about 1400°C to room temperature after exiting the drawing furnace. This part tries to contract significantly. Specifically, in normal fibers, this part is often the core part that contains a large amount of germanium as a dopant, and as a result, this core part with a large coefficient of thermal expansion will retain tensile strain after drawing. Fluctuations in the refractive index of the glass increase, resulting in an increase in fiber loss.

As a result of the above considerations, optical fibers experience an increase in loss when the glass in the cladding is very close to the core glass or when tensile strain remains in the core glass. By making the glass extremely uniform, we ensure that unnecessary tensile strain during drawing does not remain in any specific local area of the cladding. It is conceivable that the thermal distortion of the core caused by the addition of dopants can be simultaneously canceled by utilizing this.

However, it is not necessarily advantageous in terms of manufacturing costs to make a cladding portion with a very large cross-sectional area completely uniform.

(Means for Solving the Problems) Therefore, in the present invention, +11 core glass contains a dopant and has a relatively low softening temperature.

(2) A small amount of glass having a softening temperature lower than that of the outer cladding is placed around the core glass as the cladding glass in the vicinity of the core by changing the glass composition to a degree that hardly changes the refractive index of the glass.

(3) A glass having a higher softening temperature than the glass in (2) above is used as the second clad glass.

At this time, the cross-sectional area of the second clad glass is
, +21.

Note that third and fourth clad glasses are provided as necessary. In this case, the present invention prepares a quartz glass base material in which the softening temperature of the glass gradually increases from the center to the outside, and draws it to form a fiber. 1.Means for adjusting the softening temperature of quartz glass include metal oxides such as germanium, phosphorus, and boron, anions such as fluorine and chlorine, and oxygen. The refractive index that makes up the wave furnace. The perspective power of adjustment, the core is ge,'P,
The cladding contains metal oxides mainly composed of sea urchins, anions,
Oxygen is added. In that case, since the thickness of the cladding is sufficiently thick, the amount of anions and oxygen added in multiple layers is decreased sequentially from the inside to the outside, so that their softening temperature increases sequentially from the inside to the outside. I will make it happen. However, the refractive index is almost the same, that is, about ±0.02%.

(Example) Diameter 51 containing 5 wt% germania was obtained by VAD method.
, a SiO□ glass rod for the core with a length of 30 holes ff111 is prepared, and the external parts shown in Fig. 1 are attached around it according to the law.
In Figure 1, SiO□ porous glass particles are deposited to a thickness of 2 ran+, 1 is a 5102 glass rod for the core doped with Ge0g and rotated around its axis at 4 Orpm. 2 is 20017 in the axial direction of the core rod 1
A quadruple tube burner traversed at a speed of 5iC140,:l! from the center outwards. 7 minutes.

ArO, 5j2/min, H, 6J2/min, 01lOI2/
5ft glass particles are produced by the flame 3. 4 is a 5ift glass particle layer deposited around the rod l. 6 Next, the rod on which this SiO□ porous glass particles are deposited is shown in Fig. 2. The maximum temperature is 162
1011II! in an atmosphere furnace at 0°C, C12 concentration 0.5%, and helium 99.5%! It was introduced at a rate of 1/min to make it transparent and vitrified to a thickness of 10 m containing 0.3% C1.
A rod with an outer diameter of 25 fool and a first cladding glass of m was obtained. In FIG. 2, 5 is a quartz pine full tube, and 6 is an atmospheric gas supply port provided at the bottom of the quartz pine full tube 5.

7 is a gas exhaust port, and 8 is a heater. Next, on the rod on which the first cladding layer is formed, SiO□ porous glass fine particles are deposited again by the external method shown in FIG. I let it happen. The conditions at this time were the same as when obtaining the first clad glass.

Next, the rod on which the SiO□ porous glass particles were deposited was made into transparent vitrification using the furnace shown in Figure 2, and 0□ was 1%
The rod had an outer diameter of 60 mm and had a second cladding glass with a thickness of 17.5 mm. The condition at this time is the first
The procedure was the same except that the type of atmospheric gas in the furnace was changed to 99% helium and 0□1% helium compared to when obtaining the clad glass. The obtained rod was drawn at 2050°C to have a core diameter of 10.5 μm and a first cladding diameter of 65 μm.
, a fiber with a second cladding diameter of 125 μm was obtained.

Immediately after this fiberization, an ultraviolet curing resin was applied to a thickness of 62u+++ for reinforcement. Figure 3 shows the estimated values of the viscosity of the obtained fiber at a temperature of 1200°C, with the core having a viscosity of approximately 107 poise, the first cladding having a viscosity of approximately 5 x l Q l(1), and the second cladding having a It is a 10th poise, and the viscosity increases sequentially from the center to the outside.The refractive index is 1.463 for the core.
．． The first cladding is 1,459, the second cladding is 1.
Furthermore, FIG. 4 shows an investigation of the loss wavelength characteristics of the fiber. In the figure, (a) shows the loss wavelength characteristics of the fiber of the present invention, and (b) shows the loss wavelength characteristics of the fiber according to the conventional method in which the softening temperature of the cladding glass is not adjusted.

It is of low loss.

In the above embodiments of the present invention, the cladding is made of multiple layers,
An example was shown in which the residual amounts of chlorine and oxygen were adjusted.
The material is not limited to this, and similar effects can be obtained by doping with fluorine, phosphorus, or germanium.

(Effects of the Invention) As described above, in this invention, the softening temperature of an optical fiber rod is made to gradually increase from the center to the outside, so that when this rod is turned into a fiber, stress remains inside. Therefore, a fiber with low loss can be obtained.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams showing one step in an embodiment of the present invention, FIG. 3 is an explanatory diagram showing the viscosity of the fiber according to the present invention in the cross-sectional direction, and FIG. 4 is an explanatory diagram showing the viscosity of the fiber according to the present invention. 1 is a graph showing loss wavelength characteristics of a conventional fiber. In the figure, l nigermania doped core rod, 4
: 5i02 glass fine particle layer, 5: quartz pine full tube, 6: atmospheric gas supply port. Figure 1

Claims (2)

[Claims] (1) An optical fiber mainly composed of silica glass, including a core that contains at least one kind of metal oxide as a dopant and has a higher refractive index than silica glass, and a core that has a softening temperature higher than that of the core. , comprising a first cladding whose refractive index is approximately equal to that of silica glass, and a second cladding whose softening temperature is higher than that of the first cladding and whose refractive index is approximately equal to that of silica glass. optical fiber. (2) SiO_2 glass particles are deposited around the germania-doped quartz glass rod for the core, and then this is made into transparent vitrification in an anion or oxygen atmosphere to form a first cladding layer, and then a first cladding layer is formed on top of it. SiO_
2. After depositing the glass particles, the first cladding layer is made into a transparent vitrification in an anion or oxygen atmosphere to form a second cladding layer containing a larger amount of anions or oxygen than the first cladding layer. A method of manufacturing an optical fiber, comprising drawing a rod having a second cladding layer.