JPS6340744A - Optical fiber - Google Patents

Abstract

PURPOSE:To provide a low-loss optical fiber which can maintain a transmission characteristic stable for a long period of time in a hydrogen atmosphere by using core glass added with an extremely slight amt. of an alkaline (earth) metal as a hydrogen resisting agent to form the fiber. CONSTITUTION:A clad 1b having the refractive index lower than the refractive index of a core 1a consisting of the core glass formed by adding 3-10wt% dopant such as GeCl4, POCl3 or BBr3 and 0.001-15ppm alkali metal such as Li, Na, K, Rb or Cs and/or alkaline earth metal such as Mg, Ca, Sr, or Ba as the hydrogen resisting agent to a glass raw material such as; for example, SiCl4 is integrally provided to the outside of the core 1 consisting of the quartz glass, etc., and further, soot of fine particles made of synthetic quartz glass is deposited by an external deposition method, etc., to the outside thereof to form a jacket 2, by which a preform is obtd. The transparent base material vitrified by heating such preform to about 1,500 deg.C is then heated and drawn.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an optical fiber that can maintain stable transmission characteristics over a long period of time in a hydrogen atmosphere.

"Prior Art and Its Problems" Optical fibers made of quartz glass or the like are currently used as optical communication lines, for example, because they are low-loss leading waveguides.

In recent years, as optical communication networks have been developed and expanded, there has been a trend toward longer optical communication lines, and as a result, the optical fibers used in these lines are required to have even higher levels of low loss. It is being done.

Therefore, in the case of conventional optical fibers, loss can be reduced by removing impurities such as metal ions and hydroxide ions as much as possible from the quartz glass, which is the material forming the optical fiber, to increase the purity of the silica glass. I'm trying to figure it out.

Incidentally, although such optical fibers have achieved low loss properties that are sufficient to meet the above requirements, if they are exposed to a high concentration hydrogen atmosphere for a long period of time, this light Even though the silica glass forming the fiber is inert, hydrogen may be gradually absorbed from the surface of the optical fiber and gradually diffused into the core. Hydrogen diffused into the core, which is the optical transmission path, is
■Absorbs the light propagating in the core by itself, ■Acts on the G e Ot of the dopant added to the core, disturbs the electron orbit of the bonding part of this dopant, and changes the electron absorption characteristics of the bonding part. Alternatively, it combines with oxygen to form a hydroxyl group, which changes the infrared absorption characteristics due to the molecular vibration of the hydroxyl group, thereby changing the transmission amount and transmission mode of light propagating through the optical fiber.As a result, the optical fiber transmission loss was increased.

``Means for solving the problem'' Therefore, in view of the above circumstances, Inventor et al., as a result of intensive studies, found that by adding a trace amount of alkali metal and/or alkaline earth metal to the core glass, These metals prevent absorption and diffusion of hydrogen into the optical fiber over a long period of time, and also prevent the above-mentioned loss increasing effect due to hydrogen, making this optical fiber a low-loss fiber that is stable against hydrogen. I found something to do. That is, the optical fiber of the present invention is characterized in that an alkali metal and/or alkaline earth metal is added to the core glass in a range of 0.01 to 15 ppm.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of an optical fiber according to the present invention, and reference numeral 1 in the figure indicates an optical fiber.

This optical fiber 1 consists of a core La and a cladding 1b. Core LA uses glass raw materials such as 5iCQ as the main raw material, and GcC is added to this. , POCQ3, r3
It was formed by adding a dopant such as 13r3. The content of the dopant in the core la is determined depending on the refractive index difference required for the optical fiber 1, but is usually 3 to 10% by weight.

Furthermore, a hydrogen resistant agent is added to the core Ia to prevent hydrogen from bonding with oxygen in the core la to form hydroxyl groups, which causes increased loss, and to volatilize and remove hydrogen. Such hydrogen resistant agents include Ll, Na,
, alkali metals such as Rb and Cs, Mg, Ca, 5r
Examples include alkaline earth metals such as XBa, or combinations of these alkali metals and alkaline earth metals, and these hydrogen resistant agents are present in an ionic state in the core Ia. The amount of the hydrogen resistant agent added to the core Ia is in the range of 0.001 to 15 ppm. If it is less than 0.0'lppm, it is too small to have any effect of adding the hydrogen resistant agent, and the transmission loss of the optical fiber 1 increases significantly due to the hydrogen contained in the core Ia. Furthermore, if it exceeds tsppm, it is too much and not only does the effect of adding the above-mentioned hydrogen resistant agent reach a ceiling, but also the transparency of the core la decreases and the amount of transmitted light propagating within the core la also decreases. This will cause some inconvenience. Also,
The mixing ratio of the alkali metal and alkaline earth metal in the hydrogen resistant agent is appropriately determined depending on the transmission characteristics required of the optical fiber 1, the types of the alkali metal and alkaline earth metal, and the like.

A cladding lb is integrally provided on the outside of such a core la. The cladding Ib is made of quartz glass or the like having a lower refractive index than the core 1a, and its outer diameter is usually about 9 to 50 microns.

On the outside of the optical fiber 1 having such a configuration, a jacket 2 is provided to protect the tip of the fiber <l. This jacket 2 is formed by covering a cylindrical tube made of natural quartz glass or synthetic quartz glass, or by depositing soot on the surface of the clad lb.

Next, a method for manufacturing this optical fiber 1 will be explained. First, a porous glass preform is manufactured by a conventional method such as the VAD method. Next, this porous glass preform is stretched to a predetermined outer diameter, and then the surface of the glyph 4-- is etched using a surface treatment agent such as hydrofluoric acid to create irregularities on the treated surface. form and increase its surface area.

Next, this preform is sufficiently immersed in, for example, a sodium chloride aqueous solution of a predetermined concentration, and then the cladding surface of this preform is heated to about 1500 to 160 ml with an oxyhydrogen flame burner.
It is heated to about 0°C to allow sodium (hydrogen resistant agent) to permeate through the cladding surface and diffuse into the core. Here, as a method for adding the hydrogen resistant agent to the core, in the case of a hydrogen resistant agent that moves at a high speed within the core and cladding, such as the above-mentioned sodium, the immersion method described above can be used.
In the case of a hydrogen resistant agent such as an alkaline earth metal that has a low movement speed, the method for adding the hydrogen resistant agent using the phase method is as follows: First, the above porous glass is stretched to a predetermined outer diameter. The preform is placed in a sintering furnace together with a high purity alkaline earth metal salt (hydrogen resistant agent).

Next, a predetermined amount of vaporized gas obtained by heating the metal salt to a predetermined temperature is applied to a porous glass preform heated to a predetermined temperature together with a carrier gas consisting of an inert gas such as He gas or 7\r gas. By flowing over the surface, the metal penetrates through the cladding surface of the preform and gradually diffuses into the core.

Next, synthetic quartz glass soot is deposited on the cladding surface of the preform thus obtained by an external method to form a deposited layer. Next, this preform is heated to about 1500° C. to obtain a transparent vitrified optical fiber preform, and this optical fiber preform is further heated and drawn to obtain the desired optical fiber 1.

The optical fiber 1 thus obtained has a core la,
Alkali metal and or alkaline earth metal (1,0
The added alkali metal and/or alkaline earth metal suppresses the formation of hydroxyl groups due to hydrogen diffusing into the optical fiber and pushes the hydrogen to the outside. When it is dispersed, it becomes immersed in hydrogen resistance. Therefore, since this optical fiber 1 has excellent hydrogen resistance, it has a stable low loss property over a long period of time in a hydrogen atmosphere.

Hereinafter, the effects of this invention will be clarified by showing experimental examples.

"Experimental Example" (Experimental Example 1) A non-glue mode type porous glass preform was manufactured by the VAD method. This porous glass preform is made by doping S i 02 with G e 02, making it the core, and forming the cladding from 9102.
The core diameter was about 178 times the cladding diameter, and the relative refractive index difference Δ between the core and the cladding was about 0.3%. Then,
This porous glass preform was subjected to low elongation treatment so that the cladding diameter was approximately 15 mm, and then the surface of this preform was etched with a surface treatment agent such as hydrofluoric acid.

Next, the preform is immersed in a sodium chloride aqueous solution of about 1009/2 for about 5 minutes, and then the cladding surface of this preform is heated with an oxyhydrogen flame burner to about 1500 to 1500 liters.
It was heated to about 100°C to infiltrate sodium from the cladding surface. Next, a synthetic quartz glass soot was deposited on the cladding surface of the above preform by an external method to cover the jacket, and then heated to about 1500°C to make it transparent vitrified to produce an optical fiber base material. . Next, this optical fiber base material was further heated and drawn, and a two-layer coating of a modified Noricone resin coat (inside) and a Noricone resin coat (outside) was applied on the outer periphery to produce a tip fiber.

- (Hydrogen resistance test) A hydrogen resistance test was conducted on the optical fiber thus obtained. In this test, the optical fiber described above was housed in a sealed device, the device was made into a 100% hydrogen atmosphere, the temperature was set to various values, and the change in loss increase over time at each set temperature was measured. According to this test, from the above relational expression expressing the change in loss increase over time at each lj and degree, starry sky 2 in a 100% hydrogen atmosphere.
It is possible to predict the increase in loss after 25 years at 0°C.

Then, the above temperature conditions were set to 100℃, L50℃, and 200℃.
°C, measure the increase in loss at each temperature,
Changes in this increase over time were investigated, and the results are shown in the graph of FIG. This graph shows the amount of loss increase on the vertical axis and the time on the groove axis.The amount of loss increase and time are almost proportional at each temperature, and can be expressed by the following equation (A). .

Qn(Δa) = 12n(A) −(B/T)−←
3.8f2n(t) - (a) In this equation (a), (Δα) is the amount of loss increase, (T) is the temperature, (D is the elapsed time, A and B are each constants, and the second
From the graph in the figure, the loss increase 1 at each temperature 1 hour after the start of 111 constant was determined, and the constants A and B were determined by substituting the values into the above equation (a). Then (
b) Warm! 7T = 20 (°C), time (t) =
By substituting 9t)O(hr)-C25 years] into 2 and 2 in a 100% hydrogen atmosphere and at a temperature of 20°C.
The loss increase 1 after 5 years has been calculated. As a result, the increase in loss of this optical fiber was G, G (lldB/km) at a wavelength of 1.3 μm.

This value was an increase of about 1710 compared to conventional optical fiber.

(Experimental Example 2) Obtained in Experimental Example 1, and after being stretched, the cladding diameter was approximately 1
A porous glass preform with a shoulder length of 5 m was placed in a sintering furnace together with high-purity magnesium chloride. Then,
Magnesium chloride is heated to a temperature of 400°C to vaporize it, and this vaporized gas is heated to about 800°C together with He gas.
Magnesium was allowed to permeate through the cladding surface of the preform by flowing it onto the surface of the porous glass preform that had been heated to a certain temperature. The above vaporized gas and He
The combination ratio with gas was t:lCOO. Next, in the same manner as in Example 1, the cladding surface of this preform was coated with a shark throat, and then the preform was made into transparent glass and subjected to heating and drawing steps to produce a tip fiber. and,
From now on, the fiber is exposed to 100% hydrogen atmosphere and at a temperature of 2.
The increase in transmission loss m after 25 years under 0°C conditions was 0.001 dB/km at a wavelength of 1.3 μm, which was an increase in transmission loss of about 1710 compared to conventional optical fiber. .

"Effects of the Invention" As explained above, the optical fiber of the present invention has a core glass doped with an alkali metal and/or an alkaline earth metal in a range of 0.01 to 15 ppm. The metal prevents the absorption and diffusion of hydrogen into the optical fiber over a long period of time, and also prevents the hydrogen from increasing its loss, thus creating a stable, low-I element for hydrogen over a long period of time. Become something.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of the optical fiber of the present invention, and FIG. 2 is a graph showing changes over time in the amount of loss increase in the optical fiber of the present invention in a hydrogen atmosphere.

Claims (1)

[Claims] An optical fiber comprising a core glass doped with an alkali metal and/or an alkaline earth metal in a range of 0.01 to 15 ppm.