JPH0737336B2 - Optical transmitter - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical transmission body containing silica glass as a main component.

[Prior art]

Today, optical transmitters are used and applied not only in public communication but also in various fields. As the field of application expands, the required characteristics of the optical transmitters are becoming stricter. For example, one of the characteristics that hydrogen resistance is becoming severe,
In order to improve these characteristics, for example, attempts have been made to reduce the amount of phosphorus added to the core of a SiO ₂ -GeO ₂ -based optical transmission medium to zero. However, the mechanism by which the hydrogen resistance is improved has not been fully elucidated, and the control points in manufacturing have not been elucidated to this day.

[Object of the Invention]

In view of the above problems, an object of the present invention is to clarify a method for improving the hydrogen resistance of an optical transmission medium, and to provide an optical transmission medium excellent in hydrogen resistance.

[Structure of Invention]

In order to achieve the above-mentioned object, the present invention provides an optical transmission body containing silica glass as a main component, wherein the sum of the weight concentrations of alkali elements and alkaline earth elements contained in the light propagating portion of the optical transmission body is 5 p.
It is characterized by being less than or equal to pb.

Example of Invention

Embodiments of the present invention will be described in detail below with reference to the drawings.
The present inventor conducted the following experiment in order to improve the hydrogen resistance of the optical transmission medium. First, a core rod having a GI type refractive index distribution (composition is SiO ₂₎ by the VAD method, that is, the flame hydrolysis method.
-GeO ₂ , Δ ⁻ = 1%) was prepared and divided into three,
One of them was jacketed with a synthetic quartz tube synthesized by the OVD method or the like to form a clad portion. At this time, the outer diameter ratio of the two was core: clad = 50: 125. By drawing this and coating with silicone resin at the same time, the core diameter is 50 μm, the cladding diameter is 125 μm, and the coating diameter is 380 μm as shown in FIG.
The optical transmission body 1 of was obtained. Here, reference numeral 2 is a core, reference numeral 3 is a clad constituted by a synthetic quartz tube as described above, and reference numeral 4 is a coating.

When the core 2 of the light transmitter 1 was analyzed by secondary ion mass spectrometry, almost no impurities were found. Since the lower limit of detection of this analysis method is about 1 ppb, it can be presumed that it is less than that, even if impurities are present.

Next, 0.03% sodium chloride aqueous solution is applied to one of the remaining two core rods, a synthetic quartz tube of the same type as the above is jacketed by the same method, and then this is drawn and coated. The optical transmission body 1 as shown in FIG. 2 was obtained.
When the composition of the core 2 portion was examined by secondary ion mass spectrometry in the same manner as described above, 0.07 ppm of sodium was found.

Similarly, a high concentration of 0.1% sodium chloride aqueous solution is applied to the third core rod, a synthetic quartz tube of the same type as the above two is jacketed in the same manner, and the same method is used as shown in FIG. The optical transmission body 1 was obtained. When the core 2 portion of this optical transmitter 1 was analyzed by secondary ion mass spectrometry, 0.2 ppm of sodium was found.

The above three types of GI type optical transmitters 1 were placed in a hydrogen atmosphere at 200 ° C.
Exposed for hours. As a result, each showed an absorption peak value estimated to be caused by a GeOH group at a wavelength of 1.41 to 1.42 μm. A summary of these results is shown in FIG. As shown in FIG. 1, the absorption peak value increased as the amount of sodium in the core 2 increased.

Based on this result, the present inventor estimated as follows.
That is, sodium existing at the interface between the core 2 and the clad 3 disturbs the SiO ₂ —GeO ₂ glass structure, and particularly generates a precursor of defects related to germanium, and in this state, it is exposed to a hydrogen atmosphere at 200 ° C. It was inferred that upon exposure, the precursor of the defect reacts with hydrogen to generate a GeOH group, which causes a problem of increased transmission loss due to hydrogen.

Next, as shown in Fig. 1, it is about 2d even if sodium is less than 1ppb.
The increase of B / km loss is observed, and it is presumed that the cause is the intrinsic defect of SiO ₂ -GeO ₂ glass, not the one of sodium. So the sodium concentration is 10
As a result of investigating the behavior below ppb again, the arrow (5
ppb), the loss increase is about 2 dB below 5 ppb.
It was found to be almost constant as / km, and beyond this, it was found that the loss increases in proportion to the sodium weight concentration in the core.

From the above results, the present inventor has an important finding that the loss increase due to hydrogen can be prevented by reducing the sodium contamination in the part of the clad 3 inside the core 2 and in the vicinity of the core 2, that is, the light propagating portion to 5 ppb or less. Came to get.

By the way, it is a method of setting the content concentration of sodium in the core to 5 ppb or less. For example, a core rod prepared by the VAD method is immersed in a 5% hydrogen fluoride aqueous solution for about 5 minutes in advance, and this is highly purified (ion exchange + After thorough washing with distilled water, the synthetic quartz tube, that is, the VAD method, O
The synthetic quartz tube produced by the VD method or the plasma method was jacketed, or the clad portion was immediately deposited on the outer periphery of the core rod cleaned as described above by the OVD method, and the deposited portion was dehydrated. There is a method to make it transparent. All of these operations must be performed in a clean atmosphere with a cleanliness of 100 to 1000. The reason is that the core rod surface or the clad surface is contaminated by sodium, potassium, etc. in the air simply by leaving it in the air.

So far, only sodium has been described, but due to its properties, lithium, potassium, rubidium, cesium,
The same can be said for alkaline elements such as calcium or magnesium, and alkaline earth elements, and the total sum must be 5 ppb or less. Also, regarding the composition of the core 2, in addition to the SiO ₂ -GeO ₂ system glass, SiO ₂ glass or SiO _{2 -F}
The same applies to the system glass.

As described above, the hydrogen resistance of the optical transmission element is remarkably improved by setting the sum of the concentrations of the alkali element and the alkaline earth element in the light propagating portion, that is, the core portion and a part of the clad adjacent to the core, to 5 ppb or less. It became possible to do.
In addition, when the radiation resistance of the optical transmission article of the present invention was investigated, it was also found that the characteristics were improved. The reason is presumed to be the result of reducing the alkali elements and alkaline earth elements that disturb the glass structure as well as the hydrogen resistance.

〔The invention's effect〕

As described above, according to the present invention, it is possible to minimize the increase in hydrogen loss resistance of the optical transmission body.

[Brief description of drawings]

FIG. 1 is a graph showing the experimental results according to the present invention, and FIG. 2 is a transverse sectional view of an optical transmission body. 1-optical transmission body, 2-core, 3-clad

Claims (2)

[Claims] 1. A light transmission body containing quartz glass as a main component, wherein the sum of the weight concentrations of alkali elements and alkaline earth elements contained in the light propagation section of the light transmission body is 5 ppb or less. Optical transmitter. 2. The optical transmission medium according to claim 1, wherein the light propagation portion of the optical transmission medium is made of SiO ₂ --GeO ₂ .