JPS60141643A - Light transmitting material based on quartz glass - Google Patents

Abstract

PURPOSE:To obtain a light transmitting base material based on quartz glass having small difference between refractive index of core and clad and superior flexibility comprising a core made of pure quartz glass and a clad made of quartz glass doped with F and P. CONSTITUTION:A parent material for optical fiber based on quartz glass comprising a core made of pure quartz glass and a clad made of quartz glass doped with F and P having >=0.4 molar ratio of F/p. Since the refractive index of the clad is <=1.4435 and the difference between the refractive index of the clad and the core is >=0.015, the thickness of the clad can be reduced to 1mum, i.e. about 2/2 of the thickness of conventional clad, and the numerical aperature is increased to >=0.21 by using the material. Thus, a light transmitting material based on quartz glass useful as optical fiber, image guide, or image plate, etc. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION More specifically, the present invention relates to a silica glass optical transmission material comprising a core made of pure silica glass and a cladding made of quartz glass doped with fluorine and phosphorus.

For example, optical fibers and image guides (multiple fibers) are known as silica glass-based optical transmission materials, which basically consist of a core that makes up the optical transmission path and a cladding that confines light in the core. Supports are formed around the cladding if necessary. Pure silica glass is usually used for the core in view of heat resistance and light transmission loss. The cladding must have a lower refractive index than the core, and currently fused silica glass doped with boron or fluorine is used.

The larger the difference (Δn) between the refractive index of the core and the cladding, the more light leakage can be prevented even if the cladding is made thinner, and the number of openings can be increased.

Therefore, in order to increase Δn, that is, to decrease the refractive index of the cladding, various fluorine doping methods J:
A cladding made of quartz glass doped with lithium element is formed. For example, a cladding made of silica glass doped with only fluorine is formed from 5iF4 and oxygen, or a cladding made of quartz glass doped with only fluorine is formed from si C1a and a fluorine compound containing at least one of C, S, CI, and B, and oxygen is formed with fluorine and c, s, or A cladding made of quartz glass doped with B is formed.

However, it is extremely difficult to dope silica glass with fluorine, and the method described above can only dope a small amount of fluorine. From this point of view, the refractive index (1,4585) of pure silica glass can only be lowered by about 0.012 at most. Δn is 0
．． At around 0.012, light leakage cannot be prevented unless the cladding is set to 1ρ or more, and the numerical aperture is also 0.19 Pi! It can only be done once in a while.

As a result of extensive research, the present inventors have found that silica glass doped with fluorine and phosphorus, which is formed using a fluoride of phosphorus as a dopant precursor for silica glass, is smaller within a practical range. It was discovered that the material has a refractive index, and the present invention was completed.

That is, the present invention relates to a silica glass-based optical transmission material comprising a core made of pure silica glass and a cladding made of quartz glass doped with fluorine and phosphorus.

The cladding in the present invention has a refractive index of L4435 or less, and the difference in refractive index (Δn) between the core and the cladding is 0.0.
15 or more. Further, the fluorine/phosphorus ratio doped into the silica glass of the cladding is 0.4 or more.

As mentioned above, the silica glass of the cladding is doped with phosphorus as well as fluorine. Although this phosphorus acts to increase the refractive index of silica glass, the degree of this action is very small compared to the refractive index lowering effect of fluorine, and does not impair the refractive index lowering effect of fluorine.

According to the present invention, since Δn is 0.015 or more, the thickness of the cladding can be reduced to 11 Im, about half of the conventional thickness, and the numerical aperture can be further increased to 0.21 or more.

The optical transmission material of the present invention includes optical fibers, image guides,
It can be used as an image plate, etc. In particular, when the optical transmission material of the present invention is used in a quartz glass image guide made by fusing a large number of optical fibers, the outer diameter of the image guide itself can be significantly reduced because the cladding can be made thinner. , its flexibility can be greatly improved.

The optical transmission material of the present invention is produced by fabricating a silica glass optical fiber base material consisting of a core and a cladding by conventionally known external @, internal, rod-in-tube methods, etc., and then heating and stretching the base material. Manufactured by However, a fluorine compound of phosphorus is used as a dopant precursor when forming the cladding. Examples of phosphorus fluorine compounds include PFs
, PFa, etc. When using PF5 as a precursor, the difference in thermal expansion coefficient between the core and cladding must be within the allowable range [thermal expansion coefficient of pure silica glass core (5X10-7
/'C) and the thermal expansion coefficient of the cladding (2X10-"
/°C)], it is possible to reduce the 80 of the core and cladding to 0.02 or less.

If the base material is drawn individually one by one, an optical fiber can be obtained, and if many fibers are drawn simultaneously, an image guide can be obtained.

Next, an example of manufacturing the optical transmission material of the present invention will be given.

Production Example 1 (Optical Fiber) A pure quartz glass rod with a diameter of 12 mm and a clean surface was heated with a 3-layer quartz glass burner glass and a mixed gas of SLC#4 and oxygen and hydrogen (SLCM4: Ot:H2-
1: 25: 10, 'E/L/ratio) wo 6//min (71
The mixture was injected at a rate of t' and combusted, and the combustion gas was blown. The glass rod is rotated 10 times with a rotary valve, and the burner is 11I1wl.
/min to deposit the Stat soot on the surface of the glass rod. The combustion gas was blown for 200 minutes.

Then, it was heated at about 600°C in a quartz glass tube with an inner diameter of 501IIl.
PF3 gas was passed in parallel for 5 minutes at a flow rate of 0.5127 min through a glass rod with StOt soot maintained at
Vitrification was performed for 1 hour or 1 minute to produce a quartz glass optical fiber base material having a cladding made of fluorine-doped quartz glass.

The thickness of the cladding of the obtained base material was 1.9 mm,
The refractive index was 1.440 (Δn = 0.019).

Further, the fluorine/phosphorus ratio in the cladding was 0.5.

Next, this base material was heated and stretched, with a core diameter of 150 mm and a cladding thickness of 18.7 mm. An optical fiber of m was fabricated.

The Δn of this optical fiber was 0.019, which was the same as 80 in the base material, and the numerical aperture was 0.24.

In addition, the degree of cascading light in this optical fiber was investigated using the following bending loss measuring method. The measurement was performed by connecting a He-4J e laser and a light receiver with a 3711 optical fiber, and when the optical fiber was straight, the output power was <I. > and the output power (11) when the optical fiber was wound 10 times around a mandrel having an outer diameter of 519 m.

As a result, the I of the optical fiber of the present invention obtained in Example 1 was
/Io was 75%, but the I/io of a conventional optical fiber (numerical aperture 0.18) having a cladding of boron=fluorine doped quartz glass was only 55%.

Production Example 2 (Image Guide) The silica glass optical fiber base material produced in Production Example 1 was heated and stretched to an outer diameter of 300. A preform was prepared. 10,000 of these preforms were bundled and filled in a quartz skin pipe in an aligned state, and drawn at about 2,000°C to obtain a core with a core diameter of 5, an average core spacing (cladding thickness > 2.8.ca,
Core occupation rate 40%, quartz skin layer thickness 50f, outer diameter 1,
A 0 mm image guide was manufactured.

Since light leakage reduces resolution, we conducted a resolution test using this image guide.

(Resolution test) An eyepiece lens is placed at one end of a 5m long image guide, and an objective lens with a viewing angle of 20 degrees (focal length 4811) is placed at the other end, and the EIAJ test established by the Electronics Industries Association of Japan is placed at a position 360mm from the objective lens. Place chart A and place the color viewer [DNP model] behind the chart.
-■ (Using 5 inches 7FL-100WX 4)] was placed, and lines that could be visually identified were examined.

As a result, the resolution of the image guide of the present invention obtained in Example 2 was 600 lines/360 nun;
The resolution of the conventional image guide (same as the image guide of Example 2 except that Δn = 0.012 and numerical aperture 0.18) was only 200 lines/360 mII.

Further, in order to evaluate flexibility, this image guide was bent into a loop shape, the diameter of the loop was gradually reduced, and the loop diameter when the image guide broke was determined to be 18IIll.

In addition, a conventional image guide having cores with the same number of trees and the same resolution as Example 2 requires an outer diameter of at least i, 4nv, and its flexibility (loop test) is at most 281111%. There was only one.

Claims (1)

[Claims] 1. A silica glass-based optical transmission material comprising a core made of pure silica glass and a cladding made of quartz glass doped with fluorine and phosphorus. 2. PF is quartz glass doped with fluorine and phosphorus.
2. The optical transmission material according to claim 1, which is formed using s as a dopant precursor. 3. The optical transmission material according to claim 2, wherein the fluorine/phosphorus molar ratio in the cladding is 0.4 or more. 4 The refractive index of the cladding is 0.015 higher than the refractive index of the core.
The optical transmission material according to claim 3, which is smaller than the above. 5. The optical transmission material according to claim 4, wherein the optical transmission material is an image guide.