JP3108210B2 - Fluoride glass optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide for optical amplification (including an optical fiber) mainly used in a relay section of an optical communication system.

[0002]

2. Description of the Related Art An optical communication system includes a light emitting section, a relay section, and a light receiving section, and these are connected by an optical waveguide. The repeater compensates for transmission loss and pulse spread when the signal light to be transmitted propagates in the optical waveguide. Conventionally, the configuration is such that the signal light is once converted into an electric signal, compensated, and then converted into the signal light using a semiconductor laser. However, this method has a drawback that the apparatus is extremely complicated and expensive. Therefore, recently, in order to provide a low-cost relay unit, it has been considered to use a rare earth element as a light emitting source in the relay unit. Specifically, an optical waveguide is manufactured with a core portion made of a host glass doped with a rare earth element,
Attempts have been made to directly amplify signal light having a wavelength of 1.3 μm or 1.55 μm using this optical waveguide. Among these rare earth elements, the single-mode optical waveguide of ZBLAN (ZrF ₄ -BaF ₂ -LaF ₃ -AlF ₃ -NaF) based glass doped with praseodymium (Pr) in the core has a wavelength of
Attention has been focused on amplifying 1.3 μm signal light efficiently.

Usually, this kind of ZBLAN-based fluoride glass optical waveguide has a PbF ₂
On the other hand, the entire cladding is H to reduce the refractive index.
A composition doped with fF ₄ is used.

[0004]

However [0007], Hf in the cladding portion, ZBLAN based fluoride glass optical waveguide Specifically doped HfF ₄ has a clad portion composed of ZBLAN based fluoride glass not doped HfF ₄ There is a problem that the optical waveguide is easily devitrified as compared with the optical waveguide, and the optical waveguide deteriorates due to the devitrification, and breaks during drawing. However,
Hf is generally used as a substance for lowering the refractive index, and its effect has been found to be very large. At present, no substance that lowers the refractive index has been found in place of Hf, so that even if there is some problem, it must be used.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ZBLAN-based fluoride glass optical waveguide which is hardly devitrified during drawing, that is, hard to break. Therefore, according to the present invention, in a fluoride glass optical waveguide in which the clad portion is mainly made of ZBLAN-based fluoride glass and also contains Hf, the outermost layer of the clad portion does not contain Hf. A wave path is provided.

[0006]

[Action] Hf throughout the cladding portion, in the conventional method specifically doping HfF _4, be an amount of HfF ₄ doped into the cladding portion as shown in Comparative Examples 2-4 in Table 1 is trace,
The base material was found to be devitrified by crystallization. The cause of this crystallization is that the doping of HfF ₄ makes the structure of the glass more sparse, which affects the bonding of the glass surface and water, and as a result, the water on the surface of the base material is removed during drawing. This is probably due to the fact that it became impossible to crystallize easily. Therefore, it was possible to suppress the crystallization to show the outermost layer portion of the cladding as a countermeasure to the embodiment was a ZBLAN based fluoride glass not doped HfF _4.

[0007]

Embodiments of the present invention will be described below in detail. As an example, a core rod having an outer diameter of 8 mm was prepared by dissolving a ZBLAN-based fluoride glass doped with 2000 ppm of Pr and 8 mol% of PbF ₂ and casting it into a mold. Then, the core rod was stretched in an inert gas, specifically, an argon gas to obtain a core rod having an outer diameter of 3 mm. In addition, a ZBLAN-based fluoride glass doped with 40 mol% of HfF ₄ was melted and cast into a mold, and then punched to obtain a pipe for an inner layer of a clad having an outer diameter of 15 mm and an inner diameter of 3.5 mm. The core rod is inserted into the cladding inner layer pipe, and integrated by heating to about 300 ° C. in an inert gas, specifically, an argon gas, and thereafter, further stretching is repeated. Thus, a glass base material for an optical waveguide having an outer diameter of 3 mm (the ratio of the inner diameter of the clad layer to the diameter of the core portion was about 10), comprising the core portion and the inner clad layer, was obtained. Also, HfF
After dissolving ZBLAN-based fluoride glass not containing ₄
Casting, drilling this, outer diameter 10.6mm,
A pipe for the outermost layer of the clad having an inner diameter of 4.0 mm was obtained. The glass base material for an optical waveguide was disposed outside in the pipe for the outermost layer of the clad, and this was drawn at a predetermined linear velocity by a rod-in-tube method. At the time of drawing, when the number of breaks of the optical waveguide was investigated and the presence or absence of crystallization was examined by observing the broken part with a transmission electron microscope,
As shown in Table 1, an optical waveguide having a small number of breaks and no crystallization was obtained.

[0008] As a comparative example, 2000 ppm of
A core rod having an outer diameter of 8 mm was prepared by dissolving a ZBLAN-based fluoride glass doped with Pr and 8 mol% of PbF ₂ and casting it into a mold. Next, the core rod is stretched in an inert gas, specifically, an argon gas,
A core rod having an outer diameter of 3 mm was obtained. In addition, HfF ₄ is respectively contained in 0, 0.5, 10, and 40 mol% (compared to Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, respectively). ZBLAN-based fluoride glass is melted and cast into a mold. After that, a drilling process was performed to obtain a pipe for a clad part having an outer diameter of 15 mm and an inner diameter of 3.5 mm. The core rod is inserted into the cladding pipe, and the rod is inserted into an inert gas, specifically, an argon gas.
The substrate was integrated by heating to 300 ° C. to prepare a glass base material for an optical waveguide (clad diameter / core diameter ratio is about 30). These base materials were set in a drawing furnace, and the inside of the furnace was replaced with nitrogen gas, and then heated to about 300 ° C., and the drawing was performed at the same drawing speed as in the example. At this time, when the fracture of the optical waveguide was investigated and the existence of crystals was investigated by the same method as in the example, the results shown in Table 1 were obtained.

As shown in Table 1, the results of the examples and comparative examples show that the HfF ₄ -doped ZBLAN-based fluoride glass optical waveguide has a large number of breaks, and that crystallization occurs at the break points. It was found to be observed. Meanwhile, ZBLAN based fluoride glass optical waveguide entire cladding of Comparative Example 1 clad outermost according to the invention and ZBLAN based fluoride optical waveguide containing no HfF ₄ does not include HfF _4, i.e.,
Both the outermost cladding does not include the HfF ₄ ZBL
No break or crystal was observed only in the AN-based fluoride glass optical waveguide. This also indicates that providing an outermost layer not containing HfF ₄ in the optical waveguide is an effective means to prevent devitrification due to crystallization. In the examples, the clad outermost layer made of the ZBLAN-based fluoride glass not containing Hf is relatively thick.However, the outermost layer is provided by the clad inner layer containing Hf and, for example, in the air. Since the main purpose is to prevent direct contact with moisture, even if it is an extremely thin layer, the effect is sufficient.

[0010]

[Table 1]

[0011]

An object of the present invention is to provide a fluoride glass optical waveguide which is not devitrified and hardly broken at the time of drawing, that is, can be drawn long. According to the present invention, the clad portion is mainly made of ZBLAN-based fluoride glass,
Furthermore, in the optical waveguide containing Hf, a fluoride glass optical waveguide characterized in that a layer not containing Hf is provided as the outermost layer of the clad portion can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical waveguide according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an optical waveguide according to a comparative example of the present invention.

[Explanation of symbols]

1 core part 2 clad inner layer made of ZBLAN-based fluoride glass containing Hf (Example) or clad part (comparative example) 3 clad outermost layer made of ZBLAN-based fluoride glass containing no Hf

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01S 3/07 H01S 3/07 3/17 3/17 (56) References JP 5-323132 (JP, A) JP Hei 4-342441 (JP, A) JP-A-63-157110 (JP, A) JP-A-63-107841 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 13 / 04 C03B 19/02 C03B 37/012 C03C 3/32 G02B 6/00 376 H01S 3/07 H01S 3/17

Claims (1)

(57) [Claims] A cladding portion covering the core portion and having a refractive index smaller than the refractive index of the core portion;
The cladding is mainly made of ZBLAN (ZrF ₄ -BaF ₂ -LaF ₃ -AlF
₃ -NaF) -based fluoride glass and hafnium
An optical waveguide also containing (Hf), wherein the outermost layer of the cladding portion does not contain Hf.