JPH06100331A - Fluoride glass optical waveguide - Google Patents

Abstract

(57) [Summary] (Correction) [Constitution] Mainly composed of ZBLAN fluoride glass,
In a fluoride glass optical waveguide containing Pb in the core portion 1 and Hf in the cladding portion 2, the portion of the cladding portion adjacent to the core portion is made of ZBLAN-based fluoride glass containing neither Pb nor Hf. It is characterized in that the fluoride glass optical waveguide or the cladding portion is made of ZBLAN fluoride glass containing Cl in the usual composition. [Effect] It is possible to provide a ZBLAN-based fluoride glass optical waveguide with low transmission loss.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art An optical communication system comprises a light emitting section, a relay section and a light receiving section, and an optical waveguide is connected between them. This relay section compensates for transmission loss and pulse spread when the transmitted signal light propagates through the optical waveguide. Conventionally, the configuration is such that the signal light is once converted into an electric signal and compensated, and then converted into a signal light using a semiconductor laser. However, this method has a drawback in that it is expensive because the structure of the apparatus is extremely complicated. Therefore, recently, it has been attempted to manufacture an optical waveguide by using a host glass doped with a rare earth element as a core portion and directly amplify the signal light having a wavelength of 1.3 μm or 1.55 μm by this optical waveguide.

Of these rare earth elements, ZrF ₄ -BaF ₂ -LaF _3- whose core portion is doped with praseodymium (Pr) is particularly preferable.
Single-mode optical waveguides made of AlF ₃ -NaF (ZBLAN) -based fluoride glass have been attracting attention because they efficiently amplify signal light with a wavelength of 1.3 μm. The composition of the core glass of the optical waveguide is 5 to 8 m in order to increase the refractive index.
ZBLAN series fluoride glass doped with ol% lead (Pb), specifically PbF _2.
It is generally a ZBLAN-based fluoride glass doped with 40 mol% of hafnium (Hf), specifically HfF ₄ .

[0004]

However, the transmission loss of the optical waveguide manufactured by the combination of the composition of the core glass and the composition of the clad glass is as follows when the signal light having the wavelength of 1.3 μm is to be amplified. It is as high as 200 to 500 dB / km, and it was necessary to further reduce the loss for practical use.

[0005]

The purpose of the present invention is to
An object of the present invention is to provide an optical waveguide which has a smaller transmission loss than the current one when the signal light of 1.3 μm is amplified by using the optical waveguide for optical amplification and which is suitable for practical use. Therefore, according to the present invention, the core part and the clad part covering the core part are provided, and the core part and the clad part are mainly ZBLAN.
Made of fluoride glass, Pb in the core portion, in the fluoride glass optical waveguide containing Hf in the cladding portion,
There is provided a fluoride glass optical waveguide characterized in that a portion of the clad portion close to the core portion is made of ZBLAN type fluoride glass containing neither Pb nor Hf. A second configuration has a core portion and a cladding portion that covers the core portion, and the core portion and the cladding portion are mainly Z
In a fluoride glass optical waveguide containing BLAN-based fluoride glass, Pb in the core part, and Hf in the clad part, the clad part is made of ZBLAN-based fluoride glass further containing chlorine (Cl). A featured fluoride glass optical waveguide is provided.

[0006]

As a result of studying the cause of the increase in transmission loss, it was found that the main factor was an increase in Rayleigh scattering. The increase in Rayleigh scattering is caused by a change in the density and composition of the core glass in the optical waveguide, that is, a non-uniform composition of the core glass. The non-uniform composition of the core glass is caused by rapid cooling (temperature change) from a high temperature of about 2000 ° C. to room temperature accompanying drawing. In addition, the softening point of ZBLAN-based fluoride glass containing Hf in the clad part is higher than the softening point of ZBLAN-based fluoride glass containing Pb in the core part by a few degrees Celsius to 20 ° C. Thus, the core glass is drawn with low viscosity. At this time, it was found that the compressive stress from the clad part acts on the core part, and the compressive stress may cause nonuniformity of the core part glass (crystallization in some cases).

[0007] Therefore, various measures were taken to prevent the composition of the core glass from becoming non-uniform, but it was concluded that the wire drawing method involving the temperature change must be adopted at present. Therefore, as a drawing method that does not cause the composition of the core portion to be non-uniform even when drawn by the drawing method, the difference in the softening points of the adjacent layers is reduced to reduce the compressive stress generated during drawing. I thought about that. As a specific method, a buffer layer having a softening point intermediate between the core portion and the clad portion is provided between the core portion and the clad portion. The softening points of the clad part and the core part are close to each other. I considered two methods.

As a result of repeated studies on the above,
As a buffer layer between the core and the clad, specifically Pb and Hf in the clad near the core.
It has been found that a layer made of ZBLAN-based fluoride glass that does not contain is included, or that a small amount of Cl is added to the entire cladding. In general, it is known that a large amount of Cl is doped to increase the refractive index, but the amount of Cl doped according to the present invention is very small, specifically, a quantity of about a few mol% is sufficient. The rate has little effect.

[0009]

EXAMPLES Examples of the present invention will be described in detail below. First, there is neither Pb nor Hf, which has a softening point between the core and the clad between the clad and the part close to the core.
Example 1 in which a layer made of BLAN-based fluoride glass is provided will be described. It is a manufacturing method that melts the raw material and quenches it, 2000p
It contained Pr in pm, specifically PrF ₃ and 7 mol% PbF ₂ .
After making ZBLAN-based fluoride glass, it was remelted and cast into a mold to make a core rod with an outer diameter of 8 mm. The core rod was heated and stretched in an inert gas, specifically, argon gas to obtain a core rod having an outer diameter of 3 mm. Next, a ZBLAN-based fluoride glass containing neither Pb nor Hf and a ZBLAN-based fluoride glass containing 40 mol% HfF ₄ were prepared. A buffer layer pipe with an outer diameter of 12 mm and an inner diameter of 9 mm was produced by remelting ZBLAN fluoride glass containing neither Pb nor Hf and casting it in a rotating mold. The expanded core rod is inserted into the buffer layer pipe, and heated and integrated in an inert gas, specifically, an argon gas,
Thereafter, the rod was extended to an outer diameter of 3 mm to prepare a core rod with a buffer layer. A ZBLAN-based fluoride glass containing 40 mol% of HfF ₄ was used to make a clad pipe with an outer diameter of 15 mm and an inner diameter of 3.5 mm in the same manner, and the core rod with a buffer layer was placed in the clad pipe. It was inserted, heated and integrated in an inert gas, specifically, argon gas, and then stretched to prepare a single mode type optical waveguide base material. The optical waveguide base material was heated and drawn to obtain an optical waveguide. The optical waveguide has an outside diameter of 3.0 μm with a buffer layer 3 around the core portion 1.
It had a clad of 125 μm. In addition, when the transmission loss of the optical waveguide was measured with a monochromator, the signal light
It was about 105 dB / km at 1.3 μm.

Next, Example 2 in which Cl is added to the cladding to form an optical waveguide will be described. A core rod having an outer diameter of 3 mm was produced by using the same composition as in Example 1 and using the same method. In addition, the clad pipe has a NaF content of 0.2 mo in the glass composition of the clad pipe of Example 1.
The remaining 1% was replaced with NaCl, and the rest was manufactured in the same manner as in Example 1 to obtain a pipe for a clad portion having an outer diameter of 12 mm and an inner diameter of 5 mm. The core part rod and the clad part pipe were heated and integrated in an inert gas, specifically, argon gas, and then stretched to produce a single mode optical waveguide preform.
The optical waveguide base material was heated and drawn to obtain an optical waveguide.
The optical waveguide has an outer diameter of 125 μm around the core 1 having an outer diameter of 2.7 μm.
It had a cladding portion 2 of μm. In addition, when the transmission loss of the optical waveguide was measured with a monochromator, the signal light
It was about 73 dB / km at 1.3 μm.

As a comparative example, the same method and the same composition as in Example 1 were used, that is, a ZBLAN-based fluoride glass core rod containing Pr and Pb and a ZBL containing only Hf.
A pipe for a clad portion made of AN fluoride glass was produced, and an optical waveguide was obtained in the same manner as in Example 1 below. The core portion diameter of the optical waveguide was 3.2 μm, and the clad portion diameter was 125 μm. The transmission loss of the optical waveguide was measured with a monochromator, and it was about 317 dB / km when the signal light was 1.3 μm.
Met.

[0012]

[Table 1]

Since the transmission loss depends on the density of light in the optical waveguide, that is, the core diameter, it is not possible to discuss the values shown in Table 1, but between the values of Examples 1 and 2 and the comparative example. You can see that there is a big difference. In the case of Example 1,
Since the buffer layer has an intermediate refractive index between the core part and the clad part, the refractive index distribution becomes stepwise. This is to reduce the core part diameter so that there is no problem in practical use. You can However, if there is no problem, it is preferable to lower the refractive index of the buffer layer so that it is the same as that of the cladding portion, and the softening point thereof is an intermediate softening point between the core portion and the cladding portion. You may add such additives.

[0014]

EFFECTS OF THE INVENTION According to the present invention, it is mainly composed of ZBLAN type fluoride glass, Pb is contained in the core part, and Pd is contained in the clad part.
In a fluoride glass optical waveguide containing Hf, the portion of the cladding that is close to the core does not contain Pb or Hf ZBLAN
A fluoride glass optical waveguide characterized by being made of a fluoride fluoride glass, or a ZBLAN fluoride glass optical waveguide characterized by containing Cl in the clad portion, with a low transmission loss. Can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical waveguide according to a first embodiment.

FIG. 2 is a sectional view of an optical waveguide according to a second embodiment.

[Explanation of symbols]

 1 core part 2 clad part 3 buffer layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G02F 1/35 501 8106-2K H01S 3/10 Z 8934-4M

Claims (2)

[Claims] 1. A core part and a clad part covering the core part, wherein the core part and the clad part are mainly ZrF ₄
-BaF ₂ -LaF ₃ -AlF ₃ -NaF (ZBLAN) -based fluoride glass with lead (Pb) in the core and hafnium in the clad
A fluoride glass optical waveguide containing (Hf), characterized in that a portion of the clad portion close to the core is made of ZBLAN-based fluoride glass containing neither Pb nor Hf. 2. A core part and a clad part covering the core part, wherein the core part and the clad part are mainly ZBL.
A fluoride glass optical waveguide comprising an AN fluoride glass, containing Pb in the core portion and Hf in the cladding portion, wherein the cladding glass further contains chlorine (Cl). Optical waveguide.