JPH0621561A - Fluoride glass optical waveguide - Google Patents

Abstract

PURPOSE:To restrain generation of cracks, and obtain an optical waveguide having large specific refractive index difference, by using fluorine based resin for the clad part of a fluoride optical waveguide composed of core glass wherein Pr is added to ZBLAN based glass. CONSTITUTION:In a fluoride glass optical waveguide having a core part wherein ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) based fluoride glass is used as the main component and Pr is contained in it, the clad part of the fluoride glass optical waveguide is constituted of fluororesin. Fluorine based resin, e.g. tetrafluoroethylene based resin has a softening point approximate to that of the ZBLAN based glass, so that wire drawing is easy and an optical waveguide for optical amplification which has large specific refractive index difference can be obtained. Thereby an optical waveguide wherein cracks are hard to be generated and specific refractive index difference is large can be obtained.

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 repeater is for compensating the transmission loss and the spread of the pulse when the signal light to be transmitted propagates in the optical waveguide. Conventionally, the configuration has been such that the signal light is once converted into an electric signal and compensated, and then the semiconductor laser is compensated. Was used to convert to signal light. However, this method has a drawback that it is expensive because the structure of the device is extremely complicated.
Therefore, recently, a rare earth element such as Pr was used as a light emitting source, and a host glass was doped with this to form an optical waveguide.
Attempts have been made to directly amplify signal light of m or 1.55 μm.

However, Pr, specifically PrF, for example,
_The ZBLAN single-mode optical waveguide doped with ₃ is capable of optical amplification at 1.3 μm, but has a problem that the gain is low unless it is excited by a large laser with high output. This is because Pr does not absorb the 1.02 μm excitation light efficiently. Specifically, 1.3 μm
At a wavelength of 1.02 μm to obtain a gain of approx.
It is necessary to put high-power pumping light of 900 mW into the core. For this reason, it is currently practiced to reduce the diameter of the core portion of the optical waveguide and concentrate the excitation light into this core portion using a lens or the like. With such a small core diameter,
In order to maintain a predetermined single mode condition, it is desired that the relative refractive index difference Δ between the core portion and the cladding portion be 2% or more.

[0004]

However, in order to increase the relative refractive index difference Δ, the ZBLAN glass for the core portion is doped with a large amount of lead (Pb), and the ZBLAN glass for the cladding portion is mixed with a large amount. Hafnium (Hf) must be doped, but in this case, the coefficient of thermal expansion of both glasses is significantly different, and it was found that the preform cracks (cracks occur) during heat treatment. ing.

[0005]

[Object] It is an object of the present invention to provide a fluoride glass optical waveguide for optical amplification, in which the relative refractive index difference Δ between the core portion and the cladding portion can be made large and cracks do not occur during the production of the preform.

[0006]

Means for Solving the Problems The present invention is based on a ZBLAN-based fluoride glass as a main component, and in a fluoride glass optical waveguide having a core portion containing Pr, the clad portion is made of a fluorine-based resin. It is characterized by being formed.

[0007]

[Function] The technical background that led to the finding is described below. In order to increase the relative refractive index difference Δ, various dopants such as Cl and Mg were doped into the ZBLAN glass for the core and the cladding to reduce the difference in thermal expansion coefficient. However, it was not possible to completely prevent cracks. When the optical waveguide is used for optical amplification with a length of several m to 20 m, it is considered that the plastic is used as the material for forming the clad portion because the transmission loss may be relatively large. However, the softening point of ZBLAN glass is about
Normal plastic is about 200 ℃, while it is 300 ℃
Since it softens below, it was expected that drawing would be difficult even if a preform could be produced. As a result of studying various plastics, it was concluded that it is desirable to use a fluorine-based resin in the clad portion as shown in Examples described later. The reason is that the softening point is ZBLAN
This is because drawing is easy because it is close to that of the system glass, and an optical amplification optical waveguide with a large Δ can be obtained. In addition, although a tetrafluoroethylene-based resin is used in the following examples, the same effect was observed even when another fluorine-based resin was used.

[0008]

EXAMPLES Examples of the present invention will be described in detail below. ZBLAN-based glass doped with 2000 ppm of Pr was melted as glass for the core portion and cast into a mold to prepare a rod for the core portion having an outer diameter of 8 mm. Polish this surface in an inert gas,
Specifically, by heating in nitrogen gas, the outer diameter of 500
A μm core rod was produced. As the glass for the clad portion, a pipe of tetrafluoroethylene-hexafluoropropylene copolymer having an outer diameter of 32 mm and an inner diameter of 1.0 mm was used. The core part is inserted into the clad part, and in this state, both are heated to about 150 ° C in vacuum to soften the clad pipe and integrate it into a preform. A mode optical waveguide was obtained. This optical waveguide has a core diameter of 2 μm and a relative refractive index difference Δ
Was 4%. Also, when the transmission loss was measured, the wavelength
It was 1 dB / m at 1.3 μm.

The device shown in FIG. 1 was used to examine the optical amplification characteristics of this optical waveguide. Excitation light (wavelength: about 1.02 μm) from the titanium sapphire laser 1 is made incident on the single mode dummy fiber 7a via the lens 2a, and signal light having a wavelength of 1.3 μm is made incident on the dummy fiber 7b from the semiconductor laser 3 on the other side. , And these were multiplexed using the coupler 4. This light was made incident on the optical waveguide of the present invention, that is, the fiber 5 using the lens 2b, and was measured by the spectrum analyzer 6. As a result, as shown in Table 1, the wavelength of 1.3
A gain of 15 dB was obtained at μm.

[0010]

[Table 1]

As a comparative example, the outer diameter is 8 mm as in the example.
Then, a ZBLAN rod doped with 2000 ppm of Pr and 8 mol% of Pb was prepared and stretched to obtain a core rod having an outer diameter of 3 mm. Also, Hf was doped with 50 mol% to adjust the refractive index.
Outer diameter of 15 by melting ZBLAN glass and casting in a mold
A mm-sized rod was produced, and an ultrasonic drill was used to make a hole in the rod to obtain a pipe for the clad portion. The rod was inserted into this pipe, both were heated to about 300 ° C. to be integrated, and then further stretched, and an attempt was made to produce a preform for a single-mode optical waveguide. However, as shown in Table 2, there is a high probability that cracks will occur after the rod and the pipe are integrated, and it was extremely difficult to obtain a preform without cracks.
I finally got one crack-free preform,
This was drawn to obtain a fiber type optical waveguide having an outer diameter of 125 μm, a core diameter of 3 μm, and a relative refractive index difference Δ3%. When the optical amplification characteristics of this optical waveguide were examined, as shown in Table 1, the wavelength of 1.3
The gain at μm was 11 dB.

[0012]

[Table 2]

[0013]

EFFECTS OF THE INVENTION According to the present invention, since the fluorine resin is used in the cladding portion of the fluoride optical waveguide made of the core glass obtained by adding Pr to the ZBLAN glass, cracks are less likely to occur and the relative refractive index difference Δ It is possible to obtain a large optical waveguide.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical amplification characteristic evaluation device.

[Explanation of symbols]

 1 titanium sapphire laser 2 lens 3 semiconductor laser 4 coupler 5 fiber 6 spectrum analyzer 7 dummy fiber

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01S 3/07 8934-4M

Claims (1)

[Claims] 1. ZrF ₄ -BaF ₂ -LaF ₃ -AlF ₃ -NaF (ZBLAN)
In a fluoride glass optical waveguide having a core portion made of a system fluoride glass and containing praseodymium (Pr) therein, the cladding portion of the fluoride glass optical waveguide is made of a fluorine resin. Fluoride glass optical waveguide.