JPH0621560A - Fluoride glass optical waveguide - Google Patents

Abstract

(57) [Summary] [Structure] Z doped with 2000 ppm Pr and 4000 ppm Nd.
By melting BLAN glass and casting it in a mold, the outside diameter is 8
After preparing a core rod having a diameter of 3 mm, the core rod was stretched in an argon gas to obtain a core rod having an outer diameter of 3 mm. In addition, a ZBLAN glass in which a predetermined amount of Hf was doped to adjust the refractive index was melted and cast into a rotating mold to obtain a cladding pipe having an outer diameter of 15 mm and an inner diameter of 3.5 mm. The core rod is inserted into this pipe, both are integrated in an argon gas in this state, and then a single mode type optical waveguide preform created by repeating the drawing is drawn to draw a fiber type fiber. A single mode type fluoride glass optical waveguide was obtained. [Effect] Excitation with a general-purpose low-power semiconductor laser having an output wavelength other than 1.02 μm by adding Nd and Yb in addition to Pr in the core glass of the fluoride glass optical waveguide made of ZBLAN glass. Thus, a fluoride glass optical waveguide capable of high gain optical amplification at 1.3 μm 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.

[0003]

However, in a ZBLAN single mode optical waveguide doped with Pr, specifically PrF _3, for example, it is possible to amplify light at 1.3 μm, but a large laser with high output can be used. There is a problem that a high gain cannot be obtained unless it is excited by using it. In particular
In order to obtain a gain of about 10 dB at 1.3 μm, it is necessary to put pumping light with a wavelength of 100 mW or more and 1.02 μm into the core of the optical waveguide. This is possible if a titanium sapphire laser or the like is used. It is a value that cannot be achieved with the semiconductor laser of. On the other hand, the current maximum output of a single semiconductor laser is 100 to 150 mW, but due to the poor coupling efficiency with the optical waveguide, only about 30 mW can be put into the optical waveguide at most.

[0004]

[Purpose] The object of the present invention is to provide an optical waveguide for optical amplification with a high gain of 1.3 μm even if it is pumped using a general-purpose low-power semiconductor laser. Therefore, it is possible to pump at wavelengths other than 1.02 μm. It is to provide a possible fluoride optical waveguide.

[0005]

The present invention is mainly directed to ZBL.
In a fluoride glass optical waveguide made of an AN-based fluoride glass and containing at least Pr in the core glass, the fluoride glass optical waveguide is characterized in that at least Nd is also contained in the core glass.

[0006]

[Operation] At least in the core glass, by using an optical waveguide prepared by further doping Pr, specifically, for example, ZFLAN fluoride glass containing PrF ₃ with an appropriate amount of Nd fluoride,
It has been found that it can be excited by light having a wavelength other than 1.02 μm, for example, 0.8 μm.

The technical background that led to the discovery of this will be described below with some inference. In order to amplify light with a wavelength of 1.3 μm in a Pr-doped optical waveguide, it is necessary to excite with a high-power laser having a central wavelength of about 1.02 μm. In order to excite Pr in this optical waveguide with lasers of other wavelengths, higher output is required considering the electronic level of Pr. However, it is difficult to achieve this with a semiconductor laser. Therefore, we considered doping another core ion with Pr into the core glass and exciting this other ion together with the semiconductor laser. This ion efficiently absorbs energy, and if it is transmitted to the electronic level of Pr, Pr will also be easily excited and high gain amplification at 1.3 μm should be possible. In order to select this different ion, we examined the electronic structures of various ions and theoretically determined that Nd was appropriate. Based on these studies, we actually fabricated an optical waveguide of ZBLAN glass in which the core glass was doped with Pr and Nd and measured the optical amplification characteristics. I was able to get a gain.

Further, in the above study, it was experimentally found that the gain is further improved by doping the core glass with Yb. It is considered that this is because the electronic structure of Yb is between Pr and Nd, so that the energy transfer from Nd to Pr is performed more efficiently.

[0009]

EXAMPLE Example 1 of the present invention will be described in detail below.
A ZBLAN glass doped with 2000 ppm Pr and 4000 ppm Nd was melted and cast into a mold to prepare a core rod having an outer diameter of 8 mm. This rod was stretched in argon gas to obtain a core rod having an outer diameter of 3 mm. Also, to adjust the refractive index, ZBLAN glass that is doped with a certain amount of Hf is melted and cast into a rotating mold to have an outer diameter of 15 mm and an inner diameter
A 3.5 mm clad pipe was obtained. The core rod was inserted into this pipe, and in this state, both were heated to about 300 ° C. in argon gas, integrated, and further stretched to produce a single mode type optical waveguide preform. This preform was drawn to obtain a fiber type single mode optical waveguide. The core diameter of this fluoride glass optical waveguide was 3 μm, the cladding diameter was 125 μm, and the cutoff wavelength was 1.22 μm.

In order to investigate the optical amplification characteristics of this optical waveguide,
The measuring device shown in FIG. 1 was used. Excitation light from the titanium sapphire laser 1 (wavelength about 1.02 μm) and excitation light from the semiconductor laser 2 (wavelength 0.8 μm) are incident on the single mode dummy fibers 8a and 8b through the lenses 3a and 3b, respectively, Combine with the coupler 5a. Further, a signal light of 1.3 μm from the semiconductor laser 4 is incident on the dummy fiber 8c, and these are multiplexed by using the coupler 5b. This light was made incident on the ZBLAN optical waveguide of the present invention prepared by the above-mentioned procedure using the lens 3c, and the amount of amplification was measured by the spectrum analyzer 7. As a result, as shown in Table 1, a gain of 25 dB was obtained at a wavelength of 1.3 μm.

Further, as Example 2, an optical waveguide was prepared by substantially the same procedure as in Example 1, using ZBLAN glass doped with 2000 ppm Yb, 2000 ppm Pr and 4000 ppm Nd as the core glass, When the optical amplification characteristics were examined, as shown in Table 1, a gain of 28 dB was obtained at a wavelength of 1.3 μm.

As a comparative example, Nd and
ZBLAN not doped with Yb but doped with 2000ppm Pr only
Using glass based glass, in substantially the same procedure as in each of the above examples,
When an optical waveguide was prepared and its optical amplification characteristics were examined, as shown in Table 1, only a gain of 12 dB was obtained at a wavelength of 1.3 μm.

[0013]

[Table 1]

[0014]

According to the present invention, in addition to Pr, N is added to the core glass of a fluoride glass optical waveguide made of ZBLAN type glass.
d, and by containing Yb, it is possible to obtain a fluoride glass optical waveguide capable of high-gain optical amplification at 1.3 μm by excitation with a general-purpose low-power semiconductor laser having an output wavelength other than 1.02 μm. You can

[Brief description of drawings]

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

[Explanation of symbols]

 1 Titanium sapphire laser 2 Semiconductor laser 3 Lens 4 Semiconductor laser 5 Coupler 6 ZBLAN system fiber 7 Spectrum analyzer 8 Dummy fiber

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Claims (2)

[Claims] 1. The core glass or clad glass is mainly composed of ZrF ₄ --BaF ₂ --LaF ₃ --AlF ₃ --NaF (ZBLAN) type fluoride glass, and at least the core glass contains praseodymium (Pr). In a fluoride glass optical waveguide, neodymium (N
A fluoride glass optical waveguide characterized in that it also contains d). 2. The fluoride glass optical waveguide according to claim 1, wherein ytterbium (Yb) is also contained in the core glass.