JP2001358387A - Rare earth-added optical fiber and optical amplifier using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the stability of optical amplification characteristics by restraining the fluctuation of a gain due to temperature change when collectively amplifying not only light with single wavelength but also light with a plurality of wavelength using an optical fiber amplifier. SOLUTION: A conductive covering layer 4 is provided at a rare earth-added optical fiber 9 where rare earth elements have been added into a core 1. Current is allowed to flow to the conductive covering layer 4 to generate heat, thus constantly maintaining the temperature of the rare earth-added optical fiber 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-doped optical fiber used for an optical fiber amplifier or an optical repeater used in an optical communication line for multistage relay.

[0002]

2. Description of the Related Art For example, erbium-doped optical fibers (E
DF) and other optical fibers in which at least a core is doped with a rare earth element are non-linear and exhibit an optical amplification effect, and an optical fiber amplifier using this is excellent in high speed and low noise. It is frequently used in optical communication systems.

[0003]

By the way, in general, ED
Rare-earth-doped optical fibers such as F have the property that the optical amplification characteristics change when the temperature changes. Therefore, when the device is used in an environment having a temperature change, it is necessary to compensate for a change in the optical amplification characteristics due to the temperature change. For example, in an optical amplifier including a rare-earth-doped optical fiber as a component, when the environmental temperature changes, the temperature of the rare-earth-doped optical fiber itself changes, thereby changing the gain. Therefore, in order to compensate for the fluctuation of the gain and keep the gain constant, there is a method of changing the intensity of the pumping light supplied to the rare-earth-doped optical fiber according to, for example, a change in temperature.

However, there is a problem in that the fluctuation range of the gain due to such a temperature change differs depending on the wavelength of light. That is, for example, in a wavelength division multiplexing transmission system, when a plurality of lights having different wavelengths are collectively amplified by a single optical fiber amplifier, even if the temperature change is the same, the fluctuation width of the gain is different if the wavelength is different. In the method of changing the intensity of the excitation light according to the temperature change, the gain cannot be kept constant at all of the plurality of wavelengths. FIG.
Is the wavelength (unit: nm) on the horizontal axis and the gain (unit: d) on the vertical axis.
FIG. 6B is a graph showing the fluctuation of the gain at each wavelength when the environmental temperature changes from 0 ° C. to 50 ° C. in FIG.
As shown in this graph, when the ambient temperature changes from 0 to 50 ° C., for example, the light having a wavelength of 1540 nm has a gain of about 0.27 dB in the optical fiber amplifier, whereas the wavelength in the same optical fiber amplifier varies. 1546
The gain fluctuation width of the light of nm is about 0.1 dB. Therefore, for example, in this optical fiber amplifier, about 0.1 dB
If the pumping light intensity is changed so as to compensate for the fluctuation in the gain, the fluctuation in the gain can be eliminated for light having a wavelength of 1546 nm, but the gain at a wavelength of 1540 nm still fluctuates and is not constant.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is not limited to the case where light having a plurality of wavelengths is collectively amplified by a single optical fiber amplifier in addition to light having a single wavelength. And to improve the stability of optical amplification characteristics.

[0006]

In order to solve the above-mentioned problems, a rare-earth-doped optical fiber according to the present invention is characterized in that a rare-earth element is added in a core and a conductive coating layer is provided. An optical fiber device according to the present invention includes the rare-earth-doped optical fiber according to the present invention, and a means for causing a current to flow through the conductive coating layer. The optical amplifier of the present invention includes a rare-earth-doped optical fiber of the present invention, a means for flowing a current through the conductive coating layer of the rare-earth-doped optical fiber, a means for injecting excitation light into the rare-earth-doped optical fiber, It is characterized in that it is provided with a means for receiving signal light.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 is a sectional view showing one embodiment of the rare earth-doped optical fiber 9 of the present invention. In the rare-earth-doped optical fiber 9 of the present embodiment, the conductive coating layer 4 is formed on the circumference of the bare optical fiber 3 composed of the core 1 and the clad 2, and the outermost coating layer 5 is formed on the circumference. It was done. The core 1 of the bare optical fiber 3 is doped with a rare earth element such as erbium (Er).

The configuration and material of the bare optical fiber 3 can be arbitrary, but a material having low heat resistance is not preferred. In the present embodiment, the core 1 made of quartz glass is used.
An optical fiber bare wire having an outer diameter of 125 μm and having a cladding 2 and erbium added to the core is used. Further, a configuration having two clad layers having different refractive indices around the core may be adopted.

The conductive coating layer 4 is made of a material having conductivity and capable of forming a coating layer. Suitable materials include, for example, metals such as aluminum (Al) and nickel (Ni). The thickness of the conductive coating layer 4 is set so that a desired electrical resistance is obtained according to the material of the conductive coating layer 4 because the thickness of the electrical resistance of the conductive coating layer 4 changes accordingly. . The thickness of the conductive coating layer 4 is set within a range of approximately 1 μm to 100 μm. In the present embodiment, a 25 μm thick conductive coating layer 4 made of a Ni alloy is formed on the circumference of the bare optical fiber 3. As a method for forming the conductive coating layer 4, for example, a vacuum evaporation method, a sputtering method, a plasma CVD method, or the like can be used.

The outermost coating layer 5 is an insulating material,
And it is composed of a material capable of forming a coating layer. As such a material, a resin material generally used for forming a coating layer of an optical fiber can be used. Outermost coating layer 5
Plays a role as a protective layer for the bare optical fiber 3, an insulating layer for preventing a short circuit due to contact between the conductive coating layers 4, and a heat insulating layer for suppressing temperature fluctuation of the bare optical fiber 3. . The thickness of the outermost coating layer 5 can be set as appropriate, but in consideration of connectivity with other optical fibers,
It is preferable to set the outer diameter of the rare-earth-doped optical fiber 9 to be 250 μm, which is the same as that of the existing optical fiber. In this embodiment, the outermost coating layer 5 made of an ultraviolet-curable resin is formed on the periphery of the conductive coating layer 4 so that the outer diameter of the rare-earth-doped optical fiber 9 is 250 μm.

The rare-earth-doped optical fiber 9 having such a configuration
Is a part or all of the conductive coating layer 4 in the longitudinal direction.
, A Joule heat is generated in the conductive coating layer 4, and the bare optical fiber 3 is heated. The current flowing through the conductive coating layer 4 may be DC or AC. Since the amount of generated Joule heat is proportional to the square of the current intensity and the resistance of the conductor according to Joule's law, the resistance of the conductive coating layer 4 is appropriately set, and the intensity of the current is adjusted. It is possible to control the temperature of the bare optical fiber 3. Then, by adjusting the amount of heat generated in the conductive coating layer 4 of the rare-earth-doped optical fiber 9, the rare-earth-doped optical fiber 9 can be maintained at a constant set temperature. The configuration of the rare-earth-doped optical fiber 9 is not limited to the configuration shown in FIG.

The set temperature of the rare-earth-doped optical fiber 9 must be equal to or higher than the ambient temperature. When the environmental temperature fluctuates, it is necessary to set the set temperature higher than the upper limit value.
If the temperature of the rare-earth-doped optical fiber 9 becomes too high, the glass material and the coating layer material constituting the rare-earth-doped optical fiber 9 may be softened and deformed or adversely affect the characteristics. The set temperature of the optical fiber 9 needs to be within a temperature range in which such softening of the constituent material does not occur. For example, in the present embodiment, the bare optical fiber 3 is made of quartz glass, and the conductive coating layer 4 is made of N
Since the outermost coating layer 5 is formed of an i-alloy and the outermost coating layer 5 is formed of an ultraviolet curable resin, the set temperature of the rare earth-doped optical fiber 9 is preferably set within a range from the ambient temperature to about 100 ° C. or lower. In the present invention, the intensity of the current flowing through the conductive coating layer 4 is not particularly limited, but is preferably in a range of about 0.1 to 10 A.

The optical fiber device of the present invention includes the rare-earth-doped optical fiber 9 of the present invention and means for flowing a current through the conductive coating layer 4 of the rare-earth-doped optical fiber 9.
As a means for flowing a current through the conductive coating layer 4, a means for applying a DC voltage, a means for applying an AC voltage, a means for generating an induced current by an AC magnetic field, or the like can be used. Specifically, a current can be caused to flow through the predetermined portion by, for example, bringing electrodes into contact with the conductive coating layer 4 at both ends of part or all of the predetermined portion in the length direction of the rare-earth-doped optical fiber 9. In the optical fiber device, a means for measuring the temperature of the rare-earth-doped optical fiber 9 and a means for flowing a current according to the measurement result of the temperature are controlled so that the temperature of the rare-earth-doped optical fiber 9 is kept constant. It is preferable to provide control means for adjusting the intensity of the current. As a means for measuring the temperature of the rare-earth-doped optical fiber 9, for example, a thermocouple or the like can be used. In measuring the temperature of the rare-earth-doped optical fiber 9, it is important to keep the temperature of the bare optical fiber 3 constant. Therefore, the temperature of the bare optical fiber 3 is measured as the temperature of the rare-earth-doped optical fiber 9. Most preferably, the conductive coating layer 4
May be measured, or the temperature of the outermost coating layer 5 may be measured.

FIG. 2 is a schematic configuration diagram showing an example in which an optical amplifier is configured using the rare earth-doped optical fiber 9 of the present embodiment. The rare earth-doped optical fiber 9 has a core in which erbium is added. The optical amplifier of this example has a length of 1
A coil wound so as to easily store the rare earth-doped optical fiber 9 of about 0 m is used as an amplification optical fiber,
DC voltage applying means 10 is provided at both ends thereof so as to be electrically connected to the conductive coating layer 4. A light source 12 for signal light and a light source 13 for excitation light are connected to an incident end of the rare-earth-doped optical fiber 9 via an optical coupler 11. In the figure, reference numeral 12a denotes signal light, and 13a denotes pump light. A transmission optical fiber 14 is connected to the emission end of the rare earth-doped optical fiber 9. Although not shown, a means for measuring the temperature of the rare-earth-doped optical fiber and a means for controlling the DC voltage applying means 10 according to the temperature measurement result are provided. Then, while the DC voltage applying means 10 is driven to supply a current to the conductive coating layer 4 of the rare-earth-doped optical fiber 9 and the temperature of the rare-earth-doped optical fiber 9 is monitored, the measurement temperature is always set to a predetermined temperature. The current intensity is controlled so that In the optical amplifier of this example, for example, the signal light 1 having a wavelength of 1.55 μm
2a and the excitation light 13a having a wavelength of 0.5 to 1.49 μm, the signal light 12
a is amplified and emitted. In the figure, reference numeral 15 denotes an amplified signal light.

According to the optical amplifier of the present embodiment, the temperature of the rare-earth-doped optical fiber 9, which is an amplification optical fiber, can always be kept constant. Therefore, even if the environmental temperature changes, the gain of the rare-earth-doped optical fiber 9 does not change, and stable optical amplification characteristics can be obtained. Further, since the outermost coating layer 5 made of an insulating material is formed on the periphery of the conductive coating layer 4, even if the rare earth-doped optical fiber 9 is wound in a coil shape, the rare-earth-doped optical fiber 9 has a conductive coating. The layers 4 do not contact each other and no short circuit occurs. In the present embodiment,
Although the wavelength of the signal light is set to a single wavelength of 1.55 μm, regardless of the wavelength band of the signal light, since the temperature of the rare-earth-doped optical fiber 9 is always constant, the fluctuation of the gain due to the change of the environmental temperature is small. Is prevented. Therefore, the optical amplifier having such a configuration can be applied to the wavelength division multiplexing transmission system. Even when a plurality of wavelengths of light are collectively amplified, the gain does not fluctuate due to a temperature change and the optical amplification characteristics are stable. Is obtained.

[0016]

EXAMPLES Hereinafter, the effects of the present invention will be clarified by showing specific examples. Example 1 An optical amplifier having the structure shown in FIG. 2 was manufactured. The rare-earth-doped optical fiber 9 has a conductive coating layer 4 made of a Ni alloy and having a thickness of 25 μm on the circumference of the bare optical fiber 3 having an outer diameter of 125 μm and erbium added in the core 1. Approximately 35 of UV curable resin on top
One having an outermost coating layer 5 of μm was used. A tunable semiconductor laser was used as the signal light source 12, and a semiconductor laser was used as the excitation light source 13. Excitation light having a wavelength of 1480 nm is incident on the rare-earth-doped optical fiber 9, and 1540 nm, 1543 nm, and 1546 n
m, 1549 nm, 1552 nm, 1555 nm, 15
58 nm and 1561 nm signal lights were simultaneously incident, and the gain was measured when the environmental temperature changed from 0 to 50 ° C. for each wavelength. During the measurement, the temperature of the rare-earth-doped optical fiber 9 was maintained at 50 ° C. by flowing a DC current through the conductive coating layer 4 of the rare-earth-doped optical fiber 9 while appropriately adjusting it.
FIG. 3 shows the measurement results of the gain. As shown in the graph of FIG. 3, almost no change in gain due to temperature change was observed in any wavelength band.

COMPARATIVE EXAMPLE 1 A temperature change was performed in the same manner as in Example 1 except that a conventional rare-earth-doped optical fiber having no conductive coating layer 4 was used instead of the rare-earth-doped optical fiber 9. The change in gain due to was investigated. That is, an outer diameter of 125 μm with erbium added in the core.
A coating layer made of the same material as the outermost coating layer in the first embodiment is formed on the circumference of the bare optical fiber of
An optical amplifier having the configuration shown in FIG. 2 was manufactured using a rare earth-doped optical fiber having a thickness of 0 μm. However, the DC voltage applying means 10, the temperature measuring means for the rare earth-doped optical fiber, and the control means for the DC voltage applying means 10 were not provided. The same excitation light and signal light of each wavelength as those in Example 1 were applied, and the gain was measured when the environmental temperature changed from 0 to 50 ° C. for each wavelength. FIG. 4 shows the measurement result of the gain. As shown in the graph of this figure, the gain fluctuated with the change in the environmental temperature, and the fluctuation range of the gain was different for each wavelength.

[0018]

As described above, the rare-earth-doped optical fiber of the present invention has a core in which a rare-earth element is added.
It has a conductive coating layer. Therefore, the temperature of the rare-earth-doped optical fiber can be controlled by generating heat by passing a current through the conductive coating layer. Further, an optical fiber device according to the present invention includes the rare-earth-doped optical fiber according to the present invention and means for flowing a current through the conductive coating layer. Therefore, it is a device provided with a rare-earth-doped optical fiber that has an optical amplification function and can obtain a stable amplification characteristic even when the environmental temperature changes, and can be suitably used as a constituent member of an optical amplifier. In addition, by configuring an optical amplifier using the rare earth-doped optical fiber of the present invention as an amplification optical fiber, not only light of a single wavelength but also light of a plurality of wavelengths can be collectively amplified by an optical fiber amplifier. Also, it is possible to improve the stability of the optical amplification characteristic by suppressing the fluctuation of the gain due to the temperature change.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a rare earth-doped optical fiber of the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of the optical amplifier of the present invention.

FIG. 3 is a graph showing a result of examining a change in gain due to a temperature change in an example according to the present invention.

FIG. 4 is a graph showing a result of examining a change in gain due to a temperature change in a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Cladding, 3 ... bare optical fiber, 4 ... Conductive coating layer, 5 ... Outer coating layer, 9 ... Rare-earth-doped optical fiber.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takafumi Kashima 1440, Musaki, Sakura City, Chiba Prefecture Fujikura Sakura Works F-term (reference) 2H050 AB18X AD16 BB31Q BC03 5F072 AB09 AK06 FF09 JJ05 PP07 TT22 TT28 YY17

Claims (3)

[Claims] A rare earth element is added in the core,
A rare earth-doped optical fiber having a conductive coating layer. 2. An optical fiber device comprising: the rare-earth-doped optical fiber according to claim 1; and means for flowing a current through the conductive coating layer. 3. A rare earth-doped optical fiber according to claim 1, means for flowing a current through said conductive coating layer, means for exciting light to said rare-earth-doped optical fiber, and signal light to said rare-earth-doped optical fiber. An optical amplifier comprising: means for incident light.