JP2001007425A - Optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical fiber amplifier by which the flattening of the gain can be easily realized. SOLUTION: The optical fiber amplifier 1 is provided with an optical isolator 31, a photocoupler 21, a first optical fiber 11, a second optical fiber 12, a photocoupler 22 and an optical isolator 31 between its input end 1a and an output end 1b and is also provided with an excitation light source 41 connected to the photocoupler 21 and an excitation light source 42 connected to the photocoupler 22. The optical fibers 11 and 12 are respectively formed by using silica glass as host material, adding a rare-earth element such as Er element to a core region and optically connecting them. In the first optical fiber 11, Zn element is added to the core region in conjunction with the rare-earth element. In the second optical fiber 12, Al element is added to the core region in conjunction with the rare-earth element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier for supplying pumping light to an amplification optical fiber, optically amplifying signal light input to the optical fiber, and outputting the amplified signal light.

[0002]

2. Description of the Related Art An optical fiber amplifier used in a wavelength division multiplexing transmission system or the like is required to collectively amplify signal lights of a greater number of waves with a constant gain. It is required that the wavelength band be wide, and that the gain of optical amplification in the wavelength band be flat. Therefore, research and development of optical fiber amplifiers have been conducted with the aim of broadening the signal light wavelength band and flattening the gain. Erbium (E) is added to an amplification optical fiber using silica glass as a host material.
r) In addition to the rare earth element such as the element, other elements (for example, aluminum (Al) element, phosphorus (P) element, yttrium (Y) element, etc.) are added, so that the signal light wavelength band of the optical fiber amplifier is increased. It is known that broadband and gain flattening are possible.

For example, in an optical fiber amplifier disclosed in Japanese Patent Application Laid-Open No. Hei 7-147445, a first optical fiber and a second optical fiber are optically connected, and the first optical fiber is composed of an Er element and Al. The element is added, and the second optical fiber is an element to which Er element, Al element and P element are added. By doing so, the gain is flattened. The optical fiber amplifier disclosed in Japanese Patent Application Laid-Open No. H10-261828 has a weight ratio of 1.5% to 3.5%.
The gain is flattened by using an optical fiber in which the Al element is added to the core region by weight%. Further, the optical fiber amplifier disclosed in Japanese Patent Application Laid-Open No. 9-83047 has a flattened gain by cascade-connecting a plurality of optical fibers different in at least one of element types and addition amounts of rare earth elements and the like to be added. It is intended.

[0004]

However, each of the above-mentioned conventional optical fiber amplifiers has the following problems. That is, the optical fiber amplifier disclosed in Japanese Patent Application Laid-Open No.
It is difficult to obtain a desired gain spectrum because the gain spectrum is greatly affected by the ratio of the addition concentration of each element. In the optical fiber amplifier disclosed in Japanese Patent Application Laid-Open No. 10-261828, it is also difficult to obtain a desired gain spectrum because it is difficult to adjust the concentration of Al element addition. In addition, despite the fact that the signal light in the wavelength band of 1.55 μm is optically amplified using an optical fiber doped with Er element as a rare earth element, the gain of the optical amplification near the wavelength of 1.55 μm is increased. A gain dip occurs that is smaller than the gain at the surrounding wavelength. Japanese Patent Application Laid-Open No. 9-83047 does not show a specific method for realizing gain flattening.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an optical fiber amplifier capable of easily realizing gain flattening.

[0006]

An optical fiber amplifier according to the present invention comprises a plurality of optical fibers optically connected to each other by adding a rare earth element using silica glass as a host material, and pumping light to the plurality of optical fibers. An optical fiber amplifier comprising: a pumping means for supplying the optical fiber, wherein the plurality of optical fibers include first and second optical fibers in which the same rare earth element is added to each core region, and the first optical fiber is The Zn element is co-doped in the core region, and the second optical fiber is characterized in that the Al element is co-doped in the core region.

According to this optical fiber amplifier, pumping light is supplied to each of the plurality of optical fibers including the first and second optical fibers by the pumping means, and the signal light is optically amplified by the plurality of optical fibers and output. Is done. The first optical fiber in which the rare earth element and the Zn element are added to the core region has an appropriate gain because the second optical fiber in which the rare earth element and the Al element are added to the core region has a gain peak at a wavelength having a gain dip. First and second length ratios
Although the plurality of optical fibers including the above optical fiber are optically connected, the overall gain becomes flat.

Further, the optical fiber amplifier according to the present invention comprises:
The rare earth element is an Er element.
In this case, the wavelength 1.55 generally used for optical communication is used.
This is preferable because it is possible to optically amplify multi-wavelength signal light in the μm band with a small gain deviation.

Further, the optical fiber amplifier according to the present invention comprises:
The concentration of the Zn element in the core region of the first optical fiber is 1% by weight or more. In this case,
Since the gain spectrum of the first optical fiber becomes gentle, it is suitable for flattening the entire gain spectrum.

An optical fiber amplifier according to the present invention comprises:
The concentration of the Al element in the core region of the second optical fiber is 5% by weight or more. In this case,
Since the gain spectrum of the second optical fiber is stabilized, it is suitable for flattening the entire gain spectrum.

Further, in the optical fiber amplifier according to the present invention, the first optical fiber is such that any one of Ti element, Zr element, Hf element, P element and Al element is co-doped in the core region. It is characterized by. In this case, white turbidity in the Zn element added region is prevented without greatly changing the gain spectrum of the first optical fiber.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a configuration diagram of an optical fiber amplifier according to the present embodiment. The optical fiber amplifier 1 according to the present embodiment includes an optical isolator 31, an optical coupler 21, a first optical fiber 11, a second optical fiber 12, an optical coupler 22, and an optical coupler 31 between an input terminal 1a and an output terminal 1b. Isolator 3
1 is provided. The optical fiber amplifier 1 includes an excitation light source 41 connected to the optical coupler 21 and an optical coupler 2.
2 is provided with an excitation light source 42.

Each of the optical fibers 11 and 12 uses silica glass as a host material, and uses erbium (Er) element, neodymium (Nd) element and praseodymium (Pr).
A rare earth element such as an element is added to the core region and optically connected. In particular, when an Er element is added as a rare earth element, it is preferable because multi-wavelength signal light in the 1.55 μm band generally used in optical communication can be optically amplified.

The first optical fiber 11 is one in which zinc (Zn) element is co-doped in the core region in addition to the rare earth element. It is preferable that the concentration of the Zn element in the core region be 1% by weight or more because the gain spectrum of the optical fiber 11 becomes gentle. In addition, the first optical fiber 1
It is also preferable that any one of a titanium (Ti) element, a zirconium (Zr) element, a hafnium (Hf) element, a phosphorus (P) element, and an aluminum (Al) element be co-added to the core region. is there.

The second optical fiber 12 is obtained by co-doping a core region with an Al element in addition to a rare earth element. If the concentration of the Al element in the core region is 5% by weight or more, the gain spectrum of the optical fiber 12 becomes stable, which is preferable.

The optical isolator 31 allows light to pass in the direction from the input end 1a to the optical coupler 21, but does not allow light to pass in the opposite direction. The optical isolator 32 includes the optical coupler 22
Through the output end 1b, but not in the opposite direction.

The optical coupler 21 converts the 1.55 μm wavelength signal light arrived from the optical isolator 31 into the optical fiber 11.
, And the pumping light of, for example, 1.48 μm reaching from the pumping light source 41 is output toward the optical fiber 11. The optical coupler 22 outputs the signal light in the 1.55 μm band arrived from the optical fiber 12 toward the optical isolator 32, and directs, for example, 1.48 μm excitation light arrived from the excitation light source 42 toward the optical fiber 12. Output.

The optical fiber amplifier 1 according to the present embodiment includes an excitation light source 41 and an optical coupler 2 as excitation means for supplying excitation light to the optical fibers 11 and 12, respectively.
1 and a backward excitation means including the excitation light source 42 and the optical coupler 22.

The pump light output from the pump light source 41 is supplied to the optical fibers 11 and 12 via the optical coupler 21, and the pump light output from the pump light source 42 is supplied to the optical fibers 12 and Optical fiber 1
1 so that the optical fibers 11 and 12
The Er element added to each is excited to form a population inversion. 1.55 μm wavelength input to input terminal 1a
The band signal light is transmitted to the optical isolator 31 and the optical coupler 21.
Are sequentially input to the optical fiber 11 and the optical fiber 1
1 and the optical fiber 12 amplify the light. And
This optically amplified signal light is output from the output terminal 1b through the optical coupler 22 and the optical isolator 31 sequentially.

Next, an example of a method for manufacturing the optical fiber 11 in which the Er element and the Zn element are added to the core region will be described.

Ultrafine ZnO particles having an average particle diameter of about 31 nm are dispersed in pure water, and 4.1 g of the fine particles are dispersed in 50 ml of pure water.
A ZnO-containing liquid containing ZnO at a ratio of 1 is prepared.
In dispersing the ZnO ultrafine particles, it is preferable to diffuse the ZnO ultrafine particles by ultrasonic waves using an ultrasonic cleaner in order to avoid aggregation and precipitation of the ZnO ultrafine particles. Furthermore, this Zn
The O-containing liquid ErCl ₃ · 6H ₂ O and 0.005 mol / l
To prepare an Er-dissolved fine particle dispersion.

On the other hand, a soot body of silica glass is adhered to the inner wall of a silica glass tube containing 0.35% of fluorine (F) element. The bulk density of this soot body is 0.25 g / c.
m ^{3 to} about 0.30 g / cm ³ . Compared to the diameter of the soot body, the average particle diameter of the ZnO ultrafine particles is 1/10.
It is about. Then, the soot body is immersed in the Er-dissolved fine particle dispersion for 72 hours.

After the immersion, a dehydration / clarification treatment is performed. In this dehydration and clarification treatment, ZnO reacts with chlorine to form ZnC.
In order to avoid this, there is a possibility of desorption. Therefore, in order to avoid this, at a low temperature, dehydration and clearing treatment is performed with a mixed gas of chlorine and oxygen having a mixing ratio of 1: 9, and at a high temperature, dehydration is performed only with oxygen gas. It is preferable to perform a transparency process. After the dehydration and clarification treatment, a collapse treatment is performed to produce a preform. In this collapsing treatment, in order to avoid volatilization of ZnO, it is preferable to perform the collapsing treatment after depositing a GeO ₂ -added silica glass layer further inside the soot body. Then, the preform is drawn and the core diameter is 6
An optical fiber 11 having a diameter of 125 μm and a cladding diameter of 125 μm is manufactured.

It is to be noted that Z which is presumed to be due to the association of ZnO
Although clouding may occur in the nO added region, in order to avoid this, it is preferable to add any one of the Ti element, the Zr element, the Hf element, the P element and the Al element.

Next, the absorption spectrum, emission spectrum, and gain spectrum of the optical fiber 11 actually manufactured and evaluated as described above will be described with reference to FIGS.

FIG. 2 shows the first optical fiber 11 and the second optical fiber 11.
3 is a graph showing an absorption spectrum of each of the optical fibers 12. In this figure, the absorption spectrum of the optical fiber A in which only the Er element is added to the core region is also shown for reference. In this figure, the absorption spectrum of each optical fiber is standardized so that the maximum value is 1.
As can be seen from this figure, the optical fiber 11 to which the Er element and the Zn element are added has a larger increase in absorption around a wavelength of 1.49 μm than the other optical fibers.
The absorption peak wavelength of the optical fiber 11 is 1532 nm, and the optical fiber 1 doped with Er element and Al element
Although not as large as the case of 2, the wavelength is shifted to a shorter wavelength side than the absorption peak wavelength of the optical fiber A to which only the Er element is added. Further, the absorption on the longer wavelength side than the absorption peak wavelength of the optical fiber 11 is gentler than that of the optical fiber A.

FIG. 3 shows the first optical fiber 11 and the second optical fiber 11.
3 is a graph showing the emission spectrum of each of the optical fibers 12 of FIG. In this figure, the emission spectrum of the optical fiber A in which only the Er element is added to the core region is also shown for reference. Further, in this figure, the emission spectrum of each optical fiber is standardized so that the maximum value becomes 1.
As can be seen from this figure, the emission peak wavelength of the optical fiber 11 doped with Er and Zn elements is not as high as that of the optical fiber 12 doped with Er and Al, but only the Er element is doped. Is shifted to a shorter wavelength side than the light emission peak wavelength of the optical fiber A. Although the optical fiber 11 has a gentler peak than the optical fiber A, the spectral shape does not change as much as the optical fiber 12 does.

FIG. 4 shows the first optical fiber 11 and the second optical fiber 11.
6 is a graph showing a gain spectrum of each of the optical fibers 12 of FIG. In this figure, the gain spectrum of the optical fiber A in which only the Er element is added to the core region is also shown for reference. In this figure, the gain spectrum of each optical fiber is standardized so that the maximum value is 1.
As can be seen from this figure, the gain spectrum of the optical fiber 11 doped with the Er element and the Zn element is not as great as that of the optical fiber 12 doped with the Er element and the Al element, but only the Er element is doped. Compared to the case of the optical fiber A, it is gentler. Here, it should be noted that the optical fiber 11 has a gain peak near a wavelength of 1.55 μm where the optical fiber 12 has a gain dip. The optical fiber amplifier 1 according to the present embodiment achieves gain flattening by effectively utilizing this point.

FIG. 5 shows the first optical fiber 11 and the second optical fiber 11.
In addition to the gain spectrum of each optical fiber 12,
5 is a graph showing an overall gain spectrum of a first optical fiber 11 and a second optical fiber 12 cascaded. Also in this figure, the gain spectrum of each optical fiber is standardized so that the maximum value is 1. The length ratio of the optical fiber 11 and the optical fiber 12 is 1.
The overall gain spectrum in the 55 μm band is adjusted to be as flat as possible. As can be seen from this figure, the overall gain spectrum of the optical fiber 11 and the optical fiber 12 in which the optical fiber 11 and the optical fiber 12 are connected in cascade is such that the gain dip of the optical fiber 12 is compensated by the gain peak of the optical fiber 11 near the wavelength of 1.55 μm. . Wavelength 1542n
The overall gain deviation in the range from m to 1558 nm is 1%
It is about.

As described above, the optical fiber amplifier 1 according to the present embodiment optically couples the optical fiber 11 doped with Er and Zn elements and the optical fiber 12 doped with Er and Al elements. By connecting, the overall gain deviation in the 1.55 μm band can be reduced. Further, the optical fiber 12 to which the Al element is co-doped is used.
Even if the actual gain spectrum is not as designed, the overall gain deviation in the 1.55 μm wavelength band can be easily reduced by appropriately setting the length ratio of the optical fibers 11 and 12. be able to. In particular, when the concentration of the Zn element in the core region of the first optical fiber 11 is 1% by weight or more, the gain spectrum of the first optical fiber 11 becomes gentle, so that the entire gain spectrum is flattened. It is suitable for performing. Also, the second
When the concentration of the Al element in the core region of the optical fiber 12 is 5% by weight or more, the second optical fiber 1
Since the gain spectrum of No. 2 is stable, it is suitable for flattening the entire gain spectrum.

The present invention is not limited to the above embodiment, but can be variously modified. For example, a third optical fiber may be included in addition to the first optical fiber 11 and the second optical fiber 12, and these optical fibers may be optically connected at an appropriate length ratio. .

[0033]

As described above in detail, according to the present invention, pumping light is supplied to each of a plurality of optical fibers including the first and second optical fibers by the pumping means. The signal light is optically amplified and output. The first optical fiber in which the rare earth element and the Zn element are added to the core region has an appropriate gain because the second optical fiber in which the rare earth element and the Al element are added to the core region has a gain peak at a wavelength having a gain dip. Although the plurality of optical fibers including the first and second optical fibers having an appropriate length ratio are optically connected, the overall gain becomes flat.

In particular, when the above-mentioned rare earth element is an Er element, it is preferable because multi-wavelength signal light in the wavelength band of 1.55 μm generally used for optical communication can be optically amplified with a small gain deviation. .

Zn in the core region of the first optical fiber
When the concentration of the element is 1% by weight or more, the gain spectrum of the first optical fiber becomes gentle, so that the entire gain spectrum can be flattened. Also,
When the concentration of the Al element in the core region of the second optical fiber is 5% by weight or more, the gain spectrum of the second optical fiber is stabilized, so that the entire gain spectrum can be flattened.

Also, Ti element, Zr element, Hf element, P element
When any one of the element and the Al element is co-doped in the core region of the first optical fiber, the gain spectrum of the first optical fiber does not largely change and Zn
Clouding in the element addition region is prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical fiber amplifier according to an embodiment.

FIG. 2 is a graph showing an absorption spectrum of each of a first optical fiber and a second optical fiber.

FIG. 3 is a graph showing an emission spectrum of each of a first optical fiber and a second optical fiber.

FIG. 4 is a graph showing a gain spectrum of each of a first optical fiber and a second optical fiber.

FIG. 5 is a graph showing an overall gain spectrum of a cascade-connected first optical fiber and second optical fiber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber amplifier, 11 ... 1st optical fiber, 12
... Second optical fiber, 21,22 ... Optical coupler, 31,3
2 ... optical isolators, 41, 42 ... excitation light sources.

Claims (5)

[Claims] 1. An optical fiber amplifier comprising: a plurality of optical fibers optically connected to a rare earth element by using silica glass as a host material; and pump means for supplying pump light to the plurality of optical fibers. Wherein the plurality of optical fibers include first and second optical fibers in which the same rare earth element is added to each core region;
An optical fiber amplifier, wherein the first optical fiber is co-doped with a Zn element in a core region, and the second optical fiber is co-doped with an Al element in a core region. 2. The optical fiber amplifier according to claim 1, wherein said rare earth element is an Er element. 3. The optical fiber amplifier according to claim 1, wherein the concentration of Zn in the core region of the first optical fiber is 1% by weight or more. 4. The optical fiber amplifier according to claim 1, wherein the concentration of the Al element in the core region of the second optical fiber is 5% by weight or more. 5. The optical fiber according to claim 1, wherein the first optical fiber is a Ti element,
The optical fiber amplifier according to claim 1, wherein any one of the r element, the Hf element, the P element, and the Al element is co-doped in the core region.