JP2004111778A - Optical fiber for amplification and optical amplifier using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To widen the amplification band of an optical fiber for amplification. <P>SOLUTION: A core 7 comprises a whole wavelength band signal light amplifying part 7a arranged in the radial inner part of the core 7, and a long wavelength band signal light amplifying part 7b arranged at the radial outer part in the core 7. The whole wavelength band signal light amplifying part 7a is the part for amplifying the whole wavelength band light to be amplified. The long wavelength band signal light amplifying part 7b is the part for efficiently amplifying a long wavelength band light except a short wavelength band light which is hardly amplified at the radial outer side part since it is difficult for the short wavelength band light to pass through the radial outer part in the core 7. The long wavelength band signal light amplifying part 7b can be formed as the part where the concentration of a rare earth element to be added is higher than that at the radial inner part in the core 7. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an amplification optical fiber and an optical amplification device using the same.
[0002]
[Prior art]
The amplification optical fiber incorporated in the amplification optical fiber has a core to which rare earth (erbium or the like) is added, and a cladding provided radially outside the core. (For example, see Patent Documents 1, 2, and 3)
[0003]
[Patent Document 1]
Patent No. 2582592 (full text)
[Patent Document 2]
JP-A-01-09329 (full text)
[Patent Document 3]
JP-A-04-050140 (full text)
[Problems to be solved by the invention]
With the increase in the capacity of optical fiber communication, it is desired to increase the bandwidth of an optical amplifier, but a sufficient bandwidth has not yet been achieved.
[0004]
Accordingly, a main object of the present invention is to widen the amplification band of an amplification optical fiber (amplification optical fiber).
[0005]
[Means for Solving the Problems]
In order to achieve the above-described object, a first aspect of the present invention includes a core, a rare earth element added to the core, and a clad provided radially outside the core,
The core is characterized in that the concentration of rare earth added in the radially outer portion of the core is higher than that in the radially inner portion of the core. Thereby, the following operation is provided.
[0006]
In the present invention, it is possible to amplify long-wavelength band light more efficiently than short-wavelength band light by making the concentration of rare earth added at the radially outer portion of the core higher than at the radially inner portion of the core. It becomes. This is due to the fact that light propagating in an optical fiber usually has a wider mode field diameter as the wavelength becomes longer. As a result, in the present invention, the density product of the signal light in the long wavelength band side is dramatically increased as compared with the density product of the signal light in the short wavelength band side. Therefore, it is possible to form a relatively short concentration line product suitable for short wavelength band light and a relatively long concentration line product suitable for long wavelength band light in the same amplification optical fiber. As a result, it is possible to realize a wider band of the amplification optical fiber.
[0007]
It is preferable that the concentration of the rare earth element added in the radially inner portion of the core is increased as the radially outer portion of the core is increased. Accordingly, it is possible to continuously vary the concentration length product. Since the concentration-length product varies continuously in proportion to the wavelength, the concentration-length product suitable for amplification at each wavelength is set by continuously varying the concentration-length product according to the wavelength. And the amplification efficiency is improved accordingly.
[0008]
It is preferable that the concentration of the rare earth element added in the radially outer portion of the core be increased toward the radially outer side of the core. Accordingly, it is possible to continuously vary the concentration length product. Since the concentration-length product varies continuously in proportion to the wavelength, the concentration-length product suitable for amplification at each wavelength is set by continuously varying the concentration-length product according to the wavelength. And the amplification efficiency is improved accordingly.
[0009]
In a second aspect of the present invention, the core includes a core, a rare earth element added to the core, and a clad provided radially outside the core.
The core has a signal light full-band amplification portion provided at a radially inner portion of the core, and a signal light long-wavelength band amplification portion provided at a radially outer portion,
The signal light full-band amplification part is a part that amplifies the whole band light to be amplified,
The signal light long wavelength band amplification portion is a portion that amplifies long wavelength band light with high amplification efficiency except for short wavelength band light having low amplification efficiency at the radial outside portion because it is difficult to pass through the radial outside portion of the core. Is,
It has special features. Thereby, the following operation is provided.
[0010]
In the present invention, by providing the signal light long-wavelength band amplification portion at the radially outer portion of the core, the longer the light on the longer wavelength side when viewed from the light, the greater the concentration length product, and the longer wavelength light is effective. Will be amplified. As a result, in the configuration of the present invention, it is possible to effectively amplify light in a long wavelength band as compared with a normal optical fiber containing rare earth uniformly.
[0011]
Therefore, it is possible to form a relatively short concentration line product suitable for short wavelength band light and a relatively long concentration line product suitable for long wavelength band light in the same amplification optical fiber. As a result, it is possible to realize a wider band of the amplification optical fiber.
[0012]
The signal light long wavelength band amplification part can be formed as a part having a higher concentration of the rare earth added than the signal light whole band amplification part.
[0013]
It is preferable that the concentration of the rare earth element added in the radially inner portion of the core is increased as the radially outer portion of the core is increased. Accordingly, it is possible to continuously vary the concentration length product. Since the concentration-length product varies continuously in proportion to the wavelength, the concentration-length product suitable for amplification at each wavelength is set by continuously varying the concentration-length product according to the wavelength. And the amplification efficiency is improved accordingly.
[0014]
It is preferable that the concentration of the rare earth element added in the radially outer portion of the core be increased toward the radially outer side of the core. Accordingly, it is possible to continuously vary the concentration length product. Since the concentration-length product varies continuously in proportion to the wavelength, the concentration-length product suitable for amplification at each wavelength is set by continuously varying the concentration-length product according to the wavelength. And the amplification efficiency is improved accordingly.
[0015]
In the first and second aspects of the present invention, the rare earth is preferably erbium.
[0016]
Further, even when an optical amplifier is configured by incorporating the first and second amplifying optical fibers of the present invention, the same function and effect can be obtained.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing a configuration of an optical amplifier 1 incorporating an amplification optical fiber 2 according to an embodiment of the present invention.
[0018]
The optical amplifying device 1 includes an amplification optical fiber 2, WDM multiplexers 3A and 3B, pumping light sources 4A and 4B, an input end transmission optical fiber 5, and an output end transmission optical fiber 6. ing.
[0019]
The signal light is input from the input end transmission optical fiber 5 and output from the output end transmission optical fiber 6.
[0020]
An amplifying optical fiber 2 for amplifying signal light is interposed and connected between the input-end-side transmission optical fiber 5 and the output-end-side transmission optical fiber 6. The amplification optical fiber 2 is composed of a rare earth-doped optical fiber. The most suitable rare earth-doped optical fiber is an erbium-doped optical fiber, but other rare earths such as neodymium may be used.
[0021]
The WDM multiplexers 3A and 3B are provided at at least one end (both ends in the present embodiment) of the amplification optical fiber 2. The WDM multiplexers 3A, 3B are provided between the amplification optical fiber 2 and the input / output end side transmission optical fibers 5, 6. Pump light sources 4A and 4B are connected to the WDM multiplexers 3A and 3B. The WDM multiplexers 3A and 3B introduce the pump light output from the pump light sources 4A and 4B into the amplification optical fiber 2.
[0022]
As shown in FIG. 2, the amplification optical fiber 2 includes a core 7 and a clad 8 provided around the core 7.
[0023]
This optical amplifier 1 is characterized by the configuration of the core 7. The core 7 has a signal light full band amplification section 7a and a signal light long wavelength band amplification section 7b. The signal light full-band amplification portion 7a is provided on a radially inner portion of the core. The signal light long wavelength band amplification portion 7b is provided on a radially outer portion of the core 7. The signal light full band amplification section 7a is a section that amplifies the whole band light to be amplified. The signal light long wavelength band amplification portion 7b is a portion that amplifies long wavelength band light with high amplification efficiency except for short wavelength band light having low amplification efficiency at the radially outer portion because the signal light long wavelength band amplification portion 7b does not easily pass through the radially outside portion of the core 7. It is.
[0024]
The signal light full band amplification section 7a and the signal light long wavelength band amplification section 7b are configured as follows. That is, the core 7 is doped with a rare earth element such as erbium. By making the rare earth concentration different along the radial direction, the signal light full-band amplification part 7a and the signal light long-wavelength band amplification part 7b are different from each other. It is configured. Specifically, as shown in FIG. 3, a signal light full-band amplification part 7a provided at a radially inner part of the core 7 and a signal light long-wavelength band amplification part 7b provided at a radially outer part of the core 7 When compared with the above, the concentration of rare earth (erbium) is higher in the signal light long wavelength band amplification portion 7b. Further, in both the signal light full-band amplification section 7a and the signal light long-wavelength band amplification section 7b, the rare-earth addition concentration increases toward the outside of the core 7 in the radial direction. Note that, as shown in FIG. 3, the refractive index is the same for both the signal light full-band amplification section 7a and the signal light long-wavelength band amplification section 7b. In FIG. 3, the dashed line indicates the light intensity in the C band, and the two-dot chain line indicates the light intensity in the L band.
[0025]
When erbium is used as the rare earth, its maximum addition concentration (the maximum addition concentration in the signal light long wavelength band amplification portion 7b) is preferably set to the maximum possible concentration, specifically, about 1000 ppm is preferable, but up to about 3000 ppm. Can be amplified without significant performance degradation. In particular, in the L band, even at 3000 ppm, amplification can be performed with almost no reduction in amplification efficiency.
[0026]
With the above configuration, the optical amplifying device 1 can widen the amplification band. Hereinafter, the reason will be described.
[0027]
In general, in optical amplification using an amplification optical fiber, a concentration product (rare earth concentration × optical fiber length) corresponding to each wavelength (amplification wavelength) of the signal light to be amplified is required. The concentration product is proportional to the amplification wavelength, and the longer the amplification wavelength, the larger the concentration product. For example, comparing the C band (1530 to 1565 nm) and the L band (1565 to 1625 nm), the L band requires about 5 times or more the concentration length product of the C band. Therefore, if the concentration length product can be set according to each wavelength band of the signal light, it is possible to widen the amplification band of the amplification optical fiber.
[0028]
The concentration strip product is the product of the rare earth concentration and the fiber length of the rare earth doped optical fiber. Therefore, for optical fibers of the same length, the concentration-length product is proportional to the rare-earth concentration (hereinafter referred to as the effective concentration) in the core region through which the signal light actually passes. Becomes larger. The effective density is affected by the cross-sectional area of the core through which the signal light passes (hereinafter, referred to as a “passing cross-sectional area”) and the light intensity distribution in the core radial direction. When the rare earth is uniformly added to the core, the effective concentration is proportional to the cross-sectional area, and the larger the cross-sectional area, the higher the effective concentration of the rare earth. This indicates that the effective density can be controlled by changing the cross-sectional area.
[0029]
The optical amplifying device 1 focuses on the mode field diameter MFD in order to control the passage cross-sectional area. As shown in FIG. 4, the mode field diameter MFD is proportional to the wavelength of the signal light, and the longer the wavelength, the larger the mode field diameter MFD, and the shorter the wavelength, the smaller the mode field diameter MFD. Therefore, as shown in FIG. 3, the signal light on the long wavelength band side is irrespective of the radially inner portion (signal light full band amplification portion 7a) and the outer portion (signal light long wavelength band amplification portion 7b) of the core 7. While the signal light passes relatively evenly, the signal light in the short wavelength band side is biased toward the radially inner portion (the signal light full-band amplification portion 7a). Therefore, the cross-sectional area of the signal light in the long wavelength band is larger than the cross-sectional area of the signal light in the short wavelength band. It is greater than the product of the density of light.
[0030]
However, as described above, the concentration length product required for the L band (1565 to 1625 nm) is about 5 times or more the concentration length product required for the C band (1530 to 1565 nm). For this reason, it is impossible to widen the amplification band only by the increase in the product of the concentration length caused by the increase in the cross-sectional area.
[0031]
Therefore, in the optical amplifying device 1, the concentration of the rare earth added in the radially outer portion of the core 7 (the signal light long wavelength band amplification portion 7b) is higher than that in the radially inner portion of the core. This makes it possible to amplify the long wavelength band light with higher amplification efficiency than the short wavelength band light. As a result, in the optical amplifying device 1, the effective concentration of the rare earth in the signal light in the long wavelength band is significantly higher than the effective concentration of the rare earth in the signal light in the short wavelength band. As a result, in the optical amplifying device 1, the concentration product in the signal light in the long wavelength band is significantly larger than the concentration product in the signal light in the short wavelength band. Therefore, a relatively short concentration-length product suitable for short-wavelength band light (such as C-band) and a relatively long concentration-length product suitable for long-wavelength band light (such as L-band) are converted into the same amplification optical fiber. 2 can be made. As a result, the optical amplifying device 1 achieves a wider band.
[0032]
In the optical amplifying device 1, the concentration of rare earth element (erbium) added in the radially inner part of the core 7 (the signal light full-band amplification part 7 a) and the radially outer part of the core 7 (the signal light long-wavelength band amplification part 7 b). Is increased toward the outside of the core 7 in the radial direction. Thereby, in the signal light in the short wavelength band side, it is possible to continuously vary the concentration length product according to the wavelength. In the optical amplifying device 1, the concentration strip product varies continuously according to the wavelength because the concentration strip product varies continuously in proportion to the wavelength. As a result, in the optical amplifying device 1, it is possible to set the concentration length product suitable for amplification of each wavelength, and the amplification efficiency is further improved accordingly.
[0033]
Such a structure of the amplification optical fiber 2 can be manufactured as follows.
[0034]
First method When manufacturing soot to be a core, while increasing the soot density to be the central part of the core 7 (the signal light full-band amplification part 7a), the peripheral part of the core 7 (the signal light long wavelength) The soot density to be the band amplification portion 7b) is made lower than the central portion. Then, the soot thus prepared is immersed in a rare earth (erbium or the like) -containing solution to add the rare earth to the soot. As a result, the amount of rare earth added in the core peripheral portion (signal light long wavelength band amplification portion 7b) is made higher than in the core central portion (signal light full band amplification portion 7a). This is based on the fact that the low-density region in the soot has a higher rare earth concentration than the high-density region.
[0035]
Second method A quartz glass rod (to which a small amount of Ge, Er, and Al is added) that can be the core 7 is used as a seed rod at the time of manufacturing the soot, so that the peripheral portion of the core 7 (signal light length) is used. The addition amount of the rare earth element in the wavelength band amplification section 7b) is increased from the central portion of the core 7 (the signal light full band amplification section 7a). This is based on the fact that rare earth is hardly added to the center of the core 7 made of a seed rod.
[0036]
Third method When the soot is immersed in the rare earth solution, only the side surface of the soot is immersed in the solution, so that the amount of the rare earth added to the peripheral portion of the core 7 (the signal light long wavelength band amplification portion 7b). From the center of the core 7 (the signal light full-band amplification portion 7a).
[0037]
Fourth method When soot is immersed in a rare earth solution, the entire soot is immersed in the solution at one time, so that the deaeration of the central part of the soot is insufficient. The added amount of the rare earth element in the optical long wavelength band amplification section 7b) is made higher than the central portion of the core 7 (the signal light full band amplification section 7a). This is based on the fact that the rare earth does not sufficiently penetrate into the region where the degassing is insufficient.
[0038]
The arrangement structure of the signal light full band amplification part 7a and the signal light long wavelength band amplification part 7b may be configured as shown in FIG. In the configuration of FIG. 3, the signal light full-band amplification portion 7a and the signal light long-wavelength band amplification portion 7b are formed continuously in the core 7 in the radial direction. In the configuration of FIG. 5, the signal light full-band amplification portion 7a 'and the signal light long-wavelength band amplification portion 7b' are formed discontinuously in the radial direction, and rare earth elements are present between the portions 7a 'and 7b'. A portion 7c to which no addition is made is provided. The signal light long wavelength band amplification section 7b 'has a higher concentration of rare earth (erbium) than the signal light full band amplification section 7a'. Furthermore, the concentration of the rare earth element added to the signal light full-band amplification portion 7a 'becomes higher toward the outside of the core 7 in the radial direction. In the signal light full-band amplification portion 7a ', the rare earth addition concentration is constant. Regarding the refractive index, the signal light long wavelength band amplification section 7b 'is set lower than the signal light full band amplification section 7a'. In FIG. 5, the dashed line indicates the light intensity in the C band, and the two-dot chain line indicates the light intensity in the L band.
[0039]
This configuration has the following advantages. That is, it is known that the amplification characteristic of a rare-earth-doped optical fiber (especially erbium-doped optical fiber) changes rapidly around 1560 to 1570 nm. With the configuration shown in FIG. 5, it is possible to rapidly increase the mode field diameter MFD at a wavelength near 1560 to 1570 nm. As a result, the effective concentration of the rare earth element with respect to light having a wavelength band longer than 1560 to 1570 nm, and furthermore, the product of the concentration of the rare earth element can be significantly increased. It is possible to give the product of the length of the article.
[0040]
【The invention's effect】
As described above, according to the present invention, not only the amplification band of the C band and the L band can be widened, but also the amplification of both bands can be performed with one amplification optical fiber. As described above, the present invention can provide an amplifying optical fiber and an optical amplifying device capable of performing broadband amplification.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an optical amplifying device incorporating an amplifying optical fiber according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the amplification optical fiber according to the embodiment.
FIG. 3 is a diagram illustrating a rare earth concentration, a refractive index, and a light intensity of the amplification optical fiber according to the embodiment;
FIG. 4 is a diagram showing a relationship between a wavelength and a mode field diameter in an amplification optical fiber.
FIG. 5 is a diagram showing a rare earth concentration, a refractive index, and a light intensity of an amplification optical fiber according to a modified example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical amplifier 2 Amplification optical fiber 3A, 3B WDM multiplexer 4A, 4B Excitation light source 5 Input end side transmission optical fiber 6 Output end side transmission optical fiber 7 Core 7a Signal light full band amplification part 7b Signal light length Wavelength band amplification part 8 Cladding MFD mode field diameter

Claims (9)

A core, a rare earth element added to the core, and a clad provided radially outside the core,
Rare earth addition concentration of the radially outer portion of the core, higher than the radially inner portion of the core,
An optical fiber for amplification, characterized in that: The amplification optical fiber according to claim 1,
The concentration of rare earth added at the radially inner portion of the core is increased toward the radially outer side of the core,
An optical fiber for amplification, characterized in that: The optical fiber for amplification according to claim 1 or 2,
The concentration of rare earth added at the radially outer portion of the core is increased toward the radially outer side of the core,
An optical fiber for amplification, characterized in that: A core, a rare earth element added to the core, and a clad provided radially outside the core,
The core has a signal light full-band amplification portion provided at a radially inner portion of the core, and a signal light long-wavelength band amplification portion provided at a radially outer portion,
The signal light full-band amplification section is a section that amplifies the entire band light to be amplified,
The signal light long wavelength band amplification portion is a portion that efficiently amplifies long wavelength band light excluding short wavelength band light having low amplification efficiency at the radially outer portion because it is difficult to pass through the radially outer portion of the core. is there,
An optical fiber for amplification, characterized in that: The amplification optical fiber according to claim 4,
The signal light long wavelength band amplification portion is a portion where the rare earth addition concentration is higher than the signal light full band amplification portion of the core,
An optical fiber for amplification, characterized in that: The amplification optical fiber according to claim 5,
The concentration of rare earth added in the signal light long wavelength band amplification portion is increased toward the outside in the radial direction of the core,
An optical fiber for amplification, characterized in that: The amplification optical fiber according to claim 5 or 6,
The concentration of rare earth added in the signal light full-band amplification portion is increased toward the outside in the radial direction of the core,
An optical fiber for amplification, characterized in that: The amplification optical fiber according to any one of claims 1 to 7,
The rare earth is erbium,
An optical fiber for amplification, characterized in that: An optical amplification device comprising the amplification optical fiber according to any one of claims 1 to 8.

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