JP3353755B2 - Optical fiber amplifier - Google Patents

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, and more particularly to an optical fiber amplifier using a double clad type amplification optical fiber as an amplification medium.

[0002]

2. Description of the Related Art With an increase in transmission distance in an optical communication system, an optical fiber amplifier capable of directly amplifying an optical signal has been widely used.
Normally, an optical fiber amplifier includes an amplification optical fiber that amplifies an incident optical signal, an excitation light source that outputs excitation light,
It is constituted by an optical multiplexer that multiplexes the pump light with the optical signal and enters the optical fiber for amplification. Note that a rare earth element doped fiber doped with a rare earth element is used for the amplification optical fiber. For example, an erbium-doped optical fiber is used for amplifying an optical signal having a wavelength in the 1.55 μm band. The excitation light has a wavelength of 1.4.
Light having a wavelength in the 8 μm band or 0.98 μm band is used.

Conventionally, for example, when optically amplifying signal light having a wavelength in the 1.55 μm band, pumping light in the 1.48 μm band is multiplexed with the pump light, and both lights are incident on an amplification optical fiber. , 1.55 μm wavelength light and 1.48 μm wavelength light. As this optical multiplexer, a fusion type optical multiplexer in which an optical fiber is melted or an optical multiplexer composed of a dielectric multilayer film is used.

[0004] All of the above-mentioned configurations are based on the premise that the amplification optical fiber comprises a core and a single clad surrounding the core with a material having a lower refractive index than the core. On the other hand, in recent years, an amplification optical fiber called a double clad type has been introduced.
As a document describing a double clad type amplification optical fiber, for example, there is a document described in JP-A-09-205239. In the above document, the first and second claddings are formed over two layers on the outer periphery of a single mode core, and the core is doped with a four-level rare earth element. This also means that the refractive index of the second cladding is set small so as to satisfy a predetermined condition.

In order to construct an optical fiber amplifier using such a double clad type amplification optical fiber,
The signal light may be incident on the core, and the excitation light may be incident on the first clad around the core at the same time.

[0006]

In an optical transmission apparatus using an optical fiber amplifying apparatus, in order to cope with a transmission system having a longer transmission distance and an optical switching function, for example, an optical transmission apparatus has a watt-class A high output is demanded, and the application of the above-mentioned double clad type amplification optical fiber is expected to realize an optical fiber amplifier having a high gain to fulfill the demand.

The optical fiber amplifier amplifies the signal light by simultaneously injecting the signal light to be amplified into the optical fiber serving as the amplification medium and the pump light which gives the amplification medium an amplifying action. When using a double clad fiber,
It is sufficient that the signal light propagates through the core portion at the center of the fiber, and the pumping light mainly propagates through the clad portion formed to include the core outside the core.

However, there is a problem that it is difficult to couple the pumping light with high efficiency to the first cladding. As means for multiplexing the signal light and the pumping light for coupling, for example, a double-clad amplification optical fiber and a pumping light fiber are brought close to each other to form a directional coupler, and the light is coupled using evanescent coupling. There is a configuration in which the fiber output from the pumping light source is converted into an image by converting the clad portion of the double clad type amplification optical fiber using micro optics technology and coupled.

However, any of the configurations makes the structure complicated, and it is difficult to combine the excitation lights from a plurality of excitation light sources with high efficiency due to the high output, which makes it difficult to put to practical use. It is. Further, as an incidental problem, since the shape of the first clad is circular or rectangular and its size varies due to various factors, an appropriate means for easily coupling the pump light and the signal light is provided. Absent.

The optical fiber amplifier of the present invention is based on the premise that a double clad type optical fiber is used for the amplification optical fiber, and the signal light and the pump light are coupled to the amplification optical fiber with a simple configuration and with high efficiency. The purpose is to let them.

[0011]

In order to solve the above-mentioned problems, an optical fiber amplifier according to the present invention comprises a signal light optical fiber through which signal light propagates and a signal light optical fiber disposed substantially parallel to the vicinity of the signal light optical fiber. A bundle fiber including at least one pumping light optical fiber through which the pumping light propagates is used. On the other hand, the amplification optical fiber includes a core, a first cladding having a lower refractive index than the core, and a second cladding having a lower refractive index than the first cladding. An amplifying optical fiber having an optical signal for optically amplifying input signal light is used. Further, an excitation light source for outputting excitation light and inputting the excitation light to the optical fiber for excitation light is provided, and the optical fiber for signal light of the bundle fiber and the core of the amplification optical fiber are optically coupled. It is characterized by.

The end faces of the bundle fiber and the amplification optical fiber abut each other, and the signal light optical fiber of the bundle fiber and the core of the amplification optical fiber are optically coupled. Alternatively, a gradient index lens is disposed between the bundle fiber and the amplification optical fiber, and the signal light optical fiber of the bundle fiber and the core of the amplification optical fiber are optically coupled. Here, the core of the optical fiber for excitation light is arranged at a position facing the first clad of the optical fiber for amplification.

In addition, a gradient index optical fiber (graded index optical fiber) may be used instead of the gradient index lens.

[0014] The bundle fiber used in the optical fiber device of the present invention may further include a fiber ferrule, and the optical fiber for signal light and the optical fiber for pump light may both be accommodated in the fiber ferrule. In such a configuration, the optical fiber for signal light is disposed substantially at the center of the fiber ferrule, and the optical fiber for excitation light is disposed between the outer periphery of the optical fiber for signal light and the inner periphery of the fiber ferrule. The gap between the optical fiber for signal light and the optical fiber for excitation light on the inner circumference of the fiber ferrule is filled with a filler.

In the optical fiber device of the present invention, a double-clad type optical fiber is used as an amplification optical fiber, and a bundle fiber is used for inputting signal light and excitation light to the amplification optical fiber. More specifically, the bundle fiber is one in which an optical fiber for excitation light is arranged around and parallel to an optical fiber for signal light. The bundle fiber uses a fiber ferrule to house the signal light optical fiber and the excitation light optical fiber inside thereof, and is further structurally stabilized when filled with a filler.

The end faces of the bundle fiber and the amplifying optical fiber are abutted and connected in a so-called bad joint, or via a medium having a light condensing function such as a gradient index lens. An optically coupled configuration is employed. As mentioned above,
A double clad type optical fiber is used for the amplification optical fiber.On the other hand, the bundle fiber has an excitation light optical fiber arranged on the outer periphery in close proximity to the signal light optical fiber. When the core of the optical fiber for signal light is coupled, the pumping light is efficiently incident on the first cladding of the optical fiber for amplification, and this light enters the core from the first cladding. Can be caused.

In the above-mentioned configuration, when the refractive index distribution type lens is disposed between the bundle fiber and the amplification optical fiber, the core of the excitation light optical fiber is formed of the refractive index distribution type lens. If it is arranged at a position opposite to the first cladding of the amplification optical fiber, the pumping light can be excited by the first cladding of the amplification optical fiber even when condensed through the gradient index lens. Can be efficiently combined. In particular, in the gradient index lens, the length of the light emitted from the first end face near the second end face facing the first end face, that is, the pitch becomes a natural number (usually 1). What is necessary is just to select such a thing.

Here, both the bundle fiber and the amplification optical fiber used in the optical fiber amplifier of the present invention are characterized in that their end faces are formed such that the normal to the end face is oblique to the optical axis. And By doing so, it is possible to avoid the influence of the reflected return light at the connection part, and when the pump light is incident on the amplification optical fiber from the bundle fiber, the angle in the propagation direction is increased due to a slight difference in refractive index between the two. In addition, the pumping light crosses the core from the first cladding in the amplification optical fiber, so that the light can be efficiently amplified.

In the case where the bundle fiber and the amplification optical fiber are coupled via the gradient index lens, similarly to the case of the bad joint, the end face of the bundle fiber, the end face of the amplification optical fiber, and the first index of the gradient index lens are used. The first and first end faces are each formed so that the normal to the end face is oblique to the optical axis, so that the pump light efficiently crosses the core in the amplification optical fiber. You can do so.

In the above-described configuration of the optical fiber amplifier of the present invention, the bundle fiber is arranged on the input side with respect to the amplification optical fiber, and the signal light and the pump light propagate in the same direction. The light may be incident on an optical fiber (so-called forward excitation type). Conversely, on the output side, the signal light and the pump light are amplified in the opposite directions, that is, the signal light amplified and output from the amplification optical fiber is coupled to the signal light optical fiber of the bundle fiber, and The pumping light may be output from the pumping light optical fiber and incident on the amplification optical fiber (so-called backward pumping type). Furthermore, a bundle fiber can be arranged on both the input and output sides of the amplification optical fiber (so-called bidirectional pumping type).

In the above configuration, the optical fiber amplifier of the present invention is, for example, a forward pump type, and further comprises an optical isolator on the input side of the signal light optical fiber and the output side of the amplification optical fiber of the bundle fiber. Thus, the influence of the reflected return light can be avoided.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical fiber amplifier according to the present invention will be described in detail with reference to the drawings.

Before describing the configuration of the bundle fiber used in the optical fiber amplifier of the present invention and the entire configuration using the same, the double clad type amplification optical fiber used in the present invention will be described. 1 to 3
1 is a cross-sectional view showing an example of the structure of a double clad type amplification optical fiber used in an optical fiber amplifier of the present invention. In each drawing, the core portion is hatched (the same applies to FIGS. 4 and 5). The part around the core (the part without hatching) is the cladding.

The core 7a (refractive index n7) through which the signal light propagates
In a), a small amount of rare earth is added, and the periphery thereof is surrounded by a first clad 7b (refractive index n7b) and a second clad 7b.
c (refractive index n7c). In order to confine the light propagating to the core 7a, the refractive index is
It has a relationship of n7a>n7b> n7c. In general,
A circular first clad 7b is formed concentrically around a core 7a as shown in FIG. 1, and a second clad 7b is formed therearound.
Of which the clad 7c is formed is used. FIG.
Is an amplification optical fiber having a first cladding 7b having a rectangular cross section. FIG. 3 shows a configuration in which the first cladding 7b is circular but not concentric but the core 7a is eccentric. is there.

In order to optically amplify the signal light propagating through the core 7a, pump light is incident on the first cladding 7b. The pumping light has a function of exciting the rare earth element in the core 7a and amplifying the signal light. The second clad 7c is formed to confine the excitation light in the first clad 7b.

Next, the configuration of the bundle fiber used in the optical fiber amplifier of the present invention will be described.

FIGS. 4 and 5 are cross-sectional views of an example of a bundle fiber. The optical fiber 2 shown in FIG. 4 has a signal light optical fiber 2 arranged at the center and two optical fibers 2 on both sides thereof. The excitation light optical fibers 3-1 and 3-2 are arranged in parallel with the signal light optical fiber. These three optical fibers 2, 3-1 and 3-2 are cylindrical fiber ferrules 1.
, And the gap is filled with a filler 4 and fixed.

The bundle fiber shown in FIG. 5 has six excitation light optical fibers 3-1 to 3-6 arranged around a signal light optical fiber 2 arranged at the center. In the gap, like the bundle fiber shown in FIG.
The filler 4 is filled.

FIG. 6 is a side view of the above-described bundle fiber. The fiber ferrule 1 includes an optical fiber 2 for signal light and an optical fiber 3-1 for excitation light from the left side of the figure.
Are inserted and arranged in parallel. The right end of the ferrule 1 in the drawing is polished with its tips aligned.

Next, connection between the bundle fiber and the amplification optical fiber, that is, optical coupling will be described.

FIG. 7 is a diagram showing a state of connection between a bundle fiber and an amplification optical fiber used in the optical fiber amplifier of the present invention. The bundle fiber 10 shown in FIG. 6 is shown on the left side in the figure, and the amplification optical fiber 7 is shown on the right side.
It is shown. Both are the core of the optical fiber 2 for signal light of the bundle fiber 10 and the core 7 of the optical fiber 7 for amplification.
They are arranged so that a coincides with each other, that is, optically optimally couple. In the configuration shown in FIG. 7,
End faces of the bundle fiber 10 and the amplification optical fiber 7 that are abutted with each other are formed obliquely. This prevents the Fresnel reflected light at the connection point from returning to the optical fiber, and at the same time, when the pumping light enters the first clad of the amplification optical fiber 7, the light propagates obliquely through the clad due to refraction at the end face. In order to efficiently cross the core 7a.

FIG. 8 is a diagram showing the positional relationship between the two, in which the amplification optical fiber is viewed from the bundle fiber side (FIG. 7).
(A view of the side of the amplification optical fiber 7 from the AA ′ section in FIG. 3). The parts indicated by solid lines indicate the constituent parts of the bundle fiber. As described above, six excitation light optical fibers are arranged around the signal light optical fiber 2, and these are disposed inside the ferrule 1. Is housed. On the other hand, the dashed line indicates the configuration of a double clad type amplification optical fiber, in which a first clad is formed around a core 7a, and a second clad is further formed around the first clad.

Here, the optical fiber 2 for signal light and the optical fiber 7 for amplification of the bundle fiber 10 are connected such that the centers of the cores coincide. The first cladding of the amplification optical fiber is arranged so as to include the cores of the excitation light optical fibers 3-1 to 3-6 of the bundle fiber 10. Therefore, the signal light output from the bundle fiber 10 is coupled to the core 7a of the amplification optical fiber 7 with high efficiency. Then, the pump light output from the pump light optical fiber is incident on the first clad of the amplification optical fiber. The pumping light incident on the first cladding stays in the first cladding and permeates the core 7a in the process of propagating through the optical fiber, so that the amplifying optical fiber is excited.
Can be optically amplified.

The configuration in which the bundle fiber 10 and the amplification optical fiber 7 are connected by a so-called bad joint method has been described above. However, in the optical fiber amplifier of the present invention, the optical system of the bundle fiber 10 and the amplification optical fiber 7 is used. The typical connection may be configured as shown in FIG. That is, by arranging the gradient index lens 9 between the bundle fiber 10 and the amplification optical fiber 7, the two can be optically coupled to each other. The refractive index distribution type lens generally has a cylindrical shape, and is a lens in which the refractive index is distributed such that the refractive index is highest at the central axis and becomes lower toward the periphery. By using such a lens, the light incident from one end surface spreads once in the process of propagating through the lens,
Light can be condensed again by the light condensing action by the refractive index distribution.

In order to combine the two with high efficiency, the length of the gradient index lens should be such that the light emitted from one end face is just condensed on the other end face, that is, a natural number of pitches (normally Is 1 pitch).
This pitch usually varies depending on the wavelength, but may be adjusted to the wavelength of the signal light. Although the pitch slightly deviates at the wavelength of the pumping light, even in this case, the first cladding of the amplifying optical fiber 7 can couple with high efficiency because the light receiving region is wide. In the embodiment shown in FIG. 9 as well, the bundle fiber 10 is used to prevent the reflection at the end face from returning and to allow the excitation light to more efficiently traverse the core 7 a of the amplification optical fiber 7. Each end face of the optical fiber for use 7 and the gradient index lens 9 is formed obliquely.

In the above embodiment, the configuration using the gradient index lens has been described. Instead of the gradient index lens, a short gradient index optical fiber, for example, GI
A multimode fiber such as 50 can also be used. In this case as well, similarly to the configuration using the gradient index lens, by forming both end surfaces of the short optical fiber at an angle, the excitation light can be efficiently transmitted to the amplification optical fiber while avoiding the influence of the reflected return light. Across the core.

Next, the configuration of an optical fiber amplifier using this bundle fiber will be described. 10 to 12 are diagrams respectively showing the configurations of the first to third embodiments of the optical fiber amplifier of the present invention. FIG. 10 shows forward pumping, FIG. 11 shows backward pumping, and FIG. Has a configuration of an optical fiber amplifier corresponding to an input form of pump light called bidirectional pump.

In the configuration shown in FIG. 10, the bundle fiber 10 is arranged on the input side of the amplification optical fiber 7, and the pump light is input to the amplification optical fiber 7 from the same direction as the signal light. In the configuration shown in FIG. 11, the bundle fiber 10 is arranged on the output side of the amplification optical fiber 7, and the pump light is input in the opposite direction to the amplified and output signal light.

In the first embodiment, the optical isolators 6 and 8 are disposed on the input side of the bundle fiber 10 and the output side of the amplification optical fiber 7, respectively, in order to prevent the reflected light from returning. Have been. In the second embodiment, the input side of the amplification optical fiber 7 and the output side of the bundle fiber 10 are provided in order to prevent the reflected light from returning.
Optical isolators 6 and 8 are arranged respectively. Similarly, also in the third embodiment, optical isolators 6 and 8 are arranged on the input side of the bundle fiber 10 and the output side of the bundle fiber 11, respectively.

[0040]

Next, an embodiment of the optical fiber amplifier according to the present invention will be described in more detail with reference to an example.

Referring again to FIG. 10, the optical fiber amplifier of the present invention will be described. 1550 for signal light source 5
A laser emitting a wavelength in the nm band is used, and the laser output from the signal light source is optically coupled to the optical fiber 2 of the bundle fiber 10 via the optical isolator 6 already described. The bundle fiber 10 having the configuration shown in FIG. 6 is used, and the optical fiber 2 for signal light and the optical fibers 3-1 to 3-6 for excitation light are used.
Is a single mode fiber having a core diameter of 9 μm and a cladding diameter of 40 μm.

1.48 μm for the excitation light sources 4-1 to 4-6
An excitation laser that emits light of a wavelength in the (1480 nm) band is used, and is optically connected to optical fibers 3-1 to 6 composed of single mode fibers, similarly to a signal light source. The bundle fiber 10 is optically coupled by a so-called butt joint method in which the end faces of the double-clad amplification optical fiber 7 are directly butted together.

The cross-sectional structure of the double-clad amplification optical fiber 7 used in the present embodiment is such that the core 7a and the second clad 7c are concentric circles in FIG. , Φ185μm
It is. The first cladding 7b has a side of about 125 μm.
m has a substantially square shape.

On the other hand, the single mode fibers 3-1 to 3-6 for the pumping light of the bundle fiber 10 are arranged substantially concentrically with a radius of about 40 to 50 μm around the single mode fiber 2 for the signal light. This arrangement corresponds to the first clad 7 of the double clad type amplification optical fiber 7.
Any arrangement is possible as long as it is within the range of b.

A small amount of rare earth element is added to the core 7a (refractive index n7a) of the double clad type amplification optical fiber 7. In this embodiment, the optical fibers for excitation light 3-1 to 3-1
The wavelength of the excitation light input to 3-6 is in the 1480 nm band, and the one to which Er (erbium) is added as the rare earth element is used. As a rare earth element added to the double clad type amplification optical fiber, Nd (neodymium) can be used in addition to Er. In this case, the signal light wavelength is 0.8 μm band, and the wavelength of the pump LD 6 is 1. It is necessary to select the 1 μm band. In the case of Er addition, the wavelength of the excitation light is 1.48 μm (1480 nm).
In addition to the band, a 0.98 μm (980 nm) band can also be used.

A signal light (for example, wavelength = 1545 nm) having a wavelength in the 1.55 μm band is transmitted from the signal light source 5 to the optical isolator 6.
Through the core 7 of the double clad amplification optical fiber 7
a is optically incident. The pump light from the pump light sources 4-1 to 6 is supplied from the same side as the signal light via the bundle fiber 10 to the first clad 7 of the double clad amplifying optical fiber 7 from the same side.
b. At this time, a part of the excitation light also partially enters the core 7a. In the double clad type amplification optical fiber 7, the pumping light crosses the core 7a in the process of zigzag propagating inside the first cladding 7b. When the pumping light crosses the core, it converts energy into signal light via erbium. Light is amplified.

The butt joint of the bundle fiber 10 and the double clad type amplification optical fiber 7 is polished at an angle of about 8 degrees in order to reduce reflected return light. This oblique polishing prevents the return light from being reflected and helps the above-described excitation light incident on the first cladding 7b to be propagated in a zigzag manner, and also serves to cross the core 7a.

In the optical fiber amplifier having the above configuration, the pump light sources 4-1 to 4-6 each have a wavelength of 1.48 μm.
m (1480 nm) and a pump light source of 100 mW output (total pump power: 600 mW), and a signal light source of 0.15 mW (-1550 nm) at 1.55 μm (1550 nm).
0 dBm), 10 mW (+1
0 dBm), and the effect is confirmed. Also, it has been confirmed that similar effects can be obtained in the other embodiments of the present invention shown in FIGS.

[0049]

As described above, the optical fiber amplifier of the present invention uses a bundle fiber in which an excitation light optical fiber is arranged in parallel around a signal light optical fiber.
By adopting a configuration in which this is connected to a double clad amplification optical fiber, signal light and pump light can be more easily input to the double clad amplification optical fiber.

By using the above configuration, even when the shape of the first clad of the double clad type amplification optical fiber is changed, it is possible to cope only by changing the arrangement of the single mode fibers 3-1 to n of the bundle fiber 10. Also, there is an effect that the pump light and the signal light can be combined without requiring an optical design.

Further, by using a configuration in which the connection between the bundle fiber and the amplifying optical fiber is processed with an oblique end face, the pumping light incident on the first cladding of the amplifying optical fiber can cross the core. It is also possible to obtain a certain amplification effect.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of a double-clad amplification optical fiber used in an optical fiber amplifier of the present invention.

FIG. 2 is a cross-sectional view showing another example of the structure of the double clad type amplification optical fiber used in the optical fiber amplification device of the present invention.

FIG. 3 is a cross-sectional view showing another example of the structure of the double clad type amplification optical fiber used in the optical fiber amplification device of the present invention.

FIG. 4 is a sectional view showing an example of a bundle fiber used in the optical fiber amplifier of the present invention.

FIG. 5 is a cross-sectional view showing another example of the bundle fiber used in the optical fiber amplifier of the present invention.

FIG. 6 is a diagram showing a configuration of a bundle fiber used in the optical fiber amplifier of the present invention.

FIG. 7 is a diagram showing a connection state between a bundle fiber and an amplification optical fiber used in the optical fiber amplification device of the present invention.

FIG. 8 is a diagram for explaining a coupling state between a bundle fiber and an amplification optical fiber used in the optical fiber amplifier of the present invention.

FIG. 9 is a diagram showing a connection state between the bundle fiber and the amplification optical fiber used in the optical fiber amplifier of the present invention, showing a state where the bundle fiber and the amplification optical fiber are connected via a gradient index lens. .

FIG. 10 is a configuration diagram showing a first embodiment of the optical fiber amplifier of the present invention.

FIG. 11 is a configuration diagram showing a second embodiment of the optical fiber amplifier according to the present invention.

FIG. 12 is a configuration diagram illustrating a third embodiment of the optical fiber amplifier according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ferrule 2 Optical fiber for signal light 3-1 to n Optical fiber for excitation light 4-1 to n Excitation light source 5 Signal light source 6, 8 Optical isolator 7 Double clad type amplification optical fiber 7a Core 7b First clad 7c 2 clad 9 gradient index lens 10 bundle fiber 11 bundle fiber

Claims (18)

(57) [Claims] 1. An optical fiber for signal light through which signal light propagates, and an optical fiber for signal light, which is disposed in parallel near the optical fiber for signal light,
A bundle fiber including at least one optical fiber for excitation light through which the excitation light propagates, a core, and a first fiber having a lower refractive index than the refractive index of the core.
And a second cladding having a lower refractive index than the first cladding, an amplification optical fiber for optically amplifying the input signal light, and an excitation light, An excitation light source for injecting excitation light into the optical fiber for excitation light, and an excitation light source disposed between the bundle fiber and the optical fiber for amplification.
Optical fiber for the signal light of the bundle fiber
Optically coupled to the core of the optical fiber for amplification
An optical fiber amplifying device, comprising: a gradient index lens . Core wherein said excitation Hikari Mitsumochi fiber claims, characterized in that disposed in a position opposite to said first cladding of the amplification optical fiber across the gradient index lens 2. The optical fiber amplifier according to 1 . 3. The gradient index lens has a length such that light emitted from a first end face is collected near a second end face facing the first end face. Claim
The optical fiber amplifier according to claim 1 . 4. The optical fiber the amplified and the fiber bundle are both claims normal end faces, wherein the end face is formed so as to be oblique to the optical axis
The optical fiber amplifier according to any one of claims 1 to 3 . 5. A normal line of each of the end faces of the bundle fiber and the amplification optical fiber, and the first end face and the second end face of the gradient index lens are oblique to the optical axis. The said end surface is formed in this way, The description in any one of the Claims 1 thru | or 3 characterized by the above-mentioned.
Placing the optical fiber amplifier. 6. An optical fiber for signal light through which signal light propagates, and disposed in parallel near the optical fiber for signal light,
A bundle fiber including at least one optical fiber for excitation light through which the excitation light propagates, a core, and a first fiber having a lower refractive index than the refractive index of the core.
And a second cladding having a lower refractive index than the first cladding, an amplification optical fiber for optically amplifying the input signal light, and an excitation light, An excitation light source for injecting excitation light into the optical fiber for excitation light, and an excitation light source disposed between the bundle fiber and the optical fiber for amplification.
Optical fiber for the signal light of the bundle fiber
Optically coupled to the core of the optical fiber for amplification
An optical fiber amplifying device comprising: a gradient index optical fiber. The core of claim 7 wherein said excitation Hikari Mitsumochi fiber claims, characterized in that disposed in a position opposite to said first cladding of the amplification optical fiber across the gradient index lens 7. The optical fiber amplifier according to 6 . 8. The gradient index lens has a length such that light emitted from a first end face is collected near a second end face opposite to the first end face. Claim
An optical fiber amplifier according to claim 6 or claim 7 . 9. optical fiber the amplified and the fiber bundle are both claims normal end faces, wherein the end face is formed so as to be oblique to the optical axis
An optical fiber amplifier according to any one of claims 6 to 8 . 10. The bundle fiber, the end face of the amplification optical fiber, and the first of the gradient index lenses.
9. The end face of claim 6 , wherein the end face is formed such that the normal to the end face is oblique to the optical axis. To
Optical fiber amplifier according. 11. The optical fiber for signal light is arranged at the center of a fiber ferrule, and the optical fiber for excitation light is arranged around the optical fiber for signal light and between the inner circumferences of the fiber ferrule. The optical fiber amplifier according to any one of claims 1 to 10 , wherein: 12. The gap between the optical fiber for signal light and the optical fiber for excitation light on the inner periphery of the fiber ferrule is filled with a filler.
An optical fiber amplifying device as described in the above. 13. The amplifying optical fiber, wherein the bundle fiber is disposed on a side where the signal light is input to the amplifying optical fiber, and the pumping light propagates in the same direction as the signal light to the amplifying optical fiber. The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier is inputted. 14. The amplifying optical fiber, wherein the bundle fiber is disposed on a side where the signal light is output from the amplifying optical fiber, and the pumping light propagates in a direction opposite to the signal light. 2. The data is input to the
The optical fiber amplifier according to any one of claims 1 to 12. 15. The bundle fiber is disposed on both the side on which the signal light is input and the side on which the signal light is output with respect to the amplification optical fiber, and the pump light has the same propagation direction as the signal light. The optical fiber amplifier according to any one of claims 1 to 12, wherein the light is input to the amplification optical fiber from both directions of the propagation direction. 16. The optical fiber amplifying device according to claim 13, further comprising: a first optical isolator disposed on an input side of the signal light optical fiber of the bundle fiber; An optical fiber amplifier comprising: a second optical isolator disposed on an output side. 17. The optical fiber amplifier according to claim 14, further comprising: a first optical isolator disposed on an input side of the amplification optical fiber; and a signal optical fiber of the bundle fiber. An optical fiber amplifier comprising: a second optical isolator disposed on an output side. 18. The optical fiber amplifying device according to claim 15, further comprising: a first optical isolator disposed on an input side of the signal fiber optical fiber of the bundle fiber; and the signal of the bundle fiber. An optical fiber amplifier comprising: a second optical isolator disposed on an output side of an optical fiber.