JPH10104450A - Optical splitter - Google Patents

Abstract

(57) [Problem] To provide an optical branching device which is inexpensive and has a flat amplification gain. SOLUTION: A signal light which is multiplexed with pump light in a rare earth-doped optical fiber 15 for optical amplification and amplified passes through rare earth-doped optical fibers 19-1 to 19-8 on the output side, thereby being amplified. Since the signal light of the specific wavelength whose rate has been increased is optically absorbed, the amplification gain deviation is reduced. When the polarization-independent isolator 11 is inserted between the rare earth-doped optical fiber 15 for optical amplification and the optical demultiplexer 17, light reflection is suppressed and loss can be reduced. When Al ₂ O ₃ is added to the cores of the rare earth-doped optical fibers 15, 19-1 to 19-8, the amplification gain deviation can be further reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical splitter for splitting signal light input to an input port of an optical star coupler into a plurality of output ports.

[0002]

2. Description of the Related Art Various optical components have been developed with the progress of optical communication technology. An optical splitter is also one of the optical components. The optical splitter splits the signal light input to the input port of the optical star coupler into a plurality of output ports.

FIG. 5 is a block diagram of a conventional optical splitter (Japanese Patent Application Laid-Open No. 3-252628).

[0004] An optical transmission line 2 is connected to one input end of an optical multiplexer 1 shown in the figure, and the other input end of the optical multiplexer 1 is connected to an output end of a semiconductor laser diode 4 via an optical fiber 3. It is connected. The output end of the optical multiplexer 1 is connected to the input end of an optical fiber fused type optical star coupler 5, and the output ends of the optical star coupler 5 are connected to the optical fibers 6-1, 6-2.
, 6-n are connected to Er (erbium) -doped optical fiber amplifiers 7-1, 7-2,..., 7-n to form an optical branching device 8.

The optical splitter 8 splits the signal light from the optical transmission line 2 with the pumping light from the semiconductor laser diode 4 in the optical multiplexer 1 and amplifies the signal light. The branch light is emitted from each Er-doped optical fiber amplifier 7-1, 7
,..., 7-n.

[0006]

However, the conventional optical branching device 8 uses n Er-doped optical fiber amplifiers 7-1, 7-2,... It is an expensive device as a whole. In the future wavelength division multiplexing communication, it is an essential condition that the wavelength dependency of the amplification gain is flat.
± 1 dB deviation of amplification gain between nm and 1560 nm
There was a problem that is larger than.

Since the Er-doped optical fiber has a high gain, the relative refractive index difference Δ1 between the core and the clad is usually 1%.
The relative refractive index difference Δ2 of the single mode fiber and the relative refractive index difference Δ3 of the waveguide type optical star coupler are set to 0. Set to a few percent. Because usually
Matching is performed between the relative refractive index difference Δ2 and the relative refractive index difference Δ3, and a specific matching method has not been found because the relative refractive index difference Δ1 is a particularly high value. Accordingly, a mismatch in the relative refractive index difference occurs between the waveguide type optical star coupler and the Er-doped optical fiber, and reflection occurs from this portion.

An object of the present invention is to solve the above-mentioned problems and to provide an inexpensive optical splitter having a flat amplification gain.

[0009]

To achieve the above object, the present invention provides an optical splitter for splitting a signal light input to an input port of an optical star coupler into a plurality of output ports, thereby generating pump light. An excitation light source, optical multiplexing means for inputting a signal light to one input terminal and connecting the other input terminal to an output end of the excitation light source, and multiplexing the excitation light and the signal light; and connecting to an output end of the optical multiplexing means In addition, a rare earth element is added to the core and a rare earth element is added to the core to increase the refractive index, and a pumping light from the signal light multiplexed with the pumping light is connected to the rare earth doped optical fiber for the light amplification. Optical demultiplexing means for demultiplexing, an optical star coupler having an input end connected to one output end of the optical demultiplexing means, and an optical star coupler connected to an output end of the optical star coupler for reducing amplification gain deviation at a wavelength of 1530 nm to 1560 nm. To the core Those having a rare earth doped optical fiber on the output side earth element has a high refractive streamlining been added.

In the present invention, in addition to the above configuration, it is preferable that a polarization independent isolator is inserted between the rare earth-doped optical fiber for optical amplification and the optical demultiplexing means.

In the present invention, in addition to the above structure, it is preferable that both rare earth-doped optical fibers have Al ₂ O ₃ co-doped in the core.

In addition to the above configuration, the present invention provides an optical multiplexing means for multiplexing signal light and pumping light from a pumping light source, an optical demultiplexing means for demultiplexing pumping light from the signal light multiplexed with the pumping light, and At least one of the optical star couplers for splitting the signal light may be formed on a flat substrate to form a waveguide type optical component.

In the present invention, in addition to the above configuration, the waveguide type optical demultiplexing means and the waveguide type optical star coupler may be formed on the same substrate.

In addition to the above configuration, the present invention provides a polarization-independent isolator which has a relative refractive index difference (n _cr −n _cl) calculated from the refractive index n _{cr of the} core and the refractive index n _cld of the cladding of the waveguide.
_d ) An isolator that can cope with an optical fiber having / n _cr of 1.0% or more, a waveguide type optical demultiplexing means and a waveguide type optical star coupler are formed on the same substrate, and the relative refractive index difference is reduced. The relative refractive index difference of the optical fiber doped with the rare earth element is ± 0.
Preferably it is in the range of 5%.

[0015] In addition to the above structure present invention, a waveguide-type optical components, the composition of the core is _{Si x O y N z H w} (0 ≦ x, y,
z, w ≦ 2).

In addition to the above configuration, the present invention provides a waveguide type optical component, wherein the composition of the core is (Si _x Ge _y ) O ₂ (0 ≦ x, y ≦
1).

In addition to the above-described structure, the present invention uses a rare-earth-doped multi-core optical fiber having a high relative refractive index difference and having a plurality of cores doped with a rare-earth element at least in a part of an optical fiber having a core doped with a rare-earth element. Is also good.

In the present invention, in addition to the above configuration, at least a part of the waveguide type optical component may be made of a polymer.

When the signal light is amplified by being combined with the pump light in the rare-earth-doped optical fiber for optical amplification, a peak value having a high amplification factor at a specific wavelength (for example, a wavelength between 1530 nm and 1560 nm) is obtained. However, according to the optical splitter of the present invention, the signal light corresponding to the peak value is optically absorbed by passing through the rare-earth-doped optical fiber on the output side, so that the wavelength dependence of the amplification gain is flattened. . That is, an optical splitter having a small amplification gain deviation can be obtained. Further, since the signal light is preliminarily amplified and then distributed to n, the distribution deviation can be suppressed.

In other words, of the rare earth-doped optical fibers,
The rare earth-doped optical fiber for amplification is literally a fiber for optical amplification, whereas the rare earth-doped optical fiber on the output side is a fiber for reducing amplification gain deviation.

The optical splitter of the present invention is not expensive because it uses only an optical fiber without using a system called an optical amplifier on the output side of an optical star coupler. The branch loss of the optical star coupler is at most 9 to 10 dB even when the 1 × 8 optical star coupler is used, and the amplification gain of the optical fiber for optical amplification is about 40 dB.
There is no problem because the amplification gain of about B is maintained. Furthermore, it was stated that a waveguide type optical demultiplexing means and a waveguide type optical star coupler were formed on the same substrate, and that they were supported by a generally used low Δ (specific refractive index difference) waveguide type optical component. Then, a fusion technology of an optical fiber and a waveguide type optical component such as a TEC (Thermal Expanded Core) technology is required.
When optical components having different Δ are connected, a problem of light reflection occurs.

Here, the TEC technology will be described.

When the low Δ single-mode optical fiber and the high Δ rare earth-doped optical fiber are fusion-spliced by using arc discharge, the connection of the high Δ rare earth-doped optical fiber is excessively heated. GeO ₂ added to each core of the high-Δ rare-earth-doped optical fiber is diffused to the cladding side, the Δ value of the high-Δ rare-earth-doped optical fiber near the connection portion is reduced, and the mode field diameter is increased. By doing so, mode field matching with the single mode optical fiber is achieved.

The length of the mode field matching area is usually 2
５5 mm, and the longer the length is, the smaller the loss at the connection part can be.

Accordingly, the present invention provides a polarization-independent isolator, an optical demultiplexer, and a waveguide type optical star coupler, in which Δ is made substantially equal to Δ of the core of the rare-earth-doped optical fiber. Can be reduced, and the problem of light reflection does not occur.

Al ₂ O ₃ is added to the core of the rare earth doped optical fiber.
Is added, the amplification gain deviation can be further reduced.

By making the relative refractive index difference of the waveguide type optical component substantially equal to that of the rare earth-doped optical fiber, the number of times of connection by the TEC technique can be reduced, and light reflection generated at the connection portion is suppressed as much as possible. be able to.

At least one of the optical multiplexing means, the optical demultiplexing means, and the optical star coupler is formed on a flat substrate to form a waveguide type optical component, or By forming the waveguide type optical star coupler on the same substrate, the size of the optical splitter can be reduced and the loss can be reduced.

The polarization independent isolator has a relative refractive index difference (n _cr −n _cld ) / n _cr calculated from the refractive index n _{cr of the} core and the refractive index n _cld of the cladding of the waveguide of 1.0. % Of an optical fiber with a waveguide type optical demultiplexing means and a waveguide type optical star coupler formed on the same substrate and having a relative refractive index difference doped with a rare earth element. When the relative refractive index difference is within the range of ± 0.5%, the number of fusion-spliced portions is reduced, so that light reflection is suppressed and the loss can be reduced.

The waveguide-type optical components, the composition of the core is Si _x O
_{When y} N _z H _w (0 ≦ x, y, z, w ≦ 2), the relative refractive index of the core can be adjusted and the loss can be reduced.

The waveguide type optical component has a core composition of (Si _x
When Ge _y ) O ₂ (0 ≦ x, y ≦ 1), the relative refractive index of the core can be adjusted and the loss can be reduced.

When a rare earth-doped multi-core optical fiber having a high relative refractive index difference and having a plurality of cores doped with a rare earth element is used as at least a part of the optical fiber doped with a rare earth element, the amplification gain deviation is further reduced. Can be smaller.

By using a polymer for at least a part of the waveguide type optical component, the cost of the optical splitter can be reduced.

[0034]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing one embodiment of the optical splitter of the present invention.

The other end of the single mode optical fiber 10 into which signal light is incident from one end (left end in the figure) is connected to the input end 11a of the polarization independent isolator 11. An output terminal 11b of the isolator 11 is connected to one input terminal 12a of an optical multiplexer 12 as an optical multiplexer. The other input end 12 b of the optical multiplexer 12 is connected to an output end 13 a of a pump light source (for example, a semiconductor laser diode) 13.
Through an optical fiber 14. Optical multiplexer 1
The second output end 12c is connected to one end 15a of a high refractive index optical fiber (hereinafter referred to as "rare earth doped optical fiber") 15 having a core doped with a rare earth element (for example, Er). The other end 15b of the rare-earth-doped optical fiber 15 is connected to the input end 16a of another isolator 16, and the output end 16b of the isolator 16 is connected to the input end 17a of an optical splitter 17 as an optical splitter. Optical splitter 17
One output terminal 17b of the optical star coupler 18 is a 1-input n-output type (in the drawing, a 1-input 8-output type is not limited).
Is connected to the input terminal 18a of the The other output terminal 17c of the optical demultiplexer 17 is not connected. The output ends 18a to 18i of the optical star coupler 18 have a plurality of (eight, but not limited to, eight in the figure) rare earth-doped optical fibers 19-1.
To 19-8. The other ends of the rare-earth-doped optical fibers 19-1 to 19-8 are connected to ordinary single-mode optical fibers 20-1 to 20-8, respectively, to form an optical splitter 21.

Rare earth doped optical fibers 15, 19-1 to 1
In 9-8, 600p of Er was added to Ge-added SiO ₂ glass.
An optical fiber doped with pm, having a core diameter of 3 μm and a fiber length of 5 m is used.

When signal light is input to one end of the single mode optical fiber 10, the signal light passes through the isolator 11 and is multiplexed with the pump light from the pump light source 13 by the optical multiplexer 12. The signal light multiplexed with the pump light is subjected to optical amplification when passing through the rare-earth-doped optical fiber 15, and immediately thereafter passes through the isolator 16. The signal light that has passed through the isolator 16 is separated by the optical demultiplexer 17 into pump light and removed. The signal light is divided into eight by the optical star coupler 18, passes through rare-earth-doped optical fibers 19-1 to 19-8 for flattening the amplification gain, and finally to single-mode optical fibers 20-1 to 20-8. Reach. The connection between the optical multiplexer 12 and the rare-earth-doped optical fiber 15 and the connection between the rare-earth-doped optical fibers 19-1 to 19-8 and the single-mode optical fibers 20-1 to 20-8 are fusion spliced by TEC technology. Have been.

When the signal light is amplified by being combined with the pump light in the rare-earth-doped optical fiber for optical amplification, a peak value having a high amplification factor at a specific wavelength (for example, a wavelength between 1530 nm and 1560 nm) is obtained. Have. However, the optical splitter 21 according to the present invention includes the output terminals 18 b to 1
By connecting rare-earth-doped optical fibers 19-1 to 19-8 to 8i, the amplified signal light passes through the rare-earth-doped optical fibers 19-1 to 19-8 on the output side, and corresponds to the peak value. Since the signal light is optically absorbed, the wavelength dependence of the amplification gain is flattened. That is, an optical splitter having a small amplification gain deviation can be obtained. Further, since the signal light is preliminarily amplified and then distributed to n, the distribution deviation can be suppressed. For example, conventionally, the wavelength is 1530 nm to 1560 nm.
Amplification gain deviation which was about 10 dB between the optical fibers was reduced to 2 dB by using the rare earth doped optical fibers 19-1 to 19-8.
It was suppressed to about B.

Further, the optical branching device 21 of the present invention uses eight rare earth-doped optical fibers 19-1 to 19-8 instead of using eight systemized optical amplifiers, so that the cost can be reduced. Can be planned.

Further, since the optical branching device 21 of the present invention uses a single mode optical fiber having a normal relative refractive index difference on the input and output sides, it can be easily applied to a conventional optical fiber communication system. Cost reduction can be introduced.

As described above, in the present embodiment, Er is added to Ge-doped SiO ₂ glass as a rare earth-doped optical fiber.
Has been described in the case of using the 00ppm optical fiber doped, is not limited thereto, Ge added SiO ₂
5000 ppm of Al ₂ O ₃ as well as Er
An optical fiber doped with 20,000 ppm may be used.
By increasing the amount of Al ₂ O ₃ added, the wavelength 15
The amplification gain deviation between 30 nm and 1560 nm can be further reduced.

Incidentally, a waveguide type optical component in which at least one of the optical multiplexer, the optical demultiplexer and the optical star coupler is formed on a flat substrate can be used.

FIG. 2 is a block diagram showing another embodiment of the optical splitter of the present invention. Note that the same members as those of the optical branching device shown in FIG.

The difference from the optical splitter 21 shown in FIG.
The optical demultiplexer 17 and the optical star coupler 18 are connected to the flat substrate 3
That is, it is integrally formed on the upper surface of the hologram. Such an optical splitter 31 can also reduce the amplification gain deviation similarly to the optical splitter 21 shown in FIG. 1, and can be manufactured at low cost.

Here, the isolator 16 connected to the other end 15b of the rare earth-doped optical fiber 15 for optical amplification can be an isolator compatible with an optical fiber having a relative refractive index difference of 1.0% or more. In addition, the waveguide type optical demultiplexer and the waveguide type optical star coupler can be formed on the same substrate, and the relative refractive index difference between the isolators 11 and 16 is determined by the refractive index of the rare earth doped optical fiber for amplification. Rate difference ± 0.5
%. In this case, the optical branching device is such that the isolator of the optical branching device shown in FIG. 2 can cope with a relative refractive index difference of 2.0% or more, and a waveguide type optical demultiplexer and a waveguide type optical star coupler. Are formed on the same substrate, and the relative refractive index difference of the optical waveguide type component is set to 2.0%, which is the same as the relative refractive index difference of the rare-earth-doped optical fiber. ). In this case, since the rare earth-doped optical fiber, the polarization-independent isolator, the optical waveguide component, and the rare-earth-doped optical fiber have the same relative refractive index difference, the number of times of fusion using the TEC technology should be reduced. Light reflection due to fusion can be suppressed as much as possible.

[0047] Although the composition of the waveguide type optical component not specifically described, the composition of the waveguide type optical component core Si _x O _{y
N z H w (0 ≦ x} , y, z, w ≦ 2), or (Si _x
Ge _y ) O ₂ (0 ≦ x, y ≦ 1).

FIG. 3 is a block diagram showing another embodiment of the optical splitter of the present invention.

The difference from the optical splitter 21 shown in FIG.
The rare earth doped optical fiber 15 is not a single core type,
It is a multi-core type. The portion indicated by the thick line is the rare-earth-doped multi-core optical fiber 40. By using the rare earth-doped multi-core optical fiber 40, the difference in amplification gain can be further reduced. This optical splitter 41
Need not make the relative refractive index difference of the waveguide type optical star coupler 2.0%.
The relative refractive index difference is selected so that the mode field diameter, which is the optical electric field strength of the optical waveguide device, and the mode field diameter of the optical waveguide type component match.

FIG. 4 is a block diagram showing another embodiment of the optical splitter of the present invention.

The difference from the optical branching device shown in FIG. 1 is that the waveguide type optical component is formed of a polymer. Since the optical splitter 51 has the optical demultiplexer and the optical star coupler integrally formed on the substrate 50 made of a polymer, the cost can be reduced by that much.

[0052]

In summary, according to the present invention, the following excellent effects are exhibited.

The signal light multiplexed with the pump light and amplified in the rare-earth-doped optical fiber for optical amplification passes through the rare-earth-doped optical fiber on the output side, and has a specific wavelength having an increased amplification factor. Since the signal light is optically absorbed, it is possible to provide an optical branching device which is inexpensive and has a flat amplification gain.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical splitter according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the optical splitter of the present invention.

FIG. 3 is a block diagram showing another embodiment of the optical splitter of the present invention.

FIG. 4 is a block diagram showing another embodiment of the optical splitter of the present invention.

FIG. 5 is a block diagram of a conventional optical splitter.

[Explanation of symbols]

11, 16 Isolator 12 Optical multiplexer 13 Pump light source 15, 19-1 to 19-8 Rare earth doped optical fiber (E
r-doped optical fiber) 17 Optical demultiplexer 18 Optical star coupler

Claims (10)

[Claims] 1. An optical splitter for splitting a signal light input to an input port of an optical star coupler into a plurality of output ports, comprising: an excitation light source for generating an excitation light; The pumping light of the pumping light source is input to the input end of the optical multiplexing means. The optical multiplexing means multiplexes the pumping light and the signal light. The optical multiplexing means is connected to the output end of the optical multiplexing means. A rare earth-doped optical fiber for optical amplification having a refractive index, an optical demultiplexer connected to the rare earth-doped optical fiber for optical amplification, and a demultiplexer for demultiplexing the pump light from the signal light multiplexed with the pump light; Is an optical star coupler connected to one output terminal of the optical demultiplexing means, and has a wavelength of 1530 nm to 156.
An optical branching optical fiber connected to the output end of the optical star coupler for reducing the amplification gain deviation at 0 nm and having a rare-earth element added to the core and having a high-refractive-index output-side rare-earth-doped optical fiber; vessel. 2. The optical splitter according to claim 1, wherein a polarization independent isolator is inserted between the optical amplification rare earth doped optical fiber and the optical demultiplexing means. 3. The optical splitter according to claim 1, wherein said rare earth-doped optical fiber has a core co-doped with Al ₂ O ₃ . 4. An optical multiplexing means for multiplexing the signal light and the pumping light from the pumping light source, an optical demultiplexing means for demultiplexing the pumping light from the signal light multiplexed with the pumping light, and for branching the signal light. 4. The optical splitter according to claim 1, wherein at least one of the optical star couplers is formed on a flat substrate to form a waveguide type optical component. 5. The optical splitter according to claim 4, wherein the waveguide type optical demultiplexer and the waveguide type optical star coupler are formed on the same substrate. 6. The above polarization independent isolator has a relative refractive index difference (n _cr −n _cld ) / n _cr calculated from the refractive index n _{cr of the} core and the refractive index n _cld of the cladding of the waveguide. 1.0
%, Which is an optical fiber capable of coping with an optical fiber having a relative refractive index difference of not less than 1%, wherein a waveguide type optical demultiplexing means and a waveguide type optical star coupler are formed on the same substrate and the relative refractive index difference is doped with the rare earth element. The optical splitter according to claim 4, wherein the relative refractive index difference is within a range of ± 0.5%. 7. A waveguide-type optical components, the composition of the core is Si _{x
O y N z H w (0} ≦ x, y, z, w ≦ 2) optical splitter according to any one of claims 4 to 6 is. 8. The waveguide type optical component, wherein the composition of the core is (Si)
The optical splitter according to claim 4, wherein _x Ge _y ) O ₂ (0 ≦ x, y ≦ 1). 9. A multi-core rare-earth-doped optical fiber having a high relative refractive index difference and having a plurality of cores doped with a rare-earth element is used as at least a part of an optical fiber doped with a rare-earth element in a core. The optical splitter according to any one of the above. 10. The optical branching device according to claim 4, wherein at least a part of the waveguide type optical component is made of a polymer.