JP2000275451A - Optical multiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow light impinging on a refractive index gradient layer to efficiently shift into a core so as to multiplex certain wavelengths by providing a refractive index gradient clad layer. SOLUTION: A double clad fiber 10 includes a core layer 16 with the highest refractive index, a refractive-index gradient clad layer 18 located outside the core layer 16 and having a refractive index which is lower than the refractive index of the core layer 16 and decreases toward the outside, and an outer clad layer 20 located outside the refractive index gradient clad layer 18 and having a refractive index which is even lower than the lowest refractive index of the refractive index gradient clad layer 18. A multi-mode fiber 12 comprises a core layer 22 with a refractive index lower than the lowest refractive index of the refractive index gradient clad layer 18 and a clad layer 24 with the same refractive index as the outer clad layer 20. The outer clad layer 20 of the double clad fiber 10 and the clad layer 24 of the multi-mode fiber 12 are partially removed and the double clad fiber 10 and the multi-mode fiber 12 are bonded together in a bonding portion 14 at their respective side faces in such a manner that the refractive index gradient clad layer 18 makes direct contact with the core layer 22 over a predetermined range of length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplexer,
The present invention relates to an optical multiplexer that collects light incident from two different input ports and emits the light from one exit port.

[0002]

2. Description of the Related Art An optical multiplexer of this type includes a dielectric multilayer type multiplexer using a dielectric multilayer film having wavelength selectivity, and a distributed coupling type multiplexer obtained by fusing two glass fibers. There is a vessel.

[0003]

SUMMARY OF THE INVENTION Conventional optical multiplexers include:
In common, there are the following disadvantages. That is, first,
Only light having a wavelength determined by design can be combined. Second
In addition, the same wavelength or adjacent wavelengths cannot be combined.
Third, even if a plurality of multiplexers are used, a plurality of lights having the same wavelength cannot be multiplexed. Fourth, when a single mode fiber is connected to the output side, a multimode fiber cannot be connected to the input port side.

[0004] Further, in the distributed coupling type multiplexer, since the multiplexing characteristics are sinusoidal, the wavelength bandwidth that can be multiplexed is narrow.

An object of the present invention is to provide an optical multiplexer that solves such a problem.

That is, an object of the present invention is to provide an optical multiplexer capable of multiplexing light of any wavelength.

Another object of the present invention is to provide an optical multiplexer capable of multiplexing light having any wavelength including the same wavelength and a wavelength close to each other.

Another object of the present invention is to provide an optical multiplexer that can use a multi-mode fiber on the input port side when the output port side is a single mode fiber.

Another object of the present invention is to provide an optical multiplexer having a wide wavelength bandwidth.

Another object of the present invention is to provide an optical multiplexer having no limitation on the wavelength bandwidth.

[0011]

An optical multiplexer according to the present invention comprises a first optical transmission line and a second optical transmission line. The first optical transmission line includes a core layer, and an outer cladding layer having a lower refractive index than the core layer and an outer cladding layer having a lower refractive index than the inner cladding layer. I do. A second optical transmission line, a core layer having a lower refractive index than the refractive index of the inner cladding layer of the first optical transmission line, and
A cladding layer having a refractive index lower than that of the core layer; Then, the first optical transmission line and the second optical transmission line are placed on their side portions such that the inner cladding layer of the first optical transmission line and the core layer of the second optical transmission line are in contact with each other for a predetermined length. Glued.

According to such a configuration, light of the second optical transmission line is transferred to the second optical transmission line at the bonding portion simply by the refractive index, so that an arbitrary wavelength can be multiplexed. By preparing a plurality of multiplexers, it becomes possible to multiplex a plurality of wavelengths having the same wavelength.

The second optical transmission line has a gradient refractive index distribution in which the refractive index increases as the inner cladding layer of the first optical transmission line is closer to the core layer and decreases as the distance from the core layer increases. Light can be transferred to the core layer of the first optical transmission line at an early stage. This means that the length of the optical transmission line on the output side can be reduced.

By arranging the third optical transmission line having the inner cladding layer having the gradient index distribution on the output side of the first optical transmission line, the manufacturing requirements for the inner cladding layer having the gradient index distribution can be improved. Is alleviated. Therefore, it becomes easy to manufacture.

The first, second and third optical transmission lines can be realized by a fiber structure. This facilitates incorporation into an optical fiber transmission system.

[0016]

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

FIG. 1 is a longitudinal sectional view of a schematic configuration of an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG.

Numeral 10 denotes a double clad fiber having a gradient refractive index cladding, and numeral 12 denotes a multimode fiber, which are adhered at a portion 14 of the side surface surrounded by a broken line.

The double-clad fiber 10 has a core layer 16 having the highest refractive index and a refractive index outside the core layer 16 that is lower than the refractive index of the core layer 16 and gradually decreases toward the outside. It has a gradient refractive index cladding layer 18 and an outer cladding layer 20 outside the gradient refractive index cladding layer 18 and having a lower refractive index than the minimum refractive index of the gradient refractive index cladding layer 18. The number of the cladding layers may be three or more. The provision of the gradient refractive index cladding layer 18 allows the light incident on the gradient refractive index layer to be efficiently transmitted to the core layer 1.
6 can be transferred.

On the other hand, the multimode fiber 12 includes a core layer 22 having a refractive index lower than the minimum refractive index of the gradient refractive index cladding layer 18 of the double clad fiber 10, and a core layer 22.
The cladding layer 24 has a lower refractive index. As illustrated in FIG. 2, the radius of the core layer 22 of the multimode fiber 12 may be as large as the outer diameter of the gradient-index clad layer 18 of the double-clad fiber 10.

FIG. 3 shows the refractive index distribution as viewed from the line BB in FIG. The horizontal axis indicates the distance or position in the x direction with the center of the double clad fiber 10 as the origin, and the vertical axis indicates the refractive index. The refractive index of the core layer 16 of the double clad fiber 10 is n1, the maximum refractive index of the gradient refractive index cladding layer 18 is n2, the minimum refractive index is n3, and the multimode fiber 12
The refractive index of the core layer 22 is n4, the outer cladding layer 20 of the double clad fiber 10 and the multimode fiber 1
Assuming that the refractive index of the second cladding layer 24 is n5, n1> n
2>n3>n4> n5.

At the bonding portion 14, the outer cladding layer 20 of the double clad fiber 10 and the multimode fiber 1
The second cladding layer 24 is partially removed. Then, the double clad fiber 10 and the multimode fiber 12 are adhered on their side surfaces such that the refractive index gradient clad layer 18 of the double clad fiber 10 directly contacts the core layer 22 of the multimode fiber 12 within a predetermined length range. . For example, a fuser is used. Cladding layers 20, 24
If the material is made of a plastic resin, it is easy to remove a part of the material and it is easy to manufacture.

The double clad fiber 10 can be easily made into a single mode fiber by adjusting the radius of the core layer 16 and the refractive index difference between the core layer 16 and the refractive index gradient cladding layer 18. . In the following description, it is assumed that the double clad fiber 10 is a single mode fiber.

One end face 10 of the double clad fiber 10
a and the end face 12a on the same side of the multimode fiber 12.
Is an input port, and the other end face 10b of the double clad fiber 10 is an output port.

Obviously, light can enter the end face 12a of the multimode fiber 12 from either a multimode fiber or a single mode fiber. The light that has entered the multimode fiber 12 from the end surface 12a moves to the gradient-index cladding layer 18 of the double clad fiber 10 at the bonding portion 14, and further moves to the core layer 16 of the double clad fiber 10. The light once transferred to the core layer 16 propagates from the core layer 16 toward the end face 10b.

On the other hand, a fiber having a core layer similar to the double clad fiber 10, for example, a single mode fiber is connected to the end face 10a of the double clad fiber 10, and light is efficiently incident on the double clad fiber 10. it can. Light incident on the double clad fiber 10 from the end face 10a propagates through the core layer 16 toward the end face 10b. Also at the bonding portion 14, since the refractive index n4 of the core layer 22 of the multimode fiber 12 is lower than the minimum refractive index n3 of the gradient refractive index cladding layer 18, the light of the core layer 16 is guided to the core layer 22 of the multimode fiber 12. It will not be done.

In this manner, the light incident on the end face 10a of the double clad fiber 10 and the light incident on the end face 12a of the multimode fiber 12 are multiplexed by the bonding portion 14, and the other end face of the double clad fiber 10 Output from 10b.

In this embodiment, since the light is based only on the basic principle that the light is guided to a higher refractive index, it is basically independent of the wavelength. Therefore, any combination of wavelengths can be combined without limitation of the band.

The refractive index of the inner cladding layer 18 of the double clad fiber 10 decreases linearly in the radial direction, but the refractive index distribution of the inner cladding layer 18 is not limited to such an example. For example, the radius raised to the nth power (however, n
Is greater than one. ) May be changed.

FIG. 4 is a longitudinal sectional view showing a schematic configuration of a second embodiment of the present invention, and FIG. 5 is a sectional view taken along line CC of FIG.

In this embodiment, a double clad fiber 30 having two stages of two clad layers and a multimode fiber 32 are bonded at a side portion 34 thereof.

The double-clad fiber 30 has a core layer 36 having the highest refractive index, an inner cladding layer 38 outside the core layer 36 and having a lower refractive index than the core layer 36, and an outer cladding layer 38 outside the inner cladding layer 38. And an outer cladding layer 40 having a lower refractive index than that of the inner cladding layer 38. The number of the cladding layers may be three or more.

On the other hand, the multimode fiber 32
It has the same configuration as the multimode fiber 12 of the embodiment. That is, the fiber 32 includes the core layer 42 having a refractive index lower than the refractive index of the inner cladding layer 38 of the double clad fiber 30 and the cladding layer 44 having a lower refractive index than the core layer 42. As illustrated in FIG. 5, the radius of the core layer 42 of the multimode fiber 32 may be as large as the outer diameter of the inner cladding layer 38 of the double clad fiber 30.

FIG. 6 shows the refractive index distribution as viewed from the line DD in FIG. The horizontal axis indicates the distance or position in the x direction with the center of the double clad fiber 30 as the origin, and the vertical axis indicates the refractive index. The refractive index of the core layer 36 of the double clad fiber 30 is n1, the refractive index of the inner clad layer 38 is n2, the refractive index of the core layer 42 of the multimode fiber 32 is n4,
Assuming that the refractive index of the outer cladding layer 40 of the double clad fiber 30 and the refractive index of the cladding layer 44 of the multimode fiber 32 is n5, the relationship is n1>n2>n4> n5.

As in the first embodiment, the outer cladding layer 40 of the double clad fiber 30 is
And, the cladding layer 44 of the multimode fiber 32 is partially removed. Then, the double clad fiber 30 and the multimode fiber 32 are bonded on their side surfaces such that the inner clad layer 38 of the double clad fiber 30 is in direct contact with the core layer 42 of the multimode fiber 32 within a predetermined length range. For example, a fuser is used.
If the material of the cladding layers 40 and 44 is made of a plastic resin, it is easy to remove a part of the cladding layers 40 and 44, and it becomes easy to manufacture.

The double-clad fiber 30 can be easily made into a single-mode fiber by adjusting the radius of the core layer 36 and the refractive index difference between the core layer 36 and the inner clad layer 38. In the following description, it is assumed that the double clad fiber 30 is a single mode fiber.

One end face 30 of the double clad fiber 30
a and the end face 32a on the same side of the multimode fiber 32
Is an input port. The other end surface 30b of the double clad fiber 30 is connected to a double clad fiber 50 having a gradient refractive index clad layer. The end face 50b on the opposite side of the double clad fiber 50 becomes an output port.

The double-clad fiber 50 has basically the same configuration as the double-clad fiber 10, and has a core layer 52 having the highest refractive index and a core layer 52 outside the core layer 52 and having a lower refractive index than the core layer 52. And a refractive index gradient cladding layer 54 whose refractive index gradually decreases outward.
And an outer clad layer 56 having a lower refractive index than the minimum refractive index of the gradient refractive index cladding layer 54, outside the gradient refractive index cladding layer 54. The refractive index and radius of the core layer 52 and the maximum refractive index, the minimum refractive index, and the change in the radial refractive index of the refractive index gradient clad layer 54 change the optical coupling efficiency from the double clad fiber S30 to the double clad fiber 50. Set to be highest.

In the double clad fiber 50, for example, the refractive index of the core layer 52 is n1, the maximum refractive index of the gradient refractive index cladding layer 54 is n2, the minimum refractive index is n3, and the refractive index of the outer cladding layer 56 is n5. n3 is smaller than n2,
What is necessary is just to be larger than n5.

In this embodiment, the minimum refractive index of the gradient cladding layer 54 of the double clad fiber 50 can be determined independently of the refractive index of the core layer 42 of the multimode fiber 32. Becomes easier.

In this embodiment, obviously, light can be incident on the end face 32a of the multimode fiber 32 from either a multimode fiber or a single mode fiber. The light incident on the multimode fiber 32 from the end face 32a is transferred to the inner cladding layer 38 of the double clad fiber 30 at the bonding portion 34,
The transition to the core layer 36 is more gradual than in the first embodiment. When the light propagates in the longitudinal direction and reaches the double clad fiber 50, the core layer 36 of the double clad fiber 30
Is coupled into the core layer 52 of the double-clad fiber 50 and the inner clad layer 38 of the double-clad fiber 30.
Is coupled to the gradient-index cladding layer 54 of the double-cladding fiber 50. However, due to the refractive index gradient of the cladding layer 54, the light of the cladding layer 54 is rapidly transmitted to the core layer 52.
Move to In other words, the power field pattern in the radial direction becomes more focused near the center from the state expanded in the radial direction.

On the other hand, a fiber having a core layer similar to the double clad fiber 30, for example, a single mode fiber is connected to the end face 30a of the double clad fiber 30 so that light can be efficiently transmitted to the double clad fiber 30. Can be incident. Light incident on the double clad fiber 30 from the end face 30a propagates through the core layer 36. Since the refractive index n4 of the core layer 42 of the multimode fiber 32 is lower than the refractive index n2 of the inner cladding layer 38 at the bonding portion 34, the light of the core layer 36 is guided to the core layer 32 of the multimode fiber 32. There is no. The light that has propagated through the core layer 36 enters the core layer 52 of the double clad fiber 50, and is finally emitted from the end face 50b.

As described above, the light incident on the end face 30a of the double clad fiber 30 and the light incident on the end face 32a of the multimode fiber 12 are multiplexed by the bonding portion 34, and from the end face 50b of the double clad fiber 50. Output to the outside.

Also in this embodiment, since the light is based only on the basic principle of being guided to a higher refractive index, it is basically independent of the wavelength. Therefore, any combination of wavelengths can be combined without limitation of the band.

The refractive index of the inner cladding layer 54 of the double clad fiber 50 decreases linearly in the radial direction, but the refractive index distribution of the inner cladding layer 54 is not limited to such an example. For example, the refractive index distribution may be changed to the power of n (> 1) with respect to the radius.

The optical multiplexer according to the present invention can be used in a wide range of industrial fields such as optical communication, optical electronics, and medical fields, including high-power optical pumping required for fiber optical amplifiers and fiber lasers.

[0047]

As can be easily understood from the above description, according to the present invention, light of any wavelength can be multiplexed, and there is no restriction on the wavelength band. Even when a single mode fiber is used on the output port side, a multimode fiber can be used on the input port side. Since it can be realized with a simple structure, it can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a refractive index distribution of a section viewed from line BB in FIG. 2;

FIG. 4 is a longitudinal sectional view of a schematic configuration of a second embodiment of the present invention.

FIG. 5 is a sectional view taken along line CC of FIG. 4;

FIG. 6 is a refractive index distribution of a cross section taken along line DD in FIG. 5;

[Explanation of symbols]

 10: Double clad fiber 10a: Input end face 10b: Output end face end 12: Multimode fiber 12a: Input end face 14: Adhesive part 16: Core layer 18: Refractive index gradient cladding layer 20: Outer cladding layer 22: Core layer 24: Cladding Layer 30: Double clad fiber 30a: Input end face 30b: End face 32: Multimode fiber 32a; Input end face 34: Adhesive part 36: Core layer 38: Inner clad layer 40: Outer clad layer 42: Core layer 44: Cladded layer 50: Double clad fiber 50b: output end face 52: core layer 54: refractive index gradient clad layer 56: outer clad layer

Continued on the front page (72) Inventor Tetsuya Nakai 2-1-1-15 Ohara, Kamifukuoka-shi, Saitama In-house Cadidi Research Institute (72) Inventor Toshio Tani 2-1-1-15 Ohara, Kamifukuoka-shi, Saitama F-term (reference) 2K050 AB03X AB42Y AC05 AC09 AC36

Claims (10)

[Claims] 1. A core layer having an inner cladding layer having a lower refractive index than the core layer and an outer cladding layer having a lower refractive index than the inner cladding layer. A first optical transmission line, a core layer having a lower refractive index than the inner cladding layer of the first optical transmission line, and a cladding layer having a lower refractive index than the core layer. The first optical transmission line is formed such that the inner cladding layer of the first optical transmission line and the core layer of the second optical transmission line are in contact with each other for a predetermined length. An optical multiplexer, wherein the transmission line and the second optical transmission line are bonded at their side portions. 2. The refractive index increases as the inner cladding layer of the first optical transmission line is closer to the core layer of the first optical transmission line, and the refractive index decreases as the distance from the core layer increases. The optical multiplexer according to claim 1, comprising a distribution. 3. The method according to claim 1, further comprising:
It has an inner cladding layer whose maximum refractive index is lower than the refractive index of the core layer and the refractive index decreases as the distance from the core layer increases, and an outer cladding layer having a refractive index lower than the minimum refractive index of the inner cladding layer. 2. The device according to claim 1, further comprising a third optical transmission line, wherein the third optical transmission line is connected to the first optical transmission line on a multiplexed light output side of the first optical transmission line. 3.
3. The optical multiplexer according to 1. 4. The optical multiplexer according to claim 1, wherein said first optical transmission line is made of a fiber. 5. The optical multiplexer according to claim 4, wherein said first optical transmission line is made of a single mode fiber. 6. The optical multiplexer according to claim 1, wherein said second optical transmission line is made of a fiber. 7. The optical multiplexer according to claim 6, wherein said second optical transmission line is made of a multimode fiber. 8. The optical multiplexer according to claim 3, wherein said third optical transmission line is made of a fiber. 9. The optical multiplexer according to claim 8, wherein said third optical transmission line is made of a single mode fiber. 10. The optical multiplexer according to claim 1, wherein the outer cladding layer of the first optical transmission line and the cladding of the second optical transmission line are made of a plastic resin.