JP7306870B2 - Optical coupler and optical output device - Google Patents

Description

The present invention relates to optical couplers and optical output devices.

A TFB (Tapered Fiber Bundle) is known as an optical coupler (Patent Document 1). The optical coupler comprises a plurality of input optical fibers and a cladding pump optical fiber. A plurality of input optical fibers are bundled to form a bundle portion. The tip of the bundle is connected to the cladding pump optical fiber. The bundle portion has a tapered portion in which each of the plurality of input optical fibers is tapered to have a reduced cross-sectional area at the tip. According to this optical coupler, the light output from a plurality of light sources can be combined to increase the total optical power and output to the cladding pump optical fiber. This optical coupler may be applied to optical fiber lasers and optical fiber amplifiers.

U.S. Pat. No. 5,864,644

In the industrial field, there is a demand for higher power laser light. When a semiconductor laser element is used as a light source, as a method of increasing the power, the stripe width of the active layer, which is the portion that generates the laser light in the semiconductor laser element, is increased to increase the laser light output from each semiconductor laser element. There are ways to power it.

Since the beam diameter of the laser light is enlarged in the above-mentioned method of increasing the power, in order to efficiently input the laser light into the optical fiber, the fiber diameter or numerical aperture (NA) of the plurality of optical fibers of the optical coupler is is preferably increased. However, it is difficult to increase NA beyond a certain level. On the other hand, a technique for increasing the fiber diameter has not been sufficiently studied.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical coupler suitable for outputting high-power laser light and an optical output device using the same.

In order to solve the above-described problems and achieve the object, an optical coupler according to one aspect of the present invention includes a plurality of input optical fibers and an output optical fiber, the plurality of input optical fibers having a distal end. The ends of the bundle are bundled together to form a bundle, and the tip of the bundle is connected to the output optical fiber. In the bundle, each of the plurality of input optical fibers has a cross-sectional area at the tip. It has a tapered portion that is tapered so as to reduce, the numerical aperture of the output optical fiber is NAout, the numerical aperture of each of the plurality of input optical fibers is NAin, and the tapered portion is closer to the proximal side than the tapered portion. When the total cross-sectional area of the plurality of input optical fibers at the tip is ΣAi, and the cross-sectional area of the bundle portion at the tip is A, the following formula (NAout/NAin) ² <ΣAi/A
is characterized by

An optical coupler according to an aspect of the present invention is characterized in that an angle between the tapered portion and the optical axes of the plurality of input optical fibers is 0.045 radian or less.

An optical coupler according to an aspect of the present invention is characterized in that the output optical fiber has a numerical aperture of 0.22 or less.

An optical coupler according to an aspect of the present invention is characterized in that the clad layer of each of the plurality of input optical fibers at the distal end portion has a thickness of 1.7 μm or more.

In the optical coupler according to one aspect of the present invention, the thickness of the cladding layer at the tip of each of the plurality of input optical fibers is 1.9 times or more the wavelength of the light input from the base end. It is characterized by

A light output device according to an aspect of the present invention is characterized by comprising the optical coupler and a plurality of light sources each connected to a base end side of each of the plurality of input optical fibers.

A light output device according to an aspect of the present invention comprises an amplification optical fiber optically pumped by light output from the plurality of light sources, and an optical resonator, and is configured as an optical fiber laser. and

A light output device according to an aspect of the present invention is characterized in that each of the plurality of light sources is a semiconductor laser configured as a direct diode laser.

ADVANTAGE OF THE INVENTION According to this invention, it is effective in the ability to implement|achieve the optical coupler suitable for the output of a high-power laser beam.

FIG. 1 is a schematic diagram of an optical coupler according to Embodiment 1. FIG. FIG. 2 is a diagram showing the arrangement of multiple input optical fibers. FIG. 3 is a diagram showing radiation angle distributions of input light and output light. FIG. 4 is a schematic diagram of an optical coupler according to the second embodiment. FIG. 5 is a diagram showing another example of the arrangement of multiple input optical fibers. FIG. 6 is a diagram showing measurement results of radiation angle distributions of output light from a semiconductor laser element and output light from an output optical fiber. 7A is a schematic diagram of an optical coupler according to Embodiment 3. FIG. 7B is a schematic diagram of an optical coupler according to a modification of the third embodiment; FIG. FIG. 8 is a schematic diagram of a light output device according to Embodiment 4. FIG. FIG. 9 is a schematic diagram of a light output device according to Embodiment 5. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment described below. In addition, in the description of the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate, and overlapping descriptions are omitted as appropriate. Also, it should be noted that the drawings are schematic, and the relationship of dimensions of each element, the ratio of each element, and the like may differ from reality.

In Patent Document 1, NAout is the NA of the cladding pump optical fiber, NAin is the NA of each of the input optical fibers, ΣAi is the total cross-sectional area of the plurality of input optical fibers on the proximal end side of the taper portion, and the bundle at the distal end is It is described that the following formula holds when the cross-sectional area of the part is A.
(NAout/NAin) ² ≧ΣAi/A
A design that satisfies the above inequality is said to avoid excessive loss of light at the taper.

On the other hand, the inventors have found that a design that does not satisfy the above inequality can realize an optical coupler suitable for outputting high-power laser light.

(Embodiment 1)
FIG. 1 is a schematic diagram of an optical coupler according to Embodiment 1. FIG. The optical coupler 10 comprises an input optical fiber section 1 and an output optical fiber 2 .

The input optical fiber section 1 includes one input optical fiber 1a and six input optical fibers 1b as a plurality of (seven in this embodiment) input optical fibers. Here, as shown in FIG. 1, the distal end side and the proximal end side of the input optical fibers 1a and 1b are defined. The distal side and the proximal side are defined similarly in the subsequent embodiments.

FIG. 2 is a diagram showing the arrangement of the input optical fibers 1a and 1b, and is a view on arrow A as seen from the base end side in FIG. The input optical fiber 1a is arranged in the center, and the six input optical fibers 1b are arranged on the outer peripheral side of the input optical fiber 1a. The input optical fibers 1a, 1b are preferably arranged so as to be closest packed.

The input optical fiber 1a includes a core portion 1aa, a clad layer 1ab formed around the core portion 1aa, and a coating layer 1ac formed around the clad layer 1ab. The input optical fiber 1b includes a core portion 1ba, a clad layer 1bb formed around the core portion 1ba, and a coating layer 1bc formed around the clad layer 1bb. The core portions 1aa and 1ba and the clad layers 1ab and 1bb are made of glass such as quartz-based glass. The coating layers 1ac and 1bc are made of resin. The coating layers 1ac and 1bc are removed on the tip side.

Each of the input optical fibers 1a, 1b is, for example, a multimode optical fiber, but may also be a single mode optical fiber. In this embodiment, the input optical fibers 1a and 1b are assumed to be multimode optical fibers with an NA of 0.22. Note that NA may be 0.15 to 0.22.

The output optical fiber 2 is a so-called clad-pump optical fiber comprising an inner clad portion 2a and an outer clad layer 2b formed on the outer periphery of the inner clad portion 2a. The inner clad portion 2a is made of glass such as quartz-based glass. The outer clad layer 2b is made of resin. The resin is, for example, fluorine-added. The outer cladding layer 2b is removed at the distal end of the output optical fiber 2. FIG. A core portion may be provided at the center of the inner clad portion 2a. By using resin for the outer clad layer 2b, the NA of the output optical fiber 2 can be reduced to about 0.45.

A plurality of input optical fibers 1a and 1b are bundled at the tip side to form a bundle portion 1c. In the bundle portion 1c, the clad layers 1ab and 1bb of the input optical fibers 1a and 1b may be integrated. The tip portion 1ca of the bundle portion 1c is also the tip portion of the input optical fibers 1a and 1b, and is optically connected to the tip portion 2c of the output optical fiber 2 by fusion splicing or the like. A line L11 indicates the optical axis of the input optical fiber 1a and the optical axis of the output optical fiber 2. FIG. That is, they are connected so that the optical axis of the input optical fiber 1a and the optical axis of the output optical fiber 2 are aligned. The optical axis of the input optical fiber 1a is defined as the optical axes of the plurality of input optical fibers 1a and 1b.

Although the number of input optical fibers is not particularly limited, any one of 3, 7, and 19 is preferable because the positional stability of the input optical fibers when bundled is high.

The bundle portion 1c has a tapered portion 1cb in which each of the input optical fibers 1a and 1b is tapered so that the cross-sectional area is reduced at the tip portion 1ca. The cross-sectional area of the tip portion 1ca is substantially equal to the cross-sectional area of the inner clad portion 2a of the output optical fiber 2 . In this embodiment, the cross-sectional areas of the input optical fibers 1a and 1b are substantially constant from the tip of the taper portion 1cb to the tip portion 1ca. However, the tapered portion 1cb may extend to the tip portion 1ca.

The angle formed by the side surface of the input optical fiber 1a or 1b in the tapered portion 1cb with respect to the optical axis of the input optical fiber 1a (the optical axes of the plurality of input optical fibers 1a and 1b) is the side surface of the input optical fiber 1b located on the outer peripheral side. (indicated by line L12). Therefore, the angle θ between the line L11 and the line L12 is defined as the angle (taper angle) between the tapered portion 1cb and the optical axes of the plurality of input optical fibers 1a and 1b.

Here, NAout is the NA of the output optical fiber 2, NAin is the NA of each of the input optical fibers 1a and 1b, ΣAi is the total cross-sectional area of the input optical fibers 1a and 1b on the base end side of the tapered portion 1cb, and ΣAi is the tip portion. Assuming that the cross-sectional area of the bundle portion 1c at 1ca is A, the following formula (NAout/NAin) ² <ΣAi/A
holds.

As a result, when light is input from the base end sides of the input optical fibers 1a and 1b, the cross-sectional area is reduced at the tapered portion 1cb, thereby increasing the radiation angle of the light. However, the characteristic of the radiation angle after the increase is based on the characteristic of the radiation angle of the input light. Therefore, if attention is paid to the characteristics of the radiation angle of the input light, it is possible to suppress the deterioration of the light coupling efficiency with respect to the output optical fiber 2 even if ΣAi is relatively large.

For example, in the case of multimode optical fibers made of glass, non-doped silica (SiO ₂ ) is used for the large area core due to the advantage of material uniformity, and fluorine-doped silica is used for the cladding layers. There is In this case, the upper limit of the NA of the optical fiber is generally 0.22.

In this embodiment, at the tapered portion 1cb, the angle of radiation of light increases according to the reduction ratio of the taper. However, the radiation angle of the input light is dispersed over a wide range from 0 radian to the NA of the input optical fiber. It is possible to reduce the amount of light exceeding a few percent.

For example, the wavelength of input light is 915 nm, the number of input optical fibers is 19, NAin is 0.2, the fiber diameter (outer diameter of the cladding portion) is 125 μm, that is, Ai is π×(125/ 2) Assuming ² , NAout of the output optical fiber is 0.45, the fiber diameter (the outer diameter of the inner cladding portion) is 250 μm, that is, the cross-sectional area A of the bundle portion is π×(250/2) ² , (NAout/ NAin) ² = 5.0625 and ^ΣAi /A = 4.75.
is satisfied.

However, if the beam diameter of the light is expanded to increase the power, and the fiber diameter of the input optical fiber is set to 130 μm accordingly, that is, if Ai is π×(130/2) ² , then (NAout/NAin) ² = 5.0625, ΣAi/A=5.1376, and the formula described in Patent Document 1 (NAout/NAin) ² ≧ΣAi/A
is not satisfied.

On the other hand, in the present embodiment, the following formula (NAout/NAin) ² <ΣAi/A
is established. Note that this formula holds true even if the fiber diameter of the input optical fiber is larger than 130 μm. However, since there is a tapered portion, it is obvious that ΣAi/A<1 holds.

In addition, it is preferable that the taper angle is small to some extent. If the taper angle is small, the taper is gradual, so when light propagates through the taper, it prevents light from radiating from the core of the input optical fiber to the cladding layer, so that the light is confined in the core to the tip of the bundle. can be done. The taper angle is, for example, 0.045 radian or less.

In addition, although the tapered portion reduces the cross-sectional area of the bundle, the thickness of the clad layer of the input optical fiber at the tip of the bundle is increased to confine the light in the core even at the tip of the bundle. It is preferable that the thickness is above a certain level. This avoids too thin a clad layer at the tip. The thickness of the clad layer of the input optical fiber at the tip of the bundle is, for example, 1.7 μm or more.

The thickness of the cladding layer of the input optical fiber at the tip of the bundle may be set according to the wavelength of the light input from the base end, for example, 1.9 times or more the wavelength of the light. good. When the wavelength of light is 915 nm (0.915 μm), the thickness of the clad layer may be 1.7 μm or more. When the wavelength of light is 400 nm (0.4 μm), the thickness of the clad layer may be 0.8 μm or more.

FIG. 3 is a diagram showing the radiation angle distribution of the input light to the input optical fiber and the output light from the tip of the bundle. As shown in FIG. 3, the radiation angle of the output light is larger than the radiation angle of the input light, but the radiation angle distribution of the input light gradually decreases in intensity from 0 radian to 0.2 radian. there is Therefore, the distribution of the output light also gradually decreases in intensity toward 0.4 radian.

(Embodiment 2)
FIG. 4 is a schematic diagram of an optical coupler according to the second embodiment. The optical coupler 20 has a configuration in which the output optical fiber 2 in the optical coupler 10 shown in FIG. 1 is replaced with the output optical fiber 3 .

The output optical fiber 3 includes a core portion 3a, a clad layer 3b formed around the core portion 3a, and a coating layer 3c formed around the clad layer 3b. The core portion 3a and the clad layer 3b are made of glass such as silica-based glass. The coating layer 3c is made of resin. The coating layer 3c is removed on the tip side of the output optical fiber 3. FIG.

The output optical fiber 3 is a multimode optical fiber. In this embodiment, it is assumed that the output optical fiber 3 is a multimode optical fiber with an NA of 0.22. Note that NA may be 0.15 to 0.22, which is 0.22 or less.

The tip portion 1ca of the bundle portion 1c is optically connected to the tip portion 3d of the output optical fiber 3 by fusion splicing or the like. A line L21 indicates the optical axis of the input optical fiber 1a and the optical axis of the output optical fiber 3. FIG. That is, they are connected so that the optical axis of the input optical fiber 1a and the optical axis of the output optical fiber 3 are aligned.

Here, similarly to the optical coupler 10, the NA of the output optical fiber 3 is NAout, the NA of each of the input optical fibers 1a and 1b is NAin, and the cut of the input optical fibers 1a and 1b on the base end side of the taper portion 1cb is Assuming that the total area is ΣAi and the cross-sectional area of the bundle portion 1c at the tip portion 1ca is A, the following formula (NAout/NAin) ² <ΣAi/A
holds.

At the tapered portion 1cb of the bundle portion 1c, the radiation angle of light increases according to the reduction ratio of the taper. However, the radiation angle of the input light is dispersed over a wide range from 0 radian to the NA of the input optical fiber. It is possible to reduce the amount of light exceeding a few percent. As a result, when light is input from the base ends of the input optical fibers 1a and 1b, it is possible to suppress a decrease in the coupling efficiency of light to the output optical fiber 3 even if ΣAi is relatively large.

(Arrangement of input optical fiber)
FIG. 5 is a diagram showing another example of arrangement of a plurality of input optical fibers, corresponding to FIG.

The input optical fiber section 4 includes 19 input optical fibers, 1 input optical fiber 4a, 6 input optical fibers 4b, and 12 input optical fibers 4c. The input optical fiber 4a is arranged in the center, and the six input optical fibers 4b are arranged on the outer peripheral side of the input optical fiber 4a. The 12 input optical fibers 4c are arranged further outside the input optical fibers 4b. It is preferable that the input optical fibers 4a, 4b, 4c are arranged close-packed and have a circular circumference.

Each of the input optical fibers 4a, 4b, and 4c, like the input optical fiber 1a, includes a core portion, a clad layer formed on the outer periphery of the core portion, and a coating layer formed on the outer periphery of the clad layer. there is The core portion and the clad layer are made of glass such as quartz-based glass. The coating layer is made of resin. The covering layer is removed on the tip side.

Each of the input optical fibers 4a, 4b, 4c is, for example, a multimode optical fiber, but may also be a single mode optical fiber. In this embodiment, it is assumed that the input optical fibers 4a, 4b, and 4c are multimode optical fibers with an NA of 0.22. Note that NA may be 0.15 to 0.22.

A plurality of input optical fibers 4a, 4b, and 4c are bundled at their distal ends to form a bundle portion. At the bundle portion, the clad layers of the input optical fibers 4a, 4b, and 4c may be integrated. The tip of the bundle is also the tip of the input optical fibers 4a, 4b and 4c, and is optically connected to the tip 2c of the output optical fiber 2 and the tip 3d of the output optical fiber 3 by fusion splicing or the like. there is The optical axis of the input optical fiber 4a and the optical axis of the output optical fiber 2 or 3 are connected so as to coincide with each other. The optical axis of the input optical fiber 4a is defined as the optical axes of the plurality of input optical fibers 4a, 4b, and 4c.

The bundle portion has a tapered portion in which each of the input optical fibers 4a, 4b, 4c is tapered such that the cross-sectional area is reduced at the distal end portion. The cross-sectional area of the tip portion is substantially equal to the cross-sectional area of the inner clad portion 2a of the output optical fiber 2 or the cross-sectional area of the core portion 3a of the output optical fiber 3. FIG.

In this input optical fiber portion 4, the taper angle is the side surface of the input optical fiber 4c located on the outer peripheral side of the taper portion with respect to the optical axis of the input optical fiber 4a (the optical axes of the plurality of input optical fibers 4a, 4b, and 4c). is defined as the angle formed by

Here, NAout is the NA of the output optical fiber 2 or 3, NAin is the NA of each of the input optical fibers 4a, 4b, and 4c, and the total cross-sectional area of the input optical fibers 4a, 4b, and 4c on the base end side of the taper portion. is ΣAi, and the cross-sectional area of the bundle at the tip is A, the following formula (NAout/NAin) ² <ΣAi/A
holds.

Thereby, when light is input from the base end side of each of the input optical fibers 4a, 4b, and 4c, it is possible to suppress the decrease in the light coupling efficiency with respect to the output optical fiber 2 or 3. FIG.

(Example 1)
An optical coupler having a configuration similar to that of the optical coupler 10 shown in Embodiment 1 and having an input optical fiber portion including 19 input optical fibers as shown in FIG. 5 was manufactured. Then, a semiconductor laser element that outputs multimode laser light with a wavelength of 915 nm is used as a light source, and the radiation angle distribution of the output light from the output optical fiber when input from each of the input optical fibers was measured. Each semiconductor laser device was driven with a direct current. The current value was 2A.

The characteristics of the input optical fiber are as follows.
Fiber diameter: 125 μm
NA: 0.22
Number: 19 The outer diameter of the tip of the bundle portion is 250 μm. The NA of the output optical fiber is 0.45. The taper angle of the tapered portion is 0.035 radian. The thickness of the clad layer at the tip of the bundle is 3.1 μm.

FIG. 6 is a diagram showing measurement results of radiation angle distributions of output light from a semiconductor laser element and output light from an output optical fiber. The LDM indicated in the legend is the radiation angle distribution of the output light directly output from the semiconductor laser element. 250 μm shown in the legend is the radiation angle distribution of the output light output from the output optical fiber of the optical coupler of the first embodiment.

(Example 2)
An optical coupler having a configuration similar to that of the optical coupler 10 shown in Embodiment 1 and having an input optical fiber portion including 19 input optical fibers as shown in FIG. 5 was manufactured. Using the semiconductor laser element used in Example 1 as a light source, the radiation angle distribution of the output light from the output optical fiber was measured when input was made from each of the input optical fibers. Each semiconductor laser device was driven with a direct current. The current value was 2A.

The characteristics of the input optical fiber are as follows.
Fiber diameter: 125 μm
NA: 0.22
Number: 19 The outer diameter of the tip of the bundle portion is 200 μm. The NA of the output optical fiber is 0.45. The taper angle of the tapered portion is 0.04 radian. The thickness of the clad layer at the tip of the bundle is 2.5 μm.

In FIG. 6, 200 μm shown in the legend is the radiation angle distribution of the output light output from the output optical fiber of the optical coupler of the second embodiment. In Example 2, the emission angle of the output light output from the output optical fiber of the optical coupler is wider than the result of Example 1. FIG. The reason for this is thought to be that the outer diameter of the tip portion of the bundle portion is set from 250 μm to 200 μm, so that the enlargement ratio of the NA at the tapered portion is increased.

(Example 3)
An optical coupler having a configuration similar to that of the optical coupler 10 shown in Embodiment 1 and having an input optical fiber portion including 19 input optical fibers as shown in FIG. 5 was manufactured. Using the semiconductor laser element used in Examples 1 and 2 as a light source, the radiation angle distribution of the output light from the output optical fiber was measured when input was made from each of the input optical fibers. Each semiconductor laser device was driven with a direct current. The current value was 2A.

The characteristics of the input optical fiber are as follows.
Fiber diameter: 125 μm
NA: 0.22
Number: 19 The outer diameter of the tip of the bundle portion is 150 μm. The NA of the output optical fiber is 0.45. The taper angle of the tapered portion is 0.045 radian. The thickness of the clad layer at the tip of the bundle is 1.7 μm.

In FIG. 6, 150 μm shown in the legend is the radiation angle distribution of the output light output from the output optical fiber of the optical coupler of the third embodiment. In Example 3, the emission angle of the output light output from the output optical fiber of the optical coupler is wider than the result of Example 2. FIG. The reason for this is thought to be that, since the outer diameter of the tip of the bundle portion is set from 200 μm to 150 μm, the enlargement ratio of the NA at the tapered portion is increased.

In all of Examples 1 to 3, the insertion loss of the optical coupler with respect to the semiconductor laser device outputting multimode laser light with a wavelength of 915 nm was 10% or less, which was low loss characteristics at a practical level.

(Example 4)
An optical coupler having a configuration similar to that of the optical coupler 20 shown in the second embodiment and having an input optical fiber portion including 19 input optical fibers as shown in FIG. 5 was manufactured.

The characteristics of the input optical fiber are as follows.
Fiber diameter: 125 μm
NA: 0.22
Number: 19 The outer diameter of the tip of the bundle portion is 250 μm. The output optical fiber has a core diameter of 300 μm and an NA of 0.22. The taper angle of the tapered portion is 0.035 radian. The thickness of the clad layer at the tip of the bundle is 2.9 μm.

In Example 4, the maximum value of the NA of the output light and the NA of the output optical fiber are approximately the same. The light leaking from the core to the cladding layer is intentionally treated with a high-refractive-index material applied instead of the coating. By intentionally radiating the leaked light in this manner, it is possible to suppress the leaked light from being radiated to unintended locations.

In the case of Example 4, the insertion loss of the optical coupler with respect to the semiconductor laser device that outputs multimode laser light with a wavelength of 915 nm is 30% or less, which is larger than in Examples 1 to 3, but the output optical fiber Since the brightness and power density of the output light from the laser can be increased, it is suitable for outputting high-power laser light.

(Embodiment 3)
7A is a schematic diagram of an optical coupler according to Embodiment 3. FIG. The optical coupler 30 has a configuration in which the input optical fiber section 1 in the optical coupler 10 shown in FIG.

The input optical fiber section 5 includes one input optical fiber 5a and six input optical fibers 5b as a plurality of (seven in this embodiment) input optical fibers. The input optical fiber 5a is arranged in the center, and the six input optical fibers 5b are arranged on the outer peripheral side of the input optical fiber 5a. The input optical fibers 5a, 5b are preferably arranged in a close-packed manner.

The input optical fiber 5a includes a core portion 5aa, a clad layer 5ab formed around the core portion 5aa, and a coating layer 5ac formed around the clad layer 5ab. The input optical fiber 5b includes a core portion 5ba, a clad layer 5bb formed around the core portion 5ba, and a coating layer 5bc formed around the clad layer 5bb. The core portions 5aa and 5ba and the cladding layers 5ab and 5bb are made of glass such as quartz-based glass. The coating layers 5ac and 5bc are made of resin. The coating layers 5ac and 5bc are removed on the tip side.

Each of the input optical fibers 5a, 5b is, for example, a multimode optical fiber, but may also be a single mode optical fiber. The NA of the input optical fibers 5a, 5b may be 0.15-0.22.

The output optical fiber 6 is a so-called clad-pump optical fiber comprising an inner clad portion 6a and an outer clad layer 6b formed on the outer periphery of the inner clad portion 6a. The output optical fiber 6 has a tip 6c. The inner clad portion 6a is made of glass such as quartz-based glass. The outer clad layer 6b is made of resin. The resin is, for example, fluorine-added. The outer cladding layer 6b is removed at the distal end of the output optical fiber 6. FIG. A core portion may be provided at the center of the inner clad portion 6a. By using resin for the outer clad layer 6b, the NA of the output optical fiber 6 can be reduced to about 0.45.

The inner clad portion 6a has a constant diameter portion 6aa, a tapered portion 6ab, and a constant diameter portion 6ac. The constant diameter portion 6aa is located on the proximal end side of the output optical fiber 6, has a substantially constant outer diameter, and is partially removed from the outer clad layer 6b. The constant diameter portion 6ac is located on the side of the tip portion 6c of the output optical fiber 6 and has a substantially constant outer diameter smaller than that of the constant diameter portion 6aa. The tapered portion 6ab is a portion whose outer diameter increases from the constant diameter portion 6ac toward the constant diameter portion 6aa.

A plurality of input optical fibers 5a and 5b are bundled at the tip side to form a bundle portion 5c. In the bundle portion 5c, the clad layers 5ab and 5bb of the input optical fibers 5a and 5b may be integrated. The tip portion 5ca of the bundle portion 5c is also the tip portion of the input optical fibers 5a and 5b, and is optically connected to the tip portion 6c of the output optical fiber 6 by fusion splicing or the like. The optical axis of the input optical fiber 5a and the optical axis of the output optical fiber 6 are connected so as to coincide with each other. The optical axis of the input optical fiber 5a is defined as the optical axes of the plurality of input optical fibers 5a and 5b.

The bundle portion 5c has a tapered portion 5cb in which each of the input optical fibers 5a and 5b is tapered so that the cross-sectional area is reduced at the tip portion 5ca. The cross-sectional area of the tip portion 5ca is substantially equal to the cross-sectional area of the inner clad portion 6a at the tip portion 6c of the output optical fiber 6, that is, the cross-sectional area of the constant diameter portion 6ac. In this embodiment, the cross-sectional areas of the input optical fibers 5a and 5b are substantially constant from the tip of the tapered portion 5cb to the tip 5ca. However, the tapered portion 5cb may extend to the tip portion 5ca.

The taper angle is defined as the angle between the taper portion 5cb and the optical axes of the plurality of input optical fibers 5a and 5b.

Here, the NA of the output optical fiber 6 (the NA of the optical waveguide composed of the inner cladding portion 6a and the outer cladding layer 6b) is NAout, the NA of each of the input optical fibers 5a and 5b is NAin, and the NA of the taper portion 5cb is higher than that of the tapered portion 5cb. Assuming that the total cross-sectional area of the input optical fibers 5a and 5b on the base end side is ΣAi, and the cross-sectional area of the bundle portion 5c at the tip portion 5ca is A, the following formula (NAout/NAin) ² <ΣAi/A
holds.

As a result, when light is input from the base ends of the input optical fibers 5a and 5b, the tapered portion 5cb reduces the cross-sectional area, thereby increasing the radiation angle of the light. However, the characteristic of the radiation angle after the increase is based on the characteristic of the radiation angle of the input light. Therefore, if attention is paid to the characteristics of the radiation angle of the input light, it is possible to suppress the decrease in the coupling efficiency of the light to the output optical fiber 6 even if ΣAi is relatively large.

(Modification of Embodiment 3)
7B is a schematic diagram of an optical coupler according to a modification of the third embodiment; FIG. The optical coupler 30A has a configuration in which the output optical fiber 6 in the optical coupler 30 is replaced with an output optical fiber 6A.

The output optical fiber 6A includes a glass optical fiber portion 6Aa and a coating layer 6Ab formed on the outer periphery of the glass optical fiber portion 6Aa. The glass optical fiber portion 6Aa is made of glass such as quartz glass. The covering layer 6Ab is made of resin. The coating layer 6Ab is removed from the tip side of the output optical fiber 6A.

The glass optical fiber portion 6Aa has a constant diameter portion 6Aaa, a tapered portion 6Aab, and a constant diameter portion 6Aac. The constant-diameter portion 6Aaa is located on the proximal end side of the output optical fiber 6A, has a substantially constant outer diameter, and is partially removed from the coating layer 6Ab. The constant diameter portion 6Aac is located on the side of the tip portion 6Ac of the output optical fiber 6A and has a substantially constant outer diameter smaller than that of the constant diameter portion 6Aaa. The tapered portion 6Aab is a portion whose outer diameter increases from the constant diameter portion 6Aac toward the constant diameter portion 6Aaa.

The glass optical fiber portion 6Aa includes a core portion 6Aad and a clad layer 6Aae formed on the outer periphery of the core portion 6Aad. The core portion 6Aad and the clad layer 6Aae constitute a constant diameter portion 6Aaa, a tapered portion 6Aab, and a constant diameter portion 6Aac.

The output optical fiber 6A is a multimode optical fiber. In this embodiment, it is assumed that the output optical fiber 6A is a multimode optical fiber with NA of 0.22. Note that NA may be 0.15 to 0.22, which is 0.22 or less.

The tip portion 5ca of the bundle portion 5c of the input optical fiber portion 5 is optically connected to the tip portion 6Ac of the output optical fiber 6A by fusion splicing or the like. The optical axis of the input optical fiber 5a and the optical axis of the output optical fiber 6A are connected so as to coincide with each other. The cross-sectional area of the tip portion 5ca is substantially equal to the cross-sectional area of the core portion 6Aad at the tip portion 6Ac of the output optical fiber 6A.

Here, the NA of the output optical fiber 6A (the NA of the optical waveguide composed of the core portion 6Ad and the clad layer 6Ae) is NAout, the NA of each of the input optical fibers 5a and 5b is NAin, and the proximal end is closer to the taper portion 5cb than the tapered portion 5cb. Assuming that the total cross-sectional area of the input optical fibers 5a and 5b on the side is ΣAi, and the cross-sectional area of the bundle portion 5c at the tip portion 5ca is A, the following formula (NAout/NAin) ² <ΣAi/A
holds.

As a result, when light is input from the base ends of the input optical fibers 5a and 5b, the tapered portion 5cb reduces the cross-sectional area, thereby increasing the radiation angle of the light. However, the characteristic of the radiation angle after the increase is based on the characteristic of the radiation angle of the input light. Therefore, if attention is paid to the characteristics of the radiation angle of the input light, even if ΣAi is relatively large, it is possible to suppress the deterioration of the light coupling efficiency with respect to the output optical fiber 6A.

(Example 5)
An optical coupler having a configuration similar to that of the optical coupler 30A shown in the modified example of the third embodiment and having an input optical fiber portion including 19 input optical fibers as shown in FIG. 5 was manufactured.

The characteristics of the input optical fiber are as follows.
Fiber diameter: 125 μm
NA: 0.22
Number: 19 The outer diameter of the tip of the bundle portion is 250 μm. The output optical fiber has an outer diameter of 250 μm at the constant diameter portion on the distal end side, changes in the outer diameter at the tapered portion, and has an outer diameter of 300 μm at the constant diameter portion on the base end side. The NA of the output optical fiber is 0.22. As a result, it is possible to propagate light having a radiation angle characteristic corresponding to a case where the NA is smaller than 0.22 through a multimode output optical fiber with a core diameter of 300 μm and an NA of 0.22.

For example, in Examples 4 and 5, an optical coupler with 19 input optical fibers was shown. An output power of 1900 W can be obtained from a 200 μm or 300 μm NA 0.22 multimode output optical fiber.

Also, by changing the cladding diameter of the input optical fiber from 125 μm to 150 μm to fabricate an optical coupler and connecting a semiconductor laser module with an output of 200 W, a multimode output optical fiber with a core diameter of 200 μm or 300 μm and an NA of 0.22 , an output of 3800 W can be obtained.

(Embodiment 4)
FIG. 8 is a schematic diagram of a light output device according to Embodiment 4. FIG. This light output device is configured as an optical fiber laser. The optical fiber laser 100 includes a plurality of semiconductor excitation light sources 101, a plurality of optical fibers 102, an optical coupler 10, an optical fiber Bragg grating (FBG) 103, an amplification optical fiber 104, an FBG 105, and an optical coupler. 10 , a plurality of optical fibers 106 , a plurality of semiconductor excitation light sources 107 and an output optical fiber 108 . Each element is appropriately connected by an optical fiber.

A plurality of semiconductor pumping light sources 101 and 107 , which are pumping light sources, respectively output pumping light to be supplied to the amplification optical fiber 104 . The pumping light has a wavelength capable of optically pumping the amplification optical fiber 104, for example, a wavelength of 915 nm. A plurality of optical fibers 102 and 106 propagate pumping light output from semiconductor pumping light sources 101 and 107, respectively, and output the pumping light to optical coupler 10. FIG.

Each of the optical couplers 10 according to the first embodiment has a plurality of optical fibers 102 and 106 each connected to the base end side of each input optical fiber 1b, multiplexes input pumping light, and outputs light Output from the fiber 2 to the amplification optical fiber 104 .

The amplification optical fiber 104 is a YDF (Ytterbium Doped Fiber) in which ytterbium (Yb) ions, which are amplification substances, are added to a core portion made of silica-based glass, and an inner clad made of silica-based glass surrounds the core portion. This is a double-clad optical fiber in which a layer and an outer clad layer made of resin or the like are sequentially formed. The core portion of the amplification optical fiber 104 has an NA of, for example, 0.08, and is configured to propagate light emitted from Yb ions, for example, light having a wavelength of 1070 nm, in a single mode. The absorption coefficient of the core portion of the amplification optical fiber 104 is, for example, 200 dB/m at a wavelength of 915 nm. Also, the power conversion efficiency from the excitation light input to the core portion to the laser oscillation light is, for example, 70%.

The FBG 103 is connected between the output optical fiber 2 of the optical coupler 10 on the side of the plurality of semiconductor pumping light sources 101 and the amplification optical fiber 104 . The FBG 103 has a central wavelength of 1070 nm, for example, and has a reflectance of about 100% in a wavelength band of about 2 nm width around the central wavelength and around it, and almost transmits light with a wavelength of 915 nm. The FBG 105 is connected between the output optical fiber 2 of the optical coupler 10 on the side of the plurality of semiconductor pumping light sources 107 and the amplification optical fiber 104 . The FBG 105 has a central wavelength of approximately the same as that of the FBG 103, for example, 1070 nm, a reflectance at the central wavelength of about 10% to 30%, a full width at half maximum of the reflection wavelength band of about 1 nm, and almost all light with a wavelength of 915 nm. To Penetrate.

The FBGs 103 and 105 are arranged at both ends of the amplification optical fiber 104, and form optical fiber resonators for light with a wavelength of 1070 nm.

In the amplification optical fiber 104, Yb ions in the core are photoexcited by the pumping light, and light in a band including a wavelength of 1070 nm is emitted. The emitted light with a wavelength of 1070 nm causes laser oscillation due to the optical amplification action of the amplification optical fiber 104 and the action of the optical resonator constituted by the FBGs 103 and 105 .

The output optical fiber 108 is arranged on the opposite side of the FBG 105 and connected to the input optical fiber 1 a of the optical coupler 10 . The oscillated laser light (laser oscillation light) is output from the output optical fiber 108 . Output optical fiber 108 is connected, for example, to a delivery optical fiber. Laser oscillation light is propagated for a given application by a delivery optical fiber.

(Embodiment 5)
FIG. 9 is a schematic diagram of a light output device according to Embodiment 5. FIG. This light output device is configured as a direct diode laser (DDL). This DDL 200 comprises a plurality of semiconductor laser modules 201 , a plurality of optical fibers 202 , an optical coupler 20 and a delivery optical fiber 203 . Each element is appropriately connected by an optical fiber.

A plurality of semiconductor laser modules 201 each output laser light with a wavelength of 1070 nm, for example. A plurality of optical fibers 202 propagate the laser light output from each semiconductor laser module 201 and output it to the optical coupler 20 .

The optical coupler 20 according to the second embodiment has a plurality of optical fibers 202 each connected to the base end side of each of the input optical fibers 1a and 1b, multiplexes the input laser light, and outputs the output optical fiber 3 to the delivery optical fiber 203 . The delivery optical fiber 203 may be a multimode optical fiber similar to the output optical fiber 3 . A laser beam having an optical power is output from the delivery optical fiber 203 .

The optical couplers 10 and 20 in the fourth and fifth embodiments may be appropriately replaced with optical couplers according to other embodiments.

In the above embodiment, the wavelength of the laser light input to the multiplexer is, for example, 915 nm or 1070 nm. may be For example, as a semiconductor laser element, an element that outputs laser light in each wavelength band such as the 900 nm band, the 650 nm band, the 400 nm band, the infrared, the visible band, and the blue near the ultraviolet band can be used as the light source.

Moreover, the present invention is not limited by the above embodiments. The present invention also includes those configured by appropriately combining the respective constituent elements described above. Further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible.

1, 4, 5 Input optical fiber portions 1a, 1b, 4a, 4b, 4c, 5a, 5b Input optical fibers 1aa, 1ba, 3a, 5aa, 5ba, 6Aad Core portions 1ab, 1bb, 3b, 5ab, 5bb, 6Aae Cladding Layers 1ac, 1bc, 3c, 5ac, 5bc, 6Ab Coating layers 1c, 5c Bundles 1ca, 2c, 3d, 5ca, 6c, 6Ac Tip portions 1cb, 5cb, 6ab, 6Aab Tapered portions 2, 3, 6, 6A Output light Fibers 2a, 6a Inner clad portions 2b, 6b Outer clad layers 6aa, 6ac, 6Aaa, 6Aac Constant diameter portion 6Aa Glass optical fiber portions 10, 20, 30 Optical coupler 100 Optical fiber lasers 101, 107 Semiconductor excitation light sources 102, 106, 202 optical fiber 104 amplification optical fiber 108 output optical fiber 200 DDL
201 semiconductor laser module 203 delivery optical fiber

Claims (9)

a plurality of input optical fibers;
an output optical fiber;
wherein the plurality of input optical fibers are bundled at their tip ends to form a bundle portion, the tip portion of the bundle portion is connected to the output optical fiber, and the bundle portion includes the plurality of input optical fibers. each of the optical fibers has a tapered portion tapered to reduce the cross-sectional area at the distal end;
The output optical fiber has a constant outer diameter in the longitudinal direction,
NAout is the numerical aperture of the output optical fiber, NAin is the numerical aperture of the portion of each of the plurality of input optical fibers where the distal end of the bundle portion is connected to the output optical fiber, and the proximal end is larger than the tapered portion. Assuming that the sum of the cross-sectional areas of the plurality of input optical fibers at the side is ΣAi, and the cross-sectional area of the bundle at the tip is A, the connection point between the tip of the bundle and the output optical fiber is given by the following equation: (NAout/NAin) ² <ΣAi/A
An optical coupler characterized by: 2. The optical coupler according to claim 1, wherein the angle formed by said taper portion and the optical axes of said plurality of input optical fibers is 0.045 radian or less. 3. The optical coupler according to claim 1, wherein the numerical aperture of said output optical fiber is 0.22 or less. 4. The optical coupler according to claim 1, wherein the clad layer of each of said plurality of input optical fibers at said tip has a thickness of 1.7 μm or more. 4. The method according to any one of claims 1 to 3, wherein the thickness of the cladding layer at the tip of each of the plurality of input optical fibers is 1.9 times or more the wavelength of the light input from the base end. 1. An optical coupler according to claim 1. All of the core portions of the plurality of input optical fibers are included in the range of the core portion of the output optical fiber when the cross section at the connection point between the tip portion of the bundle portion and the output optical fiber is viewed in the longitudinal direction. An optical coupler according to any one of claims 1 to 5. an optical coupler according to any one of claims 1 to 6;
a plurality of light sources each connected to a base end side of each of the plurality of input optical fibers;
A light output device comprising: an amplification optical fiber optically pumped by light output from the plurality of light sources;
an optical resonator;
8. The light output device of claim 7, wherein the light output device is configured as an optical fiber laser. 8. The light output device according to claim 7, wherein each of said plurality of light sources is a semiconductor laser and configured as a direct diode laser.

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