Patent Description:
In the field of laser processing, it is important to change a beam profile of a laser beam being applied to a workpiece depending on a material or a thickness of the workpiece in order to improve processing performance such as a processing rate, a process quality, and the like. From this point of view, there has been developed in recent years a technique of forming a plurality of optical waveguides in an output optical fiber and controlling a laser beam to be introduced into each of those optical waveguides to change a beam profile of a laser beam directed to a workpiece into a desired form.

For example, <CIT> discloses an optical combiner for introducing a laser beam into an output optical fiber having a center core and an outer core located so as to surround the center core as optical waveguides, wherein the optical combiner includes a plurality of optical fibers (inner optical fibers) located on an inner side thereof so as to correspond to the center core of the output optical fiber and a plurality of optical fibers (outer optical fibers) located so as to surround the inner optical fibers with an annular arrangement to correspond to the outer core of the output optical fiber (see Figs. 8a and 8b). With the conventional arrangement disclosed in Patent Literature <NUM>, the diameter of the inner optical fibers needs to be smaller than the diameter of the outer optical fibers in order to avoid an increased diameter of the output optical fiber. When the inner optical fibers have a small diameter, the mechanical strength of the inner optical fibers is reduced, so that problems such as breakage or cutting of the optical fibers are likely to occur. Furthermore, such inner optical fibers become difficult to manufacture. Those problems make it difficult to increase the number of the inner optical fibers. Therefore, it is difficult to increase the power of a laser beam introduced into the center core of the output optical fiber, to which the inner optical fibers are connected. As a result, it is also difficult to adjust output balance between a laser beam propagating through the center core of the output optical fiber and a laser beam propagating through the outer core of the output optical fiber.

<CIT> discloses an all-fiber combiner device is described for combining multiple high power inputs, such as high power laser inputs. The device includes a first tapered fiber section made from fibers that allow for efficient size reduction of the optical signals. The output of the first tapered fiber section may then be coupled to a multimode output fiber for delivery of the combined power beam. Alternately, the first tapered section can be coupled to a second, multimode, tapered section, which provides further size reduction of the core for splicing into a final output fiber, while adding cladding to the main fiber.

The present invention has been made in view of the above drawbacks in the prior art. It is, therefore, an object of the present invention to provide an optical combiner according to independent claim <NUM>. The optical combiner can be readily manufactured with capability of directing a laser beam into each of a first optical waveguide and a second optical waveguide of an output optical fiber. Further embodiments are provided by the dependent claims.

Embodiments of an optical combiner and a laser apparatus having an optical combiner according to the present invention will be described in detail below with reference to <FIG>. In <FIG>, the same or corresponding components are denoted by the same or corresponding reference numerals and will not be described below repetitively. Furthermore, in <FIG>, the scales or dimensions of components may be exaggerated, or some components may be omitted. Unless mentioned otherwise, in the following description, terms such as "first," "second," etc. are only used to distinguish one component from another and are not used to indicate a specific order or a specific sequence.

<FIG> is a schematic block diagram showing a configuration of a laser apparatus <NUM> according to an embodiment of the present invention. As shown in <FIG>, the laser apparatus <NUM> of this embodiment has first laser sources 2A and second laser sources 2B operable to generate a laser beam, an optical combiner <NUM> to which laser beams are inputted from the respective laser sources 2A and 2B, a laser emission portion <NUM> provided on a downstream end of the optical combiner <NUM>, and a controller <NUM> operable to control the laser sources 2A and 2B. Each of the laser sources 2A and 2B and the optical combiner <NUM> are connected to each other by an optical fiber <NUM>. The optical combiner <NUM> and the laser emission portion <NUM> are connected to each other by an optical fiber <NUM>. For example, a fiber laser or a semiconductor laser can be used for the laser sources 2A and 2B. Although the laser apparatus <NUM> of this embodiment includes three laser sources 2A and six laser sources 2B, the numbers of the laser sources 2A and 2B are not limited to those values. Unless otherwise mentioned herein, the term "downstream" refers to a direction in which a laser beam propagates from each of the laser sources 2A and 2B to the laser emission portion <NUM>, and the term "upstream" refers to an opposite direction thereto.

In this laser apparatus <NUM>, first laser beams generated in the first laser sources 2A and second laser beams generated in the second laser sources 2B respectively propagate through the optical fibers <NUM> to the optical combiner <NUM>. In the optical combiner <NUM>, laser beams from a plurality of laser sources 2A and 2B are combined and outputted to the optical fiber <NUM>. A high-power laser beam L outputted to the optical fiber <NUM> is emitted from the laser emission portion <NUM>, for example, toward a workpiece.

<FIG> is a perspective view showing the optical combiner <NUM>, and <FIG> is an exploded perspective view thereof. As shown in <FIG> and <FIG>, the optical combiner <NUM> of this embodiment includes a plurality of first input optical fibers <NUM>, each of which is formed by at least a portion of the optical fiber <NUM> extending from the first laser source 2A, a bridge fiber <NUM> connected to those first input optical fibers <NUM>, an intermediate optical fiber <NUM> connected to the bridge fiber <NUM>, a plurality of second input optical fibers <NUM>, each of which is formed by at least a portion of the optical fiber <NUM> extending from the second laser source 2B, and an output optical fiber <NUM>, which is formed by at least a portion of the aforementioned optical fiber <NUM>.

As shown in <FIG> and <FIG>, in the present embodiment, the three first input optical fibers <NUM> are connected to the bridge fiber <NUM> in a state in which the input optical fibers <NUM> are held in contact with each other. Each of the first input optical fibers <NUM> has a core <NUM> and a cladding <NUM> that surrounds an outer circumference of the core <NUM>. The cladding <NUM> has a refractive index lower than a refractive index of the core <NUM>. Thus, an interior of the core <NUM> forms an optical waveguide that allows the first laser beam from the first laser source 2A to propagate therethrough. In this manner, the first input optical fiber <NUM> is configured to allow the first laser beam from the first laser source 2A to propagate through the interior of the core <NUM> and emit the first laser beam from an output end 10A (see <FIG>). Each of the first input optical fibers <NUM> has a covering layer (not shown) that surrounds an outer circumference of the cladding <NUM> at a location away from the bridge fiber <NUM>.

The bridge fiber <NUM> has a core <NUM> and a cladding <NUM> that surrounds an outer circumference of the core <NUM>. The cladding <NUM> has a refractive index lower than a refractive index of the core <NUM>. Thus, an interior of the core <NUM> forms an optical waveguide that allows the first laser beams to propagate therethrough. The bridge fiber <NUM> with such a core-cladding structure includes a first cylindrical portion <NUM> extending along an optical axis with a fixed outside diameter, a diameter reduction portion <NUM> having an outside diameter gradually reduced from the first cylindrical portion <NUM> along the optical axis, and a second cylindrical portion <NUM> extending from the diameter reduction portion <NUM> along the optical axis with a fixed outside diameter. The first cylindrical portion <NUM> has an end face that serves as a bridge input surface <NUM> to which the output ends 10A of the respective first input optical fibers <NUM> are connected by fusion splicing. An end face of the second cylindrical portion <NUM> that is located opposite to the bridge input surface <NUM> along the optical axis serves as a bridge output surface <NUM> to which an input end 30A of the intermediate optical fiber <NUM> (see <FIG>) is connected by fusion splicing. The size of the core <NUM> of the bridge fiber <NUM> on the bridge input surface <NUM> is large enough to include therein all of the cores <NUM> of the first input optical fibers <NUM>. The first input optical fibers <NUM> and the bridge fiber <NUM> are connected to each other by fusion splicing in a state in which all of the cores <NUM> of the first input optical fibers <NUM> are located within an area of the core <NUM> on the bridge input surface <NUM> of the bridge fiber <NUM>. In this manner, the bridge fiber <NUM> is configured to allow the first laser beams emitted from the output ends 10A of the first input optical fibers <NUM> to propagate through an interior of the core <NUM> and reduce the beam diameter of the first laser beams through the diameter reduction portion <NUM>. In order to suppress reflection of the first laser beams when the first laser beams are introduced into the core <NUM> of the bridge fiber <NUM> from the cores <NUM> of the first input optical fibers <NUM>, the core <NUM> of the bridge fiber <NUM> may preferably have a refractive index that is substantially the same as a refractive index of the cores <NUM> of the first input optical fibers <NUM>.

The intermediate optical fiber <NUM> has a core <NUM> and a cladding <NUM> that surrounds an outer circumference of the core <NUM>. The cladding <NUM> has a refractive index lower than a refractive index of the core <NUM>. Thus, an interior of the core <NUM> forms an optical waveguide that allows the first laser beams to propagate therethrough. The size of the core <NUM> of the intermediate optical fiber <NUM> is equal to or larger than the size of the core <NUM> of the bridge fiber <NUM> on the bridge output surface <NUM>. The bridge fiber <NUM> and the intermediate optical fiber <NUM> are connected to each other by fusion splicing in a state in which the core <NUM> of the bridge fiber <NUM> on the bridge output surface <NUM> is located within an area of the core <NUM> of the intermediate optical fiber <NUM>. In this manner, the intermediate optical fiber <NUM> is configured to allow the first laser beams propagated from the bridge fiber <NUM> to propagate through an interior of the core <NUM>. In order to suppress reflection of the first laser beams when the first laser beams are introduced into the core <NUM> of the intermediate optical fiber <NUM> from the core <NUM> of the bridge fiber <NUM>, the core <NUM> of the intermediate optical fiber <NUM> may preferably have a refractive index that is substantially the same as a refractive index of the core <NUM> of the bridge fiber <NUM>.

In the present embodiment, the six second input optical fibers <NUM> are arranged so as to surround the intermediate optical fiber <NUM> in a state in which the second input optical fibers <NUM> are held in contact with an outer circumferential surface of the intermediate optical fiber <NUM>. The adjacent second input optical fibers <NUM> are held in contact with each other. Each of the second input optical fibers <NUM> has a core <NUM> and a cladding <NUM> that surrounds an outer circumference of the core <NUM>. The cladding <NUM> has a refractive index lower than a refractive index of the core <NUM>. Thus, an interior of the core <NUM> forms an optical waveguide that allows the second laser beam from the second laser source 2B to propagate therethrough. In this manner, the second input optical fiber <NUM> is configured to allow the second laser beam from the second laser source 2B to propagate through the interior of the core <NUM> and emit the second laser beam from an output end 40A (see <FIG>). The same type of optical fibers as the aforementioned first input optical fibers <NUM> may be used for the second input optical fibers <NUM>. Each of the second input optical fibers <NUM> has a covering layer (not shown) that surrounds an outer circumference of the cladding <NUM> at a location away from the output optical fiber <NUM>.

<FIG> shows a cross-section of the output optical fiber <NUM> along with a radial refractive index distribution. As shown in <FIG>, the output optical fiber <NUM> has a center core <NUM>, an inner cladding <NUM> that surrounds an outer circumference of the center core <NUM>, a ring core <NUM> that surrounds an outer circumference of the inner cladding <NUM>, and an outer cladding <NUM> that surrounds an outer circumference of the ring core <NUM>. The inner cladding <NUM> has a refractive index lower than refractive indices of the center core <NUM> and the ring core <NUM>. The outer cladding <NUM> has a refractive index lower than a refractive index of the ring core <NUM>. Thus, an interior of the center core <NUM> forms a first optical waveguide that allows a laser beam to propagate therethrough, and the interior of the ring core <NUM> forms a second optical waveguide that allows a laser beam to propagate therethrough. In the present embodiment, the outer cladding <NUM> is formed around the ring core <NUM> as a low-refractive-index medium having a refractive index lower than the refractive index of the ring core <NUM>. Such a low-refractive-index medium is not limited to a covering layer such as the outer cladding <NUM>. For example, an air layer may be formed around the ring core <NUM> and may be used as a low-refractive-index medium. The output optical fiber <NUM> has a covering layer (not shown) that surrounds an outer circumference of the outer cladding <NUM> at a location away from the intermediate optical fiber <NUM> and the second input optical fibers <NUM>.

The output end of the intermediate optical fiber <NUM> and the output ends 40A of the second input optical fibers <NUM> are respectively connected to the output optical fiber <NUM> by fusion splicing. <FIG> is a schematic diagram showing connection of the intermediate optical fiber <NUM> and the second input optical fibers <NUM> with the output optical fiber <NUM>. In the present embodiment, the size of the center core <NUM> of the output optical fiber <NUM> is larger than the size of the core <NUM> of the intermediate optical fiber <NUM>. As shown in <FIG>, the intermediate optical fiber <NUM> and the output optical fiber <NUM> are connected to each other by fusion splicing in a state in which the core <NUM> of the intermediate optical fiber <NUM> is located within an area of the center core <NUM> of the output optical fiber <NUM> (the inner hatched area). Furthermore, the size of the ring core <NUM> of the output optical fiber <NUM> is large enough to include therein all of the cores <NUM> of the second input optical fibers <NUM>. As shown in <FIG>, the second input optical fibers <NUM> and the output optical fiber <NUM> are connected to each other by fusion splicing in a state in which all of the cores <NUM> of the second input optical fibers <NUM> are located with an area of the ring core <NUM> of the output optical fiber <NUM> (the outer hatched area).

With this configuration, a first laser beam generated by each of the first laser sources 2A propagates through the core <NUM> of the first input optical fiber <NUM> and enters the core <NUM> of the bridge fiber <NUM> from the bridge input surface <NUM> of the bridge fiber <NUM>. The laser beam that has entered the core <NUM> of the bridge fiber <NUM> propagates through the core <NUM> of the bridge fiber <NUM> while it is reflected on an interface between the core <NUM> and the cladding <NUM>. The laser beam is reduced in diameter by the diameter reduction portion <NUM> and then introduced into the core <NUM> of the intermediate optical fiber <NUM> from the bridge output surface <NUM>. The laser beam that has been introduced to the core <NUM> of the intermediate optical fiber <NUM> propagates through the interior of the core <NUM> and enters the center core <NUM> of the output optical fiber <NUM>. Then the laser beam propagates through the interior of the center core <NUM> as the first optical waveguide. The laser beam is eventually emitted from the laser emission portion <NUM> (see <FIG>). Furthermore, a second laser beam generated by each of the second laser sources 2B propagates through the core <NUM> of the second input optical fiber <NUM> and enters the ring core <NUM> of the output optical fiber <NUM>. The laser beam that has entered the ring core <NUM> of the output optical fiber <NUM> propagates through the interior of the ring core <NUM> as the second optical waveguide. The laser beam is eventually emitted from the laser emission portion <NUM> (see <FIG>).

In the present embodiment, when laser beams propagating through the cores <NUM> of the first input optical fibers <NUM> and the cores <NUM> of the second input optical fibers <NUM> are introduced into the center core <NUM> and the ring core <NUM> of the output optical fiber <NUM>, respectively, light propagating through the cores <NUM> of the first input optical fibers <NUM> is reduced in beam diameter in the bridge fiber <NUM> and then introduced into the center core <NUM> of the output optical fiber <NUM>. Therefore, the first input optical fibers <NUM> can be connected to the bridge fiber <NUM> without reduction of the diameter of the first input optical fibers <NUM>. Accordingly, the mechanical strength of the first input optical fibers <NUM> can be maintained. Thus, the optical combiner <NUM> can readily be manufactured. Furthermore, the number of the first input optical fibers <NUM> can be increased without reduction of the diameter of the first input optical fibers <NUM>. Therefore, the power of laser beams introduced to the center core <NUM> of the output optical fiber <NUM> can readily be increased. Thus, output balance between the laser beam propagating through the center core <NUM> and the laser beam propagating through the ring core <NUM> can readily be adjusted. As a result, a laser beam having a desired beam profile can be outputted from the laser emission portion <NUM> of the laser apparatus <NUM>.

Furthermore, the first laser sources 2A (e.g., an electric current supplied to the first laser sources 2A) can be controlled by the controller <NUM> to adjust outputs of the first laser beams generated by the first laser sources 2A. The second laser sources 2B (e.g., an electric current supplied to the second laser sources 2B) can be controlled by the controller <NUM> to adjust outputs of the second laser beams generated by the second laser sources 2B. Therefore, the first laser sources 2A and the second laser sources 2B can be controlled by the controller <NUM> to change a ratio of the powers of the first laser beams and the second laser beams, thereby adjusting a ratio of the first laser beams introduced to the center core <NUM> and the second laser beams introduced to the ring core <NUM> of the output optical fiber <NUM>. Thus, a profile of the laser beam outputted from the laser emission portion <NUM> of the laser apparatus <NUM> can readily be adjusted to a desired shape.

In the present embodiment, the core <NUM> of the intermediate optical fiber <NUM> is located within the area of the center core <NUM> of the output optical fiber <NUM>. Therefore, a laser beam propagating through the core <NUM> of the intermediate optical fiber <NUM> can efficiently be introduced into the center core <NUM> of the output optical fiber <NUM>. Similarly, in the present embodiment, all of the cores <NUM> of the second input optical fibers <NUM> are located within the area of the ring core <NUM> of the output optical fiber <NUM>. Therefore, laser beams propagating through the cores <NUM> of the second input optical fibers <NUM> can efficiently be introduced into the ring core <NUM> of the output optical fiber <NUM>. In this case, some of the cores <NUM> of the second input optical fibers <NUM>, not all of the cores <NUM> of the second input optical fibers <NUM>, may be located within the area of the ring core <NUM> of the output optical fiber <NUM>.

Additionally, as shown in <FIG>, an outer peripheral edge of the cladding <NUM> of the intermediate optical fiber <NUM> may preferably be located within an area of the inner cladding <NUM> of the output optical fiber <NUM> (the intermediate area between the inner hatched area and the outer hatched area). When the outer peripheral edge of the cladding <NUM> of the intermediate optical fiber <NUM> is located within the area of the inner cladding <NUM> of the output optical fiber <NUM>, all of the second input optical fibers <NUM>, which are located outside of the intermediate optical fiber <NUM>, are positioned in an area outside of the center core <NUM> of the output optical fiber <NUM>. Therefore, the laser beams propagating through the cores <NUM> of the second input optical fibers <NUM> can be inhibited from mixing with the laser beams entering the center core <NUM> of the output optical fiber <NUM> from the core <NUM> of the intermediate optical fiber <NUM>.

Furthermore, as shown in <FIG>, at least a portion of an outer peripheral edge of each of the second input optical fibers <NUM> may preferably be located within the area of the inner cladding <NUM> of the output optical fiber <NUM> (the intermediate area between the inner hatched area and the outer hatched area). When at least a portion of an outer peripheral edge of each of the second input optical fibers <NUM> is located within the area of the inner cladding <NUM> of the output optical fiber <NUM>, the intermediate optical fiber <NUM>, which is located inside of the second input optical fiber <NUM>, is likely to be located in an area inside of the ring core <NUM> of the output optical fiber <NUM>. Therefore, the laser beam propagating through the core <NUM> of the intermediate optical fiber <NUM> can be inhibited from mixing with the laser beams entering the ring core <NUM> of the output optical fiber <NUM> from the cores <NUM> of the second input optical fibers <NUM>.

For example, if reflection light returns from the laser emission portion <NUM>, it may leak within the optical combiner <NUM>. In the conventional optical combiner as disclosed in Patent Literature <NUM>, inner optical fibers and outer optical fibers are connected to the same surface of an output optical fiber. Therefore, reflection light propagating through a center core of the output optical fiber and reflection light propagating through an outer core of the output optical fiber may leak out of the one surface of the output optical fiber, resulting in an increased amount of heat locally generated. In the present embodiment, however, the first input optical fibers <NUM> are connected to the bridge input surface <NUM> of the bridge fiber <NUM>, and the second input optical fibers <NUM> are connected to the output optical fiber <NUM>. Therefore, reflection light propagating through the center core <NUM> of the output optical fiber <NUM> may leak out of the bridge input surface <NUM> of the bridge fiber <NUM>, and reflection light propagating through the ring core <NUM> may leak out of an end face of the output optical fiber <NUM>. In this manner, the reflection light propagating through the center core <NUM> and the reflection light propagating through the ring core <NUM> leak out of different surfaces. Thus, the reflection light can be dispersed to reduce local heat generation. Accordingly, the risk of failure of the optical combiner <NUM> is also reduced.

For example, when a workpiece of a thin metal plate is to be cut with the laser apparatus <NUM> according to the present embodiment, the laser apparatus <NUM> may use a laser beam L having a circular shape with a small diameter where the optical power density is higher at the center thereof. When a workpiece of a thick metal plate is to be cut, the laser apparatus <NUM> may use a beam having an annular shape with a large diameter where the spot diameter or the rate of change in optical power density is small at a location deviated from a beam waist in the laser propagation direction (the thickness direction of the workpiece). Such a beam having an annular shape with a large diameter is suitable to cut a thick plate because it is advantageous in that it can increase the optical power density at the beam waist as compared to a beam having a circular shape under the conditions of the same beam diameter and the same beam output.

In the laser emission portion <NUM>, however, if an angle at which a laser beam is emitted from the ring core <NUM> of the output optical fiber <NUM> is greater than an angle at which a laser beam is emitted from the center core <NUM> of the output optical fiber <NUM>, then the advantages of the large-diameter annular-shaped beam suitable to cut a thick plate is lessened. This is because a decrease of the power density becomes greater with a larger emission angle at a location farther away from the focal point. Therefore, if a workpiece is thicker, a power density required to cut the workpiece cannot be obtained in the thickness direction.

From this point of view, the optical combiner <NUM> may be configured such that an angle of the laser beam emitted from the ring core <NUM> of the output optical fiber <NUM> is smaller than an angle of the laser beam emitted from the center core <NUM> of the output optical fiber <NUM>. For example, when light sources with equivalent capability are used for the laser sources 2A and 2B, NA of light emitted to the ring core <NUM> of the output optical fiber <NUM> from the second input optical fibers <NUM> may be adjusted to be smaller than NA of light emitted to the center core <NUM> of the output optical fiber <NUM> from the first input optical fibers <NUM> through the bridge fiber <NUM> and the intermediate optical fiber <NUM>. In this context, NA of light refers to a value defined by NA = n sine where n is a refractive index of a core through which a beam is propagating, and θ is a propagation angle of the beam. Furthermore, the term "equivalent capability" of laser sources is used herein to mean capability in such a range so as to accept manufacturing variations. For example, if the beam parameter product (BPP) is in a range of ±<NUM> %, such laser sources have equivalent capability.

In order to reduce the NA of light emitted from each of the second input optical fibers <NUM> to the ring core <NUM> of the output optical fiber <NUM>, for example, a diameter reduction portion may be formed in the second input optical fiber <NUM> so that the second input optical fiber <NUM> has the smallest diameter at a portion where the second input optical fiber <NUM> is connected to the ring core <NUM> of the output optical fiber <NUM>. In this case, a diameter reduction rate of the diameter reduction portion of the second input optical fiber <NUM> is defined as a rate of a diameter of the core <NUM> at a portion where the second input optical fiber <NUM> is not reduced in diameter to a diameter of the core <NUM> on an end face of the diameter reduction portion of the second input optical fiber <NUM> connected to the ring core <NUM> of the output optical fiber <NUM>. For outputting a laser beam L suitable to cut a thick plate, the diameter reduction rate of the diameter reduction portion of the second input optical fiber <NUM> may preferably be lower than a rate of a diameter of the core <NUM> on the bridge input surface <NUM> of the bridge fiber <NUM> to a diameter of the core <NUM> of the intermediate optical fiber <NUM> connected to the center core <NUM> of the output optical fiber <NUM>.

Alternatively, as shown in <FIG>, an optical adjustment member <NUM> having a function of reducing an emission angle of a laser beam propagating therethrough may be provided between each of the second input optical fibers <NUM> and the output optical fiber <NUM>. Examples of such an optical adjustment member <NUM> include a Graded Index or Gradient Index (GRIN) lens member having a refractive index gradually lowered from a central axis in a radially outward direction. Such an optical adjustment member <NUM> can reduce an emission angle of a laser beam that has propagated through the core <NUM> of the second input optical fiber <NUM> before the laser beam enters the ring core <NUM> of the output optical fiber <NUM>, so that the NA of the laser beam outputted from the ring core <NUM> of the laser emission portion <NUM> can be reduced. Accordingly, when such a laser beam is used to process a workpiece W, a beam diameter and an optical power density can be inhibited from varying on a front surface of the workpiece W, within the workpiece W, and on a rear surface of the workpiece W. Thus, a laser beam L suitable to process a thick metal plate, for example, can be directed to the workpiece W.

Meanwhile, if there is a difference between an emission angle of a laser beam emitted from the ring core <NUM> of the output optical fiber <NUM> and an emission angle of a laser beam emitted from the center core <NUM> of the output optical fiber <NUM> in the laser emission portion <NUM>, then the laser beam from the ring core <NUM> and the laser beam from the center core <NUM> may overlap at a defocused location, which is deviated from a focal point of a condensing optical system, resulting in hindered processing performance. From this point of view, an optical adjustment member having a function of increasing an emission angle of a second laser beam propagating therethrough may be used instead of the optical adjustment members <NUM> illustrated in <FIG>. Examples of such an optical adjustment member <NUM> may include an optical fiber having a mode field diameter greater than a mode field diameter of the second input optical fiber <NUM>, a cylindrical lens member having a refractive index distribution in which a refractive index gradually increases from a central region toward a radially outer peripheral portion, a tapered member having a diameter gradually reduced from the second input optical fiber <NUM> along an optical axis, and a combination of two GRIN lenses.

Meanwhile, a cladding mode, which propagates through the cladding, may be generated when a laser beam leaks out of the core while it propagates through the aforementioned optical combiner <NUM>. Such a cladding mode may cause heat generation at the output optical fiber <NUM> on a downstream side of the optical combiner <NUM>. The cladding mode may be applied to an unintended area from the laser emission portion <NUM>, resulting in degraded quality of laser processing.

Particularly, when the output optical fiber <NUM> include a plurality of cores <NUM> and <NUM> as in the above embodiment, cladding modes generated when laser beams are introduced into the respective cores <NUM> and <NUM> propagate through the claddings <NUM> and <NUM> of the same output optical fiber <NUM>. Therefore, more cladding modes tend to propagate through the output optical fiber <NUM> as compared to a case where the output optical fiber <NUM> is formed by a single-core optical fiber. When a cladding mode stripper is provided in the middle of the output optical fiber <NUM> in order to remove such cladding modes, the amount of heat generated in the cladding mode stripper may increase so much that the cladding mode stripper cannot sufficiently remove the cladding modes.

Therefore, as shown in <FIG>, a first cladding mode removal portion <NUM> operable to remove cladding modes that have leaked out of the core <NUM> to the cladding <NUM> of the intermediate optical fiber <NUM> may be provided in the middle of the intermediate optical fiber <NUM>, and a second cladding mode removal portion <NUM> operable to remove cladding modes that have leaked out of the ring core <NUM> to the outer cladding <NUM> of the output optical fiber <NUM> may be provided in the middle of the output optical fiber <NUM>. With this configuration, cladding modes that have leaked to the cladding <NUM> of the intermediate optical fiber <NUM> can be removed by the first cladding mode removal portion <NUM> before entering the output optical fiber <NUM>. Therefore, the amount of heat generated in the second cladding mode removal portion <NUM> can be reduced. Any known cladding mode removal structures may be used for the cladding mode removal portions <NUM> and <NUM>.

It has been known that an emission angle of light emitted from an optical fiber increases when a load is applied to the optical fiber. In order to control an emission angle of a laser beam emitted from the center core <NUM> of the output optical fiber <NUM> and an emission angle of a laser beam emitted from the ring core <NUM> of the output optical fiber <NUM>, therefore, a first optical control portion <NUM> that controls a load applied to the intermediate optical fiber <NUM> may be provided in the middle of the intermediate optical fiber <NUM> to control the NA of light propagating through the core <NUM> of the intermediate optical fiber <NUM>. A second optical control portion <NUM> that controls a load applied to the output optical fiber <NUM> may be provided in the middle of the output optical fiber <NUM> to control the NA of light propagating through the center core <NUM> and the ring core <NUM> of the output optical fiber <NUM>. Examples of such optical control portions <NUM> and <NUM> include a device for heating or forming a temperature distribution so as to apply a load to an optical fiber, a device for providing a bend to an optical fiber, and a device for applying a lateral pressure to an optical fiber.

A load applied to the output optical fiber <NUM> by the second optical control portion <NUM> primarily exerts an influence on light propagating through the ring core <NUM>, which is located radially outside, and does not exert an influence so much on light propagating through the center core <NUM>, which is located near the center. Meanwhile, light emitted from the intermediate optical fiber <NUM> to the center core <NUM> of the output optical fiber <NUM> is influenced by a load applied to the intermediate optical fiber <NUM> by the first optical control portion <NUM>. Thus, an emission angle of a laser beam emitted from the center core <NUM> of the output optical fiber <NUM> can be controlled primarily by the first optical control portion <NUM>, and an emission angle of a laser beam emitted from the ring core <NUM> of the output optical fiber <NUM> can be controlled primarily by the second optical control portion <NUM>.

Both types of the cladding mode removal portions <NUM>, <NUM> and the optical control portions <NUM>, <NUM> may be provided as shown in <FIG>. Alternatively, one type of them may be provided. If both types of the cladding mode removal portions <NUM>, <NUM> and the optical control portions <NUM>, <NUM> are provided, cladding modes may be generated by application of loads from the optical control portions <NUM> and <NUM>. In order to efficiently remove the generated cladding modes, it is preferable to provide the first cladding mode removal portion <NUM> on a downstream side of the first optical control portion <NUM> and provide the second cladding mode removal portion <NUM> on a downstream side of the second optical control portion <NUM> as shown in <FIG>.

The aforementioned output optical fiber <NUM> is not limited to the structure illustrated in <FIG>. For example, an output optical fiber <NUM> as shown in <FIG> may be used instead of the aforementioned output optical fiber <NUM>. The output optical fiber <NUM> as shown in <FIG> has a core <NUM>, an inner cladding <NUM> that surrounds an outer circumference of the core <NUM>, and an outer cladding <NUM> that surrounds an outer circumference of the inner cladding <NUM>. The inner cladding <NUM> has a refractive index lower than a refractive index of the core <NUM>, and the outer cladding <NUM> has a refractive index lower than a refractive index of the inner cladding <NUM>. Thus, an interior of the core <NUM> forms a first optical waveguide that allows a laser beam to propagate therethrough, and an interior of the inner cladding <NUM> and the core <NUM> forms a second optical waveguide that allows a laser beam to propagate therethrough. The core <NUM> of the intermediate optical fiber <NUM> is connected to the core <NUM> of the output optical fiber <NUM> by fusion splicing, and the core <NUM> of the second input optical fiber <NUM> is connected to the inner cladding <NUM> of the output optical fiber <NUM> by fusion splicing. The output optical fiber <NUM> has a covering layer (not shown) that surrounds an outer circumference of the outer cladding <NUM> at a location away from the intermediate optical fiber <NUM> and the second input optical fiber <NUM>.

With this configuration, a laser beam that has propagated through the core <NUM> of the first input optical fiber <NUM> enters the core <NUM> of the bridge fiber <NUM> from the bridge input surface <NUM> of the bridge fiber <NUM>. The laser beam is reduced in diameter by the diameter reduction portion <NUM> and introduced into the core <NUM> of the intermediate optical fiber <NUM> from the bridge output surface <NUM>. The laser beam that has been introduced to the core <NUM> of the intermediate optical fiber <NUM> propagates through the core <NUM> and enters the core <NUM> of the output optical fiber <NUM>. Then the laser beam propagates through the interior of the core <NUM> as the first optical waveguide. The laser beam is eventually emitted from the laser emission portion <NUM> (see <FIG>). Furthermore, a laser beam that has propagated through the core <NUM> of the second input optical fiber <NUM> enters the inner cladding <NUM> of the output optical fiber <NUM> and propagates through the interior of the inner cladding <NUM> and the core <NUM> as the second optical waveguide. The laser beam is eventually emitted from the laser emission portion <NUM> (see <FIG>).

In the output optical fiber <NUM> as shown in <FIG>, the outer cladding <NUM> is formed around the inner cladding <NUM> as a low-refractive-index medium having a refractive index lower than the refractive index of the inner cladding <NUM>. Such a low-refractive-index medium is not limited to a covering layer such as the outer cladding <NUM>. For example, an air layer may be formed around the inner cladding <NUM> and may be used as a low-refractive-index medium.

In the aforementioned embodiment, a plurality of laser sources 2B and a plurality of input optical fibers <NUM> are provided. However, the number of input optical fibers <NUM> connected to a second optical waveguide of the output optical fiber <NUM> or <NUM> may be one, and the number of laser sources 2B connected to this input optical fiber <NUM> may be one. In the aforementioned embodiment, a laser source 2A is connected to each of the input optical fibers <NUM>. However, a laser source 2A may not necessarily be connected to all of the input optical fibers <NUM>. Thus, one or more laser sources 2A may be connected to one or more input optical fibers <NUM>.

Although some preferred embodiments of the present invention have been described, the present invention is not limited to the aforementioned embodiments. It should be understood that various different forms may be applied to the present invention within the technical idea thereof.

As described above, according to a first aspect of the present invention, there is provided an optical combiner that can readily be manufactured with capability of directing a laser beam into each of a first optical waveguide and a second optical waveguide of an output optical fiber. This optical combiner has a plurality of first input optical fibers each including a core, a bridge fiber having a bridge input surface connected to the cores of the plurality of first input optical fibers, a diameter reduction portion having a diameter gradually reduced away from the bridge input surface along an optical axis, and a bridge output surface located opposite to the bridge input surface along the optical axis, an intermediate optical fiber including a core connected to the bridge output surface of the bridge fiber, at least one second input optical fiber including a core, and an output optical fiber including a first optical waveguide connected to the core of the intermediate optical fiber and a second optical waveguide connected to the core of the at least one second input optical fiber.

With this configuration, light propagating through cores of a plurality of first input optical fibers is reduced in beam diameter in a bridge fiber and then introduced into a first optical waveguide of an output optical fiber. Therefore, the first input optical fibers can be connected to the bridge fiber without reduction of the diameter of the first input optical fibers. Accordingly, the mechanical strength of the first input optical fibers can be maintained. Thus, an optical combiner can readily be manufactured. Furthermore, the number of the first input optical fibers can be increased without reduction of the diameter of the first input optical fibers. Therefore, the power of laser beams introduced to the first optical waveguide of the output optical fiber can readily be increased. Thus, output balance between light propagating through the first optical waveguide and light propagating through the second optical waveguide can readily be adjusted.

The output optical fiber may include a center core, an inner cladding having a refractive index lowered than a refractive index of the center core and surrounding an outer circumference of the center core, a ring core having a refractive index higher than the refractive index of the inner cladding and surrounding an outer circumference of the inner cladding, and a low-refractive-index medium having a refractive index lower than the refractive index of the ring core and surrounding an outer circumference of the ring core. In this case, the center core forms the first optical waveguide, and the ring core forms the second optical waveguide.

An outer peripheral edge of the intermediate optical fiber may preferably be located within an area of the inner cladding of the output optical fiber. In this case, the second input optical fiber, which is located outside of the intermediate optical fiber, is positioned in an area outside of the center core of the output optical fiber. Therefore, a laser beam propagating through the core of the second input optical fiber can be inhibited from mixing with a laser beam entering the center core of the output optical fiber from the core of the intermediate optical fiber.

The core of the intermediate optical fiber may preferably be located within an area of the center core of the output optical fiber. In this case, a laser beam propagating through the core of the intermediate optical fiber can efficiently be introduced into the center core of the output optical fiber.

At least a portion of an outer peripheral edge of the at least one second input optical fiber may preferably be located within an area of the inner cladding of the output optical fiber. In this case, the intermediate optical fiber, which is located radially inside of the second input optical fiber, is likely to be located in an area inside of the ring core of the output optical fiber. Therefore, a laser beam propagating through the core of the intermediate optical fiber can be inhibited from mixing with the laser beam entering the ring core of the output optical fiber from the core of the second input optical fiber.

The core of the at least one second input optical fiber may preferably be located within an area of the ring core of the output optical fiber. In this case, a laser beam propagating through the core of the second input optical fiber can efficiently be introduced into the ring core of the output optical fiber.

The output optical fiber may include a core, an inner cladding having a refractive index lower than a refractive index of the core and surrounding an outer circumference of the core, and a low-refractive-index medium having a refractive index lower than the refractive index of the inner cladding and surrounding an outer circumference of the inner cladding. In this case, the core forms the first optical waveguide, and the core and the inner cladding form the second optical waveguide.

The at least one second input optical fiber may have a diameter reduction portion having the smallest diameter at a portion where the diameter reduction portion is connected to the second optical waveguide of the output optical fiber. In this case, a diameter reduction rate of the diameter reduction portion of the at least one second input optical fiber may be lower than a ratio of a core of the bridge fiber at the bridge input surface to a diameter of the core of the intermediate optical fiber connected to the first optical waveguide of the output optical fiber.

According to a second aspect of the present invention, there is provided a laser apparatus capable of outputting a laser beam having a desired beam profile. The laser apparatus has at least one first laser source operable to generate a first laser beam, at least one second laser source operable to generate a second laser beam, and the aforementioned optical combiner. At least one of the plurality of first input optical fibers of the optical combiner is connected to the at least one first laser source. The at least one second input optical fiber of the optical combiner is connected to the at least one second laser source.

With the aforementioned optical combiner, output balance between the laser beam propagating through the first optical waveguide and the laser beam propagating through the second optical waveguide of the output optical fiber can readily be adjusted. Therefore, a laser beam having a desired beam profile can be outputted from the laser apparatus.

Preferably, the laser apparatus may further have a controller operable to control the at least one first laser source and the at least one second laser source to adjust an output of the first laser beam generated by the at least one first laser source and an output of the second laser beam generated by the at least one second laser source. With such a controller, a ratio of outputs of the first laser beam generated by the first laser source and the second laser beam generated by the second laser source can be changed to adjust a ratio of the first laser beam introduced to the first optical waveguide of the output optical fiber and the second laser beam introduced to the second optical waveguide of the output optical fiber. Therefore, a profile of the laser beam outputted from the laser apparatus can readily be adjusted to a desired shape.

When the at least one first laser source and the at least one second laser source have equivalent capability, an emission angle of the second laser beam outputted from the second optical waveguide of the output optical fiber through the at least one second input optical fiber connected to the at least one second laser source may be smaller than an emission angle of the first laser beam outputted from the first optical waveguide of the output optical fiber through at least one of the plurality of first input optical fibers connected to the at least one first laser source.

The laser apparatus may further have a first cladding mode removal portion operable to remove a cladding mode leaking out of the core of the intermediate optical fiber and a second cladding mode removal portion operable to remove a cladding mode leaking out of the second optical waveguide of the output optical fiber. With this configuration, a cladding mode that has leaked out of the core of the intermediate optical fiber can be removed by the first cladding mode removal portion before entering the output optical fiber. Therefore, the amount of heat generated in the second cladding mode removal portion can be reduced.

The laser apparatus may further have a first optical control portion operable to control a load applied to the intermediate optical fiber so as to control an emission angle of the first laser beam propagating through the core of the intermediate optical fiber and a second optical control portion operable to control a load applied to the output optical fiber so as to control an emission angle of the second laser beam propagating through the second optical waveguide of the output optical fiber. With this configuration, an emission angle of a first laser beam emitted from the first optical waveguide of the output optical fiber can be controlled primarily by the first optical control portion, and an emission angle of a second laser beam emitted from the second optical waveguide of the output optical fiber can be controlled primarily by the second optical control portion.

This application claims the benefit of priority from <CIT> and <CIT>.

Claim 1:
An optical combiner (<NUM>) comprising:
a plurality of first input optical fibers (<NUM>) each including a core (<NUM>);
a bridge fiber (<NUM>) having a bridge input surface (<NUM>) including a single core (<NUM>) connected to the cores (<NUM>) of the plurality of first input optical fibers (<NUM>), a diameter reduction portion (<NUM>) having a diameter gradually reduced away from the bridge input surface (<NUM>) along an optical axis, and a bridge output surface (<NUM>) located opposite to the bridge input surface (<NUM>) along the optical axis;
an intermediate optical fiber (<NUM>) including a core (<NUM>) connected to the bridge output surface (<NUM>) of the bridge fiber (<NUM>);
at least one second input optical fiber (<NUM>) including a core (<NUM>); and
an output optical fiber (<NUM>) including a first optical waveguide connected to the core (<NUM>) of the intermediate optical fiber (<NUM>) and a second optical waveguide connected to the core (<NUM>) of the at least one second input optical fiber (<NUM>).