Optical combiner and laser device using the same

An optical combiner includes a plurality of input optical fibers, an output optical fiber, and a bridge fiber optically coupled to the plurality of input optical fibers and the output optical fiber. The bridge fiber includes a tapered portion whose outer diameter is reduced toward the emission end, and the outer diameter of the emission end face of the bridge fiber is smaller than the cladding outer diameter of the incident end face of the output optical fiber.

BACKGROUND OF THE INVENTION

The present invention relates to an optical combiner and a laser device using the same, which are preferable to the case of suppressing heat generation or ignition caused by return light.

Heretofore, for an optical combiner that combines light beams emitted from a plurality of laser light sources with a single optical fiber, Patent Document 1 described below is proposed, for example.

In the multiport coupler described in Patent Document 1, a signal fiber 5 in the center is integrated with a plurality of pump fibers 4 disposed around the signal fiber 5, and the diameter is reduced on the tip end side. An emitted-light confinement waveguide 7 is concentrically provided around a core 6 of the signal fiber 5 positioned in the center. The emitted-light confinement waveguide 7 has the outer diameter greater than the outer diameter of the core 6, and has the refractive index higher than the refractive index of the cladding 8 and smaller than the refractive index of the core 6.

The emitted-light confinement waveguide 7 confines return light leaking from the core of a cladding pump fiber 3 at the portion at which the cladding pump fiber 3 is connected to the end portion on the diameter reduced side, and suppresses the damage of a pumping light source caused by the return light.[Patent Document 1] Japanese Patent No. 5089950

SUMMARY OF THE INVENTION

However, in the multiport coupler, in the case where return light enters the cladding of the cladding pump fiber 3, not the core of the cladding pump fiber 3, it is not enabled to confine the return light in the emitted-light confinement waveguide 7.

Because of this, it is assumed that the return light is passed through the multiport coupler, and emitted to the signal fiber 5, which is not integrated with the multiport coupler, to cause the coating layer of the signal fiber to generate heat for degrading reliability.

It is an object of the present invention to provide an optical combiner and a laser device using the same that can improve reliability.

According to an embodiment of the present invention, there is provided an optical combiner including: a plurality of input optical fibers; an output optical fiber; and a bridge fiber disposed between the plurality of input optical fibers and the output optical fiber and optically coupled to the plurality of input optical fibers and the output optical fiber, wherein the bridge fiber includes a tapered portion whose outer diameter is reduced toward an emission end of the bridge fiber, and an outer diameter of an emission end face of the bridge fiber is smaller than a cladding outer diameter of an incident end face of the output optical fiber.

In the optical combiner, the outer diameter of the emission end face of the bridge fiber is smaller than the cladding outer diameter of the incident end face of the output optical fiber. Therefore, even though light emitted from the output optical fiber is reflected off a workpiece, for example, and the light is passed through the emission end face of the output optical fiber and emitted from the incident end face as return light, most of the light is reflected off the outer circumferential surface of the tapered portion of the bridge fiber, and emitted to the outside.

Thus, it is greatly reduced that return light enters the bridge fiber, and that return light is passed through the bridge fiber and reaches the coating layer of the input optical fiber from the incident end face. Consequently, the optical combiner can suppress the heat generation or ignition of the bridge fiber or the coating layer of the input optical fiber caused by return light.

Accordingly, the improvement of reliability of the optical combiner is implemented.

Preferably, the bridge fiber is formed of a plurality of bridge fibers optically coupled to each other, and in adjacent bridge fibers at at least one location of the plurality of bridge fibers, an outer diameter of an incident end face of the bridge fiber located on the output optical fiber side is greater than an outer diameter of an emission end face of the bridge fiber located on the input optical fiber side.

In this case, light emitted to the outside of the optical combiner is distributed to the joining portion between the joining portion between the bridge fiber and the output optical fiber and the adjacent bridge fibers. Therefore, it is possible to suppress such an event that the light emitted to the outside is concentrated on a certain location in the outside as compared with the case where light is emitted to the outside only through the joining portion between the bridge fiber and the output optical fiber.

Accordingly, it is also possible to suppress the heat generation or ignition of the members around the optical fiber caused by return light.

Moreover, preferably, the plurality of bridge fibers individually includes a core and a cladding that surrounds an outer circumferential surface of the core, and a ratio of an outer diameter of the core to an outer diameter of the cladding in the plurality of bridge fibers is smaller in a bridge fiber located more apart from an input optical fiber.

In this configuration, the end face of the bridge fiber on the output optical fiber side is always increased at the fusion-spliced point between the bridge fibers as compared with the case where a single bridge fiber in which the ratio of the outer diameter of the core to the outer diameter of the cladding is the same along the longitudinal direction is used instead of the plurality of bridge fibers. Accordingly, it is possible that return light is more distributed and emitted to the outside.

Alternatively, preferably, in the plurality of bridge fibers, light is propagated entirely through a bridge fiber to which the plurality of input optical fibers is connected, and one or two or more of bridge fibers other than the bridge fiber include a core and a cladding that surrounds an outer circumferential surface of the core.

In this configuration, it is possible to reduce the diameter difference between the outer diameter of the incident end of the bridge fiber to which a plurality of the input optical fibers is connected and the outer diameter of the bundled input optical fibers as compared with the case where the bridge fiber to which a plurality of the input optical fibers is connected has the structure including the core and the cladding.

Accordingly, it is possible to reduce the concentration of stress at the fusion-spliced point between the input optical fibers and the bridge fiber, and it is possible to improve the strength at the fusion-spliced point between the input optical fibers and the bridge fiber.

Moreover, preferably, two or more of bridge fibers are included other than the bridge fiber to which the plurality of input optical fibers is connected, and a ratio of an outer diameter of the core to an outer diameter of the cladding in the two or more of bridge fibers is smaller in a bridge fiber located more apart from the input optical fiber.

In this configuration, the end face of the bridge fiber on the output optical fiber side is always increased at the fusion-spliced point between the bridge fibers as compared with the case where a single bridge fiber in which the ratio of the outer diameter of the core to the outer diameter of the cladding is the same is used instead of two or more of the bridge fibers. Accordingly, it is possible that return light is more distributed and emitted to the outside.

Moreover, preferably, a maximum outer diameter of a bridge fiber to which the output optical fiber is connected is smaller than a maximum outer diameter of other bridge fibers.

In this configuration, it is possible to reflect return light leaked from the emission-side bridge fiber off the outer circumferential surface of the tapered portion of the incident-side bridge fiber. Therefore, it is possible to easily keep the return light away from the input optical fiber, and as a result, it is possible to further suppress the absorption of return light to the coating layer of the input optical fiber.

Moreover, a laser device according to an aspect of the present invention is a laser device including: any of the optical combiners described above; and a laser light source configured to apply laser light to the input optical fiber.

This laser device includes the optical combiner that can improve reliability, as described above. Accordingly, it is possible to implement the improvement of reliability of the laser device.

As described above, according to an aspect of the present invention, it is possible to provide an optical combiner and a laser device using the same that can improve reliability.

DETAILED DESCRIPTION OF THE INVENTION

In the following, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

(1) First Embodiment

FIG. 1is a diagram of a laser device1according to a first embodiment. As illustrated inFIG. 1, the laser device1according to the embodiment includes a plurality of laser light sources2and an optical combiner3as main components.

The laser light source2emits laser light, which is a laser diode or a Fabry-Perot fiber laser and a fiber ring fiber laser, for example.

The optical combiner3includes a plurality of input optical fibers10, an output optical fiber20, and a bridge fiber30as main components.

FIG. 2is a diagram of the cross section of the optical combiner3according to the first embodiment. As illustrated inFIG. 2, the input optical fiber10is an optical fiber that causes laser light emitted from the laser light source2to enter the bridge fiber30, and the input optical fibers10are provided in the same number as the number of the laser light sources. The input optical fibers10individually include a core11, a cladding12that surrounds the outer circumferential surface of the core11, and a coating layer13that covers the cladding12.

The refractive index of the core11is set higher than the refractive index of the cladding12. For example, the core11is made of pure quartz, and the cladding12is made of quartz doped with a dopant such as fluorine that reduces the refractive index.

The output optical fiber20is an optical fiber that causes laser light emitted from the bridge fiber30to emit in the subsequent stage. The output optical fiber20includes a core21, a cladding22that surrounds the outer circumferential surface of the core21, an outer cladding23that surrounds the outer circumferential surface of the cladding22, and a coating layer24that covers the outer cladding23.

The refractive index of the core21is set higher than the refractive index of the cladding22, and the refractive index of the cladding22is set higher than the refractive index of the outer cladding23. For example, the core21is made of silica doped with a dopant such as germanium that increases the refractive index, the cladding22is made of pure silica, and the outer cladding23is made of a polymer such as glass or a resin whose refractive index is lower than the refractive index of the cladding22.

The bridge fiber30is a glass body provided between a plurality of the input optical fibers10and the output optical fiber20and optically coupled to a plurality of the input optical fibers10and the output optical fiber20. The bridge fiber30does not have a core-cladding structure, and the entire bridge fiber30is a portion through which light is propagated.

The refractive index of the bridge fiber30is not limited more specifically. However, from the viewpoint of reducing the refraction of light incident from the input optical fiber10, preferably, the refractive index of the bridge fiber30is substantially the same as the refractive index of the core11of the input optical fiber10. For example, the first bridge fiber30is made of pure silica.

Moreover, the bridge fiber30includes a tapered portion30A whose outer diameter is reduced toward the emission end of the bridge fiber30. In the bridge fiber30according to the embodiment, the portion from a position in the midway point between the incident end and the emission end to the emission end is the tapered portion30A, and the portion from the incident end to the position in the midway point is a constant diameter portion30B whose outer diameter is constant along the length direction of the bridge fiber30.

The tapered portion30A is integrally formed with the constant diameter portion30B, and the outer diameter of the large diameter end face of the tapered portion30A is matched with the outer diameter of the constant diameter portion30B. That is, the outer diameter of the incident end face of the bridge fiber30is matched with the outer diameter of the large diameter end face of the tapered portion30A, and is the largest in the bridge fiber30. On the other hand, the emission end face of the bridge fiber30is the small diameter end face of the tapered portion30A, and the outer diameter of the emission end face is the smallest in the bridge fiber30.

The outer diameter of the emission end face of the bridge fiber30is made smaller than the cladding outer diameter of the incident end face of the output optical fiber20, and the emission end face is fusion-spliced to a part of the core21and the cladding22on the incident end face of the output optical fiber20. On the other hand, the incident end face of the bridge fiber30is fusion-spliced to the core11and the cladding12on the emission end face of the individual input optical fibers10.

It is noted that in the optical combiner3according to the embodiment, the coating layer13at one end portion fusion-spliced to the bridge fiber30is removed in the input optical fibers10, and the cladding12of the portion is exposed. Moreover, the coating layer24at one end portion fusion-spliced to the bridge fiber30is removed in the output optical fiber20, and the outer cladding23of the portion is exposed.

Next, the propagation of light in the optical combiner3will be described. In the case where laser light enters the bridge fiber30from the laser light source2through the input optical fiber10, the laser light is propagated while spreading through the bridge fiber30, and reaches the tapered portion30A.

At the tapered portion30A, the laser light is propagated while at least a part of the light is reflected off the outer circumferential surface of the bridge fiber30. It is noted that an angle of the light reflected off the outer circumferential surface of the bridge fiber30is increased with respect to the axial direction of the bridge fiber30.

The light propagated through the tapered portion30A then enters the core21of the output optical fiber20from the emission end face of the bridge fiber30, and the light is propagated through the core21and emitted from the emission end face of the output optical fiber20to the subsequent stage.

There is the case where light emitted from the output optical fiber20is reflected off a workpiece, for example, and the light enters the cladding22from the emission end face of the output optical fiber20as return light. The propagation of return light in this case will be described.FIG. 3is a schematic diagram of the propagation of return light in the optical combiner3according to the first embodiment.

As illustrated inFIG. 3, since the cladding22of the output optical fiber20is covered with the outer cladding23, the return light incident on the cladding22is propagated through the output optical fiber20from the emission end face to the incident end face of the output optical fiber20. The return light is then emitted from the cladding22on the incident end face of the output optical fiber20, and reaches the bridge fiber30.

In the embodiment, the outer diameter of the emission end face of the bridge fiber30is smaller than the cladding outer diameter of the incident end face of the output optical fiber20. Therefore, most of the light emitted from the incident end face of the output optical fiber20is reflected off the outer circumferential surface of the tapered portion30A of the bridge fiber30, and emitted to the outside.

Thus, in the optical combiner3according to the embodiment, it is greatly reduced that return light enters the bridge fiber30, or that return light reaches the coating layer13of the input optical fiber10from the incident end face through the bridge fiber30.

Consequently, the optical combiner3according to the embodiment can suppress the heat generation or ignition of the bridge fiber30or the coating layer13of the input optical fiber10caused by return light. Accordingly, the optical combiner3is provided, which can suppress heat generation or ignition caused by return light.

(2) Second Embodiment

Next, a second embodiment will be described in detail with reference to the drawings. However, in components according to the second embodiment, components the same as or equivalent to the components in the first embodiment are designated the same reference numerals and signs, and the overlapping description is appropriately omitted.

FIG. 4is a diagram of an optical combiner according to the second embodiment. As illustrated inFIG. 4, the optical combiner according to the embodiment is different from the first embodiment in that a bridge fiber is formed in a two-stage structure.

That is, the optical combiner according to the embodiment includes a first bridge fiber40and a second bridge fiber50, instead of a single bridge fiber30according to the first embodiment.

The first bridge fiber40and the second bridge fiber50are disposed between a plurality of input optical fibers10and an output optical fiber20, and are optically coupled to each other. Moreover, the first bridge fiber40in the previous stage located on the input optical fiber10side is optically coupled to the input optical fibers10, and the second bridge fiber50in the subsequent stage located on the output optical fiber20side is optically coupled to the output optical fiber20.

The first bridge fiber40does not have the core-cladding structure, and the entire bridge fiber40is a portion through which light is propagated.

The refractive index of the bridge fiber40is not limited more specifically. However, from the viewpoint of reducing the refraction of light incident from the input optical fiber10, preferably, the refractive index is substantially the same as the refractive index of a core11of the input optical fiber10.

Similarly to the bridge fiber30according to the first embodiment, the first bridge fiber40includes a tapered portion40A whose outer diameter is reduced toward the emission end of the first bridge fiber40and a constant diameter portion40B whose outer diameter is constant along the length direction of the first bridge fiber40.

The outer diameter of the incident end face of the first bridge fiber40is matched with the outer diameter of the large diameter end face of the tapered portion40A, and the incident end face is fusion-spliced to the core11and a cladding12on the emission end face of the input optical fibers10.

The second bridge fiber50includes a core51and a cladding52that covers the core51. That is, in the second bridge fiber50, the core51that is a core layer of the second bridge fiber50is a portion through which light is propagated.

The refractive index of the core51is set higher than the refractive index of the cladding52. For example, the core51is made of pure silica, and the cladding52is made of silica doped with a dopant such as fluorine that reduces the refractive index. It is noted that from the viewpoint of suppressing the refraction of light incident from the first bridge fiber40, preferably, the refractive index of the core51is set substantially the same as the refractive index of the first bridge fiber40. For example, the core51is made of pure silica.

Similarly to the bridge fiber30according to the first embodiment, the second bridge fiber50includes a tapered portion50A whose outer diameter is reduced toward the emission end of the second bridge fiber50and a constant diameter portion50B whose outer diameter is constant along the length direction of the first bridge fiber40.

The outer diameter of the incident end face of the second bridge fiber50is matched with the outer diameter of the large diameter end face (the cladding outer diameter) of the tapered portion50A, and the incident end face is fusion-spliced to the emission end face of the first bridge fiber40(the small diameter end face of the tapered portion40A). On the other hand, the emission end face of the second bridge fiber50(the small diameter end face of the tapered portion50A) is fusion-spliced to a part of a core21and a cladding22on the incident end face of the output optical fiber20.

The outer diameter of the incident end face of the second bridge fiber50is set greater than the outer diameter of the emission end face of the first bridge fiber40. Moreover, the maximum outer diameter of the second bridge fiber50is set smaller than the maximum outer diameter of the first bridge fiber40.

It is noted that in the case of the embodiment, the outer diameter of the incident end face is at the maximum in the second bridge fiber50, and the outer diameter of the incident end face is at the maximum in the first bridge fiber40. Moreover, similarly to the case of the first embodiment, the outer diameter of the emission end face of the second bridge fiber50is set smaller than the cladding outer diameter of the incident end face of the output optical fiber20.

Next, the propagation of return light in an optical combiner3will be described.FIG. 5is a schematic diagram of the propagation of return light in the optical combiner3according to the second embodiment.

As illustrated inFIG. 5, return light incident on the cladding22of the output optical fiber20is propagated through the output optical fiber20from the emission end face to the incident end face of the output optical fiber20, and reaches the second bridge fiber50.

In the embodiment, the outer diameter of the emission end face of the second bridge fiber50is smaller than the cladding outer diameter of the incident end face of the output optical fiber20. Therefore, most of the light emitted from the incident end face of the output optical fiber20is reflected off the outer circumferential surface of the tapered portion50A of the second bridge fiber50or enters the cladding52of the second bridge fiber50.

In the case where the return light is reflected off the outer circumferential surface of the tapered portion50A, the light is emitted to the outside. On the other hand, in the case where the return light enters the cladding52, the light is propagated through the cladding52, emitted from the incident end face of the second bridge fiber50, and reaches the first bridge fiber40.

In the embodiment, the outer diameter of the incident end face of the second bridge fiber50is smaller than the outer diameter of the emission end face of the first bridge fiber40. Therefore, most of the light emitted from the cladding52on the incident end face of the second bridge fiber50is reflected off the outer circumferential surface of the tapered portion40A of the first bridge fiber40, and emitted to the outside.

Thus, in the embodiment, light emitted to the outside is distributed to the joining portion between the second bridge fiber50and the output optical fiber20and the joining portion between the first bridge fiber40and the second bridge fiber50.

Therefore, the optical combiner according to the embodiment can suppress such an event that the light emitted to the outside is concentrated on a certain location in the outside as compared with the case of the first embodiment where light is emitted to the outside only through the joining portion between the bridge fiber30and the output optical fiber20.

Accordingly, the optical combiner according to the embodiment can also suppress the heat generation or ignition of the members around the optical fiber caused by return light. It is noted that similarly to the case of the first embodiment, the optical combiner according to the embodiment can also suppress the heat generation or ignition of the first bridge fiber40, the second bridge fiber50, or the coating layer13of the input optical fiber10.

Moreover, the optical combiner according to the embodiment has the structure in which the first bridge fiber40, to which a plurality of the input optical fibers10is connected, does not include the core and the cladding. In this optical combiner, it is possible to reduce the diameter difference between the outer diameter of the incident end of the first bridge fiber40and the outer diameter of the bundled input optical fibers10as compared with the case where the first bridge fiber40is formed in the structure including the core and the cladding.

For example, the size of the outer diameter of the first bridge fiber40, or the number of the input optical fibers10and the size of the outer diameter of the input optical fiber10, for example, are adjusted, so that the outer diameter of the incident end of the first bridge fiber40to be coupled to the input optical fibers10can be made substantially equal to the outer diameter of the bundled input optical fibers10.

Therefore, the concentration of stress at the fusion-spliced point between the input optical fibers10and the first bridge fiber40is reduced, and it is possible to improve the strength at the fusion-spliced point between the input optical fibers10and the first bridge fiber40.

Next, a third embodiment will be described in detail with reference to the drawing. However, in components according to the third embodiment, components the same as or equivalent to the components in the above embodiments are designated the same reference numerals and signs, and the overlapping description is appropriately omitted.

FIG. 6is a diagram of an optical combiner according to the third embodiment. As illustrated inFIG. 6, the optical combiner according to the embodiment is different from the second embodiment in that bridge fibers in two stages are formed in a core-cladding structure.

That is, the optical combiner according to the embodiment includes a first bridge fiber60having a core61and a cladding62that surrounds the outer circumferential surface of the core61instead of the first bridge fiber40according to the second embodiment.

Similarly to the first bridge fiber40according to the second embodiment, the first bridge fiber60includes a tapered portion60A whose outer diameter is reduced toward the emission end and a constant diameter portion60B whose outer diameter is constant along the length direction of the first bridge fiber60.

The outer diameter of the incident end face of the first bridge fiber60is matched with the outer diameter (the cladding outer diameter) of the large diameter end face of the tapered portion60A, and the core61on the incident end face is fusion-spliced to a core11and a cladding12on the emission end face of input optical fibers10.

It is noted that similarly to the second embodiment, the outer diameter of the incident end face of the second bridge fiber50is set greater than the outer diameter of the emission end face of the first bridge fiber60. Moreover, similarly to the second embodiment, the maximum outer diameter of the second bridge fiber50is set smaller than the maximum outer diameter of the first bridge fiber40.

In the case of the embodiment, the ratio of the outer diameter of the core61of the first bridge fiber60to the outer diameter of the cladding62is greater than the ratio of the outer diameter of the core51of the second bridge fiber50to the outer diameter of the cladding52. That is, the ratio of the outer diameter of the core to the outer diameter of the cladding is smaller in the bridge fiber located more apart from the input optical fiber10. It is noted that the ratio of the outer diameter of the core to the outer diameter of the cladding is A/B, where the outer diameter of the core is A and the outer diameter of the cladding is B.

In this optical combiner, the end face of the second bridge fiber50on the output optical fiber side is increased at the fusion-spliced point between the bridge fibers as compared with the case where a single bridge fiber in which the ratio of the outer diameter of the core to the outer diameter of the cladding is the same along the longitudinal direction is used instead of the first bridge fiber60and the second bridge fiber50. Therefore, it is possible that return light is more distributed and emitted to the outside.

Hereinabove, the embodiments are described as examples. However, the present invention is not limited to the embodiments.

For example, in the first embodiment to the third embodiment, the bridge fiber configured of the tapered portion and the constant diameter portion is applied. However, such a bridge fiber may be applied that the constant diameter portion is omitted.

In the second embodiment, the first bridge fiber40located closest to the input optical fiber is a bridge fiber through which light is propagated entirely (a bridge fiber has no core-cladding structure). Moreover, a bridge fiber other than the first bridge fiber40is a single second bridge fiber50including the core51and the cladding52.

However, two or more of the second bridge fibers50may be provided between the first bridge fiber40and the output optical fiber20as bridge fibers other than the first bridge fiber40. In the case where two or more of the second bridge fibers50are provided between the first bridge fiber40and the output optical fiber20as described above, preferably, the ratio of the core to the cladding in these second bridge fibers50is made similar to the ratio in the third embodiment.

That is, such a bridge fiber is preferable that the ratio of the outer diameter of the core51to the outer diameter of the cladding52in two or more of the second bridge fibers50is smaller in the bridge fiber located more apart from the input optical fiber10.

With this configuration, the end face of the second bridge fiber50on the output optical fiber side is increased at the fusion-spliced point between the bridge fibers as compared with the case where a single second bridge fiber50is provided. Therefore, it is possible that return light is more distributed and emitted to the outside.

Furthermore, in the case where two or more of the second bridge fibers50are provided between the first bridge fiber40and the output optical fiber20, preferably, the maximum outer diameter of the bridge fiber to which the output optical fiber is connected is smaller than the maximum outer diameter of the other bridge fibers, similarly to the second embodiment and the third embodiment.

In the third embodiment, two bridge fibers including the core and the cladding are provided between the input optical fiber10and the output optical fiber20. However, three bridge fibers or more may be provided as long as the ratio of the outer diameter of the core to the outer diameter of the cladding in the bridge fibers is smaller in the bridge fiber located more apart from the input optical fiber10.

It is noted that in the case where three bridge fibers or more are provided, preferably, the maximum outer diameter of the bridge fiber to which the output optical fiber is connected is smaller than the maximum outer diameter of the other bridge fibers, similarly to the second embodiment and the third embodiment.

Moreover, in the embodiments, the components of the laser light source2are not illustrated more specifically. However, various components may be included as long as the components emit laser light.

Furthermore, in the embodiments, the laser device1is applied including a plurality of the laser light sources2and the optical combiner3as components. For example, a resonant fiber laser device, or an MO-PA (Master Oscillator Power Amplifier) fiber laser device may be applied, and the other laser devices may be applied.

It is noted that the components of the laser device1and the optical combiner3can be appropriately combined, omitted, modified, and added with known techniques within the scope not deviating from the object of the present application, other than the content described in the embodiments or the exemplary modifications.

The present invention is usable in various fields using optical fiber combiners such as in processing fields and medical fields using laser devices.