JP2020194014A - Optical fiber and laser device - Google Patents

Abstract

To provide an optical fiber capable of bringing intensity of light propagating in a cross section close to uniformity, and a laser device using the same.SOLUTION: A delivery optical fiber 10 comprises a core 11 through which multimode light propagates, a cladding 12 enclosing an outer peripheral surface of the core, and at least one stress applying part 15 that is disposed in the cladding and applies stress to the core. The stress applying part applies stress nonuniform in a circumferential direction with a center axis C of the core 11 as a reference.SELECTED DRAWING: Figure 3

Description

The present invention relates to optical fibers and laser devices.

Fiber laser devices are used in various fields such as laser processing fields and medical fields because they have excellent light-collecting properties, high power density, and can obtain light that becomes a small beam spot.

In such a fiber laser device, it may be required to emit light having a substantially uniform light intensity in a cross section. In order to emit such light, if the intensity of the cross section of the light propagating in the core is substantially uniform at the emission end of the optical fiber, a special optical element is used for the light emitted from the optical fiber. It is possible to emit light having a substantially uniform light intensity in the cross section from the fiber optic laser device. However, in general, the intensity of the light emitted from the light source in the cross section is not uniform. Therefore, in Patent Document 1 below, the core of the optical fiber is made into a polygon, and the intensity in the cross section of the light propagating through the core of the optical fiber is made uniform.

Patent No. 5227038

However, when the shape of the core of the optical fiber is polygonal, the cross-sectional shape of the light emitted from the core is also polygonal, and the diameter of the light emitted from the core differs depending on the direction. Therefore, there is a demand for an optical fiber capable of making the intensity of the propagating light in the cross section substantially uniform by another method.

Therefore, an object of the present invention is to provide an optical fiber capable of uniformly approaching the intensity in a cross section of propagating light, and a laser apparatus using the same.

In order to solve the above problems, the optical fiber of the present invention includes a core through which multimode light propagates, a clad that surrounds the outer peripheral surface of the core, and at least one that is arranged in the clad and applies stress to the core. A stress applying portion is provided, and the stress applying portion is characterized in that a non-uniform stress is applied in the circumferential direction with reference to the central axis of the core.

In such an optical fiber, at least some higher-order mode light propagates through the core while being reflected at the interface between the core and the cladding. Further, since each stress applying portion applies non-uniform stress in the circumferential direction with reference to the central axis of the core, the refractive index changes along the circumferential direction with reference to the central axis of the core. Therefore, at least some of the higher mode light propagating through the core is refracted at different angles depending on its position in the circumferential direction of the core. Therefore, as compared with the case where the refractive index in the circumferential direction of the core is uniform, at least a part of the light in the higher-order mode is incident on the outer peripheral surface depending on the position in the circumferential direction of the core when reflected on the outer peripheral surface. Is different. Therefore, according to the optical fiber of the present invention, the intensity in the cross section of the propagating light can be made uniform as compared with the case where the refractive index in the circumferential direction of the core is uniform.

Further, it is preferable that the optical fiber includes a plurality of the stress applying portions, and the plurality of stress applying portions apply rotationally symmetric stress with respect to the central axis of the core.

Even in this case, since each stress applying portion applies non-uniform stress in the circumferential direction with reference to the central axis of the core, the stress applied to the core is in the circumferential direction with reference to the central axis of the core. It changes periodically along. Therefore, the refractive index along the circumferential direction of the core changes periodically. Therefore, as described above, the intensity in the cross section of the propagating light can be made uniform as compared with the case where the refractive index in the circumferential direction of the core is uniform. Further, such a plurality of stress applying portions are generally provided at positions equidistant from the center of the core and rotationally symmetric with respect to the center of the core, having the same coefficient of thermal expansion and the same size. Be done. In this case, the stress is balanced and it is possible to suppress the occurrence of bending stress on the optical fiber.

Further, it is preferable that the clad includes an inner clad and an outer clad, and at least one of the stress applying portions is arranged in the outer clad.

By including the inner clad and the outer clad in the clad, it is possible to add a function to the clad and reduce the cost depending on the configuration of the inner clad and the outer clad. Generally, the refractive index of the stressed portion is different from the refractive index of the clad. Therefore, by arranging at least one of the stress applying portions in the outer clad, the intensity distribution of the clad mode light can be made uniform when the clad mode light propagating in the clad propagates in the outer clad. Therefore, it is possible to suppress the propagation of the clad mode light having a high power density in a part of the clad, and it is possible to suppress the heating of the connection portion of the optical fiber, a part of the coating layer, and the like. For example, when this optical fiber is used as a delivery optical fiber that propagates a laser beam for processing, the laser beam reflected by the processed body may return to the cladding and be incident as light. In this case, it is possible to suppress the propagation of the clad mode light having a high power density in a part of the clad, so that the damage of the optical component or the like due to the return light can be suppressed. Further, when the base material for an optical fiber for manufacturing the present optical fiber is manufactured, a hole for inserting the glass body as a stress applying portion may be formed in the glass body to be a clad. In this case, when the hole is provided over the glass body that becomes the inner clad and the glass body that becomes the outer clad, the interface between the glass body that becomes the inner clad and the glass body that becomes the outer clad when forming the hole. Is prone to cracks. However, when the stress applying portion is arranged in the outer clad, the glass body to be the stress applying portion is inserted into the hole provided in the glass body to be the outer clad, so that the glass body to be the outer clad is formed. Therefore, it is possible to prevent the above-mentioned cracks from occurring during the formation of the holes.

Alternatively, the clad includes an inner clad and an outer clad, and it is preferable that at least one of the stress applying portions is arranged over the inner clad and the outer clad.

By arranging the stress applying portion over the inner clad and the outer clad, the intensity distributions of the clad mode light propagating in the inner clad and the clad mode light propagating in the outer clad can be made uniform. Therefore, it is possible to suppress the propagation of the clad mode light having a high power density in a part of the clad, and it is possible to suppress the heating of the connection portion of the optical fiber, a part of the coating layer, and the like.

Further, in order to solve the above problems, the laser apparatus of the present invention is characterized by including the optical fiber according to any one of the above and a light source that emits light incident on the optical fiber. ..

As described above, in the optical fiber of the present invention, the intensity in the cross section of the propagating light can be made uniform as compared with the case where the refractive index in the circumferential direction of the core is uniform. Therefore, the laser device provided with this optical fiber can uniformly approach the intensity in the cross section of the light emitted through the optical fiber.

Further, it is preferable that the laser device further includes a stress changing portion that changes the stress applied to the core.

By changing the stress applied to the core, the refractive index distribution of the core can be changed, and the intensity distribution of light propagating through the core can be changed. Therefore, the intensity distribution in the cross section of the light emitted from the optical fiber can be changed as compared with the case where the stress applied to the core does not change. For example, when the stress applied to the core from the stress applying portion is increased, the intensity in the cross section of the propagating light can be made closer to uniform. Further, when the stress applied to the core from the stress applying portion is weakened, it is possible to prevent the intensity of the propagating light in the cross section from becoming too uniform.

Further, it is preferable that the stress changing portion can be switched between a state in which the stress applied to the core is changed and a state in which the stress applied to the core is not changed.

Since the stress changing portion can be switched as described above, the intensity distribution in the cross section of the light emitted from the optical fiber can be switched.

Further, it is preferable that the stress changing portion can change the degree of change in stress applied to the core.

In this case, since the change in the refractive index distribution of the core can be adjusted, the intensity distribution of the light propagating in the core can be adjusted. Therefore, the intensity distribution in the cross section of the light emitted from the optical fiber can be adjusted.

Further, it is preferable that the stress changing portion changes the stress applied to the core by applying a force in the radial direction of the optical fiber from the outer peripheral side of the clad.

In this case, the direction of change in stress applied to the core can be selected by selecting the direction of the force applied from the outer peripheral side of the optical fiber.

Further, it is preferable that the stress changing portion changes the stress applied to the core by changing the temperature of the optical fiber.

Generally, the stress-applied portion in the optical fiber has a coefficient of thermal expansion different from that of the clad. Therefore, changing the temperature of the optical fiber causes the expansion and contraction rates of the stressed portion and the expansion and contraction rates of the clad to be different from each other. Therefore, the stress applied to the core can be changed without applying a force from the outside of the optical fiber.

As described above, according to the present invention, there is provided an optical fiber capable of uniformly approaching the intensity in a cross section of propagating light, and a laser apparatus using the same.

It is a figure which shows the laser apparatus in 1st Embodiment of this invention. It is a figure which shows each light source in the laser apparatus of FIG. It is a figure which shows the state of the cross section of the delivery optical fiber in the laser apparatus of FIG. It is a figure which shows the state around the core shown in FIG. It is a figure which shows the state of the light propagating in a core. It is a figure which shows the state of the cross section of the delivery optical fiber of the 2nd Embodiment of this invention. It is a figure which shows the state of the cross section of the delivery optical fiber of the 3rd Embodiment of this invention. It is a figure which shows the state of the cross section of the delivery optical fiber of the 4th Embodiment of this invention. It is a figure which shows the state of the cross section of the delivery optical fiber of the 5th Embodiment of this invention. It is a figure which shows the laser apparatus in the 6th Embodiment of this invention. It is a figure which shows the state of the stress change part of FIG. It is a figure which shows the state of the stress change part of 7th Embodiment.

Hereinafter, preferred embodiments of the optical fiber and laser apparatus according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for facilitating the understanding of the present invention, and are not for limiting the interpretation of the present invention. The present invention can be modified and improved without departing from the spirit of the present invention. For ease of understanding, some parts may be exaggerated in each figure.

(First Embodiment)
FIG. 1 is a diagram showing a laser device according to the present invention. As shown in FIG. 1, the laser apparatus 1 of the present embodiment includes a plurality of light sources 2, an optical fiber 21 that propagates light emitted from each light source 2, and a delivery optical fiber that is incident with light from the optical fiber 21. A main configuration includes a 10, a combiner 25, an optical fiber 50 connected to the delivery optical fiber 10, and an exit portion 55.

FIG. 2 is a diagram showing each light source 2 in the laser device 1. As shown in FIG. 2, in the present embodiment, each light source 2 is composed of a fiber optic laser device, and an excitation light source 40 that emits excitation light and an excitation light emitted from the excitation light source 40 are incident and excited by the excitation light. The excitation light is incident on the amplification optical fiber 30 to which the active element is added, the optical fiber 31 connected to one end of the amplification optical fiber 30, the first FBG 33 provided in the optical fiber 31, and the optical fiber 31. A combiner 35 for this purpose, an optical fiber 32 connected to the other end of the amplification optical fiber 30, and a second FBG 34 provided in the optical fiber 32 are mainly provided. A resonator is formed by the amplification optical fiber 30, the first FBG 33, and the second FBG 34, and the light source 2 of the present embodiment is a resonator type fiber laser apparatus.

The excitation light source 40 is composed of a plurality of laser diodes 41 and emits excitation light having a wavelength that excites an active element added to the amplification optical fiber 30. Each laser diode 41 of the excitation light source 40 is connected to the excitation light optical fiber 45, and the light emitted from the laser diode 41 is optically connected to the respective laser diode 41 for the excitation light optical fiber 45. Propagate. Examples of the excitation light optical fiber 45 include a multimode fiber. In this case, the excitation light propagates through the excitation light optical fiber 45 as multimode light. In this embodiment, the wavelength of the excitation light is, for example, 915 nm.

The amplification optical fiber 30 is composed of a core, an inner clad that surrounds the outer peripheral surface of the core without gaps, an outer clad that covers the outer peripheral surface of the inner clad, and a coating layer that covers the outer peripheral surface of the outer clad. .. In the present embodiment, the core of the amplification optical fiber 30 is made of quartz to which ytterbium (Yb) is added as an active element, and an element such as germanium that increases the refractive index is added as needed. Although different from the present embodiment, a rare earth element other than ytterbium may be added as an active element according to the wavelength of the amplified light. Examples of such rare earth elements include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), erbium (Er) and the like. Further, as the active element, bismuth (Bi) and the like can be mentioned in addition to the rare earth element. Further, as a material constituting the inner clad of the amplification optical fiber 30, for example, pure quartz to which no dopant is added can be mentioned. An element that lowers the refractive index, such as fluorine, may be added to the inner clad. Further, examples of the material constituting the outer clad of the amplification optical fiber 30 include a resin having a refractive index lower than that of the inner clad, and examples of the material constituting the coating layer of the amplification optical fiber 30 include the outer clad. Examples thereof include resins different from the resins constituting the above. The amplification optical fiber is a single-mode fiber, but the core diameter is the same as that of the multimode fiber so that high-power signal light can propagate through the core of the amplification optical fiber, but the single-mode fiber is used. It may be configured to propagate light. Further, the amplification optical fiber 30 may be a multimode fiber.

The optical fiber 31 has the same configuration as the amplification optical fiber 30 except that no active element is added to the core. The optical fiber 31 is connected to one end of the amplification optical fiber 30. Therefore, the core of the amplification optical fiber 30 and the core of the optical fiber 31 are optically coupled, and the inner clad of the amplification optical fiber 30 and the inner clad of the optical fiber 31 are optically coupled.

The first FBG 33 is provided in the core of the optical fiber 31. The first FBG 33 is configured by repeating a portion where the refractive index increases at regular intervals along the longitudinal direction of the optical fiber 31. By adjusting this period, the first FBG 33 reflects light in a predetermined wavelength band among the light emitted by the active element of the excited optical fiber 30 for amplification.

Further, in the combiner 35, the core of the optical fiber 45 for excitation light is connected to the inner cladding of the optical fiber 31. In this way, the excitation optical fiber 45 connected to the excitation light source 40 and the inner clad of the amplification optical fiber 30 are optically coupled via the inner clad of the optical fiber 31.

Further, in the combiner 35, the optical fiber 36 is connected to the optical fiber 31. The optical fiber 36 is, for example, an optical fiber having a core having the same diameter as the core of the optical fiber 31. One end of the optical fiber 36 is connected to the optical fiber 31, and the core of the optical fiber 36 and the core of the optical fiber 31 are optically coupled. Further, a heat conversion unit E is connected to the side opposite to the combiner 35 side of the optical fiber 36.

The optical fiber 32 has the same core as the core of the amplification optical fiber 30 except that no active element is added, and the same configuration as the inner clad of the amplification optical fiber 30 by surrounding the outer peripheral surface of the core without gaps. It is composed of a clad and a coating layer that covers the outer peripheral surface of the clad. The optical fiber 32 is connected to the other end of the amplification optical fiber 30, and the core of the amplification optical fiber 30 and the core of the optical fiber 32 are optically coupled.

The second FBG 34 is provided in the core of the optical fiber 32. The second FBG 34 has a portion in which the refractive index increases at regular intervals along the longitudinal direction of the optical fiber 32, and reflects light having at least a part of the wavelength of the light reflected by the first FBG 33 lower than that of the first FBG 33. It is configured to reflect at a rate.

Further, the optical fiber 21 shown in FIG. 1 is connected to the side opposite to the amplification optical fiber 30 side of the optical fiber 32. The configuration of the optical fiber 21 is the same as that of the optical fiber 32. By extending the optical fiber 32, a part of the optical fiber 32 may be the optical fiber 21.

The core of each optical fiber 21 is optically coupled to the core of the delivery optical fiber 10 by a combiner 25. The combiner 25 is, for example, a bridge fiber processed into a tapered shape. In this case, the core of each optical fiber 21 is connected to the end face on the large diameter side of the bridge fiber which is the combiner 25, and the core of the delivery optical fiber 10 is connected to the end face on the small diameter side of the bridge fiber which is the combiner 25. Will be done. In this way, the core of each optical fiber 21 and the core of the delivery optical fiber 10 are optically coupled via the combiner 25. The combiner 25 is not limited to the above-mentioned bridge fiber as long as the core of each optical fiber 21 and the core of the delivery optical fiber 10 are optically coupled. For example, the core of each optical fiber 21 can be used. It may be directly connected to the core of the delivery optical fiber 10.

FIG. 3 is a diagram showing a cross section of the delivery optical fiber 10. As shown in FIG. 3, the delivery optical fiber 10 is arranged in the core 11, the clad 12 that surrounds the outer peripheral surface of the core 11 without gaps, the coating layer 13 that covers the outer peripheral surface of the clad 12, and the clad 12. It is provided with a stress applying portion 15. The refractive index of the core 11 is higher than that of the clad 12. The core 11 is arranged in the center of the clad 12 and is made of quartz to which an element that increases the refractive index such as germanium is added. In this case, the clad 12 is made of, for example, pure quartz to which no dopant is added, or quartz to which a dopant that lowers the refractive index such as fluorine is added. Further, when the core 11 is made of pure quartz to which no dopant is added, for example, the clad 12 is made of quartz to which a dopant which lowers the refractive index such as fluorine is added. The coating layer 13 is made of, for example, a thermosetting resin or an ultraviolet curable resin.

The delivery optical fiber 10 is, for example, a multi-core fiber in which light of 10 or more waveguide modes propagates. For example, the diameter of the core 11 is 50 μm, and the difference in the specific refractive index between the core 11 and the clad 12 is 0.5%. In this case, the number of modes of light propagating through the delivery optical fiber 10 is about 50.

The stress applying portion 15 has a coefficient of thermal expansion different from that of the clad 12, and is a portion that applies a non-uniform stress to the core 11 in the circumferential direction with reference to the central axis C of the core 11. When the clad 12 is made of quartz to which no dopant is added, if the stress applying portion 15 is made of quartz to which fluorine or boron is added, the coefficient of thermal expansion of the stress applying portion 15 is larger than the coefficient of thermal expansion of the clad 12. If the stress applying portion 15 is made of quartz to which titanium is added, the coefficient of thermal expansion of the stress applying portion 15 is lower than the coefficient of thermal expansion of the clad 12. In this embodiment, only one stress applying portion is arranged.

FIG. 4 is a diagram showing a state around the core 11 shown in FIG. 3, and is an enlarged view showing a region surrounded by a broken line in FIG. Note that hatching is omitted in FIG. 4 in order to avoid making the figure difficult to see. When the coefficient of thermal expansion of the stress applying portion 15 is larger than the coefficient of thermal expansion of the clad 12, when the delivery optical fiber 10 is drawn and manufactured, the stress applying portion 15 is more than the clad 12 in a state where the glass is not solidified. The stress-applying portion 15 contracts more than the clad 12 when the temperature drops and the glass solidifies. Therefore, the stress applying portion 15 applies tensile stress to the core 11 as shown by an arrow. The magnitude of the stress applied to the core 11 by the stress applying portion 15 continuously changes in the core 11. In FIG. 4, a portion where the stress by the stress applying portion 15 is relatively large is surrounded by a broken line.

Further, when the coefficient of thermal expansion of the stress applying portion 15 is smaller than the coefficient of thermal expansion of the clad 12, when the delivery optical fiber 10 is drawn and manufactured, the expansion of the stress applying portion 15 is performed in a state where the glass is not solidified. The coefficient is smaller than the expansion coefficient of the clad 12, and when the temperature drops and the glass solidifies, the stress-applying portion 15 shrinks less than the clad 12. Therefore, in this case, the stress applying portion 15 applies compressive stress to the core 11 in the direction opposite to the arrow in FIG.

As shown in FIG. 4, a non-uniform stress is applied to the core 11 from the stress applying portion 15 in the circumferential direction with reference to the central axis C of the core 11.

FIG. 5 is a diagram showing a state of light propagating through the core 11. Note that hatching is omitted in FIG. 5 in order to avoid making the figure difficult to see. FIG. 5 shows the state of light propagation in a certain higher-order mode. The portion where the stress by the stress applying portion 15 shown by the broken line in FIG. 4 is relatively large is also shown by the broken line in FIG. In the portion where the stress applied by the stress applying portion 15 is large, the state of the glass crystal constituting the core 11 is different from the other portions, and the refractive index changes. When tensile stress is applied to the core 11 by the stress applying portion 15, the crystal density becomes low in the stressed portion of the core 11, and the refractive index in the portion becomes lower than the refractive index in the other portion. As described above, the magnitude of the stress applied to the core 11 is non-uniform along the circumferential direction with respect to the central axis C of the core 11, so that the refractive index distribution of the core 11 is the center of the core 11. It becomes non-uniform along the circumferential direction with respect to the axis C.

As shown in FIG. 5, the light of this higher order mode is refracted at the portion where the stress applied to the core 11 changes, and propagates through the core 11 while being reflected at the interface between the core 11 and the clad 12. Therefore, the magnitude of the incident angle of the light in the higher-order mode on the outer peripheral surface of the core 11 differs depending on the position of the core 11 in the circumferential direction. In FIG. 5, the angles of incidence θ ₁ and θ _{2 on} the outer peripheral surface of the core 11 of the higher-order mode light at two locations are shown, and the angles of incidence θ ₁ and θ ₂ are different in magnitude from each other. When compressive stress is applied to the core 11 by the stress applying portion 15, the light in the higher-order mode is refracted in a direction different from that in FIG. 5 at the portion where the stress applied to the core 11 changes, and the light is refracted with the core 11. It propagates through the core 11 while reflecting at the interface with the clad 12.

An optical fiber 50 is connected to an end of the delivery optical fiber 10 opposite to the light source 2 side. The optical fiber 50 is the same as the delivery optical fiber 10 except that it does not have the stress applying portion 15. Therefore, the core of the optical fiber 50 is not subjected to non-uniform stress in the circumferential direction with respect to the central axis C of the core 11, and the refractive index of the core is the circumference with respect to the central axis C of the core 11. Uniform in direction.

An exit portion 55 is connected to the end of the optical fiber 50 on the side opposite to the delivery optical fiber 10 side. The exit portion 55 is made of a glass rod having a diameter larger than that of the core of the optical fiber 50. The refractive index in the radial direction of the glass rod may be constant or may be lowered toward the outer peripheral side.

Next, the operation of the laser device 1 will be described.

First, in each light source 2, excitation light is emitted from each laser diode 41 of the excitation light source 40. The excitation light emitted from the excitation light source 40 enters the inner cladding of the amplification optical fiber 30 via the excitation light optical fiber 45 and the optical fiber 31. The excitation light incident on the inner clad of the amplification optical fiber 30 mainly propagates through the inner clad and excites the active element added to the core when passing through the core of the amplification optical fiber 30. The activated element in the excited state emits naturally emitted light, light of a part of the wavelength of the naturally emitted light is reflected by the first FBG 33, and the light of the wavelength reflected by the second FBG 34 of the reflected light is the first. It is reflected by 2FBG34. Therefore, the light reciprocates between the first FBG 33 and the second FBG 34, that is, in the resonator, and the light is amplified by stimulated emission when propagating through the core of the amplification optical fiber 30, and a laser oscillation state is generated. The wavelength of light at this time is, for example, 1070 nm. Then, some of the amplified light passes through the second FBG 34 and is emitted from the optical fiber 32. This light enters the core 11 of the delivery optical fiber 10 from the optical fiber 21 via the combiner 25.

Since the delivery optical fiber 10 is a multimode fiber as described above, the light incident on the core 11 of the delivery optical fiber 10 propagates through the core 11 in the multimode. At this time, at least a part of the light of the higher order mode propagates through the core 11 while being reflected at the interface between the core 11 and the clad 12. Then, the light propagating in the core 11 propagates from the delivery optical fiber 10 to the optical fiber 50, exits from the optical fiber 50, and is incident on the exit portion 55. The diameter of the light incident on the emitting unit 55 is expanded, and the light is emitted from the emitting unit 55. This emitted light is applied to the workpiece or the like.

As described above, the delivery optical fiber, which is the optical fiber of the present embodiment, has a core 11 through which multimode light propagates, a clad 12 surrounding the outer peripheral surface of the core 11, and a clad 12 arranged in the clad 12 on the core 11. At least one stress applying portion 15 for applying stress is provided, and the stress applying portion 15 applies non-uniform stress in the circumferential direction with reference to the central axis C of the core 11.

Therefore, the refractive index distribution of the core 11 becomes non-uniform along the circumferential direction. As described above, at least a part of the light propagating in the core 11 in the higher-order mode is refracted at the portion receiving the stress applied from the stress applying portion 15 and reflected at the interface between the core 11 and the clad 12. While propagating the core 11. Compared with the case where the refractive index of the light in the higher-order mode is uniform in the circumferential direction of the core 11, the incident angle to the outer peripheral surface differs depending on the position along the circumferential direction of the core 11, so that the circumference of the core 11 It reflects in different directions depending on the position along the direction. Therefore, according to the delivery optical fiber 10 of the present embodiment, the intensity in the cross section of the propagating light can be made uniform as compared with the case where the refractive index in the circumferential direction of the core 11 is uniform.

Further, in the present embodiment, there is one stress applying portion 15, and the total stress received by the core 11 from the stress applying portion 15 is non-rotationally symmetric with respect to the central axis C. Therefore, as compared with the case where rotationally symmetric stress is applied with respect to the central axis C of the core 11, at least a part of the higher-order mode light is reflected on the outer peripheral surface of the core 11 and is incident on the outer peripheral surface. Becomes more random. Therefore, the intensity of the propagating light in the cross section can be made closer to uniform.

Further, the laser device 1 of the present invention includes the delivery optical fiber 10 and a light source 2 that emits light incident on the delivery optical fiber 10. As described above, since the delivery optical fiber 10 can make the intensity in the cross section of the propagating light uniformly close, the laser device 1 provided with the delivery optical fiber 10 determines the intensity in the cross section of the light emitted through the delivery optical fiber 10. Can be brought close to uniform.

Further, in the laser device 1 of the present invention, the light emitted from the delivery optical fiber 10 is emitted from the laser device 1 via the propagating optical fiber 50. As described above, the optical fiber 50 is not provided with a stress applying portion. Therefore, in the delivery optical fiber 10, even if the stress applying portion 15 has some influence on the light propagating through the core 11, this influence can be alleviated by the optical fiber 50. When the intensity of the propagating light in the cross section of the delivery optical fiber 10 is brought close to uniform, the state of the optical fiber 50 in which the intensity of the propagating light is brought close to the cross section is generally maintained.

(Second Embodiment)
Next, the second embodiment of the present invention will be described in detail with reference to FIG. The same or equivalent components as those in the first embodiment are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified.

In the laser apparatus of the present embodiment, the configuration of the delivery optical fiber 10 is different from that of the delivery optical fiber 10 of the first embodiment. FIG. 6 is a diagram showing a cross section of the delivery optical fiber of the present embodiment. The delivery optical fiber 10 of the present embodiment is different from the delivery optical fiber 10 of the first embodiment in that the clad 12 includes an inner clad 12a and an outer clad 12b. The refractive index of the inner clad 12a is the same as that of the clad 12 of the first embodiment and is lower than the refractive index of the core 11. The refractive index of the outer clad 12b is different from that of the inner clad 12a, but may be lower or higher than that of the inner clad 12a. For example, when the core 11 is made of pure quartz to which no dopant is added and the inner clad 12a is made of quartz to which fluorine is added, if the outer clad 12b is made of quartz similar to the core 11, fluorine is added. The amount of expensive quartz used can be reduced, and the delivery optical fiber 10 can be made inexpensive.

In the present embodiment, the stress applying portion 15 is arranged over the inner clad 12a and the outer clad 12b. Further, in the present embodiment, the stress applying portions 15 are unevenly distributed on the outer clad 12b side. However, unlike FIG. 6, the stress applying portions 15 may be unevenly distributed on the inner clad 12a side.

According to the delivery optical fiber 10 of the present embodiment, the clad 12 includes the inner clad 12a and the outer clad 12b to add a function to the clad 12, and the cost depends on the configuration of the inner clad 12a and the outer clad 12b. Can be reduced.

In general, the refractive index of the stress applying portion 15 is different from the refractive index of the clad 12. Therefore, by arranging the stress applying portion 15 over the inner clad 12a and the outer clad 12b, the clad mode light propagating in the clad 12 propagates at least one of the inner clad 12a and the outer clad 12b. The intensity distribution of mode light can be made uniform. Therefore, it is possible to suppress the propagation of clad mode light having a high power density in a part of the clad 12, and it is possible to suppress the heating of the connection portion of the delivery optical fiber 10 and a part of the coating layer 13. For example, when the laser device 1 is used, the laser light reflected by the workpiece may return to the clad 12 and be incident as light. In this case, it is possible to suppress the propagation of the clad mode light having a high power density in a part of the clad 12, so that the damage of the optical component such as the light source 2 due to the return light can be suppressed.

(Third Embodiment)
Next, the third embodiment of the present invention will be described in detail with reference to FIG. The same or equivalent components as those in the second embodiment are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified.

In the laser apparatus of this embodiment, the configuration of the delivery optical fiber 10 is different from that of the delivery optical fiber 10 of the second embodiment. FIG. 7 is a diagram showing a cross section of the delivery optical fiber of the present embodiment. The delivery optical fiber 10 of the present embodiment is similar to the delivery optical fiber 10 of the second embodiment in that the clad 12 includes an inner clad 12a and an outer clad 12b, but the stress applying portion 15 is inside the outer clad 12b. It differs from the delivery optical fiber 10 of the second embodiment in that it is arranged.

According to the delivery optical fiber 10 of the present embodiment, when the stress applying portion 15 is arranged in the outer clad 12b, the clad mode light propagating in the clad 12 propagates in the outer clad 12b. The intensity distribution of can be made uniform. Therefore, it is possible to suppress the propagation of clad mode light having a high power density in a part of the clad 12, and it is possible to suppress the heating of the connection portion of the delivery optical fiber 10 and a part of the coating layer 13. Further, as in the description of the second embodiment, when the laser light reflected by the workpiece returns to the clad 12 and is incident as light, it is possible to suppress the propagation of the clad mode light having a high power density in a part of the clad 12. This makes it possible to suppress damage to optical components such as the light source 2 due to the return light.

Further, when the base material for the optical fiber for manufacturing the delivery optical fiber 10 of the present embodiment is manufactured, a hole for inserting the glass body to be the stress applying portion 15 may be formed in the glass body to be the clad 12. is there. In this case, when the holes are provided over the glass body that becomes the inner clad 12a and the glass body that becomes the outer clad 12b, the glass body that becomes the inner clad 12a and the glass that becomes the outer clad 12b when the holes are formed. Cracks are likely to occur at the interface with the body. However, in the delivery optical fiber 10 of the present embodiment, since the stress applying portion 15 is arranged in the outer clad 12b, the glass body to be the stress applying portion 15 is inserted into the hole provided in the glass body to be the outer clad 12b. Therefore, the hole is formed in the glass body to be the outer clad 12b. Therefore, it is possible to prevent the above-mentioned cracks from occurring during the formation of the holes.

(Fourth Embodiment)
Next, the fourth embodiment of the present invention will be described in detail with reference to FIG. The same or equivalent components as those in the second embodiment are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified.

In the laser apparatus of this embodiment, the configuration of the delivery optical fiber 10 is different from that of the delivery optical fiber 10 of the second embodiment. FIG. 8 is a diagram showing a cross section of the delivery optical fiber of the present embodiment. The delivery optical fiber 10 of the present embodiment is similar to the delivery optical fiber 10 of the second embodiment in that the clad 12 includes an inner clad 12a and an outer clad 12b, but a plurality of stress applying portions 15 are arranged. Is different from the delivery optical fiber 10 of the second embodiment. In the present embodiment, each of the three stress applying portions 15 is arranged at positions rotationally symmetrical with respect to the central axis C of the core 11. Further, in the present embodiment, each stress applying portion 15 has the same size and is made of the same material. Therefore, each stress applying portion 15 has the same coefficient of thermal expansion, and applies the same magnitude of stress to the core 11. When the stresses applied to the cores 11 by the respective stress applying portions 15 are combined, the stresss applied to the cores 11 by the plurality of stress applying portions 15 become rotationally symmetric with respect to the central axis C of the cores 11. However, the stress applied to the core 11 by each stress applying portion 15 is non-uniform along the circumferential direction with respect to the central axis C of the core 11. Therefore, the refractive index of the core 11 changes along the circumferential direction of the core 11.

According to the delivery optical fiber 10 of the present embodiment, each of the plurality of stress applying portions 15 is arranged at positions rotationally symmetric with respect to the center of the core 11, and the plurality of stress applying portions 15 apply the stress to the core 11. The stress is rotationally symmetric with respect to the central axis C of the core 11. As in the present embodiment, such a plurality of stress applying portions 15 generally have the same coefficient of thermal expansion and the same size, and are equidistant from the center of the core 11 and center on the core 11. It is provided at a rotationally symmetric position as a reference. In this case, the stress is balanced and it is possible to suppress the occurrence of bending stress on the delivery optical fiber 10.

(Fifth Embodiment)
Next, the fifth embodiment of the present invention will be described in detail with reference to FIG. The same or equivalent components as those in the fourth embodiment are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified.

In the laser apparatus of the present embodiment, the configuration of the delivery optical fiber 10 is different from that of the delivery optical fiber 10 of the fourth embodiment. FIG. 9 is a diagram showing a cross section of the delivery optical fiber of the present embodiment. The delivery optical fiber 10 of the present embodiment is similar to the delivery optical fiber 10 of the fourth embodiment in that the clad 12 includes the inner clad 12a and the outer clad 12b and a plurality of stress applying portions 15 are arranged. It differs from the delivery optical fiber 10 of the second embodiment in that the stress applying portion 15 is arranged at a position that is not rotationally symmetric with respect to the central axis C of the core 11. Each stress applying portion 15 applies a stress of the same magnitude to the core 11 as in the fourth embodiment. However, since the stress applying portions 15 are arranged at positions that are not rotationally symmetric as described above, when the stresses applied to the cores 11 by the respective stress applying portions 15 are combined, the plurality of stress applying portions 15 are transferred to the core 11. The applied stress is non-rotational symmetric with respect to the central axis C of the core 11.

According to the delivery optical fiber 10 of the present embodiment, the total stress from the plurality of stress applying portions 15 received by the core 11 is non-rotationally symmetric with respect to the central axis C. Therefore, as compared with the case where the stress symmetrical with respect to the central axis C of the core 11 is applied as in the delivery optical fiber 10 of the fourth embodiment, at least a part of the light of the higher order mode is the outer circumference of the core 11. The angle of incidence on the outer peripheral surface becomes more random when reflected by the surface. Therefore, the intensity of the propagating light in the cross section can be made closer to uniform.

(Sixth Embodiment)
Next, the sixth embodiment of the present invention will be described in detail with reference to FIGS. 10 and 11. The same or equivalent components as those in the first embodiment are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified.

FIG. 10 is a diagram showing a laser device of this embodiment. As shown in FIG. 10, the laser device 1 of the present embodiment is different from the laser device 1 of the first embodiment in that it includes a stress changing unit 60. The stress changing portion 60 is attached to the delivery optical fiber 10 and is a portion for changing the stress applied to the core 11 of the delivery optical fiber 10.

FIG. 11 is a diagram showing a stress changing portion 60. As shown in FIG. 11, the coating layer 13 is peeled off at the position where the stress changing portion 60 of the delivery optical fiber 10 is attached. In the present embodiment, the stress changing unit 60 includes a case 61 and a temperature changing element 62 that changes the temperature. The case 61 of the present embodiment includes a temperature changing element 62 surrounding the delivery optical fiber 10, and conducts heat between the temperature changing element 62 and the delivery optical fiber 10. Therefore, the case 61 is preferably made of a material having excellent thermal conductivity such as metal.

Examples of the temperature changing element 62 include a Peltier element and a heater. The temperature changing element 62 is electrically connected to a power source (not shown), and the temperature changing element 62 is operated by this power source.

When the temperature changing element 62 is a Peltier element, in the present embodiment, the temperature of the surface of the temperature changing element 62 on the optical fiber side rises or falls due to the voltage applied from the power source. Therefore, when no voltage is applied from the power source, the temperature of the surface of the temperature changing element 62 on the optical fiber side does not change. The switching between the rise and fall of the temperature of the surface on the optical fiber side can be realized by switching between positive and negative of the voltage applied to the temperature changing element 62. Further, by changing the magnitude of the voltage applied to the temperature changing element 62, the degree of change in the temperature of the surface of the temperature changing element 62 on the optical fiber side changes.

When the temperature changing element 62 is a heater, in the present embodiment, the temperature of the entire temperature changing element 62 rises due to the voltage applied from the power source. Therefore, when no voltage is applied from the power source, the temperature of the temperature changing element 62 does not change. Further, by changing the magnitude of the voltage applied to the temperature changing element 62, the degree of change in the temperature of the temperature changing element 62 changes.

As described above, the stress applying portion 15 has a coefficient of thermal expansion different from that of the clad 12, and when the coefficient of thermal expansion of the stress applying portion 15 is larger than the coefficient of thermal expansion of the clad 12, tensile stress is applied to the core 11. When the coefficient of thermal expansion of the stress applying portion 15 is smaller than the coefficient of thermal expansion of the clad 12, compressive stress is applied to the core 11.

When the temperature changing element 62 is a Peltier element, the stress changing portion changes the stress applied to the core 11 as follows. When the thermal expansion coefficient of the stress applying portion 15 is larger than the thermal expansion coefficient of the clad 12, if the temperature of the surface of the temperature changing element 62 on the optical fiber side rises, the stress applying portion 15 expands more than the clad 12. If the tensile stress applied to the core 11 is reduced and the temperature of the surface of the temperature changing element 62 on the optical fiber side decreases, the stress applying portion 15 contracts more than the clad 12, and the tensile stress applied to the core 11 increases. Will be done. Further, when the thermal expansion coefficient of the stress applying portion 15 is smaller than the thermal expansion coefficient of the clad 12, if the temperature of the surface of the temperature changing element 62 on the optical fiber side rises, the stress applying portion 15 expands more than the clad 12. Since it is small, the compressive stress applied to the core 11 is reduced, and if the temperature of the surface of the temperature changing element 62 on the optical fiber side drops, the contraction of the stress applying portion 15 is smaller than that of the clad 12, so that the stress is applied to the core 11. Compressive stress is increased. That is, as the temperature of the delivery optical fiber 10 rises, the stress applied to the stress applying portion is reduced, and as the temperature of the delivery optical fiber 10 decreases, the stress applied to the stress applying portion increases. Will be done.

Therefore, when the temperature changing element 62 is a heater, the tensile stress applied to the core 11 when the coefficient of thermal expansion of the stress applying portion 15 is larger than the coefficient of thermal expansion of the clad 12 due to the increase in the temperature of the heater. Is reduced, and when the coefficient of thermal expansion of the stress applying portion 15 is smaller than the coefficient of thermal expansion of the clad 12, the compressive stress applied to the core 11 is reduced.

When the stress applied to the stressed portion is increased by lowering the temperature of the delivery optical fiber 10, the change in the refractive index in the circumferential direction with respect to the central axis of the core 11 becomes large, and FIG. The degree of refraction of the higher-order mode light propagating through the core 11 shown is increased. Therefore, the intensity of the propagating light in the cross section can be made closer to uniform. In other words, even when the delivery optical fiber 10 is short, the intensity in the cross section of the propagating light can be made uniform.

Further, when the stress applied to the stress applying portion is reduced by raising the temperature of the delivery optical fiber 10, the change in the refractive index in the circumferential direction with respect to the central axis of the core 11 is reduced. The degree of refraction of the higher-order mode light propagating through the core 11 shown in 5 becomes smaller. By the way, depending on the use of the laser device, it may be preferable that the intensity of the propagating light in the cross section is not too uniform. Therefore, by reducing the degree of refraction of the light in the higher-order mode propagating through the core 11, it is possible to prevent the intensity of the propagating light in the cross section from becoming too uniform.

Since the temperature changing element 62 is operated by a power source (not shown), if a voltage is applied from the power source, the stress applied to the core 11 of the delivery optical fiber 10 is changed, and the voltage is not applied from the power source. , The stress applied to the core 11 of the delivery optical fiber 10 is not changed. That is, the stress changing unit 60 can switch between a state in which the stress applied to the core 11 is changed and a state in which the stress applied to the core is not changed. Further, the temperature changing element 62 can change the degree of change in the temperature of the delivery optical fiber 10 depending on the magnitude of the voltage applied from the power source, and can change the degree of change in the stress applied to the core 11.

As described above, the laser device 1 of the present embodiment includes a stress changing unit 60 that changes the stress applied to the core 11. Therefore, the intensity distribution in the cross section of the light emitted from the delivery optical fiber 10 can be changed as compared with the case where the stress applied to the core 11 does not change.

Further, the stress changing unit 60 of the present embodiment can switch between a state in which the stress applied to the core 11 is changed and a state in which the stress applied to the core is not changed. Therefore, the intensity distribution in the cross section of the light emitted from the delivery optical fiber 10 can be switched.

Further, since the stress change unit 60 of the present embodiment can change the degree of change in the stress applied to the core 11, the degree of change in the refractive index distribution of the core 11 can be adjusted. Therefore, the intensity distribution of the light propagating in the core 11 can be adjusted, and the intensity distribution in the cross section of the light emitted from the delivery optical fiber 10 can be adjusted.

In the present embodiment, the coating layer 13 does not have to be peeled off at the position where the stress changing portion 60 of the delivery optical fiber 10 is attached. However, the coating layer 13 is peeled off at the position where the stress changing portion 60 is attached in the delivery optical fiber 10, so that the thermal conductivity from the stress changing portion 60 to the clad 12 and the stress applying portion 15 can be improved. ..

Further, the temperature changing element 62 of the stress changing portion 60 may be in contact with the delivery optical fiber 10.

(7th Embodiment)
Next, the sixth embodiment of the present invention will be described in detail with reference to FIG. The same or equivalent components as those in the sixth embodiment are designated by the same reference numerals and duplicated description will be omitted unless otherwise specified.

The laser device 1 of the present embodiment is different from the laser device 1 of the sixth embodiment in that the configuration of the stress changing unit 60 is different from that of the stress changing unit 60 of the sixth embodiment. FIG. 12 is a diagram showing a stress changing portion 60 of the present embodiment. As shown in FIG. 11, the stress changing portion 60 of the present embodiment is different from the stress changing portion 60 of the sixth embodiment in that a force is applied in the radial direction of the delivery optical fiber 10 from the outer peripheral side of the clad 12.

The stress changing portion 60 of the present embodiment includes a case 61 and a pressing element 64. The case 61 has an opening on the delivery optical fiber 10 side, and the pressing element 64 is in contact with the delivery optical fiber 10 through the opening.

The pressing element 64 is an element that presses the delivery optical fiber 10 in the radial direction from the outer peripheral side of the delivery optical fiber 10, and examples of such an element include an actuator such as a piezo element. When the pressing element 64 is an actuator, the pressing element 64 is electrically connected to a power source (not shown), and the pressing element 64 is operated by this power source.

In the present embodiment, the pressing element 64 is arranged on a line connecting the center of the core 11 and the stress applying portion 15. That is, the pressing element 64 applies a force from the outer peripheral side of the clad 12 on the line connecting the center of the core 11 and at least one stress applying portion 15 in the radial direction of the delivery optical fiber 10. Therefore, when the pressing element 64 operates to press the delivery optical fiber 10 from the outer peripheral side of the clad 12, if the stress applying portion 15 applies a tensile stress to the core 11, the stress applied to the core 11 is applied. Is smaller, and if the stress applying portion 15 applies compressive stress to the core 11, the stress applied to the core 11 is increased.

As described above, since the pressing element 64 of the present embodiment is operated by a power source (not shown), the stress applied to the core 11 is changed depending on whether or not a voltage is applied from the power source, and the core. It is possible to switch to a state in which the stress applied to 11 is not changed. Further, the magnitude of the force for pressing the delivery optical fiber 10 can be adjusted by the magnitude of the voltage applied from this power source. That is, the degree of change in the stress applied to the core 11 can be changed depending on the magnitude of the voltage applied from the power source.

As described above, the stress changing portion 60 of the present embodiment changes the stress applied to the core 11 by applying a force in the radial direction of the delivery optical fiber 10 from the outer peripheral side of the clad 12. Therefore, by selecting the direction of the force applied from the outer peripheral side of the delivery optical fiber 10, the direction of the change in the stress applied to the core 11 can be selected.

The stress changing portion 60 of the present embodiment may be configured to mechanically apply a force in the radial direction of the delivery optical fiber 10 from the outer peripheral side of the clad 12 by using a screw or the like, unlike the above description.

Further, if the stress changing portion 60 is configured to change the stress applied to the core 11 by applying a force in the radial direction of the delivery optical fiber 10 from the outer peripheral side of the clad 12, the stress changing portion 60 may be the center of the core 11 and the stress applying portion 15. It does not have to be placed on the line connecting the.

Further, when the pressing force of the pressing element 64 is too strong, for example, a force buffer layer may be provided between the delivery optical fiber 10 and the pressing element 64. In this case, a part of the coating layer 13 or the case 61 may be used as the buffer layer.

Although the present invention has been described above by taking the above-described embodiment as an example, the present invention is not limited thereto, and can be appropriately modified.

For example, when a plurality of stress applying portions 15 are provided, the sizes, thermal expansion coefficients, and the like of at least two stress applying portions 15 may be different from each other.

Further, the number of stress applying portions 15 in the fourth and fifth embodiments is not particularly limited. Further, in these embodiments, at least one stress applying portion 15 may be arranged in the outer clad 12b.

Further, the stress changing unit 60 of the sixth and seventh embodiments may have other configurations. For example, it may not be possible to switch between a state in which the stress applied to the core 11 is changed and a state in which the stress is not changed. , The degree of change in stress applied to the core 11 does not have to be changed.

Further, the delivery optical fiber 10 may be an amplification optical fiber in which an active element excited by excitation light is added to the core 11. In this case, the clad 12 is between the clad 12 and the coating layer 13. A clad having a lower refractive index than that of the clad may be provided.

Further, each light source 2 may be a laser device having another configuration such as a solid-state laser device instead of a fiber laser device.

Further, the optical fiber 50 is not an essential configuration, and light may be directly incident on the exit portion 55 from the delivery optical fiber 10. Further, the light may be emitted directly from the delivery optical fiber 10 or the optical fiber 50 without the light emitting unit 55.

According to the present invention, according to the present invention, an optical fiber capable of uniformly approaching the intensity in a cross section of propagating light and a laser device using the optical fiber are provided, and various industries such as a fiber laser processing field and a medical field are provided. Available at.

1 ... Laser device 2 ... Light source 10 ... Delivery optical fiber 11 ... Core 12 ... Clad 15 ... Stress applying part 60 ... Stress changing part

Claims (10)

A core through which multimode light propagates and
With the clad surrounding the outer peripheral surface of the core,
At least one stress applying portion arranged in the clad and applying stress to the core,
With
The stress applying portion is an optical fiber characterized in that a non-uniform stress is applied in the circumferential direction with reference to the central axis of the core. A plurality of the stress applying portions are provided.
The optical fiber according to claim 1, wherein the plurality of stress applying portions apply rotationally symmetric stress with respect to the central axis of the core. The clad includes an inner clad and an outer clad.
The optical fiber according to claim 1 or 2, wherein at least one of the stress applying portions is arranged in the outer cladding. The clad includes an inner clad and an outer clad.
The optical fiber according to claim 1 or 2, wherein at least one of the stress applying portions is arranged over the inner clad and the outer clad. The optical fiber according to any one of claims 1 to 4,
A light source that emits light incident on the optical fiber and
A laser device comprising. The laser apparatus according to claim 5, further comprising a stress changing portion that changes the stress applied to the core. The laser apparatus according to claim 6, wherein the stress changing portion can be switched between a state in which the stress applied to the core is changed and a state in which the stress applied to the core is not changed. The laser apparatus according to claim 6 or 7, wherein the stress changing portion can change the degree of change in stress applied to the core. The stress changing portion according to any one of claims 6 to 8, wherein the stress changing portion changes the stress applied to the core by applying a force in the radial direction of the optical fiber from the outer peripheral side of the clad. Laser device. The laser device according to any one of claims 6 to 8, wherein the stress changing portion changes the stress applied to the core by changing the temperature of the optical fiber.

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