JP6806113B2 - Optical fiber laser device - Google Patents

Description

The present invention relates to an optical fiber laser apparatus.

In Patent Document 1, a polarization-retaining optical fiber in which an FBG (fiber bragg grating) is formed is connected to both ends of a polarization-retaining rare earth-added fiber to output a single-polarized laser beam. An optical fiber laser apparatus to be used is described.

JP-A-2007-273600

Conventionally, by using all the optical fibers used in the optical fiber laser apparatus as polarization-maintaining optical fibers, which is a polarization-dependent aspect, single-polarization laser light is output.

An object of the present invention is to output a single-polarized laser beam without making all the optical fibers used in the optical fiber laser device polarization-dependent.

In the optical fiber laser apparatus according to claim 1 of the present invention, a polarization-independent rare earth-added fiber to which a rare earth element is added and an end portion are connected to one end of the rare earth-added fiber to form a first FBG. The polarization-independent first fiber, the polarization-dependent polarization fiber having one end connected to the other end of the rare earth-added fiber, and the end end connected to the other end of the polarization fiber. A second fiber in which a second FBG having a reflectance lower than that of the first FBG is formed is provided.

According to the above configuration, the excitation light input to the polarization-independent first fiber excites the rare earth element of the polarization-independent rare earth-added fiber. As a result, the excited rare earth element emits naturally emitted light having a specific wavelength. This naturally emitted light is input to the polarized fiber and output from the polarized fiber to the second fiber as single-polarized light. The unipolarized light input to the second fiber is reflected by the second FBG.

The light reflected by the second FBG is amplified by reciprocating between the first FBG (first fiber Bragg grating) and the second FBG (second fiber Bragg grating) while maintaining a single polarization. Further, the monopolarized light that exceeds the oscillation condition by being amplified passes through the second FBG and is output from the second fiber as beam light.

In this way, it is possible to output single-polarized laser light without making all the optical fibers used in the optical fiber laser device polarization-dependent.

The optical fiber laser apparatus according to claim 2 of the present invention is the optical fiber laser apparatus according to claim 1, wherein the polarized fiber is a polarization-maintaining optical fiber.

According to the above configuration, by generating stress inside the polarized fiber, single-polarized laser light is output without making all the optical fibers used in the optical fiber laser device polarization-dependent. be able to.

The optical fiber laser apparatus according to claim 3 of the present invention is the optical fiber laser apparatus according to claim 2, wherein the second fiber is a polarization-maintaining optical fiber.

According to the above configuration, the light that has passed through the second FBG and is output from the second fiber as beam light is the light that is output from the polarized fiber to the second fiber. Here, the second fiber is a polarization holding type. Therefore, it is possible to prevent the plane of polarization of the output light from being tilted with respect to the plane of polarization of the input light by propagating the light through the second fiber.

The optical fiber laser apparatus according to claim 4 of the present invention is the optical fiber laser apparatus according to any one of claims 1 to 3, wherein at least a part of the polarized fiber is bent in an arc shape. It is characterized by that.

According to the above configuration, spontaneously emitted light can be output from the polarized fiber as unipolarized light by using a polarized fiber in which stress is generated inside by bending at least a part in an arc shape. ..

The optical fiber laser apparatus according to claim 5 of the present invention is the optical fiber laser apparatus according to any one of claims 1, 2 and 4, wherein the direction of the plane of polarization of the light output from the second fiber is determined. The changing member is changed based on the direction of the changing member that can be changed and output, the polarizing beam splitter into which the light output from the changing member is input, and the polarization plane of the light separated by the polarizing beam splitter. It is characterized by including a control unit that controls and changes the direction of the plane of polarization of light output from the changing member.

According to the above configuration, the light output from the second fiber is input to the polarization beam splitter via the changing member. When the plane of polarization of the light input to the polarization beam splitter points in a specific direction, the input light is output from the polarization beam splitter as usable beam light.

On the other hand, when the plane of polarization of the light input to the polarizing beam splitter does not point in a specific direction, the input light is split from the available beam light by the polarizing beam splitter. Then, the control unit controls the changing member to change the direction of the plane of polarization of the light output from the changing member based on the light separated by the polarizing beam splitter, and directs the plane of polarization to a specific direction.

In this way, the direction of the plane of polarization of the light output from the changing member can be changed based on the light separated by the polarizing beam splitter.

According to the present invention, it is possible to output a single-polarized laser beam without making all the optical fibers used in the optical fiber laser device polarization-dependent.

It is a schematic block diagram which shows the optical fiber laser apparatus which concerns on 1st Embodiment of this invention. (A) (B) It is sectional drawing which showed the polarization fiber used in the optical fiber laser apparatus which concerns on 1st Embodiment of this invention. (A) (B) It is sectional drawing which showed the optical fiber used for the optical fiber laser apparatus which concerns on 1st Embodiment of this invention, and a rare earth addition fiber. (A) (B) It is sectional drawing which showed the 1st FBG and the 2nd FBG formed in the optical fiber used in the optical fiber laser apparatus which concerns on 1st Embodiment of this invention. It is a schematic block diagram which shows the optical fiber laser apparatus which concerns on 2nd Embodiment of this invention. It is sectional drawing which showed the polarization fiber used in the optical fiber laser apparatus which concerns on 2nd Embodiment of this invention. It is a side view which showed the polarization fiber used in the optical fiber laser apparatus which concerns on 3rd Embodiment of this invention. It is a schematic block diagram which shows the optical fiber laser apparatus which concerns on 4th Embodiment of this invention.

<First Embodiment>
An example of the optical fiber laser apparatus according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 4. The arrow H shown in the figure indicates the device vertical direction (vertical direction), the arrow W indicates the device width direction (horizontal direction), and the arrow D indicates the device depth direction (horizontal direction).

(overall structure)
As shown in FIG. 1, the optical fiber laser device 10 is an optical fiber in which an excitation light source 20 that outputs excitation light in a predetermined wavelength region and a first fiber Bragg grating 32 (hereinafter, “first FBG 32”) are formed. It has 30 and a rare earth addition fiber 50. Further, the optical fiber laser apparatus 10 includes a polarized fiber 60, an optical fiber 80 on which a second fiber Bragg grating 82 (hereinafter, “second FBG82”) is formed, and a light receiving unit 96 that receives laser light.

The excitation light source 20, the optical fiber 30, the rare earth-added fiber 50, the polarization fiber 60, the optical fiber 80, and the light receiving unit 96 are arranged in this order from one side to the other in the device width direction. The optical fiber 30 is an example of the first fiber, and the optical fiber 80 is an example of the second fiber.

[Excitation light source 20]
The excitation light source 20 is, for example, a semiconductor laser or the like, and is arranged so as to face one end of the optical fiber 30 as shown in FIG. Then, the excitation light source 20 is adapted to output excitation light having no polarization characteristic toward one end of the optical fiber 30. In the present embodiment, the excitation light source 20 outputs, for example, excitation light having a wavelength of 975 [nm].

[Optical fiber 30, optical fiber 80]
− Optical fiber 30−
The optical fiber 30 is a polarization-independent optical fiber, and as shown in FIG. 1, one end faces the excitation light source 20 and stress is not generated (not applied) inside the optical fiber 30 in the device width direction. It is arranged in a straight line so as to extend. As shown in FIG. 3A, the optical fiber 30 has a core 34, a clad 36 covering the core 34, and a resin clad 38 covering the clad 36. Here, the polarization-independent optical fiber is an optical fiber that propagates light regardless of the direction in which the plane of polarization faces. For example, when light of single polarization is input, the polarization characteristic It is an optical fiber that propagates light while maintaining its properties. Specifically, it is an optical fiber that maintains single polarization and propagates light even when the polarization plane is tilted when light of single polarization is input. The plane of polarization is a plane including the direction of vibration of the electromagnetic waves constituting the light and the propagation direction of the electromagnetic waves.

The refractive index of the clad 36 is lower than that of the core 34, and the refractive index of the resin clad 38 is significantly lower than that of the clad 36. Further, examples of the material constituting the core 34 include quartz to which 1 [mol%] of germanium dioxide is added, and examples of the material constituting the clad 36 include quartz to which no dopant is added. .. Further, examples of the material constituting the resin clad 38 include an ultraviolet curable resin.

Further, in the present embodiment, for example, the outer diameter of the core 34 is 20 [μm], the outer diameter of the clad 36 is 400 [μm], and the outer diameter of the resin clad 38 is 1000 [μm]. ..

Further, the first FBG 32 formed on the optical fiber 30 has a diffraction grating 40 as shown in FIG. 4 (A). Further, the diffraction lattice 40 is arranged in the core 34 of the optical fiber 30 at regular intervals along the longitudinal direction of the optical fiber 30, and is paired with the high refractive index portion 40a having a higher refractive index than the core 34. It has a low refractive index portion 40b having the same refractive index as the core 34 between the high refractive index portions 40a of the above.

In the present embodiment, the reflection center wavelength (Bragg wavelength) of the light reflected by the first FBG 32 is, for example, 1080 [nm]. Further, the dimensions and physical property values of each part are determined so that the light is reflected by the first FBG 32 with a reflectance of 99 [%] or more.

− Optical fiber 80−
The optical fiber 80 is a polarization-independent optical fiber, and as shown in FIG. 1, the end portion faces the light receiving portion 96 and extends in the device width direction so as not to generate stress inside. It is arranged in a straight line. As shown in FIG. 3A, the optical fiber 80 has a core 84, a clad 86 that covers the core 84, and a resin clad 88 that covers the clad 86.

The outer diameter of each member of the optical fiber 80 is the same as the outer diameter of each member of the optical fiber 30, and the material constituting each member of the optical fiber 80 is the material constituting each member of the optical fiber 30. It is said to be the same. Further, in the present embodiment, the length of the optical fiber 80 is 1 [mm] 10 [mm] or less.

Further, the second FBG 82 formed on the optical fiber 80 has a diffraction grating 90 as shown in FIG. 4 (B). Further, the diffraction lattice 90 is arranged in the core 84 of the optical fiber 80 at regular intervals along the longitudinal direction of the optical fiber 80, and is paired with a high refractive index portion 90a having a higher refractive index than the core 84. It has a low refractive index portion 90b having the same refractive index as the core 84 between the high refractive index portions 90a of the above.

In the present embodiment, the reflection center wavelength (Bragg wavelength) of the light reflected by the second FBG 82 is the same as that of the first FBG 32, and is set to, for example, 1080 [nm]. Further, the reflectance of the light reflected by the second FBG 82 is lower than the reflectance of the light reflected by the first FBG 32. In the present embodiment, for example, the dimensions and physical property values of each part are determined so that light is reflected by the second FBG 82 at a reflectance of 10 [%].

[Rare earth element fiber 50]
The rare earth-added fiber 50 is a polarization-independent optical fiber, and is arranged on the opposite side of the excitation light source 20 with the optical fiber 30 interposed therebetween, as shown in FIG. Further, the rare earth-added fiber 50 is wound in a coil shape with a large diameter so that stress is not generated inside. Specifically, the aspect ratio of the cross section of the coiled portion is set to be less than or equal to a predetermined ratio. Further, as shown in FIG. 3B, the rare earth-added fiber 50 includes a core 54 to which a rare earth element has been added, a clad 56 covering the core 54, and a resin clad 58 covering the clad 56. And have.

The refractive index of the clad 56 is lower than that of the core 54, and the refractive index of the resin clad 58 is significantly lower than that of the clad 56. Further, examples of the material constituting the core 54 include quartz to which ytterbium (Yb) is added, and examples of the material constituting the clad 56 include quartz to which no dopant is added. Further, examples of the material constituting the resin clad 58 include an ultraviolet curable resin.

Further, in the present embodiment, for example, the outer diameter of the core 34 is 20 [μm], the outer diameter of the clad 36 is 400 [μm], and the outer diameter of the resin clad 38 is 500 [μm]. .. Further, the length of the rare earth-added fiber 50 is 9 [m] or more.

Further, one end of the rare earth-added fiber 50 is welded to the other end of the optical fiber 30 by arc electric discharge machining (see FIG. 1). Specifically, the core 34 and the clad 36 of the optical fiber 30 and the core 54 and the clad 56 of the rare earth-added fiber 50 are welded by arc discharge (see FIGS. 3 (A) and 3 (B)). ..

As the rare earth element added to the core 54 of the rare earth-added fiber 50, ytterbium (Yb) was used, but erbium (Er) or the like may also be used.

[Polarized fiber 60]
The polarization fiber 60 is a polarization-dependent optical fiber, and is arranged between the rare earth-added fiber 50 and the optical fiber 80 as shown in FIG. Specifically, the polarization fiber 60 is a polarization-maintaining optical fiber, which is a polarization-dependent aspect. Further, the polarization fiber 60 has a core 64, a clad 66 covering the core 64, and a resin clad 68 covering the clad 66, as shown in FIG. 2 (A). ..

Further, a pair of stress applying portions 78 are formed on the clad 66 so as to sandwich the core 64 from above and below. Specifically, the heat shrinkage ratio of the material constituting the stress applying portion 78 is much larger than that of the material constituting the clad 66. As a result, at room temperature (for example, 25 [° C.]), stress is generated (applied) to the stress applying portion 78. As described above, the optical fiber 60 is a PANDA (Polarization-maintaining AND Absorption-reducing) type optical fiber which is a polarization-maintaining type.

Here, the polarization-dependent optical fiber is an optical fiber that propagates light on a plane of polarization facing a specific direction with low loss. Further, the polarization-holding type optical fiber is an optical fiber that propagates light while holding a plane of polarization in a specific direction.

The refractive index of the clad 66 is lower than that of the core 64, and the refractive index of the resin clad 68 is significantly lower than that of the clad 66. Further, examples of the material constituting the core 64 include quartz to which 1 [mol%] of germanium dioxide is added, and examples of the material constituting the clad 66 include quartz to which no dopant is added. .. Further, as a material constituting the resin clad 68, for example, an ultraviolet curable resin can be mentioned.

Further, in the present embodiment, for example, the outer diameter of the core 64 is 20 [μm], the outer diameter of the clad 66 is 400 [μm], and the outer diameter of the resin clad 68 is 1000 [μm]. .. The length of the polarized fiber 60 is 1200 [mm] or more and 1500 [mm] or less, and the polarized fiber 60 is 70 [mm] so that stress is generated inside except for both end portions. ] It is wound in a circular coil shape with an outer diameter of 130 [mm] or more. As described above, the polarized fiber 60 is partially bent in an arc shape.

Here, as described above, the polarized fiber 60 is wound in a coil shape so that a larger stress is generated inside (so that it is applied). Therefore, as shown in FIG. 2B, the cross section of the polarized fiber 60 in the coiled portion is deformed. Specifically, the length of the coiled polarized fiber 60 in the radial direction (R direction in the figure: hereinafter “coil radial direction”) is the axial direction of the coiled polarized fiber 60 (in the figure). B direction: It is shorter than the length in the "coil axis direction"). Specifically, the aspect ratio of the cross section of the coiled portion is set to be equal to or higher than a predetermined ratio. In FIG. 2B, the degree of deformation is exaggerated so that the deformation of the cross section of the polarized fiber 60 can be easily understood.

By bending the polarization fiber 60 into a coil shape in this way, the stress generated on both sides of the core 64 is increased. As a result, the light propagating through the polarization fiber 60 is biased as unipolarized light by increasing the propagation loss of the light on the plane of polarization orthogonal to the propagation loss of the light on the specific plane of polarization. It is output from the wave fiber 60.

Further, as shown in FIG. 1, one end of the polarized fiber 60 is welded to the other end of the rare earth-added fiber 50 by arc discharge, and the other end of the polarized fiber 60 is welded to one end of the optical fiber 80. , Welded by arc discharge. Specifically, the core 64 and the clad 66 of the polarization fiber 60 and the core 54 and the clad 56 of the rare earth-added fiber 50 are welded by arc discharge. Further, the core 64 and the clad 66 of the polarization fiber 60 and the core 84 and the clad 86 of the optical fiber 80 are welded by arc discharge (see FIGS. 3 (A) and 3 (B)).

In this configuration, when light having no polarization characteristic is input to the polarization fiber 60, the propagation loss of light on the polarization plane orthogonal to the propagation loss of light on a specific polarization plane is increased. As a result, the light propagating through the polarized fiber 60 is output from the polarized fiber 60 as single-polarized light.

(Light receiving unit 96)
The light receiving unit 96 is various devices for inputting the amplified laser light, for example, an SHG element that converts the received laser light into light having a half wavelength. When the light receiving unit 96 is an SHG element, the light receiving unit 96 uses a laser beam (infrared color) having a wavelength of 1080 [nm] and a laser beam (green) having a wavelength of 540 [nm] output from the optical fiber 80. ).

(Action)
Next, the operation of the optical fiber laser device 10 will be described.

The excitation light source 20 shown in FIG. 1 outputs excitation light having a wavelength of 975 [nm] and having no polarization characteristic toward one end of the optical fiber 30. This excitation light is input to the clad 36 and the core 34 (see FIG. 3A) of the optical fiber 30. Then, the excitation light propagating through the optical fiber 30 is input to the rare earth-added fiber 50.

The excitation light input to the rare earth-added fiber 50 is absorbed by the rare earth element added to the core 54 of the rare earth-added fiber 50. As a result, the rare earth element becomes an excited state, and the excited state rare earth element emits naturally emitted light having a specific wavelength. Then, the spontaneously emitted light propagating through the core 54 (see FIG. 3B) of the rare earth-added fiber 50 is input to the polarized fiber 60.

Here, a large stress is generated in the coiled portion of the polarized fiber 60. As a result, the polarization fiber 60 outputs unipolarized light by increasing the propagation loss of light on the plane of polarization orthogonal to the propagation loss of light on the specific plane of polarization. Then, the spontaneously emitted light propagating through the core 64 of the polarized fiber 60 (see FIG. 2A) and becoming unipolar is input to the optical fiber 80.

Further, of the spontaneously emitted light input to the optical fiber 80, the light in the reflection wavelength band of the second FBG82 (1080 [nm] in this embodiment) is reflected by the second FBG82 while maintaining a single polarization. To. The light reflected by the second FBG 82 is input to the polarization fiber 60 again. Here, when propagating through the optical fiber 80 in one direction, the plane of polarization may be tilted by a certain amount. When the light incident on the optical fiber 80 from the polarized fiber 60 is reflected by the second FBG 82 and returns to the fusion point with the polarized fiber 60 again, it has the same deviation as the emitted polarization plane (polarization direction). Only the light in the propagation mode returned at the wave plane (polarization direction) leads to laser oscillation.

The single-polarized light input to the polarized fiber 60 is output from the polarized fiber 60 as single-polarized light, and is again input to the rare earth-added fiber 50.

The light re-input to the rare earth-added fiber 50 is amplified by stimulated emission of rare earth elements while maintaining a single polarization. After that, the amplified light is input to the optical fiber 30 again.

Of the light input to the optical fiber 30, the light in the reflection wavelength band of the first FBG32 (1080 [nm] in this embodiment) is reflected by the first FBG32 while maintaining a single polarization.

Further, the light reflected by the first FBG 32 is input to the rare earth addition fiber 50 again while maintaining a single polarization. The light re-input to the rare earth-added fiber 50 is amplified by stimulated emission of rare earth elements while maintaining a single polarization. After that, the amplified light is input to the polarization fiber 60 again. Here, when propagating the rare earth-added fiber 50 and the optical fiber 30 in one direction, the plane of polarization may be tilted by a certain amount. When the light incident on the rare earth-added fiber 50 and the optical fiber 30 from the polarized fiber 60 is reflected by the first FBG 32 and returns to the fusion point with the polarized fiber 60 again, the emitted polarization plane (polarization direction). ) And only the light in the propagation mode returned on the same plane of polarization (polarization direction) leads to laser oscillation.

In this way, the light reciprocates between the first FBG 32 and the second FBG 82 while propagating through the polarized fiber 60, so that the propagating light is gradually amplified while maintaining a single polarization. Then, the light exceeding the oscillation condition passes through the second FBG 82 and is output as laser light from the optical fiber 80. Further, the laser light output from the optical fiber 80 is input to the light receiving unit 96.

(Summary)
As described above, the light propagating through the polarization fiber 60 has a single polarization. Further, even if the single-polarized light propagates through the polarization-independent optical fiber 30, the polarization-independent rare earth-added fiber 50, and the polarization-independent optical fiber 80, the polarization characteristics Is maintained. As a result, all the optical fibers used in the optical fiber laser apparatus 10 are not made polarization-dependent (at least one or more polarization-independent optical fibers are used), and are single-polarized. The laser beam can be output.

Further, by arranging the polarization fiber 60 on the light receiving portion 96 side with respect to the rare earth addition fiber 50, the light output from the polarization fiber 60 and passing through the second FBG of the optical fiber 80 can be used for the rare earth addition fiber 50. It is input to the light receiving unit 96 without propagating. As a result, it is possible to prevent the plane of polarization of the light output from the polarization fiber 60 from being tilted by propagating through the rare earth-added fiber 50.

The length of the optical fiber 80 is 10 [mm] or less. Therefore, it is possible to prevent the plane of polarization of single polarization that is input from the polarization fiber 60 to the optical fiber 80, passes through the second FBG of the optical fiber 80, and is output to the receiving unit 96 from tilting (drifting). Can be done.

<Second Embodiment>
An example of the optical fiber laser apparatus according to the second embodiment of the present invention will be described with reference to FIGS. 5 and 6. In addition, about 2nd Embodiment, the part different from 1st Embodiment will be mainly described.

The optical fiber laser apparatus 210 according to the second embodiment has a polarized fiber 260 as shown in FIG. Further, the polarization fiber 260 is a polarization-dependent optical fiber, and is arranged linearly between the rare earth-added fiber 50 and the optical fiber 80 so that no internal stress is generated.

As shown in FIG. 6, the polarized fiber 260 has a circular cross section. The polarized fiber 260 has a circular core 264, a circular clad 266 that covers the core 264 and is partially chipped by the strings, and a part that covers the clad 266 is chipped by the strings. It has a circular resin clad 268 and a metal portion 262 made of metal.

The refractive index of the clad 266 is lower than the refractive index of the core 264, and the refractive index of the resin clad 268 is significantly lower than the refractive index of the clad 266. In the present embodiment, for example, the outer diameter of the core 264 is 20 [μm], the outer diameter of the clad 66 is 400 [μm], and the outer diameter of the resin clad 68 is 1000 [μm].

The metal portion 262 is arranged on one side (upper side) of the polarization fiber 260. The metal portion 262 is formed with an arcuate surface 262A and a flat surface 262B that form a part of the outer peripheral surface of the polarization fiber 260. Further, the plane 262B faces the outer peripheral surface of the core 264 in the radial direction of the polarized fiber 260.

In this configuration, when light having no polarization characteristic is input to the polarization fiber 260, the polarization fiber 260 propagates the light of the polarization plane facing a specific direction with low loss. As a result, the light propagating through the polarized fiber 260 is output from the polarized fiber 260 as single-polarized light.

As a result, the optical fiber laser device 210 can output a single-polarized laser beam without making all the optical fibers into polarization-dependent optical fibers.

<Third Embodiment>
An example of the optical fiber laser apparatus according to the third embodiment of the present invention will be described with reference to FIG. The third embodiment will be mainly described as being different from the first embodiment.

The optical fiber laser apparatus 310 of the third embodiment has a polarized fiber 360 as shown in FIG. The polarized fiber 360 is not bent in a coil shape, but is bent in a wavy shape (concavo-convex shape), so that at least a part (convex portion and concave portion) is bent in an arc shape. As a result, stress is generated inside the polarized fiber 360.

The operation of the third embodiment is the same as the operation of the first embodiment.

<Fourth Embodiment>
An example of the optical fiber laser apparatus according to the fourth embodiment of the present invention will be described with reference to FIG. In addition, about 4th Embodiment, the part different from 1st Embodiment will be mainly described.

As shown in FIG. 8, the optical fiber laser apparatus 410 of the fourth embodiment has a 1/2 wavelength plate 414 and a polarization beam splitter 416 between the optical fiber 80 and the light receiving unit 96. .. Further, the optical fiber laser apparatus 410 has a control unit 418 that rotates the 1/2 wave plate 414 based on the inclination of the polarization plane of the light separated by the polarization beam splitter 416.

The 1/2 wave plate 414 (λ / 2 plate) has a function of changing the direction of the plane of polarization of the input light and outputting the light. The polarizing beam splitter 416 (PBS: Polarizing Beam Splitter) has a function of separating light on a polarization plane that does not face a specific direction from the input light. Then, the polarization beam splitter 416 outputs the light of the polarization plane facing a specific direction to the light receiving unit 96 as beam light. The 1/2 wave plate 414 is an example of a changing member.

In this configuration, the light output from the optical fiber 80 is input to the polarizing beam splitter 416 via the 1/2 wavelength plate 414.

When the plane of polarization of the light input to the polarizing beam splitter 416 is oriented in a specific direction, the light input to the polarizing beam splitter 416 is output to the light receiving unit 96. On the other hand, when the polarization plane of the light input to the polarization beam splitter 416 does not face a specific direction, the light input to the polarization beam splitter 416 is split by the polarization beam splitter 416. Then, the control unit 418 derives the inclination with respect to the polarization plane facing the specific direction from the light of the polarization plane not facing the specific direction, and controls and rotates the 1/2 wavelength plate 414. As a result, the control unit 418 directs the plane of polarization of the light that has passed through the 1/2 wavelength plate 414 in a specific direction. Then, the light input to the polarization beam splitter 416 is output to the light receiving unit 96.

The other actions of the fifth embodiment are the same as those of the first embodiment.

Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments can be taken within the scope of the present invention. That is clear to those skilled in the art. For example, in the first, third, and fourth embodiments, the stress generated inside is increased by winding the polarization fiber 60 into a coil, but the polarization fiber 60 is deformed into another shape to be inside. The generated stress may be increased.

Further, in the above-described embodiment, in the first, third, and fourth embodiments, the polarized fiber 60 and the optical fiber 80 are separate bodies, but the light receiving portion side of the polarized fiber is linearly extended to form a first. By forming 2FBG, the polarized fiber and the optical fiber may be integrally formed.

Further, in the first, third, and fourth embodiments, the polarized fiber 60 is partially bent in an arc shape, but the entire polarized fiber 60 may be in an arc shape.

Further, in the first embodiment, the optical fiber 80 is a polarization-independent type, but the optical fiber 80 may be a polarization-maintaining type optical fiber. In this case, the light is unipolarized by propagating through the polarized fiber 60, and the light that has passed through the second FBG of the optical fiber 80 is used as laser light from the optical fiber 80 while maintaining the plane of polarization of the light. Can be output.

Further, although not particularly described in the above embodiment, the excitation light source 20 may be incident on the optical fiber from any portion.

10 Optical fiber laser device 26 Polarized fiber 30 Optical fiber (example of first fiber)
32 1st FBG
50 Rare earth element added fiber 60 Polarized fiber 80 Optical fiber (example of second fiber)
82 2nd FBG
210 Optical fiber laser device 260 Polarized fiber 310 Optical fiber laser device 360 Polarized fiber laser device 410 Optical fiber laser device 414 1/2 wave plate (example of modified member)
416 Polarization beam splitter 418 Control unit

Claims (5)

Polarization-independent rare earth-added fibers to which rare earth elements are added,
A polarization-independent first fiber in which an end is connected to one end of the rare earth-added fiber and a first FBG is formed.
A polarization-dependent polarization fiber having one end connected to the other end of the rare earth-added fiber,
A second fiber in which an end portion is connected to the other end of the polarized fiber and a second FBG having a reflectance lower than that of the first FBG is formed.
Optical fiber laser device equipped with. The optical fiber laser apparatus according to claim 1, wherein the polarized fiber is a polarization-maintaining optical fiber. The optical fiber laser apparatus according to claim 2, wherein the second fiber is a polarization-maintaining optical fiber. The optical fiber laser apparatus according to any one of claims 1 to 3, wherein at least a part of the polarized fiber is bent in an arc shape. A changing member capable of changing the direction of the plane of polarization of light output from the second fiber and outputting the light.
A polarizing beam splitter to which the light output from the changing member is input, and
A control unit that controls the changing member to change the direction of the plane of polarization of light output from the changing member based on the direction of the plane of polarization of light separated by the polarizing beam splitter.
The optical fiber laser apparatus according to any one of claims 1, 2 and 4.