JP7213499B2 - optical coupler - Google Patents

Description

The present disclosure relates to optical couplers.

An optical coupler for coupling pumping light from a plurality of pumping light sources has been proposed to increase the output power of fiber lasers (see, for example, Non-Patent Document 1). In a high-power fiber laser, pumping light from a plurality of pumping light sources is input into an optical fiber as a laser medium to cause laser oscillation. At this time, in Non-Patent Document 1, a plurality of fibers connected to an excitation light source are bundled and welded, and as shown in FIG. It was connected to an optical fiber 112 and used as an excitation output light.

If the tapered portion 111 is formed in the middle, the output angle of light on the output side will always be larger than the incident angle, effectively increasing the NA (Numerical Aperture). For this reason, a high-NA optical fiber having a larger NA than that of the input-side optical fiber must be used for the output-side optical fiber 112 .

Further, the taper inclination of the tapered portion 111 increases as the number of optical fibers connected to the tapered portion 111 increases. On the other hand, increasing the length of the tapered portion 111 goes against the demand for miniaturization of the device. Therefore, as the output power of the fiber laser increases, the inclination of the tapered portion 111 increases, and there is a problem that the NA on the output side further increases.

However, there is a limit to the amount of Ge or the like that can be added to quartz, and there is a limit to increasing the NA of a high-NA optical fiber. Therefore, there is a problem that the number of pumping light sources to be connected is limited and the pumping output cannot be increased. This problem arises not only in high output fiber lasers but also in one-to-many or many-to-many optical branching and coupling.

Tomoko Otsuki, "Special fiber technology that expands the limit of fiber laser characteristics", Journal of High Temperature Society, Vol. 35, No. 4, pp. 157-161 (2009)

An object of the present disclosure is to realize an optical coupler capable of one-to-many or many-to-many optical branching and coupling without using an optical fiber having a particularly high NA. In particular, the present disclosure aims to realize an optical coupler that enables an increase in the number of pump light sources used for pump output light without using an optical fiber having a particularly high NA.

The optical coupler of the present disclosure is
A plurality of lights emitted from a plurality of optical fibers are incident from one end of a gradient index lens, and the plurality of lights are emitted to one optical fiber connected to the other end of the gradient index lens. an optical part;
a gradient index lens disposed between the light collecting unit and the plurality of optical fibers, converting the light from the plurality of optical fibers into parallel light using a gradient index lens, and provided in the light collecting unit; a plurality of parallel light generators incident on the one end of the
Prepare.

INDUSTRIAL APPLICABILITY The present disclosure can realize an optical coupler capable of one-to-many or many-to-many optical branching and coupling without using an optical fiber having a particularly high NA. In particular, the present disclosure makes it possible to increase the number of pumping light sources used for pumping output light without using an optical fiber having a particularly high NA, so that it is possible to increase the output of a fiber laser.

An example of an optical path when using related technology. 1 shows an example of an optical coupler according to a first embodiment; 4 shows an example of the parameters of the condensing section in the present disclosure; An example of the output angle from the tapered portion is shown. 1 shows an example of an optical path of propagating light in a condensing section in the first embodiment. A first example of the distribution of each propagating light on the exit end face of the condensing section is shown. A second example of the distribution of each propagating light on the exit end face of the condensing section is shown. 3 shows a third example of the distribution of each propagating light on the exit end face of the condensing part. A first example of the arrangement of parallel light generators is shown. A second example of the arrangement of parallel light generators is shown. 1 shows an example of an optical coupler according to a second embodiment. An example of arrangement of a parallel light generator in a capillary is shown. 4 shows a modification of the optical coupler according to the second embodiment. 1 shows an example of an optical coupler according to a third embodiment; FIG. 11 shows an arrangement example of parallel light generators in the third embodiment. FIG. An example of the distribution of each propagating light on the exit end face of the condensing part is shown. 4 shows a first example of an optical coupler according to a fourth embodiment; An example of an optical path of propagating light in the first example of the optical coupler according to the fourth embodiment is shown. FIG. 11 shows a first arrangement example of a parallel light generator in a capillary according to the fourth embodiment; FIG. FIG. 12 shows a second arrangement example of the parallel light generator in the capillary according to the fourth embodiment; FIG. FIG. 12 shows a second example of an optical coupler according to the fourth embodiment; FIG. An example of an optical path of propagating light in the second example of the optical coupler according to the fourth embodiment is shown. 10 shows an example of an optical coupler according to a fifth embodiment; 11 shows an example of an optical coupler according to a sixth embodiment; An example of the distribution of each propagating light on the exit end face of the condensing part is shown. 11 shows an example of an optical coupler according to a seventh embodiment;

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In addition, in this specification and the drawings, constituent elements having the same reference numerals are the same as each other.

(First embodiment)
FIG. 2 shows an example of an optical coupler according to this embodiment. The optical coupler according to this embodiment includes a condensing section 11 and a parallel light generating section 13 . The parallel light generating section 13 is connected to the end surface 11A arranged at one end of the condensing section 11, and the optical fiber 12 is connected to the end surface 11B arranged at the other end of the condensing section 11. FIG. The parallel light generator 13 is connected at a predetermined distance from the optical axis of the gradient index lens provided in the light collector 11 . The optical fiber 12 is connected to the optical axis of a gradient index lens provided in the light condensing section 11 . The optical fiber 14 is connected to the optical axis of the gradient index lens provided in the parallel light generator 13 . Each optical fiber 14 is connected to an excitation light source 15 . These connections may use adhesives or fusion connections.

Each excitation light source 15 generates excitation light used for laser oscillation. Pumping light from each pumping light source 15 is propagated through the optical fiber 14 and enters the parallel light generator 13 . The parallel light generator 13 converts the light from the optical fiber 14 into parallel light using a gradient index lens. The condensing unit 11 converges the parallel light from the parallel light generating unit 13 onto the optical fiber 12 using a gradient index lens. This allows the present disclosure to extract multiple pump lights from the optical fiber 12 as pump output lights.

As shown in FIG. 3, the central refractive index of the light collecting portion 11 is _n0 , the refractive index distribution coefficient of the light collecting portion 11 is g, the lens length of the light collecting portion 11 is z, and the light to the light collecting portion 11 is Assuming that the distance from the optical axis OA ₁₁ of the incident light is r ₀ and the incident angle of the incident light PL ₁₃ onto the end surface 11A of the light collecting section 11 is θ ₀ , the exit angle θ ₁ from the end surface 11B of the light collecting section 11 is is obtained from the formula (1).

From equation (1), when the incident angle θ ₀ is 0°, the output angle θ ₁ of the emitted light at z=1/4 pitch is derived by equation (2).

For example, as the condensing part 11, the lens diameter D ₁₁ =0.4 mm, g=0.8 mm ⁻¹ , the central refractive index n ₀ =1.47, the lens length z=(1/4 pitch=2π/g/4 )=1.57 mm, and emitted to the optical fiber ₁₂ having a core diameter of 0.05 mm, the incident angle θ ₀ = ₀ Consider a case in which the parallel light generators 13 are arranged at an angle of . In this case, substituting the lens parameters into equation ( ₂ ), the output angle θ1 becomes 13.5°.

On the other hand, when light is collected by the tapered portion 111 as shown in FIG. 1, as shown in FIG. is four times the taper angle _θT . Therefore, as in the light condensing section 11 according to the present disclosure, light incident at a position 0.2 mm from the optical axis OA ₁₁₁ of the tapered section 111 on the end surface 111A at an incident angle of 0° Even if the number of reflections is two and the taper angle θ _T is 5°, the light is emitted from the end face 111B at an output angle of about 20°.

In this way, even if the number of reflections in the tapered portion 111 is two, the output angle from the end surface 111B when using the taper according to the related technology is It becomes larger than the condensing part 11 . Furthermore, when a large number of excitation light sources are mounted, the area of the end surface 111A increases, and the number of reflections on the tapered portion 111 further increases, so the output angle from the end surface 111B sharply increases. Therefore, when mounting a large number of excitation light sources, the NA of the optical fiber connected to the end surface 111B becomes so large that it cannot be used practically.

In the present disclosure, since a gradient index lens is used in the light collecting section 11, the output angle from the light collecting section 11 is smaller than the output angle when a taper is used, and the optical fiber 12 has a particularly high NA. There is no need to use optical fibers. Therefore, the NA of the optical fiber 12 in the present disclosure can be the same as that of the condensing section 11 . In addition, even if the number of optical fibers 14 increases, the angle of emergence from the condensing section 11 does not increase. Note that the NA of the optical fiber 12 in the present disclosure may be higher than that of the condensing section 11 .

Here, the optical fibers 12 and 14 are preferably those capable of propagating high-output light. For example, it is preferable to use a multimode optical fiber. The core diameters of the optical fibers 12 and 14 are arbitrary, but large-diameter optical fibers such as 50 μm, 62.5 μm, and 100 μm, which can transmit a large amount of light energy at once, are used. The optical fibers 14 may have a common core diameter, but the present disclosure is not limited to this, as will be described later with reference to FIG. 15 .

The optical fiber 12 may also be any optical fiber used in optical fiber amplifiers, such as a double-clad fiber. As a result, pumping light can be directly incident on the optical fiber 12 for amplification, and laser oscillation can be performed using a reflective film or FBG (Fiber Bragg Grating) inserted in the optical fiber 12 .

The graded refractive index lens used in the light condensing section 11 and the parallel light generating section 13 is a lens having a parabolic refractive index distribution from the central axis toward the outer peripheral portion. and the like, and multi-component glasses in which a refractive index distribution of square distribution is formed by ion diffusion. A GI type (graded index type) fiber can be used as the parallel light generator 13 .

The lens length L13 of the gradient index lens provided in the parallel light generator ₁₃ is the length for converting the light from the optical fiber 14 into parallel light. Such a length is, for example, a quarter pitch or a length obtained by adding an integer multiple of a half pitch.

The lens length L ₁₁ of the gradient index lens provided in the light collecting section 11 is the length for condensing the parallel light from each parallel light generating section 13 onto the optical fiber 12 . Such a length is, for example, a quarter pitch or a length obtained by adding an integral multiple of half the pitch.

FIG. 5 shows an example of the optical paths of the propagating lights PL _11#1 and PL _11#3 in the condensing section 11. As shown in FIG. A parallel light PL _13#1 is incident at a position at a distance r _13#1 from the optical axis OA ₁₁ of the end face 11A of the light collecting portion 11, and is at a distance r from the optical axis OA ₁₁ of the end face 11A of the light collecting portion 11. A parallel light PL _13#3 is incident on the position of ₁₃ #3. These PL _11#1 and PL _11#3 converge on the optical axis OA ₁₁ at a focal plane 1/4 pitch from the end face 11A.

When the lens length L ₁₁ is equal to 1/4 pitch, the propagating lights PL _11#1 to PL _11#4 are emitted from the vicinity of the optical axis OA ₁₁ at the end surface 11B. As a result, as shown in FIG. 6, the propagating lights PL _11#1 to PL _11#4 of the light condensing section 11 are emitted from the vicinity of the optical axis OA ₁₁ at the end surface 11B.

However, when the light concentrates at one point of the connecting portion between the light condensing portion 11 and the optical fiber 12, the peak intensity increases, which may cause dielectric breakdown. A flat top light intensity distribution may be desirable for the same output intensity and lower peak intensity.

Therefore, in the present disclosure, it is preferable that the lens length L11 of the gradient index lens provided in the light condensing section ₁₁ is a lens length around 1/4 pitch excluding 1/4 pitch. For example, as shown in FIG. 5, it is preferable that the lens length L11 of the gradient index lens provided in the light condensing section ₁₁ is slightly shorter than 1/4 pitch. As a result, the light intensities of the propagating lights PL _11#1 to PL _11#4 are dispersed within the range of the mode field diameter MFD ₁₂ of the optical fiber 12, as shown in FIG.

Also, the lens length L11 of the gradient index lens provided in the light condensing section ₁₁ may be slightly longer than 1/4 pitch. As a result, the light intensities of the propagating lights PL _11#1 to PL _11#4 are dispersed within the range of the mode field diameter MFD ₁₂ of the optical fiber 12, as shown in FIG.

As shown in FIG. 5, when the distances r _{13 # 1} and r _{13 # 13} are equal and the parallel lights PL _{13 # 1} and PL _{13 # 3} are symmetrical with respect to the optical axis OA ₁₁ , the light propagating at the end surface 11B Reflected light from PL _11#1 enters propagating light PL _11#13 . In particular, this reflected light occurs when the optical fiber 12 with a high NA is connected to the end face 11B.

Therefore, in the present disclosure, when the parallel light generators 13#1, 13#2, 13#3, and 13#4 are arranged on concentric circles centered on the optical axis OA ₁₁ , the parallel light generators 13# on the end surface 11A 1, 13#2, 13#3, and 13#4 are preferably shifted from point-symmetrical positions with respect to the optical axis OA ₁₁ , as shown in FIG. For example, the parallel light generator 13#3 is located at a position P _{11 #1S} point-symmetrical to the parallel light generator 13#1 with respect to the optical axis OA ₁₁ . are placed equidistant from each other. The parallel light generator 13#4 is different from the position P _11#2S point-symmetrical to the parallel light generator 13#2 with respect to the optical axis OA ₁₁ , and the parallel light generator 13#2 and the like from the optical axis OA ₁₁ . placed at a distance.

In this embodiment, an example in which the four parallel light generators 13#1 to 13#4 are arranged on the end face 11A is shown, but the present disclosure is not limited to this. For example, the number of parallel light generators 13 arranged concentrically may be an odd number such as five, as shown in FIG. By setting the number of the parallel light generators 13 arranged on the concentric circle to be an odd number, it is possible to prevent the reflected light from the end surface 11B from entering the optical path of the propagating light of the parallel light from the parallel light generators 13 . Further, according to the present disclosure, the parallel light generators 13 may be arranged on a plurality of concentric circles.

Further, FIG. 2 shows an example in which the optical fiber 14 and the excitation light source 15 are connected to all of the parallel light generators 13#1 to 13#4, but the present disclosure is not limited to this. For example, the optical fiber 14 may be connected to at least one of the parallel light generators 13#1 to 13#4.

(Second embodiment)
FIG. 11 shows an example of an optical coupler according to this embodiment. The optical coupler according to this embodiment uses a capillary type optical component in which each parallel light generator 13 is covered with a capillary 31 in the circumferential direction.

FIG. 12 shows an arrangement example of the parallel light generator 13 in the capillary 31. As shown in FIG. A through hole is provided in the capillary 31, and the parallel light generator 13 is arranged in the through hole. The end face position z31B on the other end side of the capillary 31, the end face position _z13B on the other end side of the parallel light generating section 13, and the end face position _z11A on the one end side of the light collecting section ₁₁ match.

In this embodiment, since the parallel light generator 13 is fixed by the capillary 31, the parallel light generator 13 can be #1 to 13#4 can be connected to the condensing section 11 at desired positions.

FIG. 13 shows a modification of this embodiment. In FIG. 13, a capillary type optical component is used in which the optical fiber 14 shown in FIGS. 11 and 12 is covered with a capillary 41 in the circumferential direction. By preparing in advance the capillary type optical component in which the optical fiber 14 is covered with the capillary 41 in the circumferential direction, the optical fiber 14 can be easily connected to the parallel light generators 13#1 to 13#4.

Any method can be used to manufacture the capillary optical component including the parallel light generator 13 and the capillary 31 . For example, a glass rod serving as the base material of the capillary 31 is provided with through-holes equal in number to the parallel light generating portions 13, and a gradient index lens is inserted into each through-hole and melted and drawn. Then, it is cut and polished so that the length becomes the lens length _L13 . Thereby, a capillary optical component including the parallel light generator 13 and the capillary 31 can be manufactured.

(Third Embodiment)
FIG. 14 shows an example of an optical coupler according to this embodiment. In FIG. 5, when the beam diameters of the parallel light PL _13#1 and the parallel light PL _13#3 are different, the lens length L ₁₁ of the gradient index lens provided in the light collecting unit 11 is shifted from the focal plane to 1/4 pitch. If it is shorter or longer than , there will be a difference in the beam widths of the propagating lights PL _11#1 and PL _11#3 . Therefore, the optical coupler according to this embodiment differs from the second embodiment in the lens diameter of the parallel light generator 13 . Here, the lens length L13 and refractive index distribution coefficient of the parallel light generator ₁₃ are arbitrary. For example, each parallel light generator 13 has a refractive index distribution coefficient such that the lens length L13 is the same for all the parallel light generators ₁₃ and the gradient index lenses.

FIG. 15 shows an example of the arrangement of the parallel light generators 13 on the end surface 11A. For example, the parallel light generators 13#1, 13#2, and 13#3 have a common first diameter, and the parallel light generators 13#4, 13#5, and 13#6 have a diameter larger than the first diameter. It has a small common second diameter. In this case, the core diameters of the optical fibers 14 connected to the parallel light generators 13#1, 13#2, and 13#3 are as follows: may be larger than the core diameter of

Since the parallel light generators 13#1, 13#2, and 13#3 have larger lens diameters than the parallel light generators 13#4, 13#5, and 13#6, the parallel light beams incident on the light collector 11 are The width of the parallel light generators 13#1, 13#2 and 13#3 is larger than that of the parallel light generators 13#4, 13#5 and 13#6.

FIG. 16 shows the distribution of the propagating lights PL _11#1 to PL _11#6 on the end surface 11B when the lens length L ₁₁ of the gradient index lens provided in the light condensing section 11 is shorter than 1/4 pitch. shows an example of PL _11#4 to PL _11#6 with low beam intensities are arranged in the gaps between PL _11#1 to PL _11#3 with high beam intensities. By connecting the parallel light generators 13 having different lens diameters to the end face 11A in this way, the light intensity distribution on the end face 11B can be brought closer to a flat top.

In this embodiment, an example in which the parallel light generation unit 13 is covered in the circumferential direction with the capillaries 31 is shown, but the present disclosure is not limited to this. For example, the present disclosure also includes a configuration in which the parallel light generation section 13 is directly connected to the end face 11A of the light collection section 11 without the capillary 31, as shown in FIG. Note that the distribution shown in FIG. 16 may be obtained by varying the intensity of the parallel light emitted from the parallel light generator 13 .

(Fourth embodiment)
FIG. 17 shows an example of an optical coupler according to this embodiment. 5, when the incident angle θ 13#1 of the parallel light PL _{13 #1} and the incident angle θ _{13 #3 of the parallel light PL 13#3 are} shifted from 0 degrees, as shown in FIG. and PL _11#3 are no longer focused on optical axis OA ₁₁ at the focal plane. Therefore, in the optical coupler according to the second embodiment, the incident angle of at least one parallel light is shifted from 0 degrees. Here, the lens length L13 and refractive index distribution coefficient of the parallel light generator ₁₃ are arbitrary. For example, each parallel light generator 13 has a refractive index distribution coefficient such that the lens length L13 is the same for all the parallel light generators ₁₃ and the gradient index lenses.

FIG. 19 shows an arrangement example of the parallel light generator 13 inside the capillary 31 . A through hole is provided in the capillary 31, and the parallel light generator 13 is arranged in the through hole. The end surface 11A of the condensing section 11 and the end surface 31B of the capillary 31 on the condensing section 11 side are joined, and the normal line of the end surface 31B of the capillary 31 on the condensing section 11 side and the optical axis OA of the parallel light generating section 13 are aligned. ₁₃ is equal to the incident angles θ _{13 #1} and θ _13#3 of the parallel lights PL _13#1 and PL _13#3 shown in FIG. That is, the optical axis OA ₁₃ of the parallel light generator 13 is inclined with respect to the normal to the end surface 11A of the light collector 11 .

The lens length _{L13 on the optical axis OA13 of the parallel light generator 13 is} 1/4 pitch. Both ends of the parallel light generator 13 are perpendicular to the optical axis OA ₁₃ . For this reason, the parallel light generator 13 having the optical fiber 14 connected to the optical axis OA ₁₃ at one end 13A is arranged in the through hole of the capillary 31 and fixed with a refractive index matching agent, so that the parallel light is generated at an incident angle θ ₁₃ can be made incident on the condensing portion 11 at .

In this configuration, the position z 13 B of the optical axis OA ₁₃ of the end face 13 B of the parallel light generator 13 is arranged closer to the optical fiber 14 than the position z ₃₁ B of the end face 31 _B of the capillary 31 . Further, the position z13A of the optical axis OA13 on the end face 13A of the parallel light generator ₁₃ is arranged closer to the optical fiber 14 than the position _z31A of the end face _31A of the capillary 31 is. This makes it easier to set the angle of the parallel light generator 13 with respect to the capillary 31 .

FIG. 20 shows a second arrangement example of the parallel light generator 13 inside the capillary 31 . In this arrangement example, both ends of the parallel light generator 13 are arranged on the same plane as both ends of the capillary 31 . Also in this case, the lens length _{L13 on the optical axis OA13 of the parallel light generator 13 is} 1/4 pitch.

In the case of this configuration, a through hole is provided in the base material of the capillary 31, the base material of the parallel light generating section 13 is arranged in the through hole, and the base material of the parallel light generating section 13 is melted and drawn so as to have the lens diameter of the parallel light generating section 13. It can be manufactured by separating and polishing so that the lens length L ₁₃ on the optical axis OA ₁₃ of the light generation unit 13 becomes a desired length. Therefore, the incorporation of the parallel light generator 13 into the capillary 31 can be omitted, which facilitates manufacturing.

In this embodiment, the parallel lights PL _13#1 and PL _13#3 cross the optical axis OA ₁₁ before the propagating lights PL _11#1 and PL _{11 #3} reach the focal plane. Although an example is shown with incident angles θ _13#1 and θ _13#3 of direct incidence, the disclosure is not so limited. For example, as shown in FIGS. 21 and 22, propagating light beams PL _11#1 and PL _{11 #3} cross the optical axis OA ₁₁ after reaching the focal plane. The incident angles θ _13#1 and θ _13#3 may be incident.

This embodiment also shows an example in which the parallel light generator 13 is covered with the capillaries 31 in the circumferential direction, but the present disclosure is not limited to this. For example, the present disclosure also includes a configuration in which the parallel light generation section 13 is directly connected to the end face 11A of the light collection section 11 without the capillary 31, as shown in FIG.

(Fifth embodiment)
FIG. 23 shows an example of an optical coupler according to this embodiment. In the optical coupler according to this embodiment, the capillary 31 shown in FIG. 17 is tapered. In this embodiment, the arrangement of the parallel light generator 13 in the capillary 31 is preferably as shown in FIG. As a result, the following manufacturing method can be adopted in which the incorporation of the parallel light generator 13 into the capillary 31 can be omitted.

For example, a through hole is provided in the base material of the capillary 31, the base material of the parallel light generating section 13 is placed in the through hole, and the lens diameter of the parallel light generating section 13 is adjusted to a desired incident angle by melting and drawing. , the lens length L 13 on the optical axis OA ₁₃ of the parallel light generating section 13 can be manufactured by separating and polishing so that the lens length L ₁₃ becomes a desired length.

(Sixth embodiment)
A double-clad fiber having two clad layers is used as an optical fiber for a high-power fiber laser. In this embodiment, an example in which a double-clad fiber is used as one optical fiber 12 connected to the other end 11B of the light collector 11 will be described.

FIG. 24 shows an example of an optical coupler according to this embodiment. The double clad fiber has a core CR ₁₂ surrounded by an inner clad CL ₁₂ and an inner clad CL ₁₂ surrounded by an outer clad. The double-clad fiber allows pumping light to propagate within the inner clad CL ₁₂ , thereby amplifying the propagating light in the core CR ₁₂ and enabling laser oscillation.

When the optical fiber 12 is used as an optical fiber for laser oscillation, the end face 12A of the optical fiber 12 is provided with a 100% reflective film for laser oscillation. Therefore, when the excitation light from the excitation light source 15 is incident on the core CR ₁₂ , it is reflected by the 100% reflective film provided on the end face 12A of the optical fiber 12, and the excitation light is not propagated into the core CR ₁₂ . It is reflected by the light source 15 and causes the excitation light source 15 to malfunction. Therefore, when connecting a _{double clad fiber} for laser _oscillation as the optical fiber ₁₂ , as shown in FIG. _#5 , PL _{11 and #6} are preferably selectively injected into the inner clad CL ₁₂ of the optical fiber 12 instead of the core CR ₁₂ or the outer clad of the optical fiber 12 .

In the present disclosure, by using the lens length L ₁₁ of the gradient index lens provided in the light collecting section 11, the incident angle of the parallel light from the parallel light generating section 13 to the light collecting section 11, or a combination thereof, the parallel The excitation light from the light generator 13 can selectively enter the inner clad CL ₁₂ of the optical fiber 12 . Therefore, the present disclosure makes it possible to efficiently use the pumping light from the pumping light source 15 by efficiently injecting the pumping light from the pumping light source 15 into the inner cladding CL ₁₂ of the optical fiber 12, thereby further improving the fiber laser. high output and high reliability.

(Seventh embodiment)
FIG. 26 shows an example of an optical coupler according to this embodiment. In the optical coupler according to this embodiment, a multi-core fiber is connected as the optical fiber 12 to the other end 11B of the light condensing section 11 . Accordingly, in the present disclosure, by using a multi-core fiber as the optical fiber 12, the propagating light of the plurality of optical fibers 14 is fanned into the optical fiber 12, which is a multi-core fiber, and the propagating light of each core 42 provided in the optical fiber 12 is can be fanned out to multiple optical fibers 14 .

For example, the optical fiber 12 comprises cores CO _12#1 , CO _12#2 , CO _12#3 , CO _12#4 . In this case, in this embodiment, each of the propagating lights PL _11#1 , PL _11#2 , PL _11#3 , and PL _11#4 incident from the end surface 11A of the light condensing section 11 is separated into individual cores at the other end 11B. The light is made incident on CO _12#1 to CO _12#4 . In the present disclosure, by using the lens length L ₁₁ of the gradient index lens provided in the light collecting section 11, the incident angle of the parallel light from the parallel light generating section 13 to the light collecting section 11, or a combination thereof, the parallel Propagating lights PL _11#1 , PL _11#2 , PL _11#3 , and PL _11#4 from the light generator 13 can be made incident on individual cores CO _12#1 to CO _12#4 .

In this embodiment, it is preferable that the efficiency of coupling with the cores CO _12#1 to _12#6 at the other end 11B is high. Therefore, the lens length L11 of the gradient index lens provided in the light condensing section ₁₁ is preferably 1/4 pitch or a length obtained by adding an integral multiple of 1/2 pitch. In this case, the incident position and the incident direction of each light on the end surface 11A of the light collecting section 11 are set so that the propagating light PL _11#1 to PL _11#4 are incident on the individual cores CO _12#1 to CO _12#4 . be done.

Further, in the present embodiment, it is preferable that the propagating lights do not intersect inside the light condensing section 11 . Thereby, crosstalk of each propagating light inside the condensing section 11 can be prevented. Therefore, the incident direction of each light incident from the end surface 11A of the light condensing section 11 should be directed away from the optical axis OA ₁₁ , like the incident angles θ _13#1 and θ _13#3 shown in FIG. is preferred. Alternatively, as shown in FIG. 2, each light incident from the end surface 11A of the light condensing section ₁₁ may be set parallel to the optical axis OA11.

In each of the above-described embodiments, the propagation mode of each core provided in the optical fiber 12 may be single mode or multimode.

The present disclosure can be applied to the laser processing industry and the information and communication industry.

11: Condenser 11A, 11B, 12A, 12B, 31A, 31B, 111A, 111B: End face 12, 14: Optical fiber 13: Parallel light generator 15: Excitation light source 31, 41: Capillary 111: Tapered part 112: Height NA optical fiber

Claims (13)

a plurality of parallel light generators that convert light from the plurality of optical fibers into parallel light using a first gradient index lens;
The plurality of parallel light generators are connected to one end of the second gradient index lens, and the plurality of lights emitted from the plurality of parallel light generators are directed to the other end of the second gradient index lens. a condensing part that emits light to one connected optical fiber;
with
An optical axis of the first gradient index lens and an optical axis of the second gradient index lens provided in at least one of the plurality of parallel light generators have an angle,
optical coupler. The first graded refractive index lens provided in the parallel light generation unit has a lens length of approximately 1/4 pitch, or a lens length obtained by adding an integral multiple of 1/2 pitch to approximately 1/4 pitch,
The plurality of optical fibers are each connected to an optical axis of the first gradient index lens provided in the plurality of parallel light generation units,
The optical coupler according to claim 1. The plurality of parallel light generation units are arranged at positions shifted from point-symmetrical positions with respect to the optical axis of the second gradient index lens provided in the light collecting unit,
The optical coupler according to claim 1 . The one optical fiber is a double-clad fiber with one core,
The angle is an angle at which the excitation light incident from the one end of the second gradient index lens provided in the light collecting section is incident on the inner clad provided in the double clad fiber.
The optical coupler according to claim 1. the one optical fiber is a multi-core fiber having a plurality of cores,
The angle is an angle at which each light emitted from the parallel light generator is emitted to a different core provided in the multi-core fiber,
The optical coupler according to claim 1 . The plurality of parallel light generators are covered with a common capillary in the circumferential direction,
The optical coupler according to claim 1 . The outer diameter of one end of the capillary arranged on the side of the plurality of optical fibers is larger than the outer diameter of the other end of the capillary arranged on the side of the light collecting section,
7. An optical coupler according to claim 6 . The second gradient index lens provided in the light condensing section has a lens length of approximately 1/4 pitch, or a lens length obtained by adding an integral multiple of 1/2 pitch to approximately 1/4 pitch,
The plurality of parallel light generation units are connected to positions at a predetermined distance from an optical axis of a gradient index lens provided in the light collecting unit.
The optical coupler according to claim 1 . The second gradient index lens provided in the light condensing section has a lens length near 1/4 pitch excluding 1/4 pitch, or a lens length near 1/4 pitch excluding 1/4 pitch and 1/2 pitch. has a lens length that is an integer multiple,
The plurality of parallel light generation units are connected to positions at a predetermined distance from the optical axis of the second gradient index lens provided in the light collecting unit,
The optical coupler according to claim 1 . The one optical fiber is a double clad fiber,
The second gradient index lens provided in the condensing section converts excitation light incident from the one end of the second gradient index lens provided in the condensing section into an inner portion provided in the double clad fiber. Having a lens length that makes it incident on the cladding,
The optical coupler according to claim 1 . the one optical fiber is a multi-core fiber having a plurality of cores,
The second gradient index lens provided in the light condensing section has a lens length for emitting each light emitted from the parallel light generation section to different cores provided in the multi-core fiber,
The optical coupler according to claim 1 . At least one of the plurality of parallel light generation units has a lens diameter different from that of the first gradient index lens provided in another parallel light generation unit of the plurality of parallel light generation units.
The optical coupler according to claim 1 . The circumferential direction of the plurality of optical fibers is covered with a common capillary,
The optical coupler according to claim 1 .

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