JP6122912B2 - Optical circuit device for fiber laser and fiber laser - Google Patents

Description

  The present invention relates to an optical circuit device for a fiber laser and a fiber laser.

  The stimulated emission band of rare earth elements used for oscillating fiber lasers is near infrared light. Therefore, a general fiber laser cannot visually observe the emitted light. Therefore, in a processing fiber laser, it is common to emit guide light separately from the processing laser beam in order to visually check the processing site where the laser is emitted.

  In Patent Document 1, in a fiber laser device that outputs invisible laser light through a delivery fiber, a visible laser light source generates a clad near the joint between the output fiber from which the invisible laser light is output and the delivery fiber. And a fiber laser device that irradiates the processing position of the processing object through the clad with the visible laser light when the introduction portion for introducing the visible laser light is provided and positioning of the irradiation of the invisible laser light to the processing object is performed Have been described.

  In Patent Document 2, a light source unit including a plurality of optical fibers that propagate light from a light emitting source, and an optical that irradiates an irradiated object by converging the light beams emitted from the plurality of optical fibers into one light beam. And a light irradiation device in which one light beam has a desired light intensity profile by combining the position where the end face of the optical fiber is disposed and the intensity distribution of the light beam emitted from the optical fiber. Has been.

  In Patent Document 3, an optical fiber that transmits laser light emitted from a plurality of laser oscillators is configured with a bundle fiber in which one end includes a plurality of single-core optical fibers and the other end includes a plurality of single-core optical fibers. In addition, there is described a laser beam irradiation apparatus in which a bundle fiber includes a single-core optical fiber that emits alignment visible laser light at the center and a plurality of single-core optical fibers that transmit laser light to the periphery.

JP 2013-102007 A International Publication No. 2007/007766 JP 2000-126886 A

One indicator of the beam quality of the emitted light from the laser, there are M ^2. As the value of M ² is small, the processing accuracy is high. In the fiber laser, the main factors that deteriorate the value of M ² are disturbance to the optical fiber and the complexity of the configuration of the optical system. Therefore, in order to prevent deterioration of the M ² is the configuration of the optical system from the laser resonator and the exit end, the inclusion of complex configuration than necessary is not preferable. Therefore, it is desirable that the guide light of the fiber laser is guided through the optical fiber constituting the resonator together with the laser oscillation light and emitted.

Among the fibers used for the fiber laser resonator, rare-earth-doped optical fibers represented by Yb (ytterbium) -doped optical fibers are different from optical fibers for optical communication in order to improve the characteristics of fiber lasers. Elements are often added. Therefore, a large transmission loss occurs in the visible light region due to Rayleigh scattering, absorption of additive elements, and the like. Therefore, the guide light is a configuration for guiding the resonator in order to suppress the increase of M ^2, with a large transmission loss. For this reason, a high-power visible light source is required in order to ensure sufficient luminance of the guide light at the emission end of the fiber laser.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a fiber laser optical circuit device and a fiber laser can suppress deterioration of M ^2.

In order to solve the above problems, the present invention is an optical circuit device for a fiber laser, comprising: a plurality of delivery fibers that propagate the output of a light source; and a coupler unit that combines the outputs of the plurality of delivery fibers. The coupler unit includes a first end connected to the plurality of delivery fibers, and a second end that emits an output combined by the coupler unit, and the first end and the A single core is provided between the second end and an output from all of the plurality of delivery fibers, and the single core is an infrared ray of the outputs of the plurality of delivery fibers. the has a refractive index distribution elevated M ² is capable of suppressing when the output is light incident at a particular position, a visible light input from any position other than the specific position output, the The red light incident from a specific position Provided is an optical circuit device for a fiber laser characterized by being combined with an output which is external light.

It is preferable that any position other than the specific position is a central portion in a cross section of the single core.
It is preferable that the output, which is visible light, is incident on the coupler unit from a location where the increase in M ² is the highest in actual measurement.
It is preferable that the output that is infrared light is laser light for processing, and the output that is visible light is guide light for confirming the processing position.

The present invention also provides a fiber laser including the fiber laser optical circuit device.
The delivery fiber that propagates the output that is the infrared light is connected to a fiber laser resonator including an optical fiber to which a rare earth element is added, and the path that guides the visible light outputs the visible light. It is preferable that the optical fiber is composed of an optical fiber to which a rare earth element is not added over the entire length from the visible light source to the emission end of the fiber laser.

According to the present invention, a single core coupler portion, a raised refractive index distribution capable of suppressing the M ² when entering the output is infrared light among the outputs of the delivery fiber at a particular location Therefore, it is possible to provide an optical circuit device for fiber laser and a fiber laser that can suppress the deterioration of M ² .

It is a schematic diagram which shows an example of a fiber laser. It is (a) perspective view which shows an example of the optical circuit apparatus for fiber lasers, and (b) front view of the incident side. It is a graph which shows the refractive index distribution of an Example and a comparative example. It is a graph which shows distribution of NA of an Example and a comparative example.

  Hereinafter, based on a preferred embodiment, the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows an example of a fiber laser. The fiber laser 10 includes one or a plurality of fiber laser units 11 that oscillate processing laser light. The output of the fiber laser unit 11 is propagated to the coupler unit 20 by the delivery fiber 12. When there are a plurality of fiber laser units 11, the output of each fiber laser unit 11 may be propagated through different delivery fibers 12.

  The fiber laser 10 includes a visible light source 14 that outputs visible light for guide. The output of the visible light source 14 is propagated to the coupler unit 20 by the delivery fiber 13 different from the delivery fiber 12. The fiber laser 10 only needs to have one delivery fiber 13 and one visible light source 14, respectively. Examples of the visible light source 14 include a laser diode (LD) and a light emitting diode (LED). A laser diode is preferable because high accuracy can be obtained by coherent light.

  The coupler unit 20 combines the outputs of the delivery fibers 12 and 13. The output of the coupler unit 20 is emitted from an emission end 30 such as a head via an output optical fiber 21. The output optical fiber 21 communicates from the inside to the outside of the housing 19. A fiber laser unit 11, delivery fibers 12 and 13, a visible light source 14 and the like are accommodated in the housing 19. The injection end 30 can be disposed toward an object such as processing. The fiber laser 10 may have one coupler unit 20 and one output optical fiber 21 each.

The structure of the delivery fibers 12 and 13 is not particularly limited, but a general fiber structure such as a single mode fiber (SMF) can be adopted. A general fiber structure includes a core disposed at the center of the cross section and a clad disposed at the outer periphery of the cross section, and has a refractive index profile in which the refractive index of the core is higher than the refractive index of the cladding. . The core and the clad are made of quartz glass. Quartz glass includes silica (SiO ₂ ) glass to which no dopant is added, silica glass to which a dopant such as germanium (Ge) that increases the refractive index is added, and a dopant such as fluorine (F) that decreases the refractive index. The silica glass made is mentioned.

  FIG. 2 shows an example of an optical circuit device for fiber laser. As shown in the perspective view of FIG. 2A, the coupler unit 20 emits the first end 24 connected to the plurality of delivery fibers 12 and 13 and the output combined by the coupler unit 20. Two ends 25 are provided. A portion on the first end portion 24 side of the coupler portion 20 is a large-diameter portion 22 having a substantially constant outer diameter. Further, a portion of the coupler portion 20 on the second end portion 25 side is a tapered portion 23 whose outer diameter gradually decreases from the large diameter portion 22 toward the second end portion 25.

  As shown in FIG. 2 (b), the first end portion 24 is composed of one end face, and a plurality of delivery fibers 12 and 13 are connected on the same end face. The connection structure between the coupler unit 20 and the delivery fibers 12 and 13 is not particularly limited as long as the output is optically coupled. However, fusion splicing is preferable because interface reflection can be reduced and mechanical strength can be improved.

  The coupler unit 20 has a single core between the first end 24 and the second end 25. The core has a cross-sectional area and a region where an output can be incident from all of the plurality of delivery fibers 12 and 13. The coupler unit 20 may not have a core-cladding structure and may constitute a single core whose entire cross section can propagate light. When the coupler unit 20 has a core-clad structure, a clad may be provided around a single core. The coupler unit 20 is preferably composed of the above-mentioned quartz glass.

The core of the coupler unit 20 has a refractive index distribution that can suppress an increase in M ² when an output that is infrared light among the outputs of the plurality of delivery fibers 12 and 13 is incident at a specific position. Specifically, in response to the incident position in the first end 24, a refractive index distribution such that the portion where M ² is likely locations and M ² increase is unlikely to rise occurs. A delivery fiber 12 that propagates a processing laser beam is connected to a location where M ² is unlikely to rise, and a delivery fiber 13 that propagates a guide beam is connected to a location where M ² tends to rise.

M ² is known as a factor indicating a deviation from the Gaussian beam. For example, M ² = (π / 4λ) d ₀ , where λ _{0 is} the wavelength of light in vacuum, λ is the wavelength of light in a medium having a refractive index n, d _{0 is the} beam waist diameter, and Θ is the far-field divergence angle. It can be expressed by Θ (where π is the circumference). When there is no deviation from the Gaussian beam, M ² = 1.

  The laser beam for processing is obtained as light emitted from the resonator of the fiber laser unit 11. The fiber laser resonator is a laser resonator using an optical fiber containing an active element as an amplification medium. Examples of the optical fiber for the amplifying medium include rare earth-doped optical fibers to which rare earth elements such as Yb, Nd, Er, Pr, and Tm are added. Examples of active elements other than rare earth elements include bismuth (Bi).

  Examples of the configuration of the fiber laser resonator include a Fabry-Perot resonator in which reflection parts such as fiber Bragg gratings (FBG) are provided at both ends of an optical fiber, and a ring resonator in which an optical fiber is formed in an annular shape. The rare earth doped optical fiber is used in at least a part of the optical fiber constituting the fiber laser resonator.

  As the excitation light source for the resonator, a semiconductor laser light source such as a laser diode (LD) is preferable. The wavelength of the excitation light can be selected according to the oscillation wavelength of the fiber laser, particularly the type of active element. For example, when using a Yb-doped optical fiber, the wavelength of the excitation light is, for example, 915 nm.

  The oscillation wavelength of a fiber laser is generally in the infrared region such as near infrared (wavelength of about 1 to 3 μm), although it depends on the type of rare earth element. For this reason, visible light is used as guide light for confirming the processing position in order to visually check the processing location where the infrared laser beam is emitted. When the guide light is guided in the fiber laser resonator, the guide light has a large transmission loss in the rare earth-doped optical fiber.

Therefore, in this embodiment, the guide light is incident on the coupler unit 20 from the different delivery fiber 13 without being guided in the rare earth-doped optical fiber, and is combined with the processing laser light. Since the coupler unit 20 has a refractive index distribution that can suppress an increase in M ² when incident at a specific position, the processing infrared light is incident on the coupler unit 20 from a specific position, and is used as a guide. Visible light is incident on the coupler unit 20 from any position other than the specific position.

As a portion (specific position) where M ² is difficult to rise, an outer peripheral portion in the cross section of the core of the coupler portion 20 can be cited. Further, as a portion where M ² is likely to rise (any position other than a specific position), the center portion in the cross section of the core of the coupler portion 20 can be cited. Since guide light is incident from a location where M ² is likely to deteriorate and laser light is incident from a location where M ² is unlikely to deteriorate, guide light does not propagate in rare-earth doped fibers such as Yb. Further, the loss of the guide light is suppressed, and good M ² emission light can be obtained.

In actual manufacturing, manufacturing variations occur, so even if the design is such that M ² is the worst at the center of the coupler part, the M ² is not necessarily the worst when the guide light is incident from the center of the coupler part. Absent. For this reason, it is preferable that the guide light, which is visible light, is incident on the coupler unit from a location where the increase in M ² is the highest in actual measurement. In the case where a plurality of delivery fibers are provided as the ports through which light enters the coupler section, it is preferable that the guide light is incident from a delivery fiber having the highest rise in M ² by actual measurement among these delivery fibers.

Further, when determining the position at which the processing laser light is incident on the coupler unit 20, it is possible to select a location where M ² is the lowest in actual measurement. Further, the smaller the numerical aperture (NA) value at the exit end 30 is, the smaller the amount of increase in M ^{2 and} the better the beam quality. Therefore, the incident position of the processing laser beam on the coupler unit 20 is determined as the exit end 30. It is preferable to correspond to a position where NA is small.

  The output optical fiber 21 is connected to a second end 25 that is an emission end of the coupler unit 20. The configuration of the output optical fiber 21 is not particularly limited, and examples thereof include an optical fiber having a core-clad structure such as SMF. The output optical fiber 21 may be made of the silica-based glass described above. The connection structure between the coupler unit 20 and the output optical fiber 21 is not particularly limited as long as the outputs are optically coupled, but fusion connection is preferable as described above. The core of the output optical fiber 21 preferably has a refractive index equivalent to the core of the coupler unit 20 from the viewpoint of suppressing refraction of light incident from the coupler unit 20.

  On the outer peripheral surfaces of the delivery fibers 12 and 13 and the output optical fiber 21, a coating layer (not shown) such as resin, metal plating, or carbon is provided to protect the core and clad of the optical fiber made of glass. be able to. At the place where the fusion splicing is performed, the coating layer may be peeled off before the fusion splicing. After the fusion splicing is completed, the coating layer can be formed again by applying a resin or the like.

  The coupler part 20 having a desired refractive index distribution can be manufactured by drawing a glass base material provided with a refractive index distribution in the radial direction in the same manner as the coupler part by melt drawing. The glass base material having a refractive index distribution in the radial direction is not particularly limited. For example, a CVD method (chemical vapor deposition method), an OVD method (external method), a VAD method (gas phase axis method), and an RIT method are used. It can be manufactured by the same method as the optical fiber preform, such as (rod-in-tube method).

The CVD method is a method of laminating a glass layer on the inner surface of a glass tube (tube), then reducing the diameter of the glass tube by heating, and crushing a cavity inside the glass layer to make it solid (collapse).
The OVD method is a method in which glass fine particles are deposited on the outer surface of a glass rod (rod) to form a glass soot layer, and then the glass soot layer is sintered by heating to obtain transparent glass.
The VAD method is a method for obtaining transparent glass by starting the deposition of glass particles from the tip of a starting member such as a glass rod to form a cylindrical glass soot and then sintering the glass soot by heating. is there.
The RIT method is a method in which one or a plurality of glass rods are inserted into a glass tube and the gap is closed by heating to integrate the glass rod and the glass tube.

  The refractive index distribution of the glass base material can be controlled by adding a dopant element or a compound containing the dopant element to the glass or the glass raw material when the glass of each part is generated or after the glass is synthesized. Examples of the compound containing a dopant element include fluorides, chlorides, oxides, carbonates, sulfates, and phosphates. Although the form at the time of adding a dopant element to glass or a glass raw material is not specifically limited, Gas, vapor | steam, a solution, etc. are mentioned.

  As a method of forming the coupler portion from the glass base material, the glass base material is arranged in the vertical direction, and the lower part of the glass base material is pulled downward in a state of being melted by heating, thereby forming a fiber (fiber) shape. Can pull out thin glass. The drawn glass fiber is gradually cooled in the air during drawing. After the glass has been drawn to the same extent as the large diameter portion 22 by drawing, the tapered portion 23 can be formed by further stretching the end of the glass. Even when the glass is stretched, the refractive index distribution in the radial direction is deformed in a substantially similar manner, so that the relative refractive index distribution with respect to the center of the optical axis does not substantially change.

According to the present embodiment, when a single core of the coupler unit 20 receives an output that is infrared light among outputs of the plurality of delivery fibers 12 and 13 at a specific position, an increase in M ² can be suppressed. Have a refractive index distribution. Therefore, the laser beam for processing from a specific position, the guide light from a position other than the specific position, by entering the coupler portion 20, respectively, it is possible to suppress the deterioration of M ^2.

  The delivery fiber 12 that propagates the processing laser light is connected to a fiber laser resonator that oscillates the processing laser light, while the delivery fiber 13 that propagates the guide light is connected to the fiber laser resonator. Instead, it is directly connected to the visible light source 14. Accordingly, since the attenuation of the guide light can be suppressed while the guide light propagates through the delivery fiber 13 and the coupler unit 20, sufficient guide light is sufficient at the exit end 30 without using a high-power visible light source. Brightness can be ensured.

  As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned embodiment, A various change is possible in the range which does not deviate from the summary of this invention.

  The delivery fiber 12 that propagates the output that is infrared light is connected to a fiber laser resonator including an optical fiber doped with Yb (Yb-doped fiber). On the other hand, the delivery fiber 13 that propagates the output that is visible light is preferably an optical fiber to which Yb is not added. The Yb-doped fiber causes a large transmission loss in the visible light region. For this reason, it is preferable that the guide light reaches the emission end 30 from the visible light source 14 without propagating through the Yb-doped fiber. That is, it is preferable that the path for guiding the visible light is composed of an optical fiber to which a rare earth element such as Yb is not added over the entire length from the visible light source 14 to the emission end 30.

Delivery fiber 12 and 13, as the material constituting the respective core or cladding of the coupler portion 20 and the output optical fiber 21, for example, SiO ₂ Ge is added, SiO ₂ is mentioned that pure _SiO 2, F was added It is done.

The configuration of the optical fiber having a core and a clad is not particularly limited, but (1) a combination of a SiO ₂ core doped with Ge and a pure SiO ₂ clad, and (2) SiO ₂ doped with Ge. And a combination of a SiO ₂ clad to which F is added, and (3) a combination of a pure SiO ₂ core and a SiO ₂ clad to which F is added.

In order to suppress transmission loss caused by the dopant, the material constituting the core and the clad is either one of the dopants added to SiO ₂ such as Ge, F, or pure SiO ₂ containing no dopant. It is preferable. When the core is pure SiO ₂ , loss such as Rayleigh scattering due to Ge can be reduced. When the clad is pure SiO ₂ , the cost of the additive element used for the clad can be reduced.

However, when another element is further contained as an inevitable impurity in SiO ₂ , it can be said that the dopant is one kind or does not contain the dopant. For example, when glass soot is dehydrated and sintered using a dehydrating gas such as SOCl ₂ or Cl ₂ in the production process of SiO ₂ glass, Cl may be added to SiO ₂ as an inevitable impurity. is there.

  An optical lens such as a GRIN lens (not shown) may be inserted between the end faces of the delivery fibers 12 and 13 and the first end 24 of the coupler unit 20. The optical lens may be composed of the above-described quartz glass. The connection structure between the delivery fiber and the optical lens, and between the optical lens and the coupler unit is not particularly limited as long as the output is optically coupled, but as described above, the fusion connection is preferable.

  A GRIN (Graded Index) lens has a refractive index distribution in which the refractive index decreases from the center toward the outer periphery in the radial direction. Due to this refractive index distribution, the light propagating through the GRIN lens repeats convergence and divergence at a constant period (pitch). When the length of the GRIN lens is an odd multiple of the 0.25 pitch length, the light emitted from the delivery fibers 12 and 13 can be collimated and incident on the first end 24 of the coupler unit 20. ,preferable.

  When a GRIN lens is interposed, the divergence angle of light incident on the coupler portion from the delivery fiber via the GRIN lens is smaller than the divergence angle when light is directly incident on the coupler portion from the delivery fiber. Thereby, the divergence angle of the light emitted from the coupler unit to the output optical fiber can be suppressed to be small, and the loss of light when the output is incident on the output optical fiber can be reduced.

  The configuration for reducing the divergence angle of light emitted from the delivery fiber is not limited to the GRIN lens. For example, a heat diffusion core (TEC) fiber in which a dopant such as Ge contained in the core is diffused into the cladding around the core by heating can be adopted. When the core of the delivery fiber contains a dopant such as Ge, the TEC fiber can be integrally formed with the delivery fiber by heating the end of the delivery fiber to partially form the TEC portion.

  Since the fiber laser of this embodiment has high output and high position accuracy, it can be used in various industries such as cutting, welding, marking, drilling, engraving, patterning, heating, other processing, and medical treatment for surgery. Can be used. As a laser oscillation mode, either a modulated wave such as a pulse wave or a continuous wave can be selected.

(Example)
The core of the coupler part has a refractive index distribution having a micro confinement structure. As a result, M ² is likely to deteriorate when laser light is incident on the central part of the coupler part, and M ² is less likely to deteriorate when laser light is incident on the outer peripheral part of the coupler part. did. A plurality of delivery fibers for propagating guide light or laser light were connected to the incident end of the coupler section.
Guide light is incident from the central part of the coupler part where M ² is likely to deteriorate (ie, the delivery fiber connected to the central part), and the outer part of the coupler part where M ² is difficult to deteriorate (ie, connected to the outer peripheral part). Laser beam for processing was made incident from the delivered delivery fiber). Thus, it was possible to configure the fiber laser capable of suppressing an increase in M ^2.

(Comparative example)
The core of the coupler part has a flat refractive index distribution. As a result, an optical circuit structure in which the rise in M ² is the same both when the laser beam is incident on the central portion of the coupler portion and when the laser beam is incident on the outer peripheral portion of the coupler portion is configured. did. Using this optical circuit structure, when laser light and guide light are incident on the coupler part from separate delivery fibers, the guide light is incident on the coupler part from the same delivery fiber as the laser light. ² increased (deteriorated).

(Contrast between Example and Comparative Example)
FIG. 4 shows the result of numerical calculation of the numerical aperture (NA) distribution for the coupler portion having the refractive index distribution shown in FIG. The refractive index distribution shown in FIG. 3 is the value of the relative refractive index difference (Δ) with respect to the position (μm) from the center in the large diameter portion 22 (core) of FIG. The radius of the large-diameter portion 22 is 200 μm in both the example and the comparative example. In the comparative example, Δ = 0% for the entire large diameter portion 22 (core). The refractive index distribution of the example has a fine confinement structure in which Δ is 0.02% at the maximum in a range of about 65 to 200 μm from the center, and in the region closer to the center, Δ = 0%. FIG. 4 shows the value of NA from the injection end after the diameter reduction through the tapered portion 23 of FIG. According to the example, since the position from the center is in the range of about 90 to 140 μm and has a region having a smaller NA value than the comparative example, the laser beam for processing is incident on the region where the NA has decreased. As a result, the amount of increase in M ² can be reduced and the beam quality can be improved. Since the minute confinement structure has a higher refractive index than the surroundings, incident light can be collected from the surroundings into the minute confinement structure.

DESCRIPTION OF SYMBOLS 10 ... Fiber laser, 11 ... Fiber laser unit, 12, 13 ... Delivery fiber, 14 ... Visible light source, 19 ... Housing, 20 ... Coupler part, 21 ... Output optical fiber, 22 ... Large diameter part, 23 ... Tapered part 24 ... first end, 25 ... second end, 30 ... injection end.

Claims (6)

An optical circuit device for a fiber laser, comprising: a plurality of delivery fibers that propagate the output of a light source; and a coupler that combines the outputs of the plurality of delivery fibers,
The coupler unit has a first end connected to the plurality of delivery fibers, and a second end that emits the output combined by the coupler unit,
Between the first end portion and the second end portion, a single core is provided in which output is incident from all of the plurality of delivery fibers,
It said single core has a refractive index distribution capable increase in M ² is suppressed when incident at a particular position output is infrared light among the outputs of said plurality of delivery fiber, the specific position Combining the output that is visible light incident from any position other than the output that is infrared light incident from the specific position ,
The specific position is a position where the refractive index is higher than that of the periphery at the outer periphery of the cross section of the single core.
For fiber laser beam circuit and wherein the.   2. The optical circuit device for a fiber laser according to claim 1, wherein any position other than the specific position is a central portion in a cross section of the single core. The optical circuit device for a fiber laser according to claim 1, wherein the output that is visible light is incident on the coupler unit from a place where the increase in M ² is the highest in actual measurement.   The output that is the infrared light is a laser beam for processing, and the output that is the visible light is a guide light for confirming the processing position. The optical circuit device for fiber laser as described.   A fiber laser comprising the optical circuit device for a fiber laser according to any one of claims 1 to 4.   The delivery fiber that propagates the output that is the infrared light is connected to a fiber laser resonator including an optical fiber to which a rare earth element is added, and the path that guides the visible light outputs the visible light. The fiber laser according to claim 5, comprising an optical fiber to which a rare earth element is not added over the entire length from the visible light source to the emission end of the fiber laser.

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