JP2019070599A - Light detection device and laser equipment - Google Patents

Abstract

To provide a light detection device that allows for improvement of accuracy of the detection of the intensity of each of lights propagating in both directions through an optical fiber, and laser equipment with the light detection device.SOLUTION: The light detection device comprises: a first optical fiber 10 having a first core 11 and a first clad 12; a second optical fiber 20 having a second core 21 having a diameter equal to that of the first core and connected to the first core and propagating light of a mode higher than light propagating through the first core and a second clad 22; a first clad mode stripper 15 provided outside the first clad; a first light detection unit 14 provided on one side of the first clad mode stripper in the longitudinal direction of the first optical fiber and detecting the Rayleigh scattering of the light propagating through the first optical fiber; and a second light detection unit 24 provided on the other side of the first clad mode stripper in the longitudinal direction of the first optical fiber and detecting the Rayleigh scattering of the light propagating through the first optical fiber or second optical fiber.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a light detection device and a laser device provided with the light detection device.

  The fiber laser device is used in various fields such as the laser processing field and the medical field because the fiber laser device is excellent in light-condensing property, high in power density, and capable of obtaining light as a small beam spot. In order to realize good processing quality by such a highly efficient laser device, it is required to accurately detect the intensity of light propagating through the optical fiber.

  For example, Patent Document 1 below describes a fiber laser device capable of estimating the intensity of light propagating through an optical fiber by detecting light leaking from a connection between the optical fibers. Patent Document 2 below describes a sensor unit capable of estimating the intensity of light propagating in an optical fiber by detecting Rayleigh scattering of light propagating in the optical fiber.

International Publication No. 2012/073952 International Publication No. 2014/035505

  In the fiber laser device described in Patent Document 1, the leaked light from the connection portion between the optical fibers is used, and heat is generated when the leaked light is taken out of the optical fiber. Such heat generation becomes more pronounced as the energy of light propagating through the optical fiber becomes higher. For this reason, in the fiber laser device described in Patent Document 1, as the energy of light propagating through the optical fiber increases, the effect of heat received by the detector and the route to the detector increases, and the detection result and the detection are detected. The linearity of the relationship with the intensity of light propagating in the optical fiber estimated from the result tends to be lost. Therefore, it is difficult to accurately detect the intensity of light propagating through the optical fiber.

  Further, in the sensor unit described in Patent Document 2, Rayleigh scattering is detected, and Rayleigh scattering occurs in all directions, so it is possible to determine in which direction of the optical fiber it is Rayleigh scattering of light propagating. difficult. For this reason, in the sensor unit described in Patent Document 2, it is difficult to accurately detect the intensity of light propagating in the optical fiber in a predetermined direction. Particularly in high-reflecting material processing such as metal processing, reflected light that propagates in the direction opposite to the output direction of the laser may be generated, making it difficult to accurately detect the intensity of light propagating in the optical fiber in a predetermined direction. .

  Then, an object of the present invention is to provide a light detection device which can improve detection accuracy of intensity of each light propagating in both directions of an optical fiber, and a laser device provided with the light detection device.

  In order to solve the above problems, a light detection device according to the present invention comprises: a first optical fiber having a first core and a first cladding surrounding the first core; a second core connected to the first core; A second optical fiber having a second cladding surrounding the two cores, a first cladding mode stripper provided outside the first cladding, and one side of the first cladding mode stripper in the longitudinal direction of the first optical fiber A first light detection unit disposed to detect Rayleigh scattering of light propagating through the first optical fiber; and a first light detection unit disposed on the other side of the first cladding mode stripper in a longitudinal direction of the first optical fiber; An optical fiber or a second light detection unit that detects Rayleigh scattering of light propagating in the second optical fiber, wherein the diameter of the first core and the diameter of the second core are different from each other Equal, the second core is characterized by propagating light in high-order modes than the light propagating through the first core.

  Generally, light of higher order mode tends to have higher energy at a position outside the center of the core than light of lower order mode, so it tends to become clad mode light at the connection between optical fibers. In the light detection device of the present invention, the second core propagates light of a mode higher than that of light propagating through the first core. Therefore, light propagating from the second core to the first core is clad mode light at the connection portion between the first optical fiber and the second optical fiber as compared to light propagating from the first core to the second core. easy. Thus, at least a portion of the light propagating in the first cladding as cladding mode light is emitted to the outside of the first optical fiber in the first cladding mode stripper. Therefore, the detection result of the first light detection unit disposed on one side of the first cladding mode stripper in the longitudinal direction of the first optical fiber and the detection result of the second light detection unit disposed on the other side of the first cladding mode strip A difference in the amount of light emitted by the one cladding mode stripper occurs. The magnitude of this difference depends at least on the intensity of light propagating from the second core to the first core. Therefore, the intensity of light propagating from the second core to the first core can be estimated using the difference between the detection result of the first light detection unit and the detection result of the second light detection unit. Further, in the light detection device according to the present invention, the first light detection unit detects Rayleigh scattering of light propagating bidirectionally in the first optical fiber, and the second light detection unit is the first optical fiber or the second optical fiber. Detects Rayleigh scattering of light propagating in two directions. Here, by estimating the intensity of the light propagating through the second core to the first core as described above, from the detection result of the first light detection unit or the second light detection unit, the first core to the second light are detected. The intensity of light propagating to the core side can also be estimated. Furthermore, in the light detection device of the present invention, the first light detection unit and the second light detection unit respectively detect Rayleigh scattering. For this reason, compared with the case of detecting leaked light as in the fiber laser device described in Patent Document 1, even if the intensity of light propagating through the optical fiber is high, it is estimated from the detection result and the detection result. The linearity of the relationship with the intensity of light propagating through the optical fiber can be maintained. Therefore, the light detection device of the present invention can improve the detection accuracy of the intensity of each light propagating in both directions of the optical fiber.

  The second optical fiber is disposed downstream of the first optical fiber in the propagation direction of the light from the light source that emits the light propagating through the first optical fiber, and the first light detection unit is The first cladding mode stripper is disposed upstream of the light source in the propagation direction of the light from the light source, and the second light detection unit is downstream of the first cladding mode stripper in the propagation direction of the light from the light source It is preferred that the

  Below, the upstream side of the propagation direction of the light from a light source may only be called upstream, and the downstream side of the propagation direction of the light from a light source may only be called downstream. Further, the direction from the upstream side to the downstream side may be referred to as a forward direction, and the direction from the downstream side to the upstream side may be referred to as a reverse direction.

  A second optical fiber for propagating light of a higher order mode than the first optical fiber is disposed downstream of the first optical fiber, whereby light propagating from the first optical fiber to the second optical fiber is emitted. It is suitable when low-order mode light such as the fundamental mode is emitted from the light source. By disposing the second optical fiber downstream of the first optical fiber, the light of the low order mode emitted from the light source can be propagated from the first optical fiber to the second optical fiber with low loss. On the other hand, the reflected light propagating to the opposite side to the propagation direction of the light emitted from the light source tends to include the light of the high order mode. Therefore, the light of the higher order mode of the reflected light can be made into cladding mode light at the connection portion between the second optical fiber and the first optical fiber and emitted at the first cladding mode stripper.

  Preferably, the first optical fiber is a single mode fiber.

  Since the first optical fiber is a single mode fiber, light propagating as multi-mode light from the second optical fiber to the first optical fiber is generated at the connection portion between the first optical fiber and the second optical fiber. It becomes easier to become cladding mode light. Therefore, the difference between the detection result of the first light detection unit and the detection result of the second light detection unit tends to be large, and the detection accuracy of each light propagating in both directions of the optical fiber can be further improved.

  Preferably, a second cladding mode stripper is provided outside the second cladding.

  When the cladding mode light propagating to the first cladding side in the second cladding is not removed, at least a portion of the cladding mode light propagating from the second cladding to the first cladding may propagate through the first cladding. Thus, by providing the second cladding mode stripper in the second optical fiber as described above, cladding mode light propagating to the first cladding side of the second cladding is reduced, and the first cladding is used as the second cladding. The cladding mode light propagating to the opposite side can also be reduced. Thus, by reducing the cladding mode light propagating through the first cladding, the influence of the cladding mode light on the first light detection unit is suppressed, and the light propagating through the first optical fiber by the first light detection unit Can be detected more accurately. In addition, when cladding mode light propagates to the first cladding side to the second cladding side, at least a part of the cladding mode light can propagate to the opposite side of the second cladding from the first cladding. By providing the second cladding mode stripper as described above, cladding mode light propagating through the second cladding can also be reduced.

  Further, in the longitudinal direction of the first optical fiber and the second optical fiber, the first light detecting portion and the second light detecting portion sandwiching a connection portion between the first optical fiber and the second optical fiber. Preferably, the second light detection unit detects Rayleigh scattering of light propagating through the second optical fiber.

  In the light detection device according to the present invention, as described above, cladding mode light generated at the connection portion between the first optical fiber and the second optical fiber is removed by the first cladding mode stripper in the first light detection unit. The difference between the detection result and the detection result of the second light detection unit is used. By the way, since there is a difference in the concentration of the additive between the cladding and the core, the ratio of Rayleigh scattering differs between the light propagating through the core and the light propagating through the cladding. Therefore, it is preferable that the first light detection unit and the second light detection unit each detect Rayleigh scattering of light propagating through either the core or the cladding. Here, since the second core propagates light of a mode higher than that of the first core, light propagating from the first core to the second core is propagated at the second core with the loss at the connection portion suppressed. Do. On the other hand, light propagating from the second core to the first core side is at least partially incident on the first cladding at the connection portion as described above. As described above, at least a part of the light incident on the first cladding is emitted to the outside in the first cladding mode stripper before the first light detection unit. Therefore, by disposing the first light detection unit and the second light detection unit with the connection unit interposed therebetween, the first light detection unit mainly detects Rayleigh scattering of light propagating through the first core, and the second light detection unit The light detection unit mainly detects Rayleigh scattering of light propagating through the second core. As described above, when the first light detection unit and the second light detection unit respectively detect Rayleigh scattering of light propagating mainly through the core, the detection accuracy of the intensity of each light propagating in both directions of the optical fiber is further increased. It can be improved.

  Further, it is preferable that the second light detection unit is disposed on the side opposite to the first optical fiber side with respect to a second cladding mode stripper provided on the outer side of the second cladding.

  By disposing the second light detection unit and the second cladding mode stripper in this manner, at least a portion of cladding mode light that propagates the second cladding to the side opposite to the first cladding side is a part of the second light detection unit. The light is emitted to the outside of the second optical fiber in the second cladding mode stripper in the foreground. Thus, the second light detection unit can more accurately detect the intensity of light propagating through the second core.

  Preferably, no dopant is added to the first core and the second core.

  By not adding the dopant to the first core and the second core, it is possible to suppress the occurrence of an error in the detection result in the first light detection unit and the second light detection unit due to the concentration distribution of the dopant.

  Further, the first cladding is coated with a low refractive index resin having a refractive index lower than that of the first cladding from the connection portion between the first optical fiber and the second optical fiber to the first cladding mode stripper. Is preferred.

  By covering the first cladding with the low refractive index resin as described above, the cladding mode light generated at the connection portion between the first optical fiber and the second optical fiber is prevented from leaking in the vicinity of the connection portion, It can propagate to one clad mode stripper. By suppressing light leakage in the vicinity of the connection portion in this manner, heat generation in the vicinity of the connection portion can be suppressed, and a change in the amount of light loss at the connection portion can be suppressed. Therefore, the intensity of light can be detected more accurately in the first light detection unit and the second light detection unit.

  Preferably, the outer diameter of the first cladding and the outer diameter of the second cladding are equal to each other.

  When the outer diameter of the first cladding and the outer diameter of the second cladding are equal to each other, when the first optical fiber and the second optical fiber are fusion spliced, an uneven step is formed at the connection portion Can be suppressed, and the occurrence of bending at the connection can be suppressed. Thus, the loss of light at the connection between the first optical fiber and the second optical fiber can be suppressed.

  Preferably, a mode scrambler unit is provided to reduce an energy difference between light of each mode propagating in the second core.

  By providing the mode scrambler unit that scatters the light propagating in the multi-mode light propagating core, the difference in the energy density distribution of the propagating light can be reduced in the core. For this reason, at the connection portion between the second core and the first core, the difference in the amount of loss due to the angle of the propagating light can be reduced. Thus, variations in detection results of the first light detection unit and the second light detection unit can be suppressed.

  In order to solve the above-mentioned subject, the laser device of the present invention is provided with the above-mentioned photodetection device, and at least one light source which emits the light which propagates the 1st optical fiber and the 2nd optical fiber. It features.

  As described above, according to the light detection device of the present invention, the detection accuracy of the intensity of each light propagating in both directions of the optical fiber can be improved. Therefore, according to the laser apparatus provided with the said light detection apparatus, the accuracy of control based on the intensity | strength of the light which propagates an optical fiber can be improved.

  As described above, according to the present invention, a light detection device capable of improving the detection accuracy of the intensity of each light propagating in both directions of the optical fiber and a laser device provided with the light detection device are provided.

It is a figure showing roughly the composition of the laser device concerning the embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a part of the light detection device shown in FIG. It is sectional drawing which shows roughly a part of optical detection apparatus which concerns on the modification of this invention. It is sectional drawing which shows roughly a part of optical detection apparatus which concerns on the other modification of this invention.

  Hereinafter, preferred embodiments of a light detection device and a laser device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a view schematically showing the configuration of a laser apparatus according to an embodiment of the present invention. As shown in FIG. 1, the laser device 1 of the present embodiment includes a light detection device 2, a light source 5, and a control unit CP as main components.

  The light source 5 includes an excitation light source 50, an optical combiner 53, an amplification optical fiber 55, an optical fiber 54 connected to one side of the amplification optical fiber 55, a first FBG 57 provided on the optical fiber 54, and the other of the amplification optical fiber 55. An optical fiber 56 connected to the side and a second FBG 58 provided in the optical fiber 56 are provided as main components. Further, the amplification optical fiber 55, the first FBG 57, and the second FBG 58 constitute a resonator.

  The excitation light source 50 is composed of a plurality of laser diodes 51. In the present embodiment, the laser diode 51 is, for example, a Fabry-Perot semiconductor laser made of a GaAs semiconductor and emits excitation light having a central wavelength of 915 nm. Do. Each laser diode 51 of the excitation light source 50 is connected to the optical fiber 52, and the excitation light emitted from the laser diode 51 propagates through the optical fiber 52.

  The amplification optical fiber 55 mainly includes a core, an inner cladding surrounding the outer peripheral surface of the core without a gap, an outer cladding covering the outer peripheral surface of the inner cladding, and a covering layer covering the outer cladding. It has a double clad structure. The refractive index of the inner cladding is lower than the refractive index of the core, and the refractive index of the outer cladding is lower than the refractive index of the inner cladding. As a material which constitutes a core of optical fiber 55 for amplification, elements, such as germanium (Ge) which raises a refractive index, ytterbium (Yb) etc. which are excited by excitation light emitted from excitation light source 50, for example The quartz which added the active element is mentioned. As a material which comprises the inner clad | crud of the optical fiber 55 for amplification, the pure quartz to which the dopant is not added can be mentioned, for example. An element such as fluorine (F) that lowers the refractive index may be added to the material of the inner cladding. The outer cladding is made of resin or quartz, and the resin may be, for example, an ultraviolet curable resin, and quartz may be, for example, a dopant such as fluorine (F) that lowers the refractive index so that the refractive index is lower than that of the inner cladding. Quartz is added. As a material which comprises the coating layer of the optical fiber 55 for amplification, an ultraviolet curable resin is mentioned, for example, When an outer clad is resin, it is set as the ultraviolet curable resin different from resin which constitutes an outer clad.

  The optical fiber 54 connected to one side of the amplification optical fiber 55 has a core not doped with an active element, an inner cladding surrounding the outer peripheral surface of the core without gaps, and an outer covering the outer peripheral surface of the inner cladding. It mainly comprises a cladding and a covering layer covering the outer cladding. The core of the optical fiber 54 has substantially the same configuration as the core of the amplification optical fiber 55 except that the active element is not added. The core of the optical fiber 54 is connected to the core of the amplification optical fiber 55, and the inner cladding of the optical fiber 54 is connected to the inner cladding of the amplification optical fiber 55. Further, the core of the optical fiber 54 is provided with a first FBG 57 as a first mirror. Thus, the first FBG 57 is provided on one side of the amplification optical fiber 55. In the first FBG 57, a portion in which the refractive index periodically increases along the longitudinal direction of the optical fiber 54 is repeated, and the active element of the amplification optical fiber 55 brought into the excited state by adjusting this period. Is configured to reflect light of at least some of the wavelengths of light emitted by The reflectance of the first FBG 57 is higher than the reflectance of the second FBG 58 described later, and it is preferable to reflect light of a desired wavelength among the light emitted by the active element at 90% or more, and more preferably 99% or more preferable. The wavelength of light reflected by the first FBG 57 is, for example, 1090 nm when the active element is ytterbium as described above.

  The optical fiber 56 connected to the other side of the amplification optical fiber 55 has a core not doped with an active element, a clad surrounding the outer peripheral surface of the core without a gap, and a covering layer covering the outer peripheral surface of the clad As the main configuration. The core of the optical fiber 56 is connected to the core of the amplification optical fiber 55, and the cladding of the optical fiber 56 is connected to the inner cladding of the amplification optical fiber 55. Further, the core of the optical fiber 56 is provided with a second FBG 58 as a second mirror. Thus, the second FBG 58 is provided on the other side of the amplification optical fiber 55. In the second FBG 58, a portion in which the refractive index increases with a constant period is repeated along the longitudinal direction of the optical fiber 56, and light of at least a part of wavelengths of light reflected by the first FBG 57 is lower than the first FBG 57 It is configured to reflect at reflectance. The second FBG 58 preferably reflects at least a part of the wavelength light of the light reflected by the first FBG 57 at a reflectance of 5% to 50%, and more preferably at a reflectance of 5% to 10%. .

  In the optical combiner 53, the core of each optical fiber 52 and the inner cladding of the optical fiber 54 are connected. Therefore, the optical fiber 52 through which the excitation light emitted from each of the laser diodes 51 propagates and the inner cladding of the amplification optical fiber 55 are optically coupled via the inner cladding of the optical fiber 54.

  FIG. 2 is a cross-sectional view schematically showing a part of the light detection device 2 shown in FIG. As shown in FIGS. 1 and 2, the light detection device 2 of the present embodiment includes a first optical fiber 10, a second optical fiber 20, a low refractive index resin layer 31, a first cladding mode stripper 15, and a second cladding mode. A stripper 25, a first light detection unit 14, a second light detection unit 24, a first AD conversion unit 16, a second AD conversion unit 26, a mode scrambler unit 35, and a calculation unit 40 are provided as main components.

  The first optical fiber 10 may be part of the optical fiber 56 or may be another optical fiber connected to the optical fiber 56. The first optical fiber 10 has a first core 11, a first cladding 12 surrounding the first core 11, and a first covering layer 13 surrounding the first cladding 12. The first core 11 is made of pure quartz to which no dopant is added. The first cladding 12 is made of a material having a refractive index lower than that of the first core 11. As a material which comprises the 1st clad 12, quartz to which dopants, such as fluorine (F) which lowers a refractive index, are added can be mentioned, for example. The first covering layer 13 is made of a material having a refractive index lower than that of the first cladding 12. As a material which comprises the 1st coating layer 13, ultraviolet curable resin is mentioned, for example.

  The first cladding mode stripper 15 is provided outside the first cladding 12 of the first optical fiber 10. The first cladding mode stripper 15 is not particularly limited as long as the cladding mode light propagating in the first cladding 12 can be emitted to the outside of the first optical fiber 10. The first cladding mode stripper 15 of this embodiment is configured by intermittently providing a plurality of high refractive index portions 15 h made of a resin having a refractive index higher than that of the first cladding 12 outside the first cladding 12.

  The second optical fiber 20 is disposed downstream of the first optical fiber 10 in the propagation direction of the light from the light source 5. The second optical fiber 20 has a second core 21, a second cladding 22 surrounding the second core 21, and a second covering layer 23 surrounding the second cladding 22. The second core 21 propagates light of a higher order mode than the light propagating through the first core 11. That is, the second optical fiber 20 is a multimode fiber. Also, the second core 21 is made of pure quartz to which no dopant is added. The second cladding 22 is made of a material having a refractive index lower than that of the second core 21. As a material which comprises the 2nd clad 22, quartz to which dopants, such as fluorine (F) which lowers a refractive index, are added can be mentioned, for example. The second covering layer 23 is made of a material having a refractive index lower than that of the second cladding 22. As a material which comprises the 2nd coating layer 23, an ultraviolet curable resin is mentioned, for example. In the second optical fiber 20, the diameter of the second core 21 is equal to the diameter of the first core, and the outer diameter of the second cladding 22 is equal to the outer diameter of the first cladding 12. When the outer diameter of the first cladding 12 and the outer diameter of the second cladding 22 are equal, when the first optical fiber 10 and the second optical fiber 20 are fusion-spliced, uneven steps occur at the connecting portion 30. It can be suppressed that it is formed, and the occurrence of bending in the connection portion 30 can be suppressed. Therefore, the loss of light at the connection portion 30 between the first optical fiber 10 and the second optical fiber 20 can be suppressed.

  The second cladding mode stripper 25 is provided outside the second cladding 22 of the second optical fiber 20. The second cladding mode stripper 25 is not particularly limited as long as the cladding mode light propagating in the second cladding 22 can be emitted to the outside of the second optical fiber 20. The second cladding mode stripper 25 of the present embodiment is configured by intermittently providing a plurality of high refractive index portions 25 h made of a resin having a refractive index higher than that of the second cladding 22 outside the second cladding 22.

  The first optical fiber 10 and the second optical fiber 20 are connected to each other at one end face, the first core and the second core are connected to each other, and the first cladding 12 and the second cladding 22 are connected to each other ing. The connection between the first optical fiber 10 and the second optical fiber 20 is performed, for example, by fusing the end faces of each other with an oxyhydrogen burner or the like. Further, in the vicinity of the connection portion 30 between the first optical fiber 10 and the second optical fiber 20, the first covering layer 13 and the second covering layer 23 are peeled off. The portion where the first covering layer 13 and the second covering layer 23 are peeled off is covered with the low refractive index resin layer 31 in a state where the first optical fiber 10 and the second optical fiber 20 are connected. The low refractive index resin layer 31 is formed of a low refractive index resin whose refractive index is lower than the refractive index of the first cladding 12 and the refractive index of the second cladding 22. The low refractive index resin layer 31 of the present embodiment is formed between the first cladding mode stripper 15 and the second cladding mode stripper 25. That is, the first cladding 12 and the second cladding 22 are coated with the low refractive index resin layer 31 between the connecting portion 30 and the first cladding mode stripper 15 and between the connecting portion 30 and the second cladding mode stripper 25. Ru. Such a low refractive index resin layer 31 is made of, for example, an ultraviolet curable resin.

  The mode scrambler unit 35 shown in FIG. 1 is formed in the second optical fiber 20. The mode scrambler unit 35 scatters the light propagating through the second core 21. The second optical fiber 20 is a multimode fiber, and the mode scrambler unit 35 reduces the energy difference of the light of each mode propagating in the second core 21. The mode scrambler unit 35 of the present embodiment is formed by annularly bending a part of the second optical fiber 20 as shown in FIG.

  In the present embodiment, the first light detection unit 14 is disposed outside the first optical fiber 10 and detects Rayleigh scattering of light propagating through the first optical fiber 10. In addition, the second light detection unit 24 is disposed outside the second optical fiber 20 and detects Rayleigh scattering of light propagating through the second optical fiber 20. Since Rayleigh scattering occurs in all directions, it is difficult to determine in which direction of the optical fiber it is Rayleigh scattering of light propagating only by detecting Rayleigh scattering. For example, in the case of using a laser device for high-reflecting material processing such as metal processing, reflected light that propagates in a direction opposite to the output direction of the laser may also propagate through the optical fiber. In such a case, in the light detection device 2 of the present embodiment, as will be described in detail later, the detection accuracy of the intensity of each light propagating in both directions of the optical fiber can be improved. In addition, the first light detection unit 14 is provided on the opposite side of the first cladding mode stripper 15 to the second optical fiber 20 side, and the second light detection unit 24 is provided on the first side of the second cladding mode stripper 25. It is provided on the opposite side to the optical fiber 10 side. That is, the first light detection unit 14 is disposed upstream of the first cladding mode stripper 15 in the propagation direction of the light from the light source 5, and the second light detection unit 24 is a light source than the second cladding mode stripper 25. It is arranged downstream of the propagation direction of light from 5. Preferably, the first light detection unit 14 and the second light detection unit 24 are disposed apart from the first cladding mode stripper 15 and the second cladding mode stripper 25, respectively. By arranging the first light detection unit 14 and the second light detection unit 24 separately from the first cladding mode stripper 15 and the second cladding mode stripper 25, the first light detection unit 14 and the second light detection unit 24 can be provided. The influence of the heat generated in the first cladding mode stripper 15 and the second cladding mode stripper 25 can be suppressed. The first light detection unit 14 and the second light detection unit 24 each include, for example, a photodiode.

  The first AD converter 16 is a part that AD-converts the signal from the first light detector 14 and sends it to the calculator 40. The second AD converter 26 is a part that AD-converts the signal from the second light detector 24 and sends it to the calculator 40.

  The calculation unit 40 performs calculation based on the detection result of the first light detection unit 14 sent via the first AD conversion unit 16 and the detection result of the second light detection unit 24 sent via the second AD conversion unit 26. As described later, it is a part for estimating the intensity of light propagating through the first core 11 and the intensity of light propagating through the second core 21.

  The control unit CP shown in FIG. 1 is a part that controls the light source 5 based on the signal from the calculation unit 40 as described later.

  Next, the operation and action of the laser device 1 and the light detection device 2 of the present embodiment will be described.

  First, when excitation light is emitted from each of the laser diodes 51 of the excitation light source 50, the excitation light is incident on the inner cladding of the amplification optical fiber 55 through the inner cladding of the optical fiber 54. The excitation light incident on the inner cladding of the amplification optical fiber 55 mainly propagates through the inner cladding of the amplification optical fiber 55, and the active element added to the core when passing through the core of the amplification optical fiber 55 Excite. The activated element in the excited state emits spontaneous emission light of a specific wavelength. For example, when the active element is ytterbium, the spontaneous emission light at this time is light including a wavelength of 1090 nm and having a certain wavelength band. The spontaneous emission light propagates through the core of the amplification optical fiber 55, light of a part of the wavelength is reflected by the first FBG 57, and of the reflected light, light of the wavelength reflected by the second FBG 58 is reflected by the second FBG 58 And reciprocate in the resonator. Then, when the light reflected by the first FBG 57 and the second FBG 58 propagates through the core of the amplification optical fiber 55, stimulated emission occurs and this light is amplified, and when the gain and loss in the resonator become equal, the laser It becomes oscillation state. Then, a part of the light resonating between the first FBG 57 and the second FBG 58 is transmitted through the second FBG 58 and emitted through the first optical fiber 10 and the second optical fiber 20. The light emitted from the second optical fiber 20 is irradiated to the object to be processed or the like. In addition, a part of the light irradiated to the processing object or the like may be reflected on the surface of the processing object or the like, and a part of the reflected light may return to the second optical fiber 20. The light thus reflected back to the second optical fiber 20 propagates in the second optical fiber 20 in the reverse direction.

The light emitted from the light source 5 and propagating in the forward direction through the first optical fiber 10 and the second optical fiber 20 mainly propagates through the first core 11 and the second core 21. As described above, in the first core 11, light of the fundamental mode propagates with higher energy than light of the higher mode, and in the second core 21, light can propagate in the multimode. Therefore, the light propagating in the forward direction is suppressed from loss at the connection portion 30 and enters the first core 11 to the second core 21. Therefore, the loss of the light propagating in the forward direction in the first core 11 at the connection 30 is ignored, and the intensity of the light propagating in the forward direction in the first core 11 is propagated in the backward direction by Pf and the second core 21. Assuming that the intensity of light is Pr, the intensity M2 of light obtained from Rayleigh scattering detected by the second light detection unit 24 can be expressed by the following equation (1).
M2 = Pf + Pr (1)

Also, as described above, the light returning to the second optical fiber 20 tends to be coupled into the multimode in the second core 21. In general, at the connection between optical fibers, light of a higher mode is more likely to be cladding mode light than light of a fundamental mode. For this reason, in the connection portion 30 between the first optical fiber 10 and the second optical fiber 20, light propagating in the reverse direction is likely to become cladding mode light than light propagating in the forward direction. Therefore, at least a part of the light propagating in the second core 21 in the reverse direction is likely to be incident on the first cladding 12 at the connection portion 30. At least a portion of cladding mode light that is incident on the first cladding 12 and propagates through the first cladding 12 is emitted to the outside of the first optical fiber in the first cladding mode stripper 15. Thus, the light incident from the second core 21 to the first core 11 is a part of the light propagating in the second core 21 in the opposite direction. Assuming that the ratio of light incident on the first core 11 to light propagating in the second core 21 in the reverse direction is α, the intensity M1 of light obtained from Rayleigh scattering detected by the first light detection unit 14 is It can be represented by (2). That is, the intensity of light propagating in the opposite direction in the first core 11 can be set as αPr.
M1 = Pf + αPr (2)

The detection results of the first light detection unit 14 and the second light detection unit 24 are input to the calculation unit 40 via the first AD conversion unit 16 and the second AD conversion unit 26, and the calculation unit 40 calculates the above equation (1), The calculation of (2) is performed. Further, from the above equations (1) and (2), the intensity Pf of light propagating in the first core 11 in the forward direction and the intensity Pr of light propagating in the second core 21 in the reverse direction have the following equations (3), It is asked like 4).
Pr = (M2-M1) / (1-.alpha.) (3)
Pf = (αM2-M1) / (α-1) (4)

Further, in the case of considering the connection loss of light propagating in both directions at the connection portion between the first core 11 and the second core 21, the intensity M 1 of light obtained from Rayleigh scattering detected by the first light detection unit 14 The light intensity M2 obtained from Rayleigh scattering detected by the second light detection unit 24 can be expressed by the following equations (5) and (6), respectively. Here, β is a ratio of light propagating in the forward direction in the first core 11 to the second core 21 and reaching the position detected by the second light detection unit 24, and γ is It is a ratio of the light which is incident on the first core 11 and reaches the position detected by the first light detection unit 14 out of the light propagating in the opposite direction in the two cores 21. That is, the intensity of light in the reverse direction propagating through the first core 11 can be denoted by γPr, and the intensity of light in the forward direction propagating through the second core 21 can be denoted by βPf.
M1 = Pf + γPr (5)
M2 = βPf + Pr (6)

From the above equations (5) and (6), the intensity Pf of light propagating in the first core 11 in the forward direction and the intensity Pr of light propagating in the second core 21 in the reverse direction have the following equations (7) and (7) It is asked like 8).
Pr = (γM2-M1) / (γβ-1) (7)
Pf = (. Beta.M1-M2) / (. Gamma..beta.-1) (8)

  The β and γ can be determined in advance by performing a test for propagating light in the forward direction and the reverse direction to the first optical fiber 10 and the second optical fiber 20, respectively. Specifically, first, the first optical fiber 10 and the second optical fiber 20 are connected, and a calorimeter for measuring the energy of light emitted from the downstream end surface of the second optical fiber 20 is disposed. Then, when light is propagated in the forward direction from the upstream side of the first optical fiber 10, Pf, M1, and M2 of the above equation (8) are determined by the calorimeter, the first light detection unit 14 and the second light detection unit 24. Be In addition, a calorimeter for measuring the energy of light emitted from the end face on the upstream side of the first optical fiber 10 is disposed, and light is propagated from the downstream side of the second optical fiber 20 in the reverse direction. The light detection unit 14 and the second light detection unit 24 obtain Pr, M1, and M2 of the above-mentioned formula (7). From these results, β and γ can be obtained.

  After the intensity Pf of light in the forward direction and the intensity Pr of light in the reverse direction are determined by the calculation unit 40 as described above, the controller CP performs predetermined control on the laser device 1 based on the calculation result. be able to. For example, control is performed to adjust the output from the light source 5 according to the light intensity Pf in the forward direction, or the laser light emitted from the laser device 1 is stopped when the light intensity Pf in the reverse direction exceeds the allowable value. Control can be performed.

  As described above, in the light detection device 2 of the present embodiment, the second core 21 propagates light of a higher order mode than the light propagating through the first core 11. Generally, light of higher order mode tends to have higher energy at a position outside the center of the core than light of lower order mode, so it tends to become clad mode light at the connection between optical fibers. Therefore, the light propagating in the reverse direction from the second core 21 to the first core 11 side is compared with the light propagating in the forward direction from the first core 11 to the second core 21 with the first optical fiber 10 and It is easy to become cladding mode light at the connection portion 30 with the second optical fiber 20. Thus, at least a part of the light propagating as the cladding mode light and propagating through the first cladding 12 is emitted to the outside of the first optical fiber 10 in the first cladding mode stripper 15. Therefore, the detection result of the first light detection unit 14 disposed upstream of the first cladding mode stripper 15 and the detection result of the second light detection unit 24 disposed downstream of the first cladding mode stripper 15 at least A difference in the amount of light emitted by the one clad mode stripper 15 occurs. The magnitude of this difference depends at least on the intensity of light propagating backward in the second core 21. Therefore, using the difference between the detection result of the first light detection unit 14 and the detection result of the second light detection unit 24, it is possible to estimate the intensity of light propagating in the second core 21 in the reverse direction. . Further, in the light detection device 2 of the present embodiment, the first light detection unit 14 detects Rayleigh scattering of light propagating in the first optical fiber 10 in two directions, and the second light detection unit 24 detects the second light fiber 20. Detects Rayleigh scattering of light propagating in two directions. Here, by estimating the intensity of light propagating in the reverse direction as described above, the intensity of light propagating in the forward direction is also estimated from the detection result of the first light detection unit 14 or the second light detection unit 24. You can also Furthermore, in the light detection device 2 of the present embodiment, the first light detection unit 14 and the second light detection unit 24 each detect Rayleigh scattering. For this reason, compared with the case of detecting leaked light as in the fiber laser device described in Patent Document 1, even if the intensity of light propagating through the optical fiber is high, it is estimated from the detection result and the detection result. The linearity of the relationship with the intensity of light propagating through the optical fiber can be maintained. Therefore, the light detection device 2 of the present embodiment can improve the detection accuracy of the intensity of each light propagating in both directions of the optical fiber.

  Further, in the light detection device 2 of the present embodiment, the first light detection unit 14 is disposed upstream of the first cladding mode stripper 15 in the propagation direction of the light from the light source 5, and the second light detection unit 24 is And the second cladding mode stripper 25 is disposed downstream of the propagation direction of light from the light source 5. By thus arranging the first light detection unit 14, the second light detection unit 24, the first cladding mode stripper 15, and the second cladding mode stripper 25, at least cladding mode light propagating from the upstream side to the downstream side is generated. A part is emitted to the outside of the second optical fiber 20 in the second cladding mode stripper 25 before the second light detection unit 24. Further, at least a part of the cladding mode light propagating from the downstream side to the upstream side is emitted to the outside of the first optical fiber 10 in the first cladding mode stripper 15 before the first light detection unit 14. Therefore, the first light detection unit 14 can detect the intensity of light propagating through the first core 11 more accurately, and the second light detection unit 24 more accurately determines the intensity of light propagating through the second core 21. Can be detected.

  Further, in the light detection device 2 of the present embodiment, the first core 11 and the second core 21 are not doped with the dopant, so that the concentration distribution of the dopant causes the first light detector 14 and the second light detector 24 to be formed. It can be suppressed that an error occurs in the detection result in

  Further, in the light detection device 2 of the present embodiment, the first cladding 12 is covered with the low refractive index resin layer 31 from the connection portion 30 between the first optical fiber 10 and the second optical fiber 20 to the first cladding mode stripper 15. It is done. By covering the first cladding 12 with the low refractive index resin layer 31 as described above, the clad mode light propagating in the reverse direction generated at the connection portion 30 is prevented from leaking in the vicinity of the connection portion 30, and the first cladding It can propagate to the mode stripper 15. Further, in the light detection device 2 of the present embodiment, the second cladding 22 is coated with the low refractive index resin layer 31 also from the connection portion 30 to the second cladding mode stripper 25. By covering the second cladding 22 with the low refractive index resin layer 31 in this manner, leakage of cladding mode light propagating in the forward direction generated at the connection portion 30 in the vicinity of the connection portion 30 is suppressed, and the second cladding It can propagate to the mode stripper 25. By suppressing light leakage in the vicinity of the connection portion 30 as described above, heat generation in the vicinity of the connection portion 30 can be suppressed, and a change in the amount of light loss in the connection portion 30 can be suppressed. Thus, the light intensity can be detected more accurately in the first light detection unit 14 and the second light detection unit 24.

  Further, in the light detection device 2 of the present embodiment, the mode scrambler unit 35 is formed in the second optical fiber 20, and light propagating in a multimode in the second core 21 is scattered. Therefore, the difference in the energy density distribution of the propagating light can be reduced in the second core 21. Therefore, at the connection portion between the second core 21 and the first core 11, the difference in the amount of loss due to the angle of the propagating light can be reduced. Thus, variations in detection results of the first light detection unit 14 and the second light detection unit 24 can be suppressed.

  In addition, the laser device 1 of the present embodiment includes the light detection device 2, and the light source 5 that emits light propagating through the first optical fiber 10 and the second optical fiber 20. As described above, according to the light detection device 2, the detection accuracy of the intensity of each light propagating in both directions of the optical fiber can be improved. Therefore, according to the laser device 1 including the light detection device 2, the accuracy of control based on the intensity of light propagating through the optical fiber can be improved.

  The embodiments of the present invention have been described above by way of example, but the present invention is not limited to these. For example, in the above embodiment, the second optical fiber 20 is described as being disposed downstream of the first optical fiber 10, but the second optical fiber 20 is disposed upstream of the first optical fiber 10. It may be arranged. However, the second optical fiber 20 that propagates the light of the high-order mode from the first optical fiber 10 is disposed downstream of the first optical fiber 10, whereby the first optical fiber 10 to the second optical fiber 20 side It is suitable when light of low order mode, such as a fundamental mode, is emitted from a light source which emits light propagating to the light source. Since the second optical fiber 20 is disposed downstream of the first optical fiber 10, the light of the low order mode emitted from the light source 5 has a low loss from the first optical fiber 10 to the second optical fiber 20. It can be propagated. On the other hand, the reflected light propagating to the opposite side to the propagation direction of the light emitted from the light source 5 is likely to include light of the high-order mode. Therefore, light of a higher order mode of the reflected light can be made into cladding mode light at the connection portion between the second optical fiber 20 and the first optical fiber 10 and emitted by the first cladding mode stripper 15.

  Moreover, although the said embodiment gave and demonstrated the example in which the 2nd clad mode stripper 25 is provided in the 2nd optical fiber 20, the 2nd clad mode stripper 25 is not an essential structure. However, by providing the second cladding mode stripper 25 in the second optical fiber 20, the intensity of light propagating through the optical fiber can be detected more accurately as described below. When cladding mode light propagating backward in the second cladding 22 is not removed, at least a portion of cladding mode light propagating from the second cladding 22 toward the first cladding 12 may propagate in the first cladding 12. Therefore, by providing the second cladding mode stripper 25 in the second optical fiber 20, cladding mode light propagating in the reverse direction in the second cladding 22 is reduced, and a cladding propagating in the reverse direction in the first cladding 12 Mode light may also be reduced. Thus, the clad mode light propagating in the opposite direction in the first clad 12 is reduced, whereby the influence of the clad mode light on the first light detector 14 is suppressed, and the first light detector 14 The intensity of light propagating in the optical fiber 10 can be detected more accurately. In addition, when cladding mode light propagates in the forward direction through the first cladding 12, at least a portion of the cladding mode light can propagate in the forward direction through the second cladding 22. By providing the second cladding mode stripper 25, cladding mode light that propagates in the forward direction of the second cladding 22 can also be reduced.

  Further, as shown in FIG. 3, another cladding mode stripper 25 a may be provided downstream of the second light detection unit 24. FIG. 3 is a cross-sectional view schematically showing a part of a light detection device 2a according to a modification of the present invention. In this modification, the same reference numerals are given to the same components as those in the above embodiment, and the detailed description will be omitted. Some of the reflected light emitted from the second optical fiber 20 and returned to the second optical fiber 20 may become cladding mode light. By providing another cladding mode stripper 25 a also downstream of the second light detection unit 24, cladding mode light resulting from such reflected light can be removed before the second light detection unit 24. The accuracy of the detection result of the two light detection unit 24 can be further improved.

  In the above embodiment, the first light detection unit 14 is provided on the outer side of the first optical fiber 10 and the second light detection unit 24 is provided on the outer side of the second optical fiber 20. The invention is not limited to this form. FIG. 4 is a cross-sectional view schematically showing a part of a light detection device 2b according to another modification of the present invention. In this modification, the same reference numerals are given to the same components as those in the above embodiment, and the detailed description will be omitted. The first light detection unit 14 and the second light detection unit 24 may be disposed so as to sandwich the first cladding mode stripper 15, and as shown in FIG. 4, the first light detection unit 14 and the second light detection unit 24. May be provided outside the first optical fiber 10. However, it is preferable that the first light detection unit 14 and the second light detection unit 24 be disposed with the connection portion 30 between the first optical fiber 10 and the second optical fiber 20 interposed therebetween as in the above embodiment. As described above, in the light detection device 2, the first light detection caused by the first cladding mode stripper 15 removing the cladding mode light generated at the connection portion 30 between the first optical fiber 10 and the second optical fiber 20. The difference between the detection result of the unit 14 and the detection result of the second light detection unit 24 is used. By the way, since there is a difference in the concentration of the additive between the cladding and the core, the ratio of Rayleigh scattering differs between the light propagating through the core and the light propagating through the cladding. Therefore, it is preferable that the first light detection unit 14 and the second light detection unit 24 detect Rayleigh scattering of light propagating through either the core or the clad. Here, since the second core 21 propagates light of a higher order mode than the first core 11, the loss of light propagating from the first core 11 to the second core 21 at the connection portion 30 is suppressed. The second core 21 is propagated. On the other hand, at least a part of the light propagating from the second core 21 to the first core 11 side enters the first cladding 12 at the connection portion 30 as described above. As described above, at least a portion of the light incident on the first cladding 12 is emitted to the outside in the first cladding mode stripper 15 before the first light detection unit 14. Accordingly, by arranging the first light detection unit 14 and the second light detection unit 24 with the connection unit 30 interposed therebetween, the first light detection unit 14 mainly performs Rayleigh scattering of light propagating through the first core 11. The second light detection unit 24 mainly detects Rayleigh scattering of light propagating through the second core 21. As described above, the first light detection unit 14 and the second light detection unit 24 mainly detect the Rayleigh scattering of the light propagating in the core, thereby detecting the intensity of the light propagating in both directions of the optical fiber. Can be further improved.

  Moreover, although the said embodiment demonstrated that only the 2nd core 21 propagates the light of a higher-order mode than the light which propagates the 1st core 11, the 1st optical fiber 10 may be a single mode fiber. Since the first optical fiber 10 is a single mode fiber, the light propagating as multi mode light as described above from the second optical fiber 20 to the first optical fiber 10 is the first optical fiber 10 and the first optical fiber 10. In the connection portion 30 with the two optical fibers 20, it becomes easier to become cladding mode light. Therefore, the difference between the detection result of the first light detection unit 14 and the detection result of the second light detection unit 24 tends to be large, and the detection accuracy of each light propagating in both directions of the optical fiber is further improved. obtain.

  In the above embodiment, the outer diameter of the first cladding 12 and the outer diameter of the second cladding 22 are described as being equal to each other, but the outer diameter of the first cladding 12 and the outer diameter of the second cladding 22 May be different from one another. However, when the outer diameter of the first cladding 12 and the outer diameter of the second cladding 22 are equal to each other, the loss of light at the connection portion 30 between the first optical fiber 10 and the second optical fiber 20 can be suppressed.

  Moreover, although the said embodiment gave and demonstrated the example which the dopant is not added to the 1st core 11 and the 2nd core 21, in the 1st core 11 and the 2nd core 21, the dopant which raises refractive indexes, such as germanium, etc. Etc. may be added.

  Moreover, although the said embodiment gave and demonstrated the example which the mode scrambler part 35 is provided in the 2nd optical fiber 20, the mode scrambler part 35 is not an essential structure. Further, when the mode scrambler unit 35 is provided, the mode scrambler unit 35 is not limited to the form of bending the optical fiber annularly as in the above embodiment, for example, by bending the optical fiber into a spiral or wavy line A scrambler unit 35 may be formed.

  In the above embodiment, the light source 5 is described as an example of a resonator-type fiber laser device. However, the light source 5 may be another fiber laser device or a solid-state laser device. When the light source 5 is a fiber laser device, it may be a MO-PA (Master Oscillator Power Amplifier) type fiber laser device. Further, the number of light sources 5 is not particularly limited as long as at least one light source 5 is provided.

  As described above, according to the present invention, the light detection device and the laser device capable of improving the detection accuracy of light propagating in both directions of the optical fiber are provided, and used in the field such as fiber laser device and optical fiber communication. It is expected to do.

DESCRIPTION OF SYMBOLS 1 ... Laser apparatus 2, 2, 2a, 2b ... Light detection apparatus 5 ... Light source 10 ... 1st optical fiber 11 ... 1st core 12 ... 1st clad 14 ... 1st Light detection unit 15 First clad mode stripper 16 First AD conversion unit 20 Second optical fiber 21 Second core 22 Second cladding 24 Second light detection Section 25 second clad mode stripper 26 second AD conversion section 30 connection section 31 low refractive index resin layer 35 mode scrambler section 40 calculation section CP. · Control unit

Claims (11)

A first optical fiber having a first core and a first cladding surrounding the first core;
A second optical fiber having a second core connected to the first core and a second cladding surrounding the second core;
A first cladding mode stripper provided outside the first cladding;
A first light detection unit disposed on one side of the first cladding mode stripper in the longitudinal direction of the first optical fiber to detect Rayleigh scattering of light propagating through the first optical fiber;
A second light detection unit disposed on the other side of the first cladding mode stripper in the longitudinal direction of the first optical fiber to detect Rayleigh scattering of light propagating through the first optical fiber or the second optical fiber;
Equipped with
The diameter of the first core and the diameter of the second core are equal to each other,
The light detection device according to claim 1, wherein the second core propagates light of a higher order mode than light propagating through the first core. The second optical fiber is disposed downstream of the first optical fiber in the propagation direction of light from a light source that emits light propagating in the first optical fiber,
The first light detection unit is disposed upstream of the first cladding mode stripper in the propagation direction of light from the light source.
2. The light detection device according to claim 1, wherein the second light detection unit is disposed downstream of the first cladding mode stripper in the propagation direction of light from the light source. The light detection device according to claim 1, wherein the first optical fiber is a single mode fiber. The light detection device according to any one of claims 1 to 3, wherein a second cladding mode stripper is provided outside the second cladding. In the longitudinal direction of the first optical fiber and the second optical fiber, the first light detection unit and the second light detection unit are disposed across the connection portion between the first optical fiber and the second optical fiber. And
The light detection device according to any one of claims 1 to 4, wherein the second light detection unit detects Rayleigh scattering of light propagating through the second optical fiber. The light according to claim 5, wherein the second light detection unit is disposed on the side opposite to the first optical fiber side with respect to a second cladding mode stripper provided outside the second cladding. Detection device. The light detection device according to any one of claims 1 to 6, wherein a dopant is not added to the first core and the second core. The first cladding is covered with a low refractive index resin having a refractive index lower than that of the first cladding from the connection portion between the first optical fiber and the second optical fiber to the first cladding mode stripper. The light detection device according to any one of claims 1 to 7, wherein The light detection device according to any one of claims 1 to 8, wherein an outer diameter of the first cladding and an outer diameter of the second cladding are equal to each other. The light detection apparatus according to any one of claims 1 to 9, further comprising a mode scrambler unit configured to reduce an energy difference between light of respective modes propagating in the second core. The light detection device according to any one of claims 1 to 10.
At least one light source for emitting light propagating in the first optical fiber and the second optical fiber;
A laser apparatus comprising:

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