WO2020027184A1

WO2020027184A1 - Light detecting device, and laser device

Info

Publication number: WO2020027184A1
Application number: PCT/JP2019/029971
Authority: WO
Inventors: 真一阪本; 航清山
Original assignee: 株式会社フジクラ
Priority date: 2018-07-31
Filing date: 2019-07-31
Publication date: 2020-02-06
Also published as: JP2020020652A; JP6644839B2

Abstract

A light detecting device (2) is provided with: a first cladding mode stripper (21) and a second cladding mode stripper (22) provided in an optical fiber, with a prescribed spacing therebetween; a first light detector (31) for detecting the intensity of light leaking from the optical fiber (10) between the first cladding mode stripper (21) and the second cladding mode stripper (22); and a second light detector (32) for detecting the intensity of light leaking from the optical fiber (10) on the opposite side to the first cladding mode stripper (21) side of the second cladding mode stripper (22).

Description

Photodetector and laser device

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

Fiber laser devices are used in various fields, such as laser processing and medical fields, because of their excellent light-collecting properties, high power density, and the ability to provide light with a small beam spot. In order to realize good processing quality with such a highly efficient laser device, it is required to detect the intensity of light propagating through an optical fiber. It is also known that light emitted from a fiber laser device is reflected by a processing body, reenters from a light emission port, and propagates in an optical fiber in a reverse direction. If the intensity of light propagating in the opposite direction in the optical fiber is high, the light source may be damaged, so the fiber laser device may be provided with an interlock mechanism that stops the operation of the device when the light is strong. There is. In this case, it is required to detect the intensity of light propagating in the optical fiber in the opposite direction.

For example, in Patent Document 1 below, after removing clad light propagating in the clad, a part of the light propagating in the core is leaked to the clad, and the light leaked from the core to the clad further reduces the light leaked from the clad. By detecting, the intensity of light propagating through the optical fiber is detected. By detecting such light, the intensity of light propagating in a predetermined direction through the optical fiber can be monitored.

JP-A-2017-21099

では In the fiber laser device described in Patent Document 1, the clad light is removed as described above. However, for example, the above reflected light tends to enter each of the core and the clad of the optical fiber and propagate through the core and the clad. As described above, when the reflected light propagates between the core and the clad, the amount of light propagating through the clad tends to be larger than the amount of light propagating through the core due to the difference in cross-sectional area between the core and the clad. For this reason, there is a demand to monitor the intensity of light propagating in a predetermined direction through the clad.

Therefore, an object of the present invention is to provide a photodetector capable of detecting the intensity of light propagating in a predetermined direction through a clad, and a laser device including the photodetector.

In order to solve the above problems, a photodetector according to the present invention comprises a first clad mode stripper and a second clad mode stripper provided on an optical fiber at predetermined intervals, the first clad mode stripper and the second clad mode stripper. A first photodetector for detecting the intensity of light leaking from the optical fiber between the first stripper and a mode stripper; and a light detector on a side opposite to the first clad mode stripper with respect to the second clad mode stripper. A second photodetector for detecting the intensity of light leaking from the fiber.

When the first cladding mode stripper is provided on one side of the optical fiber and the second cladding mode stripper is provided on the other side of the optical fiber at a predetermined interval, the light propagating through the cladding of the optical fiber from one side to the other side. Is absorbed by the first cladding mode stripper, and the light propagating through the cladding of the optical fiber from the other side to the one side is absorbed by the second cladding mode stripper. Therefore, between the first cladding mode stripper and the second cladding mode stripper of the optical fiber, light propagation in the cladding is suppressed. However, in this section, light can propagate through the core from one side to the other and from the other side to the one side. In other words, the first photodetector arranged in this section detects the intensity of light that leaks from the optical fiber as a part of the light propagating through the core of the optical fiber. Also, on the side opposite to the first cladding mode stripper side with respect to the second cladding mode stripper, that is, at the position where the second photodetector is provided, light can propagate the cladding from the other side to one side, and The core may propagate from one side to the other and from the other side to the one side. For this reason, the second photodetector detects the intensity of light in which a part of the light leaks from the optical fiber. That is, the difference between the intensity of the light detected by the first photodetector and the intensity of the light detected by the second photodetector is the difference between the light leaking from the optical fiber and the light propagating from the other side to the one side through the clad. Strength. The intensity of light propagating through the optical fiber has a correlation with the intensity of light leaking from the optical fiber. Therefore, the intensity of light propagating from the other side to the one side through the clad can be detected using the intensity of light detected by the first photodetector and the intensity of light detected by the second photodetector. Thus, according to the photodetector of the present invention, the intensity of light propagating in a predetermined direction through the clad can be detected.

Preferably, the photodetector further includes a subtractor for calculating a difference between the intensity of light detected by the first photodetector and the intensity of light detected by the second photodetector.

As described above, the difference between the intensity of the light detected by the first photodetector and the intensity of the light detected by the second photodetector is due to the fact that the light propagating from the other side to the one side of the cladding from the optical fiber. It becomes the intensity of the leaked light. Therefore, the intensity of the leaked light can be calculated by the subtracter, and the intensity of the light propagating from the other side to the one side through the clad can be obtained.

Further, the photodetector includes a signal output from the first photodetector, the signal indicating the intensity of light detected by the first photodetector, and the second photodetector output from the second photodetector. It is preferable to further include an adjusting unit that adjusts the level of at least one of the signals indicating the intensity of the light to be detected.

Generally, a photodetector is composed of a photodiode (PD) or the like. If there is an error in attaching the photodetector to the optical fiber, an error occurs in the intensity of light detected by the photodetector. Therefore, as described above, the adjustment unit adjusts at least one of a signal indicating the intensity of light detected by the first photodetector and a signal indicating the intensity of light detected by the second photodetector. This makes it possible to adjust the balance between the intensity of light detected by the first photodetector and the intensity of light detected by the second photodetector.

Preferably, at least one of the first photodetector and the second photodetector is thermally separated from the first cladding mode stripper and the second cladding mode stripper.

一般 General photodetectors such as photodiodes tend to have errors in the intensity of light detected due to the influence of heat. Therefore, the photodetector is more accurate than the case where the clad mode stripper and the photodetector are not thermally separated by thermally separating the cladding mode stripper and the photodetector that tend to generate heat. The intensity of light can be detected.

Further, a laser device according to the present invention includes the optical fiber, the light detection device according to any one of the above, and at least one light source that emits light propagating through the optical fiber. It is.

Such a laser device can perform an operation corresponding to the intensity of light by detecting the intensity of light propagating in a predetermined direction through the cladding of the optical fiber.

In the laser device, it is preferable that the second photodetector is disposed closer to the emission end of the optical fiber than the first photodetector.

In this case, of the light emitted from the laser device, reflected by the workpiece, and propagated in the optical fiber in the opposite direction, the intensity of the light propagated through the clad can be detected. Therefore, the interlock mechanism or the like can be operated when the intensity of light propagating through the clad is equal to or higher than a predetermined intensity. Normally, the reflected light also propagates through the core of the optical fiber. Therefore, by detecting the intensity of light propagating through the clad, the intensity of light propagating in the core in the opposite direction can also be estimated. The interlock mechanism or the like may be operated when the intensity of the light propagating in the reverse direction through the core in this way is equal to or higher than a predetermined intensity.

Further, the laser device further includes a control unit connected to the first photodetector and the second photodetector, wherein the control unit outputs the first photodetector output from the first photodetector. The operation of the light source may be controlled based on a signal indicating the light intensity detected by the second light detector and a signal indicating the light intensity detected by the second light detector output from the second light detector.

A signal output from the first photodetector and indicating the intensity of light detected by the first photodetector, and a signal output from the second photodetector and indicating the intensity of light detected by the second photodetector. When controlling the operation of the light source based on the above, the control unit, the intensity of light propagating through the cladding of the optical fiber from the second photodetector side toward the first photodetector side is a predetermined value In the case described above, the operation of the light source may be stopped.

In this way, the interlock operation for stopping the laser beam emitted from the laser device can be effectively performed.

Further, the control unit may determine a signal indicating the intensity of the light detected by the first photodetector output from the first photodetector and an intensity of the light detected by the second photodetector output from the second photodetector. When controlling the operation of the light source on the basis of the signal indicated by the control signal, the control unit determines that the intensity of light propagating through the clad of the optical fiber from the second photodetector side toward the first photodetector side is predetermined. When the value is not less than the value, the intensity of light emitted from the light source may be reduced.

にする By doing so, the intensity of the laser light emitted from the laser device can be effectively reduced.

As described above, according to the present invention, there is provided a photodetector capable of detecting the intensity of light propagating in a predetermined direction through a clad, and a laser device including the photodetector.

It is a figure showing roughly composition of a laser device concerning an embodiment of the present invention. FIG. 2 is a diagram schematically illustrating the photodetector illustrated in FIG. 1.

Hereinafter, preferred embodiments of the photodetector and the laser device according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for the purpose of facilitating the understanding of the present invention, and are not intended to limit the present invention. Therefore, the present invention can be modified and improved from the following embodiments without departing from the gist thereof. Note that, for easy understanding, the scale described in each drawing may be different from the scale described in the following description.

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

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 optical fiber 56 and a second FBG 58 provided on the optical fiber 56 are provided as main components. Further, a resonator is constituted by the amplification optical fiber 55, the first FBG 57, and the second FBG 58.

The pump 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-based semiconductor and emits pump light having a center wavelength of 915 nm. I do. Further, 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 includes, as main components, a core, an inner clad surrounding the outer peripheral surface of the core without any gap, an outer clad covering the outer peripheral surface of the inner clad, and a coating layer covering the outer clad. 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. Examples of a material constituting the core of the amplification optical fiber 55 include an element such as germanium (Ge) for increasing the refractive index, and ytterbium (Yb) excited by the excitation light emitted from the excitation light source 50. Quartz to which an active element is added can be given. As a material constituting the inner cladding of the amplification optical fiber 55, for example, pure quartz to which no dopant is added can be given. Note that 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 is, for example, an ultraviolet curable resin, and the quartz is, 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. Is added. Examples of the material constituting the coating layer of the amplification optical fiber 55 include an ultraviolet curable resin and a thermosetting resin. When the outer clad is a resin, an ultraviolet curable resin different from the resin constituting the outer clad is used. And thermosetting resins.

The optical fiber 54 connected to one side of the amplification optical fiber 55 includes a core to which an active element is not added, an inner cladding surrounding the outer peripheral surface of the core without any gap, and an outer cladding covering the outer peripheral surface of the inner cladding. A clad and a coating layer for covering the outer clad are mainly provided. The core of the optical fiber 54 has substantially the same configuration as the core of the amplification optical fiber 55 except that no active element is 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, a first FBG 57 as a first mirror is provided in the core of the optical fiber 54. Thus, the first FBG 57 is provided on one side of the amplification optical fiber 55. In the first FBG 57, a portion where the refractive index is periodically increased along the longitudinal direction of the optical fiber 54 is repeated, and by adjusting this period, the active element of the amplification optical fiber 55 in the excited state is adjusted. Are configured to reflect at least some wavelengths of the light emitted by the. The reflectance of the first FBG 57 is higher than the reflectance of a second FBG 58 described later, and it is preferable that 90% or more of the light emitted by the active element is reflected at a desired wavelength, more preferably 99% or more. preferable. The wavelength of the 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 includes a core to which the active element is not added, a clad surrounding the outer peripheral surface of the core without any gap, and a coating layer covering the outer peripheral surface of the clad. Is provided as a main configuration. The core of the optical fiber 56 has substantially the same configuration as the core of the amplification optical fiber 55 except that no active element is added. The core 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. In the core of the optical fiber 56, a second FBG 58 as a second mirror is provided. Thus, the second FBG 58 is provided on the other side of the amplification optical fiber 55. In the second FBG 58, a portion having a high refractive index is repeated at a constant period along the longitudinal direction of the optical fiber 56, and at least a part of the light reflected by the first FBG 57 has a lower wavelength than the first FBG 57. It is configured to reflect at a reflectance. The second FBG 58 preferably reflects at least some wavelengths of the light reflected by the first FBG 57 at a reflectance of 5% to 50%, 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 pumping light emitted from each laser diode 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 view schematically showing a part of the photodetector 2 shown in FIG. As shown in FIGS. 1 and 2, a photodetector 2 of the present embodiment includes an optical fiber 10, a first cladding mode stripper 21, a second cladding mode stripper 22, a first photodetector 31, and a second photodetector. 32, a first level adjustment unit 33, a second level adjustment unit 34, and a subtractor 40 as main components.

The optical fiber 10 has a core 11, a cladding 12 surrounding the core 11, and a coating layer 13 surrounding the cladding 12, and is connected to an end of the optical fiber 56 opposite to the amplification optical fiber 55 side. The core 11 has the same configuration as the core of the optical fiber 56, and the clad 12 is made of a material having a lower refractive index than the core 11. The coating layer 13 is made of a material having a lower refractive index than the cladding 12. As a material constituting the coating layer 13, for example, an ultraviolet curable resin can be used. The optical fiber 56 may be extended and the optical fiber 10 may be a part of the optical fiber 56.

The first cladding mode stripper 21 is provided outside the cladding 12 of the optical fiber 10. The first cladding mode stripper 21 is not particularly limited as long as it is configured to emit cladding mode light propagating in the cladding 12 to the outside of the optical fiber 10. The first cladding mode stripper 21 of the present embodiment is configured by intermittently providing a plurality of high refractive index portions 13h made of a resin having a higher refractive index than the cladding 12 outside the cladding 12.

The second cladding mode stripper 22 is provided outside the cladding 12 of the optical fiber 10 at a predetermined interval from the first cladding mode stripper 21. The second cladding mode stripper 22 is not particularly limited as long as it is configured to emit cladding mode light propagating in the cladding 12 to the outside of the optical fiber 10. In the present embodiment, the second cladding mode stripper 22 has the same configuration as the first cladding mode stripper 21.

{Circle around (1)} The first photodetector 31 is disposed on the side of the optical fiber 10 between the first cladding mode stripper 21 and the second cladding mode stripper 22. That is, the first photodetector 31 is separated from the first cladding mode stripper 21 and the second cladding mode stripper 22, and is shifted from the position facing the first cladding mode stripper 21 in the forward direction, and , From the position facing the second cladding mode stripper 22 in the opposite direction. The first photodetector 31 is disposed at such a position, detects the intensity of light leaking from the optical fiber 10, and outputs a signal corresponding to the detected intensity of light. The light detected by the first photodetector 31 includes light leaking from the optical fiber 10 due to Rayleigh scattering of light propagating through the optical fiber 10. The first photodetector 31 is composed of, for example, a photodiode and outputs a voltage corresponding to the intensity of incident light. In this case, the voltage becomes a signal indicating the intensity of the detected light. When the first photodetector 31 has, for example, a photodiode and an A / D converter, the first photodetector 31 outputs a digital signal indicating the intensity of the detected light.

The second photodetector 32 is disposed on the side of the optical fiber 10 on the side opposite to the first cladding mode stripper 21 side with respect to the second cladding mode stripper 22. That is, the second photodetector 32 is separated from the second cladding mode stripper 22 and is arranged at a position shifted from the position facing the second cladding mode stripper 22 in the forward direction. The second photodetector 32 is disposed at such a position and detects the intensity of light leaking from the optical fiber 10. The light detected by the second photodetector 32 includes light leaking from the optical fiber 10 due to Rayleigh scattering of the light propagating through the optical fiber 10, similarly to the light detected by the first photodetector 31. The second photodetector 32 is formed of, for example, a photodiode, and outputs a voltage corresponding to the intensity of incident light, as in the case of the first photodetector 31. In this case, the voltage becomes a signal indicating the intensity of the detected light. In the case where the second photodetector 32 has, for example, a photodiode and an A / D converter, as in the case of the first photodetector 31, the second photodetector 32 detects the detected light. A digital signal indicating the intensity of the signal is output.

In the present embodiment, the first photodetector 31 and the second photodetector 32 are arranged at a predetermined distance from the optical fiber 10. By forming a space between the first photodetector 31 and the second photodetector 32 and the optical fiber 10 in this manner, the first photodetector 31 and the second photodetector 32 and the optical fiber 10 Are thermally separated. Since the first clad mode stripper 21 and the second clad mode stripper 22 are provided outside the clad of the optical fiber 10, the first optical detector 31, the second optical detector 32, and the optical fiber 10 are thermally connected. By being separated, the first photodetector 31 and the second photodetector 32 are thermally separated from the first clad mode stripper 21 and the second clad mode stripper 22. Note that a light-transmitting and heat-insulating member may be disposed between the first optical detector 31 and the second optical detector 32 and the optical fiber 10. Examples of such a member include air, quartz, and a light-transmitting resin. Even in the configuration in which the heat-insulating member is disposed as described above, the first photodetector 31 and the second photodetector 32 are thermally separated from the first clad mode stripper 21 and the second clad mode stripper 22. Is done. Further, for example, a first heat sink that thermally contacts the first cladding mode stripper 21 and radiates heat generated by the first cladding mode stripper 21 to the outside, and a second heater that thermally contacts the second cladding mode stripper 22. And a second heat radiating plate for radiating heat generated by the second cladding mode stripper 22 to the outside. Even if the first heat radiating plate and the second heat radiating plate are separated from each other, the first light The detector 31 and the second photodetector 32 can be thermally separated from the first cladding mode stripper 21 and the second cladding mode stripper 22. In this case, when the first heat sink and the first clad mode stripper 21 are in contact with each other, and the second heat sink and the second clad mode stripper 22 are in contact with each other, the heat generated by each clad mode stripper is efficiently applied to the heat sink. It is more preferable because it can conduct. The configuration in which the first photodetector 31 and the second photodetector 32 are thermally separated from the first cladding mode stripper 21 and the second cladding mode stripper 22 is not limited to the above.

The first level adjuster 33 outputs a signal of a level having a predetermined relationship with the level of the input signal. Specifically, it outputs a signal of a predetermined multiple of the level of the input signal, or outputs a signal of a level obtained by adding a predetermined level to the level of the input signal. A signal indicating the intensity of light detected by the first photodetector 31 is input to the first level adjustment unit 33. Therefore, when the signal from the first photodetector 31 is a voltage, the first level adjuster 33 outputs, for example, a voltage obtained by applying a predetermined bias to the input voltage. When the signal from the first photodetector 31 is a digital signal, the first level adjuster 33 may be, for example, a predetermined multiple of the intensity of the light detected by the first photodetector 31 indicated by the input digital signal. And outputs a signal indicating the intensity.

The second level adjuster 34 outputs a signal having a predetermined relationship with the level of the input signal, similarly to the first level adjuster 33. A signal indicating the intensity of light detected by the second photodetector 32 is input to the second level adjustment unit 34. Therefore, when the signal from the second photodetector 32 is a voltage, the second level adjustment unit 34 outputs, for example, a voltage obtained by applying a predetermined bias to the input voltage. When the signal from the second photodetector 32 is a digital signal, the second level adjuster 34 may be, for example, a predetermined multiple of the intensity of the light detected by the second photodetector 32 indicated by the input digital signal. And outputs a signal indicating the intensity.

In the present embodiment, a case where light of the same intensity leaks from the optical fiber 10 between the portion of the optical fiber 10 where the first photodetector 31 is provided and the portion of the optical fiber 10 where the second photodetector 32 is provided Then, the first level adjusting unit 33 and the second level adjusting unit 34 are adjusted such that the first level adjusting unit 33 and the second level adjusting unit 34 output signals of the same level. That is, the first clad mode stripper 21 provided with the first photodetector 31 and the second clad mode stripper 22 provided between the first clad mode stripper 22 and the second clad mode stripper 22 provided with the second photodetector 32 are referred to as first and second clad mode strippers. When light of the same intensity propagates through the optical fiber 10 on the side opposite to the cladding mode stripper 21 side, the first level adjusting unit 33 and the second level adjusting unit 34 output signals of the same level. The first level adjuster 33 and the second level adjuster 34 are adjusted. To adjust the first level adjustment unit 33 and the second level adjustment unit 34 in this manner, the following may be performed. That is, light propagates from one side to the other side in the core 11 of the optical fiber 10. At this time, light is prevented from propagating to the cladding 12. Part of the light propagating in the core 11 leaks from the optical fiber 10 through the clad 12 due to Rayleigh scattering. The intensity of the light leaking from the optical fiber 10 varies between the first clad mode stripper 21 where the first photodetector 31 is provided and the second clad mode stripper 22 where the second photodetector 32 is provided. The first clad mode stripper 21 side and the opposite side with respect to the clad mode stripper 22 have substantially the same strength. Therefore, at this time, the first level adjusting unit 33 and the second level adjusting unit 33 are configured so that the level of the signal output from the first level adjusting unit 33 and the level of the signal output from the second level adjusting unit 34 are the same. The level adjuster 34 is adjusted. Thus, the first level adjusting unit 33 and the second level adjusting unit 34 are adjusted so as to output signals of the same level as described above.

The subtractor 40 calculates the difference between the intensity of light detected by the first photodetector 31 and the intensity of light detected by the second photodetector 32. In the present embodiment, the level of the signal indicating the intensity of the light detected by the first photodetector 31 is adjusted by the first level adjustment unit 33, and the level of the signal indicating the intensity of the light detected by the second photodetector 32 is adjusted. Is adjusted by the second level adjusting unit 34. Therefore, in the present embodiment, the subtractor 40 includes a signal indicating the intensity of light detected by the first photodetector 31 whose level has been adjusted, and the second photodetector whose level has been adjusted. The signal indicating the intensity of the light detected by the second photodetector 32 is input to the subtracter 40. Find the difference from the strength. When the signal indicating the light intensity detected by the first photodetector 31 and the second photodetector 32 input to the subtractor 40 is a voltage, the subtractor 40 determines the first photodetector from the voltage difference. A signal indicating the difference between the intensity of the light detected by 31 and the intensity of the light detected by the second photodetector 32 is output. When the signal indicating the intensity of the light detected by the first photodetector 31 and the second photodetector 32 input to the subtractor 40 is a digital signal, the subtractor 40 calculates the first photodetector 31 by calculation. And outputs a signal indicating a difference between the light intensity detected by the second light detector 32 and the light intensity detected by the second photodetector 32. It is preferable that the signal indicating this difference is a digital signal from the viewpoint that the control unit CP easily receives the signal as described later.

When the signals from the first photodetector 31 and the second photodetector 32 are voltages, if necessary, the signal between the first photodetector 31 and the subtractor 40 and the second photodetector An A / D converter may be provided between 32 and the subtractor 40.

The signal output from the subtracter 40 is input to the control unit CP shown in FIG. The control unit CP controls the light source 5. Specifically, the control unit CP controls the excitation light source 50 of the light source 5 to control on / off of each laser diode 51 and the intensity of light emitted from each laser diode 51.

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 the pumping light is emitted from each of the laser diodes 51 of the pumping light source 50, the pumping light enters the inner cladding of the amplification optical fiber 55 via the inner cladding of the optical fiber 54. The pumping 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. To excite. The active element in the excited state emits spontaneous emission light of a specific wavelength. The spontaneous emission light at this time is, for example, light having a certain wavelength band including a wavelength of 1090 nm when the active element is ytterbium. The spontaneous emission light propagates through the core of the amplification optical fiber 55, and 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. Then, it reciprocates in the resonator. 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 the light is amplified. When the gain and the loss in the resonator become equal, the laser is emitted. Oscillation occurs. Some of the light that resonates between the first FBG 57 and the second FBG 58 transmits through the second FBG 58 and propagates in the optical fiber 10 in the forward direction.

The light emitted from the light source 5 and propagating in the optical fiber 10 in the forward direction mainly propagates through the core 11, but leaks at a connection portion of the optical fiber and a part of the light propagates in the clad 12 in the forward direction. There are cases. However, light propagating from the light source 5 side through the clad 12 in the forward direction is absorbed by the first clad mode stripper 21. For this reason, on the side opposite to the light source 5 side with respect to the first clad mode stripper 21, the propagation of light in the clad 12 in the forward direction is suppressed. On the other hand, light propagating in the core 11 in the forward direction is emitted from the optical fiber 10. Light emitted from the optical fiber 10 is applied to a processing target or the like.

By the way, a part of the light irradiated to the processing object or the like is reflected on the surface of the processing object or the like, and a part of the reflected light may return to the optical fiber 10. The light reflected back to the optical fiber 10 in this manner tends to propagate in the opposite direction through the core 11 and the clad 12 of the optical fiber 10. However, light propagating in the opposite direction through the cladding 12 is absorbed by the second cladding mode stripper 22. Therefore, on the light source 5 side of the second clad mode stripper 22, light is prevented from propagating in the reverse direction through the clad 12. On the other hand, the light propagating in the core 11 in the opposite direction propagates toward the light source 5 through the position where each clad mode stripper is provided.

Here, the intensity of light propagating in the core 11 in the forward direction is Pfcore, the intensity of light propagating in the cladding 12 in the forward direction is Pfclad, the intensity of light propagating in the core 11 in the reverse direction is Prcore, and the cladding 12 Is assumed to be Prclad.

As described above, on the side opposite to the light source 5 side with respect to the first cladding mode stripper 21, light is prevented from propagating in the cladding 12 in the forward direction. 12 is prevented from propagating in the opposite direction. Therefore, between the first cladding mode stripper 21 and the second cladding mode stripper 22, light is prevented from propagating through the cladding 12. On the other hand, between the first cladding mode stripper 21 and the second cladding mode stripper 22, light propagates through the core 11 in the forward and reverse directions. Therefore, the intensity P1 of light propagating through the optical fiber 10 between the first cladding mode stripper 21 and the second cladding mode stripper 22 is represented by the following equation (1).
P1 = Pfcore + Prcore (1)

The first photodetector 31 detects the intensity of light leaking from the optical fiber 10 between the first cladding mode stripper 21 and the second cladding mode stripper 22, as described above. As described above, the light leaking from the optical fiber 10 includes the light leaking due to Rayleigh scattering, so that the intensity of the light leaking from the optical fiber 10 and the intensity of the light propagating through the optical fiber 10 are correlated. Therefore, the first photodetector 31 detects the intensity of light correlated with the intensity P1 of light propagating through the optical fiber 10 between the first cladding mode stripper 21 and the second cladding mode stripper 22.

On the side opposite to the light source 5 side with respect to the second cladding mode stripper 22, light can propagate in the cladding 12 in the reverse direction, and light propagates in the core 11 in the forward direction and the reverse direction. Therefore, the intensity P2 of light propagating through the optical fiber 10 on the side opposite to the light source 5 side with respect to the second cladding mode stripper 22 is expressed by the following equation (2).
P2 = Pfcore + Prcore + Prclad (2)

The second photodetector 32 detects the intensity of light leaking from the optical fiber 10 on the side opposite to the first cladding mode stripper 21 with respect to the second cladding mode stripper 22. Accordingly, the second photodetector 32 detects the intensity of light correlated with the intensity P2 of the light propagating through the optical fiber 10 on the side opposite to the first cladding mode stripper 21 with reference to the second cladding mode stripper 22. .

信号 The signals output from the first photodetector 31 and the second photodetector 32 have their levels adjusted by the first level adjuster 33 and the second level adjuster 34 respectively, and are input to the subtractor 40.

In the subtracter 40, as described above, the difference between the light intensity detected by the first light detector 31 and the light intensity detected by the second light detector 32 is obtained. As described above, the first photodetector 31 detects the intensity of light correlated with the intensity P1, and the second photodetector 32 detects the intensity of light correlated with the intensity P2. Therefore, the subtractor 40 obtains a value correlated with the difference between the intensity P1 and the intensity P2. That is, the subtractor 40 obtains an intensity correlated with the intensity Prclad of the light propagating in the opposite direction through the clad 12 of the optical fiber 10. Therefore, the intensity Prclad of light propagating in the opposite direction through the clad 12 can be obtained. The subtractor 40 outputs a signal indicating an intensity correlated with the light intensity Prclad, or a signal indicating the intensity Prclad.

信号 The signal output from the subtractor 40 is input to the control unit CP. The control unit CP can perform predetermined control on the light source 5 based on the intensity correlated with the light intensity Prclad determined as described above, or on the basis of the intensity Prclad. For example, when the intensity Prclad of light propagating in the reverse direction through the clad 12 is equal to or more than a predetermined value, the control unit CP controls the pump light source 50 to stop the operation of each laser diode 51, and An interlock operation for stopping the laser light emitted from 1 can be performed. Alternatively, the control unit CP controls the pumping light source 50 to reduce the intensity of light emitted from each laser diode 51 when the intensity Prclad of light propagating in the reverse direction through the clad 12 is equal to or more than a predetermined value. Thus, control for reducing the intensity of the laser light emitted from the laser device 1 can be performed.

As described above, the photodetecting device 2 of the present embodiment includes the first clad mode stripper 21 and the second clad mode stripper 22 provided on the optical fiber 10 at a predetermined interval, and the first clad mode stripper 21. Between the second cladding mode stripper 22, the first photodetector 31 for detecting the intensity of light leaking from the optical fiber 10, and opposite to the first cladding mode stripper 21 side with respect to the second cladding mode stripper 22. And a second light detector 32 for detecting the intensity of light leaking from the optical fiber 10 on the side.

As described above, between the first cladding mode stripper 21 and the second cladding mode stripper 22 of the optical fiber 10, a part of light propagating through the core of the optical fiber leaks from the optical fiber. The second photodetector detects a part of the light propagating in the opposite direction through the cladding 12 and the core on the side opposite to the first cladding mode stripper with respect to the second cladding mode stripper. A part of the propagating light detects the intensity of light leaking from the optical fiber. For this reason, using the intensity of the light detected by the first photodetector 31 and the intensity of the light detected by the second photodetector 32, the intensity of the light propagating in the opposite direction to the clad 12 is correlated with the intensity Prclad and the intensity Prclad. Strength to be obtained.

In the laser device 1 of the present embodiment, the light detection device 2 detects the intensity of light propagating in the opposite direction through the clad 12 of the optical fiber 10, and performs an interlock operation or the like according to the intensity of the light. A predetermined operation can be performed.

In addition, since the light detection device 2 of the present embodiment includes the subtractor 40 that calculates the difference between the light intensity detected by the first light detector 31 and the light intensity detected by the second light detector 32, The intensity of light propagating in the opposite direction in the cladding can be easily calculated.

Further, the light detection device 2 of the present embodiment includes a first level adjustment unit 33 that adjusts the level of a signal that is output from the first light detector 31 and that indicates the intensity of light detected by the first light detector 31, and A second level adjuster is provided which adjusts the level of a signal output from the second photodetector and indicating the intensity of light detected by the second photodetector. If there is an error in the attachment of the photodetector such as the photodiode to the optical fiber 10, an error in the intensity of the light detected by the photodetector occurs. Therefore, as in the present embodiment, the first level adjustment unit 33 adjusts the level of the signal indicating the intensity of the light detected by the first photodetector 31, and the second level adjustment unit 34 adjusts the level of the second photodetector 32. By adjusting the level of the signal indicating the intensity of light detected by the first photodetector 31, the balance between the intensity of light detected by the first photodetector 31 and the intensity of light detected by the second photodetector 32 can be adjusted.

In the present embodiment, the first photodetector 31 and the second photodetector 32 are thermally separated from the first clad mode stripper 21 and the second clad mode stripper 22. A general photodetector such as a photodiode tends to cause an error in the intensity of light to be detected due to the influence of heat. Therefore, as in this embodiment, the first clad mode stripper 21 and the second clad mode stripper 22, which tend to generate heat, are thermally separated from the first photodetector 31 and the second photodetector 32. Thus, the first photodetector 31 and the second photodetector 32 can more accurately detect the light intensity as compared with the case where the clad mode stripper and the photodetector are not thermally separated.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

For example, in the above-described embodiment, the photodetector 2 includes the subtractor 40, and the subtractor 40 determines the intensity Prclad of the light propagating in the reverse direction through the clad 12. However, the subtractor 40 is not essential. For example, a signal including the intensity of light detected by the first photodetector 31 and a signal including the intensity of light detected by the second photodetector 32 may be individually output from the photodetector 2. . In this case, the control unit CP may control the above embodiment using the respective signals.

The light detection device 2 of the above embodiment includes a first level adjustment unit 33 and a second level adjustment unit 34. However, the first level adjustment unit 33 and the second level adjustment unit 34 are not essential. In this case, when light of the same intensity leaks from the optical fiber 10 between the portion of the optical fiber 10 where the first photodetector 31 is provided and the portion of the optical fiber 10 where the second photodetector 32 is provided, It is preferable that the first photodetector 31 and the second photodetector 32 output signals of the same level. Also, different from the above embodiment, a signal indicating the intensity of light detected by the first photodetector 31 output from the first photodetector 31 and a second photodetector output from the second photodetector 32 are An adjustment unit for adjusting one level of a signal indicating the intensity of light to be detected may be provided.

In the embodiment, the first photodetector 31 and the second photodetector 32 are thermally separated from the first cladding mode stripper 21 and the second cladding mode stripper 22. However, the first photodetector 31 and the second photodetector 32 do not need to be thermally separated from the first cladding mode stripper 21 and the second cladding mode stripper 22, and the first photodetector 31 and the second One of the photodetectors 32 may be thermally separated from the first cladding mode stripper 21 and the second cladding mode stripper 22. However, in order to suppress the influence of heat generated from the first cladding mode stripper 21 and the second cladding mode stripper 22, the first photodetector 31 and the second photodetector 32 are connected to the first cladding mode stripper as in the above embodiment. It is preferable to be thermally separated from the mode stripper 21 and the second cladding mode stripper 22.

In the above-described embodiment, the first clad mode stripper 21 is provided on the light source 5 side of the optical fiber 10 with respect to the first photodetector 31, and the emission end side opposite to the light source 5 side of the optical fiber 10. Was provided with a second cladding mode stripper 22, and the intensity of light propagating in the cladding 12 of the optical fiber 10 in the reverse direction was detected. However, the second cladding mode stripper 22 is provided on the light source 5 side of the optical fiber 10, and the first cladding mode stripper 21 is provided on the emission end side opposite to the light source 5 side of the optical fiber 10, and the second light detection The device 32 may be provided on the side opposite to the first cladding mode stripper 21 side with respect to the second cladding mode stripper 22. In this case, the intensity of light propagating in the clad 12 in the forward direction can be detected.

In the above embodiment, the subtractor 40 and the control unit CP are separate blocks. However, the subtractor 40 and the control unit CP may be integrated.

Further, in the above embodiment, the example in which the light source 5 is a resonator type fiber laser device has been described, but 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. The number of the light sources 5 is not particularly limited, and it is sufficient that at least one light source 5 is provided.

As described above, according to the present invention, a photodetector capable of detecting the intensity of light propagating in a predetermined direction through a clad, and a laser device including the photodetector are provided, and a fiber laser device or an optical fiber It is expected to be used in fields such as communication.

DESCRIPTION OF SYMBOLS 1 ... Laser apparatus 2 ... Photodetection apparatus 5 ... Light source 10 ... Optical fiber 11 ... Core 12 ... Cladding 21 ... 1st cladding mode stripper 22 ... 2nd cladding Mode stripper 31 First photodetector 32 Second photodetector 33 First level adjuster 34 Second level adjuster 40 Subtractor CP Control unit

Claims

A first cladding mode stripper and a second cladding mode stripper provided on the optical fiber at predetermined intervals;
A first photodetector that detects the intensity of light leaking from the optical fiber between the first cladding mode stripper and the second cladding mode stripper;
On the side opposite to the first cladding mode stripper side with respect to the second cladding mode stripper, a second photodetector for detecting the intensity of light leaking from the optical fiber,
A light detection device comprising:
The light detection device according to claim 1, further comprising a subtractor that calculates a difference between an intensity of light detected by the first photodetector and an intensity of light detected by the second photodetector. .
A signal indicating the intensity of light detected by the first photodetector output from the first photodetector, and indicating the intensity of light detected by the second photodetector output from the second photodetector. The photodetector according to claim 1, further comprising an adjusting unit that adjusts at least one level of the signal.
4. The method according to claim 1, wherein at least one of the first photodetector and the second photodetector is thermally separated from the first cladding mode stripper and the second cladding mode stripper. The photodetector according to claim 1.
The optical fiber;
A light detection device according to any one of claims 1 to 4,
At least one light source for emitting light propagating through the optical fiber,
A laser device comprising:
The laser device according to claim 5, wherein the second photodetector is disposed closer to an emission end of the optical fiber than the first photodetector.
A control unit connected to the first photodetector and the second photodetector,
The control unit includes a signal output from the first photodetector and indicating the intensity of light detected by the first photodetector, and a light output from the second photodetector and detected by the second photodetector. 7. The laser device according to claim 5, wherein the operation of the light source is controlled based on a signal indicating the intensity of the laser beam.
The controller stops the operation of the light source when the intensity of light propagating through the cladding of the optical fiber from the second photodetector side to the first photodetector side is equal to or more than a predetermined value. The laser device according to claim 7, wherein the laser device is operated.
The controller outputs light emitted from the light source when the intensity of light propagating through the clad of the optical fiber from the second photodetector side toward the first photodetector side is equal to or greater than a predetermined value. The laser device according to claim 7, wherein the intensity of the laser beam is reduced.