JP2013197332A - Optical circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical circuit device in which the cause of decrease in output from an optical fiber for amplification can be understood by an inexpensive configuration.SOLUTION: A fiber laser device 1 includes excitation light sources 20A, 20B for supplying exciting light, and an optical fiber 12 for amplification. A first rare earth element (Yb) emitting laser oscillation light by receiving the exciting light, and a second rare earth element (Er) emitting the monitor light having a wavelength different from that of the laser oscillation light are added to the optical fiber 12 for amplification. The fiber laser device 1 further includes a light separator 40 for separating the laser oscillation light from the light passed through the optical fiber 12 for amplification, a photo-detector 42 for detecting the intensity of the laser oscillation light, a light separator 60 for separating the monitor light from the light passed through the optical fiber 12 for amplification, a photo-detector 62 for detecting the intensity of the monitor light, and a photo-darkening detection unit 70 for detecting the photo-darkening by comparing a change in the intensity of laser oscillation light with a change in the intensity of monitor light.

Description

  The present invention relates to an optical circuit device, and more particularly to an optical circuit device that can be used as a fiber laser.

  With the recent increase in the output power of fiber lasers, the power of pumping light to the rare earth element-doped optical fiber, which is a gain medium of the fiber laser, has also increased. Along with this, it has been reported that a core loss of a rare earth element-doped optical fiber increases with time and a phenomenon called photodarkening occurs in which the output of the fiber laser decreases. Although the detailed principle of the photodarkening phenomenon has not yet been elucidated, there are reports that the photodarkening phenomenon depends on the population inversion.

  FIG. 1 is a graph showing loss due to photodarkening in a rare earth element-doped optical fiber. The broken line indicates the loss of the unused Yb-doped optical fiber, and the solid line indicates the loss of the Yb-doped optical fiber when photodarkening occurs. As shown in FIG. 1, the loss due to photodarkening tends to increase as the wavelength becomes shorter than the wavelength region of visible light. Further, an increase in loss is observed even at a wavelength of about 1000 nm which is often used as an oscillation wavelength of a fiber laser using Yb as a gain medium.

  In this way, photodarkening is one of the causes of fiber laser output drop. In addition to photodarkening, photodarkening is also a cause of loss of optical components and pumping light sources (semiconductors). Laser) deterioration and failure, deviation of the optical axis system of the emitted light, and the like are conceivable. Therefore, when there is a decrease in the output of the fiber laser, it is first confirmed that there is no abnormality or deterioration in elements other than the rare earth element-doped optical fiber until it is determined whether the cause is photodarkening. After that, it was necessary to take out the rare earth element-doped optical fiber from the apparatus and evaluate it to confirm its deterioration. Normally, a high-power fiber laser has a structure in which it is difficult to take out a rare earth element-doped optical fiber for heat dissipation, and it is often difficult to take out a rare earth element doped optical fiber. As described above, much time and labor are required to identify the cause of the decrease in the output power of the fiber laser.

  As a method for detecting such photodarkening, a method is known in which the intensity of light from a monitoring light source is monitored and photodarkening is detected from fluctuations in the intensity of the light (see, for example, Patent Document 1). . However, in this method, it is necessary to connect a semiconductor laser or the like as a monitoring light source separately from the excitation light source, and it is necessary to separately add a monitoring light source, a driving circuit thereof, a harness for supplying power to the monitoring light source, and the like. As a result, not only the entire apparatus becomes large, but also the number of parts of the apparatus and the man-hours for making the apparatus increase, resulting in a problem that the cost of the apparatus increases.

JP 2010-263188 A

  The present invention has been made in view of such problems of the prior art, and provides an optical circuit device capable of grasping the cause of a decrease in output from an amplification optical fiber with a compact and inexpensive configuration. With the goal.

  According to the first aspect of the present invention, there is provided an optical circuit device capable of grasping the cause of a decrease in output from an amplification optical fiber with a compact and inexpensive configuration. This optical circuit device includes a pumping light source that supplies pumping light and an amplification optical fiber. The amplification optical fiber includes a first rare earth element that generates laser oscillation light upon receiving the excitation light supplied from the excitation light source, and a monitor having a wavelength different from that of the laser oscillation light due to the supply of the excitation light. A second rare earth element that produces light is added. The optical circuit device includes: a first optical separator that separates the laser oscillation light from the light that has passed through the amplification optical fiber; and a light intensity of the laser oscillation light separated by the first optical separator. A first light detector for detecting light, a second light separator for separating the monitoring light from the light passing through the amplification optical fiber, and light of the monitoring light separated by the second light separator A second photodetector for detecting the intensity; a change in the light intensity of the laser oscillation light detected by the first photodetector; and a change in the light intensity of the monitoring light detected by the second photodetector. And a photodarkening detector for detecting photodarkening.

  According to the second aspect of the present invention, there is provided an optical circuit device capable of grasping the cause of the decrease in the output from the amplification optical fiber with a compact and inexpensive configuration. This optical circuit device includes a pumping light source that supplies pumping light and an amplification optical fiber. The amplification optical fiber includes a first rare earth element that generates laser oscillation light upon receiving the excitation light supplied from the excitation light source, and a monitor having a wavelength different from that of the laser oscillation light due to the supply of the excitation light. A second rare earth element that produces light is added. In addition, the optical circuit device separates the monitoring light from the first photodetector that detects the light intensity of leakage light from the optical path through which the laser oscillation light propagates, and the light that has passed through the amplification optical fiber. An optical separator; a second optical detector for detecting the optical intensity of the monitoring light separated by the optical separator; a change in the optical intensity of leaked light detected by the first optical detector; A photodarkening detection unit that detects a photodarkening by comparing the change in the light intensity of the monitoring light detected by the second photodetector.

  The leakage light may be loss light at the fusion splicing portion provided on the optical path through which the laser oscillation light propagates, or may be scattered light leaking from the core of the optical fiber irradiated with ultraviolet light. . In addition, a filter that blocks light having the wavelength of the monitoring light while transmitting light having the wavelength of the laser oscillation light among the leakage light incident on the first photodetector from the optical path through which the laser oscillation light propagates May be provided.

  Further, light generated by spontaneous emission or stimulated emission of the second rare earth element due to energy transition from the first rare earth element to the second rare earth element due to the supply of the excitation light is used as the monitoring light. be able to. Alternatively, when the absorption band of the first rare earth element and the absorption band of the second rare earth element partially overlap each other, the second rare earth element is caused by the supply of the excitation light. Light generated by spontaneous emission or stimulated emission can be used as the monitoring light.

  When the wavelength of the monitoring light is longer than the wavelength of the laser oscillation light, the photodarkening detection unit causes the light intensity decrease detected by the first photodetector to be reduced by the second photodetector. It may be determined that photodarkening has occurred when the detected decrease in light intensity is greater. Further, the photodarkening detection unit is configured to perform photodarkening based on a difference between a decrease in light intensity detected by the first photodetector and a decrease in light intensity detected by the second photodetector. The progress level may be determined.

  Further, in the optical circuit device, photodarkening is detected by a bleaching light source capable of emitting bleaching light for recovering core loss of the optical fiber for amplification in which photodarkening has occurred, and the photodarkening detection unit. Accordingly, a photobleaching unit for supplying the bleaching light from the bleaching light source to the amplification optical fiber may be further provided.

  Here, light generated by spontaneous emission or stimulated emission of the second rare earth element due to energy transition from the first rare earth element to the second rare earth element due to the supply of the excitation light is used as the monitoring light. When used, Yb can be used as the first rare earth element, and Er can be used as the second rare earth element. Further, Tm can be used as the first rare earth element, and Ho can be used as the second rare earth element, or Yb can be used as the first rare earth element and Pr can be used as the second rare earth element.

  In addition, when light generated by spontaneous emission or stimulated emission of the second rare earth element resulting from the supply of the excitation light is used as the monitoring light, Yb is used as the first rare earth element, and the second rare earth element is used. Er can be used as the element. In this case, the wavelength of the excitation light is preferably 970 nm to 980 nm.

  The optical circuit device may further include a control unit that controls the intensity of excitation light of the excitation light source based on a detection result of the photodarkening detection unit.

  The concentration of the second rare earth element is preferably lower than the concentration of the first rare earth element. Further, as the above-described optical separator, any of a wavelength division multiplex coupler, a tap coupler, or a combination of a wavelength division multiplex coupler and a tap coupler can be used.

  According to the present invention, by using an amplification optical fiber to which two kinds of rare earth elements are added, in addition to laser oscillation light, monitoring light having a different wavelength can be generated. Therefore, it is possible to generate monitoring light without providing a separate light source for monitoring light, and it is possible to grasp the cause of output decrease without increasing the number of parts or enlarging the entire apparatus. As a result, the cause of the output decrease of the amplification optical fiber can be grasped at low cost.

It is a graph which shows the wavelength dependence of the loss by photodarkening. It is a schematic diagram which shows the structure of the optical circuit device in the 1st Embodiment of this invention. FIG. 3 is an energy transition diagram of an amplification optical fiber in the optical circuit device of FIG. 2. It is a figure which shows the loss wavelength characteristic of the optical fiber to which Yb and Er were added. It is a schematic diagram which shows the structure of the optical circuit device in the 2nd Embodiment of this invention. It is a schematic diagram which shows the structure of the optical circuit device in the 3rd Embodiment of this invention. It is a schematic diagram which shows the structure of the optical circuit device in the 4th Embodiment of this invention.

  Hereinafter, embodiments of an optical circuit device according to the present invention will be described in detail with reference to FIGS. 2 to 7, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 2 is a schematic diagram showing the configuration of the fiber laser device 1 as the optical circuit device according to the first embodiment of the present invention. As shown in FIG. 2, the fiber laser device 1 according to the present embodiment includes an optical resonator 10, a plurality of pumping light sources 20A for introducing pumping light into the optical resonator 10 from one of the optical resonators 10, and a pumping light source 20A. A combiner 22A that combines the excitation light from the optical resonator 10, a plurality of excitation light sources 20B that introduce the excitation light from the other of the optical resonators 10, and a combiner 22B that combines the excitation light from the excitation light source 20B. It has.

  The optical resonator 10 is connected to an amplification optical fiber 12, a highly reflective fiber Bragg grating (FBG) 14 connected to one end of the amplification optical fiber 12, and the other end of the amplification optical fiber 12. The low reflection FBG 16 is made up of. Further, a light emitting portion 32 that emits laser oscillation light is provided at an end portion of the optical path 30 that extends from the low reflection FBG 16 to the outside of the optical resonator 10.

  In the present embodiment, the excitation light sources 20A and 20B and the combiners 22A and 22B are provided on both the high reflection FBG 14 side and the low reflection FBG 16 side, which is a bidirectional excitation type fiber laser device, but the high reflection FBG 14 It is good also as installing an excitation light source and a combiner only in any one of the side and the low reflection FBG16 side.

  At least two kinds of rare earth elements are added to the core of the amplification optical fiber 12, and in this embodiment, the amplification optical fiber 12 to which Yb (ytterbium) and Er (erbium) are added is used. In this case, it is preferable to add Yb at a concentration much higher than Er. For example, it adds so that the ratio of Yb and Er may be set to 30: 1. The amplification optical fiber 12 preferably has a double clad structure including an inner clad and an outer clad lower than the refractive index of the inner clad.

  As the excitation light sources 20A and 20B, for example, a high-power multimode semiconductor laser (LD) having a wavelength of 915 nm can be used. The excitation light from the excitation light source 20A is combined by the combiner 22A and introduced into the amplification optical fiber 12 from the highly reflective FBG 14 side. Similarly, the pumping light from the pumping light source 20B is combined by the combiner 22B and introduced into the amplification optical fiber 12 from the low reflection FBG 16 side.

  The high reflection FBG 14 and the low reflection FBG 16 in the present embodiment are configured to reflect light having a wavelength of 1000 nm to 1100 nm corresponding to the wavelength of the laser oscillation light. The reflectance of the high reflection FBG 14 is preferably 90% to 100%, and the reflectance of the low reflection FBG 16 is preferably 30% or less. In the present embodiment, an example in which FBG is used as the reflecting means for causing laser oscillation in the optical resonator 10 will be described. However, a mirror can also be used as the reflecting means.

  In such a configuration, when excitation light having a wavelength of, for example, 915 nm is introduced from the excitation light sources 20A and 20B into the amplification optical fiber 12, Yb of the amplification optical fiber 12 is excited, and emitted light having a wavelength of 1000 nm band is emitted. This Yb emission light is laser-oscillated at a wavelength of 1000 nm band by the high reflection FBG 14 and the low reflection FBG 16 arranged so as to satisfy a predetermined resonance condition. A part of the laser oscillation light generated in the optical resonator 10 is reflected by the low reflection FBG 16 and returns to the amplification optical fiber 12, but most of the laser oscillation light is transmitted through the low reflection FBG 16 and emitted from the light emitting unit 32. The

  Here, as shown in FIG. 2, in the present embodiment, a part of the 1000 nm band light, that is, a part of the laser oscillation light among the light from the optical resonator 10 is placed between the light emitting part 32 and the combiner 22B. A first light separator 40 for separation is provided. A first light detector 42 is connected to the first light separator 40, and the first light detector 42 has a light intensity of the laser oscillation light separated by the first light separator 40. Is configured to detect. As the first optical separator 40, for example, a wavelength division multiplexing (WDM) coupler, a tap coupler, or a combination thereof can be used, and as the first optical detector 42, for example, a photodetector can be used. .

By the way, two kinds of rare earth elements Yb and Er are added to the core of the amplification optical fiber 12 in the present embodiment. FIG. 3 is an energy transition diagram of the amplification optical fiber 12. As shown in FIG. 3, it is known that an energy transition occurs from the energy level of ² F _5/2 of Yb ³⁺ to the energy level of ⁴ I _11/2 of Er ³⁺ (for example, WLBarnes
et al. "Er ³⁺ -Yb ³⁺ and Er ³⁺ Doped Fiber
Lasers, "Journal of Lightwave Technology, Vol. 7, No. 10, October 1989,
pp. 1461-1465). Therefore, the excitation light source 20A, the higher the energy levels of Yb ³⁺ by the excitation light from 20B, part of the energy transitions to Er ^3+, the energy levels of the Er ³⁺ is ⁴ I _11/2 Excited. The excited Er ³⁺ relaxes to ⁴ I _13/2 in a non-radiative process, emits amplified spontaneous emission (ASE) in the 1500 nm band, and transitions to the ground state ⁴ I _15/2 . Here, the spontaneous emission light amplified from Er thus emitted or the stimulated emission light generated by the spontaneous emission light is referred to as monitoring light.

  Thus, in the present embodiment, among the rare earth elements added to the amplification optical fiber 12, Yb has a role of amplifying light as a gain medium for laser oscillation light, and Er is different from laser oscillation light. It has a role of emitting light of a wavelength. Therefore, by supplying excitation light from the excitation light sources 20A and 20B to the amplification optical fiber 12, laser oscillation light having a wavelength of 1000 nm band is generated from Yb, and monitoring light of 1500 nm band is generated from Er. Here, since the high reflection FBG 14 and the low reflection FBG 16 are not configured to reflect 1500 nm band light, the monitoring light passes through the high reflection FBG 14 and the low reflection FBG 16.

  Here, as shown in FIG. 2, at the end of the optical path 50 extending from the highly reflective FBG 14 to the outside of the optical resonator 10, 1500 nm band light out of the light from the optical resonator 10, that is, a part of the monitoring light. A second light separator 60 is provided for separating the two. A second light detector 62 is connected to the second light separator 60, and the second light detector 62 determines the light intensity of the monitoring light separated by the second light separator 60. It can be detected. As the second optical separator 60, for example, a wavelength division multiplexing (WDM) coupler, a tap coupler, or a combination thereof can be used, and as the second optical detector 62, for example, a photodetector can be used. .

  As shown in FIG. 2, the fiber laser device 1 includes a photodarkening detection unit 70 connected to the first photodetector 42 and the second photodetector 62. The photodarkening detection unit 70 is a comparator to which the light intensity of the laser oscillation light detected by the first light detector 42 and the light intensity of the monitoring light detected by the second light detector 62 are input. The photodarkening is detected based on the comparison result of the comparator. The photodarkening detection unit 70 calculates changes in the light intensity of the input laser oscillation light and monitoring light, and detects photodarkening using the comparison results of these changes as follows.

  When photodarkening occurs in the optical fiber, as shown in FIG. 1, a large loss occurs in the laser output in the 1000 nm band on the short wavelength side, but there is almost no effect on the light in the 1500 nm band. Therefore, when photodarkening occurs, there is a difference between the degree of output reduction in the 1000 nm band and the degree of output reduction in the 1500 nm band. That is, the ratio of the light intensity of the laser oscillation light and the monitoring light is usually constant. However, when photodarkening occurs in the amplification optical fiber 12, the laser oscillation light having a short wavelength strongly influences the photodarkening. Since the influence of the monitoring light having a long wavelength is small, it can be estimated that photodarkening occurs when the degree of output decrease in the 1000 nm band is larger than the degree of output decrease in the 1500 nm band. On the other hand, when there is not much difference in the degree of output reduction between the 1000 nm band and the 1500 nm band, it can be said that the output reduction is low in wavelength dependence, and the cause is other than photodarkening ( For example, it can be determined that the excitation light source is deteriorated.

  The photodarkening detection unit 70 of the present embodiment detects photodarkening using the wavelength dependence of the loss due to the above-described photodarkening. That is, the photodarkening detection unit 70 compares the change in the light intensity of the laser oscillation light in the 1000 nm band with the change in the light intensity of the monitor light in the 1500 nm band. If it is greater than the decrease in intensity, it is determined that photodarkening has occurred. Furthermore, the photodarkening detection unit 70 determines that photodarkening is progressing as the difference between the decrease in the light intensity of the laser oscillation light and the decrease in the light intensity of the monitoring light increases.

  As described above, in this embodiment, by using the amplification optical fiber 12 to which two kinds of rare earth elements Yb and Er are added, in addition to the laser oscillation light, monitoring light having a wavelength different from this is generated. be able to. Therefore, it is possible to generate monitoring light without providing a separate light source for monitoring light, and it is possible to grasp the cause of output reduction without increasing the number of components and without enlarging the entire apparatus. As a result, the cause of the output decrease of the amplification optical fiber 12 can be grasped at low cost.

  In addition, by utilizing the wavelength dependence of loss due to photodarkening, it is possible to easily determine whether the cause of output decrease is due to photodarkening or due to other factors. Can be done. When the fiber laser device 1 is used for an optical fiber evaluation test, the level of photodarkening can be easily monitored.

  In the example shown in FIG. 2, the second optical separator 60 is provided on the optical path 50 extending from the highly reflective FBG 14 to the outside of the optical resonator 10, but the installation position of the second optical separator 60 is the same. It is not limited, and any location where monitoring light exists can be used. For example, the second optical separator 60 can be provided on the optical path 30 extending from the low reflection FBG 16 or inside the optical resonator 10.

  As described above, in the present embodiment, two types of rare earth elements added to the amplification optical fiber 12 are Yb (first rare earth element) that generates laser oscillation light upon receiving excitation light supplied from an excitation light source. , Er (second rare earth element) that generates monitoring light having a wavelength different from that of the laser oscillation light by energy transition from Yb is used. The combination of the first rare earth element and the second rare earth element is this. It is not limited to. As a combination of rare earth elements having similar characteristics, a combination of Tm (thulium) as the first rare earth element, a combination of Ho (holmium) as the second rare earth element, or Yb (ytterbium) as the first rare earth element, As the rare earth element 2, a combination of Pr (praseodymium) can be considered.

  In the above-described embodiment, the monitoring light is emitted from Er using the energy transition from Yb to Er generated by supplying the excitation light. However, the monitoring light can be generated from Er by other methods. . FIG. 4 shows loss wavelength characteristics of an optical fiber to which Yb and Er are added and loss wavelength characteristics of an optical fiber to which Er is added. As shown in FIG. Both absorption bands overlap at a wavelength of 980 nm. Therefore, when excitation light having a wavelength of 970 nm to 980 nm is used, both Yb and Er cause spontaneous emission and stimulated emission accompanying spontaneous emission. Light from the Yb has a wavelength of 1000 nm and from Er has a wavelength of 1500 nm. Light can be emitted, and spontaneous emission light of Er and stimulated emission light accompanying spontaneous emission can be used as monitoring light. As described above, the laser oscillation light and the monitoring light can be generated by utilizing the spontaneous emission of two kinds of rare earth elements and the stimulated emission accompanying the spontaneous emission.

  FIG. 5 is a schematic diagram showing a configuration of a fiber laser device 101 as an optical circuit device in the second embodiment of the present invention. As shown in FIG. 5, in addition to the configuration of the first embodiment, the fiber laser device 101 of the present embodiment outputs the excitation light of the excitation light sources 20A and 20B based on the detection result of the photodarkening detection unit 70. The control part 180 which controls is provided. The control unit 180 controls the drive current of the excitation light sources 20A and 20B according to the detection result of the photodarkening detection unit 70, and adjusts the intensity of the excitation light from the excitation light sources 20A and 20B. With such a configuration, the intensity of the excitation light can be adjusted in accordance with a decrease in the light intensity of the laser oscillation light and / or the monitoring light. For example, when the light intensity of the laser oscillation light and / or the monitoring light is lowered, the output state from the light emitting unit 32 can be kept constant by increasing the intensity of the excitation light from the excitation light sources 20A and 20B. it can.

  FIG. 6 is a schematic diagram showing a configuration of a fiber laser device 201 as an optical circuit device according to the third embodiment of the present invention. As shown in FIG. 6, in the fiber laser device 201 in this embodiment, a photo bleaching light source 280 is provided instead of a part of the excitation light source 20A in the first embodiment, and the output of the photo bleaching light source 280 is controlled. A photo bleaching unit 282 is added.

  The photo bleaching light source 280 emits bleaching light that recovers the core loss of the amplification optical fiber 12 in which photodarkening has occurred. As the photo bleaching light source 280, for example, a semiconductor laser (LD) having a wavelength of 407 nm can be used. The bleaching light from the photo bleaching light source 280 is combined by the combiner 22A and introduced into the amplification optical fiber 12 from the high reflection FBG 14 side. 6 shows an example in which the photo bleaching light source 280 is provided on the high reflection FBG 14 side, the photo bleaching light source 280 may be provided on the low reflection FBG 16 side.

  The photo bleaching unit 282 is connected to the photo darkening detection unit 70, and controls the photo bleaching light source 280 based on the photo darkening detection result in the photo darkening detection unit 70. That is, when photodarkening is detected by the photodarkening detection unit 70, the photobleaching unit 282 drives the photobleaching light source 280 to supply bleaching light to the amplification optical fiber 12. Thereby, recovery of the core loss of the amplification optical fiber 12 in which photodarkening has occurred is performed.

  As described above, according to the present embodiment, when photodarkening is detected in the amplification optical fiber 12, the bleaching light for recovering the core loss of the amplification optical fiber 12 is applied to the amplification optical fiber 12. Therefore, it is possible to reduce or eliminate the influence of photodarkening.

  FIG. 7 is a schematic diagram showing a configuration of a fiber laser device 301 as an optical circuit device according to the fourth embodiment of the present invention. As shown in FIG. 7, in the fiber laser device 301 in the present embodiment, a fusion splicing part 340 is provided on the optical path 30 that extends from the low reflection FBG 16 to the outside of the optical resonator 10. In the vicinity of the fusion splicing portion 340, a first photodetector 342 that detects the light intensity of the leaked light from the fusion splicing portion 340 is provided. As the first photodetector 342, for example, a photodetector can be used.

  Similarly to the first embodiment, an optical separator 60 that separates a part of the monitoring light is provided at the end of the optical path 50 extending from the highly reflective FBG 14 to the outside of the optical resonator 10. A second photodetector 62 is connected to the optical separator 60. The second optical detector 62 detects the light intensity of the monitoring light.

  In such a configuration, the laser oscillation light propagates on the optical path 30 from the optical resonator 10 toward the light emitting part 32, but a part of the laser oscillation light is leaked to the outside at the fusion splicing part 340. Leak. In addition to the laser oscillation light, the leakage light includes monitoring light from Er. If the amplification optical fiber 12 to which Yb is added at a concentration much higher than Er is used, the leakage light component is laser oscillation. Light becomes dominant, and the light intensity detected by the first photodetector 342 can be regarded as the light intensity of the laser oscillation light. Therefore, the photodarkening detection unit 70 compares the change in the light intensity of the leakage light detected by the first light detector 342 with the light intensity of the monitoring light detected by the second light detector 62. Thus, the photodarkening can be detected as in the first embodiment described above. That is, the photodarkening detection unit 70 in this embodiment determines that photodarkening has occurred when the decrease in the light intensity of the leakage light is larger than the decrease in the light intensity of the monitoring light, and the light intensity of the leakage light It is determined that the photodarkening is progressing as the difference between the decrease in the light intensity and the decrease in the light intensity of the monitoring light increases.

  If there is a concern about a decrease in detection accuracy due to the component of the monitoring light included in the leakage light, a filter 380 is interposed between the fusion splicing portion 340 and the first photodetector 342 as shown in FIG. Can be inserted. That is, if the filter 380 that transmits the wavelength of the laser oscillation light (1000 nm band) and blocks the wavelength of the monitoring light (1500 nm band) among the leaked light incident on the first photodetector 342 is inserted, the first Since only the laser oscillation light enters the photodetector 342, detection with higher accuracy is possible.

  In addition, when high-power laser oscillation light propagates, the first light detector 342 may detect light leaked from the fiber itself of the optical path 30 instead of the fusion splicing portion 340. In such a case, although it is not necessary to provide the fusion splicing part 340, more light can be obtained by using the loss light from the fusion splicing part 340 as in this embodiment.

  Furthermore, when it is desired to increase the amount of light detected by the first photodetector 342, an optical fiber having an ultraviolet light irradiated on the core is used as the optical path 30, and the scattered light leaking from the core of the optical fiber is detected by the first light. This may be detected by the instrument 342. According to such a configuration, the amount of scattered light can be increased in the ultraviolet light irradiation region.

  Needless to say, the configurations of the fusion splicing part 340, the first photodetector 342, the filter 380, and the like in this embodiment can be applied to the second and third embodiments described above.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and it goes without saying that the present invention may be implemented in various forms within the scope of the technical idea. For example, in each of the above-described embodiments, the fiber laser device has been described as an example of the optical circuit device. However, the present invention is not limited to the fiber laser, and for example, the present invention can be applied to an optical fiber amplifier. It is.

DESCRIPTION OF SYMBOLS 1 Fiber laser apparatus 10 Optical resonator 12 Optical fiber for amplification 14 High reflection FBG
16 Low reflection FBG
20A, 20B Excitation light source 22A, 22B Combiner 30 Optical path 32 Light emitting part 40 First optical separator 42 First optical detector 50 Optical path 60 Second optical separator 62 Second optical detector 70 Photodarkening detection Unit 101 fiber laser device 180 control unit 201 fiber laser device 280 photo bleaching light source 282 photo bleaching unit 301 fiber laser device 340 fusion splicing unit 342 first photodetector 380 filter

Claims (14)

An excitation light source for supplying excitation light;
A first rare earth element that generates laser oscillation light upon receiving excitation light supplied from the excitation light source, and a second rare earth element that generates monitoring light having a wavelength different from that of the laser oscillation light due to the supply of the excitation light And an optical fiber for amplification to which is added,
A first optical separator that separates the laser oscillation light from the light that has passed through the amplification optical fiber;
A first photodetector for detecting the light intensity of the laser oscillation light separated by the first light separator;
A second optical separator that separates the monitoring light from the light that has passed through the amplification optical fiber;
A second photodetector for detecting the light intensity of the monitoring light separated by the second light separator;
A photo for detecting photodarkening by comparing the change in the light intensity of the laser oscillation light detected by the first light detector and the change in the light intensity of the monitoring light detected by the second light detector. A darkening detection unit;
An optical circuit device comprising: An excitation light source for supplying excitation light;
A first rare earth element that generates laser oscillation light upon receiving excitation light supplied from the excitation light source, and a second rare earth element that generates monitoring light having a wavelength different from that of the laser oscillation light due to the supply of the excitation light And an optical fiber for amplification to which is added,
A first photodetector for detecting light intensity of leakage light from an optical path through which the laser oscillation light propagates;
An optical separator that separates the monitoring light from the light that has passed through the amplification optical fiber;
A second photodetector for detecting the light intensity of the monitoring light separated by the light separator;
Photodark that detects photodarkening by comparing the change in the light intensity of the leaked light detected by the first light detector and the change in the light intensity of the monitoring light detected by the second light detector. A scanning detection unit;
An optical circuit device comprising:   The optical circuit device according to claim 2, wherein the leakage light includes lost light in a fusion splicing portion provided on the optical path.   The optical circuit device according to claim 2, wherein the leakage light includes scattered light that leaks from a core of an optical fiber irradiated with ultraviolet light.   Of the leakage light incident on the first photodetector from the optical path, the filter further includes a filter that blocks light having the wavelength of the laser light while transmitting light having the wavelength of the laser oscillation light. The optical circuit device according to any one of claims 2 to 4.   The monitoring light is generated by spontaneous emission or stimulated emission of the second rare earth element due to energy transition from the first rare earth element to the second rare earth element due to the supply of the excitation light. An optical circuit device according to any one of claims 1 to 5.   The absorption band of the first rare earth element and the absorption band of the second rare earth element partially overlap each other, and the monitoring light is the second rare earth element resulting from the supply of the excitation light. The optical circuit device according to any one of claims 1 to 5, wherein the optical circuit device is generated by spontaneous emission or stimulated emission. The wavelength of the monitoring light is longer than the wavelength of the laser oscillation light,
The photodarkening detection unit causes photodarkening when a decrease in light intensity detected by the first photodetector is greater than a decrease in light intensity detected by the second photodetector. The optical circuit device according to claim 1, wherein the optical circuit device is determined to be.   The photodarkening detection unit proceeds with photodarkening based on a difference between a decrease in light intensity detected by the first photodetector and a decrease in light intensity detected by the second photodetector. 9. The optical circuit device according to claim 1, wherein the level is determined. A bleaching light source capable of irradiating bleaching light to recover the core loss of the amplification optical fiber in which photodarkening has occurred;
In response to detection of photodarkening by the photodarkening detection unit, a photobleaching unit that supplies the bleaching light from the bleaching light source to the amplification optical fiber;
The optical circuit device according to any one of claims 1 to 9, further comprising:   The optical circuit device according to any one of claims 1 to 10, wherein the first rare earth element is Yb and the second rare earth element is Er.   The optical circuit device according to claim 11, wherein a wavelength of the excitation light is 970 nm to 980 nm.   The optical circuit device according to any one of claims 1 to 12, further comprising a control unit that controls the intensity of excitation light of the excitation light source based on a detection result of the photodarkening detection unit. . The optical circuit device according to any one of claims 1 to 13, wherein the concentration of the second rare earth element is lower than the concentration of the first rare earth element.

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