JP2019070652A - Method for detection and detector - Google Patents

Abstract

An object of the present invention is to accurately monitor the power of output light and/or to monitor the power of return light with high accuracy. A detection method for detecting Rayleigh scattered light leaking from the side surface of an optical fiber included in a fiber laser (FL) or fiber laser system (FLS), wherein the Rayleigh scattered light detected by a detector (DD) is Based on the waveform of the Rayleigh scattered light, it is determined whether the light originates from the return light or from the output light. [Selection drawing] Fig. 1

Description

  The present invention relates to a detection method and a detection apparatus for detecting Rayleigh scattered light leaked from the side of an optical fiber.

  In the field of material processing, fiber lasers have been widely used in recent years. A fiber laser is a laser device that uses an optical fiber (hereinafter referred to as “amplifying fiber”) whose core is doped with rare earth (hereinafter referred to as “amplifying fiber”) as an amplification medium, and is a continuous oscillation type (resonator type) fiber A laser and a pulse oscillation type (MOPA type) fiber laser that intermittently outputs laser light are widely used. In addition to the fiber laser, which uses continuous or intermittent laser light as an output light, an optical fiber (hereinafter referred to as “Raman fiber”) connected to a subsequent stage of a continuous wave or pulsed wave fiber laser The Stokes light generated by stimulated Raman scattering in In either case, the output light is guided by the delivery fiber to the vicinity of the object to be processed, and is irradiated onto the object to be processed through the head portion connected to the tip of the delivery fiber.

  By the way, in a fiber laser for processing, it is necessary to monitor the power of output light in order to perform feedback control, abnormality detection and the like. As a method of monitoring the power of the output light, (1) The output light incident on the delivery fiber is branched into the irradiation output light and the monitoring output light by the coupler, and the monitoring output light is detected by the photodetector. 2. Description of the Related Art (2) A method is widely used in which a part of output light incident on a delivery fiber is leaked from a bending portion or a fusion point, and the leaked light is detected by a photodetector.

  However, the former method has a problem that the manufacturing cost is increased due to the increase of parts called couplers and the increase of the process of inserting the couplers into the delivery fiber. Also, in the latter method, there is a problem that the manufacturing cost is increased due to an increase in the step of forming a bending portion or a fusion bonding point in the delivery fiber (a bending portion or a melting portion for leakage of monitor output light In the case where a landing point is newly formed) or the problem that the place where output light is detected is limited to the vicinity of a bending portion or a fusion point (when leakage of monitor output light from an existing bending portion or a fusion point) )was there. Furthermore, these methods are methods that consume part of the output light to monitor the power of the output light. Therefore, these methods have a common problem that loss of output light inevitably occurs in order to monitor the power of output light.

  As a method for monitoring the power of the output light without causing these problems, scattered light of Rayleigh scattering in which the output light is scattered light instead of detecting the output light itself propagating in the delivery fiber A method of detecting (hereinafter, referred to as "Rayleigh scattered light") is known. Since there is a certain correspondence between the power of the output light propagating through the delivery fiber and the power of the Rayleigh scattered light generated in the delivery fiber, the power of the output light can be calculated from the power of the Rayleigh scattered light .

  Patent Document 1 discloses a sensor unit that detects Rayleigh scattered light leaked from the side surface of an optical fiber. In this sensor unit, a concave portion is disposed so that the bottom surface faces the light receiving surface of the light detector, and a configuration is employed in which Rayleigh scattered light leaked from the side surface of the optical fiber to the opposite side to the light detector It is done. The curvature of the bottom of the recess is determined so that the reflected Rayleigh scattered light is focused on the light receiving surface of the light receiving element. Therefore, in addition to the Rayleigh scattered light leaked from the side surface of the optical fiber to the photodetector side, the Rayleigh scattered light leaked from the side surface of the optical fiber to the opposite side to the photodetector enters the photodetector. As a result, it is possible to cause a sufficient amount of Rayleigh scattered light to be incident on the light detector for accurately measuring the power.

JP-A-2015-525342 (released on September 3, 2015)

  However, as in the sensor unit described in Patent Document 1, when the Rayleigh scattered light leaked from the side surface of the optical fiber is reflected to be incident on the light detector, the amount of the Rayleigh scattered light leaked from the side surface of the optical fiber is constant. Even if the positional relationship between the optical fiber, the reflector, and the light detector changes, the amount of Rayleigh scattered light entering the light detector changes.

  In particular, in the sensor unit described in Patent Document 1, a configuration is adopted in which the reflecting surface of the reflector is made concave so that the reflected Rayleigh scattered light is focused on the light receiving surface of the light receiving element. Therefore, a slight change in the positional relationship between the optical fiber, the reflector, and the light detector significantly changes the amount of Rayleigh scattered light incident on the light detector. That is, a slight change in the positional relationship between the optical fiber, the reflector, and the light detector significantly increases the error included in the monitor value (the power of the output light calculated from the detected power of the Rayleigh scattered light).

  Also, as the Rayleigh scattered light leaked from the delivery fiber contained in the fiber laser, in addition to the one derived from the output light propagating in the forward direction of the delivery fiber, the one derived from the return light propagating in the reverse direction in the delivery fiber included. For this reason, the prior art has a further problem that it is difficult to monitor the power of the output light with high accuracy and to monitor the power of the return light with high accuracy.

  The present invention has been made in view of the above-mentioned further problems, and an object thereof is to monitor the power of output light with high accuracy and / or monitor the power of return light with high accuracy. It is to realize a detection method.

  In order to achieve the above object, a detection method according to the present invention is a detection method for detecting Rayleigh scattered light leaked from a side surface of an optical fiber included in a fiber laser or a fiber laser system, which is detected by a detection device A determination step is included to determine whether the Rayleigh scattered light is derived from the return light or the output light based on the waveform of the Rayleigh scattered light.

  The detection method according to an aspect of the present invention preferably further includes an output light monitoring step of monitoring the power of the Rayleigh scattered light determined to be derived from the output light in the determination step.

  The detection method according to an aspect of the present invention preferably further includes a return light monitoring step of monitoring the power of the Rayleigh scattered light determined to be derived from the return light in the determination step.

  In the detection method according to one aspect of the present invention, in the determination step, whether the Rayleigh scattered light detected by the detection device is derived from the return light or derived from the output light is the Rayleigh. Preferably, the determination is made by comparing the width of the scattered light waveform with a predetermined reference value.

  In order to solve the above problems, a detection device according to an aspect of the present invention is a detection device that detects Rayleigh scattered light leaked from the side surface of an optical fiber included in a fiber laser or a fiber laser system. A determination means is provided for determining whether the detected Rayleigh scattered light is derived from the return light or the output light based on the waveform of the Rayleigh scattered light.

  According to the present invention, it is possible to realize a detection method which can monitor the power of output light with high accuracy and / or monitor the power of return light with high accuracy.

Fig. 1 shows a first embodiment of a detection device according to the invention; (A) is an exploded perspective view of the detection device, and (b) is a cross-sectional view of the detection device. It is a figure which shows 2nd Embodiment of the detection apparatus which concerns on this invention. (A) is an exploded perspective view of the detection device, and (b) is a cross-sectional view of the detection device. (A) is a graph which shows the light output dependence of the difference | error contained in the monitor value calculated from the power of the Rayleigh scattered light detected using the detection apparatus which concerns on an Example. (B) is a graph which shows the light output dependence of the difference | error contained in the monitor value calculated from the power of the cladding mode light detected using the detection apparatus which concerns on a comparative example. In the detection device 2 shown in FIG. 2, when the upper surface of the reflection plate is not processed (when the aluminum material is exposed), black alumite processing (non-reflection processing) and gold plating processing (reflection processing) It is a graph which shows the relationship between the offset amount from the reference (standard) position of an optical fiber, and the change rate (absolute value) of the photoelectric current output from a photodiode regarding the case where it is carried out. It is a block diagram of a fiber laser provided with the detection apparatus shown in FIG. 1 or FIG. It is a block diagram of a fiber laser system provided with a detecting device shown in FIG. 1 or FIG.

First Embodiment
A detection device 1 according to a first embodiment of the present invention will be described based on FIG. In FIG. 1, (a) is an exploded perspective view of the detection device 1, and (b) is an AA ′ cross-sectional view of the detection device 1.

  The detection device 1 is a device for detecting Rayleigh scattered light leaked from the side surface of the optical fiber OF, and includes a photodetector 11, a base plate 12, a PD holder 13, a top plate 14, a front plate 15, and a rear plate 16 Have.

  The light detector 11 is a configuration for detecting Rayleigh scattered light leaked from the side surface of the optical fiber OF. In the present embodiment, as the light detector 11, a light detector having a photodiode 11a and a DO (Diode Outline) package 11b accommodating the photodiode 11a is used. A circular through hole 13a is formed in one bottom surface of the DO package 11b, and the Rayleigh scattered light leaked from the side surface of the optical fiber OF is incident on the light receiving surface 11a1 of the photodiode 11a through the through hole 13a. Do. The anode terminal 11a2 and the cathode terminal 11a3 of the photodiode 11a are drawn out of the DO package 11b from the other bottom surface of the DO package 11b.

  The base plate 12 is a plate-like member, and is made of, for example, a metal such as aluminum. The PD holder 13 is a rectangular parallelepiped member, and is made of, for example, a metal such as aluminum. The PD holder 13 is formed with a through hole 13 a having a circular cross section from the upper surface to the lower surface. Further, on the lower surface of the PD holder 13, a groove 13b having a triangular cross section is formed from the front surface to the rear surface. The PD holder 13 is fixed to the base plate 12 using a bolt (for example, a hex socket bolt) such that the lower surface thereof abuts on the upper surface 12 a of the base plate 12.

  The optical fiber OF is accommodated in a groove 13 b formed in the PD holder 13 and is sandwiched between the base plate 12 and the PD holder 13. In the light detector 11, the light receiving surface 11a1 of the photodiode 11a is opposed to the upper surface 12a of the base plate 12 through the optical fiber OF, and the other bottom surface of the DO package 11b (the anode terminal 11a2 and the cathode terminal 11a3 are drawn out) Is inserted into the through hole 13 a formed in the PD holder 13 so that the bottom surface of the PD holder 13 is flush with the upper surface of the PD holder 13.

  The top plate 14 is a plate-like member in which a circular opening 14 a is formed, and is made of, for example, a metal such as aluminum. In the top plate 14, the anode terminal 11a2 and the cathode terminal 11a3 of the photodiode 11a pass through the opening 14a, and the bottom of the DO package 11b around the opening 14a (the bottom surface from which the anode terminal 11a2 and the cathode terminal 11a3 are drawn out) ) Is fixed to the PD holder 13 using a screw (for example, a countersunk screw) so as to press the above from above.

  The front plate 15 is a plate-like member in which the cut 15a is formed and is bent so as to be L-shaped when viewed from the side, and is made of, for example, a metal such as aluminum. The front plate 15 has a bolt (for example, a hexagonal socket) so that one of two regions separated by ridges of the surface on the mountain side abuts on the front surface of the PD holder 13 and the other abuts on the upper surface 12 a of the base plate 12. It is being fixed to the front of PD holder 13 using a bolt. The optical fiber OF is drawn to the front of the PD holder 13 through the incision 15a.

  The rear plate 16 is formed by bending a plate-like member in which the cut 16a is formed so as to be L-shaped when viewed from the side, and is made of, for example, a metal such as aluminum. The rear plate 16 has a bolt (for example, a hexagonal socket) so that one of two regions separated by ridges of the surface on the mountain side abuts on the back surface of the PD holder 13 and the other abuts on the upper surface 12 a of the base plate 12. It fixes to the back of PD holder 13 using a bolt. The optical fiber OF is drawn to the rear of the PD holder 13 through the incision 16a.

  The front plate 15 and the rear plate 16 function as a heat radiation path for dissipating the heat generated in the PD holder 13 to the base plate 12 by absorbing the light leaked from the optical fiber OF. Therefore, by providing the front plate 15 and the rear plate 16, the temperature rise of the PD holder 13 can be suppressed.

  As described above, in the detection device 1, the light receiving surface 11a1 of the photodiode 11a (an example of the "light receiving element" in the claims) and the upper surface 12a of the base plate 12 (an example of the "reflector" in the claims) (An example of the “reflection surface” in the claims) is opposed to each other via the optical fiber OF. Therefore, in addition to the Rayleigh scattered light leaking upward from the side surface of the optical fiber OF, it leaks downward from the side surface of the optical fiber OF, and then is reflected upward by the upper surface 12 a of the base plate 12 Rayleigh scattered light can be made incident on the light receiving surface 11a1 of the photodiode 11a. That is, the Rayleigh scattered light leaked from the side surface of the optical fiber OF can be more efficiently received by the photodiode 11 a than in the case where the base plate 12 which is a reflector is not present. Moreover, in the detection device 1, the top surface 12 a of the base plate 12, that is, the reflection surface that reflects the light leaked from the side surface of the optical fiber OF is flat. Therefore, compared with the case where the upper surface 12a of the base plate 12 is concave, the increase in the error included in the monitor value accompanying the change of the relative position of the optical fiber OF, the base plate 12, and the photodiode 11a can be suppressed small.

  Further, in the detection device 1, a Rayleigh scattering in which the portion surrounding the light receiving surface 11a1 of the photodiode 11a in the DO package 11b (an example of the “frame” in the claims) leaks upward from the side surface of the optical fiber OF. Reflect light downwards. Then, part of the Rayleigh scattered light reflected downward in the relevant portion of the DO package 11b is reflected upward on the upper surface 12a of the base plate 12, and is incident on the light receiving surface 11a1 of the photodiode 11a. Therefore, the Rayleigh scattered light leaked from the side surface of the optical fiber OF can be more efficiently received by the photodiode 11a.

  The thickness of the PD holder 13 is preferably set so that Rayleigh light leaked from the side surface of the optical fiber OF is most efficiently incident on the light receiving surface 11a1 of the photodiode 11a. In the present embodiment, the thickness of the PD holder 13 is such that the distance from the optical axis of the optical fiber OF to one bottom surface of the DO package 11 b (bottom surface on which the through hole 13 a is formed) is 0.7 mm. It is set.

  Further, it is preferable that the upper surface 12 a of the base plate 12 be subjected to a reflection process such as a gold plating process. Accordingly, it is possible to efficiently reflect upward the Rayleigh scattered light leaked from the side surface of the optical fiber OF as compared to the case where the top surface 12 a of the base plate 12 is not subjected to the reflection processing. Therefore, the Rayleigh scattered light leaked from the side surface of the optical fiber OF can be more efficiently received by the photodiode 11a than when the top surface 12a of the base plate 12 is not subjected to the reflection processing. As the reflection processing applied to the upper surface 12a, other than gold plating processing, processing for coating glass with an antireflective film (AR coating), processing for stainless steel processing, processing for surface treatment of white alumite to aluminum (for aluminum oxidation prevention), etc. Conceivable. However, when the reflectance of the upper surface 12a itself of the base plate 12 is sufficiently high, the reflection processing may be omitted.

  In addition, it is preferable that the surfaces of the PD holder 13, the front plate 15, and the rear plate 16 be subjected to non-reflection processing such as black alumite processing. Thus, light other than Rayleigh scattered light leaked from the optical fiber OF is received by the PD holder 13 and the front plate 15 as compared to the case where the surface of the PD holder 13, the front plate 15 and the rear plate 16 is not subjected to non-reflection processing. Alternatively, it is possible to suppress the light reflected from the surface of the rear plate 16 and being incident on the photodiode 11a. Therefore, it is possible to suppress an increase in the error included in the monitor value caused by the light other than the Rayleigh scattered light leaked from the side surface of the optical fiber OF being received by the photodiode 11a.

Second Embodiment
A detection device 2 according to a second embodiment of the present invention will be described based on FIG. In FIG. 2, (a) is an exploded perspective view of the detection device 2, and (b) is a cross-sectional view of the detection device 2 taken along the line AA ′.

  The detection device 2 is a device for detecting Rayleigh scattered light leaked from the side surface of the optical fiber OF, and includes a light detector 21, a fiber holder 22, a PD holder 23, a reflection plate 24, and a top plate 25. .

  The light detector 21 is a configuration for detecting Rayleigh scattered light leaked from the side surface of the optical fiber OF. In the present embodiment, a photodetector having a photodiode 21a (an example of a "light receiving element" in the claims) and a DO (Diode Outline) package 21b accommodating the photodiode 21a as the photodetector 21 is used. It is used. A circular opening 23a is formed on one bottom surface of the DO package 21b, and the Rayleigh scattered light leaked from the side surface of the optical fiber OF is incident on the light receiving surface 21a1 of the photodiode 21a through the opening 23a. The anode terminal 21a2 and the cathode terminal 21a3 of the photodiode 21a are drawn out of the DO package 21b from the other bottom surface of the DO package 21b.

  The fiber holder 22 is a rectangular solid member, and is made of, for example, a metal such as aluminum. The fiber holder 22 has a step 22a formed on the upper surface, and a portion (hereinafter referred to as "thin portion") ahead of the step 22a has a thickness behind the step 22a (hereinafter It is thinner than the thickness of "thick part". The thin portion of the fiber holder 22 is formed with a through hole 22 b having a circular cross section from the upper surface to the lower surface. Further, a groove 22c having a rectangular cross section is formed on the upper surface of the fiber holder 22 from the front surface to the rear surface.

  The PD holder 23 is a plate-like member whose top view shape substantially matches the thin-walled portion of the fiber holder 22 and is made of, for example, a metal such as aluminum. The PD holder 23 is formed with a circular opening 23a from the upper surface to the lower surface. The PD holder 23 uses a bolt (for example, a hexagon socket head bolt) so that the lower surface thereof is in contact with the upper surface of the fiber holder 22 and the opening 23a thereof communicates with the through hole 22b of the fiber holder 22. It is fixed to the thin portion of the fiber holder 22. The thickness of the PD holder 23 substantially matches the height of the step 22 a, and the upper surface of the PD holder 23 is flush with the upper surface of the thick portion of the fiber holder 22.

  The optical fiber OF is accommodated in a groove 25 c formed in the fiber holder 22, and is sandwiched between the fiber holder 22 and the PD holder 23. At this time, what is sandwiched between the fiber holder 22 and the PD holder 23 is a section of the optical fiber OF which does not include fusion bonding. The photodetector 21 has an opening formed in the PD holder 23 such that the other bottom surface of the DO package 21 b (the bottom surface from which the anode terminal 21 a 2 and the cathode terminal 21 a 3 are drawn out) is flush with the top surface of the PD holder 23. It is inserted from above at 23a. The photodetector 21 is pressed from above by a washer 26 b fixed to the PD holder 23 using a bolt 26 a.

  The reflection plate 24 is a member on a disk, and is made of, for example, a metal such as aluminum. The reflection plate 24 is inserted from below into the through hole 22b formed in the fiber holder 22 so that the upper surface 24a faces the light receiving surface 21a1 of the photodiode 21a via the optical fiber OF. At this time, the convex portion 24 b protruding left and right from the reflective plate 24 is engaged with the concave portion 22 d formed on the lower surface of the fiber holder 22, whereby the reflective plate 24 is positioned.

  The top plate 25 is a plate-like member whose top view shape substantially matches the thick portion of the fiber holder 22 and is made of, for example, a metal such as aluminum. The top plate 25 is fixed to the thick portion of the fiber holder 22 using a bolt (for example, a hex socket bolt) so that the lower surface thereof abuts on the upper surface of the fiber holder 22. Thus, the optical fiber OF is sandwiched between the fiber holder 22 and the top plate 25. At this time, in the optical fiber OF, a section including the fusion point P is sandwiched between the fiber holder 22 and the top plate 25. The light leaked from the fusion point P of the optical fiber OF (such as unnecessary residual excitation light) is absorbed by the fiber holder 22 to replace heat.

  As described above, in the detection device 2, the light receiving surface 21 a 1 of the photodiode 21 a (an example of the “light receiving element” in the claims) and the upper surface of the reflecting plate 24 (an example of the “reflector” in the claims) 24a (an example of the "reflecting surface" in the claims) are opposed to each other via the optical fiber OF. For this reason, in addition to the Rayleigh scattered light leaking upward from the side surface of the optical fiber OF, it leaks downward from the side surface of the optical fiber OF and then is reflected upward by the upper surface 24 a of the reflection plate 24. The Rayleigh scattered light can be made incident on the light receiving surface 21a1 of the photodiode 21a. That is, the Rayleigh scattered light leaked from the side surface of the optical fiber OF can be more efficiently received by the photodiode 21a than in the case where the reflection plate 24 which is a reflector does not exist. Moreover, in the detection device 2, the top surface 24 a of the reflection plate 24, that is, the reflection surface that reflects the light leaked from the side surface of the optical fiber OF is flat. Therefore, compared with the case where the upper surface 24a of the reflection plate 24 is concave, the increase in the error included in the monitor value accompanying the change of the relative position of the optical fiber OF, the reflection plate 24, and the photodiode 21a can be suppressed small.

  Further, in the detection device 2, a Rayleigh scattering in which a portion surrounding the light receiving surface 21a1 of the photodiode 21a in the DO package 21b (an example of a “frame” in the claims) leaks upward from the side surface of the optical fiber OF. Reflect light downwards. Then, a part of the Rayleigh scattered light reflected downward at the relevant portion of the DO package 21b is reflected upward by the upper surface 24a of the reflection plate 24, and is incident on the light receiving surface 21a1 of the photodiode 21a. . Therefore, the Rayleigh scattered light leaked from the side surface of the optical fiber OF can be more efficiently received by the photodiode 21a.

  Preferably, the thickness of the PD holder 23 is set such that Rayleigh light leaked from the side surface of the optical fiber OF is most efficiently incident on the light receiving surface 21a1 of the photodiode 21a. In the present embodiment, the thickness of the PD holder 23 is set such that the distance from the optical axis of the optical fiber OF to one bottom surface of the DO package 21b (the bottom surface on which the opening 23a is formed) is 0.4 mm. It is done.

  In addition, it is preferable that the upper surface 24 a of the reflection plate 24 be subjected to reflection processing such as gold plating. Accordingly, it is possible to efficiently reflect upward the Rayleigh scattered light leaked from the side surface of the optical fiber OF as compared to the case where the top surface 24 a of the reflection plate 24 is not subjected to the reflection processing. Therefore, the Rayleigh scattered light leaked from the side surface of the optical fiber OF can be more efficiently received by the photodiode 21a than when the top surface 24a of the reflection plate 24 is not subjected to the reflection processing. As the reflection processing to be applied to the upper surface 24a, similarly to the first embodiment, other than gold plating processing, processing for coating glass with an anti-reflection film (AR coating), stainless processing, aluminum for preventing aluminum oxidation, white alumite The process etc. which surface-treat is considered. However, when the reflectance of the upper surface 24 a itself of the reflection plate 24 is sufficiently high, the reflection processing may be omitted.

  In addition, it is preferable that non-reflection processing such as black alumite processing be performed on the surfaces of the fiber holder 22, the PD holder 23, and the top plate 25. Thus, light leaked from the fusion point P of the optical fiber OF is greater than that in the case where the surface of the fiber holder 22, the PD holder 23, and the top plate 25 is not subjected to non-reflection processing. Or, it is possible to suppress the light being reflected by the top plate 25 and being incident on the photodiode 21a. Therefore, it is possible to suppress an increase in the error included in the monitor value caused by the light leaked from the fusion point P of the optical fiber OF being received by the photodiode 21a. In particular, in the present embodiment, the PD holder 23 is mounted on the upper surface of the thin-walled portion of the fiber holder 22, and the lower surface of the PD holder 23 is mounted on the upper surface of the thick-walled portion of the fiber holder 22. It is located below the lower surface of 25. For this reason, after leaking from the optical fiber OF, part of the light propagating in the groove 22 c is blocked by the rear end 23 b of the PD holder 23. That is, the PD holder 23 is disposed such that the rear end 23 b blocks the light leaked from the fusion point P of the optical fiber OF and prevents the light from being incident on the photodiode 21 a. For this reason, the above-mentioned effect becomes more remarkable.

  Further, it is preferable that the fusion bonding point P of the optical fiber OF is embedded in the resin 27 having a refractive index higher than that of the cladding of the optical fiber OF inside the groove 22c formed in the fiber holder 22. Thus, cladding mode light (light propagating in the cladding) can be removed, and as a result, the cladding mode light can be prevented from being incident on the photodiode 21 a disposed closer to the output side than the fiber holder 22. it can. Therefore, the increase in the error included in the monitor value can be further reduced. The cladding mode light may include light leaked from the core to the cladding at the fusion point of the optical fiber OF, residual excitation light, and the like.

[Characteristics of detection device]
The characteristics of the detection device 2 according to the second embodiment will be described based on FIGS. The characteristics of the detection device 1 according to the first embodiment are also equivalent to the characteristics of the detection device 2 according to the second embodiment.

  First, with respect to the detection device 2 according to the embodiment for monitoring Rayleigh scattered light and the detection device according to the comparative example for monitoring cladding mode light, the light output dependency of the error included in the monitor value is compared. Shown in. In FIG. 3, (a) is a graph showing an estimated value of an error included in the monitor value calculated from the power of the Rayleigh scattered light obtained by the detection device 2 according to the embodiment, (b) is It is a graph which shows the estimated value of the difference | error contained in the monitor value calculated from the power of the cladding mode light obtained by the detection apparatus which concerns on a comparative example.

  While the error included in the monitor value calculated from the power of the Rayleigh scattered light is ± 1% or less as shown in FIG. 3A, the error is included in the monitor value calculated from the power of the cladding mode light. The included error is ± 10% or more as shown in (b) of FIG. This result shows that by using the detection device 2 according to the embodiment for monitoring Rayleigh scattered light, it is possible to obtain a more accurate monitor value than using the detection device according to the comparative example for monitoring cladding mode light. There is.

  Next, in the case where the upper surface 24 a of the reflection plate 24 of the detection device 2 according to the embodiment is not processed (when the aluminum material is exposed) and when black alumite processing (non-reflection processing) is performed, gold plating ( The offset amount from the reference position of the optical fiber OF (the position where the optical axis overlaps with the center of the light receiving surface 21a1 of the photodiode 21a) and the photocurrent (Rayleigh) output from the photodiode 11a It is a graph which shows the relationship with the change rate (absolute value) of (proportional to the power of scattered light).

  When the upper surface 24 a of the reflection plate 24 is not processed, it is estimated that when the optical fiber OF is offset by 1 mm from the reference position, the photocurrent output from the photodiode 11 a changes by 15%.

  On the other hand, when the upper surface 24a of the reflection plate 24 is black alumite processed, the photocurrent output from the photodiode 11a is 52.20 μA when the offset amount is 0 mm, and 42 when the offset amount is 1 mm. It was .75 μA. That is, it was confirmed that when the optical fiber OF is offset by 1 mm from the reference position, the photocurrent output from the photodiode 11a changes by 18.1%. This result means that the increase of the error included in the monitor value due to the offset of the optical fiber OF is promoted by lowering the reflectance of the upper surface 24 a of the reflection plate 24.

  When the upper surface 24a of the reflection plate 24 is gold-plated, the photocurrent output from the photodiode 11a is 94.65 μA when the offset amount is 0 mm, and 89.55 μA when the offset amount is 1 mm. The That is, it was confirmed that when the optical fiber OF is offset by 1 mm from the reference position, the photocurrent output from the photodiode 11a changes by 5.4%. This result means that the increase of the error included in the monitor value due to the offset of the optical fiber OF is suppressed by increasing the reflectance of the upper surface 24 a of the reflection plate 24.

Application Example 1
The detection device 1 according to the first embodiment and the detection device 2 according to the second embodiment can be applied to the fiber laser FL. FIG. 5 is a block diagram of the fiber laser FL.

  The fiber laser FL is connected to an amplification fiber AF whose core is doped with rare earth, a first fiber Bragg grating FBG1 functioning as a mirror connected to one end of the amplification fiber AF, and the other end of the amplification fiber AF And a second fiber Bragg grating FBG2 functioning as a half mirror, and a continuous wave fiber laser having a resonator. The laser diodes LD1 to LD6 are connected to the first fiber Bragg grating FBG1 via the pump combiner PC, and the delivery fiber DF is connected to the second fiber Bragg grating FBG2. The laser diodes LD1 to LD6 are configured to generate excitation light to be supplied to the resonator, and the delivery fiber DF is configured to guide laser light generated by the resonator to a processing target. The laser light generated by the resonator is guided through the delivery fiber DF, and then irradiated onto the object to be processed through the head H provided at the tip of the delivery fiber DF.

  The delivery fiber DF is equipped with a detection device DD for detecting the Rayleigh scattered light leaked from the delivery fiber DF. The detection device 1 according to the first embodiment and the detection device 2 according to the second embodiment can be used as the detection device DD.

  The fiber laser FL further includes a control unit (not shown). The control unit calculates a monitor value indicating the power of the output light from the power of the Rayleigh scattered light detected by the detection device DD. In addition, the control unit controls the power of the excitation light generated by the laser diodes LD1 to LD6 based on the power of the Rayleigh scattered light detected by the detection device DD so as to reduce the fluctuation of the power of the output light. Control.

  The Rayleigh scattered light leaked from the delivery fiber DF includes, in addition to the light originating from the output light propagating in the delivery fiber DF in the forward direction, the one originating in the return light propagating in the delivery fiber DF in the reverse direction. . For this reason, in order to monitor the power of the output light with high accuracy, it is preferable to suppress the incidence of Rayleigh scattered light derived from the return light on the detection device DD.

  Therefore, in the fiber laser FL, a configuration is adopted in which the cladding mode stripper CMS is provided on the output end side of the detection device DD of the delivery fiber DF. Here, with the cladding mode stripper CMS, the coating of the delivery fiber DF is removed, and the outermost cladding (the cladding in a single cladding fiber, the outer cladding in a double cladding fiber, etc.) has a refractive index higher than that of the outermost cladding. Refers to a structure covered with a high resin or the like. By providing the cladding mode stripper CMS, it is possible to suppress the return light (cladding mode light) guided through the outermost cladding of the delivery fiber DF from being incident on the detection device DD as noise. In addition to the configuration in which the cladding mode stripper CMS is provided, a configuration may be adopted in which the light guided inside the coating is leaked to the outside of the coating by removing a part of the coating of the delivery fiber DF. . Thereby, the light guided through the coating of the delivery fiber DF can be prevented from being incident on the detection device DD as noise.

  The return light guided through the core of the delivery fiber DF can not be removed even by the cladding mode stripper SMS. However, the waveforms of the Rayleigh scattered light derived from the return light and the Rayleigh scattered light derived from the output light are different. More specifically, the width (for example, half width) of the waveform of Rayleigh scattered light derived from the return light is smaller than the width of the waveform of Rayleigh scattered light derived from the output light. Therefore, (1) Whether the Rayleigh scattered light detected by the detection device DD originates from the return light or the output light, based on the waveform (for example, the width of the waveform (2) accurately monitoring the power of output light and reflected light by monitoring the power of Rayleigh scattered light determined by comparison with a predetermined reference value and (2) determined to be derived from the output light Can.

  Here, the configuration for monitoring the power of the output light with reference to the power of the Rayleigh scattered light leaked from the delivery fiber DF has been described, but the return light is referred to the power of the Rayleigh scattered light leaked from the delivery fiber DF It is also possible to adopt a configuration for monitoring the power of In this case, by omitting the cladding mode stripper CMS described above, not only the return light guided in the core of the delivery fiber DF but also the return light guided in the cladding of the delivery fiber DF is made incident on the detection device DD. A configuration may be employed, or a configuration may be employed in which only the return light guided through the core of the delivery fiber DF is incident on the detection device DD without omitting the cladding mode stripper CMS described above. (1) Whether the Rayleigh scattered light detected by the detection device DD is derived from the return light or the output light is determined based on the waveform (for example, the width of the waveform is determined in advance The power of the returned light can be monitored with high accuracy by monitoring the power of the Rayleigh scattered light that is determined by comparison with the reference value (2) and determined to be derived from the returned light.

Application Example 2
The detection device 1 according to the first embodiment and the detection device 2 according to the second embodiment can be applied to the fiber laser system FLS. FIG. 6 is a block diagram of a fiber laser system FLS.

  The fiber laser system FLS includes an output combiner OC for obtaining output light by combining a plurality of fiber lasers FL1 to FL6 and laser beams generated by the respective fiber lasers FLi, and an output obtained for the output combiner OC. It is constituted by an output fiber OF which guides the light to the object to be processed.

  The output fiber OF is mounted with a detection device DD for detecting Rayleigh scattered light leaked from the output fiber OF. The control unit (not shown) of the fiber laser system FLS calculates a monitor value indicating the power of the output light from the power of the Rayleigh scattered light detected by the detection device DD. The detection device 1 according to the first embodiment and the detection device 2 according to the second embodiment can be used as the detection device DD.

  The control unit of the fiber laser system FLS adjusts the power of the output light of each fiber laser FLi to control the power of the output light of the entire fiber laser system FLS. For example, when the power of the output light of the entire fiber laser system FLS decreases, the control unit uniformly raises the power of the output light of the individual fiber lasers FLi to thereby control the power of the entire output light of the fiber laser system FLS Maintain at rated output.

  Here, in order to maintain the power of the output light of the entire fiber laser FLS at the rated output, instead of the configuration in which the power of the output light of each fiber laser FLi is uniformly raised, the degree of degradation of the fiber laser FLi is small. You may employ | adopt the structure which raises the power of output light preferentially. Thereby, the lifetime of the entire fiber laser system FLS can be increased.

  As a method of evaluating the degree of deterioration of the fiber laser FLi, the control unit measures the degree of deterioration of the power of the output light of the fiber laser FL, the power of the output light at a certain point, and a predetermined period after that point There is a method of determining by comparing the power of the output light of. For example, the control unit compares the power of the output light at the time of system operation with the power of the output light after a predetermined period has elapsed from the time of system operation, and detects the drop width of the power of the output light. The degree of deterioration of the power of the output light of the laser FL may be determined. The control unit determines that the power of the output light of the fiber laser FL is degraded as the drop width of the power of the output light is larger.

[Items to be added]
The object of the present embodiment is to increase the error included in the monitor value as the relative position of the optical fiber, the reflector, and the light detector changes in the detection device for detecting the Rayleigh scattered light leaked from the side surface of the optical fiber Is also realized in a detection device in which the

  In order to achieve the above object, a detection device according to the present embodiment is a detection device for detecting Rayleigh scattered light leaked from a side surface of an optical fiber, comprising: a light receiving element having a light receiving surface; And a reflector having a reflection surface facing the light receiving surface, wherein the reflection surface of the reflector is flat.

  According to the above configuration, the light receiving surface of the light receiving element and the reflecting surface of the reflector face each other through the optical fiber. For this reason, in addition to the Rayleigh scattered light leaked toward the light receiving element from the side surface of the optical fiber, it leaks toward the reflector from the side surface of the optical fiber and is then reflected toward the light receiving element by the reflecting surface of the reflector. The Rayleigh scattered light can be made incident on the light receiving surface of the light receiving element. That is, the Rayleigh scattered light leaked from the side surface of the optical fiber can be more efficiently received by the light receiving element than in the case where no reflector is present. And according to said structure, the reflective surface of a reflector is flat. Therefore, the increase in the error included in the monitor value caused by the change in the relative position of the optical fiber, the reflector, and the light receiving element can be suppressed to a smaller value than when the reflective surface of the reflector is concave.

  In the detection device according to one aspect of the present embodiment, it is preferable that the reflection surface of the reflector is plated with gold.

  According to the above configuration, it is possible to cause the light receiving element to efficiently receive the Rayleigh scattered light leaked from the side surface of the optical fiber as compared to the case where the reflection surface of the reflector is not plated with gold.

  The detection device according to one aspect of the present embodiment preferably further includes a light receiving element holder for holding the light receiving element, and the surface of the light receiving element holder is preferably subjected to black alumite processing.

  According to the above configuration, light other than Rayleigh scattered light leaked from the side surface of the optical fiber (for example, light leaked from the fusion point) is reflected on the surface of the light receiving element holder and is incident on the light receiving element. It can be suppressed. Therefore, it is possible to suppress an increase in the error included in the monitor value caused by the light receiving element receiving light other than the Rayleigh scattered light leaked from the side surface of the optical fiber.

  In the detection device according to one aspect of the present embodiment, the light receiving surface of the light receiving element is preferably surrounded by a frame that reflects the Rayleigh scattered light.

  According to the above configuration, after being reflected toward the reflector by the frame, Rayleigh scattered light reflected toward the light receiving element by the reflecting surface of the reflector is incident on the light receiving surface of the light receiving element It can be done. Thus, the Rayleigh scattered light leaked from the side surface of the optical fiber can be more efficiently received by the light receiving element.

  The detection device according to one aspect of the present embodiment further includes a fiber holder that holds a section including the fusion point of the optical fiber, and the light receiving element holder is integrated with the fiber holder. Is preferred.

  According to the above configuration, the light leaked from the fusion point of the optical fiber can be converted to heat in the fiber holder and diffused to the outside.

  In the detection device according to one aspect of the present embodiment, it is preferable that the surface of the fiber holder is subjected to black alumite processing.

  According to the above configuration, it is possible to suppress that the light leaked from the fusion point of the optical fiber is reflected by the fiber holder and is incident on the light receiving element. Therefore, it is possible to suppress an increase in the error included in the monitor value, which is caused when the light leaked from the fusion point of the optical fiber is received by the light receiving element.

  In order to solve the above problems, a fiber laser according to one aspect of the present embodiment includes: an amplification fiber; and a resonator constituted by a pair of fiber Bragg gratings connected to both ends of the amplification fiber; A fiber laser comprising a delivery fiber for guiding laser light generated by a resonator, according to an aspect of the present embodiment, as a detection device for detecting Rayleigh scattered light leaked from the side surface of the delivery fiber. It has a detection device.

  According to the above configuration, a fiber laser capable of outputting a monitor value with higher accuracy than before, or a fiber that executes control with higher accuracy than before based on a monitor with higher accuracy than before A laser can be realized.

  In the fiber laser according to one aspect of the present embodiment, the delivery fiber preferably includes a cladding mode stripper on the output end side of the detection device.

  According to the above configuration, the influence of the reflected light on the monitor value can be reduced.

  In the fiber laser according to one aspect of the present embodiment, a control unit that controls the power of excitation light based on the power of Rayleigh scattered light detected by the detection device so as to reduce fluctuation of the power of output light. Preferably, it further comprises

  According to the above configuration, it is possible to realize a fiber laser that performs power control with higher accuracy than before based on a monitor value with higher accuracy than before.

  In order to solve the above-mentioned subject, a fiber laser system concerning one mode of this embodiment is a combiner which multiplexes a plurality of fiber lasers, and a laser beam generated by each of a plurality of above-mentioned fiber lasers, and the above. An output fiber for guiding output light obtained by a combiner, according to an aspect of the present embodiment, as a detection device for detecting Rayleigh scattered light leaked from the side surface of the output fiber, in a fiber laser system comprising: It has a detection device.

  According to the above configuration, based on the fiber laser system capable of outputting monitor values with higher accuracy than in the past, or based on the monitor values with higher accuracy than in the past, control with higher accuracy than before is executed. A fiber laser system can be realized.

  According to the present embodiment, it is possible to realize a detection device in which the increase in the error included in the monitor value, which accompanies the change in the relative position of the optical fiber, the reflector, and the light detector, is suppressed smaller than that in the related art.

1 Detection Device (First Embodiment)
11 photodetector 11a photodiode (light receiving element)
11a1 Photodiode's light receiving surface 11b DO package (frame)
12 base plate (reflector)
12a Top surface of the base plate (reflection surface)
13 PD holder 14 top plate 15 front plate 16 rear plate 2 detection device (second embodiment)
21 photodetector 21a photodiode (light receiving element)
21a1 Photodiode's light receiving surface 21b DO package (frame)
22 Fiber Holder 23 PD Holder 24 Reflective Plate (Reflector)
24a Reflector plate top surface (reflection surface)
25 top plate FL fiber laser P fusion point (structure for removing reflected light)
FLS fiber laser system

Claims (5)

In a fiber laser or a detection method for detecting Rayleigh scattered light leaked from a side of an optical fiber included in a fiber laser system,
The method includes a determination step of determining whether the Rayleigh scattered light detected by the detection device is derived from the return light or the output light based on the waveform of the Rayleigh scattered light.
A detection method characterized by The method further includes an output light monitoring step of monitoring the power of Rayleigh scattered light determined to be derived from the output light in the determination step.
The detection method according to claim 1, characterized in that: The method further includes a return light monitoring step of monitoring the power of Rayleigh scattered light determined to be derived from the return light in the determination step.
The detection method according to claim 1 or 2, characterized in that: In the above determination step, the waveform width of the Rayleigh scattered light is determined in advance as to whether the Rayleigh scattered light detected by the detection device is derived from the return light or the output light. Determine by comparing with the reference value,
The detection method according to any one of claims 1 to 3, characterized in that: In a detection device for detecting Rayleigh scattered light leaked from the side surface of an optical fiber included in a fiber laser or a fiber laser system,
A determination means is provided for determining based on the waveform of the Rayleigh scattered light whether the Rayleigh scattered light detected by the detection device is derived from the return light or derived from the output light. ,
A detection device characterized by

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