JP2020060658A - Optical device and laser device - Google Patents

Abstract

To provide an optical device or a laser device which suppress local heating caused by SRS light, etc.SOLUTION: An optical device 8A is used in a laser device 1A emitting laser light. The optical device comprises: a core; a cladding covering the core and having refractive index lower than the core; a first slant type FBG11a and a second slant type FBG11b formed on the core. The first slant type FBG and the second slant type FBG blocks a wavelength range of the SRS light generated by the laser light, and have transmissivities different to one another in the wavelength range.SELECTED DRAWING: Figure 1

Description

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

The maximum output of the laser device is limited by stimulated Raman scattering (SRS) that occurs nonlinearly with respect to the laser output.
Patent Document 1 below discloses forming a slant type FBG (Fiber Bragg Grating) in the core of a laser device. With this configuration, the SRS light can be selectively removed from the light propagating in the core, the signal light propagating in the core can be stabilized, and the pumping light source can be prevented from being damaged.
When the slant type FBG is formed on the core, the coating portion may be partially removed, the processing light may be applied to the core, and then the portion may be coated again by the recoating portion.

U.S. Pat. No. 9,634,462

  In the high-power laser device, when the SRS light is removed by using the slant type FBG, the removed high-power SRS light is radiated to the recoating portion or the coating portion. At this time, if the SRS light is radiated in a concentrated manner at one point, the energy absorbed at the time of transmission causes local heat generation, which may cause deterioration in the re-covered portion or the coated portion.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide an optical device or a laser device capable of suppressing local heat generation in the recoating portion or the coating portion due to SRS light.

  In order to solve the above problems, an optical device according to a first aspect of the present invention is an optical device used in a laser device that emits laser light, and covers a core and the core, and is lower than the core. A clad having a refractive index, and a first slant type FBG and a second slant type FBG formed on the core, wherein the first slant type FBG and the second slant type FBG are SRS generated by the laser light. It blocks the wavelength band of light and has different transmittances in the wavelength band.

  When the optical device according to the above aspect is used in the laser device, the transmittance of the slant type FBG located on the upstream side in the propagation direction of the SRS light is made larger than the transmittance of the slant type FBG located on the downstream side. It is possible to reduce the difference in the power of the SRS light removed on the upstream side and the downstream side. Accordingly, for example, as compared with the case where the first slant type FBG and the second slant type FBG have the same transmittance, the slant type FBG located on the upstream side intensively removes the SRS light and the re-covered portion is It is possible to suppress local heat generation.

  Here, the optical device of the above aspect further includes a third slant type FBG formed in the core, and the first slant type FBG, the second slant type FBG, and the third slant type FBG are the cores. The second slant type FBGs may be arranged in this order along the longitudinal direction of, and have a smaller transmittance than the first slant type FBG and the third slant type FBG.

  In this case, regarding the SRS light traveling from the first slant type FBG to the second slant type FBG, the power of the SRS light incident on the second slant type FBG is smaller than the power of the light incident on the first slant type FBG. Therefore, by making the transmittance of the second slant type FBG smaller than that of the first slant type FBG, it is possible to reduce the difference in the power of the SRS light shielded by the first and second slant type FBGs. In addition, the same action and effect can be obtained for the SRS light traveling from the third slant type FBG to the second slant type FBG. That is, even if the SRS light propagates in either direction in the optical device, it is possible to suppress the recoating portion or the like from locally generating heat. Therefore, the optical device having this configuration can be suitably used when the propagation direction of the SRS light cannot be specified or when the SRS light propagates bidirectionally.

  Further, three or more slant type FBGs including the first slant type FBG and the second slant type FBG are formed in the core, and the three or more slant type FBGs are arranged along the longitudinal direction of the core. While being arranged, the transmittance may gradually decrease from one side to the other side in the longitudinal direction.

  In this case, when the optical device is arranged such that the direction from the one side to the other side in the longitudinal direction and the propagation direction of the SRS light are aligned, the slant type FBG located on the downstream side in the propagation direction of the SRS light is arranged. The transmittance becomes smaller than that of the slant type FBG located on the upstream side in the propagation direction of SRS light. That is, the transmittance of the slant type FBG becomes gradually smaller along the propagation direction of the SRS light, so that the SRS light can be more surely dispersed and removed.

  A laser device according to a second aspect of the present invention includes the optical device, a laser light source that generates laser light, and an output end that outputs the laser light, and the optical device includes the laser light source. The second slant type FBG is arranged between the first slant type FBG and the output end, and the second slant type FBG has a smaller transmittance than the first slant type FBG.

  According to the laser device of the second aspect, the second slant type FBG is arranged more downstream than the first slant type FBG in the traveling direction of the SRS light generated by the laser light. Therefore, the SRS light that has not been removed (remains) by the first slant type FBG is incident on the second slant type FBG. That is, the power of the SRS light incident on the second slant type FBG is smaller than the power of the SRS light incident on the first slant type FBG. Then, since the transmittance of the second slant type FBG is smaller than that of the first slant type FBG, the power of SRS light removed by the first slant type FBG and the power of SRS light removed by the second slant type FBG , The difference between can be reduced. As a result, for example, as compared with the case where the first slant type FBG and the second slant type FBG have the same transmittance, the SRS light is intensively removed by the first slant type FBG and absorbed by the coating or the like. It is possible to suppress local heat generation. Furthermore, since the SRS light is also prevented from being emitted from the output end, the quality of the laser light becomes stable.

  A laser device according to a third aspect of the present invention includes the optical device, a laser light source that generates laser light, and an output end that outputs the laser light, and the optical device is the laser light source. The second slant type FBG, which is disposed between the output end and the second slant type FBG, is disposed closer to the laser light source than the first slant type FBG, and has a smaller transmittance than the first slant type FBG.

  According to the laser device of the third aspect, the second slant type FBG is more downstream than the first slant type FBG in the propagation direction of the SRS light (reverse SRS light) traveling toward the laser light source in the laser device. Is located in. The retrograde SRS light is generated by the SRS light generated by the laser light traveling toward the output end being reflected at the output end, or by the laser light reflected from the processing target of the laser device and re-incident at the output end. Then, the retrograde SRS light not removed (remained) by the first slant type FBG is incident on the second slant type FBG. That is, the power of the retrograde SRS light incident on the second slant type FBG is smaller than the power of the retrograde SRS light incident on the first slant type FBG. Further, since the transmittance of the second slant type FBG is smaller than that of the first slant type FBG, the power of the retrograde SRS light removed by the first slant type FBG and the retrograde SRS light removed by the second slant type FBG are The difference between the power and the power can be reduced. Thereby, for example, as compared with the case where the first slant type FBG and the second slant type FBG have the same transmittance, the retrograde SRS light is intensively removed by the first slant type FBG and is absorbed by the re-covering portion or the like. It is possible to suppress local heat generation due to the above. Further, since the retrograde SRS light is also prevented from entering the laser light source, it is possible to suppress the failure of the laser light source.

  A laser device according to a fourth aspect of the present invention includes the optical device, an excitation light source that emits excitation light, a resonator that generates laser light by the excitation light, and an output end that outputs the laser light. And the optical device is disposed between the excitation light source and the resonator, the second slant type FBG is disposed closer to the excitation light source than the first slant type FBG, and The transmittance is smaller than that of the first slant type FBG.

  According to the laser device of the fourth aspect, by the same operation as the laser device of the third aspect, the retrograde SRS light is intensively removed by the first slant type FBG and is absorbed by the re-covering portion or the like. It is possible to suppress local heat generation. Further, it is possible to suppress the retrograde SRS light from entering the pumping light source, so that it is possible to suppress the failure of the pumping light source.

  According to the above aspect of the present invention, it is possible to provide an optical device or a laser device capable of suppressing local heat generation in the recoating portion and the coating portion due to SRS light.

It is a block diagram which shows the structure of the laser apparatus which concerns on 1st Embodiment. It is a schematic diagram of the optical device of FIG. It is a graph which shows the light-shielding rate and the power of the light shielded of each slant type FBG in an Example. (A)-(c) is a graph which shows the light shielding performance of each slant type FBG which concerns on an Example. It is a block diagram which shows the structure of the laser apparatus which concerns on 2nd Embodiment.

(First embodiment)
Hereinafter, the optical device and the laser device of the first embodiment will be described with reference to the drawings.
As shown in FIG. 1, the laser device 1A includes a laser light source L that generates laser light, an output end 7, and an optical device 8A that is arranged between the laser light source L and the output end 7. . The laser light source L includes a plurality of excitation light sources 2, a combiner 3, an HR-FBG (High Reflectivity-Fiber Bragg Grating) 4, an amplification fiber 5, and an OC-FBG (Output Coupler-Fiber Bragg Grating) 6, Is equipped with. The amplification fiber 5, the HR-FBG 4, and the OC-FBG 6 form a resonator R that generates laser light by the excitation light emitted from the excitation light source 2.

  The laser device 1A of the present embodiment is a fiber laser device in which the laser light source L includes the amplification fiber 5. The type of the laser light source L can be changed appropriately. That is, the present embodiment may be applied to a laser device of a type other than the fiber laser device. For example, the present invention is also applicable to a laser device such as a semiconductor laser (DDL: Direct Diode Laser) or a disk laser in which a resonator is composed of a fiber other than an optical fiber and a laser beam emitted from the resonator is output from an output end 7. is there.

(Direction definition)
As shown in FIGS. 1 and 2, the optical device 8A includes an optical fiber 10. Hereinafter, the longitudinal direction of the optical fiber 10 (the longitudinal direction of the core) is simply referred to as the longitudinal direction X. Further, when viewed from the optical fiber 10, the output end 7 side in the longitudinal direction X is called + X side, and the excitation light source 2 side is called −X side.

The excitation light source 2 emits the excitation light toward the amplification fiber 5. As the excitation light source 2, for example, a laser diode can be used.
The combiner 3 is arranged between the excitation light source 2 and the resonator R. The combiner 3 couples the excitation light emitted by the excitation light source 2 into one optical fiber and directs it to the amplification fiber 5.

  The amplification fiber 5 has a core to which one or more kinds of active elements are added, a first cladding that covers the core, a second cladding that covers the first cladding, and a coating that covers the second cladding. are doing. The amplification fiber 5 is a double-clad fiber. As the active element added to the core, for example, a rare earth element such as erbium (Er), ytterbium (Yb), or neodymium (Nd) is used. These active elements emit light in the excited state. Silica glass or the like can be used for the core and the first cladding. A resin such as a polymer can be used for the second clad. As the coating, a resin material such as an acrylic resin or a silicone resin can be used.

The HR-FBG 4 is formed in the core of an optical fiber fusion-spliced to the −X side end of the amplification fiber 5. The HR-FBG4 is adjusted so as to reflect the light of the wavelength of the signal light of the light emitted by the active element of the amplification fiber 5 in the excited state at a reflectance of almost 100%. It has a structure in which high refractive index portions are repeated at regular intervals along the longitudinal direction.
The OC-FBG 6 is formed in the core of the optical fiber fused to the + X side end of the amplification fiber 5. The OC-FBG6 has a structure similar to that of the HR-FBG4, but is adjusted to reflect light with a lower reflectance than the HR-FBG4.

  In the amplification fiber 5, the signal light reflected by the HR-FBG 4 and the OC-FBG 6 reciprocates in the longitudinal direction of the amplification fiber 5. The signal light is amplified along with this round trip to become laser light. In this way, in the resonator R, the light is amplified and laser light is generated. Part of the laser light passes through the OC-FBG 6 and reaches the output end 7 via the optical device 8A. The optical device 8A is configured to transmit the laser light and remove at least a part of the SRS light generated by the laser light.

(Optical device)
FIG. 2 is a schematic diagram showing the configuration of the optical device 8A. As shown in FIG. 2, the optical device 8A includes an optical fiber 10. The optical fiber 10 is a single clad fiber having a core 11, a clad 12, and a coating 13. Silica glass or the like can be used for the core 11 and the clad 12. The clad 12 covers the core 11 and has a lower refractive index than the core 11. The coating 13 covers the clad 12 and has a higher refractive index than the clad 12. As the coating 13, a resin material such as acrylic resin or silicone resin can be used. These resin materials used as the coating 13 generally absorb light and generate heat.

(Slant type FBG)
A plurality of slant type FBGs 11a to 11c are formed on the core 11. The plurality of slant type FBGs 11a to 11c are arranged in series at intervals in the longitudinal direction X. In the example of FIGS. 1 and 2, the number of slant type FBGs 11a to 11c is three. The first slant type FBG 11a, the second slant type FBG 11b, and the third slant type FBG 11c are arranged in this order along the longitudinal direction X from the -X side to the + X side. However, the number of slant type FBGs formed in the core 11 may be two, or may be four or more.

  The slant type FBGs 11a to 11c are formed by partially irradiating the core 11 with a processing light beam (such as an ultraviolet laser beam) to modulate the refractive index. In this embodiment, in order to form the slant type FBGs 11a to 11c, the coating 13 is partially removed, and the processing light beam is applied to the core 11 through the removed portion. Further, the removed portion is covered with the recoating portions 14a to 14c after the slant type FBGs 11a to 11c are formed. Therefore, the outer peripheral surface of the portion of the clad 12 that covers the region of the core 11 in which the slant type FBGs 11a to 11c are formed is covered with the recoating portions 14a to 14c. If the coating 13 is made of a material that sufficiently transmits the processing light beam, the coating 13 may not be removed. In this case, the optical device 8A may not include the recoating portions 14a to 14c.

  A resin material having a refractive index higher than that of the clad 12 can be used for the recoating portions 14 a to 14 c. The material of the recoating portions 14a to 14c may be the same as or different from the material of the coating 13.

  In the longitudinal direction X, the first recoating portion 14a is arranged at a position corresponding to the first slant type FBG 11a. Similarly, the second recoating portion 14b and the third recoating portion 14c are arranged at positions corresponding to the second slant type FBG 11b and the third slant type FBG 11c. Moreover, since the slant type FBGs 11a to 11c are arranged at intervals in the longitudinal direction X, the recoating portions 14a to 14c are also arranged at intervals in the longitudinal direction X. In this way, the number and positions of the recoating portions 14a to 14c are determined according to the number and positions of the slant type FBGs 11a to 11c formed on the core 11.

  However, after the coating 13 in the range where the plurality of slant type FBGs 11a to 11c are formed is collectively removed and the plurality of slant type FBGs 11a to 11c are formed in the collectively removed portion, one re-removal is performed in the collectively removed portion. You may provide a coating part continuously. In this case, the position of the recoating portion corresponds to the position of the slant type FBGs 11a to 11c, but the number of recoating portions does not correspond to the number of the slant type FBGs 11a to 11c.

  The slant type FBGs 11a to 11c are configured to transmit light in the wavelength band of signal light used as laser light, and escape light in the wavelength band of SRS light generated by laser light from the core 11 toward the cladding 12. ing. That is, each of the plurality of slant type FBGs 11a to 11c blocks the wavelength band of the SRS light generated by the laser light.

  As schematically shown in FIG. 2, in the slant type FBGs 11a to 11c of the present embodiment, the intervals between the refractive index modulation portions in the longitudinal direction X are nonuniform. As a result, the wavelength band of the light removed from the core 11 in the slant type FBGs 11a to 11c becomes large. Therefore, the SRS light can be more reliably released toward the cladding 12. As described above, the SRS light is selectively removed from the core 11 and absorbed by the coating 13 or the recoating portions 14a to 14c, so that the quality of the signal light can be stabilized.

  Here, for example, when the SRS light is concentrated and removed by one slant type FBG, the removed SRS light is concentrated and absorbed by the coating 13 or the recoating portions 14a to 14c. As a result, the coating 13 or the recoating portions 14a to 14c may locally generate heat, which may cause deterioration or the like.

Therefore, in the present embodiment, the plurality of slant type FBGs 11a to 11c have different light blocking rates in the wavelength band of SRS light so that the SRS light is dispersed as much as possible and absorbed by the coating 13 or the recoating portions 14a to 14c.
The details will be described below.

  In the present embodiment, a case will be considered where the SRS light propagating in the optical fiber 10 toward the + X side is removed. In this case, a part of the SRS light is first removed by the first slant type FBG 11a located closest to the −X side. Then, the SRS light that has not been removed (remains) goes to the second slant type FBG 11b. Therefore, the power of the SRS light incident on the second slant type FBG 11b is smaller than the power of the SRS light incident on the first slant type FBG 11a. Similarly, the power of the SRS light incident on the third slant type FBG 11c is smaller than the power of the SRS light incident on the second slant type FBG 11b.

  That is, the power of the incident SRS light becomes smaller as the slant type FBG located closer to the + X side. On the other hand, the SRS light removed by each of the slant type FBGs 11a to 11c is absorbed by the coating 13 or the recoating portions 14a to 14c, respectively. Here, in order to suppress the local heat generation in the coating 13 or the recoating portions 14a to 14c, it is preferable that the powers of the SRS light removed by the slant type FBGs 11a to 11c are made to be close to each other (equalization). That is, it is preferable that the SRS light is not concentrated and absorbed at one point but is dispersed as much as possible and absorbed by the coating 13 or the recoating portions 14a to 14c.

From the above, it is preferable to make the transmittance of the SRS light in the wavelength band smaller in the slant type FBG located on the + X side. That is, it is preferable that each of the slant type FBGs 11a to 11c has a transmittance that gradually decreases from the − side to the + side in the longitudinal direction.
The transmittance here is the ratio of the power of the SRS light that is blocked by the slant type FBG to the power of the SRS light that is incident on a certain slant type FBG. For example, when the transmittance is 0.3, when 10 W SRS light is incident, 3 W SRS light is removed from the core 11 and 7 W SRS light remains in the core 11.

  When the transmittance is set to be smaller for the slant type FBG located on the + X side, the proportion of the SRS light to be removed decreases in the slant type FBG on the −X side where the SRS light of large power is incident, and the SRS light of small power is generated. In the incident + X side slant type FBG, the proportion of SRS light to be removed becomes large. Therefore, the power of the SRS light removed by each slant type FBG is equalized.

More specifically, the optical device 8A of the present embodiment is arranged between the resonator R and the output end 7, and the core 11 of the optical device 8A has a first slant type FBG 11a and a second slant type. The FBG 11b is formed. Since the second slant type FBG 11b is arranged closer to the output end 7 side (+ X side) than the first slant type FBG 11a, the power of the SRS light incident on the second slant type FBG 11b is incident on the first slant type FBG 11a. It is smaller than the power of SRS light.
Further, in the present embodiment, the transmittance of the second slant type FBG 11b in the wavelength band of SRS light is smaller than that of the first slant type FBGFBG 11a.

  According to this configuration, for example, the power of the SRS light removed by the first slant type FBG 11a and the second slant type FBG 11a and the second slant type FBG 11b are compared to the case where the transmittances are made equal. The difference between the power of the SRS light removed by the FBG 11b and the power of the SRS light can be reduced. As described above, by equalizing the powers of the SRS light removed by the slant type FBGs 11a and 11b, it is possible to prevent the SRS light from being concentrated and absorbed at one point such as the coating 13 and to locally generate heat. Can be suppressed. Furthermore, since the SRS light is also prevented from being emitted from the output end 7, the quality of the laser light becomes stable.

  Although the relationship between the transmittances of the first slant type FBG 11a and the second slant type FBG 11b has been described above, the same applies when three or more slant type FBGs are formed in the core 11 of the optical device 8A. That is, by setting the transmittance to be smaller for the slant type FBG located closer to the output end 7 side (+ X side), the power of the SRS light removed by the three or more slant type FBGs is equalized, dispersed, and covered 13. Etc. can be absorbed.

Next, the setting of the ideal transmittance of each slant type FBG will be described. In the following, the “light blocking rate T _i ” calculated based on the transmittance is used. The light blocking rate T _i is defined by the following mathematical formula 1.

In Formula 1, R _i represents the transmittance. For example, when the transmittance R _i = 0.9, the light blocking ratio T _i = −0.45 [dB]. Further, when the transmittance R _i = 0.5, the light blocking ratio T _i = −3.01 [dB]. As described above, the smaller the transmittance R _i (the higher the light blocking property of SRS light), the larger the absolute value of the light blocking ratio T _i . In other words, a large absolute value of the light blocking rate T _i means that the slant type FBG has a high ability to remove SRS light.

In the following description, for generalization, the number of slant type FBGs formed in the core 11 is represented by n (n = 3 in FIG. 2). Further, the position of the slant type FBG counted from the −X side is represented by i. For example, in FIG. 2, the first slant type FBG 11a corresponds to i = 1, and the third slant type FBG 11c corresponds to i = 3. Further, the light blocking rate of the slant type FBG corresponding to the position i is represented by T _i . The condition for equalizing the power removed by each slant type FBG is to satisfy the following mathematical expression (2).

By setting the light blocking rate T _i as shown in Expression (2), the power of the SRS light removed from each slant type FBG is made uniform, and the SRS light is more surely dispersed to cover the coating 13 or the recoating portion. It can be absorbed by 14a to 14c.
When i = n, the slant type FBG is located closest to the + X side, and the power of the incident SRS light in the optical device 8A is the smallest. Therefore, for the slant type FBG corresponding to i = n, it is preferable to reduce the transmittance R as much as possible to remove the SRS light toward the output end 7. That is, it is preferable that the absolute value of the light blocking rate T _n when i = n is as large as possible. Specifically, the absolute value of the light blocking ratio T _n is good greater than the absolute value of the light blocking ratio T _n-1. Thereby, the SRS light can be removed more reliably and the quality of the signal light output from the output end 7 can be stabilized.

Here, setting of the light blocking rate of the slant type FBG will be described using a specific example. In this embodiment, the number of slant type FBGs formed in the core 11 of the optical device 8A is n = 10. Then, for the slant type FBG corresponding to i = 1 to 9, the light blocking rate T _i was set so as to satisfy the mathematical expression (2). For the slant type FBG corresponding to i = 10, the light blocking rate T _i was set with the transmittance R _{i set} to 0.001. Further, the central value of the wavelength of the signal light is set to 1070 nm, and the SRS light in the wavelength band of 1100 to 1160 nm is removed. The power of the SRS light incident on the −X side end of the optical device 8A is assumed to be 100W.

FIG. 3 is a graph showing the relationship between the light blocking rate T _i of each slant type FBG set as described above and the power P _{i of the} SRS light removed from the core 11 by each slant type FBG. The horizontal axis of FIG. 3 indicates the position (i) of the slant type FBG. The first vertical axis (left side) of FIG. 3 is the light blocking rate T _i [dB] of each slant type FBG. The second vertical axis (right side) of FIG. 3 is the power P _i [W] of the SRS light removed from the core by each slant type FBG.

When calculated based on the mathematical expression (1), the light blocking rate T ₁ = −0.45 for the slant type FBG corresponding to i = 1. The power of SRS light removed by this slant type FBG is P ₁ = 10 [W].
Similarly, for the slant type FBG corresponding to i = 9, T ₉ = −3.0 [dB] and P ₉ = 10 [W]. Also, the slanted FBG corresponding to _{i = 10, T10 = -30 [} dB], the P 10 = 10 [W].

As described above, according to the setting of the present embodiment, the power P _i of the removed SRS light becomes equal for any of the slant type FBGs with i = 1 to 10. Therefore, the SRS light is uniformly dispersed and absorbed by the coating 13 and the like, and local heat generation of the coating 13 can be suppressed.

The slant type FBG provided in the optical device 8A needs to block the SRS light and transmit the signal light. Therefore, the light blocking rate T _i of the slant type FBG described above is for the wavelength band of SRS light. Hereinafter, the relationship between the wavelength band and the light blocking rate in the slant type FBG will be described with reference to FIGS.

FIG. 4A is a graph showing the light shielding performance of the slant type FBG corresponding to i = 1 in the above embodiment. The horizontal axis of FIG. 4A indicates the wavelength, and the vertical axis indicates the light blocking rate for each wavelength. In the above embodiment, it is assumed that the central wavelength of the signal light is 1070 nm and the wavelength band of the SRS light is 1100 to 1140 nm. Therefore, the light blocking rate at 1070 nm is set to be almost 0 [dB], and the signal light is set to be transmitted. On the other hand, for the wavelength band of 1100 to 1140 nm, the light blocking rate T ₁ = −0.45 [dB] is set as described in the above embodiment.

FIGS. 4B and 4C are graphs showing the light-shielding performance of the slant type FBG corresponding to i = 9 and 10 in the above embodiment. The shapes of the graphs of FIGS. 4B and 4C are similar to those of FIG. 4A, and are set so as to transmit the signal light (1070 nm) and block the SRS light (1100 to 1140 nm). The light blocking rate in the wavelength band of the SRS light is T ₉ = −3.0 [dB] when i = ₉ and T ₁₀ = −30 [dB when i = 10, as described in the above embodiment. ] Has become.
By providing such a light blocking performance, it is possible to disperse and remove the SRS light by each slant type FBG while transmitting the signal light.

The light blocking rate for each wavelength band can be set by adjusting the intensity of the ultraviolet light with which the core 11 is irradiated when the slant type FBG is formed, the irradiation time, the number of FBG forming surfaces, and the like.
Further, although the wavelength band of SRS light is assumed to be 1100 to 1140 nm in the above description, the wavelength band of SRS light differs depending on the central wavelength of signal light. Generally, the wavelength band of SRS light is a band shifted from the center wavelength of signal light to the range of +30 to +70 nm. Therefore, the light blocking characteristics of the slant type FBG may be adjusted according to the central wavelength of the signal light.

(Second embodiment)
Next, a second embodiment according to the present invention will be described, but the basic configuration is the same as that of the first embodiment. Therefore, the same reference numerals are given to the same configurations, the description thereof is omitted, and only different points will be described.

  In the present embodiment, a configuration will be described in which SRS light propagating toward the -X side (hereinafter referred to as retrograde SRS light) is removed. The retrograde SRS light is generated, for example, by SRS light traveling toward the + X side being reflected at the output end 7 or by laser light reflected by the processing target of the laser device and re-incident on the output end 7. When such retrograde SRS light reaches the pumping light source 2, it causes a failure of the pumping light source 2, and therefore is preferably removed before reaching the pumping light source 2. However, if the SRS light is concentrated and removed at one place, it causes local heat generation of the recoating portion 14, and therefore it is preferable to disperse and remove the SRS light similarly to the first embodiment.

  Therefore, in this embodiment, the retrograde SRS light is dispersed and removed. FIG. 5 is a diagram showing the configuration of the laser device 1B in this embodiment. In this embodiment, the position of the optical device is different from that in the first embodiment. More specifically, the optical device 8B is located between the combiner 3 and the resonator R. In the optical device 8B, the second slant type FBG 11b is located closer to the excitation light source 2 side (-X side) than the first slant type FBG 11a. The third slant type FBG 11c is located closer to the excitation light source 2 than the second slant type FBG 11b is.

  In other words, the second slant type FBG 11b is located downstream of the first slant type FBG 11a in the propagation direction of the retrograde SRS light. Therefore, the power of the retrograde SRS light incident on the second slant type FBG 11b is smaller than the power of the retrograde SRS light incident on the first slant type FBG 11a. Further, the transmittance of the second slant type FBG 11b is set smaller than that of the first slant type FBG 11a. Therefore, the difference between the power of the retrograde SRS light removed by the first slant type FBG 11a and the power of the retrograde SRS light removed by the second slant type FBG 11b can be reduced. Thereby, as compared with the case where the transmittances of the first slant type FBG 11a and the second slant type FBG 11b are made equal to each other, the retrograde SRS light is concentratedly removed by the first slant type FBG 11a, and the recoating portions 14a to 14c. It is possible to suppress local heat generation due to being absorbed by the like. Further, since the retrograde SRS light is also prevented from entering the pumping light source 2, the pumping light source 2 can be prevented from malfunctioning.

  Although the relationship between the transmittances of the first slant type FBG 11a and the second slant type FBG 11b has been described above, the same applies when three or more slant type FBGs are formed in the core 11 of the optical device 8B. That is, by making the transmittance of the slant type FBG located closer to the excitation light source 2 side (−X side) smaller, the power of the retrograde SRS light removed by three or more slant type FBGs is equalized and dispersed. Can be emitted from the recoating portions 14a to 14c.

  The technical scope of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, the optical device 8A of the first embodiment or the optical device 8B of the second embodiment may be applied to a bidirectional pump type laser device including a forward pump light source and a backward pump light source.

  Further, one laser device may be provided with both the optical device 8A of the first embodiment and the optical device 8B of the second embodiment. In this case, the SRS light propagating toward the + X side can be removed by the optical device 8A, while the retrograde SRS light propagating toward the -X side can be removed by the optical device 8B.

  Further, a plurality of optical devices 8A and 8B may be arranged in series in the laser devices 1A and 1B. In this case, the plurality of optical devices 8A, the optical devices 8B, or the optical devices 8A and 8B may be directly fusion-bonded to each other, or optical transmission such as an optical fiber may be provided between the optical devices. A passage may be provided.

  In addition, in the first embodiment, the transmittance of the slant type FBG located on the + X side is further reduced, so that the SRS light propagating toward the + X side is dispersed and removed from the core 11. Further, in the second embodiment, the SRS light propagating toward the −X side is dispersed and removed from the core 11 by further reducing the transmittance of the slant type FBG located on the −X side. Here, three or more slant type FBGs may be formed in one optical device, and the transmittance of the slant type FBG located closer to the center in the longitudinal direction X may be further reduced.

  In other words, the transmittance may be increased as the slant type FBG is closer to the end in the longitudinal direction X of the optical device. According to this configuration, one optical device can disperse and remove both the SRS light propagating toward the + X side and the retrograde SRS light propagating toward the −X side from the core 11. . When this configuration is applied to, for example, the laser device 1A in the first embodiment, the transmittance of the second slant type FBG 11b is made smaller than the transmittance of the first slant type FBG 11a and the third slant type FBG 11c. Similarly, in the laser device 1B according to the second embodiment, the transmittance of the second slant type FBG 11b may be smaller than the transmittance of the first slant type FBG 11a and the third slant type FBG 11c.

Further, in the first embodiment, in order to evenly remove the retrograde SRS light generated by the return light or the like, the slant type FBG having a small transmittance is arranged on the −X side of the slant type FBG having a large transmittance. Good.
Further, the optical device 8A in the first embodiment and the optical device 8B in the second embodiment have the same basic configuration except that the position and the direction in which they are arranged in the laser device are different. . That is, the optical device 8A and the optical device 8B have the same configuration when viewed alone. Considering this point, three or more slant type FBGs 11a to 11c are arranged side by side in the core 11, and the transmittance of the slant type FBGs 11a to 11c gradually decreases from one side to the other side in the longitudinal direction of the core 11. An optical device should be adopted. Then, by appropriately selecting whether the one side of the optical device is the + X side or the −X side of the laser device, the SRS light traveling toward the + X side is uniformly removed or −X. It is possible to select whether the retrograde SRS light traveling toward the side should be equalized and removed.

  In addition, it is possible to appropriately replace the constituent elements in the above-described embodiments with known constituent elements without departing from the spirit of the present invention, and the above-described embodiments and modified examples may be appropriately combined.

  1A, 1B ... Laser device 2 ... Excitation light source 3 ... Combiner 8A, 8B ... Optical device 10 ... Optical fiber 11 ... Core 11a-11c ... Slant type FBG 12 ... Clad 13 ... Coating 14a-14c ... Recoating part L ... Laser light source

Claims (6)

An optical device used for a laser device that emits laser light,
With the core,
A clad that covers the core and has a lower refractive index than the core;
A first slant type FBG and a second slant type FBG formed on the core;
An optical device in which the first slant type FBG and the second slant type FBG shield the wavelength band of SRS light generated by the laser light and have different transmittances in the wavelength band. Further comprising a third slant type FBG formed on the core,
The first slant type FBG, the second slant type FBG, and the third slant type FBG are arranged in this order along the longitudinal direction of the core,
The optical device according to claim 1, wherein the second slant type FBG has a smaller transmittance than the first slant type FBG and the third slant type FBG. Three or more slant type FBGs including the first slant type FBG and the second slant type FBG are formed in the core,
The three or more slant type FBGs are arranged side by side along the longitudinal direction of the core, and the transmittance gradually decreases from one side to the other side in the longitudinal direction. The optical device described. An optical device according to any one of claims 1 to 3,
A laser light source that generates laser light,
An output end for outputting the laser light,
The optical device is disposed between the laser light source and the output end,
The laser device in which the second slant type FBG is arranged closer to the output end side than the first slant type FBG and has the smaller transmittance than the first slant type FBG. An optical device according to any one of claims 1 to 3,
A laser light source that generates laser light,
An output end for outputting the laser light,
The optical device is disposed between the laser light source and the output end,
The laser device, wherein the second slant type FBG is arranged closer to the laser light source than the first slant type FBG, and has a smaller transmittance than the first slant type FBG. An optical device according to any one of claims 1 to 3,
An excitation light source that emits excitation light,
A resonator that generates laser light by the excitation light,
An output end for outputting the laser light,
The optical device is disposed between the excitation light source and the resonator,
The laser device in which the second slant type FBG is arranged closer to the excitation light source than the first slant type FBG, and has the smaller transmittance than the first slant type FBG.

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