JP7473365B2 - Optical devices and laser devices - Google Patents

Description

The present invention relates to optical devices and laser devices.

Laser devices are currently used in a variety of fields, including processing, automotive, and medical fields. In recent years, fiber laser devices have been attracting attention in the processing field, due to their superior beam quality and focusing ability compared to conventional laser devices (e.g., carbon dioxide laser devices). The maximum output of such laser devices is limited by stimulated Raman scattering (SRS), which occurs nonlinearly with respect to the laser output.

The following Patent Document 1 discloses a technology for reducing SRS light in a fiber laser device by forming a slant-type Fiber Bragg Grating (FBG) in the core. This technology makes it possible to selectively remove SRS light from light propagating within the core. This makes it possible to stabilize the signal light propagating within the core and prevent damage to the pump light source. When forming a slant-type FBG in the core, the coating may be partially removed, the core may be irradiated with processing light, and then that portion may be recoated with a re-coating portion.

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

However, in a high-output laser device, when a slant-type FBG is used to remove SRS light, the removed high-power SRS light is radiated to the re-coated section or the coated section. If the SRS light is concentrated and radiated at one point, localized heat generation occurs due to the energy absorbed during transmission, which may cause deterioration of the re-coated section or the coated section.

The present invention has been made in consideration of the above circumstances, and aims to provide an optical device and laser device that can suppress localized heating of the recoated portion and coated portion due to SRS light.

In order to solve the above problem, an optical device according to one aspect of the present invention is an optical device (8A, 8B) used in a laser device (1A, 1B) that outputs laser light, and includes a core (11), a cladding (12) that covers the core and has a lower refractive index than the core, and a first slant-type FBG (11b) and a second slant-type FBG (11a) formed in the core, and the first slant-type FBG and the second slant-type FBG have different light-shielding bands, which are wavelength bands that block SRS light.

In an optical device according to one aspect of the present invention, a first slant-type FBG and a second slant-type FBG having different light blocking bands, which are wavelength bands that block SRS light generated by laser light, are formed in the core. This allows the first slant-type FBG and the second slant-type FBG to disperse and remove SRS light, thereby suppressing localized heating of the recoated portion and the coated portion due to SRS light.

The optical device according to one aspect of the present invention further comprises a third slant FBG (11c) formed in the core, and the third slant FBG has a light blocking band different from the first slant FBG and the second slant FBG.

In addition, in an optical device according to one aspect of the present invention, the first slant FBG has a central band (B) that includes the central wavelength component of the SRS light among the entire wavelength band of the SRS light as its light-shielding band, the second slant FBG has a short-wavelength side band (A) that is shorter than the central band as its light-shielding band, and the third slant FBG has a long-wavelength side band (C) that is longer than the central band as its light-shielding band.

In addition, in an optical device according to one aspect of the present invention, the first slant FBG has a narrower light blocking band than the second slant FBG and the third slant FBG.

In addition, in an optical device according to one aspect of the present invention, the light blocking bands are set so that the first slant type FBG, the second slant type FBG, and the third slant type FBG can remove the same amount of energy of the SRS light.

In addition, in an optical device according to one aspect of the present invention, the first slant type FGB, the second slant type FBG, and the third slant type FBG have a light blocking band ratio set to 1:4:4.

A laser device (1A) according to one aspect of the present invention includes a laser light source (L) that generates laser light, an output end (7) that outputs the laser light, and any of the optical devices (8A, 8B) described above that are disposed between the laser light source and the output end.

A laser device (1B) according to another aspect of the present invention includes an excitation light source (2) that emits excitation light, a resonator (R) that generates laser light from the excitation light, an output end (7) that outputs the laser light, and any of the optical devices (8A, 8B) described above that are disposed between the excitation light source and the resonator.

The present invention has the advantage of being able to suppress localized heating of the recoated portion or coated portion due to SRS light.

1 is a diagram showing a configuration of a main part of a laser device according to a first embodiment of the present invention; 1 is a vertical cross-sectional view showing a configuration of an optical device according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating the transmission characteristics of a slant-type FBG provided in the optical device according to the first embodiment of the present invention. FIG. 2 is a diagram showing an example of the spectrum of SRS light generated in the laser device according to the first embodiment of the present invention. FIG. 4 is a diagram showing a configuration of a main part of a laser device according to a second embodiment of the present invention.

The optical device and laser apparatus according to the embodiments of the present invention will be described in detail below with reference to the drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. Furthermore, the present invention is not limited to the following embodiments.

First Embodiment
Laser Device
Fig. 1 is a diagram showing a main configuration of a laser device according to a first embodiment of the present invention. As shown in Fig. 1, the laser device 1A of this embodiment includes a laser light source L that generates laser light, an output end 7, and an optical device 8A arranged between the laser light source L and the output end 7. The laser light source L includes a plurality of pumping light sources 2, a combiner 3, a High Reflectivity-Fiber Bragg Grating (HR-FBG) 4, an amplification fiber 5, and an Output Coupler-Fiber Bragg Grating (OC-FBG) 6. The amplification fiber 5, the HR-FBG 4, and the OC-FBG 6 constitute a resonator R that generates laser light by pumping light emitted by the pumping light source 2.

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

The pumping light source 2 emits pumping light toward the amplification fiber 5. For example, a laser diode can be used as the pumping light source 2. The combiner 3 is disposed between the pumping light source 2 and the resonator R. The combiner 3 combines the pumping light emitted by the pumping light source 2 into one optical fiber and directs it toward the amplification fiber 5.

The amplification fiber 5 includes a core doped with one or more types of active elements, a first cladding covering the core, a second cladding covering the first cladding, and a coating covering the second cladding. The amplification fiber 5 is a double-clad fiber. As the active element doped in 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 an excited state. The core and the first cladding can be made of silica glass or the like. As the second cladding, a resin such as a polymer can be used. As the coating, a resin material such as an acrylic resin or a silicone resin can be used.

The HR-FBG4 is formed in the core of an optical fiber fused to the end of the amplification fiber 5 on the -X side. The HR-FBG4 is adjusted to reflect light of the signal light wavelength emitted by the active element of the amplification fiber 5 in an excited state with nearly 100% reflectivity, and has a structure in which high refractive index portions are repeated at a constant interval along the longitudinal direction of the HR-FBG4. The OC-FBG6 is formed in the core of an optical fiber fused to the end of the amplification fiber 5 on the +X side. The OC-FBG6 has a structure similar to that of the HR-FBG4, but is adjusted to reflect light with a lower reflectivity than the HR-FBG4.

In the amplification fiber 5, the signal light reflected by the HR-FBG 4 and the OC-FBG 6 travels back and forth in the longitudinal direction of the amplification fiber 5. As the signal light travels back and forth, it is amplified and becomes laser light. In this way, light is amplified in the resonator R to generate laser light. 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 portion of the SRS light generated by the laser light.

Optical Devices
Fig. 2 is a longitudinal sectional view showing the configuration of an optical device according to a first embodiment of the present invention. 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. The core 11 and the clad 12 can be made of silica glass or the like. 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. The coating 13 can be made of a resin material such as an acrylic resin or a silicone resin. These resin materials used as the coating 13 generally absorb light and generate heat.

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

Re-coating parts 14a to 14c can be made of a resin material with a higher refractive index than cladding 12. The material of re-coating parts 14a to 14c may be the same as or different from the material of coating 13.

In the longitudinal direction X, the re-coating portion 14a is arranged at a position corresponding to the slant FBG 11a. Similarly, the re-coating portion 14b and the re-coating portion 14c are arranged at positions corresponding to the slant FBG 11b and the slant FBG 11c, respectively. Furthermore, since the slant FBGs 11a to 11c are arranged at intervals in the longitudinal direction X, the re-coating portions 14a to 14c are also arranged at intervals in the longitudinal direction X. In this way, the number and positions of the re-coating portions 14a to 14c are determined according to the number and positions of the slant FBGs 11a to 11c formed in the core 11.

However, the coating 13 may be removed in a lump from the area where multiple slant FBGs 11a-11c are to be formed, multiple slant FBGs 11a-11c are formed in the lump-removed portion, and then one re-coating portion may be provided continuously in the lump-removed portion. In this case, the position of the re-coating portion corresponds to the position of the slant FBGs 11a-11c, but the number of re-coating portions does not correspond to the number of slant FBGs 11a-11c.

The slant FBGs 11a to 11c are configured to transmit light in the wavelength band of the signal light used as the laser light, and to allow light in the wavelength band of the SRS light generated by the laser light (e.g., 1115 to 1135 nm) to escape from the core 11 toward the cladding 12. In other words, each of the multiple slant FBGs 11a to 11c blocks the wavelength band of the SRS light generated by the laser light.

As shown diagrammatically in FIG. 2, the slant FBGs 11a-11c have non-uniform spacing between the refractive index modulation sections (sections where a refractive index change is applied) in the longitudinal direction X. This broadens the wavelength band of light that is removed from the core 11 by the slant FBGs 11a-11c. This allows the SRS light to escape more reliably toward the cladding 12. In this way, the quality of the signal light can be stabilized by selectively removing the SRS light from the core 11 and absorbing it in the coating 13 or re-coating sections 14a-14c.

Here, for example, if the SRS light is concentrated and removed using one slant-type FBG, the removed SRS light is concentrated and absorbed by the coating 13 or the re-coating. As a result, the coating 13 or the re-coating may locally heat up, possibly causing degradation.

In this embodiment, as shown in FIG. 3, the light blocking bands of the SRS light in the multiple slant FBGs 11a to 11c are made different from each other, and the SRS light is dispersed and absorbed by the coating 13 or the re-coating portions 14a to 14c. FIG. 3 is a diagram showing a schematic diagram of the transmission characteristics of a slant FBG provided in an optical device according to the first embodiment of the present invention. In FIG. 3, the horizontal axis represents the wavelength, and the vertical axis represents the transmission loss of the SRS light.

In FIG. 3, wavelength band WB1 is the wavelength band of the signal light, and wavelength band WB2 is the wavelength band of the SRS light. The wavelength band WB2 of the SRS light is on the longer wavelength side than the wavelength band WB1 of the signal light. Also, in FIG. 3, the graph shown by the solid line is a graph showing the transmission characteristics of the slant FBG 11a, the graph shown by the dashed line is a graph showing the transmission characteristics of the slant FBG 11b, and the graph shown by the dashed line is a graph showing the transmission characteristics of the slant FBG 11c.

In the example shown in FIG. 3, the transmission characteristics of the slant FBG 11a are set so that the transmission loss is large in the wavelength band WB21 on the short wavelength side of the wavelength band WB2 of the SRS light. The transmission characteristics of the slant FBG 11b are set so that the transmission loss is large in the wavelength region WB22 in the central part of the wavelength band WB2 of the SRS light. The transmission characteristics of the slant FBG 11c are set so that the transmission loss is large in the wavelength band WB23 on the long wavelength side of the wavelength band WB2 of the SRS light. The magnitude of the transmission loss of the slant FBGs 11a to 11c may be set to be the same or different. Also, the light blocking bands of the slant FBGs 11a to 11c may partially overlap.

Here, "different light-shielding bands" refers not only to cases where the light-shielding bands of the slant-type FBGs 11a to 11c are completely different, but also to cases where the light-shielding bands of the slant-type FBGs 11a to 11c partially overlap, as shown in Figure 3. In other words, it is difficult to design slant-type FBGs 11a to 11c that have transmission characteristics where the transmittance changes from 0% to 100% at a certain wavelength, and even if it were possible to design such FBGs, it would be difficult to actually manufacture them due to manufacturing errors, etc., so it is acceptable for the light-shielding bands to partially overlap.

In this embodiment, it is desirable to set the light blocking bands of each of the slant FBGs 11a to 11c so that the power (amount of energy) of the SRS light blocked by each of the slant FBGs 11a to 11c is uniform. This is because SRS light of the same power (energy) can be dispersed from each of the slant FBGs 11a to 11c and absorbed by the coating 13 or re-coating portions 14a to 14c.

Figure 4 is a diagram showing an example of the spectrum of SRS light generated by the laser device according to the first embodiment of the present invention. In Figure 4, the horizontal axis represents wavelength, and the vertical axis represents the power of SRS light. The light blocking band of the slant FBG 11b is set, for example, to a central band B that includes the central wavelength component of the SRS light among the entire wavelength band of the SRS light. The light blocking band of the slant FBG 11a is set, for example, to a short wavelength side band A that is shorter than the central band B among the entire wavelength band of the SRS light. The light blocking band of the slant FBG 11c is set, for example, to a long wavelength side band C that is longer than the central band B.

Here, the above "full wavelength band of SRS light" is, for example, a wavelength band (so-called 3σ interval) that includes 99.7% of the total power of the SRS light. Also, the above "central wavelength component of SRS light" is, for example, a wavelength component in which the optical power is maximum (or nearly maximum). In the example shown in FIG. 4, the "full wavelength band of SRS light" is 1115.0 [nm] to 1135.0 [nm], and the "central wavelength component of SRS light" is 1125.0 [nm].

The light-shielding bands of each of the slant FBGs 11a to 11c are set so that the areas obtained by integrating the graph shown in FIG. 4 over the short-wavelength side band A, the central band B, and the long-wavelength side band C are equal (area ratio is 1:1:1). Specifically, the light-shielding bands of the slant FBGs 11a, 11b, and 11c have a ratio of 4:1:4, with the central band B being set narrower than the short-wavelength side band A and the long-wavelength side band C.

For example, the light-shielding band (shorter wavelength side band A) of the slant FBG 11a is set to 1115.0 to 1124.4 [nm], the light-shielding band (central band B) of the slant FBG 11b is set to 1124.4 to 1126.8 [nm], and the light-shielding band (longer wavelength side band C) of the slant FBG 11c is set to 1126.8 to 1135.0 [nm]. By shading each band, each of the slant FBGs 11a to 11c can remove all wavelength components of the SRS light.

In this embodiment, we consider the case of removing SRS light propagating through the optical fiber 10 toward the +X side. In this case, the SRS light passes through the slant FBGs 11a, 11b, and 11c in order. Therefore, the SRS light first has its components in the short wavelength side band A shown in FIG. 4 removed by the slant FBG 11a. Next, the SRS light has its components in the central band B shown in FIG. 4 removed by the slant FBG 11b. Finally, the SRS light has its components in the long wavelength side band C shown in FIG. 4 removed by the slant FBG 11c.

The SRS light removed by each of the slant FBGs 11a, 11b, and 11c is absorbed by the coating 13 or the re-coating portions 14a, 14b, and 14c, respectively. Here, if the power (amount of energy) of the SRS light blocked by each of the slant FBGs 11a to 11c is set to be uniform, the power (amount of energy) of the SRS light absorbed by the coating 13 or the re-coating portions 14a to 14c will be uniform. This prevents the SRS light from being concentrated and absorbed at one point, such as the coating 13, and suppresses localized heat generation. In addition, the SRS light is prevented from being emitted from the output end 7, stabilizing the quality of the laser light.

As described above, in this embodiment, multiple slant FBGs 11a to 11c having different light blocking bands, which are wavelength bands that block SRS light generated by laser light, are formed in the core 11 of the optical fiber 10 that transmits laser light. This allows the SRS light to be dispersed and removed by the multiple slant FBGs 11a to 11c, thereby suppressing localized heating of the recoated portion and coated portion due to the SRS light. Furthermore, when forming the slant FBGs 11a to 11c in the core 11 of the optical fiber 10, the slant FBGs 11a to 11c can be formed individually with a gap in the longitudinal direction X. This makes it easy to manufacture the optical device 8A.

Second Embodiment
Laser Device
Fig. 5 is a diagram showing the main configuration of a laser device according to a second embodiment of the present invention. In Fig. 5, the same components as those shown in Fig. 1 are given the same reference numerals. The laser device 1A of the first embodiment shown in Fig. 1 is configured to include an optical device 8A arranged between the laser light source L and the output end 7. In contrast, the laser device 1B of this embodiment is configured to omit the optical device 8A of the laser device 1A shown in Fig. 1 and to include an optical device 8B arranged between the pump light source 2 (more precisely, the combiner 3) and the resonator R.

The laser device 1A of the first embodiment and the laser device 1B of this embodiment described above are capable of removing SRS light propagating toward the -X side (hereinafter referred to as retrograde SRS light) in addition to SRS light propagating toward the +X side. Retrograde SRS light is generated, for example, when SRS light traveling toward the +X side is reflected at the output end 7, or when laser light is reflected off the object to be processed by the laser device and re-enters the output end 7. The following mainly describes the case of removing retrograde SRS light.

If the backward SRS light reaches the excitation light source 2, it may cause a breakdown in the excitation light source 2, so it is preferable to remove it before it reaches the excitation light source 2. However, removing the SRS light in a concentrated manner in one place may lead to localized heating of the coating 13 or recoating portion, so it is preferable to remove it in a dispersed manner as in the first embodiment.

In this embodiment, the optical device 8B arranged between the excitation light source 2 (more precisely, the combiner 3) and the resonator R disperses and removes the backward SRS light. The optical device 8B has a similar configuration to the optical device 8A shown in FIG. 2. However, in the optical device 8B, three slant FBGs 11a (second slant FBG), slant FBG 11b (first slant FBG), and slant FBG 11c (third slant FBG) are arranged in this order along the longitudinal direction X from the +X side toward the -X side. The number of slant FBGs formed in the core 11 may be two, or may be four or more.

The SRS light propagating through the optical fiber 10 toward the -X side passes through the slant FBGs 11a, 11b, and 11c of the optical device 8B in that order. As a result, the SRS light first has its components in the short wavelength side band A shown in FIG. 4 removed by the slant FBG 11a. Next, the SRS light has its components in the central band B shown in FIG. 4 removed by the slant FBG 11b. Finally, the SRS light has its components in the long wavelength side band C shown in FIG. 4 removed by the slant FBG 11c.

The SRS light removed by each of the slant FBGs 11a, 11b, and 11c is absorbed by the coating 13 or the re-coating portions 14a, 14b, and 14c, respectively. Here, if the power (amount of energy) of the SRS light blocked by each of the slant FBGs 11a to 11c is set to be uniform, the power (amount of energy) of the SRS light absorbed by the coating 13 or the re-coating portions 14a to 14c will be uniform. This prevents the SRS light from being concentrated and absorbed at one point, such as the coating 13, and suppresses localized heat generation. In addition, since the backward SRS light is removed by the optical device 8B before it reaches the pump light source 2, failure of the pump light source 2 can be prevented.

As described above, in this embodiment, multiple slant FBGs 11a to 11c having different light blocking bands, which are wavelength bands that block backward SRS light generated by laser light, are formed in the core 11 of the optical fiber 10 that transmits laser light. This allows the backward SRS light to be dispersed and removed by the multiple slant FBGs 11a to 11c, making it possible to suppress localized heating of the re-coating portion and coating portion due to the backward SRS light. Furthermore, when forming the slant FBGs 11a to 11c in the core 11 of the optical fiber 10, the slant FBGs 11a to 11c can be formed individually at intervals in the longitudinal direction X. This makes it easy to manufacture the optical device 8B.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be freely modified within the scope 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 excitation type laser device equipped with a forward excitation light source and a backward excitation light source.

In addition, 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 a laser device of this configuration, the SRS light propagating from the laser light source L toward the output end 7 can be removed by the optical device 8A, while the backward SRS light propagating from the resonator R toward the excitation light source 2 can be removed by the optical device 8B.

Also, multiple optical devices 8A, 8B may be arranged in series within the laser devices 1A, 1B. In such an arrangement, multiple optical devices 8A may be directly fusion-spliced to each other, multiple optical devices 8B may be directly fusion-spliced to each other, or multiple optical devices 8A and 8B may be directly fusion-spliced to each other. Alternatively, multiple optical devices 8A may be directly fusion-spliced to each other, multiple optical devices 8B may be directly fusion-spliced to each other, or multiple optical devices 8A and 8B may be directly fusion-spliced to each other via an optical transmission path such as an optical fiber.

The arrangement of the slant FBGs 11a to 11c in the optical device 8A according to the first embodiment and the optical device 8B according to the second embodiment is arbitrary. For example, in the optical device 8A, the slant FBGs 11a to 11c may be arranged in the order of slant FBG 11c, slant FBG 11b, and slant FBG 11a from the -X side to the +X side. Alternatively, the slant FBGs 11b, slant FBG 11a, and slant FBG 11c may be arranged in the order of slant FBG 11b, slant FBG 11a, and slant FBG 11c from the X side to the +X side.

In addition, each core 11 may have two or four or more slant FBGs. For example, if the core 11 has two slant FBGs, it is preferable to divide the entire wavelength of the SRS light into two in terms of energy amount, and to make the short wavelength band and the long wavelength band into light blocking bands. This makes it possible to distribute the power of the SRS light in each slant FBG.

In addition, when the SRS light has multiple peaks in the wavelength components, for example, the short wavelength side band A and the long wavelength side band C shown in FIG. 4 may each include a peak and be set to have a narrower wavelength band than the central band.

1A, 1B... laser device, 2... excitation light source, 7... output end, 8A, 8B... optical device, 11... core, 11a... slant type FBG, 11b... slant type FBG, 11c... slant type FBG, 12... cladding, A... short wavelength side band, B... central band, C... long wavelength side band, L... laser light source, R... resonator

Claims (8)

An optical device used in a laser device that outputs laser light,
A core,
a cladding covering the core and having a lower refractive index than the core;
a first slant FBG and a second slant FBG formed in the core ;
a resin provided on an outer peripheral surface of the cladding at a position corresponding to the positions of the first slant FBG and the second slant FBG in a longitudinal direction of the core, the resin having a refractive index higher than that of the cladding;
Equipped with
The first slant FBG and the second slant FBG have different light blocking bands, which are wavelength bands that block SRS light. Further comprising a third slant FBG formed in the core,
the third slant FBG has a light blocking band different from the first slant FBG and the second slant FBG;
2. The optical device according to claim 1. the first slant FBG has a central band including a central wavelength component of the SRS light as the light blocking band among the entire wavelength band of the SRS light,
the second slant FBG has a short wavelength side band that is shorter than the central band as the light blocking band,
The third slant FBG has a long wavelength side band that is longer than the central band as the light blocking band.
3. The optical device according to claim 2. The optical device according to claim 3, wherein the first slant FBG has a light blocking band set narrower than the second slant FBG and the third slant FBG. 5. The optical device according to claim 2, wherein the first slant FBG , the second slant FBG, and the third slant FBG have their light blocking bands set such that the amounts of energy of the SRS light that can be removed are equal to each other. The optical device according to claim 5 , wherein the first slant FBG , the second slant FBG, and the third slant FBG have light blocking bands set to a ratio of 1:4:4. A laser light source that generates laser light;
an output end for outputting the laser light;
The optical device according to claim 1 , which is disposed between the laser light source and the output end;
A laser device comprising: An excitation light source that emits excitation light;
a resonator for generating laser light by the excitation light;
an output end for outputting the laser light;
The optical device according to claim 1 , which is disposed between the pump light source and the resonator; and
A laser device comprising:

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