Offset splice points in fiber laser systems
By adopting an offset-splicing fiber design in the fiber laser system, the output instability problem caused by the SRS phenomenon in high-power fiber lasers is solved, achieving high brightness and efficient material processing effects.
Patent Information
- Application Number
- CN202510365688.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-04-30
- Filing Date
- 2025-03-26
- Publication Date
- 2025-09-30
AI Technical Summary
Existing high-power fiber lasers suffer from severe stimulated Raman scattering (SRS) during material processing, resulting in output instability, efficiency loss, and beam parameter product (BPP) degradation. Existing solutions are complex and time-consuming.
The fiber laser system design with offset splicing reduces the SRS gain by misaligning the central axis of the first fiber core with the central axis of the second fiber core at the splicing point, setting the offset distance to greater than 2 microns, and propagating the laser through the larger diameter second fiber core to maintain high brightness.
The SRS content is effectively reduced to below 1%, maintaining high output brightness and spectral density, reducing transverse mode instability, and improving the quality and efficiency of material processing.
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Figure CN120728339A_ABST
Abstract
Description
[0001] CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] This patent application claims priority to U.S. Patent Application No. 63 / 571,254, filed on March 28, 2024, entitled “OFFSET FIBER CORES OF A HIGH-POWER FIBER LASER.” The disclosure of the prior application is considered a part of and incorporated by reference into this patent application. Technical Field
[0003] The present disclosure generally relates to fiber laser systems and offset splice points in fiber laser systems. Background Art
[0004] A high-power fiber laser is a fiber laser that can provide a relatively high output power. For example, the output power of a high-power fiber laser can be at least one kilowatt. Summary of the Invention
[0005] In some embodiments, a fiber laser system includes a first optical fiber including a first core having a first diameter; and a second optical fiber including a second core having a second diameter, the second diameter being larger than the first diameter, wherein: an end of the first optical fiber is connected to an end of the second optical fiber at a splice point, a central axis of the first core is not aligned with a central axis of the second core at the splice point, and an offset distance between the central axis of the first core and the central axis of the second core at the splice point is greater than 2 microns.
[0006] In some embodiments, a fiber laser system includes a first optical fiber including a first core having a first diameter; and a second optical fiber including a second core having a second diameter, wherein: an end of the first optical fiber is connected to an end of the second optical fiber at a splice point, and an offset distance between a central axis of the first core and a central axis of the second core at the splice point is greater than 2 microns.
[0007] In some embodiments, a fiber laser system includes a first optical fiber; and a second optical fiber, wherein: an end of the first optical fiber is connected to an end of the second optical fiber at a splice point, and an offset distance between a first core of the first optical fiber and a second core of the second optical fiber at the splice point allows a stimulated Raman scattering (SRS) content of an output of the fiber laser system to be less than or equal to 1%. BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Figures 1A to 1C An example implementation of a fiber laser system is shown.
[0009] Figures 2A to 2BAn example implementation of the fiber laser system described herein is shown.
[0010] Figure 3 An example diagram of a similarly configured fiber laser system is shown.
[0011] Figure 4A An example diagram of a similarly configured fiber laser system is shown.
[0012] Figure 4B An example table is shown which indicates the Figure 4A Describes data associated with a similarly configured fiber laser system.
[0013] Implementation method
[0014] The following detailed description of example embodiments refers to the accompanying drawings, in which the same reference numbers in different drawings may identify the same or similar elements.
[0015] High-power fiber lasers (e.g., kilowatt (kW) class or higher) can be used for material processing applications such as cutting, welding, engraving, marking, and / or other material processing applications. It is generally desirable that the output of a high-power fiber laser (e.g., including laser light) has high brightness to enable faster cutting speeds and better cutting quality of materials (e.g., metal or another hard material). A major limitation to the brightness of the amplified output is the increase in stimulated Raman scattering (SRS), which is a nonlinear optical effect that converts signal light to longer wavelengths within the output. High SRS content (e.g., measured as a percentage (%)) can lead to unstable output, efficiency loss, increased heating, and beam parameter product (BPP) degradation.
[0016] In some cases, the SRS gain can be mitigated by increasing the linewidth of the fiber laser, for example by using Bragg spectroscopy and increasing the fiber core size. However, this may result in BPP degradation and a reduction in spectral density. In addition, the fiber laser can be configured to have multiple peak wavelengths in the output coupler (OC) grating reflectivity spectrum, which increases the power threshold beyond which the SRS level begins to affect the output. However, this configuration requires complex fiber Bragg grating design and precise positioning of reflective components, which is difficult and time-consuming to design, manufacture and maintain. In addition, SRS filters (e.g., including tilted fiber Bragg gratings) can be used to increase the power threshold at which the SRS level begins to affect the output, but this requires additional components in the fiber laser, resulting in more complexity and optical losses (e.g., due to the additional splicing required to include the SRS filter).
[0017] Some embodiments described herein include a fiber laser system. The fiber laser system can be configured to be capable of kilowatt-class material processing. In some embodiments, the fiber laser system includes a first optical fiber and a second optical fiber, the first optical fiber including a first core and the second optical fiber including a second core. The first core has a first diameter that is smaller than a second diameter of the second core. An end of the first optical fiber is connected to an end of the second optical fiber at a splice point to allow laser light to propagate from the first optical fiber to the second optical fiber (e.g., from the first core to the second core).
[0018] The central axis of the first core is not aligned with the central axis of the second core at the splice point. That is, the center point of the cross-sectional area of the first core does not touch the center point of the cross-sectional area of the second core at the splice point. This can be referred to as an offset splice. Therefore, there is an offset distance (e.g., a non-zero offset distance) between the central axis of the first core and the central axis of the second core. The offset distance (e.g., at the splice point) meets (e.g., is greater than or equal to) an offset threshold, which reduces the peak intensity of the laser in the second fiber core and thereby minimizes the SRS gain along the length of the second fiber. In this way, the fiber laser system is able to minimize (and in some embodiments, eliminate) the SRS content in the output (e.g., including the laser) of the fiber laser system. For example, the offset distance causes the SRS content of the output to be less than or equal to a maximum allowable SRS content (e.g., associated with optimal performance of the fiber laser system), such as 1% of the output.
[0019] Furthermore, in some embodiments, the entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point. This allows efficient laser propagation from the first core to the second core, and as a result, the BPP and spectral density of the output are the same or similar to the output of a fiber laser with aligned cores. Furthermore, the offset splice point redistributes the laser's energy to other modes, making the modes incoherent and, therefore, resulting in lower transverse mode instabilities (TMI) in the output of the fiber laser system, thereby improving the quality of the output.
[0020] Figures 1A to 1C An example embodiment 100 of a fiber laser system is shown. Figures 1A to 1C As shown, the fiber laser system may include a first optical fiber and a second optical fiber. Figure 1A A first example configuration of a fiber laser system is shown, Figure 1B A second example configuration of a fiber laser system is shown, and Figure 1C A third example configuration of a fiber laser system is shown.
[0021] A fiber laser system can be configured to deliver laser light, such as a high-power laser, for use in materials processing applications such as cutting, welding, engraving, marking, and / or other materials processing applications. For example, a fiber laser system can be configured to enable kilowatt-level materials processing. In some embodiments, the fiber laser system can be a master oscillator power amplifier (MOPA), the first fiber can be an oscillator fiber, and the second fiber can be an amplifier fiber.
[0022] like Figures 1A to 1C As shown, the first optical fiber may include a first core and may optionally include a first cladding and / or a first optical fiber jacket. The first core may include glass and / or another suitable material that is configured to transmit laser light (e.g., from an input end of the first core (shown as the left side of the first core) to an output end of the first core (shown as the right side of the first core)). The first cladding may surround (e.g., circumferentially surround) the first core and be configured to confine the laser light (e.g., within the first core). The first optical fiber jacket may surround (e.g., circumferentially surround) the first core and / or the first cladding and may include a material configured to protect and / or shield the first core and / or the first cladding (e.g., a plastic material, such as polyethylene).
[0023] like Figures 1A to 1C As further shown, the first core can have a first diameter. The first diameter can be a measure of the thickness of the first core at the splice point, as further described herein. That is, the first diameter can be a measure of the thickness of the cross-sectional area of the first core at the splice point. Furthermore, the first core can have a central axis. The central axis can extend along the length of the first core (e.g., in a direction parallel to the direction of propagation of the laser light within the first core) and pass through a "center" point of the cross-sectional area of the first core at the splice point.
[0024] In addition, if Figures 1A to 1C As shown, the second optical fiber may include a second core and may optionally include a second cladding and / or a second optical fiber jacket. The second core may include glass and / or another suitable material that is configured to transmit laser light (e.g., from an input end of the second core (shown as the left side of the second core) to an output end of the second core (shown as the right side of the second core)). The second cladding may surround (e.g., circumferentially surround) the second core and be configured to confine the laser light (e.g., within the second core). The second optical fiber jacket may surround (e.g., circumferentially surround) the second core and / or the second cladding and may include a material configured to protect and / or shield the second core or the second cladding (e.g., a plastic material, such as polyethylene).
[0025] like Figures 1A to 1CAs further shown, the second core can have a second diameter. The second diameter can be a measure of the thickness of the second core at the splice point, as further described herein. That is, the second diameter can be a measure of the thickness of the cross-sectional area of the second core at the splice point. Furthermore, the second core can have a central axis. The central axis can extend along the length of the second core (e.g., in a direction parallel to the direction of laser propagation within the second core) and pass through a center point of the cross-sectional area of the second core at the splice point.
[0026] In some embodiments, the second diameter can be greater than the first diameter. Thus, the second core can be thicker than the first core (e.g., at the splice point). In some embodiments, the second diameter is greater than or equal to at least X times the first diameter (e.g., at the splice point), where X>1. For example, the second diameter can be greater than or equal to three times the first diameter (e.g., at the splice point).
[0027] The first core and the second core may also have other different characteristics. For example, the first core may be a single-mode core or a few-mode core, and the second core may be a multi-mode core. That is, the second core may be configured to support more modes than the first core is configured to support. In other words, the second core may be configured to support M modes, and the first core may be configured to support N modes, where M>N.
[0028] like Figures 1A to 1C As further shown, an end of a first optical fiber (e.g., shown as the right end of the first optical fiber) is connected to an end of a second optical fiber (e.g., shown as the left end of the first optical fiber) at a splice point. That is, the first optical fiber can be fused to the second optical fiber at the splice point, such as to facilitate efficient transmission of laser light between the first optical fiber and the second optical fiber (e.g., with minimal loss or interruption). In some embodiments, the fiber laser system can be configured to allow laser light to propagate from the first optical fiber (e.g., from the first core of the first optical fiber) to the second optical fiber (e.g., to the second core of the second optical fiber) at the splice point. That is, the fiber laser system can be configured to allow laser light to propagate from the "thinner" first core to the "thicker" second core at the splice point.
[0029] It is worth noting that the center axis of the first core is not aligned with the center axis of the second core at the splicing point. That is, the center point of the cross-sectional area of the first core does not touch the center point of the cross-sectional area of the second core at the splicing point. Figures 1A to 1C As shown, there may be an offset distance (e.g., a non-zero offset distance) between the central axis of the first core and the central axis of the second core. The offset distance may be a specific size, such as Figures 1A to 1C Vertical dimensions shown.
[0030] Figure 1AA first example configuration of a fiber laser system is shown in which the offset distance is such that the entire cross-sectional area of a first core contacts a portion of the cross-sectional area of a second core at a splice point, and wherein the portion of the cross-sectional area of the second core includes a point associated with a central axis of the second core (e.g., a center point). Figure 1B A second example configuration of a fiber laser system is shown in which the offset distance is such that the entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at a splice point, and wherein the portion of the cross-sectional area of the second core does not include a point associated with a central axis of the second core (e.g., a center point). Figure 1C A third example configuration of a fiber laser system is shown in which the offset distance is such that the entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at a splice point, wherein the portion of the cross-sectional area of the second core does not include a point associated with a central axis of the second core (e.g., a center point), and wherein an edge of the first core is aligned with (and contacts) an edge of the second core.
[0031] In some embodiments, the offset distance (e.g., at the splice point) can satisfy (e.g., can be greater than or equal to) an offset threshold. The offset threshold can be associated with, for example, a maximum misalignment value associated with splicing the first and second optical fibers together at the splice point. That is, the offset threshold can be greater than the maximum cumulative sum of potential misalignment offsets that may occur due to splicing the first and second optical fibers together at the splice point. Thus, the offset threshold can be, for example, 1 micrometer (μm) (e.g., when the maximum misalignment value is less than 1 μm), 2 μm (e.g., when the maximum misalignment value is less than 2 μm), or 3 μm (e.g., when the maximum misalignment value is less than 3 μm). Additionally or alternatively, the offset threshold can be, for example, 1% of the first diameter (e.g., when the maximum misalignment value is less than 1% of the first diameter), 5% of the first diameter (e.g., when the maximum misalignment value is less than 5% of the first diameter), or 10% of the first diameter (e.g., when the maximum misalignment value is less than 10% of the first diameter), among other examples.
[0032] In some embodiments, the offset distance can be designed to minimize the SRS content (e.g., the SRS content includes Stokes-shifted SRS content and / or anti-Stokes-shifted SRS content) of the output of the fiber laser system (e.g., the output includes laser light propagating from the first core to the second core at the splice point). For example, the offset threshold can be associated with a maximum allowable SRS content of the output. That is, when the offset distance satisfies the offset threshold, the SRS content of the output is less than or equal to the maximum allowable SRS content of the output. Thus, the offset distance can cause the SRS content of the output to be less than or equal to the maximum allowable SRS content of the output. The maximum allowable SRS content of the output can be, for example, 1%, 2%, 3%, or another percentage of the output associated with optimal performance of the fiber laser system.
[0033] As mentioned above, Figures 1A to 1C Provided as an example only. Other examples may be found in the Figures 1A to 1C Description is different.
[0034] Figures 2A to 2B An example implementation 200 of a fiber laser system described herein is shown. Figure 2A A first example configuration showing how the cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at a splice point, and Figure 2B A second example configuration is shown of how the cross-sectional area of a first core contacts a portion of the cross-sectional area of a second core at a splice point.
[0035] like Figure 2A As shown, the central axis of the first core is not aligned with the central axis of the second core at the splice point. That is, the center point of the cross-sectional area of the first core does not touch the center point of the cross-sectional area of the second core at the splice point, and there is an offset distance (e.g., a non-zero offset distance) between the central axis of the first core and the central axis of the second core. The offset distance can be a specific size, such as Figure 2A Additionally, the offset distance is such that the entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point, wherein the portion of the cross-sectional area of the second core includes a point associated with a central axis of the second core (e.g., a center point).
[0036] like Figure 2B As shown, the central axis of the first core is not aligned with the central axis of the second core at the splice point. That is, the center point of the cross-sectional area of the first core does not touch the center point of the cross-sectional area of the second core at the splice point, and there is an offset distance (e.g., a non-zero offset distance) between the central axis of the first core and the central axis of the second core. The offset distance can be a specific size, such as Figure 2B Furthermore, the offset distance is such that the entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point, wherein the portion of the cross-sectional area of the second core does not include a point associated with a central axis of the second core (e.g., a center point).
[0037] As mentioned above, Figures 2A to 2B Provided as an example only. Other examples may be found in the Figures 2A to 2B Description is different.
[0038] Figure 3An example graph 300 is shown. The example graph indicates SRS content in similarly configured fiber laser systems (e.g., MOPA fiber laser systems). The first fiber laser system includes an oscillator output fiber core (e.g., as a first core) and an amplifier input fiber core (e.g., as a second core), whose respective central axes are aligned (e.g., an offset distance between the respective central axes is zero (0) or close to zero, such as within tolerance). The SRS content (in decibels (dB)) of the first fiber laser system relative to signal power (in watts (W)) is indicated by line 302. The second fiber laser system includes an oscillator output fiber core (e.g., as a first core) and an amplifier input fiber core (e.g., as a second core), whose respective central axes are not aligned (e.g., an offset distance exists between the respective central axes, as described elsewhere herein). The SRS content (in dB) of the second fiber laser system relative to signal power (in W) is represented by line 304.
[0039] Thus, example graph 300 shows that the second fiber laser system provides a stable output for higher signal powers than the first fiber laser system (indicated by the horizontal dashed line associated with an SRS of -20 dB). For example, the second fiber laser system provides a stable output for signal powers up to at least 3375 W, while the first fiber laser system only provides a stable output for signal powers up to a maximum of 3200 W.
[0040] As mentioned above, Figure 3 Provided as an example. Other examples can be found in the Figure 3 Description is different.
[0041] Figure 4A Example graph 400 and example graph 402 are shown for similarly configured fiber laser systems (e.g., MOPA fiber laser systems). Example graph 400 indicates a wavelength offset for a desired signal output (e.g., a desired wavelength in nanometers (nm)) for a first fiber laser system that includes an oscillator output fiber core (e.g., as a first core) and an amplifier input fiber core (e.g., as a second core) whose respective central axes are aligned (e.g., an offset distance between the respective central axes is zero (0) or near zero, such as within a tolerance range). Example graph 402 indicates a wavelength offset for a desired signal output (e.g., a desired wavelength in nm) for a second fiber laser system that includes an oscillator output fiber core (e.g., as a first core) and an amplifier input fiber core (e.g., as a second core) whose respective central axes are not aligned (e.g., an offset distance exists between the respective central axes, as described elsewhere herein). Figure 4AAs shown, the first fiber laser system is affected by a 5.0% Stokes shift SRS content and a 0.3% anti-Stokes shift SRS content in the output spectrum, and therefore only 94.7% of the output spectrum is associated with the desired signal output. Figure 4B As shown, the second fiber laser system is unaffected by Stokes-shifted SRS content and anti-Stokes-shifted SRS content (or any SRS content is so small as to be undetectable at the resolution shown in example graph 402) such that 100% of the output spectrum correlates with the desired signal output.
[0042] Figure 4B An example table 404 is shown indicating data associated with a first fiber laser system and a second fiber laser system (e.g., as described above in connection with FIG. Figure 4A For example, table 404 indicates that the second fiber laser system provides a similar BPP (e.g., in millimeters by milliradians (mm-mrad)) as the first fiber laser system and has improved performance in terms of Stokes-shifted SRS content and anti-Stokes-shifted SRS content (e.g., in percentage) compared to the first fiber laser system, including during cold start. Notably, data is associated with each fiber laser system configured with a wavelength of 1079 nm using 6.5 kW of power, and the spectra associated with the fiber laser systems were collected using 2 kilohertz (kHz) modulated data sampling.
[0043] As mentioned above, Figures 4A to 4B Provided as an example only. Other examples may be found in the Figures 4A to 4B Description is different.
[0044] The above disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the embodiments. In addition, any of the embodiments described herein may be combined, unless the above disclosure clearly provides reasons why one or more embodiments cannot be combined.
[0045] As used herein, satisfying a threshold may refer to a value being greater than a threshold, greater than or equal to a threshold, less than a threshold, less than or equal to a threshold, equal to a threshold, not equal to a threshold, etc., depending on the context.
[0046] Even though particular combinations of features are referenced in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. In fact, many of these features may be combined in ways that are not specifically referenced in the claims and / or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of the various embodiments includes the combination of each dependent claim with every other claim in the claim set. As used herein, a phrase referring to "at least one" of a list of items refers to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the items.
[0047] Unless explicitly stated, any element, behavior or instruction used in this article should not be interpreted as key or essential. In addition, as used in this article, the article "one" and "an" are intended to include one or more projects and can be used interchangeably with "one or more". In addition, as used in this article, the article "the" is intended to include one or more projects related to the article "the", and can be used interchangeably with "the one or more". In addition, as used in this article, the term "set" is intended to include one or more projects (for example, related projects, unrelated projects or the combination of related and unrelated projects), and can be used interchangeably with "one or more". In the case of being intended to only one project, "only one" or similar language is used. In addition, as used in this article, the term "has / have / having" etc. are intended to be open terms. In addition, unless explicitly stated otherwise, the phrase "based on" is intended to represent "at least partially based on". In addition, as used in this article, the term "or" is inclusive when used in series, and can be used interchangeably with "and / or", unless explicitly stated otherwise (for example, if used in combination with "(of the two) any one" or "only ... one of"). Additionally, for ease of description, spatially relative terms, such as "below," "lower," "above," "upper," "left," "right," etc., may be used herein to describe the relationship of one element or feature to another element or feature as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device, apparatus, and / or element in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.
Claims
1. A fiber laser system, comprising: a first optical fiber comprising a first core having a first diameter; as well as a second optical fiber comprising a second core having a second diameter, the second diameter being greater than the first diameter, wherein: the end of the first optical fiber being connected to the end of the second optical fiber at a splice point, The central axis of the first core is not aligned with the central axis of the second core at the splice point, and An offset distance between the central axis of the first core and the central axis of the second core at the splice point is greater than 2 microns.
2. The fiber laser system of claim 1 , wherein: The first core is a single-mode core or a few-mode core; and The second core is a multimode core.
3. The fiber laser system of claim 1 , wherein: The fiber laser system is a master oscillator power amplifier MOPA system; The first optical fiber is an oscillator fiber; and The second optical fiber is an amplifier fiber.
4. The fiber laser system of claim 1 , wherein the fiber laser system is configured to allow laser light to propagate from the first optical fiber to the second optical fiber at the splice point.
5. The fiber laser system of claim 1 , wherein: The entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point.
6. The fiber laser system of claim 5, wherein: The portion of the cross-sectional area of the second core does not include a point associated with the central axis of the second core.
7. The fiber laser system of claim 5, wherein: The portion of the cross-sectional area of the second core includes a point associated with the central axis of the second core.
8. The fiber laser system of claim 1 , wherein: The stimulated Raman scattering (SRS) content of the output of the fiber laser system is less than or equal to 1%.
9. A fiber laser system, comprising: a first optical fiber comprising a first core having a first diameter; as well as a second optical fiber comprising a second core having a second diameter, wherein: The end of the first optical fiber is connected to the end of the second optical fiber at a splice point, and The offset distance between the central axis of the first core and the central axis of the second core at the splicing point is greater than 2 microns.
10. The fiber laser system of claim 9, wherein: At the splicing point, the second diameter is greater than the first diameter.
11. The fiber laser system of claim 9, wherein: At the splicing point, the second diameter is greater than or equal to three times the first diameter.
12. The fiber laser system of claim 9, wherein: The first core is a single-mode core or a few-mode core; and The second core is a multimode core.
13. The fiber laser system of claim 9, wherein the fiber laser system is configured to allow laser light to propagate from the first optical fiber to the second optical fiber.
14. The fiber laser system of claim 9, wherein: The fiber laser system is configured to be capable of kilowatt-class material processing.
15. The fiber laser system of claim 9, wherein: The entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point, the portion excluding a point associated with the central axis of the second core.
16. The fiber laser system of claim 9, wherein: The entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point, the portion including a point associated with the central axis of the second core.
17. A fiber laser system, comprising: a first optical fiber; as well as The second optical fiber, wherein: The end of the first optical fiber is connected to the end of the second optical fiber at a splice point, and The offset distance between the first core of the first optical fiber and the second core of the second optical fiber at the splice point allows a stimulated Raman scattering (SRS) content of an output of the fiber laser system to be less than or equal to 1%.
18. The fiber laser system of claim 17, wherein: The entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point, the portion excluding a point associated with a central axis of the two cores.
19. The fiber laser system of claim 17, wherein: The entire cross-sectional area of the first core contacts a portion of the cross-sectional area of the second core at the splice point, the portion including a point associated with a central axis of the second core.
20. The fiber laser system of claim 9, wherein: At the splicing point, the diameter of the second core is greater than the diameter of the first core.