Raman suppression fiber

Abstract

SOLUTION: In some implementations, a monolithic optical fiber comprises a tapered core having a first diameter at an input end and a second diameter at an output end. The tapered core comprises a first tapered region at the input end, a second tapered region at the output end, and a central region having a constant diameter that is larger than the first diameter and the second diameter. The first tapered region expands monotonically from the first diameter to the constant diameter of the central region along a length of the first tapered region, and the second tapered region contracts monotonically from the constant diameter of the central region to the second diameter along a length of the second tapered region.EFFECT: The monolithic optical fiber may be used as a delivery fiber to deliver a laser beam from a fiber laser engine to a process head.SELECTED DRAWING: None

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 203,772, filed July 30, 2021, entitled "RAMAN DEPRESSING FIBER," the disclosure of which is considered part of this patent application and incorporated herein by reference. [Technical Field]

[0002] The present disclosure generally relates to industrially applicable delivery fibers and optical fibers designed to suppress stimulated Raman scattering (SRS) gain and maintain laser brightness along the optical fiber. [Background technology]

[0003] In physics, the term scattering is commonly used to describe various physical processes in which moving particles or some form of radiation (e.g., light or sound) are forced to deviate from a straight-line trajectory by local inhomogeneities in the medium through which the particles or radiation pass. For example, Raman scattering (or the Raman effect) is the inelastic scattering of photons by a material, which means that both an exchange of energy and a change in the direction the light travels occur. Raman scattering typically involves the energy gained by molecules when incident photons from a visible laser are shifted to lower energy. Summary of the Invention [Means for solving the problem]

[0004] In some embodiments, an integrated optical fiber comprises a tapered core having an input end and an output end, and a cladding surrounding the tapered core. The tapered core comprises a first tapered region at the input end, a second tapered region at the output end, and a central region disposed between the first and second tapered regions. The first tapered region has a first core diameter at the input end, the second tapered region has a second core diameter at the output end, and the central region has a third core diameter larger than the first and second core diameters. The first and second tapered regions each have the third core diameter at their interfaces with the central region.

[0005] In some embodiments, an optical assembly comprises an optical fiber having a core and a cladding surrounding the core, the core having a constant core diameter and the cladding having a constant cladding diameter greater than the constant core diameter, the optical assembly comprising a first nonlinearity reduction device spliced ​​to the optical fiber at an input end and a second nonlinearity reduction device spliced ​​to an output end of the optical fiber.

[0006] In some embodiments, an optical assembly includes a fiber laser engine, a processing head, and an integrated delivery fiber connected to the fiber laser engine and the processing head for delivering a laser beam from the fiber laser engine to the processing head. The integrated delivery fiber includes a tapered core having an input end and an output end, and a cladding surrounding the tapered core. The tapered core has a first tapered region at the input end, a second tapered region at the output end, and a central region disposed between the first and second tapered regions. The first tapered region has an input diameter at the input end, the second tapered region has an output diameter at the output end, and the central region has a constant diameter larger than the input and output diameters. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 illustrates an example of an industrial beam delivery system. [Figure 2] FIG. 1 is a diagram illustrating an example of a delivery fiber. [Figure 3] 1A and 1B illustrate exemplary embodiments of Raman-suppressing fibers capable of mitigating stimulated Raman scattering (SRS) or other nonlinear effects. [Figure 4] 1A and 1B illustrate exemplary embodiments of fiber assemblies capable of mitigating SRS or other nonlinear effects. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following detailed description of the exemplary embodiments refers to the accompanying drawings, in which the same reference numbers in different drawings may identify the same or similar elements.

[0009] Laser material processing has many advantages, including high productivity, non-contact processing, improved quality, and high accuracy and mobility of the laser beam delivery point. Lasers are used in a variety of industrial applications, such as cutting, drilling, welding, brazing, surface annealing, alloying, and / or hardening, among others. For example, in industrial laser applications, the beam delivery system often includes an optical fiber that is used to deliver a high-power and / or high-intensity laser beam to a target.

[0010] For example, FIG. 1 illustrates an example of an industrial beam delivery system 100. As shown in FIG. 1, the industrial beam delivery system 100 may include a fiber laser engine 110 (e.g., a multi-kilowatt (kW) fiber laser engine) connected to a processing head 120 in a processing area 130 (e.g., a cutting and / or welding area) via a delivery fiber 140 having a length of typically about 10 to 50 meters (m). The delivery fiber 140 may be provided in a reinforced cable with pluggable input and output ends, and the processing head 120 is an optical assembly including a receptacle for receiving the input end of the delivery fiber 140, optics for projecting the laser output, and any laser processing accessories, such as an assist gas port, that may be required. The fiber laser engine 110 can deliver a laser through free space or via a separate optical fiber into an optical coupler unit, which can launch the laser into the delivery fiber 140. Thus, delivery fiber 140 delivers the laser to processing head 120, which can project the laser onto a workpiece within application region 130 to perform a desired laser material processing operation.

[0011] The length of the delivery fiber 140 used in industrial beam delivery systems 100 is typically long (e.g., at least 10 meters). A long delivery fiber 140 may be necessary, for example, because the processing head 120 typically accelerates rapidly within large machines, and because the gantry that moves the processing head 120 within the processing area 130 and directs the laser at the material being cut, welded, engraved, and / or otherwise processed cannot be burdened by the weight of the fiber laser engine 110 (e.g., a movable beam delivery system could move the laser within the processing area 130 without moving the fiber laser engine 110, but this system could be very heavy). Furthermore, a long delivery fiber 140 may be advantageous in that it allows the fiber laser engine 110 to be located in a well-protected area with easy maintenance access, rather than being located near the processing area 130. However, a long delivery fiber 140 can pose various challenges, including optical power loss, pulse broadening, and / or nonlinear limitations. For example, industrial applications are increasingly demanding higher laser powers (e.g., currently 15-20 kW) because higher laser powers generally result in faster material processing. However, as laser powers increase, delivering high-brightness, high-power laser light through tens of meters of optical fiber becomes increasingly difficult due to problematic nonlinear effects such as stimulated Raman scattering (SRS).

[0012] Specifically, SRS is a nonlinear optical effect in which energy from an optical pump beam is converted to longer wavelengths via vibrational and / or rotational modes, or phonons, excited in the molecules of a glass medium. While this process may be useful for certain applications (e.g., converting an optical fiber into a Raman amplifier or a tunable Raman laser), SRS is undesirable for multi-kW continuous-wave (CW) industrial fiber lasers or multi-kW quasi-CW fiber lasers used in the cutting and welding industries. For example, in industrial applications, SRS can transfer energy from one channel to an adjacent channel and / or limit the power that can propagate without undesirable losses and / or heating. These can adversely affect industrial processes and / or cause damage to equipment. As the power levels of industrial kW fiber lasers continue to increase, the SRS problem becomes more severe, creating a need for techniques to suppress SRS.

[0013] In general, the degree of SRS present in an optical fiber can be measured by the Raman gain index, which is a metric of the amount of amplification caused by SRS in a given length of optical fiber. The Raman gain index in an optical fiber is determined by multiplying the gain coefficient gR by the signal intensity integrated along the length of the optical fiber, where the signal intensity is calculated by dividing the power by the geometric area:

[0014]

number

[0015] The gain coefficient gR can be approximately 10-13 m / W, depending on the particular dopant in the glass. For example, FIG. 2 shows an example of a standard delivery fiber 200 including a core 210, a cladding 212 surrounding the core 210, and a buffer 214 surrounding the cladding 212. Generally, the standard delivery fiber 200 can have a length 220 of at least 10 m and a constant diameter 222. As described herein, the SRS effects in the standard delivery fiber 200 are described in the context of the standard delivery fiber having a length 220 of either 20 m or 30 m and a core 210 diameter 222 of either 50 micrometers (μm) or 100 μm, although other suitable values ​​for the length 220 and core diameter 222 are contemplated. As shown in FIG. 2, table 230 shows the SRS gain (in decibels (dB)) that can occur when the core 210 diameter 222 in the standard delivery fiber 200 is 50 μm. In particular, the middle column of table 230 shows the possible SRS gains at different power levels (e.g., 4 kW, 6 kW, 9 kW, and 12 kW) when length 220 is 20 m and core diameter 222 is 50 μm, while the right-most column of table 230 shows the possible SRS gains when length 220 is 30 m and core diameter 222 is 50 μm. As shown in table 230, power levels greater than 4 kW or lengths greater than 20 m result in SRS gains that do not meet a performance threshold (e.g., a 20 decibel (dB) limit) that is considered practical when core diameter 222 is 50 μm (e.g., as indicated by the shaded boxes in table 230).

[0016] Therefore, when using a standard delivery fiber 200 with a fixed power and length, a commonly adopted solution to mitigate SRS is to increase the core diameter (e.g., to 100 μm). Doing so reduces the SRS gain by increasing the effective area along the length 220 of the standard delivery fiber 200 (e.g., increasing the value of the denominator in the above equation reduces the signal strength). For example, table 232 presents SRS gain values ​​for the standard delivery fiber 200 when the core diameter 222 is 100 μm and the length 220 is 20 m or 30 m. As shown, the SRS gain value is significantly lower when the core diameter 222 is increased to 100 μm compared to when the core diameter 222 is 50 μm. However, in certain applications (e.g., industrial applications requiring a tightly focused, small spot size), a (smaller) core diameter 222 of 50 μm may be preferable, so increasing the core diameter 222 is a suboptimal solution. Furthermore, as power levels increase to 15-20 kW (or higher), SRS will increase even for a standard delivery fiber 200 with a core diameter 222 of 100 μm, which would then require a further increase in core diameter 222 to 200 μm (or higher).

[0017] Some embodiments described herein relate to Raman-suppressing (or suppressing) fibers that can reduce Raman gain without sacrificing brightness or requiring core diameter modifications (e.g., via a processing head) to deliver undesirable spot sizes in the application area. For example, in some embodiments, the Raman-suppressing fiber can be an integrated (e.g., single-piece) delivery fiber that maintains brightness and reduces SRS gain in high-power kW applications. The Raman-suppressing fiber can deliver small spot sizes (e.g., 50 μm) and high power intensities over long fiber lengths (e.g., 10-50 meters), an effect that would otherwise be limited by SRS gain. The Raman-suppressing fibers described herein are also compatible with current fiber manufacturing and / or cabling processes, thereby providing backward compatibility with existing technology. For example, as described herein, Raman-suppressing fibers can deliver high-brightness, high-power laser light through tens of meters of optical fiber with reduced nonlinear effects (e.g., reduced SRS, self-phase modulation, four-wave mixing, and / or stimulated Brillouin scattering) by reducing power density and maintaining brightness along most of the fiber length, and in a manner that is compatible with standard cabling, splicing, and the like.

[0018] FIG. 3 illustrates an exemplary embodiment of a Raman-suppressing fiber 300 capable of mitigating SRS or other nonlinear effects. For example, as noted above, the easiest way to reduce Raman gain in an optical fiber at a given power level and length is to increase the effective area along the length of the fiber (e.g., by increasing the denominator in the above equation to reduce the Raman gain index experienced by the optical fiber). However, as further described above with reference to FIG. 2, increasing the effective area (e.g., by increasing the core diameter) can sacrifice brightness and increase the spot size delivered by the optical fiber. In contrast, as shown in FIG. 3, the Raman-suppressing fiber 300 is monolithic, with both the input and output ends of the cable having a tapered core 310. As further shown, a cladding 312 surrounds the tapered core 310, and the diameter 326 of the cladding 312 may be constant or may have a tapered shape corresponding to the shape of the tapered core 310. In some embodiments, the core 310 of the Raman-suppressing fiber 300 may have a tapered length at the input and output ends that provides adiabaticity with respect to light traveling within the core 310. For example, the Raman-suppressing fiber 300 shown in FIG. 3 may have a tapered length of approximately 2 m at the input end and approximately 2 m at the output end, although other suitable tapered length values ​​are contemplated (e.g., adiabaticity with respect to light traveling within the core 310 may be achieved with a tapered length of approximately 100-200 millimeters (mm)). Furthermore, in some embodiments, the core 310 may have a central diameter 326 that is generally larger than the diameter 322 of the core 310 at the input end and the diameter 324 of the core 310 at the output end over most of the length 320 of the Raman-suppressing fiber 300, and the diameters 322 and 324 may be equal or different. For example, in some embodiments, the ratio of center diameter 326 to diameter 322 at the input end and / or diameter 324 at the output end may be between about 1.5 and 3.5 (e.g., center diameter 326 may be about twice diameter 322 at the input end and / or diameter 324 at the output end, e.g., 125 μm in an example where diameter 322 at the input end is 50 μm and diameter 324 at the output end is 50 μm).As described herein, the Raman-suppressing fiber 300 maintains brightness, delivers a more desirable smaller spot size, and is capable of being a drop-in replacement for existing fibers based on an integrated design.

[0019] As described herein, the Raman-suppressing fiber 300 can suppress SRS (e.g., reduce Raman gain) without increasing spot size or sacrificing brightness by including a tapered core 310 that increases the effective area of ​​the Raman-suppressing fiber 300 along the length 320 of the Raman-suppressing fiber 300. Furthermore, in addition to suppressing SRS gain, the Raman-suppressing fiber 300 can have one or more design parameters to maintain the brightness of a laser traveling along the length 320 of the Raman-suppressing fiber 300 (e.g., within the tapered core 310). For example, in some embodiments, the one or more design parameters may include a length of the up-taper region 330 at the input end of the Raman suppression fiber 300, a length of the down-taper region 332 at the output end of the Raman suppression fiber 300, and / or a taper ratio of the Raman suppression fiber 300 (e.g., a ratio of the diameter 326 of the core 310 in the untapered central region 334 of the Raman suppression fiber 300 to the diameter 322 of the core 310 at the input end and / or the diameter 324 of the core 310 at the output end). In some embodiments, the up-taper length 330, the down-taper length 332, and / or the taper ratio may have values ​​that are adiabatic with respect to light of the laser traveling within the core 310. For example, the uptaper length 330 at the input end of the Raman suppression fiber 300 and the downtaper length 332 at the output end of the Raman suppression fiber 300 may be approximately 100 mm to 2 m, which may be long enough to be adiabatic for light (e.g., the uptaper and downtaper lengths allow light to pass through without degradation in brightness or additional loss). Increasing the taper lengths 330, 332 to values ​​greater than 2 m generally does not improve brightness but may cause more loss due to SRS. Regarding the taper ratio of the Raman suppression fiber, the taper ratio may be approximately 1.5 to 3.5, although the taper ratio may be constrained by the minimum supportable numerical aperture (NA) of the Raman suppression fiber 300.For example, if the taper ratio is increased significantly and the NA of the light in the Raman-suppressing fiber 300 is reduced, brightness degradation may occur due to micro- and / or macrobending, higher-order mode (HOM) excitation, and / or other effects. Brightness degradation effects can become problematic for NA values ​​of about 0.05, and a taper ratio in the above range (e.g., a diameter change of about 2x or 2.5x) can counteract the problematic brightness degradation effects.

[0020] 3 and described herein, the Raman-suppressing fiber 300 may include a tapered core 310 having input and output ends, and a cladding 312 surrounding the tapered core 310. In some embodiments, a buffer 314 (e.g., a conduit contained within a fiber optic cable) may encase the Raman-suppressing fiber 300 to provide mechanical isolation, protection against damage, and / or other functionality (e.g., fiber identification), as shown in FIG. 3. In some embodiments, the tapered core 310 includes a first tapered region 330 (e.g., an up-taper region) at the input end, a second tapered region 332 (e.g., a down-taper region) at the output end, and a central region 334 disposed between the first tapered region 330 and the second tapered region 332, as shown. In some embodiments, the first tapered region 330 has a first diameter 322 at the input end, the second tapered region 332 has a second diameter 324 at the output end, and the central region 334 has a third (central) diameter 326 that is larger than the first diameter 322 and the second diameter 324. In some embodiments, the first diameter 322 may be equal to the second diameter 324, or the first diameter 322 and the second diameter 324 may have different values ​​(e.g., if the Raman-suppressing fiber 300 is used in an application requiring the output spot size to be smaller or larger than the input laser). In some embodiments, the first tapered region 330 and the second tapered region 332 each have the third diameter 326 at their interface with the central region 334.

[0021] In some embodiments, to maintain the brightness of light traveling within the tapered core 310, the first tapered region 330 and the second tapered region 332 each have a length that is adiabatic with respect to light traveling within the tapered core 310 (e.g., about 100 mm to 2 m). Furthermore, in some embodiments, the first tapered region 330 may monotonically expand (e.g., linearly or parabolically) along its length, and the second tapered region 332 may monotonically contract (e.g., linearly or parabolically) along its length. In some embodiments, the first diameter 322 at the input end and the second diameter 324 at the output end are between 50 and 200 μm, although the first diameter 322 and / or the second diameter 324 may have larger values ​​for higher powers that may be susceptible to Raman gain. Further, as described herein, the first diameter 322 may be equal to the second diameter 324, or the first diameter 322 and the second diameter 324 may have different values. In some embodiments, the Raman-suppressing fiber 300 may be monolithic, allowing the Raman-suppressing fiber 300 to be used as a drop-in replacement for existing delivery fibers with constant core diameters. In some embodiments, as shown in FIG. 3 , the cladding 312 may have a constant diameter (e.g., at least 10 m, typically about 10 m to about 50 m) along the length 320 of the Raman-suppressing fiber 300. Alternatively, the cladding 312 may have a tapered shape corresponding to the shape of the tapered core 310. Furthermore, to minimize brightness degradation and / or maintain brightness, the taper ratio of the diameter 326 in the central region 334 to one or more of the first diameter 322 at the input end or the second diameter 324 at the output end may be between 1.5 and 3.5 (e.g., depending on the minimum supportable NA).

[0022] Thus, in some embodiments, the Raman-suppressing fiber 300 can have various design characteristics that enable it to suppress SRS without increasing spot size or sacrificing brightness. For example, referring to FIG. 3, table 340 shows the SRS gain that can be experienced in a design where the core 310 has diameters 322, 324 of 50 μm at the input and output ends, a diameter 326 of 125 μm in the central region 334 (e.g., resulting in a 2.5× taper ratio), and the uptaper region 330 and downtaper region 332 have lengths of approximately 2 m. For example, in FIG. 2, table 230 presents respective SRS gain (in dB) values ​​for standard 20 m and 30 m delivery fibers with a constant 50 μm core diameter, which results in an amount of Raman gain that does not meet the threshold (e.g., greater than 20 dB) at power levels greater than 4 kW and / or lengths greater than 20 m. Raman gain that does not meet these thresholds can be canceled in a standard delivery fiber only by increasing the constant core diameter (e.g., to 100 μm, as shown by table 232). In contrast, as shown in table 340, the Raman-suppressing fiber 300 can exhibit significantly less SRS without increasing the input diameter 322 or output diameter 324 to values ​​greater than 50 μm. Thus, compared to the standard delivery fiber shown in FIG. 2 (e.g., where the core 210 and cladding 212 have constant diameters), the Raman-suppressing fiber 300 with tapered cores 310 at both the input and output ends dramatically reduces SRS gain while still delivering a desired spot size to the application. For example, comparing table 230 of FIG. 2 with table 340 of FIG. 3, the Raman suppression fiber 300 design reduces the SRS gain from 17.69 dB to 3.68 dB at 20 m length and 4 kW power, from 26.54 dB to 5.12 dB at 30 m length and 4 kW power, from 26.54 dB to 5.52 dB at 20 m length and 6 kW power, and from 39.81 dB to 7.64 dB at 30 m length and 6 kW power.Thus, as described herein, the Raman-suppressing fiber 300 can be used in any suitable application requiring SRS suppression over long fiber lengths (e.g., the Raman-suppressing fiber 300 can be used as a feeding fiber, a process fiber, a passive fiber in lasers and / or combiners, and / or in other industries aside from high-power fiber lasers). Furthermore, in addition to having application in reducing SRS gain in CW lasers as described herein, the Raman-suppressing fiber 300 can be used as a delivery fiber for other pulsed laser applications (e.g., in the nanosecond, picosecond, and / or femtosecond ranges). Furthermore, the Raman-suppressing fiber 300 can be used to reduce any nonlinear effects that may be associated with high peak power densities. In this case, such nonlinear effects may include SRS, self-phase modulation, four-wave mixing, and / or stimulated Brillouin scattering, among other examples.

[0023] As noted above, Figure 3 is provided as an example. Other examples may differ from those described with respect to Figure 3.

[0024] FIG. 4 illustrates exemplary embodiments of fiber assemblies 400, 450 capable of mitigating SRS or other nonlinear effects. As shown, fiber assemblies 400, 450 may each include a core 410, a cladding 412 surrounding the core 410, and a buffer 414 for encapsulating the core 410 and cladding 412, where the buffer 414 may have a constant diameter. Additionally, as shown, fiber assemblies 400, 450 may include nonlinearity reduction devices at opposing ends of the core 410 to mitigate SRS or other nonlinear effects (e.g., SRS, self-phase modulation, four-wave mixing, and / or stimulated Brillouin scattering, among other examples). For example, rather than designing the core 410 with up- and down-tapers to increase the effective area (e.g., as shown in FIG. 3), fiber assembly 400 may include a quarter-pitch graded-index (GI) fiber 420 spliced ​​to the input and output ends of a standard delivery fiber at respective splice points 422. Alternatively, fiber assembly 450 may include separate tapered ends 460 (e.g., tapered sections with a maximum length of about 30 mm) to mitigate SRS or other nonlinear effects, which are spliced ​​to the input and output ends of standard delivery fiber at respective splice points 462. For example, as shown, tapered ends 460 have the same diameter as core 410 at each splice point 462, but have smaller input and output diameters to increase the effective area and thereby suppress nonlinear effects without delivering undesirable spot sizes or degrading brightness.

[0025] As noted above, Figure 4 is provided as an example. Other examples may differ from those described with respect to Figure 4.

[0026] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the embodiments. Further, any of the embodiments described herein may be combined unless the above disclosure explicitly states why one or more embodiments cannot be combined.

[0027] As used herein, meeting a threshold can refer to a value greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, etc., depending on the context.

[0028] Although particular combinations of features are recited in the claims and / or disclosed herein, these combinations are not intended to limit the disclosure of various embodiments. Indeed, many of these features can be combined in ways not specifically recited in the claims and / or disclosed herein. While each dependent claim listed below may depend directly on only one claim, the disclosure of various embodiments includes each dependent claim in combination with every other claim in the set of claims. As used herein, phrases referring to "at least one of" a list of items refer to any combination of those items, including single elements. As an example, "at least one of a, b, or c" is intended to encompass a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the same item.

[0029] No element, act, or instruction used herein should be construed as critical or required unless explicitly stated. Also, as used herein, the articles "a" and "an" are intended to include one or more items and can be used interchangeably with "one or more," and the article "the" is intended to include one or more items referenced in connection with the article "the" and can be used interchangeably with "one or more." Furthermore, as used herein, "set" is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and can be used interchangeably with "one or more." When only one item is intended, the phrase "only one" or similar terminology is used. Also, as used herein, "has," "have," "having," and the like are intended to be open-ended terms. Furthermore, the phrase "based on" means "based at least in part on," unless otherwise specified. Also, as used herein, "or" is intended to be inclusive when used consecutively and can be used interchangeably with "and / or" unless expressly stated otherwise (e.g., when used in combination with "either" or "only one of").

[0030] Additionally, spatially relative terms such as "below," "lower," "upper," "upper," etc. may be used herein for ease of description 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 devices, apparatus, and / or elements in use or operation in addition to the orientation depicted in the figures. Devices may be oriented in other orientations (such as rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Claims

1. An integral optical fiber, a tapered core having an input end and an output end; a cladding surrounding the tapered core; Equipped with the tapered core has a first tapered region at the input end, a second tapered region at the output end, and a central region disposed between the first tapered region and the second tapered region; the first tapered region has a first core diameter at the input end, the second tapered region has a second core diameter at the output end, and the central region has a third core diameter greater than the first and second core diameters; the first tapered region and the second tapered region each have a third core diameter at an interface with the central region; the first core diameter at the input end and the second core diameter at the output end are between 50 and 200 micrometers; The monolithic optical fiber, wherein the cladding has a constant cladding diameter throughout the first tapered region, the central region, and the second tapered region.

2. 2. The integrated optical fiber of claim 1, wherein the first and second tapered regions have lengths such that they are adiabatic with respect to light traveling within the tapered core.

3. 10. The integrated optical fiber of claim 1, wherein the first tapered region monotonically expands along the length of the first tapered region and the second tapered region monotonically contracts along the length of the second tapered region.

4. 2. The integrated optical fiber of claim 1, wherein the first core diameter is equal to the second core diameter.

5. 2. The integrated optical fiber of claim 1, wherein a nonlinearity parameter associated with a laser beam transmitted through the integrated optical fiber satisfies a threshold based on one or more of a power level of the laser beam or a value of the first core diameter or the second core diameter.

6. 10. The integrated optical fiber of claim 1, having a length of at least 10 meters.

7. 10. The integrated optical fiber of claim 1, wherein a taper ratio of a third core diameter in the central region to one or more of a first core diameter at the input end or a second core diameter at the output end is between 1.5 and 3.

5.

8. 1. An optical assembly comprising: an optical fiber having a core; the core has a constant core diameter; a first nonlinearity reduction device spliced ​​to the input end of the optical fiber; the first nonlinearity reduction device is a first tapered element, the first tapered element having an input diameter at a first tapered end and a first core diameter at a first splice point equal to the constant core diameter, the first nonlinearity reduction device being spliced ​​to the input end of the optical fiber at the first splice point; a second nonlinearity reduction device spliced ​​to the output end of the optical fiber; the second nonlinearity reduction device is a second tapered element, the second tapered element having an output diameter at a second tapered end and the first core diameter at a second splice point equal to the constant core diameter, the second nonlinearity reduction device being spliced ​​to the output end of the optical fiber at the second splice point; the input diameter and the output diameter are each between 50 and 200 micrometers; a cladding surrounding the core, the first nonlinearity reducing device, and the second nonlinearity reducing device; the cladding has a constant cladding diameter across the core, the first nonlinearity reducing device, and the second nonlinearity reducing device; The optical assembly, wherein the constant cladding diameter is greater than the constant core diameter.

9. 9. The optical assembly of claim 8, wherein the first nonlinearity reduction device and the second nonlinearity reduction device are tapered components having a first core diameter equal to the constant core diameter at each junction point where the first and second nonlinearity reduction devices are spliced ​​to the optical fiber, and having input and output diameters, respectively, smaller than the constant core diameter.

10. 10. The optical assembly of claim 8, wherein a nonlinearity parameter associated with a laser beam transmitted through the optical assembly satisfies a threshold value based on one or more of a power level of the laser beam or a length of the optical assembly.

11. 11. The optical assembly of claim 10, wherein the nonlinearity parameter comprises Raman gain, self-phase modulation, four-wave mixing, or stimulated Brillouin scattering.

12. 1. An optical assembly comprising: a fiber laser engine; A processing head; an integrated delivery fiber connected to the fiber laser engine and the processing head, for delivering a laser beam from the fiber laser engine to the processing head; wherein the integrated delivery fiber comprises: a tapered core having an input end and an output end; a cladding surrounding the tapered core; Equipped with the tapered core has a first tapered region at the input end, a second tapered region at the output end, and a central region between the first tapered region and the second tapered region; the first tapered region has an input diameter at the input end, the second tapered region has an output diameter at the output end, and the central region has a constant diameter greater than the input and output diameters; the input diameter and the output diameter are each between 50 and 200 micrometers; The optical assembly, wherein the cladding has a constant cladding diameter across the first tapered region, the central region, and the second tapered region.

13. 13. The optical assembly of claim 12, wherein a nonlinearity parameter associated with the laser beam delivered to the processing head satisfies a threshold based on one or more of the power level of the laser beam, the length of the integrated delivery fiber, the value of the input diameter, or the value of the output diameter.

14. 14. The optical assembly of claim 13, wherein the nonlinearity parameter comprises Raman gain, self-phase modulation, four-wave mixing, or stimulated Brillouin scattering.

15. 13. The optical assembly of claim 12, wherein the first tapered region and the second tapered region each have a length that is adiabatic with respect to the laser beam delivered to the processing head.

16. 13. The optical assembly of claim 12, wherein the first tapered region monotonically expands along a length of the first tapered region and the second tapered region monotonically contracts along a length of the second tapered region.

17. 13. The optical assembly of claim 12, wherein the input diameter is equal to the output diameter. Optical assembly.

18. 9. The optical assembly of claim 8, wherein a nonlinearity parameter associated with a laser beam transmitted through the optical assembly satisfies a threshold value based on the value of the input diameter or the output diameter.

19. 9. The optical assembly of claim 8, wherein the input diameter is equal to the output diameter.

20. 9. The optical assembly of claim 8, wherein a taper ratio of the constant core diameter of the optical fiber to one or more of the input diameter at the first tapered end or the output diameter at the second tapered end is between 1.5 and 3.5.

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