Raman depressing fiber
Patent Information
- Application Number
- JP2022116447
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2021-11-03
- Filing Date
- 2022-07-21
- Publication Date
- 2025-07-10
- Estimated Expiration
- 2042-07-21
AI Technical Summary
Long delivery fibers in industrial laser systems face challenges such as optical power loss, pulse broadening, and nonlinear effects like stimulated Raman scattering (SRS), which become more severe with increasing laser powers, affecting industrial processes and equipment.
The development of Raman suppression fibers with a tapered core design that maintains brightness and reduces SRS gain without increasing spot size, featuring adiabatic taper lengths and controlled taper ratios to minimize nonlinear effects.
The Raman suppression fibers effectively suppress SRS and other nonlinear effects, maintaining high brightness and small spot sizes over long distances, compatible with existing fiber manufacturing and cabling, suitable for high-power industrial applications.
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Abstract
Description
Cross - reference to related applications
[0001] This patent application was filed on July 30, 2021, and claims the priority of U.S. Provisional Patent Application No. 63 / 203,772, entitled "RAMAN DEPRESSING FIBER". The disclosure of this prior application is considered a part of this patent application and is incorporated herein by reference.
Technical Field
[0002] This disclosure generally relates to delivery fibers that can be used for industrial applications and optical fibers designed to suppress stimulated Raman scattering (SRS) gain and maintain the brightness of a laser along the optical fiber.
Background Art
[0003] In physics, the term scattering generally refers to various physical processes in which moving particles or radiation in some form (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 matter, which means that both an exchange of energy and a change in the direction in which the light travels occur. Usually, Raman scattering involves the energy acquired by molecules when incident photons from a visible laser are shifted to lower energies.
Summary of the Invention
Means for Solving the Problems
[0004] In some embodiments, the 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 located 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 a third core diameter at their interface with the central region.
[0005] In some embodiments, the optical assembly comprises an optical fiber, the optical fiber comprising a core and a cladding surrounding the core. The core has a constant core diameter, and the cladding has a constant cladding diameter that is greater than the constant core diameter. The optical assembly comprises a first nonlinearity reduction device joined to the optical fiber at the input end, and a second nonlinearity reduction device joined to the output end of the optical fiber.
[0006] In some embodiments, the optical assembly comprises a fiber laser engine, a processing head, and an integrated delivery fiber connected to the fiber laser engine and the processing head, which delivers a laser beam from the fiber laser engine to the processing head. The integrated delivery fiber comprises 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 located 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 drawing]
[0007] [Figure 1] This figure shows an example of an industrial beam delivery system. [Figure 2] This figure shows an example of a delivery fiber. [Figure 3] This figure shows an exemplary embodiment of a Raman-suppressing fiber capable of mitigating stimulated Raman scattering (SRS) or other nonlinear effects. [Figure 4] This figure shows an exemplary embodiment of a fiber assembly capable of mitigating SRS or other nonlinear effects. [Modes for carrying out the invention]
[0008] A detailed description of exemplary embodiments follows with reference to the accompanying drawings. Identical reference numerals in different drawings may identify identical or similar elements.
[0009] Laser material processing offers numerous 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, including cutting, drilling, welding, brazing, surface annealing, alloying, and / or hardening. For example, in industrial laser applications, beam delivery systems often include optical fibers used to deliver high-power and / or high-intensity laser beams to targets.
[0010] For example, Figure 1 shows an example of an industrial beam delivery system 100. As shown in Figure 1, the industrial beam delivery system 100 typically includes a fiber laser engine 110 (e.g., a multi-kilowatt (kW) fiber laser engine) connected to a processing head 120 in a work area 130 (e.g., a cutting and / or welding area) via a delivery fiber 140 having a length of 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, an optical system for projecting the laser output, and any laser processing accessories such as an assist gas port if necessary. The fiber laser engine 110 can deliver a laser into an optical coupler unit via free space or via a separate optical fiber, and the optical coupler unit can emit a laser into the delivery fiber 140. Therefore, the delivery fiber 140 delivers the laser to the processing head 120, and the processing head 120 projects the laser onto the workpiece in the processing area 130 to perform the 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 m). For example, a long delivery fiber 140 may be necessary because the processing head 120 is usually rapidly accelerating within a large machine, and the gantry that moves the processing head 120 within the work area 130 to direct the laser onto the material being cut, welded, engraved, and / or otherwise processed cannot bear the weight load of the fiber laser engine 110 (for example, a movable beam delivery system can move the laser within the work area 130 without moving the fiber laser engine 110, but this system can be very heavy). Furthermore, a long delivery fiber 140 can be advantageous in that it allows the fiber laser engine 110 to be located in a well-protected area with easy access for maintenance work, rather than near the work area 130. However, a long delivery fiber 140 can impose various challenges, including optical power loss, pulse spread, and / or nonlinear limitations. For example, higher laser power generally leads to faster material processing, so there is a growing demand for high-power lasers (e.g., currently 15-20 kW) in industrial applications. However, as laser power increases, transmitting high-brightness and high-power laser light through optical fibers tens of meters long is becoming increasingly difficult due to problematic nonlinear effects such as stimulated Raman scattering (SRS).
[0012] In particular, 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 molecules of a glass medium. While this process may be useful for certain applications (e.g., converting optical fibers into Raman amplifiers or tunable Raman lasers), SRS is undesirable for multi-kW continuous-wave (CW) industrial fiber lasers or multi-kW quasi-continuous-wave 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 could propagate without undesirable loss and / or heating. These can negatively impact industrial processes and / or cause damage to equipment. As the power levels of industrial kW fiber lasers continue to increase, the problem of SRS becomes more serious, creating a need for techniques to suppress SRS.
[0013] Generally, the degree of signal resonance (SRS) present in an optical fiber can be measured by the Raman gain index, which is a metric for the amount of amplification caused by SRS in an optical fiber of a given length. 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. Here, the signal intensity is obtained by dividing the output by the geometric area, as shown in the following equation.
[0014]
number
[0015] The gain coefficient gR can be approximately 10–13 m / W and depends on the specific dopant in the glass. For example, Figure 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, a standard delivery fiber 200 may have a length 220 of at least 10 m and a constant diameter 222. As described herein, the effect of SRS in a standard delivery fiber 200 is explained in the context that the length 220 of the standard delivery fiber is either 20 m or 30 m, and the diameter 222 of the core 210 is either 50 micrometers (μm) or 100 μm, although other appropriate values for length 220 and core diameter 222 are possible. As shown in Figure 2, Table 230 shows the possible SRS gain (in decibels (dB)) that can occur when the diameter 222 of the core 210 in a standard delivery fiber 200 is 50 μm. In particular, the middle column of Table 230 shows the possible SRS gains that can occur at different power levels (e.g., 4kW, 6kW, 9kW, and 12kW) when the length 220 is 20m and the core diameter 222 is 50μm, while the rightmost column of Table 230 shows the possible SRS gains that can occur when the length 220 is 30m and the core diameter 222 is 50μm. As shown in Table 230, when the power level exceeds 4kW or the length is greater than 20m, SRS gains occur that do not meet the performance threshold (e.g., a limit of 20 decibels (dB)) that is considered practical for a core diameter 222 of 50μm (e.g., indicated by the shaded boxes in Table 230).
[0016] Therefore, when using a standard delivery fiber 200 with fixed output and length, a solution typically employed to reduce SRS is to increase the core diameter (e.g., up to 100 μm). Doing so increases the effective area along the length 220 of the standard delivery fiber 200, thereby reducing the SRS gain (e.g., by increasing the value of the denominator in the above equation, the signal strength decreases). For example, Table 232 shows the SRS gain values for a standard delivery fiber 200 when the core diameter 222 is 100 μm and the length 220 is 20 m or 30 m. As shown in the figure, 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, increasing the core diameter 222 is a second-best solution, as 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. Furthermore, as the output level increases to 15-20 kW (or higher), the SRS also increases even with a standard delivery fiber 200 with a core diameter of 222 and a core diameter of 100 μm. In that case, it would be necessary to further increase the core diameter of 222 to 200 μm (or higher).
[0017] Several embodiments described herein relate to Raman suppression (or suppression) fibers capable of reducing Raman gain without sacrificing brightness or requiring the delivery of undesirable size spots into the installation area by changing the core diameter (e.g., via a processing head). For example, in some embodiments, the Raman suppression fiber may be an integrated (e.g., single-piece) delivery fiber that maintains brightness and reduces SRS gain in high-power kW applications. The Raman suppression fiber can deliver small spot sizes (e.g., 50 μm) and high power intensity over long fiber lengths (e.g., 10 to 50 meters). This effect is otherwise limited by SRS gain. The Raman suppression fibers described herein are compatible with current fiber manufacturing processes and / or cable wiring processes and are therefore backward compatible with existing technologies. For example, as described herein, Raman-suppressed fibers can transmit high-brightness, high-power laser light through optical fibers tens of meters long 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 compatible with standard cable and connection technologies.
[0018] Figure 3 shows an exemplary embodiment of a Raman-suppressed fiber 300 that can mitigate SRS or other nonlinear effects. For example, as described above, the easiest way to reduce the Raman gain in an optical fiber at a given output level and length is to increase the effective area along the length of the fiber (for example, by increasing the denominator in the above equation to reduce the Raman gain index occurring in the optical fiber). However, as further described with reference to Figure 2, increasing the effective area (for example by increasing the core diameter) can come at the expense of brightness and increase the spot size transmitted by the optical fiber. In contrast, as shown in Figure 3, the Raman-suppressed fiber 300 is integrated, with both the input and output ends of the cable having tapered cores 310. Furthermore, as shown, the cladding 312 surrounds the tapered cores 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 cores 310. In some embodiments, the core 310 of the Raman suppression fiber 300 may have tapered lengths at the input and output ends that are adiabatic with respect to light traveling through the core 310. For example, the Raman suppression fiber 300 shown in Figure 3 may have tapered lengths of about 2 m at the input end and about 2 m at the output end, but other suitable tapered length values are possible (for example, adiabatic protection with respect to light traveling through the core 310 can be achieved with a tapered length of about 100 to 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 suppression fiber 300, and the diameters 322 and 324 may be equal or different. For example, in some embodiments, the ratio of the central diameter 326 to the diameter 322 at the input end and / or the diameter 324 at the output end may be about 1.5 to 3.5 (for example, the central diameter 326 may be about twice the diameter 322 at the input end and / or the diameter 324 at the output end, which is 125 μm in an example where the diameter 322 at the input end is 50 μm and the diameter 324 at the output end is 50 μm).As described herein, the Raman-suppressed fiber 300 maintains brightness, delivers a more desirable smaller spot size, and can drop-in replace existing fibers based on an integrated design.
[0019] As described herein, the Raman suppression fiber 300 can suppress SRS (e.g., reduce Raman gain) without increasing spot size or sacrificing brightness by providing a tapered core 310 that increases the effective area of the Raman suppression fiber 300 along its length 320. Furthermore, in addition to suppressing SRS gain, the Raman suppression fiber 300 may have one or more design parameters to maintain the brightness of the laser traveling along its length 320 (e.g., within the tapered core 310). For example, in some embodiments, one or more design parameters may include the length of the up-tapered region 330 at the input end of the Raman suppression fiber 300, the length of the down-tapered region 332 at the output end of the Raman suppression fiber 300, and / or the taper ratio of the Raman suppression fiber 300 (e.g., the 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 the laser light traveling through the core 310. For example, the up-taper length 330 at the input end of the Raman suppression fiber 300 and the down-taper length 332 at the output end of the Raman suppression fiber 300 may be approximately 100 mm to 2 m, and this length may be sufficient to be adiabatic with respect to light (for example, by setting the up-taper and down-taper lengths to this length, light can pass through without causing brightness degradation or additional loss). Increasing the taper lengths 330 and 332 to values greater than 2 m generally does not improve brightness but may cause more loss in SRS. Regarding the taper ratio of the Raman suppression fiber, the taper ratio may be approximately 1.5 to 3.5, but the taper ratio may be constrained by the minimum supported numerical aperture (NA) of the Raman suppression fiber 300.For example, if the taper ratio increases significantly and the NA of the light in the Raman-suppressed fiber 300 decreases, luminance degradation may occur due to micro and / or macrobends, higher-order mode (HOM) excitation, and / or other effects. This luminance degradation effect may be problematic when the NA value is approximately 0.05, and the problematic luminance degradation effect can be counteracted by setting the taper ratio within the above range (e.g., changing the diameter to approximately 2 or 2.5 times).
[0020] Therefore, as shown in Figure 3 and described herein, the Raman-suppressed 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, as shown in Figure 3, a buffer 314 (e.g., a conduit included in the optical fiber cable) can enclose the Raman-suppressed fiber 300 to provide mechanical isolation, protection against damage, and / or other functions (e.g., fiber identification). In some embodiments, as illustrated, the tapered core 310 includes a first tapered region 330 (e.g., an up-tapered region) at the input end, a second tapered region 332 (e.g., a down-tapered region) at the output end, and a central region 334 located between the first tapered region 330 and the second tapered region 332. 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, (for example, when the Raman suppression fiber 300 is used in an application where the output spot size needs to be smaller or larger than the input laser,) 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 first tapered region 330 and the second tapered region 332 each have a third diameter 326 at the 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 the light traveling within the tapered core 310 (e.g., about 100 mm to 2 m). Further, in some embodiments, the first tapered region 330 may expand monotonically (e.g., linearly or parabolically) along the length of the first tapered region 330, and the second tapered region 332 may contract monotonically (e.g., linearly or parabolically) along the length of the second tapered region 332. In some embodiments, the first diameter 322 at the input end and the second diameter 324 at the output end are 50 to 200 μm, but the first diameter 322 and / or the second diameter 324 may have larger values in the case of higher output, which may be more susceptible to the influence of 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 suppression fiber 300 may be of an integrated type, whereby the Raman suppression fiber 300 can be used as a drop-in replacement for an existing delivery fiber with a constant core diameter. 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 suppression fiber 300. Alternatively, the cladding 312 may have a tapered shape corresponding to the shape of the tapered core 310. Further, to minimize brightness degradation and / or maintain brightness, the taper ratio of the diameter 326 in the central region 334 with respect to one or more of the first diameter 322 at the input end or the second diameter 324 at the output end may be set to 1.5 to 3.5 (e.g., according to the minimum supportable NA).
[0022] Therefore, in some embodiments, the Raman-suppressed fiber 300 can have various design characteristics that enable SRS suppression without requiring an increase in spot size or a sacrifice of brightness. For example, referring to Figure 3, Table 340 shows the possible SRS gain in a design where the diameters 322 and 324 of the core 310 at the input and output ends are 50 μm, the diameter 326 in the central region 334 is 125 μm (resulting in, for example, a 2.5x taper ratio), and the up-tapered region 330 and down-tapered region 332 are approximately 2 m in length. For example, in Figure 2, Table 230 presents the respective SRS gain (in dB) values for typical 20 m and 30 m delivery fibers with a core of constant diameter 50 μm, which result in an amount of Raman gain that does not meet the threshold (e.g., greater than 20 dB) at power levels above 4 kW and / or lengths greater than 20 m. Raman gains that do not meet these thresholds can only be canceled in a standard delivery fiber by increasing the core diameter (for example, up to 100 μm, as shown in Table 232). In contrast, as shown in Table 340, the Raman-suppressed fiber 300 can exhibit a considerably smaller SRS without increasing the input diameter 322 or output diameter 324 to a value greater than 50 μm. Therefore, compared to a standard delivery fiber shown in Figure 2 (for example, when the core 210 and cladding 212 have a constant diameter), the Raman-suppressed fiber 300, which has a tapered core 310 at both the input and output ends, dramatically reduces the SRS gain while delivering the desired spot size to the application. For example, comparing Table 230 in Figure 2 with Table 340 in Figure 3, the design of Raman-suppressed fiber 300 shows that the SRS gain decreases from 17.69 dB to 3.68 dB at a length of 20 m and an output of 4 kW, from 26.54 dB to 5.12 dB at a length of 30 m and an output of 4 kW, from 26.54 dB to 5.52 dB at a length of 20 m and an output of 6 kW, and from 39.81 dB to 7.64 dB at a length of 30 m and an output of 6 kW.Therefore, as described herein, the Raman-suppressed fiber 300 can be used in any suitable application where suppression of SRS over long fiber lengths is required (for example, the Raman-suppressed fiber 300 can be used as a feeding fiber, process fiber, passive fiber in lasers and / or combiners, and / or in other industries except high-power fiber lasers). Furthermore, in addition to having applications for reducing SRS gain in CW lasers as described herein, the Raman-suppressed fiber 300 can be used as a delivery fiber for other pulsed laser applications (e.g., in the nanosecond, picosecond, and / or femtosecond ranges). Moreover, the Raman-suppressed fiber 300 can be used to reduce any nonlinear effects that may be associated with high peak power density. In such cases, such nonlinear effects may include, among other examples, SRS, self-phase modulation, four-wave mixing, and / or stimulated Brillouin scattering.
[0023] As described above, Figure 3 is provided as an example. Other examples may differ from those described with respect to Figure 3.
[0024] FIG. 4 shows exemplary embodiments of fiber assemblies 400, 450 that can reduce SRS or other non - linear 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 the cladding 412, and the buffer 414 may have a constant diameter. Further, as shown, fiber assemblies 400, 450 may include a non - linearity reduction device at opposite ends of the core 410 to reduce SRS or other non - linear effects (e.g., among others in the example, SRS, self - phase modulation, four - wave mixing, and / or stimulated Brillouin scattering). For example, instead of designing a core 410 with tapers and downtapers 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 joined to the input and output ends of a standard delivery fiber at each junction point 422. Alternatively, fiber assembly 450 may individually include a tapered end 460 (e.g., a tapered component with a maximum length of about 30 mm) to reduce SRS or other non - linear effects, and the tapered end 460 is joined to the input and output ends of a standard delivery fiber at each junction point 462. For example, as shown, the tapered end 460 has the same diameter as the core 410 at each junction point 462 and has smaller input and output diameters to increase the effective area and thereby suppress non - linear effects without delivering an undesirable spot size or degrading the brightness.
[0025] As described above, FIG. 4 is provided as an example. Other examples may be different from those described with respect to FIG. 4.
[0026] The foregoing disclosures are illustrative and explanatory, but are not intended to be exhaustive or to limit embodiments to the exact forms disclosed. Modifications and variations may be made in light of the foregoing disclosures or obtained from the practice of embodiments. Furthermore, any of the embodiments described herein may be combined unless the foregoing disclosures expressly indicate why one or more embodiments cannot be combined.
[0027] As used herein, "meeting a threshold" can mean, depending on the context, a value greater than the threshold, greater than or equal to the threshold, less than or equal to the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, etc.
[0028] While specific combinations of features are described in the claims and / or disclosed herein, these combinations are not intended to limit the disclosure of various embodiments. In fact, many of these features can be combined in ways not specifically described in the claims and / or disclosed herein. Each dependent claim listed below may depend directly on only one claim, but the disclosure of various embodiments includes each dependent claim combined with any other claim in the set of claims. As used herein, the phrase “at least one of” the list of items refers to any combination of those items, including a single element. For example, “at least one of a, b, or c” is intended to include any combination of a, b, c, ab, ac, bc, and abc, as well as any multiples of the same item.
[0029] Any elements, actions, or instructions used herein should not be construed as important or essential unless expressly stated otherwise. Furthermore, where used herein, the articles “a” and “an” are intended to include one or more items and are interchangeable with “one or more,” and where used herein, the article “the” is intended to include one or more items referred to in relation to the article “the” and is interchangeable with “one or more.” Additionally, where 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 is interchangeable with “one or more.” When only one item is intended, the phrase “only one” or similar terminology is used. Furthermore, where used herein, “has,” “have,” “having,” etc., are intended to be open-ended terms. Additionally, the phrase “based on” means “at least partially based on” unless otherwise specified. Furthermore, as used herein, “or” is intended to be inclusive when used consecutively and may be used interchangeably with “and / or” unless expressly otherwise specified (for example, when used in combination with “either” or “only one of”).
[0030] Furthermore, spatially relative terms such as "down," "lower," "upper," and "upper" may be used herein to describe the relationship between one element or feature and another, as shown in the figures, for the sake of clarity. Spatially relative terms are intended to encompass different orientations of equipment, devices, and / or elements during use or operation, in addition to the orientations depicted in the drawings. Equipment may be oriented to other orientations (90-degree rotations or other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.
Claims
1. A monolithic optical fiber, comprising: a tapered core having an input end and an output end; a cladding surrounding the tapered core; wherein the tapered core has a first tapered region at the input end, a second tapered region at the output end, and a central region provided 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 core diameter and the second core diameter; the first tapered region and the second tapered region each have a third core diameter at the interface with the central region; the first core diameter at the input end and the second core diameter at the output end are 50 to 200 micrometers; the cladding has a constant cladding diameter over the first tapered region, the central region, and the second tapered region, the monolithic optical fiber.
2. The monolithic optical fiber according to claim 1, wherein the first tapered region and the second tapered region have a length that is adiabatic to light traveling within the tapered core, the monolithic optical fiber.
3. The monolithic optical fiber according to claim 1, wherein the first tapered region expands monotonically along the length of the first tapered region, and the second tapered region contracts monotonically along the length of the second tapered region, the monolithic optical fiber.
4. The monolithic optical fiber according to claim 1, wherein the first core diameter is equal to the second core diameter, the monolithic optical fiber.
5. The monolithic optical fiber according to claim 1, wherein the non-linearity parameter related to the laser beam transmitted through the monolithic optical fiber satisfies a threshold based on one or more of the output level of the laser beam, the value of the first core diameter, or the value of the second core diameter, the monolithic optical fiber.
6. The monolithic optical fiber according to claim 1, having a length of at least 10 meters, the monolithic optical fiber.
7. The monolithic optical fiber according to claim 1, wherein the taper ratio of the third core diameter in the central region to one or more of the first core diameter at the input end or the second core diameter at the output end is 1.5 to 3.5, the monolithic optical fiber.
8. An optical assembly, comprising: comprising an optical fiber having a core, said core having a constant core diameter, comprising a first non-linearity reduction device joined to the input end of said optical fiber, said first non-linearity reduction device being a first tapered component, said first tapered component having an input diameter at a first tapered end and having a first core diameter equal to said constant core diameter at a first joining point, said first non-linearity reduction device being joined to the input end of said optical fiber at said first joining point, comprising a second non-linearity reduction device joined to the output end of said optical fiber, said second non-linearity reduction device being a second tapered component, said second tapered component having an output diameter at a second tapered end and having said first core diameter equal to said constant core diameter at a second joining point, said second non-linearity reduction device being joined to the output end of said optical fiber at said second joining point, said input diameter and said output diameter being each 50 to 200 micrometers, comprising a cladding surrounding said core, said first non-linearity reduction device, and said second non-linearity reduction device, said cladding having a constant cladding diameter over said core, said first non-linearity reduction device, and said second non-linearity reduction device, said constant cladding diameter being larger than said constant core diameter, an optical assembly.
9. The optical assembly according to claim 8, wherein said first non-linearity reduction device and said second non-linearity reduction device are tapered components having a first core diameter equal to said constant core diameter at each joining point where said first and second non-linearity reduction devices are joined to said optical fiber, and having an input diameter and an output diameter each smaller than said constant core diameter, respectively, an optical assembly.
10. The optical assembly according to claim 8, wherein a non-linearity parameter associated with a laser beam transmitted through said optical assembly satisfies a threshold based on one or more of an output level of said laser beam or a length of said optical assembly, an optical assembly.
11. The optical assembly according to claim 10, wherein said non-linearity parameter includes Raman gain, self-phase modulation, four-wave mixing, or stimulated Brillouin scattering, an optical assembly.
12. An optical assembly, a fiber laser engine, a processing head, An integrated delivery fiber connected to the fiber laser engine and the processing head, and transmitting a laser beam from the fiber laser engine to the processing head; comprising, the integrated delivery fiber is a tapered core having an input end and an output end; a cladding surrounding the tapered core; comprising The tapered core has a first tapered region at the input end, a second tapered region at the output end, and a central region provided 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 larger than the input diameter and the output diameter; The input diameter and the output diameter are each 50 to 200 micrometers; The cladding has a constant cladding diameter over the first tapered region, the central region, and the second tapered region, an optical assembly.
13. The optical assembly according to claim 12, wherein a non-linearity parameter related to the laser beam transmitted to the processing head satisfies a threshold value based on one or more of the output 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. An optical assembly.
14. The optical assembly according to claim 13, wherein the non-linear parameter includes Raman gain, self-phase modulation, four-wave mixing, or stimulated Brillouin scattering. An optical assembly.
15. The optical assembly according to 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 transmitted to the processing head. An optical assembly.
16. The optical assembly according to claim 12, 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. An optical assembly.
17. The optical assembly according to claim 12, wherein the input diameter is equal to the output diameter. An optical assembly. Claim 18. The optical assembly according to claim 8, wherein a non-linear parameter associated with a laser beam transmitted through the optical assembly satisfies a threshold value based on a value of the input diameter or the output diameter. Claim 19. The optical assembly according to claim 8, wherein the input diameter is equal to the output diameter. Claim 20. The optical assembly according to claim 8, wherein a taper ratio of the constant core diameter in the optical fiber with respect to one or more of the input diameter at the first tapered end or the output end at the second tapered end is 1.5 to 3.5.