Symmetrical fiber layout for mitigating group delay mismatch in multi-core fibers

Abstract

The invention relates to a symmetric fiber layout for mitigating group delay mismatch in a multi-core fiber. A multi-core optical fiber includes a fiber media including an input facet configured to receive seed light and an output facet configured to output amplified light and a plurality of cores arranged in the fiber media. Each core is configured to guide a respective beamlet of seed light and includes a respective gain medium for amplifying the respective beamlet into a respective beamlet of amplified light. The input facet and the output facet are parallel surfaces pointing in opposite directions. The fiber media has a plurality of bends. The number of the left-handed bends is equal to the number of the right-handed bends, so that the comprehensive bending angle of the optical fiber medium is zero. The group delays of the plurality of cores are substantially matched due to the input-output facet arrangement and due to the comprehensive bend angle of the fiber media being zero.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 684,497, filed August 19, 2024, entitled “SYMMETRIC OPTICAL FIBERLAYOUT TO MITIGATE GROUP DELAY MISMATCH IN MULTI-CORE FIBER”. The disclosure of that prior art application is considered part of this patent application and is incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to symmetrical fiber layouts for mitigating group delay in multi-core optical fibers. Background Technology

[0004] Active fiber is an optical fiber in which rare earth elements (e.g., erbium, ytterbium, or thulium) are doped within the fiber core. These rare earth elements serve as the active core material. Inside the fiber core, the rare earth dopant performs stimulated emission by converting light (e.g., laser light) into amplified light (e.g., amplified laser light). In some cases, active fiber can be used to generate laser light from pump light. As a result, the laser light is generated and / or amplified within the fiber core based on the input light. Multicore fiber (MCF) is an optical fiber containing two or more cores within a single strand. In other words, two or more cores are provided within the same fiber cladding. MCF with active cores can be used as power amplifier fibers. Summary of the Invention

[0005] In some implementations, a multi-core optical fiber includes an optical fiber medium and a plurality of cores disposed within the optical fiber medium, the optical fiber medium including an input facet configured to receive seed light and an output facet configured to output amplified light, wherein each of the plurality of cores is configured to guide a corresponding sub-bundle of seed light and includes a corresponding gain medium for amplifying the corresponding sub-bundle of seed light into the corresponding sub-bundle of amplified light, wherein the input facet and the output facet are parallel surfaces pointing in opposite directions such that the direction of travel of seed light entering the input facet is the same as the direction of travel of amplified light leaving the output facet, wherein the optical fiber medium has a plurality of bends, including one or more left-hand bends and one or more right-hand bends, wherein the number of one or more left-hand bends is equal to the number of one or more right-hand bends, such that the combined bend angle of the optical fiber medium is zero, and wherein the group delay of the plurality of cores is substantially matched due to the arrangement of the input facet and the output facet and due to the zero combined bend angle of the optical fiber medium.

[0006] In some implementations, a coherent beam combining fiber includes an optical fiber medium and a plurality of cores disposed within the optical fiber medium, the optical fiber medium including an input facet configured to receive seed light and an output facet configured to output amplified light, wherein each of the plurality of cores is configured to guide a corresponding portion of the seed light and includes a corresponding gain medium for amplifying the corresponding portion of the seed light into a corresponding portion of the amplified light, wherein the input facet and the output facet are parallel surfaces facing opposite directions such that the direction of travel of the seed light entering the input facet is parallel to the direction of travel of the amplified light leaving the output facet, wherein the optical fiber medium has a plurality of bends, including one or more left-hand bends and one or more right-hand bends, wherein the number of one or more left-hand bends is equal to the number of one or more right-hand bends, wherein the sum of the bend angles of the plurality of bends is zero, wherein the left-hand bend angles and the right-hand bend angles have opposite signs, and wherein the group delay of the plurality of cores is substantially matched due to the arrangement of the input facet and the output facet and due to the zero sum of the bend angles.

[0007] In some implementations, a coherent beam combining assembly includes a cold plate with grooves and a multi-core fiber mounted on the cold plate within the grooves. The multi-core fiber includes an fiber medium and a plurality of cores arranged within the fiber medium. The fiber medium includes an input facet configured to receive seed light and an output facet configured to output amplified light. Each of the multiple cores is configured to guide a corresponding portion of the seed light and includes a corresponding gain medium for amplifying the corresponding portion of the seed light into the corresponding portion of the amplified light. The input and output facets are parallel surfaces pointing in opposite directions, such that the direction of travel of seed light entering the input facet is the same as the direction of travel of amplified light leaving the output facet. The fiber medium has a plurality of bends, including one or more left-hand bends and one or more right-hand bends, wherein the number of the one or more left-hand bends is equal to the number of the one or more right-hand bends, such that the combined bending angle of the fiber medium is zero. Furthermore, due to the arrangement of the input and output facets and because the combined bending angle of the fiber medium is zero, the group delay of the multiple cores is substantially matched. Attached Figure Description

[0008] Figure 1 A coherent beam combination (CBC) component according to one or more implementations is shown.

[0009] Figure 2A A cross-section of the MCF is shown.

[0010] Figure 2B The bending of the MCF in the horizontal plane is shown.

[0011] Figure 3 A cross-section of the MCF is shown.

[0012] Figure 4Aand Figure 4B Various example layouts of the MCF based on one or more implementations are shown.

[0013] Figure 5 An optical fiber assembly according to one or more implementations is shown. Detailed Implementation

[0014] The following example implementation is described in detail with reference to the accompanying drawings. The same reference numerals in different drawings can identify the same or similar elements.

[0015] Fiber-based amplifiers for ultrafast lasers are typically limited by achievable peak output power due to nonlinear effects. The inherent nonlinearity of active core materials with high peak intensities leads to self-phase modulation, resulting in degradation of pulse time and spectral characteristics. One approach to extending ultrafast fiber amplifiers beyond these limitations is the use of coherent beam combining (CBC). By spatially multiplexing light within an individual core (or fiber) and coherently recombining it, the peak intensity limitation within a single core can be overcome.

[0016] "Group delay" refers to the time required for a specific group of wavelengths (or optical pulses) to travel through an optical fiber. In other words, group delay is the time delay experienced by light as it travels through the fiber. Different cores of an MCF can have different group delays, resulting in group delay differences between cores. These differences can be caused by differences in the optical path length between different channels or cores to be combined (e.g., due to variations in fiber length and / or refractive index). Since each core can guide different sub-bundles, group delay differences between cores can cause time discrepancies in the arrival times of different sub-bundles at the MCF end. However, in CBC applications, group delay differences are undesirable when sub-bundles are recombined after traveling through the MCF and can hinder proper recombining of sub-bundles to achieve peak intensity. For example, to efficiently coherently combine ultrafast pulses (e.g., ultrashort pulses on the femtosecond to picosecond scale), the group delay (time difference of arrival) between individual beams or sub-bundles should be at least an order of magnitude shorter than the pulse length of the individual beam. This level of group delay is necessary for phase control of individual beams with subwavelength accuracy, enabling efficient coherent recombining.

[0017] However, bending of the MCF can cause group delay differences within adjacent cores. If the core and the bend are aligned in the same plane, the path length difference Δs between the two sub-bundles of adjacent cores is Δs = α × ΔX, where α is the bending angle of the fiber in radians and ΔX is the core spacing. For example, for a typical U-shaped fiber layout (α = π), assuming ΔX = 100 micrometers (μm), the path length difference is Δs = π × ΔX = 314 μm. This path length difference Δs corresponds to a time delay of approximately 1 picosecond (ps), which is too large to coherently recombine ultrafast (sub-picosecond) pulses.

[0018] In principle, this time delay mismatch or group delay mismatch will not occur if the bend is orthogonal to the fiber / core plane. However, this phenomenon only applies to linear (e.g., one-dimensional) core arrays. For example, in the case of a horizontal bend, cores arranged along a vertical line will not experience relative group delay mismatch. However, for any two-dimensional core array (hexagonal grid, rectangular grid, etc.), which includes the spatial arrangement of cores along two axes (e.g., horizontal and vertical planes), the bend will cause group delay mismatch between two or more cores. Therefore, for any two-dimensional core array, it is necessary to control the group delay derived from the fiber layout geometry in order to coherently recombine ultrafast pulses.

[0019] Compared to multiple independent single-core fibers (SCFs), a single fiber with multiple cores (e.g., MCF) offers several advantages in coherent beam combining. Because the amplifier channels of an MCF lack independent mechanical degrees of freedom, it is less sensitive to vibration compared to using multiple independent SCFs. By mechanically fixing the core spacing within the MCF, optical coupling in a multi-core fiber can be facilitated using a shared set of mirrors, lenses, and diffractive optics. Furthermore, the multiple cores of an MCF share a coupling thermal environment, which can reduce potential thermal variations caused by path length differences.

[0020] In experimental demonstrations of CBC, phase control can be dynamically controlled via a feedback loop, during which the group delay is typically considered static. Group delay compensation can be performed in various ways in these demonstrations, often including conventional delay stages. To efficiently recombine laser pulses in a CBC system, a coarse-tuning method (e.g., a coarse-tuning knob) can be used to adjust the group delay to ensure temporal overlap of the pulses, and a fine-tuning method (e.g., a fine-tuning knob) can be used to adjust the phase delay to ensure constructive interference of the pulses. However, both coarse-tuning and fine-tuning methods require additional components to actively match the group delay, increasing the complexity and cost of the CBC system.

[0021] Some implementations described herein aim to passively match the group delay of various amplifier channels (e.g., in different fiber cores) in an MCF. The MCF can have a two-dimensional core array. The MCF may include an optical fiber medium and multiple cores arranged within the optical fiber medium, the optical fiber medium including an input facet configured to receive seed light and an output facet configured to output amplified light. Each core can be configured to guide a corresponding sub-bundle of seed light and may include a corresponding gain medium for amplifying the corresponding sub-bundle into a corresponding sub-bundle of amplified light. The input and output facets can be arranged as parallel surfaces pointing in opposite directions. As a result, the direction of travel of seed light entering the input facet is the same as the direction of travel of amplified light leaving the output facet. Furthermore, the optical fiber medium may have multiple bends, including one or more left-hand bends (e.g., counterclockwise bends) and one or more right-hand bends (e.g., clockwise bends). The number of left-hand bends can be equal to the number of right-hand bends, such that the combined bend angle of the optical fiber medium is zero. In other words, the sum of the bend angles of the multiple bends is zero, where the left-hand and right-hand bend angles have opposite signs.

[0022] Due to the arrangement of the input and output facets (e.g., input-output facet arrangement) and the fact that the combined bending angle of the fiber medium is zero, the group delay of multiple cores can be substantially matched. The group delay can be at least an order of magnitude shorter than the pulse duration of the seed light. In other words, any group delay mismatch between multiple cores can be at least an order of magnitude shorter than the pulse duration of the seed light. The seed light is a pulsed light comprising multiple ultrafast laser pulses having pulse durations on the femtosecond to picosecond scale. In some implementations, each of the multiple pulses has a pulse duration of less than 10 picoseconds. For example, the pulse duration of ultrafast laser pulses can be in the range of 10 femtoseconds to 10 picoseconds. Here, "pulse duration" refers to the compressed (Fourier-limited) pulse duration, corresponding to chirped pulse amplification. While the actual pulse duration in the amplifier medium can be on the nanosecond scale, the Fourier-limited compressed (or unstretched) pulse duration is relevant for the group delay in a CBC system. By passively matching the group delay between multiple cores, correct group delay can be achieved without any additional adjustment knobs or components.

[0023] Figure 1A CBC component 100 according to one or more implementations is shown. The CBC component 100 includes a frequency divider 102 (e.g., a beam splitter) for splitting seed light into corresponding sub-bundles of seed light 104, a phase modulator 106 (e.g., a phase shifter), an MCF 108 having an amplifier core 110, and a combiner 114 that amplifies the corresponding sub-bundles of seed light 104 into corresponding sub-bundles of amplified light 112, and that combines the corresponding sub-bundles of amplified light 112 into combined amplified light 116. Furthermore, the CBC component 100 may also include a phase detector 118 and a control system 120 that detects the phase of the corresponding sub-bundles of amplified light 112, and that controls the phase modulator 106 such that the phase of the corresponding sub-bundles of amplified light 112 is aligned (e.g., in-phase) based on phase misalignment detected by the phase detector 118.

[0024] MCF 108 may be a CBC fiber configured for CBC assembly 100. MCF 108 may have an fiber medium 122 including an input facet 124 configured to receive (frequency-divided) seed light and an output facet 126 configured to output amplified light (e.g., a sub-bundle of amplified light 112). Fiber medium 122 may be doped or may include doped portions for guiding pump light. In some implementations, stress bars may be arranged in fiber medium 122. Stress bars may be doped with dopants such as boron. Amplifier cores 110 may be arranged in fiber medium 122. Each amplifier core 110 may guide a corresponding sub-bundle of seed light 104 and includes a corresponding gain medium (e.g., ytterbium) for amplifying the corresponding sub-bundle of seed light 104 into a corresponding sub-bundle of amplified light 112.

[0025] The input facet 124 and the output facet 126 can be arranged as parallel surfaces pointing in opposite directions, such that the direction of travel of the seed light 104 entering the input facet 124 is the same as the direction of travel of the amplified light 112 leaving the output facet 126.

[0026] MCF 108 can have multiple bends, including one or more left-hand bends and one or more right-hand bends. Figure 1 (Not shown in the image). The number of one or more left-handed bends can be equal to the number of one or more right-handed bends, such that the combined bending angle of the fiber medium is zero. In other words, the sum of the bending angles of multiple bends can be zero, where the left-handed and right-handed bending angles have opposite signs. Therefore, the bending angles can be the same or different, as long as the sum of the bending angles is equal to zero. In some implementations, the fiber medium 122 is not twisted around the longitudinal fiber axis of the MCF 108. In some types of optical fibers, twisting of the fiber medium 122 can lead to group delay mismatch caused by path length differences due to twisting.

[0027] MCF 108 can have a symmetrical fiber layout, such that the group delay mismatch between amplifier cores 110 is essentially zero. In other words, due to the input-output facet arrangement of MCF 108 and the fact that the combined bending angle of MCF 108 is zero, the group delays of amplifier cores 110 can be substantially matched. The group delay can be at least an order of magnitude shorter than the pulse duration of the seed light (e.g., a compressed (Fourier-limited) pulse duration). In other words, any group delay mismatch between amplifier cores 110 can be at least an order of magnitude shorter than the pulse duration of the seed light. For example, due to the input-output facet arrangement of MCF 108 and the fact that the combined bending angle of MCF 108 is zero, the path lengths of amplifier cores 110 can be substantially equal, such that the group delay is at least an order of magnitude shorter than the pulse duration of the seed light.

[0028] The seed light can be a pulsed light comprising multiple ultrafast laser pulses 128 having pulse durations on the femtosecond to picosecond scale. In some implementations, each pulse 128 has a pulse duration of less than 10 picoseconds. For example, the pulse duration of an ultrafast laser pulse can be in the range of 10 femtoseconds to 10 picoseconds. Here, "pulse duration" refers to a compressed (Fourier-limited) pulse duration, corresponding to chirped pulse amplification. Therefore, each corresponding sub-bundle of the seed light 104 can include a corresponding pulse 128 that temporally overlaps with other corresponding pulses 128 of other corresponding sub-bundles of the seed light 104. Since the group delays of the amplifier cores 110 are substantially matched, each corresponding sub-bundle of the amplified light 112 can include a corresponding pulse 130 that temporally overlaps with other corresponding pulses 130 of other corresponding sub-bundles of the amplified light 112. As a result, a symmetrical fiber layout can passively match the group delays between the amplifier cores 110. By passively matching the group delays between multiple cores, correct group delays can be achieved without the need for any additional adjustment knobs or components.

[0029] As mentioned above, Figure 1 Provided as an example. Other examples may be provided with reference to [the relevant information]. Figure 1 The difference is as described. In practice, with Figure 1 Compared to the above, CBC component 100 may include more components, fewer components, different components, or components arranged differently, without departing from the above disclosure.

[0030] Figure 2A The cross-section of MCF 200 is shown. MCF 200 can correspond to a joint. Figure 1The MCF 108 and MCF 200 described herein may be a three-core fiber having three cores 201 and six surrounding stress bars 202 for polarization maintenance characteristics. The three cores 201 and the six surrounding stress bars 202 may be arranged within an fiber medium 203, such as glass. The fiber medium 203 may be surrounded by a cladding 204. The stress bars 202 may be arranged in a grid pattern. Furthermore, each core 201 may be arranged between a corresponding pair of stress bars 202. Thus, the stress bars 202 may generate birefringence for polarization maintenance of each corresponding sub-bundle of seed light in the cores 201.

[0031] As mentioned above, Figure 2A Provided as an example. Other examples may be provided with reference to [the relevant information]. Figure 2A The differences are as described. For example, different numbers of cores and / or stress bars can be used. Furthermore, the arrangement pattern of the cores and stress bars can be different from... Figure 2A The grid patterns shown are different.

[0032] Figure 2B The bending of MCF 200 in the horizontal plane is shown. A U-shaped 180-degree bend (e.g., α = π) will cause a group delay mismatch. Here, core 201 is aligned in the horizontal plane. Therefore, Figure 2B An example of an asymmetric fiber layout is shown, in which there is a group delay mismatch exceeding the acceptable margin for a CBC system.

[0033] For example, the path length difference Δs between two sub-bundles of adjacent cores is Δs = α × ΔX, where α is the bending angle of the fiber in radians, and ΔX is the core spacing. For instance, for a typical U-shaped fiber layout (α = π), assuming ΔX = 100 micrometers (μm), the path length difference is Δs = π × ΔX = 314 μm. This path length difference Δs corresponds to a time delay of approximately 1 picosecond (ps), which is too large to coherently recombine ultrafast (sub-picosecond) pulses.

[0034] The symmetrical curvature of the MCF 200 in a single plane mitigates group delay mismatch. The combined curvature angle of the MCF 200 should be zero. In other words, the curvature of the MCF 200 to the left and right should be balanced. The combined curvature angle can be the sum of all curvature angles, with left and right curvatures having opposite signs. This means that the input and output facets of the MCF 200 should be parallel and point in opposite directions, such that the direction of light entering the MCF 200 is the same as the direction of light leaving the MCF 200, and there are no unequal numbers of left-handed (or curved) and right-handed loops in the MCF 200. In contrast, a fully circular layout can result in the input and output facets of the MCF 200 pointing in opposite directions, but produces an unsatisfactory group delay mismatch of 2π×ΔX.

[0035] This geometric group delay matching method is applicable to any one-dimensional or two-dimensional array (hexagonal, rectangular grid, etc.) of multiple cores in a single fiber, regardless of the fiber cross-section orientation, provided that the cores maintain the same relative orientation to the mounting plane along the entire length of the fiber. Therefore, fiber twisting should be avoided to ensure that all cores 201 have the same path length. For a three-core (linear) arrangement corresponding to MCF 200, the stress induced by the stress bar can provide a preferred bending orientation and can automatically prevent MCF 200 twisting during assembly and installation. However, for other multi-core fiber layouts, fiber twisting should be prevented during the installation process. Other multi-core fiber layouts include stress-free non-polarization-maintaining multi-core fibers and polarization-maintaining fibers that may not have a preferred bending orientation.

[0036] In some implementations, the twist of the MCF 200 (or another type of MCF) can be monitored and controlled during assembly. When the MCF is in a stress-free (unbent) state, the default (e.g., untwisted) orientation of the fiber input (e.g., input facet) and fiber output (e.g., output facet) can be marked on the splice end caps of the MCF. During assembly, the orientation of the fiber input and fiber output can be monitored and maintained to prevent twisted orientation between the fiber input and fiber output. Before the final installation of the end caps and curing of the adhesive (which permanently bonds the fiber to the grooves of the cold plate), the fiber orientation can be fine-tuned by axially inspecting the two end cap facets to eliminate any residual twist. Therefore, the fiber core can maintain the same relative orientation to the mounting plane along the entire length of the fiber, ensuring a matching path length of the core.

[0037] As mentioned above, Figure 2B Provided as an example. Other examples may be provided with reference to [the relevant information]. Figure 2B The differences mentioned above.

[0038] Figure 3 The cross-section of MCF 300 is shown. MCF 300 can correspond to a joint. Figure 1 The MCF 108 and MCF 300 are described above. The MCF 300 can be a ten-core optical fiber with ten cores 301 and a central stress bar 302. The ten cores 301 and the central stress bar 302 can be arranged in an optical fiber medium 303, such as glass. The optical fiber medium 303 can be surrounded by a cladding 304. The central stress bar 302 can be arranged coaxially with the optical fiber axis of the MCF 300. Furthermore, the ten cores 301 can be arranged on a circle concentric with the central stress bar 302. Therefore, the cores 301 can surround the central stress bar 302. Additionally, the cores 301 can be equidistant from each other on the circle.

[0039] The central stress bar 302 can generate circularly symmetric stress (and thus birefringence) within the MCF 300, and can maintain the polarization of the core 301. Therefore, the central stress bar 302 can generate birefringence to achieve polarization maintenance for each corresponding sub-beam of the seed light in the core 301. Due to the circularly symmetric stress generated by the central stress bar 302, there is no preferred bending orientation.

[0040] The symmetrical bending of the MCF 300 in a single plane can mitigate group delay mismatch. The overall bending angle of the MCF 300 should be zero. In other words, the bending of the MCF 300 to the left and right should be balanced. The overall bending angle can be the sum of all bending angles, with left-hand and right-hand bends having opposite signs. This means that the input and output facets of the MCF 300 should be parallel and point in opposite directions, such that the direction of light entering the MCF 300 is the same as the direction of light leaving the MCF 300, and that there are no unequal numbers of left-hand loops (or bends) and right-hand loops in the MCF 300.

[0041] This geometric group delay matching method is applicable to any one-dimensional or two-dimensional array (hexagonal, rectangular grid, etc.) of multiple cores in a single fiber, regardless of the fiber cross-section orientation, provided that the cores maintain the same relative orientation to the mounting plane along the entire length of the fiber. Therefore, fiber twisting should be avoided to ensure that all cores 301 have the same path length. For a three-core (linear) arrangement corresponding to MCF 300, the stress induced by the stress bar can provide a preferred bending orientation and can automatically prevent MCF 300 twisting during assembly and installation. However, for other multi-core fiber layouts, fiber twisting should be prevented during the installation process. Other multi-core fiber layouts include stress-free non-polarization-maintaining multi-core fibers and polarization-maintaining fibers that may not have a preferred bending orientation.

[0042] In some implementations, the twisting of the MCF 300 (or another type of MCF) can be monitored and controlled during assembly. When the MCF is in a stress-free (unbent) state, the default (e.g., untwisted) orientation of the fiber input (e.g., input facet) and fiber output (e.g., output facet) can be marked on the splice end caps of the MCF. During assembly, the orientation of the fiber input and fiber output can be monitored and maintained to prevent twisting orientation between the fiber input and fiber output. Before the final installation of the end caps and curing of the adhesive (which permanently bonds the fiber to the grooves of the cold plate), the fiber orientation can be fine-tuned by axially inspecting the two end cap facets to eliminate any residual twisting. Therefore, the fiber core can maintain the same relative orientation to the mounting plane along the entire length of the fiber, ensuring a matching path length of the core.

[0043] As mentioned above, Figure 3Provided as an example. Other examples may be provided with reference to [the relevant information]. Figure 3 The differences are as described. For example, different numbers of cores can be used.

[0044] Figure 4A and Figure 4B Various example arrangements 401-406 according to one or more implementations of MCF 410a-410f are shown. Example arrangements 401-406 may relate to arrangements of MCF 200 and MCF 300. Example arrangements 401-406 can satisfy the aforementioned requirement of symmetrical bending, which mitigates group delay mismatch between the fiber cores of the MCF. For example, example arrangements 401-406 may include a balanced number of left and right bends, with a combined bend angle of zero for each MCF 410a-410f. Furthermore, the input facet 411 and output facet 412 of each MCF 410a-410f are arranged parallel to each other and pointing in opposite orientations, such that the direction of light entering the MCF is the same as the direction of light leaving the MCF. The cores of each MCF 410a-410f can maintain the same relative orientation to the mounting plane along the entire length of the fiber. Fiber length, minimum bending radius, and required footprint can ultimately determine which arrangement is advantageous. Therefore, example arrangements 401-406 can provide passive, geometry-controlled group delay, thereby mitigating group delay mismatch between cores.

[0045] As mentioned above, Figure 4A and Figure 4B Provided as an example only. Other examples may be found with reference to [the relevant source]. Figure 4A and Figure 4B The differences mentioned above.

[0046] Figure 5 An optical fiber assembly 500 according to one or more implementations is shown. The optical fiber assembly 500 can be used in a CBC assembly, such as in combination with... Figure 1 The CBC assembly 100 is described above. The fiber optic assembly 500 may include an MCF 502 and a cold plate 504, the cold plate including a groove 506. The MCF 502 can be mounted to the cold plate 504 within the groove 506. For example, the MCF 502 can be bonded to the cold plate 504 within the groove 506. Therefore, the bending shape of the MCF 502 can conform to the shape of the groove 506. The MCF 502 can be similar to... Figure 4B The example arrangement shown is 405. Furthermore, the MCF 502 may have an input facet 508 and an output facet 510, these facets having surfaces parallel to each other and pointing in opposite directions. The combined bending angle of the groove 506 and the MCF 502 can be zero to mitigate or eliminate assembly delay mismatch of the core of the MCF 502. To ensure optimal alignment, a spring clip (not shown) can hold the end cap of the MCF 502 in place on the cold plate 504.

[0047] As mentioned above, Figure 5 Provided as an example. Other examples may be provided with reference to [the relevant information]. Figure 5 The differences mentioned above.

[0048] The following provides an overview of some aspects of this disclosure:

[0049] Aspect 1: A multi-core optical fiber, comprising:

[0050] An optical fiber medium, including an input facet and an output facet, wherein the input facet is configured to receive seed light and the output facet is configured to output amplified light; and

[0051] A plurality of cores are arranged in the optical fiber medium, wherein each of the plurality of cores is configured to guide a corresponding sub-bundle of the seed light, and includes a corresponding gain medium for amplifying the corresponding sub-bundle of the seed light into a corresponding sub-bundle of the amplified light.

[0052] The input and output facets are parallel surfaces pointing in opposite directions, such that the seed light entering the input facet travels in the same direction as the amplified light leaving the output facet.

[0053] The optical fiber medium has multiple bends, including one or more left-hand bends and one or more right-hand bends.

[0054] The number of the one or more left-handed bends is equal to the number of the one or more right-handed bends, such that the combined bending angle of the optical fiber medium is zero, and

[0055] Due to the arrangement of the input and output facets and the fact that the combined bending angle of the optical fiber medium is zero, the group delay of the multiple cores is essentially matched.

[0056] Aspect 2: According to aspect 1, however, the seed light is a pulsed light, which comprises multiple ultrafast laser pulses having pulse durations on the femtosecond to picosecond scale.

[0057] Aspect 3: The multi-core optical fiber according to aspect 2, wherein the group delay is at least an order of magnitude shorter than the pulse duration of the pulse.

[0058] Aspect 4: A multi-core optical fiber according to any one of Aspects 1 to 3, wherein each corresponding sub-bundle of the seed light comprises a corresponding pulse, the corresponding pulse being temporally overlapped with other corresponding pulses of other corresponding sub-bundles of the seed light.

[0059] Aspect 5: A multi-core optical fiber according to any one of Aspects 1 to 4, wherein each corresponding sub-bundle of the amplified light comprises a corresponding pulse, the corresponding pulse being temporally overlapped with other corresponding pulses of other corresponding sub-bundles of the amplified light.

[0060] Aspect 6: A multi-core optical fiber according to any one of Aspects 1 to 5, wherein the optical fiber medium is glass.

[0061] Aspect 7: A multi-core optical fiber according to any one of Aspects 1 to 6, wherein the path lengths of the plurality of cores are substantially equal, such that the group delay is at least an order of magnitude shorter than the pulse duration of the seed light.

[0062] Aspect 8: A multi-core optical fiber according to any one of Aspects 1 to 7, wherein the path lengths of the plurality of cores are equal.

[0063] Aspect 9: The multi-core optical fiber according to any one of Aspects 1 to 8 further includes:

[0064] At least one stress bar is arranged in the optical fiber medium, wherein the at least one stress bar generates birefringence for polarization maintenance of each corresponding sub-bundle of the seed light.

[0065] Aspect 10: The multi-core optical fiber according to Aspect 9, wherein the at least one stress bar includes a central stress bar, the central stress bar being arranged coaxially with the fiber axis of the multi-core optical fiber, and

[0066] The plurality of cores are arranged on a circle concentric with the central stress bar.

[0067] Aspect 11: The multi-core optical fiber according to Aspect 9, wherein the at least one stress bar comprises a plurality of stress bars arranged in a grid pattern, and

[0068] Each of the plurality of cores is arranged between a corresponding pair of stress bars.

[0069] Aspect 12: A multi-core optical fiber according to any one of Aspects 1 to 11, wherein the optical fiber medium is not twisted around the longitudinal optical fiber axis of the multi-core optical fiber.

[0070] Aspect 13: A coherent beam combining fiber, comprising:

[0071] An optical fiber medium, including an input facet and an output facet, wherein the input facet is configured to receive seed light and the output facet is configured to output amplified light; and

[0072] A plurality of cores are arranged in the optical fiber medium, wherein each of the plurality of cores is configured to guide a corresponding portion of the seed light and includes a corresponding gain medium for amplifying the corresponding portion of the seed light into a corresponding portion of the amplified light.

[0073] The input and output facets are parallel surfaces facing opposite directions, such that the direction of travel of the seed light entering the input facet is parallel to the direction of travel of the amplified light leaving the output facet.

[0074] The optical fiber medium has multiple bends, including one or more left-hand bends and one or more right-hand bends.

[0075] The number of the one or more left-handed bends is equal to the number of the one or more right-handed bends.

[0076] The sum of the bending angles of the plurality of bends is zero, wherein the left-hand and right-hand bending angles have opposite signs, and

[0077] Due to the arrangement of the input and output facets and the fact that the sum of the bending angles is zero, the group delay of the plurality of cores is substantially matched.

[0078] Aspect 14: A coherent beam combining assembly, comprising:

[0079] Cold plate, including grooves; and

[0080] A multi-core optical fiber is installed on the cold plate and located within the groove.

[0081] The multi-core optical fiber includes:

[0082] An optical fiber medium, including an input facet and an output facet, wherein the input facet is configured to receive seed light and the output facet is configured to output amplified light; and

[0083] A plurality of cores are arranged in the optical fiber medium, wherein each of the plurality of cores is configured to guide a corresponding portion of the seed light and includes a corresponding gain medium for amplifying the corresponding portion of the seed light into a corresponding portion of the amplified light.

[0084] The input and output facets are parallel surfaces pointing in opposite directions, such that the seed light entering the input facet travels in the same direction as the amplified light leaving the output facet.

[0085] The optical fiber medium has multiple bends, including one or more left-hand bends and one or more right-hand bends.

[0086] The number of the one or more left-handed bends is equal to the number of the one or more right-handed bends, such that the combined bending angle of the optical fiber medium is zero, and

[0087] Due to the arrangement of the input and output facets and the fact that the combined bending angle of the optical fiber medium is zero, the group delay of the multiple cores is essentially matched.

[0088] Aspect 15: The coherent beam combining assembly according to aspect 14, wherein the seed light is a pulsed light comprising a plurality of ultrafast laser pulses having pulse durations on the femtosecond to picosecond scale.

[0089] Aspect 16: The coherent beam combining assembly according to aspect 15, wherein the group delay is at least an order of magnitude shorter than the pulse duration of the pulse.

[0090] Aspect 17: According to the coherent beam combining assembly of aspect 15, each corresponding sub-beam of the seed light includes a corresponding pulse, the corresponding pulse being temporally overlapped with other corresponding pulses of other corresponding sub-beams of the seed light.

[0091] Aspect 18: According to the coherent beam combining assembly of aspect 17, each corresponding sub-beam of the amplified light at the output facet includes a corresponding pulse, the corresponding pulse being temporally overlapped with other corresponding pulses of other corresponding sub-beams of the amplified light.

[0092] Aspect 19: The coherent beam combining assembly according to aspect 18, wherein the path lengths of the plurality of cores are substantially equal, such that the group delay is at least an order of magnitude shorter than the pulse duration of the seed light.

[0093] Aspect 20: The coherent beam combining assembly according to any one of aspects 14 to 19 further includes:

[0094] At least one stress bar is disposed in the optical fiber medium, wherein the at least one stress bar is configured to induce stress to provide a preferred bending orientation to the optical fiber medium and automatically prevent the optical fiber medium from twisting.

[0095] Aspect 21: A system configured to perform one or more operations according to one or more of aspects 1 to 20.

[0096] Aspect 22: An apparatus comprising components for performing one or more operations according to one or more of aspects 1 to 20.

[0097] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit implementations to the precise forms disclosed. Modifications and variations can be made based on the foregoing disclosure, or derived from the practice of implementation. Furthermore, any implementation described herein can be composed unless the foregoing disclosure expressly provides a reason why one or more implementations cannot be composed.

[0098] Although specific combinations of features are referenced in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features can be combined in ways not specifically referenced in the claims and / or not disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes combinations of each dependent claim with every other claim in the claim set. As used herein, the phrase “at least one” in the list of referenced items refers to any combination of these 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 combinations of multiple items among these.

[0099] Unless explicitly stated otherwise, no element, action, or instruction used herein should be construed as critical or necessary. Furthermore, as used herein, the articles “a” and “one” are intended to include one or more items and may be used interchangeably with “one or more.” Furthermore, as used herein, the article “described” is intended to include one or more items referenced in conjunction with the article “described” and may be used interchangeably with “one or more.” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and may be used interchangeably with “one or more.” If only one item is intended to be used, the phrase “only one” or similar language is used. Furthermore, as used herein, the terms “having,” “having,” “containing,” etc., are intended to be open-ended terms. Furthermore, unless explicitly stated otherwise, the word “based on” is intended to mean “at least partially based on.” Furthermore, as used herein, the term “or” is inclusive when used in series and may be used interchangeably with “and / or” unless explicitly stated otherwise (e.g., if used in conjunction with “any one of…” or “only one of…”). Furthermore, for ease of description, spatial relative terms (such as “below,” “lower,” “above,” “upper,” etc.) may be used herein to describe the relationship of an element or feature to other elements or features shown in the figures. In addition to the orientations shown in the figures, spatial relative terms are intended to cover different orientations of devices, equipment, and / or elements in use or operation. The device may be oriented in other ways (rotated 90 degrees or otherwise), and the spatial relative descriptors used herein may be interpreted accordingly.

Claims

1. A multi-core optical fiber, comprising: An optical fiber medium includes an input facet and an output facet, wherein the input facet is configured to receive seed light and the output facet is configured to output amplified light; as well as A plurality of cores are arranged in the optical fiber medium, wherein each of the plurality of cores is configured to guide a corresponding sub-bundle of the seed light, and includes a corresponding gain medium for amplifying the corresponding sub-bundle of the seed light into a corresponding sub-bundle of the amplified light. The input and output facets are parallel surfaces pointing in opposite directions, such that the seed light entering the input facet travels in the same direction as the amplified light leaving the output facet. The optical fiber medium has multiple bends, including one or more left-hand bends and one or more right-hand bends. The number of the one or more left-handed bends is equal to the number of the one or more right-handed bends, such that the combined bending angle of the optical fiber medium is zero, and Due to the arrangement of the input and output facets and the fact that the combined bending angle of the optical fiber medium is zero, the group delay of the multiple cores is essentially matched.

2. The multi-core optical fiber according to claim 1, wherein the seed light is a pulsed light, the pulsed light comprising a plurality of ultrafast laser pulses having pulse durations on the femtosecond to picosecond scale.

3. The multi-core optical fiber according to claim 2, wherein the group delay is at least an order of magnitude shorter than the pulse duration of the pulse.

4. The multi-core optical fiber according to claim 1, wherein each corresponding sub-bundle of the seed light comprises a corresponding pulse, the corresponding pulse overlapping in time with other corresponding pulses of other corresponding sub-bundles of the seed light.

5. The multi-core optical fiber according to claim 1, wherein each corresponding sub-bundle of the amplified light comprises a corresponding pulse, the corresponding pulse overlapping in time with other corresponding pulses of other corresponding sub-bundles of the amplified light.

6. The multi-core optical fiber according to claim 1, wherein the optical fiber medium is glass.

7. The multi-core optical fiber according to claim 1, wherein the path lengths of the plurality of cores are substantially equal, such that the group delay is at least an order of magnitude shorter than the pulse duration of the seed light.

8. The multi-core optical fiber according to claim 1, wherein the path lengths of the plurality of cores are equal.

9. The multi-core optical fiber according to claim 1, further comprising: At least one stress bar is arranged in the optical fiber medium, wherein the at least one stress bar generates birefringence for polarization maintenance of each corresponding sub-bundle of the seed light.

10. The multi-core optical fiber according to claim 9, wherein the at least one stress bar includes a central stress bar, the central stress bar being arranged coaxially with the fiber axis of the multi-core optical fiber, and The plurality of cores are arranged on a circle concentric with the central stress bar.

11. The multi-core optical fiber according to claim 9, wherein the at least one stress bar comprises a plurality of stress bars arranged in a grid pattern, and Each of the plurality of cores is arranged between a corresponding pair of stress bars.

12. The multi-core optical fiber according to claim 1, wherein the optical fiber medium is not twisted around the longitudinal optical fiber axis of the multi-core optical fiber.

13. A coherent beam combining fiber, comprising: An optical fiber medium includes an input facet and an output facet, wherein the input facet is configured to receive seed light and the output facet is configured to output amplified light; as well as A plurality of cores are arranged in the optical fiber medium, wherein each of the plurality of cores is configured to guide a corresponding portion of the seed light and includes a corresponding gain medium for amplifying the corresponding portion of the seed light into a corresponding portion of the amplified light. The input and output facets are parallel surfaces facing opposite directions, such that the direction of travel of the seed light entering the input facet is parallel to the direction of travel of the amplified light leaving the output facet. The optical fiber medium has multiple bends, including one or more left-hand bends and one or more right-hand bends. The number of the one or more left-handed bends is equal to the number of the one or more right-handed bends. The sum of the bending angles of the plurality of bends is zero, wherein the left-hand and right-hand bending angles have opposite signs, and Due to the arrangement of the input and output facets and the fact that the sum of the bending angles is zero, the group delay of the multiple cores is essentially matched.

14. A coherent beam combining assembly, comprising: Cold plate, including grooves; as well as A multi-core optical fiber is installed on the cold plate and located within the groove. The multi-core optical fiber includes: An optical fiber medium includes an input facet and an output facet, wherein the input facet is configured to receive seed light and the output facet is configured to output amplified light; as well as A plurality of cores are arranged in the optical fiber medium, wherein each of the plurality of cores is configured to guide a corresponding portion of the seed light and includes a corresponding gain medium for amplifying the corresponding portion of the seed light into a corresponding portion of the amplified light. The input and output facets are parallel surfaces pointing in opposite directions, such that the seed light entering the input facet travels in the same direction as the amplified light leaving the output facet. The optical fiber medium has multiple bends, including one or more left-hand bends and one or more right-hand bends. The number of the one or more left-handed bends is equal to the number of the one or more right-handed bends, such that the combined bending angle of the optical fiber medium is zero, and Due to the arrangement of the input and output facets and the fact that the combined bending angle of the optical fiber medium is zero, the group delay of the multiple cores is essentially matched.

15. The coherent beam combining assembly of claim 14, wherein the seed light is a pulsed light comprising a plurality of ultrafast laser pulses having pulse durations on the femtosecond to picosecond scale.

16. The coherent beam combining assembly of claim 15, wherein the group delay is at least an order of magnitude shorter than the pulse duration of the pulse.

17. The coherent beam combining assembly of claim 15, wherein each corresponding sub-beam of the seed light comprises a corresponding pulse, the corresponding pulse being temporally overlapped with other corresponding pulses of other corresponding sub-beams of the seed light.

18. The coherent beam combining assembly of claim 17, wherein each corresponding sub-beam of the amplified light at the output facet includes a corresponding pulse, the corresponding pulse being temporally overlapped with other corresponding pulses of other corresponding sub-beams of the amplified light.

19. The coherent beam combining assembly of claim 18, wherein the path lengths of the plurality of cores are substantially equal, such that the group delay is at least an order of magnitude shorter than the pulse duration of the seed light.

20. The coherent beam combining assembly of claim 14, further comprising: At least one stress bar is disposed in the optical fiber medium, wherein the at least one stress bar is configured to induce stress to provide a preferred bending orientation to the optical fiber medium and automatically prevent the optical fiber medium from twisting.

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