Polarization-maintaining multi-core optical fiber including stress application portion to substantially achieve birefringence in surrounding core

Abstract

The invention relates to a polarization-maintaining multi-core optical fiber comprising a stress applying portion to substantially achieve birefringence in the surrounding core. In some embodiments, an optical system includes a multi-core optical fiber, the multi-core optical fiber including: a cladding; a stress applying portion (SAP); and a set of at least three cores equidistant from a center of the SAP at a cross-section of the multi-core optical fiber, wherein the SAP substantially achieves birefringence in the set of at least three cores.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Patent Application No. 63 / 660,779, filed on June 17, 2024, entitled “MULTICORE FIBER WITH CENTRALSTRESS ROD TO MAINTAIN POLARIZATION,” and U.S. Patent Application No. 63 / 553,886, filed on February 15, 2024, entitled “MULTI-CORE FIBER GEOMETRY WITHOUT THERMAL GRADIENTS FOR COHERENT BEAM COMBINING.” The disclosures of these prior applications are considered a part of and incorporated by reference into this patent application. Technical Field

[0003] The present disclosure generally relates to polarization-maintaining (PM) multicore optical fibers and PM multicore optical fibers that include a stress-applying portion (SAP) to substantially achieve birefringence in the surrounding core. Background Art

[0004] PM multicore fiber is designed to maintain the polarization of signals (i.e., light) traveling through the multiple cores of the multicore fiber. Due to the multiple cores, PM multicore fiber can support high signal capacity (e.g., high data transmission capacity), and due to its polarization-maintaining properties, PM multicore fiber can maintain the polarization of signal light. Summary of the Invention

[0005] In some embodiments, an optical system includes a multi-core optical fiber comprising: a cladding; a SAP; and a set of at least three cores equidistant from a center of the SAP at a cross-section of the multi-core optical fiber, wherein the SAP substantially implements birefringence in the set of at least three cores.

[0006] In some embodiments, an optical system includes a multi-core optical fiber comprising: a cladding; a SAP; and a set of at least three cores surrounding the SAP, wherein the SAP substantially implements birefringence in the set of at least three cores, and wherein respective polarization principal axes of the set of at least three cores are radially aligned with a center of the SAP.

[0007] In some embodiments, a multi-core optical fiber includes: a cladding; a SAP; and a plurality of cores equidistant from a center of the SAP, wherein the SAP substantially implements birefringence in the plurality of cores, and wherein the center of the SAP and first and second cores of the plurality of cores are not collinear. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figures 1A to 1F is a diagram illustrating an example embodiment related to a PM multi-core optical fiber including a SAP to substantially achieve birefringence in the surrounding cores. DETAILED DESCRIPTION

[0009] The following describes example embodiments in detail with reference to the accompanying drawings. The same reference numerals in different drawings may identify the same or similar elements.

[0010] In order to maintain polarization of the multiple cores of a multi-core optical fiber (and thereby make the multi-core optical fiber a PM multi-core optical fiber), the multi-core optical fiber may include stress rods, at least two of which are placed near each core, such as in a linear arrangement (e.g., with a first stress rod and a second stress rod placed on opposite sides of the core). The stress rods include a material that has different thermal expansion properties than the material of the core or the cladding of the preformed optical fiber or the multi-core optical fiber (e.g., due to a heated fiber drawing process used to produce a PM multi-core optical fiber), which applies mechanical stress (e.g., compressive stress or tensile stress) to the core. This mechanical stress induces birefringence in the core, which enables the core to maintain the polarization of light within the core. For example, mechanical stress can be applied to the core, causing deformation, thereby changing the refractive index in different directions within the core. This change in refractive index causes birefringence in the core. The birefringence causes light entering the core that is polarized along a first polarization axis of the core or a second polarization axis of the core (e.g., orthogonal to the first polarization axis) to remain within the core. The first polarization main axis may be one of a fast polarization axis and a slow polarization axis, and the second polarization main axis may be the other of the fast polarization axis and the slow polarization axis.

[0011] However, including at least two stress rods for each core of a PM multi-core optical fiber increases the complexity of designing and forming the PM multi-core optical fiber. For example, in some cases, the PM multi-core is formed by drilling holes in a preformed optical fiber, inserting a corresponding core or stress rod into each hole, and performing a fiber drawing process (e.g., drawing the preformed optical fiber into the final PM multi-core optical fiber). Therefore, ensuring precise placement and alignment of the stress rods and cores in the preformed optical fiber is difficult. In addition, due to impurities associated with the stress rods and cores (e.g., impurities in the holes into which the stress rods and cores are inserted, or impurities in the surfaces of the stress rods and cores) and defects associated with the stress rods and cores (e.g., defects caused by scratches, cracks, bubbles, or other defects in the stress rods and cores), at least one stress rod or core may fail, which generally causes the preformed optical fiber (or the final PM multi-core optical fiber) to be unusable and therefore discarded (i.e., wasted). The likelihood of failure only increases with the number of stress rods and cores included in the preformed optical fiber.

[0012] Furthermore, including at least two stress rods for each core of a PM multi-core optical fiber can limit the number of cores that can be included in the PM multi-core optical fiber. This reduces the capacity of the PM multi-core optical fiber, which can render the PM multi-core optical fiber unsuitable for applications requiring higher capacity (e.g., in optical systems). In some cases, the size (e.g., diameter) of the PM multi-core optical fiber can be increased to include additional cores (and additional stress rods) to provide higher capacity, but this can lead to other design challenges within the optical system (e.g., based on accommodating the larger size of the PM multi-core optical fiber).

[0013] Some embodiments described herein include multi-core optical fibers (e.g., multi-core optical fibers of optical systems). The multi-core optical fiber includes a stress-applying portion (SAP) (e.g., a disk or ring shape at the cross-section of the multi-core optical fiber) and a plurality of cores surrounding the SAP (e.g., the center of the SAP and the first and second cores of the plurality of cores are not collinear). For example, the plurality of cores can be equidistant from the center of the SAP (e.g., the plurality of cores can be positioned on the circumference of an imaginary circle around the SAP, wherein the imaginary circle is centered on the center of the SAP). Therefore, the SAP (e.g., due to being surrounded by the plurality of cores) applies (or effectively applies) a mechanical stress to each core in a first direction radially aligned with the center of the SAP, which changes the refractive axis of each core (e.g., along the first direction and along a second direction orthogonal to the first direction), and thereby substantially achieves birefringence in each core. In addition, due to the birefringence, each core has a first polarization principal axis and a second polarization principal axis aligned with the first direction and the second direction, respectively. In this way, the SAP substantially achieves birefringence in the plurality of cores, which results in the corresponding first principal axis or second principal axis of the plurality of cores being radially aligned with the center of the SAP.

[0014] By using only one SAP (e.g., which substantially achieves birefringence in the multiple cores), the multi-core optical fiber is able to maintain the polarization of light within the multiple cores (e.g., when light entering the core is polarized along one of the respective first polarization principal axes or second polarization principal axes of the multiple cores), which makes the multi-core optical fiber a PM multi-core optical fiber. This reduces the complexity of designing and forming the multi-core optical fiber (e.g., compared to a conventional PM multi-core optical fiber that includes multiple stress rods). For example, because the number of SAPs that need to be included in the multi-core optical fiber is significantly smaller (e.g., compared to the typical number of stress rods), the placement and alignment of the SAP and the multiple cores in the preformed optical fiber are less challenging. In addition, the smaller number of components (e.g., due to the use of only one SAP and multiple cores) reduces the likelihood of failure. This increases the likelihood that the multi-core optical fiber will be usable (e.g., after formation) and therefore used for its intended purpose.

[0015] In some embodiments, because the SAP is equidistant from the multiple cores (e.g., because the SAP is a single central SAP), the SAP applies equal (or nearly equal) mechanical stress to each core, and the birefringence generated in the multiple cores is equal (or nearly equal) across the multiple cores (e.g., the birefringence field in each core is the same or nearly the same, such as in a direction radially aligned with the center of the SAP). This is difficult to achieve in a conventional PM multi-core fiber that includes multiple stress rods (e.g., because each rod can apply mechanical stress in a particular direction in more than one core when there is insufficient spacing from the other cores, and thus the birefringence in a particular core can be achieved by any number of rods, depending on the location of the particular core in the PM multi-core fiber). In addition, in some cases, the birefringence in the multiple cores being substantially achieved by the SAP allows at least some of the multiple cores to have polarization principal axes that are not aligned with each other, which can reduce interference between the cores (e.g., reducing crosstalk). As a result, in some cases, the multi-core fiber provides improved signal quality and integrity, which is beneficial in certain applications, such as high-capacity optical communication applications.

[0016] Figures 1A to 1F is a diagram illustrating an example embodiment 100 associated with a PM multi-core optical fiber that includes a SAP to substantially achieve birefringence in the surrounding cores. Figures 1A to 1F As shown, example embodiment 100 includes an optical system 102 (e.g., a fiber laser system, a coherent beam combining (CBC) system, and / or an optical amplifier system, etc.). Optical system 102 includes a multi-core optical fiber 104, which may include a SAP 106, a plurality of cores 108 (e.g., a group of at least two cores, a group of at least three cores, etc.), and a cladding 110. Figures 1A to 1F A cross-sectional view of a multi-core optical fiber 104 is shown associated with each example embodiment 100. The cross-sectional configuration of the multi-core optical fiber 104 extends through the length of the multi-core optical fiber 104, so references herein to Figures 1A to 1F The depicted cross-sectional views may be located at any point along the length of the multi-core optical fiber 104 .

[0017] like Figures 1A to 1FAs shown, the multi-core optical fiber 104 can include a SAP 106 and a plurality of cores 108 within the multi-core optical fiber 104 (e.g., within a cladding 110 of the multi-core optical fiber 104). The SAP 106 can be (e.g., at a cross-section of the multi-core optical fiber 104) disk-shaped (e.g., can have a filled circle), an annular shape (e.g., can have a hollow circle), or can have another type of shape. Notably, the SAP 106 can include a center 112 (e.g., a center point of the SAP 106). In some embodiments, the center 112 of the SAP 106 can be aligned with the center of the multi-core optical fiber 104 (e.g., the center point of the multi-core optical fiber 104 or the center point of the cladding 110), or, alternatively, can not be aligned with the center of the multi-core optical fiber 104. As Figures 1A to 1F As further shown, each of the plurality of cores 108 may be disk-shaped (e.g., at a cross-section of the multi-core optical fiber 104), or may have another type of shape. The SAP 106 and the plurality of cores 108 may be embedded in a cladding 110 (e.g., the cladding 110 may be a gap component in which the SAP 106 and the plurality of cores 108 are disposed, such as described herein with respect to FIG. Figures 1A to 1F described configuration).

[0018] The SAP 106 and the plurality of cores 108 may comprise different materials and, therefore, may have different thermal expansion characteristics from one another and from the cladding 110. For example, the SAP 106 may comprise boron (B)-doped glass (e.g., silica-based glass), the plurality of cores 108 may comprise ytterbium (Yb)-doped glass (e.g., silica-based glass), and the cladding 110 may comprise undoped glass (e.g., silica-based glass). Consequently, due to the different thermal expansion characteristics between the SAP 106 and the plurality of cores 108 and / or between the SAP 106 and the cladding 110, mechanical stress is applied to each core 108 (e.g., as a result of a heated fiber drawing process used to produce the multi-core optical fiber 104). As further described herein, this stress substantially causes birefringence in the cores 108.

[0019] like Figure 1A As shown, in a cross-section of the multi-core optical fiber 104, the plurality of cores 108 may surround the SAP 106 within the cladding 110. For example, the plurality of cores 108 may surround the SAP 106 in the cladding 110 such that the plurality of cores 108 are equidistant from the center 112 of the SAP 106. That is, the plurality of cores 108 may be arranged on the circumference of an imaginary circle C1 having a radius R1, the imaginary circle being centered on the center 112 of the SAP 106 (e.g., each core 108 is located at the same radial distance from the center 112 of the SAP 106).

[0020] In some embodiments, the center-to-center distance between a first core 108 and a second core 108 that are adjacent to each other (e.g., the first core 108 and the second core 108 are adjacent cores 108) among the plurality of cores 108 may be greater than or equal to 2.5 times the maximum of the first diameter of the first core 108 and the second diameter of the second core 108 (e.g., the maximum of the corresponding diameters of the adjacent cores 108). In this manner, the possibility of crosstalk between the first core 108 and the second core 108 (e.g., between adjacent cores 108) is minimized.

[0021] like Figure 1A As further shown, the SAP 106 (e.g., due to being surrounded by the plurality of cores 108) can exert mechanical stress on the plurality of cores 108 and, thus, can substantially cause birefringence in the plurality of cores 108 (e.g., the SAP 106 can cause, can primarily cause, birefringence in the plurality of cores 108). Substantially causing birefringence can include any change in birefringence that causes one or more optical properties of the plurality of cores 108 to be greater than a corresponding negligible threshold, such as greater than a negligible refractive index difference threshold (e.g., which can be 0.01×10 -3 , 0.1×10 -3 or different amounts) (eg, which defines birefringence).

[0022] Achieving substantially birefringence in each core 108 can result in the core 108 having a first polarization principal axis 114-1 (e.g., one of the fast polarization axis or the slow polarization axis) radially aligned with the center 112 of the SAP 106, and having a second polarization principal axis 114-2 (e.g., the other of the fast polarization axis or the slow polarization axis) orthogonal to the first polarization principal axis 114-1. The first polarization principal axis 114-1 and the second polarization principal axis 114-2 can be collectively referred to as the polarization principal axis 116 of the core 108. Thus, in some embodiments, a first core 108 of the plurality of cores 108 can have a first polarization principal axis 116 that is not aligned with a second polarization principal axis 116 of a second core 108 of the plurality of cores 108. For example, when the first core 108, the second core 108 and the center 112 of the SAP 106 are not collinear (for example, not arranged on the same imaginary line), the first core 108 may have a specific first polarization main axis 114-1 among the first polarization main axes 116, which is radially aligned with the center 112 of the SAP 106, and the second core 108 may have another specific first polarization main axis 114-1 among the second polarization main axes 116, which is radially aligned with the center 112 of the SAP 106, and the specific first polarization main axis 114-1 and the other specific first polarization main axis 114-1 may not be aligned (for example, may not be parallel to each other). As another example, when the plurality of cores 108 includes a group of at least three cores 108, a first core 108 in the group of at least three cores 108 may have a first polarization principal axis 116 that is not aligned with a second polarization principal axis 116 of a second core 108 in the group of at least three cores 108 (e.g., because there are first and second cores 108, 108 in the group of at least three cores that are not colinear with the center 112 of the SAP 106 and therefore must have non-aligned polarization principal axes 116). When considering the alignment between the first polarization principal axis 116 and the second polarization principal axis 116, the first polarization principal axis 114-1 in the first polarization principal axis 116 corresponding to the fast axis of the first polarization principal axis 116 can be compared with the first polarization principal axis 114-1 in the second polarization principal axis 116 corresponding to the fast axis of the second polarization principal axis 116, or the first polarization principal axis 114-1 in the first polarization principal axis 116 corresponding to the slow axis of the first polarization principal axis 116 can be compared with the first polarization principal axis 114-1 in the second polarization principal axis 116 corresponding to the slow axis of the second polarization principal axis 116.However, it is inappropriate to compare the first polarization principal axis 114-1 in the first polarization principal axis 116 corresponding to the slow axis of the first polarization principal axis 116 with the second polarization principal axis 114-2 in the second polarization principal axis 116 corresponding to the fast axis of the second polarization principal axis 116, and to compare the second polarization principal axis 114-2 in the first polarization principal axis 116 corresponding to the fast axis of the first polarization principal axis 116 with the first polarization principal axis 114-1 in the second polarization principal axis 116 corresponding to the slow axis of the second polarization principal axis 116.

[0023] Thus, the multi-core optical fiber 104 can be polarization-maintaining (e.g., the multi-core optical fiber 104 can be a PM multi-core optical fiber, and each core 108 in the plurality of cores 108 can be polarization-maintaining). For example, due to birefringence induced in each core 108 (e.g., by the SAP 106), each core 108 can maintain the polarization of light within the core 108 (e.g., in a direction aligned with the polarization principal axis 116 of the core 108). In some embodiments, the birefringence substantially achieved in the plurality of cores 108 can be equal across the plurality of cores 108. For example, because the plurality of cores 108 are equidistant from the center 112 of the SAP 106, the SAP 106 applies equal (or nearly equal) mechanical stress to each core 108, and the birefringence induced in each core 108 (e.g., by the SAP 106) can be the same (or nearly the same within a tolerance range). In other words, the (eg, birefringent) birefringent field in each core 108 may be identical or nearly identical in magnitude and / or distribution, but may be oriented differently (eg, radially aligned with the center 112 of the SAP 106).

[0024] Figure 1B Shown with Figure 1A Another example embodiment 100 is similar to the example embodiment 100 shown, wherein a plurality of cores 108 surround a SAP 106 within a cladding 110 (e.g., such that the plurality of cores 108 are equidistant from a center 112 of the SAP 106), and the SAP 106 is annular. Figure 1AThe disk-shaped SAP 106, the ring-shaped SAP 106 (e.g., due to being surrounded by the plurality of cores 108), can apply mechanical stress to the plurality of cores 108 and thus can substantially achieve birefringence in the plurality of cores 108 (e.g., the SAP 106 can cause or can primarily cause birefringence in the plurality of cores 108). Achieving substantially birefringence in each core 108 can result in the core 108 having a polarization principal axis 116 that includes a first polarization principal axis 114-1 (e.g., one of the fast polarization axis or the slow polarization axis) radially aligned with the center 112 of the SAP 106 and a second polarization principal axis 114-2 (e.g., the other of the fast polarization axis or the slow polarization axis) orthogonal to the first polarization principal axis 114-1. Thus, the multi-core optical fiber 104 can be polarization-maintaining (e.g., the multi-core optical fiber 104 can be a PM multi-core optical fiber, and each of the plurality of cores 108 can be polarization-maintaining), as described above. Furthermore, the birefringence substantially achieved in the plurality of cores 108 may be equal among the plurality of cores 108 (eg, because the plurality of cores 108 are equidistant from the center 112 of the SAP 106 ).

[0025] Figure 1C Shown with Figure 1A Another example embodiment 100 is similar to the illustrated example embodiment 100, wherein the multi-core optical fiber 104 further includes (e.g., at a cross-section of the multi-core optical fiber 104) another SAP 118 (e.g., a ring-shaped SAP) and a set of one or more cores 120 within the cladding 110. The other SAP 118 may include a center 122 (e.g., a center point of the other SAP 118), which may be aligned with the center 112 of the SAP 106. The other SAP 118 and the one or more cores 120 may include the same or similar materials as the SAP 106 and the plurality of cores 108, respectively. Accordingly, the other SAP 118 and the one or more cores 120 may have different thermal expansion properties from each other, from the SAP 106, from the plurality of cores 108, and / or from the cladding 110. Thus, due to the different thermal expansion characteristics between another SAP 118 and one or more cores 120 and / or between another SAP 118 and the cladding 110, mechanical stress is exerted in each core 120 (e.g., as a result of a heated fiber drawing process used to produce the multi-core optical fiber 104). As further described herein, this mechanical stress substantially causes birefringence in the cores 120.

[0026] like Figure 1CAs shown, the other SAP 118 can surround the SAP 106 and the plurality of cores 108 because the other SAP 118 is annular, and a set of one or more cores 120 can surround the SAP 106, the plurality of cores 108, and the other SAP 118 (e.g., within the cladding 110). For example, the set of one or more cores 120 can surround the SAP 106, the plurality of cores 108, and the other SAP 118 such that the set of one or more cores 120 are equidistant from the center 122 of the other SAP 118. That is, the set of one or more cores 120 can be arranged on the circumference of an imaginary circle C2 having a radius R2 (e.g., where R2>R1) centered on the center 122 of the other SAP 118 (e.g., each core 120 is positioned at the same radial distance from the center 122 of the other SAP 118).

[0027] In some embodiments, the center-to-center distance between a first core 120 and a second core 120 adjacent to each other (e.g., the first core 120 and the second core 120 are adjacent cores 120) in a group of one or more cores 120 may be greater than or equal to 2.5 times the maximum value of the first diameter of the first core 120 and the second diameter of the second core 120 (e.g., the maximum value of the corresponding diameters of the adjacent cores 120). In this manner, the possibility of crosstalk between the first core 120 and the second core 120 (e.g., between adjacent cores 120) is minimized.

[0028] like Figure 1C As further shown, the other SAP 118 (e.g., due to being surrounded by the set of one or more cores 120) can apply mechanical stress to the set of one or more cores 120 and, thus, can substantially effectuate birefringence in the set of one or more cores 120 (e.g., the other SAP 118 can cause or can primarily cause birefringence in the set of one or more cores 120). Furthermore, because the other SAP 118 surrounds (e.g., completely surrounds) the plurality of cores 108, the other SAP 118 can not cause (or can only minimally cause) birefringence in the plurality of cores 108. Thus, as described herein with respect to Figure 1A As described above, the birefringence induced by the SAP 106 in the plurality of cores 108 may not be affected (or may be only minimally affected) by another SAP 118 .

[0029] The other SAP 118 that substantially achieves birefringence in each core 120 can result in the core 120 having a first polarization principal axis 124-1 (e.g., one of the fast polarization axis and the slow polarization axis) radially aligned with the center 122 of the other SAP 118, and having a second polarization principal axis 124-2 (e.g., the other of the fast polarization axis and the slow polarization axis) orthogonal to the first polarization principal axis 124-1. The first polarization principal axis 124-1 and the second polarization principal axis 124-2 can be collectively referred to as the polarization principal axis 126 of the core 120.

[0030] In some embodiments, a core 108 in the plurality of cores 108 can have a principal polarization axis 116 that is aligned with a principal polarization axis 126 of a core 120 in the set of one or more cores 120. Additionally or alternatively, a first core 120 in the set of one or more cores 120 can have a first principal polarization axis 126 that is not aligned with a second principal polarization axis 126 of a second core 120 in the set of one or more cores 120. For example, when the first core 120, the second core 120, and the center 122 of another SAP 118 are not collinear (for example, not arranged on the same imaginary line), the first core 120 may have a specific first polarization main axis 124-1 among the first polarization main axes 126, which is radially aligned with the center 122 of another SAP 118, the second core 120 may have another specific first polarization main axis 124-1 among the second polarization main axes 126, which is radially aligned with the center 122 of another SAP 118, and the specific first polarization main axis 124-1 and the other specific first polarization main axis 124-1 may not be aligned (for example, may not be parallel to each other).

[0031] Thus, the multi-core optical fiber 104 can be polarization-maintaining for both the plurality of cores 108 and the group of one or more cores 120 (e.g., the multi-core optical fiber 104 can be a PM multi-core optical fiber, and each core 108 in the plurality of cores 108 and each core 120 in the group of cores 120 can be polarization-maintaining). For example, each core 120 can maintain the polarization of light within that core 120 (e.g., in a direction aligned with the principal axis of polarization 126 of the core 120) due to birefringence induced in each core 120 (e.g., by another SAP 118), and each core 108 can maintain the polarization of light within that core 108 (e.g., in a direction aligned with the principal axis of polarization 116 of the core 108) due to birefringence induced in each core 108 (e.g., by SAP 106). In some embodiments, the birefringence substantially achieved in the group of one or more cores 120 can be equal among the group of one or more cores 120. For example, because a group of one or more cores 120 are equidistant from the center 122 of another SAP 118, another SAP 118 applies equal (or nearly equal) mechanical stress to each core 120, and the birefringence induced in each core 120 can be the same (or nearly the same within a tolerance range).

[0032] Figure 1D Shown with Figure 1A Another example embodiment 100 is similar to the illustrated example embodiment 100, in which the multi-core optical fiber 104 further includes (e.g., at a cross section of the multi-core optical fiber 104) one or more additional SAPs 124 (e.g., one or more disk-shaped SAPs) within the cladding 110. The one or more additional SAPs 124 can include the same or similar material as the SAP 106. Thus, the one or more additional SAPs 124 and the plurality of cores 108 can have different thermal expansion characteristics.

[0033] like Figure 1D As shown, one or more further SAPs 128 may surround the SAP 106 and the plurality of cores 108. For example, the one or more further SAPs 128 may surround the SAP 106 and the plurality of cores 108 such that the one or more further SAPs 128 are equidistant from the center 112 of the SAP 106. That is, the one or more further SAPs 128 may be disposed on the circumference of an imaginary circle C3 having a radius R3 (e.g., where R3>R1) centered on the center 112 of the SAP 106 (e.g., each further SAP 128 is positioned at the same radial distance from the center 112 of the SAP 106).

[0034] In some embodiments, a particular another SAP 128 may be associated with a particular core 108 in the plurality of cores 108. For example, Figure 1DAs shown, the specific another SAP 128, the specific core 108, and the center 112 of the SAP 106 can be collinear (e.g., at a cross-section of the multi-core optical fiber 104), and the specific core 108 can be positioned between the specific another SAP 128 and the SAP 106. Thus, the specific another SAP 128 can also apply mechanical stress to the specific core 108, and thus can substantially achieve the birefringence in the specific core 108 that is substantially achieved (cooperatively) in the specific core 108 by the SAP 106 (e.g., because the SAP applies mechanical stress to the specific core 108, as described elsewhere herein). For example, the specific another SAP 128 can be positioned to increase the mechanical stress in the specific core 108 that is primarily generated by the SAP 106 (e.g., due to different thermal expansion characteristics between the specific core 108 and the specific core 108 and / or between the specific core 108 and the cladding 110), which enhances the birefringence that is substantially achieved in the specific core 108. Thus, a particular core 108 can have polarization principal axes 116 that include a first polarization principal axis 114-1 (e.g., one of a fast polarization axis or a slow polarization axis) that is radially aligned with the center 112 of the SAP 106, and can have a second polarization principal axis 114-2 (e.g., the other of a fast polarization axis or a slow polarization axis) that is orthogonal to the first polarization principal axis 114-1.

[0035] Figure 1E Shown with Figure 1D Another example embodiment 100 is similar to the example embodiment 100 shown, in which each of the one or more further SAPs 128 is associated with two or more cores 108 in the plurality of cores 108. For example, the further SAP 128 can be positioned such that the SAP 106 and the further SAP 128 individually and in relation to each other apply mechanical stress to two or more cores 108 in the plurality of cores 108, and thus can substantially achieve birefringence in the two or more cores 108 in the plurality of cores 108. Thus, the one or more further SAPs 128 can be positioned (e.g., on the circumference of the imaginary circle C3) such that birefringence is induced in the plurality of cores 108 such that the respective polarization principal axes 116 of the plurality of cores 108 are not radially aligned with the center 112 of the SAP 106. For example, as Figure 1E As shown, the SAP 106 associated with one or more other SAPs 128 can be configured to substantially achieve birefringence in the plurality of cores 108 such that the respective polarization principal axes 116 of the plurality of cores 108 are aligned (e.g., the respective first polarization principal axes 114-1 are aligned in the vertical direction, and the respective second polarization principal axes 114-2 are aligned in the horizontal direction, as shown in FIG. Figure 1E shown).

[0036] Figure 1F Shown with Figure 1A Another example embodiment 100 similar to the example embodiment 100 shown, wherein the multi-core optical fiber 104 includes (e.g., at a cross-section of the multi-core optical fiber 104) a first SAP 106-A and a plurality of first cores 108-A surrounding the first SAP 106-A within a cladding 110 (e.g., in a manner similar to that described herein with respect to Figure 1A In a manner similar to that described herein), and a second SAP 106-B and a plurality of second cores 108-B surrounding the second SAP 106-B within the cladding 110 (e.g., in a manner similar to that described herein with respect to Figure 1A In a manner similar to that described above, the first SAP 106 -A can have a center 112 -A, and the second SAP 106 -B can have a center 112 -B, both of which can be offset from the center of the multi-core optical fiber 104 .

[0037] like Figure 1F As shown, the first SAP 106-A (e.g., due to being surrounded by the plurality of first cores 108-A) can apply mechanical stress to the plurality of first cores 108-A, and thereby can substantially achieve a first birefringence in the plurality of first cores 108-A (e.g., the first SAP 106-A can cause or can primarily cause the first birefringence in the plurality of first cores 108-A). Substantially achieving the first birefringence in each of the first cores 108-A can result in each of the first cores 108-A having a polarization principal axis 116-A, the polarization principal axis including a first polarization principal axis 114-1-A (e.g., one of a fast polarization axis or a slow polarization axis) radially aligned with the center 112-A of the first SAP 106-A, and a second polarization principal axis 114-2-A (e.g., the other of a fast polarization axis or a slow polarization axis) orthogonal to the first polarization principal axis 114-1-A. Thus, in some embodiments, in a manner similar to that described above, a first core 108-A among the plurality of first cores 108-A may have a first polarization principal axis 116-A that is not aligned with a second polarization principal axis 116-A of another first core 108-A among the plurality of first cores 108-A.

[0038] like Figure 1FAs further shown, the second SAP 106-B (e.g., due to being surrounded by the plurality of second cores 108-B) can apply mechanical stress to the plurality of second cores 108-B and, thus, can substantially achieve the second birefringence in the plurality of second cores 108-B (e.g., the second SAP 106-B can cause or can primarily cause the second birefringence in the plurality of second cores 108-B). Substantially achieving the second birefringence in each of the second cores 108-B can result in each of the second cores 108-B having a polarization principal axis 116-B that includes a first polarization principal axis 114-1-B (e.g., one of the fast polarization axis or the slow polarization axis) radially aligned with the center 112-B of the second SAP 106-B and a second polarization principal axis 114-2-B (e.g., the other of the fast polarization axis or the slow polarization axis) that is orthogonal to the first polarization principal axis 114-1-B. Thus, in some embodiments, in a manner similar to that described above, a second core 108-B among the plurality of second cores 108-B may have a first polarization principal axis 116-B that is not aligned with a second polarization principal axis 116-B of another second core 108-B among the plurality of second cores 108-B.

[0039] supply Figures 1A to 1F As an example. Other examples can be related to Figures 1A to 1F Different from what is described.

[0040] The above disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practicing the embodiments. In addition, any embodiments described herein may be combined, unless the above disclosure clearly provides reasons why one or more embodiments cannot be combined.

[0041] Although specific combinations of features are listed in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. In fact, many of these features can be combined in ways that are not specifically listed in the claims and / or disclosed in the specification. Although each dependent claim listed below may only directly depend on one claim, the disclosure of the various embodiments includes the combination of each dependent claim with each other claim in the claim set. As used herein, the phrase "at least one" in a list of reference 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 any combination of a, b, c, ab, ac, bc, and abc, as well as multiple items in the same item.

[0042] Unless explicitly stated, otherwise any element, behavior or instruction used in this article should not be interpreted as key or essential.In addition, as used in this article, the article " one (a) " and " one (an) " are intended to include one or more projects, and can be used interchangeably with " one or more (one or more) ".In addition, as used in this article, the article " that (the) " is intended to include one or more projects quoted in combination with the article " that ", and can be used interchangeably with " one or more ".In addition, the term " set " used in this article is intended to include one or more projects (for example, related projects, unrelated projects or the combination of related and unrelated projects), and can be used interchangeably with " one or more ".If only intend to use a project, phrase " only one (only one) " or similar language is used.In addition, as used in this article, the term " has (has) ", " have (have) ", " have (having) " etc. are intended to be open terms.In addition, unless explicitly stated otherwise, otherwise " based on (based on) " word 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 expressly stated otherwise (e.g., if used in conjunction with "either" or "only one of"). Additionally, for ease of description, spatially relative terms (such as "below," "lower," "above," "upper," "left," "right," etc.) may be used herein to describe the relationship of one element or feature to other elements or features shown in the figures. Spatially relative terms are intended to encompass different orientations of the apparatus, device, and / or element in use or operation in addition to the orientation shown in the figures. The apparatus may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

Claims

1. An optical system comprising: Multi-core optical fiber, including: cladding; stress applying portion SAP; and a group of at least three cores, the group of at least three cores being equidistant from the center of the SAP in the cross section of the multi-core optical fiber, wherein the SAP substantially effects birefringence in the set of at least three cores.

2. The optical system of claim 1, wherein a first core in the set of at least three cores has a first polarization principal axis that is not aligned with a second polarization principal axis of a second core in the set of at least three cores.

3. The optical system according to claim 2, wherein: A specific first polarization principal axis among the first polarization principal axes is radially aligned with the center of the SAP; Another specific first polarization principal axis among the second polarization principal axes is radially aligned with the center of the SAP; and The specific first polarization principal axis is not aligned with the other specific first polarization principal axis.

4. The optical system of claim 1, wherein the birefringence is equal among the set of at least three cores.

5. The optical system according to claim 1 , wherein at the cross section of the multi-core optical fiber, the SAP is one of the following: disc-shaped, or Ring.

6. The optical system according to claim 1, wherein the multi-core optical fiber further comprises: another SAP surrounding the SAP and the set of at least three cores at the cross section of the multi-core optical fiber; as well as A set of one or more cores surrounds the other SAP at the cross section of the multi-core optical fiber and is equidistant from the center of the other SAP, wherein the other SAP substantially realizes birefringence in the set of one or more cores.

7. The optical system according to claim 1, wherein the multi-core optical fiber further comprises: another SAP associated with a particular core in the set of at least three cores, wherein: Centers of the another SAP, the specific core, and the SAP are collinear at the cross section of the multi-core optical fiber, and The specific core is positioned between the other SAP and the SAP at the cross section of the multi-core optical fiber.

8. The optical system according to claim 1, wherein the multi-core optical fiber further comprises: Another SAP; as well as another group of at least three cores, the another group of at least three cores being equidistant from the center of the another SAP at the cross section of the multi-core optical fiber, wherein the another SAP substantially achieves birefringence in the another set of at least three cores.

9. The optical system according to claim 1, wherein the multi-core optical fiber further comprises: First another SAP; as well as Second another SAP, which: The SAP substantially enables birefringence in the set of at least three cores in association with the first further SAP and the second further SAP such that respective principal axes of polarization of the set of at least three cores are aligned.

10. An optical system comprising: Multi-core optical fiber, including: cladding; stress applying portion SAP; and a set of at least three cores, said set of at least three cores surrounding said SAP, wherein the SAP substantially achieves birefringence in the set of at least three cores, and wherein respective principal axes of polarization of the set of at least three cores are radially aligned with the center of the SAP.

11. The optical system of claim 10, wherein the set of at least three cores are equidistant from the center of the SAP.

12. The optical system of claim 10, wherein a first core in the set of at least three cores has a first principal axis of polarization that is not aligned with a second principal axis of polarization of a second core in the set of at least three cores.

13. The optical system of claim 1, wherein the birefringence is equal among the set of at least three cores.

14. The optical system according to claim 10, wherein the multi-core optical fiber further comprises: another SAP surrounding the set of at least three cores; as well as A set of one or more cores surrounds the other SAP.

15. The optical system according to claim 10, wherein the multi-core optical fiber further comprises: Another SAP, where: A particular core is positioned closer to the SAP than the other SAP is positioned to the SAP.

16. The optical system according to claim 10, wherein the multi-core optical fiber further comprises: Another SAP; as well as a further plurality of cores surrounding said further SAP, wherein the another SAP substantially effects birefringence in the further plurality of cores.

17. A multi-core optical fiber, comprising: cladding; Stress applying part SAP; as well as a plurality of cores equidistant from the center of the SAP, wherein the SAP substantially enables birefringence in the plurality of cores, and The center of the SAP and the first and second cores of the plurality of cores are not collinear.

18. The multi-core optical fiber of claim 17, wherein the first core has a first polarization principal axis that is not aligned with a second polarization principal axis of the second core.

19. The multi-core optical fiber of claim 17, wherein the first core has a first polarization principal axis radially aligned with the center of the SAP, and the second core has a second polarization principal axis radially aligned with the center of the SAP.

20. The multi-core optical fiber of claim 17, wherein the first core has a first polarization principal axis that is aligned with a second polarization principal axis of the second core.

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