Multicore fiber optic connectors and optical communication systems

Abstract

To provide a multicore fiber connector and an optical communication system using the same that can suppress the effects of nonlinear optical phenomena in optical communication. [Solution] The multicore fiber connector comprises a first multicore fiber having a plurality of core portions including a first core portion whose effective core cross-sectional area at a predetermined wavelength is a first value, and a cladding portion surrounding the plurality of core portions, and a second multicore fiber having a plurality of core portions including a second core portion whose effective core cross-sectional area at the predetermined wavelength is a second value smaller than the first value, and a cladding portion surrounding the plurality of core portions, wherein the first core portion and the second core portion are connected in series.

Description

Technical Field

[0001] The present invention relates to a multi-core fiber connector and an optical communication system.

Background Art

[0002] In a multi-core fiber including a plurality of core portions, inter-core crosstalk may sometimes become a problem. As a method for solving this problem, there is known a method of forming a plurality of core portions into heterogeneous core portions. The heterogeneous core portions refer to core portions having mutually different effective refractive indices (for example, Patent Document 1).

[0003] Furthermore, a technology for optimally using a multi-core fiber in accordance with a communication mode (for example, bidirectional communication) has been disclosed (for example, Non-Patent Document 1).

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Non-Patent Literature

[0005]

Non-Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0006] However, the configuration of known multi-core fibers leaves room for improvement from the perspective of suppressing the influence of nonlinear optical phenomena in optical communication.

[0007] The present invention has been made in view of the above, and its object is to provide a multicore fiber connector and an optical communication system using the same that can suppress the influence of nonlinear optical phenomena in optical communication. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, one aspect of the present invention is a multicore fiber connector comprising: a first multicore fiber having a plurality of core portions including a first core portion having a first effective core cross-sectional area at a predetermined wavelength which is a first value, and a cladding portion surrounding the plurality of core portions; and a second multicore fiber having a plurality of core portions including a second core portion having a second effective core cross-sectional area at the predetermined wavelength which is smaller than the first value, and a cladding portion surrounding the plurality of core portions, wherein the first core portion and the second core portion are connected in series.

[0009] The multicore fiber connector may comprise only the first multicore fiber and the second multicore fiber as multicore fibers, and the first core portion and the second core portion may be directly connected in series.

[0010] The first multicore fiber and the second multicore fiber each include at least two core portions, and each may include a core portion in which the absolute value of the difference in the effective core cross-sectional areas of the two core portions at the predetermined wavelength is 10% or more greater than the smaller of the two effective core cross-sectional areas of the two core portions at the predetermined wavelength.

[0011] The plurality of core portions of the first multicore fiber include a third core portion whose effective core cross-sectional area at a predetermined wavelength is a third value, and the plurality of core portions of the second multicore fiber include a fourth core portion whose effective core cross-sectional area at a predetermined wavelength is a fourth value greater than the third value, and the third core portion and the fourth core portion may be connected in series.

[0012] The number of cores in the first multicore fiber or the second multicore fiber may be 19 or less.

[0013] The number of cores in the first multicore fiber or the second multicore fiber may be 2 or more and 4 or less.

[0014] In the first multicore fiber or the second multicore fiber, there may be no markers in the cladding portion that have a different refractive index from the cladding portion and do not contribute to light propagation.

[0015] One aspect of the present invention is an optical communication system comprising: a multicore fiber cable including the multicore fiber connector; a first communication device that outputs a first signal light to the first core; and a second communication device that receives the first signal light transmitted through the second core after it has been transmitted through the first core.

[0016] One aspect of the present invention is an optical communication system comprising: a multicore fiber cable including the multicore fiber connector; a first communication device that outputs a first signal light to the first core; and a second communication device that receives the first signal light transmitted through the second core after it has passed through the first core, wherein the second communication device outputs a second signal light to the fourth core, and the first communication device receives the second signal light transmitted through the third core after it has passed through the fourth core. [Effects of the Invention]

[0017] The present invention provides the effect of realizing a multicore fiber connector that can suppress the effects of nonlinear optical phenomena in optical communication. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 1. [Figure 2]FIG. 2 is a schematic cross-sectional view of the multicore fiber shown in FIG. 1 in a plane perpendicular to the longitudinal direction. [Figure 3] FIG. 3 is a diagram showing an example of the relationship between the difference in effective core area between cores and inter-core crosstalk. [Figure 4] FIG. 4 is a schematic configuration diagram of an optical communication system using the multicore fiber connector according to Embodiment 2. [Figure 5] FIG. 5 is a schematic cross-sectional view of the multicore fiber shown in FIG. 4 in a plane perpendicular to the longitudinal direction. [Figure 6] FIG. 6 is a schematic configuration diagram of an optical communication system using the multicore fiber connector according to Embodiment 3. [Figure 7] FIG. 7 is a schematic cross-sectional view of the multicore fiber shown in FIG. 6 in a plane perpendicular to the longitudinal direction. [Figure 8] FIG. 8 is a schematic configuration diagram of an optical communication system using the multicore fiber connector according to Embodiment 4. [Figure 9] FIG. 9 is a schematic cross-sectional view of the multicore fiber shown in FIG. 8 in a plane perpendicular to the longitudinal direction. [Figure 10] FIG. 10 is a schematic configuration diagram of an optical communication system using the multicore fiber connector according to Embodiment 5. [Figure 11] FIG. 11 is a schematic cross-sectional view of the multicore fiber shown in FIG. 10 in a plane perpendicular to the longitudinal direction. [Figure 12] FIG. 12 is a schematic configuration diagram of an optical communication system using the multicore fiber connector according to Embodiment 6. [Figure 13] FIG. 13 is a schematic cross-sectional view of the multicore fiber shown in FIG. 12 in a plane perpendicular to the longitudinal direction. [Figure 14] FIG. 14 is a schematic configuration diagram of an optical communication system using the multicore fiber connector according to Embodiment 7. [Figure 15] FIG. 15 is a schematic cross-sectional view of the multicore fiber shown in FIG. 14 in a plane perpendicular to the longitudinal direction. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below. In each drawing, the same or corresponding components are denoted by the same reference numerals as appropriate, and redundant explanations are omitted as appropriate. Furthermore, in this specification, the cutoff wavelength or effective cutoff wavelength refers to the cable cutoff wavelength as defined in ITU-T G.650.1 of the International Telecommunication Union (ITU). In addition, terms not specifically defined in this specification shall follow the definitions and measurement methods in G.650.1 and G.650.2.

[0020] (Embodiment 1) Figure 1 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 1. The optical communication system 1000 is a bidirectional optical communication system comprising a multicore fiber cable 100, a communication device 200, and a communication device 300.

[0021] <Multicore fiber cable> The multicore fiber cable 100 comprises a multicore fiber connector 110 according to Embodiment 1 and a structure 120. The structure 120 constitutes the multicore fiber cable 100 and is a structure for supporting and protecting the multicore fiber connector 110, and includes, for example, tension members and sheaths.

[0022] The multicore fiber connector 110 is configured by directly connecting a multicore fiber 111 and a multicore fiber 112 in series.

[0023] Figure 2 is a schematic cross-sectional view of the multicore fiber shown in Figure 1, in a plane perpendicular to the longitudinal direction. Figure 2(a) is a cross-sectional view of the multicore fiber 111, and Figure 2(b) is a cross-sectional view of the multicore fiber 112.

[0024] The multicore fiber 111 is a two-core type multicore fiber having two core portions 111a and 111b as multiple core portions, and a cladding portion 111c surrounding the core portions 111a and 111b.

[0025] The core sections 111a and 111b have, for example, a so-called step type, W type, or trench type refractive index profile. The cladding section 111c has an average refractive index lower than the maximum refractive index of the core sections 111a and 111b. In the case of a trench type refractive index profile, the core section has a center core, an intermediate layer surrounding the center core, and a trench layer surrounding the intermediate layer. The refractive index of the intermediate layer is lower than the maximum refractive index of the center core, and the refractive index of the trench layer is even lower than the refractive index of the intermediate layer and the refractive index of the cladding section.

[0026] Core portion 111a is a core portion whose effective core cross-sectional area at a predetermined wavelength is a first value. Core portion 111b is a core portion whose effective core cross-sectional area at a predetermined wavelength is a third value. The predetermined wavelength is a wavelength included in the wavelength band (used wavelength band) used as the wavelength of signal light in the optical communication system 1000. The used wavelength band is, for example, 1520 nm to 1620 nm. The predetermined wavelength is, for example, 1550 nm.

[0027] Furthermore, the absolute difference between the first and third values ​​is greater than that of the third value by more than 10%.

[0028] The multicore fiber 111 described above is an example of a first multicore fiber, core portion 111a is an example of a first core portion, and core portion 111b is an example of a third core portion. Furthermore, core portions 111a and core portion 111b are two core portions, and are an example of a core portion in which the absolute value of the difference in the effective core cross-sectional area of ​​the two core portions at a predetermined wavelength is 10% or more greater than the effective core cross-sectional area of ​​the smaller of the two effective core cross-sectional areas at a predetermined wavelength.

[0029] The multicore fiber 112 is a two-core type multicore fiber having two core sections 112a and 112b as multiple core sections, and a cladding section 112c surrounding the core sections 111a and 111b.

[0030] The core sections 112a and 112b have, for example, a so-called step type, W type, or trench type refractive index profile. The cladding section 112c has an average refractive index lower than the maximum refractive index of the core sections 112a and 112b.

[0031] Core section 112a is a core section whose effective core cross-sectional area at a predetermined wavelength is the second value. The second value is smaller than the first value, which is the effective core cross-sectional area of ​​core section 111a at a predetermined wavelength. Core section 112b is a core section whose effective core cross-sectional area at a predetermined wavelength is the fourth value. The fourth value is larger than the third value, which is the effective core cross-sectional area of ​​core section 111b at a predetermined wavelength.

[0032] Furthermore, the absolute difference between the second and fourth values ​​is more than 10% greater than that of the second value.

[0033] The multicore fiber 112 described above is an example of a second multicore fiber, core portion 112a is an example of a second core portion, and core portion 112b is an example of a fourth core portion. Furthermore, core portions 112a and 112b are two core portions, and are examples of core portions in which the absolute value of the difference in the effective core cross-sectional area of ​​the two core portions at a predetermined wavelength is 10% or more greater than the smaller of the two effective core cross-sectional areas at the predetermined wavelength.

[0034] As shown in Figure 1, core section 111a and core section 112a are directly connected in series. Also, core section 111b and core section 112b are directly connected in series.

[0035] <Communication equipment> Communication devices 200 and 300 are communication devices having a known configuration used in bidirectional communication in optical fiber communication. Communication device 200 is connected to the multicore fiber 111 side of the multicore fiber cable 100. Communication device 300 is connected to the multicore fiber 112 side of the multicore fiber cable 100. Communication device 200 is an example of a first communication device, and communication device 300 is an example of a second communication device.

[0036] The communication device 200 outputs signal light L11 of a predetermined wavelength to the core portion 111a of the multicore fiber 111. Such signal light L11 is an example of a first signal light. The core portion 111a transmits the signal light L11 and outputs it to the core portion 112a of the multicore fiber 112. The core portion 112a transmits the signal light L11 after it has been transmitted through the core portion 111a.

[0037] The communication device 300 receives signal light L12, which is signal light L11 after it has transmitted through core section 111a and then core section 112a. As signal light L11 propagates sequentially through core sections 111a and 112a, its power gradually decreases in accordance with the transmission losses of these core sections. Therefore, the power of signal light L12 is lower than the power of signal light L11.

[0038] Furthermore, the communication device 300 outputs a signal light L21 of a predetermined wavelength to the core section 112b of the multicore fiber 112. Such a signal light L21 is an example of a second signal light. The core section 112b transmits the signal light L21 and outputs it to the core section 111b of the multicore fiber 111. The core section 111b transmits the signal light L21 after it has been transmitted by the core section 112b.

[0039] The communication device 200 receives signal light L22, which is signal light L21 after the transmission of core section 112b and then core section 111b. As signal light L21 propagates sequentially through core sections 112b and 111b, its power gradually decreases according to the transmission losses of these core sections. Therefore, the power of signal light L22 is lower than the power of signal light L21.

[0040] In the optical communication system 1000 configured as described above, the multicore fiber connector 110 transmits the signal light L11 through the core section 111a, which has a relatively large effective core cross-sectional area, when the power is relatively high, and through the core section 112a, which has a relatively small effective core cross-sectional area, when the power is relatively low. This suppresses the influence of nonlinear optical phenomena in communication from communication device 200 to communication device 300. Furthermore, in the multicore fiber connector 110, the signal light L21 transmits through the core section 112b, which has a relatively large effective core cross-sectional area, when the power is relatively high, and through the core section 111b, which has a relatively small effective core cross-sectional area, when the power is relatively low. This suppresses the influence of nonlinear optical phenomena in communication from communication device 300 to communication device 200. Therefore, in the optical communication system 1000, the multicore fiber connector 110 can suppress the influence of nonlinear optical phenomena in bidirectional communication between communication device 200 and communication device 300.

[0041] Furthermore, in the multicore fiber connector 110, the effective core cross-sectional areas of core portions 111a and 111b in the multicore fiber 111 are different, making it easy to distinguish between core portions 111a and 111b when observing the cross-section of the multicore fiber 111 under a microscope. In particular, the absolute value of the difference in the effective core cross-sectional areas of core portions 111a and 111b is large, exceeding 10% of the smaller value, making identification even easier. Similarly, in the multicore fiber 112, the effective core cross-sectional areas of core portions 112a and 112b are different, and in particular, the absolute value of the difference in the effective core cross-sectional areas of core portions 112a and 112b is large, exceeding 10% of the smaller value, making it easy to distinguish between core portions 112a and 112b when observing the cross-section under a microscope. For these reasons, in the multicore fiber 111 and multicore fiber 112, even if there are no markers in the cladding portion that have a different refractive index from the cladding portion and do not contribute to light propagation, the two core portions can be easily distinguished.

[0042] Furthermore, the effective core cross-sectional areas of core sections 111a and 111b in the multicore fiber 111 are different. As a result, core sections 111a and 111b function as different types of core sections, thus reducing inter-core crosstalk. Similarly, the effective core cross-sectional areas of core sections 112a and 112b in the multicore fiber 112 are different, thus reducing inter-core crosstalk.

[0043] Through diligent research by the inventors, it has been confirmed that it is preferable for reducing intercore crosstalk if the absolute value of the difference between the effective core cross-sectional areas of the two core sections at a predetermined wavelength is 10% or more greater than the smaller of the two effective core cross-sectional areas.

[0044] For example, Figure 3 shows an example of the relationship between the difference in effective core cross-sectional area (Aeff) between cores and intercore crosstalk (XT). Note that Figure 3 shows a case where there are four core sections and the outer diameter of the cladding section is 125 μm, and XT is the average value of the four core sections. As shown in Figure 3, if the difference in Aeff between cores is 10% or more of the smaller value, it is preferable to keep the XT at a wavelength of 1550 nm and a length of 100 km below -30 dB.

[0045] (Embodiment 2) Figure 4 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 2. The optical communication system 1000A is a one-way optical communication system comprising a multicore fiber cable 100A, a communication device 200A, and a communication device 300A.

[0046] The multicore fiber cable 100A has a configuration in which the multicore fiber connector 110 in the multicore fiber cable 100 of Figure 1 is replaced with the multicore fiber connector 110A according to Embodiment 2.

[0047] The multicore fiber connector 110A is configured by directly connecting the multicore fiber 111A and the multicore fiber 112A in series.

[0048] Figure 5 is a schematic cross-sectional view of the multicore fiber shown in Figure 4, in a plane perpendicular to the longitudinal direction. Figure 4(a) is a cross-sectional view of the multicore fiber 111A, and Figure 4(b) is a cross-sectional view of the multicore fiber 112A.

[0049] The multicore fiber 111A has a configuration in which the core portion 111b of the multicore fiber 111 shown in Figure 2(a) is replaced with the core portion 111a. The multicore fiber 112A has a configuration in which the core portion 112b of the multicore fiber 112 shown in Figure 2(b) is replaced with the core portion 112a.

[0050] As shown in Figure 3, core section 111a and core section 112a are directly connected in series.

[0051] Communication devices 200 and 300 are communication devices having a known configuration used in one-way communication in optical fiber communication. Communication device 200A is connected to the multicore fiber 111A side of the multicore fiber cable 100A. Communication device 300A is connected to the multicore fiber 112A side of the multicore fiber cable 100A.

[0052] The communication device 200A outputs signal light L11 and L31 to the core section 111a of the multicore fiber 111A, respectively. The wavelength of signal light L31 is the wavelength of the wavelength band used, and may be the same as or different from the wavelength of signal light L11. The core section 111a, upon receiving signal light L31, transmits the signal light L31 and outputs it to the core section 112a of the multicore fiber 112A. The core section 112a transmits the signal light L31 after it has been transmitted through the core section 111a.

[0053] The communication device 300A receives signal light L32, which is signal light L31 after it has transmitted core section 111a and then core section 112a. As signal light L31 propagates sequentially through core sections 111a and 112a, its power gradually decreases in accordance with the transmission losses of these core sections. Therefore, the power of signal light L32 is lower than the power of signal light L31.

[0054] In the optical communication system 1000A configured as described above, the influence of nonlinear optical phenomena in one-way communication from communication device 200A to communication device 300A can be suppressed.

[0055] (Embodiment 3) Figure 6 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 3. The optical communication system 1000B is a bidirectional optical communication system comprising a multicore fiber cable 100B, a communication device 200B, and a communication device 300B.

[0056] The multicore fiber cable 100B has a configuration in which the multicore fiber connector 110 in the multicore fiber cable 100 of Figure 1 is replaced with the multicore fiber connector 110B according to Embodiment 3.

[0057] The multicore fiber connector 110B is configured by directly connecting the multicore fiber 111B and the multicore fiber 112B in series.

[0058] Figure 7 is a schematic cross-sectional view of the multicore fiber shown in Figure 6 in a plane perpendicular to the longitudinal direction. Figure 7(a) is a cross-sectional view of the multicore fiber 111B, and Figure 7(b) is a cross-sectional view of the multicore fiber 112B.

[0059] The multicore fiber 111B has a three-core configuration, with the core portion 111b shown in Figure 2(a) added to the multicore fiber 111A shown in Figure 5(a). The two core portions 111a and core portion 111b are arranged to form a regular triangular lattice in cross-section. The multicore fiber 112B has a three-core configuration, with the core portion 112b shown in Figure 2(b) added to the multicore fiber 112A shown in Figure 5(b). The two core portions 112a and core portion 112b are arranged to form a regular triangular lattice in cross-section.

[0060] As shown in Figure 6, core section 111a and core section 112a are directly connected in series. Also, core section 111b and core section 112b are directly connected in series.

[0061] Communication devices 200B and 300B are communication devices having a known configuration used in bidirectional communication in optical fiber communication. Communication device 200B is connected to the multicore fiber 111B side of the multicore fiber cable 100B. Communication device 300B is connected to the multicore fiber 112B side of the multicore fiber cable 100B.

[0062] The communication device 200B outputs signal light L11 and L31 to each of the two core sections 111a of the multicore fiber 111A.

[0063] The communication device 300B receives signal lights L12 and L32, which are signal lights L11 and L31, after the core section 111a has been transmitted and the core section 112a has been transmitted.

[0064] Furthermore, the communication device 300B outputs the signal light L21 in the wavelength band used to the core portion 112b of the multicore fiber 112B.

[0065] The communication device 200B receives the signal light L22, which is the signal light L21 after the core section 112b has been transmitted and the core section 111b has been transmitted.

[0066] In the optical communication system 1000B configured as described above, the influence of nonlinear optical phenomena in bidirectional communication between communication device 200B and communication device 300B can be suppressed. In particular, the optical communication system 1000B is a system suitable when the communication capacity from communication device 200B to communication device 300B is large. Furthermore, the multicore fiber connector 110B is also suitable from the viewpoint of the identifiability of the core portion in the cross section and the reduction of intercore crosstalk.

[0067] (Embodiment 4) Figure 8 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 4. The optical communication system 1000C is a one-way optical communication system comprising a multicore fiber cable 100C, a communication device 200C, and a communication device 300C.

[0068] The multicore fiber cable 100C has a configuration in which the multicore fiber connector 110 in the multicore fiber cable 100 of Figure 1 is replaced with the multicore fiber connector 110C according to Embodiment 4.

[0069] The multicore fiber connector 110C is configured by directly connecting the multicore fiber 111C and the multicore fiber 112C in series.

[0070] Figure 9 is a schematic cross-sectional view of the multicore fiber shown in Figure 8 in a plane perpendicular to the longitudinal direction. Figure 9(a) is a cross-sectional view of the multicore fiber 111C, and Figure 9(b) is a cross-sectional view of the multicore fiber 112C.

[0071] The multicore fiber 111C has a configuration in which the core portion 111b of the multicore fiber 111B shown in Figure 7(a) is replaced with the core portion 111a. The multicore fiber 112B has a configuration in which the core portion 112b of the multicore fiber 112B shown in Figure 7(b) is replaced with the core portion 112a.

[0072] As shown in Figure 8, core section 111a and core section 112a are directly connected in series.

[0073] Communication devices 200C and 300C are communication devices having a known configuration used in one-way communication in optical fiber communication. Communication device 200C is connected to the multicore fiber 111C side of the multicore fiber cable 100C. Communication device 300C is connected to the multicore fiber 112C side of the multicore fiber cable 100C.

[0074] The communication device 200C outputs signal light L11, L31, and L41 in the operating wavelength band to the core section 111a of the multicore fiber 111A. The wavelength of signal light L41 is in the operating wavelength band and may be the same as or different from the wavelengths of signal light L11 and L31. The core section 111a, upon receiving signal light L41, transmits the signal light L41 and outputs it to the core section 112a of the multicore fiber 112C. The core section 112a transmits the signal light L41 after it has been transmitted through the core section 111a.

[0075] The communication device 300C receives signal light L42, which is signal light L41 after the core section 111a has been transmitted and then the core section 112a has been transmitted. As signal light L41 propagates sequentially through the core sections 111a and 112a, its power gradually decreases in accordance with the transmission losses of these core sections. Therefore, the power of signal light L42 is lower than the power of signal light L41.

[0076] In the optical communication system 1000C configured as described above, the influence of nonlinear optical phenomena in one-way communication from communication device 200C to communication device 300C can be suppressed.

[0077] (Embodiment 5) Figure 10 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 5. The optical communication system 1000D is a bidirectional optical communication system comprising a multicore fiber cable 100D, a communication device 200D, and a communication device 300D.

[0078] The multicore fiber cable 100D has a configuration in which the multicore fiber connector 110 in the multicore fiber cable 100 of Figure 1 is replaced with the multicore fiber connector 110D according to Embodiment 5.

[0079] The multicore fiber connector 110D is configured by directly connecting the multicore fiber 111D and the multicore fiber 112D in series.

[0080] Figure 11 is a schematic cross-sectional view of the multicore fiber shown in Figure 10 in a plane perpendicular to the longitudinal direction. Figure 11(a) is a cross-sectional view of the multicore fiber 111D, and Figure 11(b) is a cross-sectional view of the multicore fiber 112D.

[0081] The multicore fiber 111D has a four-core configuration, with a core portion 111b added to the multicore fiber 111B shown in Figure 7(a). The two core portions 111a and the two core portions 111b are arranged to form a square grid in cross-section, and identical core portions are located diagonally opposite each other. The multicore fiber 112B has a four-core configuration, with a core portion 112b added to the multicore fiber 112B shown in Figure 7(b). The two core portions 112a and the two core portions 112b are arranged to form a square grid in cross-section, and identical core portions are located diagonally opposite each other.

[0082] As shown in Figure 10, core section 111a and core section 112a are directly connected in series. Also, core section 111b and core section 112b are directly connected in series.

[0083] Communication devices 200D and 300D are communication devices having a known configuration used in bidirectional communication in optical fiber communication. Communication device 200D is connected to the multicore fiber 111D side of the multicore fiber cable 100D. Communication device 300D is connected to the multicore fiber 112D side of the multicore fiber cable 100D.

[0084] The communication device 200D outputs signal light L11 and L31 in the wavelength band to the two core sections 111a, 111a of the multicore fiber 111D, respectively.

[0085] The communication device 300D receives signal lights L12 and L32, which are signal lights L11 and L31, after the core section 111a has been transmitted and the core section 112a has been transmitted.

[0086] Furthermore, the communication device 300D outputs signal light L21 and L51 in the operating wavelength band to each of the two core sections 112b of the multicore fiber 112D. The wavelength of signal light L51 is the wavelength in the operating wavelength band and may be the same as or different from the wavelength of signal light L21.

[0087] The communication device 200D receives signal lights L22 and L52, which are signal lights L21 and L51, after the core section 112b has been transmitted and then the core section 111b has been transmitted.

[0088] In the optical communication system 1000D configured as described above, the influence of nonlinear optical phenomena in bidirectional communication between the communication device 200D and the communication device 300D can be suppressed. Furthermore, the multicore fiber connector 110D is also suitable from the viewpoint of distinguishability of the core portion in cross-section and reduction of intercore crosstalk.

[0089] (Embodiment 6) Figure 12 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 6. The optical communication system 1000E is a bidirectional optical communication system comprising a multicore fiber cable 100E, a communication device 200E, and a communication device 300E.

[0090] The multicore fiber cable 100E has a configuration in which the multicore fiber connector 110 in the multicore fiber cable 100 of Figure 1 is replaced with the multicore fiber connector 110E according to Embodiment 6.

[0091] The multicore fiber connector 110E is configured by directly connecting the multicore fiber 111E and the multicore fiber 112E in series.

[0092] Figure 13 is a schematic cross-sectional view of the multicore fiber shown in Figure 12 in a plane perpendicular to the longitudinal direction. Figure 13(a) is a cross-sectional view of the multicore fiber 111E, and Figure 13(b) is a cross-sectional view of the multicore fiber 112E.

[0093] The multicore fiber 111E has a configuration in which one of the two core portions 111b of the multicore fiber 111D shown in Figure 11(a) is replaced with core portion 111a. The multicore fiber 112E has a configuration in which one of the two core portions 112b of the multicore fiber 112D shown in Figure 11(b) is replaced with core portion 112a.

[0094] As shown in Figure 12, core section 111a and core section 112a are directly connected in series. Also, core section 111b and core section 112b are directly connected in series.

[0095] Communication devices 200E and 300E are communication devices having a known configuration used in bidirectional communication in optical fiber communication. Communication device 200E is connected to the multicore fiber 111E side of the multicore fiber cable 100E. Communication device 300C is connected to the multicore fiber 112E side of the multicore fiber cable 100E.

[0096] The communication device 200E outputs signal light L11, L31, and L61 in the operating wavelength band to the core section 111a of the multicore fiber 111E. The wavelength of signal light L61 is in the operating wavelength band and may be the same as or different from the wavelengths of signal light L11 and L31. The core section 111a, upon receiving signal light L61, transmits the signal light L61 and outputs it to the core section 112a of the multicore fiber 112E. The core section 112a transmits the signal light L61 after it has been transmitted through the core section 111a.

[0097] The communication device 300E receives signal light L62, which is signal light L61 after it has transmitted core section 111a and then core section 112a. As signal light L61 propagates sequentially through core sections 111a and 112a, its power gradually decreases in accordance with the transmission losses of these core sections. Therefore, the power of signal light L62 is lower than the power of signal light L61.

[0098] In the optical communication system 1000E configured as described above, the influence of nonlinear optical phenomena in bidirectional communication between the communication device 200E and the communication device 300E can be suppressed. In particular, the optical communication system 1000E is a system suitable when the communication capacity from the communication device 200E to the communication device 300E is large. Furthermore, the multicore fiber connector 110E is also suitable from the viewpoint of the identifiability of the core portion in the cross section and the reduction of intercore crosstalk.

[0099] (Embodiment 4) Figure 14 is a schematic diagram of an optical communication system using a multicore fiber connector according to Embodiment 7. The optical communication system 1000F is a one-way optical communication system comprising a multicore fiber cable 100F, a communication device 200F, and a communication device 300F.

[0100] The multicore fiber cable 100F has a configuration in which the multicore fiber connector 110 in the multicore fiber cable 100 of Figure 1 is replaced with the multicore fiber connector 110F according to Embodiment 7.

[0101] The multicore fiber connector 110F is configured by directly connecting the multicore fiber 111F and the multicore fiber 112F in series.

[0102] Figure 15 is a schematic cross-sectional view of the multicore fiber shown in Figure 14 in a plane perpendicular to the longitudinal direction. Figure 15(a) is a cross-sectional view of the multicore fiber 111F, and Figure 15(b) is a cross-sectional view of the multicore fiber 112F.

[0103] The multicore fiber 111F has a configuration in which the core portion 111b of the multicore fiber 111E shown in Figure 13(a) is replaced with the core portion 111a. The multicore fiber 112F has a configuration in which the core portion 112b of the multicore fiber 112E shown in Figure 13(b) is replaced with the core portion 112a.

[0104] As shown in Figure 14, core section 111a and core section 112a are directly connected in series.

[0105] Communication devices 200F and 300F are communication devices having a known configuration used in one-way communication in optical fiber communication. Communication device 200F is connected to the multicore fiber 111F side of the multicore fiber cable 100F. Communication device 300F is connected to the multicore fiber 112F side of the multicore fiber cable 100F.

[0106] The communication device 200F outputs signal light L11, L31, L61, and L71 in the operating wavelength band to each of the core sections 111a of the multicore fiber 111F. The wavelength of signal light L71 is in the operating wavelength band and may be the same as or different from the wavelengths of signal light L11, L31, and L61. The core section 111a, upon receiving signal light L71, transmits the signal light L71 and outputs it to the core section 112a of the multicore fiber 112F. The core section 112a transmits the signal light L71 after it has been transmitted through the core section 111a.

[0107] The communication device 300F receives signal light L72, which is signal light L71 after the core section 111a has been transmitted and then the core section 112a has been transmitted. As signal light L71 propagates sequentially through the core sections 111a and 112a, its power gradually decreases in accordance with the transmission losses of these core sections. Therefore, the power of signal light L72 is lower than the power of signal light L71.

[0108] In the optical communication system 1000F configured as described above, the influence of nonlinear optical phenomena in one-way communication from communication device 200F to communication device 300F can be suppressed.

[0109] (Examples of combinations of effective core cross-sectional areas) Table 1 shows examples of combinations of effective core cross-sectional areas at a wavelength of 1550 nm in core sections with different effective core cross-sectional areas (referred to as core #1 and core #2) in the above embodiment. However, the combinations in Table 1 are just examples, and the present invention is not limited thereto.

[0110] [Table 1]

[0111] (Manufacturing method) The multicore fibers constituting the multicore fiber connector according to this embodiment can be manufactured, for example, using a method called a drilling method, as described below.

[0112] For example, core materials are manufactured using known methods such as VAD (Vapor-phase Axial Deposition) or OVD (Outside Vapor Deposition). A core material is a material that has a portion that will become part of the cladding portion, surrounding the portion that will become the core portion of a multicore fiber.

[0113] Furthermore, a cladding base material is prepared to form the majority of the cladding portion, and voids are made in it equal to the number of core portions for inserting the core base material. After making the voids, the inside of the voids may be cleaned.

[0114] Next, core materials are inserted into each void of the clad material and integrated through heat treatment or other means to form an optical fiber material. Furthermore, multicore fibers are drawn from the optical fiber material using a known drawing furnace.

[0115] (Examples) Two types of two-core multicore fibers (fiber #1 and fiber #2) were manufactured according to the manufacturing method described above. The core matrix was manufactured using the VAD method. The core portion was manufactured to have a trench-type refractive index profile. In this case, the center core was made of pure silica glass, and the intermediate layer, trench layer, and cladding portion were made of silica glass containing fluorine. The outer diameter of the cladding portion was designed to be 125 μm. The distance between the centers of the core portions (core pitch) was designed to be 48 μm.

[0116] Table 2 shows the structural parameters and optical properties of fiber #1 and fiber #2, with the cores of fiber #1 designated as core #1 and core #2, and the cores of fiber #2 designated as core #3 and core #4. The structural parameters and optical properties of each core of the multicore fiber manufactured as described above are shown in Table 2. In Table 2, "center core Δ" is the relative refractive index difference with respect to the center core, and "trench Δ" is the relative refractive index difference with respect to the trench layer. However, "cladding ratio" is a value based on the refractive index of the cladding part, and "pure silica ratio" is a value based on the refractive index of pure silica glass. Also, "cladding Δ" is the relative refractive index difference of the cladding part with respect to the refractive index of pure silica glass. Furthermore, "center core diameter 2a" indicates the outer diameter of the center core, "b / a" indicates the ratio of the outer diameter 2b of the intermediate layer to the center core diameter 2a, and "c / a" indicates the outer diameter of the trench layer 2c to the center core diameter 2a. "λcc" indicates the cutoff wavelength. "Dispersion Slope" indicates the value at the zero-dispersion wavelength. "Bending loss @1550nm / 30mmΦ" refers to the bending loss at a wavelength of 1550nm when a multicore fiber is bent to a diameter of 30mm. Furthermore, the difference in specific refractive index with respect to the cladding portion of the intermediate layer was approximately 0%.

[0117] As shown in Table 2, in fiber #1, the effective core cross-sectional area (Aeff) of core #1 and core #2 is 80 μm². 2 and 125 μm 2 Unlike the previous example, the absolute value of the difference between the two is 80 μm 2 It was more than 10%. Also, in fiber #2, the Aeff was 110 μm between core #3 and core #4. 2 It was the same.

[0118] [Table 2]

[0119] Next, two 50km long fibers #1 were prepared and fusion spliced ​​together so that the cores #1 and #2 of each fiber were connected in series, thereby manufacturing the multicore fiber connector of the embodiment. On the other hand, a 100km long fiber #2 was used as the multicore fiber of the comparative example. The connection loss in the embodiment was 0.1dB.

[0120] Table 3 shows the optical characteristics of the multicore fiber connector in the example and the multicore fiber in the comparative example. Here, "average span loss" is the transmission loss per 100 km of length. However, for the example, "average span loss" is the average of A and B, where A is ((transmission loss in the first core #1) + (transmission loss in the second core #2) + (connection loss between the first core #1 and the second core #2)) and B is ((transmission loss in the first core #2) + (transmission loss in the second core #1) + (connection loss between the first core #2 and the second core #1)). Equivalent Aeff is the effective Aeff of two or more optical fibers, calculated from a comparison with the nonlinearity of NZ-DSF. "XT" is the worst-case value of the intercore crosstalk measured under various conditions.

[0121] As shown in Table 3, the multicore fiber connector of the example had a larger equivalent Aeff compared to the comparative example, resulting in lower optical nonlinearity and better crosstalk characteristics.

[0122] [Table 3]

[0123] In the above embodiments, the number of cores in the multicore fiber constituting the multicore fiber connector is between 2 and 4, but it may be greater than 4, or 19 or less from the viewpoint of core management. However, by using two multicore fibers of equivalent design with 2 or 4 cores each, and connecting cores with different equivalent Aeffs to form the bidirectional optical communication system of Embodiment 1 or Embodiment 5, it is possible to construct a multicore fiber connector that is easy to manufacture while suppressing the effects of nonlinear optical phenomena and crosstalk.

[0124] Furthermore, in the above embodiment, the multicore fiber connector comprises only a first multicore fiber and a second multicore fiber, and the first core portion and the second core portion are directly connected in series, but the present invention is not limited thereto. For example, in another embodiment, the multicore fiber connector may comprise other multicore fibers other than the first multicore fiber and the second multicore fiber, and the first core portion and the second core portion may be indirectly connected in series with the other multicore fiber in between. In this case, a core portion with an effective core cross-sectional area equal to the value in the first core portion may be connected between the first core portion and the second core portion, or a core portion with an effective core cross-sectional area between the value in the first core portion and the value in the second core portion may be connected.

[0125] Furthermore, in the embodiments described above, in the embodiment in which the same core portion is provided within the same multicore fiber, the same core portion may be made into different core portions. In this case, the absolute value of the difference in effective core cross-sectional area between two of the different core portions may be 10% or more greater than the smaller of the two effective core cross-sectional areas of the two core portions at a predetermined wavelength. For example, one core portion 111a in the multicore fiber 111A of the multicore fiber connector 110A according to Embodiment 2 may be replaced with a core portion whose effective cross-sectional area is larger than that of core portion 112a, and the absolute value of the difference between the effective core cross-sectional area of ​​the replaced core portion and the effective core cross-sectional area of ​​core portion 111a may be 10% or more greater than the effective core cross-sectional area of ​​core portion 111a.

[0126] Furthermore, the present invention is not limited by the embodiments described above. Configurations that appropriately combine the above-described components are also included in the present invention. Moreover, further effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the embodiments described above, and various modifications are possible. [Explanation of Symbols]

[0127] 100, 100A, 100B, 100C, 100D, 100E, 100F: Multicore fiber optic cable 110, 110A, 110B, 110C, 110D, 110E, 110F: Multicore fiber connector 111,111A,111B,111C,111D,111E,111F,112,112A,112B,112C,112D,112E,112F: Multicore fiber 111a, 111b, 112a, 112b: Core section 111c, 112c: Clad section 120: Structure 200,200A,200B,200C,200D,200E,200F,300,300A,300B,300C,300D,300E,300F:Communication device 1000, 1000A, 1000B, 1000C, 1000D, 1000E, 1000F: Optical communication system L11,L12,L21,L22,L31,L32,L41,L42,L51,L52,L61,L62,L71,L72: Signal light

Claims

1. A first multicore fiber having a plurality of core portions including a first core portion whose effective core cross-sectional area at a predetermined wavelength is a first value, and a cladding portion surrounding the plurality of core portions, A second multicore fiber having a plurality of core portions including a second core portion whose effective core cross-sectional area at a predetermined wavelength is a second value smaller than the first value, and a cladding portion surrounding the plurality of core portions, Equipped with, The first core and the second core are connected in series. Multicore fiber connector.

2. The multicore fiber comprises only the first multicore fiber and the second multicore fiber. The first core and the second core are directly connected in series. The multicore fiber connector according to claim 1.

3. The first multicore fiber and the second multicore fiber each include at least two core portions, and each core portion includes a core portion in which the absolute value of the difference in the effective core cross-sectional areas of the two core portions at the predetermined wavelength is 10% or more greater than the smaller of the two effective core cross-sectional areas of the two core portions at the predetermined wavelength. The multicore fiber connector according to claim 1.

4. The plurality of core portions of the first multicore fiber include a third core portion whose effective core cross-sectional area at the predetermined wavelength is a third value. The plurality of core portions of the second multicore fiber include a fourth core portion whose effective core cross-sectional area at a predetermined wavelength is a fourth value greater than the third value, The third core section and the fourth core section are connected in series. The multicore fiber connector according to claim 1.

5. The number of cores in the first multicore fiber or the second multicore fiber is 19 or less. The multicore fiber connector according to claim 1.

6. The number of core portions in the first multicore fiber or the second multicore fiber is 2 or more and 4 or less. The multicore fiber connector according to claim 1.

7. In the first multicore fiber or the second multicore fiber, there are no markers in the cladding portion that have a different refractive index from the cladding portion and do not contribute to optical propagation. The multicore fiber connector according to claim 1.

8. A multicore fiber cable including the multicore fiber connector described in claim 1, The first core unit comprises a first communication device that outputs a first signal light, A second communication device that receives the first signal light transmitted from the second core after the first core has been transmitted, An optical communication system equipped with [the necessary components].

9. A multicore fiber cable including the multicore fiber connector described in claim 4, The first core unit comprises a first communication device that outputs a first signal light, A second communication device that receives the first signal light transmitted from the second core after the first core has been transmitted, Equipped with, The second communication device outputs a second signal light to the fourth core unit. The first communication device receives the second signal light that has transmitted the third core after transmitting the fourth core. Optical communication system.

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