Multicore optical fiber and multicore optical fiber design method

Abstract

This multicore optical fiber (FB) comprises: a plurality of cores that include a first core (C1) and a second core (C2); and a cladding (CL) that has a refractive index lower than the refractive index of the plurality of cores and is disposed so as to envelop the plurality of cores. The absolute value of a figure of merit difference (ΔFoM) between the first core (C1) and the second core (C2) is smaller than the range of variation in the signal-to-noise ratio in a receiver that processes signals transmitted through the plurality of cores. The absolute value of a group delay time difference (Δτ) of light between the first core (C1) and the second core (C2) is equal to or greater than a time related to phase noise estimation at the receiver with respect to whichever of the first core (C1) and the second core (C2) has the smaller group delay time (Δτ) of light.

Description

Multi-core optical fiber and design method for multi-core optical fiber

[0001] The present disclosure relates to a multi-core optical fiber and a method for designing a multi-core optical fiber.

[0002] Non-Patent Documents 1-3 disclose a master-slave signal processing method that reuses estimated phase noise information between channels in order to reduce power consumption in digital signal processing associated with noise removal in optical coherent transmission. In the master-slave signal processing method, the signal processing results are affected by the difference in signal quality between channels, so at least the same signal-to-noise ratio is required between channels.

[0003] Non-Patent Document 4 discloses a method for reducing not only the power consumption of signal processing but also the processing time by using a heterogeneous multicore fiber having multiple cores with different group delay times. In the method for reducing processing time, phase noise estimation is performed in a core with a small group delay time in the multicore fiber, and the estimation results are diverted to a core with a large group delay time. In the core with a large group delay time, the waiting time required for phase noise estimation can be reduced, thereby reducing processing time.

[0004] Non-Patent Document 5 discloses a multi-core optical fiber that reduces the group delay time of the guided mode by using a core structure that uses a fluorine-doped glass core or a fluorine-doped glass cladding. On the other hand, Non-Patent Document 6 discloses that fluorine-doped glass contains impurities, which increases the loss coefficient of light due to Rayleigh scattering loss. Therefore, the signal-to-noise ratio of an optical signal guided through a low-delay core deteriorates.

[0005] The signal-to-noise ratio of an optical fiber communication system is influenced by the loss, nonlinear resistance, and chromatic dispersion of the optical fiber. Non-Patent Document 7 discloses that when the difference in figure of merit between optical fibers having two different core structures, calculated by the loss, nonlinear resistance, and chromatic dispersion, is zero, the two optical fibers can achieve the same signal-to-noise ratio.

[0006] MD Feuer et al., IEEE Photonics Technology Letters, vol. 24, no. 21, pp. 1957-2012, Nov. 2012.N. Bai et al., OFC / NFOEC, Anaheim, CA, USA, 2013, pp. 1-3.L. Lundberg et al., Optical Express, vol. 27, issue 16, pp. 22226-22236, Aug. 2019.Y. Sagae et al., Journal of Lightwave technology, vol. 40, no. 1, pp. 215-221, Jan. 2022.Y. Sagae et al., Journal of Lightwave technology, vol. 37, no. 19, pp. 5028-5033, Oct. 2019.M. Ohashi et al., Journal of Lightwave technology, vol. 20, no. 5, pp. 539-543, May. 1992.A. Carena et al., Optical Express, vol. 20, no. 1, pp. 339-334, Jan. 2012.

[0007] According to the multi-core optical fiber disclosed in Non-Patent Document 5, when Rayleigh scattering loss is considered as loss, the difference in figure of merit between the normal core and the low-latency core is about 2 dB, which still results in a significant difference in transmission performance. Therefore, the signal-to-noise ratio differs between the signals transmitted through the normal core and the signals transmitted through the low-latency core, making it difficult to apply a master-slave signal processing scheme. Therefore, there is a problem that the signal processing power and the signal processing delay cannot be sufficiently reduced.

[0008] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a multi-core optical fiber and a design method for a multi-core optical fiber that can realize reduction in signal processing power and signal processing delay by applying master-slave signal processing using signals transmitted through low-latency cores.

[0009] In order to solve the above-mentioned problems, a multi-core optical fiber according to the present disclosure includes multiple cores including a first core and a second core, and a cladding having a refractive index lower than that of the multiple cores and arranged to enclose the multiple cores, wherein the absolute value of the difference in figure of merit between the first core and the second core is smaller than the fluctuation range of the signal-to-noise ratio at a receiver that processes signals transmitted through the multiple cores, and the absolute value of the optical group delay difference between the first core and the second core is equal to or greater than the time required for phase noise estimation at the receiver for the core having the smaller optical group delay time of the first core or the second core.

[0010] Furthermore, a design method for a multi-core optical fiber according to the present disclosure is a design method for a multi-core optical fiber including multiple cores including a first core and a second core, and a cladding having a refractive index lower than that of the multiple cores and arranged to encompass the multiple cores, wherein the absolute value of the figure of merit difference between the first core and the second core is set to be smaller than the fluctuation range of the signal-to-noise ratio in a receiver that processes signals transmitted through the multiple cores, and the absolute value of the optical group delay difference between the first core and the second core is set to be equal to or greater than the time related to phase noise estimation in the receiver for the core having the smaller optical group delay time of the first core or the second core.

[0011] According to the present disclosure, it is possible to provide a multi-core optical fiber and a design method for a multi-core optical fiber that can achieve a reduction in signal processing power and a reduction in signal processing delay by applying master-slave signal processing using a signal transmitted through a low-latency core.

[0012] FIG. 1B is a cross-sectional view showing the structure of a multi-core optical fiber (SI type) according to an embodiment of the present disclosure. FIG. 1C is a schematic view showing the refractive index distribution in the structure shown in FIG. 1A. FIG. 1D is a cross-sectional view showing the structure of a multi-core optical fiber (with common depression) according to an embodiment of the present disclosure. FIG. 2E is a schematic view showing the refractive index distribution in the structure shown in FIG. 2A. FIG. 1F is a cross-sectional view showing the structure of a multi-core optical fiber (trench-assisted type) according to an embodiment of the present disclosure. FIG. 3G is a schematic view showing the refractive index distribution in the structure shown in FIG. 3A. FIG. 3G is a cross-sectional view showing the structure of a multi-core optical fiber (W-type) according to an embodiment of the present disclosure. FIG. 4A is a schematic view showing the refractive index distribution in the structure shown in FIG. 4A. FIG. 4F is a first characteristic diagram showing the dependency of differential group delay and figure of merit difference on core structure parameters. FIG. 4G is a second characteristic diagram showing the dependency of differential group delay and figure of merit difference on core structure parameters. １ 1 is a diagram showing the relationship between the coefficient K and the effective cross-sectional area of ​​the second core. ２ 1 is a diagram showing the relationship between the coefficient K and the effective cross-sectional area of ​​the second core. ３ 10A and 10B are diagrams illustrating the relationship between the differential group delay (DGD) and the low-latency core arrangement; 10B and 10C are diagrams illustrating the relationship between the differential group delay (DGD) and the low-latency core arrangement; 10C and 10D are diagrams illustrating the relationship between the differential group delay (DGD) and the low-latency core arrangement;

[0013] Next, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description, the same components are designated by the same reference numerals and redundant description will be omitted.

[0014] [1. Structure of the multi-core optical fiber] The multi-core optical fiber FB according to the present disclosure includes multiple cores including a first core C1 and a second core C2, and a cladding CL that has a refractive index lower than that of the multiple cores and is arranged to encompass the multiple cores.

[0015] Here, the absolute value of the figure of merit difference between the first core C1 and the second core C2 is designed to be smaller than a predetermined value. Also, the absolute value of the optical differential group delay between the first core C1 and the second core C2 is designed to be equal to or greater than the time required for estimating the phase noise for the core with the shorter optical group delay between the first core C1 and the second core C2. The design of the "figure of merit difference" and the design of the "differential group delay" will be described later.

[0016] In the following, as an example, a case where the multi-core optical fiber FB includes four cores (multiple cores) is shown, but the number of cores is not limited to this example. Furthermore, the core structure of the multi-core optical fiber FB may be various structures. For example, it may be an SI type, a common depressed type, a trench-assisted type, or a W type.

[0017] 1-1. SI-type structure] Fig. 1A is a cross-sectional view showing the structure of a multi-core optical fiber (SI-type) according to an embodiment of the present disclosure. Fig. 1B is a schematic diagram showing the refractive index distribution in the structure shown in Fig. 1A.

[0018] The refractive index of the cladding CL is constant, and the radius and refractive index of each core may be different. By appropriately designing the radii and refractive indices of at least two of the multiple cores, the first core C1 and the second core C2, it is possible to satisfy predetermined conditions for the "figure of merit difference" and the "differential group delay time." In FIG. 1B, the radius of the first core C1 is a １ , the radius of the second core C2 is a ２ , the relative refractive index difference of the first core C1 with respect to the cladding CL is Δ １ , the relative refractive index difference of the second core C2 with respect to the cladding CL is Δ ２ It is shown that this is the case.

[0019] [1-2. Structure with Common Depression] Fig. 2A is a cross-sectional view showing the structure of a multi-core optical fiber (with a common depressed region) according to an embodiment of the present disclosure. Fig. 2B is a schematic diagram showing the refractive index distribution in the structure shown in Fig. 2A.

[0020] A common depressed region DP is arranged to encompass the multiple cores, and a cladding CL is arranged to encompass the common depressed region DP. As a result, the cladding CL encompasses the multiple cores.

[0021] The relative refractive index difference of the common depressed region DP with respect to the cladding CL is Δ Ｄand the refractive index of the common depressed region DP is smaller than the refractive index of the cladding CL. The refractive index of the common depressed region DP is the same for each core, and the radius and refractive index of each core may be different for each core. By appropriately designing the radii and refractive indexes of at least two of the multiple cores, the first core C1 and the second core C2, it is possible to satisfy predetermined conditions for the "figure of merit difference" and the "differential group delay time."

[0022] In addition, the core distance Λ and the relative refractive index difference Δ Ｄ By appropriately designing the above, it is possible to design the inter-core crosstalk and bending loss of each core for each core. In addition, the common depressed region DP provides strong light confinement, which makes it possible to suppress inter-core crosstalk compared to the SI type.

[0023] [1-3. Trench-assisted structure] Fig. 3A is a cross-sectional view showing the structure of a multi-core optical fiber (trench-assisted) according to an embodiment of the present disclosure. Fig. 3B is a schematic diagram showing the refractive index distribution in the structure shown in Fig. 3A.

[0024] The trench-assisted core has an inner cladding region outside the core and a trench region TR concentric with the core outside the inner cladding region, the refractive index of the trench region TR being smaller than the refractive index of the inner cladding region and the refractive index of the cladding CL.

[0025] The refractive index, width, and inner diameter of the trench region TR arranged around the core may be different for each core. Similarly, the refractive index and outer diameter of the inner cladding region arranged around the core may be different for each core. By appropriately designing the radii and refractive indices of at least two of the multiple cores, the first core C1 and the second core C2, it is possible to satisfy predetermined conditions for the "figure of merit difference" and the "differential group delay time."

[0026] In FIG. 3B, the relative refractive index difference of the trench region TR arranged around the first core C1 with respect to the cladding CL is Δ ｔ１ , the relative refractive index difference of the trench region TR arranged around the second core C2 with respect to the cladding CL is Δｔ２ The core distance Λ and the relative refractive index difference Δ ｔ１ , Δ ｔ２ By appropriately designing the above, it is possible to design the inter-core crosstalk, bending loss of each core, and cutoff wavelength for each core.

[0027] [1-4. W-type structure] Fig. 4A is a cross-sectional view showing the structure of a multi-core optical fiber (W-type) according to an embodiment of the present disclosure. Fig. 4B is a schematic diagram showing the refractive index distribution in the structure shown in Fig. 4A.

[0028] The W-shaped core has a low refractive index region LR concentric with the core, the refractive index of which is smaller than that of the cladding CL.

[0029] The refractive index and outer diameter of the low-refractive-index region LR disposed around the core may be different for each core. By appropriately designing the radius and refractive index of at least two of the multiple cores, the first core C1 and the second core C2, it is possible to satisfy predetermined conditions for the "figure of merit difference" and the "differential group delay time."

[0030] In FIG. 4B, the relative refractive index difference of the low refractive index region LR arranged around the first core C1 with respect to the cladding CL is Δ ｄ１ , the relative refractive index difference of the low refractive index region LR arranged around the second core C2 with respect to the cladding CL is Δ ｄ２ The core distance Λ and the relative refractive index difference Δ ｄ１ , Δ ｄ２ By appropriately designing the above, it is possible to design the inter-core crosstalk, bending loss of each core, and cutoff wavelength for each core.

[0031] [2. Core Design Area] Next, we consider the conditions that the "figure of merit difference" and "differential group delay time" must satisfy. Here, if the absolute value of the figure of merit difference between the first core C1 and the second core C2 is set to be smaller than the fluctuation range of the signal-to-noise ratio in the receiver that processes signals transmitted through multiple cores, it becomes possible to apply the master-slave signal processing method.

[0032] Furthermore, if the absolute value of the optical group delay time difference between the first core C1 and the second core C2 is set to be equal to or greater than the time required for phase noise estimation at the receiver for the core with the smaller optical group delay time out of the first core C1 and the second core C2, the waiting time required for phase noise estimation can be reduced for the core with the larger group delay time. As a result, the processing time can be reduced. For example, if the difference in reception time of the optical signal between the cores, i.e., the absolute value of the optical propagation delay time difference, is 1 / (N Ｓ L Ｓ ) μs / km or more (however, the number of transmission spans of the multi-core optical fiber FB is N Ｓ As a result, the signal processing power consumption and the signal processing delay can be reduced sufficiently.

[0033] The figure of merit difference ΔFoM between the first core C1 and the second core C2 is defined by the following equation.

[0034] Here, the chromatic dispersion, effective length, nonlinear refractive index, effective cross section, and loss coefficient of the first core C1 are respectively defined as D １ , L ｅｆｆ１ , n ２１ , A １ , and α １ The wavelength dispersion, effective length, nonlinear refractive index, effective cross-sectional area, and loss coefficient of the second core C2 are respectively set as D ２ , L ｅｆｆ２ , n ２２ , A ２ , and α ２ Furthermore, the span length of the multi-core optical fiber FB is set to L Ｓ It states that:

[0035] For example, Non-Patent Document 1 discloses the signal-to-noise ratio characteristics of signal quality in a multi-core optical fiber. According to the signal-to-noise ratio characteristics, the signal-to-noise ratio that achieves the desired signal quality differs by about 1 dB between cores of the same design.

[0036] Therefore, the signal-to-noise ratio at the receiver that processes the signal transmitted through multiple cores can fluctuate by about 1 dB due to electrical noise originating in the receiver. Therefore, by satisfying the relationship "-1 dB ≦ ΔFoM ≦ 1 dB," the effect of optical fiber characteristics on signal quality can be suppressed to a negligible level.

[0037] 5 is a first characteristic diagram showing the dependence of the differential group delay time and the difference in figure of merit on the core structure parameters. ２ is 80 μm ２ In FIG. 5, the vertical axis represents the effective cross-sectional area A of the first core C1. １ Also, the horizontal axis "Δ １ -Δ ２ " indicates the relative refractive index difference of the first core C1 with respect to the second core C2. The group delay time of the first core C1 is τ １ , the group delay time of the second core C2 is τ ２ The solid line shows the differential group delay Δτ = τ １ -τ ２ In the calculation, the guided mode LP in the first core C1 and the second core C2 is １１ The cutoff wavelength of the laser beam is set to 1530 nm or less.

[0038] In the example shown in Figure 5, the first core C1 transmits a low-delay signal because its group delay time is small. The dashed line indicates the figure of merit difference ΔFoM. In the shaded area shown in Figure 5, the relationship "-1 dB ≦ ΔFoM ≦ 1 dB" is realized.

[0039] In the above description, the design region where "-1 dB≦ΔFoM≦1 dB" has been described, but actual operation is not limited to this numerical range. The allowable range of ΔFoM may be changed as appropriate depending on the transmission capacity, transmission distance, performance of the signal processing device, etc. to which the multi-core optical fiber FB is applied. For example, when the transmission capacity or transmission distance is small, the allowable range of ΔFoM becomes wider.

[0040] 6 is a second characteristic diagram showing the dependence of the group delay time difference and the figure of merit difference on the core structure parameters. ２ is 110 μm ２In FIG. 6, the vertical axis represents the effective cross-sectional area A of the first core C1. １ Also, the horizontal axis "Δ １ -Δ ２ " indicates the relative refractive index difference of the first core C1 with respect to the second core C2. The group delay time of the first core C1 is τ １ , the group delay time of the second core C2 is τ ２ The solid line shows the differential group delay Δτ = τ １ -τ ２ The dashed line indicates the figure of merit difference ΔFoM. The guided mode LP in the first core C1 and the second core C2 １１ The cutoff wavelength of the laser beam is set to 1530 nm or less.

[0041] By comparing FIG. 5 and FIG. 6, the effective cross-sectional area A ２ It can be seen that, as the effective cross-sectional area A of the first core C1 increases, the design range shown by the hatched area fluctuates in a direction in which the absolute value of the relative refractive index difference of the first core C1 with respect to the second core C2 decreases. １ It can be seen that fluctuates in the increasing direction.

[0042] Therefore, by clearly indicating the expression of the boundary line indicated by "ΔFoM=-1 dB" in the shaded area, the design range of the core is clarified.

[0043] For simplicity, the relative refractive index difference Δ ｃｏｒｅ About "Δ ｃｏｒｅ =Δ １ -Δ ２ ", the boundary line relationship indicated by "ΔFoM=-1 dB" is expressed by the following formula.

[0044] Here, the coefficient K １ and coefficient K ２ is the effective cross-sectional area A of the second core C2 ２ is a coefficient that depends on

[0045] Furthermore, the relationship of the boundary line indicated by "ΔFoM=-1 dB" with respect to the differential group delay Δτ is expressed by the following equation.

[0046] Here, the coefficient K ３is a coefficient that depends on the differential group delay Δτ.

[0047] FIG. 7 shows the coefficient K １ 8 is a graph showing the relationship between the coefficient K and the effective cross-sectional area of ​​the second core. ２ 9 is a diagram showing the relationship between the coefficient K and the effective cross-sectional area of ​​the second core. ３ FIG. 10 is a diagram illustrating the relationship between the differential group delay and the

[0048] Coefficient K １ is the effective cross-sectional area A of the second core C2 ２ The coefficient K １ and the effective cross-sectional area A of the second core C2 ２ The relationship is expressed by the following equation:

[0049] Coefficient K ２ is the effective cross-sectional area A of the second core C2 ２ It decreases linearly with the coefficient K ２ and the effective cross-sectional area A of the second core C2 ２ The relationship is expressed by the following equation:

[0050] Coefficient K ３ decreases linearly with respect to the differential group delay Δτ. ３ The relationship between the differential group delay time Δτ and the

[0051] From the above, the effective cross-sectional area A of the second core C2 ２ and the required value of Δτ based on the transmission distance L, ｃｏｒｅ and the effective cross-sectional area A of the first core C1 １ The design conditions are expressed by the following formula: and

[0052] By realizing a low-latency core that satisfies the above formula, it is possible to apply a signal processing load reduction technique using a low-latency signal to the multi-core optical fiber FB.

[0053] [3. Arrangement of Low-Delay Cores] Fig. 10 is a diagram showing a first example of the arrangement of low-delay cores. At least one low-delay core LC that satisfies the structural conditions shown in Figs. 5 to 9 is arranged in the multi-core optical fiber FB. Here, the core structure of the multi-core optical fiber FB may be of various types. For example, it may be an SI type, a common depressed type, a trench-assisted type, or a W type.

[0054] All cores transmit signals in the same direction, and the phase noise information estimated by the low-latency core LC can be diverted to all other normal cores NC. Therefore, when there are N normal cores NC, the power consumption used for phase noise estimation is 1 / N of that when the noise information is not diverted.

[0055] Fig. 11 is a diagram showing a second example of the arrangement of low-latency cores. At least two low-latency cores LC that satisfy the structural conditions shown in Figs. 5 to 9 are arranged in the multi-core optical fiber FB. Here, the core structure of the multi-core optical fiber FB may be of various types. For example, it may be an SI type, a common depressed type, a trench-assisted type, or a W type.

[0056] Assume that a pair of a low-latency core LC and a normal core NC is created, and bidirectional transmission is performed by switching the signal transmission direction between each pair. For example, in FIG. 11 , the signal transmission direction within pair P1 is the same. Also, the signal transmission direction within pair P1 is the same. On the other hand, the signal transmission direction within pair P1 is opposite to the signal transmission direction within pair P2.

[0057] In this case, the power consumption used for phase noise estimation is 1 / 2 of that when noise information is not diverted. Also, compared to the example shown in Figure 10, bidirectional transmission can reduce crosstalk between the cores of pair P1 and pair P2 by about -20 dB. Therefore, applicability to long-distance transmission lines can be expanded.

[0058] [Effects of the Embodiments] As described above in detail, the multi-core optical fiber according to the present disclosure comprises multiple cores including a first core and a second core, and a cladding having a refractive index lower than that of the multiple cores and arranged to enclose the multiple cores. The absolute value of the figure of merit difference between the first core and the second core is smaller than the fluctuation range of the signal-to-noise ratio in a receiver that processes signals transmitted through the multiple cores. The absolute value of the optical group delay difference between the first core and the second core is equal to or greater than the time required for phase noise estimation in the receiver for the core having the smaller optical group delay time of the first core or the second core.

[0059] This allows for master-slave signal processing using signals transmitted through the low-latency core, thereby reducing signal processing power and delay, and thereby improving the efficiency of optical communication systems.

[0060] In the multi-core optical fiber according to the present disclosure, the figure of merit difference ΔFoM is When the number of transmission spans of the multi-core optical fiber is N, the relationship "-1 dB ≦ ΔFoM ≦ 1 dB" is satisfied. Ｓ The absolute value of the differential group delay is 1 / (N Ｓ L Ｓ ) μs / km or more.

[0061] Here, the chromatic dispersion, effective length, nonlinear refractive index, effective cross section, and loss coefficient of the first core are respectively represented by D １ , L ｅｆｆ１ , n ２１ , A １ , and α １ The wavelength dispersion, effective length, nonlinear refractive index, effective cross section, and loss coefficient of the second core are respectively defined as D ２ , L ｅｆｆ２ , n ２２ , A ２ , and α ２ The span length of the multi-core optical fiber is L Ｓ It was decided.

[0062] This clarifies specific design conditions for the first core and the second core, making it possible to more reliably achieve reductions in signal processing power and signal processing delays.

[0063] Furthermore, the multi-core optical fiber according to the present disclosure has and, where the differential group delay is Δτ, in the range of −10 ns / km≦Δτ<0 ns / km, The above condition may be satisfied.

[0064] Here, the guided mode LP in the first core and the second core １１ The cutoff wavelength of the cladding is set to 1530 nm or less. ０ and the refractive index of the first core is n １ and the refractive index of the second core is n ２ and the relative refractive index difference Δ ｃｏｒｅ = (n １ ２ -n ０ ２ ) / 2n １ ２ -(n ２ ２ -n ０ ２ ) / 2n ２ ２ <0%.

[0065] This clarifies specific design conditions for the first core and the second core, making it possible to more reliably achieve reductions in signal processing power and signal processing delays.

[0066] Furthermore, a design method for a multi-core optical fiber according to the present disclosure is a design method for a multi-core optical fiber including multiple cores including a first core and a second core, and a cladding having a refractive index lower than that of the multiple cores and arranged to encompass the multiple cores, wherein the absolute value of the figure of merit difference between the first core and the second core is set to be smaller than the fluctuation range of the signal-to-noise ratio in a receiver that processes signals transmitted through the multiple cores, and the absolute value of the optical group delay difference between the first core and the second core is set to be equal to or greater than the time related to phase noise estimation in the receiver for the core having the smaller optical group delay time of the first core or the second core.

[0067] This allows for master-slave signal processing using signals transmitted through the low-latency core, thereby reducing signal processing power and delay, and thereby improving the efficiency of optical communication systems.

[0068] Although the contents of the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these descriptions, and various modifications and improvements are possible, which will be apparent to those skilled in the art. The descriptions and drawings that form part of this disclosure should not be understood as limiting the present disclosure. Various alternative embodiments, examples, and operating techniques will be apparent to those skilled in the art from this disclosure.

[0069] Of course, the present disclosure includes various embodiments not described herein. Therefore, the technical scope of the present disclosure is defined only by the invention-specifying matters according to the scope of the claims that are appropriate from the above description.

[0070] C1 First core C2 Second core CL Cladding DP Common depressed region FB Multi-core optical fiber LC Low delay core LR Low refractive index region NC Normal core P1, P2 Pair TR Trench region

Claims

1. A multi-core optical fiber comprising: multiple cores including a first core and a second core; and a cladding having a refractive index lower than that of the multiple cores and arranged to encompass the multiple cores, wherein the absolute value of the difference in figure of merit between the first core and the second core is smaller than the fluctuation range of the signal-to-noise ratio in a receiver that processes signals transmitted through the multiple cores, and the absolute value of the optical group delay time difference between the first core and the second core is equal to or greater than the time related to phase noise estimation in the receiver for the core of the first core or the second core having the smaller optical group delay time.

2. The chromatic dispersion, effective length, nonlinear refractive index, effective cross section, and loss coefficient of the first core are respectively defined as D １ , L ｅｆｆ１ , n ２１ , A １ , and α １ The wavelength dispersion, effective length, nonlinear refractive index, effective cross-sectional area, and loss coefficient of the second core are respectively defined as D ２ , L ｅｆｆ２ , n ２２ , A ２ , and α ２ The span length of the multi-core optical fiber is L Ｓ The figure of merit difference ΔFoM is When the number of transmission spans of the multi-core optical fiber is N, the following relationship is satisfied: -1 dB≦ΔFoM≦1 dB. Ｓ The absolute value of the differential group delay is 1 / (N Ｓ L Ｓ 2. The multi-core optical fiber according to claim 1, wherein the optical fiber has a transmission loss of 100 s / km or more.

3. Guided mode LP in the first core and the second core １１ The cutoff wavelength of the cladding is 1530 nm or less, and the refractive index of the cladding is n ０ and the refractive index of the first core is n １ and the refractive index of the second core is n ２ and the relative refractive index difference Δ ｃｏｒｅ = (n １ ２ -n ０ ２ ) / 2n １ ２ -(n ２ ２ -n ０ ２ ) / 2n ２ ２ In the range of <0%, where the differential group delay time is Δτ, and in the range of −10 ns / km≦Δτ<0 ns / km, The multi-core optical fiber according to claim 2 , which satisfies the following:

4. A design method for a multi-core optical fiber comprising: multiple cores including a first core and a second core; and a cladding having a refractive index lower than that of the multiple cores and arranged to encompass the multiple cores, wherein the absolute value of the figure of merit difference between the first core and the second core is set to be smaller than the fluctuation range of the signal-to-noise ratio in a receiver that processes signals transmitted through the multiple cores; and the absolute value of the optical group delay time difference between the first core and the second core is set to be equal to or greater than the time related to the phase noise estimation in the receiver for the core of the first core or the second core having the smaller optical group delay time.

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