Optical communication system of MS-CPE transmission mode

Abstract

The present application provides an optical fiber. The present application aims at realizing a low-delay core capable of being applied to a main channel of an MS-CPE transmission method by a general refractive index distribution structure. The optical fiber of the present application is a single-mode optical fiber having an SI-type refractive index distribution structure, a relative refractive index difference Δ(%) of a cladding region with respect to a core region, a radius a(μm) of the core region, and a group delay time difference Δ τ satisfy "Mathematical Formula 19" and "Mathematical Formula 20", or have a W-type refractive index distribution structure, a mode field diameter MFD is 9.5-10.1 μm, a relative refractive index difference Δ1(%) of a low-refractive index layer with respect to a core, a relative refractive index difference Δ2(%) of a cladding region with respect to the core, a core radius a1, and a group delay time difference Δ τ satisfy "Mathematical Formula 41".

Description

Technical Field

[0001] This invention relates to an optical fiber for optical communication. Background Technology

[0002] In current long-distance transmission networks, optical coherent communication technology has achieved a leap in capacity. In optical coherent communication, information about the phase state of light is allocated. The phase state of the signal light varies depending on the wavelength dispersion of the optical fiber constituting the transmission channel and the phase fluctuations of the signal source, thus degrading signal quality. Therefore, in optical coherent communication, digital signal processing (DSP) for phase noise removal in the receiver is essential. Current DSPs ensure sufficient signal quality, but they also present the challenge of increased computational costs within the device.

[0003] To address this issue, Non-Patent Literature 1 proposes the following approach: One channel in the transmission channel is used as the master channel for carrier phase estimation, and the estimation results are then applied to other transmission channels for phase correction. This transmission method is also known as Master-Slave CPE (MS-CPE). MS-CPE can reduce the signal processing cost of phase estimation by the same amount as the slave channel.

[0004] On the other hand, in recent years, the requirements for reducing communication latency have increased in optical communications. Non-Patent Document 2 reports that the DSP processing time in optical coherent communication technology is about 1 μs. Reducing the latency of this DSP processing is also one of the solutions to the requirement of reducing communication latency. Therefore, Non-Patent Document 3 indicates the possibility of applying a transmission channel with reduced group delay time to the main channel of the MS-CPE, thereby reducing the DSP processing latency in the secondary channel.

[0005] Existing technical documents Non-patent literature 1: MDFeuer, LENelson, Non-patent literature 2: V. Bobrovs, S. Spolitis and G. Ivanovs, “Latency causes and reduction in optical metro networks,” Proceedings in SPIE 9009, 90080C (2014) Non-patent document 3: Y.Sagae, T.Matsui, T.Sakamoto and K.Nakajima, "Multi-functional multi-core fiber based long-haul transmission system with lowerDSP complexity," ECOC 2019, pp.1-4 (2019)

[0006] In the MS-CPE of Non-Patent Document 3, a multi-core fiber with a core whose refractive index distribution is reduced to about 1 μm and a stepped cladding is used as the optical fiber in a transmission channel that reduces group delay time. However, the core with the reduced refractive index distribution is prone to refractive index distribution deformation due to spinning tension and other factors during fiber manufacturing (making it difficult to obtain the desired effect of MS-CPE), posing a manufacturability challenge. Summary of the Invention

[0007] Therefore, in order to solve the aforementioned problems, the object of the present invention is to provide an optical fiber that improves manufacturability for use as an MS-CPE.

[0008] To achieve the above objectives, the optical fiber of the present invention uses a low-latency core as the main channel, which uses a typical refractive index distribution employed in general optical fibers.

[0009] Specifically, the first optical fiber of the present invention is an optical fiber present in an optical communication system using the MS-CPE transmission method, characterized in that... The core of radius a (μm) used in the main channel and the cladding with a relative refractive index difference Δ (%) relative to the core are of the step refractive index (SI) type refractive index distribution structure and satisfy the mathematical formula C1. [Mathematical expression C1] Wherein, Δτ (ns / km) is the group delay time difference between the master channel and the slave channel, which is the value of mathematical formula C2 when the optical signal is transmitted in the master channel and the slave channel of the optical communication system, and when the optical signal is transmitted over a distance L (km). [Mathematical expression C2]

[0010] Furthermore, the second optical fiber of the present invention is an optical fiber included in an optical communication system using MS-CPE transmission, characterized in that... The core of radius a1 (μm) for the main channel, the low refractive index layer surrounding the core and having a relative refractive index difference Δ1 (%) relative to the core, and the cladding having a relative refractive index difference Δ2 (%) relative to the core are W-type refractive index distribution structures and satisfy mathematical formula C3. [Mathematical expression C3] Wherein, MFD is the mode field diameter of the core (μm), Δτ (ns / km) is the group delay time difference between the main channel and the slave channel, which is the value of mathematical formula C2 when the optical signal is transmitted in the main channel and the slave channel of the optical communication system, and the transmission distance L (km).

[0011] The optical fiber of the present invention improves manufacturability by constructing a low-delay core with a universal refractive index distribution structure. Therefore, the present invention provides an optical fiber with improved manufacturability for use as an MS-CPE.

[0012] Furthermore, the optical fiber of the present invention is characterized in that the refractive index of the core is lower than that of pure silica glass. For example, the first optical fiber of the present invention is characterized in that the radius a (μm) satisfies mathematical formula C4, and the minimum group delay time difference Δτ is minimized. min (nm / km) satisfies mathematical formula C5, where the relative refractive index difference Δ of the core relative to pure quartz glass is... F (%) satisfies mathematical expression C6. By reducing the refractive index of the core, a larger Δτ can be achieved, which expands the application area of ​​MS-CPEs using low-delay signals. [Mathematical expression C4] [Mathematical expression C5] [Mathematical expression C6] Wherein, MFD is the mode field diameter (μm) of the core.

[0013] Furthermore, the optical fiber of the present invention is a multi-core optical fiber, which has multiple cores, one of which is the core used for the main channel.

[0014] Furthermore, the inventions described above can be combined in combination as much as possible.

[0015] The present invention provides an optical fiber that improves manufacturability for use as an MS-CPE. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating the required delay reduction for the transmission channel length of a low-latency main channel with a group delay time for achieving MS-CPE. Figure 2 This is a diagram illustrating a basic configuration example of a SI-type low-latency main channel suitable for submarine optical communication systems. Figure 3 This is a diagram illustrating the designable range of the core radius for the SI-type low-latency main channel suitable for submarine optical communication systems. Figure 4 This is a graph illustrating the Δτ dependence of K0 for the SI-type low-latency main channel applicable to submarine optical communication systems. Figure 5 This is a graph illustrating the Δτ dependence of K1 for the SI-type low-latency main channel applicable to submarine optical communication systems. Figure 6 This is a graph illustrating the Δτ dependence of K2 for the SI-type low-latency main channel applicable to submarine optical communication systems. Figure 7 This is a diagram illustrating an example of the design region (MFD=9.5μm) for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 8 This is a graph illustrating the a2 / a1 dependence of the optical characteristics of the W-type low-latency main channel suitable for submarine optical communication systems. Figure 9 This is a diagram illustrating the designable range of the core radius for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 10 This is a graph illustrating the Δτ dependence of K3 for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 11 This is a diagram illustrating an example of the design region (MFD=9.8μm) for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 12 This is a diagram illustrating the designable range of the core radius for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 13 This is a graph illustrating the Δτ dependency of K4 for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 14 This is a diagram illustrating an example of the design region (MFD=10.0μm) for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 15 This is a diagram illustrating the designable range of the core radius for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 16 This is a graph illustrating the Δτ dependency of K5 for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 17 This is a diagram illustrating the designable range of the core radius for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 18 This is a graph illustrating the MFD dependency of K6 for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 19 This is a graph illustrating the MFD dependency of K7 for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 20 This is a graph illustrating the MFD dependency of K8 for a W-type low-latency main channel suitable for submarine optical communication systems. Figure 21 This is a diagram illustrating an example of the design region (MFD=9.5μm) for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 22 This is a diagram illustrating the designable range of ΔF for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 23 This is a graph illustrating the Δτ dependence of K9 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 24 This is a diagram illustrating an example of the design region (MFD=15.0μm) for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 25 This is a diagram illustrating the designable range of ΔF for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 26 This is a graph illustrating the Δτ dependence of K10 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 27 This is a graph illustrating the MFD dependence of the minimum designable core radius for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 28 This is a graph illustrating the MFD dependence of the maximum designable core radius for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 29 This is a graph illustrating the MFD dependence of the designable minimum Δτ for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 30 This is a graph illustrating the MFD dependence of K11 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 31 This is a graph illustrating the MFD dependence of K12 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 32 This is a graph illustrating the MFD dependence of K13 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 33 This is a graph illustrating the MFD dependence of K14 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 34 This is a graph illustrating the MFD dependence of K15 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 35 This is a graph illustrating the MFD dependence of K16 for a SI-type fluorine-doped low-latency main channel suitable for submarine optical communication systems. Figure 36 This is a diagram illustrating an example of the design region (MFD=9.5μm) for a SI-type fluorine-doped low-latency main channel suitable for terrestrial optical communication systems. Figure 37 This is a diagram illustrating the designable range of ΔF for a SI-type fluorine-doped low-latency main channel suitable for terrestrial optical communication systems. Figure 38 This is a diagram illustrating an example of the design region (MFD=15.0μm) for a SI-type fluorine-doped low-latency main channel suitable for terrestrial optical communication systems. Figure 39 This is a graph illustrating the Δτ dependence of the ΔF design range for a SI-type fluorine-doped low-latency main channel suitable for terrestrial optical communication systems. Figure 40 This is a graph illustrating the MFD dependence of the minimum designable core radius for a SI-type fluorine-doped low-latency main channel suitable for terrestrial optical communication systems. Figure 41 This is a graph illustrating the MFD dependence of the designable minimum Δτ for a SI-type fluorine-doped low-latency main channel suitable for terrestrial optical communication systems. Figure 42 This is a diagram illustrating the multi-core optical fiber of the present invention. Figure 43 This is a diagram illustrating the multi-core optical fiber of the present invention. Figure 44 This is a diagram illustrating the multi-core optical fiber of the present invention. Figure 45 This is a diagram illustrating the multi-core optical fiber of the present invention. Figure 46This is a diagram illustrating the multi-core optical fiber of the present invention. Figure 47 This is a diagram illustrating the multi-core optical fiber of the present invention. Figure 48 This is a diagram illustrating the design region of the intercore distance and refractive index difference of the low-refractive-index layer in the multi-core optical fiber of the present invention. Figure 49 This is a diagram illustrating an example of the structure of the multi-core optical fiber of the present invention. Figure 50 This is a diagram illustrating an optical communication system that uses the optical fiber of the present invention as an optical transmission channel. Figure 51 This is a diagram illustrating the refractive index distribution of SI-type optical fiber. Figure 52 This is a diagram illustrating the refractive index distribution of a W-type optical fiber. Figure 53 This is a flowchart illustrating the optical fiber design method of the present invention. Detailed Implementation

[0017] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to these embodiments. Furthermore, in this specification and the accompanying drawings, elements with the same reference numerals denote identical constituent elements.

[0018] [Basic conditions] Figure 50 This diagram illustrates an optical communication system 301 employing MS-CPE transmission. The optical communication system 301 includes a transmitter 11, a receiver 12, and an optical transmission channel 50. The optical transmission channel 50 can be a single-core optical fiber, a multi-core optical fiber, a ribbon fiber with multiple fiber cores (single-mode) arranged side-by-side, or an optical cable containing multiple fiber cores (single-mode). In the case of a multi-core optical fiber, any one core is used as the master channel, and the other cores are used as slave channels. In the case of a ribbon fiber or optical cable, any one fiber core is used as the master channel, and the other fiber cores are used as slave channels. In the case of a single-core optical fiber, any wavelength is used as the master channel, and the other wavelengths are used as slave channels.

[0019] It is known that the DSP processing time is approximately 1 μs. To effectively reduce the DSP processing time of the slave channel using the MS-CPE that utilizes the low-latency signal shown in Non-Patent Document 3, it is preferable that the signal arrival time difference between the low-latency master channel and the slave channel in the receiver is greater than 1 μs. Therefore, if the signal arrival time difference between the master and slave channels in the receiver is set to s (μs), and the low-latency master channel group delay time is set to τ... m (μs / km), the group delay time of the channel is set to τ. s(μs / km), let the transmission system length (transmission channel length) be L (km), then τ is determined by equation (10). m Requirements and conditions. [Mathematical Expression 10]

[0020] If the group delay time difference between the slave channel and the master channel is set as Δτ (ns / km), then equation (10) becomes as follows. [Mathematical Expression 11]

[0021] Figure 1 This is a graph illustrating the calculated L-dependence of Δτ when s = 1 μs. MS-CPEs using low-latency signals can be achieved in the region below the straight line, where the group delay time difference is smaller than the straight line. Here, in submarine optical communication systems exceeding 1000 km, Δτ is required to be below -1.0 ns / km, and in land relay systems exceeding approximately 300 km, Δτ is required to be below -3.4 ns / km.

[0022] [Implementation Method 1] In this embodiment, a design method for realizing a low-latency main channel core in an optical fiber having an SI-type refractive index distribution structure suitable for submarine optical communication systems is described. Here, optical fiber refers to… Figure 50 The optical transmission channel 50, regarding the "core," refers to a single-core fiber with only one core, a multi-core fiber with any single core, and a ribbon fiber or optical cable with any single fiber core encased within it. SI type refers to... Figure 51 A step-index refractive index distribution structure. Figure 51 The example used a single-core fiber, but in the case of a multi-core fiber, each core has the same refractive index distribution structure.

[0023] Figure 2 This diagram illustrates the required characteristics (radius a and relative refractive index difference Δ) of the cores in the main channel. Each core is made of pure quartz glass and has a step-index (SI) refractive index distribution.

[0024] The parameter is bending loss (α) b The mode field diameter (MFD) and Δτ are assumed to be the same as those of a general cutoff-shifted fiber (ITU-T G.654) in the channel (group delay time τ). s Δτ is the bending loss α at a wavelength of 1.625 μm (λ = 4.88 μs / km). bThe calculation results of MFD are shown. The dashed and dotted lines represent the boundary lines of structures with a recommended bending loss of 2.0 dB / 100 tuns or less and an MFD of 9.5 μm or greater, respectively, in the international standard specification ITU-T G.654 for optical fibers used in long-distance transmission. The gray area enclosed by these curves has optical characteristics suitable for long-distance transmission channels and can achieve Δτ < -1.0 ns / km relative to general cutoff-displaced fibers. In this embodiment, the case where the slave channel is a type SI fiber is described, but the slave channel can also be a fiber other than a type SI fiber.

[0025] In addition, α b The core structure with a value of 2.0 dB / 100 turns is represented by the following formula. [Mathematical Expression 12] The structure with an MFD of 9.5 μm is represented by the following formula. [Mathematical Expression 13] The structure with a group delay time difference Δτ of -1.0 ns / km is represented by the following formula. [Mathematical Expression 14]

[0026] Figure 3 This is a graph illustrating the Δτ dependency of the core radius design range for the main channel. In this calculation, the core radius of the structure achieving MFD=9.5μm and Δτ=-1ns / km is set as a. max This will achieve MFD=9.5μm and α b The core radius of the structure with a value of 2.0 dB / 100 turns is set as a. min At that time, a max -a min As the design range for the core radius. According to Figure 3 It can be seen that as Δτ decreases, the range of designable core radii decreases, and the designable structure disappears at Δτ = -2 ns / km.

[0027] Regarding the core structure that realizes the time difference of delay Δτ, the relationship between Δ and a is expressed by the following formula using coefficients K0, K1, and K2 that depend on Δτ. [Mathematical Expression 15] according to Figure 4 Using Δτ, K0 is represented by the following formula in the range of -2ns / km < Δτ < -1.0ns / km. [Mathematical Expression 16] Similarly, according to Figure 5 Using Δτ, K1 is expressed by the following formula in the range of -2ns / km < Δτ < -1.0ns / km. [Mathematical Expression 17] Furthermore, similarly, according to Figure 6 Using Δτ, K2 is expressed by the following formula in the range of -2ns / km < Δτ < -1.0ns / km. [Mathematical Expression 18]

[0028] As stated above, satisfying [Mathematical Expression 19] And satisfy [Mathematical Expression 20] SI-type pure silica core optical fiber possesses optical characteristics suitable for long-distance transmission channels, and can achieve a Δτ greater than -2.0 ns / km and less than -1.0 ns / km for slave channels comparable to general-purpose cutoff-shifted optical fibers. Therefore, SI-type pure silica core optical fiber satisfying Equations 19 and 20 can realize MS-CPE using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km.

[0029] Additionally, for optical cables and ribbon fibers, "SI-type pure silica core fiber" refers to the fiber core used in the main channel, and "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, as described later, "SI-type pure silica core fiber" refers to the core used in the main channel, and "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0030] [Implementation Method 2] In this embodiment, a design method for realizing a low-latency main channel core in an optical fiber having a W-shaped refractive index distribution structure suitable for submarine optical communication systems is described. Here, optical fiber refers to Figure 50 Regarding the optical transmission channel 50, the term "core" has several meanings: single-core fiber refers to a single core, multi-core fiber refers to any single core, and ribbon fiber or optical cable refers to any single fiber core encased within it. W-type fiber refers to fiber with... Figure 52 The optical fiber with the refractive index distribution structure shown is in... Figure 52 The example used a single-core fiber, but in the case of a multi-core fiber, each core has the same refractive index distribution structure.

[0031] In transmission channels spanning thousands of kilometers, W-type refractive index fibers with a low refractive index region around the core are mostly used. Here, we consider MS-CPEs using low-latency main channels for long-distance transmission channels. If a low-latency channel can be achieved in a W-type fiber, existing manufacturing techniques can be applied, making it a preferred option.

[0032] The ratio of the relative refractive index difference Δ1 of the low refractive index layer relative to the core refractive index to the relative refractive index difference Δ2 of the cladding layer relative to the core refractive index is set as Δ1 / Δ2. Figure 7 This indicates that the bending loss is α. b The graph shows the calculated dependence of Δ1 / Δ2 on the core radius a1 when the group delay time difference is Δτ = 1.0 ns / km and the group delay time difference is 2.0 dB / 100 tuns. Here, as with general W-type fibers, the radius a2 of the low-refractive-index layer is 3 times that of a1, i.e., a2 = 3a1. In any structure, Δ1 is adjusted to make MFD = 9.5 μm.

[0033] α b Structures with a value below 2.0 dB / 100 tuns have a value greater than the dashed line in the diagram (a1), while structures with a value greater than 1.0 ns / km have a value smaller than the solid line in the diagram (a1). Therefore, α... b Structures with a voltage rating below 2.0 dB / 100 tuns and a Δτ value above 1.0 ns / km are represented by the gray area in the figure. Furthermore, the dashed line represents α. b For a structure with 2.0 dB / 100 tuns, using Δ2 / Δ1 and a1, the following relationship is satisfied: [Mathematical Expression 21] The structure with a solid line and a Δτ of 1.0 ns / km satisfies the following relationship. [Mathematical Expression 22]

[0034] Figure 8 This describes the values ​​of Δτ and α at a1=3.3, Δ2 / Δ1=0.98, and MFD=9.5μm. b A graph showing the calculated a2 / a1 dependency. The solid line represents the group delay time difference Δτ, and the dashed line represents the bending loss α. b It can be said that, in Figure 8 There are no dependencies on a2 / a1 in the design area shown.

[0035] Figure 9This graph illustrates the dependence of the designable range of the core radius on Δτ. With MFD set to 9.5 μm, the designable range of the core radius is the maximum Δ2 / Δ1. As Δτ decreases, the designable range of the core radius decreases, disappearing at -2.0 ns / km (becoming 0 μm).

[0036] Here, for a structure with a group delay time difference of Δτ, the relationship between Δ2 / Δ1 and radius a1 is, for example, the following formula. [Mathematical Expression 23] Figure 10 This is a graph illustrating the Δτ dependence of K3 at -2.0 ns / km < Δτ < -1.0 ns / km when MFD is 9.5 μm. Here, K3 satisfies the following relationship. [Mathematical Expression 24] Solving equation 21 with respect to a1 yields the minimum a1 that can be designed for Δ2 / Δ1. Substituting equation 24 into equation 23 and solving equation 23 with respect to a1 yields the maximum a1 that can be designed for Δ2 / Δ1. As described above, it has the following... [Mathematical Expression 25] The W-type pure silica core fiber possesses optical characteristics suitable for long-distance transmission channels, and achieves a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted fibers. Therefore, the W-type pure silica core fiber satisfying Equation 25 enables the implementation of MS-CPEs using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. In this embodiment, the case where the slave channel is an SI-type fiber is described, but the slave channel can also be a fiber other than an SI-type fiber.

[0037] Additionally, for optical cables and ribbon fibers, "W-type pure silica core fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "W-type pure silica core fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0038] Figure 11 This indicates that the bending loss is α. b The graph shows the calculated dependence of Δ1 / Δ2 on the core radius a1 when the group delay time difference is Δτ = 1.0 ns / km and 2.0 dB / 100 tuns. Here, compared with... Figure 7 Similarly, a2 = 3a1. In this figure, MFD = 9.8 μm.

[0039] α b Structures with a value below 2.0 dB / 100 tuns have a value greater than the dashed line in the diagram (a1), while structures with a value greater than 1.0 ns / km have a value smaller than the solid line in the diagram (a1). Therefore, α... b Structures with a voltage rating below 2.0 dB / 100 tuns and a Δτ value above 1.0 ns / km are represented by the gray area in the figure. Furthermore, the structure represented by the dashed line αb, with a voltage rating of 2.0 dB / 100 tuns, satisfies the following relationship using Δ2 / Δ1 and a1: [Mathematical Expression 26] The structure with a solid line Δτ of 1.0 ns / km satisfies the following equation. [Mathematical Expression 27]

[0040] Figure 12 This graph illustrates the dependence of the designable range of the core radius on Δτ. With MFD set to 9.8 μm, the designable range of the core radius is the maximum Δ2 / Δ1. As Δτ decreases, the designable range of the core radius decreases, disappearing at -1.46 ns / km (becoming 0 μm).

[0041] Here, for a structure with a group delay time difference of Δτ, the relationship between Δ2 / Δ1 and radius a1 is given by the following formula. [Mathematical Expression 28] Figure 13 This is a graph illustrating the Δτ dependence of K4 at -1.46 ns / km < Δτ < -1.0 ns / km when MFD is 9.8 μm. Here, K4 satisfies... [Mathematical Expression 29] The relationship is as follows. By solving mathematical expression 26 with respect to a1, we can find the minimum designable a1 for Δ2 / Δ1. Substituting mathematical expression 29 into mathematical expression 28 and solving mathematical expression 29 with respect to a1, we can find the maximum designable a1 for Δ2 / Δ1. As mentioned above, having the condition that becomes [Mathematical Expression 30] The W-type pure silica core optical fiber possesses optical characteristics suitable for long-distance transmission channels, and can achieve a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted optical fibers. Therefore, the W-type pure silica core optical fiber satisfying Equation 30 enables the implementation of MS-CPEs using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. In this embodiment, the case where the slave channel is an SI-type optical fiber is described, but the slave channel can also be an optical fiber other than an SI-type fiber.

[0042] Additionally, for optical cables and ribbon fibers, "W-type pure silica core fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "W-type pure silica core fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0043] Figure 14 This indicates that the bending loss is α. b The graph shows the calculated dependence of Δ1 / Δ2 on the core radius a1 when the group delay time difference is Δτ = 1.0 ns / km and 2.0 dB / 100 tuns. Here, compared with... Figure 7 Similarly, a2 = 3a1. In this figure, MFD = 10.0 μm.

[0044] α b Structures with a value below 2.0 dB / 100 tuns have a value greater than the dashed line in the diagram (a1), while structures with a value greater than 1.0 ns / km have a value smaller than the solid line in the diagram (a1). Therefore, α... b Structures with a voltage rating below 2.0 dB / 100 tuns and a Δτ value above 1.0 ns / km are represented by the gray area in the figure. Furthermore, the structure represented by the dashed line αb has a voltage rating of 2.0 dB / 100 tuns, and using Δ2 / Δ1 and a1, satisfies... [Mathematical Expression 31] The relationship between the solid line and the structure with a Δτ of 1.0 ns / km satisfies the following equation. [Mathematical Expression 32]

[0045] Figure 12 This graph illustrates the dependence of the designable range of the core radius on Δτ. With MFD set to 10.0 μm, the designable range of the core radius is the maximum Δ2 / Δ1. As Δτ decreases, the designable range of the core radius decreases, disappearing at -1.14 ns / km (becoming 0 μm).

[0046] Here, for a structure with a group delay time difference of Δτ, the relationship between Δ2 / Δ1 and radius a1 is given by the following formula. [Mathematical Expression 33] Figure 16 This is a graph illustrating the Δτ dependence of K5 at -1.14 ns / km < Δτ < -1.0 ns / km when MFD is 10.0 μm. Here, K5 satisfies... [Mathematical Expression 34] The relationship is as follows. By solving mathematical expression 31 with respect to a1, we can find the minimum designable a1 for Δ2 / Δ1. Substituting mathematical expression 34 into mathematical expression 33 and solving mathematical expression 33 with respect to a1, we can find the maximum designable a1 for Δ2 / Δ1. As mentioned above, it has the following... [Mathematical Expression 35] The W-type pure silica core fiber possesses optical characteristics suitable for long-distance transmission channels, and can achieve a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted fibers. Therefore, the W-type pure silica core fiber satisfying Equation 35 enables the implementation of MS-CPEs using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. In this embodiment, the case where the slave channel is an SI-type fiber is described, but the slave channel can also be a fiber other than an SI-type fiber.

[0047] Additionally, for optical cables and ribbon fibers, "W-type pure silica core fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "W-type pure silica core fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0048] Figure 17 This is a graph illustrating the MFD dependence of the designable range of the core radius a1. It shows the bending loss α for Δ2 / Δ1 = 1.00. b The designable range of core radii is below 2.0 dB / 100 tuns and Δτ is above 1.0 ns / km. As the MFD increases, the designable range of core radii decreases. At an MFD of 10.1 μm, α... b The core radius design range of less than 2.0 dB / 100 tuns and less than 1.0 ns / km disappears (becomes 0 μm). Therefore, MFD can be designed to be greater than 9.5 μm and less than 10.1 μm.

[0049] Here, using the coefficient K6 which depends on MFD, the design lower limit of the core radius a1 in mathematical formulas 17, 22 and 27 is expressed as the following formula. [Mathematical Expression 36] Figure 17 This is a graph illustrating the MFD dependency of K6. This dependency can be derived from... [Mathematical Expression 37] express.

[0050] Similarly, using coefficients K7 and K8 that depend on MFD, the design upper limit of core radius a1 in mathematical formulas 25, 30, and 35 is expressed as follows. [Mathematical Expression 38] Figure 19 This is a graph illustrating the MFD dependency of K7. This dependency can be determined by... [Mathematical Expression 39] express. also, Figure 20 This is a graph illustrating the MFD dependency of K8. This dependency is... [Mathematical Expression 40] express.

[0051] As described above, within the MFD range of 9.5 μm to 10.1 μm, it has the following properties: [Mathematical Expression 41] The W-type pure silica core fiber possesses optical characteristics suitable for long-distance transmission channels, and can achieve a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted fibers. Therefore, the W-type pure silica core fiber satisfying Equation 35 enables the implementation of MS-CPEs using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. In this embodiment, the case where the slave channel is an SI-type fiber is described, but the slave channel can also be a fiber other than an SI-type fiber.

[0052] Additionally, for optical cables and ribbon fibers, "W-type pure silica core fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "W-type pure silica core fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0053] [Implementation Method 3] The optical communication system of this embodiment is characterized in that the refractive index of the core of the optical fiber of the optical transmission channel 50 is lower than that of pure quartz glass. In Embodiments 1 and 2, the structural conditions for optical fibers using pure quartz glass as the core are described. In the SI-type and W-type structures shown in Embodiments 1 and 2, fluorine-doped glass can also be used as the core. In this case, by reducing the core refractive index, a larger Δτ can be achieved, expanding the application area of ​​MS-CPEs using low-delay signals.

[0054] In this embodiment, a method for designing a core for realizing a low-latency main channel in an optical fiber having an SI-type refractive index distribution structure with a fluorine-doped glass core is described.

[0055] Figure 21 This describes the required characteristics of the core of the main channel (radius a and relative refractive index difference Δ). F The graph shows the relative refractive index difference Δ. F It is the difference in refractive index between the fluorine-doped core and pure quartz glass. The parameters are the group delay time difference Δτ at wavelength 1.55 μm and the bending loss α at wavelength 1.625 μm. b The cutoff wavelength λc and the Rayleigh scattering loss α at wavelength 1.55 μm R Here, in each structure, the relative refractive index difference of the cladding relative to pure quartz glass is adjusted so that the MFD is 9.5 μm.

[0056] The dashed line represents the Rayleigh scattering loss of 0.17 dB / km, the same as in a general SMF. The core radius *a* satisfies... [Mathematical Expression 43] At that time, it is possible to achieve λc < 1.53 μm and α b <2.0dB / 100turns. Furthermore, in Δ F In regions smaller than the solid line, Δτ < -1.0 ns / km can be achieved. F Areas larger than the dotted line can achieve Rayleigh scattering loss below 0.17 dB / km.

[0057] Within the range of core radii in mathematical formula 43, use core radius 'a', the solid line is formed by... [Mathematical Expression 44] The expression is given. Furthermore, within the radius of the core of mathematical expression 43, the dotted line is... [Mathematical Expression 45] The expression is represented by the formula. That is, in [Mathematical Expression 46] In this process, it is possible to achieve Δτ > 1.0 ns / km and α R <0.17dB / km. Depend on Figure 21 The structure of the gray region enclosed by the curve described has optical characteristics suitable for long-distance transmission channels and can be used as a low-latency main channel with Δτ < -1.0 ns / km.

[0058] Figure 22 This explains the Δ of the main channel. F A graph showing the Δτ dependency of the design range. Figure 21 In the middle, α will be realized R =0.17dB / km and α b =2.0dB / 100turns of the structure's Δ F Let it be Δ F，min This will achieve α b =2.0dB / 100turns and the delay time difference Δτ of the structure F Let it be Δ F，max , will Δ F，max -Δ F，min Let Δ be dependent on Δτ. F The designable range. As Δτ decreases, Δ F The designable range is reduced, and the design range disappears at -14.7 ns / km (becoming 0%).

[0059] Here, regarding the structure where the group delay time difference is Δτ, Δ F The relationship with the core radius a is given by the following formula. [Mathematical Expression 47] Figure 23 This is a graph illustrating the Δτ dependence of K9 at -14.7 ns / km < Δτ < -1.0 ns / km when MFD is 9.5 μm. Here, K9 satisfies... [Mathematical Expression 48] The relationship. As mentioned above, satisfying becomes [Mathematical Expression 49] The fluorine-doped core fiber possesses optical characteristics suitable for long-distance transmission channels, and can achieve a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted fibers. Therefore, SI-type fluorine-doped core fibers satisfying Equation 49 can realize MS-CPEs using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. In this embodiment, the case where the slave channel is an SI-type fiber is described, but the slave channel can also be a fiber other than an SI-type fiber.

[0060] Additionally, for optical cables and ribbon fibers, "SI-type fluorine-doped fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "SI-type fluorine-doped fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0061] Figure 24 This also explains the required characteristics of the core of the main channel (radius a and relative refractive index difference Δ). F The figure is shown below. In this example, the relative refractive index difference of the cladding relative to the pure quartz glass is adjusted in each structure so that the MFD is 15.0 μm.

[0062] Core radius a satisfies [Mathematical Expression 50] At that time, it is possible to achieve λc < 1.53 μm and α b <2.0dB / 100turns. Furthermore, in Δ F In regions smaller than the solid line, Δτ < -1.0 ns / km can be achieved. F Areas larger than the dotted line can achieve Rayleigh scattering loss below 0.17 dB / km.

[0063] Within the range of core radii in mathematical formula 50, use core radius a, the solid line is... [Mathematical Expression 51] The expression is given. Furthermore, within the radius of the core of mathematical expression 50, the dotted line is... [Mathematical Expression 52] The expression is represented by the formula. That is, in [Mathematical Expression 53] In this process, it is possible to achieve Δτ < -1 ns / km and α R <0.17dB / km. Depend on Figure 24 The structure of the gray region enclosed by the curve described has optical characteristics suitable for long-distance transmission channels and can be used as a low-latency main channel with Δτ < -1.0 ns / km.

[0064] Figure 25 This explains the Δ of the main channel. F A graph showing the Δτ dependency of the design range. Figure 25 This explains Δ F The largest designable range of α b Δ at =2.0dB / 100 turns F A graph showing the dependence of Δτ on the designable range. As Δτ decreases, Δ... F The designable range is reduced, and the design range disappears at -18.0 ns / km (becoming 0%).

[0065] Here, regarding the structure where the group delay time difference is Δτ, Δ F The relationship between the core radius 'a' and the core radius 'a' is given by the following formula. [Mathematical Expression 54] Figure 26 This indicates that K is at -18.0 ns / km < Δτ < -1.0 ns / km when MFD is 15.0 μm. 10 A graph of the Δτ dependency. Here, K 10 satisfy [Mathematical Expression 55] The relationship. As mentioned above, satisfying becomes [Mathematical Expression 56] The fluorine-doped core fiber possesses optical characteristics suitable for long-distance transmission channels, and can achieve a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted fibers. Therefore, the SI-type fluorine-doped core fiber satisfying Equation 56 enables the implementation of MS-CPEs using low-latency signals in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. In this embodiment, the case where the slave channel is an SI-type fiber is described, but the slave channel can also be a fiber other than the SI-type fiber.

[0066] Additionally, for optical cables and ribbon fibers, "SI-type fluorine-doped fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "SI-type fluorine-doped fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0067] Figure 27 This explains α b The minimum designable core radius a is 2.0 dB / 100 turns. min A graph of MFD dependencies. min It increases linearly relative to MFD. Figure 27 The solid line can be represented by the following formula. [Mathematical Expression 57]

[0068] Figure 28 This indicates the minimum designable core radius a below λc (1.53 μm). max A graph of MFD dependencies. max It increases linearly relative to MFD. Figure 28 The solid line can be represented by the following formula. [Mathematical Expression 58]

[0069] Figure 29 This explains α b The minimum designable Δτ at 2.0 dB / 100 turns min A graph of MFD dependence. Δτ min It can be expressed by the following formula. [Mathematical Expression 59]

[0070] Here, the core radius is a min <a<a max And the designed group delay time difference is Δτ min When Δτ < -1ns / km, α R Δ is 0.17 dB / km Fmin and Δ Fmax Using the coefficient K, which depends on MFD 11 K 12 K 13 K 14 K 15 K 16 The core radius a and the group delay time difference Δτ are expressed by the following formula. [Mathematical Expression 60] [Mathematical Expression 61]

[0071] Figure 30 This explains K 11 A graph of MFD dependencies. Figure 30A straight line can be represented using MFD, as shown by the following formula. [Mathematical Expression 62]

[0072] Figure 31 This explains K 12 A graph of MFD dependencies. Figure 31 A straight line can be represented using MFD, as shown by the following formula. [Mathematical Expression 63]

[0073] Figure 32 This explains K 13 A graph of MFD dependencies. Figure 32 A straight line can be represented using MFD, as shown by the following formula. [Mathematical Expression 64]

[0074] Figure 33 This explains K 14 A graph of MFD dependencies. Figure 33 The curve can be expressed using MFD, as shown in the following formula. [Mathematical Expression 65]

[0075] Figure 34 This explains K 15 A graph of MFD dependencies. Figure 34 The curve can be expressed using MFD, as shown in the following formula. [Mathematical Expression 66]

[0076] Figure 35 This explains K 16 A graph of MFD dependencies. Figure 35 The curve can be expressed using MFD, as shown in the following formula. [Mathematical Expression 67]

[0077] As described above, relative to MFDs with a diameter greater than 9.5 μm and less than 15.0 μm, the core radius is within the range shown in equations 57 and 58. min <a<a max In the region, the designed group delay time difference Δτ is used by Δτ as shown in mathematical formula 59. min And in Δτ min When <Δτ < -1ns / km, it satisfies the condition of becoming [Mathematical Expression 68] The fluorine-doped core fiber exhibits optical properties suitable for long-distance transmission channels, and achieves a group delay time reduction of less than Δτ for the slave channel, comparable to that of general-purpose cutoff-shifted fibers. Therefore, the SI-type fluorine-doped core fiber satisfying Formula 68 enables the use of low-latency signals in MS-CPEs in long-distance transmission channels, such as submarine optical communication systems exceeding 1000 km. Furthermore, by providing a sleeve with a refractive index lower than the core region and higher than the cladding region in a manner that surrounds the structure of this embodiment, a W-type design is possible. In this embodiment, the case where the slave channel is an SI-type fiber is described, but the slave channel can also be a fiber other than the SI-type fiber.

[0078] Additionally, for optical cables and ribbon fibers, "SI-type fluorine-doped fiber" refers to the fiber core used in the main channel, while "cutoff-shifted fiber" refers to the fiber core used in the secondary channel. Furthermore, for multi-core fibers, "SI-type fluorine-doped fiber" refers to the core used in the main channel, while "cutoff-shifted fiber" refers to the core used in the secondary channel.

[0079] [Implementation Method 4] In this embodiment, fluorine-doped SI fiber, which utilizes low-latency signals and MS-CPE, is described as being used to expand the application area of ​​terrestrial relay systems. Since the terrestrial relay system is designed with a transmission channel length of approximately 100 km, based on... Figure 1 Δτ is preferably below -3.4 ns / km. Furthermore, α b Preferably, it is the same as the common SMF of 0.1 dB / 100 turns.

[0080] Figure 36 This describes the required characteristics of the core of the main channel (radius a and relative refractive index difference Δ). F (The image is shown.) The parameters are the group delay time difference Δτ at wavelength 1.55 μm and the bending loss α at wavelength 1.625 μm. b The cutoff wavelength λc and the Rayleigh scattering loss α at a wavelength of 1.55 μm. R Here, in each structure, the relative refractive index difference of the cladding relative to pure quartz glass is adjusted so that the MFD is 9.5 μm.

[0081] Radius a satisfies [Mathematical Expression 69] At that time, it is possible to achieve λc < 1.53 μm and α b <0.1dB / 100turns. Furthermore, in Δ F In regions smaller than the solid line, Δτ < -3.4 ns / km can be achieved.F Areas larger than the dotted line can achieve Rayleigh scattering loss below 0.17 dB / km.

[0082] Within the core radius *a* of Equation 69, using core radius *a*, and setting it as Δτ = -3.4 ns / km in Equations 47 and 48, the solid line is obtained. The dashed line is represented by Equation 45. That is, through... [Mathematical Expression 70] It can achieve Δτ < -3.4 ns / km and α R <0.17dB / km.

[0083] Figure 37 This explains the Δ of the main channel. F A graph showing the Δτ dependency of the design range. Figure 37 This explains Δ F The largest designable range of α b Δ at =0.1dB / 100turns F A graph showing the dependence of Δτ on the designable range. As Δτ decreases, Δ... F The designable range is reduced, and the design range disappears at -14.7 ns / km (becoming 0%).

[0084] Figure 38 This describes the required characteristics of the core of the main channel (radius a and relative refractive index difference Δ). F The figure shows the diagram. In this figure, in each structure, the relative refractive index difference of the cladding relative to the pure quartz glass is adjusted so that the MFD is 15.0 μm.

[0085] The core radius a satisfies [Mathematical Expression 71] At that time, it is possible to achieve λc < 1.53 μm and α b <0.1dB / 100turns. Furthermore, in Δ F In regions smaller than the solid line, Δτ < -3.4 ns / km can be achieved. F Areas larger than the dotted line can achieve Rayleigh scattering loss below 0.17 dB / km.

[0086] Within the core radius *a* of Equation 71, the solid line is derived using core radius *a*, set as Δτ = -3.4 ns / km in Equations 54 and 55. The dashed line within the core radius of Equation 71 is represented by Equation 52. That is, through... [Mathematical Expression 72] It can achieve Δτ < -3.4 ns / km and α R <0.17dB / km.

[0087] Figure 39 This explains the Δ of the main channel. F A graph showing the Δτ dependency of the design range. Figure 39 This explains Δ F The largest designable range of α b Δ at =0.1dB / 100turns F A graph showing the dependence of Δτ on the designable range. As Δτ decreases, Δ... F The designable range is reduced, and the design range disappears at -17.6 ns / km (becoming 0%).

[0088] Here, λc is the core radius a below 1.53 μm. max It can be represented by the mathematical formula 58. Figure 40 α b The core radius a is 0.1 dB / 100 turns. min MFD dependency. min It increases linearly relative to MFD. Figure 40 The solid line can be represented by the following formula. [Mathematical Expression 73]

[0089] also, Figure 41 This explains α b A plot of the MFD dependence of the designable minimum Δτ at 0.1 dB / 100 turns. At this point, Δτ... min It can be expressed by the following formula. [Mathematical Expression 74] Here, the core radius is a min <a<a max And the designed group delay time difference is Δτ min When α < Δτ < -3.4 ns / km R ΔF is 0.17 dB / km min and ΔF max It is represented by the mathematical formula 68.

[0090] The structure described in this embodiment extends the application area of ​​MS-CPE using low-delay signals to approximately 300 km. Furthermore, by providing a sleeve with a refractive index lower than the core region and higher than the cladding region in a manner that surrounds the structure of this embodiment, a W-type design is also possible.

[0091] [Implementation Method 5] In this embodiment, an optical communication system in which the optical transmission channel 50 is a multi-core optical fiber is described. The multi-core optical fiber in this embodiment includes at least one core structure as described in embodiments 1 to 4. (Example 1) Figure 42 This diagram illustrates a core configuration example of a multi-core optical fiber including a low-latency core. In this embodiment, the multi-core optical fiber has two or more transmission cores (52, 53) arranged on a square grid within the cladding 51. Furthermore, it is characterized in that at least one of these transmission cores (core 52) serves as the low-latency core in the structure described in embodiments 1 to 4. In this embodiment, core 52 serves as the low-latency master channel, and the other cores 53 serve as slave channels. This effectively neutralizes noise caused by interference, thus enabling stable operation of the MS-CPE using the low-latency channel in the optical communication system 300.

[0092] (Example 2) Figure 43 This is a diagram illustrating an example of a core configuration for a multi-core optical fiber, including a low-latency core. In this embodiment, the multi-core optical fiber has two or more transmission cores (52, 53) arranged in a ring shape within the cladding 51. Furthermore, it is characterized in that at least one of these transmission cores (core 52) serves as the low-latency core in the structure described in embodiments 1 to 4. In this embodiment, core 52 serves as the low-latency primary channel, while the other cores 53 serve as secondary channels. This effectively neutralizes noise caused by interference, thus enabling stable operation of the MS-CPE using the low-latency channel in the optical communication system 300.

[0093] (Example 3) Figure 44 This is a diagram illustrating an example of a core configuration for a multi-core optical fiber, including a low-latency core. In this embodiment, the multi-core optical fiber has two or more transmission cores (52, 53) arranged in a hexagonal close-packed structure within the cladding 51. Furthermore, it is characterized in that at least one of these transmission cores (core 52) serves as a low-latency core in the structure described in embodiments 1 to 4. In this embodiment, core 52 serves as the low-latency primary channel, while the other cores 53 serve as secondary channels. This effectively neutralizes noise caused by interference, thus enabling stable operation of the MS-CPE using the low-latency channel in the optical communication system 300.

[0094] (Example 4) Figure 45 This is a diagram illustrating an example of a core configuration for a multi-core optical fiber, including a low-latency core. The multi-core optical fiber of this embodiment is characterized in that a transmission core (core 52) as described in embodiments 1 to 4 is disposed at the center of the cladding 51, and two or more transmission cores 53 are disposed around it in a square lattice pattern within the cladding 51. In the multi-core optical fiber of this embodiment, core 52 is used as a low-latency primary channel, and the other cores 53 are used as secondary channels. As a result, noise caused by interference is common, thus enabling stable operation of the MS-CPE using the low-latency channel in the optical communication system 300.

[0095] (Example 5) Figure 46 This is a diagram illustrating an example of a core configuration for a multi-core optical fiber, including a low-latency core. The multi-core optical fiber of this embodiment is characterized in that a transmission core (core 52) as described in embodiments 1 to 4 is disposed at the center of the cladding 51, and two or more transmission cores 53 are disposed in a ring around it and within the cladding 51. In the multi-core optical fiber of this embodiment, core 52 is used as a low-latency primary channel, and the other cores 53 are used as secondary channels. As a result, noise caused by interference is common, thus enabling stable operation of the MS-CPE using the low-latency channel in the optical communication system 300.

[0096] (Example 6) Figure 47 This is a diagram illustrating an example of a core configuration for a multi-core optical fiber, including a low-latency core. The multi-core optical fiber of this embodiment is characterized in that a transmission core (core 52) as described in embodiments 1 to 4 is disposed at the center of the cladding 51, and four transmission cores 53 are disposed around it in a square lattice pattern within the cladding 51. Core 52 is the low-latency main channel, and cores 53 are the slave channels. Here, the low-latency main channel is of type SI, and the slave channels are of type W with a low-refractive-index layer 54 on the outer periphery of cores 53. The core radius of the low-latency main channel is set as a. m1 The core radius of the channel will be set to a. s1 Let the radius of the low refractive index layer be a. s2 Furthermore, the distance between the low-latency master channel and slave channel (the distance between the centers of core 52 and core 53) is set as Λ. Each core shares a cladding 51, and the relative refractive index difference of the cladding 51 relative to pure quartz glass is set as Δ. c Furthermore, the relative refractive index difference between the low-refractive-index layer 54 and the pure quartz glass is set as Δ. d .

[0097] Figure 48 This is an explanation about... Figure 47 The intercore distance Λ and refractive index difference Δ of the low-refractive-index layer in the multi-core optical fiber are explained in the text. d The diagram of the design area. Figure 48It is the crosstalk XT between the low-delay master channel and slave channel at a wavelength of 1.625 μm. m-s Crosstalk between channels XT s-s And leakage loss α from the channel c The intercore distance Λ and the relative refractive index difference Δ d The results of dependency calculations.

[0098] The solid line represents α. c 0.01 dB / km, dotted line indicates XT s-s -59dB / km, dashed line indicates XT m-s The structure has a crosstalk of -59 dB / km. It is known that in crosstalk XT... m-s and XT s-s When both sides are -59dB / km, communication with Quadrature Phase Shift Keying (QPSK) modulation over 10,000km can be implemented with sufficient transmission quality. Here, based on the fiber optic structure using a low-latency main channel MS-CPE that can be implemented in optical transmission systems exceeding 1,000km as described in Embodiment 1, a m1 and Δ c The values ​​were 3.4 μm and -0.4%, respectively. Furthermore, adjusting a... s1 This is to ensure that the MFD of the channel becomes 9.5 μm at a wavelength of 1.55 μm. Based on existing cutoff-shifted fiber (W-type), a s2 Set as 3a s1 The gray structure in the diagram allows for a balance between sufficient transmission quality and low loss in long-distance transmission channels.

[0099] Figure 49 This is an explanation Figure 47 The table shows an example of a multi-core fiber (MCF) structure. Core 52 of the low-latency main channel is a. m1 =3.4μm, Δ c =-0.40%. From channel core 53 for a s1 =5.0μm, low refractive index layer 54 is a s2 =15.0μm, Δ d =-0.55%. Intercore distance Λ=31μm. By adopting this structure, it is possible to achieve... Figure 48 The multi-core fiber shown exhibits excellent low XT and low loss characteristics for long-distance transmission.

[0100] At this point, the group delay time of the low-latency master channel is 4.879 μs / km, and the group delay time of the slave channel is 4.883 μs / km. This is because the group delay time difference between the low-latency master channel and the slave channel is 4 ns / km, and a transmission delay time difference of more than 1 μs can be achieved in optical transmission channels of more than 250 km.

[0101] As described above, by using this MCF in the optical transmission channel 50, an optical transmission system using a low-latency main channel can be realized even at distances of over 250km.

[0102] [Postscript] The present invention is an optical communication system 301 equipped with an optical fiber as an optical transmission channel 50 as described in embodiments 1 to 6. That is, the optical communication system of the present invention is as follows. (1) An optical communication system using MS-CPE transmission, comprising a transmitter, a receiver, and an optical transmission channel connecting them, characterized in that, in the optical fiber of the optical transmission channel, The core of radius a (μm) used in the main channel and the cladding with a relative refractive index difference Δ (%) relative to the core are of the step refractive index (SI) type refractive index distribution structure and satisfy the mathematical formula C1. [Mathematical expression C1] Wherein, Δτ (ns / km) is the group delay time difference between the master channel and the slave channel, which is the value of mathematical formula C2 when the optical signal is transmitted in the master channel and the slave channel of the optical communication system, and when the optical signal is transmitted over a distance L (km). [Mathematical expression C2]

[0103] (2) An optical communication system using MS-CPE transmission, comprising a transmitter, a receiver, and an optical transmission channel connecting them, characterized in that, in the optical fiber of the optical transmission channel, The core of radius a1 (μm) for the main channel, the low refractive index layer surrounding the core and having a relative refractive index difference Δ1 (%) relative to the core, and the cladding having a relative refractive index difference Δ2 (%) relative to the core are W-type refractive index distribution structures and satisfy mathematical formula C3. [Mathematical expression C3] Wherein, MFD is the mode field diameter of the core (μm), Δτ (ns / km) is the group delay time difference between the main channel and the slave channel, which is the value of mathematical formula C2 when the optical signal is transmitted in the main channel and the slave channel of the optical communication system, and the transmission distance L (km). [Mathematical expression C2]

[0104] (3) According to the optical fiber described in (1) and (2) above, the core has the same refractive index as pure quartz glass, but the core can be fluorine-doped glass, and the refractive index can be lower than that of pure quartz glass.

[0105] (4) The optical fiber described in (1) above is characterized in that the core has the same refractive index as pure quartz glass, but the core is fluorine-doped glass with a lower refractive index than pure quartz glass. The radius a (μm) satisfies the mathematical formula C4. The minimum group delay time difference Δτ min (nm / km) satisfies mathematical formula C5. The relative refractive index difference Δ between the core and pure quartz glass F (%) satisfies mathematical expression C6. [Mathematical expression C4] [Mathematical expression C5] [Mathematical expression C6] Wherein, MFD is the mode field diameter (μm) of the core.

[0106] (5) The optical fiber described in (1) to (4) above is characterized in that the optical fiber has a plurality of cores, one of which is the core used for the main channel.

[0107] Furthermore, this invention also provides a method for designing optical fibers as described in embodiments 1 to 6. Specifically, the design method of this invention is as follows (refer to...). Figure 53 ). (6) A method for designing optical fibers in an optical communication system using MS-CPE transmission, characterized in that, Given the signal arrival time difference s (μs) when optical signals are transmitted in the main channel and the slave channel of the optical communication system, and the transmission distance L (km) of the optical signals, calculate the group delay time difference Δτ (ns / km) between the main channel and the slave channel that satisfies mathematical formula C2 (step S01); and According to mathematical formula C1, find the radius a (μm) of the core of the optical fiber with a step refractive index (SI) type refractive index distribution structure and the relative refractive index difference Δ (%) of the cladding relative to the core (step S02). (7) A method for designing optical fibers in an optical communication system using MS-CPE transmission, characterized in that, Given the signal arrival time difference s (μs) when optical signals are transmitted in the main channel and the slave channel of the optical communication system, and the transmission distance L (km) of the optical signals, calculate the group delay time difference Δτ (ns / km) between the main channel and the slave channel that satisfies mathematical formula C2 (step S01); and According to mathematical formula C3, find the radius a1 (μm) of the core of the main channel of the optical fiber with W-shaped refractive index distribution structure, the relative refractive index difference Δ1 (%) of the low refractive index layer surrounding the core relative to the core, and the relative refractive index difference Δ2 (%) of the cladding relative to the core (step S02).

[0108] (8) The optical fiber described in (6) and (7) above is characterized in that the core has the same refractive index as pure quartz glass, but the core is fluorine-doped glass with a lower refractive index than pure quartz glass.

[0109] (9) The optical fiber according to (6) above, characterized in that, when the core has the same refractive index as pure quartz glass, but the optical fiber is fluorine-doped glass and the refractive index of the core is lower than that of pure quartz glass, Find the radius a (μm) that satisfies mathematical expression C4; Determine the minimum group delay time difference Δτ min (nm / km) to satisfy mathematical formula C5; and Find the relative refractive index difference Δ between the core and pure quartz glass. F (%) to satisfy mathematical expression C6.

[0110] (10) The optical fiber described in (6) to (9) above is characterized in that, when the optical fiber has multiple cores, one of the multiple cores is the core used for the main channel. Explanation of reference numerals in the attached figures

[0111] 11: Transmitter 12: Receiver 50: Optical transmission channel (optical fiber) 51: Cladding 52: Main channel chip 53: From the channel core 54: Low Refractive Index Layer 301: Optical Communication System

Claims

1. An optical communication system using MS-CPE transmission, comprising an optical transmission channel with optical fiber, characterized in that... Regarding the optical transmission channel, the core with radius a μm used in the main channel and the cladding with a relative refractive index difference Δ% relative to the core have a step-index refractive index distribution structure and satisfy mathematical formula C1. [Mathematical expression C1] in, Δτns / km is the group delay time difference between the master channel and the slave channel. It is the value that satisfies the mathematical formula C2 when the optical signal has been transmitted in the master channel and the slave channel of the optical communication system (in μs) and the transmission distance of the optical signal is Lkm. [Mathematical expression C2] The optical transmission channel is a single-core optical fiber, a multi-core optical fiber, a ribbon core with multiple optical fiber cores arranged in parallel, or an optical cable containing multiple optical fiber cores. In the case of a multi-core optical fiber, any one core is used as the main channel, and the other cores are used as the secondary channels. In the case of ribbon fiber and optical cable, any one optical fiber core is used as the master channel and the other optical fiber cores are used as the slave channels; in the case of single-core fiber, any wavelength is used as the master channel and the other wavelengths are used as the slave channels.

2. The optical communication system using the MS-CPE transmission method according to claim 1, characterized in that, The refractive index of the core is lower than that of pure quartz glass.

3. The optical communication system using the MS-CPE transmission method according to claim 1, characterized in that, The refractive index of the core is lower than that of pure quartz glass. The radius aμm satisfies the mathematical formula C4. The minimum group delay time difference Δτ min nm / km satisfies mathematical formula C5. The relative refractive index difference Δ between the core and pure quartz glass F % Satisfies mathematical expression C6, [Mathematical expression C4] [Mathematical expression C5] [Mathematical expression C6] Wherein, MFD is the mode field diameter (μm) of the core.

4. An optical communication system using MS-CPE transmission, comprising an optical transmission channel with optical fiber, characterized in that... Regarding the optical transmission channel, the core with radius a1μm used in the main channel, the low refractive index layer surrounding the core with a relative refractive index difference Δ1% relative to the core, and the cladding with a relative refractive index difference Δ2% relative to the core form a W-shaped refractive index distribution structure, and satisfy mathematical formula C3. [Mathematical expression C3] in, MFD is the mode field diameter of the core in μm, and Δτns / km is the group delay time difference between the master channel and the slave channel. Δτns / km is the value of mathematical expression C2, which satisfies the signal arrival time difference (sμs) when optical signals are transmitted in the master channel and the slave channel of the optical communication system, and the transmission distance of the optical signal (Lkm). [Mathematical expression C2] The optical transmission channel is a single-core optical fiber, a multi-core optical fiber, a ribbon core with multiple optical fiber cores arranged in parallel, or an optical cable containing multiple optical fiber cores. In the case of a multi-core optical fiber, any one core is used as the main channel, and the other cores are used as the secondary channels. In the case of ribbon fiber and optical cable, any one optical fiber core is used as the master channel and the other optical fiber cores are used as the slave channels; in the case of single-core fiber, any wavelength is used as the master channel and the other wavelengths are used as the slave channels.

5. The optical communication system using the MS-CPE transmission method according to claim 4, characterized in that, The refractive index of the core is lower than that of pure quartz glass.

Images