Optical fiber transmission line and transmission method

Abstract

To provide a suitable optical fiber transmission line including both of a photonic band gap fiber and an anti-resonant fiber and including branching of an optical signal, and to provide a transmission method using the same.SOLUTION: The optical fiber transmission line includes an antiresonant fiber, a plurality of photonic band gap fibers, and a branching device that receives an optical signal transmitted through the antiresonant fiber, branches the optical signal, and outputs the branched optical signal to each of the plurality of photonic band gap fibers.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber transmission line and a transmission method. [Background technology]

[0002] By transmitting light through a core that is primarily filled with air, air-core optical fibers (HCFs) have the potential to significantly reduce transmission loss compared to solid-core optical fibers. Furthermore, they offer various properties that are not possible with conventional solid-core optical fibers, such as low latency, ultra-low nonlinearity, and resistance to harsh environments, and are expected to open up many new applications.

[0003] Known examples of hole-core fibers include photonic bandgap fibers (PBGFs) and antiresonant fibers (ARFs). Non-patent documents 1 and 2 report techniques for cabling hole-core fibers. Non-patent document 3 reports a photonic bandgap fiber with a structure called a PRISM (Perturbed Resonance for Increased Single Modedness) structure. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] B. Zhu et al, “First demonstration of Hollow-Core-Fiber Cable for Low Latency Data Transmission”, OFC 2020, paper Th4B.3, (2020). [Non-patent document 2] MA Iqbal et al, “First Demonstration of 400ZR DWDM Transmission through Field Deployable Hollow-Core-Fiber Cable”, OFC 2021, paper F4C.2, (2021). [Non-patent document 3] Kazunori Takekasa, "Hole-Core Fiber Cable," Furukawa Electric Review, No. 140 (July 2021), pp. 32-39 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the known optical fiber cables, the structure of an optical fiber cable including both a photonic bandgap fiber and an antiresonant fiber has not been thoroughly studied.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a suitable optical fiber transmission line that includes both a photonic bandgap fiber and an antiresonant fiber and that includes branching of an optical signal, and a transmission method using the same. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention is an optical fiber transmission line comprising an antiresonant fiber, a plurality of photonic bandgap fibers, and a branching device that receives an input of an optical signal transmitted through the antiresonant fiber, branches the optical signal, and outputs it to each of the plurality of photonic bandgap fibers.

[0008] The antiresonant fiber may be placed in a first installation environment, and the plurality of photonic bandgap fibers may be placed in a second installation environment, and the macrobending loss of an optical fiber when placed in the second installation environment may be greater than the macrobending loss of the optical fiber when placed in the first installation environment.

[0009] The antiresonant fiber may be placed in a first installation environment, and the plurality of photonic bandgap fibers may be placed in a second installation environment, and the microbending loss of an optical fiber when placed in the second installation environment may be greater than the microbending loss of the optical fiber when placed in the first installation environment.

[0010] The branching device may be a fiber type optical branching device, a planar lightwave circuit (PLC) type optical branching device, or a spatial coupling type branching device.

[0011] The length of the antiresonant fiber may be greater than the length of the plurality of photonic bandgap fibers.

[0012] The antiresonant fiber may be laid between data centers, and the plurality of photonic bandgap fibers may be laid within the data center.

[0013] The optical fiber transmission line may include an optical fiber cable including the antiresonant fiber, and a plurality of optical fiber cables including each of the plurality of photonic bandgap fibers.

[0014] The optical fiber transmission line may include an optical fiber cable including the antiresonant fiber, and a plurality of optical fiber cords or optical fiber cords with connectors each including one of the plurality of photonic bandgap fibers.

[0015] One aspect of the present invention is a transmission method using the optical fiber transmission line, in which optical transmission is performed in the antiresonant fiber using a wavelength band wider than the wavelength band used for optical transmission in each of the multiple photonic bandgap fibers.

[0016] The branching device may wavelength-convert the optical signal transmitted through the antiresonant fiber into an optical signal in a predetermined wavelength band, and each of the plurality of photonic bandgap fibers may transmit the wavelength-converted optical signal.

[0017] The branching device may branch the optical signal transmitted through the antiresonant fiber for each wavelength band, and output the branched optical signals for each wavelength band to each of the plurality of photonic bandgap fibers. [Effects of the Invention]

[0018] According to the present invention, it is possible to realize a suitable optical fiber transmission line that includes both a photonic bandgap fiber and an antiresonant fiber and that also includes branching of an optical signal. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic configuration diagram of an optical transmission system including an optical fiber transmission line according to an embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of an antiresonant fiber taken along a plane perpendicular to the longitudinal direction thereof. [Figure 3] FIG. 3 is a schematic cross-sectional view of a photonic bandgap fiber taken along a plane perpendicular to the longitudinal direction thereof. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between bending diameter and bending loss. [Figure 5] FIG. 5 is a diagram showing an example of the relationship between wavelength and microbending loss. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. Furthermore, in each drawing, the same or corresponding components are appropriately designated by the same reference numerals, and duplicate explanations are appropriately omitted. Furthermore, terms not specifically defined in this specification shall follow the definitions and measurement methods in ITU-T G.650.1 and G.650.2 of the International Telecommunications Union (ITU).

[0021] (Embodiment) 1 is a schematic diagram of an optical transmission system 1000 including an optical fiber transmission line 100, an optical signal transmitter 200, and a plurality of optical signal receivers 300.

[0022] The optical fiber transmission line 100 includes a first cable portion 110, a plurality of second cable portions 120, and a branching device .

[0023] The first cable part 110 is an optical fiber cable including an antiresonant fiber 11 and a structure. The structure is a component that constitutes the optical fiber cable, and includes, for example, a tension member and a sheath. The first cable part 110 may also include other optical fibers, such as standard SMF, which will be described later.

[0024] FIG. 2 is a schematic cross-sectional view of an antiresonant fiber taken along a plane perpendicular to the longitudinal direction. The antiresonant fiber 11 has a structure also known as a nested antiresonant nodeless fiber (NANF). Specifically, the antiresonant fiber 11 includes an outer tube 11a made of glass and inner capillaries 11b and 11c. The outer tube 11a is covered with a resin coating. The glass cladding diameter of the antiresonant fiber 11 is the outer diameter of the outer tube 11a. To ensure reliability, the glass cladding diameter of the antiresonant fiber 11 is preferably 250 μm or less.

[0025] The inner capillaries 11b are arranged to form a regular pentagon in the cross section of the outer tube 11a. Each inner capillary 11c has a nested structure with the inner capillary 11b. An air hole core 11d is formed in the area surrounded by the inner capillaries 11b. In the antiresonant fiber 11, the antiresonant phenomenon generated by the inner capillaries 11b and 11c confines light of a predetermined wavelength band in the air hole core 11d and transmits it. The predetermined wavelength band is the wavelength band used for optical transmission.

[0026] Each second cable portion 120 is an optical fiber cable including a photonic bandgap fiber 12 and a structure. The structure is a component of the optical fiber cable, including, for example, a tension member and a sheath. The second cable portion 120 may also include other optical fibers, such as standard SMF.

[0027] FIG. 3 is a schematic cross-sectional view of a photonic bandgap fiber taken along a plane perpendicular to the longitudinal direction. The photonic bandgap fiber 12 has a PRISM structure. Specifically, the photonic bandgap fiber 12 includes a cladding 12a made of glass. The cladding 12a includes a micro-hole region 12aa. The micro-hole region 12aa includes micro-holes arranged in a triangular lattice pattern. The micro-holes form a photonic bandgap in a wavelength band including a predetermined wavelength. The micro-hole region 12aa includes a main core 12b, which is a hole core, and side cores 12c, which are hole cores, arranged on either side of the main core 12b. A resin coating is provided on the outer periphery of the cladding 12a. The glass cladding diameter of the photonic bandgap fiber 12 is the outer diameter of the cladding 12a. The glass cladding diameter of the photonic bandgap fiber 12 is preferably 250 μm or less to ensure reliability, but may be, for example, 125±25 μm. When the glass cladding diameter is 125±25 μm, the outer diameter of the coating is, for example, 250 μm. The glass cladding diameter of the photonic bandgap fiber 12 may be smaller than the glass cladding diameter of the antiresonant fiber 11.

[0028] The side core 12c is configured to optically couple with a higher-order propagation mode of a predetermined wavelength in the main core 12b. As a result, light propagating in the higher-order propagation mode in the main core 12b transfers to the side core 12c and leaks while propagating. As a result, the main core 12b propagates only the fundamental mode in the predetermined wavelength band with low loss, so the photonic bandgap fiber 12 is essentially a single-mode optical fiber. The predetermined wavelength band is the wavelength band used for optical transmission.

[0029] The size of the main core 12b is equivalent to about 19 of the minute holes that form the photonic band gap. Such a main core 12b is sometimes called a 19-cell type.

[0030] Returning to FIG. 1 , the splitter 130 has a function of receiving an input optical signal transmitted through the antiresonant fiber 11, splitting the optical signal, and outputting it to each of the photonic bandgap fibers 12. When the splitter 130 splits the signal light as it is, it may be, for example, a fiber-type optical splitter, a planar lightwave circuit (PLC)-type optical splitter, or a spatially coupled optical splitter. Alternatively, the splitter 130 may be configured to receive an optical signal, convert it into an electrical signal, split it, and further convert it into an optical signal to output it to each of the photonic bandgap fibers 12. In this case, the splitter 130 may include, for example, a photoreceiver, a signal regenerator, and a signal light source.

[0031] The optical signal transmitting unit 200 outputs an optical signal to be transmitted through the optical fiber transmission line 100 to the antiresonant fiber 11. The optical signal is, for example, a WDM (Wavelength Division Multiplexing) signal. The optical signal transmitting unit 200 is provided, for example, in a data center.

[0032] The optical signal receiving units 300 each receive an optical signal transmitted through the optical fiber transmission line 100 and output from each photonic bandgap fiber 12. The optical signal transmitting unit 200 is provided in, for example, a data center.

[0033] In the optical fiber transmission line 100, the first cable portion 110 is laid in a first installation environment E1, and thus the antiresonant fiber 11 is placed in the first installation environment E1. Also, the second cable portion 120 is laid in a second installation environment E2, and thus the photonic bandgap fiber 12 is placed in the second installation environment E2.

[0034] Examples of the first installation environment E1 include a long-distance installation environment including between data centers where bending is unlikely to occur in the optical fiber transmission line 100, an undersea installation environment, and an environment in a metro network where bending is unlikely to occur. Examples of the second installation environment E2 include a data center, an environment in a metro network where bending is unlikely to occur, an access system environment, and an FTTx (Fiber To The x) environment.

[0035] The first installation environment E1 and the second installation environment E2 will now be described. For example, assume that a certain optical fiber is a single-mode optical fiber (hereinafter referred to as standard SMF) that is standardly used in optical communications and is specified in ITU-T G.652. In this case, at least one of the following (1) and (2) holds true: (1) When the standard SMF is placed in the second installation environment E2, the macrobending loss is larger than when the standard SMF is placed in the first installation environment E1. (2) When the standard SMF is placed in the second installation environment E2, the microbending loss is larger than when the standard SMF is placed in the first installation environment E1.

[0036] In the case of (1), the first installation environment E1 is a case where the average bending diameter over the length of the optical fiber placed in that state is relatively large, for example, a bending diameter of 60 mmφ or more, which is a specified example of the bending diameter of a standard SMF. The second installation environment E2 is a case where the average bending diameter over the length of the optical fiber placed in that state is smaller than the bending diameter in the first installation environment E1, for example, a bending diameter of 50 mmφ or less. In this case, when the standard SMF is placed in the second installation environment E2, its macrobending loss will be larger than the macrobending loss when the standard SMF is placed in the first installation environment E1.

[0037] In the case of (2), the first installation environment E1 is a case where the average microbending loss over the length of the optical fiber placed in that state is relatively large, for example, when the increase in transmission loss due to microbending is equal to or greater than 0.3 dB / km@1550 nm as specified in ITU-T G.652.C. The second installation environment E2 is a case where the average microbending loss over the length of the optical fiber placed in that state is smaller than the microbending loss in the first installation environment E1, for example, when the increase in transmission loss due to microbending is less than 0.3 dB / km@1550 nm as specified in ITU-T G.652.C. The increase in transmission loss due to microbending (=microbending loss) can be measured, for example, by the fixed drum method.

[0038] In the case of the optical fiber transmission line 100, (1) and (2) hold true.

[0039] In the optical fiber transmission line 100, the length of the antiresonant fiber 11 is longer than the length of each of the photonic bandgap fibers 12.

[0040] In the optical fiber transmission line 100 configured as described above, the splitter 130 receives an input of an optical signal transmitted through the antiresonant fiber 11, splits the optical signal, and outputs it to each of the photonic bandgap fibers 12. This makes the optical fiber transmission line 100 suitable as a structure including splitting of an optical signal using a holey-core fiber.

[0041] Furthermore, in the optical fiber transmission line 100, the antiresonant fiber 11 is placed in the first installation environment E1, and the photonic bandgap fiber 12 is placed in the second installation environment E2, which has the effect of improving bending characteristics such as macrobending characteristics or microbending characteristics.

[0042] Furthermore, since both the antiresonant fiber 11 and the photonic bandgap fiber 12 are hole-core fibers, the effects of low latency, ultra-low nonlinearity, and resistance to harsh environments are also achieved.

[0043] The following explains why the configuration of the optical fiber transmission line 100 exhibits the effect of improving the bend characteristics. Figure 4 is a diagram showing an example of the relationship between the bend diameter and the bending loss per turn at a wavelength of 1550 nm for a typical photonic bandgap fiber and an antiresonant fiber having the configuration shown in Figures 2 or 3.

[0044] Moreover, Fig. 5 shows an example of the relationship between wavelength and microbending loss for a typical photonic bandgap fiber and antiresonant fiber having the configuration shown in Fig. 2 or 3. Here, the microbending loss is a value measured by the fixed drum method.

[0045] 4 and 5, the glass cladding diameter is 150 μm and the coating diameter is 250 μm. PBGF stands for photonic bandgap fiber, and ARF stands for antiresonant fiber.

[0046] As shown in Figures 4 and 5, photonic bandgap fibers tend to have relatively low macrobending and microbending losses compared to antiresonant fibers.

[0047] Therefore, in the optical fiber transmission line 100, the second cable portion 120 including the photonic bandgap fiber 12 is placed in a first installation environment E1, which can be said to be an environment that is more severe for optical fibers in terms of bending characteristics, and the first cable portion 110 including the antiresonant fiber 11 is placed in a second installation environment E2, which can be said to be an environment that is more lenient for optical fibers in terms of bending characteristics. This achieves an optical fiber transmission line 100 with good bending characteristics.

[0048] In Figure 5, the wavelengths where the microbending loss of the PBGF is relatively large correspond to the wavelength band where the transmission loss is large due to the influence of leaky modes. PBGF is known to have such a wavelength band with large transmission loss in the photonic bandgap band. On the other hand, antiresonant fiber is known to have small transmission loss over a wider band than the photonic bandgap.

[0049] Next, the reason why the optical fiber transmission line 100 is suitable as a structure including branching of an optical signal using a holey-core fiber will be explained below. The present inventors have studied structural optimization to maintain the single-mode transmission characteristics of the antiresonant fiber and the photonic bandgap fiber while also achieving bend characteristics, and have found that while the photonic bandgap fiber forms two to four low-loss wavelength bands with wavelength widths of approximately 20 to 30 nm, the antiresonant fiber can form a low-loss wavelength band with a wavelength width of approximately 300 nm.

[0050] Therefore, as an example of a transmission method in the optical transmission system 1000 using the optical fiber transmission line 100, in the antiresonant fiber 11, optical transmission is performed using a wavelength band wider than the wavelength band used for optical transmission in each of the photonic bandgap fibers 12. This makes it possible to effectively utilize the low-loss bands of each optical fiber, and the optical fiber transmission line 100 has a configuration suitable for branching optical signals.

[0051] In the first example of the transmission method, the optical signal transmitter 200 outputs a relatively wideband WDM optical signal that can be transmitted with low loss using the antiresonant fiber 11. The antiresonant fiber 11 transmits this WDM optical signal. The splitter 130 splits the WDM optical signal into wavelength bands and outputs the split signals to the respective photonic bandgap fibers 12. At this time, each of the photonic bandgap fibers 12 is configured to transmit optical signals of different wavelength bands with low loss, and the splitter 130 outputs optical signals of wavelength bands that can be transmitted with low loss through each of the photonic bandgap fibers 12 to the respective photonic bandgap fibers 12. As a result, wideband signal light can be transmitted with low loss through the optical fiber transmission line 100.

[0052] For example, if the low-loss wavelength band of the antiresonant fiber 11 is 300 nm as described above and the low-loss wavelength band of each photonic bandgap fiber 12 is 30 nm, the low-loss wavelength band of the antiresonant fiber 11 can be covered by 10 photonic bandgap fibers 12 .

[0053] In the second example of the transmission method, the optical signal transmitter 200 outputs a relatively wideband WDM optical signal that can be transmitted with low loss using the antiresonant fiber 11. The antiresonant fiber 11 transmits this WDM optical signal. The splitter 130 wavelength-converts the WDM optical signal into optical signals of a predetermined wavelength band, splits the signal, and outputs the split signals to each of the photonic bandgap fibers 12. Each of the photonic bandgap fibers 12 is configured to transmit optical signals of the predetermined wavelength band with low loss. As a result, the optical fiber transmission line 100 can transmit wideband signal light with low loss. Here, the predetermined wavelength band is, for example, the 1550 nm band. Note that the wavelength conversion may be optical wavelength conversion using a nonlinear optical effect, or electrical wavelength conversion via photoelectric conversion.

[0054] (Experimental Example 1) Two photonic bandgap fibers, one antiresonant fiber, and a fiber-type two-way branch were prepared as the air-core fibers, and an optical fiber transmission line was constructed as shown in Figure 1. The photonic bandgap fibers were each 100 m long and were 19-cell photonic bandgap fibers with a PRISM structure as shown in Figure 2. The antiresonant fiber was 1 km long and had a NANF structure as shown in Figure 3. The transmission loss of the photonic bandgap fiber at a wavelength of 1550 nm was 2.5 dB / km, and the transmission loss of the antiresonant fiber at a wavelength of 1550 nm was 1.5 dB / km.

[0055] The first installation environment for the antiresonant fiber was a bent state with an average bending diameter of 300 mm and two turns. The second installation environment for the photonic bandgap fiber was a bent state with an average bending diameter of 50 mm and two turns. The transmission loss of this optical fiber transmission line at a wavelength of 1550 nm was measured. For the measurements, standard SMF was connected to both the antiresonant fiber and the photonic bandgap fiber. The measurement light was input from the antiresonant fiber side. The results are shown in Table 1. In Table 1, the transmission loss of the optical fiber transmission line branching from the antiresonant fiber (ARF) to two photonic bandgap fibers (PBGF) was 8.87 dB for one and 8.85 dB for the other, both of which were below 10 dB, confirming that practically suitable characteristics could be obtained.

[0056] [Table 1]

[0057] In the above embodiment, the photonic bandgap fiber 12 is included in an optical fiber cable, but the photonic bandgap fiber 12 may be included in an optical fiber cord or an optical fiber cord with a connector.

[0058] Furthermore, the present invention is not limited to the above-described embodiments. The present invention also includes configurations in which the above-described components are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible. [Explanation of symbols]

[0059] 11: Antiresonant fiber 11a: Outer tube 11b, 11c: inner capillary 11d: Hole core 12: Photonic bandgap fiber 12a: Cladding part 12aa: Micropore region 12b: Main Core 12c: Side core 100: Optical fiber transmission line 110: First cable section 120: Second cable section 130: Switch 200: Optical signal transmitter 300: Optical signal receiving unit 1000: Optical transmission system E1: 1st installation environment E2:Second installation environment

Claims

1. an antiresonant fiber; a plurality of photonic bandgap fibers; a splitter that receives an input of an optical signal transmitted through the antiresonant fiber, splits the optical signal, and outputs the split optical signal to each of the plurality of photonic bandgap fibers; Equipped with Optical fiber transmission line.

2. The antiresonant fiber is placed in a first installation environment; the plurality of photonic bandgap fibers are placed in a second deployment environment; The macrobending loss of an optical fiber when the optical fiber is placed in the second installation environment is greater than the macrobending loss of the optical fiber when the optical fiber is placed in the first installation environment.

2. The optical fiber transmission line according to claim 1.

3. The antiresonant fiber is placed in a first installation environment; the plurality of photonic bandgap fibers are placed in a second deployment environment; The microbending loss of an optical fiber when the optical fiber is placed in the second installation environment is greater than the microbending loss of the optical fiber when the optical fiber is placed in the first installation environment.

2. The optical fiber transmission line according to claim 1.

4. The branching device is a fiber-type optical branching device, a planar lightwave circuit (PLC)-type optical branching device, or a spatial coupling-type branching device.

2. The optical fiber transmission line according to claim 1.

5. The length of the antiresonant fiber is longer than the lengths of the plurality of photonic bandgap fibers.

2. The optical fiber transmission line according to claim 1.

6. The antiresonant fiber is laid between data centers, and the plurality of photonic bandgap fibers are laid within the data centers.

2. The optical fiber transmission line according to claim 1.

7. an optical fiber cable including the antiresonant fiber; and a plurality of optical fiber cables including each of the plurality of photonic bandgap fibers.

2. The optical fiber transmission line according to claim 1.

8. an optical fiber cable including the antiresonant fiber; and a plurality of optical fiber cords or optical fiber cords with connectors each including one of the plurality of photonic bandgap fibers.

2. The optical fiber transmission line according to claim 1.

9. A transmission method using the optical fiber transmission line according to any one of claims 1 to 8, In the antiresonant fiber, optical transmission is performed using a wavelength band wider than the wavelength band used for optical transmission in each of the plurality of photonic bandgap fibers. Transmission method.

10. The branching device wavelength-converts the optical signal transmitted through the antiresonant fiber into an optical signal of a predetermined wavelength band, and each of the plurality of photonic bandgap fibers transmits the wavelength-converted optical signal. The transmission method according to claim 9.

11. The splitter splits the optical signal transmitted through the antiresonant fiber into optical signals for each wavelength band, and outputs the split optical signals for each wavelength band to each of the plurality of photonic bandgap fibers. The transmission method according to claim 9.

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