Core switching device and optical amplification system

Abstract

This core switching device 10 comprises: an end A and an end B which are capable of connecting the cores of MCFs having different propagation directions of signal light between adjacent cores; an end C for transmitting the signal light to an optical amplifier 30; and an end D for inputting the signal light amplified by the optical amplifier 30. The core switching device 10 guides the signal light inputted from the end A and the end B to the end C and guides the signal light inputted from the end D to the end A and the end B.

Description

Core switching device and optical amplification system

[0001] The present disclosure relates to a core switching device and an optical amplification system.

[0002] One technology to increase the transmission capacity per optical fiber is multicore fiber (MCF), which has multiple cores arranged within a single optical fiber. In optical transmission lines using MCF, crosstalk, which is signal interference between cores, is a cause of signal quality degradation. Therefore, to suppress inter-core crosstalk, a bidirectional transmission method has been proposed in which signal light with different propagation directions is arranged in adjacent cores (Non-Patent Document 1).

[0003] Long-distance transmission over optical transmission lines requires repeaters (optical amplifiers) to amplify signal light with reduced intensity. Optical amplifiers for MCF transmission can be broadly divided into two types: segmented amplification and collective amplification. In the segmented amplification method, each core of the MCF is separated using fan-out, amplified individually by an optical amplifier, and then reconnected to each core of the MCF via fan-in. In the collective amplification method, amplification is performed while maintaining the multicore structure using an amplifying multicore fiber. The collective amplification method can prevent an increase in the number of components (amplifier size), and in recent years, a multicore amplifier with small core-to-core characteristic differences has been reported (Non-Patent Document 2).

[0004] Katsunori Imamura et al., “Multicore Fiber for Bidirectional Transmission”, New Glass, Vol.31, No.118, pp.8-11 (2016). Y. Wakayama et al., “FIFO-less Core-pumped Multicore Fiber Amplifier with Fiber Bragg Grating based Gain Flattening Filter”, 2022 European Conference on Optical Communication, Th2A.5 (2022).

[0005] An optical amplifier consists of, for example, an optical isolator, a pumping light source, a pumping optical coupler, an amplifying fiber, and a gain equalizer. To ensure the characteristics of the optical amplifier, each component must be arranged in a specific order along the signal light propagation direction. When the signal light propagates in the same direction between cores in a multi-core transmission line, a collective amplification optical amplifier can be used. However, when the signal light propagates in different directions between cores, a collective amplification optical amplifier cannot be used. To amplify the signal light of a bidirectional MCF, a split-amplification method is used, which requires a fan-out device to separate each core of the MCF, multiple optical amplifiers to amplify the signal light of each core, and a fan-in device to reconnect the separated cores.

[0006] The present disclosure has been made in view of the above, and aims to achieve integration and a reduction in the number of components in a system that amplifies signal light in a multicore fiber for bidirectional transmission.

[0007] A core switching device according to one aspect of the present disclosure includes a first port capable of connecting a first plurality of cores in which the propagation direction of signal light differs between adjacent cores, a second port capable of connecting a second plurality of cores in which the propagation direction of signal light differs between adjacent cores, a third port for sending signal light to an optical amplifier, and a fourth port for inputting signal light amplified by the optical amplifier, and guides signal light input from the first port and the second port to the third port, and guides signal light input from the fourth port to the first port and the second port.

[0008] An optical amplification system according to one aspect of the present disclosure includes the above-described core switching device and an optical amplifier that amplifies signal light sent from the core switching device and inputs the signal light to the core switching device, and the optical amplifier combines the signal light with pump light and amplifies the signal light using a rare-earth-doped fiber with a multi-core structure.

[0009] According to the present disclosure, it is possible to realize integration and a reduction in the number of components in a system that amplifies signal light in a multicore fiber for bidirectional transmission.

[0010] Fig. 1 is a diagram showing an example of the configuration of an optical amplification system. Fig. 2 is a diagram showing an example in which a core switching device is configured with a planar lightwave circuit. Fig. 3 is a diagram showing an example in which a core switching device is configured with a planar lightwave circuit. Fig. 4 is a diagram showing an example in which a core switching device is configured with a planar lightwave circuit. Fig. 5 is a diagram showing an example of the configuration of an optical amplification system. Fig. 6 is a diagram showing an example of the configuration of an optical amplification system. Fig. 7 is a diagram showing an example of the configuration of an optical amplification system.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] 1 is a diagram showing an example of the configuration of an optical amplification system according to this embodiment. The optical amplification system shown in the figure includes a core switching device 10 and an optical amplifier 30. The core switching device 10 connects a bidirectional transmission MCF, converts the propagation direction of signal light propagating in both directions through the MCF, and inputs the signal light to the optical amplifier 30. The optical amplifier 30 amplifies the input signal light and inputs it to the core switching device 10. The core switching device 10 sends the amplified signal light to the MCF.

[0013] The core switching device 10 has an A-end (also called a port or terminal), a B-end, a C-end, and a D-end, and connects each of the cores of an MCF connected to the A-end and the B-end to the C-end or the D-end depending on the propagation direction of the signal light. The A-end and the B-end are connected to the cores of a bidirectional MCF in which the propagation direction of the signal light differs between adjacent cores. For example, a multi-core pigtail fiber is led out from the A-end and the B-end, and an MCF is connected to each of these pigtail fibers by fusion splicing or a connector.

[0014] The core switching device 10 guides signal light input from the cores of the MCFs connected to the A and B ends to the C end, and guides signal light input from the D end to the cores of the MCFs connected to the A and B ends. In other words, signal light input from the core connected to the A end is sent out from the C end, amplified, then input from the D end, and sent to the core connected to the B end. Signal light input from the core connected to the B end is sent out from the C end, amplified, then input from the D end, and sent to the core connected to the A end.

[0015] An optical amplifier 30 is connected between the C end and the D end. Specifically, the C end and the input of the optical amplifier 30 are connected by a fiber with a multi-core structure, and the D end and the output of the optical amplifier 30 are connected. As a result, the signal light sent from the C end is amplified by the optical amplifier 30 and input to the D end into the core switching device 10. Pigtail fibers with a multi-core structure may be led out from the C end and the D end, and the pigtail fibers and the optical amplifier 30 may be connected.

[0016] The optical amplifier 30 is a collective amplification type optical amplifier for MCF transmission. The optical amplifier 30 includes, for example, an amplification multi-core fiber 31, a pumping light source 32, a pumping light coupler 33, optical isolators 34 and 35, and a gain equalizing filter (GFF) 36. The optical amplifier 30 combines signal light with pumping light (also referred to as pump light) and amplifies the signal light in the amplification multi-core fiber 31.

[0017] The amplification multicore fiber 31 is a rare-earth-doped fiber with a multicore structure in which rare-earth ions are doped into the cores of the multicore fiber. When signal light coupled with pumping light is input to each core of the amplification multicore fiber 31, the rare-earth ions are excited, causing stimulated emission of light with the same wavelength as the signal light, thereby amplifying the signal light. When amplifying bidirectional signal light from MCFs connected to ends A and B, the amplification multicore fiber 31 has at least the same number of cores as the cores of the MCFs connected to ends A and B. In the example of FIG. 1 , two-core MCFs are connected to each of ends A and B, so the amplification multicore fiber 31 has two cores. The rare-earth ions are, for example, Yb ions, Er ions, Nd ions, and Tm ions, and may be co-doped rather than being singly doped. The rare-earth ions are selected depending on the band of the signal light to be amplified.

[0018] The pumping light source 32 outputs pumping light having a wavelength corresponding to the absorption band of the rare earth element doped in the amplification multi-core fiber 31 .

[0019] The pumping light coupler 33 couples the signal light with the pumping light from the pumping light source 32 for each core of the amplification multicore fiber 31. The number of pumping light couplers 33 is the same as the number of cores of the amplification multicore fiber 31. In the case of cladding pumping, the pumping light coupler 33 couples the pumping light to the cladding of the amplification multicore fiber 31.

[0020] The optical isolators 34 and 35 are arranged on the input and output sides of the optical amplifier 30, respectively, and serve to realize one-way transmission of the signal light.

[0021] The gain equalizing filter 36 is a filter disposed on the output side of the optical amplifier 30, and serves to flatten the gain spectrum.

[0022] The core switching device 10 can be realized by a planar lightwave circuit (PLC), a spatial optical system, or by drawing a waveguide on a glass substrate using a femtosecond laser.

[0023] FIG. 2 shows an example of a PLC-based configuration of the core switching device 10. In the example of FIG. 2, a two-core MCF is connected between terminals A and B. An optical amplifier 30 is connected between terminals C and D. The core switching device 10 includes optical waveguides connecting terminals A and B to terminals C and D. Specifically, the core switching device 10 includes an optical waveguide that guides signal light input from terminal A to terminal C, an optical waveguide that guides signal light input from terminal B to terminal C, an optical waveguide that guides signal light input from terminal D to terminal A, and an optical waveguide that guides signal light input from terminal D to terminal B. When optical waveguides cross, it is preferable to have an appropriate crossing configuration such that there is no interference between signals.

[0024] As shown in Fig. 3, a pump light multiplexer may be integrated into the core switching device 10. The core switching device 10 inputs pump light and couples the signal light with the pump light. In this case, the optical amplifier 30 connected between the C end and the D end does not need to have a configuration for combining the signal light with the pump light (a pump light source and a pump light coupler). Furthermore, the core switching device 10 may have a power coupler for pump light to split the pump light and share it.

[0025] When connecting a four-core MCF to ends A and B, a core switching device 10 can be configured using stacked PLCs as shown in Figure 4. It can also be fabricated in the same way when connecting an MCF with even more cores.

[0026] When the core switching device 10 is configured using a spatial optical system, the signal light incident from terminals A and B is guided to terminal C using lenses and mirrors, and the amplified signal light incident from terminal D is guided to terminals A and B, and the signal light is returned to the MCF from terminals A and B.

[0027] The core switching device 10 may be used for switching optical paths at connection points of transmission paths in a multi-core transmission system.

[0028] Moreover, instead of the MCF, a plurality of single-core fibers may be connected.

[0029] [Modifications] Modifications of the optical amplification system of this embodiment will be described below.

[0030] The optical amplification system in Fig. 5 is an example in which multiple MCFs are connected to each of the A and B ends of the core switching device 10. In the example in Fig. 5, M MCFs with N cores for bidirectional transmission are connected to each of the A and B ends. For each core of the MCFs connected to the A and B ends, the core that inputs the signal light to the core switching device 10 is connected to the C end, and the core from which the signal light is sent from the core switching device 10 is connected to the D end. An optical amplifier 30 having an M × N core amplification multicore fiber 31 is connected between the C end and the D end.

[0031] The optical amplification system in Fig. 6 is an example in which only signal light propagating in the same direction is redirected and amplified. In the example of Fig. 6, the core switching device 10 connects, for end A, the core whose signal light propagates to the right to end C, and for end B, the core whose signal light propagates to the right to end D. The core switching device 10 connects end A and end B for the core whose signal light propagates to the left. If M MCFs each with N cores for bidirectional transmission are connected to end A and end B, an optical amplifier 30 having an amplification multicore fiber 31 with M × N / 2 cores is connected between end C and end D.

[0032] The optical amplification system shown in Figure 7 is an example in which signal light propagating in the same direction is aggregated and amplified for each propagation direction. The lengths of the transmission paths before and after the optical amplification system are not constant, and the input intensities to the amplifiers are expected to differ, which can lead to unstable output characteristics. In such cases, the signal light is aggregated and amplified for each propagation direction.

[0033] In the example of Figure 7, for the core whose signal light propagates in the right direction, the A terminal is connected to the C-1 terminal, and the D-1 terminal is connected to the B terminal. An optical amplifier 30A is connected between the C-1 terminal and the D-1 terminal. That is, the signal light input from the A terminal to the core switching device 10 is sent out from the C-1 terminal, amplified by the optical amplifier 30A, input to the core switching device 10 from the D-1 terminal, and sent out from the B terminal. For the core whose signal light propagates in the left direction, the B terminal is connected to the C-2 terminal, and the D-2 terminal is connected to the A terminal. An optical amplifier 30B is connected between the C-2 terminal and the D-2 terminal. That is, the signal light input from the B terminal to the core switching device 10 is sent out from the C-2 terminal, amplified by the optical amplifier 30B, input to the core switching device 10 from the D-2 terminal, and sent out from the A terminal. This makes it possible to amplify the signal light collectively by individual optical amplifiers 30A and 30B for each propagation direction. The signal light may be aggregated into three or more signals, and three or more optical amplifiers may be provided.

[0034] As described above, the core switching device 10 of this embodiment includes terminals A and B that can connect cores of an MCF whose signal light propagates in different directions between adjacent cores, terminal C that transmits the signal light to the optical amplifier 30, and terminal D that receives the signal light amplified by the optical amplifier 30. The core switching device 10 guides the signal light input from terminals A and B to terminal C and the signal light input from terminal D to terminals A and B. As a result, the core switching device 10 inputs the signal light whose propagation direction differs between adjacent cores from the MCF, converts it to the same direction, and transmits it. It also inputs the amplified signal light and transmits it to the MCF. This allows the signal light with different propagation directions to be amplified using the optical amplifier 30 with a collective amplification system. As a result, the number of components can be reduced compared to a configuration with a division amplification system using a fan-in / fan-out device, and the amplifier space can be saved. If the loss in the core switching device 10 is kept at the same level as that of a fan-in / fan-out device, the amplification characteristics and power consumption are equivalent to those of the division amplification system.

[0035] The core switching device 10 of this embodiment includes terminals A and B that can connect cores of MCFs in which signal light propagates in different directions between adjacent cores, terminal C-1 that sends the signal light input from terminal A to optical amplifier 30A, terminal C-2 that sends the signal light input from terminal B to optical amplifier 30B, terminal D-1 that inputs the signal light amplified by optical amplifier 30A, and terminal D-2 that inputs the signal light amplified by optical amplifier 30B. The core switching device 10 guides the signal light input from terminal A to terminal C-1 and the signal light input from terminal D-1 to terminal B. The core switching device 10 guides the signal light input from terminal B to terminal C-2 and the signal light input from terminal D-2 to terminal A. This allows the signal light to be amplified individually by optical amplifiers 30A and 30B for each propagation direction of the signal light.

[0036] The optical amplification system of this embodiment includes a core switching device 10 that can connect MCFs in which signal light propagates in different directions between adjacent cores, and an optical amplifier 30 that amplifies the signal light sent from the C-end of the core switching device 10 and inputs it to the D-end of the core switching device 10. The optical amplifier 30 combines the signal light with pumping light and amplifies the signal light in an amplification multi-core fiber 31. This allows the signal light converted to the same direction by the core switching device 10 to be amplified collectively by the optical amplifier 30 that includes the amplification multi-core fiber 31.

[0037] 10 Core switching device 30, 30A, 30B Optical amplifier 31 Amplification multicore fiber 32 Pumping light source 33 Pumping light coupler 34, 35 Optical isolator 36 Gain equalization filter

Claims

1. A core switching device comprising: a first port capable of connecting a first plurality of cores in which the propagation direction of the signal light differs between adjacent cores; a second port capable of connecting a second plurality of cores in which the propagation direction of the signal light differs between adjacent cores; a third port for sending the signal light to an optical amplifier; and a fourth port for inputting the signal light amplified by the optical amplifier, said core switching device guiding the signal light input from the first port and the second port to the third port, and guiding the signal light input from the fourth port to the first port and the second port.

2. A core switching device as claimed in claim 1, comprising: a fifth port for sending the signal light input from said second port to a second optical amplifier; and a sixth port for inputting the signal light amplified by said second optical amplifier, said core switching device guiding the signal light input from said first port to said third port, guiding the signal light input from said fourth port to said second port, guiding the signal light input from said second port to said fifth port, and guiding the signal light input from said sixth port to said first port.

3. An optical amplification system comprising: a core switching device according to claim 1 or 2; and an optical amplifier which amplifies the signal light sent from said core switching device and inputs it to said core switching device, said optical amplifier combining the signal light with pumping light and amplifying the signal light with a rare-earth doped fiber having a multi-core structure.

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