WO2016002922A1

WO2016002922A1 - Space-oam conversion and oam combining/branching device, oam transmission system, and oam-adm network system

Info

Publication number: WO2016002922A1
Application number: PCT/JP2015/069238
Authority: WO
Inventors: 貴一 ▲浜▼本; 海松姜
Original assignee: 国立大学法人九州大学
Priority date: 2014-07-04
Filing date: 2015-07-03
Publication date: 2016-01-07
Also published as: JPWO2016002922A1

Abstract

Provided is a space-OAM conversion and OAM combining/branching device capable of increasing multicore fiber transmission channels. A space-OAM conversion and OAM combining/branching device (10) is a space-OAM conversion and OAM combining/branching device (10) that converts input single mode light into OAM mode for output, and that converts input OAM mode into single mode light for output, wherein a fundamental moment angle (θ), which is the angle of one cycle in OAM mode, satisfies the expression θ ≤ 2π × N/M (N < M), where N is the number of cores of a multicore fiber for transmitting OAM mode, and M is the number of modes to be transmitted by the multicore fiber.

Description

Spatial-OAM conversion / OAM branching device, OAM transmission system, and OAM-ADM network system

The present invention relates to a space-OAM conversion / OAM combining / branching device, an OAM transmission system, and an OAM-ADM (Add Drop Multiplexer) network system for transmitting orbital angular momentum (OAM) mode to a multi-core fiber.

Today's data traffic is increasing significantly and spatial division multiplexing (SDM) can become one of the next generation transmission technologies to keep up with the demand for such huge data traffic. Be expected. To date, several research groups have demonstrated high transmission capacity using multi-core fibers, and the data rate has already reached just under 1 Pb / s per fiber (Non-Patent Document 1).
One problem is the number of transmission channels, which is exactly the same as the number of cores “N” of a multi-core fiber (MCF). Therefore, it would be highly desirable if a significant channel increase was achieved.

For example, a conventional switching device includes a mode converter that performs mode conversion of a spatially multiplexed optical signal, and a multi-core fiber that receives the spatially multiplexed optical signal that has passed through the mode converter. The spatially multiplexed optical signal that has been mode-converted by the mode converter propagates to one of the cores of the multi-core fiber according to the mode after conversion (see, for example, Patent Document 1).

JP 2013-257521 A

The conventional switching device described in Patent Document 1 provides high-throughput spatial optical switching that does not need to be switched to a single mode at a switching node, and can only transmit an OAM mode to a multi-core fiber. It does not increase the transmission channel of multi-core fiber.

The present invention has been made to solve the above-described problems, and provides a space-OAM conversion / OAM combining / branching device and an OAM transmission system capable of increasing the transmission channels of a multi-core fiber.

In the space-OAM conversion / OAM combining / branching device according to the present invention, an input single mode light is converted into an OAM mode and output, and an input OAM mode is converted into a single mode light and output. A basic moment angle θ, which is an angle of one cycle in the OAM mode, is a conversion / OAM branching device, where N is the number of cores of the multicore fiber that transmits the OAM mode, and the number of modes that are transmitted to the multicore fiber ( When the number of channels is M, the equation θ ≦ 2π × N / M (where N <M) is satisfied.

In the space-OAM conversion / OAM branching device according to the present invention, the number of transmission channels of multi-core fibers can be increased.

(A) is explanatory drawing which shows the phase of OAM mode on N-core MCF, (b) is explanatory drawing which shows OAM mode (N: number of cores, l: charge number of OAM mode) on 6-core MCF. (C) is a graph showing a moment angle (basic moment angle is 4π / 3) as a function of charge number, and (d) is a moment angle (basic moment angle is 12π / function) as a function of charge number. 13) is a graph showing. (A) is a graph showing the phase of the a-OAM mode on the 6-core MCF (basic moment angle is 12π / 13), and (b) is on the N-core MCF by using a PHASAR element (device). FIG. (A) is a conceptual diagram of a PHASAR element for multiplexing and demultiplexing a-OAM modes, and (b) is a graph showing the relationship of the basic moment angle with respect to the radius of the Roland circle of the PHASAR element. (A) is a graph showing crosstalk in a 6-core MCF in a-OAM mode as a function of charge number by using a PHASAR element, and (b) is a charge number (when l _max = 5). It is a graph which shows the transmittance | permeability as a function. (A) is a graph showing the crosstalk as a function of the number of cores in the case of 100 ch transmission by using a PHASAR element, and (b) shows the transmission of 100 ch on the 60-core as a function of the charge number. It is a graph to show. 1 is a system configuration diagram showing a schematic configuration of an OAM transmission system according to a first embodiment. (A) is a plan view showing a schematic configuration of the space-OAM conversion / OAM combining / branching device shown in FIG. 6, and (b) is an explanatory diagram for explaining a schematic configuration of the multi-core fiber shown in FIG. (C) is sectional drawing for demonstrating arrangement | positioning of the core of another multi-core fiber, (d) is explanatory drawing for demonstrating schematic structure of a fan-in / fan-out device. (A) is a system configuration diagram showing a schematic configuration of an OAM-ADM network system according to the second embodiment, and (b) is a system configuration diagram showing a schematic configuration of the OAM-ADM system shown in FIG. 8 (a). It is. (A) is a plan view showing a schematic configuration of the ADM-through optical circuit shown in FIG. 8 (b), and (b) is a system plan view showing a schematic configuration of the OAM mode optical switch shown in FIG. 8 (b). FIG. 9C is an explanatory diagram for explaining an example of the spatial light switch unit illustrated in FIG.

(First embodiment of the present invention)
First, after explaining the problems in transmitting a normal OAM (orbital angular momentum) mode to a multi-core fiber (MCF), the new OAM mode according to the present invention is changed to the MCF. The advantages of transmitting will be described.
In the present invention, a novel method using an “advanced” orbital angular momentum (OAM) mode (hereinafter referred to as a-OAM mode) is proposed. Evaluation results show that there are more than N transmission channels on the N-core MCF (specifically, an increase in 11-mode channels corresponding to approximately twice the transmission channels on the 6-core MCF) Is shown.

1. Advanced OAM Mode on N-Core MCF The normal OAM mode (Non-Patent Document 2) is a ring-shaped field whose phase change is along the central axis, as shown in FIG. As shown in FIG. 1 (b), in order to convert this phase relationship into the N-core MCF, the phase change profile is divided into N pieces. In this way, the OAM mode can be expressed on the MCF (Non-patent Document 3). Generally speaking, a normal OAM mode having a phase change of 2π × l (l: charge number of the OAM mode) ensures an orthogonal relationship with each other when +/− l is an integer, and an infinite mode set I will provide a.
Unfortunately, in practice, there is a serious problem of degeneration of the OAM mode on the MCF.
Table 1 illustrates an example of this degeneration when the number of cores N = 6. When the charge number 1 exceeds the number of cores N (here, the number of cores N = 6), the phase relationship is exactly the same as in the case of 1−N (see the case of charge number 1 = 7). A similar degeneration occurs in the case of a negative charge number l (see the case of charge number l = −1).

Therefore, even in OAM mode, the transmission channel cannot be increased significantly on the MCF.
However, here we will focus on one advantage of MCF (the cores are isolated from each other). Each core of the MCF can be considered as being separated from each other, and therefore it is not necessary to consider the mode orthogonal state when transmitting signals along the fiber. The phase of the a-OAM mode changes along the central axis as in the normal OAM mode, but no longer has a relationship of “2π” × l.

2. Design criteria for the problem of mode degeneration In addition to the case between cases where the polarity of the charge number is different (+/−), the case of the case where the polarity of the charge number is the same appears. Accordingly, two examples will be described below.

Case 1) Cases where the polarity of the charge number is the same It should be noted about the possible “momentum angle”. (Here, the moment angle Θ is defined as an angle of one cycle in the OAM mode.) For example, in Table 1, this corresponds to 2π when the charge number l = 1, The number l = 6 corresponds to 12π.

In this case, mode degeneracy does not appear between all sets of modes, but if all moment angles Θ used (used for mode multiplexing) exceed this range, mode degeneration will not occur. Begin to appear. For example, in Table 1, the moment angle Θ of charge number 6 is 2π × 6 = 12π. Therefore, mode degeneration does not occur in the range between charge number 1 and charge number 6. However, in the case of charge number 7, the moment angle Θ is 2π × 7, which exceeds 2π × 6, and mode degeneracy appears.

In order to satisfy the conditional expression (1) while increasing the charge number, the fundamental moment angle (fundamental momentum angular) θ is examined here. In some OAM modes, the basic moment angle θ may not be 2π, but in the normal OAM mode, the basic moment angle θ is 2π. For example, if the basic moment angle θ is set to π instead of 2π, the basic moment angle θ is within the range of 2π × N as shown in Table 2, and mode degeneration is avoided up to the charge number l = 12. .

The method for setting an appropriate basic moment angle θ is as follows. In order to realize transmission exceeding M times, the basic moment angle θ is set to 2π × N / M or less. For example, in order to realize more than 2N transmission channels, the basic moment angle θ must be set as follows.

Actually, there is a case where the charge number is 0. In this case, the number of possible transmission channels is 2N + 1 times. In order to secure the case of realizing more than 3N transmission channels, the basic moment angle θ must be set as follows.

Case 2) Charge number polarity is different (+/−) Case It is proposed to generate an OAM mode using a PHASAR element described later. Both polarities in the charge number help reduce excessive losses in addition to the benefits of miniaturization.
However, by using different polarities of charge numbers, the problem of mode degeneration occurs again as charge number l = −1 in Table 1. FIG. 1C shows mode degeneracy when the basic moment angle θ is 4π / 3. As shown in FIG. 1C, the charge number 1 = 3 and the charge number 1 = −6 are in a degenerate relationship, like the charge number 1 = 4 and the charge number 1 = −5.
In practice, this problem is avoided by using the method of equation (2) of case 1. For example, if the basic moment angle θ = 2π × N / 2N = π is used again for more than 2N channels, the problem of degeneration does not occur. FIG. 1 (d) shows the moment angle Θ as a function of charge number. As shown in this figure, a non- "mode degeneration" condition is ensured.

3. Basic Evaluation of Transmission Channel Increase It has already been reported that normal OAM can be generated, multiplexed and separated using PHASAR (Non-Patent Document 5) elements (Non-Patent Document 4).
Even in the case of the a-OAM mode, as shown in FIG. 2A, the phase profile still changes linearly, so here, the possible transmission channels are evaluated based on the use of PHASAR (FIG. 2 (b)).

Since the number of arrayed waveguides in PHASAR is not limited to around 100, but limited to the number of cores “N”, one important problem of OAM mode multiplexing / demultiplexing (Mux / Demux) is its crosstalk. (Non-Patent Document 4).
In a-OAM multiplexing / demultiplexing (Mux / Demux), because of the smaller basic moment angle θ of less than 2π, the channel spacing is narrower, so there is a great concern that crosstalk will deteriorate. On the other hand, the basic moment angle θ is 2π in the normal OAM mode, but it is not necessary to be 2π in the a-OAM mode, and a smaller setting is possible.

For this reason, the use of multiple-input / multiple-output (MIMO) digital signal processing (DSP) is also taken into account. In addition, it has been demonstrated that the -4 dB worsened crosstalk on mode multiplexing can be compensated by using MIMO (Non-Patent Document 6). It is premised on the standard of talk level.

Using the beam propagation method, the crosstalk after a demux PHASAR element was simulated for a-OAM on 6-core MCF.
Crosstalk did not occur during the MCF transmission. The PHASAR element was designed using a silica-based waveguide (birefringence Δn = 0.005).
FIG. 3A is a schematic diagram of a PHASAR element that generates and multiplexes an a-OAM mode. This structure was designed as described below. The number of arrays was designed to be the number of cores of MCF (N), and the number of input ports and output ports was designed to be equal to the number of transmission channels M. The number M of transmission channels corresponds to the following equation (4).

Here, l _max is the maximum charge number. As shown in FIG. 3 (a), the arrayed waveguide and the input port to the center line of symmetry, the distance between each waveguide is set to x _a and x _in. Therefore, the basic moment angle θ of the a-OAM mode can be obtained by the following equation (5).

From this equation (5), as shown in FIG. 2A, the phase difference of each core is obtained using the following equation (6).

This phase Rowland circle determined from the radius of the optical path length difference _{_{_{(R in, R out = 2R}}} in) ( Non-Patent Document 7). The fact that the optical path length and the number of input ports are 1 is obtained by the following equation (7) when the input port interval x _in and the array waveguide interval x _a are constants (FIG. 3A). It is done.

Here, θ _a is each angle of the arrayed waveguide, θ _in is each angle of the input port, and 1 and j are position numbers of the input port and the arrayed waveguide. The optical path length difference ΔL becomes the phase difference Δφ and is obtained by the following equation (8).

Here, n _eff is the effective refractive index of the slab waveguide. The relationship between the basic moment angle and the radius of the Roland circle is determined using Equation (6), Equation (7), and Equation (8). For example, when the input port is 1, the optical path length differences (j = (N + 1) / 2 and j = (N + 1) / 2-1) are obtained by the following equation (9).

From the equations (6), (8), and (9), the relationship between the basic moment angle and the radius of the Roland circle is shown in FIG. 3 (b) (x _a = 18.5 μm, x _in = 20 μm, n _eff = 1.4532 and λ = 1.55 μm). When transmitting 9 channels (corresponding to l _max = 4) using 6-core MCF, the number of input ports is 9, the number of arrayed waveguides is 6, and the basic moment angle θ is 4π / 3. Thus, the radius of the Roland circle is set to 3145 μm (FIG. 3B). When the number of transmission channels is increased to 13 (corresponding to l _max = 6), the number of input ports is increased, the basic moment angle is 12π / 13, and the radius of the Roland circle is 4542 μm. Further, when the number of cores is increased to 12, the number of arrayed waveguides increases to 12, the basic moment angle becomes 12π / 13, and the radius of the Roland circle becomes 4542 μm.
In this way, the case where the wavelength is 1.55 μm is designed and simulated. The results and each design parameter are summarized in FIG. Here, common parameters (waveguide width = 6 μm, x _a = 18.5 μm, x _in = 20 μm, n _eff = 1.4532, and λ = 1.55 μm) were set.

As shown in these figures, the worst crosstalk is −7.3 dB when l _max (maximum value of charge number l) = 4, and −4. When the maximum value l _max = 5 of charge number l. 5 dB, and −3.1 dB in the case of the maximum value l _max = 6 of the charge number l. The actual transmission channel corresponds to 2 × l _max +1 (when the maximum value l _max of the charge number l of +/− and the charge number l = 0 are used). Therefore, the number of possible transmission channels is estimated to be 9 when the maximum value l _max = 4 of the charge number l and 11 when the maximum value l _max = 5 of the charge number l. Since the crosstalk level deteriorates to −4 dB when the maximum value l _max = 6 of the charge number l is exceeded, the number of possible transmission channels is estimated to be 11, which corresponds to almost twice the number of cores. . However, the number of possible transmission channels can be further increased by improving the performance of the PHASAR element and improving the performance of the DSP technology.

To confirm the above, the estimated transmission as a function of charge number l is shown in FIG. 4 (b) (in the case of maximum value l _max = 5 for charge number l). As shown here, if the charge number l increases, there will be an excessive loss, and thus we think it must be improved in future studies.

In addition, using this method, the evaluation was extended toward 100 ch (100 channels). FIG. 5A shows crosstalk as a function of the number of cores when realizing 100 ch.
As shown here, it can be realized on an MCF with more than 55 cores based on the same criteria. In addition, 100-channel transmission was confirmed on the 60-core MCF (FIG. 5B).
The results show that there is a possibility of exceeding 100 ch on the MCF, but in the current PHASAR device design, excess loss increases as the charge number increases, which will also improve in future work I think I have to do it.
As a precaution, when this method is used, it is not necessary to consider a ring-shaped light field profile, and the core can be laid out without being bound by rules except for crosstalk between the cores.

As described above, a new advanced OAM on N-core MCF was proposed. The possibility of more than N transmission channels based on the design criteria shown in this embodiment is presented. When a-OAM is converted to each N-core, in principle, mode-dependent delay hardly occurs when light itself propagates as a normal single mode on each core.
Thus, the described scheme has advantages in mode dependent delay. In addition to MIMO technology, we expect that further improvements in crosstalk due to improvements in PHASAR elements can contribute to promoting MCF for higher transmission capacity.

Next, a system configuration for realizing a new transmission method using the OAM mode (a-OAM mode) according to the present invention will be described with reference to FIGS. 6 and 7. FIG.
As shown in FIG. 6, the OAM transmission system 100 includes a multi-core fiber 1, a pair of optical transmission / reception systems 2, and a pair of space-OAM conversion / OAM coupling / branching devices 10 disposed on the transmission side and the reception side, respectively. And a pair of fan-in / fan-out devices 3.

As shown in FIG. 7B, the multi-core fiber 1 is provided with a plurality of cores 1a in one optical fiber, and has an increased transmission capacity and improved space utilization efficiency compared to a single-core fiber.
7B shows the multicore fiber 1 in which a plurality of cores 1a are arranged in a ring shape, the OAM mode (a-OAM mode) according to the present invention is shown in the cross section of the multicore fiber 1. It is not necessary to arrange a plurality of cores 1a in a ring shape with a clockwise or counterclockwise phase rotation, as long as they are arranged at an interval (for example, 40 μm) at which no crosstalk occurs between adjacent cores 1a. A plurality of cores 1a may be arranged irregularly.
For example, as shown in FIG. 7C, the multi-core fiber 1 is formed in a concentric shape in which a plurality of cores 1a are further arranged inside a ring in which a plurality of cores 1a are arranged in a ring shape. Compared with b), a plurality of cores 1a can be arranged in a vacant area inside the ring, and the space utilization efficiency can be increased.

The optical transmission / reception system 2 converts an electrical signal input from a terminal device (not shown) on the transmission side into an optical signal and transmits the optical signal to the space-OAM conversion / OAM combining / branching device 10. The optical signal received from the device 10 is converted into an electrical signal and output by a terminal device (not shown) on the receiving side.

The space-OAM conversion / OAM combining / branching device 10 converts single-mode light (spatial mode, Gaussian mode) input from the optical transmission / reception system 2 into an OAM mode and outputs it (combining), and a fan-in / fan-out device The OAM mode input from 3 is converted into single mode light and output (branch).
The basic moment angle θ, which is an angle of one cycle in the OAM mode, is obtained when N is the number of cores of the multicore fiber 1 that transmits the OAM mode and M is the number of modes (number of channels) that is transmitted to the multicore fiber 1. The following formula (10) is satisfied.

In particular, as shown in FIG. 7A, the space-OAM conversion / OAM branching device 10 according to this embodiment is a planar optical circuit (Planar) that realizes specific optical characteristics on a substrate by combining optical waveguides. Lightwave Circuit (PLC), comprising an input / output waveguide section 11 composed of a plurality of single mode optical waveguides 11a, an arrayed waveguide section 12 composed of a plurality of single mode optical waveguides 12a having the same optical path length, and a Roland circle The slab waveguide section 13 is connected to the input / output waveguide section 11 at one curvature surface 13a and the array waveguide section 12 is connected to the other curvature surface 13b forming the Roland circle.

Each single mode optical waveguide 11a of the input / output waveguide section 11 is connected perpendicularly to one curvature surface 13a, and each single mode optical waveguide 12a of the array waveguide section 12 is connected to another curvature surface 13b. They are connected vertically.

Further, in the slab waveguide portion 13, the curvature radius R of the Roland circle formed on the other curvature surface 13b is based on the above-described equations (7), (8), (9), and (10). Is set.
For example, when the number of single-mode optical waveguides 12a (the number of cores of the multimode fiber 1) of the arrayed waveguide section 12 is 6, and the number of transmission channels (the number of modes M transmitted to the multicore fiber) is 13, The curvature radius R of the Roland circle formed on the curvature surface 13b is 3670 μm.

The Roland circle formed on the other curvature surface 13b is centered on the midpoint of one curvature surface 13a as shown in FIG.
Further, in the slab waveguide portion 13, the Roland circle formed on one curvature surface 13a is centered on the midpoint of the slab waveguide portion 13, and the curvature radius r of the Roland circle formed on one curvature surface 13a is the center. The half of the radius of curvature R of the Roland circle formed on the other curvature surface 13b (r = R / 2).

Further, the arrayed waveguide section 12 includes N single-mode optical waveguides 12a, and the phase relationship of the OAM mode input to each single-mode optical waveguide 12a of the arrayed waveguide section 12 is Θ / N (= θ × l / N) (where Θ: moment angle, θ: basic moment angle, l: charge number in OAM mode).
For example, when the arrayed waveguide section 12 includes seven single mode optical waveguides 12a, the number of cores N of the multicore fiber 1 that transmits the OAM mode is 7, and the number of modes M that are transmitted to the multicore fiber 1 is 14. The basic moment angle θ is π from Equation (10), and the phase difference of the OAM mode input to the adjacent single mode optical waveguide 12a of the arrayed waveguide section 12 is π / 7.
Specifically, the phase of the OAM mode of charge number 0 input to the single mode optical waveguide 12a located in the center among the seven single mode optical waveguides 12a of the arrayed waveguide section 12 is defined as a reference (Θ / N = θ × l / N = π × 0/7 = 0), the phase of the OAM mode with charge numbers +1 and −1 input to the single mode optical waveguide 12a located on both sides of the single mode optical waveguide 12a is π / 7 ( = Π × 1/7) and −π / 7 (= π × (−1) / 7).
Further, the phase of the OAM mode of charge numbers +2 and -2 input to the single mode optical waveguide 12a positioned next to the single mode optical waveguide 12a to which the OAM modes of charge numbers +1 and -1 are input is 2π / 7 ( = Π × 2/7) and −2π / 7 (= π × (−2) / 7).
The phase of the OAM mode of charge numbers +3 and -3 input to the single mode optical waveguide 12a positioned next to the single mode optical waveguide 12a to which the OAM modes of charge numbers +2 and -2 are input is 3π / 7 ( = Π × 3/7) and −3π / 7 (= π × (−3) / 7).
That is, each single mode optical waveguide 12a of the arrayed waveguide section 12 has a phase relationship of 3π / 7, 2π / 7, π / 7, 0, -π / 7, -2π / 7, -3π / 7. The OAM mode is input.

As described above, the space-OAM conversion / OAM coupling / branching device 10 according to the present embodiment has a configuration including the input / output waveguide section 11, the arrayed waveguide section 12, and the slab waveguide section 13, thereby enabling single mode light. Can be continuously changed, and the number of modes transmitted to the multi-core fiber 1 can be easily increased.

The arrayed waveguide portion 12 according to the present embodiment includes a phase matching region 12b that changes the refractive index of the core of each single mode optical waveguide 12a in order to make each single mode optical waveguide 12a have the same optical path length. I have. The phase matching region 12b may be configured such that the refractive index of the core of each single mode optical waveguide 12a is changed by controlling the current, voltage, or temperature, or the medium is transformed by irradiating ultraviolet rays to change the refractive index. It may be configured to change.
The alignment accuracy among the arrayed waveguide section 12, the fan-in / fan-out device 3 and the multi-core fiber 1 can be made high. From the slab waveguide section 13 to the multi-core fiber 1 (the array waveguide section 12, the fan-in / fan-out device 3). If the lengths of the respective waveguides of the fan-out device 3) are mechanically equal, it is not necessary to provide the phase matching region 12b in the arrayed waveguide portion 12.

The fan-in / fan-out device 3 is connected to each single mode optical waveguide 12a of the arrayed waveguide section 12 in the space-OAM conversion / OAM coupling / branching device 10, and is connected to each core 1a of the multi-core fiber 1 to form a space. -Connect between the OAM conversion / OAM branching device 10 and the multi-core fiber 1.
Note that, in the fan-in / fan-out device 3 according to the present embodiment, as shown in FIG. 7 (d), N single core fibers 3a are bundled in one ferrule 3c (cylindrical connector) at one end. At the other end, the ferrule 3d is attached to each single core fiber 3a and separated at the other end, and the core 3b of each single core fiber 3a on one end side is arranged so as to coincide with each core 1a of the multicore fiber 1 Has been.

Next, the operation of the OAM transmission system 100 according to the present embodiment will be described with reference to FIGS.
In the following description, single mode light (spatial mode, Gaussian mode) is transmitted from the left optical transmission / reception system 2 in FIG. 6, and single mode light (spatial mode, Gaussian mode) is transmitted in the right optical receiving system 2 in FIG. Mode) will be described.

In the following description, the optical transmission / reception system 2 on the left side of FIG. 6 is referred to as “transmission-side optical transmission / reception system 2” with reference to the multicore fiber 1 shown in FIG. 6, and the optical transmission / reception system on the right side of FIG. 2 is referred to as “reception side optical transmission / reception system 2”.
Similarly, in the following description, the space-OAM conversion / OAM combining / branching device 10 on the left side of FIG. 6 is referred to as “transmission-side space-OAM conversion / OAM combining / branching device 10 on the basis of the multicore fiber 1 shown in FIG. The space-OAM conversion / OAM combining / branching device 10 on the right side of FIG. 6 is referred to as “receiving-side space-OAM conversion / OAM combining / branching device 10”.
Similarly, in the following description, the fan-in / fan-out device 3 on the left side of FIG. 6 is referred to as “transmitting fan-in / fan-out device 3” with reference to the multi-core fiber 1 shown in FIG. The fan-in / fan-out device 3 on the right side of FIG.

First, the transmission-side optical transmission / reception system 2 converts an electrical signal input from a transmission-side terminal device (not shown) into an optical signal, and an input / output waveguide section in the transmission-side space-OAM conversion / OAM branching device 10 The single mode light is transmitted to one single optical waveguide 11a.
The single optical waveguide 11a of the input / output waveguide section 11 in the transmission side space-OAM conversion / OAM branching device 10 propagates the input single mode light in the core, and the slab waveguide section 13 transmits the single mode light. (Position information-based signal) is output.

The slab waveguide section 13 in the transmitting side space-OAM conversion / OAM branching device 10 divides the input single mode light in a fan shape, and the phase relationship is Θ / N (Θ: moment angle, N: array waveguide section). The number of 12 single-mode optical waveguides 12a) is expanded as an OAM mode and output to each single-mode optical waveguide 12a of the arrayed waveguide section 12.

Each single mode optical waveguide 12a of the arrayed waveguide section 12 in the transmitting side space-OAM conversion / OAM branching device 10 propagates the OAM mode in the core while maintaining the phase relationship Θ / N of the input OAM mode. Output to each single-core fiber 3a of the transmission-side fan-in / fan-out device 3.

Each single-core fiber 3a of the transmission-side fan-in / fan-out device 3 maintains the phase relationship Θ / N of the input OAM mode and propagates the OAM mode in the core 3b. To enter each.

The multi-core fiber 1 maintains the phase relationship Θ / N of the input OAM mode, propagates the OAM mode in the core 1 a, and outputs it to each single-core fiber 3 a of the receiving fan-in / fan-out device 3. .

Each single-core fiber 3a of the receiving-side fan-in / fan-out device 3 maintains the phase relationship Θ / N of the input OAM mode and propagates the OAM mode in the core 3b. The signal is input to each single mode optical waveguide 12 a of the arrayed waveguide section 12 in the OAM branching device 10.

Each single mode optical waveguide 12a of the arrayed waveguide section 12 in the receiving side space-OAM conversion / OAM branching device 10 propagates the OAM mode within the core while maintaining the phase relationship Θ / N of the input OAM mode. And output to the slab waveguide section 13 respectively.

The slab waveguide unit 13 in the receiving-side space-OAM conversion / OAM branching device 10 uses the input OAM mode of the phase relationship Θ / N as single mode light, and is a single mode optical waveguide of the input / output waveguide unit 11. Branch to 11a and output (OAM mode conversion (charge number conversion)).

The single optical waveguide 11a of the input / output waveguide unit 11 in the receiving-side space-OAM conversion / OAM coupling / branching device 10 propagates the input single-mode light in the core, and the receiving-side optical transmission / reception system 2 has a single mode. Output light.
The reception-side optical transmission / reception system 2 converts the optical signal of the single mode light received from the reception-side space-OAM conversion / OAM combining / branching device 10 into an electrical signal and outputs it to a reception-side terminal device (not shown).

As described above, the space-OAM conversion / OAM combining / branching device 10 according to the present embodiment can mutually convert single mode light (spatial mode, Gaussian mode) and OAM mode, and can also convert a slab waveguide section. The curvature radius R of the Roland circle formed on the other curvature surface 13b of 13 is set based on the above-described equations (7), (8), (9), and (10), so that the multi-core fiber The number of transmission channels exceeding the number of cores of 1 can be ensured.

In addition, the OAM transmission system 100 according to the present embodiment includes a pair of space-OAM conversion / OAM combining / branching device 10, so that single mode light can be converted into OAM mode and transmitted to the multi-core fiber 1. The transmission capacity of the optical fiber can be increased without increasing the diameter of the existing multicore fiber or multimode fiber.

(Second embodiment of the present invention)
FIG. 8A is a system configuration diagram showing a schematic configuration of the OAM-ADM network system according to the second embodiment, and FIG. 8B is a schematic configuration of the OAM-ADM system shown in FIG. 8A. FIG. FIG. 9A is a plan view showing a schematic configuration of the ADM through optical circuit shown in FIG. 8B, and FIG. 9B shows a schematic configuration of the OAM mode optical switch shown in FIG. 8B. FIG. 9C is a system plan view, and FIG. 9C is an explanatory diagram for explaining an example of the spatial light switch unit shown in FIG. 9B. 8 and 9, the same reference numerals as those in FIGS. 1 to 7 denote the same or corresponding parts, and the description thereof is omitted.

As shown in FIG. 8A, the OAM-ADM network system 300 is connected between the multi-core fiber 1 for transmitting the OAM mode and a plurality of the multi-core fibers 1, and forms a ring or bus type transmission path. And an OAM-ADM system 200 for inputting / outputting single mode light to / from the transmission line.

As shown in FIG. 8B, the OAM-ADM system 200 includes an ADM / through optical circuit 20 and a first ADM / through optical circuit 20 disposed on the input side and the output side of the ADM / through optical circuit 20, respectively. A space-OAM conversion / OAM branching device 10a (input / output waveguide unit 11, arrayed waveguide unit 12, slab waveguide unit 13), an OAM mode optical switch 30, and a fan-in / fan-out device 3 are provided.

As shown in FIG. 9A, the ADM through optical circuit 20 outputs a through port 21 that allows single mode light to pass through, an add port 22 that inputs single mode light to the transmission line, and outputs single mode light from the transmission line. A planar optical circuit having a drop port 23.
FIG. 9B shows an example in which the channel located at the lowermost part is configured as a passive optical circuit that is a target of ADM (Add Drop Multiplexer). It is not limited to the position.

As shown in FIG. 8B, the first space-OAM conversion / OAM branching device 10a is connected between the ADM / through optical circuit 20 and the OAM mode optical switch 30, respectively. An input single mode light is converted into an OAM mode and output to the OAM mode optical switch 30 (combining), and an OAM mode input from the OAM mode optical switch 30 is converted into a single mode light to be converted into an ADM / through optical circuit. 20 (branch).

The fan-in / fan-out device 3 includes, as shown in FIG. 8, each single mode optical waveguide of the OAM mode optical switch 30 (the arrayed waveguide section 12 of the second space-OAM conversion / OAM branching device 10b described later). The OAM mode optical switch 30 and the multicore fiber 1 are connected to each other by connecting to the cores 1 a of the multicore fiber 1.

As shown in FIG. 8B, the OAM mode optical switch 30 is connected between the first space-OAM conversion / OAM branching device 10a and the fan-in / fan-out device 3, respectively. Replace (change charge number).
The OAM mode optical switch 30 according to the present embodiment includes a plurality of input ports 31a and output ports 31b as shown in FIG. 9B, and a spatial optical switch unit 31 that switches the optical path of single mode light. And a second space-OAM conversion / OAM branching device 10b (input / output waveguide section 11, array waveguide section 12, slab waveguide section 13).
The OAM mode optical switch 30 may be monolithically integrated in which the space optical switch unit 31 and the second space-OAM conversion / OAM combining / branching device 10b are integrated on a single substrate. The configuration may be such that the component and the component of the second space-OAM conversion / OAM combining / branching device 10b are connected.

The space optical switch unit 31 according to the present embodiment is a matrix switch (N × N space optical switch unit) that connects N inputs and N outputs in an arbitrary combination. For example, FIG. As shown in FIG. 5B, 8 × 8 unit switch elements (2 × 2 switches) 31c are connected in a mesh pattern.

As shown in FIG. 9B and FIG. 8B, the second space-OAM conversion / OAM branching device 10b is connected to the input side and the output side of the space optical switch unit 31, respectively. The single mode light input from the unit 31 is converted into the OAM mode and output to the first space-OAM conversion / OAM combining / branching device 10a or the fan-in / fan-out device 3 (combining), and the first space- The OAM mode input from the OAM conversion / OAM combining / branching device 10a or the fan-in / fan-out device 3 is converted into single mode light and output to the spatial light switch unit 31 (branching).

Here, the operation of the OAM mode optical switch 30 will be described with reference to FIG.
In the following description, the OAM mode is input to the second space-OAM conversion / OAM branching device 10b on the left side of FIG. 9B, and the second space-OAM on the right side of FIG. 9B. The case where the OAM mode is output from the conversion / OAM combining / branching device 10b will be described.
Further, in the following description, the second space-OAM conversion / OAM combining / branching device 10b on the left side of FIG. 9B is referred to as “transmission side” with reference to the space optical switch unit 31 shown in FIG. 9B. The second space-OAM conversion / OAM combination / branching device 10b on the right side of FIG. 9B is referred to as a “second space-OAM conversion / OAM combination / branching device 10b”. -This is referred to as "OAM branching device 10b".

First, each single-mode optical waveguide 12a of the arrayed waveguide section 12 in the transmitting-side second space-OAM conversion / OAM combining / branching device 10b has a phase relationship Θ / N (Θ: moment angle, N : The number of single-mode optical waveguides 12a of the arrayed waveguide section 12) is maintained, and the OAM mode is propagated in the core and output to the slab waveguide section 13, respectively.

The slab waveguide unit 13 in the second space-OAM conversion / OAM branching device 10b on the transmission side uses the input OAM mode of the phase relationship Θ / N as single-mode light (positional information base signal) to input / output signals. Branch and output to one single mode optical waveguide 11a of the waveguide section 11 (OAM mode conversion (charge number conversion)).

The single optical waveguide 11a of the input / output waveguide section 11 in the transmission-side second space-OAM conversion / OAM branching device 10b propagates the input single mode light in the core, and sends it to the space optical switch section 31. Outputs single mode light.

The spatial optical switch unit 31 outputs the input single mode light to any one single optical waveguide 11a of the input / output waveguide unit 11 in the receiving-side second space-OAM conversion / OAM branching device 10b by switching. To do.

One single optical waveguide 11a of the input / output waveguide section 11 in the second space-OAM conversion / OAM branching device 10b on the reception side propagates the input single mode light (position information base signal) in the core. The single mode light is output to the slab waveguide section 13.

The slab waveguide section 13 in the second space-OAM conversion / OAM branching device 10b on the receiving side divides the input single mode light into a fan shape, expands the phase relationship as an OAM mode of Θ / N, It outputs to each single mode optical waveguide 12a of the waveguide section 12 respectively.

Each single mode optical waveguide 12a of the arrayed waveguide section 12 in the second space-OAM conversion / OAM branching device 10b on the receiving side maintains the phase relationship Θ / N of the input OAM mode, and the OAM mode is set in the core. And the OAM mode is output from the receiving side second space-OAM converting / OAM combining / branching device 10b.

As described above, the OAM mode optical switch 30 performs mode switching (switching of charge numbers) between the OAM mode between the input OAM mode and the output OAM mode.
For example, the OAM mode optical switch 30 includes the OAM mode charge number input to the first single-mode optical waveguide 12a from the top of the arrayed waveguide section 12 of the transmission-side second space-OAM conversion / OAM combining / branching device 10b. The information on 1 is switched from the seventh single-mode optical waveguide 12a from the top of the arrayed waveguide section 12 of the receiving-side second space-OAM conversion / OAM branching device 10b by the switching of the spatial optical switch section 31. It is transferred to charge number 7 in the output OAM mode.

That is, as shown in FIG. 8B, the OAM mode optical switch 30 performs a desired OAM (with information to be dropped) via the transmitting side first space-OAM conversion / OAM combining / branching device 10a. The mode is output to the lowest position (drop port 23) of the ADM through optical circuit 22, and an unnecessary OAM mode (with information that does not need to be dropped) is set in the ADM through optical circuit 22 The output is switched to a position other than the lowest position (through port 21).

As described above, the OAM-ADM network system 300 according to the present embodiment outputs only desired OAM mode from the drop port 23 of the ADM / through optical circuit 20 by switching of the OAM mode optical switch 30 and outputs desired information. In addition, the desired OAM mode can be returned to the transmission line from the add port 22 and an unnecessary OAM mode can be passed through the through port 21 of the ADM / through optical circuit 20.

An existing ADM is a transmission device that outputs all signals from a transmission line, acquires only necessary signals from the signals, and returns (inputs) all signals to the transmission line. It becomes complicated.
On the other hand, the OAM-ADM network system 300 according to the present embodiment can output only a desired OAM mode, has a simple system configuration, and is switched by the drop port 23 ( The output of the OAM mode for the add port 22) and the through port 21 can be easily switched.

The OAM transmission system 100 according to the first embodiment described above assumes long-distance transmission using the a-OAM mode.
On the other hand, the OAM-ADM network system 300 according to the present embodiment is assumed to be used for a data center that exchanges optical signals between servers in a limited network, and is intended to increase transmission capacity. However, the present invention is not limited to the a-OAM mode, and a normal OAM mode may be used.

DESCRIPTION OF SYMBOLS 1 Multi-core fiber 1a Core 2 Optical transmission / reception system 3 Fan-in / fan-out device 3a Single core fiber 3b Core 3c, 3d Ferrule 10 Space-OAM conversion / OAM combining / branching device 10a First space-OAM conversion / OAM combining / branching device 10b Second space-OAM conversion / OAM branching device 11 Input / output waveguide section 11a Single mode optical waveguide 12 Array waveguide section 12a Single mode optical waveguide 12b Phase matching region 13 Slab waveguide section 13a One curvature surface 13b Other Curvature Surface 20 ADM / Through Optical Circuit 21 Through Port 22 Add Port 23 Drop Port 30 OAM Mode Optical Switch 31 Spatial Optical Switch Unit

31a Input Port

31b Output Port 31c Unit Switch Element 100 OA Transmission system 200 OAM-ADM system 300 OAM-ADM network system

Claims

A space-OAM conversion / OAM coupling / branching device that converts an input single mode light into an OAM mode and outputs the converted signal, and converts an input OAM mode into a single mode light for output.
The basic moment angle θ, which is an angle of one cycle in the OAM mode, is expressed by the following equation 1 where N is the number of cores of the multicore fiber that transmits the OAM mode and M is the number of modes that are transmitted to the multicore fiber. A space-OAM conversion / OAM branching device characterized by satisfying.
The space-OAM conversion / OAM combining / branching device according to claim 1,
An input / output waveguide section composed of a plurality of single-mode optical waveguides;
An arrayed waveguide section comprising a plurality of single mode optical waveguides having optical path lengths equal to each other;
A slab waveguide section in which the input / output waveguide section is connected to one curvature surface constituting the Roland circle, and the arrayed waveguide section is connected to another curvature plane constituting the Roland circle;
With
A space-OAM conversion / OAM joint branching device characterized in that a curvature radius of a Roland circle formed on the other curvature surface is set based on the equation (1).
The space-OAM conversion / OAM combining / branching device according to claim 2,
The arrayed waveguide portion is composed of N single-mode optical waveguides,
A space-OAM conversion characterized in that when the charge number of the OAM mode is l, the phase relationship of the OAM mode input to each single mode optical waveguide of the arrayed waveguide section is θ × l / N OAM joint branch device.
The space-OAM conversion / OAM combining / branching device according to any one of claims 1 to 3,
Multi-core fiber,
The space-OAM conversion / OAM combining / branching device is connected to each single mode optical waveguide of the arrayed waveguide section and connected to each core of the multi-core fiber, so that the space-OAM conversion / OAM combining / branching device and the multi-core are connected. A fan-in / fan-out device that connects the fibers,
An OAM transmission system comprising:
An OAM comprising: a multi-core fiber that transmits an OAM mode; and an OAM-ADM system that is connected between a plurality of the multi-core fibers to form a ring or bus-type transmission path and that inputs and outputs a single mode light to the transmission path. -An ADM network system,
The OAM-ADM system is
An ADM through optical circuit having a through port that allows single mode light to pass through, an add port that inputs single mode light to the transmission path, and a drop port that outputs single mode light from the transmission path;
An OAM mode optical switch disposed on the input side and the output side of the ADM-through optical circuit for switching modes between OAM modes;
The OAM mode optical switch is disposed on the input side and the output side of the ADM / through optical circuit, connected to each single mode optical waveguide of the OAM mode optical switch, and connected to each core of the multicore fiber. And fan-in / fan-out devices that connect between multi-core fibers;
The OAM mode optical switch is connected between the ADM / through optical circuit and the OAM mode optical switch, converts single mode light input from the ADM / through optical circuit into an OAM mode, and outputs the OAM mode optical switch. A first space-OAM conversion / OAM combining / branching device that converts an OAM mode input from a switch into a single mode light and outputs the single mode light to the ADM / through optical circuit;
An OAM-ADM network system comprising:
The OAM-ADM network system according to claim 5,
The OAM mode optical switch is
A spatial light switch unit having a plurality of input ports and output ports and switching the optical path of single mode light;
The space optical switch unit is connected to the input side and the output side of the space optical switch unit, converts single mode light input from the space optical switch unit into an OAM mode, and converts an OAM mode into single mode light. A second space-OAM conversion / OAM combining / branching device to output to
An OAM-ADM network system comprising: