JP2014052560A - Medium, system, and method for optical transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medium, a system, and a method for optical transmission capable of suppressing an increase in crosstalk caused by an increase in the number of cores and in transmission distance.SOLUTION: An optical transmission medium is a multicore optical fiber 53, 53' having an even number of cores 1, 2, 3, 4 as optical waveguides arranged on sides or vertices of a polygon or on a circle in a cross-section perpendicular to a propagation direction of light. The cores are grouped according to either rows or distance from the center of the cores, and adjacent cores or core groups are arranged to have at least different signal light propagation directions, core refractive indices, or signal light wavelengths.

Description

  The present invention relates to an optical transmission medium in which a plurality of cores are included in a clad, an optical transmission system including the same, and an optical transmission method thereof.

  In order to increase the capacity of optical transmission systems, not only optical transmission systems using single-core optical fibers are being studied, but optical transmission systems using multi-core optical fibers are also being studied (for example, non-patent literature). 1). In a multi-core optical transmission system, there is crosstalk between cores, but it is necessary to reduce crosstalk between cores.

  A configuration of a conventional multi-core optical transmission system is shown in FIG. 1 (see Non-Patent Document 2). The optical transmission system includes an optical transmission device 11 that inputs and transmits signals 1,..., N in order from transmission to reception, a coupler 12 that combines a plurality of transmission signals, a multi-core optical fiber 53, a plurality of It comprises a separator 14 that separates received signals and an optical receiver 15 that receives and outputs signals 1,..., N. As the number of cores increases or the transmission distance increases, the crosstalk between the cores increases. Therefore, the number of cores is limited or the transmission distance is limited as compared with an optical transmission system using a single core optical fiber.

  FIG. 1 shows an example in which a multi-core optical fiber having four cores is used, but multi-core optical fibers having other core numbers have also been reported (for example, see Non-Patent Documents 2 and 3).

T.A. Morioka, “New generation optical infrastructure technologies:‘ EXAT initial ’towers 2020 and beyond”, OECC 2009, FT-4, 2009. B. Zhu, et al. "Seven-core multicore fiber transmissions for passive optical network", OPTICS EXPRESS, Vol. 18, no. 11, pp. 11117-11122, 2010. T.A. Hayashi et al. , “Ultra-low-cross multi-core fiber feasible to ultra-long-haul transmission”, OSA / OFC / NFOEC2011, PDPC2, 2011.

  As described above, in multi-core transmission, there is a problem that crosstalk between cores increases as the number of cores increases and transmission distance increases. Therefore, in order to solve the above-described problems, the present invention provides an optical transmission medium, an optical transmission system, and an optical transmission method that can suppress an increase in crosstalk accompanying an increase in the number of cores and a long transmission distance. Objective.

  In order to achieve the above goal, the present invention provides a case where the number of cores, which are optical waveguides arranged on a plane perpendicular to the light propagation direction, is an even number and the cores can be arranged on polygon sides or vertices. Alternatively, when the number of cores is an even number and the cores can be arranged on the circumference, adjacent cores on the circumference are adjacent cores, or cores that are optical waveguides arranged on a plane perpendicular to the light propagation direction Are grouped by either one of the distance from the center of the row or the core group, and at least one of the propagation direction of light, the refractive index of the core, or the wavelength of light differs between adjacent cores or adjacent groups. I decided to make it. In this specification, “adjacent core” means the nearest core, and “adjacent group” means the nearest group.

  Specifically, the present invention is an optical transmission medium in which a plurality of cores serving as waveguides are arranged in a clad, and at least one of the cores has a refractive index different from that of other cores.

  By setting the refractive index of the core to a different value, a difference occurs in the propagation constant, so that mode coupling can be reduced. Therefore, the present invention can provide an optical transmission medium that can suppress an increase in crosstalk due to an increase in the number of cores and an increase in transmission distance.

Further, the present invention is a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
One or more cores at the same distance from the center of the core group in the cross section are taken as one group, or one or more cores on a straight line parallel to each other in the cross section are taken as one group, and the adjacent cores or The optical transmission medium is characterized in that the refractive index of the core is different between the adjacent groups.

  This optical transmission medium can reduce the sum total of crosstalk between adjacent cores.

  The present invention is an optical transmission system including the optical transmission medium and an optical transmission / reception device that propagates an optical signal to the waveguide of the optical transmission medium.

  The present invention is an optical transmission method in which an optical signal is propagated to the waveguide of the optical transmission medium using the optical transmission medium.

  The present optical transmission system and the present optical transmission method include an optical transmission medium capable of reducing mode coupling. Therefore, the present invention can provide an optical transmission system and an optical transmission method that can suppress an increase in crosstalk due to an increase in the number of cores and an increase in transmission distance.

Further, the present invention provides an optical transmission medium in which a plurality of cores serving as waveguides are arranged in a cladding,
An optical transmission / reception device for propagating an optical signal to the waveguide of the optical transmission medium by making the propagation direction or wavelength of light of at least one core different from that of the other core in the core;
Is an optical transmission system.

The present invention uses an optical transmission medium in which a plurality of cores serving as waveguides are arranged in a clad,
In the optical transmission method, an optical signal is propagated to the waveguide of the optical transmission medium by changing a light propagation direction or light wavelength of at least one core in the core different from that of another core.

  Generation of mode coupling can be suppressed by changing the light propagation direction, and crosstalk can be suppressed. Further, by changing the wavelength of light, even if leakage light occurs, it can be removed by a filter or the like, and crosstalk can be suppressed. Therefore, the present invention can provide an optical transmission system and an optical transmission method that can suppress an increase in crosstalk due to an increase in the number of cores and an increase in transmission distance.

The present invention, in a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
The optical transceiver is
One or more cores at the same distance from the center of the core group in the cross section are taken as one group, or one or more cores on a straight line parallel to each other in the cross section are taken as one group, and the adjacent cores or In the optical transmission system, an optical signal is propagated to the waveguide of the optical transmission medium by changing a light propagation direction or a light wavelength between the adjacent groups.

The present invention, in a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
One or more cores at the same distance from the center of the core group in the cross section are taken as one group, or one or more cores on a straight line parallel to each other in the cross section are taken as one group, and the adjacent cores or In the optical transmission method, an optical signal is propagated to the waveguide of the optical transmission medium by changing a light propagation direction or a light wavelength between the adjacent groups.

  The present optical transmission system and optical transmission method can reduce the total crosstalk of adjacent cores.

Further, the present invention provides an optical transmission medium in which a plurality of cores serving as waveguides are arranged in a cladding,
An optical transmission / reception apparatus for propagating an optical signal to the waveguide of the optical transmission medium by changing the optical power of at least one core in the core or the transmission speed of the optical signal from other cores;
Is an optical transmission system.

The present invention uses an optical transmission medium in which a plurality of cores serving as waveguides are arranged in a clad,
In the optical transmission method, the optical power of the at least one core or the transmission speed of the optical signal in the core is different from that of the other cores, and the optical signal is propagated to the waveguide of the optical transmission medium.

  By varying the optical power or the transmission speed of the optical signal for each core, it is possible to reduce crosstalk with respect to the optical signal propagating through the optical transmission medium. Therefore, the present invention can provide an optical transmission system and an optical transmission method that can suppress an increase in crosstalk due to an increase in the number of cores and an increase in transmission distance.

  The present invention is the optical transmission system in which the optical transmission / reception apparatus sets an optical power or a transmission rate of an optical signal corresponding to the transmission loss of the core for each of the cores.

  The present invention is the optical transmission method, wherein an optical power or a transmission rate of the optical signal is set for each core according to the transmission loss of the core.

The present invention, in a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
The optical transceiver is
In the optical transmission system, an optical power or a transmission speed of an optical signal corresponding to crosstalk from an adjacent core is set for each core.

The present invention, in a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
In the optical transmission method, an optical power or a transmission speed of an optical signal corresponding to crosstalk from an adjacent core is set for each core.

In the present invention, a plurality of the optical transmission media are arranged in parallel,
In the optical transmission system, the optical transmission / reception apparatus sets a light propagation direction in each of the cores of the optical transmission medium so that a transmission capacity required for each direction of the optical signal is obtained.

In the present invention, a plurality of the optical transmission media are arranged in parallel,
In this optical transmission method, the propagation direction of light in each of the cores of the optical transmission medium is set so as to have a necessary transmission capacity for each direction of the optical transmission medium.

  A plurality of the same optical transmission media are juxtaposed, and the number of cores set in the propagation direction of one light is the same as the number of cores set in the propagation direction of the other light, so that the optical signal can be transmitted regardless of the light propagation direction. The transmission capacity can be made the same.

  The present invention can provide an optical transmission medium, an optical transmission system, and an optical transmission method that can suppress an increase in crosstalk accompanying an increase in the number of cores and an increase in transmission distance.

It is a figure explaining the conventional optical transmission system. It is a figure explaining the optical transmission system concerning the present invention. It is a setting example of the transmission direction in a 6-core optical fiber. It is an example of the setting of the transmission direction in a 12-core optical fiber. It is an example of the setting of the transmission direction in a 7-core optical fiber. It is an example of the setting of the transmission direction in a 12-core optical fiber. It is the example of a setting of the transmission direction in 19 core optical fiber. It is a figure explaining the optical transmission system concerning the present invention. It is an example of setting the transmission direction and signal wavelength in a 7-core fiber. It is a setting example of the transmission direction and core refractive index in 19-core fiber. It is a figure explaining a group structure determination method. It is a figure explaining the optical transmission system concerning the present invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components. Further, the embodiments described below can be combined as much as possible.

(Embodiment 1-1)
FIG. 2 is a diagram illustrating the optical transmission system 301 of the present embodiment. The optical transmission system 301 includes an optical transmission medium 53 in which a plurality of cores serving as waveguides are arranged in a clad, and the light propagation direction of at least one of the cores is different from that of other cores. And an optical transceiver (62, 64) for propagating an optical signal to the waveguide of the transmission medium.

  Here, in the cross section perpendicular to the light propagation direction of the waveguide, the number of the cores is an even number and the cores are on one or more polygonal sides or vertices, or the cores Are even and the cores are on the circumference of one or more circles, the adjacent cores on the same polygon or on the same circumference are defined as adjacent cores.

  The optical transceiver (62, 64) includes one or a plurality of the cores at the same distance from the center of the core group in the cross section as a group, or one or a plurality of the cores on a straight line parallel to each other in the cross section. An optical signal is propagated to the waveguide of the optical transmission medium by setting the core as one group and changing the propagation direction of light between the adjacent cores or the adjacent groups.

  In this embodiment and the following embodiments, the optical transmission medium (53, 53 ') will be described as a multi-core optical fiber. FIG. 2 is an example of a multi-core optical fiber having four cores. The basic concept of the present invention will be described with reference to FIG. In the prior art of FIG. 1, in all the cores, signal light is transmitted from one fiber end of the multi-core optical fiber 53 (in FIG. 1, the optical transmission / reception device 62 side), and the other fiber end (in FIG. 1, the optical transmission / reception device). Signal light was output from the 64th side).

  In contrast, the optical transmission system 301 individually sets the propagation direction of the signal light for each core. The white cores (1, 3) transmit from the optical transmission / reception device 62 side to the optical transmission / reception device 64 side, and the black cores (3, 4) transmit signal light from the optical transmission / reception device 64 side to the optical transmission / reception device 62. To the side. As shown in FIG. 1, mode coupling of signal light occurs between cores in the same direction of the optical signal, but the signal light propagating through one core and the signal light propagating through the adjacent core as shown in FIG. In this case, mode coupling between signal lights does not occur. That is, crosstalk between adjacent cores can be avoided by making the propagation directions of signal light different between adjacent cores.

  In FIG. 2, the “adjacent core” is, for example, the core (2, 4) with respect to the core 1. In FIG. 2, the number of cores is an even number, and the cores can be arranged on a circumference or a polygon (in this example, a quadrangle). For this reason, the cores (2, 4) are adjacent to the core 1, and the core 3 is not an adjacent core. When the cores are arranged in a straight line on the plane perpendicular to the light propagation direction, the adjacent cores are uniquely determined. However, when arranged in a line other than the straight line as shown in FIG. 2, the core 3 is also an adjacent core. However, in the present embodiment, a circle or polygon including the core on its circumference (on the circumference or on the side or vertex of the polygon) is defined on a plane perpendicular to the light propagation direction, and on the circumference. Since the adjacent core is defined, the adjacent core can be uniquely defined.

  In addition, you may prescribe | regulate an adjacent core as follows using the space | interval of a core. That is, the core 1 and the core 3 are not “adjacent cores” because the distance between them is longer than the distance between the core 1 and the core 2. The core 1 and the cores (2, 4), which are adjacent cores, avoid the mode coupling by changing the propagation direction of the signal light, but the core 1 and the core 3 that are not adjacent cores are difficult to mode-couple, so the propagation direction of the signal light May be the same.

  In the case of FIG. 2, it can be considered that four groups are set for each core. If one or more cores on a straight line parallel to each other in a plane perpendicular to the light propagation direction are grouped into one group, core 1 is group 1, cores (2, 4) are group 2, and core 3 is group 3. It is good. As described above, the cores are grouped together, and crosstalk between the cores can be reduced by propagating the optical signal to the cores by changing the light propagation direction between adjacent groups.

  The situation where crosstalk does not change from core to core has been described above. However, as the number of core parts increases, the number of signal lights propagating in the same direction also increases, and the crosstalk between these signal lights also increases, but the amount of crosstalk varies depending on the arrangement of the core parts. . In general, the core present in the center of the fiber receives more crosstalk than the core present in the periphery. In addition, when the arrangement of the cores becomes complicated, a deviation due to a manufacturing error of the fiber is generated, and a transmission loss may be different for each core. As a result, a difference occurs in the transmission characteristics of the cores. In the worst case, only the core with the worst transmission characteristics may cause a problem that errors occur frequently in the received signal.

  In order to avoid this problem, it is effective to provide a difference in the power or transmission speed of the signal light. In other words, by transmitting signal light with higher optical power than the other core parts to the core part with poor transmission characteristics, or by propagating low-speed optical signals to the core part with poor transmission characteristics compared to other core parts. Thus, it is possible to keep the quality of the received signal uniform.

  Such adjustment of optical power or transmission speed in accordance with crosstalk between cores is not limited to the present embodiment, and is preferably applied to other embodiments of the present application.

(Embodiment 1-2)
The optical transmission system 301 includes an optical transmission medium 53 in which a plurality of cores serving as waveguides are arranged in a clad, and at least one of the cores has a wavelength of light different from that of the other cores. And an optical transceiver (62, 64) for propagating an optical signal to the waveguide of the medium.

  The optical transceiver (62, 64) includes one or a plurality of the cores at the same distance from the center of the core group in the cross section as a group, or one or a plurality of the cores on a straight line parallel to each other in the cross section. An optical signal is propagated to the waveguide of the optical transmission medium by making the core into one group and changing the wavelength of light between the adjacent cores or the adjacent groups.

  Unlike the embodiment 1-1, the present embodiment transmits light with different wavelengths of light between adjacent cores or groups. Even when the wavelength of light is different between the cores, mode coupling may occur and leakage light may occur in other cores. However, since the wavelength of the leaked light is different from that of the signal light, the leaked light can be removed by using an optical filter or an electric filter on the receiving side, and crosstalk between the cores can be reduced.

  In the case of FIG. 2, for example, the signal light of the core 1 and the core 3 is the wavelength A, and the signal light of the core 2 and the core 4 is the wavelength B. Even if the directions of the signal lights are all the same, the crosstalk between the cores can be reduced by removing the leakage light between the cores or between the groups by the optical transceiver (62 or 64).

  In addition, the wavelength A and the wavelength B may each be a single wavelength, or may be a wavelength group of a plurality of wavelengths such as a wavelength division multiplexing (WDM) signal. The same wavelength may not be included in both the wavelength A and the wavelength B.

(Embodiment 1-3)
The optical transmission system 301 includes an optical transmission medium 53 ′ in which a plurality of cores serving as waveguides are arranged in a clad, and at least one of the cores has a refractive index different from that of the other cores. Also good. When the optical transmission medium 53 ′ has an even number of cores and the cores are on one or more polygon sides or vertices in a cross section perpendicular to the light propagation direction of the waveguide, Alternatively, when the number of cores is an even number and the cores are on the circumference of one or more circles, the adjacent cores on the same polygon or on the same circumference are adjacent cores. In the cross section, one or more cores at the same distance from the center of the core group in the cross section as one group, or one or more cores on a straight line parallel to each other in the cross section as one group, The refractive index of the core is different between the adjacent cores or the adjacent groups.

  Unlike Embodiment 1-1, this embodiment differs in the refractive index of a core between groups. By setting the refractive index of each core to a different value, a difference occurs in the propagation constant, so that mode coupling between cores having different refractive indexes can be reduced. For this reason, the leak light between the said cores can be reduced, and the crosstalk between cores can be reduced.

  In the case of FIG. 2, for example, the refractive index of the core 1 and the core 3 is α, and the refractive index of the core 2 and the core 4 is β. Even if the directions of the signal lights are all the same, leakage light between cores or groups can be reduced, so that crosstalk between cores can be reduced.

(Embodiment 2)
FIG. 3 shows an optical transmission medium 53 in which six cores are arranged in a hexagonal shape. FIG. 3A shows a case of conventional multi-core optical transmission, in which signal light propagates in the same direction in the core, so that mode coupling occurs and crosstalk occurs. Each core generates crosstalk from two cores.

  FIG. 3B shows the case of multi-core optical transmission according to this embodiment. In the present embodiment, the number of cores is an even number in FIG. 3B and can be arranged on a circumference or a polygon (in this example, a hexagon). For this reason, the cores (2, 6) are adjacent to the core 1, and the cores 3 to 5 are not adjacent cores. When the cores are arranged in a straight line on the surface perpendicular to the light propagation direction, the adjacent cores are uniquely determined. However, when arranged in a line other than the straight line as shown in FIG. Become. However, in the present embodiment, a circle or polygon including the core on its circumference (on the circumference or on the side or vertex of the polygon) is defined on a plane perpendicular to the light propagation direction, and on the circumference. Since the adjacent core is defined, the adjacent core can be uniquely defined. In addition, you may prescribe | regulate an adjacent core as follows using the space | interval of a core. That is, in FIG. 3, “adjacent core” is, for example, the core (2, 6) with respect to the core 1. The cores 3 to 5 are not “adjacent cores” because their intervals are longer than the intervals between the cores 1 and 2. The core 1 and the cores (2 and 6), which are adjacent cores, avoid the mode coupling by changing the propagation direction of the signal light, but the core 1 and the cores 3 to 5 which are not adjacent cores are difficult to mode-couple, so The propagation direction may be the same.

  In the present embodiment, one or more cores on a straight line parallel to each other in a plane perpendicular to the light propagation direction are grouped. Since the signal light propagating through the adjacent cores is in the opposite direction, no mode coupling occurs between the adjacent cores, and crosstalk between the signal lights does not occur. In the present embodiment, the number of cores giving crosstalk can be reduced from 2 to 0. That is, the sum of crosstalk between cores can be reduced by making the propagation directions of signal light different in adjacent cores.

  FIG. 4 shows an optical transmission medium 53 in which 12 cores are arranged in a hexagonal shape. FIG. 4A shows the case of conventional multi-core optical transmission, and FIG. 4B shows the case of multi-core optical transmission of the present embodiment.

  In the present embodiment, the number of cores is an even number and can be arranged on a circumference or a polygon (in this example, a hexagon). For this reason, the cores (2, 12) are adjacent to the core 1, and the cores 3 to 11 are not adjacent cores. When the cores are arranged in a straight line on the surface perpendicular to the light propagation direction, the adjacent cores are uniquely determined. However, when arranged in a line other than the straight line as shown in FIG. Become. However, in the present embodiment, a circle or polygon including the core on its circumference (on the circumference or on the side or vertex of the polygon) is defined on a plane perpendicular to the light propagation direction, and on the circumference. Since the adjacent core is defined, the adjacent core can be uniquely defined. In addition, you may prescribe | regulate an adjacent core as follows using the space | interval of a core. That is, in FIG. 4B, the “adjacent core” is, for example, the core (2, 12) with respect to the core 1. The cores 3 to 11 are not “adjacent cores” because their intervals are longer than the intervals between the cores 1 and 2. The core 1 and the cores (2 and 12), which are adjacent cores, avoid the mode coupling by changing the propagation direction of the signal light, but the core 1 and the cores 3 to 11 which are not adjacent cores are difficult to mode-couple, so The propagation direction may be the same.

  That is, the number of cores that give crosstalk to the core 3, the core 4, the core 5, the core 9, the core 10, and the core 11 can be reduced from 2 to 0. Further, the number of cores that give crosstalk to the core 2, the core 6, the core 8, and the core 12 can be reduced from 2 to 1. Similar to the case of FIG. 3B, the total crosstalk between the cores can be reduced by making the propagation directions of the signal light different in the adjacent cores.

  As described above, in the present embodiment, the propagation direction of the signal light is individually set for each group of cores, and the propagation direction of the signal light is reversed between adjacent groups, so that a plurality of cores can be connected. The crosstalk between cores of the optical fiber can be greatly reduced.

  Also in this embodiment, as described in the embodiments (1-2, 1-3), even if the wavelength of light and the refractive index of the core are different for each group, the effect of reducing the sum of the crosstalk between the cores is also the same. Can be obtained.

  In the present embodiment, the core is arranged in a hexagonal shape, but may be another polygonal shape or a circular shape. Further, it is desirable that the number of cores of the multi-core optical fiber is an even number. Even when the number of cores is not an even number, the propagation direction may be determined on the assumption that the number of cores is one extra. For example, in the case of 13 cores, the propagation direction may be determined assuming that the core is 14. In this case, the propagation directions of the adjacent cores of the core 1 and the core 13 are the same, and crosstalk occurs between the adjacent cores. However, it is clear that the total crosstalk is smaller than that of the conventional example.

(Embodiment 3-1)
FIG. 5 shows an optical transmission medium 53 in which seven cores are arranged in a close-packed structure. FIG. 5A shows the case of conventional multi-core optical transmission, in which signal light propagates in the same direction in the core, so that mode coupling occurs and crosstalk occurs. The center core 1 generates crosstalk from six cores. The peripheral core generates crosstalk from the three cores.

  FIG. 5B shows the case of multi-core optical transmission according to this embodiment. In the present embodiment, one or a plurality of cores on a straight line parallel to each other in a plane perpendicular to the light propagation direction is made into one group. That is, the core 2 and the core 3 are the first group, the core 1, the core 4 and the core 7 are the second group, and the core 5 and the core 6 are the third group. The signal light propagates in the same direction in the cores of the first group and the third group, and the signal light propagates in the opposite direction in the cores of the second group. Since the signal light propagating through the core of the adjacent group is in the opposite direction, mode coupling does not occur between the groups, and crosstalk between the signal lights does not occur. In the present embodiment, the number of cores that give crosstalk to the central core 1 is reduced to two, and the number of cores that give crosstalk to the peripheral cores 2, 3, 4, 5, 6, and 7 can be reduced to one. it can. That is, the sum of crosstalk between cores can be reduced by making the propagation directions of signal light different in adjacent groups.

Embodiment 3-2
FIG. 6 shows an optical transmission medium 53 in which 12 cores are arranged in a close-packed structure. FIG. 6A shows the case of conventional multi-core optical transmission. Since mode coupling of signal light occurs between cores in the same direction, the internal cores (10, 11, 12) generate crosstalk from six cores. The peripheral cores (1 to 9) generate crosstalk from three or four cores.

  FIG. 6B shows a first case of multi-core optical transmission according to this embodiment. In the present embodiment, one group or a plurality of cores that are at substantially the same distance from the center of the core group on a plane perpendicular to the light propagation direction is defined as one group. That is, the internal cores (10, 11, 12) are the first group, and the peripheral cores (1-9) are the second group. The signal light propagates in the same direction in the first group of cores, and the signal light propagates in the opposite direction in the second group of cores. When the signal light propagating through the core is in the opposite direction with the signal light propagating through the adjacent core, mode coupling between the signal lights does not occur, so the number of cores that give crosstalk to all the cores can be reduced to two. it can. That is, the sum of crosstalk between cores can be reduced by making the propagation directions of signal light different in adjacent groups.

  FIG. 6C shows a second case of multi-core optical transmission according to this embodiment. In the present embodiment, one or a plurality of cores on a straight line parallel to each other in a plane perpendicular to the light propagation direction is made into one group. That is, the core (1, 2) is the first group, the core (3, 9, 10) is the second group, the core (4, 8, 11, 12) is the third group, and the core (5, 6, 7) is The fourth group. The signal light propagates in the same direction in the cores of the first group and the third group, and the signal light propagates in the opposite direction in the cores of the second group and the fourth group. When signal light propagating through a core is in the opposite direction to signal light propagating through another core, mode coupling between signal lights does not occur, so the number of cores giving crosstalk is reduced to one or two in all cores. can do. That is, the sum of crosstalk between cores can be reduced by making the propagation directions of signal light different in adjacent groups.

Embodiment 3-3
FIG. 7 shows an optical transmission medium 53 in which 19 cores are arranged in a close-packed structure. FIG. 7A shows a case of conventional multi-core optical transmission. In the core, signal light propagates in the same direction, so that the internal core generates crosstalk from six cores. The peripheral core generates crosstalk from three or four cores.

  FIG. 7B shows a first case of multi-core optical transmission according to this embodiment. In the present embodiment, one or a plurality of cores are provided at substantially the same distance from the center of the core group on a plane perpendicular to the light propagation direction. Although the center of the multiple core group is used as the reference point here, the center of the fiber may be used as the reference point. That is, the inner core 19 is a first group, the inner cores (13 to 18) are a second group, and the peripheral cores (1 to 12) are a third group. The first group of cores and the third group of cores propagate signal light in the same direction, and the second group of cores propagate signal light in the opposite direction. That is, a group is formed concentrically around the central core 19, and signal light is transmitted so that the light propagation directions are different between the cores of adjacent groups. Thereby, the central core 19 can avoid crosstalk from other cores. In addition, the number of cores giving crosstalk to all other cores can be reduced to two. That is, the sum of crosstalk between cores can be reduced by making the propagation directions of signal light different in adjacent groups.

  FIG. 7C shows a second case of multi-core optical transmission according to this embodiment. In the present embodiment, one or a plurality of cores on a straight line parallel to each other in a plane perpendicular to the light propagation direction is made into one group. That is, the core (1-3) is the first group, the core (4, 12, 13, 14) is the second group, the core (5, 11, 15, 18, 19) is the third group, and the core (6, 10). 16, 17) is the fourth group, and the cores (7-9) are the fifth group. The signal light propagates in the same direction in the cores of the first group, the third group, and the fifth group, and the signal light propagates in the opposite direction in the cores of the second group and the fourth group. In this way, by setting the propagation direction of light between adjacent groups as the propagation in the same direction in the cores in the group, the number of cores giving crosstalk in all the cores is reduced to one or two. Can be reduced. That is, the sum of crosstalk between cores can be reduced by making the propagation directions of signal light different in adjacent groups.

  In Embodiments 3-1 to 3-3, as described in Embodiments (1-2 and 1-3), even if the wavelength of light and the refractive index of the core are different for each group, the crosstalk between cores is the same. The effect of reducing the sum of the values can be obtained.

(Embodiment 4)
The number of cores is not the same in the two propagation directions as in the number of cores 7 of the optical transmission medium 53 in FIG. 5, the number of cores 12 in the optical transmission medium 53 in FIG. 6, and the number of cores 19 in the optical transmission medium 53 in FIG. In such a case, the capacity for transmission in the propagation direction may be different. Therefore, in the present embodiment, an optical transmission system capable of making the transmission capacity in the propagation direction the same even when the optical transmission medium 53 as described above is used will be described.

  A plurality of optical transmission media 53 are arranged in parallel, and the optical transmission / reception devices (62, 64) set the propagation direction of light in each of the cores of the optical transmission media so as to obtain a necessary transmission capacity for each direction of the optical signal. It may be set. Here, two examples of the optical transmission medium 53 will be described.

  FIG. 8 is a diagram illustrating the optical transmission system 302 according to the present embodiment. The optical transmission system 302 includes two optical transmission media 53. The optical transmission / reception devices (62, 64) set the propagation directions of light set in the respective cores of the optical transmission media 53-1, and the optical transmission media 53-. The light propagation directions set in the respective cores of the optical transmission medium 53-2 corresponding to the respective one cores are reversed.

  In this embodiment, a 7-core optical fiber is used. The optical transmission / reception device 62 transmits signal light to the optical transmission / reception device 64 using a group of cores (1, 2, 5) of the optical transmission medium 53-1, and the optical transmission / reception device 64 transmits the core ( Signal light is transmitted to the optical transmitter / receiver 62 using the groups 3, 4, 6, 7). On the other hand, the optical transmission / reception device 62 transmits signal light to the optical transmission / reception device 64 using a group of cores (3, 4, 6, 7) of the optical transmission medium 53-2. Signal light is transmitted to the optical transceiver 62 using a group of two cores (1, 2, 5). In this way, by using two systems of optical transmission media and switching the propagation direction of each core for each optical transmission medium, the number of cores in the two propagation directions in the entire optical transmission system 302 can be matched. .

  That is, even when using a multi-core optical fiber in which the number of cores is not the same in the two propagation directions, the propagation direction of each core is switched between the two systems using two systems of transmission systems, that is, the signal is transmitted in the adjacent group. By making the light propagation directions different, it is possible to reduce the sum of crosstalk between cores and realize multi-core optical transmission with the same transmission capacity in both directions.

  Here, the case where there are two optical transmission media 53 has been described. However, even if there are three or more optical transmission media 53, the transmission capacities are equal in both directions so that the propagation directions of the signal light are different in adjacent groups. Thus, the same effect can be obtained by setting the light propagation direction in each core.

  Also in this embodiment, as described in the embodiments (1-2, 1-3), even if the wavelength of light and the refractive index of the core are changed for each group, the sum of crosstalk between cores is similarly reduced, In addition, multi-core optical transmission with the same transmission capacity in both directions can be realized.

  In the above example, multi-core optical transmission with the same transmission capacity is performed bi-directionally with two optical fibers. However, the number of fibers may be two or more, and required transmission capacity in each direction. Depending on the above, the combination of transmission directions may be changed as appropriate.

(Embodiment 5-1)
As described in the above embodiment, it is possible to reduce the sum of crosstalk between cores by changing the propagation direction of the core light between adjacent groups, but the 7 cores shown in FIG. Like the optical fiber, the central core 1 has crosstalk from two cores, and the other cores have crosstalk from one core.

  In the embodiment of FIG. 9, among the groups of cores having the same propagation direction, the other cores included in the group are set to different wavelengths. As a result, even if mode coupling occurs and leakage light is generated in other cores included in the group, the wavelength of the leakage light is different from that of the signal light. Light can be removed and crosstalk can be reduced.

  FIG. 9A shows the case of conventional multi-core optical transmission. When the propagation directions of the core are the same, it is necessary to prepare three types of wavelengths A, B, and C in order to reduce crosstalk from the core using different wavelengths. However, even in this case, other cores included in the group (illustrated by broken lines [core 2 to core 6 etc.] in the figure) have the same wavelength, and thus are affected by crosstalk from other cores included in the group. It will be.

  FIG. 9B shows the case of multi-core optical transmission according to this embodiment. In the present embodiment, since the propagation directions of adjacent groups are different, the same effect can be obtained at two types of wavelengths A and B. Further, other cores included in the group of the same propagation direction can also have different wavelengths, and this embodiment can effectively use wavelength resources and realize further excellent crosstalk suppression characteristics. It is possible.

  In the embodiment of FIG. 9B, an example has been described in which the light propagation direction is different between adjacent groups and the wavelength is different within the group. As another example, the refractive index of the core is different between adjacent groups, and the light propagation direction or wavelength is different within the group, or the wavelength is different between adjacent groups, and the light propagation direction or core is different within the group. The same effect can be obtained even in a form having a different refractive index.

(Embodiment 5-2)
In the embodiment of FIG. 10, among the core groups having the same propagation direction, the cores in the group are set to different refractive indexes. By setting the refractive index of each core of the optical transmission medium 53 to a different value, a difference occurs in the propagation constant, so that mode coupling can be reduced and crosstalk can be further reduced.

  FIG. 10A shows the case of conventional multi-core optical transmission. When the propagation directions of the cores are the same, three types of refractive index cores of α, β, and γ are necessary to reduce crosstalk from other cores using different refractive indexes. However, even in this case, the other cores included in the group (illustrated by broken lines [core 2 to core 19 etc.] in the figure) have the same refractive index and are affected by crosstalk from other cores included in the group. It will be.

  FIG. 10B shows the case of multi-core optical transmission according to this embodiment. In the present embodiment, since the propagation directions of adjacent groups are different, the same effect can be obtained simply by preparing cores with two types of refractive indexes α and β. Furthermore, since the refractive indexes of the other cores included in the group in the same propagation direction are different, this embodiment can more effectively reduce crosstalk. In addition, since the number of types of refractive index is small, the requirements for refractive index accuracy in fiber manufacture can be relaxed, which is effective in reducing fiber manufacturing costs.

  In the embodiment of FIG. 10B, the example in which the light propagation direction is different between adjacent groups and the refractive index of the core is different within the group has been described. As another example, the refractive index of the core is different between adjacent groups, and the light propagation direction or wavelength is different within the group, or the wavelength is different between adjacent groups, and the light propagation direction or core is different within the group. The same effect can be obtained even in a form having a different refractive index.

(Embodiment 6)
In the first to fifth embodiments, examples of core group configurations have been described. In the present embodiment, how to determine a group configuration of cores will be described. FIG. 11 is a diagram for explaining a method for determining a core group configuration.

  In step S11, the number of groups required in the case of one core and one group is calculated. Here, “consisting of one core and one group” means that the number of cores that are optical waveguides arranged in a plane perpendicular to the light propagation direction is an even number, and the cores can be arranged on the sides or vertices of the polygon. Alternatively, when the number of cores is an even number and the cores can be arranged on the circumference, the cores on the circumference are grouped (one core and one group). In step S12, the number of necessary group types is calculated when a group is formed with one or more cores on a concentric circle from a reference point (for example, the center of a fiber or a group of multiple cores) as one group. In step S13, when there are a plurality of locations to be the reference points, the reference points are changed and step S12 is performed again. In step S14, the number of groups required when one or a plurality of cores on a parallel straight line are formed as one group is calculated. In step S15, when a group configuration is possible using parallel lines of another form, step S14 is performed again using parallel lines of another form. In step S16, a group configuration that minimizes the number of groups calculated in steps (S11, S12, S14) is selected.

  As the determining means in step S16, the maximum or minimum amount or average value of the crosstalk in the core in each group configuration is calculated by multiplying each of the required number of groups by a coefficient, and the calculated value is the minimum. A method of selecting a group configuration to be used may be used. In addition, the maximum or minimum amount of crosstalk at the core in each acceptable group configuration or an average reference value (for example, 20 dB) is determined, and the number of groups is minimized among the group configurations that satisfy the reference value. A method of selecting a group configuration may be used. When the crosstalk value is used in step S16, the crosstalk of each group configuration considered in steps (S11, S12, S14) is calculated or measured before step S16.

(Embodiment 7)
FIG. 12 is a diagram illustrating the optical transmission system 303 according to the present embodiment. The optical transmission system 303 includes an optical transmission medium (53, 53 ′) in which a plurality of cores serving as waveguides are arranged in a clad, and the optical power of at least one core or the transmission speed of an optical signal is different in the core. And an optical transmission / reception device (62, 64) for propagating an optical signal to the waveguide of the optical transmission medium (53, 53 ′).

  The optical transmitter / receiver (62, 64) can set the optical power or the transmission speed of the optical signal corresponding to the transmission loss of the core for each of the cores.

In a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
The optical transceiver (62, 64)
You may set the transmission speed of the optical power or optical signal according to the crosstalk from an adjacent core for every said core.

  As the number of core portions increases, the number of signal lights propagating in the same direction also increases, and it is inevitable that crosstalk between these signal lights also increases. Since the amount of crosstalk depends on the number of cores present in the surrounding area and the distance between them, quantitative evaluation is difficult, but in general, the core existing in the center of the fiber exists in the peripheral part. Receive more crosstalk than cores that do. For this reason, the signal propagated through the core near the center is more likely to deteriorate the quality of the received signal than the signal propagated through another core.

  In addition, when the arrangement of the cores becomes complicated, a deviation due to a manufacturing error of the fiber is generated, and a transmission loss may be different for each core. Since an increase in loss is directly linked to a decrease in reception power, this also causes deterioration in the quality of the received signal.

  When signal quality degradation in the transmission path is unacceptably large, the transmission path length of the optical transmission path (optical fiber) can be shortened to prevent signal quality degradation of the received signal. However, because of the structure of the multi-core optical fiber, all the cores have the same transmission path length, and the transmission path length cannot be shortened only for a specific core. For this reason, the transmission distance of the entire multi-core optical fiber is limited by the core having the worst transmission characteristics, and the core having the good transmission characteristics cannot fully utilize the advantages.

  In order to alleviate this problem, different types of optical signals may be input for each core. As the different types of optical signals, the first is an optical signal having different optical power. The optical power may be, for example, an optical power whose reception sensitivity is improved by a difference in crosstalk intensity from other cores with respect to a core having a high crosstalk intensity.

  As the different types of optical signals, the second is an optical signal having a different transmission rate. Since an optical signal having a low transmission speed has high reception sensitivity, an error rate can be suppressed to a low level even in a transmission path with a large crosstalk. The reduction of the transmission rate is realized by lowering the symbol rate. However, in the case of an optical QAM signal, the multi-value number may be lowered. For example, the transmission speed may be a transmission speed at which reception sensitivity is improved by a difference in intensity of crosstalk with other cores.

  An optical signal that is a combination of the first and second different optical signals with respect to a core having a large crosstalk is relatively large, and an optical signal having a relatively low transmission speed has a reception sensitivity equivalent to that of other cores. You may do it.

  When the loss of a specific core is large, a decrease in reception power can be prevented by increasing the optical transmission power only for that core.

As the optical transmission power, for example, the loss difference with other cores is increased.
Further, the transmission speed may be lowered as in the case of the core having a large crosstalk.
However, optical power that is too high causes waveform degradation due to nonlinear phenomena and increased crosstalk to other cores, so control by optical power adjustment means is necessary.

  In an actual optical transmission system, it is conceivable to use only a part of a plurality of cores at the beginning of installation, and gradually increase the number of cores to be used as demand increases. In such a case, it is desirable to select only the core with the best characteristics at the beginning of installation, and select the core in consideration of the transmission characteristics as the utilization efficiency of the core increases.

  Further, in an actual optical transmission system, a situation may occur in which the transmission amount from point A to point B is large, but the transmission amount from point B to point A is small. In such a case, it is possible to assign a core having good transmission characteristics for transmission from the point A to the point B and assign a core having poor transmission characteristics for transmission from the point B to the point A.

  FIG. 12 shows an optical transmission system 303 for such a purpose. The difference from FIG. 2 is that optical switches 100a to 100d typified by a cross-connect are provided so that a core connected between signals propagating in the same direction can be freely selected. Further, since the variable optical attenuators 101a to 101d are provided, the input power to each core can be freely changed.

(Other embodiments)
In the above-described embodiment, the case where the number of cores is 4, 6, 7, 12, 19 is shown. However, when the number of cores is changed, the crosstalk can be reduced as compared with the related art. In the above-described embodiment, the case of the hexagonal shape or the core arrangement of the close-packed structure is shown, but other shapes such as a circle may be used.

  In the above-described embodiment, the optical transmission medium is described as a multi-core optical fiber. However, an optical circuit in which an optical waveguide (core) is two-dimensionally arranged on a plane perpendicular to the light propagation direction, for example, the core row is deep. It may be a planar lightwave circuit (PLC) arranged in a plurality of stages in the direction.

  The following is a summary of the multi-core optical transmission system of this embodiment.

(1)
A plurality of transmission units for transmitting signal light, a plurality of reception units for receiving signal light, a multi-core optical fiber having a plurality of core units for transmitting signal light, and each multi-core signal light from the transmission unit A coupling unit coupled to each core of the optical fiber, and a second coupling unit coupling the signal light output from each core of the multi-core optical fiber to the receiving unit, respectively.
A multi-core optical transmission system, wherein a propagation direction of a signal propagating through at least one core of the multi-core optical fiber is opposite to an adjacent core.

(2)
The multi-core optical transmission system according to (1), wherein the core portions of the multi-core optical fiber are arranged at equal intervals, and the propagation directions of signals propagating through adjacent cores are opposite to each other.

(3)
The core part of the multi-core optical fiber is arranged in a close-packed structure, the core group is divided into rows, and the propagation direction is set to be different for each row. Transmission system.

(4)
The core part of the multi-core optical fiber is arranged in a close-packed structure, the core group is divided into concentric circles, and the propagation direction is set to be different for each concentric circle. Transmission system.

(5)
In the multi-core optical transmission system according to (1) above,
Two optical transmission systems comprising a transmission unit, a coupling unit, a multi-core optical fiber, a second coupling unit, and a receiving unit are provided,
By setting the propagation direction of the signal light of each core in one system to the reverse of the other system, the number of cores with the same propagation direction and the number of cores with different propagation directions are made equal. Multi-core optical transmission system.

(6)
In the multi-core optical transmission system according to (1) to (5) above,
A multi-core optical transmission system in which signal light of adjacent cores is set to a different wavelength in a group of cores having the same propagation direction.

(7)
In the multi-core optical transmission system according to (1) to (5) above,
A multi-core optical transmission system in which the refractive indexes of adjacent cores are set to different values in a group of cores having the same propagation direction.

(Effect of this embodiment)
In this embodiment, the propagation direction, refractive index, or wavelength of signal light is individually set for each of a plurality of cores in multi-core optical transmission, and the propagation direction, refractive index, or wavelength of signal light is different between adjacent cores. By doing so, the crosstalk between cores of a multi-core optical transmission system can be greatly reduced.

51: transmitter 52: coupler 53: multi-core optical fiber 54: second coupler 55: receiver 62, 64: optical transceivers 100a to 100d: optical switches 101a to 101d: variable optical attenuator 131: signal light on the left side Core 132 propagating from right to right: Cores 130, 131, 132 for propagating signal light from right to left: Optical transmission system

Claims (16)

  An optical transmission medium in which a plurality of cores serving as waveguides are arranged in a clad, and at least one of the cores has a refractive index different from that of other cores. In a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
One or more cores at the same distance from the center of the core group in the cross section are taken as one group, or one or more cores on a straight line parallel to each other in the cross section are taken as one group, and the adjacent cores or The optical transmission medium according to claim 1, wherein the refractive index of the core is different between the adjacent groups. The optical transmission medium according to claim 1 or 2,
An optical transceiver for propagating an optical signal to the waveguide of the optical transmission medium;
An optical transmission system comprising: An optical transmission medium in which a plurality of cores serving as waveguides are arranged in a clad;
An optical transmission / reception device for propagating an optical signal to the waveguide of the optical transmission medium by making the propagation direction or wavelength of light of at least one core different from that of the other core in the core;
An optical transmission system comprising: In a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
The optical transceiver is
One or more cores at the same distance from the center of the core group in the cross section are taken as one group, or one or more cores on a straight line parallel to each other in the cross section are taken as one group, and the adjacent cores or The optical transmission system according to claim 4, wherein an optical signal is propagated to the waveguide of the optical transmission medium by changing a light propagation direction or a light wavelength between the adjacent groups. An optical transmission medium in which a plurality of cores serving as waveguides are arranged in a clad;
An optical transmission / reception apparatus for propagating an optical signal to the waveguide of the optical transmission medium by changing the optical power of at least one core in the core or the transmission speed of the optical signal from other cores;
An optical transmission system comprising: The optical transceiver is
The optical transmission system according to claim 6, wherein an optical power or an optical signal transmission rate is set for each core according to the transmission loss of the core. In a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
The optical transceiver is
The optical transmission system according to claim 6, wherein an optical power or a transmission speed of an optical signal is set for each core according to crosstalk from an adjacent core. A plurality of the optical transmission media are arranged in parallel,
The optical transmission / reception apparatus sets a light propagation direction in each of the cores of the optical transmission medium so as to have a necessary transmission capacity for each direction of an optical signal. The optical transmission system described in 1.   An optical transmission method for propagating an optical signal to the waveguide of the optical transmission medium using the optical transmission medium according to claim 1. Using an optical transmission medium in which a plurality of cores serving as waveguides are arranged in the cladding,
An optical transmission method for propagating an optical signal to the waveguide of the optical transmission medium by making the propagation direction or wavelength of light of at least one core different from that of another core. In a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
One or more cores at the same distance from the center of the core group in the cross section are taken as one group, or one or more cores on a straight line parallel to each other in the cross section are taken as one group, and the adjacent cores or The optical transmission method according to claim 11, wherein an optical signal is propagated to the waveguide of the optical transmission medium by changing a light propagation direction or a light wavelength between the adjacent groups. Using an optical transmission medium in which a plurality of cores serving as waveguides are arranged in the cladding,
An optical transmission method for propagating an optical signal to the waveguide of the optical transmission medium by making the optical power of the at least one core or the transmission speed of the optical signal different from other cores in the core.   The optical transmission method according to claim 13, wherein an optical power or an optical signal transmission rate is set for each core according to the transmission loss of the core. In a cross section perpendicular to the light propagation direction of the waveguide,
If the number of cores is even and the cores are on one or more polygon sides or vertices, or the number of cores is even and the cores are one or more circles When it is on the circumference, when the adjacent core on the same polygon or the same circumference is an adjacent core,
The optical transmission method according to claim 13, wherein an optical power or an optical signal transmission speed is set for each core in accordance with crosstalk from an adjacent core. A plurality of the optical transmission media are arranged in parallel,
16. The light according to claim 11, wherein a light propagation direction in each of the cores of the optical transmission medium is set so as to have a necessary transmission capacity for each direction of the optical transmission medium. Transmission method.

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