JP2015159584A - Optical receiver, multi-core optical fiber, and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the crosstalk removal processing load, in an optical transmission system using a multicore optical fiber.SOLUTION: An optical receiver 15 includes a photoelectric conversion unit 151 including a plurality of core groups each collecting a plurality of cores, connected with a multicore optical fiber 13 interrupting crosstalk between core groups, and receiving a channel signal from the multicore optical fiber 13, and a crosstalk removal unit 153 computing the electric field or the strength of a channel signal transmitted from an optical transmitter 11, on the basis of the channel matrix of a channel signal of each core group, and the electric field or the strength of a channel signal received by the photoelectric conversion unit 151.

Description

  The present invention relates to an optical transmission system using a multi-core optical fiber.

  With the aim of increasing the capacity of optical transmission systems, optical transmission systems using single-core optical fibers are being studied, as well as optical transmission systems using multi-core optical fibers. In an optical transmission system using a multicore optical fiber, there is crosstalk between cores, but it is necessary to reduce crosstalk between cores.

  A configuration of a conventional first optical transmission system is shown in FIG. 1 (see Non-Patent Document 1). 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 13, and a plurality of It comprises a separator 14 that separates received signals and an optical receiver 15 that receives and outputs signals 1 ′,..., N ′. The optical receiver 15 includes a photoelectric conversion unit 151 that converts an optical signal into an electric signal, and a signal processing unit 152 that performs signal processing such as polarization separation and dispersion compensation. If not necessary, the signal processing unit 152 may be excluded from the configuration. 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.

  On the other hand, research and development of a multi-core optical fiber having a trench structure with a small crosstalk between cores is underway (see Non-Patent Document 2). Moreover, the structure of the conventional 2nd optical transmission system is shown in FIG. 2 (refer nonpatent literature 3). 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 13, and a plurality of It comprises a separator 14 that separates received signals and an optical receiver 15 that receives and outputs signals 1 ′,..., N ′. The optical receiver 15 includes a photoelectric conversion unit 151 that converts an optical signal into an electric signal, a crosstalk removal unit 153, and a signal processing unit 152 that performs signal processing such as polarization separation and dispersion compensation. If not necessary, the signal processing unit 152 may be excluded from the configuration.

  The crosstalk removing unit 153 removes crosstalk between cores using MIMO (Multi-Input Multi-Output) technology that processes a plurality of input signals to generate a plurality of output signals (Non-Patent Document 4). See). If the multi-core optical fiber 13 has n cores, a plurality of input signals and a plurality of output signals are related by an n-th order channel matrix. That is, a column vector indicating a plurality of output signals is obtained by multiplying a column vector indicating a plurality of input signals by an nth-order channel matrix. Therefore, a column vector indicating a plurality of input signals is obtained by multiplying a column vector indicating a plurality of output signals by an inverse matrix of an nth-order channel matrix. Thus, if the n-th order channel matrix is known, a plurality of input signals can be known based on a plurality of output signals, and crosstalk between cores can be eliminated.

B. Zhu, et al. "Seven-core multicore fiber transmissions for passive optical network", OPTICS EXPRESS, Vol. 18, no. 11, pp. 11117-11122, 2010. T. T. et al. Hayashi et al. , “Ultra-low-cross multi-core fiber feasible to ultra-long-haul transmission”, OSA / OFC / NFOEC2011, PDPC2, 2011. P. J. et al. Winzer et al. , “MIMO capacities and outout probabilities in spatially multiplexed optical transport systems”, OPTIC EXPRESS, Vol. 19, no. 17, pp. 16680-16696, 2011. Takeo Ohgane et al., “Intuitive MIMO System Technology”, Ohmsha, 2009.

  If the number of cores or the number of channels increases, the transmission capacity improves. However, in the crosstalk removing unit 153, the circuit scale and power consumption increase, and the matrix calculation becomes complicated. In addition, if the number of cores or the number of channels increases, the matrix operation becomes complicated in proportion to the square of the number of cores or the number of channels. For example, in order to obtain the inverse matrix of the channel matrix, if the number of cores or the number of channels is 4 in consideration of polarization multiplexing, (4 × 2) × (4 × 2) = 64 operations are sufficient. If the number of cores or the number of channels is 12, (12 × 2) × (12 × 2) = 576 operations are required.

  MIMO technology has been developed by wireless communication and is applied by optical communication. In wireless communication, the channel matrix is constantly updated in order to respond to changes in the environment at high speed. However, in optical communication, the channel matrix is constantly updated in spite of small changes in the environment. Therefore, in the crosstalk removing unit 153, the processing load is increased.

  Therefore, in order to solve the above-described problems, an object of the present invention is to reduce the processing load for removing crosstalk in an optical transmission system using a multi-core optical fiber.

  A plurality of core group portions in which a plurality of cores are combined into one group are provided, and crosstalk between the core group portions is cut off.

  Specifically, the present invention is provided with a plurality of core group parts in which a plurality of cores are grouped into one group, connected to a multi-core optical fiber in which crosstalk between the core group parts is blocked, and the multi-core optical fiber Based on the channel signal reception unit that receives the channel signal from the channel matrix, the channel matrix for the channel signal for each core group unit, and the electric field or intensity of the channel signal received by the channel signal reception unit, the optical transmission device And a channel signal calculation unit that calculates an electric field or intensity of the transmitted channel signal.

  According to this configuration, since the channel matrix is calculated for each core group part instead of performing the calculation of the channel matrix for all cores, the crosstalk elimination process is performed in the optical transmission system using the multicore optical fiber. The burden can be reduced.

  Further, the present invention provides a crosstalk between the core group units by separating a plurality of core group units in which a plurality of cores are combined into one group and the core group units without interposing other cores. A multi-core optical fiber.

  According to this configuration, since the channel matrix is calculated for each core group part instead of performing the calculation of the channel matrix for all cores, the crosstalk elimination process is performed in the optical transmission system using the multicore optical fiber. The burden can be reduced.

  The present invention is also a multi-core optical fiber characterized in that the crosstalk blocking section has a refractive index smaller than that of a clad positioned around the core.

  According to this configuration, the portion of the crosstalk amount between the channel signals that can be set to 0 can be more reliably set to 0. Therefore, in the optical transmission system using the multicore optical fiber, the crosstalk removal process is performed. The burden can be further reduced.

  According to another aspect of the present invention, there is provided an optical transmission system comprising the above optical receiver and the multi-core optical fiber.

  The present invention can reduce the processing load for removing crosstalk in an optical transmission system using a multi-core optical fiber.

It is a figure which shows the structure of the conventional 1st optical transmission system. It is a figure which shows the structure of the 2nd conventional optical transmission system. 1 is a diagram illustrating a configuration of an optical transmission system according to a first embodiment. 1 is a diagram illustrating a cross section of a multi-core optical fiber according to Embodiment 1. FIG. 1 is a diagram illustrating a cross section of a multi-core optical fiber according to Embodiment 1. FIG. 1 is a diagram illustrating a cross section of a multi-core optical fiber according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a configuration of an optical transmission system according to a second embodiment. It is a figure which shows the cross section of the multi-core optical fiber of Embodiment 2. FIG. It is a figure which shows the cross section of the multi-core optical fiber of Embodiment 2. FIG.

  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.

(Embodiment 1)
The configuration of the optical transmission system according to the first embodiment is shown in FIG. 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 13, and a plurality of It comprises a separator 14 that separates received signals and an optical receiver 15 that receives and outputs signals 1 ′,..., N ′. The optical receiver 15 includes a photoelectric conversion unit 151, a crosstalk amount storage unit 154, a crosstalk removal unit 153, and a signal processing unit 152 that performs signal processing such as polarization separation and dispersion compensation. If not necessary, the signal processing unit 152 may be excluded from the configuration.

  The photoelectric conversion unit 151 is connected to the multi-core optical fiber 13, receives a channel signal from the multi-core optical fiber 13, and corresponds to the channel signal reception unit. The crosstalk amount storage unit 154 stores a fixed amount of crosstalk between channel signals as a non-diagonal element of the channel matrix for the channel signal. The crosstalk removing unit 153 receives the channel matrix of the channel signal including the crosstalk amount between the channel signals fixedly stored by the crosstalk amount storage unit 154 as a non-diagonal element, and the photoelectric conversion unit 151 receives the crosstalk amount. Based on the electric field or intensity of the channel signal, the electric field or intensity of the channel signal transmitted by the optical transmitter 11 is calculated and corresponds to the channel signal calculation unit.

  The crosstalk amount storage unit 154 indicates the crosstalk amount between channel signals received from the cores in which the crosstalk between the cores of the multicore optical fiber 13 is not blocked, as a finite value of the channel matrix for the channel signals. As a non-diagonal element, it may be fixed and stored. The crosstalk amount storage unit 154 stores the crosstalk amount between channel signals received from the cores in which the crosstalk between the cores of the multi-core optical fiber 13 is blocked, which is 0 of the channel matrix for the channel signals. The diagonal element may be stored in a fixed manner.

  The cross section of the multi-core optical fiber of Embodiment 1 is shown in FIGS. The multi-core optical fiber 13 shown in FIG. 4 is a normal 12-core multi-core optical fiber. The multi-core optical fiber 13 shown in FIG. 5 is a multi-core optical fiber having 12 cores and a crosstalk blocking part 132. The multi-core optical fiber 13 shown in FIG. 6 is a multi-core optical fiber having 12 cores and having a low refractive index portion 133 in the crosstalk blocking portion 132. 4 to 6, the present invention is applied to a 12-core multicore optical fiber, but the present invention may be applied to a multicore optical fiber having an arbitrary number of cores.

  In the multi-core optical fiber 13 shown in FIG. 4, the core 131 closest to a certain core 131 has a maximum of 6 cores. In the multi-core optical fiber 13 shown in FIG. 5, the crosstalk blocking unit 132 blocks the crosstalk between the cores 131 by separating the cores 131 without passing through the other cores 131. The closest core 131 stays at a maximum of 3 cores. In the multi-core optical fiber 13 shown in FIG. 6, the refractive index of the low refractive index portion 133 is smaller than the refractive index of the clad positioned around the core 131, has a high crosstalk blocking effect, and is closest to a certain core 131. Stays up to 3 cores.

  Next, processing of the crosstalk removing unit 153 and the crosstalk amount storage unit 154 will be described. Since the change in the environment is small from the installation point of the optical transmission system to the use point of the optical transmission system, the change in the amount of crosstalk between channel signals is also small. Therefore, the optical receiver 15 obtains the amount of crosstalk between channel signals by measurement or calculation at the time of installation of the optical transmission system. Then, the crosstalk amount storage unit 154 stores the crosstalk amount between channel signals fixedly as a non-diagonal element of the channel matrix for the channel signal at the time of installation of the optical transmission system. Between the closest cores 131, off-diagonal elements of the channel matrix can be fixed and stored as finite values. Between the cores 131 not closest to each other, the non-diagonal elements of the channel matrix can be fixed as 0 and stored. An inverse matrix of the channel matrix can be calculated and stored.

  The crosstalk removing unit 153 receives the channel matrix of the channel signal including the crosstalk amount between the channel signals fixedly stored by the crosstalk amount storage unit 154 as a non-diagonal element, and the photoelectric conversion unit 151 receives the crosstalk amount. Based on the electric field or intensity of the channel signal, the electric field or intensity of the channel signal transmitted by the optical transmitter 11 is calculated. Specifically, the column vector indicating the electric field or intensity of the channel signal received by the plurality of photoelectric conversion units 151 is changed to the column vector indicating the electric field or intensity of the channel signal transmitted by the plurality of optical transmitters 11, and the channel matrix is changed. Multiplication. Therefore, the column vector indicating the electric field or intensity of the channel signal transmitted by the plurality of optical transmitters 11 is obtained by applying an inverse matrix of the channel matrix to the column vector indicating the electric field or intensity of the channel signal received by the plurality of photoelectric conversion units 151. Multiplication. Thereby, the crosstalk removing unit 153 can remove the crosstalk between the cores 131 that are closest to each other.

  As described above, the amount of crosstalk between channel signals is fixed and stored without being constantly updated, and the amount of crosstalk between channel signals is limited to a part of the finite value. Therefore, the processing load for removing crosstalk can be reduced in an optical transmission system using a multi-core optical fiber. Even if the number of cores or the number of channels is significantly increased, the processing load for removing crosstalk is not significantly increased.

(Embodiment 2)
FIG. 7 shows the configuration of the optical transmission system according to the second embodiment. 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 13, and a plurality of It comprises a separator 14 that separates received signals and an optical receiver 15 that receives and outputs signals 1 ′,..., N ′. The optical receiver 15 includes a photoelectric conversion unit 151, a crosstalk removal unit 153, and a signal processing unit 152 that performs signal processing such as polarization separation and dispersion compensation. If not necessary, the signal processing unit 152 may be excluded from the configuration.

  The photoelectric conversion unit 151 is connected to the multi-core optical fiber 13, receives a channel signal from the multi-core optical fiber 13, and corresponds to the channel signal reception unit. The multi-core optical fiber 13 includes a plurality of core group portions in which a plurality of cores are combined into one group, and crosstalk between the core group portions is blocked. The crosstalk removing unit 153 uses the channel matrix for the channel signal for each core group unit and the electric field or intensity of the channel signal received by the photoelectric conversion unit 151 to transmit the electric field or intensity of the channel signal transmitted by the optical transmitter 11. Corresponding to the channel signal calculation unit.

  Sections of the multi-core optical fiber according to the second embodiment are shown in FIGS. The multi-core optical fiber 13 shown in FIG. 8 is a multi-core optical fiber having 12 cores composed of three core group parts 134 and a crosstalk blocking part 135. The multi-core optical fiber 13 shown in FIG. 9 is a multi-core optical fiber having 12 cores composed of three core group parts 134 and having a low refractive index part 136 in the crosstalk blocking part 135. 8 to 9, the present invention is applied to a 12-core multicore optical fiber, but the present invention may be applied to a multicore optical fiber having an arbitrary number of cores.

  In the multicore optical fiber 13 shown in FIG. 8, the crosstalk blocking unit 135 blocks the crosstalk between the core group units 134 by separating the core group units 134 without passing through the other cores 131. The core 131 that is closest to a certain core 131 stays at a maximum of 3 cores. In the multi-core optical fiber 13 shown in FIG. 9, the refractive index of the low refractive index portion 136 is smaller than the refractive index of the cladding positioned around the core 131, has a high crosstalk blocking effect, and is closest to a certain core 131. Stays up to 3 cores.

  Next, processing of the crosstalk removing unit 153 will be described. Based on the channel matrix for the channel signal for each core group unit 134 and the electric field or intensity of the channel signal received by the photoelectric conversion unit 151, the crosstalk removing unit 153 receives the electric field of the channel signal transmitted by the optical transmitter 11 or Calculate the intensity. Specifically, the column vector indicating the electric field or intensity of the channel signal for each core group unit 134 received by the plurality of photoelectric conversion units 151 is the channel vector for each core group unit 134 transmitted by the plurality of optical transmitters 11. The column vector indicating the electric field or intensity is multiplied by the channel matrix for each core group unit 134. Therefore, the column vector indicating the electric field or intensity of the channel signal for each core group unit 134 transmitted by the plurality of optical transmitters 11 is the electric field or intensity of the channel signal for each core group unit 134 received by the plurality of photoelectric conversion units 151. Is multiplied by the inverse matrix of the channel matrix for each core group unit 134. Thereby, the crosstalk removing unit 153 can remove the crosstalk between the cores 131 that are closest to each other.

  When the multicore optical fiber 13 shown in FIG. 4 is used, (12 × 2) × (12 × 2) = 576 operations are required in consideration of polarization multiplexing in order to obtain an inverse matrix of the channel matrix. . When the multi-core optical fiber 13 shown in FIG. 8 or FIG. 9 is used, in order to obtain the inverse matrix of the channel matrix, (4 × 2) × (4 × 2) = 64 operations in consideration of polarization multiplexing. Just do it. The channel matrix for each core group unit 134 may be obtained by measurement or calculation and fixed and stored at the time of installation of the optical transmission system. The processing load for crosstalk removal can be further reduced.

  As described above, since the channel matrix is calculated for each core group part instead of performing the calculation of the channel matrix for all the cores, the crosstalk elimination is performed in the optical transmission system using the multicore optical fiber. The processing burden can be reduced. Even if the number of cores or the number of channels is significantly increased, the processing load for removing crosstalk is not significantly increased.

  The optical receiver, multi-core optical fiber, and optical transmission system according to the present invention may not increase the processing load for crosstalk removal even if the number of cores or the number of channels is increased in order to increase the capacity of the optical transmission system. it can.

11: Optical transmitter 12: Coupler 13: Multi-core optical fiber 14: Separator 15: Optical receiver 131: Core 132: Crosstalk blocking unit 133: Low refractive index unit 134: Core group unit 135: Crosstalk blocking unit 136 : Low refractive index unit 151: Photoelectric conversion unit 152: Signal processing unit 153: Crosstalk removal unit 154: Crosstalk amount storage unit

Claims (4)

Channel signal reception comprising a plurality of core group units each including a plurality of cores combined into one group, connected to a multi-core optical fiber in which crosstalk between the core group units is blocked, and receiving a channel signal from the multi-core optical fiber And
The electric field or intensity of the channel signal transmitted by the optical transmitter is calculated based on the channel matrix for the channel signal for each core group part and the electric field or intensity of the channel signal received by the channel signal receiver. A channel signal calculation unit;
An optical receiving device comprising: A plurality of core group parts that combine a plurality of cores into one group;
A crosstalk blocking unit that blocks crosstalk between the core group units by separating the core group units without passing through another core, and
A multi-core optical fiber comprising:   The multi-core optical fiber according to claim 2, wherein a refractive index of the crosstalk blocking portion is smaller than a refractive index of a clad positioned around the core. An optical receiver according to claim 1;
The multi-core optical fiber according to claim 2 or 3,
An optical transmission system comprising:

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