JP2017152984A - Optical communication system, optical transmission device and optical reception device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for realizing an optical communication system which transmits an optical signal by using a wavelength multiplexing technology and a mode multiplexing technology together.SOLUTION: An optical communication system is configured in such a manner that an optical transmission device 10 performs wavelength multiplexing and then performs mode multiplexing and that an optical reception device 30 performs wavelength demultiplexing and then performs mode demultiplexing. The optical transmission device 10 generates multiple optical signals in a fundamental mode (LP01 mode), performs wavelength multiplexing thereon and further performs mode multiplexing, thereby generating an optical signal that should be transmitted to the optical reception device. The optical reception device 30 performs wavelength demultiplexing on the optical signal that is received from the optical transmission device 10, further performs mode demultiplexing, thereby demultiplexing the multiplexed signal into multiple optical signals in the fundamental mode, and performs reception processing of the demultiplexed multiple optical signals.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical communication technique, and more particularly to an optical communication system, an optical transmission apparatus, and an optical reception apparatus to which both a mode multiplexing technique and a wavelength multiplexing technique are applied.

  As a technique for expanding the transmission capacity of an optical fiber transmission line, a space division multiplexing technique has been studied. In mode multiplexing technology, which is one of space division multiplexing, a multimode fiber that has multiple modes of optical signals that can propagate through one core of the optical fiber is used as a transmission line. By transmitting different information, the transmission capacity of the optical fiber transmission line is expanded. Patent Document 1 discloses a technique for generating a plurality of optical signals of different modes and transmitting a multiplexed signal through one core of a multimode fiber.

  An optical communication system using the mode multiplexing technique as described above is generally configured by connecting a transmission side device (optical transmission device) and a reception side device (optical reception device) by a multimode fiber. . An optical transmitter includes an optical transmitter, a converter that converts a mode of an optical signal generated by the optical transmitter from a basic mode to a higher-order mode, and a mode multiplexer that multiplexes a plurality of modes to generate a mode multiplexed signal. Consists of The optical receiver includes a mode separator that separates the received mode multiplexed signal into optical signals of individual modes, a mode converter that converts the mode of each separated optical signal to a basic mode, and an optical receiver. Is done.

Japanese Patent No. 5665967

D. Soma, et al., "2.05 Peta-bit / s super-nyquist-WDM SDM transmission using 9.8-km 6-mode 19-core fiber in full C band", 2015 European Conference on Optical Communication (ECOC 2015), September 27 2015-October 1 2015, PDP.3.2

  In an optical communication system that is currently commercialized, wavelength multiplexing technology is used to increase transmission capacity. In order to further increase the transmission capacity in an optical communication system, it is necessary to use a mode multiplexing technique in addition to the wavelength multiplexing technique. Non-Patent Document 1 shows a configuration and experimental results in which both wavelength multiplexing technology and mode multiplexing technology are employed in a laboratory environment. However, Non-Patent Document 1 merely shows an example in which basically the same information is multiplexed and transmitted, and no practical configuration example of the optical transmission device and the optical transmission device is shown.

  The present invention has been made in view of the above-described problems. It is an object of the present invention to provide a technique for realizing an optical communication system that transmits an optical signal by using a wavelength multiplexing technique and a mode multiplexing technique together.

  The present invention can be realized as, for example, an optical communication system, an optical transmission device, and an optical reception device. An optical communication system according to an aspect of the present invention is an optical communication system including an optical transmission device and an optical reception device that receives an optical signal transmitted from the optical transmission device, and the optical transmission device includes: First and second wavelength multiplexers that generate wavelength-multiplexed signals by multiplexing a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths, and the second wavelength A mode converter for converting a wavelength multiplexed signal generated by a multiplexer from the fundamental mode to a higher order mode; a wavelength multiplexed signal of the fundamental mode generated by the first wavelength multiplexer; and the higher order mode. A mode multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing the wavelength-multiplexed signal of the optical receiver, and the optical receiver receives the optical signal received from the optical transmitter ,That A wavelength separator that separates into a plurality of optical signals of different wavelengths, and a plurality of receiving units that correspond to different wavelengths and that receive optical signals of the corresponding wavelengths from the wavelength separators, respectively, Each receiving unit separates the input optical signal into the fundamental mode optical signal and the higher order mode optical signal, and the higher order mode light output from the mode separator. A mode converter that converts the signal from the higher-order mode to the fundamental mode, the fundamental mode optical signal output from the mode separator, and the fundamental mode output from the mode converter. An optical signal reception process is performed.

  An optical transmission apparatus according to an aspect of the present invention is an optical transmission apparatus that transmits an optical signal to an optical reception apparatus, and is a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths. Are multiplexed to convert the wavelength multiplexed signal generated by the first and second wavelength multiplexers that generate the wavelength multiplexed signal and the second wavelength multiplexer from the fundamental mode to the higher order mode. The light to be transmitted to the optical receiver by multiplexing the fundamental mode wavelength multiplexed signal generated by the mode converter, the first wavelength multiplexer, and the higher order mode wavelength multiplexed signal. And a mode multiplexer for generating a signal.

  An optical receiving apparatus according to an aspect of the present invention is an optical receiving apparatus that receives an optical signal transmitted from an optical transmitting apparatus, and the optical signal received from the optical transmitting apparatus is converted into a plurality of light beams having different wavelengths. A wavelength separator that separates signals, and a plurality of receiving units that correspond to different wavelengths and that receive optical signals of corresponding wavelengths from the wavelength separators, respectively, and each receiving unit includes the input A mode separator that separates the optical signal generated into a fundamental mode optical signal and a higher-order mode optical signal, and the higher-order mode optical signal output from the mode separator from the higher-order mode. A mode converter for converting into a fundamental mode, and performing reception processing of the fundamental mode optical signal output from the mode separator and the fundamental mode optical signal output from the mode converter. And wherein the door.

  An optical communication system according to another aspect of the present invention is an optical communication system including an optical transmission device and an optical reception device that receives an optical signal transmitted from the optical transmission device, and the optical transmission device. Includes first and second wavelength multiplexers that generate wavelength multiplexed signals by multiplexing a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths, and A mode converter that converts the wavelength multiplexed signal generated by the wavelength multiplexer from the fundamental mode to a higher order mode, the wavelength multiplexed signal of the fundamental mode generated by the first wavelength multiplexer, A mode multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing the wavelength-division multiplexed signal of the next mode, and the optical receiver receives the optical signal received from the optical transmitter Signal, A mode separator that separates the fundamental mode optical signal and the higher order mode optical signal, and converts the higher order mode optical signal output from the mode separator from the higher order mode to the fundamental mode. A mode converter, a first wavelength separator that separates the fundamental mode optical signal output from the mode separator into a plurality of optical signals each having a different wavelength, and the output from the mode converter. A second wavelength separator that separates the optical signal of the fundamental mode into a plurality of optical signals of different wavelengths, and corresponds to different wavelengths, and is output from the first and second wavelength separators; And a plurality of receiving units that perform reception processing of optical signals of corresponding wavelengths.

  According to the present invention, it is possible to realize an optical communication system that transmits optical signals by using both wavelength multiplexing technology and mode multiplexing technology.

1 is a block diagram showing a configuration of an optical communication system. 1 is a block diagram showing a configuration of an optical transmission device 10. FIG. FIG. 2 is a block diagram showing a configuration of an optical receiving device 30. FIG. 3 is a diagram illustrating an example of an actual device configuration of the optical transmission device 10. FIG. 3 is an explanatory diagram of an example of upgrade of the optical transmission device 10. FIG. 3 is an explanatory diagram of an example of upgrade of the optical transmission device 10. Explanatory drawing of the example of the upgrade of the optical receiver 30. FIG. The block diagram which shows the modification of a structure of the optical receiver 30. FIG.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

[Example 1]
FIG. 1 is a block diagram illustrating the configuration of the optical communication system according to the first embodiment. As shown in FIG. 1, the optical communication system includes an optical transmission device 10 and an optical reception device 30 that can communicate with the optical transmission device 10 via an optical transmission path 50. The optical transmission line 50 between the optical transmitter 10 and the optical receiver 30 includes a multimode optical fiber 51 and a multimode optical amplifier 52 for relay amplification of optical signals.

  Hereinafter, configurations of the optical transmission device 10 and the optical reception device 30 illustrated in FIG. 1 will be described in detail. The optical transmission device 10 generates a plurality of optical signals in the basic mode (LP01 mode), performs wavelength multiplexing of these, and further performs mode multiplexing to generate an optical signal to be transmitted to the optical reception device. . The optical receiver 30 performs wavelength separation of the optical signal received from the optical transmitter 10 and further performs mode separation to separate the multiplexed signal into a plurality of optical signals in the basic mode. Performs optical signal reception processing. In the present embodiment, as described above, a configuration example of an optical communication system in which the optical transmission device 10 performs mode multiplexing after performing wavelength multiplexing, and the optical receiving device 30 performs mode separation after performing wavelength separation. Indicates.

<Optical transmitter 10>
With reference to FIG. 2, the configuration of the optical transmission apparatus 10 according to the present embodiment will be described in detail. The optical transmitter 10 includes a wavelength multiplexer 15 (15a, 15b, 15c,...), A mode converter 16 (16b, 16c,...), A mode multiplexer 17, and a generation unit 20 (20-1, 20). 20-2, 20-3, ...). A maximum number of generation units 20 equal to the number of wavelengths that can be multiplexed by the wavelength multiplexer 15 are provided. The maximum number of wavelength multiplexers 15 equal to the number of modes that can be multiplexed by the mode multiplexer 17 is provided. Further, the number of mode converters 16 equal to the number of wavelength multiplexers 15 (15b, 15c,...) Corresponding to higher order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.) is provided.

The plurality of generation units 20 correspond to different wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...) And generate optical signals having corresponding wavelengths. For example, the generation units 20-1, 20-2, and 20-3 generate optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ , respectively. Hereinafter, the generation unit 20-1 will be mainly described, but the other generation units 20 may be configured in the same manner as the generation unit 20-1, except that the wavelength λ of the light generated by the light source 11 is different. Is possible.

The generation unit 20-1 includes a single light source 11, an optical branch circuit 12, an optical modulator 13 (13a, 13b,...), And an optical amplifier 14 (14a, 14b,...). The light source 11 generates and outputs fundamental mode light having a wavelength λ ₁ . The plurality of optical modulators 13 correspond to different modes, respectively, and modulate the light output from the light source 11 independently (that is, modulate with different input signals), so that the optical signal of the basic mode is obtained. Are generated respectively. In this embodiment, as an example, the optical modulator 13a corresponds to the basic mode (LP01 mode), and the optical modulator 13b corresponds to the higher-order mode (LP11a mode).

  An optical amplifier 14 for adjusting the power of the optical signal generated by each optical modulator 13 is provided at the subsequent stage of each optical modulator 13. In this embodiment, the set of the optical modulator 13 and the optical amplifier 14 corresponding to the same one mode functions as an optical transmitter (FIG. 4) corresponding to the one mode. Instead of the optical amplifier 14, an optical attenuator may be used, or both an optical amplifier and an optical attenuator may be used.

  In the generation unit 20-1, it is also possible to individually provide light sources for a plurality of optical transmitters corresponding to different modes. However, it may be technically difficult to maintain the wavelength of light output from all of these light sources at the same wavelength. For this reason, in the present embodiment, the light output from the single light source 11 is branched by the optical branch circuit 12, and the branched (divided) light is modulated by each of the optical modulators 13. A common light source 11 is used in the vessel 13.

  The plurality of wavelength multiplexers 15 (15a, 15b, 15c,...) Correspond to different modes. As an example, the wavelength multiplexer 15a corresponds to the fundamental mode, the wavelength multiplexer 15b corresponds to the higher order mode (LP11a mode), and the wavelength multiplexer 15c corresponds to the higher order mode (LP11b mode). The wavelength multiplexer 15a is an example of a first wavelength multiplexer, and the wavelength multiplexers 15 (15b, 15c,...) Other than the wavelength multiplexer 15a are examples of a second wavelength multiplexer. .

Each wavelength multiplexer 15 has a fundamental mode having different wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...) Generated by the optical modulator 13 corresponding to the same mode as the wavelength multiplexer. A plurality of optical signals are input from the plurality of generation units 20. For example, a plurality of fundamental mode optical signals having different wavelengths λ generated by the optical modulator 13 a corresponding to the fundamental mode are input from the plurality of generation units 20 to the wavelength multiplexer 15 a. A plurality of fundamental mode optical signals having different wavelengths λ generated by the optical modulator 13b corresponding to the higher order mode (LP11b mode) are input from the plurality of generation units 20 to the wavelength multiplexer 15b. . Each wavelength multiplexer 15 generates a wavelength multiplexed signal by multiplexing a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths. In this way, the plurality of wavelength multiplexers 15 respectively generate and output fundamental mode wavelength multiplexed signals.

  The wavelength multiplexed signal output from the wavelength multiplexer 15 a corresponding to the fundamental mode is input to the mode multiplexer 17. On the other hand, the wavelength multiplexed signals output from the wavelength multiplexers 15 (15b, 15c,...) Corresponding to the higher-order modes are respectively input to the mode converters 16 (16b, 16c,...). The mode converter 16 converts the wavelength multiplexed signal of the fundamental mode generated by the wavelength multiplexer 15 from the fundamental mode to a higher order mode, and outputs the converted wavelength multiplexed signal to the mode multiplexer 17. For example, the mode converter 16b converts the fundamental mode wavelength multiplexed signal from the fundamental mode to a higher-order mode (LP11a mode), and the mode converter 16c converts the fundamental mode wavelength multiplexed signal from the fundamental mode to the higher mode. Conversion to the next mode (LP11b mode).

  The mode multiplexer 17 receives the wavelength multiplexed signal of the fundamental mode generated by the wavelength multiplexer 15a and the wavelength multiplexed signal of the higher order mode output from the mode converter 16 (16b, 16c,...). Is done. The mode multiplexer 17 generates an optical signal to be transmitted to the optical receiver 30 by multiplexing the input wavelength multiplexed signals (mode multiplexing). Since the mode converter 16 and the mode multiplexer 17 are wavelength-multiplexed signals, devices having as little wavelength dependence as possible are employed for them.

  According to the above-described configuration, the optical modulator 13, the optical amplifier 14, and the wavelength multiplexer 15 need only support the fundamental mode, and there is an advantage that the mode dependency of those optical devices does not become a problem. is there. In addition, since the number of mode converters 16 and mode multiplexers 17 which are devices required for mode multiplexing is small, the introduction cost of the apparatus can be made relatively low.

  Here, in the configuration shown in FIG. 2, in order to enable the common light source 11 to be used in the optical transmitters (the optical modulator 13 and the optical amplifier 14) corresponding to all modes in each generation unit 20, the arrangement of each device is arranged. And how to actually realize the connection can be a problem. FIG. 4 is a diagram illustrating an example of an actual device configuration of the optical transmission device 10 to cope with such a problem. In this example, the optical transmission device 10 includes an optical transmitter rack in which a plurality of optical transmitters are mounted, and a multiplexer rack in which the wavelength multiplexer 15, the mode converter 16, and the mode multiplexer 17 are mounted. The

  First, in the optical transmitter rack, the optical transmitters corresponding to all modes are mounted adjacent to the same stage in units of wavelengths (that is, for each generation unit 20), and the common light source 11 is mounted in the vicinity thereof. Is done. The wavelength multiplexer 15, the mode converter 16, and the mode multiplexer 17 are mounted on a multiplexer rack that is a rack independent of these optical transmitters. Further, as shown in FIG. 2, the optical transmitter rack and the multiplexer rack are optically connected so as to realize the connection relationship between the optical transmitter (the optical modulator 13 and the optical amplifier 14) and the wavelength multiplexer 15. Connected by fiber. In this way, the actual device configuration of the optical transmission device 10 can be realized. In this embodiment, as shown in FIGS. 2 and 4, the mode converter 16 and the mode multiplexer 17 are separated from each other. However, it is also possible to adopt a configuration in which these are integrated.

<Optical receiver 30>
Next, the configuration of the optical receiver 30 according to the present embodiment will be described in detail with reference to FIG. The optical receiver 30 includes a wavelength separator 31 and a receiving unit 40 (40-1, 40-2, 40-3,...). Each receiving unit 40 includes a mode separator 32, a mode converter 33 (33b, 33c,...), An optical hybrid circuit 34, a light receiving element 35, a sampling processing unit 36, a MIMO processing unit 37, a carrier estimation unit 38, and A code reproduction unit 39 is included. The receiving units 40 are provided in the maximum number equal to the number of wavelengths separable by the wavelength separator 31, that is, the mode separator 32 is equal to the maximum number of wavelengths separable by the wavelength separator 31. There are as many as there are. The optical hybrid circuit 34 and each device subsequent thereto are provided in a number equal to the number of modes separable by the mode separator 32 at maximum. However, for the light receiving element 35, two light receiving elements corresponding to the I channel and the Q channel are provided for each mode. Also, only one MIMO processing unit 37 is provided for each receiving unit because processing is performed across all modes. Further, the number of mode converters 33 equal to the number of optical hybrid circuits 34 corresponding to higher-order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.) is provided.

The wavelength separator 31 receives a plurality of optical signals received from the optical transmitter 10 via the optical transmission line 50 and has a plurality of different single wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...). Separate into optical signals. The plurality of receiving units 40 correspond to different wavelengths λ, and optical signals having corresponding wavelengths are respectively input from the wavelength separator 31. For example, optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ are input to the receiving units 40-1, 40-2, and 40-3, respectively. Since the wavelength separator 31 is processed with a mode multiplexed signal, a device having mode dependence as small as possible is employed for the wavelength separator 31. Hereinafter, the receiving unit 40-1 will be mainly described. However, the other receiving units 40 are configured in the same manner as the receiving unit 40-1, except that the wavelength of the light generated by the local light source 41 is different. Is possible.

In the receiving unit 40-1, the mode separator 32 converts the optical signal having the wavelength λ ₁ input from the wavelength separator 31 into an optical signal in a fundamental mode and an optical signal in a higher order mode (LP11a mode, LP11b mode, etc.). To output. The optical signal in the basic mode is input to the optical hybrid circuit 34 corresponding to the basic mode. Each optical signal corresponding to the higher order mode is input to the corresponding mode converter 33 (33b, 33c,...).

  The mode converter 33 converts the high-order mode optical signal output from the mode separator 32 from the high-order mode to the basic mode and outputs the converted signal. For example, the mode converter 33b converts a high-order mode (LP11a mode) optical signal into a basic mode, and the mode converter 33c converts a high-order mode (LP11b mode) optical signal into a basic mode. The optical signal output from each mode converter 33 is input to an optical hybrid circuit 34 connected to the mode converter 33 (corresponding to a higher-order mode). The plurality of optical hybrid circuits 34 and their subsequent devices perform reception processing of the fundamental mode optical signal output from the mode separator 32 and the fundamental mode optical signal output from each mode converter 33.

  Specifically, the optical hybrid circuit 34 performs coherent detection (coherent reception) of the optical signal by mixing the input optical signal and local light. Here, each receiving unit 40 is provided with a single local light source 41. In the present embodiment, the light output from the single local light source 41 is branched by the optical branch circuit 42, and the branched (divided) light is used in each optical hybrid circuit 34, whereby a plurality of optical hybrids are used. A common local light source 41 is used in the circuit 34. As a result, the frequency deviation between the optical signal transmitted from the optical transmitter 10 and the local light can be made uniform in all the optical hybrid circuits 34.

  The optical signal output from the optical hybrid circuit 34 and obtained by coherent detection is converted into an electric signal by the light receiving element 35. The electrical signal is converted from an analog signal into a digital signal by the sampling processing unit 36. In this way, a plurality of electrical signals (digital signals) corresponding to the same wavelength and corresponding to different modes are input from the plurality of sampling processing units 36 corresponding to the different modes to the MIMO processing unit 37, respectively. The The MIMO processing unit 37 performs MIMO signal processing on a plurality of input digital signals to suppress crosstalk noise between modes, and obtains a signal corresponding to each mode obtained as a result, as a carrier signal. It outputs to the estimation part 38. Thereafter, carrier estimation processing is performed by the carrier estimation unit 38, and the transmission digital code is reproduced by the code reproduction unit 39. Thereafter, error correction processing or the like may be performed as necessary.

  In the MIMO signal processing by the MIMO processing unit 37, temporal skew between a plurality of signals input to the MIMO processing unit 37 becomes a problem. However, according to the above-described configuration, all of the optical devices used until the optical signal is converted into an electrical signal after the mode separation by the mode separator 32 can be arranged in close proximity. In the case of such an optical device arrangement, it is relatively easy to control the optical path length difference generated by the optical device, and such control is effective for the temporal skew that causes a problem in MIMO signal processing. I can deal with it.

  In addition, according to the above-described configuration, the mode separator 32 and the mode converter 33 only need to support a single wavelength, and the design and manufacture of these optical devices can be facilitated. There is an advantage that the wavelength dependence of the optical device does not become a problem. In the present embodiment, as shown in FIG. 3, the mode separator 32 and the mode converter 33 are separated from each other. However, it is also possible to adopt a configuration in which these are integrated.

  As described above, according to the present embodiment, the optical transmission apparatus 10 performs mode multiplexing after performing wavelength multiplexing, and the optical receiving apparatus 30 performs mode separation after performing wavelength separation. A system can be realized.

[Example 2]
When performing an upgrade that gradually increases the transmission capacity of the optical communication system as in the first embodiment, it is assumed that necessary devices are added in units of wavelengths or modes. In the present embodiment, a configuration example that enables such an upgrade for each of the optical transmission device 10 and the optical reception device 30 will be described. In the following, the present embodiment will be described focusing on the differences from the first embodiment.

<Upgrade of optical transmitter 10>
In the present embodiment, as in the first embodiment, the optical transmission device 10 is mounted in a rack configuration as shown in FIG. The optical transmission device 10 includes a wavelength multiplexer 15, a wavelength multiplexer 15, and a mode multiplexer 17 corresponding to the added higher-order mode in order to enable addition of a higher-order mode to be transmitted. A mode converter 16 provided therebetween can be added. Further, the optical transmitter 10 is configured such that an optical transmitter (the optical modulator 13 and the optical amplifier 14) corresponding to the added higher-order mode can be added to each generation unit 20. Further, in order to make it possible to add such an optical transmitter, each generation unit 20 of the optical transmitter 10 is configured such that the optical transmitter to be added can be connected to the light source 11 via the optical branch circuit 12. Can be done. An optical connector for connection may be provided in advance at a location where the wavelength multiplexer 15, the mode converter 16 and the optical transmitter are connected (added) in the optical transmitter 10. Note that the number of generation units 20 equal to the number of wavelengths multiplexed by the wavelength multiplexer 15 may be provided in advance, or the number of generation units 20 is increased sequentially as the number of multiplexed wavelengths increases. May be.

  The upgrade of the optical transmission device 10 can be performed in stages according to the following procedure. In the initial stage of introduction of the optical transmitter 10, as shown in FIG. 5, only the number of required wavelengths of optical transmitters corresponding to mode 1 (basic mode) are mounted on the optical transmitter rack. In addition, a wavelength multiplexer 15 a corresponding to mode 1 (basic mode) and a final mode multiplexer 17 that transmits an optical signal to the optical transmission line 50 are mounted on the multiplexer rack.

  Thereafter, when there is no wavelength that can be used in mode 1, an optical device corresponding to mode 2 (for example, LP11a mode) that is a higher-order mode is newly mounted in the optical transmitter rack and the multiplexer rack. Specifically, as shown in FIG. 6, optical transmitters corresponding to mode 2 are newly installed in the optical transmitter rack by the number of necessary wavelengths. A wavelength multiplexer 15b corresponding to mode 2 and a mode converter 16b corresponding to the wavelength multiplexer 15b are newly mounted on the multiplexer rack. By repeating such a procedure, the optical transmission device 10 can be upgraded in units of one mode and one wavelength.

<Upgrade of optical receiver 30>
In the optical receiver 30, each receiving unit 40 shown in FIG. 3 corresponds to one wavelength, and corresponds to a processing block necessary for receiving all modes of optical signals multiplexed on the one wavelength. To do. Therefore, in order to realize the upgrade of the optical receiver 30 in units of one wavelength, the optical unit and the electric circuit are added to the optical receiver 30 using the reception unit 40 shown in FIG. Good.

  In the following, with reference to FIG. 7, the upgrade of the optical receiver 30 in one mode and one wavelength unit will be described. In the present embodiment, the optical receiving device 30 includes an optical hybrid circuit 34 corresponding to the added higher-order mode and the optical hybrid circuit 34 and the mode corresponding to the added higher-order mode in order to enable addition of a higher-order mode to be received. A mode converter 33 provided between the separator 32 can be added to each receiving unit 40. Further, in order to allow such an optical hybrid circuit 34 to be added, each receiving unit 40 is configured so that the optical hybrid circuit 34 to be added can be connected to the local light source 41 via the optical branch circuit 42. ing.

  Devices other than the mode converter 33 and the optical hybrid circuit 34 to be added in each receiving unit 40 are provided in advance in each receiving unit 40. That is, each receiving unit 40 includes a mode separator 32, a local light source 41, an optical branching circuit 42, a light receiving element 35, and all electric circuits (sampling processing unit 36, MIMO processing unit 37, carrier estimation unit 38, and A code reproduction unit 39) is provided in advance.

  As shown in FIG. 7, the upgrade of the optical receiver 30 in one mode unit is realized by adding an optical device to the optical receiver 30 using the mode converter 33 and the optical hybrid circuit 34 as an expansion unit. it can. An optical connector for connection may be provided in advance at a location where the mode converter 33 and the optical hybrid circuit 34 are connected (added) in the optical receiver 30. Thereby, the upgrade of the optical receiver 30 can be easily realized as an additional package. In addition, in each receiving unit 40, when there is no mode that can be used at the corresponding wavelength, a new receiving unit 40 may be added as described above, or the number of wavelengths separated by the wavelength separator 31 The number of receiving units 40 equal to may be provided in advance.

  According to the present embodiment, each of the optical transmission device 10 and the optical reception device 30 can be upgraded step by step in one mode and one wavelength unit, and the equipment required for the initial introduction can be saved, and the initial introduction cost can be reduced. Reduction is possible.

[Example 3]
In the first and second embodiments, a configuration example in which mode separation is performed after the optical receiver 30 performs wavelength separation is described. However, a configuration in which wavelength separation is performed after the optical receiver 30 performs mode separation is described as optical communication. It can also be applied to the system. In this embodiment, a modification of such an optical communication system will be described. In the following, the present embodiment will be described with a focus on differences from the first and second embodiments.

  FIG. 8 is a block diagram illustrating a modification of the configuration of the optical receiver 30. In the optical communication system of the present embodiment, the optical transmission device 10 has the configuration shown in FIG. 2, and the optical reception device 30 has the configuration shown in FIG.

  The optical receiver 30 includes a mode separator 32, a mode converter 33 (33b, 33c,...), A wavelength separator 31 (31a, 31b, 31c,...), And a receiving unit 40 (40-1,. 40-2, 40-3, ...). Each receiving unit 40 includes an optical hybrid circuit 34, a light receiving element 35, a sampling processing unit 36, a MIMO processing unit 37, a carrier estimation unit 38, and a code reproduction unit 39.

  The wavelength separators 31 are provided in a number equal to the number of modes that can be separated by the mode separator 32 at the maximum. As many mode converters 33 as the number of wavelength separators 31 (31b, 31c,...) Corresponding to higher-order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.) are provided. In addition, the receiving units 40 are provided in a number equal to the number of wavelengths that can be separated by the wavelength separator 31 at the maximum, that is, the optical hybrid circuit 34 and each of the subsequent devices are arranged at a maximum in the mode separator 32. As many as the number of separable modes are provided. However, for the light receiving element 35, two light receiving elements corresponding to the I channel and the Q channel are provided for each mode. Also, only one MIMO processing unit 37 is provided for each receiving unit because processing is performed across all modes.

  The mode separator 32 separates the optical signal received from the optical transmission apparatus 10 via the optical transmission line 50 into an optical signal in a basic mode and an optical signal in a higher-order mode (LP11a mode, LP11b mode, etc.). Output. The fundamental mode optical signal is input to the wavelength separator 31a corresponding to the fundamental mode. Each optical signal corresponding to the higher order mode is input to the corresponding mode converter 33 (33b, 33c,...).

  The mode converter 33 converts the high-order mode optical signal output from the mode separator 32 from the high-order mode to the basic mode and outputs the converted signal. For example, the mode converter 33b converts a high-order mode (LP11a mode) optical signal into a basic mode, and the mode converter 33c converts a high-order mode (LP11b mode) optical signal into a basic mode. The optical signal output from each mode converter 33 is input to a wavelength separator 31 (31b, 31c,...) Connected to the mode converter 33 (corresponding to a higher-order mode). Since the mode separator 32 and the mode converter 33 are wavelength multiplexed signals, devices having as little wavelength dependence as possible are employed for them.

The wavelength separator 31a corresponding to the fundamental mode has a plurality of fundamental mode optical signals output from the mode separator 32, each having a different single wavelength λ (λ ₁ , λ ₂ , λ ₃ ,...). Is separated into optical signals. Further, each wavelength separator 31 (31b, 31c,...) Corresponding to the higher order mode differs from the fundamental mode optical signal output from the mode converter 33 (33b, 33c,...). The optical signals are separated into a plurality of optical signals having a single wavelength λ (λ ₁ , λ ₂ , λ ₃ ,...). The wavelength separator 31a is an example of a first wavelength separator, and the wavelength separators 31 (31b, 31c,...) Other than the wavelength separator 31a are examples of a second wavelength separator. .

The plurality of receiving units 40 correspond to different wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...), And optical signals having corresponding wavelengths are input from the wavelength separator 31. For example, optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ are input to the receiving units 40-1, 40-2, and 40-3, respectively. Each receiving unit 40 performs a receiving process of an optical signal having a corresponding wavelength λ output from the wavelength separator 31. Hereinafter, the receiving unit 40-1 will be mainly described. However, the other receiving units 40 are configured in the same manner as the receiving unit 40-1, except that the wavelength of the light generated by the local light source 41 is different. Is possible.

In the receiving unit 40-1, the fundamental mode optical signal having a single wavelength λ ₁ inputted from the wavelength separator 31a corresponding to the fundamental mode is inputted to the optical hybrid circuit 34 corresponding to the fundamental mode. In addition, an optical hybrid circuit corresponding to a higher-order mode is inputted to a fundamental mode optical signal having a single wavelength λ ₁ input from a wavelength separator 31 (31b, 31c,...) Corresponding to the higher-order mode. 34 respectively. The plurality of optical hybrid circuits 34 and their subsequent devices perform reception processing of the input basic mode optical signals. Note that reception processing by the plurality of optical hybrid circuits 34 and their subsequent devices is the same as in the first embodiment.

  According to the configuration described above, the optical devices in the wavelength separator 31 and the receiving unit 40 need only support the fundamental mode, and there is an advantage that the mode dependency of these optical devices does not become a problem. . In addition, since the number of mode separators 32 and mode converters 33, which are devices required for mode separation, is small, the introduction cost of the apparatus can be made relatively low.

10: Optical transmitter, 30: Optical receiver, 50: Optical transmission line, 51: Multimode optical fiber, 52: Multimode optical amplifier 11: Light source, 12: Optical branch circuit, 13: Optical modulator, 14: Optical Amplifier: 15: Wavelength multiplexer, 16: Mode converter, 17: Mode multiplexer, 20: Generation unit 31: Wavelength separator, 32: Mode separator, 33: Mode converter, 34: Optical hybrid circuit, 35: Light receiving element, 36: sampling processing unit, 37: MIMO processing unit, 38: carrier estimation unit, 39: code reproduction unit, 40: reception unit, 41: local light source, 42: optical branch circuit

Claims (21)

An optical communication system comprising: an optical transmission device; and an optical reception device that receives an optical signal transmitted from the optical transmission device,
The optical transmitter is
First and second wavelength multiplexers that generate wavelength-multiplexed signals by multiplexing a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths;
A mode converter for converting the wavelength multiplexed signal generated by the second wavelength multiplexer from the fundamental mode to a higher order mode;
A mode for generating an optical signal to be transmitted to the optical receiver by multiplexing the wavelength-division multiplexed signal in the fundamental mode and the wavelength-division multiplexed signal in the higher-order mode generated by the first wavelength multiplexer. A multiplexer, and
The optical receiver is
A wavelength separator that separates the optical signal received from the optical transmission device into a plurality of optical signals of different wavelengths;
A plurality of receiving units, each of which corresponds to a different wavelength, and each of which receives an optical signal of the corresponding wavelength from the wavelength separator,
A mode separator for separating the input optical signal into the fundamental mode optical signal and the higher-order mode optical signal;
A mode converter for converting the higher-order mode optical signal output from the mode separator from the higher-order mode to the fundamental mode;
An optical communication system comprising: a receiving process for the fundamental mode optical signal output from the mode separator and the fundamental mode optical signal output from the mode converter. The optical transmission device further includes a plurality of generation units that generate optical signals having different wavelengths, and each generation unit includes:
A single light source generating fundamental mode light having a single wavelength;
A plurality of optical modulators each corresponding to a different mode and using the light source in common, and independently modulating the light output from the light source, whereby the optical signal of the basic mode Each of the plurality of light modulators,
To the first wavelength multiplexer, a plurality of fundamental mode optical signals each having a different wavelength generated by an optical modulator corresponding to the fundamental mode are input from the plurality of generation units,
The second wavelength multiplexer receives a plurality of fundamental mode optical signals having different wavelengths generated by an optical modulator corresponding to the higher order mode from the plurality of generation units. The optical communication system according to claim 1. 3. The light according to claim 2, wherein each generation unit of the optical transmission device further includes at least one of an optical amplifier and an optical attenuator that adjust power of an optical signal generated by each optical modulator. Communications system. In order to allow the optical transmission device to add the higher-order mode to be transmitted,
A second wavelength multiplexer corresponding to the added higher-order mode, and a mode converter provided between the second wavelength multiplexer and the mode multiplexer can be added, and
The optical communication system according to claim 2 or 3, wherein an optical modulator corresponding to the added higher-order mode can be added to each generation unit. Each of the generation units of the optical transmission device is configured to be connectable to the light source via an optical branch circuit that branches an optical modulator to be added from the light output from the light source. The optical communication system according to claim 4. Each receiving unit of the optical receiver is
A single local light source that generates fundamental mode light having a single wavelength;
A plurality of optical hybrid circuits that respectively correspond to different modes and use the local light source in common,
The optical hybrid circuit corresponding to the fundamental mode performs coherent detection of the optical signal of the fundamental mode output from the mode separator by the light output from the local light source,
The optical hybrid circuit corresponding to the higher-order mode performs coherent detection of the optical signal of the fundamental mode output from the mode converter by the light output from the local light source. 6. The optical communication system according to any one of items 1 to 5. The optical receiver is configured to add an optical hybrid circuit corresponding to an added higher-order mode, and between the optical hybrid circuit and the mode separator, in order to enable addition of the higher-order mode to be received. The optical communication system according to claim 6, wherein a mode converter provided in the receiver is configured to be extendable to each receiving unit. Each receiving unit of the optical receiver is configured to be connectable to the local light source via an optical branch circuit that branches the optical hybrid circuit to be added to the light output from the local light source. The optical communication system according to claim 7. Each receiving unit of the optical receiver includes a light receiving element that converts an optical signal output from each optical hybrid circuit into an electrical signal, and a plurality of electrical signals that correspond to the same wavelength and correspond to different modes. The optical communication system according to claim 8, wherein an electrical circuit that performs MIMO signal processing is provided in advance. The optical communication system according to any one of claims 1 to 9, wherein an optical transmission line between the optical transmission device and the optical reception device includes a multimode optical fiber and a multimode optical amplifier. . An optical transmitter that transmits an optical signal to an optical receiver,
First and second wavelength multiplexers that generate wavelength-multiplexed signals by multiplexing a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths;
A mode converter for converting the wavelength multiplexed signal generated by the second wavelength multiplexer from the fundamental mode to a higher order mode;
A mode for generating an optical signal to be transmitted to the optical receiver by multiplexing the wavelength-division multiplexed signal in the fundamental mode and the wavelength-division multiplexed signal in the higher-order mode generated by the first wavelength multiplexer. A multiplexer;
An optical transmission device comprising: A plurality of generation units that generate optical signals having different wavelengths, respectively,
A single light source generating fundamental mode light having a single wavelength;
A plurality of optical modulators each corresponding to a different mode and using the light source in common, and independently modulating the light output from the light source, whereby the optical signal of the basic mode Each of the plurality of light modulators,
To the first wavelength multiplexer, a plurality of fundamental mode optical signals each having a different wavelength generated by an optical modulator corresponding to the fundamental mode are input from the plurality of generation units,
The second wavelength multiplexer receives a plurality of fundamental mode optical signals having different wavelengths generated by an optical modulator corresponding to the higher order mode from the plurality of generation units. The optical transmission device according to claim 11. The light according to claim 12, wherein each generation unit of the optical transmission device further includes at least one of an optical amplifier and an optical attenuator that adjust power of an optical signal generated by each optical modulator. Transmitter device. In order to allow the optical transmission device to add the higher-order mode to be transmitted,
A second wavelength multiplexer corresponding to the added higher-order mode, and a mode converter provided between the second wavelength multiplexer and the mode multiplexer can be added, and
The optical transmission device according to claim 12 or 13, wherein an optical modulator corresponding to the added higher-order mode can be added to each generation unit. Each of the generation units of the optical transmission device is configured to be connectable to the light source via an optical branch circuit that branches an optical modulator to be added from the light output from the light source. The optical transmission device according to claim 14. An optical receiver that receives an optical signal transmitted from an optical transmitter,
A wavelength separator that separates the optical signal received from the optical transmission device into a plurality of optical signals of different wavelengths;
A plurality of receiving units, each of which corresponds to a different wavelength, and each of which receives an optical signal of the corresponding wavelength from the wavelength separator,
A mode separator for separating the input optical signal into a fundamental mode optical signal and a higher-order mode optical signal;
A mode converter for converting the higher-order mode optical signal output from the mode separator from the higher-order mode to the fundamental mode;
An optical receiver that performs reception processing of the fundamental mode optical signal output from the mode separator and the fundamental mode optical signal output from the mode converter. Each receiving unit of the optical receiver is
A single local light source that generates fundamental mode light having a single wavelength;
A plurality of optical hybrid circuits that respectively correspond to different modes and use the local light source in common,
The optical hybrid circuit corresponding to the fundamental mode performs coherent detection of the optical signal of the fundamental mode output from the mode separator by the light output from the local light source,
The optical hybrid circuit corresponding to the higher-order mode performs coherent detection of the optical signal of the fundamental mode output from the mode converter, using light output from the local light source. The optical receiver described in 1. The optical receiver is configured to add an optical hybrid circuit corresponding to an added higher-order mode, and between the optical hybrid circuit and the mode separator, in order to enable addition of the higher-order mode to be received. The optical receiver according to claim 17, wherein a mode converter provided in the receiver can be added to each receiving unit. Each receiving unit of the optical receiver is configured to be connectable to the local light source via an optical branch circuit that branches the optical hybrid circuit to be added to the light output from the local light source. The optical receiver according to claim 18. Each receiving unit of the optical receiver includes a light receiving element that converts an optical signal output from each optical hybrid circuit into an electrical signal, and a plurality of electrical signals that correspond to the same wavelength and correspond to different modes. An optical circuit for performing MIMO signal processing on the optical receiver is provided in advance. An optical communication system comprising: an optical transmission device; and an optical reception device that receives an optical signal transmitted from the optical transmission device,
The optical transmitter is
First and second wavelength multiplexers that generate wavelength-multiplexed signals by multiplexing a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths;
A mode converter for converting the wavelength multiplexed signal generated by the second wavelength multiplexer from the fundamental mode to a higher order mode;
A mode for generating an optical signal to be transmitted to the optical receiver by multiplexing the wavelength-division multiplexed signal in the fundamental mode and the wavelength-division multiplexed signal in the higher-order mode generated by the first wavelength multiplexer. A multiplexer, and
The optical receiver is
A mode separator that separates an optical signal received from the optical transmission device into an optical signal in the fundamental mode and an optical signal in the higher-order mode;
A mode converter for converting the higher-order mode optical signal output from the mode separator from the higher-order mode to the fundamental mode;
A first wavelength separator that separates the fundamental mode optical signal output from the mode separator into a plurality of optical signals of different wavelengths;
A second wavelength separator that separates the fundamental mode optical signal output from the mode converter into a plurality of optical signals each having a different wavelength;
A plurality of receiving units that correspond to different wavelengths and perform reception processing of optical signals of the corresponding wavelengths output from the first and second wavelength separators. system.

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