WO2017145901A1 - Optical communication system, optical transmission device, and optical reception device - Google Patents

Abstract

This optical communication system is configured in which an optical transmission device performs wavelength multiplexing and subsequently performs mode multiplexing, and an optical reception device performs wavelength separation and subsequently performs mode separation. The optical transmission device generates a plurality of optical signals of a basic mode (LP01 mode), performs wavelength multiplexing on the optical signals, and further performs mode multiplexing on the optical signals, and thereby, generates an optical signal to be transmitted to the optical reception device. The optical reception device performs wavelength separation on the optical signal received from the optical transmission device, and further performs mode separation on the optical signal, and thereby, separates the multiplexed signal into the plurality of optical signals of the basic mode, and performs reception processing of the separated optical signals.

Description

Optical communication system, optical transmitter, and optical receiver

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

Space division multiplexing technology is being studied as a technology for expanding the transmission capacity of optical fiber transmission lines. 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 transmitter, and an optical receiver. 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 device according to an aspect of the present invention is an optical transmission device that transmits an optical signal to an optical reception device, and each of a plurality of fundamental mode optical signals that are independently modulated and have different wavelengths. The first and second wavelength multiplexers that generate wavelength multiplexed signals by multiplexing, and the mode that converts the wavelength multiplexed signals generated by the second wavelength multiplexer from the basic mode to the higher order mode An optical signal to be transmitted to the optical receiver by multiplexing the wavelength multiplexed signal in the fundamental mode and the wavelength multiplexed signal in the higher mode generated by the converter, the first wavelength multiplexer And a mode multiplexer for generating.

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. It is characterized in.

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 the higher-order mode optical signal output from the mode separator is converted 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.

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. Are a plurality of generation units for generating mode multiplexed signals each having a different wavelength, wherein each generation unit is independently modulated, and the first and second fundamental modes having a single wavelength Of the optical signals, a mode converter that converts the second optical signal from the fundamental mode to a higher-order mode; the first optical signal in the fundamental mode; and the second optical signal in the higher-order mode. A plurality of mode multiplexing signals each having a different wavelength output from the plurality of generation units, and a mode multiplexer that generates a mode multiplexed signal by multiplexing. A wavelength multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing, and the optical receiver converts the optical signal received from the optical transmitter to the optical signal in the basic mode. A mode separator that separates the signal into a higher-order mode optical signal, and a mode converter that converts 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 having different wavelengths, and the fundamental mode optical signal output from the mode converter. A second wavelength separator that separates the light into a plurality of optical signals having different wavelengths, and light of the corresponding wavelengths that correspond to different wavelengths and are output from the first and second wavelength separators, respectively. Reception of signal A plurality of receiving units for performing processing, characterized in that it comprises a.

An optical transmission apparatus according to another 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 generation units that generate mode-multiplexed signals having different wavelengths, respectively. Each generation unit is independently modulated and converts the second optical signal from the fundamental mode to the higher order mode among the first and second optical signals of the fundamental mode having a single wavelength. A mode converter that generates a mode multiplexed signal by multiplexing the first optical signal in the fundamental mode and the second optical signal in the higher order mode, and A plurality of generation units, and a wavelength multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing a plurality of mode multiplexed signals output from the plurality of generation units, each having a different wavelength. Characterized in that it comprises a.

An optical receiving apparatus according to another 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 an optical signal in a basic mode. A mode separator that separates the high-order mode optical signal, and a mode converter that converts the high-order mode optical signal output from the mode separator from the high-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, and the fundamental mode optical signal output from the mode converter, A second wavelength separator that separates a plurality of optical signals having different wavelengths, and a second wavelength separator that corresponds to a different wavelength, and that is output from the first and second wavelength separators, Perform receive processing Characterized in that it comprises a plurality of receiving units, the.

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. Are a plurality of generation units for generating mode multiplexed signals each having a different wavelength, wherein each generation unit is independently modulated, and the first and second fundamental modes having a single wavelength Of the optical signals, a mode converter that converts the second optical signal from the fundamental mode to a higher-order mode; the first optical signal in the fundamental mode; and the second optical signal in the higher-order mode. A plurality of mode multiplexing signals each having a different wavelength output from the plurality of generation units, and a mode multiplexer that generates a mode multiplexed signal by multiplexing. A wavelength multiplexer that generates an optical signal to be transmitted to the optical receiving device by multiplexing, and the optical receiving device converts the optical signal received from the optical transmitting device into a plurality of different wavelengths. A wavelength separator that separates the optical signal, and a plurality of receiving units that correspond to different wavelengths, and each receives an optical signal of a corresponding wavelength from the wavelength separator, each receiving unit, A mode separator that separates the input optical signal into the optical signal of the fundamental mode and the optical signal of the higher-order mode, and the optical signal of the higher-order mode that is output from the mode separator. A mode converter for converting from the next mode to the fundamental mode, the fundamental mode optical signal output from the mode separator, and the fundamental mode optical signal output from the mode converter. And performing reception processing.

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.

Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are denoted by the same reference numerals.

The accompanying drawings are included in the specification, constitute a part thereof, show an embodiment of the invention, and are used to explain the principle of the invention together with the description.

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. 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 an optical receiving device 30. 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. Explanatory drawing of the example of the upgrade 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, the configuration 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, 20-1). 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. However, 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).

In the subsequent stage of each optical modulator 13, an optical amplifier 14 for adjusting the power of the optical signal generated by each optical modulator 13 is provided. 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 provide light sources individually 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 basic 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. In the following, the receiving unit 40-1 will be mainly described, but the other receiving units 40 are configured in the same manner as the receiving unit 40-1, except that the wavelength of 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 higher-order mode optical signal output from the mode separator 32 from the higher-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 to 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, a 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.

Further, in the optical receiver 30 shown in FIG. 3, it is possible to adopt a configuration in which the mode converter 33 (33b, 33c,...) Does not exist. When the mode converter 33 does not exist, each optical signal corresponding to the higher order mode output from the mode separator 32 is input to the corresponding optical hybrid circuit 34. In this case, in the optical hybrid circuit 34 corresponding to the higher-order mode, the mode does not match between the input optical signal and the light output from the local light source 41. For this reason, there is a possibility that the signal-to-noise ratio (S / N) of the optical signal output from the optical hybrid circuit 34 may be reduced. However, the decrease in S / N can be compensated for by increasing the power of the local light source 41. Like.

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.

Then, when there is no wavelength that can be used in mode 1, an optical device corresponding to mode 2 (for example, LP11a mode), which 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.

Hereinafter, with reference to FIG. 7, the upgrade of the optical receiver 30 in units of one mode and one wavelength 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]
Next, configurations different from those in the first and second embodiments will be described as configuration examples of the optical transmission device 10 and the optical reception device 30 illustrated in FIG. In the optical communication system according to the third embodiment, the optical transmission device 10 generates a plurality of optical signals in the basic mode (LP01 mode), performs mode multiplexing of these signals, and further performs wavelength multiplexing, thereby providing an optical reception device. An optical signal to be transmitted to is generated. The optical reception device 30 performs mode separation of the optical signal received from the optical transmission device 10 and further performs wavelength separation to separate the multiplexed signal into a plurality of optical signals in the basic mode, Performs optical signal reception processing. In this embodiment, as described above, an example configuration of an optical communication system in which the optical transmission device 10 performs wavelength multiplexing after performing mode multiplexing and the optical receiving device 30 performs wavelength separation after performing mode separation. Indicates.

<Optical transmitter 10>
With reference to FIG. 8, 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 17 and a generation unit 20 (20-1, 20-2, 20-3,...). Each generation unit 20 includes a single light source 11, an optical branch circuit 12, an optical modulator 13 (13a, 13b,...), An optical amplifier 14 (14a, 14b,...), And a mode converter 15 (15b). , 15c,...) And the mode multiplexer 16. The generation units 20 are provided in the maximum number equal to the number of wavelengths that can be multiplexed by the wavelength multiplexer 17, that is, the mode multiplexer 16 has the maximum number of wavelengths that can be multiplexed by the wavelength multiplexer 17. A number equal to is provided. In each generation unit 20, as many optical modulators 13 and optical amplifiers 14 as the number of modes that can be multiplexed by the mode multiplexer 16 are provided. Also, the number of mode converters 15 is provided in a number equal to the number of optical modulators 13 and optical amplifiers 14 corresponding to higher-order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.).

The plurality of generation units 20 correspond to different single wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...), And generate optical signals each having a corresponding wavelength. 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. However, 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,...), An optical amplifier 14 (14a, 14b,...), And a mode converter 15 ( 15b, 15c,...) And a mode multiplexer 16. 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 fundamental mode (LP01 mode), the optical modulator 13b corresponds to the higher order mode (LP11a mode), and the optical modulator 13c corresponds to the higher order mode (LP11b mode). ).

In the subsequent stage of each optical modulator 13, an optical amplifier 14 for adjusting the power of the optical signal generated by each optical modulator 13 is provided. 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. 10) 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 provide light sources individually 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 fundamental mode optical signal (first optical signal) generated by the optical modulator 13 a corresponding to the fundamental mode and passed through the optical amplifier 14 a is input to the mode multiplexer 16. Further, the fundamental mode optical signal (second light) generated by the optical modulator 13 (13b, 13c,...) Corresponding to the higher-order mode and passed through the optical amplifier 14 (14b, 14c,...). Signal) is input to the mode converter 15 (15b, 15c,...).

The mode converter 15 converts the input optical signal having a single wavelength λ ₁ from the fundamental mode to a higher-order mode, and outputs the converted optical signal to the mode multiplexer 16. For example, the mode converter 15b converts the input optical signal from the basic mode to the higher order mode (LP11a mode), and the mode converter 15c converts the input optical signal from the basic mode to the higher order mode (LP11b). Mode).

The mode multiplexer 16 includes a fundamental mode optical signal having a single wavelength λ ₁ that has passed through the optical amplifier 14a and a single output from the mode converter 15 (15b, 15c,...). A higher-order mode optical signal having wavelength λ ₁ is input. The mode multiplexer 16 multiplexes the input optical signals (mode multiplexing) to generate a mode multiplexed signal having a single wavelength λ ₁ and outputs the mode multiplexed signal to the wavelength multiplexer 17.

To the wavelength multiplexer 17, mode multiplexed signals having different wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...) Output from the plurality of generation units 20 are input in parallel. The wavelength multiplexer 17 generates an optical signal to be transmitted to the optical receiver 30 by multiplexing (wavelength multiplexing) the plurality of input mode multiplexed signals. Since the wavelength multiplexer 17 is processed with a mode multiplexed signal, a device having mode dependency as small as possible is employed for the wavelength multiplexer 17.

According to the configuration described above, the mode converter 15 and the mode multiplexer 16 need only support a single wavelength. In general, since the mode converter and the mode multiplexer have wavelength dependency, it may be technically difficult to cover a wide wavelength band. However, according to the configuration of the present embodiment, the mode converter and the mode multiplexer need only support one specific wavelength, and there is an advantage that the design and manufacture can be facilitated. In this embodiment, as shown in FIG. 2, the mode converter 15 and the mode multiplexer 16 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 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 maximum number of wavelength separators 31 equal to the number of modes that can be separated by the mode separator 32 is provided. 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 device 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 higher-order mode optical signal output from the mode separator 32 from the higher-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. In the following, the receiving unit 40-1 will be mainly described, but the other receiving units 40 are configured in the same manner as the receiving unit 40-1, except that the wavelength of 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.

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 to 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.

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.

Here, in the configuration shown in FIG. 9, the common local light source 41 can be used in the optical receivers (the optical hybrid circuit 34, the light receiving element 35, and the subsequent electric circuit) corresponding to all modes in each receiving unit 40. Therefore, how to actually arrange and connect each device can be a problem. FIG. 10 is a diagram illustrating an example of an actual device configuration of the optical receiving device 30 for coping with such a problem. In this example, the optical receiver 30 includes a separator rack in which the wavelength separator 31, the mode converter 33, and the mode separator 32 are mounted, and an optical receiver rack in which a plurality of optical receivers are mounted. The

First, in the optical receiver rack, optical receivers corresponding to all modes are mounted adjacent to the same stage in units of wavelengths (that is, for each receiving unit 40), and a common local light source 41 is provided near them. Is implemented. Further, the wavelength separator 31, the mode converter 33, and the mode separator 32 are mounted on a separator rack that is a rack independent of these optical receivers. Further, as shown in FIG. 9, the optical receiver rack and the separator rack are provided so as to realize the connection relationship between the optical receiver (the optical hybrid circuit 34, the light receiving element 35, and the subsequent electric circuit) and the wavelength separator 31. Are connected by an optical fiber. In this way, the actual device configuration of the optical receiver 30 can be realized. In the present embodiment, as shown in FIGS. 9 and 10, the mode converter 33 and the mode separator 32 are separated from each other. However, it is also possible to adopt a configuration in which these are integrated.

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

[Example 4]
When performing an upgrade that gradually increases the transmission capacity of the optical communication system as in the third 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 differences from the third embodiment.

<Upgrade of optical transmitter 10>
In the optical transmitter 10, each generating unit 20 shown in FIG. 8 corresponds to one wavelength, and corresponds to a processing block necessary for generating an optical signal having the one wavelength. Therefore, in order to realize the upgrade of the optical transmission device 10 in units of one wavelength, the optical device may be added to the optical transmission device 10 using the generation unit 20 shown in FIG. 8 as an expansion unit.

Hereinafter, with reference to FIG. 11, the upgrade of the optical transmission device 10 in one mode and one wavelength unit will be described. In the present embodiment, the optical transmission apparatus 10 includes an optical modulator 13 corresponding to the added higher-order mode and mode multiplexing with the optical modulator 13 in order to enable addition of a higher-order mode to be transmitted. An optical amplifier 14 and a mode converter 15 provided between the generator 16 and the generator 16 can be added to each generation unit 20. Further, in order to make it possible to add such an optical modulator 13, each generating unit 20 is configured to be able to connect the optical modulator 13 to be added to the light source 11 via the optical branch circuit 12. .

Devices other than the optical modulator 13, the optical amplifier 14, and the mode converter 15 to be added in each generation unit 20 are provided in advance in each generation unit 20. That is, each generation unit 20 is provided with a light source 11, an optical branch circuit 12, and a mode multiplexer 16 in advance.

As shown in FIG. 11, the upgrade of the optical transmission apparatus 10 in one mode unit is performed by adding an optical device to the optical transmission apparatus 10 using the optical modulator 13, the optical amplifier 14, and the mode converter 15 as an expansion unit. It can be realized by doing. An optical connector for connection may be provided in advance at a location where the optical modulator 13, the optical amplifier 14, and the mode converter 15 are connected (added) in the optical transmission device 10. Thereby, the upgrade of the optical transmission device 10 can be easily realized as a package extension. Further, in each generation unit 20, when there is no mode usable at the corresponding wavelength, a new generation unit 20 may be added as described above, or the number of wavelengths multiplexed by the wavelength multiplexer 17. The number of generation units 20 equal to may be provided in advance.

<Upgrade of optical receiver 30>
In the present embodiment, as in the third embodiment, the optical receiver 30 is mounted in a rack configuration as shown in FIG. The optical receiver 30 includes a wavelength separator 31, a wavelength separator 31, and a mode separator 32, 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 therebetween can be added. Furthermore, the optical receiver 30 is configured such that an optical receiver (optical hybrid circuit 34, light receiving element 35, and subsequent electrical circuit) corresponding to the added higher-order mode can be added to each receiving unit 40. Further, in order to make it possible to add such an optical receiver, each receiving unit 40 of the optical receiver 30 can connect the optical receiver to be added to the local light source 41 via the optical branch circuit 42. Can be configured. An optical connector for connection may be provided in advance at a location where the wavelength separator 31, the mode converter 33, and the optical receiver in the optical receiver 30 are connected (added). Note that the number of reception units 40 equal to the number of wavelengths separated by the wavelength separator 31 may be provided in advance, or the number of reception units 40 is increased sequentially as the number of wavelengths to be separated increases. May be.

The upgrade of the optical receiver 30 can be performed in stages according to the following procedure. In the initial stage of the introduction of the optical receiver 30, as shown in FIG. 12, only the optical receivers corresponding to the mode 1 (basic mode) are mounted on the optical receiver rack by the required number of wavelengths. The separator rack is mounted with a wavelength separator 31a corresponding to mode 1 (basic mode) and a mode separator 32 that first receives an optical signal from the optical transmission line 50. Note that the MIMO processing unit 37, which is a part of the optical receiver, is an electric circuit that performs signal processing between modes in each receiving unit 40, and is not shown in FIG. It may be incorporated.

After that, when there is no wavelength that can be used in mode 1, an optical device corresponding to mode 2 (for example, LP11a mode), which is a higher-order mode, is newly mounted in the optical receiver rack and the separator rack. Specifically, as shown in FIG. 13, optical receivers corresponding to mode 2 are newly mounted in the optical receiver rack by the number of necessary wavelengths. In addition, a wavelength separator 31b corresponding to mode 2 and a mode converter 33b corresponding thereto are newly mounted on the separator rack. By repeating such a procedure, the optical receiver 30 can be upgraded in units of one mode and one wavelength.

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 5]
In the first and second embodiments, the configuration example in which mode separation is performed after the optical receiver 30 performs wavelength separation is described. However, as in the third and fourth embodiments, the optical receiver 30 performs mode separation. It is also possible to apply a configuration for performing wavelength separation later to an optical communication system. That is, the configuration shown in FIG. 8 can be adopted as the configuration of the optical receiver 30 in the optical communication systems of the first and second embodiments.

[Example 6]
In the third and fourth embodiments, a configuration example in which wavelength separation is performed after the optical receiver 30 performs mode separation has been described. However, a configuration in which mode separation is performed after the optical receiver 30 performs wavelength separation is described as optical communication. It can also be applied to the system. That is, the configuration shown in FIG. 3 can be adopted as the configuration of the optical receiver 30 in the optical communication systems of the third and fourth embodiments.

The present invention is not limited to the above embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

This application claims priority on the basis of Japanese Patent Application No. 2016-034708 and Japanese Patent Application No. 2016-034709 filed on Feb. 25, 2016. Incorporated into.

Claims (42)

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
A plurality of generating units for generating mode multiplexed signals each having a different wavelength, each generating unit comprising:
A mode converter that converts the second optical signal from the fundamental mode to a higher-order mode among the first and second optical signals of the fundamental mode that are independently modulated and have a single wavelength; ,
A mode multiplexer that generates a mode multiplexed signal by multiplexing the first optical signal in the fundamental mode and the second optical signal in the higher-order mode;
The plurality of generating units, including:
A wavelength multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing a plurality of mode multiplexed signals output from the plurality of generating units, each having a different wavelength;
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 that receive optical signals of the corresponding wavelengths output from the first and second wavelength separators, respectively. system. Each generation unit of the optical transmitter is
A single light source that generates 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,
An optical modulator corresponding to the fundamental mode generates the first optical signal of the fundamental mode;
The optical communication system according to claim 21, wherein the optical modulator corresponding to the higher-order mode generates the second optical signal in the fundamental mode. 23. The light according to claim 22, 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. The optical transmitter is configured such that an optical modulator corresponding to the added higher-order mode can be added to each generation unit in order to enable addition of the higher-order mode to be transmitted. An optical communication system according to claim 22 or 23. 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 24. Each receiving unit of the optical receiver is
A single local light source that generates 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 first wavelength 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 in the fundamental mode output from the second wavelength separator by the light output from the local light source. The optical communication system according to any one of claims 21 to 25. In order to allow the optical receiver to add the higher-order mode to be received,
The second wavelength separator corresponding to the added higher-order mode, and a mode converter provided between the second wavelength separator and the mode separator can be added, and
27. The optical communication system according to claim 26, wherein an optical hybrid circuit corresponding to the added higher-order mode 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. 28. The optical communication system according to claim 27. 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 communication system according to claim 28, wherein an electrical circuit that performs MIMO signal processing is provided in advance. 30. The optical communication system according to any one of claims 21 to 29, wherein an optical transmission path between the optical transmitter and the optical receiver includes a multimode optical fiber and a multimode optical amplifier. . An optical transmitter that transmits an optical signal to an optical receiver,
A plurality of generating units for generating mode multiplexed signals each having a different wavelength, each generating unit comprising:
A mode converter that converts the second optical signal from the fundamental mode to a higher-order mode among the first and second optical signals of the fundamental mode that are independently modulated and have a single wavelength; ,
A mode multiplexer that generates a mode multiplexed signal by multiplexing the first optical signal in the fundamental mode and the second optical signal in the higher-order mode;
The plurality of generating units, including:
A wavelength multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing a plurality of mode multiplexed signals output from the plurality of generating units, each having a different wavelength;
An optical transmission device comprising: Each generation unit of the optical transmitter is
A single light source that generates 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,
An optical modulator corresponding to the fundamental mode generates the first optical signal of the fundamental mode;
32. The optical transmission device according to claim 31, wherein the optical modulator corresponding to the higher order mode generates the second optical signal in the fundamental mode. The optical generation apparatus according to claim 32, 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. The optical transmitter is configured such that an optical modulator corresponding to the added higher-order mode can be added to each generation unit in order to enable addition of the higher-order mode to be transmitted. 34. The optical transmission device according to claim 32 or 33. 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. 35. The optical transmission device according to claim 34. An optical receiver that receives an optical signal transmitted from an optical transmitter,
A mode separator that separates an optical signal received from the optical transmitter 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;
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, each corresponding to a different wavelength, for receiving optical signals of corresponding wavelengths output from the first and second wavelength separators;
An optical receiving device comprising: Each receiving unit of the optical receiver is
A single local light source that generates 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 first wavelength 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 in the fundamental mode output from the second wavelength separator by the light output from the local light source. The optical receiver according to claim 36. In order to allow the optical receiver to add the higher-order mode to be received,
The second wavelength separator corresponding to the added higher-order mode, and a mode converter provided between the second wavelength separator and the mode separator can be added, and
The optical receiver according to claim 37, wherein an optical hybrid circuit corresponding to the added higher-order mode can be added to each receiver 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. 40. The optical receiver according to claim 38. 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. 40. An optical receiver according to claim 39, wherein an electrical circuit for performing MIMO signal processing 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. 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
A plurality of generating units for generating mode multiplexed signals each having a different wavelength, each generating unit comprising:
A mode converter that converts the second optical signal from the fundamental mode to a higher-order mode among the first and second optical signals of the fundamental mode that are independently modulated and have a single wavelength; ,
A mode multiplexer that generates a mode multiplexed signal by multiplexing the first optical signal in the fundamental mode and the second optical signal in the higher-order mode;
The plurality of generating units, including:
A wavelength multiplexer that generates an optical signal to be transmitted to the optical receiver by multiplexing a plurality of mode multiplexed signals output from the plurality of generating units, each having a different wavelength;
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.

Images