JP6725996B2 - Optical communication system and optical receiver - Google Patents

Description

The present invention relates to optical communication technology, and particularly relates to an optical communication system及 beauty optical receiving apparatus using the both modes multiplexing technology and wavelength multiplexing technology.

Space division multiplexing technology has been studied as a technology for expanding the transmission capacity of an optical fiber transmission line. In the mode multiplexing technology, which is one of space division multiplexing, a multimode (multimode) fiber having multiple modes of an optical signal that can propagate in one core of an optical fiber is used as a transmission line, and The transmission capacity of the optical fiber transmission line is expanded by transmitting different information. Patent Document 1 discloses a technique of generating a plurality of optical signals of different modes and transmitting the multiplexed signals 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 transmitting side device (optical transmitting device) and a receiving side device (optical receiving device) with a multimode fiber. .. The optical transmitter includes an optical transmitter, a converter for converting a mode of an optical signal generated by the optical transmitter from a fundamental mode to a higher mode, and a mode multiplexer for multiplexing a plurality of modes to generate a mode multiplexed signal. Composed of. Further, the optical receiver comprises a mode demultiplexer for demultiplexing the received mode-multiplexed signal into optical signals of individual modes, a mode converter for converting the mode of each demultiplexed optical signal into a fundamental mode, and an optical receiver. To be done.

Japanese Patent No. 56659667

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 the currently commercialized optical communication systems, wavelength division multiplexing technology is used for increasing transmission capacity. In order to further increase the transmission capacity in the optical communication system, it is necessary to use the mode multiplexing technique in addition to the wavelength multiplexing technique. Non-Patent Document 1 shows a configuration and an experimental result in which both wavelength multiplexing technology and mode multiplexing technology are adopted in a laboratory environment. However, Non-Patent Document 1 merely shows an example in which the same information is basically multiplexed and transmitted, and does not show a practical configuration example of the optical transmitter and the optical transmitter.

The present invention has been made in view of the above 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 both wavelength multiplexing technology and mode multiplexing technology.

The present invention can be realized, for example, as 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 transmitter and an optical receiver that receives an optical signal transmitted from the optical transmitter, wherein the optical transmitter is A plurality of generation units for generating mode-multiplexed signals each having a different wavelength, each generation unit being independently modulated and having a single wavelength, a first mode second optical signal and a second mode optical signal. Among these, 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 are multiplexed. And multiplexing the plurality of generation units including the mode multiplexer that generates the mode multiplex signal and the plurality of mode multiplex signals having different wavelengths, which are output from the plurality of generation units. And a wavelength multiplexer that generates an optical signal to be transmitted to the optical receiving device, wherein the optical receiving device converts the optical signal received from the optical transmitting device to the optical signal in the basic mode and the high-level optical signal. A mode converter for separating an optical signal of a next mode and an optical signal of the higher-order mode output from the mode separator, the mode converter converting the higher-order mode to the basic mode, The output of the high-order mode optical signal from the mode separator is provided before the second wavelength separator for wavelength-multiplexing the wavelength-multiplexed high-order mode optical signal. For the output of the optical signal of the fundamental mode , the mode converter, which is not provided before the first wavelength demultiplexer for wavelength demultiplexing the wavelength-multiplexed optical signal of the fundamental mode , the optical signal of the fundamental mode output from the mode separator, said first wavelength separator for separating a plurality of optical signals of different wavelengths, the optical signal of the fundamental mode output from the mode converter , said second wavelength demultiplexer for separating a plurality of optical signals having different wavelengths, corresponding to different wavelengths, output from the first and second wavelength demultiplexer, the corresponding wavelength of light And a plurality of receiving units that perform signal reception processing.

An optical receiving device according to an aspect of the present invention is an optical receiving device that receives an optical signal transmitted from an optical transmitting device, in which an optical signal received from the optical transmitting device is compared with an optical signal in a basic mode. A mode converter for separating an optical signal of a next mode and an optical signal of the higher-order mode output from the mode separator, the mode converter converting the higher-order mode to the basic mode, The output of the high-order mode optical signal from the mode separator is provided before the second wavelength separator for wavelength-multiplexing the wavelength-multiplexed high-order mode optical signal. For the output of the optical signal of the fundamental mode , the mode converter, which is not provided before the first wavelength demultiplexer for wavelength demultiplexing the wavelength-multiplexed optical signal of the fundamental mode , the optical signal of the fundamental mode output from the mode separator, said first wavelength separator for separating a plurality of optical signals of different wavelengths, the optical signal of the fundamental mode output from the mode converter , said second wavelength demultiplexer for separating a plurality of optical signals having different wavelengths, corresponding to different wavelengths, output from the first and second wavelength demultiplexer, the corresponding wavelength of light A plurality of receiving units that perform signal reception processing.

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

The block diagram which shows the structure of an optical communication system. FIG. 3 is a block diagram showing the configuration of the optical transmitter 10. FIG. 3 is a block diagram showing the configuration of an optical receiving device 30. The figure which shows the example of the actual apparatus structure of the optical receiver 30. Explanatory drawing of the example of the upgrade of the optical transmitter 10. Explanatory drawing of the example of the upgrade of the optical receiver 30. Explanatory drawing of the example of the upgrade of the optical receiver 30. FIG. 6 is a block diagram showing a modified example of the configuration of the optical receiving device 30.

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

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

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

<Optical transmitter 10>
The configuration of the optical transmitter 10 according to the present embodiment will be described in detail with reference to FIG. 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 a mode multiplexer 16. The number of generation units 20 provided is equal to the maximum number of wavelengths that can be multiplexed by the wavelength multiplexer 17, that is, the mode multiplexer 16 has a maximum number of wavelengths that can be multiplexed by the wavelength multiplexer 17. Is provided in a number equal to. In each generation unit 20, the number of optical modulators 13 and optical amplifiers 14 provided is equal to the maximum number of modes that can be multiplexed by the mode multiplexer 16. Further, the mode converters 15 are provided by the number equal to the number of the optical modulators 13 and the optical amplifiers 14 corresponding to the higher-order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.).

The plurality of generation units 20 respectively correspond to different single wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,...) And generate optical signals having the corresponding wavelengths. For example, the generation units 20-1, 20-2, 20-3 generate optical signals having wavelengths λ ₁ , λ ₂ , λ ₃ , respectively. The generation unit 20-1 will be mainly described below, but each generation unit 20 other than that 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. It is possible.

The generation unit 20-1 includes a single light source 11, an optical branching 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 a fundamental mode light having a wavelength λ ₁ . The plurality of optical modulators 13 correspond to different modes, respectively, and independently modulate the light output from the light source 11 (that is, modulate with different input signals) to obtain a basic mode optical signal. Respectively. In the present embodiment, as an example, the optical modulator 13a corresponds to the basic 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). ) Is supported.

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

In the generation unit 20-1, it is also possible to individually provide a light source for a plurality of optical transmitters corresponding to different modes. However, maintaining the wavelengths of the lights output from all the light sources at the same wavelength may involve technical difficulties. Therefore, in the present embodiment, the light output from the single light source 11 is branched by the optical branching circuit 12, and the branched (divided) light is modulated by each optical modulator 13, so that a plurality of optical modulations are performed. The common light source 11 is used in the container 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. In addition, an optical signal of the fundamental mode (second optical signal) 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 each of the mode converters 15 (15b, 15c,... ).

The mode converter 15 converts the input optical signal of the single wavelength λ ₁ from the basic mode to the 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 high-order mode (LP11a mode), and the mode converter 15c converts the input optical signal from the basic mode to the high-order mode (LP11b). Mode).

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

Mode multiplexing signals having different wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,... ), which are output from the plurality of generation units 20, are input in parallel to the wavelength multiplexer 17. The wavelength multiplexer 17 multiplexes a plurality of input mode multiplex signals (wavelength multiplex) to generate an optical signal to be transmitted to the optical receiver 30. Since the processing target of the wavelength multiplexer 17 is a mode-multiplexed signal, a device with mode dependency as small as possible is adopted as the wavelength multiplexer 17.

According to the above-mentioned structure, the mode converter 15 and the mode multiplexer 16 need only correspond to a single wavelength. Generally, since the mode converter and the mode multiplexer have wavelength dependence, 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 only need to support one specific wavelength, and there is an advantage that the design and manufacturing thereof can be facilitated. In this embodiment, as shown in FIG. 2, the mode converter 15 and the mode multiplexer 16 are separated, but it is also possible to adopt a structure in which these are integrated.

<Optical receiver 30>
Next, the configuration of the optical receiving device 30 according to the present embodiment will be described in detail with reference to FIG. The optical receiver 30 includes a mode demultiplexer 32, a mode converter 33 (33b, 33c,...), a wavelength demultiplexer 31 (31a, 31b, 31c,...) And a receiving unit 40 (40-1, 40-1). 40-2, 40-3,...). Each reception 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 number of wavelength demultiplexers 31 provided is equal to the maximum number of modes that can be separated by the mode demultiplexer 32. The number of mode converters 33 provided is equal to the number of wavelength demultiplexers 31 (31b, 31c,...) Corresponding to higher-order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.). Further, the receiving units 40 are provided at the maximum number equal to the number of wavelengths that can be separated by the wavelength demultiplexer 31, that is, the optical hybrid circuit 34 and each device in the subsequent stage have at most the mode demultiplexer 32. The number of modes that can be separated by is provided. However, with respect to the light receiving element 35, two light receiving elements corresponding to the I channel and the Q channel are provided for each mode. Further, since the MIMO processing section 37 performs processing across all modes, only one MIMO processing section 37 is provided for each receiving unit.

The mode demultiplexer 32 demultiplexes the optical signal received from the optical transmitter 10 via the optical transmission line 50 into an optical signal of a fundamental mode and an optical signal of a higher mode (LP11a mode, LP11b mode, etc.). Output. The fundamental mode optical signal is input to the wavelength demultiplexer 31a corresponding to the fundamental mode. Further, each optical signal corresponding to the higher-order mode is input to the corresponding mode converter 33 (33b, 33c,... ).

The mode converter 33 converts the high-order mode optical signal output from the mode separator 32 from the high-order mode to the basic mode and outputs the converted signal. For example, the mode converter 33b converts a high-order mode (LP11a mode) optical signal into a basic mode, and the mode converter 33c converts a high-order mode (LP11b mode) optical signal into a basic mode. The optical signal output from each mode converter 33 is input to the wavelength demultiplexer 31 (31b, 31c,...) Connected to the mode converter 33 (corresponding to a higher-order mode). The mode separator 32 and the mode converter 33 are wavelength-multiplexed signals to be processed, and therefore devices having wavelength dependency as small as possible are adopted.

The wavelength demultiplexer 31a corresponding to the fundamental mode has a plurality of fundamental mode optical signals output from the mode demultiplexer 32, each having a single different wavelength λ (λ ₁ , λ ₂ , λ ₃ ,... ). Optical signal is separated. Further, the wavelength demultiplexers 31 (31b, 31c,...) Corresponding to the higher-order modes differ from each other in the fundamental mode optical signal output from the mode converter 33 (33b, 33c,...). It is separated into a plurality of optical signals having a single wavelength λ (λ ₁ , λ ₂ , λ ₃ ,... ). The wavelength demultiplexer 31a is an example of a first wavelength demultiplexer, and the wavelength demultiplexers 31 (31b, 31c,...) Other than the wavelength demultiplexer 31a are an example of a second wavelength demultiplexer. ..

The plurality of receiving units 40 respectively correspond to different wavelengths λ (λ ₁ , λ ₂ , λ ₃ ,... ), and optical signals having the corresponding wavelengths are input from the wavelength demultiplexer 31. For example, optical signals having wavelengths λ ₁ , λ ₂ , λ ₃ are input to the receiving units 40-1, 40-2, 40-3, respectively. Each receiving unit 40 receives the optical signal of the corresponding wavelength λ output from the wavelength demultiplexer 31. Although the receiving unit 40-1 will be mainly described below, each of the other receiving units 40 should be 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 input from the wavelength demultiplexer 31a corresponding to the fundamental mode is input to the optical hybrid circuit 34 corresponding to the fundamental mode. Further, the fundamental mode optical signal having a single wavelength λ ₁ input from the wavelength demultiplexer 31 (31b, 31c,...) Corresponding to the higher-order mode is an optical hybrid circuit corresponding to the higher-order mode. 34 respectively. In the plurality of optical hybrid circuits 34 and their subsequent devices, reception processing of the input basic mode optical signal is performed.

Specifically, the optical hybrid circuit 34 performs coherent detection (coherent reception) of the input 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. The circuit 34 uses a common local light source 41. 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 obtained by the coherent detection output from the optical hybrid circuit 34 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 electric 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 different modes to the MIMO processing unit 37. It The MIMO processing unit 37 suppresses crosstalk noise between modes by performing MIMO signal processing on a plurality of input digital signals, and outputs the resulting signals corresponding to each mode as carrier waves. Output to the estimation unit 38. After that, the carrier estimation unit 38 performs carrier estimation processing, and the code reproduction unit 39 reproduces the transmission digital code. After that, error correction processing or the like may be performed as necessary.

According to the above configuration, the optical devices in the wavelength demultiplexer 31 and the receiving unit 40 only need to support the fundamental mode, and there is an advantage that the mode dependence of these optical devices does not matter. .. Further, 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. 3, 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 realize the arrangement and connection of each device can be a problem. FIG. 4 is a diagram showing 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 is composed of 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. It

First, in the optical receiver rack, the optical receivers corresponding to all modes are mounted adjacent to each other on the same stage on a wavelength-by-wavelength basis (that is, for each receiving unit 40), and a common local light source 41 is provided near them. Will be implemented. The wavelength demultiplexer 31, the mode converter 33, and the mode demultiplexer 32 are mounted on a demultiplexer rack that is a rack independent of those optical receivers. Further, as shown in FIG. 3, the optical receiver rack and the separator rack are provided so that 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. Is connected with an optical fiber. In this way, the actual device configuration of the optical receiving device 30 can be realized. In this embodiment, the mode converter 33 and the mode separator 32 are separated as shown in FIGS. 3 and 4, but it is also possible to adopt a structure in which these are integrated.

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

[Example 2]
In the case of performing an upgrade for gradually increasing 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 this embodiment, a configuration example that enables such an upgrade will be described for each of the optical transmitter 10 and the optical receiver 30. In the following, the present embodiment will be described focusing on the differences from the first embodiment.

<Upgrade of the optical transmitter 10>
In the optical transmission device 10, each generation unit 20 shown in FIG. 2 corresponds to one wavelength and corresponds to a processing block necessary for generating an optical signal of the one wavelength. Therefore, in order to realize the upgrade of the optical transmission device 10 in units of one wavelength, it is sufficient to add the optical device to the optical transmission device 10 using the generation unit 20 shown in FIG.

Hereinafter, with reference to FIG. 5, an upgrade of the optical transmitter 10 in units of one mode and one wavelength will be described. In the present embodiment, the optical transmitter 10 includes an optical modulator 13 corresponding to the higher-order mode to be added, and the optical modulator 13 and mode multiplexing in order to enable the addition of the higher-order mode to be transmitted. The optical amplifier 14 and the mode converter 15 provided between the generator 16 and each of the generators 16 can be added to each generation unit 20. Further, in order to enable the expansion of such an optical modulator 13, each generation unit 20 is configured so that the expansion target optical modulator 13 can be connected to the light source 11 via the optical branching circuit 12. ..

Devices other than the optical modulator 13, the optical amplifier 14, and the mode converter 15 that are the expansion targets in each generation unit 20 are provided in advance in each generation unit 20. That is, the light source 11, the optical branching circuit 12, and the mode multiplexer 16 are provided in advance in each generation unit 20.

As shown in FIG. 5, the upgrade of the optical transmission device 10 in the unit of one mode is performed by adding the optical device to the optical transmission device 10 with the optical modulator 13, the optical amplifier 14 and the mode converter 15 as the unit of addition. It can be realized by doing. Note that an optical connector for connection may be provided in advance in a portion of the optical transmitter 10 where the optical modulator 13, the optical amplifier 14, and the mode converter 15 are connected (added). This makes it possible to easily upgrade the optical transmission device 10 as a package extension. Further, in each generation unit 20, when there is no mode available for 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 may be added. The number of generation units 20 equal to may be provided in advance.

<Upgrade of the optical receiver 30>
In this embodiment, as in the first embodiment, the optical receiving device 30 is mounted in a rack configuration as shown in FIG. The optical receiving device 30 includes a wavelength demultiplexer 31, a wavelength demultiplexer 31 and a mode demultiplexer 32, which correspond to the added high-order mode in order to enable the addition of the higher-order mode to be received. A mode converter 33 provided between them can be added. Further, the optical receiver 30 is configured so that an optical receiver (optical hybrid circuit 34, light receiving element 35, and electric circuit in the subsequent stage) corresponding to the added higher-order mode can be added to each receiving unit 40. Further, in order to enable the extension of such an optical receiver, each receiving unit 40 of the optical receiving device 30 can connect the optical receiver of the extension to the local light source 41 via the optical branching circuit 42. Can be configured into. An optical connector for connection may be provided in advance at a location in the optical receiver 30 where the wavelength demultiplexer 31, the mode converter 33, and the optical receiver are connected (added). It should be noted that the number of receiving units 40 equal to the number of wavelengths separated by the wavelength demultiplexer 31 may be provided in advance, or the receiving units 40 may be sequentially added as the number of separated wavelengths increases. May be.

The optical receiving device 30 can be upgraded in stages by the following procedure. In the initial stage of introduction of the optical receiver 30, as shown in FIG. 6, only the optical receivers corresponding to the mode 1 (basic mode) are mounted on the optical receiver rack by the required number of wavelengths. Further, the wavelength separator 31a corresponding to the mode 1 (basic mode) and the mode separator 32 that first receives an optical signal from the optical transmission line 50 are mounted on the separator rack. 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, so that it is not shown in FIG. It may be incorporated.

After that, when there are no more usable wavelengths in the mode 1, the optical device corresponding to the mode 2 (for example, the LP11a mode) which is the higher order mode is newly mounted on the optical receiver rack and the separator rack. Specifically, as shown in FIG. 7, optical receivers corresponding to mode 2 are newly mounted on the optical receiver rack by the number of required wavelengths. Further, a wavelength separator 31b corresponding to the mode 2 and a mode converter 33b corresponding thereto are newly mounted on the separator rack. By repeating such a procedure, the optical receiving device 30 can be upgraded in units of one mode and one wavelength.

According to this embodiment, the optical transmitter 10 and the optical receiver 30 can be upgraded step by step in one mode and one wavelength, and the equipment required for the initial installation can be saved. Reduction is possible.

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

FIG. 8 is a block diagram showing a modified example of the configuration of the optical receiving device 30. In the optical communication system of the present embodiment, the optical transmitter 10 has the configuration shown in FIG. 2 and the optical receiver 30 has the configuration shown in FIG.

The optical receiving device 30 includes a wavelength demultiplexer 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 The code reproduction unit 39 is included. The maximum number of receiving units 40 is equal to the number of wavelengths that can be separated by the wavelength demultiplexer 31, that is, the number of mode demultiplexers 32 is equal to the maximum number of wavelengths that can be separated by the wavelength demultiplexer 31. It is provided by the number. The optical hybrid circuit 34 and the devices subsequent thereto are provided in a number equal to the maximum number of modes that can be separated by the mode separator 32. However, with respect to the light receiving element 35, two light receiving elements corresponding to the I channel and the Q channel are provided for each mode. Further, since the MIMO processing section 37 performs processing across all modes, only one MIMO processing section 37 is provided for each receiving unit. Further, the number of mode converters 33 provided is equal to the number of the optical hybrid circuits 34 corresponding to the higher-order modes (for example, LP11a mode, LP11b mode, LP02 mode, etc.).

The wavelength demultiplexer 31 receives a plurality of optical signals received from the optical transmission device 10 via the optical transmission path 50 and has a plurality of different 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 the corresponding wavelengths are input from the wavelength demultiplexer 31. For example, optical signals having wavelengths λ ₁ , λ ₂ , λ ₃ are input to the receiving units 40-1, 40-2, 40-3, respectively. Since the processing target of the wavelength demultiplexer 31 is a mode multiplexed signal, a device having mode dependency as small as possible is adopted as the wavelength demultiplexer 31. Although the receiving unit 40-1 will be mainly described below, each of the other receiving units 40 should be 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 reception unit 40-1, the mode demultiplexer 32 converts the optical signal of the wavelength λ ₁ input from the wavelength demultiplexer 31 into the optical signal of the fundamental mode and the optical signal of the higher mode (LP11a mode, LP11b mode, etc.). Output separately. The basic mode optical signal is input to the optical hybrid circuit 34 corresponding to the basic mode. Further, each optical signal corresponding to the higher-order mode is input to the corresponding mode converter 33 (33b, 33c,... ).

The mode converter 33 converts the high-order mode optical signal output from the mode separator 32 from the high-order mode to the basic mode and outputs the converted signal. For example, the mode converter 33b converts a high-order mode (LP11a mode) optical signal into a basic mode, and the mode converter 33c converts a high-order mode (LP11b mode) optical signal into a basic mode. The optical signal output from each mode converter 33 is input to the optical hybrid circuit 34 (corresponding to the higher-order mode) connected to the mode converter 33. In the plurality of optical hybrid circuits 34 and their subsequent devices, the 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 is performed. Note that the reception processing by the plurality of optical hybrid circuits 34 and the devices in the subsequent stages thereof is the same as that in the first embodiment.

According to the configuration described above, the mode separator 32 and the mode converter 33 need only support a single wavelength, which can facilitate the design and manufacture of those optical devices, and at the same time, enable the optical devices to be designed and manufactured. There is an advantage that the wavelength dependence of is not a problem. In addition, in this embodiment, as shown in FIG. 8, the mode separator 32 and the mode converter 33 are separated, but it is also possible to adopt a structure in which these are integrated.

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

Claims (15)

An optical communication system comprising an optical transmitter and an optical receiver that receives an optical signal transmitted from the optical transmitter,
The optical transmission device,
A plurality of generation units for generating mode-multiplexed signals each having a different wavelength, each generation 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 fundamental-mode optical signals that are independently modulated and have a single wavelength. ,
A mode multiplexer that generates a mode multiplexed signal by multiplexing the first optical signal of the fundamental mode and the second optical signal of the higher order mode;
A plurality of generation units, including:
A wavelength multiplexer that generates an optical signal to be transmitted to the optical receiving device by multiplexing a plurality of mode-multiplexed signals having different wavelengths, which are output from the plurality of generating units,
The optical receiving device,
An optical signal received from the optical transmitter, a mode separator for separating the optical signal of the fundamental mode and the optical signal of the higher 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, wherein the higher-order mode optical signal is output from the mode separator. On the other hand, for the output of the fundamental mode optical signal from the mode demultiplexer, which is provided before the second wavelength demultiplexer for wavelength demultiplexing the wavelength-multiplexed high-order mode optical signal, The mode converter, which is not provided before the first wavelength demultiplexer for wavelength demultiplexing the wavelength-multiplexed optical signal of the fundamental mode,
The first wavelength demultiplexer that demultiplexes the optical signal of the fundamental mode output from the mode demultiplexer into a plurality of optical signals of different wavelengths,
The second wavelength demultiplexer that demultiplexes the optical signal of the fundamental mode output from the mode converter into a plurality of optical signals of different wavelengths,
A plurality of receiving units that respectively correspond to different wavelengths and perform a receiving process of optical signals of the corresponding wavelengths output from the first and second wavelength demultiplexers, and optical communication. system. Each generation unit of the optical transmission device,
A single light source that produces light having a single wavelength;
A plurality of optical modulators corresponding to different modes and commonly using the light source, wherein the light signals of the fundamental mode are obtained by independently modulating the light output from the light source. A plurality of optical modulators, each of which generates
An optical modulator corresponding to the fundamental mode generates the first optical signal in the fundamental mode,
The optical communication system according to claim 1, wherein the optical modulator corresponding to the higher-order mode generates the second optical signal in the fundamental mode. The optical generator according to claim 2, wherein each generation unit of the optical transmitter further includes at least one of an optical amplifier and an optical attenuator that adjusts the 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. The optical communication system according to claim 2 or 3. Each of the generation units of the optical transmission device is configured to be connectable to the light source through an optical branching circuit that branches the light output from the light source, the optical modulator to be added. The optical communication system according to claim 4. Each receiving unit of the optical receiving device,
A single local light source that produces light having a single wavelength;
A plurality of optical hybrid circuits that correspond to different modes and that commonly use the local oscillation light source,
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 demultiplexer 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 second wavelength demultiplexer by the light output from the local light source. The optical communication system according to any one of claims 1 to 5. The optical receiving device, in order to enable the addition of the higher order mode to be received,
A second wavelength demultiplexer corresponding to the added higher-order mode and a mode converter provided between the second wavelength demultiplexer and the mode demultiplexer are configured to be expandable, and
The optical communication system according to claim 6, wherein the optical hybrid circuit corresponding to the added high-order mode is configured to be expandable to each receiving unit. Each receiving unit of the optical receiving device is configured to be able to connect the optical hybrid circuit to be added to the local light source via an optical branching circuit for branching the light output from the local light source. The optical communication system according to claim 7, wherein: Each receiving unit of the optical receiving device includes a light receiving element for converting an optical signal output from each optical hybrid circuit into an electric signal, and a plurality of electric signals corresponding to the same wavelength and corresponding to different modes. The optical communication system according to claim 8, wherein an electric circuit that performs MIMO signal processing is provided in advance. 10. The optical communication system according to claim 1, wherein an optical transmission line between the optical transmitter and the optical receiver includes a multimode optical fiber and a multimode optical amplifier. .. An optical receiving device for receiving an optical signal transmitted from an optical transmitting device,
An optical signal received from the optical transmitter, a mode separator for separating an optical signal of a fundamental mode and an optical signal of a higher 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, wherein the higher-order mode optical signal is output from the mode separator. On the other hand, for the output of the fundamental mode optical signal from the mode demultiplexer, which is provided before the second wavelength demultiplexer for wavelength demultiplexing the wavelength-multiplexed high-order mode optical signal, The mode converter, which is not provided before the first wavelength demultiplexer for wavelength demultiplexing the wavelength-multiplexed optical signal of the fundamental mode,
The first wavelength demultiplexer that demultiplexes the optical signal of the fundamental mode output from the mode demultiplexer into a plurality of optical signals of different wavelengths,
The second wavelength demultiplexer that demultiplexes the optical signal of the fundamental mode output from the mode converter into a plurality of optical signals of different wavelengths,
A plurality of receiving units that respectively correspond to different wavelengths and perform a receiving process of optical signals of the corresponding wavelengths output from the first and second wavelength demultiplexers;
An optical receiver comprising: Each receiving unit of the optical receiving device,
A single local light source that produces light having a single wavelength;
A plurality of optical hybrid circuits that correspond to different modes and that commonly use the local oscillation light source,
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 demultiplexer 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 second wavelength demultiplexer by the light output from the local light source. The optical receiver according to claim 11. The optical receiving device, in order to enable the addition of the higher order mode to be received,
A second wavelength demultiplexer corresponding to the added higher-order mode and a mode converter provided between the second wavelength demultiplexer and the mode demultiplexer are configured to be expandable, and
The optical receiving device according to claim 12, wherein the optical hybrid circuit corresponding to the added higher-order mode is configured to be able to be added to each receiving unit. Each receiving unit of the optical receiving device is configured to be able to connect the optical hybrid circuit to be added to the local light source via an optical branching circuit for branching the light output from the local light source. The optical receiving device according to claim 13, wherein: Each receiving unit of the optical receiving device includes a light receiving element for converting an optical signal output from each optical hybrid circuit into an electric signal, and a plurality of electric signals corresponding to the same wavelength and corresponding to different modes. The optical receiving apparatus according to claim 14, wherein an electric circuit that performs MIMO signal processing is provided in advance.

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