JP6120383B2 - Optical communication system - Google Patents

Description

  The present invention relates to a PON optical communication system that multiplexes a broadcast signal and a data communication signal by wavelength, branches them by an optical coupler, and transmits them to each subscriber.

  In recent years, high-speed data communication services such as the Internet using an optical fiber network called FTTH (Fiber To The Home) have been provided. As a configuration of the optical fiber network, a system called a PON (Passive Optical Network) is generally used and is also called a passive double star system. In this configuration, an optical fiber extending from the center is branched by an optical coupler, which is a passive device, and connected to each subscriber. The PON includes standards established by IEEE such as GE (Gigabit Ethernet (registered trademark))-PON and 10G-EPON using Ethernet (registered trademark) as it is, and ITUs such as G-PON and 10G-PON. There is a standard established by -T.

  In GE-PON, when there is no downstream communication data from the center OLT (Optical Line Termination) to each subscriber's D-ONU (ONU for data communication), the OLT repeats a predetermined repetition. It is specified that an idle pattern having a pattern is transmitted.

  In addition, both broadcasting service and data communication service are provided with a single optical fiber by wavelength multiplexing. When the data communication service is a GE-PON system, the broadcast signal and the communication signal interfere with each other due to the influence of the downlink data signal and the periodicity of the idle pattern, and the broadcast quality deteriorates.

  Therefore, the conventional optical communication system is configured as shown in FIG. In the optical communication system of FIG. 2, as a center device, an optical transmitter 100 that outputs a broadcast signal, an OLT 101 that outputs a downlink data signal, an optical amplifier 102 that amplifies the level of the broadcast signal, a broadcast signal, and a downlink data signal And a WDM filter 103 that outputs the wavelength multiplexed signals. The optical signal wavelength-multiplexed by the WDM filter 103 is transmitted by a single optical fiber 104, branched by an optical coupler 105, and transmitted to each subscriber's house. In the subscriber home 120 using only the broadcast service, the broadcast signal is wavelength-separated by the WDM filter 108 and then received by the V-ONU (broadcast ONU) 106. In the subscriber house 122 that uses both the broadcast service and the data communication service, the WDM filter 108 wavelength-separates the broadcast signal and the downlink data signal, and receives them by the V-ONU 106 and the D-ONU 107, respectively. Thus, even in the subscriber home 120 that uses only the broadcast service, it is necessary to provide the WDM filter 108 to transmit only the wavelength of the broadcast signal so that the broadcast signal and the downlink data signal do not interfere with each other. .

  As methods for suppressing interference between other broadcast signals and idle patterns, there are methods described in Patent Documents 1 and 2.

  Patent Document 1 describes that when there is no downstream data signal, random pattern dummy data is inserted to reduce interference with a broadcast signal.

  Patent Document 2 describes that communication signals are scrambled and transmitted to reduce interference with broadcast signals.

JP 2007-67599 A JP 2006-14227 A

  However, in the method of separating a broadcast signal by providing a WDM filter in front of the V-ONU, a WDM filter is required even for a subscriber who uses only the broadcast service, and the WDM filter is installed in all subscriber homes. It takes time and money.

  Further, in the method of Patent Document 1, it is necessary to newly install a device for inserting dummy data in the center, which again takes time and cost.

  In addition, the method of Patent Document 2 is difficult to implement because it changes the method defined by the standard.

  Therefore, an object of the present invention is to enable an optical communication system that provides both broadcasting and communication services to be constructed easily and at low cost.

In the present invention, a broadcast signal which is a digital optical signal is transmitted from an optical transmitter disposed at the center and branched by a first optical coupler, and the broadcast signal from the first optical coupler is received by a broadcast ONU to be electrically transmitted. A broadcast service to be converted into a signal and output, and a first downlink data signal, which is an optical signal, is transmitted from the first OLT arranged in the center, branched by the second optical coupler, and first downlink data from the second optical coupler A first communication service for receiving a signal by an ONU for first data communication, converting it into an electrical signal and outputting it, wherein the first OLT outputs a predetermined repetitive pattern when there is no downstream data signal in an idle state In an existing optical communication system that is operated on each core using multi-core optical fiber cables, the core is used for broadcasting services. A new optical communication system provided by additionally providing a second communication service that is faster than the communication service of the second downlink data signal, which is disposed in the center and is an optical signal having a wavelength different from that of the broadcast signal. A second OLT that outputs and outputs a random pattern in an idle state where there is no second downlink data signal, an optical multiplexer that is arranged in the center and that multiplexes and outputs the broadcast signal and the second downlink data signal, A first optical splitter that is inserted between the second OLT and the optical multiplexer and that branches the second downlink data signal; and a subscriber's home that receives both the broadcasting service and the second communication service. A wavelength separation filter that separates and outputs an optical signal from the coupler into a broadcast signal and a second downlink data signal, and a subscriber's home that receives the provision of the second communication service. In the subscriber's home to be provided for both communication service is connected to the wavelength separation filter, subscriber premises for receiving a second downlink data signal, receive offer only the second communication service without the provision of broadcasting services A second data communication ONU that is directly connected to the first optical coupler , receives the optical signal from the first optical coupler , converts the second downlink data signal into an electrical signal, and outputs the electrical signal; between the first optical coupler, a first optical coupler La and broadcast ONU and the first optical coupler and the optical transmission path Ru respectively connected to between the second data communication ONU, has to receive only broadcast signals subscribing At the customer's house , the first optical coupler and the broadcast ONU are directly connected by an optical transmission line, and the second downlink data signal is branched by the first optical branching device, and the broadcast signal output from the optical transmitter is Output from the second OLT The level difference with the second downlink data signal is adjusted to 10 dB or more, and the interference between the second downlink data signal and the broadcast signal is reduced by the level difference, and the broadcast ONU receives the optical signal from the first optical coupler . In some cases, the optical communication system is adjusted so that the second downlink data signal does not affect the broadcast signal.
In another aspect of the present invention, a broadcast signal which is a digital optical signal is transmitted from an optical transmitter and branched by a first optical coupler, and the broadcast signal from the first optical coupler is received by a broadcast ONU and converted into an electrical signal. The broadcasting service to be converted and output, and the first downlink data signal, which is an optical signal, is transmitted from the first OLT and branched by the second optical coupler, and the first downlink data signal from the second optical coupler is turned on for the first data communication ONU. The first OLT is a communication service that receives and converts to an electrical signal and outputs the electrical signal, and the first OLT is a first communication service that outputs a predetermined repetitive pattern when there is no downstream data signal. In the existing optical communication system that is operated on each core using the optical fiber, the second speed faster than the first communication service using the core used for the broadcasting service. When providing a new optical communication system by adding a communication service, a second downlink data signal, which is an optical signal having a wavelength different from that of the broadcast signal, is output, and a random pattern is generated in an idle state where there is no downlink data signal A second OLT for output and an optical multiplexer for wavelength-multiplexing the broadcast signal and the second downlink data signal and outputting to the first optical coupler are newly provided to provide both the broadcast service and the second communication service. At the subscriber's home , the optical signal branched to the first optical coupler is separated into a broadcast signal and a second downlink data signal and output, and the second downlink data signal from the wavelength separation filter is electrically output. provided a first 2 ONU data communication for converting a signal, the newly, in the subscriber premises to be provided only broadcast service, a first optical coupler without providing the wavelength separation filter Directly connected by a core wire is used between the ONU for transmission to the broadcast service, in the subscriber premises to be provided in only the second communication service, the first optical coupler and the second without providing a wavelength separation filter The data communication ONU is directly connected to the data communication ONU by a core used for broadcasting service, and the level difference between the broadcast signal output from the optical transmitter and the second downlink data signal output from the second OLT When the data signal is attenuated to adjust to 10 dB or more, the interference between the second downlink data signal and the broadcast signal is reduced by the level difference, and the broadcast ONU receives the optical signal branched to the first optical coupler In addition, there is provided an optical communication system construction method characterized in that the second downlink data signal is adjusted so as not to affect the broadcast signal.

  The fact that the downlink data signal does not affect the broadcast signal means that the broadcast can be normally reproduced on a TV receiver or the like connected to the subsequent stage of the broadcast ONU.

  As the OLT and the ONU for data communication, any system can be adopted as long as it is a PON system that outputs a random pattern in an idle state. It should be noted that it is sufficient that it is randomized at least in the idle state, and the entire downlink data signal including the idle state may be randomized. Further, the term “random” does not only mean that it is completely random, but also includes a case where the downlink data signal has such a large periodicity that it does not affect the broadcast signal. For example, methods such as G-PON and 10G-PON can be adopted.

  The level difference between the broadcast signal and the downlink data signal may be adjusted by adjusting the level of the broadcast signal with an optical amplifier, or may be adjusted by adjusting the level of the downlink data signal with an optical attenuator. Further, the level difference may be adjusted by branching at least one of the broadcast signal and the downlink data signal by an optical coupler. Specifically, the level difference is preferably 10 dB or more. This is because the interference of the downlink data signal with the broadcast signal can be sufficiently reduced.

  The optical communication system of the present invention does not require a WDM filter to be inserted before a broadcast ONU for a subscriber who uses only a broadcast service and installs only a broadcast ONU. Therefore, the optical communication system of the present invention can be realized simply and at low cost.

1 is a diagram illustrating a configuration of an optical communication system according to a first embodiment. The figure which showed the structure of the conventional optical communication system. The figure which showed the structure of the optical communication system of a modification. The figure which showed the structure of the optical communication system of a modification.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  FIG. 1 is a diagram illustrating the configuration of the optical communication system according to the first embodiment. The optical communication system according to the first embodiment provides each subscriber with both broadcast service and data communication service using a single optical fiber by wavelength multiplexing. The network between the center and each subscriber is a PON system in which a single optical fiber 14 from the center is branched by an optical coupler 15 and connected to each subscriber. In the data communication service, two-way communication is performed between the center side and each subscriber. However, the upstream communication from the subscriber to the center side has nothing to do with the present invention. In the example, the description is omitted.

  As shown in FIG. 1, in the optical communication system according to the first embodiment, an optical transmitter 10, an OLT 11, an optical amplifier 12, and a WDM filter 13 are arranged on the center side. The output side of the optical transmitter 10 is connected to the optical amplifier 12, and the output side of the optical amplifier 12 and the output side of the OLT 11 are connected to the WDM filter 13.

  The optical transmitter 10 outputs a broadcast signal that is an optical signal having a wavelength of 1550 nm. The broadcast signal is a digital signal such as terrestrial digital broadcast, BS digital broadcast, or CS digital broadcast.

  The input side of the optical amplifier 12 is connected to the output side of the optical transmitter 10, and a broadcast signal from the optical transmitter 10 is input. The optical amplifier 12 amplifies the broadcast signal and adjusts it to a predetermined output level. The specific adjustment method will be described in the operation stage of the optical communication system at the subsequent stage.

  The OLT 11 outputs a downlink data signal that is an optical signal having a wavelength of 1490 nm. The OLT 11 is a device compatible with the G-PON system, and outputs a random pattern in an idle state where there is no downstream data signal. Here, the random pattern does not mean that it is completely random, but the spectrum of the downlink data signal is spread over a wide frequency band corresponding to the bit rate, and the interference level with respect to the broadcast signal becomes sufficiently low. It also means a pattern with a large periodicity. Also, the sufficiently low interference level means that a TV receiver or the like connected to the subsequent stage of the V-ONU 16 can normally reproduce the broadcast signal. For example, a pseudo random pattern such as a PN code may be used. Note that it is sufficient that at least the idle pattern is randomized, and the entire downlink data signal including the idle state may be randomized.

  As long as the idle pattern such as GE-PON is not a fixed pattern standard and the idle pattern is a randomized standard, it may be a standard of an arbitrary system other than the G-PON system. For example, the 10G-PON system is used.

  The WDM filter 13 is connected to the output side of the optical amplifier 12 and the output side of the OLT 11, respectively, and receives a broadcast signal whose output level is adjusted by the optical amplifier 12 and a downlink data signal from the OLT 11. Then, the WDM filter 13 wavelength-multiplexes the two signals and outputs them.

  The optical coupler 15 is connected to the WDM filter 13 by a single optical fiber 14 and receives the wavelength-multiplexed optical signal from the WDM filter 13. The optical coupler 15 divides the inputted optical signal into a plurality of parts and transmits the divided optical signals to each subscriber.

  As shown in FIG. 1, subscribers who receive the broadcasting service and the data communication service can have the following three patterns. In the subscriber houses 20 to 22, devices corresponding to the respective patterns are arranged.

  One is a subscriber who receives only broadcasting service. A subscriber house 20 that receives only broadcast service is provided with a V-ONU 16 that is a broadcast ONU. The optical signal input side of the V-ONU 16 is directly connected to one end on the output side of the optical coupler 15. The V-ONU 16 receives a signal obtained by wavelength-multiplexing the broadcast signal and the downlink data signal from the optical coupler 15. The V-ONU 16 converts the wavelength-multiplexed signal, which is an optical signal, into an RF band electrical signal and outputs it.

  The other is a subscriber who receives only data communication services. A D-ONU 17 is arranged in the subscriber premises 21 that receive only data communication services. The optical signal input side of the D-ONU 17 is directly connected to one end on the output side of the optical coupler 15. The D-ONU 17 uses a PON system similar to the OLT 11, that is, a G-PON system. The D-ONU 17 receives a signal obtained by wavelength-multiplexing the broadcast signal and the downlink data signal from the optical coupler 15. The D-ONU 17 wavelength-separates the downlink data signal from the wavelength-multiplexed signal that is an optical signal, converts the signal into an electrical signal, and outputs the electrical signal.

  The other is a subscriber who receives both broadcasting service and data communication service. A V-ONU 16, a D-ONU 17, and a WDM filter 18 are arranged in the subscriber house 22 that uses both the broadcast service and the communication service. The input side of the WDM filter 18 is directly connected to one end of the output side of the optical coupler 15, and a signal obtained by wavelength-multiplexing the broadcast signal and the downlink data signal from the optical coupler 15 is input. The output side of the WDM filter 18 is connected to the optical signal input side of the V-ONU 16 and D-ONU 17, respectively. The WDM filter 18 wavelength-divides the input wavelength-multiplexed signal into a broadcast signal and a downlink data signal, and outputs them to the V-ONU 16 and the D-ONU 17, respectively.

  Instead of the WDM filter 18, an optical coupler that simply divides the optical signal may be provided. As will be described later, even if the V-ONU 16 receives an optical signal in which the broadcast signal and the downlink data signal are wavelength-multiplexed, the interference of the downlink data signal to the broadcast signal is small and does not affect the broadcast quality. is there.

  Next, the transmission / reception operation of the broadcast service in the optical communication system of the first embodiment will be described.

  In the optical communication system according to the first embodiment, the broadcast signal and the downlink data are adjusted so that the level of the broadcast signal becomes larger than the level of the downlink data signal by adjusting the output level of the broadcast signal by the optical amplifier 12 at the center. Adjust the signal level difference. The level difference is set so that the downlink data signal does not interfere with and influence the broadcast signal when the subscriber home 20 reaches the V-ONU 16. “Unaffected” means that a TV receiver or the like connected to the subsequent stage of the V-ONU 16 can normally reproduce the broadcast. Specifically, the level difference between the broadcast signal input to the WDM filter 13 and the downlink data signal may be 10 dB or more. With such a level difference, since the idle pattern of the downlink data signal is randomized, the V-ONU 16 receives the optical signal in which the broadcast signal and the downlink data signal are wavelength-multiplexed and converts it into an electrical signal. Even so, the interference of the downlink data signal to the broadcast signal is sufficiently small and does not affect the broadcast quality. In particular, if the entire downlink data signal including the idle state is randomized, it is desirable that interference of the downlink data signal to the broadcast signal can be further reduced.

  Since the downlink data signal does not affect the broadcast signal in this way, the WDM filter for transmitting only the wavelength band of the broadcast signal, which has been conventionally required to be inserted before the V-ONU 16, is the light of the first embodiment. This is not necessary at the subscriber home 20 in the communication system. That is, the optical coupler 15 and the V-ONU 16 of the subscriber's home 20 can be directly connected by the optical fiber 14 without providing a WDM filter. Therefore, the optical communication system according to the first embodiment is low-cost and has a simple configuration.

  In the optical communication system according to the first embodiment, in the case where only the broadcasting service is provided, or in the optical communication system that uses a multi-fiber optical fiber cable and provides the broadcasting service and the data communication service with each core wire, This is particularly effective when a communication service is additionally provided by wavelength multiplexing.

  For example, when a GE-PON data communication service and a broadcast service are provided with two cores, a wavelength-multiplexed XG-PON high-speed data communication service is added to the core wire on the broadcast service side. is there.

  In such a case, in the conventional optical communication system as shown in FIG. 2, since it is necessary to install the WDM filter 108 in the subscriber's house that uses only the broadcast service, the subscriber's consent for the additional provision of the data communication service. Need to get. For this reason, it takes time and the cost of the WDM filter 108 is increased.

  However, the optical communication system according to the first embodiment does not require a WDM filter in the subscriber house 20 that uses only broadcasting, and thus has the merit that it is easy to obtain the consent of the subscriber and the introduction cost is low.

[Modification]
In the first embodiment, the output level of the broadcast signal is amplified and adjusted by the optical amplifier 12, thereby adjusting the level difference between the broadcast signal and the downlink data signal and reducing the interference of the downlink data signal to the broadcast signal. However, as shown in FIG. 3, the output level of the downlink data signal is attenuated by the optical attenuator 19 or the like, and the output level of the broadcast signal is also attenuated and adjusted by the optical attenuator 19 or the like as necessary. The level difference of the data signal may be adjusted. Further, as shown in FIG. 4, at least one of the broadcast signal and the downlink data signal may be branched by the optical coupler 200 to adjust the level difference between the broadcast signal and the downlink data signal. Alternatively, by changing the error correction bit rate or changing the modulation method for one or both of the broadcast signal and the downlink data signal, the interference between the downlink data signal and the broadcast signal is reduced by adjusting the signal level difference. It may be. Of course, the level difference may be adjusted by combining these methods.

  The present invention can be applied to an optical communication system that provides both a broadcasting service such as terrestrial digital broadcasting and a high-speed data communication service such as the Internet.

10: Optical transmitter 11: OLT
12: Optical amplifier 13, 18: WDM filter 14: Optical fiber 15, 200: Optical coupler 16: V-ONU
17: D-ONU
19: Optical attenuator 20, 21, 22: Subscriber's house

Claims (6)

A broadcast signal, which is a digital optical signal, is transmitted from an optical transmitter disposed in the center and branched by a first optical coupler, and the broadcast signal from the first optical coupler is received by a broadcast ONU and converted into an electrical signal. The broadcast service to be output and the first downlink data signal, which is an optical signal, are transmitted from the first OLT arranged at the center, branched by the second optical coupler, and the first downlink data signal from the second optical coupler. Is a communication service for receiving a first data communication ONU, converting it into an electrical signal and outputting it, wherein the first OLT outputs a predetermined repetitive pattern in an idle state with no downstream data signal. In an existing optical communication system that is operated on each core using a multi-fiber cable, the core used for the broadcasting service is A new optical communication system faster second communication service is provided by adding than said to use the first communication service,
A second OLT that is arranged at the center, outputs a second downlink data signal that is an optical signal having a wavelength different from that of the broadcast signal, and outputs a random pattern when there is no second downlink data signal;
An optical multiplexer disposed at a center and wavelength-multiplexing and outputting the broadcast signal and the second downlink data signal;
A first optical splitter inserted between the second OLT and the optical multiplexer and branching the second downlink data signal;
The optical signal from the first optical coupler is separated into the broadcast signal and the second downlink data signal and is output at a subscriber's home that receives both the broadcast service and the second communication service. A wavelength separation filter that
It is arranged in a subscriber's home that receives the provision of the second communication service, and is connected to the wavelength separation filter in the subscriber's home that receives both the broadcasting service and the second communication service . In a subscriber's house that receives a downlink data signal and receives only the second communication service without receiving the broadcast service, it is directly connected to the first optical coupler, and the optical signal from the first optical coupler is received. A second data communication ONU that receives a signal, converts the second downlink data signal into an electrical signal, and outputs the electrical signal;
Between the said optical multiplexer first optical coupler, an optical transmission line Ru said first contact between the optical coupler La and the broadcast ONU and the first optical coupler between the second data communication ONU each connection to,
Have
In the subscriber premises that receive only the broadcast signal, the first optical coupler and the broadcast ONU are directly connected by the optical transmission line,
The level difference between the broadcast signal output from the optical transmitter and the second downlink data signal output from the second OLT is adjusted to 10 dB or more by branching the second downlink data signal by the first optical splitter. Then, the interference between the second downlink data signal and the broadcast signal is reduced by the level difference, and when the broadcast ONU receives the optical signal from the first optical coupler , the second downlink data signal is Adjusted so as not to affect the broadcast signal,
An optical communication system.   The level difference is adjusted by adjusting the level of the broadcast signal by the optical amplifier, further comprising an optical amplifier disposed at a center for amplifying the broadcast signal. Optical communication system.   An optical attenuator disposed at the center for attenuating the second downlink data signal; and adjusting the level of the second downlink data signal by the optical attenuator to adjust the level difference. The optical communication system according to claim 1.   The system further comprises a second optical branching device arranged at a center for branching the broadcast signal, and the level difference is adjusted by branching the broadcast signal by the second optical branching device. Item 4. The optical communication system according to Item 1.   5. The device according to claim 1, wherein the second OLT and the second ONU for data communication are devices compatible with a G-PON system or a 10G-PON system. 6. Optical communication system. A broadcast service that transmits a broadcast signal, which is a digital optical signal, from an optical transmitter, branches by a first optical coupler, receives the broadcast signal from the first optical coupler by a broadcast ONU, converts it into an electrical signal, and outputs it; The first downlink data signal, which is an optical signal, is transmitted from the first OLT and branched by the second optical coupler, and the first downlink data signal from the second optical coupler is received by the first data communication ONU to be electrically The first OLT is a communication service that converts and outputs a signal, and the first OLT is a first communication service that outputs a predetermined repetitive pattern when there is no downstream data signal using an optical fiber cable. In the existing optical communication system operated by the core wire, the first communication service is faster than the first communication service by using the core wire used for the broadcasting service. When adding a communication service to provide a new optical communication system,
A second OLT that outputs a second downlink data signal that is an optical signal having a wavelength different from that of the broadcast signal, and that outputs a random pattern when there is no downlink data signal;
An optical multiplexer that wavelength-multiplexes the broadcast signal and the second downlink data signal and outputs the multiplexed signal to the first optical coupler;
Newly established,
Wavelength at which the optical signal branched to the first optical coupler is separated into the broadcast signal and the second downlink data signal for output at the subscriber's home receiving both the broadcast service and the second communication service A separation filter; and a second data communication ONU that converts the second downlink data signal from the wavelength separation filter into an electrical signal and outputs the electrical signal;
Newly established,
In the subscriber's house receiving only the broadcast service, the first optical coupler and the broadcast ONU are directly connected by the core used for the broadcast service without providing the wavelength separation filter,
In a subscriber's house receiving only the second communication service, the core used for the broadcast service between the first optical coupler and the second data communication ONU without the wavelength separation filter is used. Connect directly,
The level difference between the broadcast signal output from the optical transmitter and the second downlink data signal output from the second OLT is adjusted to 10 dB or more by attenuating the second downlink data signal. To reduce interference of the second downlink data signal with the broadcast signal, and when the broadcast ONU receives the optical signal branched to the first optical coupler, the second downlink data signal is converted into the broadcast signal. Adjusted so as not to affect the
An optical communication system construction method characterized by the above.

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