JP5228225B2 - Optical CATV system - Google Patents

Description

  The present invention relates to an optical CATV (Cable television) system.

  In a conventional CATV downlink system, a center station (HE: Head End) and a subscriber's house are connected via a copper wire. In such a CATV system, a video signal is distributed to a subscriber's home using a channel in the UHF band up to 450 MHz. In the CATV system, there are thousands to tens of thousands of subscribers to one center station. Further, the distance from the center station to the subscriber's home may reach several kilometers. Therefore, when trying to transmit the above-mentioned signals, particularly high-frequency / broadband video signals from the center station to the subscriber's house, it is necessary to install relay amplifiers at intervals of ~ 400 m in the trunk portion. This is because the high frequency / broadband signal is attenuated.

  In recent years, in order to mitigate signal attenuation, an optical CATV system (HFC: Hybrid Fiber and Coaxial) using an optical cable in a trunk portion from a center station to a subcenter has been proposed. Thereby, the influence of inflow noise included in the upstream signal is alleviated, and the upper limit of the video signal band is expanded from 450 MHz to 770 MHz. Specifically, in the optical CATV system, a video signal is distributed as a frequency multiplexed signal using a carrier wave of 6 MHz span within a frequency band of 70 MHz to 770 MHz. Also, an empty channel in the same frequency band is used for a downlink communication signal for the Internet or the like. Furthermore, a channel in the frequency band of 10 to 55 MHz is used for an upstream communication signal.

  In recent years, all-optical use of telephone lines has become common. In the all-optical telephone line, a PON system such as a so-called GE-PON (Gigabit Ethernet-Passive Optical Network) system is adopted as the most general form. In the PON system, generally, optical fibers from 64 subscriber houses are coupled to an optical coupler, and one optical fiber is connected from the optical coupler to the center station for 64 subscriber houses. . Such a PON system has a capacity capable of transmitting not only a voice signal for a telephone but also a communication signal for the Internet or the like, and further a video signal.

  Under such circumstances, the construction of an all-optical CATV system has become a hot topic.

JP 2004-166300 A JP-A-2005-341266 JP 2006-005595 A

  The number of optical fibers connected to the center station in the PON system is enormous. Therefore, in the CATV system, if an optical fiber connection form similar to that of the PON system is adopted, it is difficult to accommodate the optical fiber in the center station. In addition, the center station does not have enough space to accommodate devices that individually process signals from a large number of optical fibers.

  Further, when adopting the configuration of the PON system in the CATV system, a difference in communication method becomes a problem. That is, in the PON system, the Ethernet frame is transmitted as it is, whereas in the CATV system, the signal is QPSK (Quaternary Phase Shift Keying) modulated by a carrier wave and QAM (Quadrature Amplitude Modulation) in both cases of uplink and downlink. The data is modulated and transmitted by a method such as modulation. Therefore, when adopting the PON system configuration in the CATV system, it is necessary to replace the equipment of the center station and the entire modem at the subscriber's house.

  An object of the present invention is to provide an optical CATV system capable of reducing the number of fibers connected to a center station and reducing the number of devices to be replaced.

  The optical CATV system of the present invention includes a CATV (Cable television) center station, an FTTH (Fiber To The Home) node device, and a plurality of optical network units for a plurality of subscriber homes. The FTTH node device is connected to the center station. The plurality of optical network units are connected to the FTTH node device. The center station transmits an image signal to the FTTH node device using an optical signal having a wavelength of DWDM (Dense Wavelength Division Multiplexing) standard via an optical fiber connecting the center station and the FTTH node device. A downlink communication signal in a frequency band of 70 MHz to 770 MHz is transmitted using an optical signal having a wavelength of another DWDM different from the wavelength of the video signal. The FTTH node device receives a plurality of optical signals corresponding to a video signal and a downlink communication signal from the center station via an optical fiber connecting the FTTH node device and the center station. Relay to the optical network unit. The plurality of optical network units receive a plurality of optical signals having different wavelengths from the FTTH node apparatus via optical fibers connecting the respective optical network units and the FTTH node apparatus, and light having wavelengths different from these wavelengths. An uplink communication signal using a time division slot dedicated to each optical network unit using a signal and using a channel in a frequency band including the frequency band of 10 to 55 MHz and lower than the frequency band of the downlink communication signal. To the FTTH node device. The optical network unit at each subscriber's home outputs BS-IF and CS-IF signals, video signals, and downlink communication signals based on the received optical signals having different wavelengths. The FTTH node device generates a multiplexed uplink communication signal by multiplexing uplink communication signals transmitted from a plurality of optical network units, and uses the optical signal having a wavelength of the CWDM standard to generate a multiplexed uplink communication signal. The data is transmitted to the center station via an optical fiber connecting the FTTH node device and the center station. The center station receives the multiplexed uplink communication signal from the FTTH node device via an optical fiber connecting the center station and the FTTH node device. Here, this CATV system is characterized in that a plurality of subscribers are grouped together and uplink communication signals from the subscribers belonging to the group are transmitted to the FTTH node apparatus at different wavelengths. Thereby, even when a plurality of subscribers are multiplexed by the FTTH node device to generate a multiplexed uplink signal, the effect of multiplexing the noise generated by the network unit at each subscriber's home can be reduced. it can.

  In the optical CATV system of the present invention, the center station and the optical network unit at the subscriber's house are connected by an optical fiber. Further, the upstream communication signal from the optical network unit at each subscriber's house is multiplexed by the FTTH node device and transmitted to the center station through one optical fiber. For example, by setting the number of time divisions for a plurality of optical network units to 256, for example, 256 optical network units can be connected to the FTTH node device. As a result, the number of optical fibers connected to the center station can be reduced with respect to the number of optical network units. Further, as the BS-IF and CS-IF signals, the video signal, the downlink communication signal, and the uplink communication signal, substantially the same signals as those in the conventional CATV system can be used, so that the modulation / demodulation employed in the conventional CATV system is possible. A device can be employed.

  The optical CATV system of the present invention includes a CATV center station, an FTTH cluster node device, a plurality of FTTH node devices, and a plurality of optical network units for a plurality of subscriber homes. The FTTH cluster node device is connected to the center station. The plurality of FTTH node devices are connected to the FTTH cluster node device. The plurality of optical network units are connected to any of the plurality of FTTH node devices. The center station uses the optical signal of the wavelength of the DWDM standard to the FTTH cluster node device via the optical fiber connecting the center station and the FTTH cluster node device, and the BS-IF and CS-IF signals, and the video A signal is transmitted, and a downstream communication signal of 70 MHz to 770 MHz is transmitted using an optical signal of another wavelength of the DWDM standard. The FTTH cluster node device receives optical signals of a plurality of wavelengths from the center station via an optical fiber connecting the center station and the FTTH cluster node device, and relays these optical signals to the plurality of FTTH node devices. . A plurality of optical network units are connected to the plurality of FTTH node devices, respectively. Each of the plurality of FTTH node devices receives a plurality of optical signals from the FTTH cluster node device via an optical fiber connecting the FTTH node device and the FTTH cluster node device, and is connected to the FTTH node device. These optical signals are transmitted to two or more optical network units. Each of the optical network units receives a plurality of optical signals from the FTTH node device via an optical fiber connecting the FTTH node device connected to the optical network unit and the optical network unit, and Using an optical signal having a wavelength different from the wavelength of the signal, an uplink communication signal including a frequency band of 10 to 55 MHz and using a frequency band lower than the frequency band of the downlink communication signal is transmitted to the FTTH node device. The plurality of optical network units separates and outputs the BS-IF and CS-IF signals, the video signal, and the downlink communication signal from the received optical signal. Different wavelengths are assigned to upstream communication signals from a group of optical network units connected to the same FTTH node device among a plurality of FTTH node devices. Each of the plurality of FTTH node devices generates a multiplexed uplink signal by multiplexing uplink communication signals transmitted from two or more optical network units connected to the FTTH node device, and has a wavelength of the CWDM standard. The multiplexed uplink communication signal is connected between the FTTH node apparatus and the FTTH cluster node apparatus using an optical signal having a wavelength different from that used by another FTTH node apparatus connected to the FTTH cluster node apparatus. The data is transmitted to the FTTH cluster node device via the optical fiber. The FTTH cluster node device receives multiplexed uplink communication signals from a plurality of FTTH node devices via an optical fiber connecting the FTTH cluster node device and the plurality of FTTH node devices, and the FTTH cluster node device and the center station Multiplexed upstream communication signals are transmitted via the optical fiber connecting the two. The center station receives a multiplexed uplink communication signal from the FTTH cluster node device via an optical fiber connecting the center station and the FTTH cluster node device.

  In the optical CATV system of the present invention, the center station and the optical network unit at the subscriber's house are connected by an optical fiber. In addition, uplink communication signals from a plurality of optical network units are multiplexed by the FTTH node device to be multiplexed uplink communication signals. Here, with a plurality of network units as a group, the upstream communication signals of the network units in the group are assigned different wavelengths. Therefore, even if a plurality of uplink communication signals are multiplexed and received in the FTTH node device, the multiplexing effect of noise generated by each network unit can be reduced. Here, the wavelength of the uplink communication signal from each network unit may correspond to one of the CWDM grid wavelengths (20 nm span), or may correspond to a wavelength of 10 nm intervals that is 1/2 of the wavelength. If the division span becomes narrow, the number of subscribers included in one FTTH node device can be increased. On the other hand, from the viewpoint of each subscriber, the time slot allocated to one subscriber decreases. The wavelength division interval and the number of subscribers in a group can be appropriately determined according to the relationship between the communication capacity and the total number of subscribers. Further, as the BS-IF and CS-IF signals, the video signal, the downlink communication signal, and the uplink communication signal, substantially the same signals as those in the conventional CATV system can be used, so that the modulation / demodulation employed in the conventional CATV system is possible. A device can be employed.

  As described above, according to the present invention, there is provided an optical CATV system that can reduce the number of fibers connected to the center station and reduce the number of devices to be replaced.

1 is a diagram schematically illustrating an optical CATV (Cable Television) system according to an embodiment. It is a figure which shows an example of the center station shown in FIG. 1 in detail. It is a figure which shows the frequency band of the video system signal and communication signal which are utilized with the optical CATV system of one Embodiment. It is a figure which shows the wavelength of the optical signal utilized with the optical CATV system of one Embodiment. It is a figure which shows the structure of the FTTH cluster node apparatus of one Embodiment. It is a figure which shows the structure of the FTTH node apparatus of one Embodiment. It is a figure which shows the structure of the quadruple O / E converter of one Embodiment. It is a figure which shows the structural example of a merger. It is a figure which shows the structure of the optical network unit of one Embodiment. It is a figure which shows the frequency band of the video system signal and communication signal which are utilized with the optical CATV system of another embodiment. It is a figure which shows the structure of the optical network unit of another embodiment. It is a figure which shows the structure of the optical network unit of another embodiment. It is a figure which shows the structure of the center station concerning another embodiment. It is a figure which shows the structure of the network unit corresponding to the center station concerning another embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a diagram schematically illustrating an optical CATV (Cable Television) system according to an embodiment. In the optical CATV system 10 shown in FIG. 1, a video signal and a downlink communication signal are transmitted from the center station 12 to a plurality of downstream subscriber houses 14. Further, upstream communication signals are transmitted from the plurality of subscriber homes 14 to the upstream center station 12.

The optical CATV system 10 may include FTTH (Fiber To The Home) node devices 16 a _{1 to} 16 a _J and a plurality of optical network units (ONUs) 18. Here, J is an integer of 1 or more. Further, the optical CATV system 10 can include FTTH node devices 16b _{1 to} 16b ₄ , an FTTH cluster node device 20, and a plurality of ONUs 18. The node devices 16a _{1 to} 16a _J and the node devices 16b _{1 to} 16b ₄ can have the same device configuration. Therefore, hereinafter, each of the node devices 16a _{1 to} 16a _J and the node devices 16b _{1 to} 16b ₄ may be collectively referred to as a node device 16.

The center station 12 and the node devices 16a _{1 to} 16a _J are connected to each other via an upstream optical fiber 22a and downstream optical fiber 22b. Each of the node devices 16a _{1 to} 16a _J is connected to the downstream side thereof by a plurality of optical fibers 26. Each optical fiber 30 is branched from the optical fiber 26 via a plurality of optical taps, that is, a plurality of optical couplers 28. Each optical fiber 30 is connected to an ONU 18 provided in a plurality of subscriber homes 14.

The center station 12 and the cluster node device 20 are connected via optical fibers 32a and 32b for downlink signals and optical fibers 34a and 34b for uplink. Each of the cluster node device 20 and the node devices 16b _{1 to} 16b ₄ is connected via an upstream optical fiber 36a and a downstream optical fiber 36b.

Similarly to the node devices 16a _{1 to} 16a _J , each of the node devices 16b _{1 to} 16b ₄ is connected to the downstream side thereof by a plurality of optical fibers 26. An optical fiber 30 is branched from the optical fiber 26 via a plurality of optical taps, that is, a plurality of optical couplers 28. The optical fibers 30 are respectively connected to the ONUs 18 provided in the subscriber homes 14. Here, the upstream and downstream optical fibers, 32a and 32b, 34a and 34b, are provided between the center station and the FTTH cluster node apparatus 20, because one is used as a working system and the other as a standby system. This is to increase the security of the system. Even if there is an accident such as disconnection in the working system, the communication between each subscriber home 14 and the center station 12 is not hindered by instantaneously switching to the standby system.

FIG. 2 is a diagram showing in detail an example of the center station shown in FIG. The center station 12 includes a cable modem (CMTS: Cable Modem Termination System) 12a _{1 to} 12a ₂ , communication optical transmitters 12b _{1 to} 12b ₂ , video optical transmitters 12c _{1 to} 12c ₂ , and communication optical receivers. and a vessel _12d 1 to 12d _2.

The CMTSs 12a ₁ and 12a ₂ are connected to an external communication network such as the Internet. For example, CMTS 12a ₁ is connected to a wide area network to provide an Internet service, and CMTS 12a ₂ is connected to a telephone line to provide an IP telephone service. This CMTS is often prepared for each service. The CMTSs 12a _{1 to} 12a ₂ receive the uplink communication signal based on the optical signal from the cluster node device 20. The CMTSs 12a _{1 to} 12a ₂ demodulate the received uplink communication signal and transmit the demodulated signal to an external network. Further, the CMTSs 12a _{1 to} 12a ₂ modulate a signal received from an external communication network to generate a downlink communication signal, and transmit the downlink communication signal to the downstream side, that is, the cluster node device 20 side.

Specifically, the optical signal from the cluster node device 20 is transmitted to the CWDM (coarse wavelength division multiplexing) filters 12e ₁ and 12e ₂ via the optical fibers 34a (working system) and 34b (standby system). The optical signal input to the filter 12e ₁ via the optical fiber 34a is demultiplexed for each wavelength by the filter 12e ₁ . Optical signal branched by the filter 12e ₁ is individually optical / electrical conversion by one of the light receiving element of the optical receiver 12d _1. Uplink communication signals transmitted through the optical fiber 34b as well, after being demultiplexed by CWDM filter 12e _2, is an optical / electrical conversion by the other light receiving element of the optical receiver 12d _1. The active system 34a and the standby system 34b can be switched by switching two optical / electrically converted signals by a switch (SW). The output of the switch becomes an upstream communication signal. In FIG. 2, a path indicated by a thick line corresponds to a propagation path of an optical signal, and a path indicated by a thin line corresponds to a propagation path of an electric signal. The upstream communication signal from the optical receiver 12d ₁ is distributed by the distributor 12n ₁ and input to the respective CMTS devices 12a ₁ and 12a ₂ , and the received upstream communication signal is a service provided by the CMTS device. If it is determined, the upstream communication signal is demodulated and sent out to a protocol on an external wide area network.

As will be described later, the optical signal transmitted from the cluster node device 20 has a wavelength that differs depending on the transmission source node device 16, that is, a wavelength corresponding to one grid wavelength based on the CWDM transmission standard. Therefore, it is necessary to equip the light receiving device 12d ₁ corresponding to the node device 16. Also, as described above, the CMTS apparatus is provided corresponding to each service to form one set, and this set is provided corresponding to the number of node apparatuses. Alternatively, as shown in FIG. 2, a CMTS device typically includes one output (downstream system) and a plurality of input (upstream system) terminals. Instead of corresponding to the number of each node device, a single CMTS device set can correspond to a plurality of node devices. In any case, since the CMTS can identify the node device 16 that is the source of the uplink communication signal in this way, the uplink communication signal is transmitted from the time slot used by the uplink communication signal. It is possible to specify from which ONU downstream the transmission is performed.

Further, the downlink communication signals from the CMTSs 12a ₁ and 12a ₂ are respectively distributed by the distributors 12m ₁ and 12m _{2 in} a number corresponding to the node devices, and then the outputs of the two CMTS devices in the example of FIG. 12o ₁ and 12o ₂ are added together, and the output is transmitted to the optical transmitters 12b ₁ and 12b ₂ . The optical transmitters 12b ₁ and 12b ₂ convert the received downlink communication signal into an optical signal by E / O conversion. The optical signal is input to the optical fibers 32a and 32b via the multiplexer 12g and the distributor 12f, and transmitted to the cluster node device 20 via the optical fibers 32a and 32b.

The optical signal from the node device 16 directly connected to the center station 12 without passing through the cluster node device 20 is received by the optical receiver 12d ₂ via the optical fiber 22a. When the center station 12 and the node device 16 are directly connected, the necessity of providing two systems, an active system and a standby system, is reduced. This is because the number of subscribers involved in one cluster node device 20 and the absolute number of subscribers involved in one node device are much larger in the former. The optical receiver 12d ₂ O / E converts the received optical signal to generate an upstream communication signal. Since there is no distinction between the working / standby systems, the optical receiver 12d ₂ does not have a changeover switch (SW) between them. The uplink communication signal is distributed by the distributor 12n ₂ and then input to the CMTSs 12a ₁ and 12a ₂ . Downlink communication signals from the CMTSs 12a ₁ and 12a ₂ are added together by the adder 12o ₂ and then input to the optical transmitter 12b ₁ . The optical transmitter 12b ₁ converts the received downlink communication signal into an optical signal by E / O conversion. The optical signal is input to the optical fiber 22b via the multiplexer 12h and transmitted to the node device 16 via the optical fiber 22b.

The center station 12 receives a video signal (BC: Broadcast) in a frequency band of 70 to 770 MHz, a BS and CS signal in a 12 GHz band, down-converts the BS and CS signals, and has a frequency of 1 GHz to 2.6 GHz. It has equipment for converting to band BS-IF and CS-IF signals. The video-system optical transmitters 12c ₁ and 12c ₂ generate optical signals by E / O converting the video signals and the BS-IF and CS-IF signals. The optical signals generated by the optical transmitters 12c ₁ and 12c ₂ are respectively amplified by the optical amplifiers 12j1 and 12j2, and then distributed to the two systems by the distributors 12k ₁ and 12k ₂ , and one of the distributed optical signals is distributed. Is input to the optical fiber 22b via the multiplexer 12h and transmitted to the node device 16 via the optical fiber 22b. The other distributed signal is input to the optical fibers 32a and 32b via the multiplexer 12g and the distributor 12f, and transmitted to the cluster node device 20 via the optical fibers 32a and 32b. .

  Refer to FIG. 1 again. In this system 10, it is assumed that 16 subscriber homes 14, that is, 16 ONUs 18 are connected to one optical fiber 26 extending from one node device 16. In addition, it is assumed that 16 optical fibers 26 extend downstream from one node device 16. Therefore, the system 10 can join 256 subscribers to one node device 16. The communication of these 256 subscribers is distinguished by time division using different time slots. Note that the number of optical fibers 26 extending from the node device 16 and the number of ONUs 18 connected to one optical fiber 26 can be appropriately set according to the number of time divisions in communication.

  In this system 10, BS-IF and CS-IF signals, video signals, and downlink communication signals are transmitted as optical signals from the center station 12 to the subscriber premises 14, and uplink communication signals are transmitted from the subscriber premises 14. It is transmitted to the center station 12 side as an optical signal. Here, different wavelengths are assigned to the optical signals for the BS-IF and CS-IF signals, the video signal, the downlink communication signal, and the uplink communication signal. As will be described later, in each subscriber home 14, the ONU 18 separates the BS-IF and CS-IF signals, the optical signal for the video signal, and the optical signal for the downlink communication signal by a wavelength separation filter. The video signal and the downlink communication signal are output from the same terminal, and each video signal is connected to a device 14d such as a television receiver in the subscriber's house 14 via the set top box 14c, while the downlink communication signal is It is connected to a device 14b such as a personal computer via a cable modem 14a.

  Hereinafter, the frequency band of the video system signal and the communication signal used in the system 10 and the wavelength of the optical signal will be described. FIG. 3 is a diagram illustrating frequency bands of video-related signals and communication signals used in the optical CATV system according to an embodiment. FIG. 4 is a diagram illustrating wavelengths of optical signals used in the optical CATV system according to the embodiment.

  As shown in FIG. 3, in the system 10, the BS-IF and CS-IF signals use channels in the frequency band of 1 GHz to 2.6 GHz. The video signal (BC: Broad Cast) uses a channel in a frequency band of 70 to 770 MHz corresponding to the video signal frequency. A downlink communication signal (NC: Narrow Cast) uses an empty channel in a frequency band of 70 to 770 MHz. The uplink communication signal uses a channel in the frequency band of 10 to 55 MHz. Note that an equivalent transmission rate of the downlink communication signal may be improved by using a plurality of unused channels in the frequency band of 70 to 770 MHz.

  As shown in FIG. 4, in the present system 10, an optical signal having a wavelength of the CWDM standard is used as an optical signal for the uplink communication signal. Specifically, 16-wavelength optical signals excluding the 1.55 μm band wavelength every 20 nm in the range of 1.29 μm to 1.61 μm are used for uplink communication signals. In the present system 10, an optical signal having a wavelength of the DWDM standard is used as an optical signal for a downstream signal. Specifically, an optical signal having a wavelength of 1555.75 nm is used for BS-IF and CS-IF signals. An optical signal having a wavelength of 1.55898 μm is used for the video signal (BC). In addition, an optical signal having a wavelength of 1.55736 μm is used for the downlink communication signal (NC).

  Hereinafter, the cluster node device 20, the node device 16, and the ONU 18 will be described in detail. FIG. 5 is a diagram showing a configuration of the cluster node device 20. The cluster node device 20 can be connected to the node device 16 corresponding to the CWDM wavelength described above on the downstream side. In the present embodiment shown in FIG. 1, four node devices 16 are connected to the cluster node device 20. As described above, in the present embodiment, since 256 subscriber houses can be connected to each node device 16, in the present system 10, for example, when eight node devices 16 are connected to the cluster node device 20. Can include a maximum of 2048 subscribers downstream of the cluster node device 20.

  As shown in FIG. 5, the cluster node device 20 includes optical amplifiers 20a and 20b, an optical switch 20c, and a branching coupler 20d as downstream elements. The optical amplifiers 20a and 20b are fiber amplifiers such as EDFA (Erbium Doped Fiber Amplifier), for example. The downstream optical signal transmitted from the center station 12 via the optical fibers 32a and 32b is amplified by the optical amplifiers 20a and 20b according to the transmission distance, and input to the optical switch 20c. The downstream optical signals from the optical amplifiers 20a and 20b are switched by the optical switch 20c and then output to the optical fibers 36b connected to the node devices 16 via the branch coupler 20d.

  In addition, the cluster node device 20 includes an optical multiplexing filter 20e and an optical coupler 20f as upstream elements. The optical signal for the uplink communication signal from the node device 16 connected to the cluster node device 20 is input to the optical multiplexing filter 20e through the optical fiber 36a. The light propagating through the optical fiber 36a has a wavelength that complies with the CWDM standard, and the optical multiplexing filter 20e multiplexes these optical signals having different wavelengths, and converts the multiplexed optical signal into an optical signal. Transmit to coupler 20f. The optical coupler 20f transmits the received optical signal simultaneously to the optical fibers 34a and 34b. With this configuration, a highly reliable system is configured corresponding to the two optical fibers 32a and 32b of the working / standby in the downstream system and corresponding to the optical fibers 34a and 34b of the working / standby in the upstream system. The

  According to the present system 10, video system signals and communication signals using the same frequency band as in the conventional CATV system are transmitted and received as optical signals, so that the cluster node device 20 does not need to be provided with electrical equipment. Therefore, the cluster node device 20 can be configured only by optical components. Therefore, the cluster node device 20 can adopt a very simple configuration.

  FIG. 6 is a diagram illustrating a configuration of an FTTH node apparatus according to an embodiment. As shown in FIG. 6, the node device 16 includes an optical amplifier 16c and an optical coupler 16d as downstream elements. An optical signal transmitted from upstream to the node device 16, that is, an optical signal including a video signal and a downlink communication signal, is amplified by the optical amplifier 16c and then input to the optical coupler 16d. The optical amplifier 16c is a fiber amplifier such as an EDFA, for example. In the present embodiment, the optical coupler 16d branches the optical signal at 1:16. Each of the branched optical signals is input to the optical multiplexing filter 16e. In the present embodiment, 16 optical multiplexing filters 16e are provided. Each of the optical multiplexing filters 16e outputs a downstream optical signal from the upstream, that is, an optical signal in the 1.55 μm wavelength band, to the optical fiber 26 connected to the optical multiplexing filter 16e. On the other hand, each of the optical multiplexing filters 16e outputs an upstream communication signal transmitted via the corresponding optical fiber 26 to an upstream element of the node device 16 described below.

  The node device 16 also includes a quadruple O / E converter 16f, a merger 16g, and two optical transmitters 16h as upstream elements. The upstream optical signal from the 16 optical multiplexing filters 16e has a band of wavelengths of 1.29 μm to 1.61 μm excluding the wavelength of 1.55 μm, and each of the four systems has a quadruple O / E converter 16f. Is input. The quadruple O / E converter 16f O / E converts the four input optical signals into four electric signals, multiplexes these electric signals and outputs them.

The merger 16g multiplexes the electric signals from the four quadruple O / E converters 16f, branches them into two, and outputs them to the two optical transmitters 16h. Each of the optical transmitters 16h generates an optical signal having a wavelength of the CWDM standard by performing E / O conversion on the input electric signal. Each of the optical transmitters 16h outputs the generated optical signal upstream. Specifically, in the case of the node devices 16a _{1 to} 16a _J , the optical signal generated by the optical transmitter 16h is transmitted to the center station 12 via the optical fiber 22a. On the other hand, in the case of the FTTH node devices 16b _{1 to} 16b ₄ , the optical signal generated by the optical transmitter 16h is transmitted to the cluster node device 20 via the two optical fibers 36a.

  Hereinafter, the quadruple O / E converter and the merger will be described in detail. FIG. 7 is a diagram illustrating a configuration of a quadruple O / E converter according to an embodiment. As illustrated in FIG. 7, the quadruple O / E converter 16 f includes four photodiodes 42, an amplifier 44, a multiplexer 46, a variable attenuator 48, and a main amplifier 50. The four photodiodes 42 receive an optical signal from the optical multiplexing filter 16e to which the photodiodes 42 are connected, and perform O / E conversion on the optical signal to generate an electrical signal. The electric signal generated by the photodiode 42 is amplified by the corresponding amplifier 44 and then multiplexed by the multiplexer 46. The electric signal from the multiplexer 46 is variably attenuated by the variable attenuator 48, amplified by the main amplifier 50, and then output upstream. A part of the signal from the main amplifier 50 becomes a monitor signal supplied to the terminal 52.

  Further, as illustrated in FIG. 7, the quadruple O / E converter 16 f may further include four switches 54 and a controller 56. In the present system 10, a communication system of TDM (Time Division Multiplex) is adopted for downlink and TDMA (Time Division Multiple Access) is adopted for uplink. That is, the ONU 18 connected to one node device 16 transmits data upstream in different time slots. Therefore, the photodiode 42 and the amplifier 44 have a time that is not used. The controller 56 stops the photodiode 42 and the amplifier 44 by opening a switch that connects the photodiode 42 and the amplifier 44 and the power supply potential Vcc during a period when the photodiode 42 and the amplifier 44 are not used. Thereby, the influence by the noise which generate | occur | produces with the photodiode 42 and amplifier 44 etc. which are not utilized is reduced. In the above example, the configuration in which the power supply of both the photodiode 42 and the amplifier 44 is turned off has been described. However, the same effect can be obtained by turning off the power supply to either one. Alternatively, in place of the above method, a disconnection / connection switching means such as a semiconductor switch is provided between the amplifier 44 and the multiplexer 46, and these switching means are disconnected during a time when the photodiode 42 and the amplifier 44 are not used. By setting the state, noise appearing at the output of the multiplexer 46 can be reduced. In this case, when each of the photodiode 42 and the amplifier 44 is used, the uplink communication signal is normally transmitted by setting the switching means to the connected state.

  FIG. 8 is a diagram illustrating a configuration example of the merger. FIG. 8A shows a configuration of an example of a merger, and FIG. 8B shows a configuration of another example of a merger. In the merger 16g shown in FIG. 8A, the electric signals from the corresponding two quadruple O / E converters 16f are multiplexed and output by the two couplers 58, respectively. Then, the electrical signals from the two couplers 58 are multiplexed together with the signals from the modem 16 m by the coupler 60 and output to the branch element 62. The branch element 62 bifurcates and outputs the input electrical signal.

  In the merger 16g shown in FIG. 8B, the electric signals from the corresponding two quadruple O / E converters 16f are multiplexed and output by the two couplers 58, respectively. The electrical signal from one of the two couplers 58 is multiplexed with the signal from the modem 16m and output. The electric signal from the other coupler of the two couplers 58 is output as it is.

  The electrical signals that are bifurcated and output by the merger 16g shown in FIG. 8A are the same. Therefore, communication is performed in a time-sharing manner according to the number of ONUs 18 connected to the node device 16, but the output from the node device 16 becomes redundant, so that the reliability is improved.

  On the other hand, the two electrical signals output by the merger 16g shown in FIG. 8B correspond to upstream communication signals from different ONUs 18. Therefore, the number of time divisions can be halved and the bandwidth of uplink communication can be increased equivalently compared to the case where the confluencer 16g shown in FIG. 8B is employed.

  Refer to FIGS. 1 and 6 again. The node device 16 directly connected to the center station 12 among the node devices 16 can use an optical signal having an arbitrary wavelength among the wavelengths of the CWDM standard described above as an optical signal for the uplink communication signal. On the other hand, the node device 16 connected to the cluster node device 20 uses optical signals having different wavelengths from among the wavelengths of the CWDM standard described above as the optical signal for the uplink communication signal. Thereby, the center station 12 can identify which node device 16 connected to one cluster node device 20 is from the downstream side. Therefore, the time division number of the uplink communication signal can be set to the number of ONUs 18 existing downstream of one node device 16.

  As illustrated in FIG. 6, the node device 16 may further include a photodiode 16k, a modem 16m, and a controller 16n. The photodiode 16k outputs an electrical signal by O / E converting the downstream communication optical signal branched from the optical amplifier 16c. The modem 16m demodulates a part of the electrical signal, that is, a downlink communication signal of a channel assigned in advance for a control signal from the center station 12. The controller 16n collects various information of the node device 16 based on the demodulated signal, and transmits the collected information to the center station as one of the upstream communication signals via the modem 16m. For example, information such as the bias current value, light intensity, and / or temperature of the optical transmitter 16h can be transmitted as the information. Alternatively, the controller 16 n controls the amplification degree adjustment of the optical amplifier 16 c mounted in the node device 16 and the optical output of the optical transmitter 16 h based on the control signal transmitted from the center station 12. In this way, the node device 16 can be remotely controlled from the center station 12.

  In the conventional system, particularly the HFC system, it is possible to remotely control the intermediate amplifier inserted in the transmission path from the center station. However, in that case, the receiver mounted in the intermediate amplifier is dedicated, and the intermediate amplifier is connected in series in the transmission path, so when the center station remotely controls a specific intermediate amplifier Therefore, it is necessary to specify an intermediate amplifier to be controlled by using so-called polling. On the other hand, the modem device 16n having the same configuration as that installed in the subscriber's house may be installed in the node device 16 shown in FIG. 6 for monitoring / control of the node device. Since the device 16 has a one-to-one correspondence with the center station, there is an advantage that it is not necessary to specify individual node devices by the polling.

  Hereinafter, the ONU 18 will be described in detail. FIG. 9 is a diagram illustrating a configuration of an optical network unit according to an embodiment. As shown in FIG. 9, the ONU 18 includes a multiplexing / demultiplexing filter 66, an optical filter 68, an optical receiver 70, a viewing control unit 72, an optical receiver 74, a variable gain amplifier 75, an amplifier 76, a directional coupler 78, A filter 80, an amplifier 82, an optical transmitter 84, an optical filter 86, a control modem 102, and a controller 104 are included.

  The multiplexing / demultiplexing filter 66 separates the upstream signal and the downstream signal. Specifically, the optical filter 66 has a bandpass characteristic that allows an optical signal having a wavelength of 1.55 μm to pass through for a downstream signal, and is a band notch filter that blocks the same band for an upstream signal. Function. Therefore, the multiplexing / demultiplexing filter 66 outputs the downstream video system signal and the downstream communication signal from the optical fiber 30 to the optical filter 68, and outputs the optical signal from the optical filter 86 to the optical fiber 30.

  The optical filter 68 is a bandpass filter, and separates an optical signal having a wavelength of 1.555575 μm and an optical signal having wavelengths of 1.555898 μm and 1.555736 μm. Referring to FIGS. 3 and 4, the optical signal with a wavelength of 1.55555 μm includes a BS-IF signal and a CS-IF signal, the optical signal with a wavelength of 1.555736 μm includes an optical signal for downstream communication, and an optical signal with a wavelength of 1.555898 μm. The optical signal includes a video signal. The optical filter 68 outputs an optical signal having a wavelength of 1.55555 μm to the optical receiver 70. On the other hand, the optical filter 68 outputs an optical signal having a wavelength of 1.555898 μm and an optical signal having a wavelength of 1.555736 μm to the optical receiver 74.

  The optical receiver 70 performs O / E conversion on an optical signal having a wavelength of 1.55555 μm, thereby generating a BS-IF signal and a CS-IF signal. The BS-IF and CS-IF signals from the optical receiver 70 are output to the terminal T1 via the viewing control unit 72. By connecting the output from the terminal T1 to the BS antenna terminal of the television receiver, satellite broadcasting (both analog and digital) can be received as it is. The BS-IF / CS-IF signal system is provided with a viewing control apparatus for controlling viewing outside the contract.

  The optical receiver 74 performs O / E conversion on an optical signal having a wavelength of 1.555898 μm and an optical signal having a wavelength of 1.555736 μm, thereby outputting a video signal of 70 MHz to 770 MHz and a downlink communication signal. The output level of these video signals and downstream communication signals is optimized by a gain variable amplifier 75 and is output to a directional coupler 78 via an amplifier 76. Therefore, the input optical signal light intensity, particularly the optical signals with wavelengths of 1.555898 μm and 1.555736 μm, is not constant due to the transmission distance or the optical coupling efficiency between the node device 16 and the ONU 18. However, the intensity of the video signal and the downlink communication signal output from the terminal T2 is kept substantially constant.

  The directional coupler 78 outputs a video signal and a downlink communication signal, that is, a signal in a frequency band of 70 MHz or more to the terminal T2. In addition, the directional coupler 78 outputs an upstream communication signal from the terminal T2, that is, a signal in a frequency band of 55 MHz or less to the filter 80. The terminal T2 is assumed to be a television receiver having a bidirectional function, a cable modem, a VoIP-compatible telephone device, and the like.

  As described above, the upstream communication signal from the terminal T2 is output to the optical transmitter 84 via the low-pass filter 80 and the amplifier 82 that pass the signal in the frequency band of 10 MHz to 55 MHz. The optical transmitter 84 performs E / O conversion on the upstream communication signal to generate an optical signal having a predetermined wavelength in the CWDM standard as described above. The optical signal generated by the optical transmitter 84 is output to the optical fiber 30 via the CWDM bandpass filter 86 and the multiplexing / demultiplexing filter 66. A plurality of ONUs 18 connected to one optical fiber 26 can use optical signals having wavelengths different from the wavelengths in the CWDM standard except for the 1.55 μm band for uplink communication signals. It is. The modem 102 has a function similar to that of the modem 16 m mounted on the node device 16. That is, a control signal is transmitted from the center station using a part of the downlink communication signal, and the controller 104 decodes this control signal, and the state of the components mounted on the ONU 18, for example, received light intensity, optical transmission The degree of change with time of components such as a laser mounted in the vessel 84 is monitored, and this information is transmitted to the center station. Alternatively, the laser drive conditions can be updated directly from the center station.

  As shown in FIG. 9, the ONU 18 can further include a controller 90. The ONU 18 transmits an upstream communication signal using a predetermined time slot. That is, the ONU 18 does not need to use a light emitting element such as a laser of the optical transmitter 84 except for a predetermined time slot. Based on the command from the controller 104 described above, the controller 90 provided between the power supply Vcc and the optical transmitter 84 is controlled to be in an open state except for the time slot assigned to the ONU 18. As a result, it is possible to prevent the light emitted from the optical transmitter 84 from becoming noise at times other than the time slot of the ONU 18. Alternatively, the controller 90 constantly monitors the output of the amplifier 82 as shown in FIG. 9 and detects the presence or absence of an upstream communication signal. Then, in a state where there is no upstream communication signal, the power Vcc of the optical transmitter 84 is automatically turned off, thereby reducing the light emitted from the optical transmitter 84 from becoming noise. In this case, the same effect can be obtained by turning off the entire power supply of the optical transmitter 84 or reducing the light output level of the laser mounted in the transmitter 84.

  As described above, in the present CATV system, a configuration is employed in which an optical signal for upstream communication transmitted from the ONU 18 at each subscriber's home is communicated using different wavelengths. As described above, the node device 16 can include a maximum of 256 subscribers, and uplink communication is performed for each subscriber using, for example, a time slot assigned to 1/256. The need to distinguish subscribers by signal wavelength is inherently sparse. However, when all the subscribers perform uplink communication using the same wavelength, the optical noise caused by the optical transmitter 84 of each subscriber home ONU 18 becomes large and normal uplink communication is hindered. In the optical CATV system, since there are different services such as the Internet and IP telephone, there is a unique time division slot signal for each service. For this reason, uplink communication signals may be transmitted simultaneously from a plurality of ONUs although frequencies are different. In other words, optical signals having the same wavelength may be transmitted at the same time. In this case, there is a problem that the optical signals collide and optical noise increases. In the present CATV system, each subscriber is grouped into 16 houses, which are grouped together, and each subscriber performs uplink communication at a different wavelength, thereby reducing noise appearing at the receiving end of the node device 16. Further, the noise that appears at the receiving end of the node device is further reduced by adding a function to the ONU 18 of each subscriber's house to stop the light emission when the upstream communication signal is “none”.

  Hereinafter, an optical CATV system according to another embodiment will be described. FIG. 10 is a diagram illustrating frequency bands of video signals and communication signals used in an optical CATV system according to another embodiment. As shown in FIG. 10, in another embodiment, the upper limit frequency of the frequency band of the downlink communication signal can be set to a frequency higher than 770 MHz. Moreover, the upper limit frequency of the frequency band of the uplink communication signal can be set to a frequency greater than 55 MHz. In this example, the downlink communication signal is transmitted through a channel in a frequency band from 70 MHz to 870 MHz. Further, the uplink communication signal is transmitted through a channel in a frequency band of 10 to 90 MHz.

  In the present embodiment, an ONU different from the above-described ONU 18 is used. FIG. 11 is a diagram illustrating a configuration of an optical network unit according to another embodiment. The ONU 18A shown in FIG. 11 further includes an amplifier 94, a filter 96, a directional coupler 98, and an amplifier 100 in addition to the same elements as the ONU 18.

  In the ONU 18A, the video signal and the downlink communication signal generated by the optical receiver 74 are branched into two, and are output to the amplifier 76 in one path. The signals output to the terminal T2 through the path including the amplifier 76 are a video signal and a downlink communication signal that use a channel in the frequency band 70 to 770 MHz, as in the conventional CATV system.

  In the other of the two paths after the optical receiver 74, the signal is output to the directional coupler 98 via the amplifier 94 and the high-pass filter 96. The high-pass filter 96 passes a signal in a frequency band of a lower limit frequency that is higher than 70 MHz to an upper limit frequency that is higher than 770 MHz. In this example, the high pass filter 96 passes signals in the frequency band of 120 MHz to 870 MHz. The signal passing through the high pass filter 96 is output to the terminal T3.

  When a modem that enables higher-speed transmission than the conventional modem is connected to the outside of the ONU 18, a system that corresponds to an extended band of 120 to 870 MHz, particularly 770 to 870 MHz as a downstream band, and 10 to 90 MHz as an upstream band Can be configured. FIG. 11 is a diagram showing the configuration of the ONU 18A at that time. Specifically, the external high-speed modem can demodulate a downlink communication signal in a 120 to 870 MHz band, and can modulate an uplink communication signal in a 10 to 90 MHz band. As a result, it is possible to extend the bandwidth of the upstream communication signal that has been particularly deficient.

  The external modem is connected to terminal T3. A 1000Base-T cable can be connected to the terminal T3. Moreover, since the 120-770 MHz band overlaps with the conventional band among the 120-870 MHz frequency bands, it is also possible to connect the same apparatus as the conventional one to the terminal T3.

  The upstream communication signal (10 to 90 MHz band) supplied from the external modem 102 to the terminal T3 is output to the optical transmitter 84 via the directional coupler 98 and the amplifier 100. The upstream communication signal output to the optical transmitter 84 is O / E converted by the optical transmitter 84 as in the case of the ONU 18. As a result, an upstream communication signal is transmitted using an optical signal having a wavelength conforming to the CWDM standard.

  In the ONU 18A, the path leading to the terminal T3 is completely separated from the downstream signal in the same frequency band (70 to 770 MHz) as in the prior art. As the optical signal corresponding to the upstream signal, an optical signal having a wavelength completely different from the wavelength of the downstream optical signal is used. As a result, according to the ONU 18A, it is possible to use a signal in a frequency band that could not be used due to overlapping with a downlink signal as an uplink communication signal. For example, if it is determined that a frequency band of about 300 MHz or more is used as the frequency band of the downlink communication signal, the frequency band for the uplink communication signal using the modem 102 can be increased to 250 MHz.

  It is possible to incorporate an external high-speed modem in the ONU. FIG. 12 shows the configuration of the ONU 18B incorporating the high-speed modem 102a. The output of the directional coupler 98 is not directly connected to the terminal T3 but is connected to the terminal T3 via the high speed modem 102a. Further, by connecting a controller 104 to the modem 102a, the high-speed modem 102a can have the function of the monitoring / controlling modem 102 shown in FIGS. That is, the control signal included in the downlink communication signal is received by the high-speed modem 102a, and the controller 104 analyzes the control signal to monitor / control each component in the ONU 18B. The monitoring information can be transmitted using any one of the channels of the extended upstream band up to, for example, 90 MHz made possible by adopting the high-speed modem 102a, or transmitted in the conventional band up to 55 MHz. It is also possible to do. Furthermore, the control signal can also be received in the extension band of 770 to 870 MHz.

FIG. 13 is a diagram showing the configuration of the center station 12B according to another embodiment. In the configuration of the center station 12 shown in FIG. 2, the video signal (BC) and the BS-IF / CS-IF signal are transmitted using different wavelengths. Since the BC signal (frequency: 70 MHz to 770 MHz) and the BS-IF / CS-IF signal (frequency: 1.0 to 2.6 GHz) are different in frequency, the possibility of collision is low. Therefore, FIG. 13 shows a configuration in which these two video signals are transmitted using one wavelength. That, BC signal and BS-IF / CS-IF signal is transmitted by the optical transmitter 12c ₁ of one in advance electrically coupled by coupler 12p. The output of the optical transmitter 12c ₁ is distributed to each of the system, the node device system 16 or cluster node device system 20, is the same as the configuration of FIG. In this case, the wavelength of the video system signal output by the optical transmitter 12c ₁ may be a 1.55575Myuemu. On the other hand, the wavelength of the communication downlink signal can be 1.55736 μm as in the configuration of FIG.

  FIG. 14 shows one configuration of the ONU 18C corresponding to the center station configuration of FIG. The optical signal from the optical fiber 30 is demultiplexed by the multiplexing / demultiplexing filter 66, and the 1.55 μm band optical signal is received by the optical receiver 70 and O / E converted. This optical signal includes both a BC signal having a frequency of 70 MHz to 2.6 GHz and a BS-IF / CS-IF signal. Then, the electrical signal converted by the optical receiver 70 is divided into two, one from the terminal T1 through the high-pass filter 72 that passes the frequency 1 to 2.6 GHz, and the other through the low-pass filter 72a that passes the frequency 70 Mz to 770 MHz. Then, the signal is output from the terminal T2 through the same configuration as the ONU 18 in FIG. The viewing control unit for restricting viewing outside the contract is provided in the system connected to the terminal T1, as in the example of FIG. In FIG. 14, the variable gain amplifier 75 is inserted only in the path of the BC signal. However, the same effect can be obtained by providing a structure immediately after the optical receiver 70 and dividing the output of the variable gain amplifier 75 into two. Can be obtained.

  The embodiment of the present invention has been described above. In the optical CATV system of the above-described embodiment, the number of optical fibers to be accommodated in the center station 12 can be reduced with respect to the number of ONUs 18 connected to one node device 16. It is possible to reduce the noise included in the upstream communication signal by distinguishing the wavelength of the upstream communication signal from the subscriber's home in the county with a plurality of subscribers as a group. In the above embodiment, the configuration in which this wavelength is made to correspond to the grid wavelength (20 nm span) of the CWDM standard has been described, but the present system is not limited to the grid wavelength of CWDM. For example, if the span width is 10 nm which is ½ of the standard, the number of subscribers included in a group can be doubled. In this case, the number of subscribers included in one node device is doubled, and the time slot allocated to each subscriber may be halved at most. What is necessary is just to determine the number of subscribers included in.

  Further, the cluster node device 20 can be interposed between the plurality of node devices 16 and the center station 12 by using optical signals having different wavelengths of the CWDM standard as optical signals for uplink communication signals. As a result, the number of optical fibers to be accommodated in the center station 12 can be reduced with respect to the number of ONUs 18 downstream of the cluster node device 20.

  Further, since a signal in the same frequency band as that of a conventional CATV system can be used, it is possible to suppress replacement of a modem device such as a modem. Furthermore, by using the frequency band shown in FIG. 10 and the ONU shown in FIG. 11, it is possible to realize higher speed communication.

10 ... optical CATV system, _12b 1, _12b 2 _... communication system optical transmitter, _12c 1, _12c 2 _... image-based optical transmitter, _12d 1, _12d 2 _... communication based optical _receiver, 12e _1, 12e 2 ... CWDM filter _{, 12f, 12k 1, 12k 2} ... optical distributor, 12g, 12h ... optical multiplexer, _12j 1, _12j 2 _... optical _{amplifiers, 12n 1, 12n 2, 12m} 1, 12m 2 ... _distributor, 12o _1, 12o ₂ ... adder, 14 ... subscriber premises, 14a ... cable modem, 14c ... set-top _{boxes, 16,16a 1 ~16a J, 16b 1} ~16b 4 ... FTTH node apparatus, 16c ... optical amplifier, 16d ... optical coupler, 16e ... optical multiplexing filter, 16f ... quadruple O / E converter, 16g ... merger, 16h ... optical transmitter, 16k ... photodiode, 16m ... mode , 16n ... controller, 18 ... optical network unit (ONU), 20 ... cluster node device, 20a, 20b ... optical amplifier, 20c ... optical switch, 20d ... branch coupler, 20e ... optical multiplexing filter, 20f ... optical coupler, 22a ... Optical fiber for upstream signal, 22b ... Optical fiber for downstream signal, 26 ... Optical fiber, 28 ... Optical coupler, 30 ... Optical fiber, 32a, 32b ... Optical fiber for downstream signal, 34a, 34b ... Optical fiber for upstream signal, 36a ... optical fiber for upstream signal, 36b ... optical fiber for downstream signal, 42 ... photodiode, 44 ... amplifier, 46 ... multiplexer, 48 ... variable attenuator, 50 ... main amplifier, 54 ... switch, 56 ... controller, 58 ... Coupler, 60 ... Coupler, 62 ... Branch element, 66 ... Multiplexing filter, 68 ... Optical filter, 70 ... Optical reception 72, high-pass filter, 72a ... low-pass filter, 74 ... optical receiver, 75 ... variable gain amplifier, 76 ... amplifier, 78 ... directional coupler, 80 ... low-pass filter, 82 ... amplifier, 84 ... optical transmitter, 86: Band pass filter, 90: Controller, 94: Amplifier, 96: High pass filter, 98: Directional coupler, 100: Amplifier, 102, 102a: Modem, 104: Controller

Claims (7)

CATV (Cable television) center station,
FTTH (Fiber To The Home) node device connected to the center station;
A plurality of optical network units respectively provided in a plurality of subscriber houses connected to the FTTH node device;
With
The center station transmits a video signal to the FTTH node device using an optical signal having a wavelength of DWDM (Dense Wavelength Division Multiplexing) standard via an optical fiber connecting the center station and the FTTH node device. , A downlink communication signal is transmitted using an optical signal having a wavelength of a DWDM standard different from the wavelength,
The FTTH node device receives the plurality of optical signals having different wavelengths from the center station, relays the plurality of optical signals to the plurality of optical network units,
The plurality of optical network units are:
Receiving the plurality of optical signals having different wavelengths from the FTTH node device;
Using an optical signal having a wavelength different from the plurality of wavelengths, an uplink communication signal including a frequency band of 10 to 55 MHz and using a frequency band lower than the frequency band of the downlink communication signal is transmitted to the FTTH node device.
In optical CATV system,
The plurality of optical network units are groups each including a part of the plurality of optical network units, and are connected to one of a plurality of optical fibers extending from the FTTH node device to the plurality of optical network units. Divided into groups including network units , the optical network units in the group are grid wavelengths conforming to the CWDM standard, each having a different wavelength and a wavelength different from the wavelength of the plurality of received optical signals. An uplink communication signal of a wavelength individually corresponding to the optical network unit of the FTTH node device,
An optical CATV system characterized by the above. The video signal includes a broadcast (BC) signal and a BS-IF / CS-IF signal,
The BC signal and the BS-IF / CS-IF signal are transmitted using one wavelength allocated in different DWDM standards.
The optical CATV system according to claim 1. The video signal includes a broadcast (BC) signal and a BS-IF / CS-IF signal,
The BC signal and the BS-IF / CS-IF signal are electrically combined and transmitted at one wavelength assigned in the DWDM standard.
The optical CATV system according to claim 1. An FTTH cluster node device that relays the plurality of optical signals to the FTTH node;
The FTTH node device performs optical / electrical conversion on uplink communication signals from a plurality of optical network units connected to the FTTH node device, and then multiplexes the converted electric signal having a grid wavelength of the CWDM standard. Converted into an optical signal and transmitted to the FTTH cluster node;
The FTTH cluster node device relays an uplink multiplexed optical signal transmitted by the FTTH node device to the center station.
The optical CATV system according to claim 1. The FTTH node device includes a modem device that receives a control signal included in the downlink communication signal, and a controller that analyzes the control signal,
The center station remotely controls the FTTH node device via the control signal.
The optical CATV system according to claim 1. The FTTH node device includes an optical receiver that optically / electrically converts the uplink communication signal, and an amplifier that amplifies the output of the optical receiver,
At least one of the optical receiver and the amplifier has a function of stopping the operation when the upstream communication signal is lost,
The optical CATV system according to claim 1.   The optical network unit according to claim 1, wherein the optical network unit includes a light emitting element, and further has a function of detecting a state in which a communication uplink signal from the optical network unit has disappeared and stopping the operation of the light emitting element. CATV system.

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