JP2003289284A - Bidirectional catv system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bidirectional CATV system for inexpensively and easily composing a bidirectional CATV system for long-distance optical transmission between a center station and to provide a plurality of optical nodes via a light transmission path. <P>SOLUTION: The bidirectional CATV system has a light distribution/synthesis closer. Outgoing light modulation signals, that are transmitted from a center station via the light transmission path are received and are distributed to a plurality of optical nodes for sending out, at the same time, incoming light modulation signals that are transmitted from each of the plurality of optical nodes are received, and the plurality of light modulation signals are synthesized and transmitted to the center station by the light distribution/synthesis closure. The center station has a separator for receiving the incoming light modulation signals that are transmitted from the light distribution/synthesis closure via the light transmission path and for separating the up signals for each optical node. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional CATV system for performing bidirectional optical transmission between a center station and an optical node connected via an optical transmission line, and particularly to a headend and an optical system in the center station. The present invention relates to an optical transmission system that performs long-distance bidirectional optical transmission with a node.

[0002]

2. Related Background Art Recently, various services such as Internet connection service and telephone service utilizing high-speed transmission performance of CATV (cable television), and video-on-demand have been provided. In order to provide these various services, a head end (center station) prepared by a CATV operator and a CATV subscriber station are connected by a communication line capable of bidirectional communication. Then, an optical fiber is connected to this communication line from the center station of the CATV operator to an optical node provided near the subscriber station, and a coaxial cable is used from the optical node to the subscriber station. The hybrid fiber / coaxial method (HFC method) is often used.

In this case, the downlink signal from the center station to the subscriber station has, for example, an emission wavelength of 1.55 provided in the center station.
It is modulated by an external modulation type optical transmitter of [μm], amplified to a predetermined level by using an amplifier such as an EDFA (erbium-doped optical fiber amplifier), and then sent to a downstream optical transmission line. Then, the downstream optical signal transmitted from this center station is received by the optical node connected to the downstream optical transmission line,
After converting into an electric signal, it is sent to the subscriber station via a coaxial cable.

On the other hand, an upstream signal such as a data signal transmitted from an information terminal such as a personal computer installed in a subscriber station or an audio signal output from a telephone is transmitted to the above-mentioned optical node via a coaxial cable. It The optical node receiving this upstream signal digitally samples this signal to convert it into a digital signal, converts it into an optical signal by a laser diode or the like, and sends it to the center station. Then, the center station receiving this upstream optical signal converts the signal output from the subscriber station into an electric signal and restores it, and then sends it out to the Internet line, telephone line or the like via a communication device or the like.

[0005]

However, in the bidirectional CATV system configured as described above, in order to transmit a downlink signal from a center station to a plurality of optical nodes, the number of optical nodes must be equal to that of the center stations. It is necessary to prepare an external modulation type optical transmitter and a fiber amplifier. Further, there is also a problem that it is necessary to prepare as many downlink / uplink optical fiber cores as the number of optical nodes, respectively, and connect the center station and a plurality of optical nodes.

When a CATV operator lays this optical fiber, there is a problem that a high cost is required for constructing a transmission line. Of course, it is conceivable to use a dark fiber such as that of a telecommunications carrier as this optical fiber, but in this case, the cost corresponding to the number of cores of the optical fiber is required. There is a problem of increasing.

Therefore, when a CATV operator constructs a two-way CATV system, the equipment of the center station
As maintenance costs and costs for optical transmission lines will be high,
There was a concern that the usage fee for the subscriber who bears the service cost would be high. The present invention has been made in view of the above circumstances, and an object thereof is to provide an inexpensive bidirectional CATV system for performing long-distance optical transmission between a center station and a plurality of optical nodes via an optical transmission line. Another object is to provide an interactive CATV system that can be easily configured.

[0008]

In order to achieve the above object, a bidirectional CATV system according to the present invention receives a plurality of downlink optical modulation signals transmitted from the center station via an optical transmission line. Optical distribution / combination that distributes and distributes to optical nodes, receives upstream optical modulation signals respectively transmitted from the plurality of optical nodes, combines the plurality of optical modulation signals, and transmits to the center station. In addition to providing a closure, the center station includes a separator that receives the upstream optical modulation signal transmitted from the optical distribution / combining closure via an optical transmission line and separates the upstream signal for each optical node. It has a feature.

The optical distribution / synthesis closure further includes an optical fiber amplifier for amplifying the downstream optical modulation signal sent from the center station, and the optical modulation signal amplified by the optical fiber amplifier to a plurality of the optical nodes. It is composed of an optical coupler for distribution and distribution, and an optical combiner for combining upstream optical modulation signals of different wavelengths respectively sent from the plurality of optical nodes and sending them to the center station.

Alternatively, the light distribution / synthesis closure is
A plurality of optical / electrical signal converters for converting the upstream optical modulation signals respectively sent from the plurality of optical nodes into electric signals, and a plurality of upstream electrics converted into electric signals by the plurality of optical / electrical signal converters. It is composed of a time-division modulator for time-division-multiplexing and synthesizing signals, and an electric / optical converter for converting the modulated signal output from the time-division modulator into an optical signal.

[0011] Preferably, the demultiplexer is configured to demultiplex, for each wavelength, upstream optical modulation signals having different wavelengths pre-allocated after a plurality of optical nodes. Alternatively, the demultiplexer is configured to demultiplex the time division multiplex modulated upstream optical modulation signal into a plurality of optical nodes.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An interactive CATV system according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a first embodiment of an interactive CATV system. In this figure, a head end serving as a center station 10 installed on the CATV operator side is connected with an optical distribution / combining closure 20 to be described later via a first optical transmission line 50. And this light distribution / synthesis closure 2
0 to a plurality of optical nodes 30 via the second optical transmission line 60.
Is further connected to the subscriber station 40 via the coaxial cable 70 from the optical node 30.

Specifically, the antenna 11 is provided at the head end.
External modulation type optical transmission for generating a downstream optical modulation signal by synthesizing a broadcast wave signal of a television or the like received by etc. and a data signal output by the communication device 12 connected to an internet line (not shown) or the like as a high frequency signal A device 13 and a fiber amplifier 14 for amplifying and transmitting the downstream optical modulation signal to the optical distribution / composition closure 20 are provided. As the fiber amplifier 14, for example, an erbium-doped optical fiber amplifier (EDFA) is used.

On the other hand, the optical node 30 is provided with a downstream optical receiver 31 and an upstream optical transmitter 32 for mutual communication with the subscriber station 40. The optical distribution / combining closure 20 and the second optical transmission line 60 are connected to each other so that they can communicate with the center station 10.
By the way, as shown in FIG. 2, the above-mentioned optical distribution / combining closure 20 receives the downstream optical modulation signal transmitted from the center station 10 through the downstream optical fiber core wire 50a,
A downstream fiber amplifier 21 that amplifies this signal and an optical coupler 22 that distributes the downstream optical modulation signal amplified by this downstream fiber amplifier 21 to each of a plurality of optical nodes 30 are provided. The downlink fiber amplifier 22 plays a role of compensating for the attenuation of the downlink signal transmitted from the center station 10 via the downlink optical fiber core wire 50a and of compensating for the distribution loss of the downlink signal distributed by the optical coupler 22.

Further, upstream optical signals of individual wavelengths are assigned to the plurality of optical nodes 30 which relay the upstream signals sent from the plurality of subscriber stations 40, respectively. Specifically, the wavelengths of the optical signals transmitted from the plurality of optical nodes 30 are assigned in advance to each optical node 30 as wavelengths that can be wavelength division multiplexed (WDM) transmitted. Then, the mixed WDM filter 2 that synthesizes the upstream optical signals of the plurality of wavelengths
3 is provided in the light distribution / synthesis closure 20.

Incidentally, in FIG. 2, the wavelengths of the upstream optical signals transmitted from the two optical nodes A and B are respectively λ1.
And λ2. On the other hand, the center station 10 is provided with the division WDM filter 15 for separating the upstream optical modulation signal wavelength-division-multiplexed by the optical distribution / combining closure 20 into the upstream signal for each optical node 30 as described above.
An upstream optical receiver 16 for converting the upstream optical modulation signal separated by the split WDM filter 15 into an electrical signal is prepared for each node.

In this embodiment, the wavelengths of upstream optical signals transmitted from a plurality of optical nodes are two wavelengths λ1 and λ2 for easy understanding, but the wavelengths are not limited to these two wavelengths. Absent. In other words, the same light distribution
A wavelength that enables WDM combining may be allocated to each of the plurality of optical nodes 30 connected to the combining closure 20.

Now, the bidirectional C configured as described above.
In the ATV system, the downstream optical modulation signal sent from the center station 10 to the optical distribution / combining closure 20 is amplified by the downstream fiber amplifier 21 provided in the optical distribution / combining closure 20 to a predetermined level. . Then, the amplified downstream optical modulation signal is distributed to each of the plurality of optical nodes 30 via the second optical transmission line 60a connected to the output port of the optical coupler 22.

That is, the light distribution / synthesis closure 20 is
It functions to amplify the downlink optical modulation signal sent from the center station 10 and distribute the downlink optical modulation signal to the plurality of optical nodes 30. Since the optical distribution / combining closure 20 is provided, only one set of the external modulation type optical transmitter 13 and the plurality of fiber amplifiers 14 may be prepared in the center station 10. That is, a plurality of optical nodes 30 are
On the other hand, the external modulation type optical transmitters 13 and the fiber amplifiers 14 for the number of units required for transmitting the downstream optical modulation signal are unnecessary. In addition, the center station 10 and the optical node 30
As for the downstream optical fiber core wire 50a between the optical fiber and the optical fiber, it is necessary to provide the same number as the number in the conventional method.
Therefore, it is sufficient to have one downlink optical fiber core wire 50a.

On the other hand, the upstream electrical signal sent from the personal computer 44 or the like of the subscriber station 40 to the center station 10 is converted into an optical modulation signal by the upstream optical transmitter 32 provided in the optical node 30. , Mixing W of light distribution / synthesis closure 20
It is given to the DM filter 21. This optical modulation signal is mixed by the mixing WDM filter 23 and is wavelength division multiplexed (WDM) transmitted as an upstream optical modulation signal to the center station 10 through the upstream optical fiber core wire 50b. Then, the center station 1 that receives the upstream optical modulation signal transmitted by the wavelength division multiplexing transmission
0 is a division WDM filter 1 provided in the center station 10.
5, the upstream optical modulation signal is separated for each wavelength (for each optical node), and the upstream optical receiver 16 prepared for each optical node 30 converts the electrical signal into an electrical signal and supplies the electrical signal to the communication device 12.

Therefore, the upstream optical modulation signals sent from the plurality of optical nodes 30 to the center station 10 are multiplexed by the optical distribution / combining closure 20, so that the upstream optical fiber core wire 50b for transmitting the upstream optical modulation signals is provided. It can be configured with one. In addition, the above-mentioned optical modulation signal is transmitted to a plurality of optical nodes 3.
An optical modulation signal that can be transmitted by wavelength division multiplexing (WDM) having different wavelengths assigned in advance for each 0 is used.

Thus, the bidirectional CA thus configured
According to the TV system, even in a bidirectional CATV system in which a plurality of optical nodes 30 are arranged, a downlink signal transmitted from the center station 10 is transmitted to a plurality of optical couplers by an optical coupler provided in the optical distribution / combining closure 20. Since it is distributed to the node 30, the center station 10 and the optical distribution / composition closure 20
The space between and can be constituted by one down optical fiber core wire 50a.

In addition, from the plurality of optical nodes 30 to the center station 1
The upstream signal sent to 0 is also wavelength-division-multiplexed and transmitted by the mixed WDM filter 23 provided in the optical distribution / combining closure 20, so that one line is provided between the optical distribution / combining closure 20 and the center station 10. The optical fiber core wire 50b for upstream can be used. That is, as described above, the number of optical fiber core wires required is extremely small as compared with the conventional bidirectional CATV system, and the external modulation type optical transmitter 13 and the fiber amplifier 14 provided in the center station 10 are provided.
You only need to prepare one for each. Therefore, the center station 10
It is possible to construct a bidirectional CATV system capable of significantly reducing the cost of the equipment and the optical transmission line and improving the reliability.

Next, a second embodiment according to the present invention will be described. FIG. 3 is a schematic configuration diagram showing a second embodiment of the interactive CATV system. This embodiment is different from the above-described first embodiment in that wavelength division multiplexing (W) is used as a method of combining upstream signals transmitted from a plurality of optical nodes 30.
The point is that time division multiplexing (TDM) is used instead of DM). Specifically, as shown in the optical distribution / combination closure 20T in FIG. 4, an optical / electrical signal converter 2 for converting an upstream signal sent from a plurality of optical nodes (not shown) into an electrical signal.
4, a TDM (time division multiplex) modulator 2 for performing time division multiplex modulation of a plurality of upstream signals converted into this electric signal.
5 and an electrical / optical converter 26 for sending the multiplex-modulated upstream signal to the upstream optical fiber core wire 50b.

On the other hand, the optical / electrical signal converter 1 for converting the upstream optical modulation signal sent from the optical distribution / combining closure 20T toward the center station 10 to the center station 10 into an electric signal.
7 and the upstream signal converted into this electrical signal to the optical node 3
A TDM demodulator 18 for separating the signal for each 0 is provided. Then, the upstream signal separated by the TDM demodulator 18 for each optical node 30 is given to the communication device 12 as in the first embodiment.

Even in the bidirectional CATV system of another embodiment configured as above, the downlink signal transmitted from the center station 10 as in the case of the first embodiment, the optical distribution / composition closure 20T. Multiple optical nodes 3 distributed by
0 to the subscriber station 40. On the other hand, an upstream signal transmitted from the subscriber station 40 to the center station 10 via the plurality of optical nodes 30 is converted into an electrical signal by the optical / electrical signal converter 24 provided in the optical distribution / combination closure 20T. To be converted. Then, the upstream modulated wave signals transmitted from the plurality of optical nodes are multiplexed by the time division multiplexing (TDM) modulator 25. Specifically, each time slot assigned to each of the plurality of optical nodes 30 is multiplexed and modulated into a carrier signal of a single frequency. And time division multiplexing (TD
M) The modulated upstream signal is an optical distribution / composition closure 20.
The optical signal is converted into an optical signal by the electric / optical converter 26 provided in T, and the upstream optical fiber core wire 50 is used as an upstream optical modulation signal.
It is transmitted to the center station 10 via b.

On the other hand, the center station 10 which has received the upstream optical modulation signal converts it into an electric signal by the optical / electrical signal converter 24. Then, as described above, this signal is time-division-multiplexed and modulated in the time slots assigned to each of the plurality of optical nodes, so that it is separated for each optical node 30 by the TDM demodulator 18 and given to the communication device 12. Thus, according to the bidirectional CATV system of the second embodiment configured as described above, the optical distribution / similar to the first embodiment described above.
The composite closure 20 distributes the downstream signals to the plurality of optical nodes 30 and multiplexes the upstream signals output from the plurality of optical nodes 30, so that each of the downstream / upstream optical fiber core wires is transmitted by one optical transmission. It can consist of roads. Further, according to the second embodiment, the plurality of optical nodes 3
It is possible to use the optical modulation wave of the same frequency without changing the wavelength of the upstream optical signal transmitted from 0 to the optical distribution / combination closure 20T, and it is not necessary to allocate the optical wavelength to each optical node 30. Therefore, the optical node 3 of the same standard
0, it is possible to construct a bidirectional CATV system that is extremely easy to install and maintain. Further, it is possible to construct a bidirectional CATV system that can significantly reduce the cost of the center station 10 and thus the optical transmission path, and can improve reliability and maintainability.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

[0029]

As described above, the bidirectional CA according to the present invention.
According to the TV system, since the optical distribution / combining closure is provided between the center station and the plurality of optical nodes, one upstream optical transmission line and one downstream optical transmission line may be prepared. Therefore, the construction / management cost of the optical transmission line can be significantly reduced. Also, since a large number of optical nodes can be operated with a small number of head-end devices, the cost related to the center station and installation and management can be significantly reduced, reliability can be improved, and installation work can be performed. It is possible to construct a two-way CATV system that is extremely easy to perform and maintain, and has great practical effects.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an interactive CATV system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a light distribution / combination closure according to an embodiment of the present invention.

FIG. 3 is a diagram showing a schematic configuration of an interactive CATV system according to another embodiment of the present invention.

FIG. 4 is a diagram showing a schematic configuration of a light distribution / combination closure according to another embodiment of the present invention.

[Explanation of symbols]

10 center stations 11 antenna 12 Communication device 13 External modulation type optical transmitter 14, 21 Fiber amplifier 15 split WDM filter 16 upstream optical receiver 17, 24 Optical / electrical signal converter 18 TDM demodulator 20 Optical distribution / synthesis closure 22 Optical coupler 23 Mixed WDM filter 25 TDM modulator 26 Electric / optical converter 30 optical nodes 40 subscriber stations 50a Downstream optical fiber core wire 50b upstream optical fiber core wire

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 7/22 H04B 9/00 G

Claims (5)

[Claims] 1. A bidirectional CATV system for performing long-distance optical transmission between a center station and a plurality of optical nodes via an optical transmission line, the system being transmitted from the center station via the optical transmission line. The downlink optical modulation signal is received and distributed to the plurality of optical nodes to be distributed, and the upstream optical modulation signals respectively transmitted from the plurality of optical nodes are received, and the plurality of optical modulation signals are combined. An optical distribution / combining closure for sending to the center station is provided, and the center station receives an upstream optical modulation signal sent from the optical distribution / composition closure via an optical transmission line, and outputs an upstream signal for each optical node. A two-way CATV system comprising a separator for separating. 2. The optical distribution / synthesis closure includes an optical fiber amplifier for amplifying a downstream optical modulation signal transmitted from the center station, and an optical modulation signal amplified by the optical fiber amplifier to a plurality of the optical nodes. An optical coupler for distributing and distributing, and an optical combiner for combining upstream optical modulation signals of different wavelengths respectively transmitted from the plurality of optical nodes and transmitting to the center station. 1. An interactive CATV system according to 1. 3. The optical distribution / synthesis closure includes a plurality of optical / electrical signal converters for converting upstream optical modulation signals respectively sent from the plurality of optical nodes into electric signals, and a plurality of the optical / electrical signals. A time-division modulator for time-division-multiplexing and synthesizing a plurality of upstream electric signals converted into electric signals by a converter, and electric / optical conversion for converting the modulated signal output from the time-division modulator into an optical signal The interactive CATV system according to claim 1, further comprising: 4. The bidirectional CATV system according to claim 1, wherein the demultiplexer demultiplexes a plurality of upstream optical modulation signals having different wavelengths for each wavelength. 5. The bidirectional CATV system according to claim 1, wherein the demultiplexer demultiplexes the time-division-multiplexed upstream optical modulation signal for each optical node.