JP4278628B2 - Optical transmission system - Google Patents

Description

The present invention relates to an optical transmission system relates especially optical transmission system for performing optical transmission of an optical access network.

  With the widespread use of broadband multimedia services such as the Internet and digital content distribution in recent years, there is a need for the construction of economical, high-speed, broadband systems for access networks. As a technology to provide services, opticalization of subscriber networks such as FTTH (Fiber To The Home) is progressing.

  As an optical fiber subscriber system, a PON (Passive Optical Network) system, in which one optical fiber is branched from the station side by an optical splitter and bidirectional communication services are provided with a plurality of subscribers, is attracting attention. I'm bathing.

  FIG. 9 is a diagram showing an outline of the PON system. The PON system 100 includes an OLT (Optical Line Terminal: optical subscriber line station apparatus) 101 arranged in a station and ONUs (Optical Network Unit: optical subscriber line termination apparatuses) 102-1 to 102 arranged in a home. -N and the optical splitter 103.

  The OLT 101 is connected to the optical splitter 103 by a single optical fiber F1. The optical fiber branched by the optical splitter 103 is connected to the ONUs 102-1 to 102-n (maximum of 32 branches in the PON).

  In such a configuration, in order to perform bidirectional communication by sharing the optical fiber F1 between one OLT 101 and the plurality of ONUs 102-1 to 102-n, the wavelength λ1 in the downstream direction (station → subscriber) and the upstream WDM (Wavelength Division Multiplex) transmission is performed in which the wavelength (λ2) in the direction (subscriber → station) is different (generally, the downstream wavelength λ1 is 1.49 μm and the upstream wavelength λ2 is 1.31 μm).

  In the downstream direction, the TDM (Time Division Multiplex) system in which the ONUs 102-1 to 102-n receive all the signals of the wavelength λ1 transmitted from the OLT 101 and read out only the information in the time slots assigned to the ONUs. Is done.

  Further, in the upstream direction, since signals of the same wavelength λ2 are transmitted from the ONUs 102-1 to 102-n, TDMA (Time Division) that controls transmission timing so as not to collide with burst signals from other ONUs. Multiplex Access) method is performed.

As a conventional PON technology, a system has been proposed in which optical branching elements are arranged in multiple stages between a center device and a user device to branch an optical signal into multiple branches (for example, Patent Document 1).
JP-A-8-242207 (paragraph numbers [0018] to [0020], FIG. 1)

  In the conventional PON system 100, the optical splitter 103 is configured to branch up to 32. Therefore, when the number of subscribers increases, a similar PON system is further constructed or a new optical fiber is connected to the OLT. In response to the increase in subscribers.

  10 and 11 are diagrams showing the configuration of the PON system corresponding to the increase in subscribers. 10 shows a case where a plurality of PON systems are constructed, and FIG. 11 shows a case where a new optical fiber is connected to the OLT 101.

  In contrast to FIG. 10, when the number of subscribers increases when the PON system 100-1 is initially operated with 32 ONUs 102-1 to 102-32, the PON system 100-that performs the same service as the PON system 100-1. 2 will be newly constructed to accommodate up to 64 ONUs. When the number of subscribers further increases, a new PON system is similarly constructed.

  In contrast to FIG. 11, when the number of subscribers increases when initially operating with 32 ONUs 102-1 to 102-32 in the PON system 100-1, a new optical splitter 103a is constructed by laying the optical fiber F2 on the OLT 101. And is connected to the ONUs 102-1 to 102-32 by an optical fiber branched from the optical splitter 103a so that it can accommodate up to 64 ONUs. When the number of subscribers further increases, new optical fibers are laid in the OLT 101 in the same manner.

  In recent years, the number of subscribers to multimedia communication has been steadily increasing, and the number of subscribers to CATV services that distribute digital contents using PON technology is expected to increase rapidly. 10 and 11 correspond to the increase in subscribers by the method described above.

  However, since a new system is constructed in FIG. 10, the expansion work becomes large and enormous costs are required. On the other hand, in FIG. 11, a new optical fiber is connected to the existing OLT 101, and a dark fiber (an optical fiber that is laid but not used) can be used as the optical fiber to be connected.

  However, when the optical fiber F1 that is already in operation is seen, a WDM signal in which only two wavelengths different in upstream and downstream are multiplexed flows, and the optical fiber F1 is sufficiently utilized for WDM transmission. In other words, in order to cope with the increase in subscribers in such an operation state, releasing the dark fiber and additionally connecting it to the OLT 101 means that the dark fiber is released wastefully. For this reason, the method of FIG. 11 is poor in line efficiency and cannot be said to be an efficient method for dealing with an increase in subscribers.

  Further, in the above-described prior art (Japanese Patent Laid-Open No. 8-242207), the optical signal is multi-branched by connecting the optical splitter in multiple stages on the optical fiber, so that it is possible to cope with the increase in subscribers.

  However, branching loss increases when the optical signal is branched by an optical splitter connected in multiple stages on the path through which the optical signal passes. Therefore, the light receiving sensitivity must be increased on the OLT side, and the optical output power must be set large on the ONU side. In other words, problems such as high cost of optical elements and increase in power consumption occur.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an optical transmission system having a network configuration that can flexibly cope with an increase in subscribers and improving the efficiency of optical fiber lines. And

To solve the above SL problem, an optical transmission system is provided. The optical transmission system includes a plurality of station devices that perform bidirectional communication with a plurality of subscriber devices belonging to a plurality of different subscriber groups by using a plurality of downlink signal lights and a plurality of uplink signal lights each having a different wavelength; A plurality of splitters for focusing a plurality of subscriber devices belonging to each of the plurality of subscriber groups, and a plurality of station side multiplexing / demultiplexing units respectively connected to the plurality of station devices are connected in a multistage manner. The plurality of subscriber units are connected in multiple stages by a multi-stage connection between a station side multiplexing / demultiplexing unit that connects each of the plurality of station devices to a common optical fiber and a plurality of subscriber side multiplexing / demultiplexing units respectively connected to the plurality of splitters. A subscriber-side multiplexing / demultiplexing unit that connects each of the subscriber devices to a common optical fiber.

  Here, the plurality of downstream signal lights and the plurality of upstream signal lights are arranged in the first wavelength band and the second wavelength band, which are different wavelength bands, respectively, and the subscriber-side multiplexing / demultiplexing unit includes a common optical fiber or A first port connected to the upper subscriber side multiplexing / demultiplexing unit, a second port connected to one of the plurality of splitters, and a third port connected to the lower subscriber side multiplexing / demultiplexing unit And a subscriber-side first filter or subscriber-side third filter connected to the first port to the third port, respectively.
  The first filter on the subscriber side transmits the transmission output of the input light from the first port to the second filter on the subscriber side, the reflected output of the input light from the first port to the third filter on the subscriber side, and from the second filter The transmission output of the input light is output to the first port, the wavelength of the downstream signal light corresponding to the subscriber group connected to the second port is transmitted, and the other plurality of downstream signal lights and the plurality of upstream signal lights To reflect.
  The second filter on the subscriber side transmits the transmitted output of the input light from the first filter to the second port, the transmitted output of the input light from the second port to the first filter on the subscriber side, and the input light from the second port. Are output to the third filter on the subscriber side, transmit light in the first wavelength band, and reflect light in the second wavelength band.
  The third filter on the subscriber side receives the reflected output of the input light from the first filter on the subscriber side as the third port, the transmitted output of the input light from the second filter on the subscriber side as the first filter on the subscriber side, The reflected output of the input light from the three ports is output to the first filter on the subscriber side, the wavelength of the upstream signal light corresponding to the subscriber group connected to the second port is transmitted, and a plurality of other upstream signal lights And reflects a plurality of downstream signal lights.
  The station side multiplexing / demultiplexing unit includes a first port connected to the common optical fiber or the upper station side multiplexing / demultiplexing unit, a second port connected to any one of the plurality of station apparatuses, and a lower station. A third port connected to the side multiplexing / demultiplexing unit, and a station-side first filter or station-side third filter connected to the first port to the third port, respectively.
  The first filter on the station side transmits the transmission output of the input light from the first port to the second filter on the station side, the reflected output of the input light from the first port to the third filter on the station side, and the input light from the second filter Are transmitted to the first port, transmit the wavelength of the upstream signal light corresponding to the station device connected to the second port, and reflect the other plurality of upstream signal lights and the plurality of downstream signal lights.
  The station-side second filter reflects the transmission output of the input light from the first filter to the second port, the transmission output of the input light from the second port to the station-side first filter, and the reflection of the input light from the second port. Outputs are respectively output to the station-side third filters, transmit light in the second wavelength band, and reflect light in the first wavelength band.
  The third filter on the station side reflects the reflected output of the input light from the first filter on the station side to the third port, the transmitted output of the input light from the second filter on the station side to the first filter on the station side, and the third port The reflected output of the input light is output to the first filter on the station side, the wavelength of the downstream signal light corresponding to the station device connected to the second port is transmitted, and the other plurality of downstream signal lights and the plurality of upstream signal lights To reflect.

The optical transmission system of the present invention includes a plurality of station apparatuses, a plurality of subscriber apparatuses, and a plurality of optical splitters that aggregate the subscriber apparatuses for each subscriber group and branch the downlink signal, and combine them. Sends the downstream signal to the common optical fiber, sends the demultiplexed upstream signal to the corresponding station device, and transmits the demultiplexed downstream signal to the common optical fiber. A two-way communication between a station and a subscriber is performed on a single common optical fiber by a subscriber-side optical multiplexing / demultiplexing unit that transmits to a corresponding subscriber device via an optical splitter. As a result, it is possible to configure a network that can flexibly cope with an increase in subscribers, and to improve the efficiency of optical fiber lines.
In addition, since a plurality of subscriber-side multiplexing / demultiplexing units arranged for each subscriber group have the same structure and are configured to efficiently perform demultiplexing of downstream signals and multiplexing of upstream signals, the system configuration is complicated. Therefore, it is possible to reduce costs.
In addition, since the plurality of station-side multiplexing / demultiplexing units arranged for each station have the same structure and are configured to efficiently perform demultiplexing of upstream signals and multiplexing of downstream signals, the complexity of the system configuration is eliminated. In addition, it is possible to reduce costs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a principle diagram of an optical transmission system. The optical transmission system 1 includes station apparatuses 10-1 to 10-n, subscriber apparatuses 20-1 to 20-m in the subscriber groups G1 to Gn, optical splitters 30-1 to 30-n, and station-side optical multiplexing / demultiplexing. It is a system that is configured by a unit 40 and a subscriber side optical multiplexing / demultiplexing unit 50 to perform optical transmission. The optical transmission system 1 can be applied to, for example, a PON of an optical access network. Hereinafter, the station device is referred to as OLT, and the subscriber device is referred to as ONU.

  The OLTs 10-1 to 10-n are connected to the station-side optical multiplexing / demultiplexing unit 40, and the station-side optical multiplexing / demultiplexing unit 40 and the subscriber-side optical multiplexing / demultiplexing unit 50 are connected via a common optical fiber Fc. The wave splitter 50 is connected to the optical splitters 30-1 to 30-n.

  The ONUs 20-1 to 20-m in the subscriber groups G1 to Gn are connected to the optical splitters 30-1 to 30-n, respectively. That is, the ONUs 20-1 to 20-m in the subscriber group G1 are connected to the optical splitter 30-1, and the ONUs 20-1 to 20-m in the subscriber group Gn are connected to the optical splitter 30-n. (The maximum number of ONU connections in one subscriber group is 32 for a PON).

  The OLTs 10-1 to 10-n transmit, to the ONU side, downlink signals to which different downlink wavelengths λ1 to λn are assigned to the subscriber groups G1 to Gn (hereinafter, downlink signals to which the downlink wavelength λx is assigned are downlink signals). λx)).

  That is, the OLT 10-1 transmits the downstream signal λ1 to the ONUs 20-1 to 20-m in the subscriber group G1, and the OLT 10-n transmits the downstream signal λn to the ONUs 20-1 to 20-m in the subscriber group Gn. Send to.

  The ONUs 20-1 to 20-m transmit, to the OLTs 10-1 to 10-n, uplink signals in which different uplink wavelengths λn + 1 to λ2n are assigned to the OLTs 10-1 to 10-n in units of the subscriber groups G1 to Gn. (Hereinafter, an upstream signal to which the upstream wavelength λy is assigned is referred to as an upstream signal λy).

  That is, the ONUs 20-1 to 20-m in the subscriber group G1 transmit the upstream signal λn + 1 to the OLT 10-1, and the ONUs 20-1 to 20-m in the subscriber group Gn transmit the upstream signal λ2n to the OLT 10-n. Send to.

  The common optical fiber Fc is a single-core optical fiber cable that converges a downstream signal and an upstream signal (a WDM signal of λ1 to λ2n flows) and is shared and used in bidirectional communication between a station and a subscriber.

  The optical splitters 30-1 to 30-n aggregate the ONUs 20-1 to 20-m for each of the subscriber groups G1 to Gn, and the downlink signals λ1 to λn for the subscriber groups G1 to Gn. Branch and output to ~ 20-m.

  The station-side optical multiplexing / demultiplexing unit 40 is arranged on the station side, and station-side multiplexing / demultiplexing units 40a-1 to 40a-n (generic names) for multiplexing the downlink signals λ1 to λn and demultiplexing the upstream signals λn + 1 to λ2n. In the case of including the station side multiplexing / demultiplexing unit 40a), the multiplexed downstream signal is transmitted to the common optical fiber Fc, and the demultiplexed upstream signal is transmitted to the corresponding OLTs 10-1 to 10-n.

  The subscriber-side optical multiplexing / demultiplexing unit 50 is arranged on the subscriber side, and subscriber-side multiplexing / demultiplexing units 50a-1 to 50a- for performing demultiplexing of the downstream signals λ1 to λn and multiplexing of the upstream signals λn + 1 to λ2n. n (in the collective case, subscriber side multiplexing / demultiplexing unit 50a), the multiplexed upstream signal is sent to the common optical fiber Fc, and the demultiplexed downstream signal is transmitted to the corresponding ONUs 20-1 to 20-m. The data is sent through the splitters 30-1 to 30-n.

  In the optical transmission system 1 as well, bidirectional communication using the common optical fiber Fc using the TDM system for the downstream band and the TDMA system for the upstream band is performed by dividing and multiplexing the upstream and downstream wavelengths as described above. Is done.

  Next, the configuration of the optical transmission system 1 when there are four subscriber groups G1 to G4 will be described, and features of the optical transmission system 1 that can flexibly cope with an increase in subscribers will be described in detail. FIG. 2 is a diagram showing the configuration of the optical transmission system. The optical transmission system 1a includes OLTs 10-1 to 10-4, ONUs 20-1 to 20-32 in the subscriber groups G1 to G4 (assuming a maximum number of 32 units are connected in one group), an optical splitter. 30-1 to 30-4, a station side optical multiplexing / demultiplexing unit 40-1, and a subscriber side optical multiplexing / demultiplexing unit 50-1. The basic connection configuration of each element is the same as that in FIG. 1, and shows a system that performs bidirectional communication between four OLTs 10-1 to 10-4 and subscriber groups G1 to G4.

  The station side optical multiplexing / demultiplexing unit 40-1 has a configuration in which the station side multiplexing / demultiplexing units 40a-1 to 40a-4 are connected in multiple stages, and the subscriber side optical multiplexing / demultiplexing unit 50-1 includes the subscriber side multiplexing / demultiplexing unit 50-1. The units 50a-1 to 50a-4 are connected in multiple stages.

  The operation in the downstream direction (OLT → ONU) will be described. Each of the OLTs 10-1 to 10-4 outputs downstream signals λ1 to λ4. The station side multiplexing / demultiplexing unit 40a-4 transmits the downlink signal λ4 to the station side multiplexing / demultiplexing unit 40a-3, and the station side multiplexing / demultiplexing unit 40a-3 receives the downlink signal λ3 transmitted from the OLT 10-3. The downstream signal λ4 is multiplexed and transmitted to the station side multiplexing / demultiplexing unit 40a-2.

  Further, the station side multiplexing / demultiplexing unit 40a-2 multiplexes the downlink signal λ2 and the downlink signals λ3, λ4 transmitted from the OLT 10-2, and transmits the multiplexed signal to the station side multiplexing / demultiplexing unit 40a-1. The multiplexing / demultiplexing unit 40a-1 multiplexes the downlink signal λ1 and the downlink signals λ2 to λ4 transmitted from the OLT 10-1 and sends out the multiplexed signal through the common optical fiber Fc.

  On the other hand, when receiving the downlink signals λ1 to λ4, the subscriber side multiplexing / demultiplexing unit 50a-1 demultiplexes the downlink signals λ1 to λ4 into the downlink signals λ1 and λ2 to λ4. The downlink signal λ1 is branched into 32 by the optical splitter 30-1 and transmitted to the ONUs 20-1 to 20-32 in the subscriber group G1, and the downlink signals λ2 to λ4 are transmitted to the subscriber side multiplexing / demultiplexing unit 50a-2. Sent to.

  When the subscriber side multiplexing / demultiplexing unit 50a-2 receives the downlink signals λ2 to λ4, the subscriber side multiplexing / demultiplexing unit 50a-2 demultiplexes the downlink signals λ2 and λ3 and λ4. The downstream signal λ2 is branched into 32 by the optical splitter 30-2 and transmitted to the ONUs 20-1 to 20-32 in the subscriber group G2, and the downstream signals λ3 and λ4 are transmitted to the subscriber side multiplexing / demultiplexing unit 50a-3. Sent to.

  When the subscriber side multiplexing / demultiplexing unit 50a-3 receives the downstream signals λ3 and λ4, it demultiplexes the respective wavelengths. The downstream signal λ3 is branched into 32 by the optical splitter 30-3 and transmitted to the ONUs 20-1 to 20-32 in the subscriber group G3, and the downstream signal λ4 is transmitted to the subscriber-side multiplexing / demultiplexing unit 50a-4. Is done.

  The subscriber side multiplexing / demultiplexing unit 50a-4 receives the downstream signal λ4 and sends it to the optical splitter 30-4. The downstream signal λ4 is branched into 32 by the optical splitter 30-4 and transmitted to the ONUs 20-1 to 20-32 in the subscriber group G4.

  Next, the operation in the upstream direction (ONU → OLT) will be described. The ONUs 20-1 to 20-32 in the subscriber groups G1 to G4 transmit the upstream signals λ5 to λ8 via the optical splitters 30-1 to 30-4 (from the ONUs 20-1 to 20-32 by TDMA). The transmission timing is controlled so that the output signals do not collide).

  The subscriber side multiplexing / demultiplexing unit 50a-4 transmits the upstream signal λ8 to the subscriber side multiplexing / demultiplexing unit 50a-3, and the subscriber side multiplexing / demultiplexing unit 50a-3 is transmitted from the subscriber group G3. The uplink signal λ7 and the uplink signal λ8 are multiplexed and transmitted to the subscriber side multiplexing / demultiplexing unit 50a-2.

  Further, the subscriber side multiplexing / demultiplexing unit 50a-2 multiplexes the upstream signal λ6 and the upstream signals λ7 and λ8 transmitted from the subscriber group G2, and transmits the multiplexed signal to the subscriber side multiplexing / demultiplexing unit 50a-1. The subscriber-side multiplexing / demultiplexing unit 50a-1 multiplexes the upstream signal λ5 and the upstream signals λ6 to λ8 transmitted from the subscriber group G1, and transmits them through the common optical fiber Fc.

  On the other hand, when receiving the upstream signals λ5 to λ8, the station side multiplexing / demultiplexing unit 40a-1 demultiplexes the upstream signals λ5 and λ6 to λ8. The upstream signal λ5 is transmitted to the OLT 10-1, and the upstream signals λ6 to λ8 are transmitted to the station side multiplexing / demultiplexing unit 40a-2.

  Upon receiving the upstream signals λ6 to λ8, the station side multiplexing / demultiplexing unit 40a-2 demultiplexes the upstream signals λ6 to λ7 and λ8. The upstream signal λ6 is transmitted to the OLT 10-2, and the upstream signals λ7 and λ8 are transmitted to the station side multiplexing / demultiplexing unit 40a-3.

  When receiving the upstream signals λ7 and λ8, the station side multiplexing / demultiplexing unit 40a-3 demultiplexes the respective wavelengths. The upstream signal λ7 is transmitted to the OLT 10-3, and the upstream signal λ8 is transmitted to the station side multiplexing / demultiplexing unit 40a-4. The station side multiplexing / demultiplexing unit 40a-4 receives the upstream signal λ8, and the upstream signal λ8 is transmitted to the OLT 10-4.

  FIG. 3 is a diagram showing an example of frequency arrangement of used wavelengths. The wavelength band used for the downstream signal is the C band of 1.5 μm band, and the wavelength band used for the upstream signal is the O band of 1.3 μm band. In the downstream direction, different wavelengths are used within the same C-band wavelength band, and in the upstream direction, different wavelengths are used within the same O-band wavelength band (for example, different wavelengths are used with a wavelength interval of 20 nm). ).

  Here, since the optical transmission system 1a in FIG. 2 is a system that performs bidirectional communication between the four OLTs 10-1 to 10-4 and the subscriber groups G1 to G4, the downstream signal is defined as the C band and within the C band. The wavelengths of the downstream signals λ1 to λ4 are set every 20 nm interval. Further, the upstream signals are set to the O band, and the wavelengths of the upstream signals λ5 to λ8 are set every 20 nm within the O band.

  In the optical transmission system 1, the wavelengths of the downstream signal and the upstream signal are set as shown in FIG. 3, and the station side multiplexing / demultiplexing unit 40a and the subscriber side multiplexing / demultiplexing unit 50a are configured as shown in FIG. It has a filter function for filtering the wavelength band and the upstream wavelength band (for example, when the station side multiplexing / demultiplexing unit 40a-4 is viewed, the received upstream wavelength λ8 is transmitted to the OLT 10-4 side, The received downstream wavelength λ4 is transmitted to the station side multiplexing / demultiplexing unit 40a-3).

  Therefore, even when a new subscriber group needs to be added when the number of subscribers increases, the station side multiplexing / demultiplexing unit 40a and the subscriber side multiplexing / demultiplexing unit 50a having such a filter function are provided. It is possible to flexibly cope with an increase in the number of subscriber groups by simply making additional connections in multiple stages corresponding to the number of new subscriber groups.

  FIG. 4 is a diagram showing a configuration of an optical transmission system corresponding to an increase in subscriber groups. The optical transmission system 1b is a configuration when the subscriber group G5 is newly increased with respect to the system configuration shown in FIG. 2 (the OLT 10-5 is also added as the subscriber group G5 increases).

  Since the subscriber group has increased by one, the station side multiplexing / demultiplexing unit 40a-5 is additionally connected to the station side multiplexing / demultiplexing unit 40a-4, and the subscriber side multiplexing / demultiplexing unit 50a-5 is added to the subscriber side multiplexing / demultiplexing. Additional connection is made to the wave unit 50a-4. Also, a new downstream signal is C-band λa, and a new upstream signal is O-band λb. FIG. 5 shows the wavelength arrangement when the subscriber group is increased by one.

  The new downlink signal λa is multiplexed (multiplexed) with the downlink signals λ1 to λ4 and transmitted to the ONU side through the common optical fiber Fc in the same manner as the operation in the downlink direction described above with reference to FIG. Further, the new upstream signal λb is combined with the upstream signals λ5 to λ8 and transmitted to the OLT side through the common optical fiber Fc in the same manner as the upstream operation described above with reference to FIG.

  As described above, the configuration of the optical transmission system 1 can flexibly cope with an increase in subscriber groups by simply connecting the station side multiplexing / demultiplexing unit 40a and the subscriber side multiplexing / demultiplexing unit 50a in multiple stages. (If the number of subscriber groups decreases, it is only necessary to remove the unit.) Large-scale expansion work as in the past becomes unnecessary, and a new optical fiber is laid (to release the dark fiber). This eliminates the need to use the existing common optical fiber Fc as it is, and enables bidirectional communication including the increased optical wavelengths of subscribers.

  Further, since the new wavelength is multiplexed and transmitted by WDM using the existing common optical fiber Fc, the line efficiency can be improved. For example, in the conventional PON system, WDM transmission of 2 waves (1 wave in the upstream and 1 wave in the downstream) is performed, but in the optical transmission system 1, 4 waves, 6 waves,... 2N waves (N waves in the uplink) Therefore, N-times line efficiency can be obtained.

  Next, a specific internal configuration of the subscriber side multiplexing / demultiplexing unit 50a will be described. FIG. 6 is a diagram showing an internal configuration of the subscriber side multiplexing / demultiplexing unit 50a. The station-side multiplexing / demultiplexing unit 40a has the same internal configuration as the subscriber-side multiplexing / demultiplexing unit 50a, except that the input / output of downlink / uplink signals is reversed, and the description thereof will be omitted.

  Subscriber-side multiplexing / demultiplexing units (hereinafter simply referred to as multiplexing / demultiplexing units in the description of FIG. 6) 50a-1 to 50a-4 have three filters (bandpass filters), and the basic structures thereof are the same. It is. However, the transmission wavelengths of these filters are different for each unit.

  The multiplexing / demultiplexing unit 50a-1 includes filters f1a to f1c. The filters f1a and f1b are filters that transmit the wavelength λ1 and reflect other wavelengths, and the filter f1c is a filter that transmits the wavelength λ5 and reflects other wavelengths. The multiplexing / demultiplexing unit 50a-2 includes filters f2a to f2c. The filters f2a and f2b are filters that transmit the wavelength λ2 and reflect other wavelengths, and the filter f2c is a filter that transmits the wavelength λ6 and reflects other wavelengths.

  The multiplexing / demultiplexing unit 50a-3 includes filters f3a to f3c. The filters f3a and f3b are filters that transmit the wavelength λ3 and reflect other wavelengths, and the filter f3c is a filter that transmits the wavelength λ7 and reflects other wavelengths. The multiplexing / demultiplexing unit 50a-4 includes filters f4a to f4c. The filters f4a and f4b are filters that transmit the wavelength λ4 and reflect other wavelengths, and the filter f4c is a filter that transmits the wavelength λ8 and reflects other wavelengths.

  In view of the flow of the downstream signal with respect to such a configuration, when the downstream signals λ1 to λ4 enter the filter f1a of the multiplexing / demultiplexing unit 50a-1, the downstream signals λ1 and λ2 to λ4 are demultiplexed. The downstream signal λ1 is transmitted through the filters f1a and f1b, and the downstream signals λ2 to λ4 are reflected by the filter f1c and dropped to the lower multiplexing / demultiplexing unit 50a-2.

  Such a signal flow continues in the same manner. That is, when the downstream signals λ2 to λ4 enter the filter f2a of the multiplexing / demultiplexing unit 50a-2, the downstream signal λ2 and the downstream signals λ3 and λ4 are demultiplexed, and the downstream signal λ2 passes through the filters f2a and f2b and is output. The downstream signals λ3 and λ4 are reflected by the filter f2c and dropped to the lower multiplexing / demultiplexing unit 50a-3.

  When the downstream signals λ3 and λ4 are incident on the filter f3a of the multiplexing / demultiplexing unit 50a-3, the downstream signal λ3 and the downstream signal λ4 are demultiplexed, and the downstream signal λ3 is transmitted through the filters f3a and f3b and output. λ4 is reflected by the filter f3c and dropped to the lower multiplexing / demultiplexing unit 50a-4. When the downstream signal λ4 is incident on the filter f4a of the multiplexing / demultiplexing unit 50a-4, the downstream signal λ4 is transmitted through the filters f4a and f4b and output.

  On the other hand, looking at the flow of the upstream signal, when the upstream signal λ8 enters the filter f4b of the multiplexing / demultiplexing unit 50a-4, the upstream signal λ8 follows the path of reflection by the filter f4b, transmission by the filter f4c, and reflection by the filter f4a. The process proceeds to the upper multiplexing / demultiplexing unit 50a-3.

  Such a signal flow continues in the same manner. That is, when the upstream signal λ7 is incident on the filter f3b of the multiplexing / demultiplexing unit 50a-3, the upstream signal λ7 is reflected by the filter f3b, transmitted by the filter f3c, and reflected by the filter f3a, and the upstream signal λ7 is reflected by the upstream signal λ8. Are added and combined to proceed to the upper multiplexing / demultiplexing unit 50a-2.

  When the upstream signal λ6 is incident on the filter f2b of the multiplexing / demultiplexing unit 50a-2, the upstream signal λ6 is reflected by the filter f2b, transmitted by the filter f2c, and reflected by the filter f2a, and the upstream signal λ6 has upstream signals λ7 and λ8. Are added and combined to proceed to the upper multiplexing / demultiplexing unit 50a-1.

  When the upstream signal λ5 is incident on the filter f1b of the multiplexing / demultiplexing unit 50a-1, the upstream signal λ5 is reflected by the filter f1b, transmitted by the filter f1c, and reflected by the filter f1a, and the upstream signal λ5 has upstream signals λ6 to λ8. Are added and combined, and upstream signals λ5 to λ8 are output from the unit.

  Here, conventionally, when a multi-branch system is constructed, in a system in which optical splitters are branched by connecting multiple stages on a path through which an optical signal passes, branch loss increases, and an OSNR (Optical Signal to Noise) increases. However, the multi-branch network is constructed for the station side multiplexing / demultiplexing unit 40a and the subscriber side multiplexing / demultiplexing unit 50a of the optical transmission system 1 using the above-described filters. By doing so, the branch loss can be remarkably reduced, and a desired OSNR can be obtained even in a multi-branch network.

  Next, modifications of the station side optical multiplexing / demultiplexing unit 40 and the subscriber side optical multiplexing / demultiplexing unit 50 will be described. In the above description, the station side multiplexing / demultiplexing unit 40a and the subscriber side multiplexing / demultiplexing unit 50a are configured to perform multiplexing / demultiplexing using a bandpass filter, but AWG (Array Wave-guide Grating) is used. ) Can also be used for multiplexing and demultiplexing. An AWG is composed of, for example, an optical circuit using an optical waveguide made of silica glass, and outputs an optical signal with a plurality of wavelengths divided into different waveguides for each wavelength, or combines light of different wavelengths into one waveguide. It can be output as a wave.

  FIG. 7 is a diagram showing the configuration of the AWG. Regarding the multiplexing / demultiplexing function of the AWG 70, the WDM signals having wavelengths λ1 to λn incident from the input waveguide 71 are spread by diffraction in the slab waveguide 72a and distributed to the respective waveguides of the phase difference waveguide 73. The light distributed and transmitted by the phase difference waveguide 73 has a phase difference (optical path difference) when reaching the slab waveguide 72b because the length of each phase difference waveguide is different.

  When the length of the phase difference waveguide 73 is adjusted to optimize the phase difference so as to exhibit the same characteristics as the grating (diffraction grating) (when wavelength decomposition is performed), the light is collected at different positions depending on the wavelength. To come.

  The light emitted from each phase difference waveguide becomes a point light source array having a phase difference at the incident end of the slab waveguide 72b, spreads by diffraction in the slab waveguide 72b, is strengthened according to the wavelength by interference, and has different emission guides. The light is condensed on the waveguide 74 and separated (divided into each wavelength) by the output waveguide 74. On the other hand, when light of different wavelengths is incident from the reverse, the light is multiplexed into one waveguide and output.

  FIG. 8 is a diagram showing an example of wavelength arrangement when AWG is used. If the AWG has an FSR (free spectral range) with a wavelength period shifted by 20 ns, it can be multiplexed / demultiplexed in the same way as the wavelength arrangement as described above with reference to FIG. And two-way communication between subscribers can be performed.

  Although the AWG is used in the above modification, the station side multiplexing / demultiplexing unit 40a and the subscriber side multiplexing / demultiplexing unit 50a are configured using WSS (Wavelength Selectable Switch). It is also possible.

(Appendix 1) In an optical transmission system that performs optical transmission,
A plurality of station devices for transmitting a downlink signal to which a different downlink wavelength is assigned for each subscriber group to a subscriber;
A plurality of subscriber devices that transmit, to the station device, an uplink signal in which a different uplink wavelength is assigned to each station device in units of subscriber groups;
A single-core common optical fiber that focuses the downlink signal and the uplink signal and shares the bidirectional signal between the station and the subscriber;
Aggregating a plurality of subscriber devices for each subscriber group, a plurality of optical splitters for branching the downlink signal for each subscriber group;
Arranged on the station side, including a station-side multiplexing / demultiplexing unit that multiplexes the downlink signal and demultiplexes the uplink signal, sends the multiplexed downlink signal to the common optical fiber, and demultiplexes the signal A station-side optical multiplexer / demultiplexer that sends an upstream signal to the corresponding station device;
A subscriber-side multiplexing / demultiplexing unit arranged on the subscriber side for performing demultiplexing of the downlink signal and multiplexing of the uplink signal, and transmitting the multiplexed uplink signal to the common optical fiber; A subscriber-side optical multiplexing / demultiplexing unit that sends the downlink signal to the corresponding subscriber device via the optical splitter;
An optical transmission system comprising:

  (Supplementary Note 2) When a new subscriber group needs to be added when the number of subscribers increases, the station side optical multiplexing / demultiplexing unit and the subscriber side optical multiplexing / demultiplexing unit are connected to the station side optical multiplexing / demultiplexing unit. By adding and connecting units in multiple stages, and adding and connecting the subscriber side multiplexing / demultiplexing units in multiple stages, a multiplexing / demultiplexing function for new subscriber groups is added, and the number of subscribers increases. 2. The optical transmission system according to appendix 1, wherein the optical wavelength to be transmitted is increased, and bidirectional communication including the increased optical wavelength is performed using only the existing common optical fiber.

  (Supplementary Note 3) Different wavelength band bands are used for the downlink signal and the uplink signal, and the station side multiplexing / demultiplexing unit uses a downlink wavelength band band used for the downlink signal and an uplink wavelength used for the uplink signal. It is configured by a filter that filters the band band, and the station side multiplexing / demultiplexing units are connected in multiple stages so that different downstream wavelengths in the same downstream wavelength band band are multiplexed for each unit, and the same upstream wavelength band The optical transmission system according to appendix 2, wherein different upstream wavelengths in the band are demultiplexed for each unit.

  (Supplementary Note 4) Different wavelength band bands are used for the downlink signal and the uplink signal, and the subscriber-side multiplexing / demultiplexing unit uses a downlink wavelength band band used for the downlink signal and an uplink used for the uplink signal. It is configured by a filter for filtering the wavelength band, and the subscriber-side multiplexing / demultiplexing units are connected in multiple stages, so that different downstream wavelengths in the same downstream wavelength band are demultiplexed for each unit, and the same upstream The optical transmission system according to appendix 2, wherein different upstream wavelengths in the wavelength band are combined for each unit.

(Additional remark 5) In the optical transmission method which performs optical transmission corresponding to increase / decrease in the subscriber to a network,
The plurality of station devices transmit a downlink signal to which a different downlink wavelength is assigned for each subscriber group to the subscriber,
The plurality of subscriber devices transmit, to the station device, an uplink signal in which a different uplink wavelength is assigned to each station device in units of subscriber groups,
Providing a single-core common optical fiber for converging the downstream signal and the upstream signal and sharing the bidirectional communication between the station and the subscriber;
Aggregating a plurality of the subscriber devices for each subscriber group, providing a plurality of optical splitters for branching the downlink signal for each subscriber group,
A station-side multiplexing / demultiplexing unit that multiplexes the downlink signal and demultiplexes the uplink signal, sends the multiplexed downlink signal to the common optical fiber, and corresponds the station corresponding to the demultiplexed uplink signal Place the station side optical multiplexing / demultiplexing section to be sent to the equipment on the station side,
Including a subscriber-side multiplexing / demultiplexing unit that demultiplexes the downlink signal and combines the uplink signal, sends the multiplexed uplink signal to the common optical fiber, and corresponds the downlink signal corresponding to the demultiplexed downlink signal A subscriber side optical multiplexing / demultiplexing unit that transmits to the subscriber device via the optical splitter is arranged on the subscriber side,
If it is necessary to add a new subscriber group when the number of subscribers increases, the station side multiplexing / demultiplexing units are additionally connected in multiple stages, and the subscriber side multiplexing / demultiplexing units are additionally connected in multiple stages. By adding a multiplexing / demultiplexing function to a new subscriber group, the optical wavelength to be transmitted is increased as the number of subscribers increases, and only the existing common optical fiber includes the increased optical wavelength. An optical transmission method characterized by performing bidirectional communication.

  (Additional remark 6) The wavelength band different from the said downstream signal and the said upstream signal is used, The said station side multiplexing / demultiplexing unit uses the downstream wavelength band used by the said downstream signal, and the upstream wavelength used by the said upstream signal It is configured by a filter that filters the band band, and the station side multiplexing / demultiplexing units are connected in multiple stages so that different downstream wavelengths in the same downstream wavelength band band are multiplexed for each unit, and the same upstream wavelength band The optical transmission method according to appendix 5, wherein different upstream wavelengths in the band are demultiplexed for each unit.

  (Supplementary Note 7) Different wavelength band bands are used for the downlink signal and the uplink signal, and the subscriber-side multiplexing / demultiplexing unit uses a downlink wavelength band band used for the downlink signal and an uplink signal used for the uplink signal. It is configured by a filter for filtering the wavelength band, and the subscriber-side multiplexing / demultiplexing units are connected in multiple stages, so that different downstream wavelengths in the same downstream wavelength band are demultiplexed for each unit, and the same upstream The optical transmission method according to appendix 5, wherein different upstream wavelengths in the wavelength band are multiplexed for each unit.

1 is a principle diagram of an optical transmission system. It is a figure which shows the structure of an optical transmission system. It is a figure which shows the example of frequency arrangement | positioning of a use wavelength. It is a figure which shows the structure of the optical transmission system corresponding to the increase in a subscriber group. It is a figure which shows wavelength arrangement | positioning when a subscriber group increases by one. It is a figure which shows the internal structure of a subscriber side multiplexing / demultiplexing unit. It is a figure which shows the structure of AWG. It is a figure which shows the example of a wavelength arrangement | positioning at the time of using AWG. It is a figure which shows the outline | summary of a PON system. It is a figure which shows the structure of the PON system corresponding to a subscriber increase. It is a figure which shows the structure of the PON system corresponding to a subscriber increase.

Explanation of symbols

1 Optical Transmission System 10-1 to 10-n Station Equipment (OLT)
20-1 to 20-m subscriber unit (ONU)
30-1 to 30-n optical splitter 40 station side optical multiplexing / demultiplexing unit 40a station side multiplexing / demultiplexing unit 50 subscriber side optical multiplexing / demultiplexing unit 50a subscriber side optical multiplexing / demultiplexing unit Fc common optical fiber G1 to Gn subscriber group λ1 ~ Λn Downstream signal λn + 1 ~ λ2n Upstream signal

Claims (2)

  A plurality of station devices that perform bidirectional communication with a plurality of subscriber devices belonging to a plurality of different subscriber groups by a plurality of downlink signal lights and a plurality of uplink signal lights each having a different wavelength;
  A plurality of splitters each for focusing a plurality of subscriber devices belonging to each of the plurality of subscriber groups;
  A plurality of station side multiplexing / demultiplexing units respectively connected to the plurality of station apparatuses are connected in a multistage manner, whereby a station side multiplexing / demultiplexing unit that connects each of the plurality of station apparatuses to a common optical fiber,
  A plurality of subscriber-side multiplexing / demultiplexing units respectively connected to the plurality of splitters, and a plurality of subscriber-side multiplexing / demultiplexing units for connecting each of the plurality of subscriber devices to a common optical fiber. ,
  The plurality of downstream signal lights and the plurality of upstream signal lights are arranged in a first wavelength band and a second wavelength band, which are different wavelength bands, respectively.
  The subscriber side multiplexing / demultiplexing unit includes a first port connected to the common optical fiber or the upper subscriber side multiplexing / demultiplexing unit, a second port connected to any one of the plurality of splitters, And a third port connected to the subscriber-side multiplexing / demultiplexing unit in the lower stage, and a subscriber-side first filter or subscriber-side third filter respectively connected to the first port to the third port ,
  The first filter on the subscriber side transmits a transmission output of input light from the first port to the second filter on the subscriber side, and a reflected output of input light from the first port to the third filter on the subscriber side. A transmission output of the input light from the second filter is output to the first port, the wavelength of the downstream signal light corresponding to the subscriber group connected to the second port is transmitted, and the other plurality Reflecting the downstream signal light and the plurality of upstream signal lights,
  The second filter on the subscriber side transmits a transmission output of input light from the first filter to the second port, and transmits a transmission output of input light from the second port to the subscriber side first filter. The reflected output of the input light from the two ports is output to the third filter on the subscriber side, the light in the first wavelength band is transmitted, the light in the second wavelength band is reflected,
  The third filter on the subscriber side receives the reflected output of the input light from the first filter on the subscriber side as the third port, and the transmitted output of the input light from the second filter on the subscriber side as the third filter on the subscriber side. The reflected output of the input light from the third port is output to the first filter to the first filter on the subscriber side, and the wavelength of the upstream signal light corresponding to the subscriber group connected to the second port is transmitted to one filter And reflecting the other plurality of upstream signal lights and the plurality of downstream signal lights,
  The station side multiplexing / demultiplexing unit includes a first port connected to the common optical fiber or the upper station side multiplexing / demultiplexing unit, a second port connected to any one of the plurality of station devices, and A third port connected to the lower station side multiplexing / demultiplexing unit and a station side first filter to a station side third filter respectively connected to the first port to the third port;
  The first filter on the station side transmits the transmission output of the input light from the first port to the second filter on the station side, and the reflected output of the input light from the first port to the third filter on the station side. The transmission output of the input light from the two filters is output to the first port, the wavelength of the upstream signal light corresponding to the station device connected to the second port is transmitted, and the other plurality of upstream signal lights And reflecting the plurality of downstream signal lights,
  The second filter on the station side transmits a transmission output of input light from the first filter to the second port, and transmits a transmission output of input light from the second port to the second filter on the station side. The reflected output of the input light from each is output to the third filter on the station side, the light in the second wavelength band is transmitted, the light in the first wavelength band is reflected,
  The station side third filter has a reflected output of input light from the station side first filter as the third port, and a transmission output of input light from the station side second filter as the station side first filter. The reflected output of the input light from the third port is output to the first filter on the station side, the wavelength of the downstream signal light corresponding to the station device connected to the second port is transmitted, and the other plurality Reflecting the downstream signal light and the plurality of upstream signal lights,
  An optical transmission system characterized by that.   By connecting a plurality of multiplexing / demultiplexing units connected to a plurality of bidirectional optical transmission apparatuses that perform bidirectional communication using a plurality of downstream signal lights and a plurality of upstream signal lights each having different wavelengths, A multiplexing / demultiplexing unit for connecting each of the bidirectional optical transmission devices to a common optical fiber,
  The plurality of downstream signal lights and the plurality of upstream signal lights are arranged in a first wavelength band and a second wavelength band, which are different wavelength bands, respectively.
  The multiplexing / demultiplexing unit includes a first port connected to the common optical fiber or the upper multiplexing / demultiplexing unit, a second port connected to any one of the plurality of bidirectional optical transmission devices, and A third port connected to the lower multiplexing / demultiplexing unit, and a first filter to a third filter respectively connected to the first port to the third port;
  The first filter transmits a transmission output of input light from the first port to the second filter, a reflection output of input light from the first port to the third filter, and an input light from the second filter. Are transmitted to the first port, transmit the wavelength of the downstream signal light corresponding to the bidirectional optical transmission device connected to the second port, and the plurality of downstream signal lights and the plurality of downstream signal lights. Reflecting the upstream signal light
  The second filter transmits a transmission output of input light from the first filter to the second port, a transmission output of input light from the second port to the first filter, and an input light from the second port. Are output to the third filter, transmit light in the first wavelength band, reflect light in the second wavelength band,
  The third filter has a reflected output of input light from the first filter as the third port, a transmitted output of input light from the second filter as the first filter, and an input light from the third port. Are output to the first filter, transmit the wavelength of the upstream signal light corresponding to the bidirectional optical transmission device connected to the second port, and the plurality of upstream signal lights and the plurality of upstream light beams. To reflect the downstream signal light,
  A multiplexing / demultiplexing section characterized by that.

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