CA2153220A1 - Fiber-optic access system for subscriber optical communication - Google Patents

Fiber-optic access system for subscriber optical communication

Info

Publication number
CA2153220A1
CA2153220A1 CA002153220A CA2153220A CA2153220A1 CA 2153220 A1 CA2153220 A1 CA 2153220A1 CA 002153220 A CA002153220 A CA 002153220A CA 2153220 A CA2153220 A CA 2153220A CA 2153220 A1 CA2153220 A1 CA 2153220A1
Authority
CA
Canada
Prior art keywords
optical
fiber
array
access system
central office
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA002153220A
Other languages
French (fr)
Inventor
Shuntaro Yamazaki
Takeshi Nagahori
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NEC Corp
Original Assignee
NEC Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by NEC Corp filed Critical NEC Corp
Publication of CA2153220A1 publication Critical patent/CA2153220A1/en
Abandoned legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/27Arrangements for networking
    • H04B10/272Star-type networks or tree-type networks
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25Arrangements specific to fibre transmission
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25Arrangements specific to fibre transmission
    • H04B10/2589Bidirectional transmission

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Computing Systems (AREA)
  • Optical Communication System (AREA)
  • Small-Scale Networks (AREA)
  • Light Guides In General And Applications Therefor (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)

Abstract

A fiber-optic access system for subscriber optical communi-cation adopting star type topology in an optical fiber network includes a central office, a plurality of optical network units, an optical interface, and a signal recogni-tion/reproduction and clock extraction IC. The optical interface is provided in the central office and includes an array optical transmission module as a package unit accom-modating a plurality of light sources and a plurality of output fiber terminals, and an array optical reception module as a package unit accommodating a plurality of optical sensors and a plurality of input fiber terminals.
The signal recognition/reproduction and clock extraction IC
is provided to each channel of the array optical reception module. The access system provided is of a scale compara-ble to that of a central office side optical interface of PDS and wide band characteristics comparable to those of a single star type system.

Description

FOR
SUBSCRIBER OPTICAL COMMUNICATION

BACKGROUND OF THE INVENTION
(1) Field of the Invention The present invention relates to a fiber-optic sub-scriber communication system using star type topology for fiber-optic networks, and more particularly to a fiber-optic access system in such a communication system.
(2) Description of the Related Art A fiber-optic subscriber communication system, partic-ularly that for telephone or like low transfer rate serv-ices, has used a passive double star (PDS) type network in order to minimize the cost of fiber-optic networks and optical interfaces in the central office (CO) side. In such a system, as shown in Fig. 1, an optical fiber 84 connected to a single optical interface (IF) 83 in the CO
81 is branched by a passive splitter 85 in the network and connected to a plurality of optical network units (ONUs) 86. Reference numeral 82 in the CO 81 denotes a switcher (SW). An optical interface 87 in each of the ONUs 86 is connected to a plurality of subscriber homes 88. Please refer to "Fiber Optic Subscriber Loop, Special Edition", IEEE Communications Magazine, February 1994, Vol. 32, No.
2. In this scheme, a plurality of ONUs 86 commonly use the 21a3Z20 1 CO-side optical interface 83 and also part of the transmis-sion line 84.
In the system that provides wide band services, the PDS scheme has not been used but a single star type fiber network has been used as shown in Fig. 2, in which the transmission line 94 is laid from the single CO 91 to each of the ONUs 96 on a one-to-one basis. In Fig. 2, the reference numeral 92 denotes a switcher; 93, 97 denote an optical interface; and 98 denotes a subscriber home.
Where the PDS is used, however, a bottle neck problem is encountered if it is intended to accommodate high rate services because of the common use of part of transmission line by all the ONUs. More specifically, in the common part of transmission line, signals between all the ONUs and the CO are multiplexed in their transmission. This means that the transfer rate necessary for the common transmis-sion line part is the multiple of the band required for the ONU by the number of ONUs. For this reason, for accommo-dating high rate services by using PDS, a super-high trans-fer rate has to be set for the optical interface, or resorthas to be had to the provision of new channels by using the wavelength multiplexing technique. With the PDS, however, it is difficult to sufficiently increase the transfer rate because the upstream line (that is, data transfer from the ONU to the CO) is of a multi-access system in the burst -- 21532~

1 mode. In addition, the above methods dictate very high cost.
Accordingly, the single star type scheme as described before is used to accommodate the high rate services. In this case, unlike the PDS, there is no bottle neck problem because there is no common transmission line part to the ONUs. However, on the CO-side, the same number of optical interfaces 93 as the number of ONUs 96 is necessary as shown in Fig. 2. Therefore, the merits of the PDS, i.e., the small scale and low cost of the CO, are lost.

SUMMARY OF THE INVENTION
An object of the invention, therefore, is to overcome the problems existing in the prior art and to provide a new fiber-optic access system for subscriber optical communica-tion, which is of a scale and a cost comparable to those of the CO-side optical interface of the PDS and wide band characteristics comparable to those of the single star type system.
According to one aspect of the invention, there is provided a fiber-optic access system for subscriber optical communication adopting star type topology in an optical fiber network, the fiber-optic access system comprising:
a central office;
a plurality of optical network units which are con-21532~Q

1 nected with the central office by optical fibers;
an optical interface which is provided in the central office and which includes an array optical transmission module as a package unit accommodating a plurality of light sources and a plurality of output fiber terminals, and an array optical reception module as a package unit accommo-dating a plurality of optical sensors and a plurality of input fiber terminals; and a circuit which is provided to each channel of the array optical reception module and which has functions of recognizing and reproducing a data signal transmitted from each of the optical network units to the central office and of extracting a clock signal synchronized with the data signal.
According to a second aspect of the invention, there is provided a fiber-optic access system for subscriber optical communication adopting star type topology in an optical fiber network, the fiber-optic access system com-prising:
a central office;
a plurality of optical network units which are located in homes and connected with the central office by optical fibers;
a plurality of optical interfaces which are provided in the central office and each of which includes an array 215322~

1 optical transmission module as a package unit accommodating a plurality of light sources and a plurality of output fiber terminals and an array optical reception module as a pack-age unit accommodating a plurality of optical sensors and a plurality of input fiber terminals; and a circuit which is provided to each channel of the array optical reception module and which has functions of recognizing and reproducing a data signal transmitted from each of the optical network units to the central office and of extracting a clock signal synchronized with the data signal.
The fiber-optic access system according to the inven-tion achieves the cost saving and band extension. The invention is predicated in the single star type structure which is excellent in the wide band characteristics. The difference of the invention from the prior art resides in the employment of array optical transmission and reception modules for the C0-side optical interface. The array optical transmission and reception modules are unit pack-ages including a plurality of optical transmission andreception circuits, respectively, and a plurality of opti-cal fiber terminals. Thus, they permit a great reduction in scale and cost compared to the case where a plurality of single optical transmission and reception modules are mounted. Thus, with the single star type structure, it is 21S322~

1 possible to realize a cost and an equipment scale which are comparable to those of the CO-side optical interface for the PDS. In another aspect, in the PDS, the signal trans-mitted from the ONU to the CO is in the burst mode, thus imposing a limitation on the transfer rate of the optical interface. Specifically, the upper limit of the transfer rate is about 150 Mb/s. This means that where there are 16 branches of the PDS, for instance, the capacity (transfer rate) of the upstream line allotted to each ONU ti.e.~ line from the ONU to the CO) is lower than 10 Mb/s. In con-trast, according to the invention, there is no such trans-fer rate limitation because the single star type scheme is adopted. However, the upper limit of the band of the array optical reception module is subject to inter-channel cross-talks. Nevertheless, it is possible to realize as hightransfer rate as about 1 Gb/s. Thus, according to the invention, it is possible to provide to the ONU an upstream line having a band which is as wide as several tens to one hundred times compared to the conventional PDS.

The array optical transmission and reception modules have heretofore been developed for the purpose of communi-cation between computers or like data link parallel trans-mission. In these uses, a plurality of parallel data signals are substantially bit-synchronized. Thus, a common clock signal has been used for the individual channels and 1 transmitted in parallel to the above mentioned parallel data signals. However, in the single star type access as used in the invention, the distance between the CO and the ONU greatly varies with each ONU. That is, there is no correlation among the upstream signals from the individual ONUs. Therefore, the CO has to extract a clock signal for each channel, and it has been impossible to use the prior art array optical reception module for data link directly.
According to the invention, a circuit having functions of identifying and reproducing a received data and extracting a clock signal, is provided for each channel of array optical reception module. Thus, it is possible to obtain a proper clock signal for each channel even if the relative position relation of the upstream signals from the individ-ual ONUs is not fixed.

BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantagesof the present invention will be apparent from the follow-ing description of preferred embodiments of the inventionexplained with reference to the accompanying drawings, in which:
Fig. 1 is a structural diagram of an example of a conventional PDS;

Fig. 2 is a structural diagram of an example of a - 21~3%20 1 conventional single star type network;
Fig. 3 is a structural diagram of a fiber-optic access system of a first embodiment according to the invention;
Fig. 4 is a diagram of an internal structure of an array optical reception module in the fiber-optic access system according to the invention;
Fig. 5 is a diagram of an internal structure of an array optical transmission module in the fiber-optic access system according to the invention;
Fig. 6 is a structural diagram of a fiber-optic access system of a second embodiment according to the invention;
Fig. 7 is a structural diagram of a fiber-optic access system of a third embodiment according to the invention;
and Fig. 8 is a diagram of a modified fiber-optic access system according to the invention.

PREFERRED EMBODIMENTS OF THE INVENTION
Now, preferred embodiments of the invention are ex-plained with reference to the accompanying drawings.
A first embodiment of the invention will now be de-scribed. In this embodiment, the feature of a first aspect of the invention is applied to an FTTC (fiber to the curb) type fiber-optic access system. The structure of the embodiment is shown in Fig. 3. In a central office (CO) 1, 215322~

l there are provided a switcher (SW) 2, an array optical transmission module (Tx) 3 and an array optical reception module (Rx) 4. The array optical transmission module 3 and the array optical reception module 4 constitute a CO-side optical interface 30. In the network system, sixteen ONUs 5 through 20 are connected. The CO-side optical interface 30 is connected to the sixteen ONUs 5 to 20 through a plurality of optical fibers 22. In each ONU, an optical reception module (Rx) 23 and an optical transmission module (Tx) 24 are provided. Each ONU includes a subscriber line interface (IF) 25, from which coaxial cables 77 extend to twenty four subscriber homes 21. Thus, 4 channels of 6 Mb/s video signal and 64 kb/s telephone service can be provided to each subscriber home 21. The data transfer rate between the CO 1 and each of the ONUs 5 through 20 is 600 Mb/s in a downstream direction for video and telephone service data for 24 homes and 1.5 Mb/s in an upstream direction for telephone service data.
The array optical reception module (Rx) 4 has an internal structure as shown in Fig. 4. A first 16-core fiber ribbon 26 has an end face secured at a position near a 16-channel array optical sensor 27. Thus, light emitted from each fiber of the fiber ribbon 26 is incident on each light-receiving portion of the array optical sensor 27.
The array optical sensor 27 has each of its signal elec-1 trodes connected to each input terminal of a 16-channel array pre-amplifier IC 28. The array pre-amplifier IC 28 has each output terminal connected to each input terminal of a 16-channel IC 29 which has functions of identifica-tion, reproduction, and clock signal extraction. From theoutput terminals 71 of the IC 29, there appear 16 channel data signals of 1.5 Mb/s transmitted from the individual ONUs and 16 channel clock signals synchronized to the respective data signals. The data signal is phase matched for each channel by using the extracted clock signal before being inputted to the switcher 2 (see Fig. 3).
The array optical transmission module (Tx) 3 has an internal structure as shown in Fig. 5. As shown therein, the optical transmission module 3 comprises a 16-channel array semiconductor laser 31, a second 16-core fiber ribbon 32, and an array laser driver IC 33. Thus, 16 channel downstream signals applied to the input terminals 72 of the driver IC 33 can be transmitted with a single module. With the structures as described above, it is possible to reduce the scale of the C0-side optical interface and realize an FTTC (fiber to the curb) access system which can provide wide band services.
A second embodiment will now be described. In the second embodiment, the feature of the first aspect of the invention is applied to an FTTH (fiber to the home) access 1 system. The structure of this embodiment is shown in Fig.
6. In a central office (C03 41, there are provided a switcher (SW) 42, twenty four array optical transmission modules 3, and twenty four array optical reception modules 4. To each array optical transmission module 3 and each array reception module 4 are connected to sixteen ONUs 43 to 58 in the subscriber homes via optical fibers 22.
Though not shown in the drawings, in each ONU, an optical reception module and an optical transmission module are provided. There are 4 channels of 6 Mb/s video signal and 1.5 Mb/s ISDN primary rate service that are provided to each home. The data transfer rate is thus 25.5 Mb/s in a downstream direction for video signal and ISDN primary rate service data, and 1.5 Mb/s in an upstream direction for ISDN primary rate service data.
The array optical reception module 3 and the array optical transmission module 4 have the same internal struc-tures as in the prece~;ng first embodiment, so they are not described any further here. The sole difference of this embodiment is that the data transfer rate is 25.5 Mb/s in a downstream direction as noted above, which is lower than in the first embodiment. When realizing an FTTH access system with the prior art single star structure, the same number of optical interfaces as the number of subscribers was necessary on the CO-side. According to the invention as 21532~

1 applied to this embodiment, the number of optical inter-faces can be reduced down to one-sixteenth.
A third embodiment of the invention will now be de-scribed. In this embodiment, the feature of a second aspect of the invention is applied to an FTTC (fiber to the curb) access system. The structure of this embodiment is shown in Fig. 7. Specifically, in this embodiment, a plurality of optical fibers 75 are used for transmission lines between the ONUs 5 to 20 and the homes 21 in the first embodiment. A subscriber-line interface 25 in each ONU (5 to 20) includes a 24-channel array optical reception module (Rx) 61 and a 24-channel array optical transmission module (Tx) 62. These modules are the same in structure as the previous array optical reception and transmission modules 4 and 3, and are different only in the number of channels and the data transfer rate. The data transfer rate is the same as that on the coaxial cable in the first embodiment, that is, 24 Mb/s in a downstream direction and 64 kb/s in an upstream direction. A feature of this embod-iment is that it is possible to increase distance coveredbecause of the use of optical fibers from each ONU to each subscriber home, thus increasing the freedom of the network design. The remainder is the same as the first embodiment, and is not described.

As has been described in the foregoing, it is possible 21S322~

1 to provide a fiber-optic access system, which can realize both the wide band characteristics and the reduction of the scale and cost of the C0-side interface. However, the invention is not limited to the three embodiments described above as, for example, the following modification is con-ceivable.
Where a central office (C0) accommodates a number of PDS systems in a PDS fiber-optic access system, a plurality of optical interfaces are necessary on the C0-side. By applying the invention, it is possible to realize small scale C0 system as in the above embodiments. However, as described before, in the PDS, the upstream line is a burst mode multi-access system. That is, the C0 side array optical reception module 4 deals with burst signal, and at the same time a multi-access control circuit is provided for each channel. The multi-access control circuit is large in scale, and sometimes it may be thought difficult to collectively mount this control circuit in the array optical reception module. In such a case, the control circuit is provided in the neighborhood of the module.
The PDS is an effective means for realizing cost reduction of telephone and other low rate services. Howev-er, where subscribers requiring high rate services such as business building coexist in a service area, it is desira-ble to use both PDS and single star in the same network.

215~220 1 In this case, CO side optical interfaces according to theinvention and CO side optical interfaces of PDSs coexist.
While, in the above embodiments, bi-directional trans-mission system based on 2-core optical fiber is used be-tween the CO and the ONU, it is possible to apply theinvention to a single-core bi-directional transmission system aiming at cost reduction. In such a case, it is possible to adopt a wavelength multiplexing technique for an upstream and a downstream, or adopt a time compression multiplexing (TCM) transmission system. Where the wave-length multiplexing system is adopted, as shown in Fig. 8, wavelength multiplexing separation couplers are connected to the individual channel fibers of the array optical transmission and reception modules 3 and 4. In this exam-ple, the downstream signal is at a wavelength of 1.5 ~m,and the upstream signal is at a wavelength of 1.3 ~m. In the case of the TCM communication system, directional couplers are used in lieu of the wavelength multiplexing separation couplers shown in Fig. 8. In this case, it is also necessary to provide each of the array optical trans-mission and reception modules 3 and 4 with a compression circuit for TCM transmission system.
While the invention has been described in its pre-ferred embodiments, it is to be understood that the words which have been used are words of description rather than 21~322Q

1 limitation and that changes within the purview of the appended claims may be made without departing from the true scope of the invention as defined by the claims.

Claims (5)

1. A fiber-optic access system for subscriber optical communication adopting star type topology in an optical fiber network, said fiber-optic access system comprising:
a central office;
a plurality of optical network units which are con-nected with said central office by optical fibers;
an optical interface which is provided in said central office and which includes an array optical transmission module as a package unit accommodating a plurality of light sources and a plurality of output fiber terminals, and an array optical reception module as a package unit accommo-dating a plurality of optical sensors and a plurality of input fiber terminals; and a circuit which is provided to each channel of said array optical reception module and which has functions of recognizing and reproducing a data signal transmitted from each of said optical network units to said central office and of extracting a clock signal synchronized with said data signal.
2. A fiber-optic access system according to claim 1, in which, for communication between said optical network units and homes, said fiber-optic access system further comprises a plurality of subscriber-line optical interfaces which are provided in said optical network units and each of which includes an array optical transmission module and an array optical reception module having configurations that are the same as those of said array optical transmission module and said optical reception module in said central office.
3. The fiber-optic access system according to claim 1, in which said array optical reception module comprises a core fiber ribbon, an array optical sensor, an array pre-amplifier IC, and a signal recognition/reproduction and clock extraction IC, which are coupled in series.
4. The fiber-optic access system according to claim 1, in which said array optical transmission module comprises a core fiber ribbon 32, an array semiconductor laser, and an array laser driver IC, which are couples in series.
5. A fiber-optic access system for subscriber optical communication adopting star type topology in an optical fiber network, said fiber-optic access system comprising:
a central office;
a plurality of optical network units which are located in homes and connected with said central office by optical fibers;
a plurality of optical interfaces which are provided in said central office and each of which includes an array optical transmission module as a package unit accommodating a plurality of light sources and a plurality of output fiber terminals and an array optical reception module as a pack-age unit accommodating a plurality of optical sensors and a plurality of input fiber terminals; and a circuit which is provided to each channel of said array optical reception module and which has functions of recognizing and reproducing a data signal transmitted from each of said optical network units to said central office and of extracting a clock signal synchronized with said data signal.
CA002153220A 1994-07-05 1995-07-04 Fiber-optic access system for subscriber optical communication Abandoned CA2153220A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP6153196A JPH0818513A (en) 1994-07-05 1994-07-05 Optical access system
JP153196/1994 1994-07-05

Publications (1)

Publication Number Publication Date
CA2153220A1 true CA2153220A1 (en) 1996-01-06

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ID=15557148

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Country Status (6)

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US (1) US5872644A (en)
EP (1) EP0691761A3 (en)
JP (1) JPH0818513A (en)
KR (1) KR0170005B1 (en)
AU (1) AU2481395A (en)
CA (1) CA2153220A1 (en)

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Also Published As

Publication number Publication date
EP0691761A2 (en) 1996-01-10
EP0691761A3 (en) 1998-04-15
KR960003566A (en) 1996-02-23
KR0170005B1 (en) 1999-03-30
AU2481395A (en) 1996-01-18
JPH0818513A (en) 1996-01-19
US5872644A (en) 1999-02-16

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