U.S. patent application number 09/152798 was filed with the patent office on 2002-07-18 for optical fiber subscriber network.
Invention is credited to CHOE, WON-HA, KIM, JIN-HAN, LEE, SOONG-HEE.
Application Number | 20020093709 09/152798 |
Document ID | / |
Family ID | 19521212 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020093709 |
Kind Code |
A1 |
KIM, JIN-HAN ; et
al. |
July 18, 2002 |
OPTICAL FIBER SUBSCRIBER NETWORK
Abstract
A wavelength division multiplexed optical fiber subscriber
network capable of expanding the number of the subscribers. In the
optical fiber subscriber network, a central office allocates a
unique combination of optical wavelengths to a subscriber upon
receipt of a service request signal from the subscriber, a
wavelength division multiplexing service requested information
together with the combined optical wavelength, and transmits the
wavelength division multiplexed optical wavelength through an
optical fiber. A plurality of optical subscriber devices optically
distributes, filters and combines the wavelength division
multiplexed optical signals received through the optical fiber to
select optical wavelengths allocated thereto and outputs the
selected optical wavelengths to corresponding subscriber
terminals.
Inventors: |
KIM, JIN-HAN; (KUMI-SHI,
KR) ; CHOE, WON-HA; (KIMHAE-SHI, KR) ; LEE,
SOONG-HEE; (KIMHAE-SHI, KR) |
Correspondence
Address: |
ROBERT F. BUSHNELL
ATTORNEY-AT-LAW
1522 K STREET, N.W.
SUITE 300
WAHINGTON
DC
200051202
|
Family ID: |
19521212 |
Appl. No.: |
09/152798 |
Filed: |
September 14, 1998 |
Current U.S.
Class: |
398/79 ;
398/167.5 |
Current CPC
Class: |
H04J 14/0227 20130101;
H04J 14/0282 20130101; H04Q 11/0067 20130101; H04Q 2011/0086
20130101; H04Q 2011/0064 20130101; H04J 14/025 20130101; H04Q
11/0062 20130101; H04J 14/0246 20130101; H04B 10/272 20130101 |
Class at
Publication: |
359/125 ;
359/167 |
International
Class: |
H04J 014/02; H04B
010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 1997 |
KR |
1997-47032 |
Claims
What is claimed is:
1. An optical fiber subscriber network, comprising: a central
office for allocating a combination of optical wavelengths to a
subscriber upon receipt of a service request signal from said
subscriber, a wavelength division multiplexing service requested
information together with a combined optical wavelength, and for
transmitting wavelength division multiplexed optical signals
through an optical fiber; and a plurality of optical subscriber
devices for optically distributing, filtering and combining said
wavelength division multiplexed optical signals received through
the optical fiber to select optical wavelengths allocated thereto
and outputting the selected optical wavelengths to corresponding
subscriber terminals.
2. The optical fiber subscriber network of claim 1, wherein said
central office comprises: an exchange for allocating a combination
of the optical wavelengths to a subscriber upon receipt of the
service request signal from said subscriber; a plurality of optical
transmitters for converting electric signals output from said
exchange to optical signals of unique wavelengths; a wavelength
division multiplexer for multiplexing the optical signals output
from said optical transmitters and transmitting the wavelength
division multiplexed optical signals to the optical fiber; and an
optical amplifier for amplifying the wavelength division
multiplexed optical signals to compensate for transmission loss for
transmission to the subscriber through the optical fiber.
3. The optical fiber subscriber device of claim 1, wherein said
optical subscriber device comprises: an optical distributor for
distributing the wavelength division multiplexed optical signals
received through an incoming optical fiber to internal optical
fibers; a fixed optical filter for filtering a wavelength group
allocated from the wavelength division multiplexed optical signals
to receive an optical wavelength group pre-allocated in said
central office; an optical receiver module connected to an output
of said fixed optical filter, for converting the optical signals
output from said fixed optical filter to electric signals; a
concentrator for switching and concentrating an output of said
optical receiver module to multimedia terminals connected to output
ports of said optical subscriber device; and an electronic signal
converter for converting an output of said concentrator so as to
connect the multimedia terminals to said concentrator.
4. The optical fiber subscriber device of claim 1, further
comprising a plurality of optical distributors placed on said
optical fiber intervening between said central office and said
optical subscriber devices, for distributing the wavelength
division multiplexed optical signals output from said central
office according to construction of a service requested
network.
5. The optical fiber subscriber device of claim 4, further
comprising an optical amplifier placed on said optical fiber
intervening between said central office and said optical subscriber
devices, for compensating for distribution loss of the wavelength
division multiplexed optical signals due to said optical
distributors.
6. The optical fiber subscriber device of claim 2, further
comprising a plurality of optical distributors placed on said
optical fiber intervening between said central office and said
optical subscriber devices, for distributing the wavelength
division multiplexed optical signals output from said central
office according to construction of a service requested
network.
7. The optical fiber subscriber device of claim 6, further
comprising an optical amplifier placed on said optical fiber
intervening between said central office and said optical subscriber
devices, for compensating for distribution loss of the wavelength
division multiplexed optical signals due to said optical
distributors.
8 An optical fiber subscriber network, comprising: a central office
for allocating a combination of optical wavelengths to a subscriber
upon receipt of a service request signal from said subscriber, and
for transmitting the wavelength division multiplexed optical
wavelength through an optical fiber, said central office
comprising: an exchange for allocating the combination of the
optical wavelengths to said subscriber upon receipt of the service
request signal from said subscriber; a plurality of optical
transmitters for converting electric signals output from said
exchange to optical signals of unique wavelengths; a wavelength
division multiplexer for multiplexing the optical signals output
from said optical transmitters and transmitting the wavelength
division multiplexed optical signals through the optical fiber; and
an optical amplifier for amplifying the wavelength division
multiplexed optical signals to compensate for transmission loss for
transmission to the subscriber through the optical fiber; and a
plurality of optical subscriber devices for optically distributing,
filtering and combining the wavelength division multiplexed optical
signals received through the optical fiber to select optical
wavelengths allocated thereto and outputting the selected optical
wavelengths to corresponding subscriber terminals.
9. The optical fiber subscriber device of claim 8, wherein said
optical subscriber device comprises: an optical distributor for
distributing the wavelength division multiplexed optical signals
received through an incoming optical fiber to internal optical
fibers; a fixed optical filter for filtering a wavelength group
allocated from the wavelength division multiplexed optical signals
to receive an optical wavelength group pre-allocated in said
central office; an optical receiver module connected to an output
of said fixed optical filter, for converting the optical signals
output from said fixed optical filter to electric signals; a
concentrator for switching and concentrating an output of said
optical receiver module to multimedia terminals connected to output
ports of said optical subscriber device; and an electronic signal
converter for converting an output of said concentrator so as to
connect the multimedia terminals to said concentrator.
10. The optical fiber subscriber device of claim 9, further
comprising a plurality of optical distributors placed on said
optical fiber intervening between said central office and said
optical subscriber devices, for distributing the wavelength
division multiplexed optical signals output from said central
office according to construction of a service requested
network.
11. The optical fiber subscriber device of claim 9, further
comprising an optical amplifier placed on said optical fiber
intervening between said central office and said optical subscriber
devices, for compensating for distribution loss of the wavelength
division multiplexed optical signals due to said optical
distributors.
12. The optical fiber subscriber device of claim 9, further
comprising a plurality of optical distributors placed on said
optical fiber intervening between said central office and said
optical subscriber devices, for distributing the wavelength
division multiplexed optical signals output from said central
office according to construction of a service requested
network.
13. The optical fiber subscriber device of claim 9, further
comprising an optical amplifier placed on said optical fiber
intervening between said central office and said optical subscriber
devices, for compensating for distribution loss of the wavelength
division multiplexed optical signals due to said optical
distributors.
Description
CLAIM FOR PRIORITY
[0001] This application makes reference to, incorporates the same
herein, and claims all benefits accruing under 35 U.S.C. .sctn. 119
from an application for OPTICAL FIBER SUBSCRIBER NETWORK earlier
filed in the Korean Industrial Property Office on the of Sep. 12,
1997, and there duly assigned Serial No. 47032/1997, a copy of
which application is annexed hereto.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to an optical fiber subscriber
network, and in particular, to a wavelength division multiplexed
(WDM) optical fiber subscriber network for serving an expanded
number of subscribers.
[0004] 2. Related Art
[0005] As high speed, high-capacity user communication services
progress along with the development of the information-oriented
society, there have been demands for a wideband communication
network capable of accommodating different types of data including
voice, data, still-image, and live-video/voice multicast
transmissions to a large number of users. One of the fast-growing
constituent of wideband communication networks is an optical fiber
subscriber network which uses optical signals to convey information
across an optical waveguide. Frequently, time-division multiplexing
(TDM) is employed to convey information from plural information
sources on a single channel. However, the transmission capacity is
limited by fiber dispersion and the need to generate high peak
power pulse.
[0006] Wavelength division multiplexing (WDM) has been recently
developed as a cost-effective way to increase the
information-carrying capacity of existing fiber optic network. A
wavelength division multiplexed (WDM) optical fiber subscriber
network employs plural optical signal channels, each channel being
assigned a particular channel wavelength. In a WDM system, signal
channels are generated, multiplexed, transmitted over a single
waveguide, and demultiplexed to individually route each channel
wavelength to a designated receiver. Through the use of optical
amplifiers, such as doped fiber amplifiers, plural optical channels
are directly amplified simultaneously, facilitating the use of WDM
systems in long distance optical systems. Exemplars of wavelength
division multiplexed optical fiber subscriber networks are
disclosed in U.S. Pat. No. 4,901,306 for Wavelength-Division
Multiplexed Optical Fiber Network issued to Gardner, U.S. Pat. No.
5,119,223 for Bidirectional Light Wavelength (LWG)
Telecommunication System And Method For Wavelength Separation Mode
(Bidirectional Wavelength Separation Mode) Between A Central
Telecommunication Location And Plurality Of Decentralized
Telecommunication Locations issued to Panzer et al., U.S. Pat. No.
5,351,146 for All-Optical Network Architecture issued to Chan et
al., U.S. Pat. No. 5,457,760 for Wavelength Division Optical
Multiplexing Elements issued to Mizrahi, U.S. Pat. No. 5,510,921
for Optical Frequency Division Multiplexing Network issued to Takai
et al., U.S. Pat. No. 5,550,818 for System For Wavelength Division
Multiplexing/Asynchronous Transfer Mode Switching For Network
Communication issued to Brackett et al., U.S. Pat. No. 5,557,439
for Expandable Wavelength Division Multiplexed Optical
Communication Systems issued to Alexander et al., U.S. Pat. No.
5,587,830 for High Capacity Optical Fiber Network issued to
Chraplyvy et al., and U.S. Pat. No. 5,717,795 for Optical
Wavelength Division Multiplexed Network System issued to Sharma et
al.
[0007] Many conventional optical fiber subscriber networks require
high density wavelength division multiplexing which uses more than
three wavelengths to increase the information-carrying capacity of
existing fiber optic network. Wavelength variable filter or WDM
multiplexer/demultiplexer must be used which requires precise
manufacturing technology. Therefore, in building subscriber
networks, there arise safety and cost problems. In particular,
there is a limitation in expanding the new subscribers or
increasing the communication speed.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is therefore an object of the present
invention to provide an improved wavelength division multiplexed
optical fiber subscriber network.
[0009] It is also an object to provide a cost-effective wavelength
division multiplexed optical fiber subscriber network.
[0010] It is another object to provide a wavelength division
multiplexed optical fiber subscriber network for supporting
expanded number of subscribers with high reliability and
flexibility.
[0011] It is yet another object to provide a wavelength division
multiplexed optical fiber subscriber network for carrying increased
number of subscribers with greater margin of safety and cost
efficiency.
[0012] These and other objects of the present invention can be
achieved by an optical fiber subscriber network including a central
office for allocating a unique combination of optical wavelengths
to a subscriber upon receipt of a service request signal from the
subscriber, wavelength division multiplexed (WDM) service requested
information together with the combined optical wavelength, and
transmitting the WDM optical wavelength through an optical fiber;
and a plurality of optical subscriber devices for optically
distributing, filtering and combining the WDM optical signals
received through the optical fiber to select optical wavelengths
allocated thereto and outputting the selected optical wavelengths
to corresponding subscriber terminals.
[0013] Preferably, the central office includes an exchange for
allocating a combination of the wavelengths to a subscriber upon
receipt of the service request signal from the subscriber; a
plurality of optical transmitters for converting electric signals
output from the exchange to optical signals of unique wavelengths;
a WDM multiplexer for multiplexing the optical signals output from
the optical transmitters and transmitting the multiplexed optical
signals to the optical fiber; and an optical amplifier for
amplifying the output of the WDM multiplexer to compensate for
transmission loss of the multiplexed optical signals being
transmitted to the subscriber through the optical fiber.
[0014] Preferably, the optical subscriber device includes an
optical distributor for distributing the WDM multiplexed optical
signals received through an incoming optical fiber to Q internal
optical fibers; a fixed optical filter for filtering a wavelength
group allocated thereto out of the WDM multiplexed optical signals
to receive an optical wavelength group pre-allocated in the central
office; an optical receiver module connected to an output of the
fixed optical filter, for converting the optical signals output
from the fixed optical filter to electric signals; a concentrator
for switching and concentrating an output of the optical receiver
module to multimedia terminals connected to output ports of the
optical subscriber device; and an electronic signal converter for
converting an output of the concentrator so as to connect the
multimedia terminals to the concentrator.
[0015] In addition, the optical fiber subscriber network includes a
plurality of optical distributors placed on the optical fiber
intervening between the central office and the optical subscriber
devices, for distributing the optical signals output from the
central office according to construction of a service requested
network. The optical fiber subscriber device may include an optical
amplifier placed on the optical fiber intervening between the
central office and the optical subscriber devices, for compensating
for distribution loss of the optical signals due to the optical
distributors.
[0016] The present invention is more specifically described in the
following paragraphs by reference to the drawings attached only by
way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] A more complete appreciation of this invention, and many of
the attendant advantages thereof, will be readily apparent as the
same becomes better understood by reference to the following detail
description when considered in conjunction with the accompanying
drawings, in which like reference symbols indicate the same or
similar elements components, wherein:
[0018] FIG. 1 is a block diagram of a first example of a typical
wavelength division multiplexed (WDM) optical fiber subscriber
network;
[0019] FIG. 2 is a block diagram of a second example of a typical
wavelength division multiplexed (WDM) optical fiber subscriber
network;
[0020] FIG. 3 is a block diagram of a third example of a typical
wavelength division multiplexed (WDM) optical fiber subscriber
network;
[0021] FIG. 4 is a block diagram of a wavelength division
multiplexed (WDM) optical fiber subscriber network constructed
according to a preferred embodiment of the present invention;
[0022] FIG. 5 is a block diagram of an optical subscriber device
(424) installed in the house of the subscriber according to a
preferred embodiment of the present invention; and
[0023] FIG. 6 is a flow chart of a central office for allocating
the services for the respective optical wavelength groups according
to a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Referring now to the drawings and particularly to FIG. 1,
which illustrates a first embodiment of typical wavelength division
multiplexed (WDM) optical fiber subscriber network. As shown in
FIG. 1, the first WDM optical fiber subscriber network includes N
subscriber devices S1-SN each having an optical transmitter 2 and
an optical receiver 4, and a star coupler 6 for star-coupling the
subscriber devices S1-SN. In operation, the optical transmitters 2
in the respective subscriber devices S1-SN output optical signals
of wavelengths .lambda..sub.1-.lambda..sub.N through optical
transmission lines (i.e., optical fibers) connected to the star
coupler 6. The star coupler 6 then couples the received optical
signals and distributes the coupled signals to the optical
transmission lines connected the optical receivers 4 in the
respective subscriber devices S1-SN. Here, the optical receivers 4
each have a wavelength selection filter for selectively passing the
optical signal of a specific wavelength.
[0025] FIG. 2 illustrates a second embodiment of a typical
wavelength division multiplexed (WDM) optical fiber subscriber
network of a PPL-type (Passive Photonic Loop type). The WDM optical
fiber subscriber network combines and distributes N wavelengths by
using WDM multiplexers 102 and 116 and WDM demultiplexers 104 and
114 and then connects the wavelengths to the respective subscriber
devices S1-SN. A central office 100 consists of N optical
transmitters 106 for transmitting the optical signals of the
wavelengths .lambda..sub.1-.lambda..sub.N, the WDM multiplexer 102
for multiplexing (combining) the optical signals output from the
optical transmitters 106 and transmitting the multiplexed optical
signals via an optical transmission line (i.e., optical fiber) 108,
a WDM demultiplexer 104 for demultiplexing the optical signals of
the wavelengths .lambda..sub.1-.lambda..sub.M transmitted upward
from the subscriber side through an optical transmission line 110,
and M optical receivers 112 for receiving the optical signals
distributed (demultiplexed) by the WDM demultiplexer 104. Further,
the subscriber side, consisting of a WDM demultiplexer 114 and a
WDM multiplexer 116 which are shared by N subscriber devices S1-SN,
is connected to the central office 100 via the optical transmission
lines 108 and 110. The WDN demultiplexer 114 at the subscriber side
distributes the optical signals of the wavelengths
.lambda..sub.1-.lambda..sub.N received through the optical
transmission line 108 to the respective subscriber devices S1-SN.
The WDM multiplexer 116 combines (multiplexes) the optical signals
of the wavelengths .lambda..sub.1-.lambda..sub.M transmitted upward
from the subscriber devices S1-SN and transmits the combined
signals to the central office 100 via the optical transmission line
110.
[0026] In downward transmission of the optical signals (from the
central office 100 to the subscriber side), the optical
transmitters 106 of the central office 100 convert the electric
signals output from the electronic circuit 118 to the optical
signals of the wavelengths .lambda..sub.1-.lambda..sub.N, and the
WDM multiplexer 102 combines the optical signals output from the
optical transmitters 106 and transmits the combined optical signals
to the WDM demultiplexer 114 through the downward optical
transmission line 108. The WDM demultiplexer 114 then distributes
the received optical signals of the wavelengths
.lambda..sub.1-.lambda..sub.N to the respective subscriber devices
S1-SN.
[0027] In upward transmission of the optical signals (from the
subscriber side to the central office 100), the subscriber devices
S1-SN transmit the optical signals of the wavelengths
.lambda..sub.1-.lambda..sub.M, and the WDM multiplexer 116 combines
the optical signals output from the subscriber devices S1-SN and
transmits the combined optical signals to the WDM demultiplexer 104
through the upward optical transmission line 110. The WDM
demultiplexer 104 then distributes the optical signals of the
wavelengths .lambda..sub.1-.lambda..sub.M to the optical receivers
112, which convert the received optical signals to the electric
signals and output the converted electric signals to the electronic
circuit 118.
[0028] FIG. 3 illustrates a third embodiment of a typical
wavelength division multiplexed (WDM) optical fiber subscriber
network which uses different wavelengths according to the types of
the distributive services. The respective subscribers use the
different wavelengths for the upward/downward communicative
services, so as to efficiently use the limited number of the
optical wavelengths.
[0029] In operation, the downward signals (transmitted from the
base station 100 to the subscriber side) are used for both the
distributive service (e.g., CATV (Cable TV)) and the communicative
service (e.g., B-ISDN (Broadband-Integrated Services Digital
Network)), whereas the upward signals (transmitted from the
subscriber side to the central office 100) are used for the
communicative service only. The downward distributive service
branches (divides) the downward signals into N signals using a
single wavelength .lambda..sub.0 and transmits the branched signals
through N optical transmission lines. The downward communicative
service (B-ISDN) allocates N unique wavelengths to the respective
subscriber devices, and the upward communicative service (B-ISDN)
also allocates the unique wavelengths to the respective subscriber
devices. Therefore, it is necessary to secure (2N+1) wavelengths in
order to accommodate N subscribers.
[0030] Specifically, the downward distributive service transmits
the downward signal for a subscriber device S1 through an optical
fiber 331 using the wavelength .lambda..sub.0, and the downward
communicative service transmits the downward signal through an
optical fiber 332 using the wavelength .lambda..sub.1. The
wavelength .lambda..sub.1 output from a WDM
multiplexer/demultiplexer 312 is combined with the wavelength
.lambda..sub.0 received through the optical fiber 331 in a WDM
multiplexer/demultiplexer 311, and the combined wavelength
.lambda..sub.0.lambda..sub.1 is transmitted to the subscriber
device S1 through an optical fiber 341. The combined wavelength is
demultiplexed into the wavelengths .lambda..sub.0 and
.lambda..sub.1 by a WDM multiplexer/demultiplexer 321 in the
subscriber device S1. Subsequently, the wavelength .lambda..sub.0
is converted to an electric signal in an optoelectric converter 322
and transmitted to a TV set, and the wavelength .lambda..sub.1 is
converted to an electric signal in an optoelectric converter 323
and transmitted to a B-ISDN terminal.
[0031] On the other hand, in the upward service, an optoelectric
converter 324 converts the electric signal from the B-ISDN terminal
to an optical signal, and the WDM multiplexer/demultiplexer 321
upward transits the converted optical signal through the optical
fiber 341. The signal on the optical fiber 341 is transmitted to an
optical fiber 334 through the WDM multiplexer/demultiplexer 311 and
then, transmitted to the central office through the WDM
multiplexer/demultiplexer 312 and an optical fiber 333. In the same
manner, the other subscriber devices S2-SN in the subscriber side
320 use two unique wavelengths.
[0032] Since the optical fiber subscriber networks as described in
FIGS. 1 to 3 employ the high density wavelength division
multiplexing which uses more than three wavelengths, the wavelength
variable filter or the WDM multiplexer/demultiplexer which requires
precise manufacturing technology must be used. Therefore, in
building many subscriber networks, there arise the safety and cost
problems. In addition, there is a limitation in expanding the new
subscribers or increasing the communication speed.
[0033] Turning now to FIG. 4 which illustrates an improved and
cost-effective wavelength division multiplexed (WDM) optical fiber
subscriber network constructed according to a preferred embodiment
of the present invention. As shown in FIG. 4, the optical fiber
subscriber network consists of a central office 410, a subscriber
side 420 including P subscribers S1-SP, and an upward/downward
optical fiber cable 440 serving as an optical communication path
for transmitting data between the central office 410 and the
subscriber side 420. Here, the upward/downward optical fiber cable
440 has distributers 422 and 430 disposed sporadically thereon.
[0034] The central office 410 includes an ATM (Asynchronous
Transfer Mode) exchange 412 which is commonly used for the wideband
communication network, N optical transmitters 414-1 to 141-N for
converting the electric signals output from the ATM exchange 412 to
the optical signals of unique wavelengths, a WDM multiplexer 416
for multiplexing the optical signals output from the optical
transmitters 414 to transmit the multiplexed optical signals
through the optical fiber cable 440, and an optical amplifier 418
for amplifying the output optical signals of the WDM multiplexer
416 to compensate for the loss of the optical signals which may be
caused by the optical fiber cable 440 and the distributors 422 and
430 during transmission of the optical signals to the subscriber
side 420.
[0035] Further, the subscriber side 420 includes P subscribers
S1-SP each having optical subscriber devices for selecting an
optical wavelength group pre-allocated to the subscriber and
outputting the selected optical wavelength group to a corresponding
terminal. The detailed construction of the optical subscriber
device 424 for the first subscriber S1 is illustrated in FIG. 5, by
way of example. FIG. 5 shows the optical subscriber device
installed in the house of the respective subscribers S1-SP
according to a preferred embodiment of the present invention.
Referring to FIG. 5, an optical distributor 502 distributes the WDM
multiplexed optical signal received from the central office 410 via
an incoming optical fiber 444-1 to Q optical fibers 512-1 to 512-Q.
A fixed optical filter 54 consists of Q fixed optical filtering
elements and each of the fixed optical filtering element filters
corresponding wavelength group out of the N WDM multiplexed optical
signals. An optical receiver module 506, disposed at the rear stage
of the fixed optical filter 504, converts the received optical
signals to the electric signals. A concentrator 508 switches or
concentrates the output of the optical receiver module 506 to the
multimedia terminals (e.g., a TV set, a telephone or facsimile, a
video conference device, and a computer or work station) connected
to output ports of the optical subscriber device 424. An electronic
signal converter 510 converts an output of the concentrator 508 to
be suitable for the multimedia terminals. In the embodiment, an ATM
exchange or a packet exchange is used for the concentrator 508.
Further, the electronic signal converter 510 uses a network
connector for connecting the computer or the work station, a CODEC
(Coder-DECoder) for connecting the TV set and the video conference
device, or a PBX (Private Branch Exchange) for connecting the
telephone or the facsimile.
[0036] In operation, the exchange 412 of the central office 410
constantly checks whether a connection request signal is received
from a certain subscriber and whether there is an extra bandwidth
to allocate to the corresponding subscriber. If there is the extra
bandwidth, the exchange 412 notifies an internal service control
layer that it is possible to accommodate the required service, and
then updates a service allocation table. When it is determined to
accommodate the service through a specific wavelength, the exchange
412 enables optical transmission modules of the optical
transmitters 414 to transmit the optical signals. The optical
signals, each having different wavelengths, transmitted from the
optical transmitters 414 are combined by the WDM multiplexer 416
and transmitted through the optical fiber cable 440. In this
situation, it is not necessary that the respective transmission
modules for the respective wavelengths should have the same
information transmission rate. Further, to compensate for the
distribution loss of the optical signals, the central office 410
may have the optical amplifier 418 at the final stage thereof, if
necessary.
[0037] Meanwhile, the WDM multiplexed optical signals output from
the central office 410 are transmitted through the optical cable
440 and branched out properly by the optical distributors 430 and
422 according to the construction of the service requested network.
Moreover, when necessary, the optical cable 440 may have further
distributors, and the portion having the greater distribution loss
may include a separate optical amplifier to compensate for the
distribution loss. The optical signals having reached the
corresponding subscriber through the distributors 430 and 422 are
distributed by the 1XQ optical distributor 502 in the subscriber
device 424 and filtered by the fixed optical filter 504 consisting
of Q optical filtering elements for passing specific wavelengths
functioning as addresses of the physical layer. The filtered Q
optical wavelengths are transmitted to the optical receiver module
506 through Q optical fibers 514-1 to 514-Q, which converts the
received optical signals to the electric signals. The output
signals of the optical receiver module 506 is transferred to the
electronic signal converter 510 via the concentrator 508 which
distributes, concentrates or switches the input signals. The
electronic signal converter 510 converts the received signals to
the signals suitable for the multimedia terminals.
[0038] FIG. 6 shows a flow chart illustrating that the central
office 410 of the optical fiber subscriber network allocates the
services for the respective optical wavelength groups according to
the present invention. In FIG. 6, reference character "j" denotes
an identification number of a group consisting of different
wavelengths and reference character "i" denotes an identification
number of the respective optical wavelengths in the respective
groups.
[0039] Referring to FIG. 6, the exchange 412 (strictly speaking, a
controller of the exchange 412) monitors the optical wavelength
groups allocated to the respective subscribers from the first group
(j=1) to the last group (j=P) at prescribed periods to check
whether a new service request signal is received (steps 602-608).
Meanwhile, if the service request signal is received from a
specific group at step 604, the exchange 412 detects the remaining
bandwidth of the optical wavelength from the first optical
wavelength (i=1) to the last optical wavelength (i=Q) and
determines whether the detected remaining bandwidth is wider than
or equal to the service requested bandwidth (steps 610-616).
Specifically, the exchange 412 first detects the remaining
bandwidth of the first optical wavelength (i=1) at step 610, and
determines whether the detected remaining bandwidth is wider than
or equal to the service requested bandwidth at step 612. If the
detected remaining bandwidth is narrower than the service requested
bandwidth at step 614, the exchange 412 performs the same operation
for the next optical wavelength (i=i+1). The same operation is
repeated even for the last optical wavelength (i=Q). Although the
remaining bandwidth is detected even for the last optical
wavelength (i=Q), if it is narrower than the service requested
bandwidth, the exchange 412 notifies the upper service control
layer that it is impossible to accommodate the requested service at
step 624, and then returns to step 602.
[0040] However, when the remaining bandwidth for any one of the
optical wavelengths is equal to or wider than the service requested
bandwidth at step 612, the exchange 412 determines the remaining
bandwidth for the optical wavelength at step 618, notifies the
upper service control layer that it is possible to accommodate the
requested service at step 620, and updates a service allocation
table of the optical wavelengths at step 622, and then returns to
step 602.
[0041] In conclusion, when N optical wavelengths are WDM
multiplexed by the WDM multiplexer, the passive optical fiber
subscriber network of the invention has a downward structure
capable of providing connection service to P subscribers (where
P>N). That is, N WDM multiplexed optical signals are transmitted
to the respective subscribers through the multistage optical
distributors 430 and 422. Then, in the subscriber device, the fixed
optical filter 504 passes a combination of Q wavelengths (where
1<Q.ltoreq.N) allocated to the subscriber. Accordingly, it is
possible to increase the number of the connectable subscribers by
allocating the combination of the multiple wavelengths rather than
a specific wavelength to each subscriber. Here, the number of the
connectable subscribers is determined by 1 P = C N Q = N ! Q ! ( N
- Q ) ! N ( 1 )
[0042] where P is the number of the connectable subscribers, N the
number of the optical wavelengths, and Q the number of the
wavelengths allocated to the subscribers as the identification
codes. Here, P has the maximum value when Q=N/2 (where N is a even
number), or Q=(N1)/2 (where N is an odd number).
[0043] For example, when N=16 and Q=4, the optical fiber subscriber
network can accommodate 1280 subscribers (P=1820). Thus, in order
to increase the number of the subscribers, it is needed to increase
the number Q of the wavelength allocated to the respective
subscribers. That is, when 8 wavelengths are allocated to the
respective subscribers (Q=8), the number P of the connectable
subscribers becomes 12870. Further, use of the optical fiber
subscriber network can reduce use of the high-priced devices such
as the wavelength variable optical filter, the
multiplexer/demultiplexer and the wavelength converter.
[0044] Further, when an existing subscriber requires the high speed
communication, it is possible to reallocate the optical wavelength
group so as to allow the subscriber to use the wavelength with
higher transmission rate or additionally allocate the wavelength
group other than the existing wavelength group.
[0045] As described above, the optical fiber subscriber network of
the invention has an increased number of the connectable
subscribers and reduces use of the wavelength variable optical
filter or the WDM multiplexer which requires the precise
manufacturing technology, thereby contributing to the reduction in
the cost of building the optical fiber subscriber network. In
addition, when a certain subscriber requires an increase in the
communication capacity or the communication speed, it is possible
to easily enhance the quality of the services by additionally
allocating the wavelengths or allocating the high-speed
wavelength.
[0046] While there have been illustrated and described what are
considered to be preferred embodiments of the present invention, it
will be understood by those skilled in the art that various changes
and modifications may be made, and equivalents may be substituted
for elements thereof without departing from the true scope of the
present invention. In addition, many modifications may be made to
adapt a particular situation to the teaching of the present
invention without departing from the central scope thereof.
Therefore, it is intended that the present invention not be limited
to the particular embodiment disclosed as the best mode
contemplated for carrying out the present invention, but that the
present invention includes all embodiments falling within the scope
of the appended claims.
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