Title: Wavelength division multiplexed (WDM) ring passive optical network (PON) with route protection for replacement of splitter based passive optical networks
Abstract: A method and apparatus for low cost upgrading on demand of an optical fiber communication system without installing additional optical fiber and minimal installation of optical circuitry at destination and distribution terminals. The upgraded systems comprise an optical data loop of a plurality of destination terminals and a single intermediate terminal.
Patent Number: 6,898,206 Issued on 05/24/2005 to Buabbud, et al.
| Inventors:
|
Buabbud; George H. (South Lake, TX);
Zuhdi; Muneer (Lewisville, TX);
Trick; Ulrich (Bad Soden, DE);
Volk; Thomas (Buseck, DE);
Wawro; Debra D. (Arlington, TX)
|
| Assignee:
|
Advanced Fibre Access Corporation (Petaluma, CA)
|
| Appl. No.:
|
876439 |
| Filed:
|
June 6, 2001 |
| Current U.S. Class: |
370/463; 370/535; 398/59 |
| Intern'l Class: |
H04L 012/66 |
| Field of Search: |
370/463,466,532,535-537
398/58-59,20,167,141-142
714/22
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Ho; Duc
Assistant Examiner: Nguyen; Phuongchau Ba
Attorney, Agent or Firm: Jones Day
Claims
1. In an existing optical network comprising a multiplicity of destination terminals,
an intermediate terminal, and a primary terminal, each of said multiplicity of
destination terminals including an optical interface unit (OIU) having an OIU input
optical connector and an OIU output optical connector and each OIU for extracting
data on lightwaves received at said OIU input optical connector and injecting data
onto lightwaves transmitted from said OIU output optical connector, each of said
destination terminals having a corresponding pair of optical fibers extending to
said intermediate terminal, each of said corresponding pairs of optical fibers
including a first fiber and a second fiber, and each of said OIU connected by said
OIU input optical connector and said OIU output optical connector to each corresponding
first fiber and second fiber, and said intermediate terminal connected to said
primary terminal by at least a primary pair of optical fibers, apparatus for providing
optical data transmission comprising:
a first conversion circuit located in said intermediate terminal having a first
conversion input optical connector and a first conversion output optical connector,
said first conversion circuit for converting optical data to electrical data and
electrical data to optical data, said first conversion circuit further including
electrical connections;
a transmission loop comprising said multiplicity of destination terminals and
said corresponding pairs of optical fibers wherein;
at each of said multiplicity of destination terminals, said first fiber of said
corresponding pair of optical fibers connected to said OIU output optical connector,
and said second fiber of said corresponding pair of optical fibers connected to
said OIU input optical connector; and
at said intermediate terminal said first fibers of said corresponding pairs of
optical fibers connected to said second fibers of other of said corresponding pairs
of optical fibers, except said first optical fiber of one of said corresponding
pairs of optical fibers is connected to said first conversion input optical connector
and said second optical fiber of another one of said corresponding pairs of optical
fibers is connected to said first conversion output optical connector; and
a second conversion circuit located in said intermediate terminal for converting
optical data to electrical data and electrical data to optical data and electrically
connected to said electrical connections of said first conversion circuit, said
second conversion circuit also optically connected to said primary pair of optical
fibers extending between said intermediate terminal and said primary terminal.
2. In an existing optical network comprising a multiplicity of destination terminals,
each of said destination terminal having a corresponding pair of optical fibers,
each corresponding pair of optical fibers having a first fiber and a second fiber,
and each of said destination terminals connected to an intermediate terminal by
its corresponding pair of optical fibers, and said intermediate terminal connected
to a primary terminal by at least a pair of primary optical fibers, apparatus for
providing upgraded optical data transmission comprising:
a first conversion circuit located in said intermediate terminal having a first
conversion output optical connector and a first conversion input optical connector
for connecting optical fibers to optically transmit and receive bidirectional data
between said intermediate terminal and said multiplicity of destination terminals,
said first conversion circuit for converting optical data to electrical data and
electrical data to optical data, said first optical conversion circuit further
including electrical connections;
a first optical interface unit (OIU) and a last OIU, said first and last OIUs
located in a first destination terminal and a last destination terminal, respectively,
said first and last destination terminals included in said multiplicity of destination
terminals, each of said first and last OIUs; including an input optical connector
and an output optical connector, said first and last OIUs for extracting and inserting
data on lightwaves traveling over optical fibers, and said lightwaves being received
at said input optical connectors and transmitted from said output connectors of
said first and last OIUs, wherein:
said first fiber of said corresponding pair of optical fibers of said first destination
terminal is connected to said first conversion output optical connector of said
first conversion circuit, and said second fiber of said corresponding pair of optical
fibers of said last destination terminal connected to said first conversion input
optical connector of said first conversion circuit, the second fiber of said corresponding
pair of optical fibers of said first destination terminal and the first fiber of
said corresponding pair of optical fibers of said last destination terminal connected
so as to form a series optical loop extending between said first conversion output
optical connector of said first conversion circuit and at least through said first
and last destination terminals and back to said first conversion input optical
connector of said first conversion circuit; and
a second conversion circuit located in said intermediate terminal for converting
optical data to electrical data and electrical data to optical data, and electrically
connected to said first conversion circuit, said second conversion circuit also
optically connected to said pair of primary optical fibers extending between said
intermediate terminal and said primary terminal.
3. The apparatus of claim 2 wherein said second fiber or said corresponding pair
of optical fibers of said first destination terminal and said first fiber of said
corresponding pair of optical fibers of said last destination terminal are connected
directly to each other.
4. The apparatus of claim 2 wherein said optical interface unit is a broadband
optical interface unit.
5. An apparatus for facilitating optical communication between a first terminal
and a first remote optical interface unit (OIU) and a second remote OIU, each remote
OIU having an OIU optical input and an OIU optical output, the first and second
remote OIUs associated with a first pair and a second pair of optical fibers, respectively,
each pair of optical fibers comprising a first fiber and a second fiber, the apparatus comprising:
an optical communication unit located within the first terminal and having an
optical communication unit input and an optical communication output, wherein:
the OIU optical input of first remote OIU is connected to the optical communication
output of the optical communication unit by the first fiber of the first pair of
optical fibers;
the OIU optical output of the second remote OIU is connected to the optical communication
input of the optical communication unit by the second fiber of the second pair
of optical fibers;
the OIU optical output of first remote OIU is connected to the second fiber of
the first pair of optical fibers;
the OIU optical input of second remote OIU is connected to the first fiber of
the second pair of optical fibers; and
the second fiber of the first pair of optical fibers and the first fiber of the
second pair of optical fibers define an optical communication loop separate from
the optical communication unit;
wherein the optical communication loop is defined by the second fiber of the
first pair of optical fibers and the first fiber of the second pair of optical
fibers by directly connecting the second fiber of the first pair of optical fibers
to first fiber of the second pair of optical fibers.
6. The apparatus of claim 5, wherein the optical communication loop is defined
by the second fiber of the first pair of optical fibers and the first fiber of
the second pair of optical fibers by intermediate OIUs each having an OIU optical
input and an OIU optical output and each intermediate OIU having a corresponding
pair of optical fibers comprising a first fiber and a second fiber.
7. The apparatus of claim 5, wherein the first and second OIUs are broadband OIUs.
8. The apparatus of claim 5, further comprising at least one optical bypass switch
associated with one of the first or second remote OIUs and connected across the
corresponding first or second pair of optical fibers.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatus associated with broadband
communications using optical fibers as the transmission media, and more specifically
to methods and apparatus for on-demand upgrading of an existing optical network
system with the capacity to service additional subscribers with broadband digital
service with no installation of additional optical fibers and minimal replacement
of existing infrastructure.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97
and 1.98
The telecommunications industry is using more and more optical or light fibers
in lieu of copper wire. Optical fibers have an extremely high bandwidth thereby
allowing the transmission of significantly more information than can be carried
by a copper wire. The carried information includes broadband digital data carrying
digital television signals, computer data, etc.
Of course, modern telephone systems require bidirectional communications where
each station on a communication channel can both transmit and receive. This is
true, of course, whether the system uses electrical wiring or optical fibers as
the transmission medium, and whether the information is simple analog voice or
broadband digital signals. Early telephone communication systems solved this need
by simply providing separate copper wires for carrying the communications in each
direction. Some early attempts at using optical fibers as a transmission medium
followed this example and also used two different optical fibers such as optical
fibers
10 and
10A in the prior art FIG. 1 for carrying the communications
in each direction. As shown, in the prior art FIG. 1, fiber
10 is connected
by an optical coupler
12 to an LED (light-emitting diode)
14 at one
end and by optical coupler
16 to a PD (photodetection diode)
18 at
the other end. Similarly, but in reverse, fiber
10A is connected by an optical
coupler
16A to PD
18 at one end and by optical coupler
12A
to LED
14 at the other end.
However, because of the extremely high bandwidths capable of being transmitted
by an optical fiber, a single fiber is quite capable of carrying communications
in both directions. One technique is WDM (wavelength divisional multiplexing) which
is shown in the prior art FIG.
2 and uses different wavelengths for each
direction of travel. Components in FIG.
2 and subsequent figures which operate
the same as shown in FIG. 1 carry the same reference numbers. In the embodiment
shown in FIG. 2, a central office
20 is connected to an immediate or RT
(remote terminal)
22 by at least one pair of optical fibers
10B.
The remote terminal
22 may be further connected to a multiplicity of destination
terminals by other pairs of optical fibers. As shown, the central office includes
a light-emitting diode
14 optically connected to fiber optics
10
by optical coupler
12 for converting electrical signals to optical signals
and a photodetection diode
18A optically connected to optical fiber
10A
by a coupler
16A for converting optical signals to electrical signals. The
fiber optics
10 and fiber optics
10A are each connected to a wavelength
division multiplexer
24 which in turn is connected by optical coupler
26
to optical fiber
10B. This arrangement is duplicated at the RDT
22
by light-emitting diode
14A, photodetection diode
18, and wavelength
division multiplexer
24A. It will, of course, be appreciated that although
the figure is shown as providing communications between a central office
20
(station
1) and a remote terminal office
22 (station
2) prior
to being further distributed to a multiplicity of destinations, the communications
system could be used for providing communications between any two types of stations,
examples include communication between two central offices, two remote terminal
offices, or between a remote office and an individual user's location, etc. A typical
communications system using an LED (light-emitting diode) and a PD (photodiode)
with a single optical fiber is disclosed in U.S. Pat. No. 5,075,791 entitled "Method
and Apparatus for Achieving Two-Way Long-Range Communication Over an Optical Fiber",
issued to Mark W. Hastings, and incorporated in its entirety hereby by reference.
Yet another technique for using a single optical fiber
10 for telephone
systems is illustrated in the prior art FIG.
3. The illustrated figure is
referred to as TCM (time compression multiplexing). The system operates at a single
frequency and uses a single optical fiber
10 and a single diode
30
and
30A at each end connected by optical couplers
32 and
32A,
respectively, for both converting electrical signals to optical signals and for
receiving optical signals and converting those optical signals to electrical signals.
TCM systems have the obvious advantage of requiring fewer components.
Still other and more advanced systems carry telephony communication (either
analog or digital) at one wavelength of light and television signals (digital and/or
analog) at another wavelength.
However, as mentioned above, optical fibers have extremely high bandwidths
and use of an optical fiber for any of the above-mentioned existing systems is
a very ineffective use of the fiber and, in fact, the available bandwidth of an
optical fiber makes it possible to use both active and passive optical transmission
techniques which can be used to carry a significantly-increased number of individual
bidirectional broadband communication channels or signals.
Of course, where early types of optical transmission systems have been installed,
it is desirable to limit the time the operation of such systems is disrupted. Further,
once an early type fiber-optic telephone system is installed, wholesale removal
and replacement with a new system would normally be prohibitive from a cost point
of view. Therefore, it would be advantageous to be able to upgrade on a demand
basis an existing fiber-optic system to also carry a significantly increased number
of broadband communication channels.
SUMMARY OF THE INVENTION
It is an object of this invention to provide methods and apparatus for upgrading
an optical communication transmission system so that it can carry a significantly-increased
number of broadband bidirectional channels.
It is another object of the invention to provide a method and apparatus to upgrade
an existing optical communication transmission system without extensive installation
of new optical fibers.
It is still another object of the invention to provide methods and apparatus
to
upgrade a communication transmission system with minimal addition of new components.
It is yet another object of the invention to allow upgrading of a optical fiber
communication transmission system to occur on an on-demand-basis.
The present invention accomplishes these and other objects in an existing optical
fiber communication system which carries information between a multiplicity of
destination terminals through a second location such as a remote or intermediate
terminal to a primary terminal such as a central office. The optical fiber communication
system includes a multiplicity of optical fiber pairs each of which has one end
which terminates one each at the multiplicity of destination terminals and terminates
at the other end at an intermediate terminal or distribution apparatus. Selected
ones of the multiplicity of destination terminals include an OIU (optical interface
unit) for extracting and injecting data with respect to light waves that are received
at an input of the optical coupler OIU which is connected to one of the fibers
of the pair associated with that terminal. Light waves receiving new data at the
OIU are then connected to the other fiber of the pair by an output optical coupler.
The communication system also includes at least a pair of optical fibers extending
between a primary terminal or location and the intermediate terminal or distribution apparatus.
To upgrade the existing optical network or communication system, an optical combining
device such as a coupler/splitter located in the intermediate terminal includes
a plurality of input optical connectors and an output optical connector. There
is also an optical separating device which may also be a coupler/splitter included
at the intermediate terminal having an input optical connector and a plurality
of output optical connectors. A transmission loop comprising a plurality of the
destination terminals which include an OIU and a like plurality of corresponding
pairs of optical fibers is formed by selectively connecting the fibers of each
pair at the intermediate terminal. To aid understanding of how the transmission
loop is formed, it is worthwhile to arbitrarily designate that the end of a first
fiber of each of the corresponding pair of fibers terminates at the intermediate
terminal with a first optical connector and the end of the second fiber of each
pair terminates at the intermediate terminal with a second optical connector. At
the destination terminal each first fiber of the plurality of pairs are connected
to the output optical connectors of the OIU and the second fiber of each plurality
of pairs are connected to the input optical connectors of the OIU.
At the intermediate or distribution terminal end, each first optical connector
of the first optical fiber of a pair of fibers is connected to the second optical
connector of the second optical fiber of another pair of fibers. This is true for
each of the plurality of pairs terminating at the intermediate terminal except
the first optical coupler of a first fiber of a selected "first" pair is connected
to the input connector of the optical combining device, and the second optical
connector of a second fiber of a "last" pair is connected to the output connector
of the optical splitting device. Lastly, an output optical connector of the combining
or coupler device is connected to a first fiber of a primary pair routed between
the intermediate terminal and a primary terminal and the input connector of the
optical separating or splitting device is connected to the second fiber of the
primary pair.
BRIEF DESCRIPTION OF THE DRAWINGS
Features of the present invention will be more fully disclosed when taken
in conjunction with the following Detailed Description of the Preferred Embodiment(s)
in which like numerals represent like elements and in which:
FIG. 1 is a block diagram of a prior art fiber optical communication system
using two fibers to obtain bidirectional communication;
FIG. 2 is a block diagram of another prior art bidirectional fiber-optic communication
system using a single transmission fiber having a light-emitting diode and a photodetection
diode at each end of the fiber;
FIG. 3 is a block diagram of a prior art fiber optical communication system
using a single fiber and a single transmit/receive diode at each end suitable for TCM;
FIG. 4 is a schematic of a prior art Passive Optical Fiber distribution network
suitable for being upgraded by the teachings of this invention.
FIG. 5 illustrates a first embodiment of the invention for upgrading the optical
network of FIG. 4 to an active optical network with minimal new equipment and without
the installation of additional optical fibers.
FIG. 6 is an enlarged illustration of how the optical loop is formed between
BOIU 66 and 68 and the corresponding pairs of optical fibers 50
and 52.
FIG. 7 illustrates another embodiment of the invention wherein the prior art
passive optical system is upgraded to handle a large number of broadband subscribers
by using 4 wavelengths of light, but continues to operate as a passive optical system.
FIGS. 8A and 8B illustrate how the route protection switches operate so as
to limit the number of customers or subscribers affected in the event of a failure
of an OIU in one of the destination terminals of either of the embodiments shown
in FIGS. 7 and 8.
FIG. 9 illustrates the operation of the Route Protection switches which protect
the system in the event the primary optical fiber failure between the intermediate
terminal and the central office.
FIG. 10 illustrates an upgrade similar to that of FIG. 7 but uses only two wavelengths
of light and an additional pair of optical fibers between the intermediate terminal
and the primary terminal.
DESCRIPTION OF THE INVENTION
Referring now to FIG. 4, there is shown a bidirectional, passive optical
network system. Elements of the system similar to elements discussed with respect
to the prior art system of FIGS. 1,
2 and
3 carry common reference
numbers. As shown, there is provided an intermediate distribution terminal
22
which is connected to optical communication equipment
40 at central office
20 by at least one primary pair of optical fibers
42, and preferably
by two primary pairs of optical fibers
42 and
44. It is not uncommon
for a spare pair of optical fibers to extend between an intermediate distribution
terminal and a central office. Intermediate distribution terminal
22 is
shown as including an optical splitter device
46 connected to one of the
optical fibers
42a of fiber pair
42 and an optical combining
device
48 connected to the other fiber
42b of fiber pair
42.
It should also be noted that, although the pair of fibers
42 are illustrated
in the figure with the two individual fibers
42a and
42b
traveling together in a common sheath, such an arrangement, although common,
is not necessary. The two individual fibers could be completely separate and independent
of each other. All that is necessary is that the two separate fibers start and
end at the same location. As indicated in FIG. 4, optical splitter device
46
and optical combining device
48 may typically be devices having a ratio
of 32:1. That is, the devices either receive light from or transmit light to thirty-two
optical fibers, and this received or transmitted light is carried by a single fiber
after either being split or combined, whichever is appropriate. For example, splitter
46 receives light carrying information from fiber
42a of fiber
pair
42 and splits the light into, for example only, thirty-two portions
which are coupled to one of the fibers of thirty-two different pairs of fibers
such as pairs
50,
52,
54,
56,
58,
60,
62 and
64 between intermediate terminal
22 and thirty-two
destination terminals such as the thirty-two OIUs (optical interface unit),
66,
68,
70,
72,
74,
76,
78 and
80
found in thirty-two destination terminals at thirty-two different locations. Likewise,
combining device
48 located in intermediate terminal
22 receives
light from the thirty-two OIUs on the other fiber of each of the fiber pairs
50
through
64, combines the received light and couples it to the single fiber
42b of fiber pair
42 such that it is transmitted to optical
communication equipment
40 at central office
20. Thus, in the example
shown in FIG. 4, there are thirty-two separate OIUs which may be installed at thirty-two
distinct and separate locations including OIU
66 through
80 which
are connected by one of the fibers of each of the thirty-two pairs of optical fibers
50 through
64 to the optical splitter device
46 in intermediate
terminal
22. The thirty-two OIUs are also connected by the other fiber of
each pair to the optical combining or coupler unit
48 which is also located
in intermediate terminal
22. It will appreciated that the thirty-two OIUs,
the thirty-two pairs of corresponding optical fibers and the 32:1 splitter unit
46 and 32:1 combining unit
48 represents a typical prior art passive
optical network system. Also, as was discussed above with respect to individual
fibers
42a and
42b which make up pair
42, it
is not necessary that the individual fibers of the pairs
50 through
64
or any other pair of optical fibers discussed herein, run side by side in a common
sheath. It is only necessary that the individual fibers in a pair start and terminate
at the same locations. Other prior art systems may use equipment which supports
a number of destination terminals and corresponding pairs of optical fibers which
is different than thirty-two.
Referring now to FIG. 5, there is shown a first embodiment wherein an existing
passive optical network such as was discussed with respect to FIG. 4 is suitable
for being upgraded to an active optical network system for carrying broadband data
signals. Those elements of FIG. 5 which are the same as those discussed with respect
to FIG. 4 continue to carry the same reference numbers. As shown, a primary pair
of optical fibers
42 having individual fibers
42a and
42b
extends between optical equipment
40 in the central office
20,
and optical to electrical conversion equipment
82 in the intermediate distribution
terminal
22. Also similar to the optical network system shown in FIG. 4,
there are included thirty-two corresponding pairs of optical fibers (including
the representative eight pairs of optical fibers
50 through
64) which
extend between intermediate terminal
22 and thirty-two separate destination
terminals, each of which in the embodiment of FIG. 5 contains a BOIU (broadband
optical interface unit) such as represented by BOIUs
66a,
68a,
70a,
72a,
74a,
76a,
78a
and
80a. In addition to optical/electrical data converting equipment
82 located in intermediate terminal
22, there are also included optical
communication units such as units
84 and
86 each of which includes
an output optical connector
88 and an input optical connector
90.
As was discussed above with respect to FIG. 4, a pair of optical fibers extend
between the intermediate terminal
22 and each of the BOIUs
66a
through
80a. As an example, the pair of optical fibers
50
include a first fiber
92 and second fiber
94, and as a further example,
and only for convenience, the first fiber
92 is shown carrying light from
to intermediate terminal
22 to BOIU
66a whereas the second
fiber
94 is shown carrying light in the opposite direction from the BOIU
66a to intermediate terminal
22.
Referring now to FIG. 6, there is shown a more detailed illustration of
the connections between the optical equipment
84, fiber optical pairs
50
and
52 and the BOIU
66a and BOIU
68a. As shown,
the first fiber
92 of optical pair
50 includes a "first" optical
connector at the intermediate end of fiber
92 such as optical connector
96 at the end of optical fiber
92 which terminates in intermediate
terminal
22. There is also included optical connector
98 on the destination
terminal end of fiber
92 which terminates at BOIU
66a. Likewise,
the second optical fiber
94 includes a "second" connector on the intermediate
terminal
22 end of fiber
94 such as optical connector
100
at the end of optical fiber
94 and optical connector
102 on the other
end which terminates at BOIU
66a. It is also noted that BOIU
66a
includes an input optical connector
104 and an output optical connector
106 which are connected to optical connectors
98 and
102,
respectively. Likewise, the optical pair
52 which extends between BOIU
68a
and intermediate terminal
22 also includes a first optical fiber
108
having a "first" optical connector
110 at the end of fiber
108 which
terminates in intermediate terminal
22 and an optical connector
112
at the end of fiber
108 which terminates at BOIU
68a. Similarly,
the second optical fiber
114 of optical pair
52 includes a "second"
optical connector
116 on the end which terminates at intermediate terminal
22 and optical connector
118 on the end of optical fiber
114
which terminates at the BOIU
68a. In the same manner as the BOIU
66a, BOIU
68a also includes an input terminal
120
and an output terminal
122.
Therefore, referring to FIGS. 5 and 6, it is seen that lightwaves carrying
data information is provided at connector
88 of optical equipment
84.
When optical connector
96 of fiber
92 is connected to optical connector
88 of optical equipment
84, light is provided from the unit
84
through the "first" optical fiber
92 to the BOIU
66a through
connector
98 on fiber
92 to input optical connector
104 on
BOIU
66a. As will be appreciated by those skilled in the art, data
carried on "first" optical fiber
92 which is appropriate for or "addressed
to" BOIU
66a will be extracted from the traveling lightwaves and
put in suitable format for further transmission or use. In addition to extracting
data from the light coming into BIOU
66 on optical fiber
92, BOIU
66a also inserts new data onto the light traveling through the unit
which exits BIOU
66a on connector
106 to connector
102
and onto "second" fiber
94 of pair
50. Thus, new data inserted by
BOIU
66a is now carried on "second" fiber
94 to connector
100 located in intermediate terminal
22. However, it is noticed that
connector
100 is not connected to the optical equipment
84, but is
instead connected to the "first" optical connector
110 on another "first"
optical fiber
108 of fiber pair
52. Then, in the same manner as was
discussed above with respect to BOIU
66a, light on "first" fiber
108 is connected through connector
112 at the destination terminal
end to input connector
120 on BOIU
68a where the appropriate
data for BIOU
68a is extracted and new data is injected onto the
light and then the light is transmitted back out of output connector
122
on BOIU
68a to connector
118 of "second" fiber
114
of optical pair
52 to "second" connector
116 at the intermediate
terminal end of optical fiber
114. "Second" optical connector
116
is then connected to a first optical connector on a first optical fiber of optical
fiber pair
54 which extends from intermediate terminal
22 to BOIU
70a. After the data is extracted from the light on the first fiber
of optical pair
54 and any new data is inserted onto the light traveling
to the second fiber of optical pair
54, it is again routed back to the intermediate
terminal
22 and then to the first fiber of optical pair
56 to BOIU
72a. The light coming from the output of BOIU
72a again
travels back to the intermediate terminal
22 on the second fiber of pair
56 wherein the second fiber of optical pair
56 has a "second" connector
at the intermediate end connected to the input terminal
90 of optical equipment
84. Thus, it is seen that there has been described a transmission loop which
extends initially from the output connector
88 of optical equipment
84
through BOIU
66a back to intermediate terminal
22 then out
to BOIU
68a back to intermediate terminal
22 then out to BOIU
70a then back to intermediate terminal
22 and then to BOIU
72a and back to intermediate terminal
22 where it is connected
to the input terminal
90 of optical equipment
84.
In the embodiment illustrated in FIG. 5, there are a plurality of units similar
to optical equipment
84, each of which is connected to a transmission loop
with four separate BOIUs in the same manner as just discussed. For example, electrical
equipment
86 in intermediate terminal
22 is part of the transmission
loop made up by BOIU
74a,
76a,
78a and
80a along with corresponding optical fiber pairs
58,
60,
62 and
64. It will also be appreciated, that although in the embodiment
discussed, there are four BOIUs for every piece of optical equipment in intermediate
terminal
86, the number of BOIUs could be greater or less than four. It
will also, of course, be appreciated that there are electrical connections between
the optical to electrical equipment
82 and the optical equipment
84
and
86. Thus, there has been described a transmission path wherein a plurality
of BOIU units are connected to a single piece of optical equipment at the intermediate
terminal
22 by means of a serial transmission loop. As will be appreciated
by those skilled in the art, it would be possible that a single communication channel
could be handled by each of the BOIU units or a large number of channels could
be handled. When the equipment is initially installed, a smaller number of channels
would be handled by each BOIU unit in a transmission loop and as new customers
request service, the number of channels handled by each BOIU unit in the loop could
increase. Eventually the number of channels being serviced by each BOIU unit could
increase to such a level that optical equipment unit
84 at the intermediate
terminal
22 could no longer handle the volume. In such a case, one of the
BOIU units may necessarily have to be taken out of the loop so that there might
be only three BOIU units in the loop because of the increased traffic. The BOIU
unit taken out of the overloaded transmission loop would then be combined into
another transmission loop and perhaps with a new piece of optical equipment similar
to that of optical equipment
84. It should be noted that each of the optical
fiber pairs
50 through
56 are handling four times the number of channels
because of the serial transmission loop than would be handled by each pair if each
BOIU unit went to a separate piece of optical equipment such as optical equipment
84. Thus, it can be seen that as more and more service is demanded and added
at the BOIU units, it is a simple matter to rearrange the transmission loops and
add equipment only as it is needed.
FIG. 7 illustrate two embodiments for upgrading an optical system which does
not require active elements, and only incorporates passive elements at the intermediate
or remote distribution terminal. For example, instead of the active elements
82,
84 and
86 which converted data from optical signals to electrical
signals and from electrical signals to optical signals, and as was discussed with
respect to FIGS. 5 and 6, the embodiment of FIG. 7 use passive elements such as
an optical coupler/splitter to combine various wavelengths of light arriving on
a plurality of optical fibers such that all of the optical signals can be carried
on a single optical fiber. Similarly, an optical coupler/splitter with CWDM (continuous
wave division multiplexing) may be used to separate the different wavelengths of
light carrying the various signals, one each onto a plurality of different optical
fibers. As an example only, a single fiber may be used to carry light having a
wavelength of 1,310 nanometers as is typically used for telephony service as well
as four different wavelengths, such as 1,510, 1530, 1,550 and 1,570 rather than
a single nominal wavelength of 1,550 nanometers.
More specifically, and as shown in FIG. 7, central office
20 is connected
to intermediate or remote distribution terminal
22 by at least two primary
optical fibers such as optical fiber pair
42 which has individual fibers
42a and
42b. Intermediate terminal
22 is also
connected to a plurality (such as thirty-two) of BOIU (broadband optical interface
unit) by a like plurality of pairs of optical fibers. It should be noted that BOIU
terminals
130 and
132 represent the first and eighth BOIUs forming
a first optical loop of eight different BOIUs. The loop is connected by a corresponding
eight pairs of optical fibers as represented by optical fiber pairs
134
and
136 in the same manner as the loop of four different BOIUs discussed
with respect to FIGS. 5 and 6. Similarly, the ninth BOIU
138 and the sixteenth
BOIU
140, along with a first optical fiber pair
142 and an eighth
optical fiber pair
144 represent a second optical loop of eight additional
BOIUs and their corresponding eight pairs of optical fibers.
Likewise, the seventeenth BOIU
146 and the twenty-fourth BOIU
148,
along with the seventeenth and twenty-fourth pairs of optical fibers
150
and
152, respectively, represent a third optical loop of eight BOIUs. Finally,
the twenty-fifth and thirty-second BOIUs
154 and
156, respectively,
with their corresponding pairs of optical fibers
158 and
160 represent
a fourth optical data loop. In the example as shown, each of the four optical data
loops carry light at slightly different wavelengths. For example, in the embodiment
shown the optical loops
1,
2,
3 and
4 operate at 1,510,
1,530, 1,550 and 1,570 nanometers of light, respectively.
As shown in FIG. 7, intermediate or remote distribution terminal
22 also
includes an optical combination device or coupler
162 having its output
side optically connected to optical fiber
42a of optical pair
42.
Also as shown, the four inputs of optical coupler
162 are fibers
134a
from optical fiber pair
134, optical fiber
142a from fiber
pair
142, optical fiber
150a from fiber pair
150 and
optical fiber
158a from fiber pair
150. Thus, it is seen that
each of the four serial transmission loops has an input to the optical coupling
device
162. In a similar manner, there is an optical separation or splitter
164 in combination with a four-way optical filter
166. The splitter/coupler
164 has its input
168 connected to optical fiber
42b of
optical fiber
42. Each of the four outputs are connected to one output of
the four-way filter
166 and are in turn connected one each to the last fiber
of each of the four loops. For example, fiber
136b from the first
loop is connected to the filter
166 and then to splitter/coupler
164
and the optical fiber
144b from the second optical loop is also connected
to filter
166 and then to coupler
164. Likewise, optical fiber
152b
from the third optical loop and optical fiber
160b from the fourth
optical loop are connected through the filter
166 to the splitter/coupler
164. Thus, it is seen that by using a 4:1 splitter/couplers
162 and
164, and by putting eight BOIUs in each loop, all thirty-two of the BOIUs
can be serviced.
It should also be noted that there is a route protection switch such as switches
170 and
172 located between each of the BOIUs and their corresponding
fiber optical pair. For example, protection switch
170 is located between
BOIU
130 and optical pair
134. Likewise, route protection switch
172 is located between BOIU
132 and optical pair
136. The
purpose of the route protection switches is that in the event a single BOIU, such
as for example BOIU
130, were to fail, the route protection switch would
operate to bypass that BOIU such that only the customers or subscribers associated
with and receiving service through BOIU
30 would lose service. The fault
protection switch simply bypasses BOIU
130 and couples the optical signal
directly from the optical fiber
134a to optical fiber
134b
of the optical pair
134. FIGS. 8A and 8B illustrate the normal light
path and the fault light path, respectively, through the fault protection switches.
Thus, the seven remaining BOIUs can continue to cover and provide service without interruption.
Also as shown, control office
20 includes an optical splitter/coupler
174 in combination with a CWDM filter
176 connected to optical fiber
42a of pair
42. Similarly, optical coupler/splitter
178
connected to optical fiber
42b of pair
42. Also as shown,
there are four optical receivers and four optical transmitters such as receiver
180 and transmitter
182. Each of the four receivers and transmitters
are for receiving and transmitting light having one of the four different wavelengths.
Thus, each receiver such as receiver
180 is coupled to the wave division
multiplexer filter
176 such that only light of the proper wavelength is
directed to the proper receiver. Similarly, each transmitter is connected to optical
coupler
178.
In an alternate embodiment, there may be a second pair
184 of primary
fibers
made up of fibers
184a and
184b. In the event there
are two pairs of fibers extending between the intermediate or remote distribution
terminal
22 in the central office
20, redundancy may be provided
such that if a fiber in the first primary pair
42 were to be cut or otherwise
damaged, a fiber in the second fiber pair
184 can take over. This is accomplished
by a pair of route protection switches
186 and
188 which are connected
so that if, for example, fiber
42a of pair
42 were to be damaged
or separated, switch
186 would activate such that the input of the optical
coupler/splitter
174 would be connected to optical fiber
184a
of fiber pair
184 rather than fiber
42a of pair
42.
Likewise, if optical fiber
42b were to be severed or damaged, then
switch
188 would activate such that the output of optical coupler
178
is routed to fiber
184b of pair
184 rather than to optical
fiber
42b of pair
42. FIG. 9 illustrates the normal and fault
positions of the route protection switches. It should be also be noted, however,
that this alternate embodiment also requires that the optical coupler/splitter
162 and
164 discussed with respect to intermediate terminal
22
should have two outputs rather than a single output as was discussed before. That
is, the optical coupler/splitters should be a 4:2 rather than a 4:1 splitter/coupler.
Thus, it is seen there has been described a method of using existing fiber optical
pairs to upgrade a system to a passive system with minimal change of equipment
and no additional fibers required to be installed.
Referring now to FIG. 10, there is shown still another alternate embodiment
of the present invention where only two single wavelengths of light 1,550 and 1,310
are used. It is noted that the four optical loops are substantially the same as
discussed with respect to FIG.
6. However, instead of a single pair
42
of fibers
42a and
42b, the primary optical fiber bundle
186 is not made up of two fibers but is made up of four fibers
186a,
186b,
186c and
186d. Further, if there
is to be redundancy of the primary fiber
186, it will be necessary to include
a second four-fiber bundle
188 made up of fibers
188a,
188b,
188c and
188d. In such an arrangement, it is not necessary
to use the CWDM filters; it is only necessary to use a 2×2 optical coupler/splitter
as indicated by optical coupler/splitters
190,
192,
194 and
196 in intermediate terminal
22, and 2×2 optical coupler/splitter
198,
200,
202 and
204 in central office. Thus, in this
arrangement, there is a fiber dedicated for each of the terminal loops each of
which carries eight BOIUs. Likewise at the central office
20 in end of fibers
186 and
188, each of the fibers are connected to its own receiver
and transmitter, such as receiver
206 and transmitter
208. To achieve
redundancy in the event of a primary fiber bundle failure in this embodiment, there
is also included four route protection switches such as switch
210 which
operate similarly to the switches
186 and
187 with respect to FIG.
7 above. Thus, in the event of one of the primary fibers of optical bundle
186,
the appropriate switch, such as switch
210, would switch positions such
that the information is now routed through the appropriate fiber of fiber bundle
188 and then back to its appropriate optical splitter
190.
The corresponding structures, materials, acts and equivalents of all means or
step; plus function elements in the claims below are intended to include any structure,
material, or act for performing the function in combination with other claimed
elements as specifically claimed.
*
