U.S. patent application number 12/106622 was filed with the patent office on 2008-09-18 for chromatic dispersion compensation system and method.
This patent application is currently assigned to Pivotal Decisions LLC. Invention is credited to Michael H. Eiselt, Mark Shtaif.
Application Number | 20080226302 12/106622 |
Document ID | / |
Family ID | 29254058 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080226302 |
Kind Code |
A1 |
Eiselt; Michael H. ; et
al. |
September 18, 2008 |
CHROMATIC DISPERSION COMPENSATION SYSTEM AND METHOD
Abstract
Dispersion compensation is provided in an optical transmission
system. An optical line couples first and second transceivers, and
a plurality of amplifiers coupled to the optical line are spaced
throughout the optical line with variable span distances. A
plurality of dispersion compensation modules include a coarse
granularity fiber, a connector, and a fine granularity fiber. A
memory is associated with the dispersion compensators to provide
information related to the value of the dispersion
compensation.
Inventors: |
Eiselt; Michael H.;
(Kirchheim, DE) ; Shtaif; Mark; (Even Yehuda,
IL) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
CIRA CENTRE, 12TH FLOOR, 2929 ARCH STREET
PHILADELPHIA
PA
19104-2891
US
|
Assignee: |
Pivotal Decisions LLC
Las Vegas
NV
|
Family ID: |
29254058 |
Appl. No.: |
12/106622 |
Filed: |
April 21, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11515331 |
Aug 31, 2006 |
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12106622 |
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11179134 |
Jul 11, 2005 |
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11515331 |
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10147397 |
May 15, 2002 |
6965738 |
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11179134 |
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60372845 |
Apr 16, 2002 |
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Current U.S.
Class: |
398/159 |
Current CPC
Class: |
G06Q 10/087 20130101;
H04B 10/2525 20130101; H04B 2210/256 20130101 |
Class at
Publication: |
398/159 |
International
Class: |
H04B 10/02 20060101
H04B010/02; H04B 10/12 20060101 H04B010/12 |
Claims
1. A method of reducing inventory of dispersion compensation
fibers, the method comprising: determining respective lengths of a
plurality of fine granularity fibers based on a dispersion
compensation accuracy of at least one fiber span in an optical
transmission system; determining respective lengths of a plurality
of coarse granularity fibers based on the determined respective
lengths of the plurality of fine granularity fibers; and stocking
the plurality of fine granularity fibers and the plurality of
coarse granularity fibers in accordance with their determined
respective lengths.
2. The method of claim 1 further comprising determining the
dispersion compensation accuracy for each fiber span in the optical
transmission system;
3. The method of claim 2, wherein a distance of each fiber span is
less than approximately 109 kilometers.
4. The method of claim 1, wherein the stocked plurality of fine
granularity fibers defines a first quantity and the stocked
plurality of coarse granularity fibers defines a second quantity
that is approximately equal to the first quantity.
5. The method of claim 1, wherein the determined respective lengths
of the plurality of fine granularity fibers are based upon 1
kilometer increments.
6. The method of claim 1, wherein the determined respective lengths
of the plurality of coarse granularity fibers are based upon 10
kilometer increments.
7. The method of claim 1, wherein each of the plurality of fine
granularity fibers are configured to compensate for dispersion in a
range of -9 kilometers to +9 kilometers.
8. The method of claim 1 further comprising manufacturing the
plurality of fine granularity fibers and the plurality of coarse
granularity fibers in accordance with their determined respective
lengths.
9. The method of claim 1 further comprising assigning an identifier
to at least one of the plurality of fine granularity fibers.
10. The method of claim 9, wherein the identifier corresponds to
the length of the respective fine granularity fiber.
11. The method of claim 9, wherein the identifier corresponds to a
resolution of the respective fine granularity fiber.
12. The method of claim 9, wherein each assigned identifier is
configured to be stored in a memory that is configured to be
attached to the respective fine granularity fiber.
13. The method of claim 1 further comprising assigning an
identifier to at least one of the plurality of coarse granularity
fibers.
14. The method of claim 13, wherein the identifier corresponds to
the length of the respective coarse granularity fiber.
15. The method of claim 13, wherein the identifier corresponds to a
resolution of the respective fine granularity fiber.
16. The method of claim 13, wherein each assigned identifier is
configured to be stored in a memory that is configured to be
attached to the respective coarse granularity fiber.
17. The method of claim 1 further comprising electronically polling
the stocked plurality of fine granularity fibers and the stocked
plurality of coarse granularity modules to generate an inventory
listing.
18. The method of claim 1, wherein determining the respective
lengths of the plurality of coarse granularity fibers is further
based on a range of dispersion that requires compensation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 11/515,331, filed Aug. 31, 2006, which is a division of
U.S. patent application Ser. No. 11/179,134, filed Jul. 11, 2005,
which is a continuation of U.S. Pat. No. 6,965,738, filed May 15,
2002, which claims the benefit of U.S. Provisional Patent
Application No. 60/372,845, filed Apr. 16, 2002, each of which is
hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] This invention relates to a dispersion compensation system
and more particularly to a chromatic dispersion compensation system
for use in optical transmission systems.
BACKGROUND
[0003] The transmission, routing and dissemination of information
has occurred over computer networks for many years via standard
electronic communication lines. These communication lines are
effective, but place limits on the amount of information being
transmitted and the speed of the transmission. With the advent of
light-wave technology, a large amount of information is capable of
being transmitted, routed and disseminated across great distances
at a high transmission rate over fiber optic communication
lines.
[0004] When information is transmitted over fiber optic
communication lines, impairments to the pulse of light carrying the
information can occur including pulse broadening (dispersion) and
attenuation (energy loss). As an optical signal is transmitted over
the fiber optic communication line, the optical signal is
transmitted at various frequencies for each component of the
optical signal. The high frequency components move through the
fiber optic material at different speeds then compared to the low
frequency components. Thus, the time between the faster components
and the slower components increase as the optical signal is
transmitted over the fiber optic communication line. When this
occurs, the pulse broadens to the point where it interferes with
the neighboring pulses; this is known as chromatic dispersion.
Chromatic dispersion compensation corrects this pulse broadening.
Various chromatic dispersion compensation apparatus and methods are
available.
[0005] In U.S. Pat. No. 6,259,845, entitled "Dispersion
Compensating Element Having an Adjustable Dispersion" and issued to
Harshad P. Sardesai, a variable dispersion compensation module is
disclosed. In the Sardesai patent, a dispersion compensation module
including segments of optical fiber of varying lengths, some of
which have a positive dispersion while others have a negative
dispersion is disclosed. Selected optical fiber segments are
coupled to one another to provide a desired net dispersion to
offset the dispersion associated with the fiber optic communication
line. The Sardesai patent allows for this variable dispersion
compensation model rather than provide a unique segment of
dispersion compensation fiber for each span. The Sardesai
dispersion compensation module functions by interconnecting the
various length of various dispersion per kilometer fibers so that
the resulting total dispersion equals the dispersion of the fiber
optic communication line span. The Sardesai dispersion compensation
module, however, has a high cost in that multiple dispersion
compensation fibers enclosed within the Sardesai compensation
module may remain unused and are therefore wasted when implemented
in the field. Further, the Sardesai dispersion compensation module
requires excessive interconnectivity between the various dispersion
compensation fibers, allowing for a greater connection loss to be
experienced.
[0006] U.S. Pat. No. 6,275,315, entitled "Apparatus for
Compensating for Dispersion of Optical Fiber in an Optical Line"
and issued to Park, et al., discloses a dispersion compensation
method in which dispersion compensation fiber is used in
conjunction with a variable dispersion module. In the Park patent,
the variable dispersion compensation module is a dispersion
compensation filter such as a reflective etalon filter. The etalon
filter is a tunable filter and thus allows for variable dispersion
compensation.
[0007] The primary focus of the fiber optic industry to correct
chromatic dispersion has followed one of two paths. The first path
was for the use of variable dispersion compensation modules as has
been disclosed in the above referenced patent/patent applications.
A second path is to manufacture dispersion compensation fibers in
varying lengths to correct for dispersion compensation. Each
varying length of the dispersion compensation fiber must be
inventoried requiring a vast amount of assets to be tied up in
inventory which is infrequently implemented. Therefore, any
advancement in the ability to reduce the number of
interconnectivity points between the dispersion compensating fibers
and to reduce the cost incurred with the highly technical variable
dispersion compensators and the high cost of inventory would be
greatly appreciated.
SUMMARY
[0008] A dispersion compensation system and method for use in an
optical transmission system to compensate for signal distortion of
an optical signal is provided. The dispersion compensation system
includes a first and second transceivers for generating and
receiving the optical signal respectively. An optical line couples
the first transceiver to the second transceiver. A plurality of
amplifiers are coupled to the optical line, spaced periodically
throughout the optical line forming span distances, wherein the
amplifiers amplify the optical signal and wherein the span
distances are variable. A plurality of dispersion compensation
modules are coupled to the plurality of amplifiers wherein the
dispersion compensation models include a coarse granularity module
having a resolution of at least 5 kilometers coupled to a
connector. The connector is also coupled to a fine granularity
module having a resolution of one kilometer. The coarse and fine
granularity modules are connected through a single connector. The
coarse granularity modules and the fine granularity modules correct
the dispersion of the optical signal accumulated in the variable
span distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A better understanding of the invention can be obtained from
the following detailed description of exemplary embodiments as
considered in conjunction with the following drawings.
[0010] FIG. 1 is a block diagram depicting an optical transmission
system according to the present invention.
[0011] FIGS. 2A, 2B, 2C, and 2D are graphical representations of an
eye diagram of an optical signal.
[0012] FIG. 3 is a block diagram depicting a dispersion
compensation module according to the present invention.
[0013] FIGS. 4A, 4B and 4C are block diagrams depicting exemplary
fiber combinations according to the present invention.
[0014] FIG. 5 is a flow chart of a dispersion compensation method
according to the present invention.
[0015] FIG. 6 is a flow chart depicting the inventory reduction of
dispersion compensation fibers method according to the present
invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0016] In the descriptions that follow, like parts are marked
throughout the specification and drawings with the same numerals,
respectively. The figures are not necessarily drawn to scale and
certain figures may be shown in exaggerated or generalized form in
the interest of clarity and conciseness.
[0017] FIG. 1 depicts an optical transmission system according to
the present invention. An optical transmission system 100 is shown
including a transmitting terminal 102 and a receiving terminal 104.
For illustrative purposes only, the optical transmission system 100
is shown in a unidirectional manner. However, as is known to those
skilled in the art, the optical transmission system 100 can
function in a bidirectional manner without detracting from the
spirit of the invention. The transmitting terminal 102 and the
receiving terminal 104 are connected through optical line 106. An
optical signal 108 is transmitted over the optical line 106. Spaced
periodically throughout the optical transmission system 100 are
in-line amplifiers 110. The in-line amplifiers 110 boost the
optical signal 108 as it is transmitted over the optical line 106.
As the optical signal 108 is transmitted over the optical line 106,
the optical signal 108 begins to experience chromatic dispersion.
Chromatic dispersion is the broadening of the optical pulse over
the various frequencies of the components of the optical signal
108. High frequency components of the optical signal move through
the optical line 106 at a different speed when compared to the low
frequency components of the optical signal 108. The longer
wave-length components move at a slower rate than the shorter
wave-length components of the optical signal 108. Therefore, the
optical signal 108 pulse broadens over time as the optical signal
is transmitted throughout the optical line 106. Chromatic
dispersion compensation is necessary to correct for this pulse
broadening impairment.
[0018] A controller 115 is resident in each in-line amplifier 110
and connects the in-line amplifiers 110(a-e) to the optical
supervisory channel 114 through transmission lines 118(a-e). The
controllers 115(a-e) receive and transmit control data for the
in-line amplifiers 110(a-e). The controller in one embodiment
includes a processor, a mass storage device, a network connection
and a memory (all not shown). However, a wide range of controllers
are implementable without detracting from the spirit of the
invention.
[0019] A dispersion compensation module 112 is coupled to the
in-line amplifiers 110 such that the optical signal 108 flows
through the dispersion compensation module 112 as the optical
signal 108 is transmitted along the optical line 106. The
dispersion compensation modules 112(a-e) are electronically coupled
to the controllers 115(a-e) and receive control data from the
optical supervisory channel 114 through transmission lines 118(a-e)
via the controllers 115(a-e). As can be seen, dispersion
compensation modules 112(a-e) are located at each in-line amplifier
110(a-e) location in the optical transmission system 100. However,
the quantity of dispersion compensation modules may be varied,
including locating dispersion compensation modules at every other
in-line amplifier or by selecting a fixed number of dispersion
compensation modules and distributing those dispersion compensation
modules at fixed intervals through the optical transmission system,
without detracting from the spirit of the invention. Thus, in one
embodiment, a dispersion compensation module 112a is shown
co-located with in-line amplifier 110a within the optical
transmission system 100. The distance between the transmitting
terminal 102 and the first in-line amplifier 110a and the distances
between a first in-line amplifiers 110 and an adjacent amplifier
110 may vary according to the physical layout of the optical
transmission system 100. Thus, the frequency of the in-line
amplifiers 110 within the optical transmission system 100 may vary
depending upon the type of fiber used in the optical line 106 and
depending upon the physical terrain that the optical transmission
system 100 must span. The distances between the transmitting
terminal 102 and the first in-line amplifier 110a, the distances
between adjacent in-line amplifiers 110 and the distances between
the receiving terminal 104 and the last in-line amplifier 110e may
vary and each distance defined is a spanned distance.
[0020] Referring now to FIGS. 2A-2D, graphical representations of
the eye diagram of an optical signal are shown. As the optical
signal 108 is transmitted over a standard optical system, a optimal
pulse shape is initially transmitted. The optimal pulse shape can
be seen in FIG. 2A. The optimal pulse shape forms an "eye" and
represents the minimum amount of chromatic dispersion of the
optical signal 108 pulse. As the optical signal 108 is transmitted
over the optical transmission network 100, the pulse begins to
broaden as is shown in FIGS. 2B and 2C. As the pulse broadens, the
distinctions between separate optical signal 108 pulses become less
discernable. As the optical signal 108 is transmitted further along
the optical line 106, the optical signal 108 continues to broaden
as is shown in FIG. 2D. Thus, as the optical signal 108 is
transmitted over the optical line 106, the optical signal 108
broadens to a point in which the information being transmitted over
the optical signal 108 is no longer discernable. Thus, the optical
signal 108 requires a chromatic dispersion correction to maintain
an adequate "eye" or pulse shape.
[0021] Referring now to FIG. 3, the dispersion compensation module
according to the present invention is shown. Current dispersion
compensation methodologies which incorporate dispersion
compensation fibers can be classified in two groups. The first
methodology includes the use of a dispersion compensation fiber in
combination with a tunable dispersion compensation filter. The
tunable compensation filter allows for the fine tuning of the
dispersion compensation module to be accomplished when the exact
amount of dispersion over a span is not known. Thus, when in the
field, the installer can adjust through the interconnection of
multiple dispersion compensation fibers within the tunable
dispersion compensation module to accomplish the level of
dispersion compensation necessary to offset the chromatic
dispersion present in the current span. Examples of this
methodology include U.S. Pat. No. 6,259,845 and U.S. Patent
Application No. US2001/0009468 discussed herein. A second
methodology requires that the exact dispersion amount of the span
be calculated and then a single piece dispersion compensation fiber
that exactly matches this specific dispersion amount be
manufactured or obtained from a current inventory and installed to
offset the chromatic dispersion of the span. A third methodology
now exists and is discussed herein.
[0022] The dispersion compensation module 112 according to the
present invention is comprised of a coarse granularity fiber 300
and a fine granularity fiber 302 interconnected with connector 304.
The coarse granularity fiber 300 compensates for the dispersion
slope of the fiber and includes multiple dispersion compensation
devices such as dispersion compensating fiber, higher order mode
devices and chirped fiber bragg gratings. The fine granularity
fiber 302 includes dispersion compensating fiber, higher order mode
devices and chirped fiber bragg gratings but further includes the
use of a standard single mode fiber (SSMF). The connector 304 is of
the type commonly known to those skilled in the art for the
connection of dispersion compensation fibers.
[0023] A memory 306 is physically coupled to the coarse granularity
fiber 300 and is coupled to the controller 115 through
communication line 312. A second memory 308 is physically coupled
to the fine granularity fiber 302 and is coupled to the controller
115 through communication line 314. The memories 306 and 308, in
one embodiment, are programmable read-only memories, preferably
electronically erasable programmable read-only memories. However,
multiple memory systems are implementable without detracting from
the spirit of the invention. Unique identifiers are stored in the
memories 306 and 308 and upon a query from the controller 115, the
unique identifiers are transmitted to the controller 115 for
retransmission across the optical supervisory channel 114. Further,
the unique identifiers are ascertainable through direct electrical
connection to the in-line amplifier 110 as would occur by
maintenance personnel in the field. The unique identifiers allow
the maintenance personnel to identify the specific coarse and fine
granularity fibers 300 and 302 installed in the dispersion
compensation module 112. Upon visual inspection, the resolution of
the coarse and fine granularity fibers 300 and 302 is difficult to
ascertain. However, if each individual fiber or each resolution or
length of the coarse and fine granularity fibers 300 and 302 are
assigned unique identifiers, the maintenance personnel only need
cross reference the unique identifier with a master list to
distinctly identify the resolution of the coarse and fine
granularity fibers 300 and 302. The coarse and fine granularity
fibers 300 and 302 are manufactured at specific lengths, then
inventoried such that through the use of only one coarse
granularity fiber, one fine granularity fiber and one connector the
dispersion accumulated in any standard span, which typically has a
range of less than 100 kilometers, can be compensated.
[0024] In one embodiment of the present invention, the coarse
granularity fibers 300 are manufactured and inventoried at lengths
which correspond to the accumulated dispersion in the optical
network 100 for lengths of 10 kilometers, 20 kilometers, 30
kilometers, 40 kilometers, 50 kilometers, 60 kilometers, 70
kilometers, 80 kilometers, 90 and 100 kilometers. The fine
granularity fibers 300 are manufactured and inventoried at lengths
which correspond to the accumulated dispersion in the optical
network 100 for lengths of 1 kilometer, 2 kilometers, 3 kilometers,
4 kilometers, 5 kilometers, 6 kilometers, 7 kilometers, 8
kilometers and 9 kilometers. Therefore for any span under 109
kilometers, the dispersion compensation module according to one
embodiment of the present invention is implemented with only one
coarse granularity fiber 300, one fine granularity fiber 302 and
one connector 304.
[0025] In another embodiment of the present invention, the coarse
granularity fibers 300 are manufactured and inventoried at lengths
which correspond to the accumulated dispersions in the optical
network 100 for lengths of 5 kilometers, 10 kilometers, 15
kilometers, 20 kilometers, 25 kilometers, 30 kilometers, 35
kilometers, 40 kilometers, 45 kilometers, 50 kilometers, 55
kilometers, 60 kilometers, 65 kilometers, 70 kilometers, 75
kilometers, 80 kilometers, 85 kilometers, 90 kilometers, 95
kilometers, 100 kilometers. The fine granulated fibers 300 are
manufactured and inventoried at lengths which correspond to the
accumulated dispersion in the optical network for lengths of -5
kilometer, -4 kilometer, -3 kilometer, -2 kilometer, -1 kilometer,
1 kilometer, 2 kilometers, 3 kilometers, 4 kilometers, 5
kilometers. Therefore, for any span under 105 kilometers, the
dispersion compensation model according to one embodiment of the
present invention is implemented with only coarse granularity fiber
300, one fine granularity fiber 302 and one connector 304. The
benefits of such systems are the reduction of manufacturing costs,
the reduction of inventory costs and the reduction of time
necessary to identify and install the dispersion compensation
module 112.
[0026] In one prior art system in which a single dispersion
compensation fiber is used to offset the chromatic dispersion
associated with any variable span under 109 kilometers, 109
different dispersion compensation fiber lengths would be necessary
to offset the chromatic dispersion accumulated in various lengths
varying from 1 to 109 kilometers. According to the present
invention, only 19 various dispersion compensation fiber lengths
would be necessary to be manufactured and inventoried. In another
prior system, a tunable dispersion compensation module is attached
to varying lengths of dispersion compensation fiber. However, the
cost of the tunable dispersion compensation modules greatly exceed
the cost of the dispersion compensation fiber itself and a tunable
dispersion compensation module is necessary for each span. Further,
the tunable dispersion compensation modules require multiple
connections between various lengths of dispersion compensation
fibers within the tunable dispersion module and therefore incur a
greater amount of loss due to each of these multiple connections.
As can be seen, the present invention provides a simplified and
cost effective method of preparing a dispersion compensation module
112 as shown.
[0027] The dispersion compensation module 112 may be assembled in
the field if the installer carries at least one each of the various
lengths of the dispersion compensation fiber according to the
present invention. Alternatively, the dispersion compensation
module 112 may be assembled at the plant if the chromatic
dispersion of the specific span is known. The dispersion
compensation module 112 is then delivered and installed in the
optical network by a field technician.
[0028] Referring now to FIGS. 4A, 4B and 4C, exemplary block
diagrams are provided showing the various coarse and fine
granularity fibers interconnected. FIGS. 4A, 4B and 4C demonstrate
various exemplary embodiments of the dispersion compensation
module. In FIG. 4A, a dispersion compensation module 112 is shown
with a coarse granularity fiber 402 equivalent to 60 kilometers of
accumulated dispersion connected through connector 404 to a fine
granularity fiber 406 equivalent to the dispersion necessary for
the accumulation of 2 kilometers of dispersion. Therefore, through
the use of the single coarse granularity fiber 402, the connector
404, and the fine granularity fiber 406 the total dispersion
accumulated in 62 kilometers of the optical line 106 can be
compensated.
[0029] In FIG. 4B, another exemplary embodiment is shown with the
coarse granularity fiber 410 equivalent to 40 kilometers of
accumulated dispersion, connected through connector 404 with the
fine granularity fiber 412 equivalent to 6 kilometers of
accumulated dispersion. Therefore, in this example, the dispersion
associated with 46 kilometers has been offset through the use of
the single coarse granularity fiber 410, fine granularity fiber 412
and a connector 404.
[0030] In FIG. 4C, an alternative embodiment is shown. The coarse
granularity fiber 416 is equivalent to the accumulated dispersion
of 80 kilometers. The coarse granularity fiber 416 is connected
through connector 404 to a fine granularity fiber 418 of an
accumulated -2 kilometers. The -2 kilometer fine granularity fiber
418 is typically a standard single mode fiber (SSMF). The fine
granularity fiber 418 is used to compensate for the over
compensation of the coarse granularity fiber 416. Therefore, in
this example, the total distance to be compensated is 78
kilometers. To accomplish this, the 80 kilometer coarse granularity
fiber 416 was coupled to a -2 kilometer fine granularity fiber 418.
The benefits of this compensation for over compensation of the
coarse granularity fiber include: lower connection losses due to
the connection of the SSMF to the coarse granularity fiber 416
where the large connector losses are experienced between the
connection of two dispersion compensation fibers; a lower power
loss is experienced as a signal flows through the SSMF as compared
to dispersion compensation fiber; and the SSMF is a lower cost than
the standard dispersion compensation fiber. Other fiber types such
as non-zero dispersion shifted fiber and silica-core fiber may be
implemented as the negative fine granularity fiber without
detracting from the spirit of the invention.
[0031] The dispersion compensation module 112 may include one
device including the coarse granularity fiber and the fine
granularity fiber, two different sub-modules, one for the coarse
granularity fiber and one for the fine granularity fiber, or the
fine granularity fiber may be integrated into the coarse
granularity fiber through connectors or splices at manufacture. A
wide range of connection possibilities exist without detracting
from the spirit of the invention.
[0032] FIG. 5 is a flow diagram of a dispersion compensation method
according to the present invention. The process begins with start
500. Next, in step 502, the physical optical network path is
identified. The developers of the optical network system identify
the route in which the optical network path will take over the
physical terrain. Next, the locations for the in-line amplifiers
110 are identified in step 504. The location of these in-line
amplifiers 110 depend upon the physical terrain and the
characteristics of the optical network.
[0033] Next, in step 506, the various distances between the in-line
amplifiers 110, the distance between the transmitting terminal 102
and the first inline amplifier 110a, and the distance between the
last in-line amplifier 110e and the receiving terminal 104 are
identified. As these distances vary, the determination of the
specific span distance for each span is necessary to determine the
accumulated dispersion over that span.
[0034] Next, in step 508, the specific fiber type which will be
used in the optical network is identified. Once this optical fiber
type has been identified, the specific characteristics of this
fiber are measured or obtained and will be used to determine the
amount of dispersion per kilometer of the optical network. The
calculation to determine the dispersion for each span in the
optical network is accomplished in step 510. This dispersion
calculation depends on the specific span distances and the fiber
type and characteristics of the fiber selected. In an alternative
embodiment, the measurement equipment will be taken out into the
field to directly measure the dispersion amount of the particular
deployed span. In this embodiment, the accuracy of the dispersion
is higher, as dispersion even in the same fiber type might differ
among different production batches and the product of span length
and average dispersion might give a less accurate result. Once the
calculated accumulated dispersion for each span is determined, the
coarse granularity fiber type is identified in step 512. The fine
granularity fiber type is identified next in step 514. The fiber
types are selected based upon the characteristics of the optical
network fiber and are selected based upon the dispersion
calculations for each span.
[0035] Next, in step 516, the coarse granularity fiber variable
distances are determined. In one embodiment, the coarse granularity
fiber variable distances are based upon 10 kilometer groupings.
Therefore, the coarse granularity fiber variable distances are 10
kilometers, 20 kilometers, 30 kilometers, 40 kilometers, etc. The
fine granularity fiber variable distances are identified in step
518. These fiber variable distances depend upon the total
dispersion amount experienced over the optical network and may
depend upon the current manufacturing or inventory of specific
variable distances. The variable distances are determined such that
one coarse granularity fiber and one fine granularity fiber are
coupled to properly compensate for the accumulated dispersion of
any span distance in the optical network, thus reducing inventory
and cost levels.
[0036] Next, in step 520, the fine and coarse granularity fibers
are intercoupled to form a dispersion compensation module 112. The
dispersion compensation module may be formed in the field,
interconnected at a assembly facility, or may be connected at
manufacturer if the manufacturer has access to the specific
variable distances. Finally, in step 522, the dispersion
compensation module is coupled to the optical network to
compensation for the chromatic dispersion accumulated in each span.
The process ends with step 524.
[0037] Referring now to FIG. 6, a method of inventory reduction of
dispersion compensation fibers is shown. The process begins with
start 600. Next, in step 602, the required dispersion compensation
accuracy is determined on a per span basis based upon transmission
system modeling. Next, in step 604, the lengths of the fine
granularity compensation fibers are determined based upon the
required compensation accuracy per span as determined in step 602.
Next, in step 606, the lengths of the coarse granularity fibers are
determined based upon the maximum length of the fine granularity
fibers and the range of dispersion that needs to be compensated.
For the lowest overall number of different fiber modules, the
number of coarse and fine granularity fibers should be
approximately equal. The necessary lengths are determined such that
only one coarse and only one fine granularity fiber can be coupled
to compensate any standard span distance.
[0038] In one embodiment, the standard span distance is less than
109 kilometers. In another embodiment, the necessary lengths of the
coarse granularity fibers are based upon 10 kilometer increments
and the fine granularity fibers are based upon 1 kilometer
increments. In another embodiment, the fine granularity fiber
compensate from a -9 kilometers to a +9 kilometers.
[0039] Next, in step 608, the optical network provider stocks only
the necessary lengths of the coarse and fine granularity fibers.
Thus, the intermittent lengths are not manufactured or inventoried
and thus the inventory is reduced thus lowering costs of
manufacture and storage. In step 609 the unique identifiers for the
coarse and fine granularity fibers 300 and 302 are determined. A
unique identifier is assigned to each individual fiber or a unique
identifier is assigned to a specific length or resolution of the
coarse and fine granularity fibers 300 and 302. The unique
identifier is stored in a memory device 306 and 308 and is
physically attached to the individual fibers. The manufactured and
stored coarse and fine granularity fibers 300 and 302 can be
electronically polled and an automatic inventory listing
determined. The process ends with step 610.
[0040] The foregoing disclosure and description of the invention
are illustrative and explanatory thereof of various changes to the
size, shape, materials, components and order may be made without
departing from the spirit of the invention.
* * * * *