U.S. patent application number 12/641842 was filed with the patent office on 2010-04-22 for local area warning of optical fiber intrusion.
This patent application is currently assigned to AT&T INTELLECTUAL PROPERTY II, L.P.. Invention is credited to Hossein Eslambolchi, John Sinclair Huffman.
Application Number | 20100097234 12/641842 |
Document ID | / |
Family ID | 42108226 |
Filed Date | 2010-04-22 |
United States Patent
Application |
20100097234 |
Kind Code |
A1 |
Eslambolchi; Hossein ; et
al. |
April 22, 2010 |
Local Area Warning of Optical Fiber Intrusion
Abstract
Disclosed is a method and apparatus which provides for alerting
of potential fiber optic cable intrusion. A stress detector located
at a fiber optic cable termination point detects stress on the
fiber optic cable and generates an alarm signal in response to the
stress detection. The alarm signal is transmitted to remote alarm
units along the fiber optic right of way via a conductive metallic
portion of the fiber optic cable (e.g., the fiber optic cable
sheath). In response to receipt of an alarm signal, the alarm units
initiate a perceptible (e.g., audible and/or visible) alarm. The
stress detector may also determine a location of the stress, and
generate an alarm signal addressed to a particular one or more
alarm units in the vicinity of the stress location.
Inventors: |
Eslambolchi; Hossein; (Los
Altos Hills, CA) ; Huffman; John Sinclair; (Conyers,
GA) |
Correspondence
Address: |
AT & T Legal Department - WS;Attn: Patent Docketing
Room 2A-207, One AT & T Way
Bedminster
NJ
07921
US
|
Assignee: |
AT&T INTELLECTUAL PROPERTY II,
L.P.
Reno
NV
|
Family ID: |
42108226 |
Appl. No.: |
12/641842 |
Filed: |
December 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11904497 |
Sep 27, 2007 |
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12641842 |
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11007042 |
Dec 8, 2004 |
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11904497 |
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Current U.S.
Class: |
340/653 |
Current CPC
Class: |
G08B 13/186
20130101 |
Class at
Publication: |
340/653 |
International
Class: |
G08B 21/00 20060101
G08B021/00 |
Claims
1-30. (canceled)
31. An alarm unit comprising: an antenna for receiving signals
radiated by a conductive metallic portion of a fiber optic cable;
means for detecting an alarm signal comprising alarm configuration
information, said alarm signal generated by a stress detection
mechanism and transmitted via said conductive metallic portion; and
means for initiating an alarm in response to receipt of said alarm
signal.
32. The alarm unit of claim 31 wherein alarm signals associated
with said alarm unit, as well as alarm signals associated with
other alarm units, are transmitted via said conductive metallic
portion, said alarm unit further comprising: means for recognizing
an alarm signal associated with said alarm unit as distinguished
from an alarm signal associated with said other alarm units; and
wherein said means for initiating an alarm is responsive to receipt
of an alarm signal associated with said alarm unit.
33. The alarm unit of claim 32 wherein said means for recognizing
an alarm signal associated with said alarm unit further comprises
means for recognizing based on a particular frequency associated
with said alarm unit.
34. The alarm unit of claim 32 wherein said means for recognizing
an alarm signal associated with said alarm unit further comprises
means for recognizing based on an indicia associated with said
alarm unit contained in said alarm signal.
35. The alarm unit of claim 34 further comprising means for
generating a visible alarm.
36. The alarm unit of claim 34 further comprising means for
generating an audible alarm.
37. The alarm unit of claim 31 wherein said conductive metallic
portion is a metallic sheath.
38. The alarm unit of claim 31 wherein said alarm configuration
information specifies a type of alarm said at least one alarm unit
is to initiate.
39. The alarm unit of claim 31 wherein said alarm configuration
information specifies a duration of alarm said at least one alarm
unit is to initiate.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to optical fiber
intrusion systems, and more particularly to providing local area
warning of optical fiber intrusion.
[0002] Recent years have seen a proliferation of telecommunication
services. With the additional services has come an increased need
for network infrastructure, including in particular, buried cables
and associated equipment. One type of cable is fiber optic cable,
which generally contains multiple optical fibers bundled together
within one cable.
[0003] Fiber optic cable is subject to damage, especially when
buried close to the surface or when located in the vicinity of a
construction site. Since a single fiber optic cable may carry a
very large amount of data, the failure of a single fiber optic
cable may result in service outage for a large number of customers.
As such, network service providers take precautions in order to
avoid such failure.
[0004] One technique for monitoring buried fiber optic cable is
disclosed in U.S. Pat. No. 5,778,114, entitled Fiber Analysis
Method and Apparatus. That patent describes a fiber intrusion
detection system for detecting an intrusion or potential intrusion
to a buried fiber optic cable. That system includes an optical
splitter for splitting an optical signal into sub-signals for
injection into opposite ends of a looped optical fiber. The signals
emanating from the opposite fiber ends are recombined at the
splitter for receipt at a detector that measures the phase
difference between the optical sub-signals. A processor compares
the phase difference measured by the detector to known phase
difference measurements associated with different types of threats.
By matching the actual phase difference to the known phase
difference measurement associated with a particular type of
intrusion, the processor can thus identify the nature of the
intrusion.
[0005] While detecting the fiber intrusion threat is important, in
order to avoid actual damage to a fiber optic cable, it is also
important to warn the potential intruder of the imminent threat.
However, an alarm at a central network location may not allow for
network provider personnel to reach the actual threat location
(e.g., construction site) in time to avoid the damage. In
recognition of this problem, the '114 patent discloses a
disturbance monitor that may be dispersed along the right-of-way of
the fiber optic cable for providing a visible and/or audible
warning in the field in response to a signal from the fiber
intrusion detection system. The '114 patent discloses a wireless
link between the fiber intrusion detection system and the
disturbance monitor for signaling an alarm condition. One
disadvantage of that configuration is that a wireless communication
link may not always be available, or such a link may provide an
unreliable communication channel.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention provides an improved technique for
alerting of potential fiber optic cable intrusion. In accordance
with the invention, an alarm signal is generated in response to
detection of a stress on a fiber optic cable. The detection may be
performed by a stress detector located at a fiber optic cable
termination point. The alarm signal is then transmitted to remote
alarm units along the fiber optic cable right of way via a
conductive metallic portion of the fiber optic cable. The use of
the fiber optic cable itself to transmit the alarm signal is an
improvement over the prior techniques which generally utilized an
unreliable wireless communication channel. In one embodiment of the
invention, the alarm signal is transmitted via the metallic sheath
of the fiber optic cable.
[0007] In addition to detecting stress, the stress detector may
also determine the location of the stress, thereby determining the
location of a potential threat to the fiber optic cable. Various
techniques for detecting the location of the stress are disclosed
herein. The system uses the location of the stress in order to
determine one or more remote alarm units which are associated with
the location in order to activate an alarm at those alarm units.
Such alarm may be, for example, an audible or visible alarm in the
vicinity of the stress which will notify people that there is
potential danger to the fiber optic cable. The one or more remote
alarm units may therefore be separately addressed such that the
stress detection mechanism may determine which individual alarm
units to be activated. There are various techniques for addressing
the individual alarm units, such as sending the alarm signals on
particular frequencies, embedding unique identifiers in the alarm
signal, or utilizing particular signal pulse patterns in the alarm
signal. Alternatively, instead of activating particular ones of the
alarm units, a global alarm may be used, to which all alarm units
are responsive, in order to active all the alarm units along the
fiber optic cable right of way.
[0008] Upon receipt of an alarm signal to which an alarm unit is
responsive, the alarm unit will activate a perceptible alarm (e.g.,
audible or visible). In one embodiment, the alarm signal may
indicate the type or duration of the alarm to be activated. In
addition, the alarm unit may contain user input/output components
to allow for configurability of the unit by a user.
[0009] These and other advantages of the invention will be apparent
to those of ordinary skill in the art by reference to the following
detailed description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows a system designed in accordance with one
embodiment of the invention;
[0011] FIG. 2 shows one embodiment of a stress detector which may
be used in accordance with the present invention; and
[0012] FIG. 3 is a block diagram of one embodiment of an alarm unit
which may be used in accordance with the present invention.
DETAILED DESCRIPTION
[0013] FIG. 1 shows a system designed in accordance with one
embodiment of the invention. FIG. 1 shows a fiber termination point
102 which terminates one end of a fiber optic cable 104. As is well
known, fiber optic cable 104 contains multiple optical fibers as
shown in FIG. 1. Optical fibers 106 are used for data communication
and would be connected to well known equipment in order to
implement data communication in a manner will known in the art. For
clarity, such well known data communication equipment is not shown
in FIG. 1. Optical fiber 110 is a looped optical fiber whose
endpoints are connected to a stress detector 108. Stress detector
108 is used to recognize stress on fiber optic cable 104.
[0014] In one embodiment, the stress detector may be of the type
described in U.S. Pat. No. 5,778,114, entitled Fiber Analysis
Method and Apparatus, which is incorporated herein by reference.
Such a stress detector (referred to in the '114 patent as Fiber
Analysis System (FAS)) is shown in FIG. 2 as stress detector 200.
The stress detector 200 includes a splitter 210 having four ports
212, 214, 216, 218. A source of light 220 having a high degree of
coherence, such as a laser, produces a relatively narrow beam of
light 242 for receipt at the splitter port 212. Upon receipt of the
beam 242 at its port 212, the splitter 210 splits the beam,
yielding two optical sub-signals at the splitter ports 214 and 216.
The sub-signals are injected into to opposite ends of the fiber 108
and traverse the fiber in opposite directions. Each optical
sub-signal exits the fiber 108 from the end opposite the end into
which the sub-signal was injected.
[0015] The optical sub-signals exiting the fiber 108 ends re-enter
the splitter ports 214 and 216, respectively, for re-combination by
the splitter 210 into a single beam 244 that exits the splitter
port 218 for receipt at a detector 240. The detector 240 detects
characteristics of the beam, and particularly, the interference
between the two optical sub-signals recombined at the splitter 210.
If the two optical sub-signals destructively interfere, then power
of the beam detected by the detector 240 is low, whereas if the
optical sub-signals constructively interfere, the power produced by
the beam is high.
[0016] Under quiescent conditions, that is, with no stresses on the
fiber 108, the optical sub-signals traveling in opposite directions
in the fiber are 180 degrees out-of-phase and cancel each other.
However, when the fiber is stressed because of vibration, the
sub-signals are not completely out of phase and do not cancel each
other. Thus, the output signal of the detector 240 will change in
response to stress on the fiber. Varying the split provided by the
splitter 210 may control the magnitude of the detected phase
difference. A 50-50 split provides the greatest sensitivity.
However, other percentages may be desired where noise is a
factor.
[0017] As taught in the aforementioned '114 patent, the particular
stresses on the fiber are characterized by a processor 280 in the
form of a computer or the like which controls the light source 220
to generate a continuous beam, a random pattern of light, or a
pulsed beam representative of a string of binary values
representing a digital word. The processor 280 is responsive to the
output signal of the detector 240 and serves to compare the
re-combined beam characteristics detected by the detector to
plurality of reference values stored in a data base 260, typically
comprised of a magnetic storage medium, such as a disk drive. For
purposes of illustration, the database 260 has been depicted in
FIG. 2 as an element distinct from the processor 280. In reality,
the database 260 may reside on a disk drive within the processor
itself. Alternatively, the data base 28 could reside on a file
server (not shown) connected to the processor.
[0018] The processor 280 communicates through an interface 282
which allows the stress detector 200 to communicate with external
devices and networks as will be described in further detail below.
Although a single interface 282 is shown, interface 282 is meant to
represent one or more interfaces through which stress detector 200
communicates with other devices.
[0019] In an alternate embodiment, the stress detector 108 may be
configured and operated as described in U.S. Pat. No. 5,194,847,
entitled Apparatus and Method for Fiber Optic Intrusion Sensing,
which is incorporated herein by reference. The '847 patent
describes an apparatus for sensing intrusion into a predefined
perimeter using a coherent pulsed light. The apparatus includes a
coherent light pulse source for injecting coherent light pulses
into an optical fiber having a predetermined length and positioned
along a predefined perimeter. Light is backscattered from the
optical fiber due to Rayleigh backscattering and coupled into an
optical receiving fiber. The backscattered light is detected by a
photodetector coupled to the optical fiber and a signal is produced
in response thereto. An intrusion is detectable as a change in the
produced signal. To increase the sensitivity of the apparatus, a
reference fiber and an interferometer may also be employed. In an
embodiment in which the stress detector 108 is configured in
accordance with the teachings of the '847 patent, optical fiber 110
would be a single, non-looped, optical fiber.
[0020] Thus, returning to FIG. 1, by using the above described
techniques, the stress detector 108 can determine whether fiber
optic cable 104 is subject to stress and the threat of intrusion.
Considering that the fiber optic cable 104 may be approximately 30
miles long (at which point it connects to another fiber termination
point (not shown) for signal regeneration or other signal
processing) it is advantageous to determine not only that the fiber
optic cable 104 is subject to stress, but the location of such
stress along the length of fiber optic cable 104. There are various
known techniques for determining the stress location along the
length of a fiber optic cable which may be used in accordance with
the present invention.
[0021] In the embodiments described above, Optical Time Domain
Reflectometry (OTDR) may be used in order to determine the location
of the intrusion along an optical fiber. In accordance with OTDR,
an optical signal is injected into one end of an optical fiber for
propagation along the fiber. The signal injected into the fiber
will reflect back from a stress point. By measuring the time
difference between the transmission of the forward signal and the
receipt of the reflected signal, the distance to the stress point
can be determined. In an embodiment in which the stress detector
108 is configured in accordance with the teachings of the '114
patent, one skilled in the art could readily incorporate well known
OTDR techniques in order to add a stress point location
determination. In an embodiment in which the stress detector 108 is
configured in accordance with the teachings of the '847 patent, it
should be recognized that OTDR and stress point location is
incorporated into the teachings of that patent.
[0022] Returning now to FIG. 1, upon a determination that a threat
to the fiber optic cable 104 exists, an alarm is to be initiated at
the location of the threat. In accordance with an embodiment of the
invention, one or more alarm units are placed in the field at known
locations. FIG. 1 shows three alarm units, 120, 122, 124 at known
locations along the fiber optic cable 104 right of way. In one
embodiment, each alarm unit may be associated with an area, or
zone, rather than a particular location.
[0023] In accordance with the invention, and to overcome the
deficiencies of prior approaches, the stress detector communicates
an alarm signal to an alarm unit via the metallic sheath (or other
metallic portion) of the fiber optic cable 104. This eliminates the
potential problems of communicating via a wireless communication
link, such as the link not always being available, or the link
providing an unreliable communication channel.
[0024] In operation, stress detector 108 will detect a stress on
fiber optic cable 104 and will determine the location of such
stress as described above. Upon such determination, the stress
detector 108 will determine which of the alarm units should
activate an alarm (e.g., those alarm units that are located in the
vicinity of the stress or potential threat). Stress detector 108
may make this determination based on information stored in
processor 280, database 260, or some other memory or storage
device. Such information will associate particular alarm units with
particular fiber optic cable locations or zones. For example, if
the stress is determined to be located at point 130 on fiber optic
cable 104, stress detector 108 may determine that alarm unit 124 is
to be activated. It is also noted that multiple alarm units may be
activated in response to a stress detection by stress detector 108.
For example, if the stress is determined to be located at point 132
on fiber optic cable 104, stress detector 108 may determine that
both alarm units 122 and 124 are to be activated. Of course,
various options are possible for determining which one or more
alarm units are to be activated upon a stress determination.
[0025] Upon a determination of which alarm unit(s) to activate, the
stress detector will initiate an appropriate signal to active the
alarm unit(s). As described above, the signaling of alarm units to
initiate activation is accomplished by sending an alarm signal to
the alarm unit(s) via the conductive metallic sheath of the fiber
optic cable 104. The application of a signal to the metallic sheath
of a fiber optic cable is currently known for use in locating
buried cable. The applied signal is generally an alternating
current (AC) signal. The location signal is propagated via the
metallic sheath and a resultant magnetic field is radiated along
the length of the fiber optic cable. The radiated magnetic field is
detectable by surface equipment. As shown in FIG. 1, in accordance
with one embodiment of the invention the stress detector 108
activates signal generator 112. Signal generator 112 applies an
appropriate AC signal to the metallic sheath of fiber optic cable
104 via connection 114.
[0026] In accordance with the present invention, the alarm units
may be individually addressed so that the stress detector may
control which of the alarm units activates its alarm. There are
various possible techniques for addressing individual alarm units.
For example, each of the alarm units, or each of the alarm units
within a particular zone, may be associated with, and responsive
to, a particular frequency. In this embodiment, the stress detector
will determine the alarm units to be activated and send appropriate
instructions to signal generator 112 in order to initiate an alarm
signal at the appropriate frequency. Another technique for
addressing individual alarm units is to associate each of the alarm
units, or each of the alarm units within a particular zone, with a
unique identifier. In this embodiment, the stress detector will
determine the alarm units to be activated and send appropriate
instructions to signal generator 112 in order to initiate an alarm
signal having embedded therein the unique identifier of the alarm
units to be activated. Yet another technique for addressing
individual alarm units is to configure the alarm units to be
responsive to a particular signal pulse pattern. One skilled in the
art will recognize that there are various alternate techniques for
addressing individual alarm units.
[0027] In certain situations it may be advantageous to activate all
alarm units associated with a fiber optic cable (i.e., a global
alarm), regardless of their associated location or zone. As such,
each alarm unit may also be responsive to a particular global alarm
signal (e.g., a particular frequency, identifier or signal pulse
pattern), which may be used to active all of the alarm units along
the fiber optic cable 104 right of way.
[0028] Further details of the configuration of an alarm unit are
shown in FIG. 3. It is to be understood that FIG. 3 is a high level
block diagram of an alarm unit used to describe the configuration
and functionality of an alarm unit in accordance with the present
invention. One skilled in the art would be able to implement an
alarm unit given this description. The overall operation of alarm
unit 300 is controlled by a processor 306 which operates to control
the alarm unit 300 by executing stored computer program code which
defines the desired operation. The stored computer program code is
stored in a storage/memory unit 312 which may be implemented using
any type of computer readable medium, including magnetic,
electrical, optical, or other type of media. Although
storage/memory unit 312 is shown in FIG. 3 as a single unit, it may
also be comprised of multiple units. Alternatively, the operation
of alarm unit 300 may be defined by the circuit or hardware
configuration of processor 306, or by any combination of hardware
and software. Alarm unit 300 also contains an antenna 302 for
receiving the signals radiated from the fiber optic cable 104 as
described above. Antenna 302 is connected to receiver 304 which
processes the received signals and provides them to processor 306.
Alarm unit 300 also contains one or more audible alarm components
308 for providing an audible alarm in the vicinity of the alarm
unit. An audible alarm component may be, for example, a loudspeaker
or siren. Alarm unit 300 also contains one or more visible alarm
components 310 for providing a visible alarm in the vicinity of the
alarm unit. A visible alarm component may be, for example, a high
intensity strobe light. The alarm unit 300 also contains a power
supply 316 for supplying power to the unit. In one embodiment, the
power supply may be a self contained battery to allow for use in
the field. The alarm unit 300 also contains user input/output
devices 320 (e.g., keyboard, mouse, buttons, indicator lights,
display screen, etc.) to allow a user to interface with the alarm
unit. For example, this user interface may be used to allow a
technician to program into storage/memory 312 the appropriate one
or more frequencies, identifiers or signal pulse patterns to which
the alarm unit 300 will be responsive.
[0029] The alarm unit 300 will be located in the vicinity of a
fiber optic cable so that the antenna 302 may receive alarm signals
radiated from the fiber optic cable as described above. The alarm
unit 300 may be placed above the ground so that the audible and
visible alarms may be detected by people in the vicinity of the
alarm unit. The antenna may also be above the ground as the alarm
signals radiated from the fiber optic cable will be detectable by
the above ground antenna. Alternatively, it is possible to place
certain portions of the alarm unit (e.g., antenna) below ground,
while leaving the audible and visible alarms above ground. Since
the alarm unit 300 may be outside and exposed to the elements for
prolonged periods, it is advantageously designed to withstand harsh
weather conditions as well as repeated installation and removal. It
is also advantageously tamper and vandal resistant. The alarm unit
300 may be mounted on top of cable marker posts, or secured to
other structures. In one embodiment, the alarm unit may be affixed
to objects by a chain which enters the unit via a marker post entry
hole, and locks into slots (or over a peg) within the housing: The
chain will be held in place by a closed door on the alarm unit
enclosure. The area containing the chain will be separated from any
battery, electronics, and antenna.
[0030] In operation, the alarm unit 300 will receive via antenna
302 signals radiated from the fiber optic cable. A received signal
will be processed by receiver 304 and passed to processor 306.
Processor 306 will determine whether the received signal is one
which should activate the particular alarm unit 300. The processing
of signals will depend upon the particular implementation. In one
embodiment, in which the alarm units are responsive to alarm
signals on particular frequencies, the processor 306 may configure
receiver 304 to only receive signals on the particular frequency
associated with the particular alarm unit. Alternatively, in the
embodiment in which the alarm units are responsive to certain
identifiers within the alarm signals, then upon receipt of an alarm
signal the processor will compare the identifier embedded in the
alarm signal with the identifier(s) to which the alarm unit is
responsive (such identifier(s) may be stored in storage/memory
312). Alternatively, in the embodiment in which the alarm units are
responsive to certain pulse patterns within the alarm signals, then
upon receipt of an alarm signal the processor will compare the
received pulse pattern in the alarm signal with the pulse
pattern(s) to which the alarm unit is responsive (such pulse
pattern(s) may be stored in storage/memory 312).
[0031] In yet other embodiments, it may be possible that signals
other than alarm signals (e.g., location or otherwise) may be
propagated by the metallic sheath of the fiber optic cable and
therefore received by the alarm unit 300 antenna 302. In such
embodiments, a preliminary test for any signal received by alarm
unit 300 may be whether or not the particular signal is an alarm
signal or some other type of signal.
[0032] In addition to alerting the alarm unit 300, an alarm signal
may also contain additional configuration information for the alarm
unit 300. For example, the alarm signal may contain information
which specifies the type (e.g., audible and/or visible) of alarm
which the alarm unit 300 is to initiate. The alarm signal may also
contain information which specifies the duration of the alarm. With
respect to alarm duration, it is also noted that a user in the
field may terminate the alarm by pressing an appropriate button
(user input 320) on the unit.
[0033] Returning to FIG. 1, fiber termination point 102 may also
contain a network interface 116 connected to stress detector 108.
Upon detection of a stress (and its location) on fiber optic cable
104, the stress detector 108 may send an alarm notification to
another entity via a network. For example, upon detection of a
stress, stress detector 108 may send an alarm notification to a
device (e.g., pager or telephone) associated with a technician or
to a central monitoring station. These alarm notifications may be
sent via network interface 116 and the public switched telephone
network (PSTN), a data network (e.g., Internet), or any other
appropriate network.
[0034] The foregoing Detailed Description is to be understood as
being in every respect illustrative and exemplary, but not
restrictive, and the scope of the invention disclosed herein is not
to be determined from the Detailed Description, but rather from the
claims as interpreted according to the full breadth permitted by
the patent laws. It is to be understood that the embodiments shown
and described herein are only illustrative of the principles of the
present invention and that various modifications may be implemented
by those skilled in the art without departing from the scope and
spirit of the invention. Those skilled in the art could implement
various other feature combinations without departing from the scope
and spirit of the invention. For example, while the above described
embodiments describe the use of the metallic sheath of the fiber
optic cable for transmitting the alarm signal, any conductive
metallic portion of a fiber optic cable could be used to transmit
the alarm signal. For example, an additional wire could be added
within the fiber optic cable sheath for such purposes.
* * * * *