U.S. patent application number 10/750448 was filed with the patent office on 2005-02-24 for method, apparatus and system for minimally intrusive fiber identification.
Invention is credited to Frigo, Nicholas J., Iannone, Patrick, Reichmann, Kenneth C..
Application Number | 20050041902 10/750448 |
Document ID | / |
Family ID | 34198143 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050041902 |
Kind Code |
A1 |
Frigo, Nicholas J. ; et
al. |
February 24, 2005 |
Method, apparatus and system for minimally intrusive fiber
identification
Abstract
A method, apparatus and system for minimally intrusive fiber
identification includes imparting a time-varying modulation onto an
optical signal propagating in an optical fiber and subsequently
detecting the presence of the time-varying modulation in the
optical signal transmitting through the fiber to identify the
fiber. In a specific embodiment of the invention, a time-varying
curvature is imposed on the fiber to be identified and the presence
of the resultant time variation in the transmitted power of a
propagating optical signal is subsequently detected for
identification of the manipulated fiber.
Inventors: |
Frigo, Nicholas J.; (Little
Silver, NJ) ; Iannone, Patrick; (Red Bank, NJ)
; Reichmann, Kenneth C.; (Hamilton, NJ) |
Correspondence
Address: |
AT&T CORP.
P.O. BOX 4110
MIDDLETOWN
NJ
07748
US
|
Family ID: |
34198143 |
Appl. No.: |
10/750448 |
Filed: |
December 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60496448 |
Aug 20, 2003 |
|
|
|
Current U.S.
Class: |
385/1 |
Current CPC
Class: |
G01M 11/35 20130101;
G01M 11/088 20130101; G02B 6/447 20130101; G02F 1/095 20130101;
H04B 10/07 20130101; G02B 6/2852 20130101; G01M 11/30 20130101 |
Class at
Publication: |
385/001 |
International
Class: |
G02F 001/01 |
Claims
What is claimed is:
1. A method for identifying an optical fiber, comprising: imparting
a time-varying modulation onto an optical signal propagating in
said optical fiber; and detecting the presence of said imparted
time-varying modulation to identify said optical fiber; wherein
said imparting and detecting do not interrupt the propagation of
said optical signal along said optical fiber.
2. The method of claim 1, wherein said time-varying modulation is
imparted on said optical signal by varying a property of said
optical fiber as a function of time.
3. The method of claim 2, wherein a curvature of at least a portion
of said optical fiber is varied as a function of time such that a
time-varying loss of power is generated in said propagating optical
signal.
4. The method of claim 3, wherein the curvature of said optical
fiber is varied by vibrating at least a portion of said optical
fiber.
5. The method of claim 4, wherein an amplitude of said vibration is
small compared to the average power of said propagating optical
signal such that said propagating optical signal is minimally
affected.
6 The method of claim 2, wherein a birefringence of at least a
portion of said optical fiber is varied as a function of time such
that a polarization of said propagating optical signal is varied as
a function of time.
7. The method of claim 6 wherein the birefringence of said optical
fiber is varied via a time-varying magnetic field.
8. The method of claim 6, wherein the birefringence of said optical
fiber is varied via a time-varying electric field.
9. The method of claim 1, wherein said time-varying modulation is
imparted on said optical signal by varying a frequency of said
propagating optical signal is varied as a function of time.
10. The method of claim 9, wherein the frequency of said
propagating optical signal is varied as a function of time through
time-varying non-linear interactions.
11. The method of claim 10, wherein said time-varying non-linear
interactions are created through the interaction of acoustic waves
with said propagating optical signal in said optical fiber.
12. The method of claim 1, wherein said time-varying modulation is
imparted on said optical signal by a source of said optical
signal.
13. The method of claim 12, wherein said time-varying modulation is
imparted on said optical signal at an intermediate point between
optical fibers in a fiber path.
14. The method of claim 1, further comprising bending said optical
fiber such that light is scattered out of said fiber to enable said
detecting.
15. An apparatus for identifying an optical fiber, comprising: at
least one modulating device for imparting a time-varying modulation
onto an optical signal propagating in said optical fiber; at least
one fiber bending device for bending said optical fiber such that
at least a portion of the optical signal is scattered out of said
optical fiber; and at least one detector, said detector receiving
the scattered portion of the optical signal for detecting the
presence of said imparted time-varying modulation to identify said
optical fiber.
16. The apparatus of claim 15, wherein said imparting and detecting
do not interrupt the propagation of said optical signal along said
optical fiber.
17. The apparatus of claim 15, wherein said optical fiber comprises
a plurality of interconnected optical fibers.
18. The apparatus of claim 15, further comprising a control unit,
said control unit comprising a memory for storing information and
program instructions and a processor for executing said
instructions to configure the apparatus to perform the steps of:
imparting a time-varying modulation onto the optical signal
propagating in said optical fiber; and detecting the presence of
said imparted time-varying modulation to identify said optical
fiber.
19. The apparatus of claim 18, wherein said control unit is further
adapted to cause a source of said optical signal to impart a
time-varying modulation onto said optical signal.
20. The apparatus of claim 15, wherein said at least one modulating
device comprises a transmitter head and said bending device and
said detector comprise a receiver head.
21. The apparatus of claim 20, wherein said transmitter head
further comprises a bending device and a detector and said receiver
head further comprises a modulating device.
22. The apparatus of claim 15, wherein said modulating device
comprises a vibrating piston and said vibrating piston varies the
curvature of at least a portion of said optical fiber as a function
of time such that a time-varying loss of power is generated in said
propagating optical signal.
23. The apparatus of claim 15, wherein said modulating device
comprises a piezo-electric transducer and said piezo-electric
transducer varies the curvature of at least a portion of said
optical fiber as a function of time such that a time-varying loss
of power is generated in said propagating optical signal.
24. The apparatus of claim 15, wherein said fiber bending device is
adjustable for varying the radius of the bend on said optical
fiber.
25. The apparatus of claim 15, wherein said fiber bending device
comprises at least one anvil.
26. The apparatus of claim 15, further comprising at least one
lightguide for guiding the scattered portion of the optical signal
to said at least one detector.
27. The apparatus of claim 26, wherein said lightguide comprises a
plexiglass lightguide.
28. The apparatus of claim 15, wherein said modulating device
comprises a means for introducing a varying magnetic field and said
means for introducing a varying magnetic field varies the
polarization of said propagating optical signal as a function of
time by varying the birefringence of said optical fiber as a
function of time.
29. The apparatus of claim 15, wherein said means for introducing a
varying magnetic field comprises a solenoid.
30. The apparatus of claim 28, wherein said detector further
comprises a polarizer.
31. The apparatus of claim 15, wherein said modulating device
comprises a means for varying the frequency of said propagating
optical signal as a function of time through non-linear
interactions.
32. The apparatus of claim 31, wherein said means for varying the
frequency of said propagating optical signal as a function of time
comprises a means for introducing acoustic waves and said means for
introducing acoustic waves varies the frequency of said propagating
optical signal as a function of time through non-linear
interactions of said acoustic waves and said propagating optical
signal.
33. The apparatus of claim 31, wherein said means for varying the
frequency of said propagating optical signal as a function of time
comprises an acoustic horn.
34. The apparatus of claim 15, further comprising at least a second
detector for detecting said time-varying modulation near the point
of modulation such that a subsequent downstream detection of said
modulation may be compared to the modulation detected near the
point of modulation for the identification of said optical
fiber.
35. The apparatus of claim 15, wherein said apparatus is
implemented to verify communications between at least two points in
a passive optical network.
36. An apparatus for identifying an optical fiber, comprising: a
means for imparting a time-varying modulation onto an optical
signal propagating in said optical fiber; a means for bending said
optical fiber such that at least a portion of the optical signal is
scattered out of said optical fiber; and a means for detecting the
presence of said imparted time-varying modulation to identify said
optical fiber.
37. The apparatus of claim 36, further comprising: a means for
guiding the scattered portion of said optical signal to said means
for detecting.
38. A system for identifying at least some of a plurality of
optical fibers, comprising: a plurality of fiber bending devices,
each of said devices connected to a respective one of said optical
fibers for bending said respective optical fiber such that at least
a portion of a respective optical signal is scattered out of a
respective optical fiber; and at least one detector, said detector
receiving the scattered portion of a respective optical signal from
a respective optical fiber for detecting the presence of a
respective imparted time-varying modulation to identify said
optical fibers.
39. The system of claim 38, wherein said respective time-varying
modulation is imparted on each of said respective optical signals
by a respective transmitter.
40. The system of claim 38, further comprising a plurality of
modulating devices, each of said devices acting on a respective one
of said optical fibers for imparting said time-varying modulation
onto a respective optical signal propagating in a respective
optical fiber.
41. The system of claim 38, further comprising control unit, said
control unit comprising a memory for storing information and
program instructions and a processor for executing said
instructions to control the components of said system to configure
the system to perform the steps of: imparting a time-varying
modulation onto a respective optical signal propagating in a
respective optical fiber; and detecting the presence of a
respective imparted time-varying modulation to identify said
optical fibers.
42. The system of claim 41, wherein said control unit generates a
control signal for causing a respective transmitter to impart a
time-varying modulation on respective optical signals to be
propagated via said plurality of optical fibers.
43. The system of claim 38, wherein said system comprises a
plurality of detectors, each of said detectors receiving the
scattered portion of a respective optical signal from a respective
optical fiber.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/496,448, filed Aug. 20, 2003, which is herein
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to fiber
identification and, more particularly, to a method, apparatus and
system for identifying fibers that minimally intrudes with optical
signals propagating therein.
BACKGROUND OF THE INVENTION
[0003] Modern telecommunications offices have evolved in recent
years to accommodate greater volumes of traffic, thus placing
larger and larger amounts of equipment (usually connected by
optical fibers) in areas of limited space. In addition to the
increasing numbers of optical fibers, traffic carried by each of
the optical fibers is also ever-increasing. As capacity increases,
problems arise in the management of the optical fibers of a
telecommunication office. Specifically, because optical fibers
transport large amounts of high bit-rate traffic, the disruption of
such traffic leads to the disruption of service to many circuits
and, as such, to many customers simultaneously.
[0004] For example, a typical telecommunications office includes a
plurality of racks of transmission equipment, each having multiple
fiber connections to transmitters and receivers in the line cards
supported in the racks. The fibers are ultimately destined for
terminals either in that specific office, at customer locations, or
in other offices. These office fibers are typically bundled and
laid in fiber trays that provide paths or conduits to junction
points such as patch panels (e.g., lightguide cross connects) which
connect the office fibers (sometimes called "jumpers") to the
outside plant (OSP) fibers which carry traffic from this office to
other destinations. Over time, the exact connection paths (i.e.,
the connection paths between ports on a lightguide cross connect to
corresponding ports on the line cards in the racks) may become
unknown ue to, for example, labels used to identify fibers falling
off), fibers being initially labeled incorrectly, or emergency
maintenance action requiring a fast response not being properly
documented. The unidentified or mis-identified fiber connections
can ultimately lead to disastrous Quality of Service conditions.
For example, assume that a technician, in the course of responding
to a (loss of light) alarm, disconnects a fiber labeled as being
connected to a port identified as the source of the alarm. If the
fiber connection is mislabeled or unknown, the technician may in
fact be disrupting a properly functioning circuit, thus creating a
new error and disruption of service and delaying the repair of the
original faulted circuit. As such, several means have been proposed
for identifying a fiber without interrupting traffic on the fiber
connection.
[0005] Such proposed means for the identification of optical
communication circuits include Local Injection (LI) and Local
Detection (LD) methods that have been used in practice for fusion
splicing. These techniques involve bending a bundle of optical
fibers in a cable at two distant locations and injecting light into
the fiber at one bent portion while detecting the injected light
that leaks from the fiber at the other bent portion. This method
however, has several disadvantages. For example, in order to inject
an adequate amount (i.e., power) of light into the coated fiber to
be later detected, the fiber must be bent with a curvature large
enough (i.e., radius of curvature small enough) to inject light
thus causing radiated light of a large power to leak from the bent
portion of the fiber to which the LI method is to be applied. This
causes deterioration of a signal that is to be transmitted by the
bent fiber. Therefore, if the LI method is applied during
transmission of an optical signal, troubles such as channel
interruption will occur in optical signal communication, and in an
extreme case, cracking might occur in the coated fiber. In
addition, if light having a power greater than a threshold level is
injected into a fiber by the LI method, the injected light may be
transmitted to an office or to subscribers resulting in the
addition of a noise component that may deteriorate an optical
signal being transmitted.
[0006] Therefore, a need exists for a method and apparatus for the
identification of optical fibers that minimally intrudes with
optical signals propagating therein.
SUMMARY OF THE INVENTION
[0007] The present invention provides methods and apparatuses for
fiber identification that minimally intrudes with a propagating
optical signal therein.
[0008] In one embodiment of the present invention, a method
includes varying a property of an optical fiber as a function of
time such that a time-varying modulation is imparted on an optical
signal propagating therein, and subsequently detecting the
time-varying modulation to identify the optical fiber. More
specifically, in one embodiment of the present invention, a
curvature of at least a portion of an optical fiber is varied as a
function of time such that a small time-varying loss of power is
generated in the propagating optical signal. The time-varying loss
of power is subsequently detected downstream to unambiguously
identify the optical fiber.
[0009] In an alternate embodiment of the present invention,
birefringence of an optical fiber is varied as a function of time
such that the polarization of an optical signal propagating therein
is varied as a function of time. A detector adapted for the
detection of the time-varied polarization (i.e., a detector
including a polarizer) subsequently detects the time-varying
polarization to identify the optical fiber.
[0010] In yet another embodiment of the present invention, a
property, such as the frequency, of an optical signal propagating
in an optical fiber is varied as a function of time. The
time-varying altered property (e.g., the frequency of the optical
signal) is subsequently detected for identification of an optical
fiber transmitting the optical signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The teaching of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0012] FIG. 1 depicts a high level block diagram of a
telecommunications office wherein an embodiment of the present
invention may be applied;
[0013] FIG. 2 depicts a high level block diagram of an embodiment
of a fiber identification device of the present invention;
[0014] FIG. 3 depicts a high level block diagram of an embodiment
of a fiber identification system in accordance with the present
invention;
[0015] FIG. 4 depicts a high-level block diagram of an embodiment
of a control unit suitable for use in the fiber identification
device of FIG. 2 and the fiber identification system of FIG. 3;
[0016] FIG. 5 depicts a high level block diagram of an alternate
embodiment of a fiber identification device of the present
invention; and
[0017] FIG. 6 depicts a high level block diagram of a passive
optical network (PON) including an embodiment of a fiber
identification device of the present invention.
[0018] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0019] Although various embodiments of the present invention herein
are being described with respect to optical fibers within a
telecommunications office, it should be noted that the optical
fibers and the telecommunications office presented herein are
simply provided as exemplary working environments wherein various
embodiments of the present invention may be applied and should not
be treated as limiting the scope of the invention. It will be
appreciated by those skilled in the art informed by the teachings
of the present invention that the concepts of the present invention
may be applied to a single or multiply-interconnected optical
fibers (or waveguides) in substantially any working environment
(local or remote) for the identification of the transmission
medium.
[0020] FIG. 1 depicts a high level block diagram of a
telecommunications office wherein an embodiment of the present
invention may be applied. The telecommunications office 100 of FIG.
1 illustratively comprises three racks of transmission equipment
102, 103, and 104, each rack having, connected to line cards
therein (not shown), the first end of a plurality of transmission
fibers 105.sub.1-105.sub.n, 110.sub.1-110.sub.n, and
115.sub.1-115.sub.n, respectively. The telecommunications office
100 further comprises a plurality of cable trays 120, and a patch
panel (illustratively a lightguide cross connect (LGX)) 125. Second
ends of the plurality of transmission fibers 105, 110 and 115 are
connected to ports on a first side of the LGX 125. A plurality of
outside plant cables 130.sub.1-130.sub.m are connected to ports on
a second side of the LGX 125. The telecommunications office 100
further comprises an embodiment of a fiber identification device
140 in accordance with the present invention. In FIG. 1, a first
portion of the fiber identification device 140 of the present
invention is illustratively located on a bottom fiber of the
transmission rack 104 and a second portion of the fiber
identification device 140 is located on a bottom fiber of the first
side of the LGX 125.
[0021] In the telecommunications office 100, at least some of the
plurality of fibers 105 may interconnect the various ports of the
line cards (not shown) of the transmission rack 102 to ports on the
first side of the LGX 125 (for traffic that is ultimately destined
to go outside the office, for example on an outside plant fiber
(OSP)). Similarly, at least some of the plurality of fibers 110 and
115 may interconnect the various ports of the line cards (not
shown) of the transmission equipment racks 103 and 104,
respectively, to ports on the first side of the LGX 125. In
operation, communication between the transmission racks 102,103 and
104 and the LGX 125 is accomplished over the transmission fibers
105,110 and 115, respectively. An application of the fiber
identification device 140 of the present invention is used to
identify to which port of the LGX 125 a particular fiber from one
of the transmission racks 102, 103 and 104 is connected or
vice-versa. For example, in FIG. 1 the fiber identification device
140 of the present invention is connected to a bottom fiber of the
transmission rack 104 and to a bottom fiber of the first side of
the LGX 125 to determine if the fiber connected to a bottom port of
the transmission rack 104 is the same fiber as the fiber connected
to a bottom port of the first side of the LGX 125.
[0022] In accordance with the aspects of the present invention, an
optical fiber is identified by imparting a time-varying modulation
on an optical signal propagating in the optical fiber and
subsequently detecting the presence of the imparted time-varying
modulation to identify the optical fiber. In the present invention,
the imparted time-varying modulation and the subsequent detection
are performed such that the propagation of the optical signal in
the optical fiber is not interrupted (described in greater detail
below). For example, in various embodiments of the present
invention an optical fiber is identified by varying a property of
the optical fiber as a function of time, and then detecting the
presence of the imparted variation in an optical signal propagating
through that fiber that is correlated to the variation of the
optical fiber property. For example, the curvature of an optical
fiber may be varied as a function of time to impart a time-varying
loss of power in an optical signal propagating therein. The
presence of the imparted time-varying loss of power is then
subsequently detected to identify the subject fiber.
[0023] In alternate embodiments of the present invention, an
optical signal is identified by imparting a time-varying modulation
on an optical signal outside of the fiber in which it is being
transmitted. For example, a time-varying modulation may be imparted
on an optical signal at an intermediate point between two sections
of fiber (i.e., at the location of a free space beam expander), and
the presence of the modulation subsequently identified in the
transmission fiber to identify the fiber path. In addition, a
time-varying modulation may be imparted on one or a plurality of
optical signals outside of a fiber or fiber path in which the
optical signals are to be transmitted. For example, a transmitter
or transmitters may be controlled to apply a distinctive additional
signal or over-modulation (i.e., time-varying modulation) of an
optical signal to be transmitted in an optical fiber or fibers to
be identified.
[0024] Finally, it should be noted that in the description of the
various embodiments herein, the use of the term "fiber" may be used
to identify a single fiber for transmitting an optical signal, or a
fiber path comprising a plurality of interconnected fibers for
transmitting an optical signal across a network. That is, the
aspects of the present invention may be implemented to identify a
single fiber transmitting an optical signal, or to identify an
optical path on a network of a plurality of interconnected fibers
possibly carrying a plurality of optical signals. The time-varying
modulation may be imparted on one or a plurality of optical signals
by varying a property of an optical fiber propagating the optical
signal. In addition a time-varying modulation may be imparted on
one or a plurality of optical signals outside of a fiber or fiber
path in which the optical signal is being transmitted (i.e.,
time-varying modulation imparted at an intermediate point between
interconnected fibers).
[0025] More specifically, a detectable unique signature is imparted
on optical signals propagating through a subject optical fiber or
optical fiber path and the imparted signature is subsequently
detected to identify the subject optical fiber or path. The
inventors herein illustratively depict three properties of light,
namely; polarization (i.e., the direction of the oscillating
electric field); frequency; and amplitude (the electric field
strength) or power (proportional to its square); that may be used
in the implementation of the invention disclosed herein. The
manipulation of the aforementioned three properties of light, which
are used to impose a detectable "signature" on the transmitted
light which is subsequently used to identify an optical fiber, are
discussed in greater detail below. Although various embodiments of
the present invention are being described herein as manipulating
three optical properties for imparting a detectable signature on an
optical signal propagating in an optical fiber, it will be
appreciated by those skilled in the art informed by the teachings
of the present invention that more seemingly sophisticated forms of
imparting a time-varying modulation on an optical signal
propagating in an optical fiber (e.g., phase modulation) and more
seemingly sophisticated forms of detection (e.g., heterodyne
detection) may be implemented within the concepts of the present
invention to identify a subject optical fiber or fiber path.
[0026] FIG. 2 depicts a high level block diagram of an embodiment
of a fiber identification device of the present invention suitable
for use in the telecommunications office of FIG. 1. The fiber
identification device 140 of FIG. 2 illustratively comprises a
lightguide (illustratively a plexiglass lightguide) 210, a fiber
bending device (illustratively a clamping anvil) 220, a detector
(illustratively a photodiode) 230, and a modulating device
(illustratively a vibrating piston) 240. FIG. 2 further depicts an
optical fiber 250 inter-positioned between the clamping anvil 220
and the plexiglass lightguide 210 to illustrate the concepts of the
present invention. For convenience, the embodiment of FIG. 2
depicts an embodiment of the present invention which combines the
aspects of modulation and detection processes in a single
device.
[0027] In the fiber identification device 140 of FIG. 2, the
vibrating piston 240, the clamping anvil 220 and the photodiode 230
are depicted as being in close proximity for illustrative purposes
and for ease of explanation. It will be appreciated by those
skilled in the art informed by the teachings of the present
invention that a vibrating piston, a clamping anvil and a
photodiode of the present invention may be as close or as far apart
as necessary to perform the identification method of the present
invention as dictated by economics of production. More
specifically, a fiber identification device in accordance with the
present invention may be comprised of a transmitter head (i.e.,
comprised of the vibrating piston 240 of FIG. 2) and a receiver
head 225 (i.e., comprised of the lightguide 210, the clamping anvil
220 and the detector 230. The transmitter head 240 may be located
on a fiber within, for example, a telecommunications office for
imparting a time-varying modulation on an optical signal
propagating in the optical fibers of the telecommunications office
while the receiver head 225 may be located hundreds of meters or
kilometers away for detecting the presence of the imparted
time-varying modulation for identification of a subject
fiber(s).
[0028] In addition, although the vibrating piston 240 of FIG. 2 is
depicted as operating on a bent portion of the subject fiber, in
alternate embodiments of the present invention wherein a
transmitter head and a receiver head are located distances apart
from each other, a vibrating piston may impart a time-varying
modulation on an optical signal by vibrating a substantially
straighter portion of the optical fiber to increase (by adding
curvature) or decrease (by reducing curvature) the bending loss
applied to an optical fiber. Furthermore, although in FIG. 2, the
modulating device is depicted as a vibrating piston, it will be
appreciated by those skilled in the art informed by the teachings
of the present invention that the modulating device may be any such
device capable of providing a mechanical vibration or biasing
curvature of the fiber. Even further, the modulating device in
other embodiments of the present invention may be substantially any
component capable of imparting a time-varying modulation on an
optical signal propagating in subject optical fibers as described
throughout this disclosure.
[0029] Furthermore, although in FIG. 2, the vibrating piston 240,
the clamping anvil 220 and the photodiode 230 are depicted as
comprising separate components, in alternate embodiments of the
present invention, the vibrating piston, the clamping anvil and the
photodiode of the present invention may comprise a single
component, multiple components or substantially any combination
thereof.
[0030] Referring back to FIG. 2, in the fiber identification device
140 the vibrating piston 240 is mechanically driven such that it
vibrates the fiber 250 and produces a time-varying curvature of the
fiber 250, and thus a time-varying loss (i.e., a power variation)
in an optical signal guided by the fiber 250 due to "bending loss".
Further downstream, a fiber to be tested for identification
(illustratively the fiber 250) is bent by the clamping anvil 220.
The basic principle is that when the fiber 250 is bent, some of the
light (i.e., traffic on the fiber or alternatively, a test signal)
is scattered out of the fiber core and subsequently out of the
fiber 250, itself. As such and as illustrated by the smaller graphs
on the lower left, the lower right, and on the top right of FIG. 2,
the power carried by the fiber's fundamental mode is essentially
divided into two components. A first component represents the
remaining signal in the fiber 250 (graph on lower right) and
continues propagating along the fiber 250. The second component
represents the portion of the signal that has been scattered out of
the fiber 250 (graph on upper right). At least a portion of this
scattered signal is collected by the plexiglass lightguide 210 and
guided to the detector 230. The detector 230 is configured to have
electronics sensitive to the corresponding frequency of the
time-varying loss imparted by the vibrating piston 240. As
illustrated in FIG. 2, the light leaving the fiber has a small ac
component to its amplitude (dithered) due to the overmodulation of
the signal propagating in the fiber 250 imparted by the vibrating
piston 240 and the detector 230 is well suited to detect power
variations at the overmodulation frequencies. Although in FIG. 2
the fiber identification device 140, is illustratively depicted as
comprising a lightguide for guiding the scattered light out of the
fiber 250, in alternate embodiments of the present invention, a
fiber identification device of the present invention does not
comprise a lightguide and, as such, the light scattered from a bent
fiber is detected directly by an included detector instead.
[0031] In accordance with the present invention, the frequency of
the dither (i.e., the frequency of the vibration imparted by the
vibrating piston 240) is well established and the dither amplitude
and static biasing curvature is chosen such that the dither
amplitude is small compared to the average power of the signal
propagating in the fiber 250 in order to minimally impact the
transmitted signal. The detector 230 needs to only sensitively
detect the presence of the time variation at the frequency imparted
by the vibrating piston 240. The detection of the consistent
presence of the time-varying signal at the imparted frequency by
the detector 230 is a clear indication that the vibrating piston
240 is acting on that particular fiber upstream and as such, the
fiber 250 is identified. That is, if the vibrating piston 240 were
not acting upstream on the particular fiber now being tested, the
detector 230 would only detect random noise within a detection
bandwidth centered about the frequency of the modulation
(dithering) imparted by the vibrating piston 240. While there would
be some spectral content at the central frequency of the detector
230 in the scattered signal of a fiber that is not being dithered,
it would be quite distinguishable from the dithered signal.
[0032] In the detection method of the present invention, there is
little need for accurate calibration. That is, it is sufficient to
detect the presence of the fundamental frequency imparted by the
vibrating piston 240 rather than its exact amplitude. Furthermore,
the detection of the present invention is an AC measurement, which
may be performed with much higher gain, discrimination, and lack of
bias drift when compared to an equivalent DC measurement. Even
further, in various embodiments of the present invention the most
pertinent information carried by the scattered, dithered signal is
the dithering frequency and its presence. As such, the filter
bandwidth of a detector, such as the detector 230 of FIG. 2, may be
restricted to a very narrow range (i.e., the detection time
constant may be on the order of seconds) since it is only necessary
to confirm the presence of the dithering frequency. Thus, the
detection of the present invention may be quite sensitive. In
short, the identification process is essentially complementary, in
a measurement sense, to an accurate power measurement.
[0033] A fiber identification device in accordance with the present
invention may further comprise a control unit. For example, the
fiber identification device140 of FIG. 2 further comprises a
control unit 275 to enhance the operation when the transmitter head
240 is remotely located from the receiver head 225. The control
unit 275 is adapted to control the transmitter head 240 and/or the
receiver head 225. For example, the transmitter head 240 may be
placed on a portion of the fiber 250 by a technician. The
technician may subsequently place the receiver head 225 downstream
on the fiber 250 at a position on the fiber 250 located hundreds of
meters or kilometers away. After placing the receiver head 225 on
the fiber 250, the technician may then remotely send a signal
(e.g., a radio or Ethernet signal) to the control unit 275 to cause
the control unit 275 to generate a control signal to begin the
time-varying modulation of the optical signal in the optical fiber
250 by starting the operation of the vibrating piston 240. The
control unit 275 may also be configured to be capable of adjusting
the amplitude (or frequency) of the vibration of the vibrating
piston 240 (or biasing curvature) to optimize the fiber
identification device 140 of the present invention by choosing an
amplitude (or frequency) of vibration that will minimally intrude
with a propagating optical signal in the fiber 250. Although in the
description directly preceding it is described that a remote signal
is sent to the control unit to generate a control signal to
initiate and control the operation and function of the transmitter
head 240, a control unit in accordance with the present invention
may either be hard wired to one or both, the transmitter head(s)
and the receiver head(s), for communication or may alternatively be
in communication with one or both, the transmitter head(s) and the
receiver head(s), via remote means.
[0034] Furthermore, in an alternate embodiment of the present
invention, a fiber identification device may comprise more than one
transmitter head. As such, a technician may place a transmitter
head on each of a plurality of fibers in, for example, a
telecommunications office and then head out to the field. The
technician may then test the fibers at a position downstream
located on the fiber hundreds of meters or kilometers away by
placing a receiver head on the fibers one at a time. The technician
may send a remote signal (e.g., a radio signal) to an included
control unit adapted to turn one of the transmitter heads on at a
time while placing the receiver head on the fibers one at a time to
detect the presence of the time-varying modulation imparted on a
respective optical signal to identify the optical fiber associated
with the transmitter head that is on. In this manner, a plurality
of fibers may be identified remotely by a technician.
Alternatively, more than one of the plurality of transmitter heads
may be turned on at once, each of the transmitter heads having a
different frequency of vibration associated with it, and as such,
the receiver head may be used to identify the presence of the
various known frequencies to identify an optical fiber associated
with the transmitter head vibrating at a specific known frequency.
Although in the description above various embodiments of the fiber
identification device of the present invention are depicted and
described as having a remotely controlled transmitter head(s), a
receiver head(s) may also be remotely controlled by sending a
remote signal (e.g., a radio signal) to an included controller for
operatively controlling the receiver head(s) (e.g., the detector(s)
and any adjustable bending devices) of the present invention.
[0035] Even further, in yet another embodiment of the present
invention, a group of fiber identification devices in accordance
with the present invention may comprise a fiber identification
system. That is, a fiber identification system of the present
invention may comprise more than one transmitter head and more than
one receiver head. For example, FIG. 3 depicts a high level block
diagram of an embodiment of a fiber identification system 300 in
accordance with the present invention. The fiber identification
system 300 of FIG. 3 comprises a plurality of transmitter heads
340.sub.1-340.sub.N (collectively transmitter heads 340), a
plurality of receiver heads 325.sub.1-325.sub.N (collectively
receiver heads 325), a plurality of optical fibers
350.sub.1-350.sub.N (collectively optical fibers 350) and a
controller 275. As in the fiber identification device 140 of FIG.
2, each of the transmitter heads 340 of the fiber identification
system 300 includes at least one modulating device, such as a
vibrating piston (not shown). Similarly, as in the fiber
identification device 140 of FIG. 2, each of the receiver heads 325
of the fiber identification system 300 of FIG. 3 includes at least
a fiber bending device (e.g., an anvil (not shown)) and a detector
(not shown). Alternatively, the receiver heads 325 of the fiber
identification system 300 of FIG. 3 may each further include a
lightguide.
[0036] The plurality of transmitter heads 340 and the plurality of
receiver heads 325 in the fiber identification system 300 of FIG. 3
may be placed on respective fibers by a technician in an attempt to
identify specific optical fibers. More specifically, a technician
may connect a transmitter head 340 on a position on each of the
plurality of optical fibers 350 that may be located in, for
example, a telecommunications office. The technician may then head
out to the field. The technician may then connect a receiver head
325 downstream on each of the plurality of fibers 350 thought to be
the same fibers or in the same fiber paths as the fibers in the
office at a position located hundreds of meters or kilometers away.
In such embodiments, the fiber identification method of the present
invention may be executed manually or automatically. For example, a
technician may send a remote signal (e.g., a radio signal) to the
control unit 275 which is adapted to control the transmitter heads
340 for turning the vibration of the transmitter heads 340 on and
off. The technician may then choose to monitor different ones of
the plurality of receiver heads 325 to identify the presence of the
time-varying modulation imparted by the specific ones of the
transmitter heads 340 to identify specific fibers.
[0037] Alternatively and for automatic operation, the control unit
275 of the present invention may be adapted to automatically
control the operation of the plurality of transmitter heads 340 and
the plurality of receiver heads 325 in substantially any
combination and frequency to identify the subject optical fibers by
iteratively controlling respective ones of the transmitter heads
340 and the receiver heads 325 to identify the presence of an
imparted respective time-varying modulation imparted on respective
propagating optical signals and as such, identify each of the
plurality of optical fibers. The control unit 275 of the present
invention keeps track of which transmitter heads 340 are operating
and at what frequencies. Each of the plurality of receiver heads
325 transmits the respective outputs of the detectors (not shown)
of the receiver heads 325 to the control unit 275. The control unit
275, knowing which detected signal was received from which receiver
head 325, is able to identify the plurality of optical fibers 350
by examining the received outputs of the receiver heads 325 and
identifying the respective time-varying modulation imparted on the
respective optical signals propagating in the respective optical
fibers 350.
[0038] Alternatively, the fiber identification system 300 of FIG. 3
may be configured to comprise a single detector for receiving the
scattered portions of the respective optical signals from the
respective optical fibers. In such an embodiment, the single
detector is configured such that it is operative to receive
respective scattered portions of the optical signals of the
respective optical fibers one at a time and to send the respective
detected information to the control unit. The control unit may then
identify the respective optical fibers from the information
received from the single detector.
[0039] Even further, in various embodiments of the present
invention, a control unit of the present invention may be adapted
to generate a control signal to cause a signal source (i.e., a
signal transmitter) to apply a distinctive additional signal or
over-modulation (i.e., time-varying modulation) of an optical
signal to be transmitted in an optical fiber or fibers to be
identified. That is, a control unit of the present invention may be
adapted to control a modulator of one or more transmitters of a
system to cause a time-varying modulation to be imparted by the
transmitters on respective optical signals to be transmitted on
respective optical fibers for subsequent identification of the
optical fibers in accordance with the present invention.
[0040] FIG. 4 depicts a high-level block diagram of an embodiment
of a control unit suitable for use in the fiber identification
device 140 of FIG. 2 and the fiber identification system 300 of
FIG. 3. The control unit 275 of FIG. 4 comprises a processor 410 as
well as a memory 420 for storing information and control programs.
The processor 410 cooperates with conventional support circuitry
430 such as power supplies, clock circuits, cache memory and the
like as well as circuits that assist in executing the software
routines stored in the memory 420. As such, it is contemplated that
some of the process steps discussed herein as software processes
may be implemented within hardware, for example, as circuitry that
cooperates with the processor 410 to perform various steps. The
control unit 275 also contains input-output circuitry 440 (i.e.,
may be remote input-output circuitry) that forms an interface
between the various functional elements communicating with the
control unit 275. For example, in the embodiment of FIG. 2, the
control unit 275 communicates with the transmitter head 240 via a
signal path S1 and to the receiver head 225 via signal path
O.sub.1.
[0041] Although the control unit 275 of FIG. 4 is depicted as a
general purpose computer that is programmed to perform various
control functions in accordance with the present invention, the
invention can be implemented in hardware, for example, as an
application specified integrated circuit (ASIC). As such, the
process steps described herein are intended to be broadly
interpreted as being equivalently performed by software, hardware,
or a combination thereof.
[0042] Although in the embodiments of fiber identification devices
and a fiber identification system in accordance with the present
invention depicted above (e.g., FIG. 2 and FIG. 3) the modulating
device is depicted as comprising a vibrating piston 240, 340,
various other means for imparted a time-varying modulation (e.g.,
time-varying loss) on an optical signal propagating along on
optical fiber, such as piezo-electric transducers, motors and
vibrators, may be implemented in a fiber identification device and
a fiber identification system in accordance with the present
invention. More specifically, the bend loss imparted in a fiber may
be characterized according to equation one (1), which follows:
.alpha.=c.sub.2 exp(-c.sub.1R), (1)
[0043] where .alpha. is the imparted loss per unit length (and can
be considered as proportional to the light scattered into the
detector), R is the fiber's radius of curvature, and c.sub.2 and
c.sub.1 are constants which are not strong functions of R, but are
functions of the fiber design and the wavelength of light
propagating in the fiber. The exponential dependence on R should be
noted. More specifically it should be noted that as R decreases,
the scattered light goes from very small values to very large
values quite rapidly. As a consequence of this exponential
dependence, a given curvature (static or biasing) at the location
of the vibrating piston may be imparted, such that small additional
changes applied make more significant variations in the loss
without the necessity of making large variations in the bend radius
of the fiber. Because of the dependence of c.sub.1 and c.sub.2 on
fiber types and wavelengths, the implication is that fiber
identification devices of the present invention may implement a
variable fiber bending device (e.g. a variable anvil, or more than
one anvil) to apply the bends at both the location of the vibrating
piston and the location of the anvil and detector.
[0044] Therefore, to exploit the advantages of the present
invention while minimizing the system impact (recalling that the
loss may vary strongly with wavelength), various embodiments of the
present invention comprise a means for providing an adjustable
bending radius to optical fibers and thus, adjustable bending
losses for varied applications. For instance, an embodiment of a
fiber identification device of the present invention may comprise
various fiber bending devices (e.g., anvils), each possessing a
different radius of curvature. As such, when an accurate DC
measurement must be made on a fiber wherein loss is not too great
an issue, a smaller radius anvil would be implemented. The smaller
radius anvil would impose more loss on the fiber, but would insure
accuracy by diverting more power to the detector. Such a method is
preferable for applications in tracing, characterizing, and
inventorying dark fibers, for example, where loss is not an
issue.
[0045] On the other hand, for applications in which loss is an
issue, such as fibers carrying high speed traffic that operate near
the margin of their power budgets, it is imperative to minimize
loss. In such applications, the modulation frequency, for example
from the vibrating piston, is well-known and thus can be easily
detected, while its magnitude may not necessarily need to be
accurately ascertained. Thus, to insure minimal loss, the radius of
curvature of the fiber bending device would be larger in order to
apply less loss to a propagating optical signal in the fiber, and
thus minimizing the time-variant component of loss. This aspect of
the present invention may be implemented by providing a set of
interchangeable fiber bending devices or by implementing adjustable
fiber bending devices that increase or decrease the radius of
curvature of the fiber in the active region via an adjustment.
Various other means for providing adjustable bending radii for
optical fibers, such as sliding clamps, levers, detents, etc., are
known and such other means may be implemented in a fiber
identification device in accordance with the present invention.
[0046] In addition, because the amount of bend loss experienced by
an optical signal depends on the wavelength of an optical signal or
the wavelengths of an optical signal (i.e., WDM signals are
comprised of various wavelengths), with the longer wavelengths
being more lossy than the shorter wavelengths, a bend radius for
scattering light out of an optical fiber in accordance with the
present invention must be carefully chosen. More specifically, a
bend radius that causes a negligible loss on a short wavelength
might cause a severe loss on a much longer wavelength. For
instance, in current coarse WDM (CWDM) systems, it is common for
there to be a 140 nm separation between the top and the bottom
wavelengths, and as such, there can be significant differences in
the bend losses that may result in catastrophic losses on the
longer wavelengths.
[0047] In the present invention, any vibration that is applied to a
fiber would preferably be applied in such a way that it does not
damage the fiber. For example it may be advantageous to configure a
subject fiber to have a freestanding section to which a vibration
in accordance with the present invention is applied. As such, the
fiber would be less susceptible to damage from the modulation.
Furthermore and with regard to the acoustic frequency of operation,
the conventional frequency choices (e.g., 270, 1000, 2000 Hz) to
commercial live fiber indicators are resistant to light leaks from
office lights, etc., at 60 Hz and 120 Hz. However, since the energy
of a vibrating fiber is proportional to the square of its velocity,
the power consumption of the bending device, such as the piston,
will scale substantially with the square of the frequency.
Accordingly, it may be advantageous to set the frequency to be even
lower than 270 Hz while recognizing the prevalence of the 60 Hz
noise sources.
[0048] In typical prior art fiber identification devices, AC tones
used to identify fibers are essentially modulated at 100% depth
(i.e., an on-off modulation at acoustic frequencies) and are
implemented on "dark fibers" carrying no traffic on live fiber.
Such deep modulation, however, surely impairs the signal
transmission. That is, the light lost in impressing the signature
tone will manifest itself as an additional time-varying loss,
closing the "eye pattern" (as familiar to those skilled in the art)
by that same amount and would completely close the eye pattern for
deep modulation. Thus, it would be preferable to have only a small
modulation depth (i.e., loss corresponding to less than a dB loss,
for example) on the signal light. As such, in various embodiments
of the present invention, the light corresponding to the logical
"1s" which leave a subject fiber after experiencing the imparted
vibrating bend loss, do not vary between 0 and 1 as they do for
100% modulation, but preferably vary between levels which are close
to 1, such as between 0.85 and 0.95 of the original amplitude. In
such an example, the fiber identification device of the present
invention would perceive a 5% insertion loss and a 10%
time-dependent loss, which, as far as system performance is
concerned, is considered a 15% loss, or approximately 0.7 dB.
[0049] FIG. 5 depicts a high level block diagram of an alternate
embodiment of a fiber identification device of the present
invention. The fiber identification device 500 of FIG. 5 comprises
substantially the same components as the fiber identification
device 140 of FIG. 2 with the addition of a second lightguide and a
second detector. The fiber identification device 500 of FIG. 5
illustratively comprises a first and a second lightguide
(illustratively plexiglass lightguides) 510.sub.1 and 510.sub.2, a
clamping anvil 520, a first and a second detector 530.sub.1 and
530.sub.2 (collectively detectors 530), and a modulating device
(illustratively a vibrating piston) 540. In the fiber
identification device 500 of FIG. 5, the first lightguide
510.sub.1, the vibrating piston 540 and the first detector
530.sub.1 comprise a transmitter head 502, and the second
lightguide 510.sub.2, the clamping anvil 520 and the second
detector 530.sub.2 comprise a receiver head 504. FIG. 5 further
illustrates an optical fiber 550.
[0050] Similar to the fiber identification device 140 of FIG. 2, in
the fiber identification device 500 of FIG. 5, the vibrating piston
540 is mechanically driven such that it vibrates the fiber 550 and
produces a time-varying curvature of the fiber 550, and thus a
time-varying loss (power variation) in the fiber 550 due to
"bending loss". The loss imparted by the vibrating piston 540
causes some light to scatter out of the fiber. In the fiber
identification device 500 of FIG. 5, the first plexiglass
lightguide 5101 collects at least a portion of the light scattered
due to the vibration of the optical fiber 550 and guides the
scattered light to the first detector 5301. The first detector
530.sub.1 detects the scattered light from the first plexiglass
lightguide 510.sub.1. The light from the first plexiglass
lightguide 510.sub.1 and detected by the first detector 530.sub.1
may be used to verify the presence and direction of light in the
optical fiber 550, that the vibrating piston 540 is operating
correctly (i.e., that the light in the optical fiber does in fact
have an imparted time-varying modulation), and/or to provide a
reference signal to compare to the time-varying modulation
subsequently detected by the second detector 530.sub.2.
Alternatively, the scattered light detected by the first detector
530.sub.1 may be used to identify how much power is being scattered
out of the fiber due to the vibration which may be used to adjust
the amplitude and the frequency of the vibration of the vibrating
piston 540 to optimize the fiber identification device of the
present invention such that a propagating optical signal is
minimally affected.
[0051] Further downstream, the fiber to be tested for
identification (presumptively the fiber 550 or a fiber connected to
it) is bent by the clamping anvil 520. As previously described,
when the fiber is bent, some of the light is scattered out of the
fiber. At least a portion of this scattered signal is collected by
the plexiglass lightguide 510.sub.2 and is guided to the second
detector 530.sub.2. As illustrated in FIG. 5 and as previously
described, the light leaving the fiber 550 has a small AC component
to its amplitude (dithered) due to the overmodulation of the signal
propagating in the fiber 550 imparted by the vibrating piston
540.
[0052] As before, the second detector 530.sub.2 needs to detect
only the presence of the time variation at the specific frequency
imparted by the vibrating piston 540. The detection of the presence
of the time-varying signal at the imparted frequency by the second
detector 530.sub.2 enables the identification of the fiber. As
previously stated, the additional detector 530.sub.1 enables the
detection and measurement of the time-varying modulation (i.e.,
signature) imparted on a propagating optical signal, the signature
to be later detected for identifying a subject optical fiber.
[0053] In alternate embodiments of the present invention, the
transmitter head 502 of the fiber identification device 500 of FIG.
5 further comprises a clamping anvil to apply a biasing curvature
and the receiver head 504 further comprises a modulating device
(e.g., a vibrating piston) such that the fiber identification
device of the present invention is capable of being used in either
direction to identify an optical fiber. That is, in a fiber
identification device in accordance with this embodiment, an
optical fiber located in the region of a receiver head may be
modulated such that a time-varying modulation is imparted on an
optical signal propagating therein. The modulated optical fiber may
then be identified upstream by a transmitter head of the fiber
identification device in accordance with this embodiment.
Alternatively, an optical fiber located in the region of the
transmitter head may be modulated such that a time-varying
modulation is imparted on an optical signal propagating therein.
The modulated optical fiber may then be identified downstream by
the receiver head of the fiber identification device in accordance
with this embodiment
[0054] In alternate embodiments of the present invention, the
polarization of light propagating in an optical fiber may be
manipulated to produce a time-varying modulation that may later be
detected to identify the optical fiber. For example, the
polarization of light may be modified by disturbing the normal
propagation of light in some way, introducing birefringence in the
fiber (i.e., changes to the index of refraction which are
non-uniform) by altering the fiber in some way, or by applying a
field that couples to a property in the fiber. For illustrative
purposes the Faraday effect, caused by magnetic fields, is
considered. For example, when an axial magnetic field is applied to
a fiber carrying an optical signal, it makes light with right
circular polarization travel at a different velocity than light
with left circular polarization. More specifically, a circular
birefringence is imparted. For linearly polarized light, applying
an axial magnetic field to a fiber carrying an optical signal
thereby makes the direction of polarization change. Various means
for applying a magnetic field, such as a solenoid, to a fiber
carrying an optical signal to produce a time-varying modulation in
the optical signal may be implemented within the concepts of the
present invention. The inventors further consider and propose that
the application of an electric field will have a similar effect as
the application of a varying magnetic field as described above. As
such, various means for applying an electric field to a fiber
carrying an optical signal to produce a time-varying modulation in
the optical signal, such as by adapting an optical fiber(s) to
comprise electrodes, may be implemented within the concepts of the
present invention.
[0055] For example, and referring to FIGS. 1, 2, 3 and 5 above, a
time-varying magnetic field may be applied to a fiber 250, 350, 550
in place of the modulation provided by the vibrating piston 240,
340, 540. A detector 230, 330, 530 would therefore be adapted to
detect the changes in the polarization of a propagating optical
signal scattered out of the fiber 250, 350, 550. For example in one
embodiment of the present invention, a detector 230, 330, 530 is
equipped with a polarizer(s) to enable the detector to detect the
polarization of the modulated propagating optical signal. In
addition, the detection would be configured to occur at the
frequency of the time-varying magnetic field. Even further, in
alternate embodiments of the present invention, similar methods and
apparatuses are implemented for identifying an optical fiber using
other types of time-varying birefringence, such as squeezing, etc.
These embodiments of the present invention have the advantage that
the time-varying "signature" may be introduced with very little
loss such that the power and frequency of a propagating optical
signal in the fiber remains substantially the same and only the
direction of polarization changes.
[0056] It should be noted however, that with this approach if a
propagating optical signal, while entering the region of the fiber
having the time-varying birefringence of the present invention, has
the same state of polarization as the birefringence (i.e. it is in
an eigenstate of the birefringence), the optical signal merely
experiences a change in velocity but does not undergo a change in
its state of polarization. Thus, a fiber identification device
configured to detect a change in polarization would fail to detect
any change. As such, it is important to ensure that the
birefringence applied does not have the same state of polarization
as a propagating optical signal (i.e., the fiber may be bent or
twisted, or fixed forms may be used to create a polarization
controller).
[0057] Although various specific methods of imparting a
time-varying modulation on a propagating optical signal are
presented herein within specific embodiments of the present
invention, it will be appreciated by those skilled in the art
informed by the teachings of the present invention that
substantially any method for imparted a time-varying modulation on
a propagating optical signal in a fiber may be used to subsequently
identify the fiber in accordance with the present invention. For
example, there are a number of non-linear interactions that may
shift the frequency of light, and such interactions may be used to
impose a known frequency shift on a propagating optical signal in a
fiber. More specifically, several optical sensor and signal
processing techniques implement the interaction of acoustic waves
and light to impart a frequency shift. That is, the light interacts
with the acoustic phonons to create light at upshifted or
downshifted frequencies. Such shifts in frequency may be
subsequently detected to identify an optical fiber in accordance
with the present invention. Such frequency shifts may be imparted
by various means, such as acoustic horns or acoustic transducers.
In addition, other means, such as a lithium-niobate phase
modulator, may be implemented to produce such non-linear
interactions.
[0058] The present invention may also be used to establish logical
continuity through devices by separating the transmit head and the
receive head. For example, FIG. 6 depicts a high level block
diagram of a passive optical network (PON). The PON 600 of FIG. 6
comprises an input branch 602, a trunk 605 and a plurality of
output branches 610.sub.1-610.sub.N (collectively output branches
610). The PON 600 of FIG. 6 further comprises a fiber
identification device comprising a transmitter head 640 and
receiver head 625 in accordance with the present invention. In the
PON 600 of FIG. 6, light from the trunk 605 is divided into the
output branches 610 and transmitted to subscribing customers (not
shown). Signals (i.e., in the form of light) from the customers is
combined in the trunk 605 and transmitted back to a head end (not
shown). Continuity of communication between the head end and the
customers may be verified in either direction implementing the
concepts of the present invention in much the same manner as
described above. For example, regarding point X which is on the
input branch 602, and point Y which is on one of the branches, the
transmit head 640 may be located near point X and the receive head
625 on point Y to establish that light was traveling from X to Y or
vice versa. This might be useful, for instance, in a situation in
which the fiber Y were one of a multiplicity of fibers in a closet,
all carrying traffic, that might be otherwise indistinguishable. As
such, communication may be verified without the need to interrupt
the operation of the PON 600.
[0059] While the forgoing is directed to various embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof. As
such, the appropriate scope of the invention is to be determined
according to the claims, which follow.
* * * * *