GB2267792A - Fault location in optical communications system - Google Patents
Fault location in optical communications system Download PDFInfo
- Publication number
- GB2267792A GB2267792A GB9310774A GB9310774A GB2267792A GB 2267792 A GB2267792 A GB 2267792A GB 9310774 A GB9310774 A GB 9310774A GB 9310774 A GB9310774 A GB 9310774A GB 2267792 A GB2267792 A GB 2267792A
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- United Kingdom
- Prior art keywords
- optical
- channel
- amplifier
- repeater
- down side
- Prior art date
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
- G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
- G01M11/3154—Details of the opto-mechanical connection, e.g. connector or repeater
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
- G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
- G01M11/3136—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR for testing of multiple fibers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/293—Signal power control
- H04B10/2933—Signal power control considering the whole optical path
- H04B10/2939—Network aspects
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/298—Two-way repeaters, i.e. repeaters amplifying separate upward and downward lines
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Chemical & Material Sciences (AREA)
- Optics & Photonics (AREA)
- Analytical Chemistry (AREA)
- General Physics & Mathematics (AREA)
- Optical Communication System (AREA)
- Monitoring And Testing Of Transmission In General (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Testing Of Optical Devices Or Fibers (AREA)
Abstract
The system has optical repeaters A1, A2,... An end channels R.T for two way communication. Fault location is conducted by measuring backscatter light at an optical transmission station 1 or 2 located at the end of the optical transmission link. Each of the repeaters A1 to An includes an optical returning circuit C, C1, D, D1b, D2b for returning the backscatter light from one channel T to the other channel R. The optical returning circuit is kept conducting and gives a suitable attenuation (between 10 log n-15 and 80-10 log n dB), so that the transmission of light through the other channel R is unaffected. If a fault occurs in the optical transmission link, a measurement signal is sent from the optical transmission station 1 or 2 to one channel T, and backscatter light caused by the fault is returned by the optical returning circuit C, C1, D, D1b, D2b to the other channel; R the fault location is determined by OTDR. <IMAGE>
Description
SPECIFICATION -c Title of the invention
Method and apparatus for finding a fault location for an optical repeater system and optical repeater
Background of the invention
This invention relates to a method and an apparatus for finding a fault location to enforce fault location finding controlled from a remote optical transmission station in case that a fault such as a breakdown of an optical fibre occurs in an optical repeater system, in which optical fibres, as a transmission media, with a plurality of repeaters inserted therebetween, transmit signals.
As a method for finding a fault location for an optical repeater system in case that a fault such as a breakdown of a cable occurs, a current-resistance measurement method for measuring resistance of a feeder line, a capacitance measurement method for measuring capacitance of a feeder line, a pulse-echo method for sending an electric pulse to a feeder line and measuring an echo from a fault location, and the like, are practically used so far in terms of electrical methods.
In another optical repeater system of regenerating repeater type in which an opto-electric conversion, a wave form rectifi
cation and the like are performed in every repeater section, a
fault location finding is performed by the repeater section unit through selectively operating a shutter type electric or optical
returning circuit installed in an optical repeater based on a
command from an optical transmission station, and through meas
uring the transmission performance of the returned optical
signal in a trunk channel. As for a section from the optical
transmission station to the first repeater, fault location
finding is performed by connecting a backscatter light measure
ment device to the optical fibre at the optical transmission
station, and by measuring the backscatter light occurring in the
optical fibre.Such fault location finding methods are ex
plained in, for example, " Optical Submarine Cable Communica
tion", Section 9, published by KDD Engineering and Consulting
which is the juridical foundation.
In recent research of optical repeater systems, a next
generation system is designed so as to use an optical amplifier
for directly amplifying an optical signal, as means for repeat
ering an optical signal, without converting the optical signal
into the electric signal in lieu of a conventional regenerating
repeater system. The optical repeater system using the new
optical amplifier can simultaneously transmit a backscatter
light occurring at an optical fibre between optical repeaters
since the optical signal is not regenerated in each optical
repeater. Therefore, a system design of the optical repeater
system is directed in consideration of an advantage of the new
optical amplifier.The repeater system includes backscatter
light measuring means for finding of a fault location, which is introduced not only to the section up to the first repeater as of the conventional regenerating repeater system described above gut also to the entire optical fibre sections constituting the optical repeater system.
Generally, it is indispensable for an optical multi-repeater system that an optical isolator is inserted in each optical repeater of the system, thereby eliminating unnecessary reflection in the optical repeater, and thereby stabilizing the transmission performance of the optical repeater system. It is therefore impossible to measure every backscatter light from entire optical fibre sections with optical repeaters normally constructed.
As a method to solve this problem, a fundamental invention has been contrived by this applicant. In the invention, an optical returning circuit for an optical signal is provided in each optical repeater, thereby returning backscatter light occurring at a section of an optical fibre connected to the output of the optical repeater into another optical fibre of a receiving side for transmitting signals in a direction opposed to that of the optical fibre, and thereby transmitting the backscatter light to an optical transmission station. The invention is disclosed in Japanese Patent Open-layed No. 2-2228, "Supervisory method and apparatus for a long distance optical communication system".
Fig. 7 shows an organization of a conventional optical repeater system including optical returning circuits for backscatter light, and Fig. 8 shows a detailed circuitry of the optical returning circuit. In Fig. 7, the numerals 1, 2 indi
cate optical transmission station, such as a shore terminal
station of a submarine cable, installed with a communication equipment for terminal station. Hereinafter, it will be ex
plained from the viewpoint of the optical transmission terminal
station 1 of the optical repeater system in which the total
number of the repeaters is n and the total number of optical
fibres is m.
The numerals Al to An are optical repeaters; the numerals 3a(1) to 3a(m) are up side optical fibres of a two way communi
cation; the numerals 3buzz to 3b(m) are down side optical fibres
of the two way communication; the numeral 4a(1) is an up side
optical amplifier of the repeater Al; the numeral 4b(l) is a
down side optical amplifier of the repeater Al; the numerals 5a(1) to 5a(m) are backscatter lights occurring in the up side
optical fibres 3a(l) to 3a(m); the numerals 5b(l) to 5b(m) are
backscatter lights occurring in the down side optical fibres
3b(l) to 3b(m); the numeral T is an up side optical channel of
the two way communication; the numeral R is a down side optical
channel of the two way communication; the numeral Bla is an
optical returning circuit to return backscatter light 5a(2)
occurring at the up side optical fibre 3a(2) into the down side
optical channel R.
The optical returning circuit Bla of the optical repeater
Al is constituted as shown in Fig. 8. The numeral 6 is an
optical divider such as an optical coupler for tapping the
backscatter light 5a(2) occurring at the up side optical fibre
3a(2) and tapping a repeater control signal from the optical
transmission station 1. The numeral 7 is an optical combiner
such as an optical coupler for coupling the backscatter light
5a(2) tapped at the optical divider 6 to the down side optical channel R. The numeral 8 is an optical shutter such as an
optical switch for isolating the down side optical channel R
from the backscatter light 5a(2). The numeral 9 is an optical
receiver for receiving the repeater control signal sent from the
optical transmission station 1.The numeral 10 is a control
circuit for controlling the optical shutter 10 to be open and
close.
For example, if a fault occurs at the up side optical fibre
3a(2), or a transmission side optical fibre, the optical trans
mission station 1 sends a command for the optical shutter 8 of
the optical returning circuit Bla to be conducting. The command
is received by the optical receiver 9 in the repeater Al, and
then, the control circuit 10 controls the optical shutter 8 to
be conducting. The optical transmission station 1 sends a
signal for measurement, and then, the backscatter light 5a(2)
occurs in the up side optical fibre 3a(2). The backscatter
light 5a(2) travels toward the optical transmission station 1 so
as to be opposed to the propagating direction of the measurement
signal in the up side optical fibre 3a(2).
The optical divider 6 branches off the backscatter light
5a(2), and then the backscatter light 5a(2) joins to the down
side optical channel R at the optical combiner 7 after passing
through the conducting optical shutter 8. The down side optical
channel R sends the backscatter light 5a(2) to the optical
transmission station 1. Therefore, it is possible to find the
fault location by observing the intensity of the backscatter
light 5a(2) on a time scale at the receiving end of the optical
transmission station 1, since, for example, in case of a cutoff fault the backscatter light from the back of the fault location
is not observed and in case of a local increment of the loss the
intensity of the backscatter light from the back of the fault
location is relatively attenuated due to the increment of the
loss.
As well as described above, finding a fault location in
case that a fault occurs in the down side optical fibre, for
example, in the fibre 3b(1), is accomplished by making the
optical shutter 8 of the optical returning circuit Blb of the
optical repeater Al to be conducting, by sending a measurement
signal from the optical transmission station 2, and by observing
the behavior of the backscatter light 5b(1) occurring at the
down side optical fibre 3b(1) caused by the measurement signal
during a certain time.
In such conventional finding methods of a fault location as
described above, however, the methods using electric means have
an ineffectual resolution power of finding location such as 1 or
2 % of the distance up to the fault point, and therefore, the
method can be applied only for the fault of the feeder line, or
the cable, and never used for detection of a fault of only
optical fibres. With the conventional apparatus for finding a
fault location of the optical repeater system using the optical
amplifier shown in Figs. 7, 8, each repeater needs a control
circuit for controlling the optical shutter in response to the
command from the optical transmission station and a receiving
circuit for receiving the command, and the optical transmission station needs a transmitting device for sending the command.As a result, as the size of the optical repeater is larger, the
Optical repeater system becomes less reliable, and a cost of the optical repeater system increases. It is therefore desirable to simplify a construction of an optical repeater of an optical repeater system while the system keeps its reliability and cost-effectiveness.
Summary of the invention
According to a first aspect of the invention, there is provided a method for finding a fault location for an optical repeater system in which an optical transmission link is constructed by at least one pair of optical fibres for two way communication with one repeater or a plurality of repeaters inserted therebetween, each of which includes at least one pair of optical amplifiers for two way communication, and in which one end of the optical transmission link is connected to an optical transmission station, the method comprising of maintaining each optical returning circuit to be normally conducting, the optical returning circuit being provided in each of the optical repeaters, connecting between the optical amplifiers of up and down side optical channels of the two way communication, and giving passing light therethrough a necessary loss not affecting the transmission of the down side optical channel and further, in case that a fault occurs in the optical transmission link, comprising of sending an optical measurement signal from
the optical transmission station to the up side optical channel,
returning backscatter light occurring in one of the optical fibre connected to an output of the optical amplifier of the up
side optical channel to the down side optical channel through
the optical returning circuit provided in respective of the
optical repeater, and measuring the backscatter light transmit
ted through the down side optical channel and received by the
optical transmission station to determine the fault location
according to the backscatter light.
For the purposes of this specification the optical return
ing circuit may connect between the outputs of the optical
amplifiers of the up and down side optical channels. The loss of
the optical returning circuit may be set to a value greater than
or equal to 10 Log (N) - 15 (dB) and less than or equal to 80
(dB) - 10 Log (N) or a value greater than or equal to 10 Log (N)
- 15 (dB) + (the gain of the optical amplifier of the down side
optical channel} (dB) and less than or equal to 80 (dB) - 10 Log
(N) + (the gain of the optical amplifier of the down side opti
cal channel} (dB) where the number of the optical repeater
mounting the optical returning circuit is N.In the case that
the optical returning circuit connects between the output of the
optical amplifier of the up side optical channel and the input
of the optical amplifier of the down side optical channel, the
loss of the optical returning circuit may preferably be set to a
value greater than or equal to 10 Log (N) - 15 (dB) + (the gain
of the optical amplifier of the down side optical channel} (dB)
and less than or equal to 80 (dB) - 10 Log (N) + (the gain of
the optical amplifier of the down side optical channel} (dB) where the number of the optical repeater mounting the optical returning circuit is N.
According to another aspect of the invention there is provided an apparatus for finding a fault location for an optical repeater system in which the apparatus includes one optical repeater or a plurality of optical repeaters, each of which is constituted of a pair of optical amplifying circuits for two way communication using optical amplifiers, and an optical returning circuit connecting between outputs of the optical amplifier of up and down side optical channels so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N) where the number of the optical repeater or repeaters mounting the optical returning circuit or circuits thereon is N, at least one pair of optical fibres for two way communication inserting the optical repeater or repeaters, and an optical transmission station including means for sending a measurement signal connected to one end of a transmission link formed by the optical repeater or repeaters and the optical fibres and means for receiving and measuring backscatter light of the measurement signal.
The apparatus may include other optical returning circuits giving a loss greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N) or a value greater than or equal to 10 Log (N) - 15 (dB) + (the gain of the optical amplifier of the down side optical channel) (dB) and less than or equal to 80 (dB) - 10 Log (N) + (the gain of the optical amplifier of the down side optical channel) (dB) where the
number of the optical repeater mounting the optical returning
circuit is N.Such other optical returning circuits connect s etween an output of said optical amplifier of the up side
optical channel and an input of said optical amplifier of the
down side optical channel or between the output of said optical
amplifier of an up side optical channel and the input of said
optical amplifier of a down side optical channel so as to be
normally conductive, in addition to or in lieu of the optical
returning circuit giving a loss greater than or equal to 10 Log
(N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N) and
connecting between outputs of the optical amplifier of the up
and down side optical channels.
According to a further aspect of the invention there is
provided an optical repeater for an apparatus for finding a
fault location for an optical repeater system whose optical
transmission link is composed of one of the optical repeater or
a plurality of the optical repeaters formed by at least one pair
of optical amplifying circuits for two way communication using
optical amplifiers and inserted in at least one pair of optical
fibres for two way communication, characterized in that the
optical repeater includes the optical amplifier of an up side
optical channel of the two way communication, the optical ampli
fier of a down side optical channel of the two way communica
tion, and an optical returning circuit connecting between out
puts of the optical amplifier of the up and down side optical
channels so as to be normally conductive and giving light pass
ing therethrough a loss greater than or equal to 10 Log (N) - 15
(dB) and less than or equal to 80 (dB) - 10 Log (N) where the
number of the optical repeater or repeaters mounting the optical
returning circuit or circuits in the optical transmission link Cs gs N.
The optical returning circuit may include a first optical
coupler disposed on a side of the up side optical channel, and
a second.optical coupler disposed on a side of the down side
optical channel and connected to the first optical coupler. The
first and second optical couplers adjust the losses according to
a ratio of tapping or coupling of light, so that a predetermined
loss of the optical returning circuit is formed by a composition
of the losses.
In lieu of the optical returning circuit connecting between
outputs of the optical amplifier of the up and down side optical
channels, the optical repeater may include a first optical
returning circuit connecting between an output of the optical
amplifier of the up side optical channel and an input of the
optical amplifier of the down side optical channel so as to be
normally conductive, and a second optical returning circuit
connecting between an input of the optical amplifier of the up
side optical channel and an output of the optical amplifier of
the down side optical channel so as to be normally conductive.
These first and second optical returning circuits give a loss
greater than or equal to 10 Log (N) - 15 (dB) + (the gain of the
optical amplifier of the down side optical channel} (dB) and
less than or equal to 80 (dB) - 10 Log (N) + (the gain of the
optical amplifier of the down side optical channel} (dB) to
light passing therethrough where the number of the optical
repeater or repeaters mounting the optical returning circuits in
the optical transmission link is N.
The first optical returning circuit may include a first } Optical coupler disposed on a side of the up side optical chan
nel, and a second optical coupler disposed on a side of the down
side optical channel and connected to the first optical coupler.
The second optical returning circuit may include a third optical
coupler disposed on the side of the up side optical channel, and
a fourth optical coupler disposed on the side of the down side
optical channel and connected to the third optical coupler. The
first to fourth optical couplers adjust the losses according to
a ratio of tapping or coupling of light, so that predetermined
losses of the first and second optical returning circuits are
formed by respective compositions of the losses.
Following is a description by way of example only and with
reference to the accompanying drawings of methods of carrying
the invention into effect:
Description of the drawings
Fig. 1 is a schematic diagram of an optical repeater system
including optical returning circuits according to Example 1 of
the invention;
Fig. 2 is a graph showing a relation between a code error
ratio and an attenuation of a crosstalk signal from the opposite
line;
Fig. 3 is a schematic diagram of an optical returning cir
cuit according to Example 2 of the invention;
Fig. 4 is a schematic diagram of the circuit of an optical
transmission station used in Examples 1, 2; Fig. 5 is a time chart for explaining the operation of the
optical transmission station shown in Fig. 4;;
Fig. 6 is a graph showing a result of an experiment about a
measurement of backscatter light in the optical transmission
station shown in Fig. 4;
Fig. 7 is a schematic diagram of a conventional optical
repeater system including optical returning circuits; and
Fig. 8 is a schematic diagram of a conventional optical
returning circuit.
Detailed description of examplary embodiments
Embodiment 1
Referring to Figs. 1, 2, Example 1 according to the inven
tion will be described. Fig. 1 shows an example of an apparatus
for finding a fault location for an optical repeater system.
The reference numbers of elements of the example are common with
those of the conventional example shown in Figs. 7, 8.
In Fig. 1, the numerals Al' to An' are optical repeaters,
and the numeral C1 is an optical returning circuit for returning
backscatter lights 5a(2) or 5b(1) occurring at an up side opti
cal fibre 3a(2) or at a down side optical fibre 3b(1), respec
tively, from an up side optical channel T to a down side optical
channel R or the opposite.
The numerals 1, 2 are optical transmission stations such as
shore terminal stations for a submarine cable installed with terminal equipment for communication. The numerals 3a(1) to
3a(m) are up side optical fibres of a two way communication.
The numerals 3buzz to 3b(m) are down side optical fibres of the
two way communication. The numerals 4a(1) and 4b(l) are up side
and down side optical amplifiers, respectively, of the optical
repeater A1'. The numerals 5a(1) to 5a(m) are backscatter
lights occurring at the up side optical fibres 3a(l) to 3a(m),
and the numerals 5b(1) to 5b(m) are backscatter lights occurring
at the down side optical fibres 3b(1) to 3b(m). The numeral T
is an up side optical channel, and the numeral R is a down side
optical channel. The numerals lla, llb are optical combiner and
divider's, or optical couplers. The internal constructions of
the optical repeaters A2' to An' are identical to the internal
construction of the optical repeater Al'.
The difference between Example 1 and the conventional
example is a construction of the optical returning circuits
C1, ... installed in the apparatus for finding a fault location
of Example 1. In the case of the optical returning circuit Cl, the optical coupler lla for branching off and returning the
backscatter light 5a(2) is disposed to the output of the up side
optical amplifier 4a(1), and the optical coupler 11b for inte
grating the backscatter light 5a(2) into the down side optical
channel R is disposed to the output of the down side optical
amplifier 4b(1). Those optical couplers lia, 11b are connected
with each other not through an active element such as an optical
shutter or the like.
In the apparatus thus constructed, the backscatter lights
5a(2), 5b(l) occurring at the up side and down side optical Fibres 3a(2), 3b(1), respectively, are returned to the channels
received by the optical transmission stations 1, 2, respective
ly, through the optical returning circuit Cl. Therefore, this
apparatus needs no optical receiver 9 for receiving a necessary
control signal and no control circuit 10, in order to operate an
optical shutter in comparison with the conventional example.
Moreover, the exclusive optical returning circuit is commonly
used for finding a fault location from the optical transmission
stations 1, 2, and the construction of the optical returning
circuit is very simple.
In operation, trunk channel communication signals travel
through all of the up side, or transmitting side, optical fibres
3a(l) to 3a(m) and the down side, or receiving side, optical
fibres 3b(1) to 3b(m) while the optical repeater system is in
service, thereby rendering the backscatter lights 5a(l) to
5a(m), 5b(1) to 5b(m) to occur at respective optical fibres.
These backscatter lights 5a(1) to 5a(m), 5b(1) to 5b(m) are
sequentially returned at respective of the optical returning
circuits C1, ..., Cn of respective of the optical repeaters Al', A2'..., An', and are accumulated to make a noise, thereby af
fecting the transmission performance of the trunk channel commu
nication signals on both of the channels.
To suppress those adequately, it is necessary to attenuate
the backscatter lights at respective of the optical returning
circuits C1, ..., Cn. If such attenuation is so strong, SNR
(Signal to Noise Ratio) of the measurement of the backscatter
lights 5a(1) to 5a(m), 5b(1) to 5b(m) is impaired at the optical
transmission stations 1,2, so that the measurement may lose its vCAccuracy. Therefore, a demanded loss value needed for respec
tive of the optical returning circuits becomes an essential
factor in the apparatus according to the invention using the
optical returning circuits being conducting normally.
Fig. 2 shows a resultant data from a simulated experiment
of a transmission performance of communication signals for an
optical channel of the optical repeater system comprising of 300
of the optical repeaters. With the experiment, a crosstalk
ratio of the communication signal leaking directly from the up
side optical channel T to the down side optical channel R inside
of the respective of the optical repeaters is changed to measure
a transmission performance of the down side optical channel R
where a trunk channel communication signal of 5 Gbps transmis
sion speed is transmitted across a transmission distance of
9,500 km.In Fig. 2, the abscissa indicates attenuation of the
communication signal cross-talking from the up side optical
channel T to the down side optical channel R per optical repeat
er, and the ordinate indicates a code error ratio of the commu
nication signal.
It is apparently understood from Fig. 2 that if the attenu
ation is set to or above 40 dB, the optical repeater system can
keep its transmission quality enough for providing communication
services. An attenuation not affecting the signal of the opti
cal fibre channel, or the trunk channel signal, depends in
theory on the number (N) of repeaters, which mount the optical
returning circuits thereon. Since the result of the experiment
indicates the case of N = 300, the attenuation can be calculated
from a formula of 10 Log(N) + 15 (dB). Now, mean power of the tackscatter light occurring at each optical fibre caused by the
trunk channel signal is considered while for instance, the
optical fibre 3a(2) shown in Fig. 1 is exemplified.
When an optical signal is sent from an incident end, or a
terminal p2, of the optical fibre 3a(2) and backscatter light
power occurring at the optical fibre 3a(2) per unit time is
observed at the terminal p2, the backscatter light 5a(2) occur
ring at each point in a longitudinal direction of the optical
fibre 3a(2) is received with a weaker power as the point goes
further from the terminal 2p. In addition to this, if the
optical signal is sent continuously, the backscatter light
occurring at each point accumulated at the terminal 2p.
Therefore, the accumulated power, or mean power, is satu
rated where the repeater system uses optical fibres longer than
a certain distance. In the case of an optical fibre communica
tion of about 30 km or above, the backscatter light is received
as a signal having a power30 dB weaker than the incident optical
signal power. Accordingly, it is assumed that a loss value
required for the loss at the optical returning circuits Cm,..., Cn of the respective optical repeaters Al' to An' according to
the invention, is a value subtracted 30 dB from the formula.If
the loss value satisfies a value greater than or equal to 10 Log
(N) - 15 (dB), the transmission performance of the trunk channel
signal is not impaired, thereby allowing to connect the optical
returning circuits C1, ..., Cn for the backscatter light in each
of the optical repeaters Al' to An' continuously.
On the other hand, as the loss is greater, it may cause a
problem on the measurement of the backscatter light of the measurement signal light when a fault location is to be found.
If the loss is over 80 (dB) - 10 Log (N), it is impossible to
measure the backscatter light. For example, at least 10 dB is
required as a loss of the backscatter light 5a(2), 5buzz in the
optical returning circuit C1 according to described above, in an
optical multi-repeater system composed of optical repeaters in
cluding 300 of returning circuits for the backscatter light.
Consequently, the optical returning circuit C1 can be de
signed so as to be continuously conducting, not so as to operate
to be open and close, by setting a value of a returning loss of
the backscatter lights 5a(2), 5b(1), in other words, a loss
value in routes from the terminal p2 to the terminal q2 and from
the terminal q2 to the terminal p2, to 10 dB or above. Although
if the number of the optical repeaters is less than or equal to
31 the necessary returning loss goes to minus (-) or means
amplification in the formula described above, the returning loss
can be 0 dB in this case because the loss greater than or equal
to a certain loss value is acceptable.
The loss of the optical returning circuit C1 is readily
adjustable by changing a ratio of tapping of and coupling be
tween the optical couplers 11a, llb. For example, use of opti
cal fibre couplers for the optical couplers, or combiner and
divider's, lla, 11b allows an easy design of a tapping ratio and
a coupling ratio. If the ratio of terminal pl to terminal p3 is
set to 2 : 1 with respect to the terminal p2 as 3, the loss of
the signal transmitted from the terminal p2 to the terminal p3
is 5 dB. Setting the loss of the optical coupler llb to 5 dB as
well as the coupler 11a readily allows the returning loss from che terminal p2 to the terminal q2 to 10 dB.
Embodiment 2
Referring to Fig. 3, Example 2 according to the invention
will be explained. Fig. 3 shows another apparatus for finding a
fault location for an optical repeater system. It is to be
noted that the elements same to those of Example 1 are assigned
with identical reference numbers, respectively, for the sake of
simplicity of explanation. In this apparatus, each optical
returning circuit has optical coupling points provided at re
spective inputs of the up side optical amplifier 4a(1) and the
down side optical amplifier 4b(1). In Fig. 3, the numeral A1" is an optical repeater: the numerals Dla, Dlb are optical re
turning circuits for returning backscatter lights 5a(2), 5b(l)
occurring at the optical fibres 3a(2), 3b(1), respectively.
In Example 2, since the returned backscatter lights 5a(2),
5b(1) are amplified by the optical amplifiers 4b(1), 4a(l), respectively, the returning loss seems to be reduced in compari
son with Example 1, so that the backscatter lights affect the
transmission performance of the optical transmission signal.
Therefore, returning losses (power of terminal p2- power of
terminal q2) of the optical returning circuits Dla and Dlb need
to be increased so as to compensate for the portion of these
optical amplifier's gain.
According to Example 1, although the number of composition
parts is increased, if a breakdown occurs at the section of the optical fibre 3a(2), since the optical fibre 3a(2) itself is cut
off and the optical amplifier 4b(2) of the optical repeater A2"
as of the next stage does not make optical noise, the SNR of the
backscatter light 5a(2) becomes better, thereby resulting in
that the measured SNR of the backscatter light at the optical
transmission station 1 is improved in comparison with that of
Example 1 shown in Fig. 1.
In Fig. 3, at the time that Example 2 is carried out , if
the loss of backscatter light at the optical returning circuit
satisfies a value equal to or greater than (10 Log (N) - 15 (dB)
+ the gain of the optical amplifier of the down side optical
channels, the transmission performance of the trunk channel
communication signal is never impaired, so that the optical
returning circuits for backscatter light arranged at respective
of the optical repeaters are connected continuously. It is to
be noted that as the loss is so increased, the backscatter light
caused by the measurement signal tends to be measured inaccu
rately at the time of finding a fault location, and if the loss
excesses the value 480(do) - 10 Log (N) + the gain of the opti
cal amplifier of the down side optical channel), the backscatter
light can not be measured at all.
Although Example 2 has a pair of the optical returning
circuits Dla, Dlb in the optical repeater A1", an exclusive
optical returning circuit in the repeater is possible. Further
more, the optical returning circuit having a loss value greater
than or equal to (10 Log (N) - 15 (dB) + the gain of the optical
amplifier of the down side optical channel) and less than or
equal to (80 (dB) - 10 Log (N) + the gain of the optical ampli nier of the down side optical channel) of Example 2 and the
optical returning circuit C1 having a loss value greater than or
equal to (10 Log (N) - 15 (do)) and less than or equal to (80
(dB) - 10 Log (N)} of Example 1 shown in Fig. 1 can be mixed to
build a transmission link.
It may be seemed that it is impossible to measure the
backscatter light 5a(1) occurring at the section of the optical
fibre 3a(1) since the backscatter light occurring at there is
not returned to the down side optical channel R, but it is
measurable if the optical returning circuit, such as the circuit Dla, normally connecting two channels is provided in the optical
transmission station 1.
Since a conventional method for the measurement of the
backscatter light can be applied to the first section of the
optical fibre, a detail description about it is omitted for
simplicity of the explanation. In addition, in the case of the
backscatter light 5b(m) occurring at the optical fibre 3b(m),
the backscatter light 5b(m) is measurable if the optical return
ing circuit normally connecting two channels is provided in the
optical transmission station 2. This modification can be applied
to Example 1. Similarly, the optical repeater A1' of Example 1
and the optical repeater A1" of Example 2 can be mixed to find a
fault location.
Embodiment 3
Referring to Figs. 4, 5, Example 3 will be explained. An apparatus having a sufficient receiving sensitivity is necessary
for the measurement of the backscatter light according to the
invention because the losses of the optical returning circuits
of Examples 1, 2 impair the SNR any way at the time of the
measurement. The apparatus of Example 3 is easily realized by
using a system described in Japanese Patent Application No.
(Hei)1-146,897, a method and an apparatus for measuring back
scatter light, which has already been filed by this applicant.
Fig. 4 shows an embodiment of a construction of the optical
transmission station for a fault location finding apparatus of
Example 3 applicable to Examples 1, 2. Fig. 5 shows the opera
tion of Example 3. In Example 3, each optical transmission
station has the optical returning circuit normally connecting
two channels installed therein. In Fig. 4, the numeral Dla is an
optical returning circuit composed of an optical divider and an
optical combiner, similar to that installed in the optical
repeater of Example 2 described above. The optical returning
circuit can normally return the backscatter light 5a(1) occur
ring at the optical fibre 3a(1) to make it measurable.
The numeral 12 is a pulse generator. The numeral 13 is an
optical transmitter including a semiconductor laser for emitting
narrow spectrum range light. The numeral 14 is an optical
divider separating a measurement signal sent to the repeater
system from a local-oscillator light (d). The numeral 15 is an
optical combiner for integrating a light signal (c) for being
received, such as the backscatter light or the like, with the
local-oscillator light (d). The numeral 16 is an optical re
ceiver for receiving a beat signal result of a heterodyne detec (tQion with the light signal (c) for being received, such as the
backscatter light or the like, integrated by the combiner 15,
and the local-oscillator light (d). The numeral 17 is a band
pass filter for picking up the beat signal.The numeral 18 is
an envelope detector for detecting the beat signal of the output
signal of the band pass filter 17. The numeral 19 is an oscil
loscope for monitoring the output of the envelope detector as of
a time scale.
The operation of the measurement of Example 3 will be
explained with referring to Figs. 4, 5. The pulse generator 12
generates a pulse signal capable of obtaining a predetermined
resolution, having a repeating period greater than or equal to a
time required for a signal traveling round between both ends of
the optical repeater system to be measured. The pulse signal
(a) is supplied to the optical transmitter 13. The optical
transmitter 13 is built so as to transmit an optical signal (b)
frequency-modulated with a predetermined amount of frequency
shift based on the pulse signal (a).
The transmitted optical signal (b) is transmitted to the
optical repeater system and is also used as a local-oscillator
light (d) for the heterodyne detection. A measurement optical
signal component (fp) modified with frequency shift according to
the pulse signal (a) is employed for measurement, and a signal
component (flo) not modified with frequency shift is employed
for a local-oscillator light for heterodyne detection. With
propagation of the measurement signal component (fp), the back
scatter light occurring at each section of optical fibres is
returned at each optical repeater, and received by the optical ransmission station as an optical signal (c) for being re
ceived.
The optical combiner 15 integrates the optical signal (c)
for being received with the local-oscillator light (d), thereby
transmitting an integrated signal to the optical receiver 16.
The optical receiver 16 performs heterodyne detection with the
two signals (c), (d) in accordance with a square character of a
photo-detector thereof, thereby converting the backscatter light
of the measurement optical signal component into an electric
signal (beat signal). This component is filtered by the band
pass filter 17, and is demodulated by the envelope detector 18.
The demodulated signal is fed to the oscilloscope 19, which
displays a behavior of intensity's variation of the received
signal on a time scale as an output wave form, thereby allowing
the system to detect the fault location. Signal processing at
the oscilloscope 19 improves the SNR when synchronized with the
pulse signal (a) and processed so as to obtain the mean value
repeatedly, and this leads to a fine result of the measurement.
In Example 3, since the measurement signal is a continuous
signal and is not a pulse signal such that used for a backscat
ter light measurement apparatus on the market, which is repre
sented by a system described in a book, for example, "Optical
Fiber", published by Ohm Shia, pages 323 to 325, the load of
each optical amplifier becomes stable, so that a fine result of
the measurement result is obtained. Fig. 6 shows an actual
result of the measurement of the backscatter light for the
optical repeater system using the apparatus for finding a fault
location of Example 1 shown in Fig. 1 and the optical transmis \C'ion din station of Example 3 shown in Fig. 4. The optical repeater system is constituted of 69 repeaters and has its overall length
of 2,250 km.
In Fig. 6, the abscissa indicates observed time, or dis
tance, and the ordinate indicates intensity of backscatter
light. The numerals S1, S2, S3 are the results of the measure
ment of the backscatter light of the optical fibres of the 37th,
38th, and 39th, counted from the optical transmission station,
respectively. The optical repeater system has a fault of snap
ping of the cable around the end of the 39th optical fibre.
This measurement can be described using the numerals de
scribed above. The backscatter lights 5a(37), 5a(38) and 5a(39)
occurring at transmission side, or up side, optical fibres
3a(37), 3a(38) and 3a(39) are returned by the optical returning
circuits installed in the optical repeaters A36, A37 and A38,
respectively, and are measured. Therefore, this measurement has
made an effectiveness of the invention sure.
In conclusion, the normally conducting optical returning
circuit for the backscatter light of each optical repeater is
constituted of the optical combiner and divider, or the optical
coupler, for tapping the backscatter light with giving a prede
termined loss at the output of the up side optical amplifier,
and the optical combiner and divider, or the optical coupler,
for joining the signal to either the output or the input of the
down side optical amplifier with giving a predetermined loss.
According to the invention, the optical repeater can be constituted simply, and finding a fault location is accomplished with high cost-performance, high resolution by measurement of fackscatter light.
It becomes unnecessary to add new media for producing a loss to the optical returning circuit by controlling ratios of tapping and coupling of the optical coupler. The loss at the optical returning circuit is readily adjusted using optical fibre couplers as means for optically integrating and separating.
Moreover, the use of a demodulating system of optical heterodyne detection as means for measuring the backscatter light allows the result of the measurement to achieve a fine SNR and to be stable, thereby enabling finding a fault location to be with a high resolution. Therefore, the invention can be applied widely as a method and an apparatus for finding a fault location for an optical repeater system in which optical fibres are used as transmission media and a plurality of optical repeaters are inserted between those optical fibres to transmit a signal, and is very effective.
Claims (14)
- A A method for finding a fault location for an optical repeat- er system in which an optical transmission link is constructed by at least one pair of optical fibres for two way communication with one repeater or a plurality of repeaters inserted therebetween, each of which includes at least one pair of optical amplifiers for two way communication, and in which one end of said optical transmission link is connected to an optical transmission station, comprising of:: maintaining each optical returning circuit to be normally conducting, said optical returning circuit being provided in each said optical repeater, connecting between said optical amplifiers of up and down side optical channels of said two way communication, and giving passing light therethrough a necessary loss not affecting the transmission of said down side optical channel; and further comprising, in case that a fault occurs in said optical transmission link, of: sending an optical signal for measurement from said optical transmission station to said up side optical channel; returning backscatter light occurring in one of said optical fibre connected to an output of said optical amplifier of said up side optical channel to said down side optical channel through said optical returning circuit provided in respective of said optical repeater; and measuring said backscatter light transmitted through said down side optical channel and received by said optical transmis sion station to determine the fault location according to said backscatter light.
- 2. A method as claimed in claim 1, characterized in that said optical returning circuit couples between said output of said optical amplifier of said up side optical channel and an output of said amplifier of said down side optical channel, and in that said loss of said optical returning circuit is a value greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N) where the number of said optical repeater mounting said optical returning circuit is N.
- 3. A method as claimed in claim 1, characterized in that said optical returning circuit couples between said output of said optical amplifier of said up side optical channel and an input of said amplifier of said down side optical channel, and in that said loss of said optical returning circuit is a value greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channel} (dB) and less than or equal to 80 (dB) - 10 Log (N) + (the gain of said optical amplifier of said down side optical channel} (dB) where the number of said optical repeater mounting said optical returning circuit is N.
- 4. A method as claimed in claim 1, characterized in that when said optical returning circuit couples between said output of said optical amplifier of said up side optical channel and an output of said amplifier of said down side optical channel, said loss of said optical returning circuit is a value greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to cD,O (dB) - 10 Log (N) where the number of said optical repeater mounting said optical returning circuit is N, and in that when said optical returning circuit couples between said output of said optical amplifier of said up side optical channel and an input of said amplifier of said down side optical channel, said loss of said optical returning circuit is a value greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channels (dB) and less than or equal to 80 (dB) - 10 Log (N) + (the gain of said optical amplifier of said down side optical channel} (dB) where the number of said optical repeater mounting said optical returning circuit is N.
- 5. An apparatus for finding a fault location for an optical repeater system in which the apparatus includes one optical repeater or a plurality of optical repeaters, each of which is constituted of a pair of optical amplifying circuits for two way communication using optical amplifiers, and an optical returning circuit connecting between outputs of said optical amplifier of up and down side optical channels so as to be normally conduc tive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N) where the number of said optical repeater or repeaters mounting said optical returning circuit or circuits is N, at least one pair of optical fibres for two way communication inserting said optical repeater or repeaters, and an optical transmission station including means for sending a measurement signal connected to one end of a transmission link formed by said optical repeater or repeaters and said optical fibres and means for receiving and measuring backscatter light of said measurement signal.
- 6. An apparatus for finding a fault location for an optical repeater system in which the apparatus includes one optical repeater or a plurality of optical repeaters, each of which is constituted of a pair of optical amplifying circuits for two way communication using optical amplifiers, and both or either of a first optical returning circuit connecting between an output of said optical amplifier of an up side optical channel and an input of said optical amplifier of a down side optical channel so as to be normally conductive and giving light passing there through a loss greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channel} (dB) and less than or equal to 80 (dB) - 10 Log (N) + (the gain of said optical amplifier of said down side optical channel} (dB), and a second optical returning circuit connecting between an input of said optical amplifier of said up side optical channel and an output of said optical amplifier of said down side optical channel so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channel) (dB) and less than or equal to 80 (dB) - 10 Log (N) + {the gain of said optical amplifier of said down side optical channel} (dB), where the number of said optical repeater or repeaters mounting said optical returning circuit or circuits in said optical transmission link is N, at Least one pair of optical fibres for two way communication inserting said optical repeater or repeaters, and an optical transmission station including means for sending a measurement signal connected to one end of a transmission link formed by said optical repeater or repeaters and said optical fibres and means for receiving and measuring backscatter light of said measurement signal.
- 7. An apparatus for finding a fault location for an optical repeater system in which the apparatus includes one of a first optical repeater or a plurality of first optical repeaters, each of which is constituted of a pair of optical amplifying circuits for two way communication using optical amplifiers, and a first optical returning circuit connecting between outputs of said optical amplifier of up and down side optical channels so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N), one of a second optical re peater or a plurality of second optical repeaters, each of which is constituted of a pair of optical amplifying circuits for two way communication using optical amplifiers, and both or either of a second optical returning circuit connecting between an output of said optical amplifier of said up side optical channel and an input of said optical amplifier of said down side optical channel so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channel} (dB) and less than or equal to 80 (dB) - 10 Log s c'N) + (the gain of said optical amplifier of said down side optical channel} (dB) and a third optical returning circuit connecting between an input of said optical amplifier of said up side optical channel and an output of said optical amplifier of said down side optical channel so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical ampli fier of said down side optical channel} (dB) and less than or equal to 80 (dB) - 10 Log (N) + (the gain of said optical ampli fier of said down side optical channel} (dB) where the number of said optical repeaters is N, at least one pair of optical fibres for two way communication inserting said first and second opti cal repeaters, and an optical transmission station including means for sending a measurement signal and means for measuring backscatter light of said measurement signal.
- 8. An optical repeater for an apparatus for finding a fault location for an optical repeater system whose optical transmis sion link is composed of one of the optical repeater or a plu rality of the optical repeaters formed by at least one pair of optical amplifying circuits for two way communication using optical amplifiers and inserted in at least one pair of optical fibres for two way communication, characterized in that said optical repeater includes: said optical amplifier of an up side optical channel of said two way communication; said optical amplifier of a down side optical channel of said two way communication; and '0jn optical returning circuit connecting between outputs of said optical amplifier of said up and down side optical channels so as to be normally conductive and giving light passing there through a loss greater than or equal to 10 Log (N) - 15 (dB) and less than or equal to 80 (dB) - 10 Log (N) where the number of said optical repeater or repeaters mounting said optical return ing circuit or circuits in said optical transmission link is N.
- 9. An optical repeater as claimed in claim 8, characterized in that said optical returning circuit is composed of a first opti cal coupler disposed on a side of said up side optical channel, and of a second optical coupler disposed on a side of said down side optical channel and connected to said first optical cou pler, and in that losses at said first and second optical cou plers are adjusted according to a ratio of tapping or coupling of light, so that a predetermined loss of said optical returning circuit is formed by a composition of said losses.
- 10. An optical repeater for an apparatus for finding a fault location for an optical repeater system whose optical transmis sion link is composed of one of the optical repeater or a plu rality of the optical repeaters formed by at least one pair of optical amplifying circuits for two way communication using optical amplifiers and inserted in at least one pair of optical fibres for two way communication, characterized in that said optical repeater includes: said optical amplifier of an up side optical channel of said two way communication; said optical amplifier of a down side optical channel of said two way communication; and both or either of: a first optical returning circuit connecting between an output of said optical amplifier of said up side optical channel and an input of said optical amplifier of said down side optical channel so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channel} (dB) and less than or equal to 80 (dB) - 10 Log (N) + (the gain of said optical amplifier of said down side optical channel} (dB); and a second optical returning circuit connecting between an input of said optical amplifier of said up side optical channel and an output of said optical amplifier of said down side optical channel so as to be normally conductive and giving light passing therethrough a loss greater than or equal to 10 Log (N) - 15 (dB) + (the gain of said optical amplifier of said down side optical channel) (dB) and less than or equal to 80 (dB) 10 Log (N) + (the gain of said optical amplifier of said down side optical channel} (dB), where the number of said optical repeater or repeaters mounting said optical returning circuits in said optical transmission link is N.
- 11. An optical repeater as claimed in claim 10, characterized in that said first optical returning circuit is composed of a first optical coupler disposed on a side of said up side optical channel, and of a second optical coupler disposed on a side of said down side optical channel and connected to said first t > optical coupler, and losses at said first and second optical couplers are adjusted according to a ratio of tapping or cou pling of light, so that a predetermined loss of said first optical returning circuit is formed by a composition of said losses, and in that said optical returning circuit is composed of a third optical coupler disposed on a side of said up side optical channel, and of a fourth optical coupler disposed on a side of said down side optical channel and connected to said third optical coupler, and other losses at said third and fourth optical couplers are adjusted according to a ratio of tapping or coupling of light, so that a predetermined loss of said second optical returning circuit is formed by a composition of said other losses.
- 12. A method for finding a fault location for an optical repeater system, substantially as hereinbefore described with reference to the accompanying drawings.
- 13. An apparatus for finding a fault location for an optical repeater system, substantially as hereinbefore described with reference to the accompanying drawings.
- 14. An optical repeater for an apparatus for an optical repeater system, substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13732692A JP2641674B2 (en) | 1992-05-28 | 1992-05-28 | Fault location method and apparatus for optical repeater system and optical repeater |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9310774D0 GB9310774D0 (en) | 1993-07-14 |
| GB2267792A true GB2267792A (en) | 1993-12-15 |
| GB2267792B GB2267792B (en) | 1996-01-10 |
Family
ID=15196063
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9310774A Expired - Fee Related GB2267792B (en) | 1992-05-28 | 1993-05-25 | Method and apparatus for finding a fault location for an optical repeater system and optical repeater |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2641674B2 (en) |
| GB (1) | GB2267792B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2282020A (en) * | 1993-09-20 | 1995-03-22 | Fujitsu Ltd | Optical transmission system including amplification |
| FR2716763A1 (en) * | 1994-02-25 | 1995-09-01 | Fujitsu Ltd | Optical amplifier repeater. |
| WO1997023965A1 (en) * | 1995-12-21 | 1997-07-03 | Alcatel Alsthom Compagnie Generale D'electricite | Improvements in fibre-break detection in optical signal transmission networks |
| US6310718B1 (en) * | 1998-03-09 | 2001-10-30 | Nec Corporation | Optical amplifying apparatus for detecting break point in optical transmission lines |
| US7068945B2 (en) | 2003-02-06 | 2006-06-27 | Fujitsu Limited | Optical amplifying and repeating method and optical amplifying and repeating system |
| EP1705811A1 (en) * | 2005-03-22 | 2006-09-27 | Fujitsu Limited | Method, apparatus, and system for evaluating faulty point in multi-stage optical amplifying and repeating transmission line |
| GB2425904A (en) * | 2005-05-03 | 2006-11-08 | Marconi Comm Gmbh | Optical network fault test apparatus which modifies a received test signal using a passive optical device to generate a response signal |
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| EP0084371A2 (en) * | 1982-01-19 | 1983-07-27 | Siemens Aktiengesellschaft | Carrier frequency system for four-wire operation |
| EP0111582A1 (en) * | 1982-12-18 | 1984-06-27 | ANT Nachrichtentechnik GmbH | Fault locating arrangement for an optical fibre cable link |
| US4972513A (en) * | 1987-07-23 | 1990-11-20 | Kokusai Denshin Denwa Kabushiki Kaisha | Multi-point optical amplification repeating system |
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Cited By (12)
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|---|---|---|---|---|
| GB2282020A (en) * | 1993-09-20 | 1995-03-22 | Fujitsu Ltd | Optical transmission system including amplification |
| US5510925A (en) * | 1993-09-20 | 1996-04-23 | Fujitsu Limited | Relay transmission system including optical amplification |
| GB2282020B (en) * | 1993-09-20 | 1998-05-27 | Fujitsu Ltd | Relay transmission system including optical amplification |
| FR2716763A1 (en) * | 1994-02-25 | 1995-09-01 | Fujitsu Ltd | Optical amplifier repeater. |
| WO1997023965A1 (en) * | 1995-12-21 | 1997-07-03 | Alcatel Alsthom Compagnie Generale D'electricite | Improvements in fibre-break detection in optical signal transmission networks |
| US6301036B1 (en) | 1995-12-21 | 2001-10-09 | Alcatel | optical signal transmission network with fiber-break detection |
| US6310718B1 (en) * | 1998-03-09 | 2001-10-30 | Nec Corporation | Optical amplifying apparatus for detecting break point in optical transmission lines |
| US7068945B2 (en) | 2003-02-06 | 2006-06-27 | Fujitsu Limited | Optical amplifying and repeating method and optical amplifying and repeating system |
| EP1705811A1 (en) * | 2005-03-22 | 2006-09-27 | Fujitsu Limited | Method, apparatus, and system for evaluating faulty point in multi-stage optical amplifying and repeating transmission line |
| US7657176B2 (en) | 2005-03-22 | 2010-02-02 | Fujitsu Limited | Method, apparatus, and system for evaluating faulty point in multi-stage optical amplifying and repeating transmission line |
| GB2425904A (en) * | 2005-05-03 | 2006-11-08 | Marconi Comm Gmbh | Optical network fault test apparatus which modifies a received test signal using a passive optical device to generate a response signal |
| US8331777B2 (en) | 2005-05-03 | 2012-12-11 | Ericsson Ab | Passive optical test termination |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9310774D0 (en) | 1993-07-14 |
| JP2641674B2 (en) | 1997-08-20 |
| JPH05336042A (en) | 1993-12-17 |
| GB2267792B (en) | 1996-01-10 |
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Effective date: 20090525 |