JP5066555B2 - Optical line fault search device - Google Patents

Description

The present invention relates to an OLT (Optical Line) in a station in a WDM-PON (Wavelength Division Multiplexing-Passive Optical Network) system.
The present invention relates to an apparatus for detecting a failure in an optical fiber line between ONUs (Optical Network Units) on a user's home side via an optical splitter from a terminal side.

  The speed of optical access systems has been remarkably increased, and about 100 times faster and wider bandwidth has been realized in the last five years, and research for further speedup is being conducted.

  PON is known as a technology for realizing this. PON is a technology that performs optical fiber communication efficiently by inserting a branch device, which is a passive element, in the middle of an optical access line and drawing each fiber branched into a plurality of subscribers into a plurality of subscriber houses. is there.

  The PON system connects the OLT of the in-station terminal device and the ONU of each user's house via a branch device, and is required to monitor the branch optical line between the OLT and a plurality of ONUs at low cost. Yes.

  One of the PON systems is WDM-PON. This WDM-PON is a system for sharing an optical fiber by assigning different optical wavelengths to each ONU. Since this method assigns one wavelength to one user, it is considered that a speed exceeding 10 Gbit / sec is possible.

  As a technique for testing the above-mentioned WDM-PON system, Patent Document 1 discloses an optical subscriber of a star coupler that branches a common optical fiber line from a center apparatus into individual optical fiber lines assigned to a plurality of subscribers. Filter means (wavelength variable filters) that transmit the wavelength of each signal light and can switch between passing and blocking the wavelength of the test light and its reflected light are inserted into each input / output terminal on the unit (ONU) side. In addition, wavelength selective reflection means (wavelength selective filter) that transmits the wavelength of each signal light and reflects the test light is provided at the input / output ends of each optical subscriber unit, and filter means for individual optical fiber line that performs communication Is the test light blocking state, the filter means of the individual optical fiber line to be tested is in the test light passing state, and the light reflection measuring device connected to the line on the center device side is set. Incident pulsed test light from (OTDR), a technique for fault testing of each individual optical fiber line on the basis of the return light is disclosed.

Japanese Patent No. 3255214

  In Patent Document 1, it is necessary to provide a wavelength tunable filter for each individual optical fiber line. When the number of branches becomes enormous, the number of wavelength tunable filters increases accordingly, resulting in a high cost.

  On the other hand, many of the WDM-PON systems use AWG (Arrayed Waveguide Grating) capable of demultiplexing into a plurality of fixed wavelengths as a branching means for branching a common optical fiber line into a plurality of individual optical fiber lines. It is conceivable to apply a test system such as that of Patent Document 1 to this, but when AWG is used in the wavelength branching section of Patent Document 1, the test light wavelength is adjusted to the signal light wavelength for each individual optical fiber line. There is a need.

  That is, in the case of the WDM-PON using the fixed wavelength demultiplexing type branching device as described above, it is necessary to vary the wavelength of light used for the failure test.

  However, when this number of wavelengths is large, it takes a very long time to inspect all the individual optical fiber lines, and it is necessary to stop communication during that time.

  The present invention solves the above-described problems and detects faults in all individual fiber lines of a WDM-PON system in which a common optical fiber line and individual optical fiber lines are connected via a wavelength-fixed branching device such as an AWG. An object of the present invention is to provide an optical line fault search device that can be performed in a short time.

In order to achieve the above object, an optical line fault searching device according to claim 1 of the present invention includes:
A telephone station that multiplexes signal lights of a plurality of different wavelengths to enter one end of a common optical fiber line (17), and separates and receives the light transmitted through the common optical fiber line for each wavelength. Side optical line terminator (10), connected to the other end of the common optical fiber line, receives signal light transmitted from the telephone station side optical line terminator, and separates it according to its wavelength, The light is incident on one end of individual optical fiber lines (18 ₁ to 18 _n ) individually provided with different lengths for each wavelength, and the signal light transmitted through the individual optical fiber lines is multiplexed to A fixed wavelength demultiplexing type branching device (15) that emits light to a common optical fiber line, and subscriber-side optical line terminators (16 _{1 to} 16 _n ) respectively connected to the other end side of the individual optical fiber line Search for obstacles in optical line of WDM-PON system An optical path fault searching apparatus,
A line coupler (21) connected to the common optical fiber line;
A broadband optical pulse generating means (22) for generating a broadband optical pulse including wavelengths of all signal lights transmitted through the common optical fiber line;
The broadband optical pulse is received by the first optical path, is incident on the WDM-PON system from the second optical path via the line coupler, and returns to the line coupler from the WDM-PON system in response to the broadband optical pulse. A coupler (23) for receiving return light in the second optical path and emitting it to the third optical path;
A light receiver (25) that receives the return light emitted from the third optical path of the coupler and converts it into an electrical signal having an amplitude corresponding to its intensity;
Broadband optical pulse generating means (22) for causing the broadband optical pulse to enter the WDM-PON system during a communication suspension period;
Time waveform acquisition means (27) for acquiring a time waveform of a signal output from the light receiver until a predetermined time elapses from a timing when the broadband optical pulse is incident on the WDM-PON system;
Reference waveform storage means (28) for storing a time waveform acquired in advance when the WDM-PON system is normal as a reference waveform;
It comprises a failure detection means (29) for searching for a failure in the WDM-PON system by comparing the time waveform newly acquired by the time waveform acquisition means and the reference waveform.

Further, an optical line failure searching device according to claim 2 of the present invention is the optical line failure searching device according to claim 1,
A wavelength equal to the signal wavelength corresponding to the specific individual optical fiber line out of the return light from the WDM-PON system when the fault detection unit detects that a specific individual optical fiber line has failed. Individual line measuring means for selectively injecting component light into the light receiver and obtaining a time waveform of an output signal of the light receiver to detect a more detailed failure of the specific individual optical fiber line ( 40).

Further, an optical line failure searching device according to claim 3 of the present invention is the optical line failure searching device according to claim 2,
The individual line measuring means is
A variable wavelength filter (41) for selectively passing light having a wavelength component equal to a signal wavelength corresponding to the specific individual optical fiber line from the wavelength component of the broadband optical pulse;
An optical switch (42) for inserting the tunable filter between the coupler and the light receiver, between the broadband pulse light source and the coupler, or between the coupler and the line coupler. 43).

Moreover, the optical-path fault searching apparatus of Claim 4 of this invention is the optical-path fault searching apparatus in any one of Claims 1-3,
The broadband optical pulse generating means includes
A broadband light source (22a) from a Super Continuum light source that emits light including spectral light that matches the wavelength of all the signal light;
It is characterized by comprising an optical pulse generating means (22b) for receiving an emitted light from the broadband light source and generating an optical pulse.

  As described above, the optical line fault searching device according to claim 1 of the present invention is used in a WDM-PON system with respect to WDM-PON systems having different lengths of individual optical fiber lines corresponding to the respective signal light wavelengths. A broadband optical pulse including all the wavelengths of the signal light is incident during the communication stop period, the return light from the WDM-PON system for the broadband optical pulse is received, and the time waveform of the received light signal is acquired. Compared with the reference waveform acquired at the normal time, the fault of the WDM-PON system is searched.

  For this reason, even if the number of branches of the WDM-PON system is enormous, failure detection can be performed in a short time with a measurement time of one line.

  According to the second aspect of the present invention, it is possible to obtain detailed information on a specific individual optical fiber line that has been detected as having failed due to a time waveform obtained collectively with a broadband optical pulse.

  According to the third aspect of the present invention, detailed information about the individual optical fiber line can be easily obtained when there is a fault by using the wavelength tunable filter and the optical switch.

Configuration diagram of an embodiment of the present invention Spectrum diagram of broadband optical pulse Signal waveform diagram for explaining the operation of the embodiment Signal waveform diagram for explaining the operation of the embodiment The figure which shows an example of an individual track | line measuring means Detailed waveform diagram obtained by individual line measuring means The figure which shows the other example of an individual track | line measuring means The figure which shows the other example of an individual track | line measuring means

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a basic configuration of a WDM-PON system and an optical line fault searching apparatus 20 to which the present invention is applied.

The WDM-PON system to be tested includes an OLT (telephone station side optical line terminating device) 10, a fixed wavelength demultiplexing type branching device 15 represented by the AWG, and a plurality of ONUs 16 _{1 to} 16 _n (subscriber side optical lines). Termination device), a single common optical fiber line 17 connecting between the OLT 10 and the branching device 15, and individual optical fiber lines 18 ₁ to 18 connecting individually between the branching device 15 and the ONUs 16 _{1 to} 16 _{n. n} . Here, it is assumed that the ONUs 16 _{1 to} 16 _n have a function of totally reflecting incident light by a mirror or the like when communication is stopped.

Here, the OLT ₁₀ combines a plurality of transceivers 11 _{1 to} 11 _n that transmit and receive signal lights having different wavelengths λ _{1 to} λ _n and signal lights from the transceivers 11 _{1 to} 11 _n to share a common optical fiber. A fixed wavelength demultiplexing type branching device 12 such as an AWG that emits light to the line 17 and demultiplexes the light from the common optical fiber line 17 for each wavelength and supplies the demultiplexed light to the transceivers 11 _{1 to} 11 _n having the corresponding wavelengths. It is comprised by.

  The light wavelength-multiplexed by the branching device 12 enters the branching device 15 through the common optical fiber line 17.

The branching unit 15 has the same configuration as that of the branching unit 12 and divides the light incident from the OLT 10 side into signal light of each wavelength λ _{1 to} λ _n and is assigned for each wavelength, and is an individual optical fiber line having a different length. The light is emitted to 18 ₁ to 18 _n and _given to ONUs 16 _{1 to} 16 _n , respectively. In addition, the signal light emitted from the ONUs 16 _{1 to} 16 _n is received via the individual optical fiber lines 18 ₁ to 18 _n , combined, and emitted to the common optical fiber line 17. Here, it is assumed that the lengths of the individual optical fiber lines 18 ₁ to 18 _n become longer in the order of subscripts.

Further, the difference in length (difference length) of each of the individual optical fiber lines 18 ₂ to 18 _n with respect to the shortest individual optical fiber line 18 ₁ is different from the pulse width (time width) of the broadband optical pulse Pw described later. The difference length is sufficiently longer than the time required for light to pass.

  The optical line fault searching device 20 for testing this WDM-PON system causes a test optical pulse to enter the WDM-PON system via a line coupler 21 connected to the common optical fiber line 17. Return light from the WDM-PON system in response to the optical pulse is made incident into the apparatus via the line coupler 21.

  As shown in FIG. 2, the broadband optical pulse generating means 22 generates a broadband optical pulse Pw including the wavelengths λ1 to λn of all signal lights transmitted through the common optical fiber line 17, and passes through the coupler 23 and the line coupler 21. To enter the WDM-PON system during the communication suspension period.

  The broadband optical pulse generating means 22 is composed of a broadband light source 22a and an optical pulse generating means 22b. As the broadband light source 22a, a super continuum light source, an SLD, or the like that emits light including spectral light that matches all signal light wavelengths λ1 to λn can be used.

  A supercontinuum light source emits light having an oscillation spectrum over a wide wavelength band by injecting a very strong seed light into a transparent medium such as glass (which tends to occur in a thin medium such as an optical fiber). It is a light source and is suitable as the broadband light source 22a.

  Further, as the optical pulse generating means 22b, an LN modulator or the like that performs pulse modulation on the broadband light emitted from the broadband light source 22a can be used. Here, it is assumed that a broadband optical pulse Pw synchronized with the modulation clock pulse C is emitted.

  The coupler 23 has three different optical paths for entering and exiting light, receives the broadband optical pulse Pw on the first optical path, and emits it from the second optical path to the line coupler 21. Further, the return light Pr from the line coupler 21 is received by the second optical path and is emitted from the third optical path to the light receiver 25.

  The light receiver 25 receives the return light Pr and converts it into an electric signal Vr having an amplitude corresponding to the intensity thereof, and inputs the signal to the A / D converter 26.

  The digital data signal D obtained by the A / D converter 26 is input to the time waveform acquisition means 27. The time waveform acquisition means 27 reciprocates from the timing at which the broadband optical pulse Pw is incident on the WDM-PON system (timing synchronized with the clock pulse C) to the end of the individual optical fiber line where the incident optical pulse is the longest. A series of signals (actually a series of data signals D) output from the light receiver 25 are stored and obtained by the incidence of the broadband optical pulse Pw a plurality of times (for example, 10 to 100 times). A time waveform from which random noise components are removed is obtained by averaging the obtained data.

  The reference waveform storage unit 28 stores a time waveform acquired in advance by the time waveform acquisition unit 27 when the WDM-PON system is normal as a reference waveform.

  The failure detection means 29 searches for a failure in the WDM-PON system by comparing the time waveform newly acquired by the time waveform acquisition means 27 with the reference waveform.

  The control unit 30 performs various types of control necessary for the measurement of the optical line fault searching device 20, and transmits the broadband optical pulse Pw to the WDM-PON system at least during a period when the WDM-PON system stops communication. A broadband optical pulse incident means for restricting the incidence of the broadband optical pulse Pw is formed during the period during which communication is performed by searching for a fault.

  Here, although the control part 30 has grasped | ascertained the communication stop period of a WDM-PON system, the following system can consider this, for example.

  That is, the control unit 30 stores the communication schedule of the WDM-PON system in advance, and the broadband optical pulse Pw is incident a predetermined number of times at a fixed period during the stop period, and the WDM-PON system via communication means (not shown). And the control unit 30 communicate with each other, receive information notifying the communication stop from the WDM-PON system side, and injecting the broadband optical pulse Pw a predetermined number of times in the fixed period, or the communication stop from the control unit 30 side This is a method in which a request is made to the WDM-PON system side, and when the WDM-PON system stops communication in response to the request, the broadband optical pulse Pw is incident a predetermined number of times at a constant period.

  In addition, as a specific technique for causing the broadband optical pulse Pw to enter the WDM-PON system during the communication suspension period and for restricting the incidence of the broadband optical pulse Pw during other periods, the broadband optical pulse Pw is generated. The output of the clock pulse C is turned on and off, or a shutter (not shown) is provided between the line coupler 21 and the coupler 23 or between the coupler 23 and the broadband optical pulse generating means 22 and the opening and closing of the shutter is controlled. .

  In the optical line fault searching device 20 configured as described above, the emission of light that hinders the communication is restricted during the period in which the WDM-PON system is communicating. A clock pulse C having a period is given to the broadband optical pulse generating means 22 and the time waveform acquiring means 27, and the broadband optical pulse Pw is generated at a constant period by the broadband optical pulse generating means 22, as shown in FIG. The light enters the WDM-PON system via the coupler 23 and the line coupler 21.

The broadband optical pulse Pw propagates from the common optical fiber line 17 to the branching device 15, and is propagated to the individual optical fiber lines 18 ₁ to 18 _n separately by the branching device 15 by each wavelength component.

Then, backscattered light (Rayleigh scattered light) of each wavelength component, Fresnel reflection component, or total reflection light by ONUs 16 _{1 to} 16 _n returns to the branching unit 15 through the individual optical fiber lines 18 ₁ to 18 _n , and the branching unit 15 And are incident on the light receiver 25 via the common optical fiber line 17, the line coupler 21 and the coupler 23.

  The waveform of the return light Pr (λ1) to Pr (λn) for each wavelength component included in the broadband optical pulse Pw (this waveform cannot be actually acquired) is normal if there is no abnormality in the line of the WDM-PON system. As shown in (b1) to (bn) of FIG. 3, Fresnel reflection components Ra (1) to Ra (n) at the exit point, Fresnel reflection components Rb (1) to Rb (n) at the branching device 15, ONU The components of total reflection Rc (1) to Rc (n) at the incident end appear in the form of pulses, and the time waveform acquisition means 27 obtains the waveform shown in FIG. (The fiber junction point is omitted).

Here, as described above, the lengths of the individual optical fiber lines 18 ₁ to 18 _n are different, and the difference length is such that light passes through the difference length with respect to the pulse width of the broadband optical pulse Pw. Therefore, the positions (distance and time) of the total reflection components Rc (1) to Rc (n) in the return light of the respective wavelength components are separated into positions separated by the difference length. Is displayed.

  Since the speed of light propagating through an optical fiber with the same characteristics changes depending on the wavelength difference, the position of Fresnel reflection also differs strictly, but this wavelength difference is a wavelength that can propagate through a normal single mode fiber with low loss. Since the difference is small within the band, the combined waveform in FIG. 3C is a waveform that overlaps each other (actually, the width slightly increases). Of course, the waveform comparison described later can be performed in the same manner even if the waveforms are obtained by separating these Fresnel reflection components.

  The waveform shown in FIG. 3 (c) is a waveform when there is no abnormality in the line of the WDM-PON system. This waveform is obtained when the line is laid, for example, and stored in the reference waveform storage means 28 in advance. Compared with the reference waveform, the waveform is almost the same when there is no disconnection or large deterioration in the line. Therefore, it is determined from this time waveform that no failure has occurred.

  The coincidence / disagreement of the time waveforms does not strictly compare the coordinate points consisting of the time axis and level axis of each time waveform, but the pattern information indicating the characteristics of the time waveform (number of peaks, approximate level, approximate position) ) And compare it.

  When it is determined that no failure has occurred as described above, the latest time waveform is updated and stored as a reference waveform. As a result, the comparison can be performed without being affected by errors due to aging.

Also, when subjected to the same measurements at a certain timing a lapse of time from the state of FIG. 3, for example, if there is a break in the middle of the individual optical fiber lines 18 _1, the returned light component of the wavelength corresponding to the line 4 is greatly attenuated at the disconnection position as shown in (b1) of FIG. 4, and the time waveform obtained by synthesizing each wavelength component is n-1 total reflections as shown in (c) of FIG. Only the components Rc (2) to Rc (n) appear (the other figures in FIG. 4 are the same as those in FIG. 3).

  Therefore, when compared with the reference waveform described above, it is found that there is no total reflection component Rc (1) for the wavelength λ1.

Therefore, failure detection means 29 determines that the disconnection failure has occurred in the middle of the individual optical fiber lines 18 _1, alarm information into to a department that manages the WDM-PON system for example via the communication means, not shown To be notified.

  In addition, disconnection faults of other individual optical fiber lines can be determined by comparison with the reference waveform in the same manner as described above, and disconnection faults of the common optical fiber line 17 can be easily determined by the absence of the Fresnel reflection component Rb. be able to.

  As described above, in the optical line fault searching device 20 according to the embodiment, all the WDM-PON systems used in the WDM-PON system have different lengths of individual optical fiber lines corresponding to the respective signal light wavelengths. The broadband optical pulse Pw including the wavelength of the signal light is incident during the communication stop period, the return light from the WDM-PON system with respect to the broadband optical pulse Pw is received, and the time waveform of the received light signal is acquired. In comparison with the reference waveform acquired at times, the WDM-PON system is searched for a fault.

  For this reason, even if the number of branches of the WDM-PON system is enormous, it is possible to detect faults in the measurement time for one line, and fault detection is much faster than the method of obtaining the time waveform sequentially for each wavelength. Can be done.

  In the above embodiment, an abnormal optical fiber line is specified, but more detailed characteristics of the line can be obtained.

  That is, when the failure detection means 29 detects that a failure has occurred in a specific individual optical fiber line, the return light from the WDM-PON system has a wavelength equal to the signal wavelength corresponding to the specific individual optical fiber line. Individual line measurement for selectively injecting component light into the light receiver 25 and acquiring the time waveform of the output signal of the light receiver 25 to detect more detailed faults in a specific individual optical fiber line Means are provided.

  For example, like the individual line measuring means 40 shown in FIG. 5, when the wavelength tunable filter 41 and the optical switches 42 and 43 are provided between the coupler 23 and the light receiver 25 to detect the presence or absence of a failure, The optical switches 42 and 43 are connected to the through side and the same measurement is performed. When a failure is detected in the individual optical fiber line 18x, the pass wavelength of the wavelength tunable filter 41 is set to the wavelength λx corresponding to the line. After setting, only the light of the wavelength λx of the return light is made incident on the light receiver 25, the time waveform as shown in FIG. 6 is obtained, and the disconnection position A that is greatly attenuated is found. The control unit 30 sets the pass wavelength of the wavelength tunable filter 41 and switches the optical switches 42 and 43.

  Further, the wavelength tunable filter 41 and the optical switches 42 and 43 are provided between the broadband optical pulse generator 22 and the coupler 23 as shown in FIG. 7, or between the coupler 23 and the line coupler 23 as shown in FIG. When the presence or absence of a fault is detected, the optical switches 42 and 43 are connected to the through side to perform the same measurement as described above. When a fault is detected in the individual optical fiber line 18x, the wavelength tunable filter 41 is set to the wavelength λx corresponding to the line, and the wavelength of incident light and return light to the WDM-PON system is limited to λx, and the same measurement as described above is performed.

DESCRIPTION OF SYMBOLS 10 ... OLT (telephone station side optical line terminator), 15 ... branching device, 16 _{1 to} 16 _n ... ONU (subscriber side optical line terminator), 17 ... common optical fiber line, 18 ₁ to 18 _n: individual optical fiber line, 20: optical line fault searching device, 21: line coupler, 22: broadband optical pulse generating means, 23: coupler, 25: light receiver, 26: A / D conversion 27... Time waveform acquisition means 30... Control unit 40. Individual line measurement means 41. Wavelength tunable filter 42 and 43.

Claims (4)

A telephone station that multiplexes signal lights of a plurality of different wavelengths to enter one end of a common optical fiber line (17), and separates and receives the light transmitted through the common optical fiber line for each wavelength. Side optical line terminator (10), connected to the other end of the common optical fiber line, receives signal light transmitted from the telephone station side optical line terminator, and separates it according to its wavelength, The light is incident on one end of individual optical fiber lines (18 ₁ to 18 _n ) individually provided with different lengths for each wavelength, and the signal light transmitted through the individual optical fiber lines is multiplexed to A fixed wavelength demultiplexing type branching device (15) that emits light to a common optical fiber line, and subscriber-side optical line terminators (16 _{1 to} 16 _n ) respectively connected to the other end side of the individual optical fiber line Search for obstacles in optical line of WDM-PON system An optical path fault searching apparatus,
A line coupler (21) connected to the common optical fiber line;
Broadband optical pulse generating means (22) for generating a broadband optical pulse including the wavelengths of all signal lights transmitted through the common optical fiber line;
The broadband optical pulse is received by the first optical path, is incident on the WDM-PON system from the second optical path via the line coupler, and returns to the line coupler from the WDM-PON system in response to the broadband optical pulse. A coupler (23) for receiving return light in the second optical path and emitting it to the third optical path;
A light receiver (25) that receives the return light emitted from the third optical path of the coupler and converts it into an electrical signal having an amplitude corresponding to its intensity;
Broadband optical pulse generating means (22) for causing the broadband optical pulse to enter the WDM-PON system during a communication suspension period;
Time waveform acquisition means (27) for acquiring a time waveform of a signal output from the light receiver until a predetermined time elapses from a timing when the broadband optical pulse is incident on the WDM-PON system;
Reference waveform storage means (28) for storing a time waveform acquired in advance when the WDM-PON system is normal as a reference waveform;
A light beam comprising a failure detection unit (29) for searching for a failure in the WDM-PON system by comparing the time waveform newly acquired by the time waveform acquisition unit and the reference waveform. Road obstacle search device.   A wavelength equal to the signal wavelength corresponding to the specific individual optical fiber line out of the return light from the WDM-PON system when the fault detection unit detects that a specific individual optical fiber line has failed. Individual line measuring means for selectively injecting component light into the light receiver and obtaining a time waveform of an output signal of the light receiver to detect a more detailed failure of the specific individual optical fiber line ( 40) The optical line fault searching device according to claim 1, wherein 40) is provided. The individual line measuring means is
A variable wavelength filter (41) for selectively passing light having a wavelength component equal to a signal wavelength corresponding to the specific individual optical fiber line from the wavelength component of the broadband optical pulse;
An optical switch (42) for inserting the tunable filter between the coupler and the light receiver, between the broadband pulse light source and the coupler, or between the coupler and the line coupler. 43) The optical line fault searching device according to claim 2. The broadband optical pulse generating means includes
A broadband light source (22a) from a Super Continuum light source that emits light including spectral light that matches the wavelength of all the signal light;
The optical line fault searching device according to any one of claims 1 to 3, further comprising: an optical pulse generating means (22b) for receiving an emitted light from the broadband light source and generating an optical pulse.

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