CN110635842B - Passive wavelength division multiplexing network optical fiber fault detection system and detection method thereof - Google Patents
Passive wavelength division multiplexing network optical fiber fault detection system and detection method thereof Download PDFInfo
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- 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]
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- 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
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
- H04B10/0791—Fault location on the transmission path
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- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
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- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0062—Network aspects
- H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
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Abstract
The invention relates to a passive wavelength division multiplexing network optical fiber fault detection system and a detection method thereof, belonging to the technical field of passive wavelength division multiplexing network optical fiber fault detection systems; the technical problem to be solved is as follows: the improvement of a passive wavelength division multiplexing network optical fiber fault detection system structure and a detection method thereof is provided; the technical scheme for solving the technical problem is as follows: the optical fiber coupling device comprises a chaotic laser generator, wherein a signal output end of the chaotic laser generator is connected with a second input end of a first optical circulator, and a signal output end of the first optical circulator is connected with an optical isolator in series and then is connected with an input end of a first optical fiber coupler; the first output end of the first optical fiber coupler is connected with the input end of the phase modulator after being sequentially connected with the polarization controller and the optical attenuator in series, and the output end of the phase modulator is connected with the first input end of the first optical circulator; the modulation interface of the phase modulator is also connected with a random signal generator; the invention is applied to optical fiber fault detection.
Description
Technical Field
The invention discloses a passive wavelength division multiplexing network optical fiber fault detection system and a detection method thereof, belonging to the technical field of passive wavelength division multiplexing network optical fiber fault detection systems.
Technical Field
Detecting the fault of the optical fiber by adopting a detection passive Wavelength division multiplexing network (WDM-PON for short), and mainly utilizing a Wavelength tunable optical pulse technology [ Optics Express, vol.15, pp.1461-1466,2007; IEEE Photonics Technology Letters, vol.20, pp.1323-1325,2008] and chaotic optical time domain reflectometry [ Journal of Lightwave Technology, vol.30, No.21, pp.3420-3426,2012; optical Fiber Technology, vol.20, pp.163-167,2014, Optics Communications, vol.350, pp.288-295,2015; optical Letters, vol.38, pp.3762-3764,2015; optics Express, vol.23, pp.2416-2423,2015], compared with the optical pulse as the optical fiber breakpoint detection light source, the detection of the optical fiber fault point by the chaotic laser can realize high-precision positioning independent of distance [ Journal of Lightwave Technology, vol.30, No.21, pp.3420-3426,2012; optics Express, vol.23, pp.15514-15520,2015; applied Optics, vol.56, No.4, pp.1253-1256,2017], which mainly derives from the random characteristic and autocorrelation characteristic of chaotic laser, applies the chaotic laser optical time domain reflection technology in the fiber fault detection of the WDM-PON network, and performs correlation operation on the probe light and the reference light to obtain a correlation peak on a correlation curve, wherein the corresponding position is the fault point position of the fiber.
At present, the techniques for implementing WDM network optical fiber fault detection by using chaotic laser as a detection light source in experiments mainly include: the Optical fiber fault detection with 24km and 2cm resolution is realized by using chaotic laser generated by an Optical feedback multimode laser [ Journal of Lightwave Technology, vol.30, No.21, pp.3420-3426,2012], the Optical fiber fault detection with online 20km and 1.8cm spatial resolution is realized by using self-feedback laser with a plurality of different wavelengths [ Optics Communications, vol.350, pp.288-295,2015], and the Optical fiber fault detection with 75km and 14cm distance resolution can be realized by using chaotic laser generated by an Optical chaotic direct modulation multimode laser [ Microwave and Optical Technology Letters, vol.57, No.11, pp.2502-2506,2015 ].
However, when the above-mentioned technology is used to detect a fault in an optical fiber, a chaotic laser band generated by optical feedback has "side lobes" (i.e., length information fed back by an external cavity), which can cause detection misjudgment, and is limited by the fact that the bandwidth of the chaotic laser generated by the modulation depth of the electrical modulation is too narrow, and thus fault location with higher precision cannot be realized; therefore, it is necessary to invent a high-precision optical fiber fault detection system based on WDM-POM to solve the problems of false alarm (misjudgment), short distance and poor precision of the existing chaotic optical time domain reflectometer technology.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to solve the technical problems that: the improved structure and method for detecting the optical fiber fault in passive wavelength division multiplexing network are provided.
In order to solve the technical problems, the invention adopts the technical scheme that: a passive wavelength division multiplexing network optical fiber fault detection system comprises a chaotic laser generator, wherein the signal output end of the chaotic laser generator is connected with the second input end of a first optical circulator, and the signal output end of the first optical circulator is connected with an optical isolator in series and then is connected with the input end of a first optical fiber coupler; the first output end of the first optical fiber coupler is connected with the input end of the phase modulator after being sequentially connected with the polarization controller and the optical attenuator in series, and the output end of the phase modulator is connected with the first input end of the first optical circulator;
the modulation interface of the phase modulator is also connected with a random signal generator;
the second output end of the first optical fiber coupler is connected with the erbium-doped optical fiber amplifier in series and then is connected with the input end of the electro-optical modulator;
the modulation interface of the electro-optical modulator is also connected with a pulse signal generator;
the output end of the electro-optical modulator is connected with the input end of the second optical fiber coupler;
a second output end of the second optical fiber coupler is connected with a first photoelectric detector through a filter, and an output end of the first photoelectric detector is connected with a correlator;
a first output end of the second optical fiber coupler is connected with a first input end of a second optical circulator, a second input end of the second optical circulator is connected with an input end of a wavelength division multiplexer, and an output end of the wavelength division multiplexer is connected with n optical network units;
the output end of the second optical circulator is connected with the input end of a third optical fiber coupler, and the first output end of the third optical fiber coupler is connected with a spectrum analyzer;
and a second output end of the third optical fiber coupler is connected with the correlator after being connected with the second photoelectric detector in series.
The ratio of the output signal power of the first output end and the second output end of the first optical fiber coupler is 80% to 20%;
the ratio of the output signal power of the first output end and the second output end of the second optical fiber coupler is 99% to 1%;
the ratio of the output signal power of the first output end and the second output end of the third optical fiber coupler is 50% to 50%.
The random signal generator is specifically a chaotic signal source, a noise signal source or a random sequence generator.
The chaotic laser generator is a weak resonant cavity Fabry-Perot laser.
A method for detecting the optical fiber fault of a passive wavelength division multiplexing network is characterized in that: the method comprises the following steps:
the method comprises the following steps: the chaotic laser generator generates a chaotic signal without time delay characteristics;
an optical signal generated by the chaotic laser generator passes through the first optical circulator, the optical isolator, the first optical fiber coupler, the polarization controller, the optical attenuator and the phase modulator and is then transmitted back to the chaotic laser generator, and the returned optical signal disturbs the chaotic laser generator to generate multimode chaotic laser;
the input end of the phase modulator receives a feedback light phase adjustment signal sent by the random signal generator at the same time, the phase adjustment signal is added into a returned laser signal, and the nonlinear action of the phase adjustment signal eliminates the correlation between the feedback light and the output light of the laser, so that the chaotic laser has the characteristic of no time delay;
step two: sending the adjusted chaotic laser signal to an erbium-doped fiber amplifier through a first fiber coupler, amplifying the signal, then entering an electro-optical modulator for pulse modulation, and sending a pulse signal by a pulse signal generator for modulating the amplified signal;
step three: the output end of the electro-optical modulator sends modulated multimode chaotic laser signals without time delay characteristics, one part of the laser signals enters a correlator as reference light through a second optical fiber coupler, and the other part of the laser signals enters a wavelength division multiplexer as detection light and then is split into optical network units of all detection branches;
if a breakpoint exists in a certain path of the optical network unit, feedback light returns to the second optical circulator along the original optical path, and the feedback light is respectively sent to the optical spectrum analyzer and the correlator by the second optical circulator;
the spectrum analyzer is used for displaying feedback wavelength and confirming which branch of the optical network unit has a breakpoint;
the correlator can obtain the fault position and the optical fiber attenuation of the corresponding optical network unit through the feedback light.
The specific method for detecting the optical fiber fault position and the optical fiber attenuation in the third step comprises the following steps:
when the fault position is detected, the correlator tests the echo signal of the nth path of optical network unit and the reference light delay time t λn To obtain the position L of the fault point λn The correlation calculation formula is:
in the above formula, c is the speed of light, n e The refractive index of the fiber core is adopted, and lambdan is the optical network unit of the nth path;
when detecting the optical fiber attenuation, the attenuation information can be read from the slope of the fault point position, and the cross correlation R (tau) of the echo signal and the reference optical signal of the nth path optical network unit is as follows:
in the above formula, Pref λ n pulse chaotic signal, pples λ n is a pulse part, Pchaos λ n is a chaotic part, Pecho λ n is an echo signal, Pbs λ n is a backscatter signal, Pr λ n is a reflection signal, and Pce λ n is an echo signal;
because the chaotic signal is a random signal, the effects generated by the cross-correlation of the pulsed light signal and the echo signal caused by the chaos, the back scattering caused by the chaotic signal and the pulse and the cross-correlation of the reflected signal can be eliminated after the subsequent average processing, and the correlation operation result of the reference light signal and the echo signal can be simplified as follows:
therefore, the attenuation information in the optical fiber is kept as the detection result of the optical fiber attenuation.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides random signal modulation phase feedback chaotic laser for WDM optical fiber fault detection, which utilizes a random signal generator to modulate chaotic laser generated by phase feedback weak resonant cavity Fabry-Perot laser (WRC-FPLD) to have wide frequency spectrum and no time delay characteristic, namely no periodic characteristic, thereby realizing the centimeter-level high-resolution multi-path optical fiber fault detection irrelevant to distance and realizing the fault discrimination without blind area and false alarm;
the laser used for generating the chaotic laser is weak resonant cavity Fabry-Perot laser (WRC-FPLD), the reflectivity of an antireflection film on the front end face of the laser is 1% -30%, the laser has a wider gain spectrum, the cavity length is 600 mu m, so the longitudinal mode interval is as small as 0.56nm, and the number of channels which can be used in a WDM system reaches 100 within the wavelength range of 1510-1570 nm;
compared with the prior art applied to the optical fiber fault detection of the WDM system, the invention not only can identify the breakpoints of the multi-path optical fiber, but also can measure the attenuation condition of the multi-path optical fiber due to the adoption of pulse modulation superposed pulse signals;
in conclusion, the invention effectively solves the problems of false alarm, misjudgment, incapability of considering long-distance high-precision fault positioning and incapability of identifying optical fiber attenuation in the conventional chaotic laser optical time domain reflectometer technology applied to optical fiber fault detection of the WDM system, and provides a comprehensive solution for optical fiber fault detection of the WDM system.
Drawings
The invention is further described below with reference to the accompanying drawings:
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a graph of a chaotic light signal after pulse modulation;
FIG. 3 is a graph of autocorrelation of a chaotic light signal without delay characteristics;
FIG. 4 is a graph showing the slope of the attenuation signal of the optical fiber;
in the figure: the device comprises a chaotic laser generator 1, a first optical circulator 2, an optical isolator 3, a first optical fiber coupler 4, a polarization controller 5, an optical attenuator 6, a phase modulator 7, a random signal generator 8, an erbium-doped optical fiber amplifier 9, an electro-optic modulator 10, a pulse signal generator 11, a second optical fiber coupler 12, a filter 13, a first photoelectric detector 14, a correlator 15, a second optical circulator 16, a third optical fiber coupler 17, a second photoelectric detector 18, a spectrum analyzer 19, a wavelength division multiplexer 20 and an optical network unit 21.
Detailed Description
As shown in fig. 1, the passive wavelength division multiplexing network optical fiber fault detection system of the present invention includes a chaotic laser generator (1), a signal output end of the chaotic laser generator (1) is connected to a second input end of a first optical circulator (2), and a signal output end of the first optical circulator (2) is connected in series with an optical isolator (3) and then connected to an input end of a first optical fiber coupler (4); a first output end of the first optical fiber coupler (4) is sequentially connected in series with the polarization controller (5) and the optical attenuator (6) and then is connected with an input end of the phase modulator (7), and an output end of the phase modulator (7) is connected with a first input end of the first optical circulator (2);
the modulation interface of the phase modulator (7) is also connected with a random signal generator (8);
the second output end of the first optical fiber coupler (4) is connected with an erbium-doped optical fiber amplifier (9) in series and then is connected with the input end of an electro-optical modulator (10);
the modulation interface of the electro-optical modulator (10) is also connected with a pulse signal generator (11);
the output end of the electro-optical modulator (10) is connected with the input end of the second optical fiber coupler (12);
a second output end of the second optical fiber coupler (12) is connected with a first photoelectric detector (14) through a filter (13), and an output end of the first photoelectric detector (14) is connected with a correlator (15);
a first output end of the second optical fiber coupler (12) is connected with a first input end of a second optical circulator (16), a second input end of the second optical circulator (16) is connected with an input end of a wavelength division multiplexer (20), and an output end of the wavelength division multiplexer (20) is connected with n optical network units (21);
the output end of the second optical circulator (16) is connected with the input end of a third optical fiber coupler (17), and the first output end of the third optical fiber coupler (17) is connected with a spectrum analyzer (19);
and a second output end of the third optical fiber coupler (17) is connected with the correlator (15) after being connected with the second photoelectric detector (18) in series.
The ratio of the output signal power of the first output end and the second output end of the first optical fiber coupler (4) is 80% to 20%;
the ratio of the output signal power of the first output end and the second output end of the second optical fiber coupler (12) is 99% to 1%;
the ratio of the output signal power of the first output end and the second output end of the third optical fiber coupler (17) is 50% to 50%.
The random signal generator (8) is specifically a chaotic signal source, a noise signal source or a random sequence generator.
The chaotic laser generator (1) is a weak resonant cavity Fabry-Perot laser.
A method for detecting the optical fiber fault of a passive wavelength division multiplexing network comprises the following steps:
the method comprises the following steps: the chaotic laser generator (1) generates a chaotic signal without time delay characteristics;
an optical signal generated by the chaotic laser generator (1) passes through the first optical circulator (2), the optical isolator (3), the first optical fiber coupler (4), the polarization controller (5), the optical attenuator (6) and the phase modulator (7) and then is transmitted back to the chaotic laser generator (1), and the returned optical signal disturbs the chaotic laser generator (1) to generate multimode chaotic laser;
the input end of the phase modulator (7) receives a feedback light phase adjustment signal sent by the random signal generator (8) at the same time, the phase adjustment signal is added into a returned laser signal, and the nonlinear effect of the phase adjustment signal eliminates the correlation between the feedback light and the output light of the laser, so that the chaotic laser has the characteristic of no time delay;
as shown in fig. 2, compared with the conventional scheme for measuring a fault point by using a pulse, the technical scheme of the invention has the advantages that the chaotic laser has the function of realizing a centimeter-level high resolution which is independent of the distance, and compared with the conventional scheme for measuring a fault point by using the chaotic laser generated by external cavity feedback, the chaotic laser generated in the scheme has no time delay characteristic, so that the fault discrimination without a blind area and a false alarm can be realized simultaneously during the distance measurement by using a correlation method, and the chaotic laser generated by the conventional external cavity feedback has the fault discrimination of the blind area and the false alarm due to the time delay characteristic during the distance measurement; compared with a DFB laser, the FP laser can generate multi-wavelength chaotic laser and can be used for detecting multi-path faults.
Step two: the adjusted chaotic laser signal is sent to an erbium-doped optical fiber amplifier (9) through a first optical fiber coupler (4), the signal is amplified and then enters an electro-optical modulator (10) for pulse modulation, and a pulse signal generator (11) sends out a pulse signal to modulate the amplified signal;
generating a detection signal, passing the non-delay characteristic laser through an amplifier and then entering an electro-optical modulator for pulse modulation, wherein the result is shown in fig. 3; the whole envelope is similar to a pulse, but the chaotic signal is modulated in a high-level part; compared with the fault test (attenuation cannot be measured by directly using chaotic signals) which is directly carried out by using chaotic light generated by external cavity feedback as probe light, the method and the device can accurately measure the attenuation existing in the light path to be measured due to the existence of pulse envelope.
Step three: the output end of the electro-optical modulator (10) sends modulated multimode chaotic laser signals without time delay characteristics, one part of the laser signals enters a correlator (15) as reference light through a second optical fiber coupler (12), and the other part of the laser signals enters a wavelength division multiplexer (20) as detection light and then is split into optical network units (21) of all detection branches;
if a breakpoint exists in a certain path of the optical network unit (21), feedback light returns to the second optical circulator (16) along the original optical path, and the feedback light is respectively sent to the optical spectrum analyzer (19) and the correlator (15) by the second optical circulator (16);
the spectrum analyzer (19) is used for displaying the feedback wavelength and confirming the optical network unit (21) of which branch has a breakpoint;
the correlator (15) can obtain the fault position and the optical fiber attenuation of the corresponding optical network unit (21) through feedback light.
The specific method for detecting the optical fiber fault position and the optical fiber attenuation in the third step comprises the following steps:
1) and (3) fault position detection: the correlator (15) tests the echo signal of the nth path optical network unit and the reference light delay time t λn To obtain the position L of the fault point λn The calculation formula of (2) is as follows:
in the above formula, c is the speed of light, n e The refractive index of the fiber core is adopted, and lambdan is the optical network unit of the nth path;
2) and (3) optical fiber attenuation detection: meanwhile, attenuation information can be read in the slope of the correlation result, because the correlation of the pulse chaotic signal and the backscattering signal caused by the pulse can keep the information of the backscattering signal; the echo signal of the nth optical network unit and the reference light are cross-correlated as follows:
the method comprises the steps of obtaining a Pref lambda n pulse chaotic signal, Ppuls lambda n as a pulse part, Pchaos lambda n as a chaotic part, Pecho lambda n as an echo signal, Pbs lambda n as a backscattering signal, Pr lambda n as a reflection signal and Pce lambda n as an echo signal.
Because the chaotic signal is a random signal, the effects generated by the cross-correlation of the pulse light signal and the echo signal caused by the chaos, the back scattering caused by the chaotic signal and the pulse and the cross-correlation of the reflected signal can be eliminated after the average processing; therefore, the correlation result of the reference signal and the echo signal can be simplified as follows:
the attenuation information in the fiber is preserved and the result is shown in fig. 4.
The invention belongs to an optical fiber fault detection technology, aims to solve the problems of misjudgment and long-distance high precision of the existing WDM-PON network optical fiber fault detection technology, and particularly provides a high-precision non-false-alarm monitoring system for WDM optical fiber fault detection.
The chaotic laser generator provided by the invention is particularly a weak resonant cavity Fabry-Perot laser, the laser generates chaotic laser by random phase modulation, and the random phase modulation can generate a random external cavity mode, so that the generated chaotic laser does not contain a time delay characteristic.
The invention adopts a WDM-PON network optical fiber fault detection method, and particularly modulates chaotic signals onto pulses by using intensity, one path of the chaotic signals is used as probe light to enter a WDM-PON for detection, the other path of the chaotic signals is used as reference light to enter a correlator, the correlator converts a correlation operation result to obtain a fault position, and a spectrum analyzer measures a fault branch.
The detection system comprises a non-delay characteristic chaotic laser pulse generation part and a network optical fiber fault detection part.
The chaotic laser generation part without the time delay characteristic comprises a weak resonant cavity Fabry-Perot laser (WRC-FPLD), the output end of the WRC-FPLD is connected with the second input end of the first optical circulator, the output end of the first optical circulator is connected with the input end of the optical isolator, the output end of the optical isolator is connected with the input end of the 20:80 optical fiber coupler, the first output (80% of the total power) of the 20:80 optical fiber coupler is connected with the input end of the polarization controller, the output end of the polarization controller is connected with the input end of the optical attenuator, the output end of the optical attenuator is connected with the input end of the phase modulator, the output end of the phase modulator is connected with the first input end of the first optical circulator, the second output (20% of the total power) of the 20:80 optical fiber coupler is connected with the input end of the erbium-doped optical fiber amplifier, and the output end of the erbium-doped optical fiber amplifier is connected with the input end of the electro-optical modulator.
The output of the random signal generator is connected with a modulation interface of the phase modulator, and the random signal generator can be a chaotic signal source, a noise signal source or a random sequence generator; the output of the pulse signal generator is connected with the modulation interface of the electro-optical modulator.
The output end of the electro-optical modulator is connected with the input end of the 1:99 optical fiber coupler, the second output end (1% of the total power) of the 1:99 optical fiber coupler is connected with the input end of the filter, the output end of the filter is connected with the input end of the first photoelectric detector, and the output end of the first photoelectric detector is connected with the correlator; a first output end (99 percent of the total power) of a 99 optical fiber coupler is connected with a first input end of a second optical circulator, a second input end of the second optical circulator is connected with an input end of a WDM (wavelength division multiplexing), a first output end of the WDM is connected with a first optical network unit, and an nth output end of the WDM is connected with an nth optical network unit; the output end of the second optical circulator is connected with the input end of the 50:50 optical fiber coupler, the first output end (50% of the total power) of the 50:50 optical fiber coupler is connected with the spectrum analyzer, the second output end (50% of the total power) of the 50:50 optical fiber coupler is connected with the input of the second photoelectric detector, and the output of the second photoelectric detector is connected with the correlator.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (6)
1. A passive wavelength division multiplexing network optical fiber fault detection system is characterized in that: the chaotic laser generator comprises a chaotic laser generator (1), wherein a signal output end of the chaotic laser generator (1) is connected with a second input end of a first optical circulator (2), and a signal output end of the first optical circulator (2) is connected with an optical isolator (3) in series and then is connected with an input end of a first optical fiber coupler (4);
a first output end of the first optical fiber coupler (4) is sequentially connected in series with the polarization controller (5) and the optical attenuator (6) and then is connected with an input end of the phase modulator (7), and an output end of the phase modulator (7) is connected with a first input end of the first optical circulator (2);
the modulation interface of the phase modulator (7) is also connected with a random signal generator (8);
the second output end of the first optical fiber coupler (4) is connected with an erbium-doped optical fiber amplifier (9) in series and then is connected with the input end of an electro-optical modulator (10);
the modulation interface of the electro-optical modulator (10) is also connected with a pulse signal generator (11);
the output end of the electro-optical modulator (10) is connected with the input end of the second optical fiber coupler (12);
a second output end of the second optical fiber coupler (12) is connected with a first photoelectric detector (14) through a filter (13), and an output end of the first photoelectric detector (14) is connected with a correlator (15);
a first output end of the second optical fiber coupler (12) is connected with a first input end of a second optical circulator (16), a second input end of the second optical circulator (16) is connected with an input end of a wavelength division multiplexer (20), and an output end of the wavelength division multiplexer (20) is connected with n optical network units (21);
the output end of the second optical circulator (16) is connected with the input end of a third optical fiber coupler (17), and the first output end of the third optical fiber coupler (17) is connected with a spectrum analyzer (19);
and a second output end of the third optical fiber coupler (17) is connected with the correlator (15) after being connected with the second photoelectric detector (18) in series.
2. The system of claim 1, wherein the system is configured to detect the fiber faults in the passive wavelength division multiplexing network, and comprises:
the ratio of the output signal power of the first output end and the second output end of the first optical fiber coupler (4) is 80% to 20%;
the ratio of the output signal power of the first output end and the second output end of the second optical fiber coupler (12) is 99% to 1%;
the ratio of the output signal power of the first output end and the second output end of the third optical fiber coupler (17) is 50% to 50%.
3. The system of claim 2, wherein the optical fiber fault detection system comprises: the random signal generator (8) is specifically a chaotic signal source, a noise signal source or a random sequence generator.
4. A passive wavelength division multiplexing network optical fiber fault detection system according to claim 3, wherein: the chaotic laser generator (1) is a weak resonant cavity Fabry-Perot laser.
5. A method for detecting the optical fiber fault of a passive wavelength division multiplexing network is characterized in that: the method comprises the following steps:
the method comprises the following steps: the chaotic laser generator (1) generates a chaotic signal without time delay characteristics;
an optical signal generated by the chaotic laser generator (1) passes through the first optical circulator (2), the optical isolator (3), the first optical fiber coupler (4), the polarization controller (5), the optical attenuator (6) and the phase modulator (7) and then is transmitted back to the chaotic laser generator (1), and the returned optical signal disturbs the chaotic laser generator (1) to generate multimode chaotic laser;
the input end of the phase modulator (7) receives a feedback light phase adjustment signal sent by the random signal generator (8) at the same time, the phase adjustment signal is added into a returned laser signal, and the nonlinear effect of the phase adjustment signal eliminates the correlation between the feedback light and the output light of the laser, so that the chaotic laser has the characteristic of no time delay;
step two: the adjusted chaotic laser signal is sent to an erbium-doped optical fiber amplifier (9) through a first optical fiber coupler (4), the signal is amplified and then enters an electro-optical modulator (10) for pulse modulation, and a pulse signal generator (11) sends out a pulse signal to modulate the amplified signal;
step three: the output end of the electro-optical modulator (10) sends modulated multimode chaotic laser signals without time delay characteristics, one part of the laser signals enters a correlator (15) as reference light through a second optical fiber coupler (12), and the other part of the laser signals enters a wavelength division multiplexer (20) as detection light and then is split into optical network units (21) of all detection branches;
if a breakpoint exists in a certain path of the optical network unit (21), feedback light returns to the second optical circulator (16) along the original optical path, and the feedback light is respectively sent to the optical spectrum analyzer (19) and the correlator (15) by the second optical circulator (16);
the spectrum analyzer (19) is used for displaying the feedback wavelength and confirming the optical network unit (21) of which branch has a breakpoint;
the correlator (15) can obtain the fault position and the optical fiber attenuation of the corresponding optical network unit (21) through feedback light.
6. The method according to claim 5, wherein the method comprises the following steps: the specific method for detecting the optical fiber fault position and the optical fiber attenuation in the third step comprises the following steps:
when the fault position is detected, the correlator (15) tests the echo signal of the nth path optical network unit (21) and the reference light delay time t λn To obtain the position L of the fault point λn The correlation calculation formula is:
in the above formula, c is the speed of light, n e The refractive index of the fiber core is adopted, and lambdan is the optical network unit of the nth path;
when detecting the optical fiber attenuation, the attenuation information can be read from the slope of the fault point position, and the cross correlation R (tau) of the echo signal and the reference optical signal of the nth path optical network unit (21) is as follows:
in the above formula, Pref λ n pulse chaotic signal, pples λ n is a pulse part, Pchaos λ n is a chaotic part, Pecho λ n is an echo signal, Pbs λ n is a backscatter signal, Pr λ n is a reflection signal, and Pce λ n is an echo signal;
because the chaotic signal is a random signal, the effects generated by the cross-correlation of the pulsed light signal and the echo signal caused by the chaos, the back scattering caused by the chaotic signal and the pulse and the cross-correlation of the reflected signal can be eliminated after the subsequent average processing, and the correlation operation result of the reference light signal and the echo signal can be simplified as follows:
therefore, the attenuation information in the optical fiber is kept as the detection result of the optical fiber attenuation.
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