CN1300956C - Light module of light time domain reflector, light time domain reflector and fibre-optical testing method - Google Patents
Light module of light time domain reflector, light time domain reflector and fibre-optical testing method Download PDFInfo
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Abstract
The present invention relates to an optical module of an optical time domain reflector, an optical time domain reflector and an optical fiber testing method. The optical module of the optical time domain reflector comprises a pulsed laser and an optical receiving converter, wherein the pulsed laser is used for emitting laser pulse with constant optical power; the optical receiving converter comprises an optical-electrical converter used for converting an optical signal into an electrical signal, an amplifying circuit used for amplifying the electrical signal and an A/D converter used for converting the electrical signal into a digital signal. An amplifying circuit provided with at least two amplifying stages and a stage switcher is used for realizing the segmented amplification of a dynamic range. The present invention can test optical fibers in a large dynamic range.
Description
Technical field
The present invention relates to the test optical fiber technology, particularly relate to a kind of optical time domain reflectometer and optical module thereof and be applied to the optical fiber test method of described optical time domain reflectometer.
Background technology
Along with the development of optical fiber communication technology, since the eighties, the fiberize of network is one of main trend of countries in the world network development always.The formation of the communication network of current various countries mainly is as the transmission basis with fiber optic network, and when building and safeguarding lightguide cable link, all to use OTDR (Optical Time DomainReflectometer, optical time domain reflectometer) carries out the test of optic fibre characteristic, OTDR also is the core technology in the on-line monitoring system of fiber optic network, its dynamic range is big more, and then the distance that can monitor and scope are big more, helps the fast quick checking barrier and the block removing of lightguide cable link.
The OTDR its working principles be by detect the back-scattering light of pulse laser on fibre circuit in time the energy distribution curve analysis of (distance) obtain the transmission characteristics such as length, decay, fault of optical fiber, promptly to light pulse of tested optical fiber input, when light pulse when fibre circuit is propagated forward, can scattering and the reflected back part signal, continuous high speed this signal of sampling out can draw the curve of the characteristics such as decay, fault of reflection optical fiber.
Because light pulse signal will be decayed in the process of transmission, the signal of scattering simultaneously and reflected back also will be decayed, and the front end of optical fiber is because the distance of optical transmission is short, and back scattered signal is big, and the distance of optical transmission is long more like this, and the signal of scattering and reflected back is just more little.As developing the OTDR of a dynamic range up to 35dB, then because detected light pulse has been transmitted one back and forth in the fibre circuit the inside, its decay is actual to be double, therefore the range of signal that needs to detect is at least 70dB, add that optical fiber initiating terminal connector has a big Fresnel reflection signal etc., need the measuring-signal scope to be generally more than the 80dB.To finish the detection of such great dynamic range signal within a certain period of time, very high technical difficulty is arranged.In addition, because present high-power pulsed laser can be launched maximum pulse and generally can not surpass 20 microseconds, peak power generally is no more than 200 milliwatts, under emission maximum luminous power condition, can calculate according to the Rayleigh scattering computing formula that back scattered optical signal power maximum is about-30dBm in the optical fiber, deduct 70dB after, the minimum light signal power that then will detect is about-100dBm, detect weak one like this, very high technical difficulty is also arranged.
A kind of prior art can consult the application people for Huawei Tech Co., Ltd, number of patent application are 00107854.2, the day for announcing be July 2 in 2003 day, be called the patent of invention (Fig. 1 with reference to) of " optical module that is used for the optical time domain reflectometer of high dynamic range ".
Described prior art is by control impuls generating laser emitted laser pulse energy size, and the test that the method for optical fiber realization areal survey is realized the OTDR high dynamic range.Described pulse laser reflector by the amplifier 11 that is linked in sequence, can select the some groups of analog switches 12 of conducting and pulse laser generator 13 to form respectively.When the previous paragraphs of measuring from the whole optical fiber of OTDR close together, because the switch a conducting of 12 li of some groups of analog switches in the control impuls laser at this moment by force of its scattering and the signal that reflects is launched the laser pulse of less energy and tested; When the interlude of measuring from the moderate whole optical fiber of OTDR distance, because its scattering and the signal strength signal intensity that reflects are moderate, at this moment control switch a, the b conducting of 12 li of some groups of analog switches, launch the laser pulse of medium energy and test; And when measuring, just control the switch a of 12 li of some groups of analog switches from the back of OTDR distance whole optical fiber far away section, all conductings of b, c are so that emission maximum laser pulse energy is tested the signal strength signal intensity that improves its scattering as much as possible and reflect.At last, above-mentioned three sections results that test respectively are stitched together, can obtain the transmission characteristic of whole optical fiber.
Described prior art can be used for the OTDR of high dynamic range, but its weak point is that the utilance of test result is lower, has reduced dynamic range indirectly.Because prior art obtains three test results by the light pulse of emission different-energy, at last three sections test results is spliced, make each test result only use original 1/3 valid data.From the OTDR principle, Ce Shi average time is lowered to original 1/3 exactly.And this test average time and dynamic range are closely related.Relation between average time (average time) and the signal to noise ratio raising amount can be represented by the formula:
N1 is respectively different average times with N2, thereby, because that the average time of test is lowered to is original 1/3, cause dynamic range to be reduced.
Summary of the invention
The technical problem that the present invention solves is to provide a kind of optical module and optical time domain reflectometer and optical fiber test method that improves average time with the optical time domain reflectometer of realization high dynamic range test optical fiber.
For this reason, the technical scheme of technical solution problem of the present invention is: a kind of optical module of optical time domain reflectometer is provided, comprises pulse laser and light-receiving transducer; Described light-receiving transducer comprise be used for light signal convert to the signal of telecommunication optical-electrical converter, be used for amplifying circuit that the aforementioned electric signal is amplified and the analog to digital converter that is used for signal of telecommunication sample conversion is become digital signal; Described pulse laser is used to launch the laser pulse with constant optical power; Described amplifying circuit has at least two and amplifies gear and gear switch device, is used to realize the dynamic range segmentation amplification of the signal of telecommunication.
Wherein, described gear switch device is some groups of switches can selecting conducting respectively.
Wherein, described amplifying circuit comprises current-to-voltage converting circuit and voltage amplifier circuit.
Wherein, described amplifying circuit also comprises the buffer of analog to digital converter.
Wherein, described at least two amplification gears are that narrow pulsewidth is amplified gear, wide pulse width amplifies gear, and wherein, wide pulse width amplifies gear and is divided into little electric current amplification gear of wide pulse width and the big electric current amplification of wide pulse width gear again.
The present invention also provides a kind of optical time domain reflectometer, and it also comprises control unit and data processing unit except comprising aforesaid optical module; Described control unit is used to control the gear switch device of the amplifying circuit of optical module; Described optical module is used for to optical fiber to be tested emission laser pulse and receives the light signal that returns from optical fiber to be tested, adopts different amplification gears that described light signal segmentation is amplified under control unit control and is converted to digital signal; Described data processing unit is used to receive the digital signal of optical module output, and according to the characteristic of described Digital Signal Analysis optical fiber to be tested.
Wherein, described control unit and data processing unit become one.
The present invention also provides a kind of optical fiber test method, is applied to the aforementioned lights time-domain reflectomer; Comprise step:
1) pulse laser is to the laser pulse of optical fiber emission constant optical power to be tested;
2) optical-electrical converter of light-receiving transducer receives the light signal that returns when described laser pulse transmits in optical fiber to be tested, is converted into current signal;
3) amplifying circuit of light-receiving transducer becomes voltage signal with the aforementioned currents conversion of signals, and amplifies described voltage signal;
4) analog to digital converter of light-receiving transducer converts the aforesaid voltage signal sampling to digital signal;
5) judge whether the gained digital signal reaches shift points, if then enter step 6); If not, do not do any operation;
6) action of control unit control gear switch device is switched the amplification gear of amplifying circuit, and is returned step 2);
7) data processing unit receives the digital signal of light-receiving transducer output and generates test curve, will comprise that the test curve of all data of shift points front and back carries out the segmentation splicing, obtains complete test result.
Wherein, described step 7) specifically comprises: adopt least square method to carry out curve fitting; Generate the gear shift increment size of gear shift front and back; Data after the gear shift are deducted the gear shift increment size; Generate complete test curve.
Wherein, the step that also comprises control unit configuration segmentation hop count and shift points position.
With respect to prior art, the invention has the beneficial effects as follows: because pulse laser of the present invention is launched the laser pulse of constant optical power all the time, each test result can be utilized whole valid data, therefore under 3 minutes the most general test case, because average time improves 3 times than prior art, dynamic range 1.2dB can be improved, the optical fiber of longer distance can be tested.Secondly, owing to carry out frequency segmentation and dynamic range segmentation amplification, can make optical time domain reflectometer finish the test of great dynamic range at signal characteristic.
Description of drawings
Fig. 1 is a kind of block diagram of generating laser of optical module of optical time domain reflectometer of prior art;
Fig. 2 is the theory diagram of optical time domain reflectometer of the present invention;
Fig. 3 is the composition frame chart of the pulse laser among the present invention;
Fig. 4 is the theory diagram of the light-receiving amplifier among the present invention;
Fig. 5 is the composition frame chart of the embodiment of light-receiving amplifier shown in Figure 4;
Fig. 6 is the flow chart of optical fiber test method of the present invention;
The optic fibre characteristic curve chart that Fig. 7 is made up of original test data;
Fig. 8 is the schematic diagram that curve shown in Figure 7 is spliced;
Fig. 9 is complete optic fibre characteristic curve chart.
Embodiment
Seeing also Fig. 2, is the theory diagram of optical time domain reflectometer of the present invention.Described optical time domain reflectometer comprises optical module 100, data processing unit 200 and control unit 300; Wherein, described optical module 100 comprise be used for by coupler 30 to the pulse laser 110 of optical fiber to be tested 20 emission laser pulses, be used for receiving from optical fiber 20 scatterings to be tested and the light signal that reflects and converting the light-receiving transducer 120 of digital signal to by coupler 30; Described control unit 300 is used to control the gear switch of light-receiving transducer 120; The digital signal of described data processing unit 200 reception light-receiving transducers 120 outputs is also treated the characteristic of measuring fiber 20 in view of the above and is analyzed.
In general, because the test pulse width range of optical time domain reflectometer is from 10ns to 20us, its signal band is to tens megahertzes from direct current; And the dynamic range that will make optical time domain reflectometer reaches 40dB, then the dynamic range of currents of handling in the light-receiving transducer 120 will reach 160dB, that is to say, the current signal that light-receiving transducer 120 is handled is the signal of a broadband, great dynamic range, must have a plurality of amplification gears, carry out frequency segmentation and dynamic range segmentation amplification according to signal characteristic.
Need to prove that described control unit 300 and data processing unit 200 can adopt discrete device, also can become one.
See also Fig. 3, described pulse laser 110 is launched constant luminous power all the time, comprises amplifier 111, metal-oxide-semiconductor 112 and pulse laser generator 113.In order to promote average time, the luminous power of described pulse laser 110 preferred constant emission maximums.
Wherein, metal-oxide-semiconductor 112 is selected the big and device at a high speed of drive current for use, satisfies the pulse that drives the 10ns width, and guarantees that pulse laser 110 can send the light of maximum power.Amplifier 111 is selected for use at a high speed, rail-to-rail output amplifier, satisfies the bandwidth of 10ns pulse and the switch of driven MOS pipe 112.Because the drive current of various pulse laser generators 113 is different, can adjust by the multiplication factor of adjusting amplifier 111.
In one embodiment of the present of invention, amplifier 111 is selected the OPA642 of TI company for use, and is provided for regulating the potentiometer of its multiplication factor in amplifier 111; Metal-oxide-semiconductor 112 is selected IRF7465 for use.
See also Fig. 4, described light-receiving transducer 120 comprises optical-electrical converter 121, current-to-voltage converting circuit 122, voltage amplifier circuit 123 and analog to digital converter 124.Described optical-electrical converter 121 is used for converting light signal to current signal; Described current-to-voltage convertor 122 is used for converting described current signal to voltage signal; Described voltage amplifier circuit 123 is used for the aforesaid voltage signal is amplified; Described analog to digital converter 124 is used for analog voltage signal converted to digital signal and be input to data processing unit 200 handling.
Described current-to-voltage convertor 122 and voltage amplifier circuit 123 are formed amplifying circuit, in the execution mode shown in Figure 4, described amplifying circuit switches by the gear switch device and amplifies gear, and frequency is divided into narrow pulse width signal and two sections amplifications of wide pulse width signal, and the wide pulse width signal also is divided into two sections amplifications.
Seeing also Fig. 5, is an embodiment of light-receiving transducer 120, and wherein, optical-electrical converter 121 is selected highly sensitive APD (avalanche photodide) detector for use; Current-to-voltage convertor 122 is selected for use and is striden group amplifier (as OPA655) composition, and the current signal that APD is exported is converted to voltage signal; Voltage amplifier circuit 123 selects for use amplifier AD8067 to form; In addition, also adopt the buffer of amplifier AD8138 as analog to digital converter 124, add a voltage bias at the input of amplifier AD8138 and signal is adjusted in the input range of analog to digital converter 124, this voltage bias value is by the incoming level central value decision of analog to digital converter 124.
Amplify in order to carry out frequency segmentation and dynamic range segmentation according to signal characteristic, adopt the gear of gear switch device (the some groups of switches 1231,1232 and 1233 that can select conducting respectively as shown in Figure 5, wherein switch 1232 and 1233 can be same device) switch current electric pressure converter 122 and voltage amplifier circuit 123.In the present embodiment, described gear is divided into narrow pulse width signal (first pulsewidth) and amplifies shelves, wide pulse width small-signal (second pulsewidth, first electric current) amplification shelves and wide pulse width large-signal (second pulsewidth, second electric current) amplification shelves.Wherein, it is 20MHz that narrow pulse width signal amplifies bandwidth Design, and it is 500KHz that wide pulse width amplifies bandwidth Design; Employing broad pulse test, but the APD switching current adopts the wide pulse width small-signal to amplify shelves during less than 100nA, otherwise, during greater than 100nA, adopt the wide pulse width large-signal to amplify shelves.Described switch 1231,1232 and 1233 can adopt analog switch.
Seeing also Fig. 6, is the flow chart of optical fiber test method of the present invention.
At first, implementation step S1, the pulse laser 110 emission laser pulses of optical module 100 are coupled into optical fiber 20 to be tested by coupler 30.
Step S2, digital signal is handled and exported to 120 pairs of light signals that return from optical fiber 20 to be tested of the light-receiving transducer of optical module 100.Specifically comprise: scattering and the light signal that reflects are by the optical-electrical converter 121 of coupler 30 input optical modules 100 in the process that described laser pulse transmits in optical fiber 20 to be tested, and optical-electrical converter 121 converts light signal to current signal; Described current signal is input to high-speed AD converter 124 through current-to-voltage converting circuit 122 and voltage amplifier circuit 123, and the voltage signal of 124 pairs of inputs of analog to digital converter is sampled and is converted to digital signal.
Judge whether to reach shift points, in this way, then enter step S3; As not, then do not carry out any operation.
Step S3, in order to realize the test of optical time domain reflectometer high dynamic range, the present invention adopts control unit 300 to switch at the amplification gear of shift points to current-to-voltage converting circuit 122 and voltage amplifier circuit 123.
The position of shift points adopts it to represent apart from the data point number of original position, the distance L of shift points (unit: rice) and shift points apart from the pass between the data point number M (unit: individual) of original position be:
L＝Res×M
Wherein, C represents light propagation rate (299792458 meter per second) in a vacuum; DS represent Data Spacing field in the SR4731 agreement (SR-4731 Issuel, February 2000, TelcordiaTechnologies, Inc), in the light propagation time of 10000 data points of expression, unit is 100pSec, promptly 10
-10Second; GI represents the Group Index field in the SR4731 agreement, and the refractive index of expression optical fiber has enlarged 100000 times, and for example when GI was 146800, the refractive index that is equivalent to optical fiber was 1.46800; Res represents measuring accuracy, the sampled point distance at interval of expression test data.
Step S4, data processing unit 200 is collected the digital signal of light-receiving transducer 120 outputs, will comprise that a test result curve of all data of gear shift front and back carries out the segmentation splicing, obtains complete test result.
See also Fig. 7, shown in curve be to have selected for use to have the amplifying circuit that third gear is selected, the initial data that data processing unit 200 collects, as can be seen, saltus step has taken place at an A and some B place in data.The reason of saltus step is in the test process, and at sampled point A, B has switched at the place gear of amplifying circuit.
According to the gear shift of amplifying circuit time-delay feature, data processing unit 200 can know that data are insecure in what data points that begin from shift points.For example, amplifying circuit gear shift time-delay needs Delay (ns of unit), and then insecure number of data points N is:
Consult Fig. 8,, after the corrupt data points N, carry out data splicing when obtaining the number of data points M of shift points apart from starting point.
Select Z data point before the M point, the size of Z is counting of being had of the decay blind area of this test data.According to the principle of least square fitting curve, obtain fit line L1.
Select Z point in M+N point back, same, according to the principle of least square fitting curve, obtain fit line L2.
Define starting point M, unreliable some end position M+N marks with straight line, is respectively the L3 among Fig. 8, L5.And define L3, the mid line L4 of L5.
At L3, the unreliable point in the L4 interval according to the linear relationship of L1, generates new desired value, and it is ExpC in the desired value at C point place.
At L4, the unreliable point in the L5 interval according to the linear relationship of L2, generates new desired value, and it is ExpD in the desired value at D point place.
Calculate C, the poor DeltaCD of 2 desired value ExpC that locate of D and ExpD.DeltaCD is the gear shift increment size of amplifying circuit.
The value of all data after the data point A is deducted DeltaCD.
For the data that have a plurality of shift points, repeatedly handle and to finish.
The spliced data and curves figure of match is the measurement curve of high dynamic range as shown in Figure 9.
The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (10)
1, a kind of optical module of optical time domain reflectometer comprises pulse laser and light-receiving transducer; Described light-receiving transducer comprise be used for light signal convert to the signal of telecommunication optical-electrical converter, be used for amplifying circuit that the aforementioned electric signal is amplified and the analog to digital converter that is used for signal of telecommunication sample conversion is become digital signal; It is characterized in that: described pulse laser is used to launch the laser pulse with constant optical power; Described amplifying circuit has at least two and amplifies gear and gear switch device, is used to realize the dynamic range segmentation amplification of the signal of telecommunication.
2, the optical module of optical time domain reflectometer according to claim 1 is characterized in that: described gear switch device is some groups of switches can selecting conducting respectively.
3, the optical module of optical time domain reflectometer according to claim 2 is characterized in that: described amplifying circuit comprises current-to-voltage converting circuit and voltage amplifier circuit.
4, the optical module of optical time domain reflectometer according to claim 3 is characterized in that: described amplifying circuit also comprises the buffer of analog to digital converter.
5, the optical module of optical time domain reflectometer according to claim 1, it is characterized in that: described at least two amplification gears are that narrow pulsewidth is amplified gear, wide pulse width amplifies gear, wherein, wide pulse width amplification gear is divided into little electric current amplification gear of wide pulse width and the big electric current amplification of wide pulse width gear again.
6, a kind of optical time domain reflectometer is characterized in that: except comprising as each described optical module of claim 1 to 5, also comprise control unit and data processing unit; Described control unit is used to control the gear switch device of the amplifying circuit of optical module; Described optical module is used for to optical fiber to be tested emission laser pulse and receives the light signal that returns from optical fiber to be tested, adopts different amplification gears that described light signal segmentation is amplified under control unit control and is converted to digital signal; Described data processing unit is used to receive the digital signal of optical module output, and according to the characteristic of described Digital Signal Analysis optical fiber to be tested.
7, optical time domain reflectometer according to claim 6 is characterized in that: described control unit and data processing unit become one.
8, a kind of optical fiber test method is applied to the aforementioned lights time-domain reflectomer; It is characterized in that, comprise step:
1) pulse laser is to the laser pulse of optical fiber emission constant optical power to be tested;
2) optical-electrical converter of light-receiving transducer receives the light signal that returns when described laser pulse transmits in optical fiber to be tested, is converted into current signal;
3) amplifying circuit of light-receiving transducer becomes voltage signal with the aforementioned currents conversion of signals, and amplifies described voltage signal;
4) analog to digital converter of light-receiving transducer converts the aforesaid voltage signal sampling to digital signal;
5) judge whether the gained digital signal reaches shift points, if then enter step 6); If not, do not do any operation;
6) action of control unit control gear switch device is switched the amplification gear of amplifying circuit, and is returned step 2);
7) data processing unit receives the digital signal of light-receiving transducer output and generates test curve, will comprise that the test curve of all data of shift points front and back carries out the segmentation splicing, obtains complete test result.
9, optical fiber test method according to claim 8 is characterized in that, described step 7) specifically comprises: adopt least square method to carry out curve fitting; Generate the gear shift increment size of gear shift front and back; Data after the gear shift are deducted the gear shift increment size; Generate complete test curve.
10, optical fiber test method according to claim 8 is characterized in that, also comprises the step of control unit configuration segmentation hop count and shift points position.
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| US8050556B2 (en) | 2007-02-21 | 2011-11-01 | Futurewei Technologies, Inc. | In-band optical frequency division reflectometry |
| CN101226100B (en) | 2008-01-31 | 2010-08-25 | 太原理工大学 | Chaos light time domain reflectometer and measuring method thereof |
| CN102201946B (en) * | 2010-03-26 | 2013-09-18 | 娄子正 | Network cable length sensing system |
| CN102301607B (en) * | 2010-03-29 | 2013-09-11 | 华为技术有限公司 | Data processing method, system and receiver |
| CN101958749B (en) * | 2010-07-24 | 2012-10-03 | 桂林聚联科技有限公司 | On-line optical cable monitoring method |
| CN102158280A (en) * | 2011-04-02 | 2011-08-17 | 王健 | Method for modulating and superposing optical time domain reflectometer (OTDR) testing signals in data transmission optical signals and OTDR testing method |
| CN102455246B (en) * | 2011-12-12 | 2014-07-02 | 山东信通电器有限公司 | Low-noise and anti-interference optical-time-domain reflectometer with secondary shielding |
| NL2007976C2 (en) * | 2011-12-15 | 2013-06-18 | Draka Comteq Bv | A method for the characterization of optical properties of an optical fiber. |
| CN107063980A (en) * | 2016-11-02 | 2017-08-18 | 北京信息科技大学 | A kind of flow cytometer scatters optical detection device |
| CN109525309A (en) * | 2018-11-27 | 2019-03-26 | 武汉光迅科技股份有限公司 | A kind of OTDR combination unit |
| CN114142920A (en) * | 2020-09-03 | 2022-03-04 | 华为技术有限公司 | Optical signal detection device and method and related equipment |
| CN114665965B (en) * | 2022-05-09 | 2022-09-20 | 北京国科天迅科技有限公司 | Light conversion device, storage medium and test system |
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| US5777727A (en) * | 1996-05-30 | 1998-07-07 | Ando Electric Co., Ltd. | OTDR measurement device |
| CN1113490C (en) * | 2000-06-27 | 2003-07-02 | 华为技术有限公司 | Optical module for light-time domain reflectometer with wide dynamic range |
| KR20030089873A (en) * | 2002-05-20 | 2003-11-28 | 한국건설기술연구원 | Otdr measurement system for landslides protection |
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| JPH0926376A (en) * | 1995-07-11 | 1997-01-28 | Advantest Corp | Otdr measuring device |
| US5777727A (en) * | 1996-05-30 | 1998-07-07 | Ando Electric Co., Ltd. | OTDR measurement device |
| CN1113490C (en) * | 2000-06-27 | 2003-07-02 | 华为技术有限公司 | Optical module for light-time domain reflectometer with wide dynamic range |
| KR20030089873A (en) * | 2002-05-20 | 2003-11-28 | 한국건설기술연구원 | Otdr measurement system for landslides protection |
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