CN111578971B - Device and method for realizing long-distance measurement by OFDR segmented acquisition - Google Patents
Device and method for realizing long-distance measurement by OFDR segmented acquisition Download PDFInfo
- Publication number
- CN111578971B CN111578971B CN202010401588.7A CN202010401588A CN111578971B CN 111578971 B CN111578971 B CN 111578971B CN 202010401588 A CN202010401588 A CN 202010401588A CN 111578971 B CN111578971 B CN 111578971B
- Authority
- CN
- China
- Prior art keywords
- optical fiber
- optical
- reference arm
- beat frequency
- fiber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 238000005259 measurement Methods 0.000 title claims abstract description 46
- 238000002168 optical frequency-domain reflectometry Methods 0.000 title claims abstract description 41
- 238000000034 method Methods 0.000 title claims abstract description 20
- 239000013307 optical fiber Substances 0.000 claims abstract description 135
- 230000003287 optical effect Effects 0.000 claims abstract description 102
- 230000035559 beat frequency Effects 0.000 claims abstract description 68
- 238000012545 processing Methods 0.000 claims abstract description 10
- 238000004891 communication Methods 0.000 claims abstract description 9
- 239000000835 fiber Substances 0.000 claims description 41
- 238000005070 sampling Methods 0.000 claims description 10
- 238000001228 spectrum Methods 0.000 claims description 10
- 238000012360 testing method Methods 0.000 claims description 7
- 238000010408 sweeping Methods 0.000 claims 1
- 238000010586 diagram Methods 0.000 description 5
- 238000012937 correction Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000012952 Resampling Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/266—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light by interferometric means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D21/00—Measuring or testing not otherwise provided for
- G01D21/02—Measuring two or more variables by means not covered by a single other subclass
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
- G01D3/028—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure
- G01D3/036—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure on measuring arrangements themselves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/268—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light using optical fibres
Abstract
The invention provides a device and a method for realizing long-distance measurement by OFDR sectional acquisition. Meanwhile, the optical fiber to be detected is divided into N sections, and the optical path of a reference arm in the main interferometer can be changed according to needs, so that the optical path difference between each section of area of the optical fiber to be detected and the reference arm is controlled within a short distance range. The method comprises the steps of measuring in a segmented mode, obtaining beat frequency signals, splicing the beat frequency signals in a distance domain, further obtaining long-distance OFDR beat frequency signals, and finally carrying out secondary data processing on the whole long-distance beat frequency signals to achieve optical communication measurement and distributed temperature strain measurement. The invention realizes OFDR long-distance measurement, and has high measurement result precision and good stability.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a device and a method for realizing long-distance measurement by OFDR sectional acquisition.
Background
Optical Frequency Domain Reflectometry (OFDR) is widely applied, and relates to optical communication measurement and distributed temperature and strain sensing. The OFDR technology has obvious advantages in short-distance measurement and sensing by virtue of the characteristics of high measurement precision and high spatial resolution. However, the OFDR technology is only suitable for short-distance measurement and sensing at present, and the maximum measurement distance is only about 200 meters in the prior art on the premise of high spatial resolution. An OFDR system capable of realizing long-distance measurement is urgently needed in the fields of optical fiber length measurement, large civil structures and the like. One of the difficulties to be considered in OFDR systems is non-linear sampling. A great deal of research effort has been directed to sampling or resampling using a secondary interferometer to ameliorate the non-linearity problem of lasers. In the short-distance measurement, the correction is carried out by using an auxiliary interferometer, and a remarkable improvement effect can be obtained. However, in long-distance measurement, not only the problem of nonlinear sampling caused by laser jitter but also the phase disturbance of the laser output need to be considered, when the optical path difference between the signal light and the reference light is large, for example, greater than 200 meters, the sampling calibration of the conventional auxiliary interferometer will fail, and a series of mathematical operations and algorithm compensation are required, which consumes a lot of computer resources and operation time. Due to errors in the correction process, the final measurement effect is further poor.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the defect of nonlinear sampling correction of an auxiliary interferometer in the long-distance measurement process in the OFDR prior art, the device and the method for realizing long-distance measurement by OFDR segmented acquisition are provided, so that the optical path difference between signal light and reference light is kept in a short-distance range during each beat frequency signal acquisition.
The technical scheme adopted by the invention for solving the technical problems is as follows: the OFDR segmented acquisition device for realizing long-distance measurement is provided, so that the optical path difference between signal light and reference light is kept in a short-distance range, and the whole long-distance measurement result is reconstructed through seamless splicing.
The device includes:
the sweep-frequency laser is used for emitting sweep-frequency laser with the laser wavelength periodically and linearly changed;
the optical fiber beam splitter is used for dividing the sweep frequency laser into two paths which respectively enter the auxiliary interferometer and the main interferometer;
the main interferometer is used for enabling the sweep frequency laser entering the main interferometer to generate beat frequency interference and generating a first beat frequency signal containing a signal to be detected; the main interferometer comprises an optical fiber device to be measured containing N sections of optical fiber regions to be measured, and a reference arm containing N optical path gears, wherein the length L of the reference arm of each optical path gearREF(N +1) and the length L of each section of optical fiber device to be testedDUTN and the length L of the reference arm of the previous gearREFN should satisfy the following relation:
LREF(N+1)≤LREFN+(LDUTN)/2，N≥1；
the auxiliary interferometer is used for enabling the sweep-frequency laser entering the auxiliary interferometer to generate beat frequency interference and generating a second beat frequency signal containing a signal to be detected; the second beat frequency signal is converted and then used as an external clock of the high-speed data acquisition card;
the data acquisition module is used for sampling the first beat frequency signal according to an external clock generated by the second beat frequency signal;
and the computer is used for processing and analyzing the sampled signals and simultaneously controlling the sweep frequency laser, the data acquisition module and the parameter setting and adjustment of the optical path of the reference arm in the main interferometer.
In connection with the above technical solution, the main interferometer is an interferometer with an adjustable optical path of a reference arm in an OFDR system, and includes a first optical fiber coupler, a first optical fiber circulator, a first reference arm and a second optical fiber coupler, one of the branching ends of the first optical fiber coupler is connected to the port a of the first optical fiber circulator, the port b and the port c of the first optical fiber circulator are respectively connected to an optical fiber device to be measured and the second optical fiber coupler to form a measurement optical path, and the other branching end of the first optical fiber coupler is connected to the first reference arm and then connected to the second optical fiber coupler to form a reference optical path; the optical signals of the measuring optical path and the reference optical path generate beat frequency interference at the second optical fiber coupler to form a first beat frequency signal; the first reference arm comprises a second optical fiber circulator and a first optical switch which are connected, and further comprises a plurality of optical fiber coils with different optical paths, wherein the optical fiber coils are connected with the first optical switch, and the other end of each optical fiber coil is connected with a Faraday rotator mirror.
According to the technical scheme, the main interferometer is a reflection type Michelson interferometer with an adjustable reference arm optical path difference in an OFDR system; the optical fiber testing device comprises a 2x2 optical fiber coupler, an optical fiber device to be tested and a second reference arm; the second reference arm comprises a second optical switch and a plurality of optical fiber coils with different optical paths, wherein the optical fiber coils are connected with the second optical switch, and the other end of each optical fiber coil is connected with a Faraday rotator mirror.
According to the technical scheme, the main interferometer is a main interferometer in an OFDR system, and comprises a first optical fiber coupler, a first optical fiber circulator, an optical fiber device to be tested and a third reference arm; the third reference arm comprises a third optical switch and a fourth optical switch, and a plurality of optical fiber coils with different optical paths are connected between the two optical switches.
According to the technical scheme, the auxiliary interferometer comprises an optical fiber isolator, a third optical fiber coupler, a first Faraday rotator mirror, a first optical fiber coil and a second Faraday rotator mirror; the optical fiber isolator is connected with one input end of the third optical fiber coupler, two output ends of the third optical fiber coupler are respectively connected with the first Faraday rotating mirror and the first optical fiber coil, and the second Faraday rotating mirror is connected with the first optical fiber coil.
The invention also provides a method for realizing long-distance measurement by OFDR sectional acquisition, which comprises the following steps:
constructing a reference arm capable of switching N optical path gears;
dividing an optical fiber area to be tested into N sections according to setting requirements, wherein the length of each section is determined according to the optical path of each gear of a reference arm; length L of reference arm of each gearREF(N +1) and the length L of each section of optical fiber device to be testedDUTN and the length L of the reference arm of the previous gearREFN should satisfy the following relation:
LREF(N+1)≤LREFN+(LDUTN)/2，N≥1；
starting scanning to obtain beat frequency signals of N sections of optical fiber areas to be detected;
splicing the N sections of beat frequency signals in a distance domain to obtain a complete section of long-distance OFDR beat frequency signal;
and carrying out secondary data processing on the whole long-distance beat frequency signal so as to realize optical communication measurement and distributed temperature strain measurement.
In connection with the above technical solution, the step of "performing range domain splicing on N segments of beat signals" specifically includes: respectively carrying out Fourier transform on the N sections of beat frequency signals to obtain a time (distance) -spectrum curve of each section of optical fiber area to be measured; the curves on each segment of time domain (distance domain) are connected from small to large in time in the first place and spliced into a whole curve time (distance) -spectrum curve; and splicing the range domain of the beat frequency signals of the N sections of optical fiber regions to be detected, which are acquired by N times of scanning.
The invention has the following beneficial effects: the invention provides an OFDR sectional acquisition device and method. And dividing a long-distance optical fiber area to be measured into N sections, and starting N times of scanning to obtain and splice N sections of measuring results into a long-distance measuring result. According to the invention, the optical path difference between the optical fiber region to be measured and the reference arm at each section meets the requirement in a short-distance range in each scanning and sampling process by controlling the optical path of the reference arm, so that the problems of phase jitter and the like caused by an OFDR system in long-distance interference and linear sampling processes are obviously improved, and higher measurement precision, more accurate result, better system anti-interference performance and better stability in a long-distance measurement process are ensured. The method can better serve the fields of long-distance optical communication measurement and distributed temperature strain measurement.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic diagram of the structure of an apparatus according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of an apparatus according to a second embodiment of the present invention;
FIG. 3 is a schematic structural diagram of an apparatus according to a third embodiment of the present invention;
fig. 4 is a schematic diagram illustrating the matching between the lengths of the reference optical path and the optical path to be measured.
In fig. 1, 1 is a swept-frequency laser, 2 is a fiber splitter, 3 is a main interferometer, 4 is an auxiliary interferometer, 5 is a data acquisition module, 6 is a computer, 31 is a first fiber coupler, 32 is a first fiber circulator, 33 is a second fiber coupler, 34 is a fiber device to be tested, and 35 is a first reference arm; in the reference arm, 351 is a second fiber circulator, 352 is a first optical switch, 353 is a first fiber coil, 354 is a first faraday rotator, 355 is a second fiber coil, 356 is a second faraday rotator, 41 is a fiber isolator, 42 is a third fiber coupler, 43 is a third faraday rotator, 44 is a third fiber coil, and 45 is a fourth faraday rotator.
In fig. 2, 3 is a main interferometer, 36 is a 2 × 2 fiber coupler, 37 is a second reference arm, and in the reference arm, 371 is a second optical switch, 372 is a fourth fiber coil, 373 is a fifth faraday rotator mirror, 374 is a fifth fiber coil, and 375 is a sixth faraday rotator mirror.
In fig. 3, 3 is the main interferometer, 38 is the third reference arm, and in the third reference arm, 381 is the third optical switch, 384 is the second optical switch, 382 is the sixth optical fiber coil, 383 is the seventh optical fiber coil.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, in the OFDR segmented acquisition apparatus according to the first embodiment of the present invention, a packet scanning laser 1, a fiber splitter 2, a main interferometer 3, an auxiliary interferometer 4, a data acquisition module 5, and a computer 6 are provided. The sweep-frequency laser 1 emits sweep-frequency laser with periodically and linearly changed laser wavelength, which is divided into two paths by the optical fiber beam splitter 2 and respectively enters the main interferometer 3 and the auxiliary interferometer 4; laser in the main interferometer 3 is divided into two beams in the first optical fiber coupler 31, one beam enters the first optical fiber circulator 32, the other beam enters the first reference arm 35, and the signal light enters the port a of the first optical fiber circulator 32 and then exits from the port b to enter the optical fiber device 34 to be measured. Backward Rayleigh scattering is generated in the optical fiber device to be detected 34, the backward Rayleigh scattering is returned by the original path of the first optical fiber circulator 32 and is emitted out from the port c, the emergent light is signal light, the signal light and the reference light passing through the first reference arm 35 are combined in the second optical fiber coupler 33, beat frequency interference is generated, and a first beat frequency signal containing a signal to be detected is generated.
The main interferometer 3 comprises an optical fiber device to be measured containing N sections of optical fiber regions to be measured, and a reference arm containing N optical path gears, wherein the length L of the reference arm of each optical path gearREF(N +1) and the length L of each section of optical fiber device to be testedDUTN and the length L of the reference arm of the previous gearREFN should satisfy the following relation:
LREF(N+1)≤LREFN+(LDUTN)/2，N≥1。
by constructing a variable reference arm, the optical path of the reference light and the optical path of the signal light are always kept within a short-distance range, and further segmented acquisition, splicing and reconstruction are realized.
In the auxiliary interferometer 4, laser enters the optical fiber isolator 41 and then enters the third optical fiber coupler 42, the laser is divided into two beams in the third optical fiber coupler 42, one beam enters the third normal tension rotating mirror 43, and the other beam enters the third optical fiber coil 44 and then enters the fourth faraday rotating mirror 45. The two optical original paths return and generate beat frequency interference in the third optical fiber coupler 42 to generate a second beat frequency signal, and the second beat frequency signal is converted and then used as an external clock or an auxiliary clock of the data acquisition module 5.
The data acquisition module 5 samples the first beat frequency signal according to an external clock generated by the second beat frequency signal, the sampled signal is processed and analyzed by the computer 6, and the computer 6 simultaneously controls the parameter setting and adjustment of the auxiliary sweep frequency laser 1, the data acquisition module 5 and the optical path of the reference arm in the main interferometer 3.
Further, as shown in fig. 1, the first reference arm 35 is a reference arm with a variable optical path length. One path of light split by the first fiber coupler 31 enters the port a of the second fiber circulator 351 in the first reference arm 35, then exits from the port b, enters the first optical switch 352, and is switched by the control of the computer 6 according to the requirement, so that channels with different optical lengths are selected. A plurality of channels of different optical lengths may be provided as desired.
The embodiment of fig. 1 is illustrated with two channels. For example, the selection is switched into the first fiber coil 353 and then into the first faraday rotator mirror 354. The light enters the first optical fiber coil 353 and the first faraday rotator 354 from the first optical switch 352, and then returns to the first optical switch 352, enters the second optical fiber circulator 351, and finally exits from the c port of the second optical fiber circulator and enters the second optical fiber coupler 33 to interfere with the signal light. Similarly, the signal may be switched to the Nth channel, for example, into the second fiber coil 355 and into the second Faraday rotator mirror 356.
Further, as shown in fig. 2, an interferometer and a reference arm according to another embodiment of the present invention are provided. The interferometer is a reflective michelson interferometer. Similarly, after passing through the 2 × 2 fiber coupler 36, the laser light is divided into two paths, one path enters the fiber device under test 34, and the other path enters the second reference arm 37. The second reference arm 27 has a plurality of switchable different optical path channels, one end of the second reference arm 37 is provided with an optical switch, and one end of the optical fiber coil with different optical paths is connected with the optical switch and the other end is connected with the faraday rotator mirror. The present embodiment as shown in fig. 2 is exemplified by two channels. The light returning along the path in the second reference arm 37 and the rayleigh scattered light returning along the path of the optical fiber device 34 to be tested make a round at the 2x2 optical fiber coupler 36, generate beat frequency interference, exit through the other incident end of the 2x2 optical fiber coupler 36, and enter the data acquisition module 5. In particular, in the reference arm 37, after the laser light enters the second optical switch 371, the channel can be selected and switched as desired. 372, 374 are fiber coils, 373, 375 are Faraday rotators.
Further, as shown in fig. 3, is a reference arm structure of a third embodiment of the present invention, a third reference arm 38 structure. Both ends of the third reference arm 38 are optical switches, and a plurality of switchable different optical path channels are included between the optical switches, for example, two channels in the embodiment of fig. 3. The laser is divided from the first optical fiber coupler 31, one path enters the first optical fiber circulator 32, the other path enters the third reference arm 38, the laser entering the reference arm passes through the third optical switch 381, then passes through different channels, passes through the fifth optical fiber coil 382 or the sixth optical fiber coil 383 with different lengths, finally reaches the fourth optical switch 384, and then enters the second optical fiber coupler 33 to generate beat frequency interference with the signal light.
It will be appreciated that the reference arm of the above embodiments may be further modified as required to achieve free switching of a plurality of different optical path channels by different structural forms.
Based on the apparatus of the above embodiment, the present invention also provides an OFDR segmented acquisition method, including the following steps:
constructing a reference arm capable of switching N optical path gears;
dividing an optical fiber area to be tested into N sections according to setting requirements, wherein the length of each section is determined according to the optical path of each gear of a reference arm; length L of reference arm of each gearREF(N +1) and each segment of light to be measuredFiber device length LDUTN and the length L of the reference arm of the previous gearREFN should satisfy the following relation:
LREF(N+1)≤LREFN+(LDUTN)/2，N≥1；
starting N times of scanning to obtain beat frequency signals of N sections of optical fiber areas to be detected;
and respectively carrying out Fourier transform on the N sections of beat frequency signals to obtain a time (distance) -spectrum curve of each section of optical fiber area to be measured. The curves in each time domain (distance domain) are connected from small to large in time in the first place and are spliced into a whole curve time (distance) -spectrum curve. Splicing the range domain of the beat frequency signals of the N sections of optical fiber regions to be detected acquired by N-section scanning, thereby acquiring a complete section of long-distance OFDR beat frequency signals;
and carrying out secondary data processing on the whole long-distance beat frequency signal so as to realize optical communication measurement and distributed temperature strain measurement.
Each beat frequency signal is independent and is data on a frequency domain, and the data needs to be subjected to FFT (fast Fourier transform) conversion and converted into data on a time domain, namely data on a distance domain of the optical fiber to be detected. In OFDR, the time domain is the range domain. After segmented acquisition, spectrum information on each segment of time domain (distance domain) is acquired, each segment of spectrum information is discrete, and N segments of spectrum information need to be spliced end to end from small to large on the distance domain, so that a complete OFDR curve can be obtained.
In the splicing process, because the length of each reference arm meets the relationship, the first splicing process of each section of independent spectral information from small to large in distance does not generate faults. But there may be overlap, i.e. two acquisitions in tandem, near the splice location. When the splicing positions of the optical fiber areas to be detected at the two ends are overlapped in a small area, any section of the overlapped part is selected.
The secondary data processing is mainly processing in the field of OFDR, for example, in the field of optical fiber communication measurement, a large amount of fourier transform, electric field intensity, reflectivity conversion and calibration are required to realize distributed insertion loss return loss measurement. In the field of distributed temperature strain measurement, spectrum cross-correlation algorithm calculation and the like are carried out on beat frequency signals, and distributed temperature strain values are obtained.
A first reference arm 35 is constructed that can switch optical paths, such as N optical path gears.
The optical fiber Device Under Test (DUT)34 is divided into N sections according to the setting requirement, and the length of each section is determined according to the optical path length of each gear of the first reference arm 35.
And starting scanning to obtain beat frequency signals of the N sections of optical fiber areas to be detected.
In order to explain the relationship between the optical path setting of the reference arm and the optical fiber region to be measured more clearly, a schematic diagram of matching the lengths of the reference optical path and the optical path to be measured is provided as shown in fig. 4. In the figure, laser light is divided into two beams of light after passing through an optical fiber coupler, one beam enters a reference arm, and the other beam enters a signal arm.FG、HIFor the reference arms of two different optical lengths,ABCDEFGis the optical fiber to be tested. Reference armFGHas a length of LREFPoint 1, G is the faraday rotator end position.ABCDEFGThe Rayleigh backscattering of the optical fiber at any position in the link generates beat frequency interference with the laser reflected by the Faraday rotating mirror at the G point position at the optical fiber coupler.
In particular, to illustrate the mixing phenomenon in OFDR systems, let usABOptical path length andBCoptical path is equal toFGThe optical lengths are consistent. Therefore, the interference of the rayleigh scattered light at the position of the point C at the point a and the laser light reflected from the faraday rotator at the point G is overlapped. Furthermore, the backward scattered light at any position in the two optical paths overlaps with the laser interference reflected by the Faraday rotator mirror at the G point. Beat frequency interference in OFDR systems, which monitors the frequency difference between signal light and reference light, cannot distinguish directions (i.e., the sign of the frequency difference). Therefore, the temperature of the molten metal is controlled,ABCthe area of the optical fiber to be measured cannot be measured, and is called a blind area.
Setting upCDThe section of optical fiber is a first area to be detected, called L DUT1, the length of optical fiber needs to be less than the maximum distance threshold set by the system. Otherwise, the next section of the optical fiber is adjacent to the section of the optical fiber, and an accurate result cannot be obtained due to phase disturbance.
After obtaining the beat signal of the first section of the optical fiber to be measured, switching to the second reference arm, i.e.HI. Similarly, the second reference arm, which has a section of fiber that cannot be measured due to the dead zone, is shown in FIG. 4ADAnd the optical fiber section is a dead zone relative to the second measurement reference arm. At this point, the system may measure a second fiber region under testDELikewise, the second fiber under test must be less than the system-set maximum distance threshold. Thus, beat signals of the first and second optical fiber areas to be measured CD and DE are obtained.
In order to achieve full link seamless connection, conditions must be met,
by analogy, beat frequency signals of N sections of optical fibers to be tested can be obtained.
And splicing the N sections of beat frequency signals in a distance domain to further obtain the long-distance OFDR beat frequency signal. And finally, performing secondary data processing on the whole long-distance beat frequency signal to realize the fields of optical communication measurement and distributed temperature strain measurement.
It should be noted that the invention only needs to match the reference arm, so that the optical path difference between the optical fiber region to be measured and the reference arm is kept within a certain distance, and the invention is also suitable for acquiring the optical fiber beat frequency signal of any section of region in the optical fiber link to be measured.
In summary, the device and method for realizing long-distance measurement by sectional OFDR acquisition provided by the invention adopt the beat frequency signal generated by the auxiliary interferometer 4 as the external clock of the data acquisition card, and realize equal-frequency interval sampling on the beat frequency signal of the main interferometer 3. Meanwhile, the optical fiber to be measured is divided into N sections, and the reference arm 35 in the main interferometer 3 can set the optical path according to the requirement, so that the optical path difference between each section of the optical fiber to be measured and the reference arm is controlled within a short-distance range, the beat frequency signals are measured in sections and acquired, and meanwhile, the beat frequency signals are spliced in a distance domain, and further the OFDR beat frequency signals of a long distance are acquired. And then, carrying out secondary data processing on the whole long-distance beat frequency signal to realize the fields of optical communication measurement and distributed temperature strain measurement.
It will be readily understood by those skilled in the art that the drawings and examples herein described are for illustrative purposes only and are not intended to limit the scope of the present invention, and that any modifications, equivalent substitutions, improvements and the like made without departing from the spirit and principles of the present invention are intended to be covered by the claims herein.
Claims (7)
1. An OFDR segmented acquisition device for realizing long-distance measurement is characterized by comprising:
the sweep-frequency laser is used for emitting sweep-frequency laser with the laser wavelength periodically and linearly changed;
the optical fiber beam splitter is used for dividing the sweep frequency laser into two paths which respectively enter the auxiliary interferometer and the main interferometer;
the main interferometer is used for enabling the sweep frequency laser entering the main interferometer to generate beat frequency interference and generating a first beat frequency signal containing a signal to be detected; the main interferometer comprises an optical fiber device to be measured containing N sections of optical fiber regions to be measured, and a reference arm containing N optical path gears, wherein the length L of the reference arm of each optical path gearREF(N +1) and the length L of each section of optical fiber region to be measuredDUTN and the length L of the reference arm of the previous gearREFN satisfies the following relation:
LREF(N+1)≤LREFN+（LDUTN）/2，N≥1；
the auxiliary interferometer is used for enabling the sweep-frequency laser entering the auxiliary interferometer to generate beat frequency interference and generate a second beat frequency signal; the second beat frequency signal is converted and then used as an external clock of the high-speed data acquisition card;
the data acquisition module is used for sampling the first beat frequency signal according to an external clock generated by the second beat frequency signal; acquiring beat frequency signals of N sections of optical fiber areas to be detected under N times of scanning of a frequency-scanning laser;
the computer is used for processing and analyzing the sampled signals, and comprises the step of splicing N sections of beat frequency signals in a distance domain to obtain a complete section of long-distance OFDR beat frequency signal; and simultaneously controlling the parameter setting and adjustment of the frequency-sweeping laser, the data acquisition module and the optical path of the reference arm in the main interferometer.
2. The apparatus of claim 1, wherein the main interferometer is an interferometer with an adjustable optical path of a reference arm in an OFDR system, and comprises a first fiber coupler, a first fiber circulator, a first reference arm and a second fiber coupler, wherein one of the branching ends of the first fiber coupler is connected to the port a of the first fiber circulator, the port b and the port c of the first fiber circulator are respectively connected to the fiber device to be measured and the second fiber coupler to form a measurement optical path, and the other branching end of the first fiber coupler is connected to the first reference arm and then connected to the second fiber coupler to form a reference optical path; the optical signals of the measuring optical path and the reference optical path generate beat frequency interference at the second optical fiber coupler to form a first beat frequency signal; the first reference arm comprises a second optical fiber circulator and a first optical switch which are connected, and further comprises a plurality of optical fiber coils with different optical paths, wherein the optical fiber coils are connected with the first optical switch, and the other end of each optical fiber coil is connected with a Faraday rotator mirror.
3. The apparatus of claim 1, wherein the principal interferometer is a reflective michelson interferometer with adjustable reference arm optical path difference in an OFDR system; the optical fiber testing device comprises a 2x2 optical fiber coupler, an optical fiber device to be tested and a second reference arm; the second reference arm comprises a second optical switch and a plurality of optical fiber coils with different optical paths, wherein the optical fiber coils are connected with the second optical switch, and the other end of each optical fiber coil is connected with a Faraday rotator mirror.
4. The apparatus of claim 1, wherein the main interferometer is a main interferometer in an OFDR system, comprising a first fiber coupler, a first fiber circulator, a fiber device under test, and a third reference arm; the third reference arm comprises a third optical switch and a fourth optical switch, and a plurality of optical fiber coils with different optical paths are connected between the two optical switches.
5. The apparatus of any of claims 1-4, wherein the auxiliary interferometer comprises a fiber isolator, a third fiber coupler, a first Faraday rotator mirror, a first fiber coil, a second Faraday rotator mirror; the optical fiber isolator is connected with one input end of the third optical fiber coupler, two output ends of the third optical fiber coupler are respectively connected with one ends of the first Faraday rotator mirror and the first optical fiber coil, and the second Faraday rotator mirror is connected with the other end of the first optical fiber coil.
6. A method for realizing long-distance measurement by OFDR segmented acquisition is characterized by comprising the following steps:
constructing a reference arm capable of switching N optical path gears;
dividing an optical fiber area to be tested of the optical fiber device to be tested into N sections according to setting requirements, wherein the length of each section is determined according to the optical path of each gear of the reference arm; length L of reference arm of each gearREF(N +1) and the length L of each section of optical fiber region to be measuredDUTN and the length L of the reference arm of the previous gearREFN satisfies the following relation:
LREF(N+1)≤LREFN+（LDUTN）/2，N≥1；
starting N times of scanning to obtain beat frequency signals of N sections of optical fiber areas to be detected;
splicing the N sections of beat frequency signals in a distance domain to obtain a complete section of long-distance OFDR beat frequency signal;
and carrying out secondary data processing on the whole long-distance OFDR beat frequency signal to realize optical communication measurement and distributed temperature strain measurement.
7. The method of claim 6, wherein the step of performing distance domain splicing on the N pieces of beat signals comprises:
respectively carrying out Fourier transform on the N sections of beat frequency signals to obtain a time-spectrum curve of each section of optical fiber area to be measured; the curves on each segment of time domain are connected from small to large in time in a first position and spliced into a whole curve time-spectrum curve; and splicing the range domain of the beat frequency signals of the N sections of optical fiber regions to be detected, which are acquired by N times of scanning.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010401588.7A CN111578971B (en) | 2020-05-13 | 2020-05-13 | Device and method for realizing long-distance measurement by OFDR segmented acquisition |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010401588.7A CN111578971B (en) | 2020-05-13 | 2020-05-13 | Device and method for realizing long-distance measurement by OFDR segmented acquisition |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN111578971A CN111578971A (en) | 2020-08-25 |
| CN111578971B true CN111578971B (en) | 2021-11-16 |
Family
ID=72124907
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202010401588.7A Active CN111578971B (en) | 2020-05-13 | 2020-05-13 | Device and method for realizing long-distance measurement by OFDR segmented acquisition |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN111578971B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113503901B (en) * | 2021-09-08 | 2022-05-10 | 武汉昊衡科技有限公司 | Device and method for eliminating measurement signal jitter of white light interferometer |
| CN114370889B (en) * | 2022-01-07 | 2023-03-14 | 南京大学 | Self-adaptive compensation measurement method for different measurement lengths in OFDR system |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102840909A (en) * | 2012-08-21 | 2012-12-26 | 天津大学 | Optical frequency domain reflection-distributed vibration frequency sensing and locating device and demodulation method |
| CN103954226A (en) * | 2014-04-03 | 2014-07-30 | 华南理工大学 | Long-distance distributed type large-measuring-range rapid response optical fiber dynamic strain sensing device |
| CN106289726A (en) * | 2016-07-14 | 2017-01-04 | 北京航空航天大学 | A kind of photon band-gap optical fiber backscattering distributed measurement method and device |
| CN107328429A (en) * | 2017-08-09 | 2017-11-07 | 武汉隽龙科技股份有限公司 | The device and method for closely sensing stability can be improved in optical frequency domain reflection technology |
| CN110338756A (en) * | 2019-05-24 | 2019-10-18 | 广州永士达医疗科技有限责任公司 | A kind of OCT image device and OCT image system suitable for multi-pass |
| CN110375782A (en) * | 2019-07-29 | 2019-10-25 | 武汉隽龙科技股份有限公司 | Improve the device and method of OFDR single sweep operation demodulation speed |
| CN110375781A (en) * | 2019-07-29 | 2019-10-25 | 武汉隽龙科技股份有限公司 | The self-adapting data acquisition system of variable measurement range in a kind of OFDR |
| CN110749420A (en) * | 2019-09-12 | 2020-02-04 | 芯华创(武汉)光电科技有限公司 | OFDR detection device |
-
2020
- 2020-05-13 CN CN202010401588.7A patent/CN111578971B/en active Active
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102840909A (en) * | 2012-08-21 | 2012-12-26 | 天津大学 | Optical frequency domain reflection-distributed vibration frequency sensing and locating device and demodulation method |
| CN103954226A (en) * | 2014-04-03 | 2014-07-30 | 华南理工大学 | Long-distance distributed type large-measuring-range rapid response optical fiber dynamic strain sensing device |
| CN106289726A (en) * | 2016-07-14 | 2017-01-04 | 北京航空航天大学 | A kind of photon band-gap optical fiber backscattering distributed measurement method and device |
| CN107328429A (en) * | 2017-08-09 | 2017-11-07 | 武汉隽龙科技股份有限公司 | The device and method for closely sensing stability can be improved in optical frequency domain reflection technology |
| CN110338756A (en) * | 2019-05-24 | 2019-10-18 | 广州永士达医疗科技有限责任公司 | A kind of OCT image device and OCT image system suitable for multi-pass |
| CN110375782A (en) * | 2019-07-29 | 2019-10-25 | 武汉隽龙科技股份有限公司 | Improve the device and method of OFDR single sweep operation demodulation speed |
| CN110375781A (en) * | 2019-07-29 | 2019-10-25 | 武汉隽龙科技股份有限公司 | The self-adapting data acquisition system of variable measurement range in a kind of OFDR |
| CN110749420A (en) * | 2019-09-12 | 2020-02-04 | 芯华创(武汉)光电科技有限公司 | OFDR detection device |
Also Published As
| Publication number | Publication date |
|---|---|
| CN111578971A (en) | 2020-08-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Froggatt et al. | Characterization of polarization-maintaining fiber using high-sensitivity optical-frequency-domain reflectometry | |
| JPH026724A (en) | Method and apparatus for testing optical transmission medium | |
| CN111578971B (en) | Device and method for realizing long-distance measurement by OFDR segmented acquisition | |
| JPH0666517A (en) | Optical interferometer | |
| CN101764646A (en) | Wavelength-encoding optical time domain reflection test device and measurement method thereof | |
| US6011615A (en) | Fiber optic cable having a specified path average dispersion | |
| US9304058B2 (en) | Measuring modal content of multi-moded fibers | |
| CN113138065B (en) | Device and method for analyzing few-mode fiber faults based on multi-mode transmission reflection | |
| CN113804412A (en) | Optical fiber device micro-chromaticity dispersion measuring device based on ring light path structure | |
| US4790655A (en) | System for measuring laser spectrum | |
| Li et al. | Measuring modal delays of few-mode fibers using frequency-domain method | |
| CN110375960A (en) | A kind of device and method based on super continuum source OTDR | |
| CN114526683B (en) | High-spatial-resolution temperature and strain optical fiber sensing system and measuring method | |
| CN114337804B (en) | Device and method for increasing length of white light interferometry link | |
| CN112880716A (en) | Multichannel optical fiber sensing system based on OFDR technology | |
| CN115711633A (en) | Phase noise accurate correction optical frequency domain reflectometer of loop structure reference interferometer | |
| CN113804298B (en) | Distributed bidirectional polarization measurement device based on matching correction light frequency domain interference | |
| CN115452014A (en) | Optical frequency domain reflectometer with noise suppression and frequency division multiplexing of multi-reference-arm structure | |
| JP2006242634A (en) | Method and apparatus for dispersion measurement of optical transmission medium | |
| Jeon et al. | Optical fiber chromatic dispersion measurement using bidirectional modulation of an optical intensity modulator | |
| JP2003322589A (en) | Method and instrument for measuring brillouin spectrum distribution | |
| RU2797693C1 (en) | Method for measuring parameters of refractive index inhomogeneities along the length of an optical fibre and an optical frequency domain reflectometer | |
| CN214951406U (en) | Multichannel optical fiber sensing system based on OFDR technology | |
| Takahashi et al. | Distributed measurement of single-way inter-modal crosstalk in spliced FMFs based on BOTDA | |
| US20230288287A1 (en) | Power coupling coefficient measuring method and power coupling coefficient measuring device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |