CN110749420B - OFDR detection device - Google Patents
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Abstract
The invention relates to the field of optical fiber sensing, in particular to an OFDR detection device, which comprises: the device comprises a sweep frequency light source, a first optical splitter, a main interferometer, a first photoelectric detector, an adjustable time delay auxiliary interferometer, a second photoelectric detector and a data processing module, wherein a light outlet of the sweep frequency light source is connected with a light inlet of the first optical splitter, a first light outlet of the first optical splitter is connected with a light inlet of the main interferometer, a light outlet of the main interferometer is connected with the first photoelectric detector, a second light outlet of the first optical splitter is connected with a light inlet of the adjustable time delay auxiliary interferometer, a light outlet of the adjustable time delay auxiliary interferometer is connected with the second photoelectric detector, the first photoelectric detector is connected with a data receiving end of the data processing module, and the second photoelectric detector is connected with a data receiving end of the data processing module. The device adopts the adjustable time delay auxiliary interferometer, and can measure the phase noise of different frequency points under different time delays, thereby compensating the phase noise of different abnormal frequency points.
Description
[ technical field ] A method for producing a semiconductor device
The invention relates to the field of optical fibers, in particular to an OFDR detection device.
[ background ] A method for producing a semiconductor device
With the widespread use of optical fiber links, the demand for fault detection equipment in long-distance optical fiber links is gradually increasing.
In order to solve the problem of fault location of a long-distance Optical fiber link, OFDR (Optical frequency domain reflection) distributed Optical fiber sensing technology is generally used for fault detection at present. However, the conventional OFDR distributed optical fiber sensing device has frequency offset due to problems such as phase noise interference, and the like, so that the positioning of the reflection point or the scattering point is not accurate enough. The OFDR detection device used at present uses a fixed delay auxiliary interferometer to compensate phase noise, can only compensate a fixed delay value, cannot adjust delay according to the change of the phase noise to accurately compensate, so that the OFDR distributed optical fiber sensing device cannot detect a plurality of reflection points or scattering points on a sensing link at the same time, and cannot quickly and accurately position fault points on the link.
[ summary of the invention ]
Aiming at the defects or improvement requirements of the prior art, the invention designs the OFDR detection device of the auxiliary interferometer with adjustable time delay capability, and solves the problem that the abnormal frequency point is difficult to accurately compensate in the OFDR system.
The embodiment of the invention adopts the following technical scheme:
in a first aspect, the present invention provides an OFDR detection apparatus, including: the optical fiber-based optical fiber frequency-sweeping device comprises a frequency-sweeping light source, a first optical splitter, a main interferometer, a first photoelectric detector, an adjustable time-delay auxiliary interferometer, a second photoelectric detector and a data processing module, wherein a light outlet of the frequency-sweeping light source is connected with a light inlet of the first optical splitter through an optical fiber, a first light outlet of the first optical splitter is connected with a light inlet of the main interferometer through an optical fiber, a light outlet of the main interferometer is connected with the first photoelectric detector through an optical fiber, a second light outlet of the first optical splitter is connected with a light inlet of the adjustable time-delay auxiliary interferometer through an optical fiber, a light outlet of the adjustable time-delay auxiliary interferometer is connected with the second photoelectric detector through an optical fiber, the first photoelectric detector is connected with a data receiving end of the data processing module through a data line, and the second photoelectric detector is connected with the data receiving end of the data processing module through a data line. The device adopts the adjustable time delay auxiliary interferometer, so that the adjustable time delay auxiliary interferometer can measure phase noise at different distances under different time delays, and the distances of different fault points are compensated with pertinence and accuracy.
Preferably, the adjustable time delay auxiliary interferometer specifically comprises: the first light outlet of the first optical splitter is connected with one end of the fixed delay interference arm, the first light inlet of the third optical splitter is connected with the other end of the fixed delay interference arm, the second light outlet of the second optical splitter is connected with one end of the adjustable delay interference arm, the second light inlet of the third optical splitter is connected with the other end of the adjustable delay interference arm, and the light outlet of the third optical splitter is connected with the second photoelectric detector. The invention adopts the adjustable time delay interference arm to realize the interference measurement of the adjustable time delay auxiliary interferometer under different time delays.
Preferably, the fixed delay interference arm is an adjustable delay optical device, a first optical port of the adjustable delay optical device is connected with a first light outlet of the second optical splitter, a second optical port of the adjustable delay optical device is connected with a first light inlet of the third optical splitter, and the adjustable delay optical device is used for generating fixed delay corresponding to sensing distance when the device applies different sensing distances; the adjustable delay optical device is adopted in the fixed delay interference arm, so that the optical signal delay of the fixed delay interference arm can be temporarily adjusted according to the distance of the sensing optical fiber on the main interferometer in the application field of the device, and the application environment adaptability of the device is improved.
Or the fixed time delay interference arm is specifically a fixed length optical fiber, one end of the fixed length optical fiber is connected with the first light outlet of the second optical splitter, the other end of the fixed length optical fiber is connected with the first light inlet of the third optical splitter, and the fixed length optical fiber is used for generating predictable fixed time delay; the invention adopts the optical fiber with fixed length to be coiled in the device, thereby avoiding an adjustable time delay optical device when the sensing distance is short and reducing the cost of the device.
Alternatively, the fixed delay interference arm comprises: the optical fiber circulator comprises a circulator, a reflector and a fixed-length optical fiber, wherein a first port of the circulator is connected with a first light outlet of a second optical splitter through the optical fiber, a second port of the circulator is connected with the reflector through the fixed-length optical fiber, a third port of the circulator is connected with a first light inlet of a third optical splitter through the optical fiber, and the reflector is used for multiplying the stroke of an optical signal in the fixed-length optical fiber. When the distance is longer, the invention can reduce the fiber coiling amount in the device by adopting the optical fiber with fixed length and the reflector.
Preferably, the time delay of the fixed time delay interference arm is the same as the time delay of the longest measurement distance of the optical fiber on the main interferometer. The longest measurement distance of the sensing optical fiber on the main interferometer is related to the line width power of the light source, the loss of the optical fiber link and the like. The fixed delay interference arm is used for compensating phase noise and frequency sweep nonlinearity.
Preferably, the adjustable delay interference arm comprises an adjustable delay optical device and an optical fiber, the light inlet of the adjustable delay optical device is connected with the second light outlet of the second optical splitter through the optical fiber, and the light outlet of the adjustable delay optical device is connected with the second light inlet of the third optical splitter through the optical fiber. The adjustable time delay optical device has small volume and light weight, and is mainly divided into manual adjustment and electric adjustment. The adjustable time delay optical device is a silicon optical structure controllable optical fiber time delay device or a piezoelectric ceramic controllable optical fiber time delay device.
Preferably, the maximum value of the adjustable time delay interference arm is not less than 2 times of the time delay caused by the length of the optical fiber line on the main interferometer. The invention needs to ensure that the adjustable range of the adjustable time delay interference arm can cover the measurement distance.
Preferably, the data processing module specifically comprises a data acquisition element and a data processing element, the data output end of the data acquisition element is connected with the data processing element through a data signal line, the first data acquisition end of the data acquisition element is connected with the first photoelectric detector through a data line, and the second data acquisition end of the data acquisition element is connected with the second photoelectric detector through a data line. According to the invention, after the time delay setting of the adjustable time delay interference arm is completed, the phase noise of the adjustable time delay auxiliary interferometer is measured and the distance compensation quantity of a fault point is calculated through the data processing unit.
Preferably, the adjustable delay optical device is a manual adjustable optical fiber delay device.
Preferably, the data processing module further comprises a control element, the adjustable delay optical device is an electric adjustable optical fiber delay device, and the control element is connected with the electric adjustable optical fiber delay device through a control signal line and used for adjusting the delay of the adjustable delay auxiliary interferometer. The invention can greatly reduce the complexity of manual adjustment when multiple fault points are determined through electric adjustment, and can also improve the speed of phase noise compensation under the multiple fault points.
Compared with the prior art, the embodiment of the invention has the beneficial effects that:
the invention can precisely compensate specific reflection points or scattering points on the optical fiber by using the adjustable time delay auxiliary interferometer.
The invention utilizes the adjustable time delay auxiliary interferometer, can realize one-time sampling of the main interferometer by measuring the phase noise of a plurality of reflection points or scattering points one by one and combining the method, and can respectively complete compensation on the plurality of reflection points at one time. The method can prevent the strong reflection point or the scattering point behind the strong reflection point from being submerged in the strong reflection event, and can remarkably improve the adaptability of the OFDR equipment to the strong reflection event.
The invention utilizes the electric adjustable delay interference arm, electrically controls and sequentially adjusts the delay value of the adjustable delay interference arm, and successively observes the phase signal of the adjustable delay auxiliary interferometer, so that the device of the invention can more quickly compensate a plurality of abnormal frequency points.
[ description of the drawings ]
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly described below. It is obvious that the drawings described below are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
Fig. 1 is a schematic structural diagram of an OFDR detection apparatus according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a preferred embodiment of an OFDR detection apparatus provided in an embodiment of the present invention;
fig. 3 is a schematic flow chart of an OFDR detection method according to an embodiment of the present invention.
[ detailed description ] embodiments
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.
The present invention is a system structure of a specific function system, so the functional logic relationship of each structural module is mainly explained in the specific embodiment, and the specific software and hardware implementation is not limited.
In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other. The invention will be described in detail below with reference to the figures and examples.
Example 1：
The specific structure of an OFDR detection apparatus of the present invention is described below with reference to fig. 1:
the method comprises the following steps: a sweep frequency light source, a first optical splitter, a main interferometer, a first photoelectric detector, an adjustable time delay auxiliary interferometer, a second photoelectric detector and a data processing module,
the optical fiber connection is adopted between the light outlet of the sweep frequency light source and the light inlet of the first optical splitter, the optical fiber connection is adopted between the first light outlet of the first optical splitter and the light inlet of the main interferometer, the optical fiber connection is adopted between the light outlet of the main interferometer and the first photoelectric detector, the optical fiber connection is adopted between the second light outlet of the first optical splitter and the light inlet of the adjustable delay auxiliary interferometer, the optical fiber connection is adopted between the light outlet of the adjustable delay auxiliary interferometer and the second photoelectric detector, the data line connection is adopted between the first photoelectric detector and the data receiving end of the data processing module, and the data line connection is adopted between the second photoelectric detector and the data receiving end of the data processing module. The device adopts the adjustable time delay auxiliary interferometer, so that the adjustable time delay auxiliary interferometer can measure phase noise at different distances under different time delays, and the distances of different fault points are compensated with pertinence and accuracy.
In some specific application scenarios of the present embodiment, as shown in fig. 1: the adjustable time delay auxiliary interferometer specifically comprises: a fixed time delay interference arm, an adjustable time delay interference arm, a second optical splitter and a third optical splitter,
the second light outlet of the first optical splitter is connected with the other end of the fixed delay interference arm, the second light outlet of the second optical splitter is connected with one end of the adjustable delay interference arm, the second light inlet of the third optical splitter is connected with the other end of the adjustable delay interference arm, and the light outlet of the third optical splitter is connected with the second photoelectric detector. The invention adopts the adjustable time delay interference arm to realize the interference measurement of the adjustable time delay auxiliary interferometer under different time delays.
In an actual application scenario, for different application conditions, a proper mode can be selected according to the practical requirement of adjustability of the fixed delay interference arm, and different devices are adopted to realize the fixed delay interference arm. In this embodiment, several implementation manners of the fixed delay interference arm are simply enumerated:
(1) in some embodiments of the present invention, the fixed delay interference arm is an adjustable delay optical device, a first optical port of the adjustable delay optical device is connected to a first optical outlet of the second optical splitter, a second optical port of the adjustable delay optical device is connected to a first optical inlet of the third optical splitter, and the adjustable delay optical device is used for generating a fixed delay corresponding to a sensing distance when the apparatus applies different sensing distances; the adjustable delay optical device is adopted in the fixed delay interference arm, so that the optical signal delay of the fixed delay interference arm can be temporarily adjusted according to the distance of the sensing optical fiber on the main interferometer in the application field of the device, and the application environment adaptability of the device is improved.
(2) In some embodiments of the present invention, the fixed delay interference arm is a fixed length optical fiber, one end of the fixed length optical fiber is connected to the first light outlet of the second optical splitter, the other end of the fixed length optical fiber is connected to the first light inlet of the third optical splitter, and the fixed length optical fiber is used for generating a predictable fixed delay; the invention adopts the optical fiber with fixed length to be coiled in the device, thereby avoiding an adjustable time delay optical device when the sensing distance is short and reducing the cost of the device.
(3) In some embodiments of the invention, the fixed delay interference arm comprises: the optical fiber circulator comprises a circulator, a reflector and a fixed-length optical fiber, wherein a first port of the circulator is connected with a first light outlet of a second optical splitter through the optical fiber, a second port of the circulator is connected with the reflector through the fixed-length optical fiber, a third port of the circulator is connected with a first light inlet of a third optical splitter through the optical fiber, and the reflector is used for multiplying the stroke of an optical signal in the fixed-length optical fiber. When the distance is longer, the invention can reduce the fiber coiling amount in the device by adopting the optical fiber with fixed length and the reflector.
The above embodiments are all able to implement an interferometer arm with a fixed time delay within an adjustable time delay auxiliary interferometer.
The adjustable delay interference arm specifically comprises an adjustable delay optical device and an optical fiber, wherein the light inlet of the adjustable delay optical device is connected with the second light outlet of the second optical splitter through the optical fiber, and the light outlet of the adjustable delay optical device is connected with the second light inlet of the third optical splitter through the optical fiber. The adjustable time delay optical device has small volume and light weight, and is mainly divided into manual adjustment and electric adjustment. The adjustable time delay optical device is a silicon optical structure controllable optical fiber time delay device or a piezoelectric ceramic controllable optical fiber time delay device.
In an actual application scene, the maximum value of the adjustable time delay interference arm is not less than 2 times of the time delay caused by the length of the optical fiber line on the main interferometer. The invention needs to ensure that the adjustable range of the adjustable time delay interference arm can cover the measurement distance.
On the other hand, as shown in fig. 2, in combination with the embodiment of the present invention, there is a preferred implementation manner for the specific structure of the data processing module: the data processing module comprises a data acquisition element and a data processing element, a data output end of the data acquisition element is connected with the data processing element through a data signal line, a first data acquisition end of the data acquisition element is connected with the first photoelectric detector through a data line, and a second data acquisition end of the data acquisition element is connected with the second photoelectric detector through a data line. According to the invention, after the time delay setting of the adjustable time delay interference arm is completed, the phase noise of the adjustable time delay auxiliary interferometer is measured and the distance compensation quantity of a fault point is calculated through the data processing unit.
In an actual application scenario, aiming at the flexibility of the adjustable delay interference arm in adjusting the delay, different devices can be adopted to realize the adjustable delay interference arm according to the automatic adjustment requirement and the manual adjustment requirement of the adjustable delay interference arm. In this embodiment, several implementation manners of the adjustable delay interference arm are simply enumerated:
(1) in some embodiments of the present invention, the adjustable delay optical device is a manually adjustable optical fiber delay device, and the manually adjustable optical fiber delay device has better delay continuity.
(2) In some embodiments of the present invention, the data processing module further includes a control element, the adjustable delay optical device is an electrically adjustable optical fiber delay device, and the control element is connected to the electrically adjustable optical fiber delay device through a control signal line for adjusting the delay of the adjustable delay auxiliary interferometer. The invention can greatly reduce the complexity of manual adjustment when multiple fault points are determined through electric adjustment, and can also improve the speed of phase noise compensation under the multiple fault points.
Example 2：
The present invention provides, in addition to the OFDR detection apparatus described in embodiment 1, an OFDR detection method, which can be applied to the detection apparatus described in embodiment 1, and therefore, the explanation of the corresponding method step features made in the embodiment of the present invention can find a corresponding implementation subject in embodiment 1, as shown in fig. 3, the method includes:
s1: the beat frequency signals of 1 sweep frequency period collected on the main interferometer are converted from time domain to frequency domain to obtain the frequency domain data sequence of the main interferometer,
s2: screening data of the frequency domain amplitude value of the frequency domain data sequence which is higher than a preset threshold value as a main interferometer abnormal frequency point data sequence, wherein the main interferometer abnormal frequency point data sequence comprises abnormal frequency point frequency values corresponding to abnormal frequency points;
s3: calculating the time delay corresponding to each abnormal frequency point in the main interferometer abnormal frequency point data sequence,
s4: sequentially adjusting the time delay of the adjustable time delay interference arm, detecting and demodulating to obtain phase signal data of the adjustable time delay auxiliary interferometer under different time delays to obtain a phase signal data sequence,
s5: calculating an auxiliary reference signal data sequence corresponding to each abnormal frequency point by using the phase signal data sequence,
s6: and calculating a corrected frequency value corresponding to each frequency point in the main interferometer abnormal frequency point data sequence according to the main interferometer abnormal frequency point data sequence, the phase signal data sequence, the auxiliary reference signal data sequence and the time delay value of the adjustable time delay interference arm.
The main interferometer abnormal frequency point data sequence comprises the frequency F of each main interferometer abnormal frequency pointkWhere k is the anomaly frequencyThe serial number of the main interferometer abnormal frequency point data sequence is clicked,
in an actual application scenario, a way of calculating the time delay corresponding to each abnormal frequency point in the data sequence of the abnormal frequency points of the main interferometer is specifically as follows: because the modulation parameters of the sweep frequency light source are a known stable parameter combination, the time delay of the abnormal frequency point can be calculated by using the sweep frequency light source parameter combination, the first frequency corresponding to the abnormal frequency point and the speed of the light in the optical fiber medium according to the OFDR existing technology, preferably, the preset threshold value can be-30 db, and the abnormal frequency point is a frequency point of which the frequency domain amplitude value in the frequency domain data sequence of the main interferometer is higher than the preset threshold value. In step S4, detecting and demodulating to obtain a phase signal data sequence of the adjustable delay auxiliary interferometer under different delays, specifically: the optical detection converts beat frequency optical signals generated by the adjustable delay auxiliary interferometer into electric signals, the data processing module finishes the acquisition and demodulation processing of the beat frequency electric signals of two interference arms of the adjustable delay auxiliary interferometer to obtain phase signals, and the phase signals are signals of corresponding phases of interference signals generated by the adjustable delay auxiliary interferometer on a time domain.
In an actual application scenario, the time delay of the adjustable time delay interference arm is sequentially adjusted, specifically: if the length of the abnormal frequency point data sequence of the main interferometer is 0, setting the time delay value of the adjustable time delay interference arm as a first time delay value; and if the length of the abnormal frequency point data sequence of the main interferometer is greater than or equal to 1, calculating a second time delay value sequence, and sequentially setting the adjustable time delay interference arms as the second time delay value sequence. The second sequence of delay values is noted as: tau is1～τkAnd recording a phase signal data sequence obtained by detecting and demodulating the adjustable delay auxiliary interferometer as follows: x (t-tau)1)～X(t-τk) Wherein t is a sampling period duration, and the auxiliary reference signal data sequence is recorded as: x1(t)～Xk(t)，
In some embodiments of the invention, the first delay value τ0The calculation formula is as follows:
τ0＝L·c·2·n，
wherein, L is the length of the wiring of the sensing optical fiber link, c is the propagation speed of the optical signal in the sensing optical fiber link, and n is the optical refractive index of the optical fiber medium in the sensing optical fiber link. Because the sensing optical fiber is connected to the main interferometer, the wiring length can be obtained by the requirements or tests of the construction site environment.
In some embodiments of the invention, the second sequence of delay values is: and the difference value sequence of the time delay of the fixed time delay interference arm and the time delay corresponding to each abnormal frequency point in the abnormal frequency point data sequence of the main interferometer.
In an actual application scene, the maximum time delay value of the fixed time delay interference arm is not less than 2 times of the single-pass time delay caused by the optical fiber transmission on the main interference arm.
In some embodiments of the present invention, the delay of the fixed delay interferometer arm is 2 times the single-pass delay caused by the transmission fiber on the main interferometer arm.
In practical application scenarios, the auxiliary reference signal X corresponding to the kth abnormal frequency point in the auxiliary reference signal data sequencekThe formula for calculation of (t) is:
where t is the sampling period duration, τkIs the time delay value of the adjustable time delay interference arm corresponding to the k-th abnormal frequency point, X (t-tau)k) Time delay tau corresponding to the k-th abnormal frequency pointkAnd detecting and demodulating the obtained phase signal by using the lower adjustable delay auxiliary interferometer.
In an actual application scenario, a calculation formula of the corrected frequency value f corresponding to the kth abnormal frequency point is as follows:
wherein, FkThe abnormal frequency value corresponding to the k-th abnormal frequency point, X' (t-tau)1) Detecting and demodulating the phase signal X (t-tau) obtained by the adjustable time delay auxiliary interferometer corresponding to the first abnormal frequency point1) Time differential calculation result of (1), τkCorresponding to the k-th abnormal frequency pointDelay value, tau, of adjustable delay interference arm1Is an adjustable delay interference arm delay value X 'corresponding to the first abnormal frequency point'k(t) is an auxiliary reference signal X corresponding to the kth abnormal frequency pointk(t) time differential calculation result.
In some embodiments of the present invention, the time differential can be mathematically processed as a result of dividing the phase signal of the main interferometer by the corresponding time.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. An OFDR detection apparatus, comprising: a sweep frequency light source, a first optical splitter, a main interferometer, a first photoelectric detector, an adjustable time delay auxiliary interferometer, a second photoelectric detector and a data processing module,
the optical fiber connection is adopted between the light outlet of the sweep frequency light source and the light inlet of the first optical splitter, the optical fiber connection is adopted between the first light outlet of the first optical splitter and the light inlet of the main interferometer, the optical fiber connection is adopted between the light outlet of the main interferometer and the first photoelectric detector, the optical fiber connection is adopted between the second light outlet of the first optical splitter and the light inlet of the adjustable time delay auxiliary interferometer, the optical fiber connection is adopted between the light outlet of the adjustable time delay auxiliary interferometer and the second photoelectric detector, the data receiving end of the data processing module is connected with the first photoelectric detector through a data line, and the data receiving end of the data processing module is connected with the second photoelectric detector through a data line;
the data processing module comprises a control element, the adjustable delay auxiliary interferometer comprises an adjustable delay interference arm, the control element is connected with the adjustable delay interference arm through a control signal line, and the control element sequentially adjusts the delay of the adjustable delay interference arm according to the delay corresponding to each abnormal frequency point in the abnormal frequency point data sequence of the main interferometer.
2. The OFDR detection apparatus of claim 1, wherein: the adjustable time-delay auxiliary interferometer specifically comprises: a fixed time delay interference arm, an adjustable time delay interference arm, a second optical splitter and a third optical splitter,
the first optical splitter second light outlet and the second optical splitter are connected through an optical cable, the second optical splitter first light outlet is connected with one end of the fixed delay interference arm, the third optical splitter first light inlet is connected with the other end of the fixed delay interference arm, the second optical splitter second light outlet is connected with one end of the adjustable delay interference arm, the third optical splitter second light inlet is connected with the other end of the adjustable delay interference arm, and the third optical splitter light outlet is connected with the second photoelectric detector.
3. The OFDR detection apparatus of claim 2, wherein:
the fixed delay interference arm is specifically an adjustable delay optical device, a first optical port of the adjustable delay optical device is connected with a first light outlet of the second optical splitter, a second optical port of the adjustable delay optical device is connected with a first light inlet of the third optical splitter, and the adjustable delay optical device is used for generating fixed delay corresponding to sensing distance when the device applies different sensing distances;
or the fixed-length time delay interference arm is specifically a fixed-length optical fiber, one end of the fixed-length optical fiber is connected with the first light outlet of the second optical splitter, the other end of the fixed-length optical fiber is connected with the first light inlet of the third optical splitter, and the fixed-length optical fiber is used for generating predictable fixed time delay;
or, the fixed delay interference arm includes: circulator, speculum, fixed length optic fibre, No. one port of circulator with link to each other by optic fibre between the first light-emitting port of second beam splitter, No. two ports of circulator with by between the speculum fixed length optic fibre links to each other, No. three ports of circulator with link to each other by optic fibre between the first income light-emitting port of third beam splitter, the speculum is used for doubly increasing the stroke of light signal in fixed length optic fibre.
4. The OFDR detection apparatus of claim 3, wherein: the time delay of the fixed time delay interference arm is the same as the time delay of the longest measuring distance of the optical fiber on the main interference arm.
5. The OFDR detection apparatus of claim 2, wherein: the adjustable time delay interference arm comprises an adjustable time delay optical device and an optical fiber,
the light inlet of the adjustable time delay optical device is connected with the second light outlet of the second optical splitter through an optical fiber, and the light outlet of the adjustable time delay optical device is connected with the second light inlet of the third optical splitter through an optical fiber.
6. The OFDR detection apparatus of claim 5, wherein: the maximum value of the adjustable time delay interference arm is not less than 2 times of the time delay caused by the length of the optical fiber sensing circuit on the main interferometer.
7. The OFDR detection apparatus of claim 2, wherein: the data processing module specifically comprises a data acquisition element and a data processing element,
the data output end of the data acquisition element is connected with the data processing element through a data signal line, the first data acquisition end of the data acquisition element is connected with the first photoelectric detector through a data line, and the second data acquisition end of the data acquisition element is connected with the second photoelectric detector through a data line.
8. The OFDR detection apparatus of claim 7, wherein: the adjustable time delay optical device is a manual adjustable optical fiber time delay device.
9. The OFDR detection apparatus of claim 7, wherein: the data processing module also comprises a control element, the adjustable time delay optical device is specifically an electric adjustable optical fiber time delay device,
the control element is connected with a control port of the electric adjustable optical fiber delay device through a control signal line and used for adjusting the delay of the adjustable delay auxiliary interferometer through the control element.
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