AU2020103661A4 - A distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator - Google Patents
A distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator Download PDFInfo
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- 239000000835 fiber Substances 0.000 title claims abstract description 244
- 238000005259 measurement Methods 0.000 title claims abstract description 45
- 230000005540 biological transmission Effects 0.000 claims abstract description 25
- 238000012545 processing Methods 0.000 claims abstract description 22
- 239000013307 optical fiber Substances 0.000 claims abstract description 7
- 230000003287 optical effect Effects 0.000 claims description 44
- 238000003491 array Methods 0.000 claims description 20
- 239000002131 composite material Substances 0.000 claims description 4
- 238000012544 monitoring process Methods 0.000 abstract description 10
- 238000005516 engineering process Methods 0.000 abstract description 7
- 238000009826 distribution Methods 0.000 abstract description 5
- 101150087426 Gnal gene Proteins 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 13
- 230000001427 coherent effect Effects 0.000 description 7
- 238000000034 method Methods 0.000 description 6
- 230000008901 benefit Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 230000036541 health Effects 0.000 description 3
- 238000011161 development Methods 0.000 description 2
- 238000005305 interferometry Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000002120 advanced silicon etching Methods 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
-
- 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
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
- G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
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Abstract
The invention belongs to the fiber sensing technology field, relates to a distributed fiber strain
measurement system based on an adjustable-cavity-length F-P white light interferometric
demodulator, which can be used for real-time monitoring and measurement of physical quantities
such as multipoint quasi-distributed strain or quasi-temperature distributions. It comprises a
broad spectrum light source, a four-port fiber circulator, a fiber coupler with dual-port
connections, an adjustable-cavity-length F-P white light interferometric demodulator, a three
port fiber circulator, a first transmission fiber and a second transmission fiber, a first fiber sensor
array and a second fiber sensor array, a first photodetection signal amplifier and a second
photodetection signal amplifier, and a first signal processing unit and a second signal processing
unit. The invention has a high stability of the light source and increased utilization of the light
source power.
1/5
DRAWINGS
Signal 12
processing unit 2
10
4 A 2 6
Adjustable-cavity-length F-P white
light interferometric demodulator P
Reflection h
scanning mirror --- Sensor array
1 55
A 9 ~~~Three-port fiberL-------
-Collimator optic circulator
Optical fiber 9
- - --- -- -- - Sensor array
-- Four-port fiber optic L-------
0,circulator
PD,
1 1
13 Si gnal
processing unit 1
FIG. 1
Description
1/5 DRAWINGS
Signal 12 processing unit 2
10 4 A 2 6 Adjustable-cavity-length F-P white light interferometric demodulator P
Reflection h scanning mirror -- Sensor array
A 9 ~~~Three-port fiberL------- -Collimator optic circulator
1 55 Optical fiber 9
- - -- -- -- - Sensor array
-- Four-port fiber optic L------- 0,circulator PD, 1 1
13 Signal processing unit 1
FIG. 1
A distributed fiber strain measurement system based on an adjustable-cavity-length F-P white
light interferometric demodulator
[0001] The invention belongs to the fiber sensing technology field, particularly relates to a
distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light
interferometric demodulator, which can be used for real-time monitoring and measurement of
physical quantities such as multipoint quasi-distributed strain or quasi-temperature distributions.
[0002] One of the advantages of fiber white light interferometers is that they can be easily
multiplexed. Multiple sensors have a single interferometric signal in their respective coherence
lengths, avoiding the need for more complex time or frequency multiplexing techniques to
process signals. In recent years, white light interferometric sensing technology has been
developing vigorously, and one of the highlights has been the development of a variety of
multiplexing-based fiber sensors and measurement systems for the measurement of physical
quantities such as strain, temperature, and pressure. The background of the development of
multiplexing technology is that in actual measurement and testing applications, the sensing of a
single physical quantity and a single location is far from satisfying the requirements of perceiving the state of the whole or system, which often requires online or real-time measurement of the distribution of multiple or multipoint physical quantities. For example, the nondestructive inspection and monitoring of large structures (hydroelectric power stations, dams, bridges, etc.) to determine their safety requires that fiber-optic sensors be implanted in critical areas and that monitoring networks be constructed to extract stress, strain, and temperature information from them. As a result, the number of sensors is usually in the dozens or hundreds, and if the test system is connected with only a single point sensor, the cost of the test will undoubtedly be greatly increased, and the reliability of the system will be reduced. With multiplexing technology, the same demodulation system is used to interrogate measurement information from multiple sensors, which not only greatly simplifies the complexity of the system, but also ensures the measurement accuracy and reliability. At the same time, due to the use of multiplexing technology, the cost of a single point sensor is reduced, thus making the test cost much lower, improving the cost performance, and making the fiber sensor more advantageous compared to traditional sensors.
[0003] White interferometric fiber sensors can effectively avoid the limitations and problems
encountered with very long coherent lengths of signals from narrowband laser sources. One of
the main advantages of space division multiplexing (SDM) white interferometric fiber sensors is
the ability to measure absolute length and time delay. In addition, due to the short coherence
length of the sensing signal, time-varying interference from system stray light can be eliminated.
Another advantage of SDM white light interferometry is that it allows multiple sensors to be
coherently multiplexed in a single signal without the need for relatively complex time division
multiplexing or frequency division multiplexing techniques. SDM is achieved by using a
scanning interferometer (such as a Michelson interferometer) to match the signal light to the
optical path of the reference light. If the optical paths of the two signal lights match, white light
interference strips are observed in the output signal of the interferometer. Absolute measurements
can be made with high accuracy, and parameters that can be measured include position,
displacement, strain, and temperature.
[0004] In practical applications, especially in building structure monitoring, long-range, multipoint, quasi-distributed measurements of the building structure are often required. However, for conventional fiber white light interferometer structures, the length of the sensing fiber is limited by the tuning range of the variable scanning arm. In addition, even when long tuning ranges are available, the transmission loss of the optical signal over long spatial light paths can be significant.
[0005] To solve the above problems, in 1995 Wayne V. Sorin and Douglas M. Baney of H-P, Inc. disclosed a multiplexing method for a white light interference sensor based on an optical path autocorrelator (U.S. Patent: Patent No. 5557400), which is based on a Michelson interferometer structure, using the optical path difference formed by the optical signal between the fixed arm and the variable scanning arm of the Michelson interferometer, and the reflected light signal optical path difference between the front and back of the fiber sensor, match the them to achieve the optical path autocorrelation to obtain the white light interference signal of the sensor. Then, multiplexing of optic sensors is accomplished by matching each sensor in multiple beginning-to end-connected serial fiber sensor arrays one by one with variable sizes of optical path difference between the scanning arm and the fixed arm.
[0006] In addition, the applicant published a low coherence twisted Sagnac-like fiber deformation sensing device in 2007 and 2008 (Chinese patent no. 200710072350.9) and the SDM Mach-Zehnder cascade fiber interferometer and its measurement method (Chinese patent no. ZL 200810136824.6) are primarily used to solve the problem of damage resistance in the deployment of fiber sensor arrays. The applicant published afiber Mach-Zehnder and a Michelson interferometer array combined measurer (Chinese patent no. ZL 200810136819.5), and a twin array Michelson fiber white light interferometry strain gauge (Chinese patent no. ZL 200810136820.8), which are designed to solve the problem of temperature interfering measurement and simultaneous measurement of temperature and strain in white light fiber interferometer multiplexing. The applicant published a simplified multiplexing white light interferometric fiber sensing demodulation device (Chinese patent no. ZL 200810136826.5) and a distributed fiber white light interferometric sensor array based on a tunable Fabry-Perot resonant cavity (Chinese patent no. ZL 200810136833.5), which introduces circular cavity and
F-P cavity optical path autocorrelators to simplify the topology of multiplexed interferometers,
constructing common optical paths, and improving temperature stability. The applicant also
published a dual reference length low coherence fiber circular network sensing demodulator
(Chinese patent application no. 200810136821.2) that introduces a 4x4 fiber coupler optical path
autocorrelator, intended to solve the problem of simultaneous measurement of multiple reference
sensors.
[0007] However, in the aforementioned SDM based interferometer structures, which has a large
power attenuation and a low light source utilization, only a small portion of the signal light
generated by the light source reaches the sensor array and is received by the detector to form an
interference signal. In the optical path structure published by W.V.Sorin, when the light signal
reflected by the sensor array passes through the fiber coupler 1, only half of the light enters the
Michelson autocorrelator, and the other half of light is lost along the optical path connected to
the light source. In addition, the light entering the Michelson autocorrelator is reflected by the
mirror, when passing through the coupler 2, only half of the light enters the photodetector, and
the other half feeds back into the coupler 1. Therefore, only about 1/4 of the light source power
contributes to the sensing process. Also, the light feedback passing coupler 1 enters the light
source, although the type of light source used is broad spectrum light, it is not very sensitive to
feedback compared to a laser light source. However, excessive signal power feedback, especially
for sources with large spontaneous radiation gain such as SLDs and ASEs, the feedback light will
cause a rather loud noise of the light source.
[0008] The purpose of the present invention is to provide a simple structured, easy operated
distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator.
[0009] The purpose of the invention is achieved by the followings:
[0010] A distributed fiber strain measurement system based on an adjustable-cavity-length F-P
white light interferometric demodulator, it comprises a broad spectrum light source 1, a four-port
fiber circulator 2, a fiber coupler with dual-port connections 3, an adjustable-cavity-length F-P
white light interferometric demodulator 4, a three-port fiber circulator 5, a first transmission fiber
6 and a second transmission fiber 7, a first fiber sensor array 8 and a second fiber sensor array 9,
a first photodetection signal amplifier 10 and a second photodetection signal amplifier 11, and a
first signal processing unit 12 and a second signal processing unit 13. The light emitted from the
broad spectrum light source 1 is injected into the adjustable-cavity-length F-P white light
interferometric demodulator 4 via the fiber coupler 3 after passing the four-port fiber circulator
2. The adjustable-cavity-length F-P white light interferometric demodulator generates two
interrogation light signals with adjustable optical path, which pass the three-port fiber circulator
and the four-port fiber circulator, respectively, then fed into the first fiber sensor array 8 and the
second fiber sensor array 9 via the first transmission fiber 6 and the second transmission fiber 7.
The interference signal light reflected by the first fiber sensor array 8 passes the first
transmission fiber 6 again, then it is picked up and amplified by the first photodetection signal
amplifier 10 via the three-port fiber circulator 5. Finally the signal is being processed by the first
signal processing unit 12 and a measurement result is provided. The interference signal light
reflected by the second fiber sensor array 9 passes the second transmission fiber 7 again, then it
is picked up and amplified by the second photodetection signal amplifier 11 via the four-port
fiber circulator 2. Finally the signal is being processed by the second signal processing unit 13
and a measurement result is provided.
[0011] The adjustable-cavity-length F-P white light interferometric demodulator couples and
connects a Sagnac circular optical path structure with an F-Pfiber interferometer with adjustable cavity length via two dual-port 2x2 fibers, respectively. The F-P fiber interferometer consists of an optical fiber coated with a total reflector 42 at one end and afiber selfoc lens collimator 43 connected at the other end. The fiber selfoc lens collimator is fixed on the base of a precise sliding platform and a planar optical mirror 44 is fixed on the sliding platform facing the fiber selfoc lens collimator, constructing an F-P interferometer with an adjustable optical path.
[0012] The fiber sensor array is constituted of basic fiber sensor arrays, the fiber sensor array is constituted of multiple fiber sensors connected from beginning to the end, and each fiber sensor is constituted of single-mode fiber of any lengths. A fiber sensor array is a series of single-mode fiber segments of varying lengths that form a serial array connected from beginnings to ends, or adding a strobe connection for a 1xM multiplex fiber switch constructs the M fiber sensor array into a roving array of M linear fiber sensor array, or a bus type fiber sensing network topology, a star fiber sensing network topology, and a composite star fiber sensing network topology via 1xN star fiber couplers, where N = 2, 3, 4....
[0013] The present invention has the following advantages:
[0014] The present invention discloses a low coherent multiplexing distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator. It can be used for real-time monitoring and measurement of physical quantities such as multipoint quasi-distributed strain or quasi-temperature distribution, and can be widely used in the health monitoring of large, intelligent structures. It uses a Sagnac fiber structure to connect an F-P interferometer with adjustable cavity length as a demodulation interferometer to the optical path of the system. By using two fiber circulators to connect the fiber sensor array and photodetector, all the reflected signals from the fiber sensor are coupled to the photodetector. Compared with the previous technology, the use of the fiber circulators eliminate the signal feedback back to the light source, improve the stability of the light source, and enhance the utilization of the light source power, enabling all the light emitted by the light source to be utilized, and further improve the multiplexing capability of the sensing system.
[0015] FIG. 1 is a schematic diagram of the structure of a low coherent multiplexing distributed
fiber strain measurement system based on an adjustable-cavity-length F-P white light
interferometric demodulator.
[0016] FIG. 2 is a schematic diagram of the structure of an adjustable-cavity-length F-P white
light interferometric demodulator.
[0017] FIG. 3 (a) is the schematic diagram of the structure of the topology of a linear array fiber
sensor network, while FIG. 3(b) is a schematic diagram of the topology of a switch-type parallel
linear array fiber sensor network.
[0018] FIG. 4 is a schematic diagram of the structure of the topology of a fiber strain sensor
array network.
[0019] FIG. 5 is a schematic diagram of an embodiment of a low coherent multiplexing
distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light
interferometric demodulator, where both the fiber sensor arrays are using simple linear arrays.
[0020] The invention is further described below in conjunction with the embodiments:
[0021] The invention proposes a distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator. Its characteristic is: it comprises a broad spectrum light source 1, a four-port fiber circulator 2, a fiber coupler with dual-port connections 3, an adjustable-cavity-length F-P white light interferometric demodulator 4, a three-port fiber circulator 5, transmission fibers 6 and 7, fiber sensor arrays 8 and 9, photodetection signal amplifiers 10 and 11, and signal processing units 12 and 13. The invention can be used for real-time monitoring and measurement of physical quantities such as multipoint quasi-distributed strain or quasi-temperature distribution, which can be widely used in areas such as large scale health monitoring of smart structures.
[0022] FIG. 1 is a schematic diagram of the structure of a low coherent multiplexing distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator. It comprises a broad spectrum light source 1, a four-port fiber circulator 2, a fiber coupler with dual-port connections 3, an adjustable-cavity-length F-P white light interferometric demodulator 4, a three-port fiber circulator 5, transmission fibers 6 and 7, fiber sensor arrays 8 and 9, photodetection signal amplifiers 10 and 11, and signal processing units 12 and 13.
[0023] FIG. 2 is a schematic diagram of the structure of an adjustable-cavity-length F-P white light interferometric demodulator. The adjustable-cavity-length F-P white light interferometric demodulator couples and connects a Sagnac circular optical path structure with an F-P fiber interferometer with adjustable cavity length via two dual-port 2x2 fibers 3 and 41, respectively. The F-P fiber interferometer consists of an optical fiber coated with a total reflector 42 at one end and a fiber selfoc lens collimator 43 connected at the other end. The fiber collimator 43 is fixed on the base of a precise sliding platform and a planar optical mirror 44 is fixed on the sliding platform facing the fiber collimator 43, constructing an F-P interferometer with an adjustable optical path.
[0024] FIG. 3 (a) is the schematic diagram of the structure of the topology of a linear array fiber sensor network, while FIG. 3(b) is a schematic diagram of the topology of a switch-type parallel linear array fiber sensor network.
[0025] FIG. 4 is a schematic diagram of the structure of the topology of a fiber strain sensor array network. The fiber sensor network used in the system is constituted of basic fiber sensor arrays, the fiber sensor array is constituted of multiple fiber sensors connected from beginning to the end, and each fiber sensor is constituted of single-mode fiber of any lengths with fiber ferrules on both ends. Form a series of single-mode fiber segments of varying lengths into a serial array connected from beginnings to end and uses the 1xN (N = 2, 3, 4...) star fiber couplers, to form a linear array fiber sensing network topology as shown in the figure, a bus type fiber sensing network topology, a star fiber sensing network topology, and a composite star fiber sensing network topology.
[0026] FIG. 5 is a schematic diagram of an embodiment of a low coherent multiplexing distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light interferometric demodulator, where both the fiber sensor arrays are using simple linear arrays. In the figure, 8 and 9 are the linear fiber sensor arrays.
[0027] The quasi-distributed fiber strain measurement system comprises a broad spectrum light source 1, a four-port fiber circulator 2, a fiber coupler with dual-port connections 3, an adjustable-cavity-length F-P white light interferometric demodulator 4, a three-port fiber circulator 5, transmission fibers 6 and 7, fiber sensor arrays 8 and 9, photodetection signal amplifiers 10 and 11, and signal processing units 12 and 13. In the system, the light emitted from the broad spectrum light source 1 is injected into the adjustable-cavity-length F-P white light interferometric demodulator 4 via the dual-port fiber coupler 3 after passing the four-port fiber circulator 2. The interferometric demodulator generates two interrogation light signals with adjustable optical path, which pass the three-port fiber circulator 5 and the four-port fiber circulator 2, respectively, then fed into the fiber sensor arrays 8 and 9 via the transmission fibers
6 and 7. The interference signal light reflected by the sensor array 8 passes the transmission fiber
6 again, then it is picked up and amplified by the photodetection signal amplifier 10 via the
three-port fiber circulator 5. Finally the signal is being processed by the signal processing unit 12
and a measurement result is provided. In the meantime, the interference signal light reflected by
the fiber sensor array 9 passes the transmission fiber 7 again, then it is picked up and amplified
by the photodetection signal amplifier 11 via the four-port fiber circulator 2. Finally the signal is
being processed by the signal processing unit 13 and a measurement result is provided.
[0028] Since the fiber sensor array is formed by N segments offibers in series connected from
beginning to end, it forms a sensor array consisting of N fiber sensors. The length of each
sensing fiber is 11, 12, ..., IN, which is close to the length of the two optical path difference Lo generated in the adjustable-cavity-length F-P white light interferometric demodulator, each fiber
has a different length, and satisfies the following relationship:
nL0 +X1 =nlj , j =1, 2,...N (1)
[0029] In the formula, n is the refractive index of the fiber core, and there is li # lj, and thus Xi#
Xj, that is, each sensor corresponds to its own independent spatial position. When a distributed
strain is applied to the sensing fiber, the length of each sensor changes from 11 to 1 1+A11, 12 to
1 2 +Al 2 , ..., and IN to IN+AIN, respectively, then the distributed strain is obtained as follows
_ A/ A/ 2 AIN (2) 1 2 N
[0030] By repeatedly scanning the optical path changes, for any ith sensor, the average strain across each fiber can be measured by measuring the change Al, = in the sensor length li n' divided by the known length li.
[0031] To realize the adjustment of optical path difference and the matching of scanning, the
invention constructed a F-P white light interferometric demodulator with adjustable cavity
length, as shown in FIG. 2. The white light interferometric demodulator couples and connects a
Sagnac circular optical path structure with an F-P fiber interferometer with adjustable cavity
length via two dual-port 2x2 fibers, respectively. In which, the F-P fiber interferometer consists
of an optical fiber coated with a total reflector 42 at one end and a fiber selfoc lens collimator 43
connected at the other end. The fiber selfoc lens collimator 43 is fixed on the base of a precise
sliding platform and a planar optical mirror 44 is fixed on the sliding platform facing the fiber
selfoc lens collimator 43, constructing an F-P interferometer with an adjustable optical path. The
white light interferometric demodulator serves two purposes, one is to divide the incident beam
into two paths with a certain optical path difference, and the other is to adjust the cavity length of
the F-P interferometer by moving the optical mirror, thereby changing the optical path difference
between the two optical signals and achieving a matching measurement of the optical path
change of each fiber sensor in thefiber sensor array.
[0032] To further expand the number of fiber sensors, the present invention may also increase the
number of fiber sensing arrays to M arrays in the system shown in FIG. 1, such that the fiber
sensing system may add a gated connection of a 1xM multipath fiber, which will construct an
NxM fiber sensor matrix with M fiber sensor arrays containing N fiber sensors per row, as shown
in FIG. 3.
[0033] In order to meet various sensing measurement needs, the demodulation system used in the
present invention is capable of adapting to various fiber sensing network configurations. We
know that a fiber sensing network consists of a basic fiber sensor array consisting of a number of fiber sensors connected in series at the beginning and end, each fiber sensor consists of a single mode fiber of any length with fiber ferrules at both ends. A series of single-mode fiber segments of varying lengths are connected together to form a serial array, and a 1xN (N = 2, 3, 4...) star fiber coupler can be used to form a bus type fiber sensing network topology, a star fiber sensing network topology, and a composite star fiber sensing network topology as shown in FIG. 4.
[0034] FIG. 5 is a schematic diagram of an embodiment of a low coherent multiplexing
distributed fiber strain measurement system based on an adjustable-cavity-length F-P white light
interferometric demodulator. The system comprises a broad spectrum light source 1, a four-port
fiber circulator 2, a fiber coupler with dual-port connections 3, an adjustable-cavity-length F-P
white light interferometric demodulator 4, a three-port fiber circulator 5, transmission fibers 6
and 7, fiber sensor arrays 8 and 9, photodetection signal amplifiers 10 and 11, and signal
processing units 12 and 13. The light emitted from the broad spectrum light source 1 is injected
into the adjustable-cavity-length F-P white light interferometric demodulator 4 via the fiber
coupler 3 after passing the four-port fiber circulator 2. The interferometric demodulator
generates two interrogation light signals with adjustable optical path, which pass the three-port
fiber circulator 5 and the four-port fiber circulator 2, respectively, then fed into the fiber sensor
arrays 8 and 9 via the transmission fibers 6 and 7. The interference signal light reflected by the
fiber sensor array 8 passes the transmission fiber 6 again, then it is picked up and amplified by
the photodetection signal amplifier 10 via the three-port fiber circulator 5. Finally the signal is
being processed by the signal processing unit 12 and a measurement result is provided. In the
meantime, the interference signal light reflected by the fiber sensor array 9 passes the
transmission fiber 7 again, then it is picked up and amplified by the photodetection signal
amplifier 11 via the four-port fiber circulator 2. Finally the signal is being processed by the
signal processing unit 13 and a measurement result is provided.
[0035] When the system is in operation, the F-P white light interferometric demodulator with
adjustable cavity length will scan and match each fiber sensor of different lengths by adjusting
the optical path difference and methods of scanning and matching. The white light interferometric demodulator has two functions, one is to split the incident light beam into two paths with a certain optical path difference, and the other is to adjust the cavity length of the F-P interferometer by moving the optical mirror, thereby changing the optical path difference between the two light signals to match and measure the optical path change of each fiber sensor in the fiber sensor array.
[0036] In the system, 8 and 9 are two simple linear fiber sensor arrays, each fiber sensor array is composed of a series of standard single-mode fiber cut into fiber segments of approximately equal length to be cascaded, in which the length of each fiber is different Li#Lji, j= 1, 2, ... , N, then each segment of the fiber can be seen as an independent optical fiber deformation measurement instrument, which forms a quasi-distributed fiber measurement system, as shown in FIG. 5. The system can be used for quasi-distributed strain measurements as well as for implementing quasi-distributed temperature measurements. It can be widely used in the field of intelligent structural health monitoring in civil engineering.
Claims (3)
1. A distributed fiber strain measurement system based on an adjustable-cavity-length F-P
white light interferometric demodulator, it comprises a broad spectrum light source (1), a four
port fiber circulator (2), a fiber coupler with dual-port connections (3), an adjustable-cavity
length F-P white light interferometric demodulator (4), a three-port fiber circulator (5), a first
transmission fiber (6) and a second transmission fiber (7), a first fiber sensor array (8) and a
second fiber sensor array (9), a first photodetection signal amplifier (10) and a second
photodetection signal amplifier (11), and a first signal processing unit (12) and a second signal
processing unit (13). Its characteristic is: the light emitted from the broad spectrum light source
(1) is injected into the adjustable-cavity-length F-P white light interferometric demodulator (4)
via the fiber coupler (3) after passing the four-portfiber circulator (2). The adjustable-cavity
length F-P white light interferometric demodulator generates two interrogation light signals with
adjustable optical path, which pass the three-port fiber circulator and the four-portfiber
circulator, respectively, then fed into the first fiber sensor array (8) and the second fiber sensor
array (9) via the first transmission fiber (6) and the second transmission fiber (7). The
interference signal light reflected by the first fiber sensor array (8) passes the first transmission
fiber (6) again, then it is picked up and amplified by thefirst photodetection signal amplifier (10)
via the three-port fiber circulator (5). Finally the signal is being processed by the first signal
processing unit (12) and a measurement result is provided. The interference signal light reflected
by the second fiber sensor array (9) passes the second transmission fiber (7) again, then it is
picked up and amplified by the second photodetection signal amplifier (11) via the four-port
fiber circulator (2). Finally the signal is being processed by the second signal processing unit
(13) and a measurement result is provided.
2. As claimed in claim 1, a distributed fiber strain measurement system based on an
adjustable-cavity-length F-P white light interferometric demodulator, its characteristic is that: the
adjustable-cavity-length F-P white light interferometric demodulator couples and connects a
Sagnac circular optical path structure with an F-P fiber interferometer with adjustable cavity length via two dual-port 2x2 fibers, respectively. The F-P fiber interferometer consists of an optical fiber coated with a total reflector (42) at one end and afiber selfoc lens collimator (43) connected at the other end. The fiber selfoc lens collimator is fixed on the base of a precise sliding platform and a planar optical mirror (44) is fixed on the sliding platform facing the fiber selfoc lens collimator, constructing an F-P interferometer with an adjustable optical path.
3. As claimed in claim 1, a distributed fiber strain measurement system based on an
adjustable-cavity-length F-P white light interferometric demodulator, its characteristic is: the
fiber sensor array is constituted of basic fiber sensor arrays, the fiber sensor array is constituted
of multiple fiber sensors connected from beginning to the end, and each fiber sensor is
constituted of single-mode fiber of any lengths. A fiber sensor array is a series of single-mode
fiber segments of varying lengths that form a serial array connected from beginnings to ends, or
adding a strobe connection for a 1xM multiplex fiber switch constructs the M fiber sensor array
into a roving array of M linear fiber sensor array, or a bus typefiber sensing network topology, a
star fiber sensing network topology, and a composite star fiber sensing network topology via 1xN
star fiber couplers, where N = 2, 3, 4....
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114062275A (en) * | 2021-11-18 | 2022-02-18 | 国网安徽省电力有限公司电力科学研究院 | Spatial domain multiplexing demodulation instrument and method of optical fiber photoacoustic sensor |
| CN114111750A (en) * | 2021-11-15 | 2022-03-01 | 天津大学 | Method for expanding measurement range of white light interference system |
-
2020
- 2020-11-25 AU AU2020103661A patent/AU2020103661A4/en not_active Ceased
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114111750A (en) * | 2021-11-15 | 2022-03-01 | 天津大学 | Method for expanding measurement range of white light interference system |
| CN114111750B (en) * | 2021-11-15 | 2022-11-18 | 天津大学 | Method for expanding measurement range of white light interference system |
| CN114062275A (en) * | 2021-11-18 | 2022-02-18 | 国网安徽省电力有限公司电力科学研究院 | Spatial domain multiplexing demodulation instrument and method of optical fiber photoacoustic sensor |
| CN114062275B (en) * | 2021-11-18 | 2024-04-30 | 国网安徽省电力有限公司电力科学研究院 | Spatial domain multiplexing demodulation instrument and method for optical fiber photoacoustic sensor |
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