CN101122477A - Optical fibre grating digital demodulation method and system based on autocorrelation principle - Google Patents
Optical fibre grating digital demodulation method and system based on autocorrelation principle Download PDFInfo
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Abstract
The invention discloses a fiber grating digital demodulation method and system based on the autocorrelation principle. The invention solves the problems of present fiber grating sensor system demodulation technology of low measuring precision, poor real-time performance, insufficient reuse ability, high price, unsatisfied engineering practical needs, etc. The invention has the advantages of high measuring precision, fast scanning speed, good real-time performance, strong reuse ability, high performance-price ratio, strong utility, etc. The structure of the invention includes a light source and at least a fiber grating sensor. Through a coupling device, the light source is connected with the fiber grating sensors which are successively linked in series. At the same time, the coupling device also can be connected with a tunable filter, which is linked with a photoelectric detector. The photoelectric detector is successively connected with a preamplifier and a digital-analog converter. The digital-analog converter is connected with the input terminal of a digital controller. The output terminal of the digital controller is connected with the controlling input terminal of the tunable filter via an electromechanical controller and an electromechanical modulation system in turn.
Description
Technical Field
The invention relates to a fiber grating digital demodulation method and a system thereof based on an autocorrelation principle.
Background
The fiber grating sensor is a wavelength modulation type device, has compact structure and strong anti-interference capability, is convenient for forming a fiber sensing network by utilizing multiplexing (wavelength division, time division and space division) technology to carry out large-area multipoint measurement, has wide application prospect in many fields of communication, building, machinery, medical treatment, aerospace, navigation, mining industry and the like, and is greatly developed in recent years.
At present, the theoretical research on fiber grating sensing has achieved great success, the mature fiber grating manufacturing process has also enabled the fiber grating sensor to have small-batch production capability, and how to reduce the cost, perfect demodulation and multiplexing technology, and meet the requirement of high-precision application in engineering has become an urgent problem to be solved.
The fiber grating demodulation technology is a fiber grating wavelength drift high-resolution detection technology, and mainly aims to monitor the reflection spectrum of a sensing grating in real time, analyze the change of the encoding wavelength and convert the change into an electric signal for output, and the essence is the problem of resolution and measurement of different encoding lights in a beam of light. The ideal detection method should meet the following requirements:
(1) The measuring range is large and the resolution is high. In practical application, the detection range of the wavelength drift is often required to reach a nanometer level, the measurement resolution is sub-picometer to several picometers, namely, the dynamic measurement range is 1000: 1 to 100000: 1.
(2) The reusability is good. The fiber grating sensing system mainly comprises a light source, a fiber grating sensor and a demodulation system. By sharing the light source and the demodulation system, the cost of the fiber grating sensing system is greatly reduced along with the increase of the number of the multiplexing sensors, so that the cost of the whole system is reduced.
(3) The real-time performance is good. In order to meet the requirement of real-time signal monitoring in engineering, a demodulation system is required to have a high demodulation rate so as to track the change of a detected signal in time.
(4) The universality is strong. In order to meet the requirements of fiber grating sensing systems of different scales, the demodulation system is required to be capable of adapting to the measurement system formed by fiber grating sensors of different wavelengths and different quantities, namely, the demodulation system has universality independent of a specific fiber grating sensor.
At present, the technology has been extensively and deeply studied at home and abroad, and many demodulation schemes have been proposed from different aspects, but the common methods are mainly a filtering method, an interference method and a tunable light source scanning method, as shown in the attached table 1. In comparison, the research in the aspect is more mature abroad, and the technology and the product are advanced; while the country is still in the research and development stage, and the corresponding products mainly depend on imports, so advanced technologies and products with independent property rights are urgently needed.
TABLE 1 comparison of Primary demodulation technique Performance
| Demodulation method | Measuring range | Resolution ratio | Reusability | Real time property | Cost performance ratio | General applicability | |
| Filtering method | Edge filtering method | Narrow in width | AIn general terms | Difference (D) | Good taste | Is low with | Difference between |
| Tunable filtering method | Width of | In general | In general | In general | In general terms | Good taste | |
| Interference method | In general | Height of | In general | Good, but not suitable for static measurements | Is low in | In general | |
| Tunable light source scanning method | In general | Height of | Good taste | In general | High (a) | Good taste | |
As can be seen from the attached table 1, the existing demodulation method has complex technology, low cost performance and is difficult to accept in the common field; or the real-time performance is poor, the resolution ratio is low, and the requirements of engineering measurement are difficult to adapt, so that the requirements of practical application cannot be completely met. In particular, the drawbacks of the prior art are mainly manifested in the following aspects:
(1) The problem of high-resolution detection under a strong noise background is difficult to solve. In the fiber grating sensing system, the spectral width of the sensing grating is only 0.07-0.6 nm, and the reflected signal light energy is only a very tiny part of the system light source, so that a demodulation device is required to have a high signal-to-noise ratio to ensure the resolution required by the system. However, most of the existing demodulation technologies adopt a light intensity detection method, and the problem of high-resolution detection under a strong noise background is difficult to solve.
(2) The number of multiplexing sensors is limited, and the scale of a sensing network is difficult to adapt to actual requirements. By sharing the light source and the demodulation system, the cost of the fiber grating sensing system is greatly reduced along with the increase of the number of the multiplexing sensors, and therefore the fiber grating sensing system has the advantages over the traditional electromechanical sensing system. However, the existing demodulation technology only supports 20-40 multiplexing sensors, the multiplexing capability of the fiber grating sensing network is very limited, and the scale requirement of large and complex monitoring targets cannot be met.
(3) The real-time detection problem is difficult to solve. Real-time detection requires that a demodulation system has a relatively high signal demodulation rate, and can well measure both static signals and dynamic signals, while the prior art cannot simultaneously meet the requirements of the two aspects. This is also a bottleneck that limits the entry of fiber grating sensing systems into engineering applications.
Disclosure of Invention
The invention aims to solve the problems that the conventional demodulation technology of the fiber grating sensing system is low in measurement precision, poor in real-time performance, insufficient in multiplexing capability, high in price, incapable of meeting the actual requirements of engineering and the like, and provides a fiber grating digital demodulation method and a system based on an autocorrelation principle, which have the advantages of high measurement precision, high scanning speed, good real-time performance, strong multiplexing capability, high cost performance, strong universality and the like.
In order to achieve the purpose, the invention adopts the following technical scheme:
a fiber grating digital demodulation system based on the autocorrelation principle comprises a light source and at least one fiber grating sensor, wherein the light source is connected with the fiber grating sensors which are sequentially connected in series through a coupling device, the coupling device is also connected with a tunable filter, the tunable filter is connected with a photoelectric detector, the photoelectric detector is sequentially connected with a preamplifier and a digital-to-analog converter, and the digital-to-analog converter is connected with the input end of a digital controller; the output end of the digital controller is connected with the control input end of the tunable filter through the electromechanical controller and the electromechanical modulation system in sequence.
The system obtains a required demodulation result through a digital processing method based on the autocorrelation analysis of the measurement signal; the coupling device is a 2 x 2 coupler, and the light source is a broadband light source; the tunable filter is a device with adjustable central wavelength, such as a Bragg grating, a long-period grating, an F-P cavity and the like; the fiber grating sensor is any wavelength modulation type grating sensor, such as a Bragg grating sensor, a long-period grating sensor and the like, the shapes of spectral lines of the grating sensors at different measuring points can be the same or different, and the measuring ranges can be overlapped or not overlapped; the digital controller is a controller which takes a DSP or FPGA or ARM chip as a core.
A fiber grating digital demodulation method based on the autocorrelation principle comprises the following steps,
1) Light emitted by the broadband light source enters the fiber bragg grating sensing array through the coupler, and enters the tunable filter after being reflected;
2) Under the action of an electromechanical modulation system, a tunable filter modulates the reflected light of a sensing grating containing measurement information into a signal which changes along with a time period, and then the signal is sent to a photoelectric detector for photoelectric conversion to obtain a time signal sequence with the period change;
3) The sequence signal is pre-amplified, converted to digital and analog, and then sent to a digital signal processor for operation to obtain the fiber grating wavelength drift amount to be measured, so as to achieve the purpose of demodulation.
In the step 1), the reflection spectrum or the transmission spectrum of the fiber grating sensor and the tunable filter are both Gaussian distribution, that is to say
In the formula, λ S Is the center wavelength of the fiber grating, B S Is its half high bandwidth, R S Is the reflectivity of the center wavelength, λ M Is the center wavelength of the tunable filter, B M Is its half high bandwidth, R M Is the reflectance of the center wavelength.
In the step 2), during single-point demodulation, the time signal sequence of the periodic variation entering the photodetector is as follows:
in the above formula, I 0 、R S 、B S 、R M 、B M Are all time invariant system constants, and λ S And λ M Is over timeFunction of change, wherein S The change with time reflects the change of the measured physical quantity with time, namely the quantity to be measured, and lambda M The variation with time is set by the variation law of the electromechanical modulation system, and is generally linear, that is to say
λ M ＝λ M0 +K M t
In the formula of M0 The initial center wavelength of the tunable filter corresponds to the lower limit of measurement; k M Is the scan rate; t is an element of [0, T ∈ []And T is a scanning period.
In the step 3), during single-point demodulation, the wavelength drift amount of the fiber bragg grating is as follows:
according to the relation formula of P in two adjacent scanning periods
P K (t)＝K S exp{-a 2 [λ S (KT)-λ M0 -K M t] 2 }
P K+1 (t)＝K S exp{-a 2 [λ S (KT+T)-λ M0 -K M t] 2 Is provided with
In the formula
Is a system constant, λ S (KT) denotes the center wavelength, λ, of the measurement grating in the Kth scanning period S And (KT + T) represents the central wavelength of the measurement grating in the K +1 th scanning period, and the central wavelength of the measurement grating cannot change in the same scanning period.
The above formula shows that the self-correlation of the output signal of the photoelectric detector is used for measuring the shift variation lambda of the central wavelength of the grating S K -λ S K+1 The autocorrelation function J = P is calculated from the measured time series K+1 (t)*P K (t), the increment of the central wavelength drift of the measured grating can be calculated
Further obtain the central wavelength drift of the measured grating
The purpose of demodulation is achieved.
In the step 1), during multi-point demodulation, the signal entering the photoelectric detector PD is
Wherein i =1,2, \8230, N is the number of multiplexed sensing gratings in the measuring system, and λ Si 、B Si 、R Si Then the reflectivity at the center wavelength, half-height bandwidth, and center wavelength of the ith sensing grating.
In the step 3), during multi-point demodulation, the convolution of the signals in two adjacent scanning periods is used to determine the autocorrelation function as
Where τ ∈ [0, t), let τ take different values, the following system of equations can be obtained:
solving the equation system can obtain the increment of the central wavelength drift of the N sensing gratings:
further obtaining the central wavelength drift of each sensing grating
The purpose of demodulation is achieved.
The demodulation method of the invention has the advantages that: the fiber grating autocorrelation digital demodulation method is a universal novel digital demodulation method based on time sequence analysis, can realize high-resolution multipoint fast demodulation of dynamic and static parameters by means of strong signal processing capacity of a modern digital processing system, and has low cost and strong universality. Specifically, the following points are mainly included:
(1) The measurement resolution is high, and high-precision measurement can be realized under the background of strong noise. Different from the prior art, the demodulation technology is based on the autocorrelation operation of the signal, and the measurement precision completely depends on the operational capability of the signal processor, so that the result with the measurement precision far higher than that of the prior demodulation technology can be obtained under the condition of low signal-to-noise ratio.
(2) The reusability is good. Different from the prior art, the demodulation technology of the invention obtains the wavelength drift of the multiplexing sensor by comparing the waveform changes of the modulation signals in adjacent periods, so that when in multiplexing, spectral lines of multiplexing sensors with different measuring points are allowed to have the same shape (for example, different measuring point sensors are allowed to have the same central wavelength), and the multiplexing sensors with different measuring points are also allowed to have the same wavelength change range (for example, 1550nm-1555 nm), thereby greatly improving the multiplexing capability of the system. Theoretically, the number of multiplexing sensors of the demodulation technology can be unlimited, and the demodulation technology is limited by the construction mode of a light network and the operational capability of a digital signal processor in practical application.
(3) The real-time performance is good. Different from the prior art which can only track signals of a few Hz to dozens Hz, the demodulation technology of the invention adopts a soft measurement method, has fast demodulation speed, can track signals of kilohertz magnitude and can completely meet the requirement of real-time monitoring.
(4) The cost performance is high. The prior art has a strong dependence on specific optics, which is largely imported and therefore costly. The demodulation technology of the invention adopts a digital method, thereby reducing the dependency on optical devices to a certain extent, effectively reducing the system cost and improving the cost performance of the system.
(5) The universality is strong. Different from the prior art, the demodulation technology only requires that the reflected signal can be received by the photoelectric detector when in use, and does not need the system to provide a measurement reference, so that the demodulation technology has no special requirements on parameters such as the central wavelength of the grating sensor, the wavelength interval of adjacent sensors and the like, has stronger universality and is easy for engineering application.
Drawings
FIG. 1 is a schematic diagram of a fiber grating sensor transmission demodulation system according to the present invention;
FIG. 2 is a schematic diagram of a fiber grating sensor reflection demodulation system according to the present invention;
FIG. 3 is a waveform diagram of a signal received by the photodetector during a Kth scanning period;
FIG. 4 is a waveform diagram of signals received by the photodetector during the K +1 th scanning period;
FIG. 5 is a waveform diagram of the Kth signal received by the photodetector;
FIG. 6 is a waveform diagram of the K +1 signal received by the photodetector.
The system comprises a light source 1, a fiber grating sensor 2, a 3.2 multiplied by 2 coupler, a tunable filter 4, a photoelectric detector 5, a preamplifier 6, a digital-to-analog converter 7, a digital controller 8, an electromechanical controller 9 and an electromechanical modulation system 10.
Detailed Description
The invention is further described with reference to the following figures and examples.
In fig. 1 and fig. 2, the fiber grating autocorrelation digital demodulation system includes a broadband light source 1 and a plurality of fiber grating sensors 2 connected in series in sequence, the light source 1 is connected to the fiber grating sensors 2 through a 2 × 2 coupler 3, and the coupling device is also connected to a tunable filter 4, the tunable filter 4 is connected to a photodetector 5, the photodetector 5 is connected to a preamplifier 6 and a digital-to-analog converter 7 in sequence, and the digital-to-analog converter 7 is connected to an input end of a digital controller 8 using a DSP chip; the output end of the digital controller 8 is connected with the control input end of the tunable filter 4 through an electromechanical controller 9 and an electromechanical modulation system 10 in sequence. The tunable filter 4 can be a Bragg grating, a long-period grating, an F-P cavity and the like; the fiber grating sensor 2 may be a bragg grating sensor, a long period grating sensor, or the like. The system of the present invention may be used in both projection and reflection demodulation systems.
The demodulation method of the present invention is that,
light emitted by the broadband light source enters a Fiber Bragg Grating (FBG) sensing array through a 2 x 2 coupler, and enters the tunable filter after being reflected. Under the action of an electromechanical modulation system, the tunable filter modulates the reflected light of the sensing grating containing the measurement information into a signal which changes along with a time period, and then the signal is sent to a photoelectric detector for photoelectric conversion, so that a time signal sequence with the period change is obtained. The sequence signal is sent to a Digital Signal Processor (DSP) for operation after preamplification and digital-to-analog conversion (ADC), and the fiber bragg grating wavelength drift amount required to be measured is obtained, so that the purpose of demodulation is achieved.
For simplicity, consider the case of single point demodulation first.
It is assumed that the reflection spectra of the fiber grating sensor and the tunable filter are both Gaussian distribution, i.e.
In the formula, λ S Is the center wavelength of the fiber grating, B S Is its half high bandwidth, R S Is the reflectivity of the center wavelength, λ M Is the center wavelength of the tunable filter, B M Is its half high bandwidth, R M Is the reflectance of the center wavelength.
Then in the circuit shown in fig. 1, the signal that finally enters the photodetector PD is:
in the above formula, I 0 、R S 、B S 、R M 、B M Can be regarded as a time-invariant system constant, and S and λ M Is a function of time, wherein the time variation of λ S reflects the time variation of the measured physical quantity, which is the quantity to be measured, and λ M The variation with time being set by the law of variation of the electromechanical modulation system, generally linear, i.e.
λ M ＝λ M0 +K M t (4)
In the formula of lambda M0 The initial central wavelength of the tunable filter corresponds to the lower limit of measurement; k M Is the scan rate; t is an element of [0, T ∈ []And T is a scanning period.
Consider the relationship of P in two adjacent scan periods. The following two formulas are shown:
P K (t)＝K S exp{-a 2 [λ S (KT)-λ M0 -K M t] 2 }(5)
P K+1 (t)＝K S exp{-a 2 [λ S (KT+T)-λ M0 -K M t] 2 }(6)
in the formula
Is a system constant, λ S (KT) denotes the center wavelength, λ, of the measurement grating during the Kth scanning period S (KT + T) indicates the center wavelength of the measurement grating in the K +1 th scanning period. It should be noted that it is assumed here that the center wavelength of the measurement grating does not change within the same scanning period.
Convolution is carried out on the two formulas 5 and 6, namely
It can be seen that the autocorrelation of the output signal of the photodetector is the variation lambda of the shift of the central wavelength of the measurement grating S K -λ S K+1 So that its autocorrelation function J = P is simply calculated from the measured time series K+1 (t)*P K (t), the increment of the central wavelength drift of the measured grating can be calculated
Further obtain the central wavelength drift of the measured grating
The purpose of demodulation is achieved.
Next, consider the case of multi-point demodulation.
According to the principle of linear superposition, if there are multiple sensing gratings in the measurement system shown in FIG. 1, the signal entering the photodetector PD is
Wherein i =1,2, \8230, N is the number of multiplexed sensing gratings in the measuring system, and λ Si 、B Si 、R Si It is the reflectivity at the center wavelength, half-height bandwidth, and center wavelength of the ith sensing grating.
Also convolving the signals in two adjacent scanning periods, having
Wherein tau is 0, T). If τ is taken to be a different value, the following system of equations can be obtained:
solving the equation system can obtain the increment of the central wavelength drift of the N sensing gratings:
further obtaining the central wavelength drift of each sensing grating
Demodulation examples
In the system shown in fig. 1, it is assumed that the wavelength tuning range of the tunable filter is 1550-1560nm, the half-height bandwidth is 0.1nm, the scanning period is 1s, and the scanning rate is 10nm/s. Also for simplicity, it is assumed that there are only two multiplexed sensors FBG1 and FBG2 in the system.
(1) The first condition is as follows: the central wavelengths of the multiplex sensors are different
Under the condition of neglecting noise, the initial central wavelength of the FBG1 is assumed to be 1552nm, and the half-height bandwidth is assumed to be 0.2nm; the initial center wavelength of FBG2 is 1553nm and the half-height bandwidth is 0.3nm. In the k-th scanning period, assuming that the external parameters are not changed, the signal received by the photodetector is as shown in fig. 3; in the k +1 th scanning period, assuming that the external parameter changes, the central wavelength of FBG1 becomes 1552.001nm and the central wavelength of FBG2 becomes 1552.999nm, the signal received by the photodetector at this time is as shown in fig. 4.
Respectively taking tau by adopting the method provided by the invention 1 ＝0.01s，τ 2 =0.02s, the convolution of two adjacent cycles is calculated according to equation (10), and the resulting nonlinear system of equations is solved, resulting in:
(2) Case two: the central wavelengths of the multiplexed sensors are the same
Under the condition of ignoring noise, the initial central wavelength of the FBG1 is assumed to be 1552nm, and the half-height bandwidth is assumed to be 0.2nm; the initial center wavelength of FBG2 is 1552nm and the half-height bandwidth is 0.3nm. In the k-th scanning period, assuming that the external parameters are not changed, the signal received by the photodetector is as shown in fig. 5; in the k +1 th scanning period, if the external parameters are changed, the central wavelength of FBG1 is 1552.001nm and the central wavelength of FBG2 is 1551.998nm, then the signal received by the photodetector at this time is as shown in fig. 6.
By adopting the method provided by the invention, tau is respectively taken 1 ＝0.01s，τ 2 =0.02s, the convolution of two adjacent cycles is calculated according to equation (10), and the nonlinear system of equations thus obtained is solved, resulting in:
(3) Case three: the change ranges of the central wavelengths of the multiplexing sensors have coincidence
Under the condition of ignoring noise, the initial central wavelength of the FBG1 is assumed to be 1552nm, and the half-height bandwidth is assumed to be 0.2nm; the initial center wavelength of FBG2 is 1552nm and the half-height bandwidth is 0.3nm. From the k-th scanning period, the change of the central wavelength of the sensor caused by the change of the external parameters is assumed as follows:
| scanning period | Center wavelength of 1# sensor | Center wavelength of 2# sensor |
| K | 1552.000 | 1552.000 |
| K+1 | 1552.001 | 1551.998 |
| K+2 | 1552.002 | 1552.001 |
| K+3 | 1552.003 | 1552.000 |
| K+4 | 1552.001 | 1551.999 |
| K+5 | 1551.999 | 1552.000 |
| K+6 | 1551.997 | 1551.998 |
By adopting the method provided by the invention, tau is respectively taken 1 ＝0.01s，τ 2 And =0.02s, the demodulated changes of the central wavelength of the sensor are as follows in sequence:
| |
1# |
2# sensor center wavelength |
| K | 1552.000 | 1552.000 |
| K+1 | 1552.001 | 1551.984 |
| K+2 | 1552.002 | 1551.983 |
| K+3 | 1552.002 | 1552.000 |
| K+4 | 1552.001 | 1551.982 |
| K+5 | 1552.988 | 1551.998 |
| K+6 | 1551.979 | 1551.989 |
Claims (8)
1. A fiber grating digital demodulation system based on the autocorrelation principle comprises a light source (1) and at least one fiber grating sensor (2), and is characterized in that: the light source (1) is connected with the fiber grating sensors (2) which are sequentially connected in series through a coupling device, the coupling device is also connected with a tunable filter (4), the tunable filter (4) is connected with a photoelectric detector (5), the photoelectric detector (5) is sequentially connected with a preamplifier (6) and a digital-to-analog converter (7), and the digital-to-analog converter (7) is connected with the input end of a digital controller (8); the output end of the digital controller (8) is connected with the control input end of the tunable filter (4) through the electromechanical controller (9) and the electromechanical modulation system (10) in sequence.
2. The fiber grating digital demodulation system based on the autocorrelation principle as claimed in claim 1, wherein: the system obtains a required demodulation result through a digital processing method based on the autocorrelation analysis of the measurement signal; the coupling device is a 2 x 2 coupler, and the light source (1) is a broadband light source; the tunable filter (4) is a device with adjustable center wavelength; the fiber grating sensor (2) is a grating sensor of any wavelength modulation type, the shapes of the spectral lines of the grating sensors at different measuring points can be the same or different, and the measuring ranges can be overlapped or not overlapped; the digital controller (8) is a controller which is formed by taking a DSP or FPGA or ARM chip as a core.
3. A demodulation method of the fiber grating digital demodulation system based on the autocorrelation principle as claimed in claim 1, wherein: the method comprises the following steps of,
1) Light emitted by the broadband light source enters the fiber bragg grating sensing array through the coupler, and enters the tunable filter after being reflected;
2) Under the action of an electromechanical modulation system, a tunable filter modulates the reflected light of a sensing grating containing measurement information into a signal which changes along with a time period, and then the signal is sent to a photoelectric detector for photoelectric conversion to obtain a time signal sequence with the period change;
3) The sequence signal is pre-amplified, converted to digital and analog, and then sent to a digital signal processor for operation to obtain the fiber grating wavelength drift amount to be measured, so as to achieve the purpose of demodulation.
4. The demodulation method of the fiber grating autocorrelation digital demodulation system as claimed in claim 3, wherein: in the step 1), the reflection spectrum or the transmission spectrum of the fiber grating sensor and the tunable filter are both Gaussian distribution, that is to say
In the formula, λ S Is the center wavelength of the fiber grating, B S Is its half high bandwidth, R S Is the reflectivity of the center wavelength, λ M Is the center wavelength of the tunable filter, B M Is its half high bandwidth, R M Is the reflectance of the center wavelength.
5. The demodulation method of the fiber grating autocorrelation digital demodulation system as claimed in claim 3, wherein: in the step 2), the time signal sequence of the periodic variation entering the photoelectric detector is as follows:
in the above formula, I 0 、R S 、N S 、R M 、B M Are all time invariant system constants, and λ S And λ M Is a function over time, where S The change with time reflects the change of the measured physical quantity with time, namely the quantity to be measured, and lambda M The variation with time being set by the law of variation of the electromechanical modulation system, generally linear, i.e.
λ M ＝λ M0 +K M t
In the formula of M0 The initial center wavelength of the tunable filter corresponds to the lower limit of measurement; k M Is the scan rate; t is an element of [0, T ∈ []And T is a scanning period.
6. The demodulation method of the fiber grating autocorrelation digital demodulation system as claimed in claim 3, wherein: in the step 3), during single-point demodulation, the wavelength drift amount of the fiber bragg grating is as follows:
according to the relation of P in two adjacent scanning periods
P K (t)＝K S exp{-a 2 [λ S (KT)-λ M0 -K M t] 2 }
P K+1 (t)＝K S exp{-a 2 [λ S (KT+T)-λ M0 -K M t] 2 }
Is provided with
In the formula
Is a system constant, λ S (KT) denotes the center wavelength, λ, of the measurement grating in the Kth scanning period S (KT + T) represents the central wavelength of the measurement grating in the K +1 th scanning period, and the central wavelength of the measurement grating cannot change in the same scanning period;
the output signal of the photoelectric detector is self-correlated by measuring the shift variation lambda of the central wavelength of the grating S K -λ S K+1 Can calculate the increment of the central wavelength drift of the measured grating according to the function (b)Further obtain the central wavelength drift of the measured grating
The purpose of demodulation is achieved.
7. The demodulation method of the fiber grating autocorrelation digital demodulation system according to claim 3, wherein: in the step 1), during multi-point demodulation, the signal entering the photoelectric detector PD is
Wherein i =1,2, \8230, N is the number of multiplexed sensing gratings in the measuring system, and λ Si 、B Si 、R Si It is the reflectivity at the center wavelength, half-height bandwidth, and center wavelength of the ith sensing grating.
8. The demodulation method of the fiber grating autocorrelation digital demodulation system as claimed in claim 3, wherein: in the step 3), during multi-point demodulation, the convolution of the signals in two adjacent scanning periods is used to determine the autocorrelation function as
Where τ ∈ [0, t), let τ take different values, the following system of equations can be obtained:
by solving the equation set, the increment of the central wavelength drift of the N sensing gratings can be obtained:
further obtaining the central wavelength drift of each sensing grating
The purpose of demodulation is achieved.
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| CN101383677B (en) * | 2008-10-14 | 2013-03-27 | 山东大学 | Star type optical fiber grating sensing network based on CDMA multiplexing and demodulation method |
| CN104061875A (en) * | 2014-07-09 | 2014-09-24 | 中国科学院半导体研究所 | High-precision fiber bragg grating demodulation method based on Hilbert transformation and bispectrum estimation |
| CN105823497A (en) * | 2016-05-24 | 2016-08-03 | 北京信息科技大学 | Fiber grating reflection spectrum demodulation algorithm based on signal autocorrelation matching |
| CN108645431A (en) * | 2018-05-30 | 2018-10-12 | 西安工业大学 | A kind of fitting Peak Search Method for the long correlation demodulation of optical fiber Fabry-Perot sensor chamber |
| CN110412038A (en) * | 2019-07-17 | 2019-11-05 | 天津大学 | A kind of damage location identification of structures system based on single fibre grating and neural network |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| KR100351187B1 (en) * | 2000-11-07 | 2002-09-05 | 이호준 | an signal processing device of multi fiber bragg grating sensor using CDMA |
| CN1256570C (en) * | 2004-12-07 | 2006-05-17 | 天津大学 | Method for realizing multi-channel optical fibre raster sensor high-sensitivity measurement |
| CN100494909C (en) * | 2006-11-07 | 2009-06-03 | 武汉理工大学 | High speed optic fiber grating wavelength demodulating system |
| CN201075010Y (en) * | 2007-09-07 | 2008-06-18 | 李东升 | Optical fiber grating digital demodulation system based on self-correlation principle |
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Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101383677B (en) * | 2008-10-14 | 2013-03-27 | 山东大学 | Star type optical fiber grating sensing network based on CDMA multiplexing and demodulation method |
| CN104061875A (en) * | 2014-07-09 | 2014-09-24 | 中国科学院半导体研究所 | High-precision fiber bragg grating demodulation method based on Hilbert transformation and bispectrum estimation |
| CN104061875B (en) * | 2014-07-09 | 2017-03-08 | 中国科学院半导体研究所 | High precision optical fiber grating demodulation method based on Hilbert transform and bi-spectrum estimation |
| CN105823497A (en) * | 2016-05-24 | 2016-08-03 | 北京信息科技大学 | Fiber grating reflection spectrum demodulation algorithm based on signal autocorrelation matching |
| CN105823497B (en) * | 2016-05-24 | 2017-12-19 | 北京信息科技大学 | A kind of fiber grating reflection spectrum demodulating algorithm based on signal autocorrelation matching |
| CN108645431A (en) * | 2018-05-30 | 2018-10-12 | 西安工业大学 | A kind of fitting Peak Search Method for the long correlation demodulation of optical fiber Fabry-Perot sensor chamber |
| CN108645431B (en) * | 2018-05-30 | 2020-08-07 | 西安工业大学 | Fitting peak searching method for cavity length correlation demodulation of optical fiber Fabry-Perot sensor |
| CN110412038A (en) * | 2019-07-17 | 2019-11-05 | 天津大学 | A kind of damage location identification of structures system based on single fibre grating and neural network |
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