CN114598394B - Real-time compensation method for frequency modulation signal intensity error of OFDR system - Google Patents
Real-time compensation method for frequency modulation signal intensity error of OFDR system Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 22
- 238000002168 optical frequency-domain reflectometry Methods 0.000 title claims 7
- 230000003287 optical effect Effects 0.000 claims abstract description 17
- 238000009826 distribution Methods 0.000 claims description 6
- 230000009466 transformation Effects 0.000 claims description 3
- 238000005259 measurement Methods 0.000 abstract description 8
- 230000007274 generation of a signal involved in cell-cell signaling Effects 0.000 abstract description 7
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- 239000013307 optical fiber Substances 0.000 abstract description 5
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- 230000003321 amplification Effects 0.000 description 1
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- 238000002474 experimental method Methods 0.000 description 1
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical group [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/58—Compensation for non-linear transmitter output
- H04B10/588—Compensation for non-linear transmitter output in external modulation systems
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Abstract
The invention discloses a real-time compensation method for frequency modulation signal intensity errors of an Optical Frequency Domain Reflectometer (OFDR) system, and belongs to the field of optical fiber sensing. Comprising the following steps: A. collecting an OFDR system frequency modulation signal and extracting signal data according to a signal period; B. extracting the amplitude variation of each period of data; C. superposing the periodic data; D. downsampling by a moving average; E. linearly interpolating and downsampling again to make the final sampling point number consistent with the frequency modulation signal point number to obtain compensation quantity; F. the compensation quantity feedback control modulation signal generation unit is adopted to realize real-time compensation of the intensity error; G. and evaluating the compensation effect. The method aims at compensating the frequency modulation signal intensity error of the OFDR system by collecting the frequency modulation signal intensity information in real time and combining the method, effectively reduces the attenuation of the frequency modulation signal intensity along with the increase of frequency, improves the signal-to-noise ratio of the system, and further improves the measurement range, the measurement precision and the spatial resolution of the OFDR system.
Description
Technical Field
The invention relates to the field of optical fiber sensing, in particular to a real-time compensation method for the intensity error of a frequency modulation signal of an OFDR system.
Background
In recent years, with the development of internet and mobile communication technologies, internet of things technology for 'everything interconnection' has been attracting more and more attention. High-performance sensors, serving as a core sensing layer of the Internet of things, have increased market demands. The optical reflectometer is taken as an important component in the field of optical fiber sensing, can be used for realizing distributed sensing and is widely applied to an Internet of things system, and an Optical Frequency Domain Reflectometer (OFDR) technology is an indispensable part of the optical reflectometer with unique advantages.
The OFDR technology is based on frequency modulation continuous wave technology (FMCW), and adopts a frequency domain positioning mode, and is mainly divided into two types of incoherent detection and coherent detection. In the mainstream coherent detection method, a beam of linear sweep frequency light with high coherence property is generally divided into two paths, one path is used as measurement light to be injected into an optical fiber to be detected, the other path is used as reference light for coherent amplification, and the frequency of a radio frequency signal formed by the interference of the measurement light and the reference light is different through the difference of the arrival time of the Rayleigh scattering return light signal of the measurement light at different positions of the optical fiber, so that the position distinction is realized on a frequency domain.
One of the most important components in the OFDR system is a sweep frequency light source, and the performance of the sweep frequency light source directly determines the performance of the whole OFDR system. Swept optical sources typically have a linear sweep characteristic, i.e., the instantaneous frequency of the output optical signal varies linearly with time. The implementation method of the sweep frequency light comprises two modes of internal modulation and external modulation, wherein the internal modulation adopts a tunable laser, and the driving current or the temperature of the laser is changed to realize frequency modulation; the external modulation adopts a single-frequency laser, and the modulation signal loaded on the external optical modulation device is changed to realize frequency modulation.
The external modulation scheme avoids the use of expensive tunable lasers, has the advantage of low cost, and has wider application scenes. In the external modulation scheme, the performance of the modulation signal greatly influences the overall performance of the OFDR system, the attenuation of the intensity of the modulation signal to a certain extent along with the increase of frequency is one of unavoidable problems, the imbalance of the intensity reduces the signal to noise ratio of the system, and in order to realize the measurement of long distance and high spatial resolution, the compensation of the intensity error of the modulation signal is particularly important.
Disclosure of Invention
The invention aims to provide a real-time compensation method for the frequency modulation signal intensity error of an OFDR system, which aims at solving the problem that the intensity of a modulation signal is changed along with the frequency in the existing external modulation OFDR system.
The invention provides the following technical scheme:
a real-time compensation method for the intensity error of a frequency modulation signal of an OFDR system comprises the following steps:
A. an analog-to-digital converter is adopted to obtain frequency modulation signal data of an OFDR system, and the data is extracted into { signal } according to a signal period i } n Wherein, signal i Frequency modulation signal data representing the ith period, n represents the total number of periods, and n is more than 2;
B. the frequency modulation signal data of each period is subjected to Hilbert transformation to obtain amplitude information of each period, which is recorded as { envelope } i } n Wherein, envelope i Amplitude information representing the frequency modulated signal data of the i-th period;
C. since the noise in the amplitude information conforms to the Gaussian distribution and to the independent same distribution, the average value is 0, each inventlope i The addition can reduce the influence of noise and record The width of the existing endlope_mean is smaller than any endlope i And in an envelope i Is defined by a center of (a);
D. the running average downsampling is performed on the inventlope_mean: taking a sliding window with the window size of w, taking the average from the first point of the enavelope_mean to the w point of the first downsampling point, taking the average from the w-k/2 point of the enavelope_mean to the w-k+w/2 point of the kth downsampling point, and taking the average from the last point to the last w points of the enavelope_mean; the sampled point is recorded as an inventlope_down sample;
E. performing linear interpolation on the points of the inventlope_down sample, interpolating the points to m points according to the requirement, and downsampling the points actually required by the frequency modulation signal, wherein the points are marked as inventiope_compensation and are compensation reference quantities;
F. the original quantity { envelope ] of the frequency modulated signal i } n And taking the point of the invente_compensation as a reference, and performing feedback control on the frequency modulation signal generating unit to obtain a new compensated frequency modulation signal.
Preferably, the method further comprises the step G. The compensated frequency modulation signals are collected, and if the compensation requirement is not met, the steps A-G are repeated.
Preferably, the OFDR system adopts an external modulation method, the frequency modulation signal is used for modulating a single frequency signal into a linear sweep frequency signal, and the modulated signal is used as a driving signal to be loaded on an external light modulation device to realize scanning of optical frequency, so that frequency modulation continuous wave ranging is realized.
Preferably, the frequency modulation signal generating unit consists of an FPGA and a DDS, and the control of the intensity of the frequency modulation signal is realized by adjusting the amplitude of the output signal of the DDS in real time according to the compensation reference quantity.
Compared with the prior art, the method has the advantages that the error of the frequency modulation signal intensity of the OFDR system is compensated in real time, the compensation reference quantity and the attenuation trend of the modulation signal intensity have good consistency, the attenuation generated by the increase of the frequency modulation signal intensity along with the increase of the frequency is effectively reduced, the signal-to-noise ratio of the OFDR system is improved, and finally the measurement range, the measurement precision and the spatial resolution of the OFDR system are improved.
Drawings
Fig. 1 is a schematic diagram of the linear swept optical signal generation principle in an OFDR system.
Fig. 2 is a time domain diagram of a fm signal before compensation.
Fig. 3 is a time domain diagram of a fm signal for a single period prior to compensation.
Fig. 4 is a graph comparing the inventlope and inventlope_mean.
Fig. 5 is an effect diagram of the inventiope_complete and inventiope_mean.
Fig. 6 is a time domain diagram of the compensated fm signal.
Detailed Description
According to the invention, the compensation reference quantity is obtained by combining the real-time modulation signal intensity information with the corresponding compensation algorithm, and the modulation signal generation unit is controlled in a feedback manner according to the compensation reference quantity, so that the real-time compensation of the modulation signal intensity error is realized.
The method for compensating the frequency modulation signal intensity error of the OFDR system in real time is specifically described below with reference to the accompanying drawings.
As shown in fig. 1, the principle of generating a linear swept optical signal in an externally modulated OFDR system is as follows: the single-frequency laser emits single-frequency optical signals and enters the optical modulation unit, the modulation signal generation unit generates modulation signals and inputs the modulation signals into the optical modulation unit, the single-frequency optical signals are modulated into linear sweep-frequency optical signals, meanwhile, the modulation signals are processed in real time by the compensation unit, and the compensation reference quantity obtained after the processing is fed back to control the modulation signal generation unit, so that real-time compensation of the intensity errors of the modulation signals is realized. The single-frequency laser adopted in the example has the wavelength of 1550nm and the line width of 1kHz, the light modulation unit is a lithium niobate IQ modulator, and the modulation signal generation unit mainly comprises an FPGA, a DDS and a processing circuit.
The real-time compensation method for the frequency modulation signal intensity error of the OFDR system comprises the following steps:
A. obtaining frequency modulation signal data of an OFDR system by adopting an analog-to-digital converter, and extracting the data into { signal ] according to the signal period i } n Where the subscript i represents the ith period and n represents the total number of periods, n=8 is chosen in this example.
B. Signal data for each period i Performing Hilbert transformation to obtain amplitude information of each period of data, and correspondingly marking as { envelope } i } n 。
C. Since the noise in the amplitude information conforms to the Gaussian distribution and to the independent same distribution, the average value is 0, each inventlope i The addition can reduce the influence of noise and record The width of the existing endlope_mean is smaller than any endlope i And is approximately at envelope i The average value of the noise is equal to the average value of the noise, and the average value of the noise is equal to the average value of the noise.
D. Downsampling the average of the running of the running_mean, namely taking a sliding window with the window size of w, averaging the first point to the w of the running_mean of the first downsampling point, averaging the w-k/2 to w k+w/2 of the running_mean of the kth downsampling point, and averaging the last point to the last w points of the running_mean; the down-sampled point is the inventiope_downsampled point.
E. The point of the inventiope_down sample is subjected to linear interpolation, the point is interpolated to m points according to the requirement, and then the point actually required by the frequency modulation signal is downsampled, and the point is marked as the inventiope_compensation, namely the compensation reference quantity.
F. And taking the original quantity of the frequency modulation signal as a reference feedback control frequency modulation signal generation unit by taking an endslope_compensation point to obtain a new compensated frequency modulation signal.
G. And (3) collecting the compensated frequency modulation signals, and repeating the steps A-G if the frequency modulation signals do not meet the requirements. Those skilled in the art can set the requirements to be satisfied according to the actual situation.
FIG. 2 is a time domain diagram of the periodic modulated signal before compensation; as shown in fig. 3, which is a time domain diagram of the modulated signal in a single period before compensation, wherein the abscissa is time, and the abscissa also represents frequency, the modulated signal intensity can obviously fluctuate and decay with the increase of the frequency.
As shown in fig. 4, which is a comparison graph of the inventiope and the inventiope_mean, it can be seen that the effect of noise can be effectively reduced by superposition.
As shown in fig. 5, which is an effect diagram of the compensation_compensation and the compensation_mean, it can be seen that the compensation reference quantity has good consistency with the attenuation trend of the modulation signal intensity, so that the modulation signal intensity error can be effectively compensated by feeding back the compensation reference quantity to the modulation signal generating unit.
As shown in fig. 6, which is a time domain diagram of a compensated modulation signal, the compensation method of the present invention can effectively compensate the intensity error of the modulation signal, and realize uniform distribution of the signal intensity on different frequency components.
In summary, the error of the modulated signal strength in the OFDR system may be compensated in real time by the method of the present invention. The compensation method provided by the invention is established on the basis of simulation and experiment, and has good compensation effect.
The foregoing is merely a preferred embodiment of the present invention, and the scope of the claimed invention is not limited thereto. The present invention is capable of other and further embodiments and its several details are capable of modification and variation in light of the present invention, as will be apparent to those skilled in the art, without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (4)
1. The real-time compensation method for the frequency modulation signal intensity error of the OFDR system is characterized by comprising the following steps of:
A. obtaining frequency modulation signal data of the OFDR system by adopting an analog-to-digital converter, extracting the signal data according to the signal period, and recording the signal data as { signal } i } n Wherein, signal i Frequency modulation signal data representing the ith period, n represents the total number of periods, and n is more than 2;
B. the frequency modulation signal data of each period is subjected to Hilbert transformation to obtain amplitude information of each period, which is recorded as { envelope } i } n Wherein, envelope i Amplitude information representing the frequency modulated signal data of the i-th period;
C. since the noise in the amplitude information conforms to the Gaussian distribution and to the independent same distribution, the average value is 0, each inventlope i The addition can reduce the influence of noise and record The width of the existing endlope_mean is smaller than any endlope i And in an envelope i Is defined by a center of (a);
D. the running average downsampling is performed on the inventlope_mean: taking a sliding window with the window size of w, taking the average from the first point of the enavelope_mean to the w point of the first downsampling point, taking the average from the w-k/2 point of the enavelope_mean to the w-k+w/2 point of the kth downsampling point, and taking the average from the last point to the last w points of the enavelope_mean; the sampled point is recorded as an inventlope_down sample;
E. performing linear interpolation on the points of the inventlope_down sample, interpolating the points to m points according to the requirement, and downsampling the points actually required by the frequency modulation signal, wherein the points are marked as inventiope_compensation and are compensation reference quantities;
F. the original quantity { envelope ] of the frequency modulated signal i } n And taking the point of the compensation reference quantity as a reference, and feeding back and controlling the frequency modulation signal generating unit to obtain a new compensated frequency modulation signal.
2. The method for compensating the intensity error of the frequency modulated signal of the OFDR system according to claim 1, further comprising the step of G. Collecting the compensated frequency modulated signal, and if the compensation requirement is not met, repeating the steps A-G.
3. The method for compensating the intensity error of the frequency modulation signal of the OFDR system according to claim 1 is characterized in that the OFDR system adopts an external modulation method, the frequency modulation signal is used for modulating a single frequency signal into a linear sweep frequency signal, and the modulated signal is used as a driving signal to be loaded on an external optical modulation device to realize the scanning of the optical frequency, so as to realize the frequency modulation continuous wave ranging.
4. The method for compensating the frequency modulation signal intensity error of the OFDR system according to claim 1, wherein the frequency modulation signal generating unit is composed of an FPGA and a DDS, and the control of the frequency modulation signal intensity is realized by adjusting the amplitude of the output signal of the DDS in real time according to the compensation reference quantity.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5168213A (en) * | 1990-03-13 | 1992-12-01 | Hewlett-Packard Company | Swept signal analysis instrument and method |
| JP2001308815A (en) * | 2000-04-18 | 2001-11-02 | Victor Co Of Japan Ltd | Method and device for generating transmission signal |
| CN110487313A (en) * | 2019-08-02 | 2019-11-22 | 哈尔滨工业大学 | Light source frequency sweep Nonlinear Self-tuning method in optical frequency domain reflection technology |
| CN111397644A (en) * | 2020-03-26 | 2020-07-10 | 南京大学 | Laser nonlinear tuning effect compensation system and compensation method for optical frequency domain reflectometer |
| CN113804404A (en) * | 2021-08-16 | 2021-12-17 | 广东工业大学 | Light source frequency sweep nonlinear correction method for optical frequency domain polarization crosstalk measurement |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US9319141B2 (en) * | 2010-04-06 | 2016-04-19 | Nec Corporation | Optical transmitting/receiving system and timing extracting method in optical transmitting/receiving system |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5168213A (en) * | 1990-03-13 | 1992-12-01 | Hewlett-Packard Company | Swept signal analysis instrument and method |
| JP2001308815A (en) * | 2000-04-18 | 2001-11-02 | Victor Co Of Japan Ltd | Method and device for generating transmission signal |
| CN110487313A (en) * | 2019-08-02 | 2019-11-22 | 哈尔滨工业大学 | Light source frequency sweep Nonlinear Self-tuning method in optical frequency domain reflection technology |
| CN111397644A (en) * | 2020-03-26 | 2020-07-10 | 南京大学 | Laser nonlinear tuning effect compensation system and compensation method for optical frequency domain reflectometer |
| CN113804404A (en) * | 2021-08-16 | 2021-12-17 | 广东工业大学 | Light source frequency sweep nonlinear correction method for optical frequency domain polarization crosstalk measurement |
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