CN117804590A - Signal equalization device and method for optical fiber sensing device - Google Patents
Signal equalization device and method for optical fiber sensing device Download PDFInfo
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Abstract
The invention belongs to the field of optical fiber sensing, and particularly relates to a signal equalization device and method of an optical fiber sensing device. The pulse light modulated by the invention enters the optical circulator after power amplification by the pulse light amplifying unit, and is incident into the optical fiber to be tested; the optical pulse returns to the optical circulator through the signal light which is subjected to Rayleigh scattering by the optical fiber to be detected, and then the optical pulse is interfered with the local oscillation light which is separated by the light source transmitting unit after passing through the optical signal equalizing and amplifying unit, the interference light is converted into an electric signal through the photoelectric detection unit, and the electric signal is collected and demodulated through the control collecting unit; the output end of the control acquisition unit is respectively connected with the equalization amplifying unit and the pulse modulation unit; and controlling the current curve output by the acquisition unit to control the optical signal equalization amplifying unit. The system of the invention has simpler working process and is convenient for system realization.
Description
Technical Field
The invention belongs to the field of optical fiber sensing, and particularly relates to a signal equalization device and method of an optical fiber sensing device.
Background
At present, most of the fields of optical fiber sensing are based on the coherent Rayleigh scattering principle, and the characteristic that an optical fiber is sensitive to sound (vibration) is utilized, when external vibration acts on a sensing optical fiber, the refractive index and the length of the optical fiber are slightly changed due to an elasto-optical effect, so that the phase of a transmission signal in the optical fiber is changed, and the light intensity (phase) is changed, so that the detection of a vibration event can be detected.
The optical fiber sensing system can reduce the transmitted power and generate loss due to scattering inside the optical fiber. In the case of a limited peak power of the probe light pulses, the shorter the pulse width, the smaller the average power, which in turn affects the other 2 index sensitivities and sensing distances, since the phase term signal-to-noise ratio directly determines the strain sensitivity and sensing distance in the fiber optic sensing system by demodulating the phase of the rayleigh back-scattered signal (Rayleigh Backscattering, RBS) to obtain the external vibration signal. The phase term is calculated from the intensity of the RBS, which in turn is determined by the energy of the probing light pulse. Therefore, in the optical fiber sensing system, the strain sensitivity and resolution are necessarily reduced while the sensing distance is increased.
In order to obtain a longer detection distance, the conventional optical amplifier performs constant amplification (similar multiplication amplification factor) on the whole of the transmitted or received optical signal, so that the signal strength is lower and the signal-to-noise ratio is lower at a position where the optical fiber distance is longer as the signal of the optical source is larger, under the condition that the input range of the detector and the acquisition system is required to be very high, the signal-to-noise ratio of the signal at the front end after the front end is saturated is very low, which is the most common problem in long-distance application.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a signal equalization device and a signal equalization method of an optical fiber sensing device. The device and the method can linearly amplify according to the intensity or the distance of the optical signal, so that the signal intensity is kept in a certain specified range, and the balanced amplification of the signal intensity of the whole optical fiber link is realized. Therefore, the signal intensity of the whole optical fiber link can be always kept in the optimal working range of the photoelectric detector and the acquisition system, the problems of front-end signal saturation and low back-end signal under a long-distance scene are effectively solved, and meanwhile, the algorithm analysis and processing of data are more convenient.
The technical scheme of the invention is as follows: the utility model provides a signal equalization device of optical fiber sensing device, includes light source emission unit, pulse modulation unit, pulse light amplification unit, optical circulator, the optic fibre that awaits measuring, optical signal equalization amplification unit, optical signal receiving detection unit, control acquisition unit, and the continuous light that light source emission unit sent is through pulse modulation unit, its characterized in that: the modulated pulse light enters an optical circulator after power amplification by a pulse light amplifying unit, and is incident into an optical fiber to be tested; the optical pulse returns to the optical circulator through the signal light which is subjected to Rayleigh scattering by the optical fiber to be detected, and then the optical pulse is interfered with the local oscillation light which is separated by the light source transmitting unit after passing through the optical signal equalizing and amplifying unit, the interference light is converted into an electric signal through the photoelectric detection unit, and the electric signal is collected and demodulated through the control collecting unit; the output end of the control acquisition unit is respectively connected with the equalization amplifying unit and the pulse modulation unit; the current curve output by the control acquisition unit controls the optical signal equalization amplification unit, and the current curve is as follows:
wherein:
alpha is the attenuation coefficient of the optical fiber; p (P) 0 Peak power for the transmit pulse; alpha rs Is the Rayleigh scattering coefficient of the optical fiber; s is S rs Is the backward Rayleigh scattering coefficient of the optical fiber; v g Is the transmission rate of the light beam within the fiber; w is the emission pulse width; t is a time coefficient; a T sampling time period; g is a correction coefficient.
A signal equalizing apparatus of an optical fiber sensing device as described above, characterized in that: the optical fiber to be measured is a common single-mode optical fiber, a multimode optical fiber or a scattering enhancement optical fiber.
A signal equalizing apparatus of an optical fiber sensing device as described above, characterized in that: the light source emitting unit is a narrow linewidth light source and emits signal light and local oscillation light which are separated by a coupler of 1 to 2.
A signal equalizing apparatus of an optical fiber sensing device as described above, characterized in that: the pulse modulation unit is a semiconductor optical amplifier, an electro-optical modulator or an acousto-optic modulator.
A signal equalizing apparatus of an optical fiber sensing device as described above, characterized in that: the receiving detection unit is a photoelectric detector.
A signal equalizing apparatus of an optical fiber sensing device as described above, characterized in that: the pulse light amplifying unit is a semiconductor amplifier or an erbium-doped fiber amplifier.
The invention also discloses a signal equalization method of the optical fiber sensing device, which is characterized in that: the method comprises the following steps:
s1: the light emitted by the narrow-linewidth light source is divided into signal light and local oscillation light through a coupler, the signal light forms pulse light after continuous narrow-band coherent light modulation through a pulse modulation unit, and the signal of the pulse modulation unit is controlled by the output of a control acquisition unit;
s2: the pulse light enters the optical circulator after being subjected to power amplification with fixed gain by the pulse light amplifying unit, then enters the optical fiber to be detected, returns to the optical circulator after being subjected to Rayleigh scattering by the optical fiber, and then enters the optical signal equalizing amplifying unit;
s3: the optical signal equalization amplifying unit performs equalization amplification on signals, and then performs optical coupling interference with a local oscillator and enters the optical signal receiving and detecting unit; the equalization amplifying process is as follows: the optical signal equalization amplifying unit is composed of a semiconductor amplifier and a driving circuit, the acquisition unit is controlled to output synchronous electric pulse signals and current control signals, the current control signals are realized by two methods including, but not limited to, using a digital potentiometer or a digital-to-analog converter (DAC), a current curve output by the acquisition unit is controlled to control the optical signal equalization amplifying unit, and the current curve is:
wherein: alpha is the attenuation coefficient of the optical fiber; p (P) 0 Peak power for the transmit pulse; alpha rs Is the Rayleigh scattering coefficient of the optical fiber;S rs is the backward Rayleigh scattering coefficient of the optical fiber; v g Is the transmission rate of the light beam within the fiber; w is the emission pulse width; t is a time coefficient; a T sampling time period; g is a correction coefficient;
s4: after analog-digital conversion is carried out on the acquisition card of the control acquisition unit, data demodulation is carried out, and the phase and amplitude change of the signal light are restored and output.
The signal equalization method of the optical fiber sensing device is characterized by comprising the following steps of: in the process of testing the Rayleigh scattering curve, the modulation signal modulated by the light pulse is used as a synchronous signal, the driving current of the light signal equalization amplifying unit is controlled and regulated, and the driving current in the acquisition process is regulated according to the amplitude of the actually tested optical fiber Rayleigh scattering signal, so that the amplitude of the whole optical fiber signal is kept to be reasonable.
The beneficial effects of the invention are as follows: the system has a simpler working process and is convenient for system realization; and the driving current in the acquisition process is regulated according to the signal amplitude, so that the signal amplitude of the whole section of optical fiber is kept at a reasonable value, the front-end signal saturation caused by the overlarge amplification factor is avoided, and the signal-to-noise ratio of the rear-end signal is too low after the overlarge amplification factor is too low.
Drawings
Fig. 1 is a functional block diagram of the present invention.
Fig. 2 is a schematic diagram of the operation of the conventional method.
Fig. 3 is a schematic diagram of the operation of the present invention.
Detailed Description
The technical scheme of the invention is further specifically described below with reference to the accompanying drawings and the detailed description.
As shown in FIG. 1, the signal equalization device of the optical fiber sensing device comprises a light source emitting unit, a pulse modulation unit, a pulse light amplifying unit, an optical circulator, an optical fiber to be tested, an optical signal equalization amplifying unit, an optical signal receiving and detecting unit and a control acquisition unit. Continuous light emitted by the light source emission unit passes through the pulse modulation unit, the continuous light is modulated into a pulse light signal with a certain repetition frequency, the modulated pulse light enters the optical circulator after being subjected to power amplification by the pulse light amplification unit, and the pulse light is incident into an optical fiber to be detected; the output end of the control acquisition unit is respectively connected with the equalization amplifying unit and the pulse modulation unit. The optical fiber to be tested can be a common single-mode optical fiber, a multimode optical fiber and a scattering enhancement optical fiber, the signal light of the optical pulse subjected to Rayleigh scattering by the optical fiber to be tested returns to the optical circulator, and then is interfered with the local oscillation light separated by the light source emission unit after passing through the optical signal equalization amplification unit, the interference light is converted into an electric signal by the photoelectric detection unit, and the electric signal is collected and demodulated by the control collection unit.
Before the scattered signal light is coherent with the local oscillation light of the light source, the signal light passes through an equalizing amplifying unit. The equalizing amplification unit does not amplify the signal light with a fixed gain, but gradually increases the amplification factor in the time t1 to t2 after the pulse is emitted. In the invention, the light speed c and the refractive index of the optical fiber are fixed, the time t1 is determined by the control output of the control board, and the time t2 is determined by the length of the optical cable. the time t1 is the time when the rayleigh scattering signal generated from the optical pulse to the optical fiber starting position reaches the equalizing amplifier, and the time t2 is the time when the rayleigh scattering signal generated from the optical pulse to the optical fiber ending position reaches the equalizing amplifier. The control acquisition unit sends control signals to the pulse modulation unit and the equalization amplification unit simultaneously, so that control of the starting moment can be realized, and the working ending moment of the equalization amplifier is determined by the length of the optical cable. Therefore, the working process of the system is simpler, and the system is convenient to realize.
The light source transmitting unit is a narrow linewidth light source, the pulse modulation unit is a semiconductor optical amplifier or an electro-optical modulator or an acousto-optic modulator, and the receiving and detecting unit is a photoelectric detector. The light source transmitting unit transmits a signal light and a local oscillation light which are separated by using a coupler of 1-2. The pulse light amplifying unit is a pulse light signal amplifier with fixed gain, and the pulse light amplifying unit is a semiconductor amplifier or an erbium-doped fiber amplifier.
The invention also discloses a signal equalization method of the optical fiber sensing device, which adopts the device and comprises the following steps:
s1: the light emitted by the narrow-linewidth light source is divided into signal light and local oscillation light through a coupler, the signal light forms pulse light after continuous narrow-band coherent light modulation through a pulse modulation unit, and the signal of the pulse modulation unit is controlled by the output of a control acquisition unit;
s2: the pulse light enters the optical circulator after being subjected to power amplification with fixed gain by the pulse light amplifying unit, then enters the optical fiber to be detected, returns to the optical circulator after being subjected to Rayleigh scattering by the optical fiber, and then enters the optical signal equalizing amplifying unit;
s3: the optical signal equalization amplifying unit performs equalization amplification on signals, and then performs optical coupling interference with a local oscillator and enters the optical signal receiving and detecting unit; the equalization amplifying process is as follows: the optical signal equalization amplifying unit is composed of a semiconductor amplifier and a driving circuit thereof, and the semiconductor driving amplifier has the characteristics that under the condition of a certain temperature, the larger the driving current is, the larger the gain multiple is generated. The control acquisition unit outputs a synchronous electric pulse signal as an acquired time t1, and the driving current of the semiconductor laser in the time t2, t1 to t2 of the acquisition end time can be set according to the attenuation curve of the fiber Rayleigh scattering. The current curve output by the control acquisition unit controls the optical signal equalization amplification unit, and the current curve is as follows:
wherein:
alpha: attenuation coefficient of the optical fiber;
P 0 : peak power of the transmit pulse;
α rs : the Rayleigh scattering coefficient of the fiber;
S rs : the backward Rayleigh scattering coefficient of the fiber;
v g : the transmission rate of the light beam within the optical fiber;
w: a transmit pulse width;
t: is a time coefficient;
t: sampling time period;
g, correcting the coefficient, wherein mA/mW;
s4: after analog-digital conversion is carried out on the acquisition card of the control acquisition unit, data demodulation is carried out, and the phase and amplitude change of the signal light are restored and output. The current control signal of the present invention includes but is not limited to being implemented using two methods of a digital potentiometer or digital to analog converter (DAC),
in the working process of the invention, if nonlinear loss occurs in the optical cable, the Rayleigh scattering intensity curve of the optical cable can be collected under the condition of fixed gain, and the actual corresponding attenuation curve is fitted in the same way, so that the current setting curve is obtained according to the method.
The actual implementation process of the device and the method of the invention is as follows: in the process of testing a Rayleigh scattering curve, a modulation signal modulated by light pulses is used as a synchronous signal, the driving current of an optical signal equalization amplifying unit is controlled and regulated, and the driving current in the acquisition process is regulated according to the signal amplitude, so that the amplitude of the whole section of optical fiber signal is kept at a reasonable value, the front-end signal saturation caused by overlarge amplification factor is avoided, and the signal-to-noise ratio of the rear-end signal is too low after the amplification factor is too small; as shown in fig. 2 and 3. Compared with the corresponding adjustment by using the method of grating reflectivity and the like, the method has the advantages of relatively simple system, low cost and easy realization.
Claims (9)
1. The utility model provides a signal equalization device of optical fiber sensing device, includes light source emission unit, pulse modulation unit, pulse light amplification unit, optical circulator, the optic fibre that awaits measuring, optical signal equalization amplification unit, optical signal receiving detection unit, control acquisition unit, and the continuous light that light source emission unit sent is through pulse modulation unit, its characterized in that: the modulated pulse light enters an optical circulator after power amplification by a pulse light amplifying unit, and is incident into an optical fiber to be tested; the optical pulse returns to the optical circulator through the signal light which is subjected to Rayleigh scattering by the optical fiber to be detected, and then the optical pulse is interfered with the local oscillation light which is separated by the light source transmitting unit after passing through the optical signal equalizing and amplifying unit, the interference light is converted into an electric signal through the photoelectric detection unit, and the electric signal is collected and demodulated through the control collecting unit; the output end of the control acquisition unit is respectively connected with the equalization amplifying unit and the pulse modulation unit; the current curve output by the control acquisition unit controls the optical signal equalization amplification unit, and the current curve is as follows:
wherein: alpha is the attenuation coefficient of the optical fiber; p (P) 0 Peak power for the transmit pulse; alpha rs Is the Rayleigh scattering coefficient of the optical fiber; s is S rs Is the backward Rayleigh scattering coefficient of the optical fiber; v g Is the transmission rate of the light beam within the fiber; w is the emission pulse width; t is a time coefficient; a T sampling time period; g is a correction coefficient.
2. The signal equalizing apparatus of an optical fiber sensing device according to claim 1, wherein: the optical fiber to be measured is a common single-mode optical fiber, a multimode optical fiber or a scattering enhancement optical fiber.
3. The signal equalizing apparatus of an optical fiber sensing device according to claim 1, wherein: the light source emitting unit is a narrow linewidth light source and emits signal light and local oscillation light which are separated by a coupler of 1 to 2.
4. The signal equalizing apparatus of an optical fiber sensing device according to claim 1, wherein: the pulse modulation unit is a semiconductor optical amplifier, an electro-optical modulator or an acousto-optic modulator.
5. The signal equalizing apparatus of an optical fiber sensing device according to claim 1, wherein: the receiving detection unit is a photoelectric detector.
6. The signal equalizing apparatus of an optical fiber sensing device according to claim 1, wherein: the pulse light amplifying unit is a semiconductor amplifier or an erbium-doped fiber amplifier.
7. A signal equalization method of an optical fiber sensing device is characterized in that: the method comprises the following steps:
s1: the light emitted by the narrow-linewidth light source is divided into signal light and local oscillation light through a coupler, the signal light forms pulse light after continuous narrow-band coherent light modulation through a pulse modulation unit, and the signal of the pulse modulation unit is controlled by the output of a control acquisition unit;
s2: the pulse light enters the optical circulator after being subjected to power amplification with fixed gain by the pulse light amplifying unit, then enters the optical fiber to be detected, returns to the optical circulator after being subjected to Rayleigh scattering by the optical fiber, and then enters the optical signal equalizing amplifying unit;
s3: the optical signal equalization amplifying unit performs equalization amplification on signals, and then performs optical coupling interference with a local oscillator and enters the optical signal receiving and detecting unit; the equalization amplifying process is as follows: the optical signal equalization amplifying unit is composed of a semiconductor amplifier and a driving circuit, the acquisition unit is controlled to output synchronous electric pulse signals and current control signals, the current curve output by the acquisition unit is controlled to control the optical signal equalization amplifying unit, and the current curve is as follows:
wherein: alpha is the attenuation coefficient of the optical fiber; p (P) 0 Peak power for the transmit pulse; alpha rs Is the Rayleigh scattering coefficient of the optical fiber; s is S rs Is the backward Rayleigh scattering coefficient of the optical fiber; v g Is the transmission rate of the light beam within the fiber; w is the emission pulse width; t is a time coefficient; a T sampling time period; g is a correction coefficient;
s4: after analog-digital conversion is carried out on the acquisition card of the control acquisition unit, data demodulation is carried out, and the phase and amplitude change of the signal light are restored and output.
8. The method for signal equalization of an optical fiber sensing device of claim 7, wherein: in the process of testing the Rayleigh scattering curve, the modulation signal modulated by the light pulse is used as a synchronous signal, the driving current of the light signal equalization amplifying unit is controlled and regulated, and the driving current in the acquisition process is regulated according to the signal amplitude, so that the amplitude of the whole section of optical fiber signal is kept to be reasonable.
9. The method for signal equalization of an optical fiber sensing device of claim 7, wherein: the current control signal is realized by a digital potentiometer or a digital-to-analog converter.
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