CN112129243A - Quasi-distributed optical fiber torsion angle measuring device and method based on photoelectric oscillator - Google Patents
Quasi-distributed optical fiber torsion angle measuring device and method based on photoelectric oscillator Download PDFInfo
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Abstract
The invention provides a quasi-distributed optical fiber torsion angle measuring device and method based on a photoelectric oscillator, which can be applied to the field of multipoint torque measurement. The invention realizes the selection of different sensing positions by the wavelength division multiplexing technology. When a specific sensing position is selected, two photoelectric oscillators with the same structure are formed, wherein one photoelectric oscillator is a reference photoelectric oscillator, and the other photoelectric oscillator is a measurement photoelectric oscillator. The two photoelectric oscillators share the long optical fiber delay module through the wavelength division multiplexing technology to form a mutual reference structure. The microwave signals with the same frequency generated by the two photoelectric oscillators are subjected to phase discrimination to obtain the phase fluctuation of the microwave signals caused by the optical fiber torsion angle, so that a phase demodulation mode of the optical fiber torsion angle is formed. The wavelength of a tunable laser module in the photoelectric oscillator is tuned and measured, and the sensing positions are sequentially selected, so that quasi-distributed measurement is realized. Finally, the method realizes the multi-point measurement and the quasi-distributed optical fiber torsion angle measurement based on the photoelectric oscillator and insensitive to temperature.
Description
Technical Field
The invention belongs to the field of quasi-distributed optical fiber measurement and sensing, and particularly relates to a quasi-distributed optical fiber torsion angle measurement method based on a photoelectric oscillator.
Background
The torque is a key parameter for representing the internal torsion and the internal damage degree of engineering structures such as bridges, buildings, train tracks and the like, and the measurement of the torque is one of important measurement methods for realizing the torque measurement by measuring the torsion angle of the optical fiber. The realization of multipoint torque measurement and analysis of the structural body is an important technical means for improving the structural safety and the system efficiency. The high-precision, quick and multipoint torque measurement has great significance for detecting the health state of the structure and reducing safety accidents.
The optical fiber sensor has the advantages of compact structure, light weight, high measurement sensitivity, electromagnetic interference resistance and the like, so that the optical fiber torque sensing gradually replaces the traditional torque sensing method based on the electronic technology to become the mainstream technology. Typically, torque measurement is achieved by measuring the fiber twist angle. Conventional torque sensors are largely classified into the following two categories: the torque sensor is based on an electrical method, and is easily interfered by electrical noise and temperature; and secondly, the torque sensor based on the electromagnetic induction phenomenon is large in size and is easy to be interfered by electromagnetic waves. The optical fiber torque sensor has the advantages of compact structure, light weight, high measurement sensitivity, electromagnetic interference resistance and the like, and is widely applied to torque measurement. Currently, fiber optic twist sensing modules are typically fiber gratings such as long period fiber gratings, fiber bragg gratings, phase shifted fiber bragg gratings, and interferometers such as Mach-Zehnder, sagnac, and the like.
In recent years, optoelectronic oscillators have been used in the field of optical fiber sensing to enable high-speed, high-resolution measurement of physical parameters. However, optoelectronic oscillator based sensors are susceptible to environmental factors such as temperature. Furthermore, the sensor based on the optoelectronic oscillator is usually a single-point measurement system, and cannot realize multi-point measurement. Therefore, the realization of multipoint, accurate and rapid measurement of the fiber torsion angle based on the photoelectric oscillator without being influenced by environmental factors such as temperature and the like is an urgent technical problem to be solved.
Disclosure of Invention
The invention aims to solve the problems that the influence of external factors such as temperature on a measurement result is difficult to eliminate and the signal demodulation speed is low in the prior art, so that high-precision real-time torque measurement is difficult to meet and multi-point measurement cannot be realized.
In order to achieve the above object, the quasi-distributed fiber torsion angle measuring device based on a photoelectric oscillator of the present invention includes a reference photoelectric oscillator, a measurement photoelectric oscillator, a microwave phase discrimination module, and a signal processing module, wherein an output microwave signal of the reference photoelectric oscillator and an output microwave signal of the measurement photoelectric oscillator are simultaneously input into the microwave phase discrimination module, and the microwave phase discrimination module outputs an output phase discrimination result to the signal processing module, wherein:
the reference photoelectric oscillator is used for eliminating the influence of external factors including temperature on the distance and the measurement result of the related parameters thereof;
the measurement photoelectric oscillator is used for comparing with the reference photoelectric oscillator to obtain a value to be measured;
the microwave phase discrimination module is used for discriminating the microwave signal from the reference photoelectric oscillator and the microwave signal from the measurement photoelectric oscillator;
the signal processing module is used for calculating the frequency spectrum information of the microwave signal from the frequency spectrum measuring module and the real-time frequency of the intermediate frequency signal measured by the frequency counting module through a formula to obtain the distance and related parameters thereof;
the invention uses a reference photoelectric oscillator and a measuring photoelectric oscillator, the initial oscillation frequencies of the two photoelectric oscillators are the same, the initial loop delays of the two photoelectric oscillators are equal, the phase difference of the two photoelectric oscillators is always zero, and the influence of environmental factors such as temperature on the output frequencies of the two photoelectric oscillators is the same, so that the measuring result is not influenced by the environmental factors such as temperature; the demodulation signal is the microwave signal phase difference of the two photoelectric oscillators, the measurement difficulty is low, and the demodulation cost is low.
Further, the reference optoelectronic oscillator includes a laser module 1, a polarization control module 1, a polarization modulation module 1, an optical filtering module 1, a wavelength division multiplexing module 01, a delay sensing module, a wavelength division multiplexing module 02, a polarizer module 1, an optoelectronic detection module 1, a microwave amplification module 1, a microwave filtering module 1, and a microwave coupling module 1, wherein:
a laser module 1 for generating an optical signal;
the polarization control module 1 is used for controlling an included angle between linearly polarized light input into the polarization control module 1 and a main shaft of the polarization modulation module 1;
a polarization modulation module 1 for modulating an input optical signal using a microwave signal;
the optical filtering module 1 is configured to perform filtering processing on the optical signal from the polarization modulation module 1, where the filtered optical signal only has a carrier and one of the optical signals outside a first-order sideband;
the wavelength division multiplexing module 01 is used for combining the optical signal from the optical filtering module 1 and the optical signal from the optical filtering module 2 into a beam of optical signal;
the delay sensing module is used for selecting a sensing position and enabling the two photoelectric oscillators to have the same time delay;
the wavelength division multiplexing module 02 is used for demultiplexing the synthesized optical signal and dividing the optical signal into two paths, wherein one path enters the polarizer module 1, and the other path enters the polarizer module 2 in the measuring photoelectric oscillator;
the polarizer module 1 is used for combining two optical signals with orthogonal polarization directions of x and y;
the photoelectric detection module 1 is used for converting the optical signal from the polarizer module 1 into a microwave signal;
the microwave amplification module 1 is used for amplifying the microwave signal from the photoelectric detection module 1;
the microwave filtering module 1 is used for filtering the microwave signal from the microwave amplifying module 1;
the microwave coupling module 1 is used for dividing a microwave signal from the microwave filtering module 1 into two beams, one beam is fed back to the polarization modulation module 1, and the other beam is output to the microwave phase discrimination module;
further, the measurement optoelectronic oscillator includes a tunable laser module 2, a polarization control module 2, a polarization modulation module 2, an optical filtering module 2, a wavelength division multiplexing module 01, a delay sensing module, a wavelength division multiplexing module 02, a polarizer module 2, a photodetection module 2, a microwave amplification module 2, a microwave filtering module 2, and a microwave coupling module 2, wherein:
a tunable laser module 2, tunable, for generating an optical signal of continuously varying output wavelength;
the polarization control module 2 is used for controlling an included angle between linearly polarized light input into the polarization control module 2 and a main shaft of the polarization modulation module 2;
a polarization modulation module 2 for modulating an input optical signal using a microwave signal;
the optical filtering module 2 is used for filtering the optical signal from the polarization modulation module 2, and the filtered optical signal only remains a carrier and one of the optical signals outside a first-order sideband;
the wavelength division multiplexing module 01 is used for combining the optical signal from the optical filtering module 1 and the optical signal from the optical filtering module 2 into a beam of optical signal;
the delay sensing module is used for selecting a sensing position and enabling the two photoelectric oscillators to have the same time delay;
a wavelength division multiplexing module 02 for demultiplexing the synthesized optical signal into two paths of optical signals with different wavelengths, the wavelength is lambda0Into a polarizer module 1 at a wavelength λ1～λnAny optical signal within the range enters the polarizer module 2;
the polarizer module 2 is used for combining two optical signals with orthogonal polarization directions of x and y;
the photoelectric detection module 2 is used for converting the optical signal from the polarizer module 2 into a microwave signal;
the microwave amplification module 2 is used for amplifying the microwave signal from the photoelectric detection module 2;
the microwave filtering module 2 is used for filtering the microwave signal from the microwave amplifying module 2;
the microwave coupling module 2 is used for dividing the microwave signal from the microwave filtering module 2 into two beams, one beam is fed back to the polarization modulation module 2, and the other beam is output to the microwave phase discrimination module;
further, the delay sensing module includes an optical fiber delay module and an optical fiber torsion angle sensing position, the optical fiber delay module has n +1, the optical fiber torsion angle sensing position has n, n is a natural number, the above n +1 optical fiber delay modules are alternately connected with the n optical fiber torsion angle sensing positions, the n +1 optical fiber delay module transmits the optical signal into the wavelength division multiplexing module 02, wherein:
the optical fiber delay module is used for providing an energy storage medium for the reference photoelectric oscillator and the measurement photoelectric oscillator;
when the wavelength of the optical signal transmitted by the optical fiber delay module 1 is consistent with the working wavelength of the wavelength division multiplexing module in the optical fiber torsion angle sensing position, the optical fiber torsion angle sensing position is selected.
A selected fiber optic twist angle sensing position for providing a measurement location;
the other unselected optical fiber torsion angle sensing positions are taken as an optical fiber delay module;
the invention selects the sensing position of the optical fiber torsion angle by sending optical signals with different wavelengths by the adjustable laser module 2, thereby realizing the multipoint measurement of the optical fiber torsion angle;
further, taking the fiber torsion angle sensing position 1 as an example, the structure, connection mode and function of each module in the fiber torsion angle sensing position are the same as those of the fiber torsion angle sensing position 1, the fiber torsion angle sensing position 1 includes a wavelength division multiplexing module 11, a reference light delay module 1, a fiber torsion angle sensing module 1 and a wavelength division multiplexing module 12, the fiber delay module is connected to one end of the wavelength division multiplexing module 11, the other end of the wavelength division multiplexing module 11 is connected to the reference light delay module 1 and the fiber torsion angle sensing module 1, the other end of the reference light delay module 1 is connected to the wavelength division multiplexing module 12, the other end of the fiber torsion angle sensing module 1 is connected to the wavelength division multiplexing module 12, and the other end of the wavelength division multiplexing module 12 is connected to the next fiber delay module, wherein:
the wavelength division multiplexing module 11 is used for transmitting the optical signal from the optical fiber delay module to the reference light delay module 1;
the reference light delay module 1 is used for matching the initial loop delays of the two photoelectric oscillators to ensure that the initial loop delays of the two photoelectric oscillators are equal;
a wavelength division multiplexing module 12 for inputting the optical signal from the reference light delay module 1 to the next optical fiber delay module;
the optical fiber torsion angle sensing module 1 is used for sensing the torsion angle of the optical fiber and reflecting the torsion angle of the optical fiber into passing light
A change in the polarization angle of linearly polarized light of the fiber;
the reference light delay module 1 is used for ensuring that the initial feedback loop delays of the two photoelectric oscillators are the same and eliminating the influence of the loop delays on the measurement result;
the invention also provides a quasi-distributed optical fiber torsion angle measuring method based on the photoelectric oscillator, which comprises the following steps:
A. in a reference optoelectronic oscillator, a laser module generates a light having a wavelength λ0The optical signal is controlled by the polarization control module 1, controls the included angle between the linearly polarized light input into the polarization control module 1 and the main shaft of the polarization modulation module 1, and then is input into the polarization modulation module 1, and the wavelength is lambda0The optical signal is modulated by the microwave signal in the polarization modulation module 1; the optical signal modulated by the microwave signal is filtered by the optical filter module 1, and the optical signal except the carrier and one of the first-order side bands is filtered; the filtered optical signal is input into an optical fiber delay module 1 through a wavelength division multiplexing module 01, the optical fiber delay module 1 transmits the optical signal to optical fiber torsion angle sensing positions, the working wavelength of the wavelength division multiplexing module at each optical fiber torsion angle sensing position is different, when the working wavelength of the wavelength division multiplexing module in each optical fiber torsion angle sensing position is the same as the wavelength of the optical signal transmitted to the optical fiber torsion angle sensing position, the optical fiber torsion angle sensing position is selected as a measuring position, the other optical fiber torsion angle sensing positions are equivalent to an optical fiber delay module, the optical signal output by the optical fiber delay module 1 passes through the selected optical fiber torsion angle sensing position, and then is transmitted to the next wavelength division multiplexing module through a reference optical delay module and the optical signal transmitted by the next wavelength division multiplexing moduleAfter passing through the rest of the optical fiber delay modules and the unselected optical fiber torsion angle sensing positions, the signals are demultiplexed through the wavelength division multiplexing module 02 after passing through one optical fiber delay module, one beam of optical signal after demultiplexing is transmitted into the polarizer module 2 in the measurement photoelectric oscillator, and the other beam of optical signal with the wavelength of lambda0The optical signal is transmitted into the polarizer module 1; the polarizer module 1 transmits an optical signal into the photoelectric detection module 1, the photoelectric detection module 1 converts the received optical signal into a microwave signal, the microwave signal is amplified by the microwave amplification module 1 and filtered by the microwave filtering module 1, the filtered microwave signal is divided into two beams by the microwave coupling module 1, one beam of the microwave signal is transmitted to the microwave phase discrimination module, and the other beam of the microwave signal is transmitted to the polarization modulation module 1 to form a photoelectric feedback loop of the reference photoelectric oscillator;
B. in a measuring photoelectric oscillator, a tunable laser module 2 generates an optical signal of which output wavelength is continuously changed within a certain range and inputs the optical signal to a polarization control module 2, the wavelength range being λ1～λnN is a natural number; the polarization control module 2 controls the included angle between the linearly polarized light input into the polarization control module 2 and the main shaft of the polarization modulation module 2, then the linearly polarized light is input into the polarization modulation module 2, the optical signal is modulated by the microwave signal in the polarization modulation module 2, the optical signal modulated by the microwave signal is filtered by the optical filter module 2, the optical signals except the carrier wave and one of the first order side bands are filtered, the filtered optical signal is input into the optical fiber delay module 1 through the wavelength division multiplexing module 01, the optical fiber delay module 1 transmits the optical signal to the optical fiber torsion angle sensing position, the working wavelength of the wavelength division multiplexing module at each optical fiber torsion angle sensing position is different, when the working wavelength of the wavelength division multiplexing module at the optical fiber torsion angle sensing position is the same as the wavelength of the optical signal transmitted to the optical fiber torsion angle sensing position, the optical fiber torsion angle sensing position is selected as the measuring position, the other optical fiber torsion angle sensing positions are equivalent to an optical fiber delay module, the optical signal output by the optical fiber delay module 1 passes through the wavelength division multiplexing module in the selected optical fiber torsion angle sensing position and then is transmitted to the next wavelength division multiplexing module through the reference light delay module, and the optical signal transmitted by the next wavelength division multiplexing module passes through the other optical fiber torsion angle sensing positionsAfter the optical fiber delay module and the unselected optical fiber torsion angle sensing position are sensed, the optical fiber torsion angle sensing position passes through the optical fiber delay module and is demultiplexed by the wavelength division multiplexing module 02, and the wavelength is lambda after demultiplexing0Is transmitted into a polarizer module 1 in a reference optoelectronic oscillator, with a wavelength of lambda1～λnAny optical signal in the range is transmitted into the polarizer module 2; the polarizer module 2 transmits an optical signal into the photoelectric detection module 2, the photoelectric detection module 2 converts the received optical signal into a microwave signal, the microwave signal is amplified by the microwave amplification module 2 and filtered by the microwave filtering module 2, the filtered microwave signal is divided into two beams by the microwave coupling module 2, one beam of the microwave signal is transmitted to the microwave phase discrimination module, and the other beam of the microwave signal is transmitted to the polarization modulation module 2 to form a photoelectric feedback loop of the measurement photoelectric oscillator;
the reference photoelectric oscillator and the measurement photoelectric oscillator in the steps A and B have the same structure. The feedback loop lengths of the two photoelectric oscillators are the same, and the optical fiber delay module is shared by the two photoelectric oscillators; the time delay of the reference light time delay module is the same as the time delay of the optical fiber torsion angle sensing module; the microwave filtering module 1 and the microwave filtering module 2 are both band-pass microwave filters, and key indexes such as central frequency, 3dB bandwidth and the like are the same. Because the two photoelectric oscillators have the same structure and the initial oscillation frequencies of the two photoelectric oscillators are the same, the influence of external factors including temperature on the measurement result of the torsion angle is eliminated.
C. And D, carrying out phase discrimination on the microwave signal transmitted to the phase frequency discrimination module in the step A and the microwave signal transmitted to the phase frequency discrimination module in the step B in a microwave phase discrimination module, inputting an output phase discrimination result into a signal processing module by the microwave phase discrimination module, and finally demodulating the optical fiber torsion angle in the optical fiber torsion angle sensing position.
Further, in the step B, when the wavelength of the wavelength division multiplexing module in the optical fiber torsion angle sensing position is different from the wavelength of the optical signal transmitted into the optical fiber torsion angle sensing position, the optical signal transmitted into the optical fiber torsion angle sensing position passes through the wavelength division multiplexing module in the optical fiber torsion angle sensing position and then is transmitted into the reference optical delay module, and the reference optical delay module transmits the optical signal into the next wavelength division multiplexing module and then transmits the optical signal to the next optical fiber delay module;
further, in step B, the method further includes: when the linearly polarized light with the included angle of 45 degrees between the polarization control module 2 and the main shaft of the polarization modulation module 2 is input into the polarization modulation module 2, the output light field of the polarization modulation module 2 is
Wherein ExRepresenting the sum E of the intensities of the light fields with perpendicular x-polarization directions in the output light field of the optical filter module 2yRepresents the y-direction perpendicular light field intensity in the output light field of the optical filter module 2; j represents an imaginary number; omeganRepresenting the angular frequency, omega, of the optical carriermRepresenting the angular frequency of the microwave signal; γ represents the phase modulation depth; t represents time;
represents ExAnd EyIs controlled by the dc bias of the input polarization modulation module 2;
further, in step B, the method further includes: the output light field of the optical filter module 2 is
Wherein ExRepresenting the intensity of the light field perpendicular to the x-polarization direction in the output light field of the optical filter module 2, EyRepresents the intensity of the light field in the output light field of the optical filter module 2, in which the y polarization direction is perpendicular; j represents an imaginary number; omeganRepresenting the angular frequency, omega, of the optical carriermRepresenting the angular frequency of the microwave signal; j. the design is a squaren(γ) represents an nth order bessel function of the first type; t represents time;
represents ExAnd EyThe phase difference of (a); γ represents the phase modulation depth;
further, in step B, the method further includes: suppose the optical signal polarization angle of the optical fiber in the input optical fiber torsion angle sensing module is phi, and the intensity is EiThe input optical field of the optical fiber torsion angle sensing module is
Assuming that the fiber torsion angle is theta, the input optical field of the fiber torsion angle sensing module is
Optical signal polarization angle alpha of optical fiber in output optical fiber torsion angle sensing module ═ phi-CPhi- (1-A/2) theta, whereinCRepresents circular polarization retardation; a represents the relationship between the circular birefringence of the optical fiber and the torsion angle of the optical fiber; phi represents the phase difference of the light field intensities in the output light field of the optical filter module 2, wherein the x and y polarization directions are vertical;
further, the output voltage of the photo-detection module 2 is
When in use
At this time, the output voltage of the photodetection module 2 is V (t). varies.. alpha.cos (. omega.)mt+2φ-(2-A)θ+π/2)J0(γ)J-1(γ), wherein- (2-A) represents a correlation coefficient of linear correlation between the twist angle of the optical fiber in the optical fiber twist angle sensing module and the phase of the output microwave signal of the measurement opto-electronic oscillator, ExRepresenting the intensity of the light field perpendicular to the x-polarization direction in the output light field of the optical filter module 2, EyIndicating that the y-polarization direction is perpendicular in the output light field of the optical filter module 2The intensity of the light field; omegamRepresenting the angular frequency of the microwave signal; j. the design is a squaren(γ) represents an nth order bessel function of the first type; t represents time;
represents ExAnd EyThe phase difference of (a); gamma represents the phase modulation depth, so that the optical fiber torsion angle theta can be obtained according to the output voltage of the photoelectric detection module 2;
the output light field of the polarization modulation module 2 is the input light field of the optical filter module 2, the output light field of the optical filter module 2 is the input light field of the optical fiber torsion angle sensing position, the output voltage of the photoelectric detection module 2 can be obtained from the output light field of the selected optical fiber torsion angle sensing position, and the optical fiber torsion angle theta can be obtained from the output voltage of the photoelectric detection module 2.
The two photoelectric oscillators share the long optical fiber delay line through the wavelength division multiplexing technology to form a mutual reference structure, so that the influence of external factors such as temperature on the optical fiber torsion angle measurement structure is eliminated, and finally, the real-time optical fiber torsion angle measurement based on the insensitivity of the temperature of the photoelectric oscillators is realized.
The reference photoelectric oscillator and the measurement photoelectric oscillator have the same structure. The lengths of feedback loops of the two photoelectric oscillators are the same, and the optical fiber delay module and the optical fiber torsion angle sensing position which are hundreds of meters to kilometers in length are shared by the two photoelectric oscillators; the reference light delay module is used for ensuring that the initial feedback loop delays of the two photoelectric oscillators are the same; the microwave filtering module 1 and the microwave filtering module 2 are both band-pass microwave filters, and key indexes such as central frequency, 3dB bandwidth and the like are the same. Because the two photoelectric oscillators have the same structure and the initial oscillation frequencies of the two photoelectric oscillators are the same, the key indexes of the central frequency, the bandwidth and the like of the microwave filtering module 1 and the microwave filtering module 2 are the same; therefore, the influence of environmental factors such as temperature on the oscillation frequencies of the two photoelectric oscillators is the same, so that the influence of the environmental factors such as temperature on the measurement result is eliminated.
The invention realizes the multi-point optical fiber torsion angle measurement based on the wavelength division multiplexing technology; the mutual reference structure is utilized to eliminate the influence of external factors such as temperature and the like on the measurement result of the torsion angle of the optical fiber. The low-phase-noise high-frequency microwave signal generated by the photoelectric oscillator is used for realizing the measurement of the torsion angle of the optical fiber, so that the measurement sensitivity is improved. The optical signal with different wavelengths emitted by the adjustable laser module 2 is used for selecting the sensing position of the optical fiber torsion angle, so that the multipoint measurement of the optical fiber torsion angle is realized; the microwave signal phase difference of the two photoelectric oscillators is used as the fiber torsion angle demodulation quantity, so that the measuring speed is improved. Finally, the method realizes the quick optical fiber torsion angle measurement based on the photoelectric oscillator, insensitive to temperature, quasi-distributed and high in speed.
Drawings
FIG. 1 is a schematic diagram of a quasi-distributed optical fiber torsion angle measuring device based on a photoelectric oscillator;
FIG. 2 is a schematic illustration of an optical fiber twist angle sensing position 1;
FIG. 3 is a schematic illustration of the fiber optic twist angle sensing position 2;
FIG. 4 is a schematic illustration of an optical fiber twist angle sensing position n;
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Fig. 1 is a schematic diagram of a quasi-distributed optical fiber torsion angle measuring device based on a photoelectric oscillator according to the present invention. As shown in fig. 1, the present invention includes a reference optoelectronic oscillator, a measurement optoelectronic oscillator, a microwave phase discrimination module, and a signal processing module; the reference photoelectric oscillator comprises a laser module 1, a polarization control module 1, a polarization modulation module 1, an optical filtering module 1, a wavelength division multiplexing module 01, a delay sensing module, a wavelength division multiplexing module 02, a polarizer module 1, a photoelectric detection module 1, a microwave amplification module 1, a microwave filtering module 1 and a microwave coupling module 1; the measuring photoelectric oscillator comprises a tunable laser module 2, a polarization control module 2, a polarization modulation module 2, an optical filtering module 2, a wavelength division multiplexing module 01, a delay sensing module, a wavelength division multiplexing module 02, a polarizer module 2, a photoelectric detection module 2, a microwave amplification module 2, a microwave filtering module 2 and a microwave coupling module 2.
In the embodiment, the laser generates an optical signal, and the optical signal passes through the polarization controller and is input into the polarization modulator; the polarization modulator transmits an optical signal into the optical filter, the optical filter transmits the optical signal into the wavelength division multiplexer, the optical signal is transmitted to the single-mode optical fiber through the wavelength division multiplexer, and the optical signal transmitted into the single-mode optical fiber is continuously transmitted into the wavelength division multiplexer; in the reference photoelectric oscillator, a wavelength division multiplexer transmits an optical signal into an optical delay line, the optical delay line transmits the optical signal into the wavelength division multiplexer, in the measurement photoelectric oscillator, the wavelength division multiplexer transmits the optical signal into an optical fiber torsion angle sensor, and the optical fiber torsion angle sensor transmits the optical signal into the wavelength division multiplexer; the wavelength division multiplexer transmits the optical signal into a single mode fiber, the optical signal transmitted by the single mode fiber passes through the wavelength division multiplexer, the wavelength division multiplexer demultiplexes the transmitted optical signal and transmits the demultiplexed optical signal into a polarizer, the polarizer transmits the optical signal to a photoelectric detector, and the photoelectric detector converts the optical signal into a microwave signal; the microwave signal is amplified by a radio frequency/microwave broadband low noise amplifier, filtered by a microwave band-pass filter and passes through a microwave/radio frequency coupler, the microwave/radio frequency coupler divides the microwave signal into two paths, one path of the microwave signal is output to a broadband double-balanced mixer, the other path of the microwave signal is fed back to a polarization modulator, and finally a photoelectric feedback loop of two electric oscillators is formed; the broadband double-balanced mixer transmits the phase discrimination result to the DSP digital signal processor.
When the wavelength of the wavelength division multiplexer in the optical fiber torsion angle sensing position is different from the wavelength of the optical signal transmitted into the optical fiber torsion angle sensor, the optical signal transmitted into the optical fiber torsion angle sensing position passes through the wavelength division multiplexer in the optical fiber torsion angle sensing position and then is transmitted into the optical delay line, and the optical delay line transmits the optical signal into the next wavelength division multiplexer and then transmits the optical signal to the single-mode optical fiber;
when linearly polarized light with an included angle of 45 degrees between the polarization controller and the main shaft of the polarization modulator is input into the polarization modulator, the output light field of the polarization modulatorIs composed of
Wherein ExRepresenting the intensity sum E of the light field perpendicular to the x-polarization direction in the output light field of the optical filteryRepresenting the intensity of a light field perpendicular to the y-direction in the output light field of the optical filter; j represents an imaginary number; omeganRepresenting the angular frequency, omega, of the optical carriermRepresenting the angular frequency of the microwave signal; γ represents the phase modulation depth; t represents time;
represents ExAnd EyIs controlled by the dc bias of the input polarization modulator;
the output light field of the optical filter is
Wherein ExRepresenting the intensity of the light field in the output light field of the optical filter, perpendicular to the direction of the x-polarization, EyRepresenting the intensity of a light field in the output light field of the optical filter, in which the y polarization direction is perpendicular; j represents an imaginary number; omeganRepresenting the angular frequency, omega, of the optical carriermRepresenting the angular frequency of the microwave signal; j. the design is a squaren(γ) represents an nth order bessel function of the first type; t represents time;
represents ExAnd EyThe phase difference of (a); γ represents the phase modulation depth;
suppose that the optical signal input into the optical fiber torsion angle sensor has a polarization angle phi and an intensity EiThe input optical field of the optical fiber torsion angle sensor is
Assuming that the fiber torsion angle is theta, the input optical field of the fiber torsion angle sensor is
Optical signal polarization angle alpha phi-CPhi- (1-A/2) theta, whereinCRepresents circular polarization retardation; a represents the relationship between the circular birefringence of the optical fiber and the torsion angle of the optical fiber; phi represents the phase difference of the light field intensities of the output light field of the optical filter, wherein the x and y polarization directions are vertical;
the output voltage of the photodetector is
When in use
The output voltage of the photodetector is V (t). varies.. alpha.cos (. omega.)mt+2φ-(2-A)θ+π/2)J0(γ)J-1(γ), wherein- (2-A) represents a correlation coefficient in which the fiber twist angle in the fiber twist angle sensor is linearly related to the phase of the output microwave signal of the measuring opto-electronic oscillator, ExRepresenting the intensity of the light field in the output light field of the optical filter, perpendicular to the direction of the x-polarization, EyRepresenting the intensity of a light field in the output light field of the optical filter, in which the y polarization direction is perpendicular; omegamRepresenting the angular frequency of the microwave signal; j. the design is a squaren(γ) represents an nth order bessel function of the first type; t represents time;
represents ExAnd EyThe phase difference of (a); gamma represents the phase modulation depth, so that the optical fiber torsion angle theta can be obtained according to the output voltage of the photoelectric detector;
fig. 2-4 are schematic diagrams of the fiber torsion angle sensing position of the present invention. As shown in fig. 2 to 4, the optical fiber torsion angle sensing position includes a wavelength division multiplexing module, a reference light delay module, an optical fiber torsion angle sensing module, and a wavelength division multiplexing module.
In this embodiment, single mode fiber links to each other with wavelength division multiplexer one end, and the wavelength division multiplexer other end links to each other with optical delay line, optic fibre torsion angle sensor, and the other end of optical delay line links to each other with wavelength division multiplexer, and the other end of optic fibre torsion angle sensor links to each other with wavelength division multiplexer, and the wavelength division multiplexer other end links to each other with single mode fiber, and structure, the connected mode homogeneous phase of optic fibre torsion angle sensing position are the same.
Claims (11)
1. Quasi-distributed optical fiber torsion angle measuring device based on photoelectric oscillator, its characterized in that: the microwave phase discrimination device comprises a reference photoelectric oscillator, a measurement photoelectric oscillator, a microwave phase discrimination module and a signal processing module, wherein an output microwave signal of the reference photoelectric oscillator and an output microwave signal of the measurement photoelectric oscillator are simultaneously input into the microwave phase discrimination module, and the output phase discrimination result is output to the signal processing module by the microwave phase discrimination module.
2. The quasi-distributed optical fiber torsion angle measuring apparatus based on the optoelectronic oscillator according to claim 1, wherein: the reference photoelectric oscillator comprises a laser module 1, a polarization control module 1, a polarization modulation module 1, an optical filtering module 1, a wavelength division multiplexing module 01, a delay sensing module, a wavelength division multiplexing module 02, a polarizer module 1, a photoelectric detection module 1, a microwave amplification module 1, a microwave filtering module 1 and a microwave coupling module 1; the laser module 1 generates a laser beam with a wavelength λ0The optical signal input polarization control module 1, the polarization control module 1 transmits the optical signal to the polarization modulation module 1 and then the optical signal is filtered by the optical filtering module 1, the filtered optical signal is transmitted to the wavelength division multiplexing module 01, then the wavelength division multiplexing module 01 transmits the optical signal to the delay sensing module, the delay sensing module transmits the optical signal to the wavelength division multiplexing module 02 and then transmits the optical signal to the polarizer module 1, the polarizer module 1 transmits the optical signal to the photoelectric detection module 1, the photoelectric detection module 1 converts the optical signal into a microwave signal, the microwave signal is amplified by the microwave amplification module 1 and then filtered by the microwave filtering module 1, and the microwave signal passes through the microwave coupling module 1 and is filtered by the microwave coupling module 1The block 1 divides the microwave signal into two beams, wherein one beam is transmitted into the microwave phase discrimination module, and the other beam is fed back to the polarization control module 1 to form a photoelectric feedback loop of the reference photoelectric oscillator.
3. The quasi-distributed optical fiber torsion angle measuring apparatus based on the optoelectronic oscillator according to claim 1, wherein: the measuring photoelectric oscillator comprises a tunable laser module 2, a polarization control module 2, a polarization modulation module 2, an optical filtering module 2, a wavelength division multiplexing module 01, a delay sensing module, a wavelength division multiplexing module 02, a polarizer module 2, a photoelectric detection module 2, a microwave amplification module 2, a microwave filtering module 2 and a microwave coupling module 2, wherein the tunable laser module 2 generates a wavelength lambda1The optical signal is input into a polarization control module 2, the polarization control module 2 transmits the optical signal to a polarization modulation module 2, then the optical signal is filtered by an optical filtering module 2, the filtered optical signal is transmitted into a wavelength division multiplexing module 01, then the wavelength division multiplexing module 01 transmits the optical signal into the delay sensing module, the delay sensing module transmits the optical signal into the wavelength division multiplexing module 02 and then transmits the optical signal into the polarizer module 2, after the polarizer module 2 transmits the optical signal into the photoelectric detection module 2, the photoelectric detection module 2 converts the optical signal into a microwave signal, the microwave signal is amplified by the microwave amplification module 2 and then filtered by the microwave filtering module 2, and the microwave signal is divided into two beams by the microwave coupling module 2 through the microwave coupling module 2, one of the beams is transmitted into the microwave phase discrimination module, and the other beam is fed back to the polarization control module 2 to form a photoelectric feedback loop of the reference photoelectric oscillator.
4. The optoelectronic oscillator based quasi-distributed optical fiber torsion angle measuring apparatus according to claim 2 or 3, wherein: the delay sensing module comprises n +1 optical fiber delay modules and n optical fiber torsion angle sensing positions, wherein n is a natural number, the n +1 optical fiber delay modules are alternately connected with the n optical fiber torsion angle sensing positions, and the n +1 optical fiber delay modules transmit optical signals into the wavelength division multiplexing module 02.
5. The optoelectronic oscillator based quasi-distributed optical fiber torsion angle measuring apparatus according to claim 2 or 3, wherein: the optical fiber torsion angle sensing position 1 comprises a wavelength division multiplexing module 11, a reference light delay module 1, an optical fiber torsion angle sensing module 1 and a wavelength division multiplexing module 12, wherein the optical fiber delay module is connected with one end of the wavelength division multiplexing module 11, the other end of the wavelength division multiplexing module 11 is connected with the reference light delay module 1 and the optical fiber torsion angle sensing module 1, the other end of the reference light delay module 1 is connected with the wavelength division multiplexing module 12, the other end of the optical fiber torsion angle sensing module 1 is connected with the wavelength division multiplexing module 12, the other end of the wavelength division multiplexing module 12 is connected with the next optical fiber delay module, and the structure and the connection mode of the optical fiber torsion angle sensing position are the same.
6. The quasi-distributed optical fiber torsion angle measuring method based on the photoelectric oscillator is characterized by comprising the following steps of: the method comprises the following steps:
A. in a reference optoelectronic oscillator, a laser module generates a light having a wavelength λ0The optical signal is controlled by the polarization control module 1, controls the included angle between the linearly polarized light input into the polarization control module 1 and the main shaft of the polarization modulation module 1, and then is input into the polarization modulation module 1, and the wavelength is lambda0The optical signal is modulated by the microwave signal in the polarization modulation module 1; the optical signal modulated by the microwave signal is filtered by the optical filter module 1, and the optical signal except the carrier and one of the first-order side bands is filtered; the filtered optical signal is input into the optical fiber delay module 1 through the wavelength division multiplexing module 01, the optical fiber delay module 1 transmits the optical signal to the optical fiber torsion angle sensing position, the working wavelength of the wavelength division multiplexing module at each optical fiber torsion angle sensing position is different, when the working wavelength of the wavelength division multiplexing module in the optical fiber torsion angle sensing position is the same as the wavelength of the optical signal transmitted to the optical fiber torsion angle sensing position, the optical fiber torsion angle sensing position is selected as a measuring position, the other optical fiber torsion angle sensing positions are equivalent to an optical fiber delay module, the optical signal output by the optical fiber delay module 1 is subjected to wavelength division multiplexing in the selected optical fiber torsion angle sensing positionAfter the module is used, the optical signal transmitted by the next wavelength division multiplexing module passes through the rest optical fiber delay modules and the unselected optical fiber torsion angle sensing positions and then is demultiplexed by the wavelength division multiplexing module 02 after passing through one optical fiber delay module, one optical signal after demultiplexing is transmitted into a polarizer module 2 in the measurement photoelectric oscillator, and the other optical signal with the wavelength of lambda0The optical signal is transmitted into a polarizer module 1; the polarizer module 1 transmits an optical signal into the photoelectric detection module 1, the photoelectric detection module 1 converts the received optical signal into a microwave signal, the microwave signal is amplified by the microwave amplification module 1 and filtered by the microwave filtering module 1, the filtered microwave signal is divided into two beams by the microwave coupling module 1, one beam of the microwave signal is transmitted to the microwave phase discrimination module, and the other beam of the microwave signal is transmitted to the polarization modulation module 1 to form a photoelectric feedback loop of the reference photoelectric oscillator;
B. in a measuring photoelectric oscillator, a tunable laser module 2 generates an optical signal of which output wavelength is continuously changed within a certain range and inputs the optical signal to a polarization control module 2, the wavelength range being λ1～λnN is a natural number, the polarization control module 2 controls an included angle between linearly polarized light input into the polarization control module 2 and a main shaft of the polarization modulation module 2, then the linearly polarized light is input into the polarization modulation module 2, an optical signal is modulated by a microwave signal in the polarization modulation module 2, the optical signal modulated by the microwave signal is filtered by the optical filter module 2, optical signals except a carrier wave and one first-order side of the carrier wave are filtered, the filtered optical signal is input into the optical fiber delay module 1 through the wavelength division multiplexing module 01, the optical fiber delay module 1 transmits the optical signal to the optical fiber torsion angle sensing position, and the wavelength division multiplexing modules at each optical fiber torsion angle sensing position have different working wavelengths; when the working wavelength of the wavelength division multiplexing module in the optical fiber torsion angle sensing position is the same as the wavelength of the optical signal transmitted to the optical fiber torsion angle sensing position, the optical fiber torsion angle sensing position is selected as the measuring position, the other optical fiber torsion angle sensing positions are equivalent to an optical fiber delay module, the optical signal output by the optical fiber delay module 1 passes through the wavelength division multiplexing module in the selected optical fiber torsion angle sensing position and then passes through the wavelength division multiplexing moduleThe optical fiber torsion angle module is transmitted into the next wavelength division multiplexing module, an optical signal transmitted by the next wavelength division multiplexing module passes through the rest optical fiber delay modules and the unselected optical fiber torsion angle sensing positions, then passes through one optical fiber delay module and is demultiplexed by the wavelength division multiplexing module 02, and the wavelength after demultiplexing is lambda0Is transmitted into a polarizer module 1 in a reference optoelectronic oscillator, with a wavelength of lambda1～λnAny optical signal in the range is transmitted into the polarizer module 2; the polarizer module 2 transmits an optical signal into the photoelectric detection module 2, the photoelectric detection module 2 converts the received optical signal into a microwave signal, the microwave signal is amplified by the microwave amplification module 2 and filtered by the microwave filtering module 2, the filtered microwave signal is divided into two beams by the microwave coupling module 2, one beam of the microwave signal is transmitted to the microwave phase discrimination module, and the other beam of the microwave signal is transmitted to the polarization modulation module 2 to form a photoelectric feedback loop of the measurement photoelectric oscillator;
C. and D, carrying out phase discrimination on the microwave signal transmitted to the phase frequency discrimination module in the step A and the microwave signal transmitted to the phase frequency discrimination module in the step B in a microwave phase discrimination module, inputting an output phase discrimination result into a signal processing module by the microwave phase discrimination module, and finally demodulating the optical fiber torsion angle in the optical fiber torsion angle sensing position.
7. The quasi-distributed optical fiber torsion angle measurement method based on the optoelectronic oscillator according to claim 5, wherein: in the step B, when the wavelength of the wavelength division multiplexing module in the optical fiber torsion angle sensing position is different from the wavelength of the optical signal transmitted into the optical fiber torsion angle sensing position, the optical signal transmitted into the optical fiber torsion angle sensing position passes through the wavelength division multiplexing module in the optical fiber torsion angle sensing position and then is transmitted into the reference optical delay module, and the reference optical delay module transmits the optical signal into the next wavelength division multiplexing module and then transmits the optical signal to the next optical fiber delay module.
8. The quasi-distributed optical fiber torsion angle measurement method based on the optoelectronic oscillator according to claim 5, wherein: in step B, the method also comprises: when the linearly polarized light with the included angle of 45 degrees between the polarization control module 2 and the main shaft of the polarization modulation module 2 is input into the polarization modulation module 2, the output light field of the polarization modulation module 2 is
Wherein ExRepresenting the sum E of the intensities of the light fields with perpendicular x-polarization directions in the output light field of the optical filter module 2yRepresents the y-direction perpendicular light field intensity in the output light field of the optical filter module 2; j represents an imaginary number; omeganRepresenting the angular frequency, omega, of the optical carriermRepresenting the angular frequency of the microwave signal; γ represents the phase modulation depth; t represents time;
represents ExAnd EyIs controlled by the dc bias of the input polarization modulation module 2.
9. The quasi-distributed optical fiber torsion angle measurement method based on the optoelectronic oscillator according to claim 5, wherein: in step B, the method further comprises: the output light field of the optical filter module 2 is
Wherein ExRepresenting the intensity of the light field perpendicular to the x-polarization direction in the output light field of the optical filter module 2, EyRepresents the intensity of the light field in the output light field of the optical filter module 2, in which the y polarization direction is perpendicular; j represents an imaginary number; omeganRepresenting the angular frequency, omega, of the optical carriermRepresenting the angular frequency of the microwave signal; j. the design is a squaren(γ) represents an nth order bessel function of the first type; t represents time;
represents ExAnd EyThe phase difference of (a); γ represents the phase modulation depth.
10. The quasi-distributed optical fiber torsion angle measurement method based on the optoelectronic oscillator according to claim 5, wherein: in step B, the method further comprises: suppose the optical signal polarization angle of the optical fiber in the input optical fiber torsion angle sensing module is phi, and the intensity is EiThe input optical field of the optical fiber torsion angle sensing module is
Assuming that the fiber torsion angle is theta, the input optical field of the fiber torsion angle sensing module is
Optical signal polarization angle alpha of optical fiber in output optical fiber torsion angle sensing module ═ phi-CPhi- (1-A/2) theta, whereinCRepresents circular polarization retardation; a represents the relationship between the circular birefringence of the optical fiber and the torsion angle of the optical fiber; phi denotes the phase difference of the light field intensities in the output light field of the optical filter module 2 with perpendicular x and y polarization directions.
11. The quasi-distributed optical fiber torsion angle measurement method based on the optoelectronic oscillator according to claim 5 or 7, wherein: the output voltage of the photoelectric detection module 2 is
When in use
The output voltage of the photodetection module 2 is y (t) ° cos (ω)mt+2φ-(2-A)θ+π/2)J0(γ)J-1(γ) wherein- (2-A) represents lightCorrelation coefficient of linear correlation between the fiber torsion angle in the fiber torsion angle sensing module and the phase of the output microwave signal of the measurement optoelectronic oscillator, ExRepresenting the intensity of the light field perpendicular to the x-polarization direction in the output light field of the optical filter module 2, EyRepresents the intensity of the light field in the output light field of the optical filter module 2, in which the y polarization direction is perpendicular; omegamRepresenting the angular frequency of the microwave signal; j. the design is a squaren(γ) represents an nth order bessel function of the first type; t represents time;
represents ExAnd EyThe phase difference of (a); γ represents the phase modulation depth, and thus the fiber twist angle θ can be obtained from the output voltage of the photodetection module 2.
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