Disclosure of Invention
The application provides a broadband characteristic testing device and method for an optical fiber current sensor, and solves the problem of requirements for testing and verifying high-frequency characteristics, step response characteristics and other complex waveforms of the optical fiber current sensor.
The application provides a wide band characteristic testing arrangement of optic fibre current sensor includes: the system comprises a Faraday phase shift equivalent device, a high-frequency \ step signal source and an electronic transformer calibrator;
the Faraday phase shift equivalent device is used for converting a high-frequency or step voltage signal generated by the high-frequency/step signal source and an optical signal of the optical fiber current sensor to be detected into equivalent Faraday phase shift and sending the equivalent Faraday phase shift to the optical fiber current sensor to be detected;
the high-frequency \ step signal source is respectively connected with the Faraday phase shift equivalent device and the electronic transformer calibrator and generates a high-frequency or step voltage signal;
the electronic transformer calibrator is respectively connected with a high-frequency \ step signal source and a data output port of a tested optical fiber current sensor, receives a voltage signal of the high-frequency \ step signal source, receives a digital output signal of the tested optical fiber current sensor, synchronizes the voltage signal and the digital output signal, and then performs frequency response calculation and step response calculation to obtain the broadband characteristic of the tested optical fiber current sensor.
Preferably, the measured optical fiber current sensor and the faraday phase shift equivalent device are connected by fusion through a polarization maintaining optical fiber of the measured optical fiber current sensor and a polarization maintaining tail fiber of the faraday phase shift equivalent device.
Preferably, the faraday phase shift equivalent device is composed of an optical path and a circuit part, and the optical path part includes: the polarization maintaining optical fiber, the phase modulator, the optical fiber delay loop L2, the 1/4 wave plate and the optical fiber reflector;
the circuit part includes: AD converter, integral operation, proportion regulation and DA converter.
Preferably, the phase modulator is configured to apply an equivalent phase shift to the current.
The application also provides a method for testing the broadband characteristic of the optical fiber current sensor, which comprises the following steps:
the high-frequency \ step signal source generates a high-frequency or step voltage signal;
the Faraday equivalent device applies equivalent Faraday phase shift to the high-frequency or step voltage signal and the measured optical fiber current sensor;
the electronic transformer calibrator receives a voltage signal of a high-frequency \ step signal source and a digital output signal of a tested optical fiber current transformer, synchronizes the voltage signal and the digital output signal, and then performs frequency response calculation and step response calculation to obtain the broadband characteristic of the tested optical fiber current sensor.
Preferably, the faraday equivalent device applies equivalent faraday phase shift to the high-frequency or step voltage signal and the measured optical fiber current sensor, and comprises:
a modulator of the Faraday equivalent device applies equivalent Faraday phase shift to the high-frequency voltage signal or the step voltage signal;
a modulator of the Faraday equivalent device applies equivalent phase shift to a measured optical fiber current sensor; the equivalent phase shift includes an offset phase shift and a feedback phase shift.
Preferably, the modulator of the faraday equivalent arrangement applies an equivalent faraday phase shift to the high frequency voltage signal or the step voltage signal, and comprises:
the AD converter collects a high-frequency voltage signal or a step voltage signal;
performing integral operation on the signal to obtain a step wave of each application period of the modulator;
after the step wave is corrected, the step wave is applied to a modulator through a DA converter to generate equivalent Faraday phase shift.
The application provides a wide band characteristic testing arrangement of optic fibre current sensor includes: the system comprises a Faraday phase shift equivalent device, a high-frequency \ step signal source and an electronic transformer calibrator; the Faraday phase shift equivalent device is used for converting a high-frequency or step voltage signal generated by the high-frequency/step signal source and an optical signal of the optical fiber current sensor into equivalent Faraday phase shift and sending the equivalent Faraday phase shift to the optical fiber current sensor; the high-frequency \ step signal source is respectively connected with the Faraday phase shift equivalent device and the electronic transformer calibrator and generates a high-frequency or step voltage signal; the electronic transformer calibrator is respectively connected with a high-frequency \ step signal source and a data output port of the optical fiber current sensor, receives a voltage signal of the high-frequency \ step signal source, receives a digital output signal of the optical fiber current sensor, synchronizes the voltage signal and the digital output signal, and then performs frequency response calculation and step response calculation to obtain the broadband characteristic of the optical fiber current sensor, thereby solving the problem of the requirements on testing and verification of the high-frequency characteristic, the step response characteristic and other complex waveforms of the optical fiber current sensor.
Detailed Description
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. This application is capable of implementation in many different ways than those herein set forth and of similar import by those skilled in the art without departing from the spirit of this application and is therefore not limited to the specific implementations disclosed below.
A broadband characteristic testing apparatus for an optical fiber current sensor, as shown in fig. 1, includes: the system comprises a Faraday phase shift equivalent device, a high-frequency \ step signal source and an electronic transformer calibrator;
the Faraday phase shift equivalent device is used for converting a high-frequency or step voltage signal generated by the high-frequency/step signal source and an optical signal of the optical fiber current sensor to be detected into equivalent Faraday phase shift and sending the equivalent Faraday phase shift to the optical fiber current sensor to be detected;
the high-frequency \ step signal source is respectively connected with the Faraday phase shift equivalent device and the electronic transformer calibrator and generates a high-frequency or step voltage signal;
the electronic transformer calibrator is respectively connected with a high-frequency \ step signal source and a data output port of a tested optical fiber current sensor, receives a voltage signal of the high-frequency \ step signal source, receives a digital output signal of the tested optical fiber current sensor, synchronizes the voltage signal and the digital output signal, and then performs frequency response calculation and step response calculation to obtain the broadband characteristic of the tested optical fiber current sensor.
The optical fiber current transformer is characterized in that a scheme schematic diagram is shown in fig. 2, the current is detected by utilizing an optical interference principle, light emitted by a light source passes through a coupler and is converted into linearly polarized light at a polarizer, and the linearly polarized light is uniformly distributed on two orthogonal axes (namely a fast axis and a slow axis) of a polarization maintaining optical fiber to be independently transmitted through a 45-degree polarization maintaining optical fiber melting point. After passing through the lambda/4 wave plate, the linearly polarized light which is orthogonal to each other is respectively converted into left-handed circularly polarized light and right-handed circularly polarized light, and the circularly polarized light enters the sensing optical fiber for transmission. Under the action of a magnetic field generated by the current to be measured, a Faraday magneto-optical effect is generated between two beams of circularly polarized light which are synchronously transmitted, and a transmission phase difference is generated. Two beams of circularly polarized light are transmitted to the end of the sensing optical fiber and reflected by the reflector and then returned back along the original optical path, so that the circularly polarized light is received againThe magnetic field generated by the current influences the Faraday magneto-optical effect, and the phase difference is doubled. The returned circularly polarized light is restored into linearly polarized light after passing through the lambda/4 wave plate for the second time, but the polarization directions are interchanged (namely the transmission axes of the linearly polarized light originally transmitted in the fast axis and the slow axis are interchanged at the moment). When the phase difference is transmitted back to the 45-degree melting point, linearly polarized light on the fast axis and the slow axis respectively forms interference distribution, an optical signal on one working axis is filtered after passing through the extinction direction of the polarizer, only an interference optical signal in the polarization direction is reserved and returns to the coupler, and finally, the interference optical signal carrying Faraday phase difference information enters the photoelectric detector through the coupler. Because the two interfered linearly polarized light beams have the same optical path, the optical path structure has complete space reciprocity, and the phase difference between the two linearly polarized light beams
![Figure BDA00023282811700000513](https://patentimages.storage.***apis.com/74/0d/d3/fc0b1352498d16/BDA00023282811700000513.png)
Only affected by current, can be formulated as:
in the formula (1), F represents the optical phase difference of single-path circularly polarized light in the sensing optical fiber due to Faraday effect, V represents the Verdet constant of the sensing optical fiber, N represents the turn number of the sensing optical fiber, and I is the measured current value.
The interference light intensity signal of the return photodetector can be expressed as:
in the formula, P0For light source output power, α is the optical path loss.
Applying a high frequency intrinsic phase difference between two optical signals using a phase modulator
(typically a square wave signal of amplitude + - π/2 with a period of 2 τ, where τ is the transit time, representing the first and second times the optical signal is in the optical pathTime difference of twice passing through the phase modulator), when
When the interference light intensity signal is a straight line, the peak pulse generated when the modulation phase is suddenly changed is ignored due to the even function characteristic of the interference light intensity, and the modulated interference light intensity signal is a straight line
And meanwhile, the modulated interference light intensity becomes a square wave signal with the same frequency and phase as the modulation signal. Adding a feedback phase difference to the phase modulator
Regulating
When the amplitude of the square wave signal of the interference light intensity is zero, the requirements are met
At this time
And
equal in size and opposite in sign, will
The measured current value can be calculated as the demodulation output of the optical phase difference and substituted by formula (1), which is the basic principle of phase modulation demodulation and closed loop feedback technology, and the process can be expressed as follows:
by the phase modulation and demodulation and closed loop feedback technology, the original sampling rate of the FOCT reaches over 100kHz, so that the FOCT has the technical condition of quick response.
The application provides an optic fibre current sensor wide band characteristic testing arrangement, it is measured optic fibre current sensor and Faraday phase shift equivalence device, and the polarization-maintaining fiber optic fibre that keeps through being measured optic fibre current sensor links to each other with the butt fusion of keeping of Faraday phase shift equivalence device. The measured optical fiber current sensor consists of a light source collector, a photoelectric detector, a beam splitter, a polarizer, a 45-degree melting point, a phase modulator, an optical fiber delay ring and a signal processing circuit board.
The faraday phase shift equivalent device is composed of an optical path and a circuit part, as shown in fig. 3, the optical path part comprises: the polarization maintaining optical fiber, the phase modulator, the optical fiber delay loop L2, the 1/4 wave plate and the optical fiber reflector; the circuit part includes: AD converter, integral operation, proportion regulation and DA converter. A phase modulator for applying an equivalent phase shift to the current. The integral operation and the proportion adjustment are logic units which can be programmed by FPGA, and the FPGA controls the AD converter and the DA converter to work. The working principle of the polarization maintaining fiber laser is that two beams of linearly polarized light are input into a device along a fast axis and a slow axis of a polarization maintaining fiber, are converted into two beams of leftwards-handed circularly polarized light and rightwards-handed circularly polarized light by an 1/4 wave plate after passing through a phase modulator and a fiber delay ring, are transmitted to a reflector through a reflector fiber, are converted into the rightwards-handed circularly polarized light and the leftwards-handed circularly polarized light after being reflected by the reflector, and are converted into two beams of linearly polarized light through a 1/4 wave plate, but transmission paths are exchanged, namely the fast axis polarized light is transmitted through the slow axis when returning. The two polarized light exchange paths return to the tested fiber current sensor.
Since the lengths of the fiber delay loop L2 and the fiber mirror are determined, the time difference between the two times of light passing through the phase modulator, i.e. the transit time τ of the polarized light, can be accurately calculated. The phase shift introduced by the phase modulator is related to the optical path transit time τ and the voltage difference. Assuming that the light beam passes through the phase modulator clockwise at time t, the modulation voltage is V (t), and the corresponding modulation phase shift is
When the light beam passes through the phase modulator anticlockwise at the moment of (t + tau) after being reflected, the modulation voltage is V (t + tau), and the corresponding modulation phase shift is
Where τ is the path transit time. In the whole process, the two phase shifts are opposite in direction, and the total phase shift introduced by the phase modulator can be expressed as
From the above, the step wave can be used to generate equivalent phase shift
After the AD converter collects high-frequency or step input signals, accumulation integration is carried out to form the step height of the digital step wave. As shown in fig. 4, the sampling values at t, t + τ, t +2 τ, t +3 τ are respectively V1, V2, V3, V4, which are accumulated to form a digital step wave, and the digital step wave is applied to the DA converter after being scaled, as shown in fig. 5, the step width is equal to the transit time τ, and the step height determines the equivalent faraday phase shift introduced between the two coherent lights
The resulting equivalent faraday phase shift is consistent with a high frequency or step input signal as shown in figure 6.
The present application also provides a method for testing a broadband characteristic of an optical fiber current sensor, as shown in fig. 7, including:
step S101, the high-frequency \ step signal source generates a high-frequency or step voltage signal.
In step S102, the faraday equivalence device applies equivalent faraday phase shift to the high-frequency or step voltage signal and the measured fiber current sensor.
By analyzing the dynamic response performance of the faraday phase shift equivalent device, a data model of each large device is established, as shown in fig. 8.
As can be seen in FIG. 8, the current flowing through the fiber optic sensing loop will produce a Faraday phase shift
By means of a modulatorBiased phase shift
And feedback phase shift
To ensure the stability of the system, the feedback coefficient is generally less than 1, and therefore
For high frequency signals or sudden change signals, the closed loop feedback will bring the bandwidth of the system to be reduced.
Due to the current source device performance limitation, it is difficult to obtain a desired high frequency
The signal, and therefore the high frequency performance of the system, is verified by applying an equivalent phase shift through the modulator, the principle of which is shown in fig. 9.
The high-frequency signal generator generates a high-frequency voltage signal or a step voltage signal, and the high-frequency voltage signal or the step voltage signal is collected by the AD converter. Because the Faraday phase shift generated by the current is a nonreciprocal phase shift, and the phase shift applied by the modulator is a reciprocal phase shift, in order to apply an equivalent nonreciprocal phase shift, two beams of interference light are required to be utilized for transmission delay, and a modulator signal is applied in a step wave mode. Therefore, it is necessary to perform an integration operation on the AD signal, calculate a step wave for each application period, perform a proportional correction, and apply the result to the modulator 2 through the DA converter, thereby generating an equivalent faraday phase shift.
Step S103, the electronic transformer calibrator receives a voltage signal of the high-frequency \ step signal source and a digital output signal of the measured optical fiber current transformer, and performs frequency response calculation and step response calculation after synchronizing the voltage signal and the digital output signal, so as to obtain the broadband characteristic of the measured optical fiber current sensor.
The device and the method for testing the broadband characteristics of the optical fiber current sensor meet the requirements of relevant standards and flexible and straight projects on frequency response characteristic tests of the optical fiber current sensor, carry out frequency response tests by an equivalence method, examine the frequency response characteristics of the optical fiber sensor and make up for the defects of the previous domestic detection means. And (3) performing a step response test by using an equivalent method, examining the step response characteristic of the optical fiber sensor and making up the defects of the previous domestic detection means. And the sensing characteristic test of the optical fiber current sensor under other complex waveforms can be carried out by an equivalent method.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention.