A quasi-reciprocal optical voltage sensor based on harmonic phase demodulation

Abstract

The application provides a quasi-reciprocal optical voltage sensor based on harmonic phase demodulation, and belongs to the technical field of high-voltage measurement and optical sensing technology.The voltage sensor comprises, which are sequentially connected, a light source, a fiber coupler, a polarizer, a 45-degree fusion splice, a phase modulator, a polarization-maintaining fiber delay line, a 45-degree Faraday rotator, a fiber collimator, a lithium niobate crystal and a reflective film.The voltage sensor further comprises, which are sequentially connected, a photodetector, a lock-in amplifier and an upper computer; and the photodetector is further connected with the fiber coupler, and the lock-in amplifier is further connected with the phase modulator.The application directly extracts and demodulates the phase information of light waves, avoids errors caused by bias elements and light intensity fluctuations, and effectively breaks through the technical bottleneck of the traditional optical voltage sensor in the range and linearity.

Description

Technical Field

[0001] This invention belongs to the field of high voltage measurement and optical sensing technology, specifically, it relates to a quasi-reciprocal optical voltage sensor based on harmonic phase demodulation. Background Technology

[0002] In modern power systems such as smart grids, ships, and railways, the accuracy and reliability of voltage measurement are the core foundation for ensuring the safe and stable operation of the system. Traditional voltage sensors, limited by physical mechanisms, generally suffer from inherent defects such as bottlenecks in insulation performance, susceptibility to electromagnetic interference, and hysteresis effects. In contrast, optical voltage sensors based on the electro-optic effect of lithium niobate crystals use all-dielectric optical fiber as the transmission carrier, and the sensing probe has no metal conductive structure. This not only significantly improves insulation strength and resistance to electromagnetic interference, but also fundamentally eliminates the effects of hysteresis. With these significant inherent advantages, optical voltage sensors have now become the mainstream development trend of precision voltage measurement technology in next-generation complex electromagnetic environments.

[0003] However, existing bulk crystal optical voltage sensors still face many challenges in practical engineering applications, mainly in the following aspects: ① Poor operating point stability: Traditional optical intensity demodulation schemes typically require a quarter-wave plate connected in series within the sensing unit to provide a fixed quadrature bias phase in order to achieve linear output. However, in complex environments, manufacturing errors of optical components, packaging stress, and natural birefringence drift due to temperature fluctuations can cause the quadrature bias point to shift, severely weakening the long-term operational stability of the system.

[0004] ② It is susceptible to environmental interference, and the optical intensity demodulation scheme is extremely sensitive to changes in optical path loss and fluctuations in light source power. Although compensation methods such as dual-path division are used, it is still difficult to completely eliminate measurement errors caused by non-sensor factors such as fiber bending and connector aging.

[0005] ③ Linearity conflicts with measurement range; the intensity signal of the interference output exhibits a non-linear sinusoidal relationship with the measured voltage. To ensure measurement accuracy, the system typically operates only in the quasi-linear region of the sine curve, which significantly compresses the effective measurement range. Once the measured voltage approaches or exceeds the half-wave voltage of the crystal, the system will produce severe non-linear distortion.

[0006] ④ Lack of reciprocity: Existing non-reciprocal or partially reciprocal structures are unable to effectively suppress common-mode noise in the optical path, resulting in a low system signal-to-noise ratio, which is difficult to meet the requirements of high-precision voltage measurement. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention proposes a quasi-reciprocal optical voltage sensor based on harmonic phase demodulation. By directly extracting and demodulating the phase information of the light wave, it avoids the errors introduced by bias elements and light intensity fluctuations, thereby effectively breaking through the technical bottlenecks of traditional optical voltage sensors in terms of range and linearity.

[0008] This invention is achieved through the following technical solution: A quasi-reciprocal optical voltage sensor based on harmonic phase demodulation: The voltage sensor includes a light source, an optical fiber coupler, a polarizer, a 45° fusion splice, a phase modulator, a polarization-maintaining optical fiber delay line, a 45° Faraday rotator, an optical fiber collimating lens, a lithium niobate crystal, and a reflective film connected in sequence. The voltage sensor also includes a photodetector, a lock-in amplifier, and a host computer connected in sequence; the photodetector is also connected to an optical fiber coupler, and the lock-in amplifier is also connected to a phase modulator.

[0009] Furthermore, the lock-in amplifier includes a lock-in demodulation module; the lock-in demodulation module is used to extract the amplitudes of the first harmonic component and the second harmonic component; The phase-locked demodulation module includes a first digital low-pass filter, a second digital low-pass filter, a third digital low-pass filter, a fourth digital low-pass filter, a first square calculation module, and a second square calculation module.

[0010] A control method for an optical voltage sensor with harmonic phase demodulation: the method includes the following steps: Step 1: The light emitted by the light source is polarized into linearly polarized light through the fiber coupler and polarizer; the linearly polarized light is evenly split into two orthogonal linearly polarized beams through a 45º fusion splice; they enter the phase modulator respectively, and the phase modulator applies initial phase modulation to the linearly polarized light, the modulation signal of which comes from the internal reference signal of the lock-in amplifier. Step 2: Two orthogonally polarized beams pass through a polarization-maintaining fiber delay line and are coupled to a fiber collimator via a 45° Faraday rotator. The two outgoing orthogonally polarized beams enter a lithium niobate crystal, propagate along its optical axis, reach the reflective film, and return. The Pockels phase shift is then doubled. The returning orthogonally polarized beams pass through the 45° Faraday rotator and are rotated another 45°, causing the polarization directions of the two beams to exchange. They are then coupled through a 45° fusion splice, resulting in interference. Step 3: After the photodetector converts the optical signal into an electrical signal, it is sampled into a digital signal by the data acquisition card and transmitted to the phase-locked demodulation module; Step 4: The amplitudes of the first and second harmonic components extracted by the phase-locked demodulation module are transmitted to the host computer; the amplitudes of the first and second harmonic components are demodulated to obtain the Pockels phase shift through the division and arctangent operation modules of the host computer.

[0011] Furthermore, in step 1, the initial phase modulation signal applied to the phase modulator comes from the reference signal of the lock-in amplifier.

[0012] Furthermore, in step 2, the lithium niobate crystal adopts a modulation method in which light passes through along the z-direction and a voltage is applied along the y-axis; Since the two orthogonally polarized beams return after reaching the reflective film, the phase difference generated by the Pockels effect of the lithium niobate crystal is doubled.

[0013] Furthermore, in step 3, specifically: The light intensity signal carrying the high-frequency modulation signal enters the lock-in amplifier. The signal under test and the two first-harmonic quadrature reference signals generated by the lock-in amplifier enter the first phase-sensitive detector branch for multiplication. The two signals pass through the first low-pass filter and the second low-pass filter respectively to obtain the DC component of the signal, and then enter the first square calculation module to calculate the amplitude and phase of the first harmonic component. The signal under test and two quadrature reference signals of second harmonic generation generated by the lock-in amplifier enter the second phase-sensitive detector branch for multiplication. The two signals pass through the third low-pass filter and the fourth low-pass filter respectively to obtain the DC component of the signal, and then enter the second square calculation module to calculate the amplitude and phase of the second harmonic component.

[0014] Furthermore, it also includes step 5, where the host computer converts the demodulated Pockels phase shift into the corresponding voltage value according to the pre-calibrated system proportional coefficient, and calculates the amplitude of the measured power frequency voltage to complete the voltage measurement.

[0015] A computer device system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above-described method. A computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implement the steps of the above-described method.

[0016] A computer program product includes a computer program / instructions that, when executed by a processor, implement the steps of the method described above.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention, based on the working principle of optical voltage sensors, proposes a quasi-reciprocal optical voltage sensor that can eliminate the influence of light source intensity fluctuations and is independent of orthogonal operating points. Furthermore, the introduction of a high-frequency modulation signal effectively suppresses low-frequency noise, making it suitable for various applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a quasi-reciprocal optical voltage sensor based on harmonic phase demodulation according to the present invention; Figure 2 This is a flowchart illustrating the harmonic phase demodulation algorithm; Figure 3 This is a comparison chart of the amplitudes of the demodulated signals when different amplitudes of power frequency voltage are applied to the voltage sensor; Among them, 1 is the light source, 2 is the fiber coupler, 3 is the polarizer, 4 is the 45° fusion splice, 5 is the phase modulator, 6 is the polarization-maintaining fiber delay loop, 7 is the 45° Faraday rotator, 8 is the fiber collimator, 9 is the lithium niobate crystal, 10 is the reflective film, 11 is the photodetector, 12 is the lock-in amplifier, 13 is the host computer, 14 is the first low-pass filter, 15 is the second low-pass filter, 16 is the third low-pass filter, 17 is the fourth low-pass filter, 18 is the first square calculation module, 19 is the second square calculation module, 20 is the phase-locked demodulation module, 21 is the division operation module, and 22 is the arctangent operation module. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0021] Reference Figure 1 As shown, this invention proposes a quasi-reciprocal optical voltage sensor based on harmonic phase demodulation. The voltage sensor includes a light source 1, an optical fiber coupler 2, a polarizer 3, a 45° fusion splice 4, a phase modulator 5, a polarization-maintaining fiber delay loop 6, a 45° Faraday rotator 7, an optical fiber collimating lens 8, a lithium niobate crystal 9, and a reflective film 10 connected in sequence. A photodetector 11, a lock-in amplifier 12, and a host computer 13 are connected in sequence. The photodetector 11 is connected to the optical fiber coupler 2, and the lock-in amplifier 12 is connected to the phase modulator 5.

[0022] An optical voltage sensor based on harmonic phase demodulation includes the following steps: Step 1: The light emitted by the light source 1 is polarized into linearly polarized light through the fiber coupler 2 and the polarizer 3; the linearly polarized light is evenly split into two orthogonal linearly polarized beams through the 45° fusion point 4 between the polarizer and the integrated optical phase modulator; the beams then enter the phase modulator 5 respectively. The function of the phase modulator 5 is to apply initial phase modulation to the linearly polarized light, and its modulation signal comes from the internal reference signal of the lock-in amplifier 12. Step 2: Two orthogonally polarized beams pass through the polarization-maintaining fiber delay line 6, and are coupled to the fiber collimating lens 8 via a Faraday rotator 7 with a rotation angle of 45°. The two outgoing orthogonally polarized beams enter the lithium niobate crystal 9, propagate along the optical axis of the lithium niobate crystal 9, reach the reflective film 10, and return. Then, the Pockels phase shift is doubled. The returning orthogonally polarized beams pass through the Faraday rotator 7 and are rotated again by 45°, causing the polarization directions of the two orthogonally polarized beams to be exchanged. They are then coupled through the 45° fusion splice 4, resulting in interference. A photodetector 11 is used to detect the intensity of the interference light.

[0023] Step 3: After the photodetector 11 converts the optical signal into an electrical signal, it samples it as a digital signal through the data acquisition card; the phase-locked demodulation module 20 includes a first digital low-pass filter 14, a second digital low-pass filter 15, a third digital low-pass filter 16, a fourth digital low-pass filter 17, a first square calculation module 18, and a second square calculation module 19. The phase-locked demodulation module 20 is used to extract the amplitude of the first harmonic component and the second harmonic component; Step 4: The amplitude values ​​of the first harmonic component and the second harmonic component extracted by the phase-locked demodulation module 20 are sent to the host computer 13. The host computer 13 is used to demodulate the amplitude values ​​of the first harmonic component and the second harmonic component after performing division operation module 21 and arctangent operation 22 to obtain the Pockels phase shift.

[0024] Specifically, in step 1, the initial phase modulation signal applied to the phase modulator 5 comes from the reference signal of the lock-in amplifier, and the high-frequency modulation signal can be expressed as:

[0025] in, K m For modulation depth, ω m The modulation frequency; Specifically, in step 2, the lithium niobate crystal 9 uses light transmission along the z-axis to avoid the initial phase difference caused by the crystal's natural birefringence. When a voltage is applied along the axis, it will not cause rotation of the optical axis. Therefore, the lithium niobate crystal 9 in this invention employs a modulation method of light transmission along the z-axis and voltage application along the y-axis.

[0026] Since the two orthogonally polarized beams return after reaching the reflective film, the phase difference generated by the Pockels effect of lithium niobate is doubled.

[0027] The light intensity detected by the photodetector is:

[0028] in, I in For input light intensity, α For optical path loss, δ ( t The phase difference is caused by the Pockels effect. τ For transit time; the introduction of a high-frequency carrier signal can also achieve frequency conversion, reducing 1 / f The impact of noise.

[0029] Specifically, in step 3, such as Figure 2 The demodulation process diagram shown illustrates that the light intensity signal carrying the high-frequency modulation signal enters the lock-in amplifier 12. The signal under test and two first-harmonic quadrature reference signals generated by the lock-in amplifier 12 enter the phase-sensitive detector module for multiplication. The two signals pass through the first low-pass filter 14 and the second low-pass filter 15 respectively to obtain the DC component of the signal, which enters the first square calculation module 18 to calculate the amplitude and phase of the first harmonic component. The signal under test and two second-harmonic quadrature reference signals generated by the lock-in amplifier 12 enter the phase-sensitive detector module for multiplication. The two signals pass through the third low-pass filter 16 and the fourth low-pass filter 17 respectively to obtain the DC component of the signal, which enters the second square calculation module 19 to calculate the amplitude and phase of the second harmonic component.

[0030] The amplitudes S1 and S2 of the first harmonic signal extracted by the lock-in amplifier can be expressed as:

[0031] in, J 1, J 2 represents the first-order Bessel function and the second-order Bessel function, respectively.

[0032] Specifically, in step 4, the phase signal demodulated by the host computer after the divider and arctangent operation is:

[0033] To verify the effectiveness of the proposed phase demodulation method, according to the formula, the modulation depth of the high-frequency modulation signal was set to 1 rad and the modulation frequency to 1 kHz. Different amplitudes of power frequency sinusoidal voltage signals were applied to the sensor, and the amplitude comparison results of the obtained phase demodulated signals are as follows: Figure 3As shown in the formula, the phase demodulation result is not affected by light intensity and does not require the system to operate at an orthogonal operating point, making it more applicable and able to meet the voltage measurement needs of multiple scenarios.

[0034] A computer device system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above-described method. A computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implement the steps of the above-described method.

[0035] A computer program product includes a computer program / instructions that, when executed by a processor, implement the steps of the method described above.

[0036] The memory in the embodiments of this application can be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory. Non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. Volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate synchronous DRAM (DDR SDRAM), enhanced synchronous DRAM (ESDRAM), synchronous linked DRAM (SLDRAM), and direct rambus RAM (DR RAM). It should be noted that the memory of the methods described in this invention is intended to include, but is not limited to, these and any other suitable types of memory.

[0037] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired means such as coaxial cable, optical fiber, digital subscriber line, DSL, or wireless means such as infrared, wireless, microwave, etc. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium such as a floppy disk, hard disk, magnetic tape; an optical medium such as a high-density digital video disc, DVD; or a semiconductor medium such as a solid-state disk, SSD, etc.

[0038] In implementation, each step of the above method can be completed by integrated logic circuits in the processor's hardware or by instructions in software. The steps of the method disclosed in the embodiments of this application can be directly implemented by a hardware processor, or by a combination of hardware and software modules in the processor. The software modules can reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory, and the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, detailed descriptions are omitted here.

[0039] It should be noted that the processor in the embodiments of this application can be an integrated circuit chip with signal processing capabilities. During implementation, each step of the above method embodiments can be completed by the integrated logic circuits in the processor's hardware or by instructions in software form. The processor can be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this application can be directly embodied as execution by a hardware decoding processor, or as execution by a combination of hardware and software modules in the decoding processor. The software modules can be located in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above methods.

[0040] The foregoing has provided a detailed description of the quasi-reciprocal optical voltage sensor based on harmonic phase demodulation proposed in this invention, and has elucidated the principles and implementation methods of this invention. The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A quasi-reciprocal optical voltage sensor based on harmonic phase demodulation, characterized in that: The voltage sensor includes a light source (1), an optical fiber coupler (2), a polarizer (3), a 45° fusion splice (4), a phase modulator (5), a polarization-maintaining fiber delay line (6), a 45° Faraday rotator (7), an optical fiber collimating lens (8), a lithium niobate crystal (9), and a reflective film (10) connected in sequence. The voltage sensor also includes a photodetector (11), a lock-in amplifier (12), and a host computer (13) connected in sequence; and the photodetector (11) is also connected to an optical fiber coupler (2), and the lock-in amplifier (12) is also connected to a phase modulator (5).

2. The optical voltage sensor according to claim 1, characterized in that: The lock-in amplifier (12) has a lock-in demodulation module (20); the lock-in demodulation module (20) is used to extract the amplitude of the first harmonic component and the second harmonic component; The phase-locked demodulation module (20) includes a first digital low-pass filter (14), a second digital low-pass filter (15), a third digital low-pass filter (16), a fourth digital low-pass filter (17), a first square calculation module (18), and a second square calculation module (19).

3. A control method for an optical voltage sensor based on harmonic phase demodulation as described in claim 1 or 2, characterized in that: The method includes the following steps: Step 1: The light emitted by the light source (1) is polarized into linearly polarized light through the fiber coupler (2) and polarizer (3); the linearly polarized light is evenly split into two orthogonal linearly polarized beams through the 45º fusion splice (4); they enter the phase modulator (5) respectively, and the phase modulator (5) applies initial phase modulation to the linearly polarized light, the modulation signal of which comes from the internal reference signal of the lock-in amplifier (12); Step 2: Two beams of orthogonally polarized light pass through a polarization-maintaining fiber delay line (6), and are coupled to a fiber collimating lens (8) via a 45º Faraday rotator (7); the two beams of orthogonally polarized light exiting the fiber enter a lithium niobate crystal (9), propagate along the optical axis of the lithium niobate crystal (9), reach a reflective film (10) and return, and then the Pockels phase shift is doubled; the returning orthogonally polarized light passes through a 45º Faraday rotator (7) and is rotated 45° again, so that the polarization directions of the two beams of orthogonally polarized light are exchanged; and they are coupled through a 45º fusion splice (4) and interference occurs; Step 3: The photodetector (11) converts the optical signal into an electrical signal and then samples it into a digital signal through the data acquisition card and transmits it to the phase-locked demodulation module (20). Step 4: The amplitude of the first harmonic component and the amplitude of the second harmonic component extracted by the phase-locked demodulation module (20) are transmitted to the host computer (13); the Pockels phase shift is demodulated from the amplitude of the first harmonic component and the amplitude of the second harmonic component by the division operation module (21) and the arctangent operation module (22) of the host computer (13).

4. The control method for the optical voltage sensor according to claim 3, characterized in that: In step 1, the initial phase modulation signal applied to the phase modulator (5) comes from the reference signal of the lock-in amplifier (12).

5. The control method for the optical voltage sensor according to claim 4, characterized in that: In step 2, the lithium niobate crystal (9) is modulated by transmitting light along the z-direction and applying voltage along the y-axis; Since the two orthogonally polarized beams return after reaching the reflective film, the phase difference generated by the Pockels effect of the lithium niobate crystal (9) is doubled.

6. The control method for the optical voltage sensor according to claim 5, characterized in that: In step 3, specifically: The light intensity signal carrying the high frequency modulation signal enters the lock-in amplifier (12). The signal to be measured and the two first-harmonic quadrature reference signals generated by the lock-in amplifier (12) enter the first phase-sensitive detector branch for multiplication. The two signals pass through the first low-pass filter (14) and the second low-pass filter (15) respectively to obtain the DC component of the signal, and then enter the first square calculation module (18) to calculate the amplitude and phase of the first harmonic component. The signal under test and the two double-frequency quadrature reference signals generated by the lock-in amplifier (12) enter the second phase-sensitive detector branch for multiplication. The two signals pass through the third low-pass filter (16) and the fourth low-pass filter (17) respectively to obtain the DC component of the signal, and then enter the second square calculation module (19) to calculate the amplitude and phase of the second harmonic component.

7. The control method for the optical voltage sensor according to claim 6, characterized in that: The method further includes: Step 5: The host computer (13) converts the demodulated Pockels phase shift into the corresponding voltage value according to the pre-calibrated system proportional coefficient, and calculates the amplitude of the measured power frequency voltage to complete the voltage measurement.

8. A computer device system, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 3 to 7.

9. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method according to any one of claims 3 to 7.

10. A computer program product comprising a computer program / instructions, characterized in that, When executed by a processor, the computer program instructions implement the steps of the method according to any one of claims 3 to 7.

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