A method for noise suppression of an all-fiber current sensor

Abstract

The application discloses a kind of all-fiber current sensor noise suppression method, light emitted by light source successively passes through coupler, polarizer, phase modulator, polarization maintaining optical fiber, 1 / 4 wave plate, sensing optical fiber and mirror, and the light reflected by mirror successively passes through sensing optical fiber, 1 / 4 wave plate, polarization maintaining optical fiber, phase modulator, polarizer and coupler, and then enters balanced photodetector positive port M, and the other outlet of coupler is electrically connected with balanced photodetector negative port N through optical attenuator.By adjusting the optical power of input light passing through coupler directly to photodetector through optical attenuator, and replacing common photodetector with balanced photodetector, the purpose of suppressing optical noise and photodetector common-mode noise is achieved, and the signal-to-noise ratio of output signal is improved.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic current measurement technology, specifically relating to a noise suppression method for an all-fiber optic current sensor. Background Technology

[0002] As an emerging technology, fiber optic current sensors have demonstrated strong potential to replace traditional electromagnetic current transformers. Their advantages include small size, light weight, wide dynamic range, fast response speed, absence of magnetic saturation, safety and environmental friendliness, and digital output, aligning with the future development direction of smart grids and offering broad application prospects. Currently, improving the signal-to-noise ratio (SNR) of the output signal, especially in weak current measurement, is crucial for further enhancing the competitiveness of fiber optic current sensors.

[0003] In their paper "Noise Analysis and Signal-to-Noise Ratio Optimization Design of Fiber Optic Current Transformers" (Hu Bei, Xiao Hao, Li Jianguang, et al. Noise Analysis and Signal-to-Noise Ratio Optimization Design of Fiber Optic Current Transformers [J]. High Voltage Engineering, 2017, 43(2):654-660.), Hu Bei et al. of the China Electric Power Research Institute comprehensively analyzed the noise sources of optical signals, signal detection noise, and noise introduced by the external environment. They proposed ways to improve the system signal-to-noise ratio, such as increasing the received optical power of the detector, increasing the number of turns of the sensitive fiber of the sensor head, and selecting a suitable closed-loop feedback phase modulation bias operating point. However, this scheme did not address the noise at its source.

[0004] The Chinese invention patent, "Closed-Loop Control Method and Device for Noise Suppression of Fiber Optic Current Transformer System" (application number: 200810104927.4), introduces a disturbance input signal into the mathematical model of the fiber optic current transformer system and uses a control algorithm to process the input signal feedback, thereby suppressing optical path noise. This scheme suppresses optical noise to a certain extent, but its effect on detector noise reduction is limited.

[0005] Chinese invention patent "A Real-Time Random Noise Filtering Method for Fiber Optic Current Transformers Based on Time Series" (application number 201610006839.5) proposes a real-time random noise filtering method for fiber optic current transformers based on time series, which improves the effectiveness of the data through mean filtering. This scheme can filter out signal noise; however, the mean algorithm increases the response time of the current transformer, affecting its real-time response when the power network's operating state changes abruptly. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the above-mentioned technologies by providing a noise suppression method for an all-fiber current sensor, which can effectively filter out optical noise and photodetector noise without affecting data processing speed and improving the signal-to-noise ratio of the output signal.

[0007] To achieve the above objectives, the noise suppression method for the all-fiber current sensor designed in this invention involves the light emitted from the light source passing sequentially through a coupler, a polarizer, a phase modulator, a polarization-maintaining fiber, a quarter-wave plate, a sensing fiber, and a reflector. The light reflected back from the reflector passes sequentially through the sensing fiber, the quarter-wave plate, the polarization-maintaining fiber, the phase modulator, the polarizer, and the coupler before entering the positive port M of the balanced photodetector. The other outlet of the coupler is connected to the negative port N of the balanced photodetector through an optical attenuator.

[0008] Furthermore, the noise suppression method is as follows:

[0009] Step 1: Measure the optical power at the positive port M of the balanced photodetector.

[0010]

[0011] Among them, P DC n represents the DC component of the optical signal. 11 For positive port M-photon noise, n 12 The relative intensity noise of the positive port M;

[0012] Step two: Measure the optical power reaching the negative port N, and adjust the optical attenuator to make the optical power reaching the negative port N the same as the optical power measured at the positive port M. That is, the optical power measured by the optical power meter at the negative port N is the same as the optical power measured at the positive port M. for:

[0013]

[0014] Where, n 13 For negative port N-photon noise, n 14 The relative intensity noise at the negative port N is, and

[0015]

[0016] Step 3: The optical signals at the positive port M and the negative port N pass through a balanced photodetector to complete photoelectric conversion and differential calculation to form the output voltage Δu;

[0017] Δu=u + -u - =k T P AC Formula 13.

[0018] Furthermore, the specific measurement process in step one is as follows:

[0019] When the polarization plane of the linearly polarized light generated by the measured current rotates by an angle of θ rad, the optical signal P arriving at the positive port M at this time... M for:

[0020]

[0021] In Equation 1, k p P is the optical path loss coefficient. in The light power of the light source; P is the phase difference generated by the beam passing back and forth through the phase modulator; DC P represents the DC component of the optical signal. AC The AC component of the optical signal; n 11 For positive port M-photon noise, n 12 The relative intensity noise of the positive port M;

[0022] Positive port M-photon noise n 11 Standard deviation σ 11 for:

[0023]

[0024] In the formula, P in ρ is the optical power of the light source; h is Planck's constant, h = 6.63 × 10⁻⁶. -34 J·s; Δf is the measurement bandwidth; c is the speed of light in vacuum; λ is the wavelength of light in vacuum;

[0025] Positive port M relative intensity noise n 12 Standard deviation σ 12 for

[0026]

[0027] In the formula, P in λ is the optical power of the light source; Δf is the measurement bandwidth; c is the speed of light in vacuum; λ is the wavelength of light in vacuum; Δλ is the spectral width.

[0028] As shown in equations 2 and 3, the optical noise reaching the positive port M is related to the optical power of the input light source. Therefore, the optical power reaching the positive port M of the balanced photodetector is measured and used as a reference power to adjust the optical attenuator. The measured optical power at the positive port M is...

[0029]

[0030] Furthermore, the calculation process of the output voltage Δu in step three is as follows: During the photoelectric conversion process of the optical signals at the positive port M and the negative port N through the photodiode, electronic noise is introduced. At this time, the voltages at the two ports of the balanced photodetector are respectively:

[0031]

[0032] In the formula, u +The voltage measured at position M of the positive port of the balanced photodetector is derived from the voltage obtained after photoelectric conversion of the optical signal from the current sensing optical path; k T U is the photoelectric conversion coefficient of the photodetector. - U1 is the voltage measured at position N of the negative port of the balanced photodetector, and this voltage comes from the voltage of the optical signal in the direct optical path after photoelectric conversion; u1 is the electronic noise generated by the current sensing optical signal during photoelectric conversion; u2 is the electronic noise generated by the direct optical path during photoelectric conversion.

[0033] Electronic noise includes shot noise and thermal noise, i.e.

[0034]

[0035] In the formula, u 11 For the shot noise of the positive port M, u 21 For shot noise at negative port N, u 12 Thermal noise of positive port M, u 22 The thermal noise of the negative port N;

[0036] Shot noise u at negative port N 21 Standard deviation σ 21 for:

[0037]

[0038] In the formula, e is the electron charge, Δf is the measurement bandwidth, and R K k is the transimpedance of the detector, measured in Ω. iv The photodetector's responsivity is expressed in A / W; Pout is the received optical power, expressed in W; i dark It is the dark current of the detector, measured in amperes (A).

[0039] Thermal noise of negative port N 22 Standard deviation σ 22 for:

[0040]

[0041] In the formula, k is the Boltzmann constant, k = 1.38 × 10 -23 J / K; T is the thermodynamic temperature, in K; Δf is the test bandwidth; R q Effective resistance;

[0042] Equations 9 and 10 show that electronic noise is related not only to the system characteristics but also to the optical power received by the balanced photodetector. In step two, the optical attenuator is adjusted so that the optical power reaching both receiving ends of the balanced photodetector is the same.

[0043]

[0044] Therefore, Equation 7 can be rewritten as:

[0045]

[0046] By utilizing the differential function of the balanced photodetector, the output voltage Δu is:

[0047] Δu=u + -u - =k T P AC Formula 13.

[0048] Furthermore, in step three, the balanced photodetector adopts a dual-tube differential TIA structure, in which two photodiodes with identical performance are respectively loaded onto the input terminals of the dual-ended TIA of the balanced photodetector, and a voltage output is formed after differential synthesis.

[0049] Compared with the prior art, the present invention has the following advantages: The present invention introduces an optical attenuator to adjust the optical power of the input light directly reaching the photodetector through the coupler, and replaces the ordinary photodetector with a balanced photodetector, thereby suppressing optical noise and detector common-mode noise and improving the signal-to-noise ratio of the output signal. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the noise suppression structure of the all-fiber current sensor of the present invention;

[0051] Figure 2 for Figure 1 Schematic diagram of a balanced photodetector.

[0052] 1. Light source; 2. Coupler; 3. Polarizer; 4. Phase modulator; 5. Polarization-maintaining fiber; 6. Quarter-wave plate; 7. Sensing fiber; 8. Mirror; 9. Optical attenuator; 10. Balanced photodetector. Detailed Implementation

[0053] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0054] like Figure 1 The noise suppression method for the all-fiber current sensor shown involves the following steps: the light emitted from the light source 1 passes sequentially through coupler 2, polarizer 3, phase modulator 4, polarization-maintaining fiber 5, quarter-wave plate 6, sensing fiber 7, and reflector 8. The light reflected back from the reflector 8 passes sequentially through sensing fiber 7, quarter-wave plate 6, polarization-maintaining fiber 5, phase modulator 4, polarizer 3, coupler 2, and the positive port M of the balanced photodetector 10 before being transmitted to the data processing system. Simultaneously, the other outlet of coupler 2 is connected to the negative port N of the balanced photodetector 10 through optical attenuator 9.

[0055] The specific noise suppression process is as follows:

[0056] Step 1: When the polarization plane of the linearly polarized light generated by the measured current rotates by an angle of θ rad, the optical signal P arriving at the positive port M at this time... M for:

[0057]

[0058] In Equation 1, k p P is the optical path loss coefficient. in The light power of the light source; P is the phase difference generated by the beam passing back and forth through the phase modulator; DC P represents the DC component of the optical signal. AC The AC component of the optical signal; n 11 For positive port M-photon noise, n 12 The relative intensity noise is at the positive port M.

[0059] Positive port M-photon noise n 11 Standard deviation σ 11 for:

[0060]

[0061] In the formula, P in ρ is the optical power of the light source; h is Planck's constant, h = 6.63 × 10⁻⁶. -34 J·s; Δf is the measurement bandwidth; c is the speed of light in vacuum; λ is the wavelength of light in vacuum.

[0062] Positive port M relative intensity noise n 12 Standard deviation σ 12 for

[0063]

[0064] In the formula, P in λ is the optical power of the light source; Δf is the measurement bandwidth; c is the speed of light in vacuum; λ is the wavelength of light in vacuum; Δλ is the spectral width.

[0065] As shown in Equations 2 and 3, the optical noise reaching the positive port M is related to the optical power of the input light source. Therefore, the optical power reaching the positive port M of the balanced photodetector is measured and used as a reference power to adjust the optical attenuator. Since the optical power meter measures the average optical power over a period of time, the AC optical signal is suppressed. The optical power measured at the positive port M is...

[0066]

[0067] Step two: Measure the optical power reaching the negative port N using an optical power meter, and adjust the knob of the optical attenuator until the optical power reaching the negative port N is the same as the optical power measured at the positive port M. At this point, the optical power measured by the optical power meter at the negative port N is... for:

[0068]

[0069] Where, n 13 For negative port N-photon noise, n 14 The relative intensity noise is at the negative port N. Equations 2 and 3 show that photon noise and relative intensity noise are related to the properties of the light source. Therefore...

[0070]

[0071] Step three: The optical signals at the positive port M and the negative port N pass through a balanced photodetector to complete photoelectric conversion and differential calculation. For example... Figure 2 The balanced photodetector shown employs a dual-transistor differential TIA structure. Two photodiodes with identical performance are respectively applied to the input terminals of the balanced photodetector's dual-terminal TIA, and after differential combining, a voltage output is formed. During the photoelectric conversion process of the optical signal at the positive port M and the negative port N through the photodiodes, electronic noise is introduced. At this time, the voltages at the two ports of the balanced photodetector are as follows:

[0072]

[0073] In the formula, u + The voltage measured at position M of the positive port of the balanced photodetector is derived from the voltage obtained after photoelectric conversion of the optical signal from the current sensing optical path; k T U is the photoelectric conversion coefficient of the photodetector. - U1 is the voltage measured at position N of the negative port of the balanced photodetector, and this voltage comes from the voltage of the optical signal after photoelectric conversion in the direct optical path (the light source passes through the coupler and the optical attenuator in sequence); u2 is the electronic noise generated by the current sensing optical signal during the photoelectric conversion process; u3 is the electronic noise generated by the direct optical path during the photoelectric conversion process.

[0074] Electronic noise includes shot noise and thermal noise, i.e.

[0075]

[0076] In the formula, u 11 For the shot noise of the positive port M, u 21 For shot noise at negative port N, u 12 Thermal noise of positive port M, u 22 This represents the thermal noise at the negative port N.

[0077] Shot noise u at negative port N 21 Standard deviation σ 21 for:

[0078]

[0079] In the formula, e is the electron charge, Δf is the measurement bandwidth, and R K k is the transimpedance of the detector, measured in Ω. iv The photodetector's responsivity is expressed in A / W; Pout is the received optical power, expressed in W; i dark It is the dark current of the detector, measured in amperes (A).

[0080] Thermal noise of negative port N 22 Standard deviation σ 22 for:

[0081]

[0082] In the formula, k is the Boltzmann constant, k = 1.38 × 10 -23 J / K; T is the thermodynamic temperature, in K; Δf is the test bandwidth; R q This is the effective resistance.

[0083] Equations 9 and 10 show that electronic noise is related not only to the system characteristics but also to the optical power received by the balanced photodetector. In step two, rotating the optical attenuator knob ensures that the optical power reaching both receiving ends of the balanced photodetector is the same.

[0084]

[0085] Therefore, Equation 7 can be rewritten as:

[0086]

[0087] By utilizing the differential function of the balanced photodetector, the voltage Δu output to the data processing system is:

[0088] Δu=u + -u - =k T P AC Formula 13

[0089] This approach eliminates the effects of optical and electronic noise, suppresses system noise, improves the system's signal-to-noise ratio, and enhances data processing accuracy.

Claims

1. A noise suppression method for an all-fiber optic current sensor, characterized in that: The light emitted by the light source (1) passes sequentially through the coupler (2), polarizer (3), phase modulator (4), polarization-maintaining fiber (5), quarter-wave plate (6), sensing fiber (7), and mirror (8). The light reflected back by the mirror (8) passes sequentially through the sensing fiber (7), quarter-wave plate (6), polarization-maintaining fiber (5), phase modulator (4), polarizer (3), and coupler (2) before entering the positive port of the balanced photodetector (10). M The other outlet of the coupler (2) is connected to the negative port of the balanced photodetector (10) via the optical attenuator (9). N Electrical connection; The noise suppression method is as follows: Step 1: Measure the positive port of the balanced photodetector (10) M The optical power is : Formula 4 in, P DC This is the DC component of the optical signal. n 11 Positive port M Photon noise, n 12 Positive port M Relative intensity noise; Step 2, measure the distance to the negative port. N The optical power is adjusted by regulating the optical attenuator to ensure that the light reaches the negative port. N Optical power and positive port M The measured optical power is the same, that is, the optical power meter measures the power reaching the negative port. N optical power for: Formula 5 in, n 13 negative port N Photon noise, n 14 negative port N Relative intensity noise, and Formula 6; Step 3, Positive Port M Negative port N The optical signal passes through a balanced photodetector, where photoelectric conversion and differential calculation are performed to form the output voltage. ; Formula 13 k T denoted as the photoelectric conversion coefficient of the photodetector. P AC It is the AC component of the optical signal.

2. The noise suppression method for an all-fiber current sensor according to claim 1, characterized in that: The specific measurement process in step one is as follows: When the polarization plane of the linearly polarized light generated by the measured current rotates by an angle of θ When rad, the positive port is reached. M light signal P M for: Formula 1 In Equation 1, k p This is the optical path loss coefficient. P in Δ is the optical power of the light source. φ The phase difference generated when the beam passes through the phase modulator round trip; P DC This represents the DC component of the optical signal; P AC The AC component of the optical signal; n 11 Positive port M Photon noise, n 12 Positive port M Relative intensity noise; Positive port M Photon noise n 11 Standard deviation σ 11 for: Formula 2 In the formula, P in The light power of the light source; h Let be Planck's constant. h= 6.63×10 -34 J·s;Δ f For measuring bandwidth; c The speed of light in a vacuum; λ The wavelength of light in a vacuum; Positive port M Relative intensity noise n 12 Standard deviation σ 12 for Formula 3 In the formula, P in Δ is the optical power of the light source. f For measuring bandwidth; c The speed of light in a vacuum; λ wavelength of light in a vacuum ； Δ λ Spectral width; As can be seen from equations 2 and 3, the positive port is reached. M The optical noise is related to the optical power of the input light source. At this time, the measurement reaches the positive port of the balanced photodetector. M The optical power is used as a reference optical power to adjust the optical attenuator; positive port M The measured optical power is : Formula 4.

3. The noise suppression method for an all-fiber current sensor according to claim 2, characterized in that: The output voltage in step three The calculation process is as follows: at the positive port M Negative port N During the photoelectric conversion of the optical signal through the photodiode, electronic noise is introduced. At this time, the voltages at the two ports of the balanced photodetector are: Formula 7 In the formula, u + To balance the positive port of the photodetector M The voltage measured at the location, and this voltage comes from the voltage after photoelectric conversion of the optical signal in the current sensing optical path; k T denoted as the photoelectric conversion coefficient of the photodetector. u - To balance the negative port of the photodetector N The voltage measured at the location, and this voltage comes from the voltage of the optical signal after photoelectric conversion in the direct optical path; u 1 represents the electronic noise generated during the photoelectric conversion of the current-sensing optical signal; u 2 represents the electronic noise generated during the photoelectric conversion process in the direct optical path; Electronic noise includes shot noise and thermal noise, i.e. Formula 8 In the formula, u 11 Positive port M shot noise, u 21 negative port N shot noise, u 12 Positive port M thermal noise, u 22 negative port N Thermal noise; negative port N shot noise u 21 Standard deviation σ 21 for: Formula 9 In the formula, e For electron charge, Δ f To measure bandwidth, R K Transimpedance of the detector, in Ω; k iv The responsivity of the photodetector is expressed in A / W. P out is the received optical power, measured in watts (W). i dark It is the dark current of the detector, measured in amperes (A). negative port N thermal noise u 22 Standard deviation σ 22 for: Formula 10 In the formula, k Boltzmann's constant, k = 1.38×10 -23 J / K; T Thermodynamic temperature, unit: K Δ f To test bandwidth, R q Effective resistance; Equations 9 and 10 show that electronic noise is related not only to the system characteristics but also to the optical power received by the balanced photodetector. In step two, the optical attenuator is adjusted so that the optical power reaching both receiving ends of the balanced photodetector is the same. Formula 11 Therefore, Equation 7 can be rewritten as: Formula 12 By balancing the differential function of the photodetector, the output voltage is... for: Formula 13.

4. The noise suppression method for an all-fiber current sensor according to claim 1, characterized in that: In step three, the balanced photodetector adopts a dual-tube differential TIA structure, in which two photodiodes with the same performance are respectively loaded onto the input terminals of the dual-ended TIA of the balanced photodetector, and a voltage output is formed after differential synthesis.

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