Optimization method for phase-generated carrier parameter of interferometric fiber optic sensor

Abstract

This invention discloses a method for optimizing phase generation carrier parameters in an interferometric fiber optic sensor, belonging to the field of fiber optic sensing and signal demodulation technology. This invention selects three core key parameters—laser pump current, modulation frequency, and interferometer optical path difference—as experimental factors, and sets three different level values ​​for each factor. By using a standard orthogonal array, only nine representative experimental combinations need to be executed, output noise collected, and range analysis performed on the test data to quantify the dominant influence of each parameter on noise. This allows for the rapid selection of the optimal levels for each factor to form a globally optimal parameter set, which is then verified through supplementary experiments. This invention significantly reduces the number of experiments and costs, providing a standardized optimization process that can quickly and accurately identify the globally optimal parameter combination that minimizes system output noise, effectively improving the overall performance of the fiber optic sensor.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing and signal demodulation technology, specifically relating to a method for optimizing phase generation carrier parameters of an interferometric fiber optic sensor. Background Technology

[0002] Interferometric fiber optic sensors are widely used in underwater acoustic detection, earthquake monitoring, and industrial inspection due to their high sensitivity and resistance to electromagnetic interference. Phase-carrier demodulation (PCM) is an effective passive homodyne demodulation scheme. Because it overcomes signal fading and offers advantages such as large dynamic range and high linearity, it has become one of the mainstream demodulation schemes.

[0003] However, despite the significant advantages of PGC demodulation technology, in weak signal detection scenarios, the system's noise floor suppression capability remains the core technical bottleneck determining the sensor's minimum detectable signal (resolution). The output noise of an interferometer system is not determined by a single noise source, but rather by the complex interplay of optical, electrical, and algorithmic parameters. The three most critical core physical parameters are: fiber laser pump current, carrier modulation frequency, and interferometer optical path difference. The fiber laser pump current directly determines the output optical power and dominates the system's relative intensity noise (RIN) level and the position of the laser relaxation oscillation peak in the spectrum. Too low a current leads to shot noise dominating, while too high a current may introduce additional mode competition noise. The carrier modulation frequency directly affects the demodulation bandwidth, aliasing noise suppression, and effective modulation depth (C-value). An inappropriate frequency selection, especially when it falls within the fiber laser's relaxation oscillation peak, will cause a severe amplification of the RIN. The interferometer optical path difference is the main physical pathway for converting laser phase noise into system output intensity noise; the larger the optical path difference, the higher the introduced phase noise floor.

[0004] Currently, parameter adjustments for PGC demodulation systems largely rely on manual, single-parameter trial-and-error adjustments based on the experience of experimenters. This involves fixing the optical path difference and carrier frequency, adjusting the pump current individually to find the minimum noise point, and then fixing the current again while monotactically adjusting the carrier frequency. However, these three key parameters exhibit strong nonlinear interactions at the physical level. First, the pump current and carrier frequency are deeply coupled; adjusting the pump current directly causes a frequency shift in the relaxation oscillation peak of the fiber laser. This means that a carrier frequency that was originally in a low-noise "safe zone" may unexpectedly fall into a high-noise relaxation oscillation region simply due to fine-tuning the pump current. Second, the pump current and optical path difference influence each other. Fine-tuning the pump current to optimize RIN inevitably causes a slight temperature drift in the laser's center wavelength. In an interferometer with a fixed physical arm length difference, the wavelength drift is equivalent to changing the absolute optical path difference and phase offset point of the system's actual operation. Finally, the optical path difference and carrier frequency together determine the modulation efficiency. Changes in the optical path difference directly alter the system's sensitivity to frequency noise and change the effective modulation depth, necessitating recalibration of the carrier frequency and modulation amplitude. The single-factor rotation method completely severs the dynamic relationship between the pump current, the interferometer optical path difference, and the carrier frequency. This results in traditional optimization and debugging being not only extremely inefficient and time-consuming, but also prone to getting trapped in local optima, making it impossible to approach the system's theoretical low-noise limit from a global perspective.

[0005] In summary, existing interferometric fiber optic sensor systems lack a systematic optimization mechanism that can comprehensively manage multidimensional coupling parameters. Summary of the Invention

[0006] The purpose of this invention is to provide a method for optimizing the phase generation carrier parameters of an interferometric fiber optic sensor based on orthogonal experiments. By utilizing orthogonal experimental design, the number of experiments is greatly reduced, and the influence weight of each parameter on the output noise is determined through range analysis, thereby quickly locking in the globally optimal parameter combination.

[0007] The objective of this invention can be achieved through the following technical solutions: The method for optimizing the phase generation carrier parameters of an interferometric fiber optic sensor includes the following steps: S1: Select the laser pump current I, carrier modulation frequency f, and interferometer optical path difference L as factors for the orthogonal experiment, and set at least 3 different level values ​​for each factor; S2: Based on the number of factors and the number of levels, a standard orthogonal array is selected for experimental design to obtain multiple sets of parameter configurations containing different combinations of levels for each factor; S3: Build an experimental system for phase generation and carrier demodulation of an interferometric fiber optic sensor, and set the pump current of the laser, the carrier modulation frequency and the optical path difference of the interferometer in sequence according to the parameter configuration designed in step S2. Under each set of parameter settings, collect the output signal of the interferometer and measure the noise power of the output signal. S4: Calculate the noise power of each factor at different levels, determine the optimal level of each factor based on the magnitude of the noise power, calculate the range of each factor, and determine the order of importance of each parameter's influence on the output noise based on the magnitude of the range. S5: Combine the optimal levels of each factor to form the globally optimal set of phase generation carrier demodulation parameters.

[0008] As a further embodiment of the present invention, in step S1, the level of the laser pump current is located within the stable single-mode operating range of the fiber laser. The relaxation oscillation peak generated by the selected pump current level does not fall within the carrier modulation frequency set by the system or the frequency band of the signal under test.

[0009] As a further embodiment of the present invention, in step S1, the carrier modulation frequency level is in a frequency region where the modulation efficiency is flat. The selected carrier modulation frequency is greater than twice the highest frequency of the signal under test.

[0010] As a further aspect of the present invention, in step S4, the noise power of each factor at different levels is S. ij Where i is the factor index and j is the level index, the factor is selected to make the noise power S ij The minimum level is the optimal setting for this parameter.

[0011] As a further aspect of the present invention, in step S4, the larger the range, the more dominant the corresponding factor is, and the more significant its impact on the noise.

[0012] As a further aspect of the present invention, if the globally optimal phase generation carrier demodulation parameter set is not within the original orthogonal experimental combination, a supplementary verification experiment is initiated, and its verification noise floor is calculated. The verification noise floor should be lower than the noise values ​​of all independent experiments measured in step S4.

[0013] The beneficial effects of this invention are: This invention employs an orthogonal experimental design, requiring only 9 experiments to systematically evaluate the impact of three key parameters, which greatly reduces the number of experiments, time, and cost compared to the comprehensive experimental method (27 experiments).

[0014] This invention can clearly reveal the main effect trend and relative importance of each parameter on system noise (through range analysis), and can detect the interaction between parameters, thereby avoiding the drawback of the single-variable debugging method being prone to local optima, and helping to find the optimal combination of parameters globally or approximately globally.

[0015] This invention provides a standardized optimization process that does not rely on the personal experience of operators. The optimization process is clear, recordable, and repeatable, making it easy to promote and apply in different laboratory or production environments.

[0016] This invention provides a powerful tool for debugging, calibration, and performance limit exploration of PGC demodulation systems, which helps to quickly improve the actual performance indicators of fiber optic sensors and is of great significance for the research and development and production of high-performance fiber optic sensors. Attached Figure Description

[0017] The invention will now be further described with reference to the accompanying drawings.

[0018] Figure 1 This is an overall flowchart of the method of the present invention.

[0019] Figure 2 This is a schematic diagram of a typical interferometric fiber optic sensor PGC demodulation system. Detailed Implementation

[0020] 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.

[0021] Methods for optimizing carrier parameters in phase generation of interferometric fiber optic sensors, such as... Figure 1 As shown, it includes the following steps: S1: Three key parameters affecting the output noise of the interferometric fiber optic sensor are selected as factors for the orthogonal experiment, and at least three different level values ​​are set for each factor; where: Factor A: laser pump current ; Factor B: Carrier modulation frequency ; Factor C: Interferometer optical path difference ; The determination of the laser pump current level needs to refer to the threshold power of the fiber laser to ensure that the level value is within the stable single-mode operating range of the fiber laser. At the same time, the effect of the pump current magnitude on the relaxation oscillation frequency of the fiber laser must be considered to ensure that the relaxation oscillation peak excited by the selected pump current level deviates from the carrier modulation frequency set by the system and the frequency band of the signal under test, so as to avoid introducing additional relative intensity noise.

[0022] The determination of the carrier modulation frequency level needs to take into account the characteristics of the frequency modulation efficiency of the fiber laser used as a function of frequency, and avoid frequency regions where the modulation efficiency drops sharply. Meanwhile, the selection of the carrier modulation frequency level also needs to be combined with the frequency of the signal under test and the data sampling frequency of the system to ensure that the selected carrier modulation frequency is greater than twice the highest frequency of the signal under test to avoid spectral aliasing.

[0023] In one specific embodiment of the present invention, three different levels are set as shown in the table below: The pump current levels were 80 mA, 100 mA, and 120 mA; the carrier modulation frequency levels were 10 kHz, 20 kHz, and 30 kHz; and the optical path difference levels were 3 m, 5 m, and 7 m.

[0024] S2: Based on the determined number of factors (3) and number of levels (3), select a standard orthogonal array. Experimental design was performed. The orthogonal array contains 9 experimental combinations, each representing a specific parameter configuration, as shown below: S3: Build as follows Figure 2 The diagram shows a typical experimental system for PGC demodulation of an interferometric fiber optic sensor. This system should include: a fiber laser, a signal generator, a Michelson fiber optic interferometer, a photodetector, a data acquisition card, and the PGC demodulation algorithm program.

[0025] The demodulation experimental system operates by changing the pump current. And changing the carrier modulation frequency through a signal generator The light emitted from the source is then applied to the fiber laser for direct internal modulation. The light is split into two beams of equal intensity by a 1-to-2 coupler, which then enter the reference and sensing arms of the Michelson interferometer. The beams are reflected back into the circulator by the Faraday rotating mirror and output to the photodetector. The photodetector converts the two signals into electrical signals, which are then acquired by a data acquisition card and processed in a computer.

[0026] Following the nine parameter combinations listed in the orthogonal array in step S2, precisely set the laser pump current, the carrier modulation frequency of the carrier signal generator, and the optical path difference of the interferometer in sequence; after stabilizing under each parameter setting, acquire the final output signal of the interferometer. The noise power is obtained by integrating the noise power spectral density of the output signal. S4: Calculate the noise power of each factor at different levels. That is, the first The factor of the first The noise power corresponding to each level; The values ​​of i and j are both in the range of (1, 2, 3); Based on noise power The magnitude of each factor determines its optimal level; specifically, the level that minimizes noise power is selected. The minimum level is the optimal setting for this parameter. Calculate the range of each factor = , , , , According to the range The magnitude of the parameter determines the order of their influence on the output noise. The larger the value, the more dominant the factor is, and the more significant its impact on noise. S5: For each factor A, B, and C, select the level position with the minimum noise power as the optimal configuration for that factor, and then directly combine these three optimal levels to form the globally optimal PGC demodulation parameter set.

[0027] Configure the system hardware with the optimal PGC demodulation parameter set synthesized above. If this parameter set is not within the original 9 sets of orthogonal experimental matrices, start a supplementary verification experiment and calculate its verification noise floor. This verification noise floor should be lower than the noise values ​​of all 9 sets of independent experiments measured in step S4, thereby confirming that the parameter configuration is the globally optimal solution that minimizes the output noise of the fiber optic interferometer.

[0028] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for optimizing phase generation carrier parameters in an interferometric fiber optic sensor, characterized in that, Includes the following steps: S1: Select the laser pump current I, carrier modulation frequency f, and interferometer optical path difference L as factors for the orthogonal experiment, and set at least 3 different level values ​​for each factor; S2: Based on the number of factors and the number of levels, a standard orthogonal array is selected for experimental design to obtain multiple sets of parameter configurations containing different combinations of levels for each factor; S3: Build an experimental system for phase generation and carrier demodulation of an interferometric fiber optic sensor, and set the pump current of the laser, the carrier modulation frequency and the optical path difference of the interferometer in sequence according to the parameter configuration designed in step S2. Under each set of parameter settings, collect the output signal of the interferometer and measure the noise power of the output signal. S4: Calculate the noise power of each factor at different levels, determine the optimal level of each factor based on the magnitude of the noise power, calculate the range of each factor, and determine the order of importance of each parameter's influence on the output noise based on the magnitude of the range. S5: Combine the optimal levels of each factor to form the globally optimal set of phase generation carrier demodulation parameters.

2. The method for optimizing phase generation carrier parameters of an interferometric fiber optic sensor according to claim 1, characterized in that, In step S1, the level of the laser pump current is within the stable single-mode operating range of the fiber laser. The relaxation oscillation peak generated by the selected pump current level does not fall within the carrier modulation frequency set by the system or the frequency band of the signal under test.

3. The method for optimizing phase generation carrier parameters of an interferometric fiber optic sensor according to claim 1, characterized in that, In step S1, the carrier modulation frequency level should be in a frequency region where the modulation efficiency is flat; The selected carrier modulation frequency is at least twice the highest frequency of the signal under test.

4. The method for optimizing the phase generation carrier parameters of an interferometric fiber optic sensor according to claim 1, characterized in that, In step S3, measuring the noise power of the output signal specifically involves integrating the noise power spectral density of the output signal to obtain the noise power.

5. The method for optimizing phase generation carrier parameters of an interferometric fiber optic sensor according to claim 1, characterized in that, In step S4, the noise power of each factor at different levels is S. ij Where i is the factor index and j is the level index, the factor is selected to make the noise power S ij The minimum level is the optimal setting for this parameter.

6. The method for optimizing the phase generation carrier parameters of an interferometric fiber optic sensor according to claim 1, characterized in that, In step S4, the range R of each factor i = max(S i1 , S i2 , S i3 ) - min(S i1 , S i2 , S i3 Range R i The larger the value, the more dominant the factor is, and the more significant its impact on noise.

7. The method for optimizing the phase generation carrier parameters of an interferometric fiber optic sensor according to claim 1, characterized in that, If the globally optimal phase generation carrier demodulation parameter set is not within the original orthogonal experimental combination, a supplementary verification experiment is initiated, and its verification noise floor is calculated. The verification noise floor should be lower than the noise values ​​of all independent experiments measured in step S4.

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