A dynamic phase compensation demodulation method and system for a phi-otdr system

Abstract

The application discloses a kind of dynamic phase compensation demodulation method and system for Φ-OTDR system, belong to distributed optical fiber sensing technical field.The method includes: first, interference signal is divided into four paths, respectively, zero frequency processing, one frequency mixing, one frequency quadrature mixing and two frequency mixing, through the energy extraction and difference operation of quadrature signal, eliminate carrier phase delay influence;Second, using the recurrence relation of Bessel function, combined with differential and difference operation, real-time calculation modulation depth and eliminate light intensity disturbance, finally restore the phase to be measured.The application overcomes the nonlinear distortion of traditional PGC demodulation algorithm from the root, significantly improves the system anti-interference robustness and phase demodulation accuracy, can realize the rapid, high-fidelity recovery of high-frequency dynamic vibration event along the whole optical fiber.The application can be widely applied to perimeter security, rail transit, long-distance pipeline early warning and ocean sensing and other fields.

Claims

1. A dynamic phase compensation demodulation method for Φ-OTDR systems, characterized in that, For interferometric signals with carrier phase delay acquired by the Φ-OTDR system, the following process is used to demodulate the interferometric signals and obtain their phase: The carrier phase delay compensation includes: dividing the interference signal into four paths; performing zero-frequency processing on one path to obtain a first baseband signal; mixing the other three paths with a first-harmonic carrier, a first-harmonic quadrature carrier, and a second-harmonic carrier, respectively, and filtering out high-frequency components to obtain a second, third, and fourth baseband signal; based on the second and third baseband signals, eliminating the influence of carrier phase delay on amplitude through energy extraction operations of quadrature signals to obtain a first intermediate signal; based on the second and third baseband signals, extracting carrier phase delay information through difference operations of quadrature signals, and using the carrier phase delay information to correct the fourth baseband signal to obtain a second intermediate signal that eliminates the influence of carrier phase delay; wherein, the interference signal with carrier phase delay is represented as: ； In the formula, B represents the interference signal; C represents the light intensity perturbation; φ(t) represents the modulation depth; ω represents the phase to be measured. c θ represents the carrier frequency; θ represents the carrier phase delay; t represents time. The first baseband signal, the second baseband signal, the third baseband signal, and the fourth baseband signal are respectively represented as follows: ； ； ； ； In the formula, Indicates the first baseband signal. Indicates the second baseband signal. Indicates the third baseband signal. Indicates the fourth baseband signal; Indicates a low-pass filter; Represents the harmonic coefficient; Represents the zeroth-order Bessel function of the first kind; and These are the first-order Bessel function of the first kind and the second-order Bessel function of the first kind, respectively. The energy extraction operation includes: squaring the second baseband signal and the third baseband signal respectively, adding them together, and then taking the square root; the first intermediate signal is represented as... : ； The difference operation includes: dividing the square difference between the second baseband signal and the third baseband signal by the sum of squares to obtain the carrier phase delay information as: the double angle cosine value of the carrier phase delay; The step of correcting the fourth baseband signal using the carrier phase delay information includes: dividing the fourth baseband signal by the double cosine of the carrier phase delay to obtain the second intermediate signal, denoted as: : ； In the formula, The value representing the double-angle cosine of the carrier phase delay; Compensation for modulation depth and light intensity disturbances includes: differentiating the first intermediate signal to obtain a first differential signal; performing a differential operation between the first baseband signal and the second intermediate signal to obtain a third intermediate signal; differentiating the third intermediate signal to obtain a second differential signal; calculating the modulation depth using the recursive relationship of Bessel functions based on the first intermediate signal, the first differential signal, the third intermediate signal, and the second differential signal; eliminating the influence of light intensity disturbances based on the second differential signal and the first intermediate signal to obtain a fourth intermediate signal; recovering the differential signal of the phase to be measured based on the fourth intermediate signal and the modulation depth, and then performing integration and filtering to obtain the phase to be measured, which is unaffected by carrier phase delay, modulation depth fluctuations, and light intensity disturbances; wherein the modulation depth C is calculated according to the following formula: ； In the formula, Indicates the first differential signal; Indicates the third intermediate signal; This represents the second differential signal.

2. The dynamic phase compensation demodulation method for a Φ-OTDR system according to claim 1, characterized in that, The fourth intermediate signal is represented as : ； In the formula, The differential signal representing the phase to be measured.

3. A dynamic phase compensation demodulation system for Φ-OTDR systems, characterized in that, The system is used to implement the dynamic phase compensation demodulation method for a Φ-OTDR system as described in claim 1 or 2; the system includes: The interference signal acquisition module is used to acquire the interference signal with carrier phase delay that is collected and transmitted by the Φ-OTDR system; The phase demodulation module includes a phase delay compensation submodule and a modulation depth / intensity perturbation compensation submodule; The phase delay compensation submodule is used to compensate for carrier phase delay; it includes: dividing the interference signal into four paths; performing zero-frequency processing on one path to obtain a first baseband signal; mixing the other three paths with a first-harmonic carrier, a first-harmonic quadrature carrier, and a second-harmonic carrier respectively, and filtering out high-frequency components to obtain a second baseband signal, a third baseband signal, and a fourth baseband signal; based on the second and third baseband signals, eliminating the influence of carrier phase delay on amplitude through energy extraction operations of quadrature signals to obtain a first intermediate signal; based on the second and third baseband signals, extracting carrier phase delay information through difference operations of quadrature signals, and using the carrier phase delay information to correct the fourth baseband signal to obtain a second intermediate signal that eliminates the influence of carrier phase delay; The modulation depth / light intensity disturbance compensation submodule is used to compensate for modulation depth and light intensity disturbances; it includes: differentiating the first intermediate signal to obtain a first differential signal; performing a differential operation between the first baseband signal and the second intermediate signal to obtain a third intermediate signal; differentiating the third intermediate signal to obtain a second differential signal; calculating the modulation depth using the recursive relationship of Bessel functions based on the first intermediate signal, the first differential signal, the third intermediate signal, and the second differential signal; eliminating the influence of light intensity disturbances based on the second differential signal and the first intermediate signal to obtain a fourth intermediate signal; recovering the differential signal of the phase to be measured based on the fourth intermediate signal and the modulation depth, and then performing integration and filtering to obtain the phase to be measured that is not affected by carrier phase delay, modulation depth fluctuation, and light intensity disturbances.

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