CN-121997222-A - Method for estimating tilt-length coupling coefficient in the presence of optical path noise in spatial gravitational wave detector

CN121997222ACN 121997222 ACN121997222 ACN 121997222ACN-121997222-A

Abstract

The invention discloses a tilt-length coupling coefficient estimation method when optical path noise exists in a space gravitation wave detector, which belongs to the technical field of noise analysis and data processing of the space gravitation wave detector, and combines a convolutional neural network and a self-adaptive time delay interference technology when optical path noise abnormality occurs in one or more optical links of the space gravitation wave detector, automatically identifies the links polluted by the optical path noise through the convolutional neural network, then constructs a time delay interference observed quantity capable of inhibiting the contribution of the polluted links, automatically screens out the optimal time delay interference combination to realize the complete cancellation of laser frequency noise and the effective avoidance of the abnormal links, and simultaneously, can estimate the tilt-length coupling coefficient with high precision by introducing an edge likelihood function regression method without assuming a noise power spectrum density model, thereby realizing the effective subtraction of the tilt-length noise and greatly improving the sensitivity and reliability of gravitation wave signal extraction.

Inventors

CHEN HAOKANG
WANG PANPAN
SHAO CHENGGANG

Assignees

华中科技大学

Dates

Publication Date: 20260508
Application Date: 20260112

Claims (9)

1. A method for estimating a tilt-length coupling coefficient in the presence of optical path noise in a spatial gravitational wave detector, comprising: S1, acquiring phase measurement data of each optical link of a space interferometer and angle jitter measurement data provided by a satellite-borne attitude control system; S2, performing short-time Fourier transform on the phase measurement data to obtain a power spectrum density image, and inputting the power spectrum density image into a convolutional neural network to perform abnormal link identification to obtain an optical link with abnormal optical path noise; s3, selecting an optimal time delay interference combination based on the optical link with the optical path noise abnormality, so that the influence of the optical link with the optical path noise abnormality can be completely counteracted and eliminated after time delay interference is performed based on the optimal time delay interference combination; S4, performing time delay interference based on the optimal time delay interference combination to obtain an interference output signal, and performing frequency domain power spectrum regression analysis based on the interference output signal and the angle jitter measurement data by using an edge likelihood function to obtain an optimal estimated value of an inclined-length coupling coefficient, wherein the inclined-length coupling coefficient represents the coupling degree between the angle jitter and the equivalent length change.
2. The method of claim 1, wherein the convolutional neural network comprises an input layer, a plurality of convolutional layers, a pooling layer, a fully-connected layer and an output layer, wherein the input layer is used for receiving power spectral density images of phase measurement data of each optical link, the convolutional layers are used for extracting frequency domain features of the power spectral density images, the pooling layer is used for performing feature dimension reduction on the frequency domain features output by the convolutional layers, the fully-connected layer is used for performing nonlinear mapping on the dimension reduction features output by the pooling layer, and the output layer is used for mapping the output of the fully-connected layer into noise state labels corresponding to each optical link.
3. The tilt-length coupling coefficient estimation method according to claim 1 or 2, wherein an optimal time delay interference combination is selected based on the optical link with optical path noise abnormality so that the influence of the optical link with optical path noise abnormality can be completely canceled by laser frequency noise and removed after time delay interference based on the optimal time delay interference combination, specifically comprising: Based on time delay operators corresponding to optical path lengths of different optical links and polynomial coefficients of the time delay operators, representing phase measurement data of each optical link in the space gravitational wave detector as a linear superposition form of various noise items including laser frequency noise and optical path noise, and obtaining a linear constraint equation set under the laser frequency noise cancellation condition; Setting the time delay operator polynomial coefficient corresponding to the optical link with the optical path noise abnormality to 0 as an additional constraint condition; And solving the linear constraint equation set based on the additional constraint condition to obtain the optimal time delay interference combination.
4. The method of estimating a tilt-length coupling coefficient in the presence of optical path noise in a spatial gravitational wave detector of claim 3, wherein said system of linear constraint equations is: Wherein, the Representing an optical link Is used to calculate the time delay value of the time delay value, Representing an optical link Is the reverse link of (a) Is used to calculate the time delay value of the time delay value, And (3) with Respectively optical links And A time delay operator polynomial of (c).
5. The method for estimating tilt-length coupling coefficient in the presence of optical path noise in a spatial gravitational wave detector according to claim 1 or 2, wherein performing frequency domain power spectral regression analysis using an edge likelihood function based on the interference output signal and the angular jitter measurement data to obtain an optimal estimated value of the tilt-length coupling coefficient, specifically comprising: Setting a plurality of estimated values for the tilt-length coupling coefficient; Weighting the angle jitter measurement data based on each estimated value of the tilt-length coupling coefficient respectively to obtain tilt-length noise estimated components corresponding to the corresponding estimated values, and removing the tilt-length noise estimated components corresponding to the estimated values from the interference output signals to obtain residual signals corresponding to the estimated values; converting residual signals corresponding to all estimated values into frequency domains, and calculating average power spectrum densities of the residual signals at all sampling frequencies; And calculating an edge likelihood function value corresponding to each estimated value based on the average power spectral density of the residual signal corresponding to each estimated value at each sampling frequency and the edge likelihood function, and selecting an estimated value corresponding to the maximum edge likelihood function value as the optimal estimated value of the tilt-length coupling coefficient.
6. The method of estimating tilt-length coupling coefficients in the presence of optical path noise in a spatial gravitational wave detector of claim 5, wherein said edge likelihood function is: Wherein, the Representing edge likelihood functions with respect to tilt-length coupling coefficients; In an optical link representing a transmitting end TX and a receiving end RX, tilt-length noise dithers from angle Tilt-length coupling coefficient to the interference phase, Respectively representing the angle jitter components of the device gesture in two mutually orthogonal directions, and representing the micro-angle deviation of the optical platform or the optical element relative to the ideal gesture; representing the discrete fourier transform result of the residual signal at frequency k; an average power spectral density at frequency k for the residual signal; the value of the theoretical noise power spectrum model at frequency k; as the number of independent spectrum segments for estimation; And C is a constant term which is independent of parameters.
7. A tilt-length coupling coefficient estimation system in the presence of optical path noise in a spatial gravitational wave detector, comprising: the data acquisition unit is used for acquiring phase measurement data of each optical link of the space interferometer and angle jitter measurement data provided by the satellite-borne attitude control system; The abnormal link identification unit is used for carrying out short-time Fourier transform on the phase measurement data to obtain a power spectrum density image, and inputting the power spectrum density image into a convolutional neural network to carry out abnormal link identification to obtain an optical link with abnormal optical path noise; The time delay interference selection unit is used for selecting an optimal time delay interference combination based on the optical link with the optical path noise abnormality, so that the influence of the optical link with the optical path noise abnormality can be completely counteracted and eliminated after the time delay interference is carried out based on the optimal time delay interference combination; The coupling coefficient estimation unit is used for carrying out time delay interference based on the optimal time delay interference combination to obtain an interference output signal, carrying out frequency domain power spectrum regression analysis based on the interference output signal and the angle jitter measurement data by using an edge likelihood function to obtain an optimal estimated value of an inclined-length coupling coefficient, wherein the inclined-length coupling coefficient represents the coupling degree between angle jitter and equivalent length change.
8. An electronic device comprises a computer readable storage medium and a processor; The computer-readable storage medium is for storing executable instructions; The processor is configured to read executable instructions stored in the computer readable storage medium and perform the method of any one of claims 1-6.
9. A computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, the computer instructions for causing a processor to perform the method of any one of claims 1-6.

Description

Method for estimating tilt-length coupling coefficient in the presence of optical path noise in spatial gravitational wave detector Technical Field The invention belongs to the technical field of noise analysis and data processing of a space gravitational wave detector, and particularly relates to a tilt-length coupling coefficient estimation method when optical path noise exists in the space gravitational wave detector. Background Gravitational waves are space-time ripples caused by large-mass celestial body movements, and can carry information in the depth of universe. Spatial gravitational wave detection programs (such as LISA, violin and taiji) detect low frequency gravitational wave signals by constructing laser interferometers on the order of millions of kilometers in space. Because the space environment can effectively avoid the interference of ground environment noise, the space gravitational wave detector plays an irreplaceable role in the aspect of low-frequency gravitational wave observation, and the frequency blank of ground detection is made up. However, in the actual detection process, the phase noise caused by the unstable frequency of the laser is far higher than Yu Yinli wave signal intensity, and the noise must be suppressed by a time delay interference technology. The spatial gravitational wave detector employs millions of kilometers of inter-satellite interference technology, the sensitivity of which depends on the suppression and calibration of various residual noise. With current noise subtraction technology support, at low frequency bands (< 0.01 Hz), it is mainly dominated by proof mass residual acceleration noise. At mid-band (0.01-1 Hz), optical path noise and tilt-length coupling become key factors limiting sensitivity. Tilt-length noise is generated by the angular jitter of the optical element mapped to equivalent length variations by geometric coupling, which can be suppressed by measuring the coupling coefficient and subtracting its contribution from the data. It should be noted that the tilt-length noise describes an equivalent measurement noise form generated under a known physical mechanism. Specifically, when angular jitter (also referred to as tilt noise) occurs in an optical element or an optical platform, the angular jitter is converted into an equivalent optical path length change through a geometric coupling relationship due to non-ideal factors such as a limited spot size, a wavefront curvature, an optical axis offset, and an adjustment error in an optical system, and thus the angular jitter appears as a noise component indistinguishable from a real length change in interferometric phase readout. Thus, tilt-length noise is used to emphasize that angle jitter, after being mapped by the optical system, is ultimately reflected in interferometry as the physical nature of length noise, which is the result of coupling between the angle disturbance and the equivalent length change, rather than the pure angle noise itself. If the tilt-length coupling noise is not removed, the tilt-length coupling noise is directly overlapped in the interference measurement result, and the spectrum characteristic of the tilt-length coupling noise in the intermediate frequency range is overlapped with the effective frequency range of the optical path noise and the gravitational wave signal, and is difficult to distinguish by a simple filtering or frequency domain separation method, so that noise background is raised, the signal-to-noise ratio of the gravitational wave signal is further reduced, and the reliability of system sensitivity evaluation and subsequent scientific data analysis is affected. It can be seen that it is necessary to estimate the tilt-length coupling coefficient to reconstruct the equivalent length noise introduced by the angular jitter using the coupling coefficient and subtract the noise component from the time-delayed interference output signal to improve the spatial-power-wave detector interferometry accuracy and suppress the main noise source in the intermediate frequency range. However, when the optical path noise is increased, the power spectral density and the tilt-length noise are in a similar form in the intermediate frequency range, so that the conventional spectrum-based distinguishing method cannot reliably separate the two, and the tilt-length coefficient estimation error is increased, thereby influencing the recovery of the gravitational wave signal. Optical path noise, among other things, originates from small changes in optical path length in the optical system, which may be caused by thermal expansion of the structure due to temperature gradients, deformation or stress relaxation of the optical elements, errors in the assembly of the optical components, wavefront distortion, and micro-vibration of the mechanical support structure. Because the accuracy of the tilt-length coupling coefficient estimation algorithm depends on the measurement accuracy of angle j