Abstract
In this paper, the power spectrum resolution problem of dual-frequency coherent mixing signals is analyzed when the Doppler frequency difference is small. The power spectrum function formula of the four optical coherent mixing signals is obtained using statistical theory and the Wiener–Khinchin theorem. The influence of delay time and light source line width on the power spectrum of dual-frequency coherent signals is analyzed using this formula. The results show that delay time only affects the peak of the power spectrum of the coherent signal. An increase in the line width of the light source broadens the signal power spectrum and reduces the peak value. The necessary condition for distinguishing the Doppler frequency difference is that the theoretical Doppler frequency difference is greater than 1/5 times the line width of the light source.
Highlights
Compared to direct detection technology, laser coherent detection technology greatly improves the signal-to-noise ratio and detection sensitivity
The power spectrum of the signal is related to the line width of the source, the delay time and the Doppler frequency difference
When the Doppler frequency difference is small, the power spectrum of the dual-frequency signal has a resolution limit. If it is less than the power spectrum resolution limit, the microwave beat signal cannot be obtained by optical second-order mixing or electric signal mixing
Summary
Compared to direct detection technology, laser coherent detection technology greatly improves the signal-to-noise ratio and detection sensitivity. We use statistical theory and the Wiener–Khinchin theorem to obtain the power spectrum function of dual-frequency light, and analyze the relationship between the Doppler spectrum of dual-frequency light and line width, frequency shift, delay time and motion speed. It provides theoretical support and reference for the research and application of dual-frequency laser coherent detection technology. The structure of the dual-frequency laser coherent detection system is shown in Figure 1.The time understand the correlation between Doppler shift resolution, Doppler frequency difference, and domain signal of the dual-frequency local oscillator can be expressed as E01 (t) and E02 (t), where: source line width. The influence of the line width of the light source on the spectral resolution performance of Equations (4) and (5) is analyzed, under the condition of a small Doppler shift
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