Doppler asymmetric spatial heterodyne spectroscopy (DASH) has significant advantages in the passive measurement of wind fields. Wind speed measurement accuracy depends heavily on the phase inversion accuracy of DASH interference fringes. However, the errors in the conventional phase inversion algorithm in the DASH technique make it difficult to obtain the phase of DASH interferometric stripes with high accuracy. The error mechanism of the conventional phase inversion algorithm in the DASH technique is dissected from both theoretical derivation and numerical simulation. It is found that the effect of spectrum leakage on the inversion phase error is greater compared with the window function used for isolating spectrum features. Based on the analysis, an optimization measure by improving the recovered spectrum is proposed and verified by numerical simulation. Comparative simulation results with existing phase inversion algorithms show that our optimized processing method has significant advantages, regardless of whether dealing with single or multiple spectral lines. The research results indicate that our proposed optimization measure can effectively improve the phase inversion accuracy, obtain more accurate wind field data, and contribute to the development of the DASH technique in the field of high accuracy passive measurement of global wind fields for the middle and upper atmosphere.
A real-time hybrid optoelectronic analog-to-digital converter (HOE-ADC) based on optical sampling and electronic quantization is proposed and experimentally demonstrated. In the proposed HOE-ADC, a broadband semiconductor laser is intensity modulated by electronic pulses to generate an optical sampling pulse train. The optical sampling pulse is split into multiple channels with different optical fiber delay, and the analog signal is modulated on the multichannel optical sampling pulses using a Mach–Zehnder modulator array. By broadening the optical pulses, which can be done by employing optical-fiber chromatic dispersion, the bandwidth of the sampled pulse is reduced to match the sample rate of a low-speed electronic ADC, where the broadened optical sampling pulses are quantified. The nonlinearity of optical devices is calibrated through digital signal processing. A four-channel HOE-ADC is experimentally demonstrated. A sampling rate of 12 GS / s and a system bandwidth of 10 GHz are achieved. The effective number of bit (ENOB) for a 1.5-GHz target analog signal is measured to be 5.9 bit. Further, the primary influence factors, such as delay errors, for the performance of ENOB are also discussed.
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