Research on single optical path difference crossfading technology for a coherent-dispersion spectrometer

An asymmetric common-path coherent-dispersion spectrometer (CODES) has the advantages of high stability and high throughput. It holds great potential in fields such as exoplanet exploration, cosmic redshift drift measurement, atmospheric remote sensing, and wind velocimetry. However, due to factors such as atmospheric disturbances, thermomechanical drifts, environmental vibrations, and the imperfect alignment of detector pixels, the interference spot will be displaced relative to the detector pixels. This leads to random wavelength shifts, which severely constrain detection accuracy. Therefore, this paper proposes a crossfading method based on a single optical path difference (OPD). Leveraging the dual-output characteristics of the CODES, the ordinary spectrum and the interference spectrum are separated. Then the response characteristics of the two spectra to drift are analyzed, and the principle of crossfading based on these characteristics is investigated. Furthermore, the influence of the OPD on the crossfading results is explored, and a method for selecting the OPD is provided. On this basis, a method for optimizing weights based on phase residuals in the frequency domain to realize crossfading is proposed, and the high-frequency splicing as well as spectral equalization are completed. This method effectively suppresses drift while improving spectral resolution. The results of theoretical simulations indicate that, under the parameters described in this paper, the proposed method enables a twofold enhancement in spectral resolution compared with the ordinary spectrum, along with an improvement of more than a factor of 240 in the stability of the CODES. It effectively mitigates the stability problems caused by random external environmental disturbances and provides a new solution for high-sensitivity spectral measurement technology.