Spectral flattening system for astronomical calibration sources based on a digital micromirror device

Large intensity fluctuations across different wavelengths limit the performance of modern calibration sources (e.g., laser frequency combs and Fabry-Perot etalons) for high-precision radial-velocity spectrographs. To address this issue, a digital micromirror device-based spectral-flattening system is presented. A parallel wavelength-calibration method is developed to reconstruct the column-to-wavelength mapping and improve the calibration rate relative to conventional sequential scanning. A segmented closed-loop feedback strategy is implemented to achieve rapid convergence and stable spectral output. For a supercontinuum input with a spectral dynamic range of ∼14 dB over 540-760 nm, the spectrum is flattened to -6.6 dB relative to the maximum-throughput spectrum, with a maximum flattening error of 0.21 dB relative to the target attenuation level. Continuous closed-loop operation maintains an error below 1 dB over 2 h, sufficient for typical multi-hour calibration sequences.