Design of a digital tunable stellar spectrum calibration source based on a digital micromirror device

•A spectral tunable radiometric calibration source with dual operating modes (monochromatic light and wide spectrum) is proposed.•The cylindrical collimating beam expanding system is used to reduce the aperture of the spectral modulation system, and improves the spectral modulation accuracy and spectral resolution.•The simulation accuracy (point by point scanning) of target spectrum is between 2.8% and 5.1% in broad-band mode. The output monochromatic full width at half maximum (FWHM) is between 2.75 nm and 3.86 nm in narrow-band mode.