The simulation and experiment results of the sodium MOF transmission functions. (a) and (b) show the transmission functions of Na D MOF with a center peak and with two wing peaks, respectively. Panel (c) shows the sodium MOF filter that has a single peak in the Fraunhofer D2 line center, enabling chromospheric filtering. The red solid line is the Fraunhofer line and the blue and black solid line are the MOF transmission functions.