2025 OIC Manufacturing “Road Runner” Challenge [Invited]

Measurements of the fabricated optical filters submitted to the Manufacturing Challenge (MC) organized for Optica's Topical Meeting on Optical Interference Coatings held in Tucson, AZ, in May 2025, are presented. For this ninth MC, participants were asked to design and deposit, on a provided substrate, a filter with transmittance (<i>T</i>) and front- and back-reflectance (<i>R</i>) spectra (with light incident from the front and back, respectively) matching target values specified in the 400 nm to 1100 nm spectral interval. The challenge problem was selected to require at least one absorbing layer in the design in order to ensure a good performance. Six teams from three countries participated and submitted a total of 10 samples, all coated on both sides, with total thicknesses ranging from 3589 nm to 8088 nm and comprised of 31 to 135 layers. The entries were measured at four independent laboratories; the resulting merit function values obtained when comparing the measured spectra to the targets were used to rank the filters and determine a winner. In the analysis of the results, observations will be made about coating design, fabrication, and measurement.