We used first-principles methods to investigate how oxygen vacancy defects affect the optical properties of YBa₂Cu₃O_7−δ (0 < δ < 1), a high-temperature superconductor with potential applications in optical detectors. We calculated the electronic structure of YBa₂Cu₃O_7−δ with different amounts of oxygen vacancies at three different sites: Cu–O chains, CuO₂ planes, and apical oxygens. The formation energy calculations support the formation of oxygen vacancies in the Cu–O chain at higher concentrations of vacancy defects, with a preference for alignment in the same chain. The presence of oxygen vacancies affects the optical absorption peak of YBa₂Cu₃O_7−δ in different ways depending on their location and concentration. The optical absorption peaks in the visible range (1.6–3.2 eV) decrease in intensity and shift towards the infrared spectrum as oxygen vacancies increase. We demonstrate that oxygen vacancies can be used as a powerful tool to manipulate the optical response of YBa₂Cu₃O_7−δ to different wavelengths in optical detector devices.