Exact and numerical design of non-polarizing edge filters

Multilayer dielectric thin films have polarization effects at non-normal incidence. In this letter, specifications include s- and p-polarization transmittance (T_s,(p)> 95% at 790-808 nm), s- and p-polarization reflectance (R_s,(p) > 95% at 814-860 nm), angle of incidence (AOI) = 45°, air as incident medium, and BK7 glass as substrate. Based on the two chosen materials (Ta₂O₅ and SiO₂), non-polarized edge filters are carried out using the design methods of the detuned multiple half-wave filters (exact design) and the needle optimization (numerical design). Exact design has a total of 112 layers and 12 cavities; optical thickness is 126 quartwaves at 860 nm. Numerical design has a total of 107 layers and 8 cavities; optical thickness is 91 quartwaves at 850 nm. Hence, the numerical design has less layers and thickness, thus meeting the same specifications of the exact design.