Reduced angle-shift infrared bandpass filter coatings

Infrared optics are often expected to perform over a wide range of angles of incidence, over a selected bandpass. For the best performance, it is often desired that the shift of spectral features, and the splitting between s and p polarizations, be minimized. These issues can be mitigated to a large extent by design, particularly over a narrow range of angles. However, the availability of high index materials throughout a stack design can greatly improve the performance at a given coating thickness, or greatly reduce the overall thickness required to achieve a design. Here we discuss several designs that have been achieved via hydrogenated silicon in multilayers, which demonstrate improved performance at oblique angles of incidence.