Analysis of broadband short-wave-pass (SWP) beamsplitters. Final report

摘要

Frequently, optical systems require the separation of incident radiation in length bands. Optical thin film filters are commonly used for this purpose. Separation can be achieved by reflecting, transmitting, or absorbing radiation at various wavelengths. This paper addresses one type of thin film filter, the short wave pass filter. This type of filter transmits short wavelength radiation and reflects longer wavelengths. Other methods for achieving wavelength separation of radiation include optical thin film long wave pass filters which are the complement of short wave pass filters. These reflect short wavelength radiation and transmit long wavelengths. Combining selective transmission or reflection with absorption is another method. A common example of this type of separation filter is colored glass. Specifically, the design of broadband short-wave-pass (SWP) is described here. The requirement which complicates the design of this type of filter is the need to transmit radiation over a broad short wavelength region. While numerousmethods are available to the designer, simple concepts are stressed. The approach is to look at two basic design concepts for reflecting long wavelengths and. then add performance enhancing features for transmitting the shorter wavelengths. Comparisons of performance with and without such features are presented. Improving performance frequently means adding complexity to the design which, in turn, translates into more difficulty in manufacture. Throughout this paper such produceability concerns are mentioned. By comparing relative performance benefits to complexity of specific designs, it becomes clear that trade-offs are very common when employing SWP's as wavelength separators. The primary conclusion is simple: try to avoid use of SWP's in designing optical systems which require separation of radiation over broad wavelength regions.