Comparison of several shortwave pass filter designs.
The simplest shortwave pass filter design consists of repetitions of the basic period of the form (0.5L H 0.5L), where L and H refer to quarterwaves of low and high index materials at a particular wavelength. Such a filter has a passband limited by the first- and third-order rejection bands. The width of the passband can be extended to shorter wavelengths by further subdividing the basic period using materials of intermediate indices. Alternate shortwave pass filter designs can be obtained by approximating a continuous index profile in which the natural log of the refractive index follows a sinusoidal profile. Films with such a continuous index profile are commonly called rugate filters. Four discrete index approximations to the rugate filter are compared. They are found to differ with respect to the bandwidth of the shortwave passband.
Carniglia
C K
CK