Abstract

Design theory, manufacture, and performance are discussed for a "notch" filter. Notches are necessarily those minus–filters (Thelen 1971), structurally tapered to compensate gross dispersion adjacent to the notch wavelength. Alternatively, compensation can be provided without tapering by a single HERPIN-period at each interface: we find this to be both practicable and adequate, but quite sensitive to refractive index. For the notch, per se, we prefer the particular non-quarterwave stack (described by Thelen) which has one layer index identical to the substrate. The accompanying index is not restricted and, whatever its value, bandwidth is easily varied by adjusting thickness ratio in the stack. Substrate antireflection is provided at the outer surface, and we find that the two-layer half/quarter (or W-type) coating is best to compensate notch dispersion (we assume because the constituent half/quarter indexes straddle the substrate index).

© 1984 Optical Society of America