Narrowband high-reflection filters with wide and low-reflection sidebands.

Narrowband high-reflection filters with the structure sub|H(LH)(m1)alpha L(HL)(m2)Cr(beta)M|air are proposed. The effects of the Cr layer and the matching stack consisting of dielectric multilayer on the reflection characteristics of the filters are analyzed. The distribution of the internal electric field and the optical absorption is also calculated. The analysis indicates that the improvement of the sidebands could be reached by applying the matching stack without impairing the maximal reflectance and half-width of the reflection band. Wide and flat reflection sidebands could be realized by applying a relatively thicker metal layer. However, lowering the sideband reflection could only be achieved by adding appropriate matching stacks. Large m(1)-m(2) could increase the maximal reflectance, while large m(2) or n(H)/n(L) would reduce the width of the reflection band. In the Cr layer, the least average intense electric field occurred at the central wavelength, the relatively high electric field intensity exists at the wavelengths outside the central wavelength region. The optical absorption of the filter depends strongly on the electric field intensity inside the Cr layer.