Metal-Dielectric Bandpass Filter

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This filter transmits a fairly narrow band of wavelengths centered at 870 nm.

Plot of metal-dielectric design

This design is for normal incidence on a BK7 (ordinary) glass substrate. Three materials are used: Au, SiO2, and TiO2. Starting with a thin, one-layer design, TFCalc's needle/tunneling method produced a sequence of designs of increasing complexity. The design (whose performance is shown above) consists of 8 layers. Designs with as few as 4 layers are possible. However, those designs have lower transmittance and a wider pass band.
Here is the design, with the first layer closest to the substrate and thickness given in nm:
    AU        23.33
    SIO2     121.94
    TIO2      94.24
    SIO2     302.57
    TIO2      94.24
    SIO2     127.87
    AU        24.97
    TIO2     101.94
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