Design of dielectric multilayer bandpass filters using fundamental thickness of layers

The general design principle of the dielectric multilayer bandpass filters proposed by the authors is applied to the case where only the fundamental thickness of dielectric layers are used. The actual design procedure, layer structure, necessary formulation in the design, conditions, and design examples are presented. Further, with respect to various combinations of the parameters, 900 filters are designed and their characteristics are verified to show the distribution of their design errors. In actual designs, the objectives are third‐, fifth‐, and seventh‐order Butterworth and Chebyshev filters (0.5‐dB and 1‐dB ripples) using SiO2 and TiO2 and the center wavelength of 1.3 μm. The percentage bandwidths are taken to be up to 10 percent with angles of incidence up to 30 deg with P or S polarizations. It is understood that, when the bandwidth is set to be less than 5 percent or when it is set in the range of 5 to 10 percent, it is possible to achieve designed filters with percentage bandwidth errors below 1 percent and 3 percent, respectively. In all Butterworth filters, the insertion loss at the center wavelength was below 0.04 dB. For the objective ripple in Chebyshev filters set at 0.5 dB, the maximum ripples of all filters distribute within 0.15 to 2 dB while, in the case of 1‐dB objective ripple, they are in the range from 0.4 to 2.3 dB.