Narrow frequency sharp angular filters with integral times of quarter wavelength layer structure, which can be fabricated with commonly used coating machines and work in visible and near infrared, are designed. These filters possess not only a narrow frequency pass band but also a sharp angular pass breadth in visible and near infrared. The experimental result agrees with the theoretical calculations well. These dual functional filters have many potential applications.
Based on the optical thin film interference theory, a novel thin film multi-half-wave multi-frequency filtering technology applied to DWDM interleaver, a comb-like filter, is proposed in this report. A flexible on-demand design of arbitrary frequency spacing can be easily obtained by this thchnology. The parameters of this thin film structure have been analyzed and optimized, and a specific expression for these thin film structure has been described. 50G-spaced and 100G-spaced DWDM interleavers with flat-top passband consisting of less than 30 layers have been designed and fabricated. The process of fabrication is also discussed in this paper. These thin film interleavers have the advantages of good stability, arbitrary wavelength spacing between the adjacent channels, rectangular shape of the pass-band, less layers, low cost, and easy encapsulation, which would make it more attractive to use in DWDM system. The above-mentioned technology exhibits the flexibility in design and the advantages of thin film coating, which will have more applications besides interleaver.