It is a well-known fact that optical components used in the thermal infrared would be disabled without antireflection coatings due to the serious Fresnel reflections on their surfaces. The antireflection coating consisting of a single inhomogeneous layer with graded-index is an important solution. In our investigation, the combinatorial materials libraries were synthesized to explore the composition dependence of the durability and antireflection characterization of graded-index layers deposited from four rare-earth fluorides LaF 3 , PrF 3 , ErF 3 and SmF 3 , admixed with a different amount of BaClF. It was demonstrated that the layers are robust enough to withstand normal handling and environmental conditions, furthermore, the best antireflection approach for the Ge surfaces can be achieved for the BaClF-LaF 3 layer with a BaClF concentration x = 0.51, through the high-throughput characterization of the robustness and the spectral transmittance of the elements in the libraries. Because the optimized characteristics of a Gaussian index profile followed by a quintic-profile can be created in the layers, an effective refractive index around 1.2 can be achieved, which is lower than those of infrared low-index coating materials used commonly.

Cut-off filters are usually operating at oblique incidence and exhibit polarization dependence properties. We propose a simple approach to design cut-off filters with low linear polarization sensitivity (LPS) based on dielectric-metal-dielectric (DMD) stacks. The designing method is derived from the theory of optical film characteristic matrix. The admittance loci of the film are adjusted to achieve similar spectral properties of s- and p-polarized light at oblique incidence. Different film structures are designed non-polarizing at different angles of incidence with the method. The results show that the designing method is efficient for designing non-polarizing cut-off filters, which are widely used in non-polarizing optical system.

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