Optical thin films and interferential filtering

In the free-space sector, optical thin films remain indispensable in many sectors. This is due to the maturity they have acquired over the last thirty years, and to the diversity and complexity of the optical functions they perform: simultaneous constraints on intensity and phase, polarization, achromaticity or resonance, stability at incidence... The strength of this type of component also lies in the diversity of substrates (glass, crystals, plastics) and deposited materials (oxides, sulfides, nitrides, fluorides, metals), which enable it to address wide spectral ranges (UV/VIS/PIR/MIR). Moreover, this field is virtually the only one to benefit from sophisticated synthesis software based on the latest optimization techniques (genetic algorithms, simulated annealing, needle method, etc.). While spectacular progress was made in the manufacture of filters for microelectronics, high-speed optical telecommunications and biomedical applications in the 2000s, technology has progressed even further over the last five years, particularly in the area of process automation, and today makes it possible to deposit several hundred layers with nanometric precision. These advances have been accompanied by increasingly sophisticated metrology, including flux resistance, which has become a real issue in the context of photonic integration and the increasing power of laser sources. At the same time, non-optical constraints (hardness, adhesion, environmental sensitivity, aging, self-cleaning) have taken on considerable importance, particularly in the field of consumer applications.

This article is devoted to calculating the optical response of a multilayer system: reflection, transmission and absorption, wavefront and polarization, pulse duration... We use the complex admittance method, which offers the advantage of analytical calculation to better understand and predict phenomena. The results can be used to rapidly program the spectral profile of a component, and are immediately generalizable to the study of resonances and guided modes.