Interference multilayer antireflection coatings for two wavelengths in the near infra red

The investigation deals with analysis of antireflection coatings of two transparent materials with high (H) and low (L) refractive index for two wavelengths 1.30 mum and 1.55 mum in the near IR on glass/silica substrates. The results are obtained by numerical optimisation approach which algorithms are realised using programming language DELPHI. The initial structures of LHL three-layer and LHLH four-layer coating (optimised for both wavelengths) are modifications of double-layer antireflection coating for one wavelength 1.4 mum. It is shown that the highest transmittance near 1.30 and 1.55 mum (practically equal to 100%) shows LHLH four-layer coating structure. The total physical and optical thickness of optimised LHLH four-layer coating is smaller than corresponding value for optimised LHL three-layer coating. Four-layer LHLH coating is more stable with respect to small n and d variations and corresponding transmittance changes are less than in case of LHL three-layer coating.