Development of 1.90-2.10μm Absorption Bandpass Filters
The design and optimization theory,the process parameter improvements in preparation,and the product testing methods of 1.90-2.10μm absorption bandpass filters are introduced.Ge and SiO are selected as high and low refractive index coating materials,respectively,and a matching layer is added to the film system by matching the equivalent refractive index.The TFCalc software is used to optimize the film system and smoothly eliminate the notch.A 1.90-2.10μm absorption bandpass filter with 10 layers and a total thickness of 2798 nm is developed,with a passband transmittance greater than 92%at a center wavelength of 2.0μm and an average transmittance of less than 0.8%at cutoff bands of 1.0-1.60μm and 2.50-3.89 μm.This type of filter film has fewer layers and a smaller thickness,which can significantly shorten the vacuum preparation time of the filter,improve the control accuracy of the film layer,and meet the needs of mass production.
Central wavelengthBandpass filterEquivalent refractive indexMatching layerMem-brane designProcess parameters
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