1 February 1999 Near-infrared bandpass filters from Si/SiO2 multilayer coatings
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Design optimization and experimental studies of bandpass optical filters useful in the near-IR region from 1200 to 2000 nm are carried out. It is seen that the use of Si/SiO2 multilayer coating in the form of a multicavity Fabry-Perot (F-P) filter, either alone or in combination with a long-wave-pass (LWP) filter, on an intrinsic silicon (Si) substrate simplifies the filter configuration, obviating the use of the conventional cemented filter configuration. The filter manufacturing studies demonstrate the production of filters with high in-band optical transmittance T>0.90 and excellent rejection T<0.001 from 400 to 2000 nm. The spectral stability of the filters with respect to temperature is found to be sensitive to substrate temperature; the higher the substrate temperature, the higher is the spectral stability. For filters deposited at a substrate temperature of 600 K, the spectral stability is in the range of 2.27 to 1.58x 104 K, over a filter temperature from 298 to 373 K, which is mainly dictated by the refractive index coefficient (RICFT) of Si films.
S. Ajith Kumar, C. L. Nagendra, H. Ganesha Shanbhogue, G. K. M. Thutupalli, "Near-infrared bandpass filters from Si/SiO2 multilayer coatings," Optical Engineering 38(2), (1 February 1999). https://doi.org/10.1117/1.602098 . Submission:

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