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The design of the conventional optical filter what are the characteristics?

by:HENGXIANG     2020-11-17
Optical filter has specific wavelengths of light transmission, but the colored glass filter more precise. Interference filter can provide precise control of nanometer level with different wavelengths of light transmission and deadline. Neutral density filter and polarization filter can also be used for specific imaging scene to improve performance. In order to correctly use filter, the designer must understand the advantages and limitations of all kinds of filter. Conventional ultra narrow-band filter structure is similar to the commonly used design Fabry - Perot interferometer structure, namely in two high reflective film is sandwiched between a spacer layer ( Cavity) , reflective film consists of center a quarter wave long membrane layer, spacer layer thickness for half the center wavelength of integer times. This simple single cavity structure filter performance is poorer, passband shape for the triangle. To meet the requirements of lightning detection using, ultra narrow band filter design USES two cavity or three cavity structure, it is using coupling layer will be more than one single cavity structure together, in order to get close to the rectangular passband. For multi-cavity structure, the bandwidth of the filter is mainly determined by the membrane material index of refraction, membrane structure and number of cycles, spacer layer material and structure as well as the coupling layer material and structure. In the preliminary design result is determined, by adjusting the spacing layer and the coupling parameter, the bandwidth of the filter can be fine-tuning in order to get the results meet the design requirements. Is divided into thin film absorption filter and thin-film interference filter two kinds. The former is on the specific material base, using chemical etching exactly on the need of the absorption line wavelengths. Generally through a longer wavelength, used for infrared filter. The latter is in a film base, alternately formed by vacuum coating method has a certain thickness of the refractive index in either high or low refractive index of metal - Medium - Metal film, or the dielectric film, constitute a kind of low-level times, multi-stage tandem - solid method Perot interferometer. Epidural filter not only refers to the film hardness, more important is the laser damage threshold, so it is widely used in laser systems, MianRuan membrane filter is mainly used in biochemical analyzer. Band-pass type: selected wavelengths of light, as light outside passband. The optical indicator is mainly the center wavelength ( CWL) , half the bandwidth ( FWHM) 。 Can be divided into narrowband and broadband. Such as narrow-band filter diagindex. nbf - 808 808. Short wave pass ( Also called low wave pass) : short on the selected wavelengths of light through, longer than the wavelength of light. Such as infrared end filter, IBG - 650. Relevant tags: optical filter
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