Fundamentals of Optical Filter Films

Many people who are new to filters do not understand the basic principles of optical filter films, this article will briefly explain.


1. The working principle of optical filter films


Filters are made by adding special dyes to plastic or glass substrates or by evaporating optical films on their surfaces to attenuate (absorb) certain wavelengths of light waves or pass light waves with a precise selection of a small range of wavelengths, while reflecting them. (or absorb) other unwanted bands. By changing the structure of the optical filter and the optical parameters of the film layer, various spectral characteristics can be obtained, so that the filter can control, adjust and change the transmission, reflection, polarization or phase state of the light wave.


2. The classification of optical filter films


The classification method of filters is generally classified according to the spectral band, spectral characteristics, film material, application characteristics and other characteristics. Filters can be classified into bandpass filters (such as NBF-808, BPF940, etc.) according to their spectral characteristics, cut-off filters (such as IBG-650), dichroic filters (such as semi-transparent mirrors), Neutral density filters, reflective filters, etc.; optical filters can be classified into ultraviolet band filters, visible light filters and infrared band filters according to the spectral band classification; filters are classified according to the application film material It can be divided into soft film filter and hard film filter; according to the application characteristics, the filter can be divided into medical biochemical instrument filter, fluorescence microscope filter, police multi-band hard film filter, etc. 


3. The function of optical filter films


As far as the optical lens is concerned, the filter on it is generally coated. A special optical filter film is used to allow part of the light to pass through or block part of the light to pass through. Now there is also the kind of double-peak filter, which is a double-channel coating. It is coated with two layers of film, so as to have the effect of two optical filters, such as IR650+950, which allows 650nm visible light to enter during the day, and 950nm wavelength infrared light to enter at night, but both are do not affect each other.


Our common filters include low-pass filters, infrared filters, infrared cut-off filters, narrow-band filters and beam splitters. For example, the low-pass filter is mainly used in CCD and CMOS, and its function is: the first filter out the infrared light in the light; the second trimming progress.


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