What is an interference filter?

Sep. 04, 2019

What is an interference filter?

Filters are very useful, said the optical lens supplier. It's widely used in photography, but also in all aspects of our lives, some photography masters shot landscape painting, why the main scene is always so prominent, how to do it? That's where the filters come in. For example, if you want to shoot a yellow flower with your camera, the background is blue sky and green leaves. If, however, put a yellow filter in front of the cameras, blocking part of scattering leaves green, blue sky scattering of blue light, and let chrysanthemum scattering through the yellow light of a lot of, so, chrysanthemum is very obvious, highlights the theme of "flower", therefore, in today's era of science and technology development, people's quality of life also in constant ascension, more and more demand for high-tech, use the filter are also constantly increased, types have been increasing, today we're going to meet one of these, interference filter, interference filter is what? The following changchun city borida photoelectric technology for everyone to learn the knowledge of interference filter.

Interference filter is a kind of optical film with the most kinds and complex structure. Its main function is to segment spectral bands. The most common interference filters are cut-off filters and bandpass filters.

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Bandpass filter

A cutoff filter can divide the spectrum under consideration into two parts, one that does not allow light to pass through (called the cutoff region) and the other that requires full light to pass through (called the bandpass region). According to the position of the passband in the spectral region, it can be divided into two types: long wave pass and short wave pass. The simplest structure of interference filters is respectively, where H and L represent thick high and low refractive index layers respectively, and m represents period number. Membrane systems with the above structures are called symmetric periodic membrane systems. If the considered spectral region is very wide or the ripple of passband transmittance is very high, the membrane structure will be more complex.

Bandpass Filter allows only one segment of the spectrum to pass through, while the rest of the spectrum is filtered out. According to the structure of the interference filters, they can be divided into fabry-perot filter, multi-cavity filter and induced-permeability filter. The fabry-pero type filter is a kind of filter matched on both sides of the metal membrane with appropriate dielectric membrane system to increase potential transmittance, reduce reflection and increase passband transmittance. Although the pass-band performance of the interference filter is not as good as that of the all-dielectric filter, it has a very wide cut-off property, so it has great application value. Especially in the ultraviolet region, the advantages of the interference filter are more obvious when the dielectric material generally absorbs more.

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