What Is the Type of Filter?

Feb. 24, 2021

Filters are made of plastic or glass sheets and then add special dyes, red filters can only let red light through, and so on. The transmittance of the glass is about the same as the air, all colored light can pass, so it is transparent, but after dyeing, the molecular structure changes, the refractive index also changes, the passage of certain colors of light has changed. For example, if a beam of white light passes through a blue filter, a beam of blue light is emitted, while green light and red light are very little, and most of them are absorbed by the filter.The next filter supplier will briefly introduce you.

Filters are, as the name suggests, optical devices used to select the desired radiation band. 

Filters are broadly divided into two categories.

1. Color filters, which are various colors of flat glass or bright film, the transmission bandwidth of hundreds of angstroms. Mostly used in broadband photometry or mounted in the stellar registers, to isolate overlapping spectral levels. Its main feature is that the size can be made quite large.

2. Thin film filters, thin film filters can be divided into thin film absorption filters and thin film interference filters of two kinds.

 Infrared Filter

The former is on a specific material base, chemical etching so that the absorption line is located exactly at the required wavelength. Generally, the wavelength of transmission is longer, and it is mostly used as infrared filter.


The latter is on a certain substrate, using vacuum coating method alternately formed with a certain thickness of high refractive index or low refractive index of metal-dielectric-metal film or full dielectric film composition. The choice of material, thickness and tandem of the film layers is determined by the desired central wavelength and transmission bandwidth λ.


The classification of thin film filters is to be classified by spectral band, spectral characteristics, film layer material, and application characteristics.

Spectral bands: UV filters, visible filters,infrared filters.

Spectral characteristics: bandpass filters, cutoff filters, spectral filters, neutral density filters, reflection filters.

Film materials: soft film filters, hard film filters.


Hard film filters not only refer to the hardness of the film, but also its laser damage threshold, so it is widely used in laser systems, while soft film filters are mainly used in biochemical analyzers.


Bandpass type: The light in the selected band passes through and the light outside the band is cut off. The optical index is mainly the center wavelength (CWL), half bandwidth (FWHM): divided into narrow band and wide band.

Short wavelength pass type (also called low wavelength pass): light shorter than the selected wavelength passes through, and light longer than that wavelength cuts off.

Long wavelength pass type (also called high wavelength pass): light longer than the selected wavelength passes through, and light shorter than that wavelength cuts off .

Tian Cheng optics can supply long-wave pass filter, short wave pass filter, wide band pass filter, narrow band pass filter, super narrow band pass filter and high reflection filter etc. It covers 1um to 40 um.

Tian Cheng Optics Co., Ltd. was founded in 2007 and located in Changchun city where is very famous base of optics research and development in China, We mainly manufacture high precision optical components such as spherical lens, cylindrical lens, prism, filter, window, mirror, beamsplitter, waveplate, polarizer, rod Lens and micro optics. Our products were approved by many special companies from United Kingdom, Germany, Austria, Switzerland, Italy, Ireland, Sweden, Australia, Israel, U.S.A. etc.



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