The band-pass filter is also called interference filter. Is to eliminate unwanted stray light, only need to light through, such as rice and beans mixed together. You'd better put them all down to only through a rice sieve, filter, to distinguish between the. This band pass filter is to play this role.

From spectral curves said, can let the light from a wavelength or wavelength through, similar to the great wall shape (from the shape of pulse) or approximation to Z are called bandpass and "Z" often called long wave or short wave.

The width of the band is divided into two types: narrow band and wide band. Narrow band filters, for example, half of the bandwidth 20nm spectrum through the narrow band, if you want to 40nm, 100nm bandwidth is also called narrow band, not against the.

From the spectra of the length (regional): ultraviolet, visible, near infrared, infrared and far infrared band pass filter (commonly called UV 180~400nm visible light 400 ~ 700nm, near infrared 700~3000nm, infrared 3000nm~10um.

NOUN interpretation:

1) the center wavelength (CWL): the use of the wavelength of the peak value is 850nm, such as light source LED light, the center wavelength is 850nm demand.

2) transmittance (T): hypothesis was 100%, passes through the filter some loss for the initial value, through the assessment that only 85% of the, it can put the filter transmittance only 85%, simply said that the number of losses, everybody wants to do all things loss of the smaller the better.

(3) peak transmittance (Tp) >85%.

4) semi bandwidth (FWHM): simple is the highest transmission rate of 1 / 2 place corresponding wavelength, with a wavelength of about value subtraction, for example, the peak is the best 90%, 1 / 2 is 45%, 45% of the corresponding wavelength around is 800 nm and 850 nm and the bandwidth is 50nm.

(5) the cut-off rate (Blocked): the corresponding transmission rate. Due to the rate of 0%, it is very difficult to know that the sun can make the underground tree into carbon, only rely on this thin film to cover up everything is very difficult, can only choose it through the smaller the better. The smaller the spectral transmittance is, the better.

6) cutoff band: minimum area of acceptable wavelength.

(7) (coating hard): oxide material plating (e.g., Ta2O5, SiO2, etc.).

8) piamater: removing oxide materials, such as fluoride (MgF2), sulfide, commonly used, such as aluminum, gold and silver.

9) increase through the film (AR): less reflective coating, increase the wear of light, so that the most effective use of light energy.

10) BBAR: back broadband penetration film.