The filter with cutoff region on both sides of the transmission band of the spectral characteristic curve is called a bandpass filter. Bandpass filter is an important optical thin film element, which has been widely used in chemistry, spectroscopy, laser, astrophysics, optical fiber communication, biology and other fields. The spectral curve of the band-pass filter prepared by the principle of light wave interference, the spectral transmission region near the wavelength is called the passband of the filter, usually on both sides of the cut-off region, and there may be a by-pass band around the cut-off region, usually need to use colored glass, absorption film or cut-off filter to eliminate the by-pass band.

Bandpass filters are roughly divided into broad band filters and narrow band filters according to spectral characteristics, two kinds of filters are usually combined, the application of light wave interference principle to prepare bandpass filters, and bandpass filters have been widely used in various fields.